DOI:10.13374/.issn1001-053x.2011.05.005 第33卷第5期 北京科技大学学报 Vol.33 No.5 2011年5月 Journal of University of Science and Technology Beijing May 2011 含Nb低碳钢的中间冷却及回火工艺对MA组织的 影响 余伟四陈涛焦多田蔡庆伍 北京科技大学高效轧制国家工程研究中心，北京100083 ☒通f信作者，E-mail:yuwei@(nercar.usth.edu.cm 摘要利用热膨胀仪对低碳含铌钢(0.028%C0.25%Si-1.82%Mn-0.085%Nb)进行热处理模拟，即950℃正火后快速冷 却到中间温度350~550℃，随后进行不同加热速率、保温温度及保温时间的回火处理.采用光学显微镜、扫描电镜和图像分 析方法，分析了不同回火条件下组织中的马氏体一奥氏体(M)形貌、尺寸及分布.结果表明：回火前的终冷温度在贝氏体相 变温度区间及提高回火升温速率，会增加回火组织中MA的体积分数，MA体积分数最高达到7.9%.提高回火温度和延长回 火时间，MA的体积分数会出现峰值.回火后，MA平均尺寸在0.77~1.48μm.提高终冷温度、升温速率、回火温度和延长回火 时间，会使回火后的MA粗大，并呈多边形化.MA的体积分数和平均尺寸主要受中间冷却过程结束时未转变奥氏体量、回火 过程中铁素体向残余奥氏体碳扩散程度以及回火后残余奥氏体稳定性的影响. 关键词低碳钢：铌：马氏体；奥氏体：回火：冷却：相变；微观组织 分类号TG162.83 Effects of intermediate cooling and tempering process on martensite-austenite constituents in niobium-bearing low carbon steel YU Wei☒，CHEN Tao,JIAO Duo-+ian,CAI Qing-+eu National Engineering Research Center for Advanced Rolling Technology,University of Seience and Technology Beijing,Beijing 100083,China Corresponding author,E-mail:yuwei@nercar.ustb.edu.cn ABSTRACT Heat treatment processes were simulated with a thermo-analyse simulator for niobium-bearing low carbon steel (0.028%C-0.25%Si-1.82%Mn-0.085%Nb).In the processes,the samples were cooled down to a final cooling temperature of 350 to 550C after being normalized at 950C,then reheated at different ratios,and tempered at different temperatures for different holding time periods.The morphology,the size and distribution of martensite-austenite (MA)constituents obtained under different tempering conditions were investigated by optical microscopy,scanning electron microscopy (SEM)and image analysis.The results show that the enhancement of reheating ratio and the final cooling temperature in the range of bainite transition lead to an increase of MA volume frac- tion,and the maximum volume fraction of MA constituents is up to 7.9%.Tempering at high holding temperature for long holding time can result in an occurrence of the volume fraction peak of MA constituents.The average grain size of MA constituents is 0.77 to 1.48 um after tempering.MA grains grow up and tend to be in polygonal shape when the final cooling temperature,reheating ratio and holding temperature increase and the holding time prolongs.The volume fraction and average grain size of MA constituents are mainly affected by the quantity of untransformed austenite after intermediate cooling,the evolution of carbon diffusion from ferrite to retained austenite during tempering and the stability of retained austenite after tempering. KEY WORDS low carbon steel;niobium;martensite;austenite:tempering:cooling:phase transitions:microstructure 随着高强度管线钢、高强度工程机械用钢等 高强度钢的应用范围扩大，要求钢材除了具备高 收稿日期：2010-06-07 基金项目：“十一五”国家科技支撑计划资助项目(No.2006BAE03A06)第 33 卷 第 5 期 2011 年 5 月 北京科技大学学报 Journal of University of Science and Technology Beijing Vol． 33 No． 5 May 2011 含 Nb 低碳钢的中间冷却及回火工艺对 MA 组 织 的 影响 余 伟 陈 涛 焦多田 蔡庆伍 北京科技大学高效轧制国家工程研究中心，北京 100083 通信作者，E-mail: yuwei@ nercar． ustb． edu． cn 摘 要 利用热膨胀仪对低碳含铌钢( 0. 028% C--0. 25% Si--1. 82% Mn--0. 085% Nb) 进行热处理模拟，即 950 ℃ 正火后快速冷 却到中间温度 350 ～ 550 ℃，随后进行不同加热速率、保温温度及保温时间的回火处理． 采用光学显微镜、扫描电镜和图像分 析方法，分析了不同回火条件下组织中的马氏体--奥氏体( MA) 形貌、尺寸及分布． 结果表明: 回火前的终冷温度在贝氏体相 变温度区间及提高回火升温速率，会增加回火组织中 MA 的体积分数，MA 体积分数最高达到 7. 9% ． 提高回火温度和延长回 火时间，MA 的体积分数会出现峰值． 回火后，MA 平均尺寸在 0. 77 ～ 1. 48μm． 提高终冷温度、升温速率、回火温度和延长回火 时间，会使回火后的 MA 粗大，并呈多边形化． MA 的体积分数和平均尺寸主要受中间冷却过程结束时未转变奥氏体量、回火 过程中铁素体向残余奥氏体碳扩散程度以及回火后残余奥氏体稳定性的影响． 关键词 低碳钢; 铌; 马氏体; 奥氏体; 回火; 冷却; 相变; 微观组织 分类号 TG162. 83 收稿日期: 2010--06--07 基金项目:“十一五”国家科技支撑计划资助项目( No． 2006BAE03A06) Effects of intermediate cooling and tempering process on martensite-austenite constituents in niobium-bearing low carbon steel YU Wei ，CHEN Tao，JIAO Duo-tian，CAI Qing-wu National Engineering Research Center for Advanced Rolling Technology，University of Science and Technology Beijing，Beijing 100083，China Corresponding author，E-mail: yuwei@ nercar． ustb． edu． cn ABSTRACT Heat treatment processes were simulated with a thermo-analyse simulator for niobium-bearing low carbon steel ( 0. 028% C-0. 25% Si-1. 82% Mn-0. 085% Nb) ． In the processes，the samples were cooled down to a final cooling temperature of 350 to 550 ℃ after being normalized at 950 ℃，then reheated at different ratios，and tempered at different temperatures for different holding time periods． The morphology，the size and distribution of martensite-austenite ( MA) constituents obtained under different tempering conditions were investigated by optical microscopy，scanning electron microscopy ( SEM) and image analysis． The results show that the enhancement of reheating ratio and the final cooling temperature in the range of bainite transition lead to an increase of MA volume frac￾tion，and the maximum volume fraction of MA constituents is up to 7. 9% ． Tempering at high holding temperature for long holding time can result in an occurrence of the volume fraction peak of MA constituents． The average grain size of MA constituents is 0. 77 to 1. 48 μm after tempering． MA grains grow up and tend to be in polygonal shape when the final cooling temperature，reheating ratio and holding temperature increase and the holding time prolongs． The volume fraction and average grain size of MA constituents are mainly affected by the quantity of untransformed austenite after intermediate cooling，the evolution of carbon diffusion from ferrite to retained austenite during tempering and the stability of retained austenite after tempering． KEY WORDS low carbon steel; niobium; martensite; austenite; tempering; cooling; phase transitions; microstructure 随着高强度管线钢、高强度工程机械用钢等 高强度钢的应用范围扩大，要求钢材除了具备高 DOI:10.13374/j.issn1001-053x.2011.05.005