Study on tool steels with ultrahigh carbon and ultrahigh chromium prepared by vacuum hot-pressing

Tool steels with the ultrahigh C and Cr (2.6% C and 26% Cr, mass fraction) were produced by the vacuum hot-pressing (VHP) in this study. Based on the differential scanning calorimetry analysis, two VHP temperatures (1100 ℃ and 1150 ℃) are selected which are much lower than the melting point. The bulk steels with the density of 7.45~7.47 g∙cm⁻³ are obtained by VHP at 1100 ℃ and 1150 ℃, respectively, exhibiting the full densification and good metallurgical bonding between powders. The average carbide sizes in the bulk steels obtained by VHP at 1100 ℃ and 1150 ℃ are 3.5 μm and 5.5 μm, and the maximum carbide sizes are 6.0 μm and 8.5 μm, respectively. After quenching at 1150 ℃ and tempering at 500 ℃, the average hardness values of the bulk steels obtained by VHP at 1100 ℃ and 1150 ℃ are approximately HRC 62.6 and HRC 60.8, and the average three-point bending strengths are 2060 MPa and 1850 MPa, respectively. After quenching at 1150 ℃ and tempering at 550 ℃, the average hardness values of the bulk steels obtained by VHP at 1100 ℃ and 1150 ℃ are approximately HRC 55.2 and HRC 53.6, and the average three-point bending strengths are 2490 MPa and 2320 MPa, respectively. At the same quenching and tempering conditions, the higher three-point bending strengths of the bulk steels obtained by VHP at 1100 ℃ can be attributed to the smaller carbide sizes.