How to pickle stainless steel

Welding stainless steel (stainless steel) methods and features in accessible language | Tiberis

Welding stainless steel has its own distinctive features. From our article you will learn a lot of useful information about this process in a few minutes. In one place we have collected basic data on welding methods and important nuances when carrying out work. Read and apply the acquired knowledge in practice. The Tiberis welding equipment store is always happy to share its secrets with you and is happy to help with practical advice.

Stainless steel - what kind of material is it?

At all times, the main enemy of iron products was rust. It can turn the most durable structures into a pile of useless scrap metal. Due to oxidation in the open air, precision instruments become unusable and huge structures are destroyed.

But just over a century ago, people managed to find an excellent rust remover. In 1913, English researcher Harry Brierley created the world's first (according to officially recognized version) stainless steel. It contained 12.8% chromium and 0.24% carbon. Although the first experiments with iron and chromium alloys began to be carried out back in 1820.

Stainless steel has pronounced anti-corrosion properties. Stainless steel acquires these characteristics when certain metals are added to its melt. Most often, chromium, nickel, manganese and molybdenum are used for such purposes.

There are 3 main groups of stainless steel according to their chemical composition:

1. Chromium (have increased strength) These are the cheapest types of stainless steel. They are less amenable to processing due to low ductility.
2. Chrome-nickel (differ in greater ductility). The most popular and widest group of stainless steel. The addition of nickel stabilizes the alloy structure and gives the steel weak magnetic properties.
3. Chromium-manganese-nickel. Adding manganese to the alloy increases strength while maintaining the ductility of steel.

Each of these groups contains dozens and even hundreds of grades of stainless steels, which can differ significantly in their properties.

For example, chromium steels with the minimum permissible (12-14%) chromium content are widely used in the manufacture of valves in units and in the production of ordinary kitchen utensils.

At the same time, chromium steels with a chromium content of 25-33% have excellent heat resistance. Therefore, they are used in metallurgy to create equipment for metal smelting.

In addition, stainless steels are differentiated by their physical structure. Among the many types, the most famous are ferritic, austenitic and martensitic steels.

Where are the different types of stainless steel used?

The scope of application of stainless steel affects literally all aspects of human life. The most popular chromium-nickel authensitic steels are used in large quantities for the production of fasteners (bolts and nuts). Coins are often made from these alloys, for example, Ukrainian 1,2 and 5 kopecks. Autensites are quite easy to heat treat, including welding.

Ferritic alloys are widely used in the chemical industry. High resistance to many types of acids and high temperatures allows these types of steel to be used for the manufacture of huge tanks in chemical plants.

But welding ferritic steel products is much more difficult. Significant resistance to high temperatures makes these alloys inconvenient for welding with the most common welding methods (MMA, MIG/MAG, TIG).

But at home, ferrites are very rare.

Martensitic steels are widely used in the production of tools. Kitchen knives are made from martensitic steel grades. Like their authentic counterparts, they can be welded without any problems.

What methods are used to weld stainless steel?

Stainless steel can be welded in a variety of ways. But 3 main technologies are most often used:

1. Manual arc welding with consumable electrodes (MMA). This method is most common at home, because... inverters for RDS are affordable for every welder. It is of the lowest quality, so it is practically not used on an industrial scale.
2. Semi-automatic wire welding in a protective gas environment (MIG/MAG), semi-automatic welding machines are perfect for this. The most effective method: fast, forming an even seam. Better suited for thicker parts.
3. Welding with non-consumable electrodes in an inert gas environment (TIG), most often using inverters for argon arc welding. More preferable when welding thin workpieces. Recommended for welding high pressure pipes..

In addition, stainless steel welding can be carried out using less common methods. These include:

1. Spot and roller welding.
2. Plasma welding.
3. Laser welding.

But the use of these technologies is limited by the high cost and complexity of the process. Therefore, they are used exclusively when it is necessary to weld parts that require high precision or when processing difficult-to-weld materials.

Features of welding stainless steel or how to avoid defects when welding stainless steel

Welding stainless steel has its own nuances, which are determined by the properties of this material:

1. The presence of chromium in the steel composition. This metal, when exposed to high temperature, reacts with carbon to form chromium carbide, thereby reducing the strength of the welded joint. Therefore, the welding site is quickly cooled (sometimes even with ordinary water).
2. Reduced thermal conductivity. In this connection, the welding current must be reduced by 15-20% compared to the process of processing conventional steel.
3. Increased metal expansion coefficient. Therefore, it is necessary to constantly monitor the size of the gap between the parts being welded.
4. High electrical resistance. For this reason, electrodes with chromium-nickel rods have a limited (up to 350 mm) length.

These four main features of stainless steel welding must always be taken into account when starting work. Only by fulfilling the above conditions can you achieve high-quality results. Otherwise, you are guaranteed the formation of defects.

What should high-quality equipment and materials be for welding stainless steel?

