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Influence of Vanadium on Fracture Splitting Property of Medium Carbon Steel

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Journal of Iron and Steel Research International 2016年第5期23卷 475-483页

作者： Wei-jun HUI Cheng-wei SHAO Yong-jian ZHANG Si-lian CHEN Han DONG School of Mechanical Electronic and Control Engineering Beijing Jiaotong University Beijing 100044 China Central Iron and Steel Research Institute Beijing 100081 China

The fracture splitting property of medium carbon steel 37MnSiS microalloyed with V up to 0. 45% was investigated by using simulated fracture splitting test,for the development of new crackable medium carbon steel to manufacture high performance connecting rod. Conventional high carbon steel C70S6 was used for comparison. The results show that the volume fraction of both ferrite and V-rich M（ C,N） particles increases,and the pearlite interlamellar spacing decreases with increasing V content,which in turn results in gradual increase of strength and decrease of ductility and impact energy. The fracture splitting property of the tested steel could be improved significantly due to the increase of V content mainly through the precipitation hardening mechanism of fine M（ C,N） precipitates. The fraction of brittle cleavage fracture in the crack initiation area increases noticeably with increasing V content and full brittle cleavage fracture surface could be obtained when V content was increased to 0. 45%. It is concluded that medium carbon steel with V content higher than about 0. 28% possesses not only comparable or even higher mechanical properties with those of conventional steel C70S6,but also excellent fracture splitting property,and therefore,is more suitable to fabricate high performance fracture splitting connecting rod.

关键词： microalloyed medium carbon steel fracture splitting vanadium precipitation hardening microstructure

development of Nb-V-Ti Hot-Rolled high Strength Steel With Fine Ferrite and Precipitation Strengthening

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Journal of Iron and Steel Research International 2009年第4期16卷 72-77页

作者： YI Hai-long DU Lin-xiu WANG Guo-dong LIU Xiang-hua State Key Laboratory of Rolling technology and Automation Northeastern University Shenyang 110004 Liaoning China

A hot-rolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductile-brittle transition temperature （DBTT） lower than -70℃ has been developed in laboratory. The results show that adopting finishing rolling temperature of around 800℃ is rational, and coiling temperature is between 400 and 500℃ The strength of developed 700 MPa hot-rolled high strength steel is derived from the cumulative contribution of fine grain size, dislocation hardening and precipitation hardening. The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength, and good elongation and toughness are predominantly due to fine grain ferrite.

关键词： high strength steel precipitation hardening ductile-brittle transition temperature fine grain strengthening

Correlation between Primary and Secondary Recrystallization Texture Components in Low-temperature Reheated Grain-oriented Silicon Steel

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Journal of Iron and Steel Research International 2016年第11期23卷 1234-1242页

作者： Gong-tao LIU Zhi-qiao LIU Ping YANG Wei-min MAO School of Materials Science and Engineering University of Science and Technology Beijing

Low-temperature slab-reheated grain-oriented silicon steel is characterized by a sharp {411}〈148〉 primary recrystallization texture. To date, the influence of this texture on secondary recrystallization is not clear. Microtextures in primary and secondary reerystallized sheets of low-temperature reheated grain-oriented silicon steel were examined using electron backscatter diffraction. By comparing the textures and microstructures of specific primary reerystallized grains neighboring secondary grains with those of other primary grains, the influences of primary re- crystallization textures and microstructures on the orientations of secondary grains were investigated. Results show that for low-temperature reheated graiworiented silicon steel, the primary recrystallization sheet comprises { 411 } 〈148〉, {111}〈112〉, and {001}〈120〉 texture componems. During secondary recrystallization, the {111}〈112〉 primary recrystallized grains were easily consumed by abnormally grown Goss, deviated Goss, Brass, or {210}〈001〉grains ;the { 411 }〈148〉 primary recrystallized grains were more resistant to being swallowed; and the {001} 〈120 grains were the most resistant to being consumed. For a particular primary grain, the distribution of its surrounding grain boundaries determined how easily it is consumed during secondary recrystallization. Primary grains surrounded by 20°- 45° grain boundaries were consumed much earlier than those having grain boundaries above 45°, which is in accordance with high-energy grain boundary theory. In addition, special ∑9 boundaries between {411}〈148〉 and Goss grains move more slowly than ∑9 boundaries between {111 }〈112〉 and Goss grains, which is attributed to the different positions of 〈110〉 rotation axis with respect to the normals of grain boundaries.

