발간논문

Home > KJMM 논문 > 발간논문

The microstructure and tensile properties of low carbon 2% Mn steel and 2% Mn-Nb-V steel that had been cold rolled by different degrees of reduction, were studied after aging treatment at 500, 600 and 700℃ for 60 minutes The specimens of 50% cold reduction show higher strength than those of 25% cold reduction, when aged at 500 and 600℃. However, this trend is reversed when they are heat treated at 700℃, in the temperature range of α＋γ region of those steels. Effects of aging treatments at 600℃ are also investigated for the periods of times up to 3,000 minutes. By increasing the aging time the ferrite grains recrystallize progressively and become equiaxed, and the carbides coarsen. Carbides in Mn-Nb-V steel are analyzed as V₄C₃and NbC by the election diffraction method.

keyword :

Splitting behavior of tensile specimens of low carbon 2% Mn steel and 2% Mn-Nb-V steel that had been cold rolled and aging treated were studied. The occurrence of splitting depends on steel composition, degree of cold reduction and aging treatment conditions. The susceptibility to splitting is closely related to the weakness of ferrite grain boundaries This weakness is attributed to elongation of the ferrite grains in the direction of cold rolling and also to precipitation and growth of carbides at the grain boundaries during the aging treatment.

keyword :

The behavior of retained austenite during cyclic heat treatment and deformation in medium carbon Mn-Si steel was investigated using electron microscope. The orientation relation between the austenite and martensite satisfies both K-S and N-W relationships. Austenite was retained as thin films when quenched from γrange and as isolated islands when quenched from (α＋γ) range. The amount of retained austenite tends to decrease with increased quench temperature upto 1100℃. The retained austenite was mostly strain induced transformed to martensite in the early stage (1-5%) of tensile deformation The strain hardening exponent and total elongation were increased with increased volume fraction of retained austenite.

keyword :

The influence of the second stage cold reduction ratio on the orientation of the recrystallized matrix in grain-oriented Si-Steel containing MnS ppt is investigated. The average deviation from ideal (110)[001] orientation in high temperature annealed specimen is reduced according to the increase of intensity of the (111) [112] component in the final texture of cold rolled strip and the intensity of the (111) [112] component has its maximum value when the second stage cold reduction ratio is 65%. It is also found that the temperature of the secondary recrystallization increases with grain coarsening of the primary matrix because the driving force for the secondary recrystallization, due to grainboundary energy, decreases.

keyword :

The behavior of static and cyclic creep of Ni-35Cu alloy are investigated at 485 K (0.43 Tm) and 450 MPa. The effect of stress amplitude on the cyclic creep behavior is studied by measuring the friction stress and the activation energy for the creep. Cyclic creep acceleration is observed and the cyclic creep rate increases with the stress amplitude. The activation energy for cyclic creep is slightly lower than that for static creep and the activation energy for cyclic creep deformation is not affected by the stress amplitude. In the cyclic creep deformation, the fact that the activation energy is not significantly affected by the stress amplitude means the deformation mechanism is independent of the stress amplitude. From the above results, it is considered that the cyclic creep rate is controlled by the friction stress level and the recovery rate during unloading by the dislocation core diffusion.

keyword :

The effect of nitrogen on the mechanical properties of Ni-free austenitic stainless steel has been studied at low temperature range between R.T. and -196℃. Ni in conventional austenitic stainless steel is replaced by Mn and N. Tensile strength and 0.2% offset yield strength increase with N content and the values of Charpy V-notch impact also increase with N content. The effect of N on the mechanical properties is considered to be due to the Cottrell effect and the stability of austenite. The mechanical properties of Fe-Mn-Cr-N alloy are competitive with the standard austenitic stainless steel, type 304 at the temperature from R.T to -130℃.

keyword :

keyword :

keyword :

keyword :