The choice of equipment for welding stainless steel should be made based on the characteristics of this material.

It is best to use welding electrodes made from the same grade of stainless steel as the work being welded. Then the process of melting the metal occurs evenly, providing a high-quality result.

When welding with wire, it is also necessary to select it based on the material of the workpieces being welded. The difficulty is that it is impossible to determine “by eye” a specific grade of stainless steel. To do this, you need to carry out complex spectral analysis in a specialized laboratory. If you encounter such a problem, it is best to look for information on the website of the manufacturer of the product being welded.

Processing products before welding - what and how to do

Processing of stainless steel products before welding is carried out in the following order:

1. The surface of the product is cleaned of dirt. A steel brush is usually used for this.
2. Treatment is carried out with a solvent (white spirit, special liquid or acetone). The absence of grease on the surface of the part increases the stability of the arc.
3. The surface to be welded is treated with an anti-spatter agent. As a result, after welding, the need for mechanical surface treatment simply disappears.

The only significant difference in the preparation of stainless steel products is the need for a gap between the edges of the parts. It provides free shrinkage.

How are stainless steel products processed after welding?

Stainless steel after welding is subject to mandatory additional processing. Ignoring this rule can very quickly lead to negative consequences: corrosion and a decrease in the strength of the product.

Pre-treatment after welding can be performed by the following methods:

• Mechanical cleaning of the weld. This operation is mainly intended to improve the appearance of the product. Produced with hard steel brushes.
• Sandblasting. Pursues the same goals. After doing this, the seam looks even more beautiful.
• Grinding. Allows you to achieve a perfectly smooth seam surface.

But all these pre-treatment methods only affect the appearance of the product. To effectively protect the welding site from destruction, more effective methods are needed - passivation and etching.

Pickling is the treatment of the welding site with chemically active substances (acids or special liquids). Acids eat away scale, which can cause rust.

Passivation is the application of a special agent to the welding site, under the influence of which a protective film of chromium oxide is formed on the metal surface.

Only after chemical treatment can the welding site reliably resist corrosion.

Features of welding stainless steel with other materials

The danger that exists when welding stainless steel with other materials lies in mixing them. As a result, the properties of a dissimilar weld may deteriorate sharply. The seam becomes hard and brittle, and cracks form in it.

To avoid such a development of events, it is necessary:

1. Use high-alloy or nickel-based alloys as an additive.
2. Be sure to calcinate the electrodes before welding and thoroughly clean the surfaces of the products.
3. Do not preheat the welding area before starting work.
4. Use electrodes designed for welding high-alloy steel.

In the weld, it is desirable to achieve as little as possible the presence of the base metal (particles of the original products melted during welding). Its component should not exceed 40% of the total mass. The rest is electrodes or filler wire, depending on the type of welding.

conclusions

Welding stainless steel, although it is a rather complex process, can be carried out efficiently even at home.

For a positive result you need:

1. Correctly take into account the characteristics of stainless steel welding.
2. Select the most suitable (available) welding method.
3. Carefully treat the welding area before and after finishing work.
4. Use high-quality welding equipment and consumables.

All these points can be easily implemented if you have the desire. And Tiberis store specialists are always ready to offer their assistance in choosing the most suitable welding equipment. Contact us - welding work is much easier and more efficient with us.

Source: https://www.tiberis.ru/stati/svarka-nerzhavejushhej-stali

Treatment of stainless steel after welding

Stainless steels are actively used in industry for the manufacture of containers and pipelines for aggressive liquids. In everyday life, kitchen utensils and beautiful heated towel rails are made from this metal.

The mirror surface has an attractive appearance, and the product can serve for a very long time. But to achieve such an effect on the finished structure, it is necessary to properly process the stainless steel welds. If this is not done, the weld areas will turn yellow and black, or they may even rust.

Why is this happening? What mechanical and chemical processing methods are there?

Reasons for processing

In the manufacture of various stainless steel structures, methods of welding metals with an electric arc in an environment of inert gases are used.

To do this, use a tungsten non-consumable electrode and a supply of pure argon to protect the weld pool from interaction with the environment. You can also create a seam using semi-automatic machines, where an arc burns between the tip of the wire and the product.

A mixture of argon and carbon dioxide is supplied from the burner nozzle. The wire is pushed by a special mechanism, the speed of which is adjusted depending on the thickness of the metal and the current strength.

Although the seams are strong and even, they have an unattractive appearance and therefore need to be processed. The junction itself may have a bluish-mirrored hue. The peri-suture zone is often yellow. With a scaly pattern, black marks may be visible in the grooves. And over time, such places even rust.

All this happens due to overheating in the welding zone. High temperatures from an electric arc promote burnout of alloying elements and deplete this area. As a result, it changes color and becomes more vulnerable to external influences. The film formed on the surface has little resistance to an aggressive environment, therefore, when it comes into contact with working fluids at chemical plants, it becomes a weak point and becomes covered with corrosion.

