45CrNiMoVA钢脉冲磁处理的强化机理
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Strengthening Mechanism of 45CrNiMoVA Steel by Pulse Magnetic Treatment
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通讯作者: 梁志强,liangzhiqiang@bit.edu.cn,主要从事精密磨削、微细刀具设计与制造和抗疲劳制造技术的研究
收稿日期: 2020-10-10 修回日期: 2021-04-09 网络出版日期: 2021-09-27
基金资助: |
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Corresponding authors: LIANG Zhiqiang, associate professor, Tel:
Received: 2020-10-10 Revised: 2021-04-09 Online: 2021-09-27
作者简介 About authors
栾晓圣,男,1992年生,博士生
采用脉冲磁场对珠光体态和回火马氏体态45CrNiMoVA钢分别进行了磁化处理,基于纳米压痕实验结果,分析了脉冲磁处理对残余应力、硬度和弹性模量的影响规律;基于磁滞回线的测量和磁力显微镜的观察结果,分析了脉冲磁处理对磁畴微观组织结构的影响。结果表明,脉冲磁处理能够引起试样表面残余压应力增加;脉冲磁处理后珠光体态和回火马氏体态45CrNiMoVA钢硬度分别增加1.85%和1.84%;脉冲磁处理对珠光体态下的弹性模量影响较小,但对回火马氏体态下的弹性模量影响较大,脉冲磁处理后回火马氏体态的弹性模量增加4.48%;磁化过程中,磁畴运动引起微区材料的应力应变是导致材料力学性能强化的主要机制。
关键词:
Understanding the mechanism of the effects of magnetization treatment on the mechanical properties of materials for applications in magnetic field-assisted machining and magnetic treatment strengthening is of great significance. Pearlite and tempered martensite 45CrNiMoVA steels were magnetized by a pulsed magnetic field. Nanoindentation experiments were conducted to examine the effects of a pulsed magnetic field on the residual stress, hardness, and elastic modulus. The effect of pulsed magnetic treatment on the microstructure of the magnetic domain was analyzed by measuring the hysteresis loop and via magnetic microscopy. A magnetic pulse treatment could increase the residual compressive stress on the sample surface. The hardness of pearlite and tempered martensite 45CrNiMoVA steel was increased by 1.85% and 1.84%, respectively, after the magnetic pulse treatment. The magnetic pulse treatment had an insignificant effect on the elastic modulus of pearlite 45CrNiMoVA steel but had a considerable effect on tempered martensite 45CrNiMoVA steel. After the magnetic pulse treatment, the elastic modulus of the tempered martensite 45CrNiMoVA steel increased by 4.48%. In the magnetization process, the stress and strain of the micro-region material caused by the movement of the magnetic domains was the main mechanism responsible for strengthening the mechanical properties of 45CrNiMoVA steel.
Keywords:
本文引用格式
栾晓圣, 梁志强, 赵文祥, 石贵红, 李宏伟, 刘心藜, 祝国荣, 王西彬.
LUAN Xiaosheng, LIANG Zhiqiang, ZHAO Wenxiang, SHI Guihong, LI Hongwei, LIU Xinli, ZHU Guorong, WANG Xibin.
磁场辅助材料加工能够降低刀具磨损,减小工件材料变形阻力。Azhiri等[3]发现磁场辅助车削AISI D2钢能够改善加工表面完整性,实现表面粗糙度降低、变质层厚度减小、表层微观组织结构优化的优良效果。El Mansori等[4]对比了铁磁性刀具和非铁磁性刀具在干切削铁磁性碳钢过程中磨损量受磁场的影响,证明了磁场辅助切削能够增加刀具的抗磨损性。Dehghani等[5]研究了30CrNiMo8合金钢磁场辅助切削中刀具磨损和切削力的变化,发现磁场导致刀具磨损降低94%,切削力减小100 N,认为磁场促进了切削区域材料的位错运动,增加了材料的变形能力。Muju和Ghosh[6]指出外磁场对变形体的作用增强了位错的迁移率,从而提高了2个摩擦固体中磁导率较高的固体的磨损率,揭示了磁场如何影响两接触体之间的复杂作用机理。
