等径角挤压变形奥氏体不锈钢的组织演变

 用实验方法研究了奥氏体不锈钢在等径角挤压冷变形(路径RC)过程中组织变化。实验结果表明：当剪切方向与孪晶带方向成一定角度时，在剪切力的作用下，孪晶逐渐由大块孪晶→由剪切带分割的孪晶(楼梯状)→小块状→奥氏体亚晶或马氏体晶粒；部分孪晶在剪切力作用下，剪切带可直接碎化成具有大角度位向差的细小晶粒(奥氏体亚晶+马氏体晶粒)，可发生马氏体相变；当剪切方向与孪晶带方向相同时，孪晶带区域也可发生马氏体转变；3道次变形后，具有明显特征的孪晶已很少，此后继续进行剪切变形，孪晶碎化组织(含马氏体)和奥氏体剪切滑移带(含碎化晶粒)的变形以剪切滑移方式进行，当奥氏体的滑移遇到阻力时，可局部形成局部形变孪晶来协调变形；随变形道次的增加，马氏体转变也越多，在多次剪切以及道次中的交叉滑移作用下，马氏体板条逐渐被高密度位错墙分割而碎化成细小的晶粒；8道次变形后，可获得60~230 nm的等轴晶粒。     

TA2钛／Q345R钢钎焊用钎料研究

选用AgSO．5Cu35．2Mn8．01Ni4．95Si0．380．1、Ag60．5Cu26．2Mn8．01Ni4．95Si0．380．1、AS65．5Cu21．2Mn8．0-Ni5Si0．380．1和AgT0．5Cu16．2Mn8．0Ni4．95Si0．380．1为钎焊料,对TA2钛与Q345R钢进行TIG-熔焊连接实验,结合光学显微观察、焊缝显微硬度分析及接头拉伸强度测试,研究了4种钎料对TA2钛与Q345R钢的钎焊效果的影响。结果表明,Ag65．5Cu21．2Mn8．0Ni5SiO．3130．1钎料的焊接质量最好,无论是钢侧还是钛侧都无裂纹产生,也无碳化物以及其他脆性化合物生成,且钎料与母材有明显互扩散现象。     

Interfacial Microstructure of Al-Sn-Pb Alloy/Steel During Liquid-Solid Bonding Rolling

Studies were conducted on the interfacial microstructure of a steel/liquid aluminium and its evolution during the bonding rolling process. The effects of wetting time and deformation on the diffusion layer and on the bonding strength were examined. By means of electron microscopy and electron probe analysis, it was found that the diffusion layer is mainly composed of FeAI3. For a steel temperature of 250℃ and an aluminium temperature of 850 ~C, the diffusion layer was formed within 3 s, and the shear strength of the samples increased after 8 to 14 s. Although the interface was not damaged, it was deformed notably. For an aluminium temperature of 750℃ and a wetting time of 11 to 17 s, the shear strength of the interface remained high, but the interface was obviously broken during rolling, leading to reduced bonding strength.     

Microstructure and Texture Evolution During Cold Rolling of 316L Stainless Steel

Metallurgical and Materials Transactions A - The evolution of the deformation microstructure and the local crystallographic orientations are investigated for 10, 30, 50, and 80 pct cold...     

On Characterizing a Composite Microstructure in 316LN Stainless Steel Weld Metal and a New Damage Micromechanism During Creep

The austenitic stainless steel weld metal fabricated by multipass welding exhibits a composite microstructure. Microstructural characterization of the weld metal revealed that there are two distinct regions on either side of the weld-pass interface. The variations in dislocation substructure and delta ferrite morphology are the two microstructural attributes which delineate these regions. The generation of subsequent thermal cycles during the fabrication of multipass weld joint is the paramount factor influencing the formation of the composite microstructure. During creep exposure, the extent of creep cavitation and propagation varies substantially in these two regions due to differences in their microstructures. This results in preferential damage during creep exposure of austenitic stainless steel weld metal.     

