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Effects of austenite on the uniform corrosion in the solution of 1 N H2SO4 were investigated through the electrochemical polarization test. Two phases structures of martensite and austenite were obtained by annealing treatment at the range of 500℃~700℃ for 10min. in 70% cold- rolled 202 stainless steel. Volume fraction of reversed austenite increased rapidly with an increase of annealing temperature. Uniform Corrosion was occur mainly on martensite phase in 202 austenitic stainless steel with two phase of austenite and martensite. Corrosion current density increased with an increase of volume fraction of austenite, therefore uniform corrosion was affected by volume fraction of austenite
Effect of tempering treatment on the mechanical properties of 12Cr heat resistant steel with ferrite phase was investigate in this study. As time and temperature of tempering treatment were increase, C and Cr contents in matrix structure were decreased. Due to increase of the amount of Cr26C6 type carbides. It was confirmed in mechanical properties experimental that tensile strength and hardness were decreased, while elongation and impact value were, increased with increasing the time and temperature.
This study was carried out to investigate the effect of aging treatment on the mechanical properties and damping capacity of 12Cr heat resistant steel with ferrite phase. While hardness values in ferrite phase was not changed, that in martensite phase was dramatically dropped in early stage of aging treatment and then gradually decreased with increase of aging time. As aging treatment was carried out, the precipitation was not detected in ferrite phase, while carbides were precipitated in martensite phase. With increasing the aging time, tensile strength eventually decreased while impact toughness increased rapidly in the early stage of aging and then gradually increased. Besides, it was confirmed that damping capacity was not changed in the early stage of aging and then gradually increased with increase of aging time. (Received October 20, 2010; Revised November 9, 2010; Accepted December 7, 2010)
The effect of grain size on the damping capacity of Fe-26Mn-2Al alloy studied in this paper has been investigated after changing the microstructure by cold rolling and changing grain size. Micro structures in Fe-26Mn-2Al at room temperature consist of a large quantity of austenite and a small quantity of ε and α' martensite. And ε and α' martensite was increased by increasing the degree of cold rolling. The content of deformation induced martensite was increased with increasing the degree of cold rolling. Damping capacity was linearly increased with increasing ε martensite content, which suggests that stacking faults and ε martensite variant boundaries are the principle damping sources. With increasing the grain size in Fe-26Mn-2Al alloy, the damping capacity was increased due to increasing the volume fraction of ε martensite by decrement in stability of austenite phase. With decreasing the grain size, the content of deformation induced martensite was decreased and the damping capacity was decreased.
This study was carried out to investigate the effect of reverse transformation on the mechanical properties in high manganese austenitic stainless steel. Over 95% of the austenite was transformed to deformation-induced martensite by 70% cold rolling. Reverse transformation became rapid above an annealing temperature of 550℃, but there was no significant transformation above 700℃. In addition, with an increasing annealing time at 700℃, reverse transformation was induced rapidly, but the transformation was almost completed at 10 min. There was a rapid decrese in strength and hardness with annealing at temperature above 550℃, while elongation increased rapidly above 600℃. At 700℃, hardness and strength decreased rapidly, and elongation increased steeply with an increasing reverse treatment time up to 10 min, whereas there were no significant change with a treatment time after 10 min. The reverse-transformed austenite showed an ultra-fine grain size less than 0.2 ㎛, which made it possible to strengthen the high manganese austenitic stainless steel.
This study was carried out to investigate the effect of reverse transformation on the damping capacity in high manganese austenitic stainless steel. α′-martensite was formed with the specific direction and surface relief by deformation. Over 95% of the austenite phase was transformed to deformation-induced α′-martensite by 70% cold rolling. Reverse transformation became rapid above an annealing temperature of 550℃, but there was no significant transformation above 700℃. In addition, with increasing annealing time at 700℃, reverse transformation was induced rapidly, but the transformation was almost completed at 10 min. Damping capacity was increased up to 700℃, and than unchanged with the increasing annealing temperature. Damping capacity increased steeply with an increasing reverse treatment time up to 10min, whereas there were no significant change with a treatment time of more than 10 min. Damping capacity increased with an increasing the reversed austenite and was strongly affected by reversed austenite.
The effect of forging start temperature, forging ratio on the microstructure and mechanical properties of B7B4 steel ware investigated. Microstructure of centrifugal casted B7B4 steel consisted of martensite and ferrite phase. The volume fraction of ferrite increased with increase of forging start temperature and decreased with increase of forging ratio. Tensile strength and hardness decreased with higher of forging start temperature, while impact value and elongation increased with higher of forging start temperature. With increase of forging ratio, tensile strength rapidly increased up to the forging ratio of 30%, and then slowly increased, but elongation was decreased. Hardness and impact value rapidly increased with increase of forging ratio.