AISI4340高强钢在含氧和/或Cl^(-)高温水中的应力腐蚀行为

采用慢拉伸应力腐蚀试验与应力腐蚀裂纹扩展试验,对AISI4340钢在含饱和氧和/或0.1 mol·L^(-1)的100℃水中的应力腐蚀行为进行研究。结果表明:100℃水中存在的氧或C一均可以增大AISI4340钢的应力腐蚀倾向,但在含Cl^(-)并除氧的100℃水中的应力腐蚀倾向不显著,慢拉伸断口依旧保留部分韧性断裂特征,而在含饱和氧的高温水中AISI4340钢发生完全脆性断裂,应力腐蚀倾向显著;氧或Cl^(-)均可提高AISI4340钢在100℃水中的应力腐蚀裂纹扩展速率,氧与Cl^(-)之间存在交互作用,二者共存显著提高了应力腐蚀倾向,并导致开裂后裂纹快速扩展。

阶梯钻加工高强度钢AISI4340的钻头几何参数优化

为得到阶梯钻加工AISI4340的钻头最优几何参数,提高AISI4340的加工质量,减小加工过程中的轴向力,采用DEFORM-3D对阶梯钻加工高强度钢AISI4340的过程进行了模拟,采用回归正交试验和多元非线性回归法分别建立了试验因素第一顶角、第二顶角、螺旋角与轴向力的回归模型。在MATLAB中应用遗传算法分别得到了两组不同的优化组合,对优化后的钻头几何参数进行仿真和实验验证,对加工质量进行分析,确定了阶梯钻加工AISI4340的钻头最优几何参数组合,为阶梯钻在实际加工AISI4340中选择合理的刀具几何参数提供了参考。

AISI 4340钢制螺栓的失效分析

AISI 4340钢制螺栓在静止状态发生断裂,经过外观检查、宏观观察、微观观察、能谱分析、金相观察及硬度检测等方法,综合分析确定了该固定螺栓的断裂性质,并分析其发生断裂失效的原因。结果表明:螺栓断裂性质为氢脆断裂,定量分析了螺栓装配工艺对螺栓氢脆产生的影响。提出应从固定螺栓本身的功能特性出发,选用合适材料和装配工艺,控制热处理工艺,降低该型螺栓发生氢脆断裂的风险。

超高压容器用钢AISI4340的包辛格系数

提出按单层超高压自增强容器塑性层预应力实测值确定钢材包辛格系数的方法;基于试验数据,分析了超高压容器用钢AISI4340的包辛格系数.研究表明:(1)AISI4340的包辛格系数是一个常数,其大小与塑性层的位置和容器自增强压力的大小无关.(2)AISI4340钢包辛格系数的平均值为0.967 1.(3)2项工程实例验证文中方法的合理性.

基于应变梯度塑性理论的AISI4340微细铣槽研究

针对AISI 4340合金钢在微尺度加工时的力学特点,基于Johnson-Cook模型,结合应变梯度塑性理论,建立适用于微细铣削加工的AISI 4340本构模型,并根据刀具材料的物理性能建立微铣刀的仿真模型,采用任意拉格朗日-欧拉(ALE)自适应网格技术进行微细铣槽的有限元仿真,得到了不同转速、不同进给量下微细铣削过程中铣削力的大小,并与相应的物理实验结果进行对比,验证了所建模型的正确性,为微细铣削的进一步研究奠定了基础。

AISI 4340钢干滑动摩擦磨损特性研究

室温条件下,采用CFT-Ⅰ型多功能材料表面综合性能测试仪对AISI 4340钢进行了往复干摩擦磨损试验,研究了其摩擦磨损特性.采用扫描电子显微镜(SEM)和能谱仪(EDS)对磨痕和亚表层进行了观察和检测,分析了磨损表面微观形貌、亚表层塑性变形和碳氧元素含量演化.结果表明:磨损形式以磨粒磨损为主,并伴随轻微黏着磨损和剥落磨损;磨损表面分布着长度、宽度、深度不一的划痕以及鳞片状和颗粒状磨屑;磨损表面出现轻微氧化,磨屑呈现不同程度的碳富集和氧化;亚表层出现明显摩擦影响层,距表层越近,塑性变形越明显,晶界角逐渐汇聚于表面,在表面处趋于平行;往复运动导致塑性变形方向不一致,磨痕中部,塑性变形向某位置聚集.

