不同表面处理工艺对高强螺栓钢组织及性能的影响

发布时间：2018-09-18 10:17

【摘要】：本文采用调质处理+低温气体多元共渗+电镀锌复合处理工艺,不仅使45钢和20MnTiB合金钢的力学性能得到了提升,还显著提高了其耐腐蚀性能和耐疲劳性能。该工艺主要用于高强螺栓的表面处理,试样表面美观,具有较高的硬度、抗拉强度以及良好的冲击韧性,同时还有很好的防腐性能和较高的疲劳强度,该新型复合处理工艺具有重要的工业价值。分别对8.8级高强螺栓钢(调质态45钢)和10.9级高强螺栓钢(调质态20MnTiB钢)进行三种不同的表面处理(多元共渗、镀锌处理、复合处理),利用激光共聚焦、超景深三维显微镜、X射线衍射(XRD)等分析测试技术,对不同表面处理后的两种高强螺栓钢试样进行了显微组织和宏观形貌观察,分析了其表层的物相组成,测定了镀锌层和多元渗层的结合强度及其常规力学性能,采用中性盐雾腐蚀试验和高频疲劳试验分析评价了其防腐性能和疲劳性能,通过扫描电镜(SEM)分析了其拉伸和疲劳断裂机理。试验结果表明:45钢复合处理后,晶粒更加细小,渗镀层组织均匀致密,镀锌层与多元渗层的结合强度良好,渗镀层厚度为50μm;经XRD分析得出样品表面存在有Zn(镀锌层)、氮化物(Fe3N)、碳化物(Fe3C)和氧化物(Fe3O4),其中碳化物和氮化物起到弥散强化的作用;渗镀层的显微硬度最大可达到636HV0.025左右,大约是基体显微硬度的两倍;抗拉强度为830MPa,提高到原材的1倍;冲击吸收功为32.9J,是原材的78%;其抗盐雾时间845h后保护等级达到9级(观察面开始出现少许点状红锈),防腐时间达到了原材的170倍左右;缺口试样的条件疲劳极限为369MPa,较原材的缺口试样有所提升。20MnTiB合金钢复合处理后,由于合金元素的影响,其渗镀层厚度仅仅28μm;渗镀层的物相主要有Zn(镀锌层)、氮化物(Fe3N)、氧化物(Fe203)和碳化物(Fe3C)等。渗镀层显微硬度最高可达到756HV0.025,抗拉强度可达到904MPa,提高到原材的1.1倍,冲击吸收功为166.5J,表现为较好的冲击韧性,但较调质态有所下降,其抗盐雾时间846h后保护等级达到9级,得到了大幅度的提高,缺口试样的条件疲劳极限为382MPa,较原材的缺口试样有所提高。
[Abstract]:In this paper, the mechanical properties of 45 steel and 20MnTiB alloy steel have been improved, and the corrosion resistance and fatigue resistance of 45 steel and 20MnTiB alloy steel have also been improved. The process is mainly used for the surface treatment of high strength bolts. The surface of the sample is beautiful, with high hardness, tensile strength and good impact toughness, at the same time, it also has good anticorrosive property and high fatigue strength. The new composite treatment process has important industrial value. Three different surface treatments (multicomponent co-infiltration, galvanizing treatment and composite treatment) were carried out on 8.8-grade high strength bolt steel (quenched and tempered 45 steel) and 10.9 grade high strength bolt steel (quenched and tempered 20MnTiB steel). The microstructure and macroscopic morphology of two kinds of high strength bolted steel specimens after different surface treatment were observed by means of X ray diffraction (XRD) and other techniques. The phase composition of the surface layer was analyzed. The bonding strength and conventional mechanical properties of galvanized and multicomponent coating were measured. The corrosion resistance and fatigue performance of zinc coating were evaluated by neutral salt spray corrosion test and high frequency fatigue test. The tensile and fatigue fracture mechanisms were analyzed by scanning electron microscope (SEM). The results show that the grain size is finer, the microstructure of the coating is uniform and compact, and the bonding strength between the galvanizing layer and the multicomponent layer is good. The thickness of percolation coating is 50 渭 m. XRD analysis shows that there are Zn (galvanized layer), nitride (Fe3N), carbide (Fe3C) and oxide (Fe3O4) on the surface of the sample, in which carbides and nitrides play the role of dispersion strengthening, and the microhardness of the coating can reach about 636HV0.025. The tensile strength is 830MPa, which is twice as high as that of the original material. The impact absorption energy is 32.9J, which is 78% of the original material, and the protective grade is 9 after the salt spray resistance time is 845h (the observed surface begins to appear a little spot red rust), and the anticorrosion time is about 170 times of the original material. The fatigue limit of the notched specimen is 369MPa. Compared with the notched specimen of the original material, the fatigue limit of the notched specimen is increased. 20MnTiB alloy steel after composite treatment, due to the effect of alloying elements, The coating thickness is only 28 渭 m. The main phases of the coating are Zn (galvanizing layer), nitride (Fe3N), oxide (Fe203) and carbides (Fe3C). The microhardness and tensile strength of the permeable coating can reach 756HV0.025 and 904MPa, which can be increased to 1.1 times of the original material, and the impact absorption energy is 166.5J. the impact toughness of the coating is better, but it is lower than that of the tempering state. The protective grade of the coating is 9 after the salt spray resistance time is 846 hours. The fatigue limit of the notched specimen is 382 MPA, which is higher than that of the original notched specimen.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1;TG178

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