High strength quenched and tempered steels find a variety of application in structures including pipeline, mining equipments, cranes and off shore- platforms. where they offer weight savings combined with toughness and weldability. The Austenite transformation characteristics of the steel is studied in this article. Its schematic continuously cooling transformation (CCT) and isothermal transformation and critical transformation temperature are measured by Formaster-F type dilatometer. The mechanical properties, namely, tensile ductility, charpy impact energy at different heat-treatment procedure are studied the other properties such as tensile and impact and drop weight tear test(DWTT) at low temperature, fracture toughness from the original are researched systematically. the corresponding microstructure and carbide distribution in matrix are studied by electron microscopies, X-ray diffraction and TEM. the effects of microstructure on the properties are discussed in detail. In the view of the results, the critical rate of cooling for martensite transformation is 9.3 ℃/S, the critical transformation temperature is 420 ℃, this steel has good hardenability. for isothermal transformations, more transforming time is desired since alloy element adding in steel and carbide formed hold carbon diffusion and redistribution of alloy element. The possibility of improving heat treatment procedure and controlling the content of different phase is offered. As temptering temperature increase (550-650 ℃), tensile strength and yield strength and notch tensile strength and hardness gradually decrease byu growing of carbide and droping of dislocation harded functions. There is temper brittleness tempering at 600 ℃ in transeverse samples, the longistitude is not. It have proved that the microstructure of hot-rolling steel has orientation. For transeverse samples tough-brittle temperature is 17 ℃ measured by DWTT. Compared with the Welten60 steel. This steel have high-strength and more good plastics and less crack expand energy. The different of properties between the transverse and longititude from the quenched-tempered steel and temper brittleness and appearance of split in tensile at low temperature for element heterogentity are discussed.
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