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The anisotropy of bulk formability in hot-rolled AISI 1040 steel bars has been evaluated using upset and bend tests in longitudinal, circumferential, and radial directions. The index of workability is improved approximately 65 pct by aligning the critical tensile stresses parallel to inclusion plane and elongation (longitudinal direction). The lowest workability is attained in the radial direction where tensile stresses are perpendicular to the plane of inclusions. In the circumferential direction, tensile stresses are parallel to the plane of inclusions, though perpendicular to inclusion elongation, leading to intermediate workability. Tensile ductilities in the principal directions are compared with the three workability levels. Tension fracture data agree with the forming limit line in the radial direction. In the other directions, however, the tension test progressively overestimates workability as the workability level increases.  相似文献   

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The effects of varying finish rolling temperature (FRT) and cooling rate on the mechanical properties of hot rolled plates of an experimental low-alloy Ti-V steel were studied. Fracture toughness was evaluated for various types of specimens at slow and high deformation rates. However, the transition temperatures determined by the various tests do not always correlate. Therefore, it is recommended that fracture toughness be evaluated by both static and dynamic testing. Following a low cooling rate, the best plate properties are obtained at the lowest FRT in the austenite-ferrite range, although occurrence of delaminations at this temperature may be detrimental for specific applications. Higher cooling rates produce higher strength but lower toughness than lower cooling rates in plates with the same FRT.  相似文献   

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Cavity formation from inclusions in ductile fracture of A508 steel   总被引:3,自引:0,他引:3  
Experiments were performed on A508 class 3 steel in order to determine the conditions for cavity formation from elongated MnS inclusions. Circumferentially notched tensile specimens were employed in order to investigate the effect of negative hydrostatic pressure. The results of finite element calculations and metallographic observations on polished sections were used to evaluate the conditions required for cavity initiation. Tests were performed at different temperatures in both longitudinal and short transverse direction. The results can be explained in terms of a local critical stress independent of temperature. This local stress is tentatively calculated using an extension of Eshelby’s theory for inclusions proposed by Berveiller and Zaoui.  相似文献   

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The effect of tensile prestrain on the ductile fracture behavior of an interstitial-free (IF) steel has been studied using primarily (1) the analysis of void density by optical microscopy, (2) characterization of the size of dimples by scanning electron microscope (SEM) and image analyzer, and (3) estimation of strain hardening behavior of a series of prestrained tensile specimens, loaded until fracture. The variation of void density with local plastic strain around the necked region of the specimens indicated the existence of two types of void nucleation pertaining to inclusions and precipitate particles. The critical strain for void nucleation (ε{inn}) for the precipitate particles initially increases and then decreases with the increase in percentage prestrain. This phenomenon has been explained using the strain hardening exponent and nature of dislocation-particle interaction. The nature of variation of the average size of the dimples and that of ε{inn} with prestrain are found to be similar. The dimple size thus bears a proportional relationship with the void, nucleation strain ε{inn} and hence the former can be used to predict (ε{inn}) for IF steel.  相似文献   

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The effects of hydrogen on ductile fracture were investigated in a spheroidized steel similar to AISI 1520, containing negligible amounts of P and S, using notched bend bar tests. The effects of hydrogen were exhibited either in the form of enhanced plastic instability along characteristic slip traces in mode II or of enhanced, strain-controlled, local crack tip processes. The contri-bution of enhanced plastic instability, however, was only apparent under conditions in which flow localization also occurred without hydrogen. The role of plastic instability near the crack tip was found to be dominant in these bend bar tests, whereas it was small or negligible in previous tests in axisymmetric tension. Microstructural effects were rationalized in terms of a critical, local concentration of hydrogen. The intrinsic effect of hydrogen appeared to be the enhancement of strain-controlled fracture processes. Formerly with Carnegie Mellon University.  相似文献   

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The thermostatting of alloy-steel coils after hot rolling in a continuous broad-strip mill is considered. A technological chart of slow controlled cooling of the coils is developed. Measures are proposed for the production of high-quality and highly profitable steel coils without additional capital expenditures or operating costs.  相似文献   

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Central Scientific-Research Institute of Ferrous Metallurgy. Kommunarsk Mining-Metallurgical Institute (KGMI). Kommunarsk Metallurgical Combine. Translated from Metallurg, No. 10, pp. 36–37, October, 1989.  相似文献   

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A refined method has been developed for measurement of the localized surface strains during axial compression of cylinders. The method has been applied to 1045 steel cylinders in various conditions to study fracture under combined stress states. Because the refined measurement method is used, perturbations are observed in the strain path which would otherwise not be apparent. These perturbations precede surface fracture in every case. It is shown that geometric similarities exist between the strain perturbations in upsetting and those in trough formation preceding fracture in stretch forming of sheet material. In addition, metallographic examination of transverse sections of the upset cylinders reveals the presence of subsurface void formations prior to fracture. It is concluded that the surface fractures in upset cylinders involve localized necking of material between inhomogeneities, and it is suggested that an accurate model of this behavior may give some understanding of the influence of material parameters on fracture.  相似文献   

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The concept of dividing microvoid coalescence (MVC) ductile fracture into three constituent processes, nucleation, growth, and coalescence, is discussed, with emphasis on needs for additional analytical and experimental work. Statistical and stochastic aspects of the problem are presented. Recent work on modeling of local strains during ductile fracture, and particularly as components of fracture toughness, is summarized and discussed in light of current knowledge of ductile fracture. Such local strain modeling is especially attractive because it permits micromechanisms of fracture to be explicitly included in the fracture model. This paper is based on a presentation made at the symposium “Stochastic Aspects of Fracture” held at the 1986 annual AIME meeting in New Orleans, LA, on March 2-6, 1986, under the auspices of the ASM/MSD Flow and Fracture Committee.  相似文献   

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在热轧集装箱用钢的钢卷表面发现有细条状和近似圆点状的2种缺陷.通过对这2种缺陷进行EPMA、SEM和EDS等分析,并结合现场的轧制工艺情况,对这2种缺陷形成原因进行综合分析.分析结果表明:这2种缺陷都是在轧制过程中形成,由于集装箱用钢含Si量较高,造成除鳞难以去除,轧制油的油污与氧化铁皮压入形成了一种近似圆点的复合缺陷.  相似文献   

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The patenting process of three hot-rolled steels with carbon mass contents of 0.70% 0.90% was studied.The effect of the quenching temperature on the cementite lamellar distance in the steel was evaluated on the basis of microstructural characterization and mechanical property tests.The patenting treatment of high-carbon hot-rolled strip and its application in springs were discussed.  相似文献   

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60kg汽车用热轧高扩孔钢生产与应用   总被引:1,自引:0,他引:1  
针对传统60 kg高强钢无法满足特殊用户使用要求的现状,宝钢采用低碳低硫的成分及特定的精炼方式,结合特殊的热轧工艺,开发出一种新型60 kg高扩孔钢。通过比较分析60 kg高扩孔钢和传统60 kg高强钢的化学成分、生产工艺、金相组织、力学性能,发现高扩孔钢具有更好的综合力学性能。扩孔裂纹传播特征及扩孔裂纹扩展的机理分析表明,由于传统高强钢存在珠光体及带状特征,加速了扩孔裂纹的萌生及快速扩展;而高扩孔钢以多边形铁素体为主,有效阻碍了裂纹的扩展,因此组织均匀性是获得高扩孔率的关键因素之一。最后,以车轮轮辐为例介绍60 kg高扩孔钢的应用,60 kg高扩孔钢冲压轮辐中心孔及螺栓孔等关键部位成形良好,并通过用户成形认证。  相似文献   

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