含Al超纯铁素体不锈钢再结晶行为、成形性和高温抗氧化性能研究

发布时间：2018-04-11 17:08

本文选题：铁素体不锈钢 + 再结晶　；参考：《上海大学》2016年博士论文

【摘要】：铁素体不锈钢由于仅含少量镍或不含镍,在镍资源越来越紧张的今天,正逐步替代奥氏体不锈钢,在汽车,家电等领域获得广泛应用,成为一种资源节约型的绿色环保不锈钢材料。但是与奥氏体不锈钢相比,铁素体不锈钢在力学,成形性,耐蚀,抗氧化等方面仍然存在一定的不足。近年来,随着不锈钢冶炼技术和精炼技术的发展和应用,使得铁素体不锈钢中的C,N等有害元素含量大幅降低,超纯铁素体不锈钢的耐蚀性能获得有效提高。研究发现,在钢液凝固过程中,Al不但能促进非均匀异质形核,提高等轴晶比例,降低板材各向异性,而且还能在热处理过程中细化晶粒,提高板材力学性能。更为重要的是,当Al达到一定含量时,可以在不锈钢表面形成一层致密的富Al_2O_3氧化膜,大幅提高不锈钢的抗高温氧化性能。本文主要研究了合金元素Al对超纯铁素体不锈钢的再结晶行为、成形性能和1000oC等温氧化行为的影响。通过采用金相显微镜、XRD衍射、SEM扫描电镜、TEM透射电镜、EBSD背散射衍射及Thermo-Calc热力学平衡相图计算等技术手段研究了微观组织结构的演变规律。主要结论如下:1)Al可以显著降低429超纯铁素体不锈钢的再结晶温度,冷轧退火后的平均晶粒大小随着Al含量的增加有少量增加,这主要是因为再结晶温度和夹杂物的面积分数的显著降低。室温拉伸抗拉强度和屈服强度随着Al含量的增加而线性提高,延伸率变化不大,但是塑性应变比先增加后减少,含0.16 wt.%Al样品呈现出最高的塑性应变比r=1.62。Al含量的增加可以显著改善429超纯铁素体不锈钢的高温拉伸和压缩力学性能。随着Al含量的提高,基体和晶界夹杂物类型从单相的TiN演变成复合MgO·Al_2O_3-TiN颗粒,并且夹杂物的平均大小有少量的增加而面积比例分数降低。Al含量的增加可以显著改善抗点蚀性能。2)冷轧和退火后429超纯铁素体不锈钢表层和中心层的织构从α+γ织构演变成完全的γ织构,并且0.16 wt.%Al的加入提高了(111)[-1-12]和(111)[-2-35]织构的强度,但是当Al含量进一步增加到1.51 wt.%时γ织构强度反而降低了。厚度方向的γ织构随着Al含量的增加,从(111)[1-21]转到(111)[3-52],且0.16 wt.%的Al可以显著提高γ织构的强度。不含Al样品冷轧退火后γ-织构在室温拉伸后消失了,而含0.16 wt.%Al样品中γ-织构仍然占主导,111//ND的最高强度为4.6。含1.51 wt.%Al样品室温拉伸后(111)[0-11]织构强度显著降低。含0.16 wt.%Al的429超纯铁素体不锈钢具有最强γ织构。3)429超纯铁素体不锈钢1000oC氧化增重曲线呈现典型的抛物线规律。氧化较短时间后,不含Al样品呈球状形貌的局部区域优先氧化,随着氧化时间的增加表面氧化膜扩展到整个样品表面且球状氧化产物长到一起,氧化产物顶端存在一些细小的孔洞。随着Al含量的增加,表面氧化膜形貌较为均匀,氧化产物呈颗粒状形貌。氧化膜呈现出多层结构,外层氧化膜富含Fe_2O_3和少量的Fe_3O_4,外层氧化膜下方有Cr_2O_3,中间层氧化膜富含Fe_2O_3和Cr_2O_3,内层氧化膜富含Fe_3O_4。随着Al含量的提高,氧化膜厚度减少,低Al含量样品高温抗氧化性能的改善主要依靠Cr_2O_3。当Al含量增加到1.51 wt.%时,氧化较短时间后样品表面出现了富Al_2O_3的氧化膜,随着氧化时间的增加,氧化膜厚度增加不显著。1.51 wt.%Al样品表层下形成的具有保护性的、均匀的、完整的、富Al_2O_3的氧化膜,显著提高429超纯铁素体不锈钢的高温抗氧化性能。
[Abstract]:Ferritic stainless steel due to only small amounts of nickel or nickel free, in nickel resources increasingly tense today, is gradually replacing the austenitic stainless steel, widely used in automobiles, household appliances and other fields, become green stainless steel material is a kind of resource saving. But compared with austenitic stainless steel, ferritic stainless steel in mechanics, forming property, corrosion resistance, anti-oxidation and other aspects still exist some shortcomings. In recent years, with the development and application of stainless steel smelting and refining technology, the ferritic stainless steel of C, N and other harmful elements were significantly reduced, the corrosion resistance of ultra pure ferritic stainless steel was effectively improved. The study found that in liquid steel during the solidification process of Al can not only promote the inhomogeneous nucleation, increase the proportion of equiaxed grains, reduce material anisotropy, but also refine the grain in the heat treatment process, improve the mechanical properties of the plate more. It is important that when Al reached a certain level, Al_2O_3 rich oxide film can form a dense layer on the surface of stainless steel, greatly improve the oxidation resistance of stainless steel. This paper mainly studies the alloy element Al on ultra pure ferritic stainless steel recrystallization behavior, forming property and 1000oC isothermal oxidation behavior by means of metallographic. Microscope, XRD diffraction, scanning electron microscopy and transmission electron microscopy SEM, TEM, EBSD technology and Thermo-Calc back scattering diffraction thermodynamic equilibrium phase diagram calculation and research the evolution of the microstructure. The main conclusions are as follows: 1) the recrystallization temperature of Al can significantly reduce the 429 ultra pure ferritic stainless steel, the average grain size with the cold rolling and annealing the increase of the content of Al increased slightly, mainly because of the decreased area fraction of recrystallization temperature and inclusions. The tensile tensile strength and yield strength with With the increase of Al content, linear increase, elongation rate changed little, but the plastic strain ratio increased first and then decreased, containing 0.16 wt.