棒材四道次连轧过程中轧件变形的三维有限元模拟

采用全三维大变形热力耦合弹塑性有限元法对实际的四机架合金钢棒材连轧过程中轧件的变形进行了模拟 ,模拟结果与实际情况基本吻合 .     

Simplification of heat treatment process in a tool steel by aluminium addition

A novel concept for simplification of heat treatment process in a tool steel by the addition of aluminium has been proposed in this research. The addition of 1.08?wt-% aluminium leads to an approximately fully pearlitic state, of which the cementite lamellae are largely spheroidised. Excessive addition of 1.58?wt-% aluminium would result in the formation of a large amount of δ-ferrite. These results are mainly attributed to the synthetic effect of aluminium on the driving force of pearlite transformation and the inter-spacing distance between the proeutectoid carbides. The mechanical properties’ analyses show that aluminium has promising potential to substantially simplify the processing method for developing a relative low-cost mould steel without the concomitant mechanical properties’ reductions.     

Finite element simulation of the steel plates hot rolling process

In this paper we discuss our finite element procedure for simulating the hot rolling of flat steel products. We couple an Eulerian rigid‐viscoplastic model of the steel plates deformation to a Lagrangian elastic model of the rolls deformation. This latter model incorporates the bending deformation of the work rolls supported by the back‐up rolls and the flattening of the contact areas (Hertz problem) via an enhanced beam model. The finite element model is validated comparing its predictions with actual industrial measurements and then it is used to analyse different rolling set‐ups. Copyright © 2001 John Wiley & Sons, Ltd.     

Texture comparison of an ordinary IF steel and a high-strength IF steel under ferritic rolling and high-temperature coiling

The present work was performed to investigate the texture difference of an ordinary Ti-IF steel and a high-strength Ti-IF steel under ferritic hot rolling and high-temperature coiling. Comparing with the completely recrystallized textures of the ordinary IF steel, the textures of the high-strength IF steel were still deformed textures. The texture difference for the two steels is related to high P content in the high-strength IF steel which prevents the recrystallization during the coiling process. For the ordinary IF steel, the texture components were mainly very weak {001}110 orientation at the surface, and partial 110//RD (rolling direction) textures focused on {223}110 orientation and 111/ND (normal direction) texture at the mid-section and 1/4-section. For the high-strength IF steel, the texture components were mainly of {110}001 orientation at the surface and of a sharp 110//RD texture from {001}110 to {223}110 and weak 111/ND texture at the mid-section and 1/4-section.     

Thermodynamic constitutive model for load-biased thermal cycling test of shape memory alloy

This paper presents a three-dimensional calculation model for martensitic phase transformation of shape memory alloy. Constitutive model based on thermodynamic theory was provided. The average behavior was accounted for by considering the volume fraction of each martensitic variant in the material. Evolution of the volume fraction of each variant was determined by a rate-dependent kinetic equation. We assumed that nucleation rate is faster for the self-accommodation than for the stress-induced variants. Three-dimensional finite element analysis was conducted and the results were compared with the experimental data of Ti–44.5Ni–5Cu–0.5 V (at.%) alloy under bias loading.     

Shape memory and thermo-mechanical properties of shape memory polymer/carbon fiber composites

In this study, chopped carbon fiber reinforced trans-1, 4-polyisoprene (TPI) was developed via a proposed new manufacturing process with the aim of improving weak mechanical properties of bulk TPI bulk. Specimens of the developed shape memory polymer (SMP) composites were fabricated with carbon fiber weight fraction of 5%, 7%, 9%, 11% and 13%, respectively. Measured are the effects of chopped carbon fiber and temperature on: (a) shape recovery ratio and rate; (b) stress–strain relationship; (c) maximum tensile stress, strain and Young’s modulus; and (d) maximum stress and residual strain under a constant strain cyclic loading. In addition, SEM micrographs were also presented to illustrate the fracture surface. The present experimental results show that the SMP with 7% carbon fiber weight fraction appears to perform best in all the tests. This indicates that the 7% carbon fiber weight fraction could be the optimum value for the SMP developed using the proposed manufacturing process.     

新型钢板滚切剪剪切机构运动学分析

通过对新型滚切剪空间剪切机构的原理分析,建立以关键点坐标为变量的剪切机构显式三维非线性轨迹方程,并对确定导向杆与机架铰接点位置的求解理论给予修正。以某大型钢厂2 800 mm单轴双偏心滚切剪的研发项目为依托,对剪切机构的运动轨迹进行模拟仿真。上下剪刃重叠量、刀弧水平偏移量的计算结果表明,应用显式轨迹方程组及修正的导向杆约束理论,是提高轨迹求解精度、优化杆件尺寸、降低刀弧水平位移量、提高剪刃重叠量均匀度的重要手段。现场剪机重叠量、刀弧水平综合位移量的实际值及高质量的钢板剪切断面也证实了上述剪切机构运动学理论及导向点约束修正理论的正确性。     

