稀土对C-Mn钢中针状铁素体形成的影响
发布时间：2019-06-04 18:40
【摘要】：稀土在钢中的应用自上世纪60年代起一直得到国家的重视。稀土加入钢中可起到脱氧、脱硫和变质夹杂等作用,生成大量高熔点、弥散、细小的夹杂物。稀土夹杂物能够诱导晶内针状铁素体形核,细化钢的组织,提高钢的强韧性。然而目前关于钢中添加稀土促进晶内针状铁素体的形成国内外还缺乏系统深入研究。本论文以稀土氧化物冶金技术为背景,通过向C-Mn钢中加入少量稀土,系统研究稀土处理C-Mn钢后夹杂物和显微组织的变化规律、钢成分和稀土夹杂物协同作用与热处理制度对晶内针状铁素体形成的影响,阐明稀土处理得到晶内针状铁素体组织的控制条件,并探究稀土处理对钢焊接热影响区组织和性能的影响规律,为拓展稀土在钢中的应用领域提供科学依据和技术支撑。稀土对C-Mn钢中夹杂物和显微组织的影响研究表明,本实验条件下向C-Mn钢中添加0.017 wt%的稀土后,FactSage软件热力学计算与扫描电子显微镜及透射电子显微镜检测发现钢中的主要夹杂物为RE2O2S和MnS的复合夹杂及少量硅铝酸盐夹杂,尺寸明显细化。1100℃水冷试样组织由马氏体转变为大量的晶内针状铁素体。在稀土处理方式上,对晶内针状铁素体形成而言,稀土La和Ce复合处理优于单一稀土添加,La和Ce最佳复合质量比约为3：1。稀土处理C-Mn钢后晶内针状铁素体形核核心尺寸主要集中在1 μm～4 Um,且这些核心主要是在钢液中形成的。稀土加入钢中后保温约5 min时,尺寸在1 μm～4μm夹杂物数量百分比最高,最有利于获得大量的有效核心。钢中C,Mn和Al与稀土处理协同作用对晶内针状铁素体形成的影响研究表明,改变C和Mn含量对稀土处理后钢中夹杂物种类、数量和尺寸影响不大。本实验条件下能与稀土处理协同作用获得大量晶内针状铁素体的C含量范围在0.1 wt%-0.18 wt%,Mn含量范围约为0.75 wt%～1.31 wt%。热力学计算与实验结果表明本实验条件下C-Mn钢中A1含量超过0.004 wt%时,能够使0.017 wt%稀土处理钢中的稀土夹杂物种类转变为REAlO3和RE2S3。同时A1含量越高,奥氏体向铁素体转变的开始温度越高,钢中夹杂物数量越少,不利于针状铁素体组织的生成。钢中不同种类的稀土夹杂物诱导晶内针状铁素体形核效果研究结果表明,诱导晶内针状铁素体形核最有效的纯稀土夹杂物种类是RE2O2S,晶格错配度计算表明RE2O2S夹杂诱导针状铁素体形核是由于其与a-Fe间的低晶格错配度。C-Mn钢中RE2O2S夹杂有MnS依附析出形成复合形核核心时,由于低晶格错配度和Mn元素贫乏区两种机理共同作用,RE2O2S与MnS复合夹杂诱导晶内针状铁素体的形核能力明显强于纯RE2O2S夹杂。热处理过程对稀土处理C-Mn钢中针状铁素体形成的影响研究表明,稀土处理C-Mn钢晶内针状铁素体形成的最佳奥氏体化温度约为1100℃,1100℃奥氏体化最佳保温时间约在20 min-30 min,有利于晶内针状铁素体形核的奥氏体晶粒尺寸约为150 1μm,冷却速率范围在2℃/s-8℃/s。不同方式稀土处理C-Mn钢后获得晶内针状铁素体的最佳奥氏体晶粒尺寸及冷却速率差别不大。当钢中A1含量升高为0.027 wt%时,晶内针状铁素体形成的最佳冷却速率范围变窄到2℃/s-5℃/s。稀土处理对钢中原始奥氏体晶粒长大有明显的抑制作用,1100℃下保温40 min后,钢中奥氏体晶粒长大不明显,尺寸约为150 μm。利用Gleeble热模拟机模拟研究了焊接热输入对稀土处理的15 mm厚钢板焊接热影响区组织和性能的影响,结果表明,在稀土处理C-Mn钢中,焊接热输入为25 kJ/cm时热影响区显微组织主要是贝氏体,热输入线能量在50kJ/cm～100 kJ/cm范围内热影响区中晶内针状铁素体组织含量随着热输入线能量的增大而增多。在焊接热输入为100 kJ/cm时稀土处理钢热影响区由于形成了较多的晶内针状铁素体,其室温冲击韧性与母材相差不大,明显的改善了焊接热影响区的室温冲击韧性。不同方式稀土处理钢的显微组织和冲击韧性在各热输入线能量下差别不大,焊接热输入线能量在75 kJ/cm和100 kJ/cm时复合稀土处理钢热影响区冲击韧性略高于单一稀土处理钢。测定了稀土处理C-Mn钢焊接热影响区的连续冷却转变曲线,发现稀土处理钢获得晶内针状铁素体的At8/5范围为40 s-600 s。铝脱氧C-Mn钢稀土处理后焊接过程能够获得晶内针状铁素体的△t8/5范围变窄到100 s～300 s,较难得到晶内针状铁素体组织,其热影响区在焊接热输入为75 kJ/cm和100 kJ/cm时容易形成粗大的晶界铁素体和贝氏体／魏氏体组织。
[Abstract]:The application of rare-earth in steel has been valued by the state since the 1960s. The addition of rare earth into the steel can play a role in deoxidization, desulfation and metamorphic inclusion, so as to generate a large amount of high melting point, dispersion and fine inclusions. The rare-earth inclusion can induce the nucleation of acicular ferrite in the crystal, refine the structure of the steel, and improve the strength and toughness of the steel. However, there is a lack of systematic in-depth study on the formation of acicular ferrite in the crystal by adding rare earth to the steel. In this paper, by adding a small amount of rare earth to the C-Mn steel, the change of the inclusions and the microstructure of the rare-earth-treated C-Mn steel and the effect of the synergistic effect of the steel composition and the rare-earth inclusion on the formation of the acicular ferrite in the crystal are