退火对齿轮钢枝晶偏析及元素扩散的影响
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摘要
为了研究退火工艺对20CrMnTi齿轮钢铸坯的枝晶形貌、合金元素(碳,硅,铬和锰)分布及其扩散的影响,利用光学显微镜(OM)对退火前后铸坯枝晶形貌进形了比较,利用电子探针(EPMA)对元素的分布进行了定量分析,并使用Thermo-Calc软件中的Dictra模块进行了模拟验证。研究结果表明,退火工艺使20CrMnTi齿轮钢铸坯的枝晶形貌显示得更加完整清晰,测量退火后铸坯中的二次枝晶间距为55μm。铸坯中碳元素存在上坡扩散,偏析系数变大,偏析系数变化量?kC为0.666;硅元素存在轻微的上坡扩散,偏析系数变化量?kSi为0.041 5;锰元素扩散更加均匀,偏析系数变化量为?kMn为-0.141;铬元素扩散得更加均匀,偏析系数变化量为?kCr为-0.106。模拟结果显示,铸坯在保温温度为680℃,保温时间为2 h的退火工艺条件下,碳原子发生了上坡扩散,产生偏析现象;硅、铬、锰原子无明显扩散变化。
In order to study the effects of annealing process on the dendritic morphology of 20 CrMnTi gear steel slab,the distribution of alloying elements(C,Si,Cr and Mn)and its diffusion,the optical microscope(OM)was used to shape the dendrites before and after annealing. The appearance was compared and the distribution of the elements was quantitatively analyzed using an electron probe(EPMA),and the simulation was performed using the Dictra module in the Thermo-Calc software. The results showed that the dendritic morphology of the 20 CrMnTi gear steel slab was more complete and clear,and the secondary dendrite spacing in the slab after annealing was measured to be 55 μm. The C element in the slab had an upward slope,the segregation coefficient became larger,the variation of the segregation coefficient was ?kC=0.666. The Si element had a slight uphill diffusion,the variation of the segregation coefficient was ?kSi=0.041 5. The Mn element diffusion was more uniform,and the variation coefficient of the segregation coefficient wasΔkMn=-0.141. The Cr element also diffused more uniformly and the variation coefficient of the segregation coefficient was ΔkCr=-0.106. The simulation results showed that under the annealing condition of slab temperature of 680 ℃ and holding time of 2 h,C atoms were up-slope and diffuse,resulting in segregation. Si,Cr and Mn atoms had no obvious diffusion changes.
In order to study the effects of annealing process on the dendritic morphology of 20 CrMnTi gear steel slab,the distribution of alloying elements(C,Si,Cr and Mn)and its diffusion,the optical microscope(OM)was used to shape the dendrites before and after annealing. The appearance was compared and the distribution of the elements was quantitatively analyzed using an electron probe(EPMA),and the simulation was performed using the Dictra module in the Thermo-Calc software. The results showed that the dendritic morphology of the 20 CrMnTi gear steel slab was more complete and clear,and the secondary dendrite spacing in the slab after annealing was measured to be 55 μm. The C element in the slab had an upward slope,the segregation coefficient became larger,the variation of the segregation coefficient was ?kC=0.666. The Si element had a slight uphill diffusion,the variation of the segregation coefficient was ?kSi=0.041 5. The Mn element diffusion was more uniform,and the variation coefficient of the segregation coefficient wasΔkMn=-0.141. The Cr element also diffused more uniformly and the variation coefficient of the segregation coefficient was ΔkCr=-0.106. The simulation results showed that under the annealing condition of slab temperature of 680 ℃ and holding time of 2 h,C atoms were up-slope and diffuse,resulting in segregation. Si,Cr and Mn atoms had no obvious diffusion changes.
引文
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[2]刘辉,王阳,孙庆,等. 700 MPa大梁钢拉伸断后分层现象的解析[J].钢铁,2017,52(11):52.(LIU Hui,WANG Yang,SUN Qing,et al. Analysis of delamination of 700 MPa beam steel after tensile fracture[J]. Iron and Steel,2017,52(11):52.)
[3]李聚宝,李岩,张有余,等.双相区热处理对430铁素体不锈钢热轧板组织和性能的影响[J].钢铁研究学报,2017,29(1):62.(LI Ju-bao,LI Yan,ZHANG You-yu,et al. Effect of heat treatment in two-phase zone on microstructure and properties of 430 ferritic stainless steel hot rolled sheet[J]. Journal of Iron and Steel Research,2017,29(1):62.)
[4]曹重,邹荣,吴光耀,等.微合金化控轧控冷钢筋纵向金相组织研究[J].钢铁,2013,48(6):61.(CAO Zhong,ZOU Rong,WU Guang-yao,et al. Study on longitudinal metallographic structure of microalloyed controlled rolling and controlled cold steel bars[J]. Iron and Steel,2013,48(6):61.)
