The 10 most-cited articles in 鐵と鋼 : 日本鐡鋼協會々誌, 2020

In order to examine the effects of soft-fine particle peening (Soft-FPP) on the fatigue properties of gas carburized SCM420H steel, rotating bending fatigue tests were conducted for carburized SCM420H steels treated with FPP using shot particles having different hardness. The Soft-FPP treated steels pre-treated with carburizing showed higher fatigue life and fatigue strength at 107 cycles compared with the only-carburized steels. This is attributed to the increase of surface hardness and the generation of compressive residual stress induced by FPP. The carburized steels treated with FPP failed in the subsurface fracture mode from the singular microstructure beneath the carburized layer in the long life region. The transition stress for the carburized steels treated with FPP, at which the surface fracture mode changed to the subsurface one, tended to increase with the hardness of shot particles used in FPP. Furthermore, the release behavior of residual stress induced by FPP during fatigue tests was also examined. There were no noticeable differences in compressive residual stress…

Elastic stiffness c11, c12 and c44 are key parameters in the analysis of elastic deformation behaviors. In order to determine the values of these parameters, Young’s modulus of single crystal; E100, E110 and E111 are needed as well as Young’ modulus Ep and Poisson’s ratio ν in poly-crystal. In this paper, the values of Young’s modulus in single crystalline iron are summarized and then elastic stiffness was estimated for pure iron under the conditions; Ep=208.2 GPa and ν=0.291 that are reliable values for isotropic poly-crystalline iron. As a result, it is found that Young’s modulus of single crystalline iron should be as follows: E100=127.8 GPa, E110=214.3 GPa, E111=276.6 GPa. From these values, elastic stiffness of iron is calculated at c11=228.1 GPa, c12=135.0 GPa, c44=113.2 GPa. Diffraction Young’s modulus of iron can be estimated on the basis of Kröner model by applying the values of elastic stiffness. It is also confirmed that the average value of diffraction Young’s modulus agrees with the value of Young’s modulus Ep (208.2 GPa) of ideal poly-crystalline iron.

This research centers on elucidating the relationship between void nucleation sites and the morphology/distribution of the surrounding phase in dual-phase steel during the initial stages of ductile fracture. Characteristic features of voids and surrounding ferrite/martensite grains were observed through a three-dimensional (3D) optical microscope analysis with the aid of serial sectioning. The characterized 3D distribution and morphology of ferrite/martensite surrounding the voids were set as an input for a finite flement (FE) simulation to obtain the hydrostatic pressure and equivalent plastic strain in the ferrite and martensite phases during tensile deformation. Experimental results showed that some of the voids present in the ferrites were surrounded by the flat-shaped martensites, which were elongated along both rolling direction (RD) and transversal direction (TD). These flat-shaped martensites were existed along the tensile direction. The FE simulation showed that the ferrite grains sandwiched between the harder martensites are more susceptible to void nucleation; this is due…

This paper gives an overview of developments in the field of non-oriented electrical steels that are widely used in motor cores in recent years, focusing mainly on texture control. ND//<100> texture is recognized as the ideal texture for application to motor cores. To obtain a suitable texture, precise control is required during each manufacturing process. This involves adjusting the chemical components during the steel making, fine temperature and reduction control during hot rolling, temperature control during hot-band annealing, temperature and reduction control during cold rolling and heating rate and temperature control during final annealing. High silicon Fe-Si alloy containing 6.5 mass% Si has been recognized as a promising core material for high frequency applications. When producing high silicon steel by the continuous chemical vapor deposition (CVD) siliconizing process, materials with a gradient Si concentration in the sheet thickness direction have been found to display superior high-frequency iron loss.

Thermodynamic analysis of the Fe-Mo-B ternary system was performed using the CALPAHD approach coupled with the first-principles calculation, and effect of Mo addition in steels on the grain boundary segregation tendency of B was discussed by means of the grain boundary phase model. The calculated phase diagrams and thermodynamic properties well reproduced the experimental data as well as the results of the first-principles computation, and thus the parameter set with high accuracy for this ternary system was evaluated. Grain boundary segregation behavior of B and Mo was analyzed by means of the parallel tangent scheme. The Gibbs energy of the liquid phase obtained in the present work was adopted for that of the grain boundary phase. According to the model, the amount of segregated B in grain boundaries decreased with descending temperature. This phenomenon is due to the formation of boride phases such as Fe2B and τ2 phases in the iron matrix.