Effects of molybdenum content on the structure and mechanical properties of as-cast Ti-10Zr-based alloys for biomedical applications

The effects of molybdenum on the structure and mechanical properties of a Ti-10Zr-based system were studied with an emphasis on improving the strength/modulus ratio. Commercially pure titanium (c.p. Ti) was used as a control. As-cast Ti-10Zr and a series of Ti-10Zr-xMo (x = 1, 3, 5, 7.5, 10, 12.5, 15, 17.5 and 20 wt.%) alloys prepared using a commercial arc-melting vacuum pressure casting system were investigated. X-ray diffraction (XRD) for phase analysis was conducted with a diffractometer. Three-point bending tests were performed to evaluate the mechanical properties of all specimens. The experimental results indicated that these alloys had different structures and mechanical properties when various amounts of Mo were added. The as-cast Ti-10Zr has a hexagonal α′ phase, and when 1 wt.% Mo was introduced into the Ti-10Zr alloy, the structure remained essentially unchanged. However, with 3 or 5 wt.%, the martensitic α″ structure was found. When increased to 7.5 wt.% or greater, retention of the metastable β phase began. The ω phase was observed only in the Ti-10Zr-7.5Mo alloy. Among all Ti-10Zr-xMo alloys, the α″-phase Ti-10Zr-5Mo alloy had the lowest elastic modulus. It is noteworthy that all the Ti-10Zr and Ti-10Zr-xMo alloys had good ductility. In addition, the Ti-10Zr-5Mo and Ti-10Zr-12.5Mo alloys exhibited higher bending strength/modulus ratios at 20.1 and 20.4, respectively. Furthermore, the elastically recoverable angles of these two alloys (26.4° and 24.6°, respectively) were much greater than those of c.p. Ti (2.7°). Given the importance of these properties for implant materials, the low modulus, excellent elastic recovery capability and high strength/modulus ratio of α″ phase Ti-10Zr-5Mo and β phase Ti-10Zr-12.5Mo alloys appear to make them promising candidates.     

Application of nanoengineering to research and development and production of high strength steel sheets

Abstract

The design concepts and properties of three unique high strength steel sheets developed utilising nanoengineering are reviewed. The first steel is developed by optimising the distribution of nanoprecipitates and exhibits low yielding ratio in spite of being strengthened by grain refinement and precipitation hardening. The second is the ferrite single phase tensile strength 780 MPa grade advanced high strength steel sheet utilising the thermally stable nanosized precipitates, which possesses significantly well balanced elongation and stretch flangeability. These two were already commercialised. The last is the ultrahigh strength steel, of which the formability is enhanced by optimising the combination of hard phases. The steel consists of bainite, retained austenite and tempered martensite and exhibits 35% of elongation with 1470 MPa of tensile strength. Although further optimisation of the composition and the processing are needed to produce and commercialise the steel, the results indicate that the approach has the potential to improve formability dramatically.     

Structure and hot-rolled reinforcement rods properties evolution in the process of long service life

The physical nature of mechanical properties of hot-rolled reinforcement rods degradation during long-life operation is established by methods of transmission diffraction electron microscopy. It is shown that strength and plasticity properties decrease is due to cementite plates cutting and dissolution, microcracks formation process as a result of interstitial phase inclusions creation in the near-surface layer of material.     

Strain hardening behavior of a TRIP/TWIP steel with 18.8% Mn

Tensile tests were carried out to study the strain hardening behavior of a TRIP/TWIP steel with 18.8% manganese. The results indicated that the true stress-strain curve can be divided into 4 stages in tension testing. Material is in an elastic region when the true strain is below 0.06. In the initial stage of the plastic deformation (? = 0.06-0.14), ?-martensite was preliminarily formed, and that austenite transformed to α-martensite through the ?-martensite formation. When the true strain was between 0.14 and 0.35, the stacking fault energies were elevated by the increase of strain energy, deformation twinning occurred instead of the ?-martensite formation. The second derivative of the stress-strain curve satisfied the condition d²σ/d?² > 0. Twinning induced plasticity dominated this stage. In the last plastic deformation stage (? = 0.35-0.45), γ → α transformation occurred at the crossing of twins, and α-martensite grew along the thickness of the twinned regions.     

Dynamic impact behavior of Ni-rich and Ti-rich shape memory alloys

Stress vs. strain curves of two kinds of Ti–Ni shape memory alloys under dynamic compressive loading condition were obtained by the split Hopkinson pressure bar experiment. One is Ni-rich, 50.75Ni–49.25Ti (at%), alloy and the other is Ti-rich, 49.5Ni–50.5Ti (at%). The former exists as austenite phase to show superelastic behavior at the room temperature, and the latter is martensitic phase at the room temperature. The dynamic stress–strain curves were compared with quasi-static compressive test results. The Ni-rich specimen displayed a much higher stress level at the high strain rate than at the quasi-static test, but the Ti-rich specimen exhibited a stress level alike in the two types of tests. Temperature measurement on the surface of the impact specimens was carried out during the impact test. The temperature rising was about 3–5 °C in the considered test conditions.     

