A Concise Guide to Welding Stainless Steel

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.

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. Why use 98%Ar+2%O2 shielding gas for solid stainless steel welding wire?

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 a word, hope this article will be helpful to your application in actual production and manufacturing.