双锥度薄壁钢锭模的研制

根据锭模在使用过程中温度场与应力场的分布原理及钢锭的轧制制原理，进行了新型试验模的设计，使锭模在使用过程中受热较均衡，各部位所受热应力基本趋于一致；并保证所浇钢锭在轧制时头部形成较浅的鱼尾。达到提高锭模使用寿命和提高钢锭成坯率的目的。     

金属陶瓷工作层钢锭模的试验分析

金属陶瓷工作层钢锭模的试验及结果分析表明，金属陶瓷用于钢锭模能使锭模浇铸过程中模体温度分布和升温较均匀平稳，铸毕打水前后模体温差小，从而提高锭模使用寿命。金属陶瓷用于钢锭模工作层是可行的，能满足生产要求。     

钢锭模内吹氩提高镇静钢质量的原理

本文从理论上分析了采用锭模吹氩对提高镇静钢质量的作用。锭模吹氩工艺有去气,去夹杂物方面的效果,并可以改善钢锭铸态组织,减少皮下气泡,还探讨了锭模吹氩对钢锭化学成分和宏观偏析的影响。     

钢锭模技术的发展现状及其趋势

叙述了为提高钢锭模寿命在改善钢锭模材质，改革锭模设计，改善锭模内表层结构，和运用系统工程管理四个方面开展钢锭模技术研究的情况，且其理论研究也在进一步深入。     

高炉铁水直接浇铸钢锭模研试

本文系统地介绍了武钢高炉铁水钢锭模的研究过程，突出了锭模解剖取样和理化性能检验等内容，并对试验和检验结果进行了分析和讨论，提出了进一步改进的措施。     

采用钢质钢锭模

为了减少在制造钢锭模时的消耗和改善钢锭的质量,研究所研究了一种贯通型钢质八角钢锭模铸造新工艺,它与活动底板组合使用,用于浇注4.6～8.2吨的钢锭。钢质钢锭模是按照“锭模套锭模”的方法铸成的。金属型模可用大尺寸的铁质或钢质钢锭模代替。钢质钢锭模的壁厚应是钢锭平均直径的0.14～0.16,而铁质模应是平均     

钢锭冷凝过程数学模型及应用

本文建立了钢锭冷凝过程的二维数学模型,采用了修正温度回升,Ｃ－Ｎ辐射边界热流、分区时间长步等新方法,应用该模型对武钢Ｄ４８１３、Ｃ８８１２、Ｄ８０９８、Ｃ９２１３四种锭型钢锭的冷凝过程进行了计算,并用实测钢锭、钢锭模表面温度的方法进行了验证,计算值、实测值一致性良好。制定出了该四种锭型的“钢锭传搁时间表”,通过分析钢锭的传搁过程,首次提出了对先浇注钢锭的装炉温度进行修正的方法。另外,还成功地研究出     

钢锭锭型与锭模设计中的关键参数研究

钢锭是当前一种应用较为广泛的基础性材料,是当前经济发展中十分重要的材料。但是我国在对钢锭进行设计生产的过程中却表现出较多的问题,尤其是在高端的钢锭设计生产中表现出来的问题更加的明显。因此,在实际设计生产中需要加强对钢锭锭型和锭模设计的改进和优化,从而减少其中存在的问题。基于此本文重点对钢锭锭型与锭模设计中的关键参数展开研究,希望能够提升钢锭锭型与锭模设计的整体质量。     

影响大型钢锭锭模使用寿命的因素

讨论了10t以上钢锭锭模的材质、结构设计、制作工艺及使用对钢锭模使用寿命的影响，提出了提高钢锭模使用寿命的措施。     

J_b12.23t扁钢锭模热应力分析

钢锭模热应力是产生锭模裂纹的主要原因,直接影响锭模寿命。钢锭模热应力的大小与锭模形状,材料性能、注温、环境温度等有关。以前由于热应力连续体模型建立相当困难,难以求得连续解,而实验测定也相当费事,一般只能测定模壁表面应力,因此这方面的研究甚少。近年来,由于电子计算机的发展和应用,使采用有限单元法数值解析热应力成为可能,且其结果与实测值有较好的吻合。本文用有限单元法计算热应力的结果,分析J_b12.25t扁锭锭模热应力分布情况。     

