Effect Of Rare Earth Ce On Microstructure And Thermal Fatigue Properties Of H13 Steel

At present,the development speed of the world’s manufacturing industry is getting faster and faster,and China’s manufacturing industry is also showing a thriving scene under the leadership of this drive.However,there is still a certain gap between the types and properties of existing hot work die steels in China and international high-quality die steels.In order to adapt to the development of the manufacturing industry,in view of the problems existing in the actual production of die steel,the composition improvement and process optimization are carried out,so as to improve the service life and reduce the production cost,which provides a certain theoretical basis for the research of die steel in my country.This experiment takes H13 steel as the research object,smelts 7 kinds of test steels with different Ce content,and conducts different heat treatment experiments on them.The microstructure and uniformity,thermal fatigue properties and mechanical properties of the experimental steels are studied.result:Through the observation of the microstructure of the test steel,the addition of rare earth Ce plays a role in improving the microstructure in the steel.When the Ce content is0.026%,the improvement effect on the microstructure in the steel is the most significant,and the grain refinement effect is the most obvious.At the same time,the addition of rare earth Ce plays a positive role in improving the dendrite segregation in steel.Through the study of the heat treatment process,the quenched and tempered structure after quenching at 1040°C and tempering at 580°C has the most uniform microstructure and the smallest grains,so it is used as the preparatory heat treatment before the thermal fatigue cycle.The results of thermal fatigue cycle at 700℃ show that the crack initiation of the test steel is mainly caused by the combined effects of stress concentration of prefabricated notch,pits generated by oxidation reaction,inclusions with uneven shape,and structural defects existing in the matrix.The addition of rare earth Ce can play the role of metamorphic inclusions and strengthen grain boundaries,so that the shape of the originally uneven inclusions is gradually transformed into spherical and ellipsoidal shapes,reducing stress concentration and hindering the initiation of cracks.During the thermal fatigue cycle,the crack propagates forward after initiation,and the power of its propagation is mainly provided by the thermal stress of the cooling and heating cycle.The tip is extended forward.The addition of rare earth Ce plays a role in hindering the crack growth.When the rare earth content is 0.026%,the obstacle to the crack growth rate is the most obvious,which is 16.6% slower than that without the addition of rare earth.The influence of rare earth Ce content on the mechanical properties of the test steel showed a trend of first increasing and then decreasing.When the rare earth content is260 ppm,its mechanical properties are the best,and its quenching and tempering hardness,tensile strength and impact toughness are: 650.6HV,391.4HV,1332 MPa,21.5Ak/(J·cm-2),respectively.Has the best comprehensive mechanical properties.