Study On Quenching And Tempering Process For900MPa High Strength Low Alloy Steel Plate

In21century, steel is also the main material in modern society. With the development of society, the higher requirement of steel production process has been put forward to reduce the cast and energy consumption, improve the mechanical properties of steel. Direct quenching process can use waste heat after rolling and be organically combined deformation and heat treatment, thus effectively improving the overall performance of steel. In recent years, direct quenching and tempering processes in the production of thick steel plate is gradually increased, promoting the thick steel plate production methods which relying solely on the alloying and off-conditioning turned the traditional model of micro alloying and thermomechanical treatment technology combination of new model. Not only can this multiplied the strength of steel, but also in low temperature toughness, weldability, inhibiting crack propagation, uniform cooling plate and the shape control is superior compared to the conventional process.In this paper, the high strength low alloy steel has been studied, for the regulations on the different microstructure and properties between DQ-T and RQ-T, by combining the thermal simulation techniques, laboratory hot rolling and heat treatment experiments. The article includes the following main parts and results:(1)The curves of continue cooling transformation under deformation and no deformation have been obtained by thermal simulating tests on MMS-300, According to the thermal expansion test and micrographs observation, both the continuous cooling transformation regulations and the effect of different deformation conditions and cooling conditions on phase transition behavior and transformation products were researched.(2)According to the DQ-T experiments, the mechanical properties and organization of the test steel at different tempering temperatures were analysed and researched. When the optimal quenching temperature is900℃and tempering temperature is600℃, the mechanical properties and organization are the best match value.(3)By the DQ and off line tempering experiments, the mechanical properties and organization of the test steel at different direct quenching temperatures were analysed and researched, the mechanical properties and organization at the quenching temperature range850～910℃are determined to the best match value. At the same time comparing the DQ-T and RQ-T, we find out that the mechanical properties of the test steel using DQ-T is better than the one using RQ-T.(4)After the welding joints experiment, the measured mechanical property can be seen, the mechanical properties of the weld line are worse than the base metal. The Akv(-40℃) on HAZ are better than the one on weld line, and the tensile specimens were broken in weld line. There are some problems of the welding materials.we need to research it deeper..