In today’s industry, stainless steel has become a widely used material, and its unique corrosion resistance and high strength make it suitable for many applications, such as food processing, pharmaceuticals, aerospace, etc. However, the process of welding stainless steel requires special skill and knowledge to ensure the quality and stability of the welded joint. This article is intended to provide a concise guide to the basics and techniques of welding stainless steel for those wishing to learn the skill. Whether you are an engineer, a technician, or a DIY enthusiast, you can find useful information and advice in this article to ensure you get the best results when welding stainless steel.
About Stainless Steel
Stainless steel is an alloy material consisting of iron, chromium, nickel, and other alloying elements. It gets its name from its corrosion-resistant properties. Stainless steel materials can be divided into many different types, each with different chemical compositions and properties. Among them, the most commonly used types are 304 and 316 stainless steel.
Type 304 stainless steel is typically used in room-temperature applications such as food processing equipment, medical equipment, construction materials, etc. It contains 18% chromium and 8% nickel and has good corrosion resistance and plasticity.
316 stainless steel contains 2%-3% molybdenum, which makes it have higher corrosion resistance and chloride corrosion resistance, and is usually used in marine and chemical equipment.
Regardless of the type of stainless steel, they all have high strength and wear resistance and can be processed and plastically deformed by heat treatment and cold working. These characteristics make stainless steel widely used in industrial production. However, due to the high hardness and chemical composition of stainless steel, welding stainless steel requires special skills and knowledge to ensure the quality and stability of welded joints.
Preparation Before Welding Stainless Steel
Preparation before welding is one of the most important steps in welding stainless steel. Proper preparation ensures the stability of the welding process and the quality of the welded joint. Before welding stainless steel, the following two preparations need to be done:
Prepare the Surface for Welding
The preparation of the welding surface is one of the important factors to ensure the quality of welding. Before welding stainless steel, it is necessary to remove grease, dirt, and oxides on the welding surface, lest these impurities have an adverse effect on welding. Generally speaking, it can be cleaned with a brush, sandpaper, or other cleaning tools. If you are welding larger stainless steel components, you will need to use a grinder or other mechanical tool for surface preparation.
Prepare Suitable Welding Equipment and Welding Materials
Selecting the proper welding equipment and welding consumables is critical to the success of the welding process. When welding stainless steel, it is necessary to select welding equipment and materials suitable for stainless steel. Generally speaking, the use of argon arc welding or plasma arc welding is a more common choice. At the same time, it is necessary to select the appropriate welding current, electrode, welding wire, etc. according to the material type and thickness of the stainless steel. When selecting welding materials, it is necessary to ensure that the chemical composition of the welding materials matches the stainless steel base material to ensure the quality and stability of the welded joints.
Before welding stainless steel, it must be ensured that the surface and material preparation has been done and that the welding equipment has been set to the appropriate parameters. These preparations can help the welding process to run smoothly and ensure the quality and stability of the welded joint.
Choose the Proper Welding Method
When welding stainless steel, it is very important to choose the appropriate welding method. Different welding methods have different advantages and disadvantages for different types of stainless steel. The following are several common welding methods:
Argon Arc Welding
Argon arc welding is one of the most commonly used methods for welding stainless steel. It uses pure argon as a shielding gas to prevent air contamination of the welding area. Argon arc welding is suitable for most types of stainless steel and can weld thinner stainless steel components. The welding quality of argon arc welding is high, the welding joint is flat, and there are no oxides and other impurities in the weld.
Plasma Arc Welding
Plasma arc welding is a high-energy welding method that uses plasma as the welding source. The plasma can provide enough heat to melt the stainless steel and produce good fusion in the welded joint. Plasma arc welding is commonly used to weld thicker stainless steel components, and it can weld large pipes, vessels, and other equipment.
TIG Welding
TIG welding is a manual welding method that uses a thin welding wire and a handheld argon arc torch for welding. TIG welding can control the speed and temperature of welding, so it is very suitable for welding small and delicate stainless steel components. The advantage of TIG welding is that the welded joint is flat and free of oxides and other impurities, but it requires a highly skilled operator to control the quality and speed of the weld.
Choosing the proper welding method depends on the type of stainless steel, its thickness, application, and other factors. Before welding stainless steel, it is necessary to evaluate different welding methods and choose the most suitable method to ensure the quality and stability of welded joints.
Perform Welding
When welding stainless steel, the welding needs to be performed according to the following steps:
Clean Welding Area
Before welding stainless steel, the welding area needs to be cleaned to ensure the quality of the welded joint. Any grease, dust, or other contaminants can negatively affect welding. Therefore, detergents and solvents are used to clean the welding area before welding.
