The generation of stress and strain during the quenching of steel plates in polyalkylene glycol solutions

An examination has been made of the effect of increasing polyalkylene glycol concentration on the generation of thermal stress and strain in steel plates of a high hardenability steel 835M30, using a viscoelastic-plastic mathematical model. The results obtained from these quenched specimens suggest that the residual stresses and strains were not greatly affected by concentrations of the proprietary Aquaquench 1250 within the range 5% to 25%, although the addition of up to 5% of this solution did markedly reduce the residual stress and strain. At the same time the reduction in the Aquaquench 1250 from 25% to 5% greatly reduced the duration of the vapour blanket stage of the quench, so it might be possible to produce a fully martensite structure in a lower hardenability steel without adversively affecting the level of stress and strain at the end of the quench.     

Characterization and modeling of quenching-induced residual stresses in the nickel-based superalloy IN718

The residual stress fields in pieces of quenched IN718 superalloy have been characterized by neutron diffraction. The samples were in the form of cylindrical rods of length sufficient to ensure that steady-state conditions prevail at the midsection. Quenching the samples in air, water, and oil generated various residual stress fields. The interfacial heat-transfer coefficients were estimated using an inverse-modeling technique. The findings were rationalized with an elastic-plastic finite-element model that included temperature-dependent properties. The hoop and axial stresses are the most significant components of the stress field and arise from the plastic deformation occurring at the periphery of the cylindrical sections, the extent of which depends strongly upon the severity of the quench. The model is used to examine the residual stress fields to be expected in a turbine-disc forging of idealized geometry.     

Effect of quench rate on microstructure and tensile properties of ALSL 4320 and 4340 steels

A study has been made of the effect of quench rate on the microstructure and tensile properties of two commercial AISI 4320 and 4340 steels having fully martensitic structures. The steels were quenched from various temperatures from 1323 to 1473 K, at two different quench rates using iced brine (fast quench treatments) and oil held at 373 K (slow quench treatments). Tensile properties of these steels, after double-tempering at 473 K with intermediate quenching and refrigeration, were determined at ambient temperature (293 K) using an Instron test machine. The microstructural changes accompanying these quench rates were examined by means of optical and thin-foil transmission electron microscopic techniques. In the 4320 steel with a relatively high Ms temperature, the slow quench treatments compared to the fast quench treatments increased both the 0.2 pct proof stress and the ultimate tensile strength at similar total elongation levels, regardless of the prior austenite grain size, while the strength data of the slowly quenched steels exhibited a large scatter as the prior austenite grain size increased. However, in the 4340 steel with a relatively low Ms temperature tensile properties were less sensitive to quench rate, while the slow quench treatments compared to the fast quench treatments increased slightly only the 0.2 pct proof stress. From microstructural results, it is suggested that the beneficial effect on the strength of the slowly-quenched steels is caused by a dispersion-hardening effect due to carbon segregation or fine carbide precipitation in the martensite during the quench(i.e., autotempering).     

P110级石油套管淬火组织形态对残余应力的影响

以降低P110级石油套管淬火冷却过程中的热应力和组织应力为目的,提出了水淬+空冷和水淬+空冷+水淬两种冷却方式。利用逐层钻孔法测试了不同工艺下的残余应力,分析了淬火组织特征和残余应力对裂纹产生和扩展的影响。结果表明:直接淬火工艺的淬火组织为板条马氏体和孪晶马氏体共存,且孪晶马氏体的含量较多。水淬+空冷和水淬+空冷+水淬两种工艺的淬火组织为板条马氏体、下贝氏体和不同程度的残余奥氏体,水淬+空冷+水淬工艺中还有少量孪晶马氏体。水淬+空冷、水淬+空冷+水淬两种冷却方式和直接淬火工艺相比,钢管内的切向和轴向残余应力均减小,从而易减小钢管的变形,以及降低和缓解了钢管内微裂纹的产生和扩展趋势。     

Solidification of Nb-Ge alloys in long drop tubes

The 30 m and 100 m long drop tubes at the Marshall Space Flight Center have been used to obtain large undercooling in Nb-Ge alloys. Electron beam melting has been used to obtain drops approximately 2.5 mm in diameter. In the 30 m tube many specimens fell the length of the tube without solidifying, and were ultimately liquid quenched in oil. The amount of undercooling prior to the quench was usually around 0.13T;m. In the 100 m tube, freezing generally initiated during free fall, and the maximum undercooling was around 0.22Tm. Microstructures were characterized by a combination of X-ray diffraction, optical microscopy, and scanning electron microscopy with energy dispersive analysis by X-rays. A variety of interesting microstructures was observed.     