磁处理能够使材料产生强化效果,提升疲劳寿命。Miller[7]和Nikiforov等[8]分别证实了磁处理后刀具寿命提高175%,耐磨性提高1.8~2倍。Çelik等[9]研究了磁处理对AISI 4140钢疲劳寿命的影响,结果表明,在疲劳裂纹萌生阶段,外加磁场使磁畴规则取向和分布导致滑移带的形成推迟,提高了疲劳寿命。Kida等[10]对中碳低合金钢试样疲劳裂纹尖端区域进行磁化,发现磁场变化与塑性变形区有很强的相关性。Fahmy等[11]发现脉冲磁场施加在低碳钢试样上能够增加其疲劳寿命(可能还有疲劳极限),提出疲劳寿命的提高是由于外磁场对磁畴的影响,进而对位错活动的影响,最终导致裂纹萌生的延迟。Shao等[12]发现脉冲磁处理后合金钢的接触疲劳寿命提高了42.11%,认为在脉冲磁场作用下,位错、析出物和磁畴的微观结构变得更加均匀。许擎栋等[13]分析了脉冲磁场处理后位错分布更加均匀的原因是:脉冲磁场引起位错钉扎处的电子能态发生转变,使钉扎处空位或杂质原子易于移动。脉冲磁场处理能够消除材料内有害的残余拉应力[12,14~16],这也有利于结构件疲劳寿命提升。
总结以上研究可以发现,在合理的磁处理条件下,材料的变形、损伤和断裂机制会受到磁场的影响,原有的应力-应变关系发生改变,宏观强度、硬度和残余应力发生变化,进而影响摩擦磨损、疲劳断裂等性能。超高强度钢45CrNiMoVA在高承载结构件中有广泛应用,其加工损伤、疲劳断裂问题严重影响装备的使用安全。为进一步挖掘45CrNiMoVA钢结构件抗疲劳性能提升的潜力,揭示其力学性能受磁场的影响作用规律,对于指导其抗疲劳加工具有重要意义,而目前相关研究鲜有报道。本工作采用脉冲磁场对不同组织状态下的45CrNiMoVA钢进行磁化处理,基于纳米压痕实验结果,分析了脉冲磁场处理对残余应力、硬度和弹性模量的影响规律,基于磁畴运动理论揭示了脉冲磁场处理强化作用机理。
1 实验方法
1.1 试样材料
试样材料为超高强度钢45CrNiMoVA,测得其元素含量(质量分数,%)为:Ni 1.4,Mo 1.0,Cr 0.9,Si 0.9,C 0.42,Mn 0.6,V 0.2,Fe余量。其中,铁磁性元素Fe和Ni是引起该材料磁场响应的主要元素。低温回火后试样材料的力学性能参数[17]为:抗拉强度(
图1
图1
不同热处理条件下45CrNiMoVA钢的微观组织
(a) pearlite (P), annealed
(b) tempered martensite (TM)
Fig.1
The microstructures of 45CrNiMoVA steel under different heat treatment conditions
1.2 实验方案
从相同直径、2种热处理条件(退火态和淬火+回火态)下的45CrNiMoVA钢棒料(相近区域,以保证组织均匀性)上分别切割2块试样(尺寸为10 mm × 8 mm × 6 mm),将试样镶嵌,表面打磨、抛光,干燥备用。磁化处理实验在自行搭建的脉冲磁场磁化处理实验平台上进行,设备结构示意图如图2所示,气隙间距可调,可产生0~1.7 T连续可调脉冲磁场,采用CH-1600高精度Gauss计测量磁场强度。本次实验采用的脉冲磁化处理参数为:正弦波、频率10 Hz、磁场强度1 T和磁化处理时间20 min。相同的磁化参数下分别对珠光体态试样1和回火马氏体态试样3进行磁化处理,试样2和试样4分别为相应的对照组,磁化处理过程中脉冲磁场方向垂直于试样抛光面,表1为实验方案。
图2
图2
脉冲磁化处理设备结构示意图
Fig.2
Structure diagram of pulse magnetization processing equipment
表1 45CrNiMoVA钢脉冲磁化处理实验方案
Table 1
Specimen label | Microstructure of specimen | Magnetization state |
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1 | Pearlite | Magnetization |
2 | Unmagnetized | |
3 | Tempered martensite | Magnetization |
4 | Unmagnetized |
图3
图3
典型纳米压痕载荷-位移曲线及重要的加载/卸载参数示意图
Fig.3
Typical nanoindentation load-displacement curve (a) and important parameters (b) (h—displacement, P—loading,
其中,
通过X-350型X射线衍射仪(XRD)对磁处理前后试样表面残余应力进行检测,参数包含:倾斜固定ψ法(ψ为试样表面法线与衍射晶面法线的夹角),交相关法定峰,靶材CrKα,ψ角为0°和45°,衍射晶面(211),管电压20 kV,管电流5 mA,扫描范围145°~168°,步距0.2°。采用MPMS-XL-7磁学性质测量系统测量45CrNiMoVA钢材料的磁滞回线(试样尺寸为直径2 mm、厚2 mm),以定量分析其磁化性能。采用Dimension FastScan型磁力显微镜(MFM)对45CrNiMoVA钢试样表面磁畴结构形貌进行观察,扫描范围20 μm × 20 μm,扫描速率0.503 Hz,扫描时探针抬起距离测试表面的高度为120 nm。
2 实验结果
2.1 脉冲磁化处理对残余应力的影响
