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Influence of microstructures on Polarization Resistance and Hydrogen-Induced Cracking of a micro-alloyed steel Submitted to Different Cooling Rates

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Journal of Iron and steel Research International 2011年第S1期18卷 168-172页

作者： González M R Martins de Araújo D S Goldenstein H Alonso-Falleiros N Departamento de Engenharia Metalúrgica e de Materiais EscolaPolitécnicaUniversidade de Sao Paulo-SP-Brasil

The effect of different microstructures on the polarization resistance (Rp) and the hydrogen-induced cracking (HIC) of a micro-alloyed steel austenitized and submitted to different cooling rates was *** 19.1 x 6 x 2 mm,containing the whole thickness of the plate were extracted from a 20 mm plate and heat treated on a quenching dilatometer,were submitted to Rp and HIC corrosion *** Rp and HIC tests followed as close as possible ASTM G59 and NACE standard TM0284-2003,in this case,modified only with regard to the size of the *** samples transformed from austenite by a slow cooling (cooling rate of 0.5℃.s-1) showed higher susceptibility to hydrogen-induced cracking,with large cracks in the middle of the sample propagating along segregation bands,corresponding to the centerline of the plate *** cooling rates of 10℃.s-1,only small cracks were found in the matrix and micro cracks nucleated at non-metallic *** higher cooling rates (40℃.s-1) very few small cracks were detected,linked to non-metallic *** result suggests that structures formed by polygonal structures and segregation bands (were eutectoid microconstituents predominate) have higher susceptibility to *** predominantly formed by acicular ferrite make it difficult to propagate the cracks among non-oriented and interlaced acicular ferrite *** segregation bands containing eutectoid products also help inhibit cracking and crack propagation;segregation bands can function as pipelines for hydrogen diffusion and offer a path of stress concentration for the propagation of cracks,frequently associated to non-metallic *** resistance essays performed on the steel in theas received condition,prior to any heat treatment,showed larger differences between the regions of the plate,with a considerably lower Rp in the *** austenitization heat treatments followed by cooling rates of 0.5 e 10℃.s-1 made more uniform the

关键词： hydrogen induced cracking polarization resistance micro-alloyed steel control cooling

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Influence of Ti(C,N)precipitates on austenite growth of micro-alloyed steel during continuous casting

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China Foundry 2017年第5期14卷 421-428页

作者： Liu Yang Yang Li Zheng-liang Xue Chang-gui Cheng The State Key Laboratory of Refractories and Metallurgy Wuhan University of Science and TechnologyWuhan 430081China steelmaking Plant of WISCO Wuhan 430083China

Austenite grain size is an important influence factor for ductility of steel at high temperatures during continuous casting. Thermodynamic and kinetics calculations were performed to analyze the characteristics of Ti(C,N) precipitates formed during the continuous casting of micro-alloyed steel. Based on Andersen-Grong equation, a coupling model of second phase precipitation and austenite grain growth has been established, and the influence of second precipitates on austenite grain growth under different cooling rates is discussed. Calculations show that the final sizes of austenite grains are 2.155, 1.244, 0.965, 0.847 and 0.686 mm, respectively, under the cooling rate of 1, 3, 5, 7, and 10 ℃·s^(-1), when ignoring the pinning effect of precipitation on austenite growth. Whereas, if taking the pinning effect into consideration, the grain growth remains stable from 1,350 ℃, the calculated final sizes of austenite grains are 1.46, 1.02, 0.80, 0.67 and 0.57 mm, respectively. The sizes of final Ti(C,N) precipitates are 137, 79, 61, 51 and 43 nm, respectively, with the increase of cooling rate from 1 to 10 ℃·s^(-1). Model validation shows that the austenite size under different cooling rates coincided with the calculation results. Finally, the corresponding measures to strengthen cooling intensity at elevated temperature are proposed to improve the ductility and transverse crack of slab.

关键词： micro-alloyed steel Ti(C,N) precipitation austenite grain pinning effect

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Research on Behavior of Secondary Phase Particles Precipitation and Dissolution in micro-alloyed steel in Process of Continuous Casting

Research on Behavior of Secondary Phase Particles Precipitat...

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“第十届中国钢铁年会”暨“第六届宝钢学术年会”

作者： Zhang Qiaoying Zhang Jian Liu Guoping Wang Litao Maanshan Iron ＆ steel Co. Ltd.