Heated towel rails sometimes rust at the welding points due to the presence of a small electrical voltage in the pipes, which interacts with the material of the product and continues to weaken the weld. This also happens due to the wrong choice of stainless steel for a specific type of product.

For example, instead of grade 304, which is rich in chromium, manufacturers use stainless steel 201, which is cheaper, but whose composition replaces chromium with manganese. It is difficult to distinguish them visually, but with prolonged work in contact with liquids, this will appear as red spots.

Therefore, the correct choice of steel grade and subsequent processing of stainless steel is the key to a long, attractive appearance of the product.

Mechanical grinding

The good corrosion properties of stainless steel contribute to its extensive use in environments where liquids are used. Such products last longer than mild steel.

And the shine and mirror appearance of the surface allow you to install structures in prominent places, improving the overall design of the room or facade. External railings and ramps, parking racks, and various heated towel rails are made from stainless steel.

Despite contact with water and welding work on the products, all these elements retain their beautiful appearance. This is achieved through several types of processing.

One of them is mechanical grinding, which removes the top oxide layer on the weld, which is the weak point of the structure, and also eliminates color transitions and irregularities in the weld joint. This process occurs in the following sequence:

1. Using a grinder and a thick grinding wheel, the waves of the metal seam and its convexities protruding beyond the general plane of the surface are erased. This way you can quickly smooth out the seam, but the grinder leaves behind rough grooves from the abrasive and overheated areas with dark spots.
2. To remove these defects more carefully, you can use petal wheels for an angle grinder. The process will take a little longer, and more consumables will be spent for a large volume of work, but the risks will remain smaller.
3. Next, a grinding machine called Rebir is used. It has a straight shape, an electric motor and a handle to hold it. Petal circles (KSL) are put on the end, but their arrangement differs from the circles on the grinder. Thanks to the wide structure of the sandpaper pieces, it is possible to apply more pressure to the workpiece and cover a wide area. KSLs come in different calibers depending on the amount of abrasive used. To process stainless steel after welding, first use “40” and then “zero”. This eliminates all grooves from previous tools. The coating becomes monochromatic and matte.

Work should be carried out in a respirator, since dust from the abrasive and particles of removed metal float in the air. The grinder must also protect his eyes, for which he wears clear glasses.

Stainless steel heats up from friction with grinding wheels, so the worker must wear gloves to avoid burns. As an analogue of manual grinding, sandblasting units are used, where sand granules are supplied under air pressure, removing the top oxide from the metal.

This is used in enterprises with a large turnover of products. It is not advisable to install such equipment at home.

Polishing

The next stage of stainless steel processing is polishing the welding area, and the entire product, to give the final shine. This further cleans the surface, making it smooth and solid, which prevents the influence of aggressive liquids from the outside.

First, the welding seams are processed with a disk containing vulcanite. This is a rubber-like material, the circle of which is mounted on a drill. Using vulcanite it is possible to give the seam the desired depth and shape, “sawing it down” to create a concave structure. The material is gentle on steel. After this, polishing paste is applied to the already sanded surface.

It may have a diamond composition. Regular GOI paste will do. A felt circle is placed on the drill and longitudinal movements are made over the entire surface. To thoroughly polish the welding areas, small circles are used, which are convenient for reaching areas in corner joints.

Work is carried out until a mirror surface is obtained and there are no matte spots.

Acids and gels

To remove all color transitions after welding and eliminate the oxide layer that promotes corrosion, stainless steel is etched. This refers to the acidic type of material treatment. You can use sulfuric or hydrochloric acid. Analogs, such as fluoride or nitrogen, are also suitable. They are available in the form of gels and pastes. There are also special aerosols. The procedure goes like this:

1. After welding, scale and debris are removed from the surface. A metal brush is used for this.
2. The product is allowed to cool to a temperature of 50 degrees.
3. The composition is applied from above or the structure is immersed in a container with an acidic agent.
4. After 30 minutes, wash off the acid with plenty of water.

It is important for the worker to wear a respirator, since there will be a large amount of vapor in the air that is dangerous to the respiratory system. It is also necessary to protect the skin on your hands by wearing rubber gloves. If acid comes into contact with an open area of ​​skin, rinse the area quickly and thoroughly with plenty of water.

Another processing method is electrochemical etching. To do this, use a container with acid. Two wires emanate from the current source, which are placed into the liquid through a resistance. The product is attached to the “plus”, which consists of a lead plate. The “minus” of the lead plate drops freely into the acid. Closing the voltage in the composition promotes the separation of oxides from the surface of the stainless steel, but prevents oversaturation of hydrogen. The procedure lasts up to 8 minutes.

Thanks to a variety of methods for processing stainless steel, you can achieve a beautiful appearance at the welding site. This is a painstaking process that requires diligence and perseverance, but thanks to such measures, a mirror-like surface is created that will not rust in the future due to the weak oxide layer.