Effect of boundary conditions and workpiece geometry on residual stresses and microstructure in quenching process

In this study, the internal and residual stress states in quenched C60 steel cylinders are analyzed both numerically and experimentally in order to investigate the effects of boundary conditions (such as quench severity and temperature of quench bath) and specimen geometry. Specimen geometry has been analyzed by introducing a hole in a cylinder and varying hole diameter and its eccentricity. In the numerical analysis, the finite element method is applied and both temperature gradients and phase transformations are considered. Experiments include microstructural examination and X-ray measurements of residual stresses of the first kind. It has been found that the value of the convective heat transfer coefficient is very critical to obtain simulation results close to real ones. For instance, when a constant value obtained as the mean of a temperature dependent distribution is used for this parameter, residual stresses are seriously underestimated (up to 40%). The temperature of the quench bath affects directly the convective heat transfer coefficient. The lower the bath temperature, the higher are the resulting residual stresses. Under the same quenching conditions, if the diameter of the hole is greater than a critical value, a transition occurs from the shallow hardening case to the through hardening case, i.e., the residual stress distribution is reversed. On the other hand, for a constant hole diameter, if the eccentricity ratio reaches a critial value, a complex residual stress state results, i.e., compressive/tensile stress transition regions along the circumference are observed.     

The Effect of Aging on the Relaxation of Residual Stress in Cast Aluminum

Most cast aluminum-engineered components are water quenched after the solution-treatment cycle of the casting process. This rapid water quenching has the potential to induce high residual stresses in regions of the castings. Reducing the amount of residual stress can have a promising effect on the life of the component. This study was conducted to quantify how aging affects the amount of residual stress in an aluminum casting. An engineered high residual stress test sample and quenching technique has been developed, and a relaxation study has been completed. The study focused on four different temperatures: 463 K, 493 K, 513 K, and 533 K (190 °C, 220 °C, 240 °C, and 260 °C) and a range of aging times (0.3 to 336 hours). The aging data were used to verify a stress relaxation model. The results indicated that as the aging temperature increased, the amount of relaxation of the residual stress increased.     

Fatigue and microstructural properties of quenched Ti- 6Al- 4V

The mechanical properties and microstructures of Ti-6A1-4V were determined for specimens heat treated at temperatures from 843 °C to 1065 °C for 10 minutes and water quenched; these properties were compared with those of α-β annealed specimens. Specimens heat treated at 900 °C and water quenched had higher fatigue lives by a factor of four to ten relative to the other treatments; in addition, this treatment resulted in high ductility, yield strength, tensile strength, and elastic modulus. Micro-structure studies utilizing optical and transmission microscopy showed that the improved fatigue lives were a result of a strain induced transformation of retained β to martensite. The amount of retainedβ and its relative stability were shown to depend upon the heat treatment temperature. The lower the heat treatment temperature below theβ transus the smaller the amount ofβ phase present before the quench and the richer theβ phase inβ stabilizer. The greater the concentration ofβ stabilizer in theβ phase the greater the probability that theβ phase was retained. High heat treatment temperatures resulted in a greater amount ofβ that was less stable and more probable to transform to martensite during a water quench.     

