Fabrication And Microstructure-property Relationship Investigation Of PM High Chromium Cast Iron With Cr/C=7.2

In this paper, the powder metallurgy sintering Cr/C=7.2 high chromium cast iron pressing-sintering、heat treatment and abrasion resistance has been systematically studied, which can explore a new way of thinking and technology for preparation performance and wear-resistant high chromium cast iron.Fist, we studied the suppression performance of high chromium cast iron powder preparation by aerosol technology. The results suggested that the formability of pure high chromium cast iron powder was poor, but it could be effectively improved by adding formative agent. Comparing the effect of improving the blank sample quality between two different formative agent—namely paraffin and zinc stearate, the result showed that pressed density increased with increasing compacting pressure, when the compacting pressure was over 350MPa, the increase of pressed density was not obvious and prone to defects such as hierarchical. Blank samples were easily stick to the mold while using zinc stearate as formative agent, however, it is more beneficial to obtain high-density blank sample without defects while using paraffin as formative agent. As paraffin added quantity to 3 wt%, pressing pressure of 350 MPa, we can obtain high quality billet which density up to 75% of the relative density.In order to obtain high density products the supersolidus liquid phase sintering technology has been adopted. With the help of DSC detection and phase diagram analysis, we discovered the sintering temperature of high chromium cast iron powder was between 1250℃ to 1270℃. The result of experiment showed that the growth of carbide became more and more obvious as an increase of sintered temperature, sintered density and hardness were parabolically related with sintered temperature. Carbide precipitation increased gradually and had a growing phenomenon as an increase of holding time, but it was not as obvious as the effect of sintered temperature. The density increased gradually with the increase of holding time but the range was not great, Meanwhile carbide precipitation increase gradually and have grew up phenomenon.Major in powder metallurgy sintering high chromium cast iron matrix is martensite and the tiny carbide evenly distributed in the matrix. Comparing with high chromium cast iron produced by cast, the carbide in those produced by powder metallurgy distributed in the matrix with a fine, uniform and bacilliform morphology. Among factors, which influenced size of carbon, sintered temperature occupied first place, holding time came second.Through the sintering experiment to get the best sintering process were: 1264℃ 120min, when the density is 7.65 g/cm3, hardness、bending strength and impact toughness are 66.4 HRC、1199 MPa and 4.6 J/cm2 respectively.The wear resistance of high chromium cast iron was result of carbide and matrix. Suitable heat treatment should be taken in order to obtain highly wear resistance. The heat treatment processes of high chromium cast iron could be divided into hardening, tempering and sub-critical heat treatment. In these experiments, we compared distinct heat treatment temperature’s effect on microstructure and mechanical property, we also analyzed XRD patterns coming from different heat treatment states.The quenching process of sintering high chromium cast iron is:930℃～1120℃ 120min+air cooling. The results showed that with improvement of hardening temperature, carbide precipitation increased gradually and had a growing phenomenon, sharp-corner carbon in a sintered state became tact. With the increase of hardening temperature, impact toughness and bending strength decreased in a small range and then increased, the highest impact toughness、bending strength and hardness were 3.6 J/cm2、1075 MPa and 63.3HRC respectivelyThe quantity of carbide increased and then decreased with increasing tempering temperature, The secondary carbide precipitation phenomenon is obvious. Impact toughness and bending strength increased after the first reduce, the highest impact toughness and bending strength of 3.88 J/cm2 and 1169 MPa respectively when the tempering temperature was 650℃.When the temperature of sub-critical heat treatment was lower than 450℃, carbide did not change obviously, When the temperature was over 450℃, the carbide increased gradually and became much finer and more uniform, When the temperature arrived at 650℃, the carbide had a growing phenomenon. The impact toughness and bending strength decreased accompanying with increase of sub-critical heat treatment’s temperature, and the highest impact toughness and bending strength were 4.1 J/cm2 and 1520 MPa respectively when the sub-critical heat treatment’s temperature was 350℃.XRD pattern showed that the matrix structure of high chromium cast iron in a sintered state could obtain a majority of martensite, then by instable heat treatment and sub- critical heat treatment, retained austenite reduced further. Quenching experiments showed that Cr/C=7.2 powder metallurgy of high chromium cast iron can be water quench and there is no defects such as crack、metal shed that happened in cast high chromium cast iron.Experiments use SiC for grinding grain, on a planetary ball mill 0～30 h abrasion experiment was carried. The result suggested that under the condition of hard abrasive wear TiC base steel bonded carbide wear is bigger than high chromium cast iron, casting and powder metallurgy sintering high chromium cast iron wear is quite. The wear mechanism of TiC-based steel-bonded cemented carbide and high chromium cast iron obtained by powder metallurgy method was primary fatigue delamination wear, and the wear mechanism of cast high chromium cast iron was a combination of multiple plastic-deformation, fatigue wear and micro fracture.