The Evolution Of Microstructure And Mechanical Properties During Heat Treatment Of Low Carbon Medium Manganese Steel

The steel containing 3-10%manganese is called medium manganese steel.Compared with high manganese steel,the steel has the advantages of simple production and low cost;Compared with the low manganese steel,due to the relatively more manganese,expanded austenite transformation zone,bring more convenience to control the performance and the microstructure of the steel.With the development of science and technology,the smelting and other problems of manganese steel are solved gradually,the study of medium manganese steel become the focus of attention.In this paper the microstructure and properties of low carbon medium manganese steel(0.12C-3Mn)during heat treatment were studied.The evolution law of microstructure and properties of the steel after rolling is analyzed by the conventional quenching-tempering(Q-T),quenching-partitioning(Q-P),and the intercritical heat treatment(Q-Q-T).The wear resistance properties of the steel was analyzed under the condition of the conventional off-line quenching-tempering and quenching and tempering heat treatment.The main research contents and conclusions are as follows:(1)The continuous cooling transformation behavior of experimental steel under different cooling conditions is studied,obtained the continuous cooling transformation(CCT)curves of experimental steel under no deformation condition,and the changes of the hardness with cooling rates of the steel were analyzed.The results show that:The continuous cooling transformation curves of the experimental steel are mainly composed of three parts of the bainite transformation zone at low cooling rate,the martensitic transformation zone at middle cooling rate,and the martensitic transformation zone at high cooling rate;The steel has good quenching permeability and obtained martensite at 5?/s cooling rate;the hardness of the steel increases with the increase of the cooling rates,and the hardness changed not obvious when the cooling rate is greater than 5?/s.(2)The microstructure and mechanical properties of the rolled experimental steel after the conventional quenching-tempering(Q-T)were studied,and the wear performance of the experimental steel was analyzed.The results show that:The optimal mechanical properties are obtained when the steel quenched at 780? and tempered at 250 ?.The tensile strength of is 1316MPa,yield strength is 1113MPa,elongation is 13%,room temperature impact power reached 95 J,the wear resistance is 1.18 times of conventional low alloy wear-resistant steel.(3)The microstructure and mechanical properties of the rolled experimental steel after the conventional quenching-partitioning(Q-P)were studied,and the wear performance of the experimental steel was analyzed.The results show that:The optimal mechanical properties are obtained when the steel quenched at 300? and partitioned at 250?.The tensile strength of is 1240MPa,yield strength is 865MPa,elongation is 15%,-40 temperature impact power reached 20J,the wear resistance is 1.04 times of conventional low alloy wear-resistant steel.(4)The microstructure and mechanical properties of the rolled experimental steel after the intercritical heat treatment(Q-Q'-T)were studied,The morphology and distribution of retained austenite during intercritical heat treatment changed with intercritical quenching temperatures and tempering temperatures were studied The results show that:The steel obtained optimal TS×T.EL is 28GPa%when intercritical quenched at 720 ? and tempered at 680 ?,The temperature of the intercritical tempering has a great influence on the content of the retained austenite.The content of retained austenite increased from 6%to 15%with the increase of tempering temperature.The intercritical quenching temperature of the critical heat treatment has a certain effect on the distribution and morphology of the retained austenite.When the temperature of the intercritical quenching temperature is 700?,the retained austenite is small and the main distributed on the grain boundary;When the temperature of the intercritical quenching temperature is 720 ?,the retained austenite is big and the main distributed on the grain boundary;When the temperature of the intercritical quenching temperature is 740?,The large remnant austenite and the fine austenite existed simultaneously,the bulk retained austenite was mainly distributed on the grain boundary,while fine retained austenite was mainly distributed in the interphase.