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Effect of Adding Nitrogen on Microstructure and Property of Vanadium Microalloyed Reinforcing Bar Steel

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Journal of Iron and Steel Research International 2003年第2期10卷 45-50页

作者： LIU Shu-ping yang cai-fu ZHANG Yong-quan Central Iron and Steel Research Institute

The relation between stacking fault overlap and martensitic nucleation in Fe-17Mn-10Cr-5Si-4Ni alloy was studied. The arrayed structure of dislocations and characteristics of ε-martensite formation under stress were in-situ observed by TEM. The results reveal that ε-martensite nucleates at the top of stacking faults overlapped band, where the ordered arrayed structure of Shockley partial dislocations exists. External stress promotes ε-martensitic nucleation ability because of accelerated ordering of Shockley partial dislocations in stacking faults overlapped band.

关键词： stacking fault overlap nucleation location stress-induced ε-martensite

A Model for Precipitation Kinetics in Vanadium Microalloyed Steel

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Journal of Iron and Steel Research International 2010年第2期17卷 36-42页

作者： FANG Fang YONG Qi-long yang cai-fu SU Hang Structure Material Institute Central Iron and Steel Research Institute Beijing 100081 China

Small dispersoid particles inhibit recrystallization which is critical in controlling the grain structure of many high strength low alloy steels. A general kinetic model has been developed to predict precipitation of V（C, N） in vanadium microalloyed steels with a series of carbon and nitrogen contents. The solubility product and driving force of carbonitrides precipitated in austenite as well as the interracial energy and other parameters can be evaluated to predict Nucleation rates-Temperature （NrT） and Precipitation-Time-Temperature （PTT） diagram. By using stress relaxation tests and fitting with Avrami equation, it is possible to draw PTT diagrams. The predictions of the model coincide with results of experimental investigation on V（C, N） precipitation in austenite. The nose temperature is around 850 ℃ obtained by experiment which is different from the prediction of the model and the difference is 30 ℃, and nitrogen has more effect on the shape of ＂C＂ curve of PTT diagram than carbon that makes ＂C＂ curve move leftward significantly.

关键词： kinetic calculation model PTT curve stress relaxation nitrogen

Microstructure and Precipitation Behavior in HAZ of V and Ti Microalloyed Steel

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Journal of Iron and Steel Research International 2009年第3期16卷 68-72,77页

作者： FANG Fang YONG Qi-long yang cai-fu SU Hang China Iron and Steel Research Institute Group Beijing 100081 China

Three steels containing 0.05%C-0.1%V-0.01%N （steel V-LN）,0.05%C-0.1%V-0.02%N （steel V-HN）,and 0.05%C-0.1%V-0.02%N-0.01%Ti （steel V-HN-Ti）,which were all essentially vanadium microalloyed steels,were subjected to simulating the microstructure of a coarse grained heat affected zone （CGHAZ）. The process involved reheating to 1 350 ℃,rapid cooling to room temperature,and varying the welding heat input from 15 kJ/cm to 54 kJ/cm,including four cooling rates of t8/5 equal to 7.5 s,20 s,40 s,100 s,and the relationship of heat input to t8/5 was calculated by Quiksim software. The microstructure and precipitation of vanadium and titanium carbon nitrides are studied. The results indicate that the microstructure consists of granular bainite and some side plate ferrite in the grain boundary when the steels are produced with the highest heat input. As the heat input decreased,numerous polygonal ferrites and grain boundary ferrites appeared,and the size apparently increased. When the steel contained high nitrogen,it was considerably easier to form martensite-austenite island,which was even worse for the toughness and other properties of the steel. For the limitation of cooling time,vanadium carbon nitrides could not precipitate sufficiently,but as titanium was added,the unmelted or precipitated TiN on cooling absorbed some fraction of nitrogen in the matrix and made more precipitate positions for the round V（C,N）,and thus several useful round particles could be seen in titanium-contained steel,and most of them were around TiN. By this experiment,we can conclude that with the help of titanium,nitrogen-enhanced steel had a better prior austenite grain size,was considerably easier to precipitate,reduced free nitrogen in the matrix effectively,and provided a very effective mechanism for restriction grain growth in the HAZ.

