Orthogonal test method was used to optimize the heat treatment process for three kinds of specimens with diameters of ∅30,∅32 and ∅36 mm in order to determine the suitable heat treatment process parameters to meet the bolt strength grade 10.9,where the heat treatment process of 35 CrMo steel was investigated by using single-factor method,and that the hardness of the core reaching half martensite hardness was used as the basis for quenching,that the 1/2 radius and core hardness were used as the evaluation indexes.The results show that the optimal heat treatment parameters are the quenching temperature of 860 ℃,the holding time of 50 min,and the water-soluble quenching liquid for quenching,the tempering temperature of 480 ℃,and the tempering time of 80 min.After heat treatment with the optimized process,the hardness,tensile strength,yield strength,elongation and percentage reduction of area of all the specimens with three different diameters can meet the mechanical property requirements of 10.9 grade high strength bolts.
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