Study On Design, Preparation And Properties Of 2200MPa Grade Low Alloy Steel

With the constant increase of demand and requirement for ultrahigh strength steel in the high technology fields of aerospace,national defense,energy,national economic construction,ultrahigh strength steel with high toughness,excellent welding performance and good resistance to high bullet penetration becomes to the development direction of steel.The aim of this paper is to develop new type ultrahigh strength low alloy steel with 2200MPa as well as high toughness.The important results are as following:1.A new type of low alloy ultrahigh strength steel 30Cr2NiSi2Mn2Mo was successfully prepared in the research.The superiority of mechanical properties with the ultimate tensile strength of more than 2200MPa,elongation more than 8.4%,reduction in area more than 34%and impact toughness obtained at-40? more than 13J is revealed in the paper which fulfill and leapfrog the excellent combination of high strength and toughness.The cost of the new low alloy ultrahigh strength steel is comparable with other low alloy ultrahigh strength steel but much lower compared with 2000MPa of maraging steel and secondary hardening ultrahigh steel.2.A systemic study on the influence of austenitization heat treatment and tempering heat treatment on the microstructure and mechanical properties of the new low alloy ultrahigh strength steel 30Cr2NiSi2Mn2Mo is made in the research.The strength and HRC increase firstly and then decrease while impact toughness obtained at-40?improves obviously with increasing the austenitization temperature.Strength and HRC decrease with raising the tempered temperature,a sharp loss is found in the toughness when tempered during 300?-400? which indicates that the tempered martensite brittleness is occurred.The results show that the optical heat treatment process of the new type of low alloy high strength steel was austenitized at 920? for 1 h,oil quenching,and subsequently tempered at 200? for 2h,air cooling.3.The new designed low alloy ultrahigh strength steel 30Cr2NiSi2Mn2Mo has excellent welding properties.The ultimate tensile strength of the welded joint after heat treatment is more than 2100MPa.4.The new designed low alloy ultrahigh strength steel 30Cr2NiSi2Mn2Mo has excellent resistance to high speed impact protection performance which is much better than the represented international leading deputy high hardness armored steel MARS240 made by French.