摘要
利用热模拟技术并结合SEM和TEM分析方法,研究了含钒超低碳贝氏体钢(ULCB)在轧后快速加热回火过程中不同回火温度对其组织、显微硬度及析出行为的影响.结果表明:未经回火的试验钢组织为板条贝氏体+粒状贝氏体;经高温回火后,组织中出现了多边形铁素体,随回火温度的增加,板条贝氏体数量减少,多边形铁素体数量增加.在600℃以下回火时,析出相主要是沿位错析出;在600℃以上时,以晶界析出和沿位错线析出两种方式存在.高的加热速率、较短的保温时间不利于位错的回复消失以及碳元素和钒元素的扩散,故随回火温度的增加,析出相的数量增多,但尺寸变化不明显.基体中存在两种尺寸的纳米级析出相:一种是只含有V,尺寸在15～20 nm的V(C,N);另一种含有V、Cr两种元素,尺寸在10 nm以下具有面心立方结构的(V,Cr)(C,N)复合析出相.当回火温度为600℃时,试验钢具有最高的硬度值,332 HV.试验钢硬度的变化是回火后贝氏体组织粗化、位错亚结构的回复软化以及第二相析出的强化机制综合作用的结果.
The effects of different tempering temperatures under rapid heating on precipitation behavior,microstructure and micro-hardness of vanadium-bearing ULCB steel were investigated by using thermal simulation,scanning electron microscope（SEM） and transmission electron microscope（TEM）.The results show that the main microstructures of tested steel are lath bainite and granular bainite before tempering,and polygonal ferrite appears after high temperature tempering.The amount of the lath bainite decreases and polygonal ferrite increases as tempering temperature increasing.The second phase particles mainly precipitate at dislocations when the tempering temperature is below 600 ℃,and above 600 ℃,they are precipitating along the grain boundaries and at dislocations.With the increase of tempering temperature,the amount of precipitation increases and the particles size does not show a clear change.This is because the higher heating rate and shorter holding time is unfavorable to the recovery of high density dislocations and diffusion of carbon and vanadium elements.There are two kinds of different sizes of the nanometer-sized precipitate particles in matrix,one is vanadium carbonitride,of which the size is from 15 nm to 20 nm,another is enriched with Cr and V and it is smaller than 10 nm.It seems that this carbide can maintain the face-centered cubic structure.After tempering at 600 ℃,the micro-hardness of tested steel is the highest,which is about 332 HV.The micro-hardness variation is ascribed to the comprehensive mechanism including lower bainite coarsening,the recovery softening process of dislocation substructure and precipitation strengthening of the second phase in bainite during tempering.
出处
《材料科学与工艺》
EI
CAS
CSCD
北大核心
2013年第3期33-40,共8页
Materials Science and Technology
基金
国家高技术研究发展计划资助项目(2012AA03A508)
关键词
组织
纳米级析出相
回火温度
显微硬度
快速加热回火
microstructure
nanometer-sized precipitate
tempering temperature
micro-hardness
rapid heating tempering
