Mn系贝氏体/马氏体复相钢的研究及应用进展

Mn系贝氏体／马氏体复相钢因其工艺简单、性能良好和价格低廉等优点而得到了广泛的重视。本文回顾了Mn系贝氏体／马氏体复相钢近几年来在微观组织、强韧化机理、延迟断裂及疲劳性能等方面所取得的研究成果，简要介绍了Mn系贝氏体／马氏体复相钢在不同领域的应用情况与进展。     

建筑用耐火H型钢性能与组织的研究

对工业试制耐火H型钢的力学性能和微观组织进行了研究。分析了回火温度及时间对微观组织的影响,探讨了耐火钢的高温强化机理。结果表明,建筑用耐火H型钢在室温时的显微组织为多边形铁素体、少量珠光体和少量马氏体的混合组织,细小、弥散分布的马氏体组织是建筑用耐火H型钢保持良好高温性能的一个主要原因。高温下良好的组织稳定性有利于提高耐火H型钢的高温性能。thermo-calc热力学软件计算结果表明．Mn、Mo、Cr等合金元素能大量固溶在渗碳体中,形成合金渗碳体,有利于阻止高温回火组织粗化,保持良好的高温性能。     

Multi-phase microstructure design of a low-alloy TRIP-assisted steel through a combined computational and experimental methodology

The multiphase constitution of a transformation-induced plasticity (TRIP)-assisted steel with a nominal composition of Fe–1.5Mn–1.5Si–0.3C (wt.%) was designed, utilizing a combination of computational methods and experimental validation, in order to achieve significant improvements in both strength and ductility. In this study, it was hypothesized that a microstructure with maximized ferrite and retained austenite volume fractions would optimize the strain hardening and ductility of multiphase TRIP-assisted steels. Computational thermodynamics and kinetics calculations were used to develop a predictive methodology to determine the processing parameters in order to reach maximum possible ferrite and retained austenite fractions during conventional two-stage heat treatment, i.e. intercritical annealing followed by bainitic isothermal transformation. Experiments were utilized to validate and refine the design methodology. Equal channel angular pressing was employed at a high temperature (950 °C) on the as-cast ingots as the initial processing step in order to form a homogenized microstructure with uniform grain/phase size. Using the predicted heat treatment parameters, a multiphase microstructure including ferrite, bainite, martensite and retained austenite was successfully obtained. The resulting material demonstrated a significant improvement in the true ultimate tensile strength (～1300 MPa) with good uniform elongation (～23%), as compared to conventional TRIP steels. This provided a mechanical property combination that has not been exhibited before by low-alloy first-generation high-strength steels. The developed computational framework for the selection of heat treatment parameters can also be utilized for other TRIP-assisted steels and help design new microstructures for advanced high-strength steels, minimizing the need for cumbersome experimental optimization.     

马氏体钢中BL/M和AR/M复相组织调控方法及对性能影响的研究现状

综述了提高钢铁材料性能的马氏体钢中下贝氏体/马氏体(B_L/M)和残留奥氏体/马氏体(A_R/M)复相组织的调控方法及其强韧化机理等方面的研究进展。针对贝氏体等温淬火、淬火-配分(Q&P)、淬火-配分-回火(Q-P-T)等新型热处理工艺对微观组织特征和力学性能影响的研究现状进行了总结,并分析了钢铁材料复相组织调控工业化应用需重点突破的问题。     

Multiscale mechanics of TRIP-assisted multiphase steels: I. Characterization and mechanical testing

The mechanical behaviour of transformation-induced plasticity (TRIP)-assisted multiphase steels is addressed based on three different microstructures generated from the same steel grade. The mechanisms responsible for the work-hardening capacity and the resulting balance between strength and resistance to plastic localization are investigated at different length scales. The macroscopic mechanical response is determined by simple shear, uniaxial tension, Marciniak and equibiaxial tension supplemented by earlier tensile tests on notched and cracked specimens. It is shown that the transformation rate reaches a maximum for stress states intermediate between uniaxial tension and equibiaxial tension. At an intermediate length scale, the true in situ flow properties of the individual ferrite–bainite and retained austenite phases are determined by combining neutron diffraction and digital image correlation. This combined analysis elucidates the partitioning of stress and strain between the different constitutive phases. Based on these results, supplemented by transmission electron microscopy and electron backscattered diffraction observations, a general overview of the hardening behaviour of TRIP-assisted multiphase steels is depicted.     

