【作者】 冯浩； 李花兵； 姜周华； 焦卫超； 代晶；

【Author】 FENG Hao;LI Huabing;JIANG Zhouhua;JIAO Weichao;DAI Jing;School of Metallurgy,Northeastern University;

【机构】 东北大学冶金学院；

【摘要】 航空发动机被誉为高端制造业领域"皇冠上的明珠",其主轴承作为支撑高低压转子平稳运转的核心部件,在高速、高温、重载及受力复杂的服役条件下运转,主轴承材料本身的质量和性能直接影响到发动机性能、寿命和可靠性。根据主轴承的服役工况条件,航空轴承钢需具有耐高温、耐腐蚀、高硬度、高断裂韧性、高滚动接触疲劳寿命及高尺寸稳定性。目前已发展的三代航空轴承钢,均无法满足航空轴承对耐蚀性的迫切需求。传统的不锈轴承钢9Cr18Mo,在凝固过程中会生成粗大的共晶碳化物,降低其硬度、耐蚀性、疲劳强度等。随着高推重比航空发动机技术的发展,主轴承转速和工作温度不断提高,以及舰载机长期在苛刻海洋环境中服役对耐蚀性的需求,极大地推动了高性能、长寿命和高可靠性新型航空轴承钢的研发进程。研究表明,由于氮在晶界偏聚的趋势小,且氮化物细小且分布均匀,能提高马氏体不锈钢的强度、硬度、耐腐蚀性能和疲劳寿命,并且基本不降低韧性。德国基于降碳增氮的理念,利用加压电渣重熔开发了高氮马氏体不锈钢Cronidur 30,已成功应用于航天飞机燃料泵轴承、飞机发动机主轴承、起落架滚珠丝杠、直升机旋转斜盘轴承等。然而,如何合理匹配马氏体不锈钢中的碳氮含量,获得细小、均匀的显微组织以及高强韧性、高耐蚀性的性能,是一个需要解决的问题。本文利用电子背散射衍射、透射电镜、扫描电镜等手段,研究碳氮调控对高氮不锈轴承钢中残余奥氏体、孪晶马氏体及析出相的影响规律。结合拉伸实验、冲击试验和断口观察,阐明以氮代碳对强度、冲击韧性和断裂机制的影响规律,并结合组织演变,揭示其作用机制。利用浸泡腐蚀实验和形貌观察,研究以氮代碳对其耐晶间腐蚀性能的影响规律。研究结果表明,以氮代碳能避免晶界上粗大碳化物的形成,使析出相类型由M₂₃C₆变为M₂₃C₆+M₂N,继而又转变为M₂N。以氮代碳使有效晶粒尺寸、γ_R和α’_TM的含量先升高后降低,而碳氮化物含量的变化趋势则正好相反。高的γ_R含量能提高马氏体不锈钢的冲击韧性,但也会降低其强度。以氮代碳使马氏体不锈钢强度先降低后升高,并且断裂机制由典型的脆性断裂转变为了韧性与脆性混合型断裂。以氮代碳显著提高0.35C-0.37N钢的冲击韧性,比0.50C-0.16N和0.20C-0.54N钢分别高出了一倍和两倍,而其强度仍可保持在较高水平。以氮代碳先增强后降低实验钢的耐晶间腐蚀性能,主要与碳氮化物析出含量和析出相类型转变有关。0.35C-0.37N钢兼具良好的力学性能和较强的耐晶间腐蚀性能。更多还原

【Abstract】 The aerospace engine is recognized as the jewel in the crown of the high-end manufacturing.The main bearing is the key component to sustain the stable and reliable operation of high-and-low pressure rotor,and has to endure high speed,high temperature,high load and complex force.The quality and performance of the material for main bearing could directly affect the performance,service life and reliability of the engine.Based on the service condition of the main bearing,the aerospace bearing steels must possess high temperature resistance,corrosion resistance,high hardness,high fracture toughness,high rolling contact fatigue life and high dimensional stability.The current three generations aerospace bearing steels could not meet the urgent demand of corrosion resistance for aerospace bearings.The conventional high carbon martensitic stainless steels 9 Cr18Mo would precipitate coarse eutectic carbides during solidification,which would reduce its hardness,corrosion resistance and fatigue strength,etc.With the development of aerospace bearing with high thrust-weight ratio,the rotation rate and working temperature of main bearing were increased.Moreover,the demanding for corrosion resistance of the carrier-based planes,which serve in the harsh marine environment for long term,has substantially promoted the R & D process of new aerospace bearing with high performance,long service life and high reliability.Previous researchers indicated that due to the low segregation tendency of nitrogen,the tiny nitrides spread uniformly in steels,which could enhance the strength,hardness,corrosion resistance and fatigue life,and almost not reduce the toughness of martensitic stainless steels.Based on the idea of increasing nitrogen and decreasing carbon,the high nitrogen martensitic stainless steel Cronidur30 was developed using pressurized electroslag remelting in Germany,and had been successfully used in fuel pump bearing of aerospace plane,main bearing of airplane,landing gear ball screw and rotary swash plate bearing,etc.However,the question of how to reasonably match the carbon and nitrogen contents in martensitic stainless steels to obtain tiny and uniform microstructure as well as high strength-toughness and high corrosion resistance is still needed to be solved.This paper investigated the influence of carbon-nitrogen regulation on retained austenite,twinned martensite and precipitates by using EBSD,TEM and SEM,etc.Combined with the tensile test,impact test and fracture observation,the effect of partial substitution of C by N on strength,toughness and fracture mechanism was revealed.In addition,the influence of partial substitution of C by N on intergranular corrosion resistance（IGC） was studied using immersion corrosion tests and morphology observation.The results showed that the partial substitution of C by N avoided the formation of coarse carbides located on the grain boundaries,and the sequence of precipitation was M₂₃C₆ to M₂₃C₆+M₂ N and finally to M2 N.The partial substitution of C by N first raised and then dropped the effective grain size,the fraction of γR and α’_TM,while the variation of the amount of carbonitrides was just the opposite.The high fraction of γ_R was confirmed to confer the impact toughness of high nitrogen stainless bearing steels significantly,though the strength was lowered.The partial substitution of C by N first dropped then raised the strength of high nitrogen stainless bearing steels,whereas it caused the variation of fracture characteristics from the typical brittle to a mixed ductile and brittle mode.The partial substitution of C by N resulted in the substantial increase of impact toughness of 0.35 C-0.37 N steel,which was two or three times higher than 0.50 C-0.16 N and 0.20 C-0.54 N steels,even at the high strength level.The partial substitution of C by N first enhanced and then deteriorated the IGC resistance.The 0.35 C-0.37 N high nitrogen stainless bearing steel possessed good combination of mechanical properties and IGC resistance.更多还原