The Effect of Vacuum-Carbosintering on the Microstructure and Mechanical Properties of Pre-Alloyed Powder Metallurgy Steel Parts

Abstract

This study investigated the simultaneous applicability of sintering (S) and vacuum carburizing (VC) processes of pre-alloyed powder metallurgy (PM) steel parts by vacuum-carbosintering (VCS) method in industrial-type low-pressure vacuum carburizing (LPVC) furnaces. In this context, the specimens were subjected to S, S + VC (VCS) and direct VCS heat treatments after warm pressing (WP). Subsequently, mechanical tests and microstructure characterization were carried out. In the specimens, a density value of 6.39 g/cm(3) was obtained after WP. This value increased to 6.74 g/cm(3) after VCS heat treatment, but this increase remained limited. A final density value of 7.32 g/cm(3) was obtained after SVC heat treatment. While VCS specimens had a surface carbon concentration of 1.798 wt.%C, SVC specimens have a surface carbon concentration of 1.179 wt.%C. The carbon concentration decreased from the surface to the center, and this decrease occurred faster in VCS specimens. While VCS specimens had a case depth of similar to 2 mm, SVC specimens had a case depth of similar to 2.5 mm. After VC heat treatment, SVC specimens had a surface hardness of 517.7 HV1.0. VCS specimens had a surface hardness of 478.1 HV1.0. S specimens had the lowest hardness value (98.1 HV1.0). The lowest three-point bending strength was obtained as 192.3 MPa in S specimens. These specimens exhibited a uniform elongation of 3.5%. VC heat treatment increased the three-point bending strength of the specimens. The highest three-point bending strength was obtained as 248 MPa in SVC specimens. This value was 157 MPa in VCS specimens. Both specimens did not exhibit uniform elongation. The results of the study showed that the S and VC processes of PM steel parts can be successfully applied simultaneously using the VCS method in industrial-type LPVC furnaces. [GRAPHICS] .