Microcracking and fatigue in a carburized steel

A carburized coarse-grained AISI 8620 steel was subjected to three postcarburization heat treatments: a) direct oil quench from the carburizing temperature (1700°F), b) direct oil quench, reheat to 1550°F and oil quench, and c) slow cool, reheat to 1550°F and oil quench, reheat to 1450°F and oil quench. The latter two treatments refined the austenitic grain size over that resulting from the direct quench and caused a reduction in the size of the marten-site plates and of the number and/or size of the microcracks within the plates. The refine-ment of the microstructure and the reduction of the number of microcracks resulted in greatly improved fatigue resistance,i.e., from fatigue limits of 140 to 250 ksi maximum cyclic stress for the direct quench and double reheat conditions, respectively. Subcritical crack growth was transgranular, but the mode of unstable crack propagation was mixed transgranular and intergranular in the direct quench and single reheat specimens. Obser -vations of microcrack coalescence and fracture surface features suggest that microcracks are instrumental in the transgranular mode of failure. C. A. Apple, formerly Postdoctoral Fellow, Lehigh University, Bethlehem, Pa. 18015     

淬火油再生提高淬火工效

淬火油质量的好坏直接影响到成形后弹簧片弧高的稳定及力学性能的优劣。通过淬火油的再生，使淬火油达到超速淬火油标准，可抑制淬火钢板异常变形，稳定淬火弧高，提高淬透性，确保得到良好的淬火组织。提高了热处理淬火工效20％左右。     

考虑成卷-展平过程的冷弯残余应力分析

 从不考虑材料冷作硬化（理想弹塑性体）与考虑冷作硬化（双线性随动硬化）两个方面对带坯在成卷、开卷、展平、塑性弯曲及回弹过程中产生的应力进行了解析分析,获得了冷弯残余应力沿厚度方向上的分布,随后对比研究了考虑硬化与不考虑硬化对冷弯残余应力分布的影响,并将理论计算结果与实测残余应力进行了对比。结果表明,理想弹塑性模型和硬化模型预测的残余应力分布形式几乎一致;成卷上存在屈服时,纵向残余应力由内外表面向板厚中心方向呈非线性分布（成卷上无屈服时呈线性分布）,横向残余应力呈近似线性分布;在变形外区主要为残余拉应力（横向残余应力在外侧有极小部分受压区）,内区主要为残余压应力（横向残余应力在内侧有极小部分受拉区）;横、纵向残余应力最大值均在中性层位置;研究结果与试验测量结果基本一致。     

热处理对超级13Cr不锈钢组织及拉伸性能的影响

 为了研究热处理工艺对超级13Cr不锈钢组织及拉伸性能的影响,采用了光学显微镜、X射线衍射仪、透射电子显微镜、显微硬度测试及应变速率拉伸等试验方法。结果表明,经过水淬和油淬处理的超级13Cr不锈钢组织及拉伸性能相差不大。但相比于水淬,采用油淬的试样经回火处理后塑性得到更大提升。淬火试样经回火处理后,组织变为回火索氏体。随着回火温度升高,材料的塑性先增加后减小,硬度与强度变化则相反。620 ℃回火试样含有逆变奥氏体,强度塑性组合较好。二次回火能够增加超级13Cr不锈钢中逆变奥氏体含量,但塑性变化不明显,强度下降较大。     

Behavior of Pultruded Fiber-Reinforced Polymer Beams Subjected to Concentrated Loads in the Plane of the Web

Results of the behavior of pultruded fiber-reinforced polymer (FRP) I-shaped beams subjected to concentrated loads in the plane of the web are presented. Twenty beams with nominal depths from 152.4 to 304.8?mm were tested in three-point bending with a span-to-depth ratio of four. Load was applied to the top flange directly above the web—12 without bearing plates and 8 with bearing plates of varying width and thickness. All test specimens failed with a wedgelike shear failure at the upper web-flange junction. Finite-element results support experimental findings from strain gauge and digital image correlation data. Bearing plates increased beam capacity by 35% or more as a function of bearing plate width and thickness. Bearing plates increased average shear stress in the web at failure from 17.4 to 27.2?MPa—below the accepted value of in-plane shear strength (69?MPa). A design equation is presented, and predicted capacities are compared with experimental results. The average value of experimental capacity to predicted capacity is 1.12 with a standard deviation of 0.11 and coefficient of variation (COV) of 0.10 for sections up to 304.8?mm deep.     

