A method for observing tridimensional morphology of sulfide inclusions by non-aqueous solution electrolytic etching

Three-dimensional investigation of sulfides is required in order to improve the mechanical properties of steel by controlling the sulfides in the steel.A method including its principles and device is introduced for the investigation of threedimensional morphology of sulfides.The method is suitable for gear steel,free cutting steel,non-quenched steel,tempered steel(ws≥0.02 wt.%),etc.The influences of current density,time,and temperature on the exposure degree of sulfide inclusions were investigated by using 16MnCrS5 steel.The best parameters of electrolytic etching of sulfur steel,as found by experimentation,are as follows:current density,37.5-52.5 mA/cm2;time,30-35 min;and temperature,—10 to 0℃.Under these conditions,the three-dimensional morphology of sulfide inclusions in sulfur-bearing steel can be exposed effectively.

Analysis of precipitation behavior of MnS in sulfur-bearing steel system with finite-difference segregation model

To further reveal the influence of micro-segregation on the precipitation behavior of MnS in sulfur-bearing steel system, a coupled model of micro-segregation and MnS precipitation was established by the finite-difference method based on various calculation domains and the solid diffusion degrees, and a new controlled diffusion equation with more stable convergence was also used. 49MnVS3 and 1215 steels were used to analyze the influence of calculation domain, segregation model and S content on the precipitation behavior of MnS. The calculation results were verified by a high- temperature confocal laser scanning microscope （HT-CLSM）. The results show that the domain has little effect on the precipitation temperature, precipitation solid fraction and precipitation amount of MnS, but affects the precipitation location and segregation of the solutes. For low- and medium-sulfur steels, the temperatures calculated by the diffusion control growth （DCG） model and the Lever model were nearly identical, whereas the temperature calculated by the Scheil model was lower. However, for high-sulfur steels, the precipitation temperatures calculated by three segregation models were nearly same. The precipitation solid fraction is more reasonable to describe the precipitation behavior of MnS. The precipitation behavior of MnS, observed by the HT-CLSM, matches well with that in the DCG model.

Thermodynamic analysis of improvement of converter gas by injecting pulverized coal into vaporization cooling flue

In order to improve the calorific value and the recovery yield of converter gas during the steelmaking process, a novel and thermodynamically admissible process was proposed. This method involved injecting pulverized coal into the vaporization cooling flue of a converter, and the approach was developed based on an industrial 30 t converter. The effects of temperature, O2 content, and the volumetric ratio of CO to CO2 on the conversion of the mixed components of gas were analyzed using thermodynamic calculations. Furthermore, the effect of the injection rate on the quality and quantity of gas was investigated. The results show that the O2 and CO2 components of flue gas decrease as the injection rate increases, whereas the CO and H2 components synchronously increase. With the injection rate of 30 kg min-1, the 02 and CO2 components of the gas decreased by 64.12 and 41.19%, respectively, while the CO and H2 increased by 20.09 and 236.84%, respectively, and the recovery time of gas increased by 11.61%, compared to non-injection.

Thermal analysis of walls in a new-type billet caster tundish with a vacuum shell

To reduce thermal loss from molten steel in a tundish during continuous casting production, a new tundish fabricated by welding radiation-proof steel plates onto the steel plates of the exterior walls of a billet caster tundish was proposed. This new tundish was used to investigate the effect of pressures inside the vacuum chamber on the uniformity of the temperature of molten steel and the thermal conditions of the vacuum layer. The results show that the conversion radiation coefficient is not sensitive to pressure and its value at high temperatures is merely 1.5 times greater than that at low temperatures. Pressure is the key factor af- fecting additional factor of conversion convection. This factor is more than 100 times greater at 10-5 Pa than at 10-2 Pa, and the temperature at inner points at 10-2 Pa is, on average, 4 K higher than that at 10-5 Pa. Meanwhile, the local temperature difference of the inlet at 10-2 Pa is 1 K higher than that at 10-5 Pa. Thus, the proposed vacuum billet caster tundish can achieve low superheat teeming of steel because of the ther- mal preservation capability of the vacuum, which helps to reduce the tapping temperature and improve the uniformity of the temperature of steel.