Source: https://svarkalegko.com/tehonology/obrabotka-shvov-nerzhavejki.html

Stainless steel pickling: indications, etching methods and materials

Stainless steel often requires surface treatment to achieve the desired aesthetic or performance properties. Treatment with shot blasting and sandblasting devices is limited due to the high probability of hardening.

Modern production uses etching of stainless steel, after preliminary thermal or mechanical treatment. The complexity of this process, compared to conventional black, low-alloy steels, is explained by the presence of a chromium oxide film that acts as a protective barrier.

It is this that forms hard scale that does not interact well with reagents. Technological influences may cause color changes on the surface. These include welding, soldering, and other operations involving high temperatures. Iridescent tarnish can be removed by etching.

For different chemical compositions of stainless steel, individual pickling methods and compositions have been developed, taking into account the influence of the steel elements, to achieve maximum results.

The predominant methods of etching stainless steels are alkaline and acid, which can be intensified by electrolysis or proceed without it.

Immersion treatment with high concentration acids

The procedure is carried out in specialized areas, since it is associated with the release of saturated acid vapors that are hazardous to health. The technology includes several stages.

1. Dissolving scale by immersing the welded assembly in a bath with a solution of sulfuric (6-8% by volume) and hydrochloric (2-4%) acids. The mixture is heated to 60-80 degrees and left for half an hour. Electrolytic submersible etching helps to destroy the oxide film faster: current is passed through the bath, and the product is connected to the positive or negative pole
2. Intensive rinsing in water.
3. Immersion in a container where nitric (weight fraction -10-20%) and hydrofluoric (1-2%) acids are mixed.
4. Rinse with plenty of water.

Treatment with ready-mixed acids

Preparations for etching welds are produced in the form of pastes, sprays, gels, concentrates containing from 2 to 4 acidic components. It is most convenient to use thick paste-like mixtures. They are laid in a thicker layer, are better retained on vertical surfaces, and their activity manifests itself already at +10°C. The most effective pastes are SAROX TS-K 2000, Avesta BlueOne, Stain Clean (ESAB).

Etching is performed in this order:

1. Removing dirt, rust, degreasing the product with any detergent. The cleansing agent is applied for 30 minutes.
2. Etching. Cover the seams with etching gel or paste, covering 20 cm to the left and right, spray the spray over the entire surface of the product. The exposure time ranges from 10 to 90 minutes - it depends on the concentration of the drug, the chemical composition of the steel, the thickness of the scale, and the ambient temperature.
3. Passivation. A substance is applied that creates a stable layer of chromium oxide on the surface of the stainless steel. Exposure time – 30-60 minutes.

Source: https://instanko.ru/drugoe/travlenie-nerzhavejki.html

Acid etching

The maximum effect of etching stainless steel with acids is achieved by sequential interaction of the stainless steel surface in baths with two types of acids - sulfuric and nitric. The sequence of stages is as follows

1. Degreasing, removal of large snags, scale
2. Pickling in a sulfuric acid bath (concentration 10-12%) or sulfuric acid bath (8% sulfuric acid, 4% hydrochloric acid). In this case, corrosion of scale and roughness on the surface occurs. The ideal temperature for the process is between 60 and 80 degrees Celsius. Monitoring this parameter is important for process control. The duration of treatment depends on the steel grade, the presence of a controlled ratio, and the concentration of acids. If the bath is depleted, pitting corrosion may occur. For example, steel with 18% Cr, 8% Ni requires 23 to 45 minutes of pickling in a sulfuric acid bath. Reducing the processing time by half can be achieved if this operation is carried out in a controlled atmosphere.
3. Rinsing with plenty of running water
4. Immersion of the workpiece in a bath filled with a solution of nitric acid and hydrofluoric acid (10 - 20, 1-2 weight percent, respectively). At a bath temperature of 60–70 degrees, the treatment time is 7–15 minutes.
5. Repeated rinsing with large volumes of water

The presented method is basic and has many variations. Etching in one nitrate bath with an admixture of hydrofluoric acid increases the etching time to 30 minutes. Sodium fluoride can act as a substitute for hydrofluoric acid. Increasing the concentration of hydrofluoric acid to 10% allows the process to be carried out at low temperatures, avoiding preliminary immersion in sulfuric acid.

Reducing the etching time in sulfuric acid can be achieved by adding no more than 5% sodium chloride. This move gives the desired effect in 15 minutes, but at the same temperature, about 80 degrees Celsius.

Be careful: if it is necessary to carry out the procedure in a room with insufficient aspiration, replace the components of the second stage of etching. Acids produce harmful fumes when etching. A solution of ferrous sulfate (7%) and hydrofluoric acid (2%) is proposed as a replacement.   

To correctly select the acid etching method, you need to know and take into account the state of the oxide film on the surface of stainless steel. Appearance can tell you about the composition of the film. The green color of the scale indicates a high content of chromium oxides. Accordingly, the action of acidic environments will be difficult and will require more time.