Interfacial Reactions During Titanium Dissolution in Liquid Iron: A Combined Experimental and Modeling Approach

The dissolution behavior of Ti in liquid Fe has been investigated experimentally and theoretically within the framework of inclusion formation in steel. In the experimental study, Ti cylinders have been immersed into liquid Fe and, subsequently, water-quenched. Macroscopic observation of quenched samples shows the initial solidification of an Fe shell around the Ti. Microstructural analysis of the Fe-Ti interfacial area with a scanning electron microscope equipped with an energy dispersive X-ray spectrometer reveals that a reaction zone develops in a three-step process: formation of a first liquid eutectic layer rich in Ti, formation of a second eutectic layer rich in Fe, and then mixing of both layers. The reaction zone grows in thickness up to 40 pct of the original sample radius and dissolves both parts of the Ti sample and the Fe shell. A simplified, one-dimensional, implicit finite volume model has been used to describe these phenomena theoretically. Good qualitative agreement is achieved between experiment and model. The model has been used to estimate the influence of original addition size, preheating, convection, and superheating on the required melt-back time.     

Influence of Zn Coating on Interfacial Reactions and Mechanical Properties During Laser Welding-Brazing of Mg to Steel

To investigate the influence of Zn coating on the joining of magnesium alloy AZ31?to Zn-coated steel, dissimilar metal joining both with and without Zn coating was performed by the laser welding-brazing (LWB) process. Welding characteristics including joint appearance, identification of interfacial reaction layers, and mechanical properties were comparatively studied. The results indicated that the presence of Zn coating promoted the wetting of liquid filler wire on the steel substrate. Heterogeneous interfacial reaction layers formed along the interface between the Mg alloy and Zn-coated steel, whereas no distinct reaction layer and increased concentration of Al were identified at the interface between the Mg alloy and noncoated steel. The maximum tensile-shear strength of Mg/steel lap joint with Zn coating reached 180?N/mm, which was slightly higher than that achieved without Zn coating (160?N/mm). Failure of joint in both cases occurred at the interface; however, the fracture mode was found to differ. For Zn-coated steel, the crack propagated along the Mg-Zn reaction layer and Fe-Al phase, with little Mg-Zn reaction phases remaining on the steel side. As for noncoated steel, some remnants of the seam adhered to the steel substrate.     

2205双相不锈钢连铸坯加热过程组织转变

对2205双相不锈钢连铸坯试样在1 220、1 240、1 260、1 280℃保温10、20、30和40 min进行加热处理,通过光学显微镜和铁素体仪试验分析2205双相不锈钢的组织和铁素体含量随保温时间和加热温度的变化情况.结果表明,2205双相不锈钢连铸坯试样在相同的保温时间下,随着加热温度的升高,铁素体含量逐渐增加,1 260℃时奥氏体晶粒明显变得粗大;在相同的加热温度下,随着保温时间的延长,铁素体的含量逐渐减少.     

含镍铁素体冷轧不锈带钢的微观组织

为了拓宽铁素体不锈钢的应用范围,利用金相显微镜、电子背散射衍射技术(EBSD)和透射电镜(TEM),研究含镍铁素体冷轧不锈带钢的微观组织结构,分析了其形成原因及对力学性能的影响.结果表明,由于镍等奥氏体形成元素带来的相变,细化了铁素体组织,且在一定的热处理工艺下可以得到具有较高应力、由铁素体亚晶和小晶粒组织构成的弥散组织,该组织均匀分布在铁素体基体上,起到了“第二相”强化的作用,从而在保证铁素体不锈钢较好塑性的同时,大大提高了其强度.     

