Universal Hardness Test to Rate the Sintering Degree of P/M Steel fromDiffusion-Bonded Powder

摘要

Various standards specify the properties of PM materials to be achieved by usual industrialrnprocesses. In some cases, however, even if the properties of PM parts supplied by differentrnmanufacturers, and based on a same raw material, fulfil the specifications, operating failures occurrnfor some of them. The observed differences may derive from different sintering levels, i.e. fromrnunsuited process conditions, not covered by standards. In other words, this uncontrolled factor,rncould justify the observed differences. The intensity of the sintering process, and the consequentrn"mesostructure", namely the combined pattern of porosity feature, micro-constituents type andrndistribution, and diffusion level of alloy additions, may be the reason of the observed behaviour'srndifference. On this assumption, the universal hardness testing method has been applied to a wellknownrnferrous material, low-carbon steel from diffusion-bonded (1.75% Ni, 1,5% Cu, 0.5% Mo,rncarbon), with the aim of detecting the effect of different sintering conditions, (at 1120 ℃ or 1250rn℃; from 20 to 120 minutes) on elastic and plastic properties that the new method enables torndetect. The results show a positive influence of sintering intensity on the so-called plasticrnproperties. The effect on the elastic properties appears less pronounced. The changes ofrnmicrostructure agree with the observed enhancement of mechanical performances. The researchrnconfirms that the universal hardness method is suitable to classify and differentiate PM materials,rneven heat treated, and to reveal process changes.