Microstructure and mechanical properties of a rapid solidified boron- modified duplex stainless steel

Two duplex stainless steels 2205 and 2205 with 2.5?wt-% B addition prepared by a fast solidification technique were investigated. The samples were arc melted and cast in a cylindrical mould with varying diameters in a single cavity that provided different cooling rates. The hardness increased in both cases for smaller diameters, however, there was a different profile from the surface to the centre in case of 2205 with 2.5?wt-% B. The microstructural investigation indicated that boron addition led to the formation of hard borides and grain refinement. Different boride morphologies that varied with the cooling rates were identified. The compression strength at room temperature improved by a factor of 3.5 with boron addition without considerably decreasing the ductility.     

Fatigue behaviour of duplex stainless steel reinforcing bars subjected to shot peening

The influence of shot peening on the fatigue properties of duplex stainless steel reinforcing bars manufactured using both hot- and cold-rolled processes was studied. The S-N curves of the bars before and after the shot-peening process were determined, showing that shot peening improves the fatigue behaviour of the rebars. This improvement is essentially due to the introduction of a compressive residual stress field in the surface of the reinforcing bars, but also to the smoothing of the surface flaws and cold working generated during the manufacturing process. This improvement is much greater in the case of the hot-rolled bars, mainly as a result of their much higher ability for plastic deformation, whereas cold-rolled bars had a much higher hardness. A more severe peening action capable of promoting greater plastic deformation on the bar surface is judged necessary to improve the fatigue resistance of cold-rolled rebars.     

Microstructure and mechanical and electrochemical properties of martensitic weld deposits developed for welding of a 12%Cr duplex stainless steel

Abstract

The microstructure and mechanical and electrochemical properties of martensitic weld deposits developed for the welding of a duplex 12% Cr corrosion resisting steel, as well as the experimental procedures used, are described. During the development, it was found that weld metals having matching compositions (and thus duplex structures) to those of 3CR12 had very poor impact properties. This was largely because of the inability to control weld metal grain size. By increasing the proportion of austenite stabilising elements, to produce a predominantly low carbon martensitic weld deposit, it was found that acceptable toughness (≥30 J at 20°C) could be achieved in the as welded condition. The electrochemical properties were designed to be similar to, yet slightly more noble than, those of the wrought 3CR12 plate, thus guarding against possible inhomogeneities in the as cast structure. Cost was also an important consideration throughout the development of these closely matching consumables, since the austenitic filler metals used (e.g. AWS E 309 Mo) were substantially more expensive than the parent plate. It has been shown that cost effective, metallurgically compatible filler metals for 3CR12 can be produced.

MST/651     

Microstructure and mechanical properties of NiAl produced in the SHS process induced by low-temperature hydrostatic extrusion

A stoichiometric nickel aluminide intermetallic alloy produced by self-sustained high-temperature synthesis (SHS) induced to the green compacts of the mixture of elemental Ni and Al powders by mechanical heavy deformation during low-temperature hydrostatic extrusion has been investigated. The process was performed with the high strain rate (>10² s^?1) at the low temperature (～500°C). To reduce the porosity, grain size and non-homogeneity of the obtained material a further high-temperature (～950°C) hydrostatic extrusion was applied. Mechanical properties of the material were measured on the samples cut out from extruded rods in the longitudinal and transverse directions. Elastic anisotropy (elastic tensor) was determined using a resonant ultrasound spectroscopy (RUS) method applied to small cylindrical samples of the material. Its value described as the ratio of the coefficients of linear compressibility in transverse and longitudinal directions was at the level of 2 for extruded material even after annealing. Plastic anisotropy of the material was determined in uniaxial compression tests using an acoustic emission (AE) method for monitoring early stages of microcracking process in the samples under investigation. The phenomenon of the yielding point was observed for the samples compressed in the direction of extrusion.     

Microstructure and mechanical properties of resistance upset butt welded 304 austenitic stainless steel joints

Resistance upset welding (UW) is a widely used process for joining metal parts. In this process, current, time and upset pressure are three parameters that affect the quality of welded products. In the present research, resistance upset butt welding of 304 austenitic stainless steel and effect of welding power and upset pressure on microstructure, tensile strength and fatigue life of the joint were investigated. Microstructure of welds were studied using scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis was used to distinguish the phase(s) that formed at the joint interface and in heat affected zone (HAZ). Energy dispersive spectroscopy (EDS) linked to the SEM was used to determine chemical composition of phases formed at the joint interface. Fatigue tests were performed using a pull–push fatigue test machine and the fatigue properties were analyzed drawing stress-number of cycles to failure (S–N) curves. Also tensile strength tests were performed. Finally tensile and fatigue fracture surfaces were studied by SEM. Results showed that there were three different microstructural zones at different distances from the joint interface and delta ferrite phase has formed in these regions. There was no precipitation of chromium carbide at the joint interface and in the HAZ. Tensile and fatigue strengths of the joint decreased with welding power. Increasing of upset pressure has also considerable influence on tensile strength of the joint. Fractography of fractured samples showed that formation of hot spots at high welding powers is the most important factor in decreasing tensile and fatigue strengths.     