热处理对双真空冶炼AISI 4340钢显微组织和拉伸性能的影响

采用光学显微镜、透射电镜和拉伸实验等研究了不同热处理状态的双真空冶炼AISI 4340钢的显微组织与拉伸性能,并与普通冶炼AISI 4340钢的强度-塑性进行对比。结果表明:淬火态双真空冶炼AISI 4340钢的微观组织主要由板条和片层孪晶马氏体组成,板条内位错密度较高;经350℃回火后有大量碳化物析出,且仍观察到片层孪晶马氏体;随着回火温度继续升高,逐渐形成回火索氏体。随着回火温度升高,双真空冶炼AISI 4340钢中片层孪晶马氏体逐渐分解消失以及板条内位错密度下降导致其强度降低,而析出碳化物的球化则是塑性提高的主要原因。与普通冶炼工艺相比,双真空冶炼显著降低了AISI 4340钢中夹杂物含量,从而提高其塑性;淬火态和350℃回火态双真空冶炼AISI 4340钢强度-塑性同步提高的一个原因是纳米级片层孪晶马氏体的存在。

高速铣削AISI 4340合金结构钢时涂层刀具磨损机理研究

针对AISI 4340合金结构钢难加工的特点,选用PVD硬质合金涂层刀具进行高速干铣削试验,选用扫描电子显微镜(SEM)观察失效刀具表面的磨损形貌特征,选用能谱分析仪(EDS)分析磨损刀具表面的元素分布及含量,揭示刀具的磨损机理。研究结果表明:刀具寿命与切削参数选取有关,随着切削速度的增加,刀具磨损加快,刀具寿命降低。硬质合金涂层刀具的主要磨损形式是前刀面磨损和后刀面磨损,前刀面磨损机理主要是粘结磨损、涂层剥落、切削刃微崩刃;后刀面磨损机理主要是磨粒磨损、粘结磨损、扩散磨损、微裂纹。

Occurrence of Dynamic Shear Bands in AISI 4340 Steel under Impact Loads

In this study, occurrence of adiabatic shear bands in AISI 4340 steel under high velocity impact loads is investigated using finite element analysis and experimental tests. The cylindrical steel specimen subjected to impact load was divided into different sections separated by nodes using finite element method in ABAQUS environment with boundary conditions specified. The material properties were assumed to be lower at the section where the adiabatic shear bands are expected to initialize. The finite element model was used to determine the maximum flow stress, the strain hardening, the thermal softening, and the critical strain for the formation of adiabatic shear bands. Experimental results show that deformed bands were formed at low strain rates and there was a minimum strain rate required for formation of transformed band in the alloy. The experimental results also show that cracks were initiated and propagated along transformed bands leading to fragmentation under the impact loading. The susceptibility of the adiabatic shear bands to cracking was markedly influenced by strain-rates. The simulation results obtained were compared with experimental results obtained for the AISI 4340 steel under high strain-rate loading in compression using split impact Hopkinson bars. A good agreement between the experimental and simulation results was obtained.

Experimental Investigation of Laser Surface Hardening of AISI 4340 Steel Using Different Laser Scanning Patterns

Laser surface transformation hardening becomes one of the most modern processes used to improve fatigue and wear properties of steel surfaces. In this process, the material properties and the heating parameters are the factors that present the most significant effects on the hardened surface attributes. The control of these factors using predictive modeling approaches to achieve desired surface properties leads to conclusive results. However, when the dimensions of the surface to be treated are larger than the cross-section of the laser beam, various laser-scanning patterns are involved. This paper presents an experimental investigation of laser surface hardening of AISI 4340 steel using different laser scanning patterns. This investigation is based on a structured experimental design using the Taguchi method and improved statistical analysis tools. Experiments are carried out using a 3 kW Nd: YAG laser source in order to evaluate the effects of the heating parameters and patterns design parameters on the physical and geometrical characteristics of the hardened surface. Laser power, scanning speed and scanning patterns (linear, sinusoidal, triangular and trochoid) are the factors used to evaluate the hardened depth and the hardened width variations and to identify the possible relationship between these factors and the hardened zone attributes. Various statistical tools such as ANOVA, correlations analysis and response surfaces are applied in order to examine the effects of the experimental factors on the hardened surface characteristics. The results reveal that the scanning patterns do not modify the nature of the laser parameters’ effects on the hardened depth and the hardened width. But they can accentuate or reduce these effects depending on the type of the considered pattern. The results show also that the sinusoidal and the triangular patterns are relevant when a maximum hardened width with an acceptable hardened depth is desired.

