Study on tool steels with ultrahigh carbon and ultrahigh chromium prepared by vacuum hot-pressing
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摘要: 采用真空热压技术制备了含有超高碳和铬（2.6%C，26%Cr，质量分数）的模具钢。基于差示扫描量热分析曲线，选取两个远低于熔点的温度（1100 ℃和1150 ℃）进行热压，分别制造出几乎完全致密、粉末之间冶金结合良好的块体钢，密度为7.45～7.47 g∙cm−3；对应热压温度1100 ℃ 和1150 ℃，热压态钢中平均碳化物尺寸分别为3.5 μm和5.5 μm，最大碳化物尺寸分别为6.0 μm和8.5 μm。经1150 ℃淬火、500 ℃回火，1100 ℃ 和1150 ℃热压钢的平均硬度分别为HRC 62.6和HRC 60.8，平均三点弯曲强度分别为2060 MPa和1850 MPa；经1150 ℃淬火、550 ℃回火，1100 ℃ 和1150 ℃热压钢硬度分别为HRC 55.2和HRC 53.6，平均三点弯曲强度分别为2490 MPa和2320 MPa。在相同淬火和回火条件下，1100 ℃热压钢的三点弯曲强度较高，原因是淬火回火后钢中碳化物尺寸较小。Abstract: 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.
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Key words:
- vacuum hot-pressing /
- powder metallurgy /
- high carbon and high chromium /
- tool steels /
- carbides
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图 1 粉末升温和降温的差示扫描量热分析曲线
Figure 1. DSC curves of the powders in the heating and cooling process
图 2 粉末和热压态钢X射线衍射图谱
Figure 2. X-ray diffraction patterns of the powders and as-VHP steels
图 3 原始粉末显微形貌：（a）低倍；（b）高倍
Figure 3. Microstructures of the raw powders: (a) lower magnification; (b) higher magnification
图 5 热压态抛光面光学显微形貌：（a）1100 ℃;（b）1150 ℃
Figure 5. Optical microstructures of the polished surfaces of the as-VHP steels: (a) 1100 ℃; (b) 1150 ℃
图 6 热压态试样显微组织形貌：（a）1100 ℃;（b）1150 ℃
Figure 6. Microstructures of the as-VHP steels: (a) 1100 ℃; (b) 1150 ℃
图 7 淬火+回火态试样显微形貌：（a）1100 ℃热压，1150 ℃淬火，500 ℃回火；（b）1150 ℃ 热压，1150 ℃淬火，500 ℃回火；（c）1100 ℃热压，1150 ℃淬火，550 ℃回火；（d）1150 ℃热压，1150 ℃淬火，550 ℃回火
Figure 7. Microstructures of the as-VHP steels after quenching at 1150 ℃ and tempering: (a) VHP at 1100 ℃ and tempering at 500 ℃; (b) VHP at 1150 ℃ and tempering at 500 ℃; (c) VHP at 1100 ℃ and tempering at 550 ℃; (d) VHP at 1150 ℃ and tempering at 550 ℃
图 8 热压块体钢1150 ℃淬火、500 ℃和550 ℃回火后的硬度
Figure 8. Hardness of the VHP steels after quenching at 1150 ℃ and tempering at 500 ℃和550 ℃
图 9 热压钢1150 ℃淬火、500 ℃和550 ℃回火后的三点弯曲强度
Figure 9. Three-point bending strength of the VHP steels after quenching at 1150 ℃ and tempering at 500 ℃和550 ℃
表 1 原料粉末化学成分（质量分数）
Table 1. Chemical composition of the raw powders
% C Cr V Mo Nb Fe 2.6 26.0 2.3 1.1 1.4 余量 
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