冷轧工作辊热凸度及其对板形影响

冷轧过程中工作辊的热凸度变化是决定带材板形质量的重要因素,研究分析工作辊的热变形及其对板形的影响对于提高带材质量有着重要的意义.以某厂1 450 mm冷连轧生产线为研究对象,运用大型有限元分析软件ANSYS与LS-DYNA分别建立四机架与五机架的工作辊二维热凸度有限元仿真模型和三维有限元轧制仿真模型,并将2个仿真模型相...     

The effect of the thermal path to reach isothermal temperature on transformation kinetics

Experimentally determined isothermal transformation (IT) diagrams are valid only for a precisely described experimental condition; they are dependent on these conditions(e.g., the thermal path) and do not simply characterize the transformation. The concept of the true IT diagram, which depends only on the material considered and which characterizes the transformation independently of the experiment’s condition, is presented. On the basis of the true IT diagram, it is possible to predict and derive (1) the influence of the thermal path to reach isothermal temperature on transformation kinetics, (2) the kinetics of the transformation during continuous change of temperature, and (3) the influence of the temperature at which heat treatment starts on the experimental transformation diagram. Factors that influence a shape of experimental diagrams are discussed. It has been found that the most important ones are the shape of the true transformation diagram and the sign of temperature change (plus for heating, minus for cooling). Experimental transformation kinetics depend on overall activation energy, rate constant, and the time exponent derived for true transformation kinetics. Formerly with the Laboratory of Metallurgy, Delft University of Technology, 2628 AL Delft, The Netherlands     

焊接热循环参数对大线能量焊接用钢EH40热影响区组织和性能的影响

利用热模拟技术及光学显微镜、透射电镜研究了焊接热循环参数对大线能量焊接用船板钢热影响区组织和性能的影响.发现模拟焊接热影响区组织主要由粒状贝氏体、铁素体和珠光体组成,且随着峰值温度和冷却时间的变化,热影响区的组织发生较大的变化;热影响区的冲击韧性总体水平较高,均在200 J以上,冲击韧性并不随着峰值温度和冷却时间的增加而单调变化;热影响区M-A岛的数量、尺寸、分布和形态影响热影响区的韧性.      

热连轧机轧辊热辊型及冷却制度研究

针对热带钢连轧机由于带钢规格变化(主要指窄料和宽料)导致轧辊热辊型的大幅度波动,对轧辊温度场、热凸度和冷却效应进行了分析。采用有限差分法对轧辊温度场和热凸度进行了数值模拟,计算值和实测值吻合较好。进而应用该模型根据来料规格、压下规程等因素来确定工作辊冷却水轴向分布,为热带钢连轧机工作辊冷却系统的改造提供了可靠依据。     

Isotherm velocity in the axial zone of a continuously cast steel ingot

The behavior of the isotherm velocity in a continuously cast solidifying steel ingot is analyzed. An expression is obtained to describe the accelerated motion of isotherms near the thermal center of a cooled body (the center of symmetry of the body) without a phase transition. In the axial zone of the solidifying ingot, where the thermal overheating is insignificant, the isotherm velocity is caused by the action of two opposing factors: (i) the accelerated motion of isotherms that is characteristic of bodies cooled without a phase transition when the thermal center is approached and (ii) the release of the heat of phase transition. As a result, in the axial zone of an ingot made of a low-carbon steel (the initial carbon concentration C ₀ ≤ 0.2%), the liquidus isotherm velocity is almost constant, whereas the isotherm motion at the end of solidification is sharply accelerated, as in the case of purely thermal cooling. For high-carbon steels (C ₀ ≥ 1.0% C), the liquidus isotherm velocity increases, and the velocity of the isotherm at the end of solidification is constant (the effect of the eutectic transformation manifests itself). As a consequence, in low-carbon steels, the pool calculated from the liquidus and pouring-boundary isotherms has the shape of an acute-angled wedge, and the pool calculated from the isotherm of the end of solidification has a rounded shape. In contrast, in high-carbon steels, the pool shape calculated from the liquidus and pouring-boundary isotherms is rounded, and the pool shape calculated from the isotherm of the end of solidification is wedgelike. As a result of the analysis, a mathematical procedure is proposed for the calculation of the isotherm velocity in the two-phase zone and the shape and position of the pool bottom (from the corresponding isotherms) in a continuously cast solidifying steel ingot.     

