论文部分内容阅读
钢的烧结硬化是一种快速发展的粉末冶金工艺,它能够通过足够快的烧结后冷却速率来产生具有“烧结态”马氏体组织的高强度材料。烧结硬化日趋广泛的应用需要对达到必要的硬度与强度所需的冷却速率有更深入的了解。由于不同几何尺寸零件内部冷却速率与其组成物的热导率和表面积/体积比有关,故从两个方面进行了研究。第一部分模拟了在工业装置中进行的烧结硬化的冷却阶段,通过数值方法计算了棱柱试样的等温面。试样密度分别设为6.8 g/cm~3和7.0 g/cm~3,试样为不同高度的等截面棱柱体,其质量从200 g到近2 000 g不等。第二部分对这些烧结硬化棱柱试样进行试验研究,结合数值分析结果 ,对微观组织的性能、显微硬度、宏观硬度和强度等进行了深入研究。结果表明,显微组织依赖于由数值模型预测的等温面,与显微硬度和力学性能是相符合的。此外发现,能够完全烧结硬化的试样质量达到了200 g,而且看来表面积/体积比是关键因素。最后,数值分析和试验表明,孔隙能影响粉末冶金零件的冷却速率,因而在定义粉末冶金钢的淬透性时应考虑孔隙因素。
Sinter hardening of steel is a rapidly evolving powder metallurgy process that produces high-strength materials with “sintered” martensite by fast enough post-sintering cooling rates. The increasing use of sinter hardening requires a deeper understanding of the cooling rates required to achieve the necessary hardness and strength. Due to the different cooling rate of the internal geometry of the parts with the thermal conductivity and surface area / volume ratio of the composition, so from two aspects of the study. The first part simulates the cooling stage of the sinter hardening in an industrial plant and calculates the isothermal surface of a prismatic sample numerically. The sample densities were set at 6.8 g / cm ~ 3 and 7.0 g / cm ~ 3, respectively. The specimens were of different heights with equal cross-sections and their masses ranged from 200 g to nearly 2,000 g. The second part of these sintered hardened prismatic samples for experimental study, combined with numerical analysis of the microstructure properties, microhardness, macroscopic hardness and strength were in-depth study. The results show that the microstructure relies on the isothermal surface predicted by the numerical model, which is consistent with the microhardness and mechanical properties. In addition, it was found that the mass of sample that can be fully sintered and hardened reached 200 g, and it appears that the surface area / volume ratio is the key factor. Finally, numerical analysis and experiments show that the porosity can affect the cooling rate of powder metallurgy parts, so pore factors should be considered when defining the hardenability of powder metallurgy steel.