Microstructural creep damage in welded joints of 316L stainless steel

The present work has been undertaken to study creep damage in welded joints. The complex dual phase microstructure of 316L welds are simulated by manually filling a mould with longitudinally deposited weld beads. Most of the moulded specimens were then aged for 2000 hours at 600°C. High resolution scanning electron microscopy was extensively used to examine the microstructure of the welded material before and after ageing. Columnar grains of austenite constitute a matrix in which thin dendrites of δ-ferrite can be found. The ageing generates the precipitation of carbides, resulting in less transformation in the material. Smooth and notched creep specimens were cut from the mould and tested at 600°C under different stress levels. The creep life of the simulated welded material is shown to be lower than that of the base material. Microstructural observations reveal that creep cavities are preferentially located along the austenite grain boundaries. This analysis of intergranular damage on test specimens is conducted to obtain a predictive damage law which could be used to calculate the lifetime of welded joints.     

Creep crack growth in type 316 stainless steel and its weldment

The creep crack growth behaviour of type 316stainless steel and its weldment in the temperature range 600° to BOOoe has been studied under plane stress conditions. The creep crack growth (eeG) rate bears a relation with sheloa;d point deflection (LPD) rate independent of the load. The parameters stress mtenstty factor, K,and the energy rate line integral C*,have been correlated with the e.eG rate. At 600⁰e tsecrack growth takes place along the interface between austemte and thsdelta fernte: At 700° and BOOoe sigma phase formation is dominant and crack growth tS along the Stgma phase and austenite.     

A fatigue and creep study in austenitic stainless steel 316L used in exhaust pipes of naval gas turbines

Exhaust pipes of naval gas turbines are made of thin wall tubing of stainless steel grade AISI 316L. The tubes are fabricated by butt welding of different sections with longitudinal and circumferential joints. The plate thickness is about 4.0 mm, and the working temperature varies between 600 °C and 400 °C in the critical zones of the pipe, in the lower and central areas, respectively. The loadings in the tube induce high‐temperature fatigue and creep‐fatigue cracks have nucleated and propagated in the tube near some welded joints. The paper presents FCGR data obtained in CT specimens of used material taken from the pipes and tested at RT, 335, 500 and 600 °C. Preliminary creep data obtained in tension, in thin‐sheet specimens (about 4 mm thickness), also taken from the conduct wall and tested at 500, 550 and 600 °C are also given. These results are crucial to perform a fatigue‐creep interaction life assessment of the critical parts of the structure in the near future. Finally, the paper presents results of research work to investigate carbide precipitation and formation in virgin thin‐sheet specimens subjected to several types of thermal exposures. In some cases, 3–4 d was the time interval between exposures. Grain size measurements were carried out together with microstructural observations in the SEM. The influence of time, temperature and time interval between thermal exposures was assessed comparing the microstructures.     

316L不锈钢冠脉支架制造工艺的研究

研究了激光精细雕刻冠状动脉血管支架的制造工艺,对冠脉支架结构设计原则、激光精细雕刻加工参数、热处理工艺进行了探讨.并给出一种冠脉支架结构,进行切割实验,分析了影响切口质量因素及真空热处理工艺、电化学工艺对冠脉支架样品质量的影响.     

Modelling tail effects in creep-crack initiation and growth for 316L stainless steel

For complex loading history (creep and fatigue) applied to engineering components, assessment procedures generally estimate the crack initiation and growth by using the summation of continuous fatigue and pure creep crack growth rates. This text deals with the pure creep correlation established in laboratory tests and applied to components subjected to creep-fatigue loading. The trend of the creep opening displacement history superimposed onto the crack progress is sufficient to predict what kind of tail effect will occur when plotting ? vs. C*. The exponent of this correlation is demonstrated to be very close to unity, whatever creep stage is concerned. The contribution of either the material behaviour or the crack extension to the ? -C* correlation is discussed.     

