Since there are many generation factors for surface cracks on steel products manufactured by the processes of continuous casting through billet rolling, it is important for their prevention to identify the process where the surface cracks are generated. In this study, the formation mechanism of the oxide particles in the subscale layer around surface cracks of steel products was investigated towards establishing an estimation method of crack generation temperature. It was found that, the average radius leveled off corresponding with its exposed temperature after enough holding time. The average radiuses were 0.2 μm and 0.3 μm for 1473K and 1573K, respectively. Those oxide particles were consisted of MnO·SiO2 and MnO·Cr2O3 phases. Their formation and growth mechanism was as follows: Firstly, MnO·SiO2 precipitates at the internal oxidation reaction front. Then, MnO·Cr2O3 forms on the MnO·SiO2 particles. The existence of these two phases played an important role to determine the terminal value of the average radius.
Air leak repairs were carried out to increase a production rate at the No. 3 sintering plant in Nagoya Works of Nippon Steel. 83 vol% of air leaks were found to be localized on pallet trucks and dead plates based on oxygen concentration measurement. Through deliberate repairs of such leakage, the sinter production rate was increased by 5 mass%.
Titanium deoxidation experiments of sulfur bearing molten steel were carried out with CaO–SiO2–TiO2–S slag at 1873K and the kinetic analysis on basis of the coupled reaction model was applied. Thermochemical software was introduced into the model to achieve the activity coefficient in wide range slag compositions. Sulfur contents in both metal and slag were calculated from the sulfide capacity based on the optical basicity model. The behavior of major components such as titanium, sulfur and so on in both metal and slag were clarified experimentally and analytically. The present modeling study suggested that the reduction rate of titanium in metal was not strongly affected by the initial CaO/SiO2 ratio or TiO2 composition of flux. The model was extended to handle both TiO2 and Ti2O3 simultaneously and the calculated results showed good agreements with the experimental results.
Parts of iron plate materials excavated from the Maisaki site at Tsuruga city of Fukui prefecture were analyzed by scientific methods of the element analysis and the metallographic observation. In the element analysis, a combustion infrared absorption method for determination of carbon and sulfur in iron plates, and a neutron activation analysis (NAA) for determination of 37 trace elements were used. In the metallographic observation, the metal structures were investigated by an optical microscope and an electron probe micro analyzer (EPMA). Carbon concentration in iron samples were low carbon steel or medium carbon steel of about 0.1–0.5%. The existence of ferrite and pearlite structures and non-metallic inclusions were observed in the samples by the optical microscope. An existence of titanium being an index of the origin of Japanese iron sand was not confirmed in these non-metallic inclusions by the EPMA mapping images. As a ratio of arsenic (As) concentration to antimony (Sb) concentration, As/Sb value were less than 1.0, the origin of the samples were estimated, namely, it is concluded that the iron plate materials were brought in Japan from ancient Korea made from iron ore as a raw material.
Coke for iron-making is produced by pyrolysis of coals in coke oven. COG (Coke Oven Gas) by carbonizing is used as energy source in steel works. Waste plastics recycling process using coke ovens is mixed with coals and carbonized in coke oven. Though the process is in operation, the effect to COG is still uncertain. Then first, in order to identify secondary decomposition of pyrolysis products of plastics such as light oil, tar, and gas and analyze more intimate behavior of plastics during pyrolysis, experimental system which has warm-up part for primary decomposition and heating part for secondary decomposition was developed. This experimental system has a Fourier transform-infrared spectrometer (FT-IR) as detector and can monitor the several kinds of gases, such as hydrocarbons, CO and CO2 simultaneously, continuously and simply. Secondly, behavior of secondary pyrolysis of plastics was analyzed. Finally, behavior of pyrolysis of mixed sample composed by plastics and coals was analyzed and each pyrolysis product was evaluated on enrichment of calory. In consequence, this paper reports that gas process of evolution, amounts of evolved gases, and compositions of evolved gases have additive property. Thus, there is no effect by mixing plastics resulting from the evolved gases during pyrolysis.
