Influences of Asymmetric Reduction Rolling on the Microstructure and Mechanical Properties of AZ91

The influence of asymmetric reduction rolling （ARR） on the microstructure, texture and mechanical properties of AZ91 was investigated. The microstructural characteristics of the AZ91 sheet processed by symmetric roiling （SR） were the twins, intersection of twins and dynamic recrystalization （DRX） grains around the coarse grains and within the twins. However, the amount of twins and DRX grains in ARRed AZ91 was much smaller than that in SRed AZ91. The SRed AZ91 after annealing exhibited fine DRX grains and some coarse grains with a size of ~ 100 pro. The grains in ARRed AZ91 after annealing were much finer and more homogeneous than those in SRed AZ91 after annealing. The intensity of basal texture of ARRed AZ91 after annealing was lower than that of SRed AZ91 rolling after annealing. The average Schmid factor of ARRed AZ91 is 0.34, which is higher than that of SRed AZ91. The yield strength and ultimate tensile strength of the ARRed AZ91 sheet were inCreased to 16.1% and 31.8% compared to SRed AZ91 sheet, from 155 to 180 MPa, and from 220 to 290 MPa, respectively. The improvement of mechanical properties in ARRed AZ91 after annealing was attributed to much finer, more homogeneous DRX grains and weaker basal texture.

INFLUENCE OF COLD ROLLING REDUCTION ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF TWIP STEEL

The influence of cold rolling reduction on microstructure and mechanical properties of the TWIP （ttwinning induced plasticity） steel was investigated. The results＇ indicated that the steel had better comprehensive mechanical properties when cold rolling reduction was about 65.0% and the annealing temperature was 1000℃. The tensile strength of the steel is about 640MPa and the yield strength is higher than 255MPa, while the elongation is＇ above 82%. The microstructure is composed of austenitic matrix and annealing twins at room temperature, at the same time, a significant amount of annealing twins and stacking faults＇ are observed by transmission electron microscopy （TEM）. Mechanical twins play a dominant role during deformation, and result in exceUent mechanical properties.

INFLUENCE OF COLD ROLLING TECHNOLOGY ON TEXTURE EVOLUTION OF IF STEEL

Two kinds of cold rolling experiments, single cold rolling and double cold rolling, were carried out on one titanium stabilized interstitial free (IF) steel that has been warm rolled at ferrite temperature. The main aim was to investigate the evolution of rolling and annealing textures from the well known behavior observed under single cold rolling condition to the less understood double cold rolling by using orientation distribution function (ODF). In the twice cold rolled samples, the annealing texture comprises only single {111}(110-112) r-fibre texture when it subjected to moderate reduction in the first round of rolling. Accordingly both the once cold rolled sample and the twice cold rolled sample with heavy reduction in the first round of rolling have much complex texture components. They are related to the formation of initial {111} subgrain and the priority growth of stable {111} nucleus.

Influence of Edge Rolling Reduction on Plate-Edge Stress Distribution During Finish Rolling

Dimensions of one kind of stainless steel plate before finish rolling were obtained through analysis of the rough rolling processes by finite element method and updated geometrical method. The FE models of finish rolling process with a front edge roll were built, and influences of the edge rolling reduction on the stress change in the plate edge during finish rolling were analyzed. The results show that when the edge rolling reduction is increased from 0 mm to 2 mm, the compressive stress in plate corner clearly increases in edge rolling process, and the zone of tensile stress during whole rolling decreases; when the edge rolling reduction is increased from 2 mm to 5 ram, the compressive stress in the plate corner seldom changes, and the compressive stress decreases after the horizontal rolling.

Intercritical Rolling Induced Ultrafine Lamellar Structure and Enhanced Mechanical Properties of Medium-Mn Steel

The medium-Mn steel with ferrite and austenite structure was rolled in the intercritical region down to dif- ferent rolling reduction. The microstructure and mechanical properties of the rolled steels were investigated by scan- ning electron microscopy, transmission electron microscopy, X-ray diffraction and tensile tests. It was found that the ferrite and austenite structure gradually evolved into an ultrafine structure from the random directional lath structure to lamellar structure with lath longitudinal direction parallel to the rolling direction with increasing rolling strain. It was found that the thickness of the laths was gradually refined with increasing rolling strain. The lath thickness is about 0. 15 9m stored with high density dislocations and the austenite volume fraction of the steel is about 24% after 80% rolling reduction. Furthermore, it was interesting to find that yield strength, tensile strength and total elongation of the 80% rolled medium-Mn steel are about 1000 MPa, 1250 MPa and 24%, respectively, demonstrating an excellent combination of the strength and ductility. Based on the microstructure examination, it was proposed that the grain refinement of the medium-Mn steels could be attributed to the duplex structure and the low rolling temperature. Analysis of the relationship between the microstructure and the mechanical properties indicated that the high yield strength mainly resulted from the ultrafine grain size and the high density dislocation, but the improved ductili- ty may be attributed to the large fractions of austenite retained after intercritical rolling.

