Microstructure Evolution Of Weathering Steel Cu-P-Cr-Ni-Mo By Rolling Simulating

New type dual-phase weathering steel Cu-P-Cr-Ni-Mo has a relatively broadapplication prospects on the railway locomotive and car industry for its excellent coldformability and weatherability. However, at present, the grain of steel microstructure isrelatively bulky, which weakened the strength level. It have important researchsignificance by using TMCP (thermo-mechanical control process) to refining the grainsize and achieve the effect of grain refining strengthening, further excavate the steelprobability, hardened steel mechanical properties.The microstructure evolution of dual-phase region of Cu-P-Cr-Ni-Mo weatheringsteel was investigated by using Gleeble3500simulator in the temperature range from700℃to950℃, reduction of30%,50%,70%and strain rate of5s-1. The results ofmetallographic analyse shown that the grain size of ferrite and the volume fraction ofmartensite reduces as deformation temperature decreasing and deformation reductionincreasing.The grain size of ferrite was not uniform if the reduction is small. Fine uniformferrite grains can be obtained in a larger reduction (70%) with the hot deformation ofdual-phase region of experimental steel. Because of the deformation induced ferritetransformation refine ferrite caused by heavy deformation, fine ferrite grains can beobtained with the deformation of critical zone and grows rapidly in the subsequent heattreatment. The perfect microstructure with the ferrite grain size of3.2μm and themartensite volume fraction of8.3%can be obtained with deformed temperature of775℃,reduction of70%, and cooling rate of3℃/s.The microstructure refinement supplies an alternative approach to improve thestrength of low carbon steel without loss of room temperature ductility. Themicrostructure evolution of Cu-P-Cr-Ni-Mo weathering steel in multi-pass hotdeformation in the intercritical region or austenite single-phase region was investigated bymeans of hot compression simulation. The results indicated that smaller grains can beobtained under the conditions of general large strain through multi-pass deformation in the(γ+α) range than in the austenite single-phase region and the fine ferrite grains of1.8μm can be achieved in the (γ+α) range. The second phase distributed being lath form on theferrite matrix and turned thinner with the passes increasing. Microstructural analysisshown that at the ahead passes deformation, the strain was large enough to lead strainenhanced ferrite transformation and promoted large number of ferrites nucleation,precipitation and refinement. The continuously dynamic recrystallization of ferrite isresponsible for the ferrite grains refinement at the latter passes deformation. A lot ofsubgrains appeared and the misorientation angle between subgtrains continuously increaseled the formation a large amount of high angle grain boundaries (HAGBs) and the coarsegrains were segmentate.