Experimental investigation on corrosion and hardness of ion implanted AISI 316L stainless steel

The AISI 316L stainless steel has been widely used both in artificial knee and hip joints in bio-medical applications. In the present study AISI 316L SS was implanted with two different ions: nitrogen and helium at 100 keV with a dose of 1 × 10¹⁷ ions/cm² at room temperature. The crystallographic orientation and surface morphology were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM). The effects of ion implantation on the corrosion performance of AISI 316L stainless steel was evaluated in 0.9% NaCl solution using electro chemical test both on the virgin and implanted samples. The subsequent Tafel analysis shows that the ion implanted specimens were more corrosion resistant when compared to the bare specimens. Microhardness was also measured by Vickers method by varying the loads. The results of the studies indicated that there was a significant improvement in both corrosion resistance and hardness of implanted samples.     

316L不锈钢加工硬化机制及孪生行为

对固溶处理后的316L不锈钢试样进行了拉伸实验,根据Ludwik真应力应变模型对拉伸实验曲线进行了非线性拟合,并用Crussard-Jaoul法计算和分析了Ludwik模型中的加工硬化指数（n）,同时通过对拉伸试样的微观组织观察,分析了316L不锈钢的加工硬化机制.实验结果表明：316L不锈钢在拉伸变形过程中加工硬化非...     

大口径316L不锈钢管数控弯曲回弹规律研究

针对Φ123 mm×3.97 mm×350 mm规格的大口径316L厚壁不锈钢管,基于显/隐式弹塑性有限元仿真结合实验研究,对其数控弯曲卸载后的回弹现象进行了研究.采用单向拉伸试验和三维数字散斑动态应变测量方法获得了大口径316L不锈钢管大应变范围(真应变为49.02%)的力学性能参数,通过摩擦磨损实验获得管材316L不锈钢与45钢模具材料在不同压力和转速条件下的摩擦系数.基于ABAQUS平台,建立了大口径316L不锈钢管弯曲、抽芯、卸载回弹全过程数控弯曲有限元模型,并实验验证了所建模型的可靠性.研究表明,大口径316L不锈钢管回弹现象显著,在350 mm弯曲半径(相对弯曲半径D/t为2.846)条件下达到7.2°左右.芯棒伸出量e、芯球个数n和弯曲角度θ对卸载回弹有显著影响.     

The effect of pre-strain on tensile behaviour of 316L austenitic stainless steel

ABSTRACT

The effect of pre-strain on tensile behaviour of 316L austenitic stainless steel was investigated, focusing on strain rate sensitivity, temperature sensitivity and strain hardening. Experimental data showed that strain rate sensitivity, temperature sensitivity and strain hardening were weakening with pre-strain. Meanwhile, the variation of microstructure with pre-strain was observed by optical microscopy, scanning electronic microscopy and X-ray diffraction. Then, the mechanical properties of pre-strained material were correlated with the increase in dislocation density and mechanical twinning with pre-strain. Finally, an improved Arrhenius-PS model considering the effect of pre-strain was developed.

This paper is part of a thematic issue on Nuclear Materials.     

316L不锈钢表面聚氨酯多孔涂层的制备及其生物性能研究

利用湿法相转化原理在316L不锈钢表面制备聚氨酯涂层时，空气湿度和溶液浓度是影响涂层形貌的两个主要因素．涂层表面形貌的观察结果表明：空气湿度增大或者溶液浓度减少，都有增大涂层表面孔径的趋势，而且可以加深孔的深度．通过控制空气湿度和溶液浓度，孔径可以在几个微米到30多个微米的范围内变化．通过亲疏水性测量、血小板粘附试验和动态凝血试验考察了涂层的血液相容性．以316L不锈钢作为参照组进行对比分析，结果可知：PU多孔涂层表面为超疏水性，明显降低了血小板在材料表面的粘附，延长了动态凝血时间，表现出良好的血液相容性．     

316L不锈钢在海水中的阴极极化行为研究

为了探索316L不锈钢阴极保护有效控制电位,利用动电位极化曲线及恒电位极化法研究了316L不锈钢在天然海水和模拟闭塞液中的阴极极化行为,通过失重法研究了不同电位恒电位极化对316L不锈钢在模拟闭塞液中腐蚀控制的效果.研究表明:316L不锈钢在海水中适宜的阴极保护电位为-0.6～-0.9 V(vs.SCE),模拟闭塞液中...     

