刀剪用高碳马氏体不锈钢生产过程组织演变行为研究

发布时间：2018-05-16 07:20

本文选题：马氏体不锈钢 + 电渣重熔　；参考：《北京科技大学》2016年博士论文

【摘要】：国产刀剪在锋利度、耐磨性、使用寿命等方面与进口刀剪相比还存在明显差距,而且国内的有关研究,特别是高碳刀剪材料的研究,还比较有限。因此,本文以刀剪用高碳马氏体不锈钢7Cr17MoV为研究对象,针对其在生产过程中组织、碳化物及性能的演变开展模拟计算及实验研究,以期为高品质马氏体不锈钢刀剪材料的生产和应用提供合理依据和指导。论文的主要研究内容和结论如下：利用Thermo-calc软件计算分析了7Cr17MoV不锈钢凝固过程中各相的析出规律和演变行为,得到含铬量为17%的Fe-C平衡相图。随着凝固的进行,铁素体、奥氏体、碳化物等各相中的元素含量不断发生变化。M7C3碳化物从奥氏体中脱溶析出,随后向M23C6碳化物转变,碳化物中Cr含量不断增加。7Cr17MoV不锈钢平衡凝固过程最终组织为87%的铁素体和13%的M23C6碳化物。通过电渣重熔7Cr17MoV不锈钢实验研究发现,电渣重熔后,基体组织由马氏体和网状碳化物转变为马氏体、残余奥氏体和离散分布的碳化物,碳化物的形貌和分布获得有效改善。通过调整渣系组成和渣量,提高了材料中夹杂物的去除效率。采用Gleeble-3500热模拟试验机,研究了7Cr17MoV不锈钢的热压缩变形行为。结果表明：随着应变的增加,应力首先迅速增加,随后缓慢增加,达到峰值后,缓慢下降趋于平稳。高的变形温度和低的应变速率有利于动态再结晶的发生,峰值应力随着应变速率的降低和变形温度的增加而减小。随着变形温度的升高、变形速率的减小和冷却速度的增加,材料的微观组织细化。同时,建立了材料热变形时的流变应力本构方程。轧制对7Cr17MoV中组织、碳化物及性能的影响研究表明,7Cr17MoV钢轧制退火组织为珠光体和碳化物,热轧板材中碳化物有明显偏聚现象,冷轧后板材组织变得更加均匀和细化,碳化物偏聚现象明显减轻。随着冷轧厚度的减小,碳化物尺寸减小,数量增加,分布更加均匀。轧制不改变碳化物的类型。随着冷轧厚度的减小,7Cr17MoV的抗拉强度和屈服强度先降低后增加,断后延伸率显著增加。拉伸断口处可见韧窝和第二相粒子,第二相粒子主要是碳化物和氧化物夹杂。对7Cr17MoV不锈钢冷轧薄带热处理的研究结果表明：随着淬火温度的升高,马氏体长大,残余奥氏体含量增加,未溶碳化物减少,材料硬度增加,耐蚀性能增加。当淬火温度增加到1150℃时,材料硬度下降明显,耐蚀性能下降。淬火保温时间对材料的组织性能影响较小。随着回火温度的升高,组织中残余奥氏体分解,碳化物析出,材料硬度降低,抗拉强度下降,断后延伸率先增加后降低,最终得出材料最优热处理工艺为：淬火温度1050℃-1100℃,保温时间大于15 min,随后在200℃-250℃回火,材料的综合性能最优。热处理后,材料的硬度值大于55 HRC,抗拉强度大于1800 MPa,规定塑性延伸强度大于1400MPa,断后延伸率大于4%,自腐蚀电位大于-0.25 V,自腐蚀电流小于2.0×10-8 A/cm2。
[Abstract]:There is a significant difference in the sharpness, wear resistance and service life of the domestic knives and scissors compared with the imported knives and scissors, and the domestic research, especially the high carbon knife and scissors, is still relatively limited. Therefore, the high carbon martensitic stainless steel 7Cr17MoV is used as the research object in this paper, and the carbide and the carbide are organized in the process of production. The simulation calculation and experimental study are carried out to provide reasonable basis and guidance for the production and application of high quality martensitic stainless steel knife and scissors. The main contents and conclusions of this paper are as follows: the Precipitation Law and evolution behavior of each phase in the solidification process of 7Cr17MoV stainless steel are calculated and analyzed by Thermo-calc software. To the Fe-C equilibrium phase diagram with a chromium content of 17%, the content of elements in each phase of ferrite, austenite, carbide and so on is constantly changing with the solidification..M7C3 carbides are dissoluble from austenite, and then to M23C6 carbides, and the content of Cr in the carbides continuously increases the final microstructure of the.7Cr17MoV stainless steel in the equilibrium solidification process of 87% iron. Through the experimental study on the remelting of 7Cr17MoV stainless steel by electroslag remelting, it is found that the matrix microstructure is transformed from martensite and reticulate carbide to martensite, residual austenite and dispersed carbide, the morphology and distribution of carbides are effectively modified after remelting of electroslag remelting, and the material is improved by adjusting the composition of slag system and the amount of slag. The thermal compression deformation behavior of 7Cr17MoV stainless steel was studied by Gleeble-3500 thermal simulation test machine. The results showed that with the increase of strain, the stress first increased rapidly, and then slowly increased, after reaching the peak, the slow descent tended to be stable. The high deformation temperature and low strain rate were beneficial to the dynamic re junction. The peak stress decreases with the decrease of the strain rate and the increase of the deformation temperature. With the increase of the deformation temperature, the decrease of the deformation rate and the increase of the cooling rate, the microstructure of the material is refined. At the same time, the constitutive formula of the rheological stress in the thermal deformation of the material is established. The rolling of the microstructure, carbides and properties in 7Cr17MoV The study shows that the microstructure of 7Cr17MoV steel annealed is pearlite and carbide, and the carbide has obvious segregation phenomenon in hot rolled sheet. The structure of the plate becomes more uniform and refined after cold rolling, and the segregation phenomenon of carbide decreases obviously. With the decrease of the cold rolling thickness, the size of carbide decreases, the quantity is increased and the distribution is more uniform. Rolling is not changed. The type of carbide. With the decrease of the cold rolling thickness, the tensile strength and yield strength of 7Cr17MoV first decrease and then increase, and the elongation after fracture increases significantly. The second phase particles are mainly carbide and oxide inclusions at the tensile fracture. The results of the study on the heat treatment of the cold rolled strip of 7Cr17MoV stainless steel show that: As the quenching temperature increases, the martensite grows, the retained austenite content increases, the undissolved carbide decreases, the material hardness increases, and the corrosion resistance increases. When the quenching temperature increases to 1150 C, the hardness of the material decreases obviously and the corrosion resistance decreases. The heat preservation time has little effect on the fabric properties. With the increase of tempering temperature, the microstructure of the material is increased. The residual austenite decomposition, carbide precipitation, material hardness and tensile strength decrease, the elongation after fracture first increases and then decreases. Finally, the optimum heat treatment process of material is: quenching temperature 1050 -1100 C, heat preservation time greater than 15 min, and then tempering at 200 c -250 C, the material has the best comprehensive performance. After heat treatment, the hardness value of the material More than 55 HRC, tensile strength is greater than 1800 MPa, the specified plastic extension strength is greater than 1400MPa, the elongation after fracture is more than 4%, the corrosion potential is greater than -0.25 V, and the corrosion current is less than 2 x 10-8 A/cm2.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG142.71;TG335;TG161

【参考文献】