纳米压痕载荷-位移曲线可以反映材料的残余应力状况。45CrNiMoVA钢在不同组织状态下的纳米压痕载荷-位移曲线如图4所示,相比于未磁化处理的试样,磁化处理后试样的载荷-位移曲线发生向上的偏移,载荷最大值Pmax增加。根据Suresh和Giannakopoulos[21]对压痕过程中残余应力的分析,材料残余应力对载荷-位移曲线的影响可以用图5表示,在固定压入深度为h的条件下,材料压入区域残余拉应力的释放会导致载荷-位移曲线从X到Y的变化,接触力从P1到P2增大;而如果材料压入区域带有残余压应力,则会出现载荷-位移曲线从Z到Y的变化,接触力从P3到P2减小。基于X射线表面残余应力测量结果(图6),珠光体态和回火马氏体态试样磁化处理前表面分别为残余压应力,得出磁化处理后珠光体态和回火马氏体态试样的载荷-位移曲线分别向上偏移的原因是磁化处理导致45CrNiMoVA钢试样表面残余压应力变大。
图4
图4
磁化处理前后45CrNiMoVA钢的纳米压痕加载-位移曲线
(a) pearlite
(b) tempered martensite
Fig.4
Nanoindentation curves of magnetized and unmagnetized 45CrNiMoVA steels
图5
图5
残余应力对纳米压痕载荷-位移曲线的影响规律
Fig.5
The influence of residual stress (
图6
图6
磁化处理前后45CrNiMoVA钢表面残余应力的变化
Fig.6
The surface residual stress changes of magnetized and unmagnetized 45CrNiMoVA steels
磁化处理导致试样纳米压痕尺寸减小,以未磁化处理试样的纳米压痕
表2 基于纳米压痕曲线的残余应力计算结果
Table 2
Microstructure | Magnetization state | nm | nm | nm | nm2 | mN | mN | MPa | |
---|---|---|---|---|---|---|---|---|---|
P | Unmagnetized | 1.73 | 122.54 | 1909.31 | 2031.85 | 89317820 | 293.21 | 5.56 | 62.2 |
Magnetization | 1.71 | 125.83 | 1889.34 | 2015.17 | 87458085 | 298.77 | |||
TM | Unmagnetized | 1.71 | 262.41 | 1994.11 | 1731.70 | 73476586 | 622.51 | 4.25 | 57.8 |
Magnetization | 1.76 | 256.16 | 1978.27 | 1722.10 | 72660224 | 626.76 |
2.2 脉冲磁化处理对硬度的影响
图7所示为磁化处理分别对珠光体态和回火马氏体态45CrNiMoVA钢硬度的影响。相比于未磁化处理试样,磁化处理后的珠光体态和回火马氏体态试样硬度分别增加了1.85%和1.84%,2种组织状态下的硬度受磁处理影响差别不大。
图7
图7
磁化处理对45CrNiMoVA钢硬度的影响
(a) pearlite
(b) tempered martensite
Fig.7
Changes of hardness of magnetized and unmagnetized 45CrNiMoVA steels
式中,
式中,
2.3 脉冲磁化处理对弹性模量的影响
图8所示为磁化处理对45CrNiMoVA钢弹性模量的影响。磁化处理导致珠光体态45CrNiMoVA钢弹性模量减小0.63%,而回火马氏体态下的弹性模量增加4.48%,可见2种组织状态下45CrNiMoVA钢弹性模量受磁场的影响不同,考虑实验误差的影响,磁处理对珠光体态下的弹性模量影响较小,而对回火马氏体态下的弹性模量影响较大。
图8
图8
磁化处理对45CrNiMoVA钢弹性模量的影响
(a) pearlite
(b) tempered martensite
Fig.8
Changes of elastic modulus of magnetized and unmagnetized 45CrNiMoVA steels
式中,
2.4 基于磁畴运动理论的分析及脉冲磁处理前后表面磁畴结构形貌
图9
图9
45CrNiMoVA钢的磁性能及分析
(a) measurement results of hysteresis loop
(b) schematic diagram of domain motion in different magnetization stages
Fig.9
Magnetic properties and analysis of 45CrNiMoVA steel
图10
图10
磁化处理对45CrNiMoVA钢磁畴结构形貌的影响
(a) unmagnetized pearlite
(b) magnetized pearlite
(c) unmagnetized tempered martensite
(d) magnetized tempered martensite
Fig.10
Changes of magnetic domain structures and morphologies of 45CrNiMoVA steel
铁磁材料的磁化本质是磁畴运动[12,34,35],图9b所示为45CrNiMoVA钢不同磁化阶段的磁畴运动示意图,包含畴壁的位移和磁矩的转动。在磁化初始阶段,磁畴运动以可逆畴壁位移为主,对材料力学性能影响微弱;随着外磁场增大,畴壁位移需要克服材料内应力、杂质、晶界、位错等不均匀分布产生的阻力,形成不可逆畴壁位移;随着外磁场进一步增加,畴壁位移基本结束,磁化强度的增加依赖磁矩的转动,磁矩向外磁场方向转动,直至饱和。巴克豪森效应[34] (Barkhausen effect)认为磁化过程中畴壁的位移是一个不连续的过程,畴壁位移过程中遇到钉扎点,外磁场缓慢增加难以使其移动,而当外磁场达到临界点,畴壁突然移动到平衡位置,产生大量“跳跃”巴克豪森信号,相对应地,磁致应变量发生突变、位错塞积开动。