Low cycle fatigue life enhancement of 316 L stainless steel by nitrogen alloying

Tests carried out at room temperature on 316 L stainless steels with different nitrogen contents show that nitrogen improves the low cycle fatigue resistance of the materials. However, saturation occurs when nitrogen content is above 0.12 weight per cent. The microstructural aspect is also studied; the deformation is more difficult and more planar when nitrogen is present. Moreover, nitrogen delays the formation of cells. A single relation, derived from the Manson-Coffin formula, describes the low cycle fatigue behaviour of these steels by taking into account plastic strain range and nitrogen content.     

Structure and wear resistance of the composite layers produced by glow discharge nitriding and PLD method on AISI 316L austenitic stainless steel

The rapid technical development enhances the demands on constructional materials in terms of their resistance to frictional wear, resistance to corrosion and erosion, high hardness, high tensile and fatigue strength. These demands can be satisfied by e.g. applying various surface engineering techniques that permit to modify the microstructure, phase and chemical composition of the surface layers of the treated parts. A prospective line of the development of surface engineering is the production of composite layers by combining various surface engineering methods. The paper presents the results of examinations of the phase composition and frictional wear resistance of the layers produced by hybrid processes, i.e. such that combined glow discharge assisted nitriding performed at 450 °C and 550 °C with a pulsed laser deposition of boron nitride coatings (PLD method). It has been shown that the boron nitride coatings formed on nitrided AISI 316L steel increase its frictional wear resistance.     

水导激光加工对316L不锈钢微观形貌的影响规律

水导激光加工是一项利用水光纤将激光引导到材料加工表面的新颖加工技术,具有几乎无微裂纹、热影响区小、无污染、重熔层少、加工精度高和光束平行等优点。为研究不同水导激光加工工艺参数对微观形貌的影响,探索水导激光与物质的相互作用机理。本文采用自主研发的水导激光加工系统对316L不锈钢薄片试件进行切槽和打孔实验;使用Zeiss Vert.A1金相显微镜观察加工试件的二维形貌;使用Leica DVM6超景深显微镜和Bruke Contour Elite I白光干涉仪观察试件的三维微观形貌。实验结果表明：无论是对试件进行切槽还是打孔实验,均会在加工区域产生一定宽度的沉积层,且沉积层的大小不随加工时间和加工次数变化,其宽度约为13.5 µm;通过观察试件加工区域的二维形貌,发现打孔试件的dr和切槽试件的wl也不随加工试件和加工次数变化;通过观察切槽试件加工区域的三维形貌,其截面呈倒梯形。     

表面纳米化对316L不锈钢性能的影响

对316L不锈钢进行表面机械研磨处理(SMAT),研究表面组织变化对其硬度和在0.5 mol/LNaCl介质中腐蚀性能的影响.结果表明:通过SMAT可以在316L不锈钢表面制备出纳米结构层,随着处理时间的增加,表面纳米晶组织逐渐由单一的奥氏体相过渡到奥氏体与马氏体两相共存;表面纳米化和马氏体相变能够明显地提高316L不锈钢的表层硬度,使表面粗糙度略有下降;表面机械研磨处理降低了316L不锈钢在0.5mol/L NaCl腐蚀介质中的耐蚀性能.因为316L不锈钢表面纳米晶组织容易钝化,形成的钝化膜不稳定,提高了溶解速度.     

