数值模拟在镁合金焊接接头深冷处理中的应用

利用所建立的有限元模型,对焊接接头进行深冷处理前后的温度场分析,再把模型转化成结构单元进行应力应变场分析。计算结果表明:深冷处理后,受焊接热源影响的焊缝及附近区域横向残余应力和纵向残余应力均增大,距焊缝较远的母材区产生了预压应力;深冷处理后,横向和纵向残余变形均减小。     

深冷处理对18Ni马氏体时效钢性能及组织的影响

通过采用固溶、深冷及时效等处理方式,对18Ni马氏体时效钢进行了不同热处理工艺试验,研究了深冷处理对18Ni马氏体时效钢性能及组织的影响。结果表明,18Ni马氏体时效钢经深冷处理后硬度能有效提高;随着深冷处理时间的延长,材料的性能仍有所提升。深冷处理能使材料中的残余奥氏体向马氏体转变,但不能完全消除残余奥氏体。     

浅析焊接残余应力及其消除方法

简介了焊接残余应力危害的特点，影响因素、测量及消除残余应力的几种方法，重点论述爆炸法消除焊接残余应力的有关问题。     

冷轧铜板带残余应力成因及消除方法浅析

文章从冷轧铜合金板带残余应力的产生原因及消除方法等方面,综述了铜合金板带残余应力研究现状;指出深入了解冷轧铜合金板带残余应力的产生原因,研究高精度铜带箔残余应力的控制及消除工艺方法并在生产中产业化应用已经刻不容缓.     

层间残余应力对带夹层复合板组织性能影响

利用层间真空涂覆技术在不锈钢复合板间添加充型夹层会产生层间残余应力,在后续热轧成形过程中可能受层间残余应力影响导致复合板组织与力学性能发生变化。不锈钢复合板层间残余应力由充型夹层凝固过程中层间热应力与相变应力共同作用产生,拟通过轧前热处理对层间残余应力进行消除,采用数值模拟与试验验证相结合的方法制定轧前热处理工艺,通过层间真空压差涂覆、轧前热处理及热轧试验制备消除与未消除层间残余应力的2种不锈钢复合板,利用金相观测、硬度测试、界面能谱扫描及拉伸、剪切等表征及性能测试试验分析层间残余应力对复合板组织性能的影响。研究结果表明,在保证基层、夹层、复层组织不变的情况下,消除层间残余应力的轧前处理工艺为加热至400℃,保温3.5 h,缓慢冷却;经过轧前处理,层间残余应力消减了96.3%;相较于未消除层间残余应力的复合板,消除层间残余应力复合板轧后夹层应力显著增强,晶粒细化81.7%,同时,消除层间残余应力能够提升复合板剪切强度13.3%、拉伸强度3.9%、断后伸长率4%及夹层界面显微硬度3.5%。研究内容通过消除层间残余应力提升了带充型夹层复合板的整体性能,可为相关铸造成型构件性能的提升提供理论...     

爆炸法消除100t转炉炉壳中腰环缝的焊接残余应力

采用爆炸技术消除武钢平改转工程两台１００ｔ转炉的７０ｍｍ厚２０ｇ炉壳中腰环缝的焊接残余应力，残余应力消除率大于６２％，不仅消除残余应力效果显著，而且快速简便，为工程进展节约了大量的时间和费用。     

浅谈振动法消除残余应力的应用及其影响因素

目的 阐述了振动法消除工件残余应力的机理以及影响因素，提出振动法消除工件残余应力的方法及应用时须注意的问题。结果 残余应力实质上是金属材料内部晶体位错运动引起的，振动法在消除残余应力及稳定尺寸方面有一定的效果。结论 该技术实用性好，应用前景好，具有很好的经济和社会效益，可广泛应用于普通焊接件和铸件。     

深冷处理对硬质合金高速冲压模具材料性能的影响

本文以牌号为GF30H的硬质合金高速冲压模具材料为研究对象,对不同深冷处理时间的材料的硬度、抗弯强度、耐磨性、断裂韧性进行了研究。研究结果表明:深冷处理能有效提高材料的维氏硬度、抗弯强度、耐磨性以及断裂韧性。深冷处理时间是重要的工艺参数,对GF30H来说,2～4h为最佳的深冷处理时间。材料性能变化主要是由于深冷处理引起Co相马氏体相变、材料表面残余应力变化和WC晶粒度变化。     

残余应力测试方法的研究进展

综述了测量残余应力的方法,主要有机械释放法和非破坏性无损伤测量法以及消除残余应力的方法,并提出合理的选择。     

温度拉伸法消除焊接应力的数值模拟

课题主要研究焊接残余应力的分布规律及如何控制和消除有害残余应力.     