%Al samples exhibited the highest plastic strain ratio of the increase of the content of r=1.62.Al can significantly improve the high temperature tensile 429 ultra pure ferritic stainless steel and compressive mechanical properties. With increasing Al content. The type of inclusion matrix and grain boundary evolution from single-phase TiN into composite MgO Al_2O_3-TiN particles, and the average size of the inclusions have a small amount of increased area percentage decreased the content of.Al can significantly improve the pitting corrosion resistance of.2 cold rolling and annealing textures) 429 ultra pure ferritic stainless steel surface and the center layer from the alpha + gamma texture texture completely evolved into gamma, and 0.16 wt.%Al were higher (111) and [-1-12] (111) [-2-35] texture intensity, but when the Al content increases further to 1.51 wt.% gamma texture intensity While reducing the thickness direction of the gamma texture. With the increase of Al content, from (111) to [1-21] (111) [3-52], and 0.16 wt.% Al can significantly improve the gamma texture intensity. Al free samples of cold rolled and annealed after gamma texture in tensile and disappeared, while the samples containing 0.16 wt.%Al gamma the texture still dominates, the highest intensity of 111//ND 4.6. containing 1.51 wt.%Al samples (111) after room temperature tensile strength of [0-11] texture decreased significantly. 429 ultra pure ferritic stainless steel containing 0.16 wt.%Al has the strongest gamma texture.3) 429 ultra pure ferritic stainless steel 1000oC oxidation weight curve exhibits a typical parabolic law. The oxidation of short time after excluding Al samples showed local preferential oxidation of spherical appearance, with the increase of oxidation time of surface oxide film is extended to the entire surface of the sample and the spherical oxidation products grown together, the top hole oxidation products exist some small Al with. With the increase of the content of oxide film on the surface, more uniform morphology, granular morphology of oxide film. The oxidation product presents a multi-layer structure, the outer film is rich in Fe_2O_3 and a small amount of Fe_3O_4, the outer film below Cr_2O_3, middle layer rich in Fe_2O_3 and Cr_2O_3, the inner oxide film is rich in Fe_3O_4. with the increase of Al content, reduce the thickness of the oxide film, low Al content high temperature oxidation samples to improve the performance of Cr_2O_3. mainly depends on when the content of Al increased to 1.51 wt.%, the oxidation of a short time after the emergence of the Al_2O_3 rich oxide film sample surface, with the increase of oxidation time, the thickness of the oxide film did not significantly increase.1.51 wt.%Al sample surface formed under protective, uniform, full, rich Al_2O_3 the film, significantly improve the oxidation resistance of 429 ultra pure ferritic stainless steel.

【学位授予单位】：上海大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG142.71

【参考文献】