Explain the heat treatment effect of casting parts, forging parts and welding parts
The three methods of metal processing have one thing in common. They are hot working, which are different in temperature and range of processing. Ductile cast iron is widely used because of its brittleness and poor impact. Heat treatment of cast iron usually adopts the annealing process, reduce the casting effect: 1 because of the internal stress caused by the thermal expansion and contraction, reduce the deformation after machining, decrease surface hardness, improve machining conditions;
2 improve the crystal structure, enhance the formation and stability of spherical carbon crystal;Forgings are generally stress bearing members, and most of them are made of high strength medium carbon steel (alloy), which is formed by forging and fine crystalline. After the shell is annealed or quenched and tempered, the mechanical properties of the shell are more superior, and it has better strength and better elasticity;Welding materials.
Good welding of low carbon steel (alloy), probably because the weld workpiece rigidity, fast cooling, the weld internal crystallization of brittle microstructure (martensite), so after welding or welding process welding using self heat, reasonable arrangement of weld, welding seam and heat affected zone heat treatment. The welding heat treatment is often used to preheat before welding, after welding withasbestos cloth covering slow cooling annealing, reach the purpose, its main function is to reduce the internal stress, improve the weld microstructure of martensite formation, reduce brittle tendency, preventing welding cracks.