발간논문

Home > KJMM 논문 > 발간논문

Behaviors of the thermal expansion, high temperature deformation and mechanical properties after vacuum annealing have been studied in Fe-36.5% Ni-(0.2∼0.6)% Mn Invar alloys. Regardless of the difference of Mn content, the thermal expansion coefficients are not changed and those at room temperature are below 10^(-6). The yield stress and the ultimate compressive stress at 1000℃ are not changed with Mn content while the peak strain continuously increases with Mn content. The yield stress at room temperature after annealing is slightly decreased with Mn content, and the lowest yield stress of 205. 8㎫ is obtained an alloy containing 0.48% Mn by annealing at 1200℃. At annealing of 1200℃ the yield stress and the ultimate tensile stress as well as the elongation show the lowest values and these are discussed as the combined effects of the grain growth, the amount of MnS and the development of cube texture.

keyword :

The effect of texture and dislocation structure change on deformation behaviors in a corss-rolled steel was studied by texture measurements and TEM obsevations. The cross rolling experiment was performed through 60 or 90?rotation from the initial rolling direction. The reduction degree of the initial rolling was 30% and that of the final rolling was up to 80% The orientation change was calculated by Taylor`s deformation theory to analyze the development of the preferred orientations in the rolling texture. A rotation of microbands into the rolling direction in the longitudinal section was found by the cross rolling, while microbands became parallel to the rolling plane during the normal rolling deformation. Though shear band was not shown in the normal rolled specimen at 80% reduction, it formed in the cross rolled specimens at reductions higher than 70%. The rotation of the rolling direction at 30% reduction resulted in the corresponding rotation of the preferred orientations in the rolling texture. A marked change was shown in the texture of the corss rolled specimens of 50 % total reductions. Irrespective of cross rolling angles, the rolling texture of 80% total reduction could be described by a {111}//ND and a $lt;110$gt;//RD fiber.

keyword :

Various 97Fe-3Cu(wt%) sintered specimens were prepared from mechanically mixed powders and Cu coated powders. Cu-coated Fe powders were prepared by electroless platings (reducing and ion exchange method.) The ion exchange method resulted in better coating of Cu on Fe powder than the reducing plating method. The compacts of Cu-coated Fe powder by ion exchange showed the highest sintered density. The tensile strength and hardness of sintered compacts increased by about 10 and 5D%, respectively, when using Cu-coated Fe powder instead of mechanically mixed Fe-Cu powder. The coating of Cu on Fe powder appears therefore to be useful to improve the sinterability and mechanical properties of Fe-Cu base sintered products.

keyword :

Polycrystalline powders containing 50at% Cu and 50at% Ti have been mechanically alloyed by using rotatory ball mill under the Ar atmosphere. The microstructural change of the Cu_50Ti_50 powder with milling time can be divided into four steps such as initial, cold welding, equiaxed particle formation and steady state periods. The microhardness was increased with milling time and reached about Hv 300 after the steady state. The size of crystallite was decreased at decreased rate with machanical alloying. The amorphization started at the steady state period and completed after about 30 hrs. of milling. The amorphous phase with CuTi composition was obtained.

keyword :

The effect of hydrogen on tensile strength in dual phase steels, which have different martensite volume fraction and martensite morphology, was studied by load-elongation test. Tensile strength was decreased with increasing hydrogen charging density. If martensite volume fraction and hydrogen charging density was increased, total elongation in step quenched structure was decreased much more than that in intercritical annealed structure. When hydrogen was introduced in intercritical annealed specimen, the void was bigger than non hydrogen-charged specimen during plastic deformation. When hydrogen was introduced in the step quenched specimen and intercritical annealed specimen, the void in the step quenched specimen was bigger than that in the intercritical annealed specimen during plastic deformation.

keyword :

Equilibrium concentrations of various hydrocarbon species which existed in the vapor for growing solid carbon is calculated and a phase diagram for the carbon-hydrogen system is obtained using the thermodynamic quasi-equilibrium model. These calculations show that methane is the sole reaction product at temperatures below 1000℃, acethylene is, however, the dominant hydrocarbon speies above 2000℃. The CVD phase diagram shows that high methane concentrations and low total pressures decrease the lower temperature limit required to obtain any deposit. The fraction of carbon deposited from methane-hydrogen mixtures changes rapidly from practically zero at lower temperature limit to close to 100% over a couple of hundred degrees, then to decrease to zero at higher temperature limit.

keyword :