Microstructure and properties of ultrafine grain nickel 200 after hydrostatic extrusion processes

This paper presents the results of the studies of the structure and properties of ultrafine grained nickel 200 obtained by hydrostatic extrusion processes. Microstructure was characterized by means of optical microscopy and electron transmission microscopy. Corrosion resistance was studied by impedance and potentiodynamic methods using an AutoLab PGSTAT 100 potentiostat in 0.1 M Na₂SO₄ solution and in acidified (by addition of H₂SO₄) 0.1 M NaCl solution at pH = 4.2 at room temperature. Microhardness tests were also performed. The results showed that hydrostatic extrusion produces a heterogeneous, ultrafine-grained microstructure in nickel 200. The corrosive resistance tests showed that the grain refinement by hydrostatic extrusion is accompanied by a decreased corrosive resistance of nickel 200.     

Effects of hydrostatic extrusion on the mechanical and thermal properties of polypropylene

The structure change in spherulites for hydrostatically extruded polypropylene (PP) was studied by the use of internal friction measurements and thermophotometry tests. The onset temperature of the -loss peak of the PP sample decreases with increasing reduction in area, R. For the extrudates below R=50%, the peak temperature of -loss shifts to lower temperature. The and absorptions for the extrudates up to R=50% become broad and overlap with each other. The intensity of the -loss peak, _max, is maximum for the extrudate with R=50%. The results of tan , damping, and the intensity of the -loss peak indicate that the mechanism of molecular chain deformation is divided into two stages, below and above R=50%. The results are due to spherulitic changes, i.e. the shape of spherulites changed from spherical to elliptical in the extrudates above R=50% and the spherulite with R=50% changed from coarse structure to a finer one by the imposition of hydrostatic pressure.     

Effect of rolling deformation and solution treatment on microstructure and mechanical properties of a cast duplex stainless steel

The present study deals with the effect of rolling deformation and solution treatment on the microstructure and mechanical properties of a cast duplex stainless steel. Cast steel reveals acicular/Widmanst?tten morphology as well as island of austenite within the $\boldsymbol\delta $ -ferrite matrix. Hot rolled samples exhibit the presence of lower volume percent of elongated band of $\boldsymbol\delta $ -ferrite ( $\boldsymbol\sim $ 40%) and austenite phase which convert into finer and fragmented microstructural constituents after 30% cold deformation. By the solution treatment, the elongated and broken crystalline grains recrystallize which leads to the formation of finer grains (<10? $\boldsymbol\mu $ m) of austenite. X-ray diffraction analysis has corroborated well with the above-mentioned microstructural investigation. Enhancement in hardness, yield strength and tensile strength values as well as drop in percent elongation with cold deformation increases its suitability for use in thinner sections. 30% cold rolled and solution treated sample reveals attractive combination of strength and ductility (25·22?GPa%). The examination of fracture surface also substantiates the tensile results. The sub-surface micrographs provide the potential sites for initiation of microvoids.     

超声振动作用下镁-钢焊缝组织演变及力学性能研究

本文旨在通过引入超声振动辅助,实现镁合金和镀锌钢的可靠连接,扩大镁-钢复合构件应用范围。本文在镁合金与镀锌钢的TIG熔钎焊过程中引入超声波振动,并通过金相显微镜、扫描电镜、硬度计和拉伸机等设备对镁-钢接头微观组织和力学性能进行检测,研究超声波功率对镁合金/镀锌钢接头质量的影响。实验结果表明:超声波振动辅助焊接工艺可以有效改善镁/钢接头的焊缝成形,消除接头熔焊区域的气孔等缺陷。研究表明:在焊接过程中引入1 000 W功率进行超声振动后,接头熔焊区的平均晶粒尺寸由初始的51 μm下降到23.2 μm,晶粒细化效果显著;超声振动辅助焊接工艺改善了接头钎焊区反应层的形态,使钎焊区MgZn反应层厚度更均匀,并可以提高接头熔焊区的显微硬度;当超声波功率为1 000 W时,接头力学性能达到3 735 N,相比未施加超声波振动的接头(3 270 N),力学性能提高了14.2%。超声振动辅助工艺可以有效改善镁/钢焊缝的显微组织,提高接头力学性能,实现镁/钢异种金属的可靠连接。     