Residual Stress Analysis in Deep Drawn Twinning Induced Plasticity (TWIP) Steels Using Neutron Diffraction Method

In Twinning Induced Plasticity (TWIP) steels, delayed fracture occurs due to residual stresses induced during deep drawing. In order to investigate the relation between residual stresses and delayed fracture, in the present study, residual stresses of deep drawn TWIP steels (22Mn-0.6C and 18Mn-2Al-0.6C steels) were investigated using the finite element method (FEM) and neutron diffraction measurements. In addition, the delayed fracture properties were examined by dipping tests of cup specimens in the boiled water. In the FEM analysis, the hoop direction residual stress was highly tensile at cup edge, and the delayed fracture was initiated by the separation of hoop direction and propagated in an axial direction. According to the neutron diffraction analysis, residual stresses in 18Mn-2Al-0.6C steel were about half the residual stresses in 22Mn-0.6C steel. From the residual strain measurement using electron back-scatter diffraction, formation of deformation twins caused a lot of grain rotation and local strain at the grain boundaries and twin boundaries. These local residual strains induce residual stress at boundaries. Al addition in TWIP steels restrained the formation of deformation twins and dynamic strain aging, resulting in more homogeneous stress and strain distributions in cup specimens. Thus, in Al-added TWIP steels, residual stress of cup specimen considerably decreased, and delayed fracture resistance was remarkably improved by the addition of Al in TWIP steels.     

Effect of heat treatment process on impact wear property and mechanism of SKD11 steel

The microstructure, mechanical property, phase of SKD11 steel after vacuum heat treatmentor deep cryogenic heat treatment were studied by means of OM, hardness tester, impact tester and XRD.The impact wear properties of SKD11 steel under the two heat treatments were tested by MLD- 10 dynamic load- bearing wear tester. The impact wear mechanism was also analyzed. The results show that the microstructures of SKD11 steel after the two heat treatmentsare composed of tempering martensite, retained austenite and carbide. The hardness after cryogenic treatment is 1HRC higher than that of the vacuum treatment and impact toughness decreases lightly. Under impact wear conditions, the weight loss of the sample during deep cryogenic treatment is lower than that of the vacuum treatment, which shows better wear resistance. In the studied wear time, the wear mechanism of the sample after vacuum treatment is high stress surface fatigue and abrasive wear, and the wear mechanism of the sample after cryogenic treatment is slight abrasive wear.     

深冷处理在金属材料中的应用及研究进展

概述了金属材料深冷处理技术的发展历程,介绍了深冷处理的工艺、机理,并对深冷处理技术的应用发展趋势作了探讨。     

The relaxation of residual stresses with postweld heat treatment in a high-performance weld measured with neutron diffraction

The residual stresses in a cylindrical weldment of HP-9-4-30 steel were measured with neutron diffraction in the as-welded (AW) state and after postweld heat treatment (PWHT). Large residual stresses are present in the interior of the material in the as-welded condition. The maximum principal stresses measured were found around the edges of the cap-pass heat-affected zone and reached up to 1045 MPa (76 pct of the base metal yield strength) in the as-welded condition. The principal stress directions for the residual stress tensors do not in general follow the hoop, axial, and radial axes of the weld and change from position to position within the weld, although the highest values are generally in the hoop direction. The postweld heat treatment relaxed the largest residual stresses, with the maximum value being 30 pct of the base metal yield stress. The need for position-dependent stress-free standards and the implications of stress gradients over the measurement volumes are discussed.     