Effect of cold rolling and annealing on microstructure and properties of a new resource-saving duplex stainless steel Fe–19Cr–0.6Al–12Mn

An Fe-19Cr-0.6Al-12Mn duplex stainless steel with an optimized alloy composition of Ni replaced by Mn and Cr partially replaced by Al was developed to avoid the edge cracking, which is a common defect in the hot rolling of traditional twophase stainless steels. The newly developed duplex stainless steel could be hot-rolled in the single-phase ferrite (α) region by controlling rolling temperature and the single-phase ferrite microstructure was retained on water cooling. To obtain the two-phase stainless steel product with ferrite and austenite (γ) microstructure, cold rolling and annealing were carried out,and appropriate cold rolling reduction and annealing process parameters were determined. The significant impact of annealing on microstructure, mechanical properties and pitting resistance of the experimental steel was studied. It was observed that with the increase in cold rolling reduction, the number of γ nucleation points was dramatically increased leading to the precipitation of more γ at α grain boundaries after annealing. During annealing at 800 ℃ and with the increase in annealing time, the austenite fraction was increased with a lower rate and remained almost constant when the annealing time was greater than 4 h. With the increase in annealing temperature, the austenite fraction decreased gradually in the temperature range of 750-860 ℃. Good combination of strength, ductility and excellent pitting resistance was obtained by cold rolling to 80% reduction and annealing at 800 ℃ for 4 h. Grain refinement and the existence of Σ3 boundaries played a vital role in improving the pitting resistance of the experimental steel. With good combination of strength, ductility and corrosion resistance, the newly developed duplex stainless steel is expected to be a new resource-saving dual-phase stainless steel.

Influences of the Texture Characteristic and Interdendritic LPSO Phase Distribution on the Tensile Properties of Mg–Gd–Y–Zn–Zr Sheets Through Hot Rolling

The Mg–Gd–Y–Zn–Zr alloy sheets with different texture characteristics and distribution of the interdendritic long periodstacking ordered(LPSO) phases were fabricated through altering the final rolling reduction(FRR). The results showed that the texture characteristic was closely related to FRR and affected the tensile properties of the resulted sheets to some extent. The Schmid factor(SF) of the basal 〈a〉 slip improved with further FRR, which was ascribed to that the dynamic recrystallization(DRX) grains expand into the deformed grains with basal texture. However, the improvement of the tensile yield strength(TYS) with further FRR indicates that the strengthening effect from DRX grains surpasses the weakening effect from the elevated SF. The formation of the line-distributed interdendritic 14 H-LPSO phases can also affect the tensile properties of the resulted sheets. The line-distributed interdendritic 14 H-LPSO phases along rolling direction(RD) can act as reinforcing fiber and contribute to the higher TYS along RD and 45° to some extent, which resulted in the higher TYS along 45° compared with that along transverse direction(TD) for each resulted sheet under the circumstance of approximate basal 〈a〉 and pyramid 〈c + a〉 friction stress. Thus, the tensile yield strength is not only related to the texture, but also depends on the grain size and line-distributed interdendritic LPSO phases. The micro-cracks spread perpendicular to the tension direction, and thus, the larger cracks form within the line-distributed 14 H-LPSO phases during tension along TD, which accounts for the lower fracture elongation along TD.

Modeling flow stress and grain size of GCr15 bearing steel at hightemperature deformation near end of solidification

Hot-core heavy reduction rolling is an innovative technology for continuous casting billet at the end of solidification.The deformation characteristics of GCr15 bearing billet were investigated over the temperature range of 1000-1300℃ with the strain rate of 0.001-10 s^(-1) by the Gleeble 3800 thermo-mechanical simulator.Firstly,the true stress-strain data are calibrated by the friction correction method to acquire accurate parameters near the solidus.Then,the Laasraoui-type constitutive model and dynamic austenite grain size model are established by the thermal compression results and corrosion experimental results,and the predicted values of the experimental interval are obtained by using the models.Meanwhile,the accuracy of models is verified by comparing the predicted curves with the experimental data.Last but not the least,the dynamic parameters between solidus and liquidus are predicted by the two models,and the difficulty of experimental collecting near the melting point is solved.