Describe the role of heat treatment of castings, forgings and welded parts

1. Eliminate the stress caused by thermal expansion and contraction inside the casting, reduce the deformation after machining, reduce the surface hardness, and improve the machining conditions;

2. Improve its crystalline organisation, enhance the formation and stability of spherical carbon crystals; forgings are generally strength stress components, the material is mostly high-strength medium-carbon steel through the forging to make the metal shaped, crystalline fine.

3. After forging the shell to take annealing or tempering heat treatment, so that its mechanical properties are more superior, both better strength, but also has a better elasticity;

4. Welded parts materials are mostly weldable good mild steel, its weld may be due to the rigidity of the workpiece, fast cooling, weld internal crystallisation of brittle organisation, so after welding or welding process to use the welding of their own heat, a reasonable arrangement of the weld, the weld and heat-affected zone heat treatment.

5. Heat treatment of welded parts is often used before welding preheating, after welding with asbestos cloth covered slow cooling, to achieve the purpose of annealing treatment, its role is mainly to reduce the internal stress of the workpiece, improve the weld crystalline organisation, reduce the brittle tendency to the formation of martensite organisation, to prevent weld cracks.