Study On Composition Design And Heat-treatment Technics Of Ultra High Strength Steel

Ultra high strength steel with ultra high strength and ultra high toughness characteristics,have been applied to aerospace, military and other field with special requirements on theproperties. And it is widening application range, its performance is also put forward higherrequirements, its preparation process and strength has been unable to fully meet the needs ofsome special equipment. In this paper, design4chemical compositions of alloy steel, J-Matsoftware is applied to simulate the parameters and performance of designed alloy steel, andsmelt and prepare alloy steel specimen by the intermediate frequency induction furnace.Through metallographic microscope, SEM, EDS, Rockwell hardness tester and universalmaterial tensile machine and other methods of analysis and testing we study the influence andmechanism of different heat treatment process and alloy elements on Microstructure andmechanical properties.Research results show that, the designed alloy steel with high nickel content containchromium and molybdenum and other strong carbide forming elements, so that the CCTcurves pearlite zone substantially right and is very narrow, so the steel casting organization iscomplex phase structure of martensite and bainite and retained austenite, and its hardness canreach HRC55.The designed alloy steel samples employe annealing process at640℃for30h, obtainingthe pearlite,and4kinds of alloy steel’s hardness can drop to around HRC30, basically meetingthe requirement of processing. Alloy steel containing nickel can make the transition point offerrite and pearlite right, and delay martensite and bainite decomposition, resulting in theannealed structure containing martensite and bainite.By making different process of quenching and tempering treatment on4kinds of thealloy steel, we finally obtains the best ingredients: alloy steel carbon content in0.6-0.65%, thecontent of nickel in3.5-3.6%, chromium content in1.6-1.7%, silicon content in0.25-0.35%,manganese content in0.45-0.55%, molybdenum content in0.35-0.45%. The optimum heattreatment process is:at860℃for0.5h then air cooling+170℃temperingfor2h, temperedmicrostructure is tempered martensite. After heat treatment the tensile strength of alloy steelwith the optimum composition is1781MPa, its elongation is6.65%..