No abstract

Strong deoxidation and weak deoxidation are two kinds of deoxidation methods frequently applied in steelmaking. In the present study, high‐carbon chromium bearing steels are smelted with a strong deoxidizer and a weak deoxidizer, respectively in industrial trials. The generation mechanism of inclusions is analyzed, and the inclusion stability diagrams of the Fe–Si–Al–Mg–Mn–O system at 1873 and 1843 K are calculated. The very high cycle fatigue life of bearing steels deoxidized with different deoxidizers is also experimentally compared. The results showed that the evolution routes of inclusion in high‐carbon chromium bearing steels deoxidized by Si and Al are CaO–Al2O3–SiO2 → CaO–Al2O3–SiO2–MgO and Al2O3 → CaO–Al2O3–SiO2–MgO, respectively. The Al content in steel is controlled by different methods when different deoxidizers are applied. The effect of the oxide inclusions generated during Si deoxidization on the fatigue life is lower than that during Al deoxidization, even if the total oxygen content is slightly higher. This effect suggests that it is not accurate to evaluate the fatigue life of steels with the total oxygen content, and it is also desirable to produce bearing steels with the Si deoxidation method.

The three-dimensional morphologies of inclusions in gear steel 18CrNiMo7-6 forging were investigated by a non-destructive extraction method, and the cleanliness of radial positions was analyzed, mainly including the variation of total oxygen content and the distribution of size and quantity of inclusions. In addition, fatigue performance was tested using an ultrasonic fatigue machine to investigate the fatigue characteristics of the steel. The results show that the quantity density of inclusions per unit volume in gear steel 18CrNiMo7-6 decreases exponentially with increasing size, oxide inclusions with a size less than 8 μm account for more than 90%, while sulfide inclusions account for more than 85%. The average value of the oxygen content can reflect the level of inclusions that were evenly distributed in the molten steel, and the accumulative total oxygen content increases significantly with increasing inclusion size. The fatigue specimen failed after the stress exceeded the critical value, and fatigue failure hardly occurred when the stress was below the critical value. Meanwhile, large-sized nondeformable inclusions such as Al2O3-CaO in gear steel 18CrNiMo7-6 are closely related to fatigue failure. It is recommended that the area from the center to the 1/2 radius with low cleanliness should be avoided, while the area from the 3/4 radius to the edge with high cleanliness should be selected during the machining of the gear.

A: Alumina ceramics are commonly used as high-voltage insulation materials. The alumina ceramic will turn yellow after being irradiated with a certain amount of X-rays. Based on this phenomenon, we focused on the study of the yellowing mechanism and the effect of X-ray irradiation on the electrical insulation properties of alumina ceramics. The results indicate that after X-rays irradiating on the alumina ceramic, the color becomes yellow due to the generation of color centers; within an irradiation dose of 3 mGy, X-rays have no adverse effect on the electrical insulation properties of the alumina ceramic.