关键词： grain-oriented silicon steel secondary recrystallization texture low-temperature slab reheating

Carbide Evolution in high Molybdenum Nb-microalloyed H13 Steel during Annealing Process

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Journal of Iron and Steel Research International 2015年第4期22卷 330-336页

作者： Tian-sheng LI Fu-ming WANG Chang-rong LI Guo-qing ZHANG Qing-yong MENG State Key Laboratory of Advanced Metallurgy University of Science and Technology Beijing School of Mechanical Engineering Hunan Institute of Technology School of Materials Science and Engineering University of Science and Technology Beijing

Based on the Thermo-Calc thermodynamic software, the type of equilibrium precipitated carbides and their contents in high Mo Nb-microalloyed H13 steel （NMH13 steel） were calculated. The composition, morphology, and distribution of carbides after spheroidal annealing of two forged experimental steels were comparatively examined by means of optical microscopy （OM）, scanning electron microscopy （SEM）, electron dispersive spectroscopy （EDS） and transmission electron microscopy （TEM）. VC, M23 C6 and M6C are identified in H13 steel after spheroidizing annealing, while （V,Nb）C, M23C6 , M2C and M6C are observed in NMH13 steel. Moreover, it is found that the ad- dition of Nb significantly enhances the stability of MC phase and the high Mo content accelerates the precipitation of small rod-shape M2C phase in NMH13 steel. The amount of the fine carbides in NMH13 steel obviously increased with M2 C and M6 C precipitated from the ferrite phase, which is in accordance with the results of thermodynamic cal- culations.

关键词： niobium microalloying high molybdenum H13 steel spheroidizing annealing carbide

Hot Deformation Behavior of Vanadium-microalloyed Medium-carbon Steel for Fracture Splitting Connecting Rod

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Journal of Iron and Steel Research International 2015年第7期22卷 615-621页

作者： Wei-jun HUI Si-lian CHEN Cheng-wei SHAO Yong-jian ZHANG Han DONG School of Mechanical Electronic and Control EngineeringBeijing Jiaotong University Central Iron and Steel Research Institute

Single compression tests were carried out with a Gleeble-3800 thermal simulator to investigate hot deform- ation behavior of two vanadium-microalloyed medium-carbon steels for fracture splitting connecting rod. The tests were performed to a total true strain of 0.92 at true strain rates ranging from 10-2 to 10 s-1 and deformation temper- ature of 900--1 150 ℃, The results show that hot deformation behavior of the tested steels is similar to that of con- ventional medium-carbon microalloyed steels and dynamic recrystallization is easier to occur at higher deformation temperature and lower strain rate. The austenite deformation resistance and activation energy of deformation increase with increasing vanadium content from 0.15% to 0. 28% and thus the starting time of dynamic recrystallization was delayed. Finer recrystallized austenite grain could he obtained at higher strain rate, lower deformation temperature and higher vanadium content. TEM observation of the specimens quenched just before and after deformation reveals that vanadium is mainly in dissolved solute condition in austenite and thus affects the dynamic recrystallization behavior of the tested steels mainly through solute-drag effect.

关键词： vanadium microalloyed medium-carbon steel hot deformation dynamic recrystallization fracture splitting connected rod

high Temperature Oxidation Resistance of 9Ni Steel

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Journal of Iron and Steel Research International 2014年第10期21卷 956-963页

作者： Yi-zhi LIU Cai-fu YANG Feng CHAI Tao PAN Hang SU Institute of Engineering Steel Central Iron and Steel Research Institute

Oxidation rates and scale/steel interface configuration of 9Ni steels were investigated at 1000--1 250 ℃ in air. The results revealed that Cu addition caused high temperature oxidation resistance to deteriorate. high tempera ture oxidation rates increased and scale/steel interface configuration became complicated due to Cu addition. Scale/ steel interface appeared to be network above certain temperature. Temperature required to form network scale/steel interface dropped more than 100 ℃ for 1.5% Cu-containing steel. （Fe,Ni,Cu）x Oy in inner oxidation layer dissocia ted to Fe-Ni-Cu phase and released active oxygen which can react with base steel easily. So the inner oxidation layer became the second source of oxidizing agent besides atmosphere. Internal stress at austenite grain boundary caused local oxide to fragment. So the scale/steel interface appeared to be network. Liquid Si-rich phase formed at sufficient ly high temperature. Penetration of the liquid Si-rich phase along austenite grain enhanced austenite grain oxidizing.

