关键词: 高硼钢, 热处理, 硼化物, 硬度, 变形行为

Abstract: In order to improve the machinability of high boron steel, the effect of heat treatment(1100 ℃×60 h, air cooling) on the as cast high boron steel was studied by using scanning electron microscopy, X-ray diffraction, and hardness tester. The results show that eutectic borides in the as cast and heat treated high boron steel are composed of Cr₂B and (FeCr)₂B phases. The borides in the as cast high boron steel exhibit elongated dendritic structures, while the borides after long time heat treatment appear as a coarse and short rod shape, which is due to the boride redissolving during high temperature heat treatment, and then reaggregating and precipitating at the undissolved boride during cooling. After heat treatment, the volume fraction of boride decreases from 58.2% in as cast to 40.9% in heat-treated state, while the hardness of borides decreases from 422.0 HV0.01 to 348.6 HV0.01. Because the heat treatment significantly improves the hot workability of the high boron steel, the high boron steel does not crack in a single pass compression deformation with 20% reduction in the range of 850-1100 ℃, and the maximum peak true stress is 384.2 MPa. The mechanical properties of the rolled high boron steel basically reach the level of 304B7 steel, with a yield strength of ≥297 MPa, a tensile strength of ≥504 MPa, and an elongation of ≥3.65%.

Key words: high boron steel, heat treatment, boride, hardness, deformation behavior