How to eliminate the defects of steel castings
As a result of the cooling of high temperature liquid directly into the mold, the steel casting china have many defects in itself.
Coarse lamellar pearlite often occurs, surrounded by thick and thick ferrite network, or bulky ferrite grain.
②The widmanstatten structure
The ferrite appears with the needle, the brittleness is bigger.
③Heterogeneity of dendrite segregation.
2.The method of elimination
Steel casting defects will greatly reduce the mechanical properties, machinability variation during subsequent heat treatment, the deformation and cracking, the hardness is insufficient, only to take pre heat treatment, in order to eliminate the defects, improve machinability, good organization and preparation for the final quenching do.
①Low carbon steel by normalizing treatment to obtain uniform ferrite and fine pearlite;
②Medium carbon steel and medium carbon alloy steel were prepared by full annealing or isothermal annealing to obtain ferrite + lamellar pearlite;
③In order to eliminate casting stress, low temperature annealing treatment should be adopted;
④ for large castings the dendrite segregation by diffusion annealing to offset. But there should be a complete annealing or normalizing, to refine grain, improve mechanical properties, improve the machining performance.
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