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.
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 fraction, 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.
出处
《北京科技大学学报》
EI
CAS
CSCD
北大核心
2011年第5期550-556,共7页
Journal of University of Science and Technology Beijing
基金
"十一五"国家科技支撑计划资助项目(No.2006BAE03A06)
关键词
低碳钢
铌
马氏体
奥氏体
回火
冷却
相变
微观组织
low carbon steel
niobium
martensite
austenite
tempering
cooling
phase transitions
microstructure