The behavior of secondary phase particles precipitation in micro-alloyed steel in process of continuous casting has been studied by numerical *** secondary phase precipitation possibility was analysed in molten steel,solidification process,and *** secondary phase precipitation rule and interactant rule were found in molten steel,solidification process,austenite+ferrite and *** paper is the condition of dynamics of the secondary phase precipitation.

关键词： micro-alloyed steel secondary phase particles precipitation

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Technology Development for Controlling Slab Transverse Corner Crack of Typical micro-alloyed steels

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Journal of Iron and steel Research International 2015年第2期22卷 99-105页

作者： Hui ZHANG Chun-zheng YANG Ming-lin WANG Hong-biao TAO He-ping LIU Xue-bing WANG Central Iron and steel Research Institute Shougang Jingtang United Iron and steel Co. Ltd.

A mathematical model for simulating the fluid flow, heat transfer and solidification in the conventional mold and the chamfer mold, together with a finite element stress-strain model in the straightening process of both molds, were established for the typical niobium, vanadium, and titanium micro-alloyed steels. On the basis of both numerical analysis, the mold copper plate with an optimum chamfered shape was designed and applied in industrial tests. The predicted results from numerical simulation of fluid flow, heat transfer and solidification in the conven tional mold and the chamfer mold show that the increased chamfered angle leads to an approximately linear increase o[ the slab surface temperature, but it also causes strong flow near the slab corner. Very small chamfered length can lead to a significant increase of the temperature near the slab corner. However, with further increasing the chamfered length, the temperature of the slab corner increased slightly. The calculated results from the finite element analysis of stress-strain during the straightening process show that at the same slope width, the tangential strain on the slat） edges and corners is minimum when the chamfered angle is 30° and 45°, which is only 40° to 46° of rectangular slabs with the same cross-section area. At the same chamfered angle of 30°, when the chamfered length is controlled between 65-85 mm, the tangential strain on the part of the slab edges and corners is relatively smaller. Industrial test results show that the slab corner temperature at straightening segment increases about 100 ℃ by using chamfer mold compared to the conventional molds. The slab transverse corner cracks have been reduced more than 95° in comparison with those in the conventional mold.

关键词： micro-alloyed steel transverse corner crack chamfer mold slab

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Development of Tailored Structure and Tensile Properties of Thermomechanical Treated micro alloyed Low Carbon Dual Phase steel

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Materials Sciences and Applications 2020年第12期11卷 851-866页

作者： Hany Khalifa G. M. Megahed Taher El-Bitar Mohamed A. Taha Faculty of Engineering Ain-Shams University Cairo Egypt EZZ steel Cairo Egypt Central Metallurgical R & D Institute (CMRDI) Helwan Cairo Egypt

Direct hot rolled dual phase steel production represents a challenging route, compared with cold rolled and intercritical annealing process, due to complex and sophisticated control of the hot strip mill processing parameters. Instead, high technology compact slab production plant offers economic advantages, adequate control and prompt use of the advanced thermomechanical controlled rolling. The current work aims to obtain different structures and tensile properties by physical simulation of direct hot rolled niobium micro alloyed dual phase low carbon steel by varying the metallurgical temperatures of hot strip mill plant. This starts with adaptation of the chemical analysis of a low carbon content to fall far from the undesired peritectic region to avoid slab cracking during casting. Thermodynamic and kinetics calculations by Thermo-Calc 2020 and JMat pro software are used to define the transformation’s temperatures Ae1 and Ae3 as well as processing temperatures;namely of reheating, finishing rolling, step cooling and coiling temperatures. The results show that the increase of finishing rolling temperature from 780°C to 840°C or decreasing either of step cooling duration at ferrite bay from 7 to 4 seconds, enhances yield and tensile strengths, all due to more martensite volume fraction formation. The yield and tensile strengths also increase with decreasing coiling temperature from 330°C to 180°C, which is explained due to the increase of dislocation densities resulted from the sudden shape change during martensite formation at the lower coiling temperature in additional to the self-tempering of martensite formed at higher coiling temperatures which soften the dual phase steel.