铸造热锻模具钢的研究与应用

简述了精铸热锻模具国内外应用状况,对铸造模具钢的研究进展进行了研究。铸造热锻模具钢的开发研究对铸造热锻模的应用是至关重要的,铸造热锻模具钢的研究大致分为三个阶段,第一个阶段主要是直接采用商用锻造模具钢;第二阶段,是在原锻造模具钢的基础上采用微合金化,或加入单元素合金化,提高某一方面的性能;第三阶段是以性能要求为基础,结合铸态金属的性能特点及铸造工艺要求,进行全面的合金化设计,该类铸造模具钢更能满足热锻模的要求,具有高的性能和寿命。同时指出了当前精铸模具应用中存在的问题,并提出了建议。     

Effect of Sn Micro-alloying on Recrystallization Nucleation and Growth Processes of Ferritic Stainless Steels

We investigated the effect of Sn micro-alloying on recrystallization nucleation and growth processes of ferritic stainless steels. The as-received hot rolled sheets were cold rolled up to 80% reduction and then annealed at 740–880 °C for 5 min. The cold rolling and recrystallization microstructures and micro-textures of Sn-containing and Sn-free ferritic stainless steels were all determined by electron backscatter diffraction. Our Results show that Sn micro-alloying has important effects on recrystallization nucleation and growth processes of ferritic stainless steels. Sn micro-alloying conduces to grain fragmentation in the deformation band, more fragmented grains are existed in Sn-containing cold rolled sheets, which provides more sites for recrystallization nucleation. Sn micro-alloying also promotes recrystallization process and inhibits the growth of recrystallized grains. The recrystallization nucleation and growth mechanism of Sn-containing and Sn-free ferritic stainless steels are both characterized by orientation nucleation and selective growth, but Sn micro-alloying promotes the formation of γ-oriented grains. Furthermore, Sn micro-alloying contributes to the formation of Σ13b CSL boundaries and homogeneous γ-fiber texture. Combining the results of microstructure and micro-texture, the formability of Sn-containing ferritic stainless steels will be improved to some extent.     

Correlation of Yield Strength and Tensile Strength with Hardness for Steels

Hardness values as well as yield and tensile strength values were compiled for over 150 nonaustenitic, hypoeutectoid steels having a wide range of compositions and a variety of microstructures. The microstructures include ferrite, pearlite, martensite, bainite, and complex multiphase structures. The yield strength of the steels ranged from approximately 300 MPa to over 1700 MPa. Tensile strength varied over the range of 450-2350 MPa. Regression analysis was used to determine the correlation of the yield strength and the tensile strength to the diamond pyramid hardness values for these steels. Both the yield strength and tensile strength of the steels exhibited a linear correlation with the hardness over the entire range of strength values. Empirical relationships are provided that enable the estimation of strength from a bulk hardness measurement. A weak effect of strain-hardening potential on the hardness-yield strength relationship was also observed.     

