Heat affected zone of 15Cr1Mo1V steel after repair welding and intermediate tempering was simulated by Gleeble-3500 thermal simulation testing machine.The effect of intermediate tempering on the microstructure and mechanical properties of the heat affected zone of the long-term serviced 15Cr1Mo1V steel after repair welding was studied by means of metallographic observation,scanning electron microscopy analysis,microhardness test and impact test.The results show that the microstructure of serviced state is composed of ferrite+granular bainite+intragranular dispersed carbide+grain boundary chain carbide.After repair welding,the microstructure of tempering zone is basically the same as that of long-term serviced state.The microstructure of incomplete transformation zone and complete transformation zone is ferrite+granular bainite+pearlite+granular grain boundary carbide,but there is dispersed carbide in the crystal of incomplete transformation zone.The coarse grain zone is composed of flat noodles bainite+a small amount of granular bainite.After intermediate tempering,there is an increase in carbides at the grain boundaries of the tempering zone.The carbides precipitated in the incomplete and complete phase transformation zones continuously aggregate and grow at the grain boundaries,while a large number of chain like carbides appear at the grain boundaries of the coarse grain zone.After repair welding,except for the high hardness of the coarse grain zone,the hardness level of the other heat affected zones is not significantly different from the serviced state.After intermediate tempering,the hardness value of the coarse grain zone remains at the level after repair welding,and the hardness of the other heat affected zones has slightly increased.Due to the presence of pearlite structure in the incomplete and complete phase transformation zones,the impact property is lower,while the impact property of the tempered zone and coarse grain zone is better.After intermediate tempering,the impact property of the tempered zone and coarse grain zone decreases,while the impact property of other heat affected zones is improved.
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