基于Deform-3D软件对AISI4340钢Ф600mm铸坯开坯工艺参数的模拟数值

利用Deform-3D软件对AISI4340钢Φ600 mm铸坯至300 mm×300 mm坯的开坯过程工艺参数进行了数值模拟。通过对加热温度、轧制速度、压下率、2道次压下对铸坯心部变形和材料流动影响的研究,分析了开坯成形过程中心部等效应力和材料变形特点,获得了Φ600圆连铸坯开坯成300 mm方坯的成形规律。结果表明:在1 070~1 140℃内,加热温度对心部的应变影响较小,变化幅度在2.3%左右。当轧制速度选1.0~2.0 m/s、总压下量一定的情况下,先大后小更利于心部缺陷的焊合。

永磁风力发电机AISI 4340材料主轴锻件工艺试制

介绍了永磁风力发电机AISI 4340材料主轴锻件的技术条件,工艺试制方案,通过各项性能检测数据的比较,摸索出制造永磁风力发电机主轴锻件的可行工艺。

AISI 4340钢高温磨损机理和微观结构研究

在高温条件下采用球面往复摩擦磨损方式,研究了温度对AISI 4340低合金高强度钢摩擦磨损机理和磨损过程中微观结构的影响。结果表明,摩擦系数随温度的升高而先增大后减小,摩损率随温度升高而先减小后增大。磨痕表面分布有形貌不同的磨削痕迹和鳞片状、颗粒状磨屑,磨痕表面及其亚表层均出现明显的塑性变形。高温条件下,环境温度越高,表面摩擦系数越大,表面粗糙度越高,晶粒细化现象越明显,硬度越高,耐磨性越好。温度较低时,磨损机制主要是磨粒磨损和黏着磨损;温度较高时为磨粒磨损、黏着磨损和疲劳剥落三者兼具的形式。

淬火速度对AISI4320和4340钢显微组织和拉伸性能的影响

本文研究了淬火速度对两种具有全马氏体组织的商用AISI4320和4340钢的显微组织和拉伸性能的影响 试验钢以两种不同的冷却速度自1323～1473K的不同温度淬火。快速淬火处理采用冰盐水,慢速淬火处理采用373K的油。试验钢经473K双重回火,中间快冷和冷冻。使用Instron试验机测定室温下的拉伸性能。不同淬火速度产生的显微组织的变化用光学和薄膜透射电子显微镜技术进行观测。M_s温度较高的4320钢经缓慢淬火处理后,无论原奥氏体晶粒度大或小,其0.2％屈服强度和极限拉伸强度均比晶粒度相同的快速淬火处理钢高,面总延伸率相似。但随着原奥氏体晶粒度增大,慢淬钢强度数据的分散度变大。M_s温度较低的4340钢对淬火速度不敏惑,与快淬处理相比,慢淬处理仅使0.29％屈服强度稍有提高。根据显微组织观察的结果提出,慢淬之所以提高钢的强度,是淬火(即自回火)时碳偏聚或微细碳化物在马氏体基体上析出造成弥散硬化的结果。

Numerical Investigation of Laser Surface Hardening of AISI 4340 Using 3D FEM Model for Thermal Analysis of Different Laser Scanning Patterns

Laser surface hardening is becoming one of the most successful heat treatment processes for improving wear and fatigue properties of steel parts. In this process, the heating system parameters and the material properties have important effects on the achieved hardened surface characteristics. The control of these variables using predictive modeling strategies leads to the desired surface properties without following the fastidious trial and error method. However, when the dimensions of the surface to be treated are larger than the cross section of the laser beam, various laser scanning patterns can be used. Due to their effects on the hardened surface properties, the attributes of the selected scanning patterns become significant variables in the process. This paper presents numerical and experimental investigations of four scanning patterns for laser surface hardening of AISI 4340 steel. The investigations are based on exhaustive modelling and simulation efforts carried out using a 3D finite element thermal analysis and structured experimental study according to Taguchi method. The temperature distribution and the hardness profile attributes are used to evaluate the effects of heating parameters and patterns design parameters on the hardened surface characteristics. This is very useful for integrating the scanning patterns’ features in an efficient predictive modeling approach. A structured experimental design combined to improved statistical analysis tools is used to assess the 3D model performance. The experiments are performed on a 3 kW Nd:Yag laser system. The modeling results exhibit a great agreement between the predicted and measured values for the hardened surface characteristics. The model evaluation reveals also its ability to provide not only accurate and robust predictions of the temperature distribution and the hardness profile as well an in-depth analysis of the effects of the process parameters.

ANN Based Model for Estimation of Transformation Hardening of AISI 4340 Steel Plate Heat-Treated by Laser

Quality assessment and prediction becomes one of the most critical requirements for improving reliability, efficiency and safety of laser surface transformation hardening process (LSTHP). Accurate and efficient model to perform non-destructive quality estimation is an essential part of the assessment. This paper presents a structured and comprehensive approach developed to design an effective artificial neural network (ANN) based model for quality estimation and prediction in LSTHP using a commercial 3 kW Nd:Yag laser. The proposed approach examines laser hardening parameters and conditions known to have an influence on performance characteristics of hardened surface such as hardened bead width (HBW) and hardened depth (HD) and builds a quality prediction model step by step. The modeling procedure begins by examining, through a structured experimental investigations and exhaustive 3D finite element method simulation efforts, the relationships between laser hardening parameters and characteristics of hardened surface and their sensitivity to the process conditions. Using these results and various statistical tools, different quality prediction models are developed and evaluated. The results demonstrate that the ANN based assessment and prediction proposed approach can effectively lead to a consistent model able to accurately and reliably provide an appropriate prediction of hardened surface characteristics under variable hardening parameters and conditions.

