This paper reviews studies on the prediction of ductile fracture during metal forming using an ellipsoidal void model and some other models proposed by the author and some relevant studies. Section 2 discusses the research on the theory of voids for predicting ductile fracture during metal forming. Section 3 summarizes the simulation method for predicting ductile fracture during metal forming using the ellipsoidal void model, and Section 4 summarizes the simulation result on the ductile fracture prediction during metal forming using the ellipsoidal void model. Section 5 shows the applicability of the ellipsoidal void model and the simulation result on the ductile fracture prediction during metal forming using some other models.

Surface inspection of steel products is very important for quality assurance. Many automatic in-line surface inspection systems using the camera technique have already been installed in sheet production lines. However, automatic surface inspection of steel products such as steel pipes and thick plates has not advanced because the entire product surface is covered with uneven mill scale, and it is difficult to distinguish the pattern of the mill scale from defects with concave-convex shapes in images of the camera.

The authors developed a new surface inspection system using the twin illumination and subtraction technique, which emphasizes only concave-convex defects while canceling the pattern of the mill scale covering these types of steel products. An optical approach to enhance the detection performance of this system was already reported in connection with the development of a steel plate surface inspection technology. This paper discusses the development of a new image processing technique to detect defects from obtained images in order to satisfy the conditions of introducing automatic inspection systems at steel production lines. Concretely, a high-speed bright-dark pattern detection algorithm using expansion and conjunction processing was developed, and improved the processing speed by 22.6 times relative to the conventional simple method. An effective new original feature, overlap ratio of bright parts, was also developed, resulting in a 5.15% improvement in the classifier concordance rate relative to that without the proposed features. The developments described above have realized automatic surface inspection systems suitable for introduction in steel production manufacturing processes.

Main application of steelmaking slag is a base course material. In order to utilize slag as a base course material, it is necessary to have various characteristics in the criteria, and the modified California Bearing Ratio (CBR) value which evaluates the performance as a base course material is an important index in comparison with other competitors. Although it is expected that various factors such as properties and granularity affect CBR characteristics and compaction properties, the particle properties and granularity of steelmaking slag is different on each refining process which produce steelmaking slag. In addition, until now, X-ray CT measurement for slag base course material and effect of particle property have not been examined. Therefore, in this study, measurement of the internal phenomena of the steelmaking slag base course material by micro-focused X-ray CT and various measurement were carried out. It was revealed that the particle strength of porous particles is lower than that of dense real particles regardless of particle size and the subbase bearing capacity did not differ as much as the particle strength difference. In addition, from the mechanism by which the stress propagates and elastic finite element analysis by using X-ray CT, it was considered that the distribution of the stress was changed by the dispersion of the particle strength of each grain, and it affected the property of base course material which was the integral value of the effective stress.

The effect of C content in steels on the formation of an Al-containing carbide layer by an Al pack method at 980°C was investigated. The continuous layer consisting of an outer β-FeAl and inner Fe₃AlC layers was formed on Fe-1.2C (in wt.%) by a short process time. An α-Fe(Al) layer with Fe₃AlC precipitates was formed below the β-FeAl layer on Fe-0.7C after 16 h of process, thereafter an Fe₃AlC layer was formed between the β-FeAl and α-Fe(Al) + Fe₃AlC layers after 25 h. The β-FeAl and α-Fe(Al)+ Fe₃AlC layers were formed on Fe-0.1C, but a continuous Fe₃AlC layer was not developed after longer treatment. A continuous Fe₃AlC layer formed by an Al pack method was explained by carbon enrichment at the α-Fe(Al)/γ-Fe(C) interface due to an inward growth of the α-Fe(Al) layer.

The effects of retained austenite upon softening during low-temperature tempering at 373 K were investigated using martensitic carbon steels with and without retained austenite. To increase the amount of retained austenite, 10 mass% Ni was added to the base carbon steel (Fe-0.3C alloy). During tempering, the hardness decreased more rapidly in the Ni-added steel containing 6 vol.% retained austenite than in the base steel without retained austenite. Analyses of the microstructure and the carbon content in the solid solution (i.e., the solute carbon concentration) revealed that the retained austenite tended to suppress carbide precipitation and significantly reduced the solute carbon concentration in the martensitic matrix. We demonstrated that retained austenite acts as an effective absorption site for solute carbon in the martensitic matrix; however, the partitioned carbon is unevenly localized near the martensite/austenite interface, owing to the poor diffusivity at 373 K.

Automotive suspension springs are required to be high-strength and lightweight, and currently have a maximum strength of 2000 MPa. In addition, they must have high resistance to hydrogen embrittlement in the service environment. From previous researches, Si addition or rapid tempering improve the hydrogen embrittlement resistance of low alloy steel. In this study, we investigated the hydrogen embrittlement properties of steel samples with different Si contents and tempering rates and the effects of the fine iron carbides and retained austenite on its properties for 2000 MPa suspension spring steel. JISSUP7 (2.0Si) and SAE9254 (1.4Si) spring steels were tempered at different tempering rates by induction (IH) and furnace heating (FH) methods. Four-point bending tests under corrosion cycles were performed on these steels, and the time to failure was measured. The results show that the 2.0Si-IH steel with higher Si content and higher tempering rate has the longest fracture life and highest resistance to hydrogen embrittlement, even with relatively high diffusible hydrogen content. The size and volume fraction of iron carbides and retained austenite were evaluated by TEM, EBSD, and synchrotron XRD, and the 2.0Si-IH steels were found to have the smallest size and the highest volume fraction of fine iron carbides Fe_2-3C(ε) and the highest amount of retained austenite. It is considered that the fine iron carbides of Fe_2-3C(ε) work as hydrogen trap sites and that their high dispersion suppresses dislocation movement. They suppress hydrogen accumulation in stress concentrated areas and are expected to improve resistance to hydrogen embrittlement.

High phosphate slag fertilizer (SHP) contains phosphorous, calcium, magnesium and silicon, expected to be effective in supplying plant nutrients and improving soil acidity. We clarified the characteristics and effects of the SHP as a fertilizer. Nippon Steel Corporation prepared the SHP prototypes by concentrating phosphorus through high-temperature processing. Five types (SHP12, SHP15, SHP18-1, SHP18-2, SHP27-2) were examined through dissolution test, pot cultivation experiment, and evaluation of improving effect on soil acidity. The SHP12 was insoluble in water but soluble in various acids and most SHP contained more than 95% of acid-soluble phosphate and silicate. Above-ground growth and phosphate uptake of spinach was higher in the SHP12 plot than in no-phosphate, ammonium phosphate and fused phosphate plots, indicating that phosphorus in the SHP12 could be absorbed more easily than the common phosphate fertilizers. Above-ground growth and phosphate uptake of wheat was also high in the SHP12 and SHP15 plots, which was comparable to ammonium phosphate plot. However, the SHP27-2 had little effect as a phosphate fertilizer. The SHP12 and SHP15 could be expected to supply calcium and silicon as well as phosphorous. Although most SHP showed the same ability to improve soil acidity as calcium carbonate, it might be necessary to avoid excessive increase in soil pH depending on the soil condition and the ability of SHP. We can conclude that if the composition of the SHP is optimized, it can be used as a fertilizer with multiple effects depending on soil types, nutrient status, and crop types.