(1) preheating can reduce the cooling rate after welding, and facilitate the diffusion of hydrogen in weld metal and avoid hydrogen-induced cracks. It also reduces the hardening degree of weld seam and heat-affected zone and improves the cracking resistance of welded joints. (2) preheating can reduce welding stress. Uniformly local preheating or overall preheating can reduce the temperature difference between welded parts (also known as temperature gradients). In this way, on the one hand, the welding stress is lowered, the welding strain rate is reduced, and the welding cracks are avoided. (3) preheating can reduce the degree of restraint of welding structure, to reduce the degree of restraint of angular joints is particularly evident, with the increase of preheating temperature, the crack incidence decreases. The effect of heat treatment after welding of cast aluminium heater is: eliminating the heat stress produced by welding, the microstructure of uniform weld seam and heat-affected zone. Refining weld and hot-affected areas of the grain, excluding weld in the welding process of hydrogen embrittlement, through heat treatment can make the weld metal and metal materials better fusion (often welded materials and masterbatch of the steel bar inconsistent, by heating diffusion, better combination).