Application of the cohesive zone model for analysing the edge crack propagation of steel sheet in the cold rolling process

In the cold rolling process, the expansion and coalescence of micro‐defects can make steel sheet quality descend and create edge crack in the steel sheet. And the edge crack can cause the strip rupture completely. In this research, the cohesive zone model (CZM) was used to analyse the initiation and propagation of edge crack in the cold rolling process with the non‐reversing two‐high mill. A bi‐linear traction–separation law was utilized which is primarily given by the CZM parameters including the cohesive stress, T, and the cohesive energy, Γ. Compared with other popular models such as the Gurson–Tvergaard–Needleman (GTN) model, the CZM presents certain advantages because it requires a smaller number of parameters to be defined. Comparison results of the experiments and simulation illustrated that the CZM can provide accurate prediction for the propagation of edge crack in the cold rolling process. Parametric analysis was carried out and showed that the extent of the crack propagation increases with the increasing of the reduction ratio.     

冷连轧机动态过程特性的建模与仿真

 在分析冷连轧机组生产过程基础上，建立了冷连轧机动态过程特性的数学模型，在模型中采用新的轧机辊系负载方程，并完成了冷连轧机组的仿真软件． 分析了热轧带钢性能参数波动以及板厚控制系统设定参数扰动对板带厚度精度的影响．     

轧制工艺对316L不锈钢组织和耐蚀性能的影响

为探索改善不锈钢耐腐蚀性能的途径,对316L不锈钢施加相同变形量的同步轧制和异步轧制,利用X射线衍射、透射电镜观察、电化学测量和扫描电镜表面观察研究了轧制工艺对钢的显微组织和腐蚀性能的影响.结果表明,经过异步轧制后显微组织中出现大量孪晶界,优化了晶界结构,在酸性介质中的晶间腐蚀敏感性明显减轻;而经过同步轧制后,样品呈现出高位错密度的显微组织,在酸性介质中的耐腐蚀性能降低.异步轧制后耐蚀性能得到改善是由于大量孪晶界的形成优化了晶界结构.     

13MnNiMoNbR钢板在卷制过程中的断裂分析研究

通过试验室运用检测手段,对材料断裂分析作出的试验结果,进行真实全面的科学认证。     

铜包铝复合材料轧制变形过程模拟及轧制力计算公式

基于对铜包铝双金属复合材料轧制变形过程进行的有限元模拟,建立了双金属复合材料轧制变形分区模型,可分为弹性区、单材料塑性区、后滑区、揉轧区和前滑区.以铜的体积分数为变量,对不同铜含量的铜包铝复合材料的轧制过程进行模拟,在单一材料轧制力理论计算公式的基础上,提出了双金属复合材料轧制力的理论计算公式,通过对铜包铝复合材料轧制的试验和不同压下率下的铜包铝双金属复合材料轧制成形的有限元模拟,对所推导出的轧制力公式进行了验证.     

Magnetic properties of grain oriented ultra-thin silicon steel sheets processed by conventional rolling and cross shear rolling

A new procedure consisting of the cross shear rolling (CSR) and the subsequent tertiary recrystallization annealing under dry hydrogen atmosphere was developed to produce the grain oriented ultra-thin silicon sheets less than 0.1 mm with high magnetic property performance. For comparison, the conventional rolling (CR) was also used to process the grain oriented ultra-thin silicon steel sheets. The effect of processing parameters on magnetic properties of the grain oriented ultra-thin silicon steel sheets was investigated. With the increase of annealing temperature and holding time, magnetic properties of the sheets processed by both rolling methods reach saturation as the result of the proceeding of the tertiary recrystallization. The thin sheets rolled by CSR did achieve better magnetic properties than those rolled by CR.     

Surface nanocrystallization of SAE 1008 steel by single and multipass thread rolling process

In this study, the layers are investigated which are obtained on the surfaces of the single and multi‐pass thread rolled screws. It is observed that deformation is more homogenous depending on the pass number and thread laps failure do not form on the 3‐passed threads. A nanocrystallized layer that thicknesses and size depends on deformation amount is determined on the surfaces of the thread rolled SAE 1008 steel. While top of this layer has finer grain sizes, depending on the deformation amount grains coursed and oriented by the deformation direction. The finer grains are observed in the single pass thread rolled sample as size of 136 nm at the 15 μm inside from the surface of the root of the thread. Compared with bulk material, significant hardness increase is observed on the surfaces of the all thread rolled samples. The effect of pass number on the hardness is very low, increases of the pass number, hardness increases slightly. But thicknesses of layer are enhanced to increase the pass number.