关键词： precipitate weld input toughness nitrogen

Consensus of Second-order Multi-agent Systems with Nonsymmetric Interconnection and Heterogeneous Delays

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International Journal of Automation and computing 2011年第4期8卷 421-428页

作者： Hong-Yong yang fu-cai Wang Si-Ying Zhang School of Information Science and Engineering Ludong University Yantai 264025 PRC

In this paper, a consensus algorithm of multi-agent second-order dynamical systems with nonsymmetric interconnection and heterogeneous delays is studied. With the hypothesis of directed weighted topology graph with a globally reachable node, decentralized consensus condition is obtained by applying generalized Nyquist criterion. For the systems with both communication and input delays, it is shown that the consensus condition is dependent on input delays but independent of communication delays.

关键词： Consensus nonsymmetric interconnection second-order multi-agent systems heterogeneous delays.

Evaluation of Cracking Resistance of Copper-Bearing Age Hardening Steel Weldment

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Journal of Iron and Steel Research International 2007年第3期14卷 56-62页

作者： CHAI Feng yang cai-fu SU Hang ZHANG Yong-quan XU Zhou School of Materials Science and Engineering Shanghai Jiaotong University Shanghai 200030 China Institute of Structural Materials Central Iron and Steel Research Institute Beijing 100081 China

The weldability of a low-carbon copper-bearing age hardening steel was evaluated using cracking suscepti- bility calculation, HAZ maximum hardness measurement, and Y-groove cracking evaluation test. The results show that the hardenability characteristics and cold cracking susceptibility of the steel are very low. The results also indicate that a crack-free weldment can be obtained during the welding of this type of steel even at an ambient temperature as low as -5 ℃ as well as in an absolute humidity lower than 4 000 Pa without any preheat treatment. A slight preheat treatment can prevent the joint from cracking when welding is carried out at lower ambient temperature or higher absolute humidity.

关键词： copper-bearing age hardening steel weldability cracking resistance Y-groove cracking test

Effect of Magnesium on Inclusion Formation in Ti-Killed Steels and Microstructural Evolution in Welding Induced Coarse-Grained Heat Affected Zone

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Journal of Iron and Steel Research International 2009年第1期16卷 69-74页

作者： CHAI Feng yang cai-fu SU Hang ZHANG Yong-quan XU Zhou Central Iron and Steel Research Institute Beijing 100081 China Shanghai Jiaotong University Shanghai 200030 China

Effects of Mg on the chemical component and size distribution of Ti-bearing inclusions favored grain refinement of the welding induced coarse-grained heat affected zone （CGHAZ）, with enhanced impact toughness in Ti-killed steels, which were examined based on experimental observations and thermodynamic calculations. The results indicated that the chemical constituents of the inclusions gradually varied from the Ti-O＋Ti-Mg-O compound oxide to the Ti-Mg-O＋MgO compound oxide and the single-phase MgO, as the Mg content increased from 0.002 3M to 0.006%. A trace addition of Mg （approximately 0. 002%） led to the refinement of Ti-bearing inclusions by creating the Ti-Mg-O compound oxide and provided favorable size distribution of the inclusions for acicular ferrite transformation with a high nucleation rate in the CGHAZ, and a high volume fraction of acicular ferrite was obtained in the CGHAZ with enhanced impact toughness. Otherwise, a high content of Mg （approximately 0. 006%） produced a single-phase MgO, which was impotent to nucleate an acicular ferrite, and a microstructure comprised of a ferrite side plate and a grain boundary ferrite developed in the CGHAZ. The experimental results were confirmed by thermodynamic calculations.

关键词： non-metallic inclusion magnesium acicular ferrite coarse-grained heat affected zone (CGHAZ)

Effect of Tempering Temperature on Microstructure and Mechanical Properties of Steel Containing Ni of 9%

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Journal of Iron and Steel Research International 2011年第9期18卷 47-51,58页

作者： ZHAO Xi-qing PAN Tao WANG Qing-feng SU Hang yang cai-fu yang Qing-xiang State Key Laboratory of Metastable Materials Science and Technology Yanshan UniversityQinhuangdao066004HebeiChina Division of Structural Material Research Central Iron and Steel Research InstituteBeijing 100081China

