Hui Guo

Application of support vector machine in the prediction of mechanical property of steel materials

Abstract The investigation of the influences of important parameters including steel chemical composition and hot rolling parameters on the mechanical properties of steel is a key for the systems that are used to predict mechanical properties. To improve the prediction accuracy, support vector machine was used to predict the mechanical properties of hot-rolled plain carbon steel Q235B. Support vector machine is a novel machine learning method, which is a powerful tool used to solve the problem characterized by small sample, nonlinearity, and high dimension with a good generalization performance. On the basis of the data collected from the supervisor of hotrolling process, the support vector regression algorithm was used to build prediction models, and the off-line simulation indicates that predicted and measured results are in good agreement.

Prior knowledge-based fuzzy Support Vector Regression

A new method was proposed for incorporating prior knowledge in the form of fuzzy knowledge sets into Support Vector Machine for regression problem. The prior knowledge of Fuzzy IF-THEN rules can be transformed into fuzzy information to generate fuzzy kernel, based on which FSVR (Fuzzy Support Vector Regression) is introduced. The merit of FSVR is that it can incorporate with prior knowledge represented by fuzzy IF-THEN rules to improve the performance of the conventional SVR in incomplete numeral dataset for training. The simulation results are feasible.

Nucleation of Bainite on Allotriomorphic Ferrite/Austenite Interface in a Low Carbon Steel

. A low carbon steel is austenitized and isothermally held at 680°C to form allotriomorphic ferrite and followed by a holding at lower temperature to form bainite. The morphology of allotriomorphic ferrite/bainite interfaces is studied using optical microscope. Three kinds of combination are observed: Type I: interface on one side is clear while on the other side, unclear; Type II: unclear on both sides; Type III: clear on both sides. Clear interface indicates a large difference in the orientation between the bainite and the ferrite, and unclear interface, a very small difference. The statistical counting shows that the ratio of Type I is about 80-82%, and that of Type II, 7-8%, and Type III, 9-11%. It is observed that this ratio does not change with the austenite grain size and bainite forming temperature. And the clear and unclear side of allotriomorphic ferrite may have different influence on the nucleation rate of bainite at allotriomorhic ferrite/prior austenite interface.

Effect of zirconium addition on the austenite grain coarsening behavior and mechanical properties of 900 MPa low carbon bainite steel

Abstract The ultra-fine bainitic microstructure of a 900 MPa low carbon bainitic Cu-Ni-Mo-B steel was obtained by a newly developed relaxation precipitation control (RPC) phase transformation processing. In a pan-cake like prior-austenite grain, the microstructure consisted of lath bainite, a little of abnormal granular bainite, and acicular ferrite. The effect of zirconium carbonitrides on the austenite grain coarsening behavior was studied by transmission electron microscopy (TEM). The results show that, the lath is narrower with increasing cooling rate. The ratio of all kinds of bainitic microstructure is proper with the intermediate cooling rate; and Zr-containing precipitates distribute uniformly, which restrains austenite grain growing in heat-affected welding zone.

Two-body abrasion wear mechanism of super bainitic steel

The abrasion wear resistance and wear mechanism of super bainitic steel austempered at different temperatures and time have been investigated by two-body abrasion testings, scanning electron microscopy, X-ray diffraction, transformation electron microscopy and electron backscattering diffraction. The results show that the two-body abrasion wear mechanism is predominantly micro-ploughing abrasion, and the wear resistance is decreased with increasing isothermal temperature which is attributed to the decreased hardness caused by a higher retained austenite content and the coarsening of the microstructure. The sample austempered at 230°C for 2u2005h with the higher amount of retained austenite and lower carbon concentration exhibits excellent wear resistance, and the transformation induced plasticity effect is observed during wear process which is beneficial for the improving of hardness and wear resistance.

