Weldability of stainless steel forgings
For stainless steel forgings, the first thing to understand its weldability, because most of the stainless steel forgings are weldments. The welding characteristics of various stainless steels are as follows:
1) Austenitic stainless steel forgings have good corrosion resistance, good plasticity and toughness, as well as good weldability, no quenching hardening and few cold cracks. Due to large thermal expansion and cold contraction, hot cracks and large welding deformation may occur. During welding, stress corrosion failure, 475 ° C brittleness, σ phase precipitation embrittlement and intergranular corrosion should be prevented.
2) Martensitic stainless steel forgings have a strong hardening tendency and are prone to cold cracks. When the welding joint is heated beyond 1150 ° C, the grains in the steel will grow significantly; if the cooling rate is too fast or too slow, it may cause joint embrittlement, and also cause 475 ° C embrittlement; the tendency of intergranular corrosion is small; the hardening tendency of 30cr13, 40cr13, 68cr17 and 95Cr18 is stronger, and the welding performance is worse.
3) Ferritic stainless steel forgings have no quenching hardening phenomenon. When the heating temperature is higher than 950 ° C, the grains in the weld and heat affected zone are very coarse, and the grains can not be refined by post weld heat treatment, resulting in cold cracks, which are prone to 475 ° C embrittlement and σ phase precipitation embrittlement, and the intergranular corrosion tendency of the joint is large.
4) AUSTENITIC FERRITIC duplex stainless steel forgings have good weldability, no preheating, no heat treatment after welding, no welding cracks. However, when the proportion of ferrite is large, the phenomenon of brittleness at 475 ° C may occur, and the phenomenon of σ phase embrittlement will occur in high chromium duplex stainless steel.
For stainless steel, the structural damage cases caused by cracks, embrittlement, intergranular corrosion, knife corrosion, pitting corrosion and stress corrosion in the welding zone often occur. Therefore, the welding characteristics of various stainless steel forgings should be mastered and correctly selected, and then the welding parameters of all kinds of steel should be strictly implemented to avoid accidents.