Finite-Element Simulation of Conventional and High-Speed Peripheral Milling of Hardened Mold Steel

A finite-element model (FEM) with the flow stress and typical fracture is used to simulate a hard machining process, which before this work could not adequately represent the constitutive behavior of workpiece material that is usually heat treated to hardness levels above 50 Rockwell C hardness (HRC). Thus, a flow stress equation with a variation in hardness is used in the computer simulation of hard machining. In this article, the influence of the milling speed on the cutting force, chip morphology, effective stress, and cutting temperature in the deformation zones of both conventional and high-speed peripheral milling hardened mold steel is systematically studied by finite-element analysis (FEA). By taking into consideration the importance of material characteristics during the milling process, the similar Johnson–Cook’s constitutive equation with hardened mold steel is introduced to the FEM to investigate the peripheral milling of hardened mold steel. In comparison with the experimental data of the cutting force at various cutting speeds, the simulation result is identical with the measured data. The results indicate that the model can be used to accurately predict the behavior of hardened mold steel in both conventional and high-speed milling.     

Thermomechanical finite-element model of shell behavior in continuous casting of steel

A coupled finite-element model, CON2D, has been developed to simulate temperature, stress, and shape development during the continuous casting of steel, both in and below the mold. The model simulates a transverse section of the strand in generalized plane strain as it moves down at the casting speed. It includes the effects of heat conduction, solidification, nonuniform superheat dissipation due to turbulent fluid flow, mutual dependence of the heat transfer and shrinkage on the size of the interfacial gap, the taper of the mold wall, and the thermal distortion of the mold. The stress model features an elastic-viscoplastic creep constitutive equation that accounts for the different responses of the liquid, semisolid, delta-ferrite, and austenite phases. Functions depending on temperature and composition are employed for properties such as thermal linear expansion. A contact algorithm is used to prevent penetration of the shell into the mold wall due to the internal liquid pressure. An efficient two-step algorithm is used to integrate these highly nonlinear equations. The model is validated with an analytical solution for both temperature and stress in a solidifying slab. It is applied to simulate continuous casting of a 120 mm billet and compares favorably with plant measurements of mold wall temperature, total heat removal, and shell thickness, including thinning of the corner. The model is ready to investigate issues in continuous casting such as mold taper optimization, minimum shell thickness to avoid breakouts, and maximum casting speed to avoid hot-tear crack formation due to submold bulging.     

A Constitutive Equation for Grain Boundary Sliding: An Experimental Approach

Although grain boundary sliding (GBS) has been recognized as an important process during high-temperature deformation in crystalline materials, there is paucity in experimental data for characterizing a constitutive equation for GBS. High-temperature tensile creep experiments were conducted, together with measurements of GBS at different strains, stresses, grain sizes, and temperatures. Experimental data obtained on a Mg AZ31 alloy demonstrate that, for the first time, dynamic recrystallization during creep does not alter the contribution of GBS to creep during high-temperature deformation. The experimentally observed invariance of the sliding contribution with strain was used together with the creep data for developing a constitutive equation for GBS in a manner similar to the standard creep equation. Using this new approach, it is demonstrated that the stress, grain size, and temperature dependence for creep and GBS are identical. This is rationalized by a model based on GBS controlled by dislocations, within grains or near-grain boundaries.     

Thermomechanical Framework for the Constitutive Modeling of Asphalt Concrete

This study is concerned with the constitutive modeling of asphalt concrete. Unlike most constitutive models for asphalt concrete that do not take into account the evolution of the microstructure of the material, this study incorporates the evolution of the microstructure by using a framework that recognizes that a body’s natural configurations can evolve as the microstructure changes. The general framework, on which this study is based, is cast within a full thermomechanical setting. In this paper, we develop models within the context of a mechanical framework that stems from the general framework for models based on the full thermodynamic framework and the resulting equations represent a nonlinear rate type viscoelastic model. The creep and stress relaxation experiments of Monismith and Secor are used for validating the efficacy of the model, and it is found that the predictions of the theory agree very well with the available experimental results. The advantages of using such a framework are many, especially when one wants to model the diverse mechanical and thermodynamic response characteristics of asphalt and asphalt concrete.     