A Study on Cu and Nb Precipitation during High Temperature Tempering in Low Carbon Steels

The microstructure evolution and precipitation behavior of two low carbon steels are studied, with 0.05C-0.77%Nb added in one steel and (0.03C-)1.63Cu-0.74%Nb added in the other as a comparison. In the Cu-Nb steel tempered at 600°C for 18 hrs, there are two peaks in the particle size distribution figure, one between 2-3nm formed by NbCN precipitates, and the other, 10-12nm for Cu precipitates. The TEM observation on carbon replica shows that the average particle diameter of NbCN precipitate is 2.81±0.78nm in C-Nb steel, while 4.23±0.95 nm in Cu-Nb steel with lower carbon. The analysis shows that this size increase of NbCN not only decreases the precipitation strengthening, but also weakens significantly the pinning effect on the dislocations, which results in a more serious microstructure softening in Cu-Nb steel.

Influence of Austenite Grain Size on the Crystallography of Allotriomorphic Ferrite in a Low Carbon Steel

The influence of prior austenite grain size on the crystallography of allotriomorphic ferrite is investigated in a low carbon steel. The results show that as the prior austenite grain size decreasing, the fraction of allotriomorphic ferrites that do not keep K-S orientation relationship with any surrounding prior austenite grains is increased. It is observed that such ferrites usually form at the grain edges or grain corners. It is known that with the grain size decreasing, the fraction of grain edges and corners increases. It is suggested that the free energy of the defects at such nucleation sites is higher than that at grain faces, and the nucleation barrier of ferrite is lower. As a result, the possibility for the ferrite to form that does not have orientation relationship with all surrounding austenite grains is increased at such sites.

Influence of Allotriomorphic Ferrite under Different Growth Modes on the Variant Selection of Bainite in a Low Carbon Steel

A Fe-0.05C-2.94Mn-1.87Si steel is heat treated using a two-stage isothermal holding process to obtain allotriomorphic ferrite and bainite. Two kinds of allotriomorphic ferrite are obtained, one with only carbon partitioning and the other, alloying element partitioning. It is observed that the allotriomorphic ferrite stimulates the adjacent bainite to select the similar variant on the side where near K-S relationship is maintained between ferrite and prior austenite. The longer the border length of the allotriomorphic ferrite, the larger the stimulated bainite area. The statistical measurement shows that the alltriomorhpic ferrite with alloying element partitioning stimulates such bainite variant selection as well as that with only carbon partitioning.

Selective role of bainitic lath boundary in influencing slip systems and consequent deformation mechanisms and delamination in high-strength low-alloy steel

Abstract We elucidate here the deformation behaviour and delamination phenomenon in a high-strength low-alloy bainitic steel, in terms of microstructure, texture and stress evolution during deformation via in situ electron back-scattered diffraction and electron microscopy. Furthermore, the selective role of bainitic lath boundary on slip systems was studied in terms of dislocation pile-up and grain boundary energy models. During tensile deformation, the texture evolution was concentrated at {1 1 0}<1 1 1> and the laths were turn parallel to loading direction. The determining role of lath on the deformation behaviour is governed by length/thickness (l/t) ratio. When l/t > 28, the strain accommodates along the bainite lath rather than along the normal direction. The delamination crack initiated normal to (0 1 1) plane, and become inclined to (0 1 1) plane with continued strain along (0 1 1) plane and lath plane. This indicated that the delamination is not brittle process but plastic process. The lack of dimples at the delaminated surface is because of lack of strain normal to the direction of lath. The delaminated (0 1 1) planes were associated with cleavage along the (1 0 0) plane.

Low Temperature Mechanical Properties of Power Transmission Tower Steel

The tensile and impact tests were used to study the mechanical properties under different temperatures of 300 mm large-scale angle steel at different positions, especially the tensile strength, yield strength, total elongation and impact toughness in the range of-40 oC to 20 oC. The results showed that different regions had great differences in the microstructures and impact toughness, in which the size of edge region was the smallest and the impact toughness was the best. However, the coarsened grain of heat affected zone at weld region had deteriorated to the low temperature impact toughness. When the impact energy was 34 J, the ductile-brittle transition temperature of weld, center, vertex and edge were-7.2 oC, -33.0 oC, -31.5 oC and far less than-40 oC, respectively. Meanwhile, because the banded structure was detrimental to the ductility, the elongation of rolling direction was lower than vertical direction. The strength of weld region was higher than other locations, but the elongation was obviously decreased.