P91钢的形变强化行为

采用静力拉伸试验法研究了P91钢在566 ℃和室温时的形变强化与组织结构变化规律.结果表明,P91钢在室温条件下拉伸时自屈服至颈缩前的均匀塑性变形过程中的形变强化分3个阶段,颈缩至断裂前的局集塑性变形过程中的形变强化也分3个阶段.而在566 ℃时自屈服至颈缩前的均匀塑性变形过程中的形变强化为2个阶段.在局集塑性变形过程中,回火板条马氏体顺拉伸方向伸长变形的相对伸长量与颈缩量成双对数线性关系,马氏体板条束的位向朝拉伸方向转动的位向角与颈缩量也成双对数线性关系.塑性变形时位错组态出现胞状结构,随塑性变形量的增大,位错胞尺寸减小,并且顺拉伸方向伸长.形变强化能力决定了该钢在室温时的抗过载能力强.     

Strain hardening and heterogeneous deformation during twinning in Hadfield steel

We identify the role of deformation twinning and twin–twin intersections on the strain hardening behavior of Hadfield steel single crystals using strain field measurements. In situ and ex situ strain field measurements resolved at micrometer length scales are obtained using digital image correlation. Ex situ measurements reveal that macroscopic twin-bands, which are composed of a mixture of fine twin-lamella and matrix material, generate approximately 30% axial strain. This measurement is comparable to strain predictions based on twinning crystallography. In situ measurements reveal that primary and secondary twins may nucleate simultaneously, but the primary twin-system remains predominantly active with increased deformation. The intersection of primary and secondary twin-systems was directly linked to an increase in the strain hardening response.     

Parametric optimization of power in hydrostatic extrusion

The process of hydrostatic extrusion has gained great popularity in recent years because of its simplicity and low cost. The material to be extruded is in contact with the die only, whilst in conventional extrusion the material is in contact with three components, the ram, the chamber, and the die. Therefore, the power required to extrude the product is less in hydrostatic extrusion. Added to this, the frictional losses are kept to a minimum because of the hydrodynamic lubrication that takes effect at relatively high extrusion speeds, which prevents the product from coming into contact with the die.

In this study, an analytical model for studying hydrostatic extrusion is introduced. The model is used to investigate various parameters affecting extrusion, these parameters being: the die cone angle, the reduction ratio (the ratio of the billet diameter to the product diameter), the friction coefficient, the extrusion and back-pressure ratio, and the die shape. The model is extended to optimize the aforementioned parameters for securing a better product, and effecting minimum power requirement and small frictional losses. In order for it to gain recognition, the model was substantiated experimentally employing three commonly used engineering materials, the analytical and the experimental results being found to be in good agreement.     

Effect of warm extrusion on structure and properties of steel 20Kh

Conclusion Warm extrusion of steel 20Kh at 600–800° makes it possible to obtain a structure with high strength and ductile characteristics: _0.2=40–50 kg/mm², _b=50–60 kg/mm², =60–75%.Voroshilovgrad Machine Construction Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 56–57, March, 1976.     

铁素体马氏体双相钢动态加载下的应变硬化行为

利用拉伸Split Hopkinson bar实验装置,对双相钢进行不同应变率下的动态拉伸实验,并应用Johnson-Cook本构模型,对双相钢的动态拉伸性能及应变硬化行为进行分析。结果表明,双相钢具有明显的应变率敏感性;与静态加载类似,在动态加载条件下,双相钢具有较高的初始应变硬化率,随着应变的增加,应变硬化率先迅速下降,而后趋于平缓。     

Properties of high-strength titanium alloys after hydrostatic extrusion

Conclusion Alloys VT3-1, VT22, and VT15 can be deformed by hydrostatic extrusion at room temperature. The deformability of alloy VT22 is highest. Quenching from 700–750° and hydrostatic extrusion with 20–30% deformation + aging at 500–550° for 1–2 h produces the optimal combination of high strength and good ductility.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 74–76, March, 1976.     

镁合金温静液挤压研究

针对镁合金常温塑性较差、结构件强度较低的问题,进行了镁合金温静液挤压研究.采用动力学分析方法,推导了镁合金静液挤压力计算公式.在理论分析和试验研究的基础上,研制出了镁合金温静液挤压模具.在3150kN液压机上进行了镁合金温静液挤压工艺试验,得到了质量优良、强度较高的温静液挤压试件.     

Strain hardening of low-carbon manganese steels

Conclusions Low-carbon steels with a high manganese content (3–5%) are highly susceptible to strain aging, which is accompanied by hardening due to precipitation of finely dispersed cementite particles. The increase of the manganese content, due to the displacement character of the transformation of austenite, increase the amount of carbon in solution and leads to precipitation hardening similar to the intermediate transformation activated by cold plasmic deformation. The dispersed structure formed in this case ensures high strength and ductility of the material.Moscow Automobile Factory. Moscow Evening Metallurgical Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 47–51, September, 1980.     

Strain hardening of low-carbon martensitic steels

The strengthening of low-carbon martensitic steels at stages of uniform and localized deformation has been considered. The experimental data have been approximated using the Ludwik equation and linear dependence. The micro- and fine structure of experimental heats of steels and characteristics of strength, ductility, and toughness have been presented. True strain-true stress curves have been constructed. Strengthening indices for stages of uniform and localized deformation have been calculated. The procedure of calculating the plastic-deformation zone in front of the crack tip has been suggested.     

Cyclic hardening of KhVG steel

Ural Railroad Car Plant Production Union. Ufa Aviation Institute. Nizhnetagil Branch of Urals Polytechnic Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 33–34, September, 1992.     

In-flow hardening of low-carbon steel

Conclusions 1. Shapes from low-carbon steels of the St3 type can be hardened to σ_y≥500 MPa in a line of small- and medium-section mills by the method of interrupted quenching by turbulent water streams. 2. High service and technological properties are provided in the rolled stock with σ_y≥500 MPa under the condition that the surface hardness is limited to ≤320HV. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 36–38, September, 2000.     

Selective hardening in E52100 steel

A process involving the use of an argon thermal plasma jet to facilitate selective hardening of a high- carbon steel (E52100) has been studied experimentally. Cylindrical hollow specimens (approximately 8.0 cm OD by 6.0 cm ID by 9.0 cm long) were treated during this process by rapidly heating the central section of these samples to 870 °C, soaking at 870 °C for 1.0 to 2.0 min and then rapidly quenching the samples. All samples were continuously turned at an angular velocity of about 6 rev/sec during each trial run to promote uniform changes in temperature. A noncontact infrared sensor was also used to monitor and facilitate specimen temperature control throughout the heating and soaking phases of each test trial. The heat treated specimens were sectioned longitudinally, polished, and used to obtain microhardness profiles for several of these heat treated specimens. This work indicated that complete and relatively uniform through hardening was achieved in all of the test specimens. A significant advantage of this process over other more conventional hardening methods involves the very rapid heat transfer rates that are possible between a plasma jet flame and the heated object. An additional and somewhat related advantage is that undesirable overheating of specimen sections (adjacent to the heat treated zone) by conduction can be minimized. This effect may permit the production of selectively hardened steel objects that cannot be produced using more conventional technology.