多阶段压下规程分配方法在控温轧制中的应用

针对中厚板不同轧制阶段的特点,将开发出的多阶段中厚板压下规程分配方法采用变道次等负荷分配法和凸度-板形矢量分析法进行规程优化计算,用于控温过程压下规程分配。可最大程度地利用轧机能力,并可保证轧件板形和内在质量。目前在首钢不仅可稳定地在线应用,并轧制出Q460、Z15、DH36等高性能产品。     

Influence of Processing and Heat Treatment on Corrosion Resistance and Properties of High Alloyed Steel Coatings

Corrosion and abrasive wear are two important aspects to be considered in numerous engineering applications. Looking at steels, high-chromium high-carbon tool steels are proper and cost-efficient materials. They can either be put into service as bulk materials or used as comparatively thin coatings to protect lower alloyed construction or heat treatable steels from wear and corrosion. In this study, two different corrosion resistant tool steels were used for the production of coatings and bulk material. They were processed by thermal spraying and super solidus liquid phase sintering as both processes can generally be applied to produce coatings on low alloyed substrates. Thermally sprayed (high velocity oxygen fuel) coatings were investigated in the as-processed state, which is the most commonly used condition for technical applications, and after a quenching and tempering treatment. In comparison, sintered steels were analyzed in the quenched and tempered condition only. Significant influence of alloy chemistry, processing route, and heat treatment on tribological properties was found. Experimental investigations were supported by computational thermodynamics aiming at an improvement of tribological and corrosive resistance.     

多相流动淡水体系中碳钢的冲刷腐蚀行为

利用圆桶式冲刷腐蚀实验机 ,在含砂淡水体系中进行了几种碳钢的冲刷腐蚀失重实验和线性极化电阻测试 ,讨论了冲刷腐蚀作用的机理 .结果表明水流速度加快 ,含砂粒径增大 ,冲刷腐蚀失重增加 ;但当水流速度、砂粒粒径超过一定范围后 ,冲蚀失重的增加变得不明显 .碳钢在水体流动条件下的极化电阻比静态下要小得多 ,在两相含砂水流中的极化电阻比单相水流中小 .实验条件下 ,碳钢的冲刷腐蚀是机械磨损和电化学腐蚀共同作用的结果 ,但随着水流速度的增加 ,机械冲刷的贡献逐渐占主导     

Simultaneous chromizing-aluminizing coating of austenitic stainless steels

Chromium and aluminum were simultaneously co-deposited by diffusion into austenitic stainless steel substrates, by a single-step, pack-cementation process. The mechanism for the formation of diffusion-coated products on 304 and 316 stainless steels and on Incoloy 800 is discussed. The morphologies of the phases formed at the surface, i.e., an external beta layer and an underlying multiphase interdiffusion zone, are presented. The formation of the brittle, , outer layer was minimized by variations in the pack composition and activator. The coated 304 and 316 steels exhibited excellent scaling resistance upon oxidation in air at 1000°C.     

Transpassivation of Fe-Cr-Ni stainless steels

A transpassivation model was proposed for Fe-Cr-Ni stainless steels. In this model, the important steps and processes involved in transpassivation were illustrated. With some reasonable assumptions, transpassivation behaviours were predicted, such as the changes in film composition, film thickness, anodic current density and AC impedance spectrum in transpassive and secondary passive regions. It was demonstrated that these theoretical predictions were in good agreement with experimentally observed transpassivity of Fe-Cr-Ni stainless steels.     

Structure formation in laser carboborochromizing of steel Kh12M

Investigation of the processes of structure formation in laser alloying of steels and alloys is important. Surface strengthening of low- and intermediate-alloy steels by laser alloying with the use of multi-component paste coatings is of special interest.     

多相混输管道内侧的腐蚀试验

应用CFL-1型动态腐蚀试验环道系统,研究了几种管线钢在多相混输管道内不同流动状态下的腐蚀速率以及不同工艺条件下的段塞流的腐蚀速率,了解各种流型的腐蚀特性及温度、压力等工艺参数对混输管道内腐蚀的影响规律.     

Multiscale mechanics of TRIP-assisted multiphase steels: II. Micromechanical modelling

The stress and strain partitioning between the different phases of transformation-induced plasticity (TRIP)-aided multiphase steels is evaluated using a mean field homogenization approach. The change of the austenite volume fraction under straining is predicted using a micromechanics-based criterion for the martensitic transformation adapted to the case of small, isolated, transforming austenite grains. The parameters of the model are identified from the mechanical response and transformation kinetics measured under uniaxial tension for two steels differing essentially by the austenite stability. The model is validated by comparing the predictions with tests performed under different loading conditions: pure shear, intermediate biaxial and equibiaxial. An analysis of the effect of the austenite stability on strength and ductility provides guidelines for optimizing properties according to the stress state.     