Intermediate mechanical cleaning between two baths is recommended if descaling is difficult.

Electrolytic etching

One option common in modern factories is electrolytic etching. A workpiece or part placed in an acid bath is connected to a positive or negative terminal. When current passes through the surface of stainless steel, oxygen is released. The gaseous phase has a mechanical effect on the oxide film. This helps speed up the processing process and the quality of the resulting surface.

Etching with ready-made pastes

Modern industry offers a variety of stainless steel pickling pastes . Their main purpose is local processing of welds, the consequences of changes in the uniformity of surface coloring under the influence of temperature. The principle of working with such pastes is simple and can be used even in small workshops.

• Apply the paste in a thick layer up to 2 cm, using a brush
• Exposure 60-90 minutes
• Water jet rinsing

The use of pastes is advisable for processing welding seams of stainless steel grades. The treated seam is able to resist corrosion even in the damp conditions of a car wash.

Alkaline etching

Treating the surface of stainless steel with molten caustic soda is called alkaline etching. It should be noted that during this process the oxide film is destroyed, while the chemicals do not react with the metal. An increase in temperature promotes corrosion of the oxide film, improving the quality of the treated surface. Rapid cooling in liquid also helps to improve the treated surface.  

It is almost impossible to achieve 100% results with this type of processing. Residual films from chromium oxides, nickel and iron oxides are possible on the metal. Among the recommendations for final finishing of such defects is a short-term treatment in a nitrate bath.

Alkaline etching methods

The following methods are distinguished:

• Aging in soda. sodium nitrate should fluctuate between 20-40%, heated to a temperature of 460-500 degrees Celsius. Etching in such an environment lasts for 15 minutes. Some austenitic grades of stainless steel are prohibited from being heated above 450 degrees. This can lead to intergranular corrosion. This is followed by a rinsing step in a large amount of water, followed by a 5-minute immersion in a sulfuric acid bath and up to 10 minutes in a nitrate bath.
• Known in England since the first half of the 19th century, the etching method is combined with passing an electric current through the part being etched. At a current density of 11 A/m2, 15 seconds is sufficient. This reaction rate is associated with the electrolysis process. The release of sodium and hydrogen at the cathode contributes to the reduction of oxides. The reduced metal is deposited on the surface. This type of etching allows you to obtain degreased metal, characterized by purity and uniformity. This method uses soda. Variations are possible with the composition and addition of calcium chloride. This method is used for etching flat, rod blanks, and drawn products.
• Treatment with sodium hydrides is based on reduction by exposing the metal to sodium and hydrogen. The presence of sodium hydride is achieved by the interaction of hydrogen and sodium, which is in a molten state. A cylinder without a bottom plane is placed in molten caustic soda. The top plane has a hole. Sodium is poured into this hole, it reacts on the surface of the bath. A stream of hydrogen is passed through a spot of sodium on caustic soda. A hydride is formed and diffuses throughout the bath. Achieving the required concentration of 1-2% sodium hydride occurs within controlled threshold values. In the absence of an air separation product, dissociated ammonia is used. The parts are heated in such a bath to 400 degrees Celsius. Stainless steels show good pickling results with this technique and duration of 4-17 minutes. After etching, it is recommended to thoroughly rinse the parts. If necessary, carry out additional treatment in a nitrate bath. Given the high cost of this method, its obvious advantage is the fact that the metal does not interact with the etchant. Metal losses are minimal. Lower process temperatures reduce coolant costs and reduce operational safety.

Read also: Polishing stainless steel: techniques and tools

There are certain rules that must be followed for any of the presented methods. Among them, priority is the treatment of the metal surface before etching, removal of the oxide film, and degreasing. The etching process is no less important.

Bath materials   

Choosing the right material for making etching baths is a difficult task for chemists and materials scientists.

Recommended containers:

• ceramic coated
• glass covered brick
• wood, lead-coated concrete
• rubber derivatives
• Certain grades of stainless steel for acid baths.

nitrogenous with impurities of hydrofluoric or hydrochloric acid allows the use of the same materials. The only exceptions are lead as a coating, ceramics with a high silicon content, due to their interaction.

It is quite possible to use steel in alkali baths, monitoring the progress and intensity of electrolysis in close proximity to the material.

Under certain conditions and acid content, its temperature, and nature, it is possible to use stainless steel grades for pickling tanks. Such, for example, as 8Х18Н8М or 10Х20Н25М4.

From the information provided in this review, we can conclude that the processing mode, the chemical composition of the bath, the need for additional mechanical processing, and the use of electrolysis should be determined based on specific initial conditions (steel grade, state of the oxide film, technological capabilities) and regulated in the context of the expected final result .

Source: http://solidiron.ru/steel/travlenie-nerzhaveyushhejj-stali-pokazaniya-metody-travleniya.html

Stainless steel pickling

Pickling stainless steel is an important process that ensures the removal of the top layer of material and restoration of the original state.

