Ze Xi Yuan

EFFECTS OF ZIRCONIUM ON MICROSTRUCTURES AND MECHANICAL PROPERTIES OF MICROALLOYED STEELS

The effects of Zr on the microstructures and mechanical properties of microalloyed steels have been investigated by mechanical tests and microstructural observations. The microstructures in the Zr-doped steels are ferrite plus pearlite, which is similar to those in the Zr-free steel. With the increase in the Zr content, the lamellar structure reduces and even disappears. Sulfides and silicates that exist in the Zr-free steel are modified into fine oxides in the Zr-bearing steel. When the Zr contents range from 0.01wt% to 0.03wt%, the low temperature toughness of the steel can be substantially improved while its room-temperature strength and ductility have no apparent change. The refinement of ferrite grain size by the addition of zirconium is one of the main reasons for this toughness improvement.

Effect of Micro-Alloying Elements of Ti, Nb and B on Recrystallization Behavior of Cold-Rolled Interstitial-Free Steel Sheets

The effect of micro-alloying elements of niobium and boron and titanium on recrystallization behavior is researched after the cold rolled IF steels are annealed at high temperature. The results show that there is high density dislocation in the cold rolled steel and the microstructure is fibrous tissue. The recrystallization grains appear when the cold steel annealed at 655 °C and then the grains grow up with the annealing temperature increased to 840 °C. The recrystallization temperature and time of B-Ti-IF steel is lower than that of Nb-Ti-IF and Ti-IF steels. The recrystallization activation energy of Nb-Ti-IF steel is 181.7KJ/mol which is 56.6KJ/mol larger than that of B-Ti-IF steel.

Effect of Annealing Temperature on Phosphorus Segregation at Grain Boundary in a Ti-IF Steel

The concentration of phosphorus at grain boundary of the Ti-IF steel annealed for 180sec at 780°C、810°C and 840°C respectively is measured by auger electron spectroscopy (AES). The results show that the segregation concentration of phosphorus at grain boundary decreases with increasing annealing temperature from 780 to 840°C. The maximum phosphorus concentration at grain boundary is 13.5at% or so for the specimen annealed for 180sec at 780°C. Most of the grains are intergranular crack and there are a few secondary crack for the samples annealed at 780°C and 810°C. The grains grow up and the cleavage planes increase with increasing the annealing temperature from 780 to 840°C.

Influence of Sizing and Cooling Process on Properties of N80-1 Seamless Casing Using Steel 40Mn2V and the Process Parameter Control

nfluence of process parameters such as deformation strain and temperature in sizing, and pipe cooling rate on strength, impact toughness and microstructure in steel 40Mn2V was investigated, by hot simulation test, tensile test, impact test and microstructure observation test. The quantitative relationship between strength values and process parameters was analyzed using software Matlab, and the formulas with higher accuracy were established. It is indicated that strength, impact toughness and microstructure are mainly influenced by sizing deformation temperature and pipe cooling rate. Bainite transformation, the main cause of bad impact toughness occurs when pipe cooling rate reaches or exceeds a critical value. To satisfy the property requirements of N80-1 casing when steel 40Mn2V is used, a suitable sizing temperature shall be controlled in the range of 695~870°C when pipe cooling rate is at or below 0.6°C/s, and in the range of 695~820°C when pipe cooling rate is above 0.6°C/s but not exceed 1.1°C/s.

Study of V2O5 Direct Alloying Reductants

Based on the thermodynamic calculation, the reductants to reduce V2O5 were selected, 0.1% V were added into steels by reducing V2O5 during the smelting process. The yielding rate of vanadium was calculated by chemical analysis data. The yielding rate is 98.17% when using Si+20%C as reductant and is about 94.94% when using Al+Mg as the reductant. By comparing the inclusion morphology and composition, contrasts the Brinell hardness and tensile strength of steels using different reductants, it was found that when using Si+20%C reductant, the inclusions in the steel is larger in amount, smaller in size and higher in Brinell hardness and tensile strength.

Research and Development of High Strength Architectural Heavy Plates

This paper provides a detailed description of high strength architectural heavy plates with 80mm in thickness developed at Wuhan Iron and Steel（Group）Corporation(WISCO). The chemical composition of plates contains mainly C-Mn-Nb-V-Ti with proper content of other alloys, and the thermal-mechanical controlled process and normalizing treatment were applied. The results show that the base plates manufactured at WISCO have a good match of high strength, good through-thickness characteristic, low yield ratio and low temperature toughness with fine microstructure, and the fracture transition temperature is about -40°C. The welding plate also has high strength and good low temperature toughness which comprehensively meet the technical requirement of large-scale architectural buildings.

Effect of Strain Rate on Dynamic Recrystallization Behavior for V Micro-Alloy High-Carbon Steel

Isothermal constant strain rate compression tests on high-carbon steel are carried out under strain rate of 1s-1, 10s-1 and 50s-1 respectively and deformation of 0.7 using the THERMECMASTOR-Z thermal simulator at a temperature of 1000°C. The austenite grain morphology before and after deformation and the true stress-strain curves during the deformation process are analyzed. The experimental results show that increased strain rate can obviously contribute to the grain refinement, and when the strain rate is at low level (e.g. 1s-1)，increased strain rate can further help refine the grains. And under the same temperature conditions, as the deformation rate rises, peak stress will move toward the direction of strain increment，thus the dynamic recrystallization is not apt to occur.

Influence of Vanadium on Microstructures and Mechanical Properties of High Strength Normalized Steel

Considering the specialities of high strength normalized steel, the main roles of vanadium in normalized steel were investigated. The results show that adding vanadium can improve the strength and deteriorate the impact energy, but for vanadium steel, the strengths increase and the impact energies have no changing regulation with increasing vanadium. The microstructures of experimental steels are composed of polygonal ferrite and pearlite, vanadium can not refine ferrite grain size, most of them dissolve into the matrix, and the forms of precipitation in vanadium steel are complex carbonitrides. Grain refinement plays a greater role in improving the low temperature toughness of high strength normalized steels, the strength index is firstly considered in designing this kind of steels.

600MPa Grade TMCP Steel with Low Yield Ratio and Excellent Weldability

A new lower cost 600MPa TMCP steel with high strength,good low temperature impact toughness,low yield ratio and excellent weldability has been developed successfully by design of alloy composition and thermal mechanical control process technology, and the welding heat affected zone(HAZ) have been investigated. The systematic studies show that the new developed steels gather high strength, high low temperature toughness, good seismic performance(low yield ratio) and excellent weldability, and the base steels have a good match of strength and toughness. A large number of fine acicular ferrite in HAZ can ensure that the welding plate has high strength and good low temperature impact toughness. The comprehensive performance of steel can meet fully the high-technical requirements of large-scale engineering.

Comparative Study on the Cyclic Corrosion Test of Rail Steel U68CuCr and U75V

A further investigation into the determination of corrosion resistance behavior has been carried out through a series of cyclic corrosion tests in order to comparatively study the corrosion rates of rail steel U68CuCr and U75V under different cycle conditions. The results indicate that U68CuCr possesses better corrosion resistance than U75V. According to macroscopic view, colors of U68CuCr surfaces are all lighter than those of U75V in the same group. Moreover, the grains at the rust layer of U68CuCr specimens show much finer and denser microstructure than U75V. Besides, cracks on the rust layer of U75V specimens are found.