【作者】 李冲；

【导师】 龚文邦；

【作者基本信息】 武汉纺织大学 ， 机械工程， 2021， 硕士

【摘要】 等温淬火球墨铸铁(ADI)是一种具有独特奥铁体微观组织的新型高性能工程材料,代表了铸铁冶金学的新成就,是钢铁材料领域适合制造高端装备关键零部件和轻量化创新极具竞争优势的新型工程材料。本文研究了通过表面淬火的方式,在保证ADI心部高韧性与高塑性的前提下进一步提高其表面硬度与耐磨性。针对牌号为QTD1050-6的ADI感应加热表面淬火过程中的温度、组织、应力的变化进行数值模拟,并对数值模拟结果进行实验验证,为ADI表面淬火工艺提供参考。通过对比ADI感应淬火前后组织与性能的变化,来分析表面淬火对ADI组织与性能的影响。首先基于感应加热表面淬火原理,电磁感应原理与涡流效应,考虑QTD1050-6试样的尺寸,选择了高频感应加热表面淬火。其次,通过麦克斯韦方程组构建了ADI感应加热表面淬火过程中的电磁场数学模型。基于傅里叶方程与能量守恒原则构建了温度场数学模型。通过分析ADI表面淬火过程中,基于表层高碳奥氏体向马氏体的转变过程为扩散性相变,应力变化在热弹塑范围内进行分析,构建了组织场与应力场的数学模型。基于Jmatpro模拟了牌号为QTD1050-6ADI的热物性参数,通过有限元分析软件Deform对牌号为QTD1050-6的ADI试样感应加热表面淬火过程中的电磁场、温度场、组织场、应力场进行耦合数值分析。基于Deform的ADI感应加热表面淬火数值模拟结果表明:在加热过程中,ADI试样升温速度随着离表层的距离的增大而减小,当温度达到801℃时,表层的铁素体开始奥氏体化,经过3秒后完成表层奥氏体化,接着淬火时,表层迅速转变成马氏体;表层的硬度大幅提高,淬火后表面硬度为55.2HRC,淬硬层深度为2.1mm;在模拟升温奥氏体化与淬火过程中,出现两个应力峰值,分别出现在升温与降温速度最快的时间点,第一个峰值出现在1.5s,其应力为424MPa。第二个峰值出现在5s,其应力峰值为309MPa。对QTD1050-6试样进行表面淬火实验,结果表明:表层奥铁体组织淬火后转变成马氏体组织,淬火后试样硬度为55.6HRC,淬硬层深度经过测量为1.9mm;由此可见,数值模拟结果与实验结果吻合。对表面淬火后的试样与未表面淬火的试样进行摩擦磨损实验,其结果为:经过6×1h,试验力200N,转速为60rad/min的摩擦磨损实验后,未经过淬火ADI的磨损量为67.2mg,摩擦系数约0.4;而淬火后的ADI试样,磨损量仅为21.5mg,摩擦系数约0.5;感应加热表面淬火可以大幅提高ADI试样的表面硬度与耐磨性。通过对比表面淬火前后组织的变化,表面淬火前其表层基体组织为奥铁体;表面淬火后,表面基体组织为针状马氏体,表面淬火大幅提高试样表面硬度与耐磨性,淬火后心部仍保留原奥铁体组织,保证了心部的塑性与韧性。更多还原

【Abstract】 Austempered ductile iron(ADI)is a new type of high-performance engineering material.Its matrix structure is acicular ferrite and high-carbon austenite.Compared with ordinary ductile iron,ADI has good plasticity,wear resistance,With the characteristics of higher strength,it has been widely used at home and abroad.However,ADI cannot have both high strength and wear resistance at the same time with high toughness and plasticity.This paper studies the method of surface quenching to improve the surface hardness and wear resistance of ADI under the premise of ensuring the toughness and plasticity of the ADI core.Since the matrix structure of ADI is austenitic,it is completely different from the matrix of ordinary ductile iron,and its surface heat treatment process and the corresponding process must be different from ordinary ductile iron.In this paper,computer numerical simulation technology is used to perform finite element analysis on the changes of temperature,structure and stress in the ADI surface quenching process of QTD1050-6,and the numerical simulation results are verified through experiments,which provide a reference for the ADI surface quenching process.By comparing the changes in the structure and comprehensive properties of ADI before and after induction quenching,the influence of ADI surface quenching on the structure and comprehensive properties of ADI is analyzed.This article first studied the principle of ADI’s induction heating surface quenching.Based on the principle of electromagnetic induction and the eddy current effect,considering the size of the QTD1050-6 sample,high-frequency induction heating surface quenching was selected.Secondly,the mathematical model of electromagnetic field in the ADI surface quenching process is constructed through Maxwell’s equations.A mathematical model of the temperature field is constructed based on the Fourier equation and the principle of conservation of energy.By analyzing the ADI surface quenching process,the transformation process of surface high-carbon austenite to martensite is a diffusive phase transformation,and the stress field is analyzed in the range of thermoelastic plastic,and a mathematical model of the structure field and the stress field is constructed.The thermal properties of QTD1050-6 are calculated based on Jmatpro,and the electromagnetic field,temperature field,structure field,and stress field of QTD1050-6 in the induction heating surface quenching process of QTD1050-6 are coupled and analyzed through the finite element analysis software Deform,and experimental verification is carried out.The numerical analysis of ADI induction heating surface quenching based on Deform shows that during the heating process,the increasing speed of the surface temperature of ADI decreases with the increase of the distance from the surface.When the temperature reaches 801℃,the ferrite of the surface layer begins to oxidize.The surface layer is rapidly transformed into martensite when it becomes intensified and quenched,and at the same time the hardness of the surface layer is greatly increased.In the numerical simulation of induction heating and quenching of QTD1050-6,the two peaks of the sample stress appeared at the time points where the heating and cooling speeds were the fastest,respectively.The first peak appeared at 1.5s and its stress was 424 MPa.The second peak appears in 5s,and its peak stress is 309 MPa.Experiments show that after surface quenching,the surface hardness of QTD1050-6 ADI is changed from 34.0HRC to 54.1HRC.The surface hardness obtained by numerical simulation is 55.2HRC,and the error is within the allowable range.After surface quenching of QTD1050-6 sample,the surface matrix structure changed from austenite to martensite and graphite,and the hardened layer was 2mm,which was consistent with the numerical simulation results.After 6×1h,the test force is 200 N,the speed is 60rad/min friction and wear experiment,the wear amount of ADI without quenching is 65 mg,and the friction coefficient is about 0.4,while the wear amount of the quenched ADI sample is only 20 mg,friction The coefficient is about 0.5.Surface hardening can greatly improve the surface hardness and wear resistance of ADI specimens.By comparing the changes of the structure before and after quenching,the matrix structure on the surface before quenching is acicular ferrite,high-carbon austenite and spheroidal graphite.After quenching,the surface matrix structure is acicular martensite and graphite balls.By surface quenching,the martensite generated on the surface of the ADI sample can greatly improve the surface hardness and wear resistance of the sample.At the same time,the core part still retains the original ausferrite structure,ensuring the core part’s plasticity and toughness.更多还原