A Hybrid Optimization Approach of Single Point Incremental Sheet Forming of AISI 316L Stainless Steel Using Grey Relation Analysis Coupled with Principal Component Analysiss

We investigated the parametric optimization on incremental sheet forming of stainless steel using Grey Relational Analysis(GRA) coupled with Principal Component Analysis(PCA). AISI 316L stainless steel sheets were used to develop double wall angle pyramid with aid of tungsten carbide tool. GRA coupled with PCA was used to plan the experiment conditions. Control factors such as Tool Diameter(TD), Step Depth(SD), Bottom Wall Angle(BWA), Feed Rate(FR) and Spindle Speed(SS) on Top Wall Angle(TWA) and Top Wall Angle Surface Roughness(TWASR) have been studied. Wall angle increases with increasing tool diameter due to large contact area between tool and workpiece. As the step depth, feed rate and spindle speed increase,TWASR decreases with increasing tool diameter. As the step depth increasing, the hydrostatic stress is raised causing severe cracks in the deformed surface. Hence it was concluded that the proposed hybrid method was suitable for optimizing the factors and response.

活性屏离子渗碳设备研制及在不锈钢工件上的应用

为了解决离子渗均匀性差的问题,开发了一种工业级大尺寸活性屏离子渗技术,并研制了设备。采用低温离子渗碳工艺对AISI316L奥氏体不锈钢汽车涡轮增压器用输出销进行表面强化,工件经过435℃低温渗碳30 h后的测试结果显示,炉内工件架不同部位24个样品的硬度为917~1279 HV0.05,渗层厚度16.7~27.1μm,盐雾试验720 h后没有生锈,符合产品技术要求。该结果证明,活性屏离子渗在低温渗碳方面具有优越性,可以同时实现不锈钢工件的表面高硬度和强耐腐蚀性。

变接触长度限制接触刀具车削不锈钢时的切削力及切削性能研究

AISI 316L奥氏体不锈钢作为典型的难加工材料,存在着加工效率低和加工过程热-力载荷大的问题。现有关于改善不锈钢加工性能的若干方法,如采用润滑措施、设计刀具表面结构等,均存在明显缺陷,例如,切削液的大量使用不利于环境和人体健康,刀具表面结构的不合理设计反而会加剧刀具磨损。针对现有方法无法很好改善奥氏体不锈钢加工过程热-力载荷大等问题,文中设计了一种新型变接触长度的限制接触刀具,用于加工AISI 316L奥氏体不锈钢,其与传统限制接触刀具相比可以有效减小切削力和摩擦系数。研究中首先基于非等距剪切区模型和切削力学理论,建立了用于预测变限制接触长度的限制接触刀具在车削时的切削力半解析模型;然后,在硬质合金刀具前刀面上通过线切割和微细电火花加工出常规和新设计的限制接触形状(矩形以及梯形限制接触形状),并进行了大量实验用于验证预测模型。结果表明:利用所建立的半解析模型预测出的切削力与实验数据吻合较好;与传统限制接触刀具相比,变限制接触长度的刀具能明显减小切削力。此外,文中还对比分析了传统和变接触长度的限制接触刀具在干切削条件下对切削性能的影响,发现变限制接触长度的刀具比传统限制接触刀具能更有效地降低切削温度和减少刀具磨损。文中研究结果可为切削难加工材料的刀具的设计提供参考。

Behavior of AISI 316L Steel Subjected to Uniaxial State of Stress at Elevated Temperatures

This paper presents an experimental investigation on an AISI 316L stainless steel regarding mechanical properties and short uniaxial creep tests at elevated temperatures. The short time creep tests were carried out under different but constant stresses. The obtained data of ultimate tensile strength, yield strength, creep curves and effects of elevated temperatures on mechanical properties were presented. For a selected rheological model, material parameters were obtained. As a justification, such rheological model is implemented in the finite element procedure for an uniaxially stressed specimen in selected environmental conditions.

Microstructure and Fracture Behavior of 316L Austenitic Stainless Steel Produced by Selective Laser Melting

Selective laser melting is an additive manufacturing method based on local melting of a metal powder bed by a high power laser beam. Fast laser scans are responsible for severe thermal gradients and high cooling rates which produce complex hydrodynamic fluid flow. These phenomena affect crystal growth and orientation and are believed to be the cause of material spattering and microstructural defects, e.g. pores and incompletely melted particles. In this work, the microstructure and texture of 316L bars built along two different orientations and the effect of different distribution of defects on their mechanical response and failure mechanisms were investigated. Partially molten powder particles are believed to be responsible for the scattering in elongation to failure, reduced strength, and premature failure of vertical samples.

Effect of heat input on microstructure and mechanical properties of dissimilar joints of AISI 316L steel and API X70 high-strength low-alloy steel

The microstructure and mechanical properties of dissimilar joints of AISI 316L austenitic stainless steel and API X70 high-strength low-alloy steel were investigated.For this purpose,gas tungsten arc welding（GTAW）was used in three different heat inputs,including 0.73,0.84,and 0.97 kJ/mm.The microstructural investigations of different zones including base metals,weld metal,heat-affected zones and interfaces were performed by optical microscopy and scanning electron microscopy.The mechanical properties were measured by microhardness,tensile and impact tests.It was found that with increasing heat input,the dendrite size and inter-dendritic spacing in the weld metal increased.Also,the amount of delta ferrite in the weld metal was reduced.Therefore,tensile strength and hardness were reduced and impact test energy was increased.The investigation of the interface between AISI 316L base metal and ER316L filler metal showed that increasing the heat input increases the size of austenite grains in the fusion boundary.A transition region was formed at the interface between API X70 steel and filler metals.

Microstructure evolution and mechanical properties of 316L austenitic stainless steel with aluminum addition by warm rolling

Microstructure evolution and mechanical properties of 316L austenitic stainless steel with aluminum addition by warm rolling at 550 ℃ were investigated. It is found that sample is composed of an ashen austenite matrix, a gray black ferrite phase and a small number of NiCx. The average grain sizes are 21.62, 19.66 and 19.49 μm for samples with the rolling deformation of 30%, 50% and 70%, respectively. The yield strength and tensile strength of samples with solid solution time of 30 min and deformation of 70% are higher. The fracture modes are similar and belong to toughness fracture. The fracture surfaces of the samples are composed of relatively large equal-axis ductile dimples （5-15 μm） and fine scattered ones around the dimples （〈 5 μm）. As the rolling deformation increases, the quantity of subgrain boundary increases and the 〈 101 〉 orientation is more prominent. {001 } 〈 110 〉 rotation-cube textures are present in ferrite phase of samples and weak Goss texture is formed in austenite pole images.