Ultrasonic Characterization of Strain Hardening Behavior in AISI 316L Austenitic Stainless Steel

The present work is aimed at characterizing the strain hardening behavior of AISI 316L austenitic stainless steel using ultrasonic velocity measurements. For this purpose, microstructural studies and ultrasonic velocity measurements were carried out on the samples deformed to different levels of strain at room temperature. Strikingly, the ultrasonic velocity?Cstrain plot of the alloy exhibited a three-stage behavior that was similar to the strain hardening rate?Cstrain response of the alloy. At strains lower than about 0.06 (stage A), a falling regime of velocity was observed that was related to the increase of dislocations density. This stage was followed by a stage of a nearly constant velocity (stage B). The initiation of this stage was concurrent with the onset of deformation twinning in the microstructure. Beyond a strain of about 0.2, the second falling regime of velocity (stage C) was developed. The occurrence of this stage was attributed to the difficulty of new twins formation with an increasing strain.     

Microstructural Evolutions During Reversion Annealing of Cold-Rolled AISI 316 Austenitic Stainless Steel

Metallurgical and Materials Transactions A - Microstructural evolutions during reversion annealing of a plastically deformed AISI 316 stainless steel were investigated and three distinct stages...     

316L奥氏体不锈钢的氮合金化

采用金相显微镜、XRD、拉伸试验机及高低温冲击试验机等,并结合Thermo-calc软件计算研究了氮对316L奥氏体不锈钢微观组织、析出相、力学性能和耐点蚀性能的影响.结果表明:氮合金化能够抑制316L不锈钢中σ相和Chi相的析出,增加Cr2N的析出倾向,对奥氏体晶粒细化不明显;氮的添加能够提高316L不锈钢的室温强度和-100℃以上温度的夏比冲击功,降低-100℃以下的夏比冲击功,但对室温拉伸塑性影响不明显.此外,氮能够改善316L不锈钢的耐点蚀能力.     

不锈钢表面激光熔覆镍基合金层研究

采用多层多道搭接的激光熔覆方法在0Cr18Ni10Ti不锈钢表面上分别熔覆两种镍基合金涂层.1#合金涂层的硬度在HRC34左右,无开裂;2#合金涂层的硬度在HRC47左右,易开裂.采用硬度较低的1#合金涂层作为过渡层成功解决了2#合金涂层的开裂问题,成功制备出大面积较厚涂层.经光学显微镜(OM)、X射线衍射(XRD)、扫描电子显微镜(SEM)以及能谱(EDS)分析可知,大面积熔覆层的表层主要由γ-Ni枝晶、块状γ-Ni和M12C型碳化物增强相组成.显微硬度测试表明,表层平均硬度达HV0.2583,自熔覆层表层至基体,显微硬度逐渐降低.     

316L不锈钢换热器的失效原因分析

利用化学法、金相法、SEM和EDX等方法,分析了苯酚中间再沸器316L不锈钢换热器管束和筒体失效材料的化学成分、显微组织、夹杂物水平、腐蚀产物的成分和裂纹形貌等.结果表明316L不锈钢的化学成分、显微组织和夹杂物都符合标准,换热器管束和筒体失效的主要原因是Cl-诱导的应力腐蚀开裂,此外,苯酚在裂纹处的结晶与溶解加速了应力腐蚀裂纹的扩展.针对上述应力腐蚀问题提出了相应的改进措施.     

Characterization of Passive Film Formed on AISI 316L Stainless Steel after Magnetoelectropolishing in a Broad Range of Polarization Parameters

The aim of the paper is to present the changes in the surface film composition on AISI 316L stainless steel (SS) after electropolishing (EP) and magnetoelectropolishing (MEP) in a broad range of the process conditions. The X‐ray photoelectron spectroscopy surface analyses were performed to reveal the effect of MEP. The EP process has been performed under natural convection (in a stagnant electrolyte), much above the polarization plateau. A series of experiments were carried out on AISI 316L SS samples in accordance with the five‐level composite rotary statistical plan with the variables being the magnetic field intensity B (mT), and the anodic current density i (A dm^?2). XP high resolution spectra have been obtained on AISI 316L SS surface concerning Fe 2p, Cr 2p, O 1s, S 2p, P 2p, and C 1s, respectively. The Cr:Fe ratio regarding both metallic M and compound X was also studied and calculated. At the end, the summary results of Cr/Fe = f(B, i) in relation to the corrosion potential, have been compared. The conclusions, concerning the selection of MEP process conditions, regarding the optimum Cr/Fe ratio and corrosion behavior, have been formulated. It was found the Cr:Fe ratio well correlates with the pitting corrosion potential. MEP process can modify not only the rate of dissolution to a determined extent, but also control the corrosion behavior and Cr:Fe ratio results.     