Notch fatigue behaviour of low-temperature gaseous carburised 316L austenitic stainless steel

ABSTRACT

The influence of low-temperature gaseous carburisation on notch fatigue behaviour of 316L steel under cyclic axial loading was investigated. After carburisation, the carburised case was well distributed at the surface region and was not influenced by the notch geometry. Low-temperature carburisation considerably enhanced the notch fatigue performance, which led to 32% and 44% increase in the endurance limits for the specimens with stress concentration factors K _t?=?1.91 and 3.91, respectively. The notch sensitivity of 316L steel reduced after carburisation. Irrespective of the applied stress amplitude, the fatigue crack nucleation sites were always at the notch root surface for the untreated specimens. For the carburised specimens, fatigue cracks nucleation changed from surface at high-level stress to subsurface at low-level stress.     

Enhanced tensile properties of 316L steel via grain refinement and low-strain rolling

Excellent strength–ductility synergy of metallic materials is significant for their industrial applications. This study presents a fine-grained 316L stainless sheet (average grain size of ～5?µm) with a good combination of strength and ductility achieved via low-strain cold rolling (rolling strain of 30%). The fabricated steel sheet exhibits maximum yield strength and ultimate tensile strength values of 1045 and 1080?MPa, respectively, with a uniform elongation of 7%. Experimental results confirm that the high density of dislocations, strain-induced martensitic phase, and deformation twins together contribute to the high strength of the rolled stainless steel. Moreover, its good ductility is attributable to the strain-induced martensitic transformation and deformation twins.     

A preliminary study of laser cladding of AISI 316 stainless steel using preplaced NiTi wire

NiTi wire of diameter 1 mm was preplaced on AISI 316 stainless steel samples by using a binder. Melting of the NiTi wire to form a clad track on the steel substrate was achieved by means of a high-power CW Nd:YAG laser using different processing parameters. The geometry and microstructure of the clad deposit were studied by optical microscopy and scanning electron microscopy (SEM), respectively. The hardness and compositional profiles along the depth of the deposit were acquired by microhardness testing and energy-dispersive spectroscopy (EDS), respectively. The elastic behavior of the deposit was analyzed using nanoindentation, and compared with that of the NiTi wire. The dilution of the NiTi clad by the substrate material beneath was substantial in single clad tracks, but could be successively reduced in multiple clad layers. A strong fusion bonding with tough interface could be obtained as evidenced by the integrity of Vickers indentations in the interfacial region. In comparison with the NiTi cladding on AISI 316 using the tungsten inert gas (TIG) process, the laser process was capable of producing a much less defective cladding with a more homogeneous microstructure, which is an essential cladding quality with respect to cavitation erosion and corrosion resistance. Thus, the present preliminary study shows that laser cladding using preplaced wire is a feasible method to obtain a thick and homogeneous NiTi-based alloy layer on AISI 316 stainless steel substrate.     

轧制工艺对316L不锈钢组织和耐蚀性能的影响

为探索改善不锈钢耐腐蚀性能的途径,对316L不锈钢施加相同变形量的同步轧制和异步轧制,利用X射线衍射、透射电镜观察、电化学测量和扫描电镜表面观察研究了轧制工艺对钢的显微组织和腐蚀性能的影响.结果表明,经过异步轧制后显微组织中出现大量孪晶界,优化了晶界结构,在酸性介质中的晶间腐蚀敏感性明显减轻;而经过同步轧制后,样品呈现出高位错密度的显微组织,在酸性介质中的耐腐蚀性能降低.异步轧制后耐蚀性能得到改善是由于大量孪晶界的形成优化了晶界结构.     

Fatigue of additively manufactured 316L stainless steel: The influence of porosity and surface roughness

The fatigue behaviour of additively manufactured (AM) 316L stainless steel is investigated with the main emphasis on internal porosity and surface roughness. A transition between two cases of failure are found: failure from defects in the surface region and failure from the internal defects. At low applied load level (and consequently a high number of cycles to failure), fatigue is initiating from defects in the surface region, while for high load levels, fatigue is initiating from internal defects. Porosities captured by X‐ray computed tomography (XCT) are compared with the defects initiating fatigue cracks, obtained from fractography. The fatigue data are synthesised using stress intensity factor (SIF) of the internal and surface defects on the fracture surface.