Mechanical properties of quenching,intercritical quenching and tempering （QLT） treated steel containing Ni of 9% were evaluated from specimens subject to various tempering temperatures. The detailed microstructures of steel containing Ni of 9% at different tempering temperatures were observed by optical microscope （OM） and transmission electron microscope （TEM）. The volume fraction of austenite was estimated by XRD. The results show that high strength and cryogenic toughness of steel containing Ni of 9% are obtained when the tempering temperature are between 540 and 580 ℃. The microstructure keeps the dual phase lamellar structure after the intercritical quenching and there is cementite created in the Ni-rich constituents when tempering temperature is 540 ℃. When tempering temperatures are between 560 and 580 ℃,the reversed austenites （γ′） grow up and the dual phase lamellar structure is not clear. The γ′ becomes instable at 600 ℃. When tempered at temperature ranging from 500 to 520 ℃,the increase of dislocation density in the lamellar matrix makes both tensile strength and yield strength decrease. When tempered at 540 ℃ and higher temperature,the yield strength decreases continuously because the C and alloying elements in the matrix are absorbed by the cementite and the γ′,so the yield ratio is decreased by the γ′. There are two toughness mechanisms at different tempering temperatures. One is that the precipitation of cementite absorbs the carbon in the steel which plays a major role in improving cryogenic toughness at lower temperature. Another is that the γ′ and the purified matrix become major role at higher tempering temperature. When the tempering temperature is 600 ℃,the stability of γ′ is decreased quickly,even the transformation takes place at room temperature,which results in a sharp decrease of Charpy-V impact energy at 77 K. The tempering temperature range is enlarged by the special distribution of cementite and the lamellar structure.

关键词： steel containing Ni of 9% tempering temperature cementite reversed austenite cryogenic toughness

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Chemistry and Process Optimization of V-Microalloyed N80-Class Seamless Casing Tube

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Journal of Iron and Steel Research International 2010年第3期17卷 72-78页

作者： PAN Tao yang cai-fu MA Yue XUE Dong-mei ZHANG Yong-quan Division for Structural Materials Central Iron and Steel Research Institute Beijing 100081 China

The complex effects of different nitrogen （N） contents and thermal routines on the microstructure and mechanical properties of 33Mn2V steels for N80-Class seamless casing tube application were investigated using Gleeble simulation technique. The results showed that the N additions of 0. 014 %- 0. 021 % in the steels for the in-line normalization process （ILNP） increased the strength while the toughngss remained at a high level as compared with the steel with N content of 0. 005 %. It was also revealed that the N addition of 0. 021%could enhance the performance combination of strength and toughness in the steels by using 700 ℃ as the cooling interrupted temperature （CIT） for the non in-line normalizing process （NILNP）. It was further evidenced that the toughness was improved at expense of strength to some degree in all the steels by decreasing reheating temperature for the ILNP, while an increase of CIT for NILNP severely impaired the toughness and slightly improve the strength in the high-N steel with N content of 0. 021%. This can be attributed to the dissolution and precipitation behavior of V（C,N）. The optimization of V （C,N） precipitation could be achieved by enhancing N. The precipitation of V（C, N） in austenite was promoted by cooling to a certain temperature lower than the A,1 for the ILNP. The V（C,N） particles formed in austenite contrib- uted to grain refinement by the VN-induced nucleation of intragranular ferrite, but as a result the effect of precipitation on strengthening would become weaker due to a decrease of the precipitation of V in ferrite.

关键词： seamless tube in-line normalizing V-N microalloying reheating mechanical properties Gleeble simulation

Prediction of Deformation-Induced γ→α Transformation of 16MnNb Steel

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Journal of Iron and Steel Research International 2003年第4期10卷 59-62页

作者： YUN Bing PAN Hao yang cai-fu SHEN Jun-chang SU Hang Central Iron and Steel Research Institute

Based on the nucleation and growth theory together with the influence of deformation on driving force and nucleation site,a numerical model was developed for predicting deformation-induced transformation(DIT).The numerical results of DIT of 16 MnNb steel was presented and compared with the experimental *** calculated results are in agood agreement with the experimental ones,and the best calculated result is obtained when the constantα=0.25 for steel 16 MnNb.

关键词： 16MnNb steel phase transformation computer simulation microstructure deformation