热处理对AISI4340钢风机主轴性能的影响

对AISI 4340钢风机主轴进行了热处理工艺试验,测定了热处理后主轴的力学性能。结果表明,锻造后经860℃正火和640℃回火,850℃淬火和540℃回火处理后,主轴的力学性能为：抗拉强度1250 MPa,屈服强度1 140 MPa,断后伸长率14.5%,断面收缩率55%,-40℃冲击吸收能量38.5-41.3 J,表面硬度40-42 HRC,符合技术要求。此外,采用专用夹具、垂直装炉和预冷淬火,有效减小了主轴的热处理畸变。

Single Track Laser Surface Hardening Model for AISI 4340 Steel Using the Finite Element Method

Laser surface hardening becomes one of the most effective techniques used to enhance wear and fatigue resistance of mechanical parts. The characteristics of the hardened surface depend on the physicochemical properties of the material as well as the heating system parameters. To adequately exploit the benefits presented by the laser heating method, it is necessary to develop a comprehensive strategy to control the process parameters in order to produce desired hardened surface attributes without being forced to use the traditional and fastidious trial and error procedures. This study presents a comprehensive approach used to build a simplified model for predicting the hardness profile. A finite element method based prediction model for AISI 4340 steel is investigated. A circular shape with a Gaussian distribution is used for modeling the laser heat source. COMSOL MULTIPHYSICS software is used to solve the heat transfer equations, estimate the temperature distribution in the part and consequently predict the hardness profile. A commercial 3 kW Nd:Yag laser system is combined to a structured experimental design and confirmed statistical analysis tools for conducting the experimental calibration and validation of the model. The results reveal that the model can effectively lead to a consistent and accurate prediction of the hardness profile characteristics under variable hardening parameters and conditions. The results show great concordance between predicted and measured values for the dimensions of hardened and melted zones.

Numerical Investigation by the Finite Difference Method of the Laser Hardening Process Applied to AISI-4340

This paper presents a numerical and experimental analysis study of the temperature distribution in a cylindrical specimen heat treated by laser and quenched in ambient temperature. The cylinder studied is made of AISI-4340 steel and has a diameter of 14.5-mm and a length of 50-mm. The temperature distribution is discretized by using a three-dimensional numerical finite difference method. The temperature gradient of the transformation of the microstructure is generated by a laser source Nd-YAG 3.0-kW manipulated using a robotic arm programmed to control the movements of the laser source in space and in time. The experimental measurement of surface temperature and air temperature in the vicinity of the specimen allows us to determine the values of the absorption coefficient and the coefficient of heat transfer by convection, which are essential data for a precise numerical prediction of the case depth. Despite an unsteady dynamic regime at the level of convective and radiation heat losses, the analysis of the averaged results of the temperature sensors shows a consistency with the results of microhardness measurements. The feasibility and effectiveness of the proposed approach lead to an accurate and reliable mathematical model able to predict the temperature distribution in a cylindrical workpiece heat treated by laser.

Hardness Profile Prediction for a 4340 Steel Spline Shaft Heat Treated by Laser Using a 3D Modeling and Experimental Validation

Laser surface transformation hardening becomes one of the most effective processes used to improve wear and fatigue resistance of mechanical parts. In this process, the material physicochemical properties and the heating system parameters have significant effects on the characteristics of the hardened surface. To appropriately exploit the benefits presented by the laser surface hardening, it is necessary to develop a comprehensive strategy to control the process variables in order to produce desired hardened surface attributes without being forced to use the traditional and fastidious trial and error procedures. The paper presents a study of hardness profile predictive modeling and experimental validation for spline shafts using a 3D model. The proposed approach is based on thermal and metallurgical simulations, experimental investigations and statistical analysis to build the prediction model. The simulation of the hardening process is carried out using 3D finite element model on commercial software. The model is used to estimate the temperature distribution and the hardness profile attributes for various hardening parameters, such as laser power, shaft rotation speed and scanning speed. The experimental calibration and validation of the model are performed on a 3 kW Nd:Yag laser system using a structured experimental design and confirmed statistical analysis tools. The results reveal that the model can provide not only a consistent and accurate prediction of temperature distribution and hardness profile characteristics under variable hardening parameters and conditions but also a comprehensive and quantitative analysis of process parameters effects. The modelling results show a great concordance between predicted and measured values for the dimensions of hardened zones.