Takuro Masumura 교수

The remarkably high work-hardening rate in high-nitrogen austenitic stainless steels is generally believed to be due to the promotion of dislocation accumulation by nitrogen addition. However, analysis of dislocation accumulation behavior by the modified Williamson-Hall/Warren-Averbach method reveals that no difference to the increment of the dislocation density during deformation exists between austenitic steels with and without nitrogen. Since cross slipping is markedly suppressed in high-nitr

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 v

(Friction stress) k G b Burgers vector 2-5) 6) (2) 7) 8) 3) (2) 9) 10 15 m -2 (2)

The effects of C and N on the work-hardening behaviors were compared in metastable austenitic steels in which varied amounts of C and N were separately added (Fe-18%Cr-8%Ni-(C,N) alloys). Although both C and N suppressed deformation-induced martensitic transformation during tensile deformation due to their austenite-stabilizing effect, they enhanced the work hardening of the steels. Comparison of C-added and N-added steels revealed that C addition more increased the work-hardening rate than N ad

Md30 is defined as the temperature at which 50 vol.% of α’-martensite is formed at a true tensile strain of 0.3 in metastable austenitic steels. The effect of C concentration on Md30 is known to be identical to that of N, as shown by Nohara’s equation. However, we found that Md30 of C-added steel is lower than that of N-added steel, which indicates that the effect of C concentration on the mechanical stability of austenite is more significant than that of N. In addition, the relationship between

The electrical resistivity of low-carbon martensitic steels was measured to estimate the carbon concentration in the solid solution. Since electrical resistivity is influenced not only by solute carbon but also by substitutional elements, lattice defects, and second phase, the effects of these factors need to be subtracted from the total electrical resistivity to obtain an accurate solute carbon concentration via this method. Consequently, the effects of dislocations and grain boundaries were mu

Md30 is defined as the temperature at which 50 vol.% of α’-martensite is formed at a true tensile strain of 0.3 in metastable austenitic steels. It has been generally believed that the effect of carbon content on Md30 was estimated to be identical to that of nitrogen as shown by Nohara’s equation. However, we found in this study that Md30 in carbon-added steel is lower than that in nitrogen-added steel, which indicates that the effect of carbon content on the mechanical stability of austenite is

In Modified Williamson-Hall / Warren-Averbach (MWH/WA) method, the estimation of parameter α is of vital importance for obtaining other parameters accurately. Almost all researchers use the procedure for determining parameter α proposed by Ungár et al. (route 1), which includes the rough approximation. On the other hand, Takebayashi et al. suggested an improved procedure (route 2) which could give more precise results. By comparing above two routes, it is found that route 1 can result in overest

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 t

Age hardening in stable austenitic stainless steel wires with a chemical composition of Fe–18%Cr–12%Ni and different N contents was investigated to clarify the role of N. Age hardening could be enhanced by increasing the drawing ratio and N content. The highest age-hardening effect was observed at 800 K in the N-bearing specimens. In addition, severe drawing induced low-temperature age hardening at 450–600 K. Differential scanning calorimetry (DSC) analysis revealed that age hardening at 800 K m

Electrical resistivity of low-carbon martensitic steels was measured to estimate the carbon concentration in solid solution. Since electrical resistivity is influenced not only by solute carbon but also by substitutional elements, lattice defects and second phase, the effects of these factors need to be subtracted from total electrical resistivity, in order to obtain the accurate solute carbon concentration by this method. As a result, the effects of dislocations and grain boundaries were much s

The Williamson-Hall (WH) plots are the basic approach for the dislocation characterization. However, the elastic anisotropy affects full width at half maximum in diffraction peaks and this makes the dislocation characterization difficult. In order to correct the effect of elastic anisotropy, Ungár developed a unique methodology using the contrast factor, so called the modified Williamson-Hall (mWH) method. On the other hand, authors developed a new methodology termed as “direct-fitting (DF) meth