To calculate the dislocation density of tempered low-carbon martensitic steels (Fe-0.15%C alloy) by the direct-fitting/modified Williamson-Hall (DF/mWH) method, the unknown parameter A in tempered martensite was investigated. In the DF/mWH method, the dislocation density ρ is defined as ρ=2φ2/(πA2b2). Here, φ and b correspond to the slope of the DF/mWH plot and the magnitude of the Burgers vector, respectively. In low-carbon martensitic steels tempered at 573 - 873 K, φ and ρ were estimated by the DF/mWH method and the modified Williamson-Hall/Warren-Averbach method, respectively. As a result, these parameters decreased with increasing tempering temperature. By substituting φ and ρ in the above equation, the parameter A can be obtained as a function of the tempering parameter λ as follows:

Reduction behavior of various multi-component calcium ferrites at 900°C were investigated by using in situ X-ray diffraction (XRD) and X-ray absorption spectroscopy. Intermediate components were determined by XRD, and change in X-ray absorption spectra of Fe and Ca K-edges were analyzed to determine reaction rate constants. SFCA-I (Ca3(Ca,Fe)(Fe,Al)16O28) and SFCA (Ca2(Fe,Ca)6(Fe,Al,Si)6O20) consist of layered structure of spinel and pyroxene. Early stage of reduction reaction, diffraction peaks of spinel structure were observed which indicating SFCA-I and SFCA decomposed into these units at the first step of the reduction reactions. The spinel was reduced sequentially into FeOx then Fe. Intermediate component, Ca2(Fe,Al)2O5 originated in pyroxene module was hard to reduce and reaction was controlled by decomposition of this phase. Reduction of SFCA-I started later than SFCA (with 5.7 mol% Al2O3) under hydrogen gas reduction condition at 900°C. SFCA with a high aluminum content indicated lower reducibility than that with a low one.

The pop-in phenomenon as a plasticity initiation during nanoindentation was analyzed to investigate the effect of solute carbon on the plastic deformation for Fe-C binary alloys and interstitial free (IF) steel. The maximum shear stress τc calculated from the critical pop-in load increases as solute carbon concentration increases. Based on a model in which the elementary step of pop-in is the nucleation of a dislocation loop, it is considered that solute carbon increases the resistance to the growth of a dislocation loop, thus higher stress is necessary for the nucleation. Frequency distributions of the pop-in load shows two peaks when the sample includes solute carbon. One peak on the lower load corresponds to the nucleation at a region of solute carbon free. The other peak on the higher load is attributed to the nucleation at a region with solute carbon. Displacement burst during pop-in Δh decreases with increase in solute carbon concentration. Considering that the Δh is proportional to the number of dislocations, it is concluded that solute carbon decreases the mean free path of…

To recover the barren coast or degraded paddy field, the supply of nutrient elements such as Fe is effective. Since steelmaking slag contains various kinds of potent elements, it is expected to be used as an environmental restoration material. The dissolution mechanism of various elements from slag and the influence of surrounding organic matters and microorganisms must be clarified to utilize steelmaking slag in these methods effectively. In this research, the dissolution tests were conducted by using synthesized CaO-SiO2-FeO-Al2O3-P2O5 amorphous slag samples and aqueous solutions containing gluconic acid. Concentration of various elements in the solution, especially Fe, increased by the addition of gluconic acid. To evaluate the effect of gluconic acid on the dissolution behavior quantitatively, the existence forms of various elements in the solution were thermodynamically estimated based on the experimental results. The maximum ratio of chelated iron to total iron was 97%, indicating that the increase in iron concentration by adding gluconic acid was owing to the formation of…

The demand for a reliable and quantitative method to determine phase fractions has been increasing due to the developments of multi-phase materials, such as TRIP steels. The authors conducted a mutual verification between the two methods for phase fraction analysis, the saturation magnetization measurement and the newly developed neutron diffraction technique, neutron-diffraction-based Rietveld texture analysis (NDRTA). The chemical compositions of the current samples were Fe-18Cr-8Ni-1Mn-0.5Si (mass%) with 0, 0.1 or 0.2 mass% of C or N. The α’-martensite volume fractions analyzed by both methods showed a good linear correspondence. The analysis based on the saturation magnetization measurement required an accurate evaluation of the volume saturation magnetization of α’-martensite, which was a function of the chemical composition. The comparison with the result of NDRTA can be an effective method to calibrate the volume saturate magnetization of α’-martensite, especially in the case that a fully transformed standard sample cannot be obtained. NDRTA is also an effective method to…