2205双相不锈钢管焊接工艺评定

铁素体-奥氏体双相不锈钢,简称即双相不锈钢(DSS),具有优良的力学性能和耐蚀性能,2205(也称22Cr)双相不锈钢管材在石油及天然气工业、海洋工程、化学工业等行业具有广泛的用途。该材料焊接有许多技术特点,工艺参数对接头的组织和性能有很大影响。对D508×15.9mm规格钢管制管纵缝和现场环焊缝焊接工艺评定进行介绍。     

Wear resistance and anti-sticking properties of duplex treated forming tool steel

The aim of this work was to investigate the potential of using hard physical vapour deposition (PVD) coatings on forming tools, as well as to determine the influence of plasma nitriding on the load-carrying capacity and wear resistance of coated tool surfaces. A load-scanning test rig was used for evaluation, where duplex treated cold work tool steel samples were loaded against soft austenitic stainless steel and hardened ball bearing steel, respectively. Four different coatings (TiN, TiB₂, TaC and DLC) and two substrate treatments (hardening and plasma nitriding in two different gas mixtures) were included.Plasma nitriding alone significantly improved the friction, wear, and anti-sticking properties of the tool steel. PVD coating, and especially PVD coating of nitrided tool steel further improved the performance. Therefore, from the point of view of tool life as well as work peace surface quality, the DLC coating with its excellent anti-sticking properties and sufficiently good wear resistance represent the best solution for forming tool applications of austenitic stainless steel.     

双相不锈钢00Cr22Ni5Mo3N缸套制造工艺

介绍特种发动机的双相不锈钢00Cr22N i5Mo3N缸套的制造工艺分析研究,解决缸套制造的三个工艺难点:确定缸套离子氮化后的内孔最大变形量mδax;最大变形量mδax给磨削加工带来的影响;缸套外圆、内孔同轴度/圆柱度及表面粗糙度的控制。     

Optimization of surface roughness,cutting force and tool wear of nitrogen alloyed duplex stainless steel in a dry turning process using Taguchi method

In this work, the dry turning parameters of two different grades of nitrogen alloyed duplex stainless steel are optimized by using Taguchi method. The turning operations were carried out with TiC and TiCN coated carbide cutting tool inserts. The experiments were conducted at three different cutting speeds (80, 100 and 120 m/min) with three different feed rates (0.04, 0.08 and 0.12 mm/rev) and a constant depth of cut (0.5 mm). The cutting parameters are optimized using signal to noise ratio and the analysis of variance. The effects of cutting speed and feed rate on surface roughness, cutting force and tool wear were analyzed. The results revealed that the feed rate is the more significant parameter influencing the surface roughness and cutting force. The cutting speed was identified as the more significant parameter influencing the tool wear. Tool wear was analyzed using scanning electron microscope image. The confirmation tests are carried out at optimum cutting conditions. The results at optimum cutting condition are predicted using estimated signal to noise ratio equation. The predicted results are found to be closer to experimental results within 8% deviations.     

Microstructure and tribological behaviour of nitrocarburizing-quenching duplex treated steel

This paper explores salt bath nitrocarburizing and nitrocarburizing-quenching duplex treatment technologies. For comparison, a quenching-tempering treatment was also conducted. By means of metallographic examination, microhardness tests and X-ray diffraction analysis, the microstructures, phase structures, surface hardnesses and hardness profiles of 1045 steel treated by several techniques were investigated. The ball-on-block and ring-on-block apparatuses were employed to investigate the friction coefficient and wear-resistance respectively. The surface roughness was also measured by a profilometer. The experimental results indicate that a higher sub-surface hardness and a superior hardness profile are obtained by nitrocarburizing-quenching duplex process. This in turn improves the wear-resistance and fatigue strength, although the surface hardness is somewhat lower compared with that obtained by nitrocarburizing. It also demonstrates that the -phase formed on the steel surface has significant effects on reducing friction and improving wear-resistance. X-ray diffraction analysis shows that the phases at the nitrocarburized specimen surface are mainly -compound [Fe₃(N,C)] and small amounts of Fe₄N(γ′) and Fe_2–3(N,C). While the phases at the nitrocarburized-quenched specimen surface are very different from those at the nitrocarburized specimen. In this case, the -compound has decomposed almost completely and the nitrogen and carbon diffuse to the γ-Fe at the temperature of quenching to form the supersaturated solid solution which will become martensite containing nitrogen and carbon along with retained austenite after subsequent water cooling.     