studied by adding a small amount of rare earth to the C-Mn steel. The control condition of the acicular ferrite in the crystal is obtained by the rare-earth treatment, and the influence of the rare-earth treatment on the microstructure and the properties of the heat-affected zone of the steel is investigated, and the scientific basis and the technical support for the application of the rare-earth in the steel are provided. The effect of rare-earth on the inclusion and microstructure of C-Mn steel shows that after adding 0.017 wt% of rare-earth to C-Mn steel under the condition of this experiment, FactSage software thermodynamic calculation and scanning electron microscope and transmission electron microscope have found that the main inclusions in the steel are the composite inclusions of RE2O2S and MnS and a small amount of aluminosilicate inclusions, and the size is obviously refined. The structure of the water-cooled sample at 1100 鈩，
本文编号：2492918
[Abstract]:The application of rare-earth in steel has been valued by the state since the 1960s. The addition of rare earth into the steel can play a role in deoxidization, desulfation and metamorphic inclusion, so as to generate a large amount of high melting point, dispersion and fine inclusions. The rare-earth inclusion can induce the nucleation of acicular ferrite in the crystal, refine the structure of the steel, and improve the strength and toughness of the steel. However, there is a lack of systematic in-depth study on the formation of acicular ferrite in the crystal by adding rare earth to the steel. In this paper, by adding a small amount of rare earth to the C-Mn steel, the change of the inclusions and the microstructure of the rare-earth-treated C-Mn steel and the effect of the synergistic effect of the steel composition and the rare-earth inclusion on the formation of the acicular ferrite in the crystal are studied by adding a small amount of rare earth to the C-Mn steel. The control condition of the acicular ferrite in the crystal is obtained by the rare-earth treatment, and the influence of the rare-earth treatment on the microstructure and the properties of the heat-affected zone of the steel is investigated, and the scientific basis and the technical support for the application of the rare-earth in the steel are provided. The effect of rare-earth on the inclusion and microstructure of C-Mn steel shows that after adding 0.017 wt% of rare-earth to C-Mn steel under the condition of this experiment, FactSage software thermodynamic calculation and scanning electron microscope and transmission electron microscope have found that the main inclusions in the steel are the composite inclusions of RE2O2S and MnS and a small amount of aluminosilicate inclusions, and the size is obviously refined. The structure of the water-cooled sample at 1100 鈩，
本文编号：2492918
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