Brazing properties of various stainless steels

Welding Characteristics of Various Types of Stainless Steel

Stainless steel is a highly versatile material used in various industries. It is well-known for its corrosion resistance and its ability to be welded and fabricated into strong products. Welding stainless steel requires skill, practice and some specialized welding knowledge. This article will discuss the welding characteristics of various types of stainless steel and how to achieve a successful weld.

Different Types of Stainless Steel

Stainless steel is made up of different alloys of chromium, nickel and molybdenum. The makeup of stainless steel determines its welding characteristics. Type 304 stainless steel is one of the most widely used alloys in stainless steel fabrication. It is a non-magnetic austenitic stainless steel and is relatively non-hardenable on weld heat-affected zones. Type 309 stainless steel is magnetic due to the addition of chromium-nickel and is used in welding dissimilar steels and for applications demanding high erosion-corrosion resistance. Type 316 stainless steel is a non-magnetic stainless steel and is used for welding molybdenum-bearing austenitic steels, particularly highly corrosion resistant austenitic steels.

Welding Techniques

When welding stainless steel, it is important to use the correct welding techniques in order to achieve a successful weld. Utilizing popular advanced solutions such as TIG welding (Tungsten Inert Gas), which is suitable for most stainless steel welding applications and MIG/MAG welding (Metal Inert Gas/Metal Active Gas) welds, which are appropriate for more demanding applications such as welding under water, is recommended. It is also important to use the correct materials such as flux-cored wires, flux and cored electrodes, as well as properly selected shielding gases.

Welding Characteristics

The weldability of various types of stainless steel is influenced by its composition and microstructure. When welding Type 304 stainless, there is no significant loss of strength and ductility in the weld region even after long-term exposure at elevated temperatures. The ferritic component of the weld helps to resist hot cracking, which can be a problem when welding highly austenitic materials. For Type 309 stainless, a pre-heat of the weld area is recommended to reduce hot cracking concerns. Type 316 stainless is more resistant to hot cracking, but is still susceptible to hot cracking at extreme temperatures due to its higher molybdenum content.

Welding Considerations

When welding stainless steel, there are some important considerations to keep in mind. Water cooling should be avoided when welding as it can cool the weld area too quickly, causing the material to become hardened and more difficult to weld. Preheat and post-heat treatments are recommended to optimize weld integrity and to minimize distortion and reduce residual stresses. Lastly, proper welding techniques and materials should be used in order to achieve the highest quality weld and to avoid weld failure.

Conclusion

Welding stainless steel can be challenging and requires proper technique and knowledge to ensure a successful weld. Different alloys of stainless steel have varying welding characteristics, so it is important to understand the composition of the stainless steel in order to choose the right welding method. Following the considerations and welding techniques outlined in this article will help to ensure a successful weld when working with stainless steel.

Welding is an important process in many steel manufacturing processes, and although welding of stainless steels is often seen as more difficult than welding of mild steel, advances in filler metals have made this much more accessible. The following article details the properties of stainless steel and the most suitable welding techniques.

Stainless steels are relatively low carbon steels with a chromium content of at least 10%. This chromium content gives the steel its key corrosion resisting properties and also helps to form a passive layer of chromium oxide on its surface.

Welding of stainless steels generally has a higher heat input compared to mild steel. This is because the thermal conductivity of stainless steel is lower than that of mild steel. Additionally, stainless steels have a higher coefficient of thermal expansion compared to mild steels and this can lead to distortion. This distortion can be further exacerbated when welding stainless steel to mild steel.

The two most common welding processes for stainless steel are MIG (metal inert gas) welding and TIG (tungsten inert gas) welding. MIG welding is used for thinner sections of stainless steel while TIG welding is used for welding thicker sections. When welding stainless steels, the use of filler metal is required. This filler metal should match the composition of the base material, typically with a slightly higher ferrite content than the base material.

The main benefits of welding stainless steels are their excellent corrosion and heat resistance, strength and low maintenance requirements, making them an ideal choice for a wide variety of applications. In summary, welding of stainless steel is possible, however it requires greater levels of attention to detail due to its higher heat input and coefficient of thermal expansion. By paying attention to the materials, the technique and using suitable filler metals, it is possible to produce sound welds in stainless steel.