2205双相不锈钢氢致开裂行为的试验分析与模型预测

开展了2205双相不锈钢(Duplex stainless steel,DSS)氢致开裂(Hydrogen assisted cracking,HAC)行为的研究,考察了组织形态对2205双相不锈钢中氢致裂纹萌生和扩展的影响.结果表明,横向组织中的氢致裂纹扩展的长度比纵向组织中的裂纹更明显,裂纹优先萌生的位置在铁素体相...     

Ductility loss of hydrogen-charged and releasing 304L steel

The mechanical properties and fracture behavior of 304L austenitic stainless steel after cathodic hydrogen charging and hydrogen spontaneously releasing are investigated by tensile tests. Flat tensile specimens were cathodic hydrogen charged at various current densities. For each density, two specimens were charged at the same condition. When the charging process completed, one specimen was tensile immediately to fracture and the other was aged to release the hydrogen out of it and then was also tensile to fracture. The resulting tensile properties and micrographs of fracture surfaces of these specimens were evaluated and compared. The results show ductility loss occurred in the hydrogen-charged specimens and the loss increased as the current density increasing. After hydrogen releasing, the specimens recovered a certain extent but not all of its original ductility. Scanning electron microscope (SEM) micrographs of fracture surfaces reveal that irreversible damage had developed in the hydrogen-releasing specimens during the releasing process rather than the charging process. This consequence can be ascribed to the high tensile stress caused by non-uniform hydrogen distribution during hydrogen releasing.     

Fine structure characterization of martensite/austenite constituent in low‐carbon low‐alloy steel by transmission electron forward scatter diffraction

Transmission electron forward scatter diffraction and other characterization techniques were used to investigate the fine structure and the variant relationship of the martensite/austenite (M/A) constituent of the granular bainite in low‐carbon low‐alloy steel. The results demonstrated that the M/A constituents were distributed in clusters throughout the bainitic ferrite. Lath martensite was the main component of the M/A constituent, where the relationship between the martensite variants was consistent with the Nishiyama–Wassermann orientation relationship and only three variants were found in the M/A constituent, suggesting that the variants had formed in the M/A constituent according to a specific mechanism. Furthermore, the Σ3 boundaries in the M/A constituent were much longer than their counterparts in the bainitic ferrite region. The results indicate that transmission electron forward scatter diffraction is an effective method of crystallographic analysis for nanolaths in M/A constituents.     

2.25Cr-1Mo钢回火脆化对氢脆的影响

用冲击试验和电化学充氢方法研究了长期服役的2．25Cr-1Mo钢的回火脆化和氢脆问题．并对试样进行了显微组织分析和断口电镜扫描。结果表明：回火脆化程度不高的母材对氢脆的影响较小，断口形貌为准解理和少量的沿晶断裂；回火脆化程度较严重的焊缝对氢脆的影响较大，断口形貌为沿晶断裂。对于母材．回火脆化与氢脆的关系为线性相加；对于焊缝，回火脆化大大加剧了氢脆的程度。     

316L不锈钢抗氢脆性能研究

用光学显微镜、电子显微镜、俄歇电子谱／二次离子质谱表面分析仪等结合拉伸试验，研究了316L奥氏体不锈钢及其电子束焊缝在650℃充氘后组织、微区成分变化与性能的关系，以及拉伸应力与氘分布的关系。结果表明，高温气相充氘后，316L奥氏体不锈钢及其电子束焊缝抗氢脆性能明显下降。晶界、孪晶界析出大量碳化物，但拉伸断口形貌并未呈沿晶断裂；晶界上未发现S、P等痕量元素的偏聚，却产生了富Cr、Mo的贫Ni层，这表明晶界成分的变化减弱了晶界析出物对氢脆的影响。电子束焊缝塑性下降，拉伸时从该处断裂。拉伸静水应力梯度分布导致氘在拉伸试样断口处富集。     

EBSD and TEM investigation of the hot deformation substructure characteristics of a type 316L austenitic stainless steel

