贝氏体等温淬火对Dievar热作模具钢高温摩擦磨损性能的影响

利用贝氏体等温淬火工艺在Dievar钢中制备不同体积比例的贝/马复相微观组织，通过对显微组织、宏观/微观硬度、磨面形貌、磨屑和磨损率的分析进一步研究了贝/马复相Dievar热作模具钢的高温摩擦磨损性能并探讨其磨损机制。结果表明，Dievar钢中下贝氏体含量随等温淬火保温时间的延长而增加，其中保温3、5、10 min时下贝氏体体积占比分别为32%、45%、63%。贝/马复相试样相比于传统油淬试样具有更高的回火抗性，不同等温试样硬度值均高于传统油淬试样硬度值。同等磨损条件下，等温淬火Dievar钢相较于常规热处理Dievar钢耐磨性更加优异。在400～600℃高温摩擦磨损试验条件下，Dievar钢表面氧化物为Fe₂O₃和Fe₃O₄。Dievar钢400～500℃高温磨损机制为磨粒-轻微氧化磨损；随着温度升高，氧化物颗粒尺寸变大，磨粒磨损加剧。当温度升至600℃时，常规油淬试样磨损机制为磨粒-氧化磨损，以磨粒磨损为主；而等温淬火试样磨损机制则以氧化磨损为主。

Effect of austempering on high temperature frictional wear property of Dievar hot working die steel

Mixed microstructure with different volume fractions of lower bainite and martensite was produced in Dievar steel by austempering, and then the high temperature frictional wear performance and mechanism of the Dievar steel were investigated based on the microstructure identification, hardness evaluation, worn surface morphology and wear rate analysis. The results show that the volume fraction of lower bainite in the Dievar steel increases with the increase of austempering time, where the bainitic volume fractions are 32%, 45% and 63% with isothermal holding for 3, 5 and 10 min respectively. Compared to the conventional oil quenched specimens, the specimens with the mixed microstructure have higher tempering resistance. The hardness values for austempered specimens are higher than that of oil quenched ones. In addition, the austempered specimens exhibit better wear resistance compared to the conventional oil quenched ones under the same wear condition. Under the high temperature friction and wear test conditions of 400-600 ℃, the surface oxides of the Dievar steel are Fe₂O₃ and Fe₃O₄. The high temperature wear mechanism at 400-500 ℃ for the Dievar steel is abrasive-slight oxidation wear. As the temperature increases, the size of oxide particles becomes larger and the abrasive wear is strengthened. When the temperature approaches to 600 ℃, the high temperature wear mechanism for the conventional oil quenched specimens is still maintained as abrasive-oxidation wear, mainly abrasive wear, however, it alters to the oxidation wear for the austempered specimens.