Guangzhou Zhujiang Steel Co.

Guangzhou, China

Guangzhou Zhujiang Steel Co.

Guangzhou, China
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Huo X.-D.,Jiangsu University | Mao X.-P.,Guangzhou Zhujiang Steel Co. | Lu S.-X.,Jiangsu University | Lin Z.-Y.,China Institute of Technology | Chen Q.-L.,China Institute of Technology
Beijing Keji Daxue Xuebao/Journal of University of Science and Technology Beijing | Year: 2011

Optical microscopy, electron microscopy and electrolytically extracted phase analysis, in combination with thermodynamic calculations, were used to study precipitates and their precipitation behavior in Ti-microalloyed high strength steel produced by CSP process. It is found that many micron-sized cubic TiN particles and a large number of nanometer precipitates exist in the steel. The mass fraction of MX phases (M=Ti, Mo, Cr; X=C, N) in the steel is 0.0927%, in which particles smaller than 10 nm account for 26.9%. Thermodynamic calculations show that titanium nitride has been almost completely precipitated from the steel during or before soaking, but titanium carbide hardly precipitates before tandem rolling. Decreasing the contents of nitrogen and sulfide and controlling the coiling temperature can increase the volume fraction of titanium carbide, and decreasing the γ→α transformation temperature can prevent fine carbides from growing. These results indicate that the precipitation hardening resulting from nanometer particles is about 156 MPa and the effect can be raised through controlling the chemical composition and rolling parameters.


Mao X.,Guangzhou Zhujiang Steel Co | Mao X.,China Institute of Technology | Chen Q.,China Institute of Technology
Proceedings of the 10th International Conference on Steel Rolling | Year: 2010

This paper expounds microalloyed steels produced by thin slab easting and direct rolling process (hereinafter referred to as TSCR), which focus on the physical metallurgy characteristics of Ti, V, Nb microalloyed steels, including; the precipitation ride of microalloying elements, microslruclure characteristics and strengthening mechanism. The research shows that Ti precipitates throughout the entire process from casting to coiling, in 700 MPa grade Ti microalloyed steel, the mass fraction of less than 10 nm particles accounts for 33.7% of the total mass fraction of MC phases, the microslruclure is quasi-polygonal territe wilh less pearlile, the smallest lerrile grain size is 2.9μm, grain refinement is the main way of strengthening; the great quantity of V(C, N) precipitates with less TiN or (Ti, V) (C, N) were found in the slab of V microalloyed steel, and its average grain size is about 40 nm, calculations show that these precipitates can inhibit the growth of deformed austenite in the subsequent hot rolling process and fine lerrile, the ferrile grain size of 550 MPa grade V microalloyed steel is 3.0 ∼4.0 μm; Mixed grain tend to appear in Mb microalloyed steel in TSCR, the key measures to solve the problem is to avoid deformation in the partially recrystallized zone. Currendy, 450 ∼ 700 MPa grade high-strength steel were developed by Ti microalloying, 275 ∼ 550 MPa high-strength steel were developed by V microalloying, and high-strength automotive structural steel QSlE340 ∼ 460 TMs, pipeline steel X52 ∼X65 as well as oil casing steel J55 were developed by Nb microalloying.


Wang Z.,Tsinghua University | Wang Z.,Control Iron and Steel Research Institute, China | Mao X.,Guangzhou Zhujiang Steel Co. | Yang Z.,Tsinghua University | And 5 more authors.
Materials Science and Engineering A | Year: 2011

The strain-induced precipitation kinetics of TiC in a 0.05% C-0.10% Ti HSLA steel was investigated by two-stage interrupted compression method. The precipitation-time-temperature (PTT) diagram for TiC precipitation was obtained by analyzing the softening kinetics curves of deformed austenite, which was confirmed to be of validity by employing transmission electron microscopy (TEM). Experimental results showed that the PTT diagram for TiC precipitation exhibited a typical "C" shaped and the nucleation of strain-induced TiC precipitation was a very rapid process in the temperature range 900-925 °C. The relatively severe deformation applied on the steel was considered to be the main factor resulting in the fast kinetics of TiC precipitation. The TiC precipitates were heterogeneously distributed in either a chain-like or a cell like manner, implying that the precipitates nucleated on dislocations or on dislocation sub-structures, which were produced by deformation. The growth of TiC precipitates approximately followed a parabolic law. In addition, the coarsening of strain-induced TiC precipitates had already started before the completion of precipitation. © 2011 Elsevier B.V.