Thiol self-assembly super thin films have attracted attention from the viewpoint of surface design, e.g. chemical sensors, molecular devices and corrosion preventive films at a molecular level. On the other hand, chromate coatings on zinc coated steel sheets have been widely applied as an economical method of corrosion prevention. In response to recent environmental regulation, e.g., RoHS Directives, chromate-free coatings have been developed and applied to electrical appliances. However, a thinner chromate-free coating is required for the purpose of obtaining a better electro-conductivity, which influences the electromagnetic shielding performance of digital electrical appliances. In this paper, the corrosion resistance and film structure of alkane- and triazine- thiol self-assembly super thin layers on zinc coated steel sheets were investigated. The mechanism of corrosion prevention by the thiol layers was discussed in order to obtain a new design concept of thinner chromate-free coatings with high corrosion resistance. The alkanethiol layers showed high water-repellency and poor corrosion resistance, and the triazinethiol layers with three thiol groups per molecular showed relatively poor water-repellency and excellent corrosion resistance in spite of very small thickness such as a few monolayer thickness, which result from suppressing oxygen reduction reaction according to electrochemical measurement. It was found from XPS analysis that alkanethiol molecules combined to Zn form layers without decomposition, and triazinethiol molecules combined to Zn and the part of these molecules decomposed to form a new network structure.
Electrochemical study on cut edge corrosion of prepainted Zn coated (GI) and 55%Al–Zn coated (GL) steels has been performed in wet–dry cyclic conditions in order to clarify the difference of their degradation mechanisms. In addition, the role of chromate in the primer coating to the cut edge corrosion has been also investigated. Maximum width of delaminated polymer coating from the cut edge for GI and GL specimens was evaluated under wet–dry cyclic conditions. The cyclic tests were carried out for 1000 h by change of relative humidity, where the salt of NaCl or MgCl2 was deposited on the specimen every 48 h. The cut edge corrosion test under NaCl deposit indicated that the delamination of the GL specimen progressed at a higher rate than the GI. This is attributed to difference of corrosion morphology of their coatings from cut edge. The delamination was inhibited under MgCl2 deposit, especially for the GI specimen. The chromate in the primer coating inhibited the delamination for the GL specimen. The electrochemical corrosion monitoring was also performed under condition of alternate exposure to immersion in NaCl solution and drying at 60% RH and 25°C. On the basis of the results of the delamination tests and electrochemical measurements, the mechanism of cut edge corrosion for GI and GL and role of chromate in the primer coating were discussed.
Hydrogen desorption behaviors of pure iron with a body-centered-cubic (bcc) lattice and Inconel 625 with a face-centered-cubic (fcc) lattice were examined during tensile deformation using a quadrupole mass spectrometer in a vacuum chamber integrated with a tensile testing machine. Hydrogen and water desorption was continuously detected simultaneously under the application of a tensile load and strain to the specimens. Hydrogen desorption promoted by tensile deformation can be found by deducting both fragment hydrogen dissociated from H2O and H2 desorbed under unloading from the total hydrogen desorption out of hydrogen-charged specimens during tensile deformation. Hydrogen desorption from hydrogen-charged specimens was detected under various strain rates of 4.2×10−5/s, 4.2×10−4/s and 4.2×10−3/s. Hydrogen desorption did not increase under elastic deformation. In contrast, it increased rapidly at the proof stress when plastic deformation began, and reached its maximum, then decreased gradually for both pure iron and Inconel 625. This desorption behavior is considerable related to hydrogen dragging by dislocation mobility. The desorbed hydrogen contents promoted by tensile deformation were measured using thermal desorption analysis (TDA). The TDA results showed that the desorbed hydrogen content differed at each strain rate. The largest desorbed hydrogen content promoted by tensile deformation was 16% of the initial hydrogen content in pure iron with high hydrogen diffusion rate when it was deformed at a strain rate of 4.2×10−4/s. In contrast, that of Inconel 625 with low hydrogen diffusion rate was 9% of the initial hydrogen content when it was deformed at a strain rate of 4.2×10−6/s. This deference of the desorbed hydrogen content transported by dislocations depended on the balance between the hydrogen diffusion rate and moving dislocation velocity.