An in situ high-energy X-ray diffraction study of micromechanical behavior of multiple phases in advanced high-strength steels

The micromechanical behavior of high-strength steels with multiple phases was characterized using the in situ high-energy X-ray diffraction technique. For the materials investigated, the {2 0 0} lattice strains of the constituent phases (ferrite, bainite and martensite) with similar crystal structures were determined by separating their overlapped diffraction peaks and then examining the respective changes in peak positions during deformation. Based on those experimental data, the anisotropic elastic and plastic properties of the steels were simulated using a self-consistent model for predicting the grain-to-grain and phase-to-phase interactions. The constitutive laws for describing the elastic and plastic behavior of each constituent phase were directly obtained by comparing the predicted lattice strain distributions with the measured ones. The transmission electron microscopy observations of the microstructure development verified the partitioning of plastic strains among different phases. The present investigations provide a fundamental understanding of the stress partitioning of soft and hard phases, and the different work-hardening rates of the multiphase steels.     

Analysis of higher-order corrections to the interface kinetics in the multiphase field method

The multiphase field method has been developed in material science on the mesoscopic scale as a powerful tool to simulate complex microstructure formation. There are different model formulations in the multiphase field method for the analysis of the microstructure that develops in low-carbon steels, such as γ-to-α transformation. One is the general type derived rigorously from a free-energy formulation, and another is the antisymmetric type where only dual interface interaction is taken into account. The difference between them reflects the higher-order corrections of the interface kinetics. In this paper, a comparative study of them is performed in detail. First, we show the relationship between them analytically, and then we compare their multiphase field modeling for grain growth and γ-to-α transformation numerically using equivalent model parameters in two dimensions. As a result, although we find that both models give almost the same results for the volume fraction of α-phase, they have different morphologies near triple junctions. These differences are caused by higher-order corrections of the interaction between grains.     

Current Challenges and Opportunities Toward Understanding Hydrogen Embrittlement Mechanisms in Advanced High-Strength Steels: A Review

Hydrogen embrittlement(HE) is one of the most dangerous yet most elusive embrittlement problems in metallic materials. Advanced high-strength steels(AHSS) are particularly prone to HE, as evidenced by the serious degradation of their load-bearing capacity with the presence of typically only a few parts-per-million H. This strongly impedes their further development and application and could set an abrupt halt for the weight reduction strategies pursued globally in the automotive industry. It is thus important to understand the HE mechanisms in this material class, in order to develop effective H-resistant strategies. Here, we review the related research in this field, with the purpose to highlight the recent progress, and more importantly, the current challenges toward understanding the fundamental HE mechanisms in modern AHSS. The review starts with a brief introduction of current HE models, followed by an overview of the state-of-the-art micromechanical testing techniques dedicated for HE study. Finally, the reported HE phenomena in different types of AHSS are critically reviewed. Focuses are particularly placed on two representative multiphase steels, i.e., ferrite–martensite dual-phase steels and ferrite–austenite medium-Mn steels, with the aim to highlight the multiple dimensions of complexity of HE mechanisms in complex AHSS. Based on this, open scientific questions and the critical challenges in this field are discussed to guide future research efforts.     

Methodological fundamentals of the evaluation of the weldability of structural materials using oil and gas pipes as an example

A method for evaluating weldability is proposed, and processes of welding petrochemical equipment with a wall thickness of 20–200 mm and pipelines produced from steels of almost all strength grades, starting with carbon and low-alloy steels, hot-rolled and normalized steels, steels strengthened by heat treatment and advanced low-carbon high-strength steels of the K65–K75 type, are outlined.