Papers by Author: Lin Xiu Du

Abstract: We use the cellular automaton (CA) modeling to investigate the ferrite nucleation on the austenite grains. On the basis of the thermodynamics and kinetics of phase transformation from austenite to ferrite, the CA modeling demonstrates that the size of nucleated ferrite grains is increased with increasing of cooling rates, and nucleation process is finished instantly at a given cooling rate. The initial austenite grain size plays an important role in the obtained ferrite nucleation number, and the potential nucleation cells are increased.

Abstract: In the this paper, the compositions design with low carbon and addition of sulfur and manganese which can enhance fish-scale resistance by MnS as hydrogen trap was adopted to produce DC03EK cold-rolled enamel steel. The effect of sulfur and manganese contents on formability and fish-scale resistance of DC03EK cold-rolled enamel steel was investigated. Results show that yield strength, ultimate tensile strength, elongation, work hardening exponent and average plastic strain ratio of the steel with sulfur content of 0.024wt% and manganese content of 0.22wt% is 133 MPa, 310 MPa, 36.8%, 0.22 and 1.46, respectively, showing the well formability. And its hydrogen penetration time and diffusion coefficient is higher than 12 min and lower than 9.26×10^-7 cm²/s, respectively, showing excellent fish-scale resistance. However, for the steel with sulfur content of 0.012wt% and manganese content of 0.12wt%, even though better formability is obtained, the fish-scale resistance is poor with hydrogen penetration time of 4.7 min and hydrogen diffusion coefficient of 2.36×10^-6 cm²/s which is far from the expectation of steel for enamel.

Abstract: Generally, three typical behaviors are recognized in hot-deformation of austenite. However, considering that those austenite grains involved in single-pass deformation are mostly on the scale of dozens of micrometers or even much larger than that, it is meaningful to investigate hot-deformation behaviors of austenite grains smaller than 10μm. In the current paper, austenite grains of different sizes were prepared through repetitive treatment of rapid reheating and quenching with changing the holding temperature and/or holding time. Kinds of true stress-true strain curves at 900oC and 950oC indicate that austenitic deformation can be gradually coordinated by grain boundary behaviors, such as grain boundary sliding and/or diffusion. Simultaneously, the macroscopic deformation is more likely to be dominated through co-operation grain boundary sliding (CGBS).

Abstract: By controlled rolling and cooling process, a Mn-Ti high strength steel with yield strength on the order of 700MPa had been developed successfully. The microstructure consists of fine lath shaped bainite and ferrite. The strengthening factors of this steel are attributed to the tiny interlocked distribution of bainite lath and titanium carbide precipitation. When the amount of bainite is more than 70%, the yield strength of steel is higher than 700MPa, and good mechanical performances are obtained. As a result of presence of finely dispersed bainite slabs the plasticity of steel is improved, with the steel’s elongation being about 19%. Many tiny TiC precipitates are observed under transmission electron micrograph, and these particles result in precipitation strengthening.

Abstract: A method of obtaining nanocrystallized bulk steels through phase transformation was investigated. Firstly, the austenite grain size of a microalloyed steel was refined to 1~3μm through repeatly heating and quenching; secondly, the samples with ultrafined austenite grains were heavily deformed at different temperature, and the uniform microstructures with some 0.1~0.3μm equiaxed ferrites were obtained.

Abstract: TMCP treatments were carried out on B510L steel followed by using a pilot rolling mill. Effects of finish rolling temperature and coiling temperature on mechanical properties and microstructures of the steel were analyzed. The tensile and impact properties were measured and the microstructures were observed by OM, TEM and SEM. With a proper control of rolling and cooling conditions, the yield strength of 500MPa was obtained, which was much higher than that in normal production. The yield ratio and ductility of the experimental steel were also reasonable. It was revealed that a good combination of ferrite with bainite microstructure was ideal for good mechanical properties. It was also concluded that the strengthening mechanisms included solution hardening, fine ferrite grain hardening, bainite hardening and precipitation hardening. This work can provide an experimental basis for industrial productions.