Abstract
In order to improve mechanical properties of sinter-forged Cr bearing low alloy steel, effects of primary sintering of preforms and secondary sintering after forging on mechanical properties were examined for spherical powder having the porous surface layer (CP) and conventional P/M steel powder of under 100 mesh size (FP). Results were summarized as follow:
1) Oxygen contents of CP and FP preforms were 50-60 and 100110 ppm respectively at the primary sintering temperature of 1250°C for 60 min.
2) At the forging temperature of 1100°C, the densities of both CP and FP sinter-forged steels were saturated at the forging pressure of 9 t/cm2.
3) The impact strength of CP sinter-forged steels was influenced by the mean free path of small pores, as well as oxygen content.
4) The secondary sintering plays an important role for increasing the impact strength of both CP and FP sinter-forged steels. With increasing sintering temperature, residual pores became spherical and impact strength increased. The impact strength of the sinter-forged steels sintered under the secondary sintering conditions (for example at 1250°C for over 30 min) was located in the range of 13.5-15 kg-m/cm2. while those of CP and FP sinter-forged steels (without the secondary sintering) were 8-9 and 8.5-9.5 kg-m/cm2 respectively.
5) Tensile strength and hardness of both CP and FP sinter-forged steels were not influenced by the sintering conditions.