Prepare Welding Materials
Welding stainless steel requires the use of specialized welding consumables that have similar properties and chemical compositions to stainless steel. When selecting welding materials, the type, thickness, and application of the stainless steel need to be considered. The choice of welding material also depends on the type of welding method.
Adjust Welding Equipment
Before welding, the welding equipment needs to be adjusted to ensure that it can meet the requirements of welding stainless steel. This includes selecting the proper welding gun, the proper welding current and voltage, and the proper gas flow.
Start Welding
Once the prep work is complete, welding of stainless steel can begin. During the welding process, the welding speed and temperature need to be controlled to ensure the quality and stability of the welded joint. At the same time, it is necessary to keep the welding area clean and use shielding gas to prevent the welding area from being polluted by air.
Complete Welding and Subsequent Processing
Once welding is complete, the welded joint needs to be inspected to ensure it meets the requirements. If the welded joint is defective, it needs to be repaired. Before subsequent processing, the welded joint needs to be cooled to avoid thermal deformation. Subsequent treatments include grinding and polishing the welded joints to improve their appearance and corrosion resistance.
Soldering needs to be performed with care, speed, and temperature of the weld to ensure the quality and stability of the welded joint. Any improper operation may affect the quality and performance of the welded joint, so it needs to be operated according to the specific welding requirements.
Quality Control and Postprocessing
After welding stainless steel, quality control, and post-processing are required to ensure the quality and durability of the welded joint.
QC
Welded joints require quality control to ensure they meet requirements. Common quality control methods include X-ray testing, ultrasonic testing, and eddy current testing, among others. These methods can detect cracks, pores, inclusions, and other defects in welded joints to ensure the quality of welded joints.
Post-Processing
It is necessary to wait for the welded joint to cool completely before post-processing. Post-processing includes grinding, polishing, pickling, and electrochemical polishing. Grinding and polishing smooth the surface of welded joints and improve their appearance and corrosion resistance. Pickling removes contaminants and oxides from welded joints to improve their corrosion resistance. Electrochemical polishing can make the surface of welded joints smoother.
packaging and Shipping
Once welded joints pass quality control and post-processing, they need to be packaged and shipped. Moisture-proof, anti-corrosion, and shock-proof materials need to be used in packaging to avoid damage to welded joints during transportation.
In conclusion, for welding stainless steel, quality control, and post-processing are very important. Only through these measures can the quality and durability of welded joints be ensured and thus meet the various application requirements.
Eight Precautions for Stainless Steel Welding
1. Chromium stainless steel has certain corrosion resistance (oxidizing acid, organic acid, cavitation), heat resistance, and wear resistance. It is usually used for power stations, chemicals, petroleum, and other equipment materials. The weldability of chromium stainless steel is poor, so attention should be paid to the welding process and heat treatment conditions.
2. Chromium 13 stainless steel has greater hardenability after welding and is prone to cracks. If the same type of chromium stainless steel electrode (G202, G207) is used for welding, preheating above 300°C and slow cooling treatment at about 700°C after welding must be carried out. If the weldment cannot be subjected to post-weld heat treatment, chromium-nickel stainless steel electrodes (A107, A207) should be used.
3. Chromium 17 stainless steel, to improve the corrosion resistance and weldability, an appropriate amount of stability elements Ti, Nb, Mo, etc. are added appropriately, and the weldability is better than that of chromium 13 stainless steel. When using the same type of chromium stainless steel electrode (G302, G307), it should be preheated above 200°C and tempered at about 800°C after welding. If the weldment cannot be heat treated, chromium-nickel stainless steel electrodes (A107, A207) should be used.
4. When chromium-nickel stainless steel is welded, carbides are precipitated after repeated heating, which reduces corrosion resistance and mechanical properties.
5. Chromium-nickel stainless steel electrodes have good corrosion resistance and oxidation resistance and are widely used in chemical, fertilizer, petroleum, and medical machinery manufacturing.
6.
7. The electrode should be kept dry when in use. The calcium-titanium type should be dried at 150°C for 1 hour, and the low-hydrogen type should be dried at 200-250°C for 1 hour (do not repeat the drying multiple times, otherwise the coating will easily crack and peel) to prevent the welding rod Skin sticky oil and other dirt, so as not to increase the carbon content of the weld and affect the quality of the weldment.
8. To prevent corrosion between the eyes due to heating, the welding current should not be too large, about 20% less than the carbon steel electrode, the arc should not be too long, the interlayer cooling is fast, and the narrow welding bead is better.
