【作者】 何福善；

【导师】 张茂勋；

【作者基本信息】 福州大学 ， 材料加工工程， 2003， 硕士

【摘要】 本研究探讨了深冷处理对高铬铸铁性能的影响。通过洛氏硬度、冲击疲劳试验、疲劳磨损试验和微切削磨损试验等手段较为系统地探索了深冷处理工艺次序、高温淬火过程、延时深冷及回火过程等处理工艺对高铬铸铁宏观性能的影响，得出了一系列的对比结果，并在微观上进行了讨论。研究结果表明，适当的深冷处理可显著提高高铬铸铁的硬度、抗冲击疲劳性能。淬回火工艺和深冷处理工序对高铬铸铁性能有一定的影响，铸态-淬火-深冷处理-回火的处理工艺可获得比铸态-深冷处理-淬火-回火的处理工艺更好的综合机械性能，即更好的硬度、抗冲击疲劳性能、抗微切削磨损和抗疲劳磨损性能等。随着淬火温度下保温时间的延长，高铬铸铁的硬度和抗冲击疲劳性能都有一定的提高，但1.5小时后变化趋势不大，微切削磨损抗力呈下降趋势，抗疲劳磨损性能在保温1.5小时时表现最好。淬火温度下高温缓冷的热处理工艺与直接空冷相比，不论是材料的力学性能还是抗磨损性均不如后者。淬火与深冷处理时间间隔对高铬铸铁性能有显著影响，其中硬度值随间隔时间的延长下降较快，但2天后变化就不明显了，冲击疲劳性能在短期内下降幅度不大，疲劳磨损变化规律与硬度相反，直接深冷的单位磨损量最大，此后呈下降趋势，但变化幅度不大。经高温缓冷后深冷处理的高铬铸铁硬度随着回火温度的提高先升高后降低，峰值硬度出现在450℃上，而冲击疲劳抗力恰恰相反；350℃回火的微切削磨损性能最差，250℃回火的最佳；疲劳磨损抗力在350℃~450℃的中温回火时最低，在500℃回火时最高。深冷处理对提高高铬铸铁性能的作用机制主要表现在深冷处理促进基体中残余奥氏体的分解，促使基体中的碳以微细碳化物形式析出而起到弥散强化以及在回火过程中促进马氏体分解。其中残余奥氏体的分解和微细碳化物的析出是关键因素。深冷处理后马氏体中碳化物的析出程度、深冷前残余奥氏体的量及稳定化程度等将都直接影响高铬铸铁的性能。更多还原

【Abstract】 In this paper, the effects of cryogenic treatment on the properties of High-Chromium Cast Iron (short for HCCI) were studied. By the means of the Rockwell hardness test, repeated impact-fatigue test, surface fatigue test and scratching abrasion test, the influence of the various technique processes including cryo-treating sequence, elevated temperature quenching, time-lapse cryo-treating and tempering on the performance of HCCI have been investigated. And microscopic structure and mechanism have been discussed.The results showed that the proper cryo-treatment can improve the hardness and repeated impact-fatigue resistance of HCCI remarkably. The process of quenching-cryotreating-tempering had better general mechanical performance than that of cryotreating-quenching-tempering. Holding in the quenching temperature, the hardness and the times of the repeated impact-fatigue had a certain boost, but the change was smaller after 1.5 hours. Scratching abrasion resistance had the reverse trend and surface fatigue resistance reached a peak value when holding 1.5 hours. The method of slow cooling after the quenching temperature resulted in worse mechanical performance and wear resistance than cooling in the air directly. There were evident affects of time-lapse cryo-treat after quenching on the properties of HCCI. Hardness of the alloy deceased rapidly with the interval extending, but the trend was minishing after 2 days. The repeated impact-fatigue times dropped in a slower rate. Surface fatigue resistance was the other way round the rule of the hardness, and the weightlessness was largest in method of direct cryo-treat following quenching. After slow-cooling from the quenching temperature and cryo-treating, the hardness of HCCI appeared up and down in the conditions of different tempering temperature, the highest value existed in 450℃. Repeated impact-fatigue resistance worked on the opposite operation. 350℃ and 250℃ are the worst and best temperature for the scratching abrasion resistance respectively. The weightlessness of surface fatigue arrived to most on the medium tempering temperature of 350℃ and 450℃, the optimal wear resistance came forth when tempered on 500℃.The main function mechanism of cryo-treatment acting on the HCCI were retained austenite decomposition, ultra-fine disperse carbides precipitation and martensite micro-decomposition in the matrix. Therein, both retained austenite decomposition and carbides precipitation were the key factors in the cryo-treating process. The extent of carbides precipitated, the amount and stability of retained austenite before cryo-treating would affect the properties of the cryo-treating HCCI directly.更多还原