The effect of steam treatment and precipitation hardening on the mechanical properties and wear resistance of sintered iron and iron-copper alloys
Steam treatments reduce porosity(1) of sintered iron and sintered iron-base alloy products and provide them with increased compressive strength, hardness, resistance to wear and corrosion. The aims of the present investigation were: (a) to examine the influence of copper content and process variables on the response of sintered iron to steam treatment. (b) to explore the possibility of combining steam treatment with precipitation hardening in sintered iron/copper alloys. (c) to survey the influence of process parameters on the mechanical and wear properties of these materials. Samples prepared from - 100# A.S.C. iron powder and - 100# pre-alloyed powder containing 2,4,6 and 8% copper, pressed to densities of 6.0, 6.4, 6.8 g/cc and sintered for 1 hour at 1120 oC were treated in superheated steam and inert gas at 525 oC for periods ranging from 5 to 100 minutes and under vacuun for 500 hours. The main results of the investigation were: (i) Addition of copper in amounts of 2 to 8% slightly improves the resistance of iron to steam oxidation. (ii) During ageing in steam, the hardness increased due to simultaneous precipitation of copper from solution and formation of and void filling by layers of iron oxide. The results indicated that maximum benefit is for Fe - 2% Cu alloy and steam ageing of higher copper content alloys reduces the effect of precipitation of copper. (iii) Steam treatment of sintered. pure iron improvesthe wear properties but the effect of this treatment on Fe-Cu. alloys is not pronounced and sometimes disadvantageous. (iv) Steam oxidation of sintered pure iron improved radial-crushing stress (R.C.S.) but this treatnent reduced the R.C.S. of iron-copper alloys.