• 한국재료학회지
• /
• 제29권3호
• /
• pp.189-195
• /
• 2019

The effect of C, Mn, and Al additions on the tensile and Charpy impact properties of austenitic high-manganese steels for cryogenic applications is investigated in terms of the deformation mechanism dependent on stacking fault energy and austenite stability. The addition of the alloying elements usually increases the stacking fault energy, which is calculated using a modified thermodynamic model. Although the yield strength of austenitic high-manganese steels is increased by the addition of the alloying elements, the tensile strength is significantly affected by the deformation mechanism associated with stacking fault energy because of grain size refinement caused by deformation twinning and mobile dislocations generated during deformation-induced martensite transformation. None of the austenitic high-manganese steels exhibit clear ductile-brittle transition behavior, but their absorbed energy gradually decreases with lowering test temperature, regardless of the alloying elements. However, the combined addition of Mn and Al to the austenitic high-manganese steels suppresses the decrease in absorbed energy with a decreasing temperature by enhancing austenite stability.

• 한국재료학회지
• /
• 제26권7호
• /
• pp.353-358
• /
• 2016

The hydrogen embrittlement of two austenitic high-manganese steels was investigated using tensile testing under high-pressure gaseous hydrogen. The test results were compared with those of different kinds of austenitic alloys containing Ni, Mn, and N in terms of stress and ductility. It was found that the ultimate tensile stress and ductility were more remarkably decreased under high-pressure gaseous hydrogen than under high-pressure gaseous argon, unlike the yield stress. In the specimens tested under high-pressure gaseous hydrogen, transgranular fractures were usually observed together with intergranular cracking near the fracture surface, whereas in those samples tested under high-pressure gaseous argon, ductile fractures mostly occurred. The austenitic high-manganese steels showed a relatively lower resistance to hydrogen embrittlement than did those with larger amounts of Ni because the formation of deformation twins or microbands in austenitic high-manganese steels probably promoted planar slip, which is associated with localized deformation due to gaseous hydrogen.

• 한국재료학회지
• /
• 제27권6호
• /
• pp.318-324
• /
• 2017

In this study, two Fe-30Mn-0.2C-(1.5Al) high-manganese steels with different surface conditions were hydrogen-charged under high temperature and pressure; then, tensile testing was performed at room temperature in air. The yield strength of the 30Mn-0.2C specimen increased with decreasing surface roughness(achieved via polishing), but that of the 30Mn-0.2C-1.5Al specimen was hardly affected by the surface conditions. On the other hand, the tendency of hydrogen embrittlement of the two high-manganese steels was not sensitive to hydrogen charging or surface conditions from the standpoints of elongation and fracture behavior. Based on the EBSD analysis results, the small decrease in elongation of the charged specimens for the Fe-30Mn-0.2C-(1.5Al) high-manganese steels was attributed to the enhanced dislocation pile-up around grain boundaries, caused by hydrogen.

• 열처리공학회지
• /
• 제29권4호
• /
• pp.176-180
• /
• 2016

In this study, a microstructural investigation was conducted on the cracking phenonmenon occurring during hot rolling of Fe-23Mn high-manganese steels with different aluminium and carbon contents. Particular emphasis was placed on the phase stability of austenite and ferrite dependent on the chemical composition. An increase in the aluminum content promoted the formation of ferrite band structures which were easily deformed or cracked. In the steels containing high carbon contents of 0.4 wt.% or higher, on the other hand, the volume fraction and thickness of ferrite bands decreased and thus the cracking frequency was significantly reduced. Based on these findings, it is said that the microstructural evolution occurring during hot rolling of high-manganese steels with different aluminium and carbon contents plays an important role in the cracking phenomenon. To prevent the cracking, therefore, the formation of second phases such as ferrite should be minimized during the hot rolling by the appropriate control of the chemical composition and process parameters

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2001년도 춘계학술대회 논문집
• /
• pp.807-810
• /
• 2001

Fatigue crack growth tests were carried out using high manganese cast steel under constant amplitude loading. Crystal grain size of the material is about 1000$\mu\textrm{m}$. For this material, the fatigue crack growth mechanism of high manganese steel was clarified from results such as observation of crack growth path and fracture surface. $\Delta$$K_{th}$ is about 8MPa$\surd$m which is quiet large as compared to the general structural steels and the crack growth rate is lower than the general structural steels especilly in the low $\Delta$K regsion. The reason of this behavior is crack closure due to fracture surface roughness.

• 열처리공학회지
• /
• 제31권6호
• /
• pp.283-289
• /
• 2018

This present study deals with the hydrogen embrittlement properties of austenitic Fe-30Mn-0.2C(-1.5Al) high-manganese steels for cryogenic applications. They were electrochemically charged with hydrogen and then subjected to tensile tests for evaluating hydrogen embrittlement behavior. Tensile test results showed that after hydrogen charging the tensile strength and elongation of the Al-free steel were more remarkably decreased with increasing current density when compared to the Al-added steel. After hydrogen charging of the Al-added steel, it was found that the measured hydrogen content was small and silver particles were relatively less decorated. Therefore, the Al-added steel has a superior hydrogen embrittlement resistance to the Al-free steel because the addition of Al suppresses the injection of hydrogen during electrochemical hydrogen charging.

• 한국재료학회:학술대회논문집
• /
• 한국재료학회 1996년도 재료학회 춘계학술발표회
• /
• pp.6-6
• /
• 1996

• Archives of Metallurgy and Materials
• /
• 제66권4호
• /
• pp.1007-1011
• /
• 2021

The microstructure and mechanical properties of hot-rolled Fe-9Mn-0.2C medium-manganese steels with different Al, Cu, and Ni contents were investigated in this study. Based on the SEM, XRD, and EBSD analysis results, the microstructure was composed of martensite, band-type delta ferrite, and retained austenite phases depending on the Al, Cu, and Ni additions. The tensile and Charpy impact test results showed that the sole addition of Al reduced significantly impact toughness by the presence of delta-ferrite and the decrease of austenite stability although it increased yield strength. However, the combined addition of Al and Cu or Ni provided the best combination of high yield strength and good impact toughness because of solid solution strengthening and increased austenite stability.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
• /
• pp.933-934
• /
• 2006

The present study examines the sintering behaviour and effect of manganese addition both mechanically-blended and mechanically alloyed on Cr-Mo low alloyed steels to enhance the mechanical properties. Mn sublimation during sintering provides some specific phenomena which facilitate the sintering of alloying elements with high oxygen affinity. First step is the optimization of milling time to attain a master alloy with 50% of Mn which is diluted in Fe-1.5Cr-0.2Mo water atomized prealloyed powder by normal mixing. These mixtures are pressed to a green density of $7.1g/cm^3$ and sintered at $1120^{\circ}C$ in $90N_2-10H_2$ atmosphere.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집A
• /
• pp.205-210
• /
• 2001

Fatigue crack growth tests were carried out using high manganese cast steel under constant amplitude loading. Average crystal grain sizes of the material are $200{\mu}m$ and $1000{\mu}m$. For this material, ${\Delta}K_{th}$ is about $8MPa{\sqrt{m}}$ which is quiet large as compared to the general structural steels and the crack growth rate is lower than the general structural steels especilly in the low ${\Delta}K$ regsion. The reason of this behavior is crack closure due to fracture surface roughness and fretting oxide. The relationship between da/dN and the ${\Delta}K_{eq}$ was represented by narrow band regardless of the stress ratio.