The Effect Of Boron On Structures And Properties Of High Chromium White Cast Iron

From the view of decreasing the contents of Mo, Ni and other precious metal elements, reducing production costs and increasing wear-resistance, an experiment study for adding boron to substitute partial Mo and Ni in KmTBCr20Mo has been conducted. By observing the microstructure and testing the results of impact toughness, hardness, wear resistance of high-Cr white cast iron with variable boron, we analyzed the effect of boron on structure, mechanical properties and wear resistance in the state of casting and heat treatment, and then we carried out analyzing impact fracture and wear pattern, while we explained fracture and abrasion mechanism of high chromium white cast iron with boron.The results showed as follow:(1) B combined boride or boron-carbide in place of partial C, which made eutectic point of high-chromium white cast iron shift to the left, and the structure might transit from hypoeutectic alloy to hypereutectic over-eutectic in the boron content range of0.033to0.67(mass,%);(2) B improved harden ability characteristic of the high-chromium white cast iron, small quantity of martensite would be obtained when in state of casting;(3) When boron content was0.09%, the size of carbide was thinnest, in shape of particle, and the fragmentation level to the martensitic matrix was small, so the impact toughness was the maximum; when boron content was0.32%, the size of carbide increased, in shape of blocks and short rod, and the distribution was uniform; when boron content exceed0.32%, the impact toughness decreased as the boron content increased;(4) When in state of casting, as the content of B increased, carbide volume fraction increased and improved significantly the hardness of samples; no marked effect has been found in the samples after heat treatment, but the hardness of high-chromium white cast iron was the highest after1000℃quenching hold3h+air cooling and260℃hold3h drawing temper;(5) When boron content was0.32%after1050℃quenching hold3h+air cooling and260℃hold3h drawing temper, the impact toughness was5.2J/cm2, the hardness was57.4HRC, the relative wear resistance was1.081, the relevant mechanical properties and wear resistance of high-chromium white cast iron with boron was similar to the high-chromium white cast iron with much Mo and Ni (ak was5.5J/cm2, HRC53.3, the relative wear resistance wasl).Our study improved that the production of high-chromium white cast iron using B in place of precious elements Mo, Ni was entirely feasible as long as adding proper amount of boron, and adopting suitable processing of heat treatment.