Influence of Mode of Metal Transfer on Microstructure and Mechanical Properties of Gas Metal Arc-Welded Modified Ferritic Stainless Steel

This article describes in detail the effect of the modes of metal transfer on the microstructure and mechanical properties of gas metal arc-welded modified ferritic stainless steel (SSP 409M) sheets (as received) of 4 mm thickness. The welded joints were prepared under three modes of metal transfer, i.e., short-circuit (SC), spray (S), transfer, and mix (M) mode transfer using two different austenitic filler wires (308L and 316L) and shielding gas composition of Ar + 5 pct CO₂. The welded joints were evaluated by means of microstructural, hardness, notched tensile strength, Charpy impact toughness, and high cycle fatigue. The dependence of weld metal microstructure on modes of metal transfer and filler wires has been determined by dilution calculation, WRC-1992 diagram, Cr_eq/Ni_eq ratio, stacking fault energy (SFE), optical microscopy (OM), and transmission electron microscopy (TEM). It was observed that the microstructure as well as the tensile, Charpy impact, and high cycle fatigue of weld metal is significantly affected by the mode of metal transfer and filler wire used. However, the heat-affected zone (HAZ) is affected only by the modes of metal transfer. The results have been correlated with the microstructures of weld and HAZ developed under different modes of metal transfer.     

奥氏体不锈钢的组织超细化技术

在试验的基础上研究了获得奥氏体不锈钢超细组织的方法,研究结果表明,原始晶粒尺寸为100 μm的304N不锈钢经1道次等径角挤压变形 退火工艺处理后,晶粒尺寸可显著细化到2～7 μm,强度可提高50%以上,而塑性并不降低;增加等径角挤压变形的道次,经退火后可获得更细小、均匀的再结晶晶粒.     

Effect of Treatment Time on the Microstructure of Austenitic Stainless Steel During Low-Temperature Liquid Nitrocarburizing

The effect of treatment time on the microstructure of AISI 304 austenitic stainless steel during liquid nitrocarburizing (LNC) at 703 K (430 °C) was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Experimental results revealed that the modified layer was covered with the alloy surface and the modified layer depth increased extensively from 2 to 33.4 μm with increasing treatment time. SEM and XRD showed that when the 304 stainless steel sample was subjected to LNC at 703 K (430 °C) for less than 4 hours, the main phase of the modified layer was expanded austenite. When the treatment time was prolonged to 8 hours, the abundant expanded austenite was formed and it partially transformed into CrN and ferrite subsequently. With the increased treatment time, more and more CrN precipitate transformed in the overwhelming majority zone in the form of a typical dendritic structure in the nearby outer part treated for 40 hours. Still there was a single-phase layer of the expanded austenite between the CrN part and the inner substrate. TEM showed the expanded austenite decomposition into the CrN and ferrite after longtime treatment even at low temperature.     

Deformation Behavior and Evolution of Microstructure and Texture During Hot Compression of AISI 304LN Stainless Steel

Deformation behavior of hot-rolled AISI 304 LN austenitic stainless steel was studied by hot axisymmetric compression tests at 1173 K, 1273 K, and 1373 K (900 °C, 1000 °C, and 1100 °C) at strain rates of 0.01, 0.1, and 1 s^?1. The flow curves were examined to understand the deformation characteristics. The influence of Zener–Holloman parameter was analyzed using appropriate constitutive models. The activation energy for deformation was found to be 473 kJ/mol. Quantitative microstructural analysis was carried out using Electron backscattered diffraction. Compression at 1173 K (900 °C) at all true strain rates gave rise to partially dynamic recrystallized microstructure with strong α-fiber texture. The deformation texture is characterized by the formation of Brass component, and partial dynamic recrystallization (DRX) led to the development of Goss, S, and ube components. Necklace structure of small equiaxed recrystallized grains could be observed surrounding the large, elongated deformed grains. Compressions at 1273 K and 1373 K (1000 °C and 1100 °C) resulted in fully recrystallized microstructure consisting of mostly Σ3 and Σ9 coincidence site lattice high-angle boundaries. Compression at 1273 K (1000 °C) leads to the formation of low-intensity diffused α-fiber. DRX was confirmed by the presence of Goss, S, Cube, and rotated Cube components. Compression performed at 1373 K (1100 °C) resulted in nearly random texture with traces of α-fiber and prominent Cube/rotated Cube components. The microstructures of the 1173 K (900 °C)-compressed samples were partitioned using grain size and misorientation criteria to quantify DRX.     