Huo X.-D.,Jiangsu University | Mao X.-P.,Guangzhou Zhujiang Steel Co. | Lu S.-X.,Jiangsu University
Journal of Iron and Steel Research International | Year: 2013

In order to develop cold rolled Ti-microalloyed steel strips, the effects of annealing temperature on recrystallization behavior of experimental steel were researched by optical microscopy (OM), transmission electron microscopy (TEM) and Vickers hardness test. The annealing treatment could be divided into three distinct stages: recovery, recrystallization and grain growth. Recrystallization took place from 933 to 1033 K, during which a large number of recrystallized grains appear and hardness drops sharply. The morphology and size of TiN particles nearly remained unchanged at different stages of processing. With increasing annealing temperature, nanometer precipitates coarsened and the dislocation density was significantly reduced. In comparison with annealing time, annealing temperature was more crucial for recrystallization of cold rolled Ti-microalloyed steel. It could be concluded that the pinning force of nanometer particles on dislocations increased the recrystallization temperature. At higher annealing temperature, recrystallization took place because of precipitates coarsening caused by Ostwald ripening. © 2013 Central Iron and Steel Research Institute.


Huo X.,Jiangsu University | Mao X.,Guangzhou Zhujiang Steel Co. | Chai Y.,Guangzhou Zhujiang Steel Co.
Materials Science Forum | Year: 2011

Titanium microalloyed steel whose grain size is around 3μm has been developed by CSP process. Samples after different plastic deformation were obtained by suddenly stopping the six-stand finishing train during tandem rolling. Experimental results and analysis show that plastic deformation during tandem rolling plays a major role for grain refinement. With the successive severe strain, microstructure of the same stock during tandem rolling is further refined because of repeated recrystallization at higher temperature and strain accumulation at lower temperature. Technological features of CSP process, such as large reduction per pass, rapid cooling after rolling and high solidification and of thin slab, are important reasons for obtaining ultafine-grained structure. Besides these, chemical composition of titanium microalloyed steel has beneficial effects on grain refinement.


Huo X.,Jiangsu University | Lv S.,Jiangsu University | Mao X.,Guangzhou Zhujiang Steel Co. | Chen Q.,Guangzhou Zhujiang Steel Co.
Advanced Materials Research | Year: 2011

New 700MPa hot rolled ultra-high strength steels were successfully developed by using Ti micro-alloying technology in CSP line. Experimental methods, such as OM, TEM and chemical phase analysis, were used to study the experimental steel. The microstructure is composed of quasi-polygonal ferrite grains, whose average grain size is about 4μm. Large number of nanometer TiC particles distribute along dislocations. The mass fraction of MX phase is 0.0793wt%, in which the particles smaller than 10nm account for 33.7%. The contribution of precipitation hardening resulting from nanometer particles is calculated as approximate 158MPa. © (2011) Trans Tech Publications, Switzerland.


Mao X.,Guangzhou Zhujiang Steel Co. | Huo X.,Jiangsu University | Sun X.,Control Iron and Steel Research Institute, China | Chai Y.,Guangzhou Zhujiang Steel Co.
Journal of Materials Processing Technology | Year: 2010

A new hot rolled titanium-microalloyed steel with yield strength of 700 MPa has been developed by CSP (compact strip production) process based on commercial weather resistant steel. EBSD results showed that the average size of its grains with high angle boundaries (>15°) was 3.3 μm. High-density dislocations and large number of nanometer particles were observed in the steel product by TEM. X-ray analysis on the electrolytically extracted phase from the steel indicated that fraction of MX phase was 0.0793 wt%, in which the particles smaller than 10 nm accounted for 33.7%. The contribution of precipitation hardening resulting from nanometer particles was calculated as approximate 158 MPa. The commercial weather resistant steel, reference steel for comparison with 450 MPa yield strength, was also prepared and investigated. It can be concluded that grain refinement is still a major strengthening mechanism in this high strength steel, but precipitation hardening of nanometer TiC precipitates is the dominant factor to increasing the yield strength in new developed steel compared with the reference steel. © 2010 Elsevier B.V.