The bottom line is that after certain work is carried out, defects in the form of welds, oxides and scales can form on the surface of the stainless steel, which can significantly spoil the appearance of the material, as well as worsen the operational and aesthetic properties. A distinctive feature of steel is the presence of an oxide-chrome film, the purpose of which is to protect the top layer.

It is because of this that the above defects arise, which are difficult to interact with reagents. If such troubles occur, you can correct the situation by using a special procedure - etching stainless steel.

Stainless steel pickling procedure

Chemical and electrochemical treatment or etching is considered one of the best ways to clean the top layer of stainless steel. This procedure perfectly cleans the steel surface from welds, eliminates various types of deformations, and also helps strengthen the structure of the alloy after heat treatment. In addition to cleaning properties, the procedure ensures the restoration of the passive layer of steel, which is necessary to protect the alloy from structural destruction at elevated temperatures.

The essence of cleaning 12x18n10t steel is the chemical interaction of the top layer with a concentrated acid solution. Typically, hydrochloric or sulfuric acid is used, after which a mixture of molten alkali is used. The acid cleaning process has two stages: first of all, the metal is treated with a basic acid composition, and finally the alloy is kept in a bath with a solution of nitric acid.

When processing stainless steel, you should strictly follow the stages of the technological process. The container with the solution in which the alloy is placed should process only the upper layers of the metal, further eliminating existing damage. It is not recommended to allow changes in the macrostructure of stainless steel, as iron may lose its original properties.

Application of etching

The etching process is widely used in production during the cleaning of the upper layers of steel from welds, scale, oxides and rust. It is used when searching for internal defects by removing the top layer of the workpiece or to study the structure of the metal.

This procedure cleans the material, thereby increasing the adhesion of the top layer. This is necessary for the successful connection of a metal workpiece with another surface, after which a paint, enamel, galvanic layer or other protective coating is applied.

This type of processing not only ensures quick cleaning of the workpiece, but also creates a specified pattern on the top layer of metal. Using etching, you can cut out a channel of any thickness or create a complex image.

Processing of large workpieces and rolled products is also possible. You can easily adjust the processing depth down to microns, making it possible to process surfaces with complex areas and small grooves.

The procedure is used to carry out analysis that determines the formation of intercrystalline corrosion in stainless steel.

In addition, this process is widely used during the processing of carbon, low-alloy and high-alloy steels, non-ferrous metals and titanium. This technology is indispensable when processing small metal parts, watch gears. It is used to manufacture semiconductor chips and printed circuit boards in electronics.

This processing method ensures the formation of a conductive channel on the microcircuits. In aircraft manufacturing, etching plays an important role, since through this process the thickness of metal sheets is reduced, thereby reducing the weight of the aircraft. This operation also plays a big role in applying drawings and inscriptions.

Etching produces a relief image created by destroying a metal surface according to specific patterns. In everyday life, the operation helps clean the pipeline.

The following types of processing are used at home and at production sites:

• Acid cleaning;
• Electrolytic cleaning;
• Cleaning with pastes.

Pickling stainless steel at home - Machine tools, welding, metalworking

Stainless steel often requires surface treatment to achieve the desired aesthetic or performance properties. Treatment with shot blasting and sandblasting devices is limited due to the high probability of hardening.

Modern production uses etching of stainless steel, after preliminary thermal or mechanical treatment. The complexity of this process, compared to conventional black, low-alloy steels, is explained by the presence of a chromium oxide film that acts as a protective barrier.

It is this that forms hard scale that does not interact well with reagents. Technological influences may cause color changes on the surface. These include welding, soldering, and other operations involving high temperatures. Iridescent tarnish can be removed by etching.

For different chemical compositions of stainless steel, individual pickling methods and compositions have been developed, taking into account the influence of the steel elements, to achieve maximum results.

The predominant methods of etching stainless steels are alkaline and acid, which can be intensified by electrolysis or proceed without it.

DIY stainless steel matting

Processing of stainless steel, which can be performed using various methods and technologies, allows not only to provide products made of this metal with the required parameters and quality characteristics, but also to give their surface an attractive appearance. By correctly selecting and using various processing methods, stainless steel alloys are used to produce products for various purposes that fully meet the requirements for them.

Mechanical processing of stainless steel with electric tools allows you to quickly remove roughness from the surface

Sanding and polishing (satinizing)

Thanks to a whole list of advantages, stainless steel is equally successfully used for the manufacture of products for both practical and purely decorative purposes.

To give their surface an attractive appearance, as well as to achieve the required level of roughness, they are often subjected to grinding and polishing, which are referred to by one general term - satin.

These processing methods received this name due to the fact that after their implementation, the surface of the stainless steel resembles satin or satin fabric in its texture.

Processing a weld seam on a stainless steel begins with removing the surface to small scratches using a grinder with a flap wheel

In addition to giving the surface of a stainless steel product an attractive appearance, grinding can eliminate surface defects in the metal or make them almost invisible. Both grinding and polishing of stainless steel can be done manually or using special devices powered by an electric or pneumatic drive. The most common devices used for grinding include:

• belt type pneumatic file;
• drum-belt type sander;
• other devices that require the use of sanding belts.