[5]张迎晖,赖泓州,赵鸿金.钢中带状组织的研究现状[J].轧钢,2014,31(3):45.(ZHANG Ying-hui,LAI Hong-zhou,ZHAO Hong-jin. Research status of banded structure in steel[J]. Steel Rolling,2014,31(3):45.)
[6]陈世杰,孙维,汪开忠,等. 18CrNiMo7-6齿轮钢带状组织控制及其对力学性能的影响[J].钢铁研究学报,2016,28(9):76.(CHEN Shi-jie,SUN Wei,WANG Kai-zhong,et al. Band structure control of 18CrNiMo7-6 gear steel and its effect on mechanical properties[J]. Journal of Iron and Steel Research,2016,28(9):76.)
[7]董鹏莉,尚海霞,王华.铸坯及板卷典型质量缺陷成因与控制技术[J].中国冶金,2017,27(6):7.(DONG Peng-li,SHANG Hai-xia,WANG Hua. Typical quality defect cause and control technology of slab and plate[J]. China Metallurgy,2017,27(6):7.)
[8]赵岩,蔡晓辉,刘振宇.连续退火参数对980 MPa级冷轧双相钢组织和性能的影响[J].钢铁研究学报,2015,27(2):55.(ZHAO Yan,CAI Xiao-hui,LIU Zhen-yu. Effect of continuous annealing parameters on microstructure and properties of 980 MPa grade cold rolled dual phase steel[J]. Journal of Iron and Steel Research,2015,27(2):55.)
[9]胡昕明,高强,乔馨,等.正火温度对09MnNiDR钢组织性能的影响[J].钢铁,2011,46(3):71.(HU Xin-ming,GAO Qiang,QIAO Xin,et al. Effect of normalizing temperature on microstructure and properties of 09MnNiDR steel[J]. Iron and Steel,2011,46(3):71.)
[10] WANG X L,WANG Z Q,MA X P,et al. Analysis of impact toughness scatter in simulated coarse-grained HAZ of E550 grade offshore engineering steel from the aspect of crystallographic structure[J]. Materials Characterization,2018,140:312.
[11]吴俊平,靳星,龙木军,等.含钛微合金钢低温冲击韧性波动的原因与改进[J].中国冶金,2017,27(12):59.(WU Junping,JIN Xing,LONG Mu-jun,et al. Cause analysis and improvement of undulation of low temperature impact property for Ti microalloyed steel[J]. China Metallurgy,2017,27(12):59.)
[12]柳得橹,邵伟然,孙贤文,等.钢的表面带状组织及其引起的冷弯裂纹[J].工程科学学报,2005,27(1):42.(LIU De-lu,SHAO Wei-ran,SUN Xian-wen,et al. Surface band structure of steel and its induced cold bending crack[J]. Journal of Engineering Science,2005,27(1):42.)
[13]李科敏,杨玉军,王志刚,等. GH350合金铸锭元素偏析及其均匀化热处理[J].钢铁研究学报,2012,24(7):54.(LI Kemin,YANG Yu-jun,WANG Zhi-gang,et al. Segregation and homogenization heat treatment of GH350 alloy ingots[J]. Journal of Iron and Steel Research,2012,24(7):54.)
[14] Thompson S W,Howell P R. Factors influencing ferrite/pearlite banding and origin of large pearlite nodules in a hypoeutectoid plate steel[J]. Metal Science Journal,2013,8(9):777.
[15]张延玲,刘海英,阮小江,等.中低碳齿轮钢中合金元素的偏析行为及其对带状组织的影响[J].北京科技大学学报,2009,31(增刊1):199.(ZHANG Yan-ling,LIU Hai-ying,RUAN Xiao-jiang,et al. Segregation behavior of alloying elements in medium and low carbon gear steels and their effects on banded structure[J]. Journal of University of Science and Technology Beijing,2009,31(s1):199.)
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[17]李吉东,许庆太,孙中强,等. SPHE连铸坯夹杂物的检验和分析[J].连铸,2012,1(6):36.(LI Ji-dong,XU Qing-tai,SUN Zhong-qiang,et al. Inspection and analysis of inclusions in SPHE continuous castings[J]. Continuous Casting,2012,1(6):36.)
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[19]王新华.钢铁冶金:炼钢学[M].北京:高等教育出版社,2007.(WANG Xin-hua. Iron and Steel Metallurgy:Steelmaking[M].Beijing:Higher Education Press,2007.)
[20] Vannier I,Combeau H,Lesoult G. Numerical model for prediction of the final segregation pattern of bearing steel ingots[J].Materials Science and Engineering:A,1993,173(1/2):317.