Due to the influence of welding metallurgical conditions and different heating and cooling rates, the micro structure of weld and heat affected zone will be uneven, which will indirectly and directly affect the mechanical properties of welded joints. Therefore, it is very necessary to preheat before welding.

Heat treatment of steel

1.Preheating is an effective measure to prevent cold crack, hot crack and hardening structure in heat affected zone. When welding carbon steel, low alloy steel, heat-resistant steel with high carbon content and ordinary low carbon steel members with high rigidity, due to the fast cooling speed of the weld, hardened structure is easy to generated in the weld and heat affected zone, which leads to the generation of cracks. Therefore, the welding parts must be preheated. Preheating can slow down the cooling speed and prevent the weld from cracking.

Annealing of steel tube

2.When welding the confined welded joint area, due to the rapid cooling and heating, shrinkage stress will be generated in the joint area, which will cause cracks. Preheating the joint area before welding can reduce shrinkage stress and prevent cracks.

3.When welding in low temperature areas,preheating is also necessary to prevent cracks.

4.Preheating can also remove oil, water and other factors that affect the quality of the weld, and can also promote the escape of hydrogen in the weld, so as to prevent the formation of pores and other defects, and also prevent the generation of cracks.

Preheating before welding is an effective method to prevent welding cracks.As professional supplier of prefabrication pipeline,weldment or cladding, Hebei HaiHao Group accept all kinds welding works.Welcome your inquiry.Email:sales@haihaogroup.com