关键词： 9Ni steel high temperature oxidation scale/steel interface Thermo-Calc calculation

Effect of Niobium on Dynamic Recrystallization Behavior of 5%Ni Steel

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Journal of Iron and Steel Research International 2013年第6期20卷 38-44页

作者： LEI Xiao-rong DING Qing-feng CHEN Yuan-yuan RUI Xiao-long LI Shu-rui WANG Qing-feng State Key Laboratory of Metastable Materials Science and technology Yanshan University Research and development Center Wuhan Iron and Steel Company

The single-pass hot compressions of two 5%Ni steels with and without niobium addition at different temperatures of 800-1 150℃and strain rates of 0.01-1s-1 were performed by using a Gleeble-3500 thermal simulator and the effect of niobium on the dynamic recrystallization （ DRX ） behavior was *** results showed that the niobium addition of 0.04% can retard DRX in 5%Ni steel significantly by increasing the activation energy for DRX from 394 to 462kJ / *** critical strain required for starting DRX in 5%Ni steel was increased by 0.04-0.10 with niobium addition when the steel was deformed at a strain rate of 0.01s-1 and temperatures varied from 950 to 1 000℃.The critical temperature required for starting DRX in 5%Ni steel was also increased from 1 000 to 1 050℃ with niobium addition when the steel was deformed at a strain rate of 0.1s-1 .Such a retarded DRX occurring in Nb-added 5%Ni steel can be attributed to the pinning effect of precipitates containing niobium.

关键词： 5%Ni steel dynamic recrystallization niobium precipitation pinning effect

Hot Deformation Behavior of GH738 for A-USC Turbine Blades

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Journal of Iron and Steel Research International 2015年第11期22卷 1043-1048页

作者： Li WANG Gang YANG Ting LEI Shu-biao YIN Lu WANG Faculty of Metallurgical and Energy Engineering Kunming University of Science and Technology Central Iron and Steel Research Institute Kunming Metallurgy College

The hot deformation characteristics of GH738 superalloy over the temperature range of 1000 °C to 1 200 °C and strain range of 0.01 s^-1 to 10.0 s^-1 under a strain of 1.0 s^-1 were investigated through hot compression tests with a Gleeble-1500 simulation machine. The flow stress reached peak value before flow softening occurred. The average apparent activation energy（Q） of GH738 was calculated to be 430 k J/mol, and the stress index（n） is approximately 4.08. The processing map was developed based on flow stress data and dynamic materials model（DMM）. The map shows a dynamic recrystallization（DRX） domain in 1 050 °C to 1150 °C and 0.01 s^-1 to 1.0 s^-1 strain rate range with a peak efficiency of 45%, which is considered to be the optimum region for hot working. Moreover, the materials undergo flow instability in the temperature range of 1000 °C to 1050 °C and strain range of 1.0 s^-1 to 10.0 s^-1, and adiabatic shear bands can be observed in this domain.

关键词： hot deformation GH738 processing map turbine blade ultra-supercritical technology

Effect of Niobium on Isothermal Transformation of Austenite to Ferrite in HSLA Low-Carbon Steel

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Journal of Iron and Steel Research International 2007年第3期14卷 51-55页

作者： CAO Jian-chun LIU Qing-you YONG Qi-long SUN Xin-jun Department of Materials and Metallurgy Engineering Kunming University of Science and Technology Kunming 650093 Yunnan China Institute of Structural Materials Central Iron and Steel Research Institute Beijing 100081 China

Using thermomechanical simulation experiment, the kinetics of the isothermal transformation of austenite to ferrite in two HSLA low-carbon steels containing different amounts of niobium was investigated under the conditions of both deformation and undeformation. The results of optical microstructure observation and quantitative metallography analysis showed that the kinetics of the isothermal transformation of austenite to ferrite in lower niobium steel with and without deformation suggests a stage mechanism, wherein there exists a linear relationship between the logarithms of holding time and ferrite volume fraction according to Avrami equation, whereas the isothermal transformation of austenite to ferrite in high niobium steel proceeds via a two stage mechanism according to micrographs, wherein, the nucleation rate of ferrite in the initial stage of transformation is low, and in the second stage, the rate of transformation is high and the transformation of residual austenite to ferrite is rapidly complete. Using carbon extraction replica TEM, niobium carbide precipitation for different holding time was investigated and the results suggested that NbC precipitation and the presence of solute niobium would influence the transformation of austenite to ferrite. The mechanism of the effect of niobium on the isothermal transformation was discussed.

关键词： niobium transformation ferrite austenite