Effect Of Miscrostructure And Properties Of Deformed Austenite And Tempering In High Carbon Alloy Steel

The purpose of this paper is to study the microstructure and mechanical properties of high carbon alloy steels after isothermal quenching and tempering.The miscrostructure and mechanical properties were analyzed and confirm the best isothermal quenching and tempering process.DIL–402C type thermal expansion instrument has been applied to the determination of the steel Ac1 and Ac3,the steel cold austenitizing after predeformation of Ms points and different temperature of the isothermal holding time were measured by Gleeble–3800 thermal simulation testing machine,according to the simulated data to develop a corresponding isothermal quenching process.By optical microscope,scanning electron microscope(SEM),transmission electron microscopy(TEM)and X–ray diffraction on the microstructure and morphology of isothermal quenching samples for analysis.Mechanical properties such as hardness and tensile test and impact toughness,were measured for different austempering process samples,confirming the best isothermal quenching process.The poor performance of a group of isothermal quenching samples have different temperature tempering structure and mechanical properties test,confirming the best tempering process.The test results show that the steel sample phase transition point Ac1,Ac3 and Ms were 780 ?,820 ?and 210 ? respectively.Experimental steel at 240~320 ? isothermal quenching,the organization of the sample by lath of bainite ferrite and film–like and blocks of residual austenite.With the increase of isothermal quenching temperature,the residual austenite content increased,at the same time a large amount of residual austenite block.From the determination of the mechanical properties of analysis,with the increase of isothermal quenching temperature,impact energy and ductility are rised gradually,but they are decreased reaching a certain temperature;Hardness,tensile strength and yield strength are reduced gradually.Material obtained by 320 ? isothermal quenching heat preservation of 250~450 ? for 1 h after tempering heat treatment,the organization of the sample by lath of bainite ferrite and film–like and blocks of residual austenite.In the research of the tempering temperature range,impact energy gradually decreased;Hardness unchanged;Higher tensile strength reduced first;Yield strength and elongation are rising before.260 ? isothermal quenching process is the best in the research of the isothermal quenching temperature range,the impact energy for 44 J,hardness value for 55.7±1.3 HRC,tensile strength and yield strength of 2162 MPa and 1243 MPa,the elongation is 11.14 % and the formability reached to 24084 MPa,%.300 ? tempering process is the best in the research of the tempering temperature range,the impact energy for 47.5 J,hardness value for 49.4±0.8 HRC,tensile strength and yield strength of 1718 MPa and 1331 MPa,the elongation is 19.33 % and the formability reached to 33209 MPa,%.