Effect of Heat Input on Microstructure and Corrosion Behavior of Duplex Stainless Steel Shielded Metal Arc Welds

In the present work, UNS S32750 super duplex stainless steel sheets were welded by shielded metal arc welding process with E2595 electrode using two different heat inputs, 0.54 and 1.10 kJ/mm. Microstructural investigations (optical and scanning electron microscopy) showed very small differences in the heat affected zone for both the heat inputs. The weld metals showed presence of three different morphologies of austenite—Widmanstatten, intra-granular and grain boundary austenite along with ferrite. Ferrite content in the weld region was also nearly same and did not change significantly with the increase in heat input. Both the weldments showed similar mechanical properties (ultimate tensile strength, impact strength and hardness) and failed in a ductile manner. Electrochemical studies in 3.5% NaCl solution showed the degree of sensitization to less than 1% and nearly same pitting potential for both heat inputs. Since the effect of heat input on the weld behavior was negligible, low heat input may be preffered for welding UNS S32750 super duplex stainless steel.     

TiC强化304不锈钢的显微组织和性能

对原位合成TiC强化304不锈钢的显微组织和性能进行了研究。试验结果表明:在304不锈钢中产生TiC颗粒后,热处理态组织中的孪晶得到明显细化,同时出现了很多纳米级的未固溶的方形颗粒Cr23C6和圆形颗粒TiC。TiC颗粒的产生,使304不锈钢强度有较大提高而塑性有一定的下降。在TiC强化钢磨损过程中,TiC颗粒暴露于磨损表面起承载和形成油膜的作用,从而保护基体不发生严重磨损。随着钢中TiC含量的增加,强度和磨损性能的提高越明显。     

不锈钢与铝炉中钎焊保护气体选择的研究

通过对钎焊过程中金属氧化物稳定性及其还原机理的分析,表明在炉中钎焊异种金属不锈钢与铝的过程中,选择合适的保护气氛有利于获得稳定的焊接质量。选择还原气体氨分解气(或氢气)作保护气氛,有助于钎焊过程顺利进行,但使用时存在安全问题。炉中钎焊不锈钢与铝使用钎剂时,无论采用氨分解气还是惰性气体纯氮气作保护气氛,对焊接质量几乎无影响,钎焊样品的焊缝强度均可达65MPa。选择惰性气体氮气作保护气氛,可极大地提高钎焊过程的安全性,并降低成本。     

不锈钢中钛、钼联合测定

不锈钢中钛和钼量测定，通常都是由两个分析人员，各自单独进行测定的。钛大多采用高灵敏度显色荆——变色酸，在硫酸介质中显色进行测定。该络合物十分稳定。且钢中常存元素几乎都没有干扰。钼通常采用硫握酸盐光度法。还原剂通常采用的有氯化亚锡、抗坏血酸、硫脲等。其中以抗坏血酸最为理想，因为它是一种较弱的还原剂，钼只被还原到五价，且该钼络合物色泽十分稳定，灵敏度也较高。作者经过多年细心观察和思考，发现钛和钼的显色介质都在硫酸介质或瞵酸和硫酸混合酸介质中，因此只要在完成钛的定量比色测定后，在其试样溶液中，移取部分试液，稍作调整，加入适量的硫磷混合酸，即能达到和控制在原单独测定钼时的显色酸度，经多次实践检验证明，分析结果几乎和原单独测定钼的结果．完全一致。     

Mass Transfer and Weld Appearance of 316L Stainless Steel Covered Electrode During Shielded Metal Arc Welding

The mass transfer and the weld appearance of 316L stainless steel covered electrodes during shielded metal arc welding were investigated. According to the experimental measurements on the deposited metal and the observations on the welding process, the mass transfer coefficient of the nickel was found to be in the range of 88.09 to 99.41 pct, while those of molybdenum, chromium, manganese, and silicon are in the ranges of 84.60 to 92.51 pct, 71.59 to 77.64 pct, 20.88 to 30.15 pct, and 6.72 to 10.47 pct, respectively. Some relationships between the mass transfer and the flux coating ingredient/welding current were established. The formability properties of the weld, including the spreadability, spattering, slag detachability, and oxidation tint on the weld surface, were also discussed based on the tested data and the observations.