In continuous casting process, evenness of solidification is one of the most important issues of steel quality. Molten steel is solidified at water-cooled mold and followed by secondary water cooling zones. To analyze the phenomenon of width direction’s unevenness of solidification, it is important to visualize the flow pattern of spray water. Computational fluid dynamics is useful but grid based methods for example FVM, FDM, and FEM are not appropriate because of complex free surfaces. So, the particle based method called MPS has been applied. One of the characteristic patterns of roll arrangement was modeled, and spray water flow was calculated. As a result, according to the water rate of spray, the accumulated water on rolls overflows. The accuracy of the numerical model has been verified by the experiment which consists of the acrylic plate and rolls and spray nozzles. Computational results of water flow rate at the position of roller bearings and edges of slab agreed well with experimental results. The heat transfer coefficients between water and slab surface were estimated by this calculated results, and the solidification was also calculated. It was found that uneven water flow affected the solidification unevenness.
Alumina clusters extracted from molten steel and a cast slab at our plant were analyzed by SEM and TEM. It was found that a small amount of liquid FeO could accelerate the clustering of alumina inclusions in aluminum-killed steel because of the strong liquid-capillary negative pressure of liquid FeO. The sources of the FeO are most likely oxygen contamination from ferroalloy additives, residual steel adhering to the refractory surfaces of ladles and vessels, and air entrainment.
Hot-dip galvanized steel sheets are often used for automobile exterior body panels to enhance the corrosion performance. The requirements for their surface appearance from automakers have become higher recently. Especially, a uniform coating layer of zinc is required. In a continuous hot-dip galvanizing line (CGL), a pair of gas wipers, which are installed just above the zinc pot, is used to control the thickness of the coating layer. The strip vibration at the gas wipers causes the uneven coating thickness in the traveling direction, while the cross-bow of the strip leads to the unevenness in the width direction. The behavior of the strip at the gas wipers should be stable for the uniform coating layer. In order to make the strip stable and flat, a strip vibration and shape control technique using electromagnets has been developed. It greatly contributes to produce hot-dip galvanized steel sheets with excellent surface appearance.
This study was intended to investigate the effect of the amount of Mg and Si addition in the Al-Si coating in order to improve corrosion resistance of Aluminized steel sheets.
A salt spray test using formed specimens proved that Al-8mass%Si-6mass%Mg-coated steel sheet having less cracks in the alloy layer after forming has the best corrosion resistance.
This outdoor exposure test using unformed specimens for 10 years proved that corrosion weight loss of Al-8mass%Si-6mass%Mg-coated steel sheet was reduced to approximately 30% less than that of Aluminized steel sheets and approximately 70% less than that of 55% aluminum-zinc alloy-coated steel sheets; thereby, it was possible to confirm that Al-8mass%Si-6mass%Mg-coated steel sheet has favorable corrosion resistance under a long-term atmospheric environment.
This is supported to be the protective effects caused by corrosion products mixed with Si and Mg, since the current value of the cathode polarization method of the specimen of Al-8mass%Si-6mass%Mg-coated steel sheet after the outdoor exposure test in an artificial rain solution were reduced by approximately 40% less than that of aluminized steel sheet.
Cold-rolled and annealed ferrite-martensite dual phase (DP) steel sheets are a useful material for automotive applications because of their excellent balance of strength and ductility. Although few research papers have examined the crystallography and microstructure of lath martensite in DP steel, the characteristics of lath martensite have been investigated in single-phase martensitic steel. In the present study, the crystallography and microstructure of lath martensite in a ferrite-martensite dual phase were studied using electron microscopy and electron diffraction analysis, and the crystallographic orientation relationship between the ferrite and martensite was analyzed. The main results are as follows: (1) The lath martensite in DP steel consists of some number of packets, and these packets consist of blocks. This structure is the same as the microstructure of single-phase lath martensite. (2) The habit planes of the martensite laths in a packet tend to be parallel to the close-packed plane of the adjacent ferrite grain, whose fraction is about 30%.