Probe Pulse Conditions and Solidification Parameters for the Dissimilar Welding of Inconel 718 and AISI 316L Stainless Steel

Metallurgical and Materials Transactions A - The present work addresses the weldability of dissimilar materials Inconel 718 and AISI 316L stainless steel through metallurgical and mechanical...     

Comparison of Continuum Damage Laws Under Uniaxial Creep for an AISI 316 Stainless Steel

Parameters of five popular continuum damage models are fit to match their creep rate and time to rupture predictions with that of a validated micro-mechanisms based model at a high nominal stress for an austenitic stainless steel. Their predictions are then compared with that of the micro-mechanisms based model at lower stress levels. The creep-strain rate and time to failure predictions of the model due to Wen et al. (Eng Fract Mech 98:169–184, 2013) best agrees with that of the micro-mechanisms based model in the regime of dominance of creep deformation processes. At still lower stress levels, where cavitation-rate is determined by diffusion processes, the Wen et al. model predictions of creep lifetimes become excessively non-conservative. A correction based on a formula due to Cocks and Ashby (Prog Mater Sci 27:189–244, 1982) has been proposed for this regime.     

Influence of Inclusion and Specimen Orientations on Intergranular Corrosion Testing of AISI 316LN Stainless Steel

Fabricated components must be free from sensitization for using these in critical applications in aggressive environments. During fabrication of a hollow bar from solid bar, deep hole drilling was employed which introduces residual stresses. Stress-relieving heat treatment was employed by heating the hollow bar from room temperature to 1,065°C @ 40°C/h and soaking at 1,065°C for 1 h followed by cooling @ 40°C/h as well as 70°C/h. To detect the susceptibility to IGC, specimens were taken from both circumferential direction as well as longitudinal direction and subjected to ASTM A 262 Practice E test. In U bend, the specimens from the circumferential direction failed whereas longitudinal specimens did not fail. However specimens of both orientations showed Step structure in Practice A test indicating that no carbide has nucleated during the stress-relieving heat treatment ensuring that the cooling rates are faster than the critical cooling rates and the material is not susceptible to IGC. EDAX studies indicated the presence of numerous MnS inclusions enriched in chromium which might have led to chromium depletion around the inclusions resulting in poor passivity at these locations. This study presents the influence of orientation of MnS inclusions in causing failure in U bend test. The need to select specimens of correct orientation during IGC testing is emphasized in this investigation.     

Effects of Process Parameters on the Tensile-Shear Strength of Pulsed Laser Welded Thin 316L Stainless Steel Foils

In this research, the parameters of pulsed Nd:YAG laser welding on the lap-joint of a 316L stainless steel foil were optimized through the response surface methodology with the aim of enhancing the tensile-shear strength. For this purpose, the effects of peak power, pulse-width, and frequency were investigated. The results showed that the analysis of welding parameters in the form of a simple combination of pulse energy could not completely predict welding properties, and the above-mentioned statistical method could appropriately be employed to balance the parameters by modeling and presenting a second-order polynomial. In this model, with the increased power and pulse-width, the strength first increased and then it decreased, and its maxima occurred at a power of 260 W and a pulse-width of 3 ms. The most important parameters affecting this model have been found to be power and pulse-width with impacts of 65 and 25%, respectively. In addition, microscopic studies showed that decrease in strength was because of the undercut and lack of penetration.     

Influence of Marine Aerobic Biofilms on Corrosion of 316L Stainless Steel

The influence of marine aerobic biofilms on the corrosion of 316 L stainless steel(SS) in aerated and deaerated seawater was studied by electrochemical impedance spectroscopy(EIS), potentiodynamic polarisation curves, current-potential curves and scanning electron microscopy with energy-dispersive spectroscopy(SEM-EDS). EIS and SEM-EDS results showed that the aerobic biofilms inhibited 316 L SS corrosion within the test duration. Comparison of results under aerated and deaerated conditions revealed that O2 enhanced the inhibition efficiency of the aerobic biofilms. This result indicated that living cells were necessary for the aerobic biofilms to inhibit the corrosion of 316 L SS. Polarization curves indicated that the biofilms mainly inhibited anode action. Current-potential curves under deaerated conditions showed that electron transfer processes occurred between microorganisms and electrodes. Moreover, 316 L SS as an electron acceptor was protected from corrosion.     

