Advanced Materials Research Vols. 194-196

Abstract: B610CF steel is a newly steel, and is widely used. The test data of tensile strength for B610CF steel is fitted several kinds of probability statistical models. In this paper, the correlation coefficient method and K-S method were used to test the fitting effects. It is concluded that three-parameter Weibull distribution is the optimal distribution for the test data, and the security tensile strength of 48mm B610CF steel is 627.54MPa under the condition of 99.9% reliability. Through the study of tensile strength confidence interval for B610CF steel, it is obtained that confidence interval is [601.47MPa, 644.86MPa] under the condition of 99.9% reliability and 80% confidence level. The results are important for the structural reliability analysis of B610CF steel.

Abstract: OM, SEM, TEM and XRD were used to analyze microstructure and oxidation layer of 430 stainless steel during hot rolling, and microstructure characteristic and oxidation layer evolution rule under high temperature deformation were studied. It is shown that microstructure after each pass under laboratory rolling condition is composed of austenite and ferrite, but there are significant differences in the size, morphology and distribution of dual phase microstructure. Oxidation layer of each pass consists mostly of Fe₂O₃, Fe₃O₄ and FeCr₂O₄. Thickness of surface oxide film decreases from 12μm to about 4~5μm as rolling pass increases. Compared to experimental result of laboratory rolling, because high-pressure descaling is used in practical production, meanwhile deformation amount is higher and surface quality of roller is better, oxidation layer of finished product is uniform, distributes continuously and has strong internal bonding force with matrix.

Abstract: In order to guide the rolling process in industry, the effect of heat treatment temperatures and holding times on the structure and mechanical properties of the hot-rolling plate of Fe-42% Ni (4J42) was studied. The results about the metallography show that with the increasing of the heating temperature, the grain sizes of all the samples grow. Furthermore, the phenomenon of twin crystal in grains is more and more obvious. The mechanical tests show that with the increasing of the temperature and the holding time, 4J42’s tensile strength declines; when the heat temperature is 1000°C, holding times have little effect on its elongation; when the holding time is less than 8min, the hardness of 4J42 declines at different temperatures. Combine the requirements in industry with the experiment results, we found that 1000°C, 8min is appropriate to the rolling process of 4J42 alloy.

Abstract: The dynamic coefficient of thermal expansion for steel Q235 during cooling was investigated using experimental measurements and model calculations. The coefficient of thermal expansion under 1400°С was measured with a thermal dilatometer. The coefficient was derived from a segregation model of two-phase zone for of temperature range of 1400°С to zero-strength temperature (ZST). The obtained results reveal that the coefficient of thermal expansion shows two jumps in the temperature zone of the peritectic reaction and the eutectoid reaction. The anti-expansion phenomenon caused by the eutectoid reaction in the cooling process corresponds to the low-temperature crack-sensitive area. Therefore, the slab straightening process should be avoided in this temperature range during continuous casting.

Abstract: The TMCP and bake hardening experiments were carried out for the test steel，the microstructure analyses，mechanical properties and bake hardenability test were carried out by using SEM, TEM and tensile test machine. The results show that small volume fraction of bainite microstructure increased will improve BH value in the microstructure of F+P(little). compared with the microstructure that consists of ferrite mainly，which consists of bainite mainly has a higher BH value. The microstructure that consists of ferrite mainly shows the trendy of BH that increased first and then decreased, along with pre-strain increased. The microstructure that consists of bainite, under the condition of higher pre-strain, with the pre-strain increased, the BH value shows the trendy of increasing. While the BHT value is increasing monotonously.

Abstract: Effect of ultrasonic treatment time on inclusions in high carbon steel with the addition of pure rare earth Ce was investigated. The results showed that ultrasonic treatment could disperse, refine and remove inclusions in molten high carbon steel with rare earth. With the increase of ultrasonic treatment time, total oxygen content of high carbon steel and average diameter of inclusions decreased evidently, inclusions in high carbon steel could be removed in a certain degree, but the number of the inclusions increased significantly. Total oxygen content (mass fraction) of high carbon steel, equivalent number I and average diameter d of inclusions in ingot was respectively 59×10⁶, 134 entries•mm^-2 and 2.91 μm when the ultrasonic treatment time was 60 s, at the same time, the percentage of inclusions with diameter D＜2.31 μm is up to more than 43 % of the total.

Abstract: The thermal expansion curves are measured by Gleeble-1500 thermomechanical simulator for Cr-Mo steel during continuous cooling transformation at the cooling rate ranging from 1°/s to 90° /s, and CCT curve is also determined; The thermal expansion curves of continuous cooling transformation are measured under the axial compressive stresses (40MPa, 80MPa and 120MPa) at the cooling rates of 50° /s, 70° /s and 90° /s respectively, then the CCT curves with applied compressive stress are determined. The transformation microstructures of steel after continuous cooling with and without stress are observed by SEM and TEM, and the hardness is measured by Vickers hardness tester. The results show that the Bs is increased and Bf is decreased owing to the effect of applied compressive stress; At the meantime the microstructure is also changed, with increasing applied compressive stress, the quantity of granular bainite, bulk ferrite and carbide increase gradually except lath bainite，the lath width of lath bainite becomes narrower gradually, and original grain boundaries become bent from straight; The hardness of transformation structure becomes lower with increasing applied compressive stress exceeding 40Mpa after continuous cooling.

Abstract: Oxygen injector is oxygen supply equipment for steelmaking process. Based on the numerical simulation of the flow field of a new coherent jet oxygen injector and traditional supersonic oxygen injector, the authors contrasted the axial and radial velocity decay of them. After a discussion on the influence of structural parameters on the jets, the authors pointed the impact of the jet characteristics of oxygen injector due to structural wear from the angle of practical operation.

Abstract: AZ91D Magnesium alloy matrix composites (MMC) were fabricated by squeezing-infiltration casting with the preform made of crystallined aluminum silicate short fibers as reinforcement and aluminum phosphate as binder at high temperature. Drying sliding friction and wear resistance of the MMC were examined by means of MM200 wear tester ( block-on-ring configuration) against a hardened alloy steel counterface with 53HRC under loadings of 10 N,30 N and 50 N at 0.47 m/s and 0.92 m/s, and the wear morphology of the tested specimens was observed by scanning electronic microscope ( SEM ). The results indicate that wear mechanism of the MMC is characterized by abrasive wear with loadings 10 N and 30 N at 0.47m/s; while it is characterized by abrasive wear with slight flaking wear under loadings of 50 N at 0.47m/s, and it exhibits combined wear of abrasive wear with slight adhesive wear under loadings of 50 N at 0.94 m/s, increasing the wear resistance of the MMC.

Abstract: The aging hardening curves of Al₂O₃-SiO_2(sf) / AZ91D composites (MMCs) with different volume fraction were got, and the aging behaviors of the composites were investigated with Vickers hardness measurement, differential scanning calorimetry (DSC), transmission electron microscope (TEM) after solution treated at 415°C for 10h , and water quenched at room temperature, afterwards aged at 175°C for 0 -38h with a 2h interval. The result shows that there are three aging peaks at aging hardening curve of the composites, and that four types of β-Mg₁₇Al₁₂ precipitates were responsible for the aging peaks. Volume fraction of the composite affects effect of aging hardening, but does not change trend of the aging hardening curve.