At home, sanding is most often done by hand, which may require sanding sheets or tools called sanders. Unlike the conditions of home workshops, in manufacturing enterprises, stainless steel grinding is carried out using special equipment.

Stainless steel grinding begins with grit 180, then 320 and 600, and ends with polishing with a felt wheel.

When hand grinding tools are used to grind stainless steel, the processing is performed in the following sequence.

1. If stainless steel parts were connected by welding, then burn marks and weld seams are removed from their surface.
2. The part of the surface that will be sanded first should be limited using adhesive aluminum tape (it is glued in two or three layers).
3. The area of ​​the surface that is not sealed with protective tape is processed using a reciprocating grinding motion, and the pressure exerted on the tool should not be too strong.
4. After achieving the required grinding result, the already processed part is sealed with aluminum tape, and the area that borders it is subjected to processing.

In cases where the use of grinding is impractical, grinding sheets are used to process stainless steel. To correctly select such a grinding tool based on its grain size, use trial rough parts.

For grinding and polishing stainless steel, lathes on which special wheels are installed can also be used. You can perform such finishing operations using a lathe both in production and at home, if such equipment is available in your home workshop. To effectively perform these technological operations, even the simplest models of lathes can be used.

Etching method

Pickling is a fairly common method for processing stainless steel products.

This technological operation, which makes it possible to remove various defects from the surface of a stainless steel product, is used to eliminate welding marks after performing heat treatment, as well as processing parts using plastic deformation methods.

In addition, etching allows you to remove tarnish from the stainless steel, and also renews the passive layer on it, which protects the metal from the effects of elevated temperatures.

To perform etching in production conditions, aqueous solutions of acids or molten alkaline media are used.

When using acidic media, etching is performed in two stages, the first of which involves treating stainless steel with a sulfuric acid solution, and the second with a solution based on nitric acid.

To perform alkaline etching, a stainless steel product is placed in a melt of caustic soda, which, without changing the structure of the steel, effectively destroys the oxide film formed on its surface.

You can return the metallic shine to a stainless surface and restore the loss of chromium after welding using etching paste.

At home, etching is performed using special pastes that have a jelly-like consistency. When using such pastes, it should be borne in mind that in addition to hydrofluoric and nitric acid, their composition includes hydrochloric acid, as well as chlorides, which pose a danger to human health, so they should be handled with extreme caution.

Paste for etching stainless steel should be applied only to a thoroughly cleaned and degreased part, for which it is washed with warm water and treated with any available detergent. After a short exposure (from 10 to 60 minutes), the etching paste is washed off, for which ordinary running water is also used. Pastes for etching stainless steel are applied with acid-resistant brushes and special plastic spatulas.

Large areas of stainless steel surfaces are treated with etching sprays using jet spraying

This paste provides reliable protection of stainless steel from the negative effects of temperature, and also eliminates all surface defects of welded joints. Conveniently, this paste, which effectively processes a steel product in just 10 minutes, can be used for etching vertical surfaces as well.

Using such a paste, the exposure time of which on the surface of the product should be about 45 minutes, you can not only eliminate minor defects in welded joints, but also clean the stainless steel from traces of corrosion and give it a beautiful metallic shine. When choosing such a composition, you should keep in mind that it can only be used for processing stainless steel at an ambient temperature of at least +50.

Source: https://moy-instrument.ru/podelki/matirovanie-nerzhaveyushhej-stali-svoimi-rukami.html

Grinding stainless steel after welding: technology, equipment and materials, nuances

A large number of novice welders are surprised by the fact that rust appears on the surface of stainless steel. After all, it would seem impossible. The very name “stainless steel” says that stainless steel does not change its properties over time.

But the reason is not at all in the characteristics of the material, but in violations of processing rules - the lack of grinding in particular. Or no seam treatment at all after welding.

Small factories often hire inexperienced employees who do not know all the nuances of robots with different materials.

Skipping the preparatory or final stage of working with stainless steel, as a result we receive a low-quality product. In small enterprises, product quality is not properly controlled.

Then a product with untreated seams will end up on the market. This leads to subsequent corrosion of the material. Yes, these issues do not arise in large enterprises. But in a small workshop it occurs. Therefore, we will immediately clarify all the stages of grinding.

Grinding

One of the main methods of processing seams after welding is grinding. In the photo below you can see the difference before and after the procedure.

After grinding, stainless steel looks much neater. She acquired a shine and well-groomed appearance. The metal becomes much stronger and better quality.

There are two main types of sanding: modern and classic. Each has its own pros and cons. Some speed up the work process. Others make the seams stronger. You can find all the necessary information about each method in this article.

A file, sandpaper or any other sanding tool is the main thing we need, regardless of the sanding method.