9 Major Problems of Stainless Steel Welding
1. What are stainless steel and stainless acid-resistant steel?
Answer: The content of the main element “chromium” in the metal material (other elements such as nickel and molybdenum are also required) can make the steel in a passivated state and have the characteristics of stainless steel. Acid-resistant steel refers to steel that resists corrosion in strongly corrosive media such as acid, alkali, and salt.
2. What is austenitic stainless steel? What are the commonly used grades?
Answer: Austenitic stainless steel is the most widely used and has the most varieties. like:
〈1〉18-8 series: 0Cr19Ni9 (304) 0Cr18Ni8 (308)
〈2〉18-12 series: 00Cr18Ni12Mo2Ti (316L)
〈3〉25-13 series: 0Cr25Ni13 (309)
〈4〉25-20 series: 0Cr25Ni20 etc.
3. Why is there a certain technological difficulty in welding stainless steel?
Answer: The main process difficulty is: <1> Stainless steel materials have strong thermal sensitivity, and the residence time in the temperature zone of 450-850℃ is slightly longer, and the corrosion resistance of welds and heat-affected areas is seriously reduced. 〈2〉 Hot cracks are prone to occur. 〈3〉Poor protection, serious high-temperature oxidation. 〈4〉The linear expansion coefficient is large, resulting in large welding deformation.
4. Why do we need to take effective process measures for welding austenitic stainless steel?
Answer: The general process measures are: <1> We must strictly select welding materials based on the chemical composition of the base metal. 〈2〉Small current, fast welding; small wire energy, reduce heat input. <3> Thin-diameter welding wire, welding rod, non-oscillating, multi-layer, and multi-pass welding. 〈4〉Forced cooling of welding seam and heat-affected zone reduces the residence time of 450-850℃. 〈5〉Argon gas protection on the back of TIG weld. <6> Welds in contact with corrosive media are finally welded. 〈7〉Passivation treatment of welding seam and heat-affected zone.
5. Why should we use 25-13 series welding wires and electrodes for welding austenitic stainless steel, carbon steel, and low-alloy steel (dissimilar steel welding)?
Answer: For welding joints of dissimilar steels connected with austenitic stainless steel, carbon steel, and low alloy steel, 25-13 series welding wires (309, 309L) and welding rods (Austenitic 312, Austrian 307, etc.) must be used as the weld deposit metal. If other stainless steel welding consumables are used, a martensite structure will be produced on the fusion line of carbon steel and low alloy steel, which will cause cold cracks.
6.
Answer: When using solid stainless steel wire for MIG welding, if pure argon gas protection is used, the surface tension of the molten pool will be large, and the weld will be poorly formed, showing a “humpback” weld shape. Add 1-2% oxygen to reduce the surface tension of the molten pool, and the weld seam is formed smooth and beautiful.
7. Why is the surface of the solid stainless steel wire MIG welded seam black?
Answer: The MIG welding speed of solid stainless steel wire is relatively fast (30-60cm/min). The shielding gas nozzle has run to the front molten pool area. The welding seam is still in a state of red hot and high temperature. black. The pickling passivation method can remove the black skin and restore the original surface color of stainless steel.
8. Why do solid stainless steel welding wires need to use a pulsed power supply to achieve jet transition and spatter-free welding?
Answer: When using solid stainless steel wire for MIG welding, φ1.2 wire can realize jet transfer only when the current I≥260—280A; droplets below this value are short-circuited transfer, with large splashes, and generally cannot be used. Only by using a pulsed MIG power supply with a pulse current greater than 300A, can the pulse droplet transition under a welding current of 80-260A be realized without spatter welding.
9. Why is the flux-cored stainless steel welding wire protected by CO2 gas? Don’t need a pulsed power supply?
Answer: Currently commonly used flux-cored stainless steel welding wire (such as 308, 309, etc.), the welding flux formula in the welding wire is developed according to the welding chemical metallurgical reaction under the protection of CO2 gas, so it cannot be used for MAG or MIG welding; Pulsed arc welding power source.
In Conclusion
In this article, we have covered the basics and procedures for welding stainless steel. First, we learned about the properties of stainless steel and the types of stainless steel, and their applications. Then, we introduce the preparation work before welding in detail, including cleaning, clamping, preheating, and selecting appropriate welding materials. Then, we explore different welding methods, including TIG welding, MIG welding, and shielded arc welding, and analyze the characteristics and scope of application of each. Next, we introduce the precautions and quality control methods during the welding process, as well as the post-processing and packaging methods after welding. Finally, we emphasize the importance of quality control and post-processing to ensure the quality and durability of welded joints.
In a word, this article provides you with a concise and practical stainless steel welding guide, hoping to be helpful to your application in actual production and manufacturing.