【作者】 韩波；

【导师】 张福成；

【作者基本信息】 燕山大学 ， 材料学， 2010， 硕士

【摘要】 本文的目的是研究低合金含Al纳米贝氏体辙叉钢的微观组织、力学性能和耐磨性,以及含Al贝氏体钢氢脆现象的第一性原理的计算,为新型贝氏体辙叉钢的设计提供依据,同时从微观角度来研究钢中的氢脆现象。本文以铁路上使用的贝氏体辙叉钢的成分为依据,在满足其各项性能指标的基础上,设计出含Al贝氏体辙叉钢用材。通过对其常规力学性能的测试,得出理想的正火-回火工艺。通过对组织和力学性能的分析,得出理想的等温淬火工艺。通过纳米压痕和纳米划痕实验,对不同热处理工艺下试样的微观力学性能进行研究。利用X射线衍射仪(XRD)、光学显微镜(OM)和透射电镜(TEM)对处理后试样的相组成和组织进行了研究,然后测定了不同热处理工艺下试样的干摩擦磨损性能。最后,利用第一性原理的密度泛函理论,研究了含Al贝氏体钢中的氢脆现象。研究结果表明:本实验材料的最佳正火-回火工艺为:900℃奥氏体化0.5 h,350℃回火2 h。最佳等温淬火工艺为:920℃奥氏体化1 h,350℃等温淬火10 h。试样经正火-回火处理后,硬度值为63.2 HRC,韧性为46.9 J/cm2;经等温淬火处理后,硬度值为47 HRC,韧性为85.4 J/cm2;等温淬火处理后材料的性能满足铁路线路辙叉用钢标准。纳米划痕和压痕试验表明,等温淬火后试样的摩擦系数及微观硬度小于正火-回火处理后的试样,弹性模量大于正火-回火处理后的试样。在载荷为200 N、300 N,转速为200 r/min的条件下,等温淬火后试样的失重小于高速钢标准试样,其耐磨性较好。通过第一性原理对不同铝、硅含量的铁单胞的形成能进行计算,结果表明,钢中可以用Al代替Si作为促进贝氏体转变过程的元素;氢原子进入铝作为置换原子的铁单胞后,体系的相对形成能值大于硅作为置换原子的铁单胞,这说明氢原子更加容易进入铁硅单胞,因此,含Al贝氏体钢比含Si贝氏体钢氢脆敏感性低。更多还原

【Abstract】 The aim of the present dissertation is to investigate the microstructure, mechanical properties and the wear resistance of nano-bainite in low-alloyed Al-containing steels using for crossing, and to calculate hydrogen embrittlement in Al-containing bainitic steels with the first-principles, in order to provide basic data in designing the crossing of new kinds of bainitic steels, and to research hydrogen embrittlement in microcosmos.In this paper, according to chemical constituents of crossing used in high-speed railways and with meeting demand of performance, we have designed the bainitic steels Al-contained used for crossing. With the test of the conventional mechanical properties, we find the optimal craft of normalizing and tempering; By the analysis of microstructure and mechanical properties, the craft of austempering can be gained. Through the nanoindentation and nanoscratch, we can study microcosmic properties of Al-containing bainitic steels. The phase composition and microstructural morphology were studied by X-ray diffractometer, optical microscope and transmission electron microscope. At last, the wear-resistance under the condition of dry sliding friction and wear is also measured.The results show that,the optimal craft of normalizing and tempering is austenitized at 900℃for 0.5 h, then tempered at 350℃for 2 h;The craft of austempering is austenitized at 920℃for 1h, then isothermally quenched at 350℃for 10 h;After normalized and tempered, the rockwell hardness of specimen is 63.2 HRC, the impact toughness is 46.9 J/cm2; After austempered, the rockwell hardness of samples is 47 HRC, the impact toughness is 85.4 J/cm2; The mechanical properties of specimen austempered can meet the demand of the crossing in the railway. The results of the nanoindentation and nanoscratch have shown that friction coefficient and micro-hardness of specimen austempered are less than that normalized and tempered, and the elastic modulus of samples austempered is bigger than that normalized and tempered. With the load of 200 N or 300 N and the spin rates of 200 r/min, the mass loss of samples austempered is less than standard samples of high speed steel, which indicates that the wear-resistant of samples austempered is better.According to first principles, we can calculate the formation energy of FCC structure of Fe with different content of Al or Si. The results show that Al by which replacing Si in steels can accelerate bainitic transformation; When H atom enters into the FCC structure of Fe with Al atom as replaceable atom, the relative formation energy of Fe-Al system is bigger than that of Fe-Si system, which indicates that it is more stabile that H atom enters into Fe-Si system. Consequently, the hydrogen embrittlement of bainitic steel containing Al is lower than that of bainitic steel containing Si.更多还原