We can use our own strength or use a grinding machine. The latter is faster and more convenient to work with, but at home you can simply use sandpaper and your own hands for sanding.

Grinding is carried out in two stages. The first approach involves rough grinding, when the surface needs to be made as smooth as possible, without obvious irregularities.

If you work with a grinding machine, you need to use a disc after working through all the seams. This is in general, and then we will analyze the whole process in detail step by step.

Sanding Basics

To begin with, we suggest clarifying how stainless steel seams are polished. First, pay attention to the safety rules.

Using a special protective mask, overalls and welding glasses will prevent dirt and dust from getting into your nose and eyes.

If you need to get rid of deep scratches or obvious irregularities, you should use grinding heads with abrasive belts.

Selecting the desired width of the tape, focusing on the surface we are working with. The larger the surface volume of the product, the wider the tape used should be.

As mentioned earlier, stainless steel must be processed in several approaches.

A minimum of two passes is made, but in large enterprises four and five passes of grinding are done to increase the quality of the original product. This is where professional tools will help you.

Next we will talk about abrasive sanding belts. They come on a fabric or paper base. Based on the quality of the steel itself, we select the grain size of the tape, since there is no single correct and universal recommendation for choice.

There are also waterproof versions of the tape. It is used for wet sanding of seams.

It will be good to have a grinder and wood glue for work. With the help of the first, you can remove the sagging that occurs after welding, and with the help of the second, you can strengthen and level it. It is applied to the seam and treated with an abrasive tape.

Next, you need to sand the surface several more times. It must be thoroughly cleaned of metal dust and glue residues after each grinding stage. As a result, you will have a shiny, smooth product, without scratches or defects.

Next, we will need grinding paste and a grinding wheel, which is made of a soft material. Felt is best. The quality of the mouth is not so important; you can even make it yourself using instructions from the Internet.

Stainless steel processing

Pickling is one of the most popular methods for treating stainless steel seams. Here hydrochloric, sulfuric or nitric acids are used. For comfort, take acid in the form of a spray or paste, because the liquid version is not so convenient.

For etching, we practice using a thick paste, applying it in a thick layer with a special brush.

Be sure to ventilate the room in which you work with acids, since they have a very specific odor and negatively affect the human respiratory tract.

When using liquid acid, you must strictly follow safety rules. The first step is to rinse the surface of the part under water, then place the part in a container with acid.

Then rinse the part again. After reading the acid instructions, you can find out in detail the required immersion time for the part.

Again, we draw your attention to the safety rules. Never neglect your protective mask and suit. Let me explain why. Stainless metal, when working with acids, emits steam.

It poses a huge danger to human skin and respiratory tract!

The electrolytic method is another method for etching seams on stainless steel. We place the pre-washed part in a container with liquid acid and connect a current source, which can be constant or alternating.

A passivator may also be useful. This substance has special characteristics. It puts stainless steel into a passive state.

Using a passivator, you can clean seams inexpensively. As with acid, you apply it directly to the seams or dip the part in a container.

Let's sum it up

Now you know all the basics about how to clean stainless steel after welding and polish it to a perfect, smooth state.

This is what separates a professional from a beginner. An expert in his field looks comprehensively at the entire scope of work, while a beginner pays attention only to creating a seam, forgetting about all the stages of work.

Share your own grinding experience in the comments, it is very important for novice welders. How do you treat seams after welding? How do you prepare stainless steel? We are waiting for your answers. Good luck in your endeavors!

Source: https://prosvarku.info/tehnika-svarki/shlifovka-nerzhavejki-posle-svarki

Stainless steel processing methods: the most popular options

Processing of stainless steel, which can be performed using various methods and technologies, allows not only to provide products made of this metal with the required parameters and quality characteristics, but also to give their surface an attractive appearance. By correctly selecting and using various processing methods, stainless steel alloys are used to produce products for various purposes that fully meet the requirements for them.

Mechanical processing of stainless steel with electric tools allows you to quickly remove roughness from the surface

Other methods of processing stainless steel products

Products made from stainless steels are often chrome-plated, which allows:

• give them an attractive appearance;
• increase resistance to mechanical stress (friction, shock, etc.);
• significantly increase their corrosion resistance.

Meanwhile, a high-quality chrome plating operation can only be performed under production conditions, since its implementation requires not only special consumables and special equipment, but also the availability of appropriate knowledge and skills.

The photo shows stainless steel welds after treatment with 85% phosphoric acid - the result of etching looks no worse than mechanical polishing

At home, you can perform another operation that allows you to give the surface of a stainless steel product an attractive appearance - bluing. Such processing can be performed using one of the following methods:

• acid exposure;
• use of alkalis;
• application of thermal influence.

Of course, the simplest and most affordable method of finishing steel products is painting them, which can also be done using various technologies and consumables.

Source: http://met-all.org/stal/obrabotka-nerzhaveyushhej-stali-travlenie-shlifovanie-satinirovanie.html