Mao X.-P.,Guangzhou Zhujiang Steel Co. | Mao X.-P.,Wuhan University of Science and Technology | Chen Q.-L.,Control Iron and Steel Research Institute, China | Li C.-Y.,Control Iron and Steel Research Institute, China
Kang T'ieh/Iron and Steel | Year: 2012

Thin slab casting and direct rolling process (hereinafter referred to as "TSCR"), characterized by high liquid steel solidification rate, low heating temperature and short stay time in the roller-hearth furnace and high pass reduction, was helpful to inhibit the segregation of chemical composition, refine the non-metallic inclusions, lower surface decarburization, reduce the inter-laminar distance of pearlite, and alleviate to some extent the problems that traditional production process had in producing high-medium carbon steel strips. Consequently, TSCR was a suitable process for producing high-quality high-carbon strips. The microstructure of high carbon steel produced by TSCR process was investigated by optical microscope, scanning electron microscopy and other methods. The results show that: maximum carbon segregation rate is 1.16, much lower than 2.0 of traditional process, its single face decarburization depth is less than 1.0% of strip's thickness, only 30%-60% of that of traditional process, its pearlite inter-laminar distance is much smaller than that of traditional process, which are favorable for increasing the overall performance of the materials. High-medium carbon steels, such as high quality carbon steel, high carbon tool steel, spring steel, alloy structure steel and alloy tool steel, with carbon content up to 1.0%, can be produced by TSCR process and can also be widely used in industries such as automotive manufacturing, engineering machinery, special equipment, high-end blade and special tools.


Huo X.-D.,Jiangsu University | Mao X.-P.,Guangzhou Zhujiang Steel Co. | Dong F.,Jiangsu University
Beijing Keji Daxue Xuebao/Journal of University of Science and Technology Beijing | Year: 2013

Keeping chemical composition and other parameters unchanged, the effects of coiling temperature (625 and 579°C) on the microstructure and properties of Ti-microalloyed high strength steel were investigated during compact strip production (CSP). Experimental results of mechanical properties show that compared with steel strips coiled at 625°C, the yield strength of steel strips coiled at 579°C decreases by 205 MPa, but the impacting energy at -20°C increases from 11.7 J to 47 J. Optical microscopy and electron microscopy were used to study the microstructure and precipitates in the steel. It is found that the primary microstructural constituent of steel strips coiled at 625°C is ferrite grains, but the microstructure of steel strips coiled at 579°C is finer and characterized with bainite grains. The volume fraction of nanometer carbides in steel strips significantly reduces with decreasing coiling temperature, which weakens the precipitation hardening effect and causes a marked reduction of strength. However, the toughness is improved due to grain refinement and volume fraction decreasing of precipitates. Coiling temperature needs to be strictly controlled, because it is a more important parameter of producing Ti-microalloyed high strength steel.


Fu J.,University of Science and Technology Beijing | Fu J.,Key Laboratory for Ferrous Metallurgy and Resources Utilization | Fu J.,Wuhan University of Science and Technology | Li G.,Key Laboratory for Ferrous Metallurgy and Resources Utilization | And 5 more authors.
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2011

This article summarizes the state of the art of the comprehensive strengthening mechanism of steel. By using chemical phase analysis, X-ray small-angle scattering (XSAS), room temperature organic (RTO) solution electrolysis and metal embedded sections micron-nano-meter characterization method, and high-resolution transmission electron microscopy (TEM) observation, the properties of nanoscale cementite precipitates in Ti microalloyed high-strength weathering steels produced by the thin slab continuous casting and rolling process were analyzed. Except nanoscale TiC, cementite precipitates with size less than 36 nm and high volume fraction were also found in Ti microalloyed high-strength weathering steels. The volume fraction of cementite with size less than 36 nm is 4.4 times as much as that of TiC of the same size. Cementite with high volume fraction has a stronger precipitation strengthening effect than that of nanoscale TiC, which cannot be ignored. The precipitation strengthening contributions of nanoscale precipitates of different types and sizes should be calculated, respectively, according to the mechanisms of shearing and dislocation bypass, and then be added with the contributions of solid solution strengthening and grain refinement strengthening. A formula for calculating the yield strength of low-carbon steel was proposed; the calculated yield strength considering the precipitation strengthening contributions of nanoscale precipitates and the comprehensive strengthening mechanism of steels matches the experimental results well. The calculated σ s = 630 to 676 MPa, while the examined σ s = 630 to 680 MPa. The reason that "ultrafine grain strengthening can not be directly added with dislocation strengthening or precipitation strengthening" and the influence of the phase transformation on steel strength were discussed. The applications for comprehensive strengthening theory were summarized, and several scientific questions for further study were pointed out. © 2011 The Minerals, Metals & Materials Society and ASM International.

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