图10所示为MFM测得的45CrNiMoVA钢试样脉冲磁处理前后表面磁畴结构形貌,图中亮暗程度反映了磁力探针受磁场力作用下的相位变化(单位为“毫度”),局部亮暗均匀区域即代表一个磁畴单元。受材料组织晶粒不均匀的影响,45CrNiMoVA钢的磁畴结构型式杂乱。相对珠光体态组织,回火马氏体态组织更为细碎,导致其磁畴呈“碎畴”形态分布。相比于未磁化处理试样(图10a和c),脉冲磁化处理后(图10b和d)整个图像亮暗分布更为均匀,过渡区更为平滑,表明脉冲磁化处理导致表面磁畴分布更加均匀,这是在脉冲磁场作用下,磁畴克服材料内部阻碍后运动,重新排布的结果。在初始试样内部存在残余压应力的条件下,当外界磁场强度大于位错增殖所需的临界场强,磁畴的这种不可逆运动就会引起微区应力、应变,促进位错增殖、积聚,使位错密度提高,宏观表现为残余压应力和硬度的增大。弹性模量的变化可能与材料在磁化过程中总能量密度改变有关,根据铁磁学理论[35],当材料未受外应力和外磁场作用时,总能量密度(
式中,
3 结论
(1) 在初始试样表面为残余压应力的条件下,脉冲磁化处理使45CrNiMoVA钢表面残余压应力增大,这是磁场导致位错增殖的结果。
(2) 脉冲磁化处理使珠光体态和回火马氏体态45CrNiMoVA钢硬度分别增加1.85%和1.84%,这主要与磁场对位错和碳化物的影响作用有关。
(3) 脉冲磁化处理对珠光体态下的弹性模量影响较小,但对回火马氏体态下的弹性模量影响较大,磁化处理后回火马氏体态45CrNiMoVA钢弹性模量增加4.48%,这可能与材料内部总能量密度受磁场影响改变有关。
(4) 45CrNiMoVA钢力学性能受脉冲磁场强化作用的本质为磁畴克服材料内部不均匀引起的微区应力、应变,进而导致位错运动、增殖,宏观上表现为残余压应力、硬度和弹性模量的增加。
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纳米压痕法测量残余应力的研究现状
[J].
Residual stresses in DLC/Si and Au/Si systems: application of a stress-relaxation model to the nanoindentation technique
[J].
A new method for estimating residual stresses by instrumented sharp indentation
[J].
Influence rule of steel GCr15 in process of cold ring rolling-quenching by magnetic treatment
[J]. J.
磁处理对GCr15轴承环冷轧-淬火残余应力影响规律
[J].
Study on the relationship between magneto-vibration and residual stress in steel materials
[J].
钢铁材料中残余应力与磁致振动的相互作用关系
[J].
Pulsed magnetic field-induced martensitic transformation in an Fe-21Ni-4Mn alloy
[J].
F6-21Ni-4Mn合金强脉冲磁场诱发马氏体相变的研究
[J].
Effects of a strong magnetic field on the phase stability of plain carbon steels
[J].
Influence of pulsed magnetic treatment on microstructures and mechanical properties of M42 high speed steel tool
[J].
脉冲磁化处理对M42高速钢刀具组织和力学性能的影响
[J].
Magnetic domain-twin boundary interactions in Ni-Mn-Ga
[J].
An investigation on the mechanical property changing mechanism of high speed steel by pulsed magnetic treatment
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Magnetic field effects on twin dislocations
[J].
Influence of high magnetic field on carbides and the dislocation density during tempering of high Chromium-containing steel
[J].
Magnetic field sensitive functional elastomers with tuneable elastic modulus
[J].
Diffusion-controlled mechanical property-enhancement of Al-20wt.%Si ribbon annealed under high static magnetic fields, from the microscale to the atomic scale
[J].
Stress and magnetic field-dependent Young's modulus in single crystal iron-gallium alloys
[J].
Research on magnetic domain wall dynamic behaviors for stress characterization
[D].
基于磁畴动态行为特征的应力表征研究
[D].
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