We have developed an analytical method which enables highly precise and rapid quantitative analysis of ultra low sulfur contained in steel sample. The developed method is “ultraviolet fluorescence method after combustion”, which combined high frequency induction furnace and the continuous UV fluorescence analyzer of sulfur dioxide. Despite easy operation like the conventional IR method, the newly developed method showed high sensitivity and good precision. The quantitation limit of sulfur in steel was 0.5 mass ppm. In addition, it was shown that this equipment has sufficient stability as a process control analysis apparatus of the iron mill which continues operation without resting.
It is well known that the corrosion resistance of steels is improved by the addition of alloying elements. For stainless steels, a large amount of Cr is added to obtain good corrosion resistance and the addition of rare metals such as Mo and Ni etc. are applied for further improvement of the corrosion resistance depending on corrosion environments.
On the other hand, we investigated the effects of combining the addition of alloying elements and surface treatment aiming to develop new corrosion resistant steel at lower cost by reducing the content of alloying elements.
We found that 6% Cr contained steel with inorganic zinc primer showed excellent anti-rust resistance in high chloride environments. Besides, the apparent rust area and maximum corrosion depth of 6% Cr contained steel were largely reduced by the addition of Al.
The mechanisms of decrease of carbon concentration on the surface layer after gas carburizing with increasing Si concentration was investigated using three kinds of steel whose compositions were based on JIS SCr420 varying the Si concentration (0.25%Si steel, 1%Si steel, 2%Si steel). The carbon concentration on the surface layer after gas carburizing decreased with the increase of the Si concentration, and especially that of 2%Si steel was substantially low. The carbon concentration on the surface layer after gas carburizing of 1%Si steel was nearly equal to the thermodynamic calculation value simulating the gas carburizing reaction, whereas that of 2%Si steel was much lower. This substantial change seemed to come from the oxide formation at the surface, that is, 2%Si steel was different from the other steels in oxide formation at the surface, and the oxide of 2%Si steel densely covered the surface. These results reveal that the carbon concentration on the surface layer decreased according to the effect of the inhibition of the carburizing reaction by the oxide layer in 2%Si steel in addition to the effect of the thermodynamic interaction between Si and carbon.
A grain growth model based on a two-dimensional local curvature multi-vertex model in the presence of pinning particles was developed. This model is a physical model which pursues the minimum total grain boundary energy as the evaluation function, where the unpinning conditions are as follows. The first unpinning condition is that the total energy of the unpinned grain boundary is smaller than the total energy of the pinned grain boundary. The second unpinning condition is that the energy of the grain boundary necessary to surpass the energy barrier is assumed to be smaller than the jumping energy, which is presumably assisted by thermal lattice vibration. Using only the first condition, the Zener pinning effect caused by the finely dispersed particles during normal grain growth was reproduced. With the second condition, the selective abnormal grain growth was reproduced when the abnormally grown grain was surrounded by the grains with low-energy grain boundaries.
To reveal the influence of magnetic anisotropy on hysteresis loss of electrical steel sheet, hysteresis loss of non-oriented electrical steel sheet with various Si and Al contents and same grain diameter, 100 μm, was analyzed by the hysteresis loss model we advanced in other times. In the result, the influence of magnetic anisotropy was be able to evaluated in isolation from the influence of inner stress or texture etc. on hysteresis loss. Hysteresis loss was proportional to magnetic anisotropy constant. This reason was inferred that as the magnetic anisotropy constant decreases, the energy of magnetic wall decreases, then the magnetic wall was difficult to be pinned by precipitates or grain boundaries.