【作者】 程四华；

【导师】 吴迪； 许云波；

【作者基本信息】 东北大学 ， 材料加工工程， 2009， 硕士

【摘要】 一直以来,国外长期使用的100kg级高强钢板一般采用高合金化、淬火加高温回火调质热处理的工艺制造。为增加钢的淬透性,必须向钢中加入大量的Cr、Mo、Ni、Cu等贵重合金元素;同时调质高强钢的热处理工艺复杂,在成本、能耗等方面缺乏优势。本文采用TMCP技术开发100kg级高强钢板,不仅在合金成本、生产工艺上具有极大优势,而且符合当前冶金行业“节能降耗”的总体发展趋势。通过研究不同TMCP工艺下实验钢的微观组织、第二相粒子析出和位错强化等规律,优化最佳的生产工艺,为工业化大生产提供必要的指导。论文的主要工作如下:(1)采用单道次压缩实验,研究了冷却速度和驰豫对组织的影响。结果表明,冷却速度在0.5℃/s～20℃/s范围内都有贝氏体组织生成。当冷却速度小于10℃/s时,主要为粒状贝氏体组织;当冷却速度为20℃/s时,以下贝氏体组织为主,出现不规则形状的M/A岛和少量板条贝氏体。冷却速度为30℃/s时,为贝氏体和马氏体的混合组织,M/A组元细小且分散。(2)通过实验室热轧实验,研究了精轧温度、终轧温度、冷却速度以及热处理等工艺对实验钢组织和性能的影响。结果表明,100kg高强钢的控轧控冷最佳工艺参数为:(a)加热温度1200℃;(b)采用两阶段控轧,一阶段开轧温度1050～1100℃,二阶段开轧温度820～890℃;(c)轧后快冷,终冷温度在200～300℃,冷速30～50℃/s。(3)扫描、透射、复型等精细组织分析表明,变形后驰豫一定时间有利于微合金元素的析出。随着驰豫时间的延长,析出物逐渐增多,且弥散化程度提高。驰豫过程中析出物有两类,一类为尺寸在50～100nm之间的Nb、Ti析出物,呈方形;另一类为细小弥散分布尺寸小于10nm的Nb析出物,呈小椭圆形。大量的弥散析出物钉扎在晶粒内部的位错线上,有利于析出强化和冲击韧性的提高。(4)设计了不同温度的回火实验,研究了回火温度对实验钢组织和性能的影响。结果表明,轧态钢板组织为典型贝氏体和马氏体板条,板条内部含有高密度的位错,板条界面为残余奥氏体或薄膜状碳化物;回火温度较低时,与轧态组织相似;随着回火温度的升高,贝氏体板条逐渐合并,开始有碳化物析出;回火温度超过600℃时,碳化物在板条界内界外大量析出,板条界退化、消失,钢板强度大幅降低。更多还原

【Abstract】 All of these days,100kg Grade high Strength Steel used beyond the seas have been produced under the conditions that high alloying and quenching and tempering.To improve hardenability,lots of alloying agent such as Cr,Mo,Ni,Cu were plunged into the steel;at the same time,Technology for Heating Processing of the quenched and tempered steel was complicated,so it was not superior at cost and Energy consumption.This paper exploits 100kg Grade high Strength Steel under TMCP conditions,not only having the dominant position at the alloyed cost and process,but also conforming to the tendency to save energy lower energy consumption and reduce pollutants discharge in Metallurgy industry.The paper study the microstructure,the second phase particle precipitating,dislocations strengthening in different TMCP conditions to optimize the technological condition for lager industrialized production.The main works involved as follows:(1) When single press test is taken,the influence of the colling rate and relaxation are researched,The results show that bainite is to take shape among 0.5℃/s～20℃/s.The microstructure is mainly granular bainite when the colling rate is less than 10℃/s;when the colling rate is 20℃/s,the microstructure is mainly acicular ferrite,granular bainite,and irregular M/A and fewer lath bainite.when 20℃/s,the microstructure is bainite and martensite,and the M/A is minute and dispersive.(2) The controlled rolling and controlled cooling test in experiment were carried out,the effect of finish rolling temperature,cooling rate and heat treatment process on the microstructure and mechanical properties of tested were studied.The results show that the recommended processing parameters for industrial production are:(1) the reheating temperature is 1200℃;(2) two stages controlled rolling is adopted,in which the first stage rolling started at 1050～1100℃and the second stage rolling started at 820～890℃;(3) rapid cooling after final rolling,finish cooling temperature is 200～300℃,cooling rate is 30～50℃/s.(3) The transmission electron microscope,scanning electron microscope and replica method were used to study the fine microstructure.The results show that relaxing for different time afte deformation was useful to the grain refining.With the time passed,the quantity of educts and level of dispersion were gradually increased.There were two kinds of educts,the one was square that was educt with Nb/Ti and the size was between 50nm and 100nm;the other was small ellipse that was educt with Nb and the size was less than 10nm.Lots of disperse educts anchored dislocation in grain,and they were not be different from the tradition in grain boundary.so precipitation strength were obvious.(4) Different temperature tempering test were carred out to study the tempering temperature on the microstructure and mechanical properties.The results show that the microstructure as rolled were typical lath bainite and martensite,and in the lath were high density dislocation,between the lath interface were residual austenite;After tempering the width of laths were gradually widened;with tempering temperature ascending,there were educts in/out the martensite lath;when the tempering temperature was above 600℃,the educts were abundantly precipitate and the laths were broken down,so the strength was reduced.更多还原