The evolution of crystallographic texture and deformation substructure was studied in a type 316L austenitic stainless steel, deformed in rolling at 900 °C to true strain levels of about 0.3 and 0.7. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used in the investigation and a comparison of the substructural characteristics obtained by these techniques was made. At the lower strain level, the deformation substructure observed by EBSD appeared to be rather poorly developed. There was considerable evidence of a rotation of the pre‐existing twin boundaries from their original orientation relationship, as well as the formation of highly distorted grain boundary regions. In TEM, at this strain level, the substructure was more clearly revealed, although it appeared rather inhomogeneously developed from grain to grain. The subgrains were frequently elongated and their boundaries often approximated to traces of {111} slip planes. The corresponding misorientations were small and largely displayed a non‐cumulative character. At the larger strain, the substructure within most grains became well developed and the corresponding misorientations increased. This resulted in better detection of sub‐boundaries by EBSD, although the percentage of indexing slightly decreased. TEM revealed splitting of some sub‐boundaries to form fine microbands, as well as the localized formation of microshear bands. The substructural characteristics observed by EBSD, in particular at the larger strain, generally appeared to compare well with those obtained using TEM. With increased strain level, the mean subgrain size became finer, the corresponding mean misorientation angle increased and both these characteristics became less dependent on a particular grain orientation. The statistically representative data obtained will assist in the development of physically based models of microstructural evolution during thermomechanical processing of austenitic stainless steels.     

双相钢的研究现状及应用前景

介绍了目前国内外双相钢的生产工艺及研究应用状况,阐述了双相钢的显微组织特征及其综合机械性能,讨论了双相钢在我国生产的主要问题,并提出了对我国加速开发、研制、生产双相钢的建议。     

TEM analysis of centreline sulphide precipitates modified by titanium additions to low carbon steel

Elongated inclusions, particularly MnS, contribute significantly to reduced ductility and toughness in hot rolled steel but earlier research indicated that these properties can be improved by titanium additions. Such additions to a steel result in titanium being dissolved in manganese sulphide or MnS being replaced by TiS and/or titanium carbosulphides. In the present study, a steel was designed to decrease alloying element segregation and to evaluate the effect of titanium on centreline sulphide precipitates. Precipitates were identified by using scanning electron microscopy and characterized by the use of transmission electron microscopy following sample preparation by focused ion beam milling techniques. Iron–titanium‐sulphides form in close proximity to MnS precipitates that contain iron. Evidence is provided that an increase in the titanium content of steel leads to an increase in the percentage of titanium contained in the iron sulphides and a decrease in the iron content of MnS inclusions.     

EBSD investigation of the microstructure and texture characteristics of hot deformed duplex stainless steel

The microstructure and crystallographic texture characteristics were studied in a 22Cr‐6Ni‐3Mo duplex stainless steel subjected to plastic deformation in torsion at a temperature of 1000 °C using a strain rate of 1 s^?1. High‐resolution EBSD was successfully used for precise phase and substructural characterization of this steel. The austenite/ferrite ratio and phase morphology as well as the crystallographic texture, subgrain size, misorientation angles and misorientation gradients corresponding to each phase were determined over large sample areas. The deformation mechanisms in each phase and the interrelationship between the two are discussed.     

CBED and LACBED characterization of crystal defects

Convergent‐beam electron diffraction (CBED) obtained with a focused incident beam is well known for the identification of the point and space groups but it can also be used for the analysis of stacking faults and antiphase boundaries. Large‐angle convergent‐beam electron diffraction (LACBED) is performed with a large defocused incident beam and is well adapted to the characterization of most types of crystal defects: point defects, perfect and partial dislocations, stacking faults, antiphase boundaries and grain boundaries. Among the advantages of these methods with respect to the conventional transmission electron microscopy methods, are that one or few patterns are required for a full analysis and the interpretations are easy and unambiguous. The LACBED technique is particularly useful for the analysis of dislocations present in anisotropic and beam‐sensitive materials.     

Structure and morphology of the in situ composites of a liquid crystalline polymer and polycarbonate

In situ composites were prepared via melt blending of a liquid crystalline polymer (LCP) and polycarbonate using a twin screw extruder. The structure and morphology of these composites were analysed using both transmission electron microscopy (TEM) and scanning electron microscopy. The LCP phases were able to orientate and form in situ submicrometre fibres during the extrusion and post-extrusion drawing. TEM images as well as selected-area diffraction patterns were obtained from the materials. The effects of both composition, i.e. LCP content, and post-extrusion draw-down ratio on the development of the in situ formed LCP fibres were studied in detail. A skin–core morphological differentiation is observed in these materials where well-defined LCP fibres of higher aspect ratios were formed in the skin region. However, a significant amount of unelongated LCP particles were found coexisting with the less well-defined fibres in the core region of the extrudates. This skin–core differentiation was found to be dependent on the composition and the processing conditions, e.g. draw ratio. In this instance, electron microscopy is proven to be a powerful technique not only for direct observation of the formation, dimensions and morphology of the in situ LCP fibres, but also for the qualitative and quantitative characterization of the molecular orientation and crystalline structures in these fibres using selected-area electron diffraction. It is observed that the skin–core differentiation becomes more distinct in the in situ composites containing a higher percentage of LCP but diminishes when the material is processed at higher post-extrusion draw ratio.     

