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.

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。

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。

阶梯钻钻削AISI4340的轴向力和刀具温度研究

针对高强度钢AISI4340钻削过程中存在轴向力大、钻削温度高、刀具磨损严重等问题,课题组在普通麻花钻的基础上设计了一种阶梯钻,利用DEFORM-3D有限元软件对阶梯钻钻削AISI4340的过程进行仿真研究,对阶梯钻的轴向力形成理论进行分析,研究主轴转速、进给量和顶角等3个因素对轴向力和钻头最高温度的影响规律,并与普通麻花钻进行对比。结果表明:主轴转速对轴向力的影响最小,顶角对钻头最高温度的影响最小,阶梯钻在降低轴向力和减小刀具磨损方面比麻花钻更有优势;同时发现,当阶梯钻主轴转速取2 500 r·min^(-1),进给量取0.1 mm·r^(-1),第1顶角取118°时,得到的轴向力最小,钻头温度分布较为理想。研究的结果对实际钻削AISI4340参数的选择提供了一定的参考。

A Predictive Modeling Based on Regression and Artificial Neural Network Analysis of Laser Transformation Hardening for Cylindrical Steel Workpieces

Laser surface hardening is a very promising hardening process for ferrous alloys where transformations occur during cooling after laser heating in the solid state. The characteristics of the hardened surface depend on the physicochemical properties of the material as well as the heating system parameters. To exploit the benefits presented by the laser hardening process, it is necessary to develop an integrated 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 modelling approach for predicting the hardened surface physical and geometrical attributes. The laser surface transformation hardening of cylindrical AISI 4340 steel workpieces is modeled using the conventional regression equation method as well as artificial neural network method. The process parameters included in the study are laser power, beam scanning speed, and the workpiece rotational speed. The upper and the lower limits for each parameter are chosen considering the start of the transformation hardening and the maximum hardened zone without surface melting. The resulting models are able to predict the depths representing the maximum hardness zone, the hardness drop zone, and the overheated zone without martensite transformation. Because of its ability to model highly nonlinear problems, the ANN based model presents the best modelling results and can predict the hardness profile with good accuracy.

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.

热处理对AISI4340钢临界点及CCT曲线的影响

采用热膨胀法测定了AISI4340钢的固态相变点,观察了组织和硬度,研究了不同热处理状态对临界点和奥氏体连续冷却转变曲线(CCT曲线)的影响。结果表明,试验钢具有较好的淬透性,冷速为0.03℃/s时得到单一贝氏体组织,冷速为0.03~0.78℃/s之间得到马氏体和贝氏体混合组织,冷速大于0.78℃/s时相变组织都为马氏体。不同热处理状态对ATSI4340钢的A_(c1)、A_(c3)有影响,而CCT曲线没有明显差别。弥散分布、介稳定的组织具有较低的A_(c1),原始组织对A_(c1)的影响比A_(c3)大。

Shear Band Formation in AISI 4340 Steel Under Dynamic Impact Loads:Modeling and Experiment

In this study, the occurrence of the adiabatic shear bands in AISI 4340 steel under high velocity impact loading was investigated using finite element analysis and experimental tests. The cylindrical specimen subjected to the impact load was divided into different regions separated by nodes using finite element method in ABAQUS environment with boundary conditions specified. The material properties were assumed to be lower in the region where the probability of strain localization is high based on prior experimental results in order to initialize the formation of the adiabatic shear bands. The finite element model was used to determine the maximum flow stress, the strain hardening, the thermal softening, and the time to reach 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 the formation of the transformed band in the alloy and the cracks were initiated and propagated along the transformed bands leading to fragmentation under the impact loading. The susceptibility of the adiabatic shear bands to cracking was markedly influenced by the strain-rates and the initial material microstructure. The simulation results obtained were compared with the experimental results obtained from 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.