Use of neutron and synchrotron X-ray diffraction for evaluation of residual stresses in a 2024-T351 aluminum alloy variable-polarity plasma-arc weld

The residual stress fields associated with variable-polarity plasma-arc (VPPA) welds in 2024-T351 aluminum alloy plates have been measured nondestructively using neutron and synchrotron X-ray diffraction. Neutron diffraction allows in-depth measurements of the full strain tensor to be made in thick components; synchrotron X-rays allow for rapid measurements of strains inside components, although their penetration is less than that of the neutrons and constraints arising from the diffraction geometry generally lead to only two strain components being easily measurable. Hence, a combination of the two techniques, applied as described herein, is ideal for a detailed nondestructive evaluation of residual stresses in plates. The residual stresses in a 12-mm-thick VPPA-welded aluminum 2024-T351 alloy plate have been measured using neutron diffraction. The stresses were then remeasured by a combination of neutron and synchrotron X-ray diffraction after the plate had been reduced in thickness (or, skimmed) to 7 mm by machining both sides of the weld, mimicking the likely manufacturing operation, should such welds be used in aerospace structures. A strong tensile residual stress field was measured in the longitudinal direction, parallel to the weld, in both the as-welded and skimmed specimens. There was only a slight modification of the residual stress state on skimming.     

Influence of heat transfer on the development of residual stresses in quenched steel cylinders

In this paper results of systematic FE-calculations about the influence of characteristic points of the temperature dependent heat transfer coefficient, especially the Leidenfrost point and the point of maximum heat transfer coefficient on the development of residual stresses are discussed. The numerical investigations were carried out for SAE 1045 and 4140 steel cylinders with 10 and 20 mm 0 quenched in water and oil, respectively. In this work experimentally determined h, T-curves are linearly approximated in the successive stages of heat transfer. Changes of the Leidenfrost-temperature do not influence the middle plane residual stresses of the cylinders investigated. Increasing maximum heat transfer coefficients and low temperatures of maximum heat transfer coefficient, respectively, cause higher magnitudes of residual stress. The development of residual stresses is determined by the temperature dependent gradient of the heat flux density δq/δT in the temperature range of martensitic transformation. Increasing Leidenfrost-temperatures cause more homogeneous stress and residual stress states at the surface of quenched cylinders due to the symmetrical cooling of the sample in axial as well as in radial direction. In particular, it was shown that during immersion cooling of cylindrical parts the heat transfer is locally dependent. Simulating immersion cooling this dependence has to be considered using effective local heat transfer coefficients.     

Investigation on the Effect of Mold Constraints and Cooling Rate on Residual Stress During the Sand-Casting Process of 1086 Steel by Employing a Thermomechanical Model

In this study, the effects of mold constraints and cooling rate on residual stress were analyzed during the shaped casting process. For this purpose, an H-shaped sample was designed in which the contraction of its middle portion is highly restricted by the mold during the cooling process. The effects of an increasing cooling rate combined with mold constraints were analyzed by reducing the thickness of the middle portion in the second sample. A three-dimensional coupled temperature-displacement analysis was performed in finite-element code ABAQUS to simulate residual stress distribution, and then numerical results were verified by the hole-drilling strain-gauge method. It was concluded that the mold constraints have a greater effect on the values of residual stress than the cooling rate (thin section) in steel sand casting. Increasing the cooling rate would increase the amount of residual stress, only in the presence of mold constraints. It is also suggested that employing the elastic-plastic stress model for the sand mold will satisfy the experimental results and avoid exaggerated values of residual stress in simulation.     

The effect of austenitizing temperature on the microstructure and mechanical properties of as-quenched 4340 steel

The effect of austenitizing temperature on both the plane strain fracture toughness,K _IC , and the microstructure of AISI 4340 was studied. Austenitizing temperatures of 870 and 1200°C were employed. All specimens austenitized at 1200°C were furnace cooled from the higher austenitizing temperature and then oil quenched from 870°C. Transmission electron microscopy revealed an apparent large increase in the amount of retained austen-ite present in the specimens austenitized at the higher temperature. Austenitizing at 870°C resulted in virtually no retained austenite; only minor amounts were found sparsely scat-tered in those areas examined. A considerably altered microstructure was observed in specimens austenitized at 1200°C. Fairly continuous 100 to 200Å thick films of retained austenite were observed between the martensite laths throughout most of the area exam-ined. Additionally, specimens austenitized at 870°C contained twinned martensite plates while those austenitized at 1200°C showed no twinning. Plane strain fracture toughness measurements exhibited an approximate 80 pct increase in toughness for specimens austen-itized at 1200°C compared to those austenitized at 870°C. The yield strength was unaffected by austenitizing temperature. The possible role of retained austenite and the elimination of twinned martensite in the enhancement of the fracture toughness of those specimens austen-itized at the higher temperature will be discussed.     