Microstructure, corrosion and mechanical properties of 304 stainless steel containing copper, silicon and nitrogen

The effects of 0.086–0.336% nitrogen additions on the microstructure, corrosion and mechanical properties of type 304 austenitic stainless steel (SS) containing 2% copper and 2–3% silicon were studied. This study was carried out using scanning electron microscope (SEM), potentiodynamic, weight loss, hardness number and ball-punch bulge measurements. Mutual effects between Si and N were observed in the matrix of SS. Nitrogen offset the ferrite-forming tendencies of Si and was more efficient than Ni as austenitizer, but Si decreased the solubility of N in solid solution. N additions improved the pitting resistance of SS in acidic and neutral chloride solutions. This was more evident in more aggressive solutions than in solutions with low chloride concentrations. Segregation of second N-rich phases, like Cr₂N, in SS containing 2% Cu, 3% Si and 0.237% N was occurred. This steel exhibited less pitting corrosion resistance than the plain 304 SS in most chloride solutions under study. Addition of 2% Si to 304 SS containing Cu has negative effect on the mechanical behavior. But presence of N improved the mechanical strength of steel irrespective of the drop solubility of N affected by Si.     

Microstructure,mechanical and corrosion properties of friction stir welded high nitrogen nickel-free austenitic stainless steel

Friction stir welding (FSW) was applied to a 2.4 mm thick high nitrogen nickel-free austenitic stainless steel plate using tungsten–rhenium (W–Re) tool. The high-quality weld was successfully produced at a tool rotational speed of 400 rpm and a traveling speed of 100 mm/min. The microstructure, mechanical and corrosion properties of the weld were studied. The nitrogen content of the weld was almost identical to that of base metal (BM). FSW refined grains in the stir zone (SZ) through dynamic recrystallization and led to increase in hardness and tensile strength within the SZ, while the ductility was slightly decreased. The failure of tensile specimens occurred in the BM. TEM results revealed precipitates of Cr₂₃C₆ of size ~ 1 μm in the SZ, although their content was small. The precipitation of Cr₂₃C₆ and increase in δ-ferrite in the SZ led to small decrease in both pitting and intergranular corrosion resistance.     

Microstructure, mechanical properties and chemical degradation of brazed AISI 316 stainless steel/alumina systems

The main aims of the present study are simultaneously to relate the brazing parameters with: (i) the correspondent interfacial microstructure, (ii) the resultant mechanical properties and (iii) the electrochemical degradation behaviour of AISI 316 stainless steel/alumina brazed joints. Filler metals on such as Ag–26.5Cu–3Ti and Ag–34.5Cu–1.5Ti were used to produce the joints. Three different brazing temperatures (850, 900 and 950 °C), keeping a constant holding time of 20 min, were tested. The objective was to understand the influence of the brazing temperature on the final microstructure and properties of the joints. The mechanical properties of the metal/ceramic (M/C) joints were assessed from bond strength tests carried out using a shear solicitation loading scheme. The fracture surfaces were studied both morphologically and structurally using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The degradation behaviour of the M/C joints was assessed by means of electrochemical techniques.

It was found that using a Ag–26.5Cu–3Ti brazing alloy and a brazing temperature of 850 °C, produces the best results in terms of bond strength, 234 ± 18 MPa. The mechanical properties obtained could be explained on the basis of the different compounds identified on the fracture surfaces by XRD. On the other hand, the use of the Ag–34.5Cu–1.5Ti brazing alloy and a brazing temperature of 850 °C produces the best results in terms of corrosion rates (lower corrosion current density), 0.76 ± 0.21 μA cm⁻². Nevertheless, the joints produced at 850 °C using a Ag–26.5Cu–3Ti brazing alloy present the best compromise between mechanical properties and degradation behaviour, 234 ± 18 MPa and 1.26 ± 0.58 μA cm⁻², respectively. The role of Ti diffusion is fundamental in terms of the final value achieved for the M/C bond strength. On the contrary, the Ag and Cu distribution along the brazed interface seem to play the most relevant role in the metal/ceramic joints electrochemical performance.     

Effect of intermetallic precipitations on the properties of duplex stainless steel

The corrosion resistant group of ferritic austenitic duplex steels shows a rather complex precipitation and transformation behavior that affects the mechanical and corrosive properties. Most critical, concerning the change of properties, are the precipitations in the temperature field of 650–950 °C.     

