Study On Thermal Fatigue Behavior Of H13 Steel With Different Microstructure And Properties

Mold is the core component of manufacturing production,which directly determines the quality and production cost of products.The quality of the mold directly depends on the performance of the mold material,in order to improve the comprehensive mechanical properties and thermal fatigue life of hot work die steel,and promote the development of China's mold industry,our group based on H13 steel and the service environment requirements of hot work die,through new types of bainite / Martensite multiphase heat treatment process,two kinds of B/M multiphase H13 steels were obtained,code-named QBT1-H13 steel and QBT2-H13,and compared with traditional HT heat treatment process H13 steel(named HT-H13).The structure and mechanical properties of H13 steel under three heat treatment processes were studied.The evolution of the structure,mechanical properties and thermal fatigue behavior of three heat treatment processes were discussed.The thermal fatigue crack initiation and propagation mechanism of B/M multiphase H13 steel was revealed.Thermal fatigue life of three heat treatment process H13 steels were predicted.Research indicates:1)The structure of HT-H13 steel is tempered sorbite,the structure of QBT1-H13 steel is tempered sorbite and a small amount of lower bainite multiphase structure,and the structure of QBT2-H13 steel is tempered sorbite and a large number of Lower bainite multiphase structure.The hardness and tensile strength of Q13 H13 steel and QBT2 H13 steel are significantly better than HT H13 steel.In addition,QBT1-H13 steel and QBT2-H13 steel have better plastic toughness than HT-H13 steel.2)The martensite lath in the HT-H13 steel and the QBT1-H13 steel gradually merged with the increase of the number of thermal fatigue,and preformed carbides continued to coarsen.The combination of martensite laths and carbide coarsening made the two heat treatment process H13 steels softens rapidly during thermal fatigue,and their mechanical properties decrease.However,Due to Supersaturated bainite dissolves out in thermal fatigue and precipitates a large amount of fine dispersed carbides,which occurred second phase strengthening,and delayed the coarsening of Preformed carbides,QBT2-H13 steel did not show obvious softening behavior during thermal fatigue.In addition,due to Lower bainite merged and formed polygonal ferrite structure during thermal fatigue,the plasticity of the two B/M multiphase process H13 steels after thermal fatigue are significantly better than that of HT-H13 steel.3)The crack growth rate of the H13 steel in two B/M multiphase processes is significantly lower than that in the HT process.The main reason is that on the one hand,the lower bainite lath and the martensitic lath in the B/M multiphase structure have a large-angle interface.This large-angle interface makes the crack propagation require more energy,thereby slowing the crack growth rate.On the other hand,the formation of lower bainite reduces the second phase particles on the substrate,thereby reducing the source of cracks.In addition,the precipitation of fine and dispersed second-phase particles during the thermal fatigue process in B/M multiphase structure can hinder the growth of microcracks,and at the same time reduce the coarsening rate of preformed carbides and reduce the initiation of microcracks.According to reasonable prediction model calculation,the thermal fatigue life of QBT1-H13 steel and QBT2-H13 steel respectively reached 2800 and 3500 times,which is obviously better than that of HT-H13 steel.In summary,H13 steel under the QBT2 process has the best comprehensive mechanical properties and thermal fatigue properties.