Ni55Mn25Ga18Ti2高温形状记忆合金的热循环稳定性

选择双相韧化的Ni?Mn?Ga?Ti高温形状记忆合金为研究对象。制备了淬火态Ni₅₅Mn₂₅Ga₁₈Ti₂高温形状记忆合金,并对其在室温至480 ℃之间进行高达500次的相变热循环,获得了5, 10, 50, 100和500次热循环态样品。采用X射线衍射、扫描电镜、能谱仪、同步热分析仪及室温压缩等实验方法,研究了淬火态和热循环态合金样品的微观组织、相变行为、力学及记忆性能,进而分析其热循环稳定性。研究结果表明:经500次循环后,Ni₅₅Mn₂₅Ga₁₈Ti₂合金相结构和显微组织未发生明显变化,均为由非调制四方结构的板条马氏体相和面心立方富Ni的γ相组成的双相结构;随着循环次数增加,马氏体相变温度几乎不变,逆马氏体相变温度和相变滞后在循环5次后趋于稳定;抗压强度及压缩变形率波动幅度较小;形状记忆性能下降,但形状记忆应变仍保持在1.4%以上;Ni₅₅Mn₂₅Ga₁₈Ti₂高温形状记忆合金显示出良好的热循环稳定性。      

Simulation of thermal history of work rolls of finishing stand in hot strip mill: a numerical approach

Abstract

The work rolls in the finishing stands of any hot strip mill (HSM) experiences thermal shock owing to changes in temperature from initial boundary conditions. The thermal expansion owing to the change of temperature is a major contributing factor to the final shape or the profile of the strip generated at different stands of finishing stands of the HSM. A mathematical model has been developed for the prediction of temperature profile for the surface and the inner depth of the roll in the finishing stand of a HSM. The numerical result from the model calculates the temperature profile in each stand of six finishing stands of the HSM and the corresponding thermal expansion at different stands. The temperature profile and the thermal expansion of the work rolls for a complete rolling schedule have been found from this model. The measurement of the thermal expansion has been found to match closely with the calculated one.     

Marangoni convection in weld pool in CO<Subscript>2</Subscript>-Ar-shielded gas thermal arc welding

Small CO₂ additions of 0.092 to 10 vol pct to the Ar shielding gas dramatically change the weld shape and penetration from a shallow flat-bottomed shape, to a deep cylindrical shape, to a shallow concave-bottomed shape, and back to the shallow flat-bottomed shape again with increasing CO₂ additions in gas thermal arc (GTA) welding of a SUS304 plate. Oxygen from the decomposition of CO₂ transfers and becomes an active solute element in the weld pool and reverses the Marangoni convection mode. An inward Marangoni convection in the weld pool occurs when the oxygen content in the weld pool is over 80 ppm. Lower than 80 ppm, flow will change to the outward direction. An oxide layer forms on the weld pool in the welding process. The heavy oxide layer on the liquid-pool surface will inhibit the inward fluid flow under it and also affects the oxygen transfer to the liquid pool. A model is proposed to illustrate the interaction between the CO₂ gas and the molten pool in the welding process.     

多孔基定形复合相变材料传热性能提升研究进展

先进的相变储能材料是推动储能技术发展的核心和关键,在促进新能源开发和提高能源利用率中起着至关重要的作用。因在相变过程中具有高储能密度和小体积变化等优势,相变材料中应用最多的是固?液相变材料。然而在其相变过程中会发生固态向液态的转变,为了避免其在液相状态下的泄露,需要加以定形才能使用。多孔基复合相变材料在有效防止固液相变发生泄露的同时,还需兼顾定形复合相变材料传热性能的提升。本文针对这个问题进行了大量的调研,对近年来国内外在提高多孔基定形复合相变材料传热性能方面的研究进行了综合分析,介绍了三种强化传热的方法,分别是使用高导热多孔材料做载体材料、掺杂高导热纳米材料做添加剂以及构筑高导热多级结构多孔材料,并对提升复合相变材料传热性能研究方法的前景作了展望。      

Methods of Increasing the Thermal Resistance of Articles Made from Ceramic with Two-Sided Protective Coating

