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金属学报  2017, Vol. 53 Issue (2): 129-139    DOI: 10.11900/0412.1961.2016.00237
  本期目录 | 过刊浏览 |
1000 MPa级Nb-Ti微合金化超高强度钢加热制度研究
惠亚军1,2(),潘辉1,李文远1,刘锟1,陈斌1,崔阳1
1 首钢技术研究院薄板研究所 北京 100043
2 首钢总公司绿色可循环钢铁流程北京市重点实验室 北京 100043
Study on Heating Schedule of 1000 MPa Grade Nb-Ti Microalloyed Ultra-High Strength Steel
Yajun HUI1,2(),Hui PAN1,Wenyuan LI1,Kun LIU1,Bin CHEN1,Yang CUI1
1 Sheet Metal Research Institute, Shougang Research Institute of Technology, Beijing 100043, China
2 Beijing Key Laboratory of Green Recyclable Process for Iron & Steel Production, Shougang Group, Beijing 100043, China;
引用本文:

惠亚军,潘辉,李文远,刘锟,陈斌,崔阳. 1000 MPa级Nb-Ti微合金化超高强度钢加热制度研究[J]. 金属学报, 2017, 53(2): 129-139.
Yajun HUI, Hui PAN, Wenyuan LI, Kun LIU, Bin CHEN, Yang CUI. Study on Heating Schedule of 1000 MPa Grade Nb-Ti Microalloyed Ultra-High Strength Steel[J]. Acta Metall Sin, 2017, 53(2): 129-139.

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摘要: 

采用OM、TEM和EDS分析技术,研究了1000 MPa级Nb-Ti微合金化超高强度钢在不同加热温度下保温不同时间时奥氏体晶粒粗化行为与微合金元素碳氮化物溶解行为。结果表明,铸坯中存在尺寸与形状明显不同的3类析出物:尺寸大于1 μm的方形TiN粒子;尺寸在500 nm以下的球形、椭球形或方形Nb、Ti复合析出物;少量方形或椭球形TiS或Ti(C, S)析出物。随着温度的升高,原始奥氏体晶粒尺寸呈现出单调增大的趋势,当加热温度超过1200 ℃时奥氏体晶粒发生快速长大,而析出物数量不断减少、尺寸逐渐增大、Ti/Nb原子比逐渐升高,EDS显示均为Ti、Nb复合析出。随着保温时间的延长,原始奥氏体平均晶粒尺寸呈抛物线规律长大,小尺寸的球形、椭球形的析出物逐渐溶解,大尺寸方形析出物数量逐渐增加且棱角变得模糊。综合考虑加热温度和保温时间对Nb、Ti微合金元素的固溶行为和奥氏体晶粒粗化行为的影响,1000 MPa级Nb-Ti微合金化超高强度钢的加热温度和保温时间分别为1250 ℃和80 min较合适。

关键词 Nb-Ti微合金化1000MPa级超高强度钢加热制度晶粒长大析出物    
Abstract

In the production process of ultra-high strength steel, heating schedule of casting slab is one of primary controlling parameters in hot rolling techniques. Heating temperature and holding time affect the prior austenite grain size and the solution of microalloyed elements directly, which both affect austenite recrystallization, precipitation and mechanical properties. A plenty of researches have been made to get better understanding and controlling the austenite grain size or precipitation behavior during austenitizing process over the past half a century, but it lacks systematic researches. Hence it is very important to confirm a reasonable heating schedule. In this work, the austenite grain coarsening behavior and microalloying carbonitrides dissolving behavior in 1000 MPa grade Nb-Ti microalloyed ultra-high strength steel during isothermal holding at different temperatures were studied by OM, TEM and EDS. The results showed that the precipitates in the slab can be obviously classified into three kinds by their size and shape. The average dimension of the bigger cubic precipitates is over 1 μm, and that of the smaller spherical, ellipsoid or cubic precipitates is below 500 nm or less. EDS results showed that the bigger cubic precipitates are TiN, and the smaller spherical, ellipsoid or cubic precipitates are mainly composed of Nb, Ti composite precipitates and a bit of TiS or Ti (C, S). With the increasing of holding temperature, increase of the original austenite grain size showed a monotonous increase trend, and the austenite grain grows rapidly when the heating temperature exceeds 1200 ℃; the amount of precipitates decreased and their size increased, the atomic ratio of Ti/Nb increased gradually, and EDS results showed all the precipitates contain Nb, Ti elements. With the increasing of holding time, the average austenite grain grew up in parabolic law, the amount of small sized spherical and ellipsoid precipitates dissolved gradually, and that of the large sized cubic precipitates increased gradually and their edges become blurred. The effects of heating temperature and holding time on austenite grain size and precipitation behavior were considered synthetically, the heating temperature at 1250 ℃ by holding 80 min will be more appropriate for the 1000 MPa grade Nb, Ti microalloyed ultra-high strength steel.

Key wordsNb-Ti microalloying    1000 MPa grade ultra-high strength steel,    heating schedule    grain growth    precipitate
收稿日期: 2016-06-15     
图1  加热温度对1000 MPa级Nb-Ti微合金化超高强度钢原始奥氏体晶粒尺寸和晶粒度级别的影响
图2  1000 MPa级Nb-Ti微合金化超高强度钢不同加热温度保温40 min时奥氏体晶粒形貌的OM像
图3  1000 MPa级Nb-Ti微合金化超高强度钢在1150和1250 ℃保温不同时间时奥氏体平均晶粒尺寸和晶粒度级别
图4  1000 MPa级Nb-Ti微合金化超高强度钢在1150 ℃保温不同时间时奥氏体晶粒形貌的OM像
图5  1000 MPa级Nb-Ti微合金化超高强度钢在1250 ℃保温不同时间时奥氏体晶粒形貌的OM像
图6  1000 MPa级Nb-Ti微合金化超高强度钢原始试样中析出物TEM像与EDS分析
图7  1000 MPa级Nb-Ti微合金化超高强度钢在不同加热温度下保温40 min后析出物的TEM像与EDS分析
图8  1000 MPa级Nb-Ti微合金化超高强度钢在不同加热温度下保温40 min后析出物尺寸分布图
图9  1000 MPa级Nb-Ti微合金化超高强度钢在1150 ℃保温不同时间后析出物的TEM像
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