The effect of cryogenic cooling on the tensile properties of metal-matrix composites

Tensile specimens machined from metal-matrix, oriented-fiber composites (aluminum alloy reinforced with high strength stainless steel wire) were heated to 260°C and cooled in air to produce a tensile residual stress state in the matrix. Some of the test pieces were cooled to the temperature of boiling nitrogen, held at temperature for fifteen minutes, and then air warmed to room temperature. All test pieces were subsequently strain cycled in tension and the resulting stress-strain behavior was recorded. The results indicated cryogenic refrigeration extended the first stage (totally elastic) behavior of these materials. It was shown that the beneficial effects of the cryogenic treatment resulted from an alteration of the residual stress state brought about by plastic flow of the matrix. Finally, it was shown that these effects could be computed by rigorous analytical methods.     

Influence of Cryoprocessing on Mechanism of Carbide Development in Cobalt-Bearing High-Speed Steel (M35)

Cryogenic treatment has been used commonly to high-speed tool steels to enhance the wear resistance of the materials. In the current research study, specimens of complex alloyed high-speed tool steel (M35) were hardened at 1473 K (1200 °C), triple tempered at 673 K (400 °C) and then cryogenically treated at 88 K (?185 °C) for varying lengths of period starting from 16 to 48 hours of cryosoaking followed by soft tempering at 373 K (100 °C). These treated specimens were studied as a function of cryosoaking period for their electrical resistivity, residual compressive stress, and its correlation with carbide density was established. TEM analysis indicated carbide size 0.156 to 1 μm, which confirms that the cryogenic treatment enhances the precipitation of finer carbides. Lower residual stresses in the higher carbide density regimes identified in 2D contour map were explained by the stress relaxation in the matrix through precipitation of incoherent carbides.     

Determination of Bulk Residual Stresses in Electron Beam Additive-Manufactured Aluminum

Additive-manufactured aluminum alloy deposits were analyzed using neutron diffraction to characterize the effect of intermediate stress relief anneal heat treatment on bulk residual stresses in the final part. Based on measured interplanar spacing, stresses were calculated at various locations along a single bead, stacked wall deposit. A comparison between an uninterrupted deposited wall and an interrupted, stress-relieved, and annealed deposited wall showed a measureable reduction in residual stress magnitude at the interface with a corresponding shift in stress character into the deposit. This shift changes the interface stresses from purely compressive to partially tensile. The residual stress profile varied along the length of the deposit, and the heat-treatment procedure reduced the overall magnitude of the stress at the interface by 10 through 25 MPa. These results are interpreted in terms of thermal gradients inherent to the process and compared with prior residual stress-characterization studies in additive-manufactured metallic structures.     

Optimization of the range of elastic behavior of unidirectional composites by prestraining

The effect of tensile prestrain on the stage I tensile yield stress has been studied both analytically and experimentally for composites whose stress-strain curves obey the rule of mixtures. The mathematical analysis provides a means for calculating the optimum amount of prestrain, the residual stresses (in the direction of the fibers) in the matrix and fiber materials after unloading from the prestraining, and the stage I yield stress in the composite after the prestrain treatment. It is shown that the improvement in stage I yield stress by prestraining is due to the development of negative residual stresses in the matrix. The stage I yield stress in composites with negligible residual stresses in the as-fabricated condition can usually be improved by a factor of two by prestraining; the amount of improvement is even greater if the as-fabricated composites have the usual state of residual stress,i.e., tension in the matrix. Experimental studies on 2024 aluminum-tungsten composites (filament-wound; hot-pressed) having tungsten fiber volume fractions between 0.08 and 0.40 verified the mathematical analysis. The stage I yield stresses measured in these composites after a prestrain of 4.2 × 10⁻³ were in good agreement with predicted values. Improvements of up to a factor of six were found in the stage I yield stress as a result of prestraining.     

Effect of Cryogenic Treatment on Properties of Cr8-Type Cold Work Die Steel

 Effect of cryogenic treatment on the properties of Cr8-type cold work die steel was investigated. The results show that cryogenic treatment increases hardness by decreasing retained austenite, but the degree depends on the austenitizing temperature. When quenching at lower austenitizing temperature, the steel can obtain higher toughness by cryogenic treatment substituting conventional treatment process. Cryogenic time has little effect on cryogenic treatment. Conversely, cryogenic temperature has a greatly effect on cryogenic treatment that the effect of cryogenic treatment is more obvious with decreasing cryogenic temperature. In addition, deep cryogenic treatment improves the wear resistance by precipitating more homogeneous MC and M6C-carbides.