待矫直板材板形缺陷解析表征

 目前待矫直板材缺陷类型及程度的判断仍然是依赖现场工作人员的经验,具有很大的不确定性。为了获得待矫直板材残余应变（应力）的大小及分布,根据薄板大挠度屈曲理论和最小势能原理,建立了基于浪形几何参数的反解计算模型。通过实测的浪形几何参数和预设挠曲函数,对引起边浪、中浪（肋浪）等典型的浪形缺陷的残余应变（应力）进行求解,并与实测值进行对比。结果表明,残余应变（应力）的分布与浪形几何形状相对应,但压应力宽度略小于屈曲宽度,即紧邻压应力的拉应力区也产生了挠曲;几何非线性及后屈曲强度对浪形状态的影响是显著的;求解过程与板厚无关,所需几何参数较少,便于现场应用。     

Reduction of Residual Stress and Improvement of Dimensional Accuracy by Uphill Quenching for Al6061 Tube

The purpose of this study is to reduce the residual stress and machining distortion of an Al6061 tube by using uphill quenching. During uphill quenching, solid-solution heat-treated aluminum parts are usually immersed in LN₂ at 77 K (?196 °C), followed by the rapid heating of the parts, to produce a new residual stress that is opposite in nature to the original. The uphill quenching method used in this study employed two types of heating methods: boiling water at 373 K (100 °C) and high-velocity steam at 448 K (175 °C). First, FE-simulation coupled with a CFD analysis was performed to predict the residual stress of the backward hot-extruded Al6061 tube with the following dimensions: Ø200 mm × h200 mm × t10 mm. Experiment of uphill quenching was also conducted to measure the residual stress using the boiling water and high-velocity steam uphill quenching methods. The predicted residual stresses were compared with the experimental results obtained via micro-indentation and saw-cutting tests, and a deviation of about 10.4 pct was found. In addition, the experimental results showed that uphill quenching could relieve up to 91 pct of the residual stress induced by water quenching. Finally, the dimensional accuracy of uphill quenched tubes was evaluated by measuring the roundness after the machining process, which showed that the uphill quenching method could improve the dimensional accuracy of an Al6061 tube by reducing the residual stress.     

The effect of residual strain on the diastolic function of the left ventricle as predicted by a structural model

The unloaded heart is not stress-free. It is subjected to residual stress and strain. Their extent and influence on the global performance of the left ventricle and on local phenomena in the ventricular wall are studied by model simulation. The analysis focuses on the equatorial region of the ventricle, with an approximate thick-walled cylindrical geometry. The in vivo myocardium is considered to be incompressible, consisting of fibers embedded in a fluid matrix, with transmurally varying anisotropic microstructure in accordance with morphological characteristics. The results show that residual strain is transmurally distributed with a pattern and magnitude which agree well with measurements. The calculated residual strains are within mean +/- one standard deviation of the measured ones. Their magnitude was found to increase with increasing opening angle and with increasing wall thickness. The residual strain was found to have several effects on ventricular function: At volumes higher than the reference one it gives rise to more uniform transmural distributions of stress and intramyocardial pressure; it causes about 50% increase in the ventricular compliance at high volumes and doubles the suction of atrial blood at low volumes, thus facilitating the diastolic filling. In addition, residual strains cause bias of in vivo measured strains from their true values. This may significantly affect physiological interpretation of measured ventricular deformations. In conclusion, the present structural analysis predicts that residual strain has favorable effect on left-ventricular diastolic performance, and gives rise to more uniform ventricular stress distribution.