Heat treatment refers to a kind of metal hot working process in which materials are heated, insulated and cooled in solid state to obtain the expected structure and properties. The whole heat treatment is a metal heat treatment process that heats the whole workpiece and cools it at a proper speed to obtain the required metallographic structure and change its whole mechanical properties. The effect of spheroidal graphite on the matrix is small, so the mechanical properties of nodular cast iron mainly depend on the matrix structure. Therefore, the mechanical properties of nodular cast iron can be significantly improved by heat treatment.
Annealing
The cast internal stress of the de stress annealing ductile iron is about twice as large as that of the gray iron. For ductile iron castings without any other heat treatment, stress relief annealing should be carried out. The purpose of graphitization annealing graphitization annealing is to decompose the free cementite in the as cast structure and the eutectoid cementite in the pearlite, obtain the ductile iron with high plasticity ferrite matrix, eliminate the casting stress and improve its processability.
Normalizing
The purpose of normalizing is to obtain the pearlite based matrix structure, refine the grains of stainless steel strip, and improve the strength, hardness and wear resistance of nodular cast iron. Normalizing can be divided into high temperature and low temperature normalizing. High temperature normalizing for thick wall castings should be air-cooled or even spray cooled to ensure pearlite ductile iron. Low temperature normalizing is to heat the casting to 840-860 ℃, keep the temperature for 1-4h, and then out of the furnace to obtain the nodular cast iron with pearlite + ferrite matrix. The thermal conductivity of nodular cast iron is poor, and the internal stress of the castings is large after normalizing. Therefore, a stress relief annealing should be carried out after normalizing.
Heat treatment plays an important role in mechanical manufacturing. Proper heat treatment can significantly improve the mechanical properties of steel and prolong the service life of machine parts. Nantong heat treatment process can not only strengthen metal materials, fully tap the potential of materials, reduce structural weight, save materials and energy, but also improve the quality of mechanical products and extend the service life of machine parts. In addition, heat treatment can also make the surface of workpiece have special physical and chemical properties such as wear resistance and corrosion resistance.
On 2018-08-08 11:45:46