The influence of the size and shape of the parts of containers made of laminar ceramic on the thermal resistance of containers is qualitatively estimated. The coefficient in the estimation formula for thermal resistance which expresses the influence of shape and size on the thermal resistance of manufactured articles is broken down into several factors. These factors depend on the properties, shape, and size of the ceramic base and coating and the boundary between them. A model that shows how to reduce the influence of the individual factors in the thermal resistance formula on the thermal resistance of the entire article is proposed. A method of reducing this influence by soldering articles from individual parts of simplified shape is developed. Comparative tests of vessels made of quartz ceramic with a protective coating of Nb₂O₅ and assembled according to the proposed method were conducted. Qualitative observations of acoustic emission in the cooling process demonstrated that based on the proposed model, a substantial increase in the thermal resistance of vessels can be achieved by manufacturing the vessels from laminar ceramic.__________Translated from Poroshkaya Metallurgiya, Nos. 3–4(442), pp. 49–54, March–April, 2005.     

Formation of the thermodeformational properties of Mn-Cu-based alloys having the two-way shape memory effect

The specific features of the thermodeformational behavior of Mn-Cu-based alloys with the two-way shape memory effect are revealed, and their connection with the diffusionless fcc → fct phase transition and the forming structure is discussed. The mechanism of the reversible thermal deformation caused by directed internal stresses is considered. The factors that affect the temperature interval of the highest thermal sensitivity and the value of reversible and specific thermal deformation are found, and the possibilities of their change by additional alloying and heat treatment are studied.     

The liquidus surface of the system titanium-copper-silver

Conclusions The liquidus surface of the system titanium-copper-silver was studied by metallographic and thermal analysis methods. Projections were constructed of liquidus surface isotherms on the plane of the concentration triangle, and the shape of the simultaneous-crystallization curves of various phases (boundary curves) was determined.Translated from Poroshkovaya Metallurgiya, No. 4 (88), pp. 44–48, April, 1970.     

轧辊的热膨胀对辊型的影响

本文以1300 mm热轧机为研究对象,对其生产过程辊形随温度的变化进行实测,分析研究轧辊的热膨胀对板形的影响.     

The influence of γ′ on the recrystallization of an oxide dispersion strengthened superalloy-ma 6000e

The requirement of large, recrystallized, highly elongated grains is of primary importance to the development of suitable high temperature properties in oxide dispersion strengthened superalloys. In the present study the recrystallization behavior of MA 6000E, a recently developed Y₂O₃ strengthened superalloy produced by mechanical alloying, was examined using transmission and replication microscopy. Gradient and isothermal annealing treatments were applied to extruded and hot rolled product. It was found that conversion from a very fine (0.2 μm) grain structure to a coarse (≅10 mm) grain structure is controlled by the dissolution of the gamma prime phase, while grain shape was controlled primarily by the thermal gradient. The fine uniform oxide dispersion appeared to have only a secondary influence in determining the grain shape as columnar grains could be grown transverse to the working direction by appropriate application of the thermal gradient.     

Phase Transformation and Shape Memory Effect of Ti(Pt, Ir)

The martensitic transformation and shape memory effect of Ti₅₀(Pt, Ir)₅₀ with 5?C37.5 at. pct Ir were investigated using differential thermal analysis (DTA), high-temperature X-ray diffraction (HT-XRD), and compression tests. The austenite finish temperature, A _f, increased with increasing Ir content from 1331?K (1058?°C) in Ti-50 at. pct Pt to 1491?K (1218?°C) in Ti-12.5Pt-37.5Ir. The structure of the parent and martensite phases was identified as B2 and B19 in all tested alloys. A large strain recovery rate was obtained in Ti₅₀(Pt, Ir)₅₀ with 10 to 30 at. pct Ir. The highest shape recovery ratio was 57?pct in Ti-25Pt-25Ir after deformation at 1123?K (850?°C), followed by heating to above A _f. Using HT-XRD, the dependence of lattice parameter change on Ir content and temperature was investigated. The volume change during phase transformation from B2 to B19 was estimated using the lattice parameter of the B2 and B19 phases. Strain recovery is discussed along with volume change and lattice parameter change.     

