Weldability of 35CrMo steel

35CrMo steel is a heat-resistant steel with pearlite structure, which has high thermal strength (δb≥440MPa) and oxidation resistance at high temperatures, and has a certain resistance to hydrogen corrosion. Due to the high content of Cr, C and other alloying elements in 35CrMo steel, the hardening tendency of 35CrMo steel is obvious and the weldability is poor.

Because the addition of chromium and molybdenum alloying elements to 35CrMo steel increases the carbon equivalent, increases the hardening tendency of 35CrMo steel, improve the hardness of welding heat-affected zone, and easily produces welding cold cracks. Due to the difference in the content of carbon and alloy elements in the base metal and the weld metal for 35CrMo steel, when the heat-affected zone of the base metal in the delayed phase transformation undergoes austenite to martensite transformation, hydrogen remains in the martensite in a supersaturated state, resulting in hydrogen-induced cracking.

When the carbon content and alloying elements in the weld metal of 35CrMo steel are high, it is possible that the heat-affected zone of the base metal will undergo phase transformation before the weld of 35CrMo steel, and hydrogen will diffuse from the heat-affected zone to the weld, so that the hydrogen in the weld is in an excessive state. saturation. When the weld of 35CrMo steel transforms into martensitic structure after cooling, weld cold cracks will occur. Therefore, preheating before welding and heat treatment after welding should be carried out during welding of 35CrMo steel.