Organization Refine Swap Carbon Cr-mo Steel Quality In The Mechanical Properties Of Impact

The effect of ultra-fine microstructure on the mechanical properties of medium-carbon Cr-Mo steel was studied with optical microscope, TEM and SEM. The study was divided into three parts. First, analyzed the quality and mechanical properties of casting slab; second, ultra-fine microstructure was obtained by circle heating-quenching treatment, and its effect on mechanical properties is discussed in this paper; third, studied the recrystallization and grain refinement of tested steel through thermal simulate test.The macrograph of slab indicated that we can increase the quality of casting slab by decreasing the teeming temperature, using electromagnetic stirring and soft reduction technique in continuous casting proceeding. And the high qualities of slab bring us the high mechanical properties of steel.Studied on different austenite grain sizes of quenched and tempered steel, we can see, grain refinement is an efficient method to improve both strength and toughness, but the influence of grain size on strength is not obvious to quenched and tempered steel. The toughness has greatly improved with decreasing the austenite grain size, especially of the low temperature toughness. And the ductile-brittle transition temperature was improved by grain refinement. But there is a little decrease with the ductility. These results indicated that strengthen bring by pure grain refinement is limited to quenched and tempered medium carbon steel, and the main purpose of grain refinement is to improve the toughness. Furthermore, the increasing range of toughness brought by grain refinement differ from different parts (surface and center) and different directions (transverse and lengthways) because the size, distance and shape of inclusions are different.We can obtain the fine grain size about 10um by two paths deformation. So the grain refinement can be obtained by control rolling and cooling in practice production.