Creep of Polymer Matrix Composites. I: Norton/Bailey Creep Law for Transverse Isotropy

This research concerns polymer matrix composite (PMC) materials having long or continuous reinforcement fibers embedded in a polymer matrix. The objective is to develop comparatively simple, designer friendly constitutive equations intended to serve as the basis of a structural design methodology for this class of PMC. Here (Part I), the focus is on extending the deformation model of an anisotropic deformation/damage theory presented earlier. The resulting model is a generalization of the simple Norton/Bailey creep law to transverse isotropy. A companion paper (Part II) by the writers deals with damage and failure of the same class of PMC. An important feature of the proposed deformation model is its dependence on hydrostatic stress. Characterization tests on thin-walled tubular specimens are defined and conducted on a model PMC material. Additional exploratory tests are identified and carried out for assessing the fundamental forms of the multiaxial creep law.     

Finite element simulation of quench hardening

In this study, an efficient finite element model for predicting the temperature field, volume fraction of phases and the evolution of internal stresses up to the residual stress states during quenching of axisymmetrical steel components is developed and implemented. The temperature distribution is determined by considering heat losses to the quenching medium as well as latent heat due to phase transformations. Phase transformations are modelled by discretizing the cooling cuves in a succession of isothermal steps and using the IT-diagrams. For diffusional transformations both Scheil's additivity method and Johnson-Mehl-Avrami equation are used, while Koistinen-Marburger equation is employed for martensitic transformation. Internal stresses are determined by a small strain elasto-plastic analysis using Prandtl-Reuss constitutive equations. Considering long cylinders, a generalized plane strain condition is assumed. The computational model is verified by several experimental measurements and by comparison with other known numerical results. Case studies are performed with St50, Ck45 and C60 type of solid and hollow steel components. The complete data and result sets provided for the verification examples establish a basis for benchmark problems in this field.     

Simplifications and improvements in unified constitutive equations for creep and plasticity—I. Equations development

An improved version of the MATMOD unified constitutive equations for creep and plasticity is developed. The new physical-phenomenological model, MATMOD-BSSOL, is the first version of the equations that is capable of modeling both solute strengthening and complex strain softening phenomena, but it combines the capabilities of previous versions in a way that simplifies the equations and minimizes the number of material constants. The major improvement present in MATMOD-BSSOL is the way in which solute strengthening is treated; both athermal flow stress plateaus and Class I steady state creep are simulated via the effects of solute concentration on the evolution of short range back stresses, which are already present in the equations to treat directional strain hardening. The physical significance of this new approach to modeling solute effects and the way in which it unifies the low and high temperature behavior of alloys are discussed.     

Creep of Polymer Matrix Composites. II: Monkman-Grant Failure Relationship for Transverse Isotropy

This research concerns polymer matrix composite (PMC) materials having long or continuous reinforcement fibers embedded in a polymer matrix. The objective is to develop comparatively simple, designer friendly constitutive equations intended to serve as the basis of a structural design methodology for this class of PMC. Here (Part II), the focus is on extending the damage/failure model of an anisotropic deformation/damage theory presented earlier. A companion paper (Part I) by the writers deals with creep deformation of the same class of PMC. The extension of the damage model leads to a generalization of the well known Monkman/Grant relationship to transverse isotropy. The usefulness of this relationship is that it permits estimates of (long term) creep rupture life on (short term) estimates of creep deformation rate. The current extension also allows estimates of failure time for various fiber orientations. Supporting exploratory experiments are defined and conducted on thin-walled specimens fabricated from a model PMC. A primary assumption in the damage model is that the stress dependence of damage evolution is on the transverse tensile and longitudinal shear traction acting at the fiber/matrix interface. We conjecture that a supplemental mechanism of failure is the extensional strain in the fiber itself. The two postulated mechanisms used in conjunction suggest that an optimal fiber angle may exist in this class of PMC, maximizing the time to creep failure.