The influence of martensite shape,concentration, and phase transformation strain on the deformation behavior of stable dual-phase steels

A continuum model is developed to examine the influence of martensite shape, volume fraction, phase transformation strain, and thermal mismatch on the initial plastic state of the ferrite matrix following phase transformation and on the subsequent stress-strain behavior of the dual-phase steels upon loading. The theory is developed based on a relaxed constraint in the ductile matrix and an energy criterion to define its effective stress. In addition, it also assumes the martensite islands to possess a spheroidal shape and to be randomly oriented and homogenously dispersed in the ferrite matrix. It is found that for a typical water-quenched process from an intercritical temperature of 760 °C, the critical martensite volume fraction needed to induce plastic deformation in the ferrite matrix is very low, typically below 1 pct, regardless of the martensite shape. Thus, when the two-phase system is subjected to an external load, plastic deformation commences immediately, resulting in the widely observed “continuous yielding” behavior in dual-phase steels. The subsequent deformation of the dual-phase system is shown to be rather sensitive to the martensite shape, with the disc-shaped morphology giving rise to a superior overall response (over the spherical type). The stress-strain relations are also dependent upon the magnitude of the prior phase transformation strain. The strength coefficienth and the work-hardening exponentn of the smooth, parabolic-type stress-strain curves of the dual-phase system also increase with increasing martensite content for each selected inclusion shape. Comparison with an exact solution and with one set of experimental data indicates that the theory is generally within a reasonable range of accuracy. Formerly Visiting Professor, Department of Mechanical and Aerospace Engineering, Rutgers University     

热连轧精轧高速钢轧辊重复上机初始辊形预报

针对热连轧精轧高速钢轧辊重复上机时存在残留磨损辊形和残留热辊形影响初始辊形的问题,分析了残留磨损辊形和残留热辊形对板形控制精度的影响及难点,得出轧辊温度场是高速钢轧辊重复上机初始热辊形最佳表征方式的结论,提出高速钢轧辊下机后空冷过程温度场建模思路,并建立轧辊空冷过程温度场计算模型。在此基础上,基于热连轧生产线二级系统框架,研究形成了高速钢轧辊重复上机初始辊形预报技术设计方案,并在首钢京唐公司1 580 mm热连轧生产线应用。应用结果表明,该技术对实现热连轧精轧高速钢轧辊更高效应用和提高板形控制精度有显著效果。     

中厚板规程负荷分配中轧辊凸度协调分配方法

在中厚板轧机无液压弯辊条件下,为防止传统等负荷分配方法造成的板形问题,提出一种轧辊凸度协调负荷分配方法。分析了轧辊凸度对板形的影响,通过轧辊热凸度和轧辊磨损软测量模型得到了实时轧辊凸度,根据轧辊凸度的变化而调整规程板形系数以获得更加合理的负荷分配规程和良好的板形控制效果。实际应用结果表明,应用该方法后中浪和边浪等板形问题明显减少,具有良好的应用价值。     

冷连轧升降速过程板形控制工艺润滑制度优化

 冷连轧机组在带钢升降速过程中,轧制速度会出现频繁的、较大程度的波动,轧制变形区的摩擦因数也会随之发生较大的波动,引起轧制压力来回波动,从而造成升降速阶段的板形相较平稳阶段的板形而言呈现出大幅度变差的问题。工艺制度优化对于摩擦因数引起的板形问题非常有效,因此,首先分析了不同乳化液浓度、初始温度和流量下的带钢在升降速过程中板形的变化过程。针对升降速阶段板形缺陷,采用分段离散法将带钢分别沿横向和纵向分成若干条元,提出升降速过程中板形横向目标函数和纵向目标函数,进而构造出升降速过程中板形动态变化目标函数,实现对轧制过程中板形波动在横向和纵向上的综合控制。由于乳化液浓度和初始温度在轧制过程中无法改变,所以结合板形目标函数,以带钢不发生打滑和热划伤、各机架轧制力不超过限定轧制力为约束条件,提出乳化液浓度和初始温度优化设定函数;乳化液流量优化针对频繁变化的局部浪形缺陷能够起到有效控制,因此乳化液流量一般随轧制速度呈非线性变化,以出口板形波动最小为控制函数,以不发生打滑和热划伤、各机架乳化液总量不超限为约束条件,提出乳化液流量跟随速度优化函数。最后将优化模型应用于国内某钢厂冷连轧机组,根据优化前后轧制力分布、带钢板形云图可知现场应用效果良好。