| In recent years, in order to meet the requirements of material strength, toughness and other in industrial production, omestic and foreign experts continue to explore and develop new high strength steel. At the beginning of twenty-first Century, professor Bhadeshia obtained bainite with good strength and toughness in low temperature quenching, and low temperature of bainite steel research attention. In this paper, the design of isothermal quenching process suitable to high silicon high carbon steel can be bainite transition at low temperature. Chooses the content of Si in the specimen is 0.75, which is using the Si element can strongly inhibit the precipitation of cementite. This study was carried out on the ZG75Si2Mnl.5CrB steel under different process parameters of isothermal quenching, in order to provide theoretical basis for optimizing heat treatment process. The current research about low bainite is less, especially the understanding of impact toughness and wear resistance. The research aims to expand the bainite transformation theory, enrich the ways to strengthen the high silicon high carbon steel, provide a theoretical basis for the practical production and application of bainitic steel.This paper is to carry on the observation and study on mechanical properties of microstructure of ZG75Si2Mnl.5CrB steel which is obtained after different quenching process. High carbon high silicon cast steel at low temperature isothermal quenching can occurbainite transformation, to obtain the sub nanometer grade bainite. Lath bainite ferrite^ a small amount of martensite and residual austenite determine the sample with high toughness and high strength, however, little research on low temperature bainite. Therefore, this study different parameters of the isothermal quenching process of ZG75Si2Mnl.5CrB steel heat treatment, in order to provide theoretical basis for optimizing heat treatment process.In the experimental process, first of all to the design of alloy composition, in order to meet the test in the lower bainite transformation temperature occurs, and after isothermal quenching material has a better comprehensive mechanical properties, designed the ZG75Si2Mnl.5CrB steel. First of all, through the phase transition point determination, measurement of specimen of the Ms temperature is about 170℃ design of heat treatment process for the sample in 920℃austenitic 30min, at 220 ℃、240 ℃、260℃ and 280℃respectively insulation 2 min,30 min,2 h and 5 h. Under the metallurgical microscope observed that needle shape bainite ferrite and bright color of residual austenite, in the 280℃ insulation 5h bainite serious coarsening; under the SEM can be observed more clear lath bainite ferrite, claiming the growth of the bainite transformation occurred in shear; XRD diffraction experiment can use the formula to calculate the residual austenite content in the organization. The microstructure of samples after the isothermal quenching is bainite ferrite, film of residual austenite and martensite,specimens under 920℃ austenitizing 30 min at 220℃,240℃,260℃ and 280 ℃ heat preservation after 2 h, residual austenite volume is 3.23%～11.07%, the rules of with the increase of isothermal quenching temperature, sample of bainite transformation speed.In the test of mechanical properties, samples after isothermal quenching, high strength and hardness of the whole specimen, in the isothermal time phase at the same time, with the increase of heat preservation temperature, strength and hardness of the specimen decreased, the isothermal temperature is 240 ℃, with the holding time increased the tensile strength decreased continuously, and the hardness for the overall performance of the decline, but there is a rising. In the dry wear experiments, isothermal temperature is 260 ℃, isothermal time is 30min, the abrasion resistance of the sample is relatively good, in the measurement of friction and wear coefficient of the isothermal temperature is 260 ℃, isothermal time is 30min, the load is 20N,sample minimum wear coefficient is 0.3542. |
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