Microstructure and mechanical properties of Mg -2Gd -3Y -0.6Zr alloy upon conventional and hydrostatic extrusion

The Mg-12Gd-3Y-0.6Zr (wt. %) alloy was subjected to conventional and hydrostatic extrusion in two subsequent steps. The best combination of mechanical properties (strength and ductility) was achieved by RT hydrostatic extrusion following conventional extrusion at 430 °C, with the ultimate tensile strength (UTS), tensile yield strength (TYS) and elongation being 485 MPa, 413 MPa and 5.2% at room temperature. The texture results of extruded rods indicate that the c-axis of most grains was aligned preferentially perpendicular to the extrusion direction, forming a typical extrusion Mg fiber texture.     

Effect of heat input on microstructure and mechanical properties of dissimilar joints between super duplex stainless steel and high strength low alloy steel

In the present study, microstructure and mechanical properties of UNS S32750 super duplex stainless steel (SDSS)/API X-65 high strength low alloy steel (HSLA) dissimilar joint were investigated. For this purpose, gas tungsten arc welding (GTAW) was used in two different heat inputs: 0.506 and 0.86 kJ/mm. The microstructures investigation with optical microscope, scanning electron microscope and X-ray diffraction showed that an increase in heat input led to a decrease in ferrite percentage, and that detrimental phases were not present. It also indicated that in heat affected zone of HSLA base metal in low heat input, bainite and ferrite phases were created; but in high heat input, perlite and ferrite phases were created. The results of impact tests revealed that the specimen with low heat input exhibited brittle fracture and that with high heat input had a higher strength than the base metals.     

S32750双相不锈钢相界与晶界特征对其力学性能和耐蚀性能的影响EI北大核心CSCD

通过固溶处理获得不同初始组织状态的S32750双相不锈钢样品,然后进行厚度压下量80%的冷轧变形和1050℃的退火处理,采用SEM-EBSD和XRD技术研究合金相界与晶界特征以及相组成分布情况,并利用拉伸实验、纳米压痕和双环电化学动电位再活化法(DL-EPR)分析不同初始状态样品的组织对力学性能与耐晶间腐蚀性能的影响规律。结果表明:高温固溶处理的合金样品经冷轧退火后晶粒细小均匀,两相分布接近1∶1,且相界占内界面(晶界+相界)比例较高,同相晶粒团簇程度最低,表现出优异的综合力学性能。合金样品经敏化处理后,σ相易沿α相晶界析出,高温固溶并经轧制退火后的样品中,由于α晶界比例较少且满足K-S取向关系的相界比例较高则又表现出良好的晶间腐蚀抗力。因此,通过适当的工艺来调控合金的相界与晶界分布可以实现材料强度和晶间腐蚀抗力的同步改善。     

Mechanical properties and textures of duplex stainless steel rolled worked by asymmetric rolling

Laboratory asymmetric rolling trials have been developed at different temperatures on EN 1.4462 duplex steel grades imposing different reduction ratios and different asymmetric rolling ratio. The samples have been also subjected to a subsequent solution quenching. The asymmetric rolling operations have been performed in order to impose significant shear strains in the bulk regions of the rolled sheets, because during the traditional rolling the shear strains tend to become very weak and theoretically null at the middle point of the thickness. The mechanical properties, the pointed out anisotropy, the micro-structural features and the texture characteristics have been discussed as a function of the imposed operative parameters: thermal level, reduction ratios, rolling ratios and possible application of solution quenching after the rolling.     

Processing of duplex stainless steel by WEDM

This study investigates the manufacturing process of 2205 duplex stainless steel by wire electrical discharge machining where the effects of pulse-on time (PONT), wire tension and pulse-off time (POFT) on surface finish, kerf width, and material removal rate (MRR). It was found that the kerf width was unchanged with the change of PONT at long pulse-of time and higher wire tension. However, it decreased initially and then increased due to the rise of PONT at low values of wire tension and POFT. Low wire tension and PONT, POFT and contributed towards widest kerf. Longer PONT increased MRR due to higher machining/processing speed. Lower wire tension and shorter POFT increased MRR more than that of higher wire tension and POFT. Craters and recast layer were on the machined surfaces at all machining conditions. Increased PONT raised surface roughness at the lower POFT and tension in the wire. The surface finish at high wire tension and longer PONT is always better than that at smaller PONT and lower tension in the wire. The microstructure underneath the recast layer remains unchanged and the failure of wire electrode occurred at higher wire tension, longer PONT and shorter POFT.