Nonlinear optimization strategy based on multivariate prediction capability ratios: Analytical schemes and model validation for duplex stainless steel end milling

Given the complex nature of their phenomena and interactions, industrial processes often have multiple variables of interest, usually grouped into critical-to-quality and critical-to-performance characteristics. These variables often have significant correlations, which make engineering problems multivariate. For this reason, Response Surface Methodology, coupled with multivariate techniques, has been widely used as a logical roadmap for modeling and optimization of the characteristics of interest. However, the variability and prediction capability of the numerical solutions obtained are almost always neglected, reducing the likelihood that numerical results are indeed compatible with observable process improvements. To fill this gap, this paper proposes a nonlinear multiobjective optimization strategy based on multivariate prediction capability ratios. For this, rotated Factor Analysis is used as the multivariate technique for grouping process characteristics and composing capability ratios, so that the prediction variance is taken as the natural variability of the process modeled and the expected value distances to the nadir solutions of the latent variables are taken as the allowed variability. Normal Boundary Intersection method, combined with Generalized Reduced Gradient algorithm, is used as the numerical scheme to maximize the prediction capability of Pareto optimal solutions. To illustrate the feasibility of the proposed strategy, we present a case study of end milling without cutting fluids of duplex stainless steel UNS S32205. Rotatable Central Composite Design, with three cutting parameters, was employed for data collection. Traditional multivariate and proposed approaches were compared. The results demonstrate that the proposed optimization strategy is able to provide solutions with satisfactory prediction capability for all variables analyzed, regardless of their convexities, optimization directions, and correlation structure. In addition, while critical-to-quality characteristics are more difficult to control, they have been favored by the proposed optimization regarding prediction capability, which was a desirable result.     

On the accuracy of lattice-distortion analysis directly from high-resolution transmission electron micrographs

Lattice‐distortion analysis from high‐resolution transmission electron micrographs offers a convenient and fast tool for direct measurement of strains in materials over a large area. In the present work, we have evaluated the accuracy of the strain measurement when the effects of the realistic experimental variables are explicitly taken into account by the use of image simulation techniques. These variables are focal setting and variation, local thickness and orientation of the sample, as well as misalignments of the sample and the incident beam. The evaluation reveals that consistency of image features and contrast within the micrographs is desired for the analysis to eliminate effects of the variations of local focus value and specimen thickness. After proper orientation of a crystalline specimen, the misorientation of the object will not notably influence the strain measurement even though a local bending may exist within the sample. However, the incident beam of the microscope needs to be aligned carefully as the beam misalignment may introduce a notable artefact around the interface region.     

30CrMnSiA高强度钢氢脆断裂机理研究

试验结果表明：30CrMnSiA高强度钢的下贝氏体组织具有最小的氢脆敏感性,贝氏体组织的氢脆断口特征是准解理,而索氏体、屈氏体则主要是沿晶;同时分析了以上三种氢脆断口形貌特征及其断裂机理;氢促进了位错的运行与增殖,从而影响裂纹的萌生与扩展。     

TEM characterization of precipitates in the segregated regions of a low-carbon, low-manganese, titanium-added steel

A concentric solidification technique has been employed to simulate sulphide precipitation at the centreline of a continuously cast low-carbon, low-manganese, titanium-added steel slab. Selected precipitates were identified using transmission electron microscopy following sample preparation by focused ion beam milling techniques. FeTiS₂ and hexagonal MnS containing iron atoms form in close proximity to each other in super-saturated areas of the concentrically solidified sample. The presence of FeTiS₂ precipitates in low-carbon steel has been verified for the first time, and the crystal structure determined by electron diffraction analysis as a trigonal CdI₂-type with a P 3 m1 space group and lattice parameters of a = 0.341 nm and c = 0.569 nm.