关键词： micro-alloyed steel Dual Phase steel Thermomechanical Simulation Thermomechanical Rolling Compact Slab Production CSP Hot Strip Mill HSM

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Effect of Mo on the continuous cooling transformation behavior of Nb-Ti micro-alloyed low carbon steel

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Baosteel Technical Research 2011年第3期5卷 46-50页

作者： LI Bing ZHENG Lei Structural steel Division Research Institute Baoshan Iron ＆ Steel Co. Ltd. Shanghai 201900 China

The effect of molybdenum on the continuous cooling transformation behavior of the micro-alloyed low carbon steel containing niobium and titanium was investigated by a Gleeble 3800 thermo-mechanical simulator. The phase transformation temperature of the steel at various cooling rates was detected. The microstmcture was observed by optical microscope （OM） and scanning electronic microscope （ SEM）, and its Vickers hardness was tested. Based on these, its dynamic continuous cooling transformation （CCT） diagrams were determined. The results show that the transformation temperature from deformed austenite to acicular ferrite （AF） is decreased when Mo is added, and the formation of pro- eutectoid ferrite （F） and pearlite （P） is either inhabited or postponed. Mo can also enlarge the range of the cooling rate in forming AF, and refine the microstructure effectively.

关键词： micro-alloyed steel Mo continuous cooling transformation

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Influences of Alloying Elements on Oxidation Behavior of steels and microstructure of Oxide Scales

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Journal of Iron and steel Research International 2016年第3期23卷 231-237页

作者： Hui-bin WU Di WANG Peng-cheng ZHANG Jin-ming LIANG Sheng LIU Di TANG National Engineering Research Center for Advanced Rolling Technology University of Science and Technology Beijing

In order to figure out the oxidation behavior of steels during heating,five micro-alloyed steels were subjected to continuous and isothermal oxidation using the thermo gravimetric analyzer and the Gleeble-3500thermo-mechanical *** microstructure of oxide scales,especially the thickness fractions of Fe2O3,Fe3O4 and FeO layers,was analyzed using the scanning electron microscope（SEM）,electron probe microanalyzer（EPMA）and electron backscattered diffraction（EBSD）*** micro-alloyed steels containing alloying elements（Si,Cr,Ni and Cu）show a higher oxidation resistance compared with the low carbon *** is found that alloying elements accumulated at scale/substrate interface during high temperature *** elements function in two ways in the oxidation of steels：one is enhancing the scale/substrate interface and consequently suppressing the blister of scales;and the other is impeding the outward diffusion of iron cations from substrate to scales,resulting in the decrease of oxidation *** the diffusion of iron cations is impeded,the thickness fractions of Fe2O3 and Fe3O4of micro-alloyed steels are more than those of low carbon steels.

关键词： micro-alloyed steel high temperature oxidation oxidation kinetics microstructure oxide scale

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Effects of Vanadium on Structure and Tensile Properties of Tempcore steel Bars

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Materials Sciences and Applications 2022年第5期13卷 342-357页

作者： Hany Khalifa A. El-Kady EZZ steel Cairo Egypt

Thermomechanical processing is a metallurgical operation to produce high-strength steel bars (rebars), through combining plastic deformation with thermal processes like heat treatment, water quenching, heating, and cooling at various rates into a single process. Ribbed reinforcing steel bars (rebars) are used for the reinforcement of concrete structures. Tempcore is a unique process to produce high-yield-strength rebars from mild steel without addition of a high weight percentage of costly alloying elements. The strength of rebar originates from the formation of a surface layer consisting of quenched and tempered martensite that surrounds a core composed of ferrite and pearlite. The economic advantages of this process are significant in comparison to those processes requiring alloying elements or further metal working to improve the mechanical properties. However, when there is a limitation in the water-cooling capacity, the required volume fraction of the martensite layer can’t be accomplished particularly when rolling bigger diameters of 32 mm - 40 mm at a higher rolling speed to maintain high productivity. Accordingly, a small addition of microalloying elements vanadium or niobium could be used in combination with Tempcore process to obtain high-strength steel rebars. In this contribution, 0.06 weight percentage of vanadium is added to the Tempcore treated rebars to satisfy ASTM A 706 Standard of Rebar Grade 80 PSI [550 MPa]. In order to decrease the trials in the steel plant floor, thermodynamics equilibrium calculations are predicted by Thermo-Calc, CCT, TTT diagrams are calculated by JMat Pro and the kinetics evolution of the vanadium carbonitrides precipitates are predicted by the computational database Mat Calc. High yield strength and tensile strength are obtained due to the effect of fine dispersions of nanometer-scale vanadium carbonitrides precipitates inspected by transmission electron microscope.

关键词： Tempcore micro-alloyed steel Precipitation Hardening Thermodynamics of Equilibrium Kinetics of Formation

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