扫描速度对激光快速成型316L不锈钢组织性能的影响

研究了在激光功率900W条件下，扫描速度对激光快速成型不锈钢零件组织，性能的影响，在各扫描速度下，所成型的不锈钢薄壁板件的组织均为枝晶组织，随扫描速度提高，不锈钢薄壁板的定向生长树枝晶组织细化，枝晶间距变小，同时其沿X方向的机械性能（抗拉强度及硬度）降低。     

316L不锈钢的疲劳裂纹扩展行为试验

 工程构件普遍承受疲劳载荷,从而导致疲劳失效。针对由316L不锈钢制成的标准紧凑拉伸试样,开展了一系列疲劳裂纹扩展试验。试验内容包括不同应力比下的常幅加载和在常幅加载过程中引入单个拉伸过载峰。试验结果表明：316L不锈钢具有很强的应力比效应,裂纹扩展速率随应力比的增大而增大。在引入单个拉伸过载峰后,观察到出现迟滞效应前发生了短暂的加速扩展现象。通过一种新的双参数模型来描述材料的应力比效应,并使用改进的Wheeler模型对过载后的裂纹扩展行为进行预测。预测结果表明：该方法能够更好地描述不同工况下316L不锈钢的疲劳裂纹扩展行为。     

Corrosion Characteristics of Ni-Based Hardfacing Alloy Deposited on Stainless Steel Substrate by Laser Cladding

Metallurgical and Materials Transactions A - In this study, corrosion characteristics of a nickel-based Ni-Mo-Cr-Si hardfacing alloy having 32Mo, 15Cr, and 3Si (wt pct) as alloying...     

Gas Tungsten Arc Welding of 316L Austenitic Stainless Steel with UNS S32205 Duplex Stainless Steel

In the present work, dissimilar welding between UNS S32205 duplex stainless steel (DSS) and 316L austenitic stainless steel (ASS) was performed by using gas tungsten arc welding and ER2209 filler at two different heat inputs (0.52 and 0.98 kJ/mm). Microstructures were characterized using reflected light optical microscope and scanning electron microscope. Micro-hardness and tensile properties were measured across the weld for both the heat inputs. The microstructure of the welded region was primarily austenitic (for both heat inputs) with Widmanstätten morphology. The grain size of the heat affected zone on DSS side was very large (~200 µm) for the high heat input sample with the presence of partially transformed austenite and acicular austenite. The precipitation of intermetallic phases and carbides was not observed for both the heat inputs. The proportion of ferrite in the weld metal (as measured by feritscope) was higher for the high heat input sample than the low heat input sample. During the tensile test, fracture occurred in 316L ASS base metal (because of its lower strength) in ductile manner. For high heat input welds, the impact tested sample showed the presence of fine spherical precipitates rich in Cr, Mn and Fe in the fracture surface of weld metal.     

Fe-Mo-B Enhanced Sintering of P/M 316L Stainless Steel

Liquid-phase enhanced sintering of powder metallurgy（P/M）316L stainless steel by addition of sintering aids was studied.2%-8% of pre-alloyed Fe-Mo-B powder with two different particle sizes was added as sintering aids,and the specimens were sintered in vacuum at 1 200-1 350 ℃.The results show that the fine Fe-Mo-B powder（5-10 μm）has stronger activated effect.The sintered density increases with the increase in sintering aid content or sintering temperature.Warm compaction has a better effect on the control of dimensional precision of compacts.The prealloyed Fe-Mo-B powder deviated from Mo2FeB2 component can also be sintering aid of P/M 316L stainless steel.     

Effect of Welding Current and Time on the Microstructure,Mechanical Characterizations,and Fracture Studies of Resistance Spot Welding Joints of AISI 316L Austenitic Stainless Steel

This article aims at investigating the effect of welding parameters, namely, welding current and welding time, on resistance spot welding (RSW) of the AISI 316L austenitic stainless steel sheets. The influence of welding current and welding time on the weld properties including the weld nugget diameter or fusion zone, tensile-shear load-bearing capacity of welded materials, failure modes, energy absorption, and microstructure of welded nuggets was precisely considered. Microstructural studies and mechanical properties showed that the region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. Electron microscopic studies indicated different types of delta ferrite in welded nuggets including skeletal, acicular, and lathy delta ferrite morphologies as a result of nonequilibrium phases, which can be attributed to a fast cooling rate in the RSW process. These morphologies were explained based on Shaeffler, WRC-1992, and pseudo-binary phase diagrams. The optimum microstructure and mechanical properties were achieved with 8-kA welding current and 4-cycle welding time in which maximum tensile-shear load-bearing capacity or peak load of the welded materials was obtained at 8070 N, and the failure mode took place as button pullout with tearing from the base metal. Finally, fracture surface studies indicated that elongated dimples appeared on the surface as a result of ductile fracture in the sample welded in the optimum welding condition.