How to Weld Stainless Steel Pipe Ferritic?

As a Welded Pipe Stainless Steel Supplier, share with you.

Stainless Steel Pipe Ferritic generally has a pure ferrite structure at room temperature, which is not very high in strength, ductility and good toughness; if it is heated to high temperature, a small amount of austenite structure may also appear (lower for chromium Steel) or no austenite structure appears at all. Therefore, under the effect of thermal cycling during welding, there may be a small or no martensitic structure. Therefore, this type of steel does not have the problem of significantly reduced strength or quench hardening after welding, and even a small amount of martensitic structure can be solved by post-weld heat treatment. It can be said that the room temperature strength of this type of steel welded joints is not the main contradiction of welding; moreover, because its welding thermal expansion problem is far less than that of austenitic stainless steel, its hot and cold cracking problems are also not very prominent. Generally speaking, , Ferritic stainless steel is not as good as austenitic stainless steel, which mainly means that during the welding process, the plasticity and toughness of the welded joint may be reduced, that is, the problem of embrittlement occurs. As with the welding of other types of stainless steel, how to ensure that ferritic stainless steel welded joints have the same corrosion resistance as the base metal, and the embrittlement of welded joints that may occur during long-term service at high temperatures must be paid attention to.

Stainless Steel Tube ASTM A268

The thermal expansion coefficient of ferritic stainless steel is similar to that of carbon steel, which is smaller than that of austenitic stainless steel. In addition, intercalations such as S and P are more soluble in ferrite. Si and Nb is ferrite forming elements. Therefore, the weld seam It is not easy to form a low melting point eutectic during crystallization, and the hot cracking tendency is much smaller than that of austenitic stainless steel. At the same time, the amount of martensite formed in the welding heat affected zone exceeding the critical temperature is also very small, so the hardenability tendency is also small, so , ferritic stainless steel is less sensitive to delayed cracks than martensitic stainless steel, and it can be said that its process weldability is good.

Ferritic stainless steel is a Fe-Cr-C ternary alloy. Cr and additional elements such as Al, Nb, Mo and Ti are used to prevent the formation of austenite during welding heat. Therefore, the ferrite stainless steel does not undergo the quenching phenomenon of austenite to martensite during cooling after welding. However, the near-slot zone in the heat-affected zone formed by welding heat promotes coarse ferrite grains due to the high temperature, which significantly reduces the toughness of the joint, and it is impossible to directly improve it by heat treatment. This is the difficulty in welding ferritic stainless steel.

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