Effect of Ausforming Strain on the Microstructural Evolution of Lath Martensite in Low Carbon Steel

B. B. He,Q. W. Guan 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.10

Dislocation engineering is a novel alloy design strategy to produce advanced high strength steels with both high strength andgood ductility, which can be accomplished through an ausforming process. The present work studies the effect of ausformingstrain on the evolution of lath martensite microstructure in low carbon steel by detailed transmission electron microscopyobservation. Ausforming strain determines the length of the martensite blocks and the substructure in the lath martensite. The large ausforming strain (20%–45%) reduces the martensite blocks and leads to the development of dislocation cellstructure, both of which are absent in the ausformed martensite with a small ausforming strain (5%–10%). The formationof the dislocation cell structure in the prior austenite grains after the large plastic deformation inhibits the propagation ofmartensite and thus reduces the length of martensite blocks. Irrespective of the ausforming strain, the plastic deformation ofaustenite grains does not lead to an obvious change of martensite lath width. The large ausforming strain slightly enhancesthe auto-tempering of martensite on the aspect of precipitates density. The coarse precipitates formed close to the lathboundaries after small ausforming strain of 5% is absent in the martensite with large ausforming strain (20%–45%), whichis ascribed to the presence of intensive dislocations generated by elevated ausforming strain can facilitate the pipe diffusionof carbon. The present finding serves as the microstructural basis for the application of the dislocation engineering conceptin the design of advanced high-strength steel with the martensite as the intrinsic component.

오스테나이트계 스테인리스강의 강도 및 감쇠능에 마치는 미세조직의 영향

손동욱(D. U. Son),김재환(J. W. Kim),이종문(J. M. Lee),강창룡(C. Y. Kang) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-

The effect of the phases of v, α' and ε martensite, which constitute the structure of the 316L stainless steel with austenite structure at room temperature, on the damping capacity and tensile properties has been investigated. Various fraction of these phases were formed depending on the cold work degree, namely the volume fraction of ε martensite showed maximum value about at 20% cold rolling. while the volume fraction of α' martensite continuously rose according to the increase of cold rolling. The behavior of damping capacity with increasing the degree of cold rolling is the same as that of E martensite. The maximum value of damping capacity showed near at 20% cold rolling formed the largest volume fraction of ε martensite phase. With increasing the volume fraction of α' martensite, tensile strengths increased and elongation decreased due to the increment in the volume fraction of martensite induced by deformation. The damping capacity and elongation is strongly controlled by the volume fraction of E martensite with liner relationship. however, the effect of damping capacity on the volume fraction of α' martensite and austenite phase was not observed. while, tensile strength was controlled by the volume fraction of α' martensite.

Fe-Mn-Al 합금의 감쇠능 및 인장성질에 미치는 가공유기 마르텐사이트 상의 영향

엄정호(J. H. Eom),강창룡(C. Y. Kang),김창규(C. K. Kim) 한국동력기계공학회 2006 한국동력기계공학회 학술대회 논문집 Vol.- No.-

The damping capacity and strength of Fe-25Mn-2Al and Fe-25Mn-6Al alloy have been investigated for the development of new materials with high strength and damping capacity. The results obtained from this study as follow : The microstructure in Fe-25Mn-2Al and Fe-25Mn-6Al at room temperature consist of a large quantity of the austenite structure and a small quantity of a' and e martensite, and α' and ε martensite was increased by increasing the degree of cold rolling. Two specimens of cold rolled Fe-Mn-Al alloys have the microstructure that were α' and ε martensite phase, and increasing the degree of cold rolling, the volume fraction of ε martensite decreased after rising to maximum value at specific level of cold rolling, the volume fraction of α' martensite slowly increased and then dramatically increased from the point of decreasing ε martensite volume fraction. The damping capacity is strongly affected by the content of ε martensite, but the other phase such as α' martensite and austenite phase is not, actually exhibit little effect on damping capacity. The tensile strength increases and the elongation decreases with increasing the volume fraction of α' martensite, consequently they are proved that tensile strength is mainly affected by the content of α' martensite.

Fe와 V이 Zr-0.8Sn 합금의 $\beta{\rightarrow}\alpha$ 상변태 특성에 미치는 영향

오영민,김선진,O, Yeong-Min,Kim, Seon-Jin 한국재료학회 2000 한국재료학회지 Vol.10 No.9

Zr-0.86Sn 합금이 $\beta{\rightarrow}\alpha$상변태 특성에 미치는 Fe와 V의 영향을 광학현미경과 투과전자현미경으로 연구하였다. 공냉의 경우에는 V의 첨가량이 증가함에 다라 $\beta{\rightarrow}\alpha+\beta$변태온도가 감소하여 미세한 $\alpha$-lath들의 폭을 더욱 감소시켰으나, Fe의 경우에는 첨가량이 증가함에 다라 오히려 $\alpha$-lath의 폭이 약간 증가하였다. 수냉의 경우에는 모든 합금에서 martensite 미세구조를 보였다. 수냉한 Zr-0.8Sn, Zr-0.8Sn-0.1Fe, Zr-0.8Sn-0.2Fe, Zr-0.8Sn-0.4Fe, Zr-0.8Sn-0.1V 그리고 Zr-0.8Sn-0.2V 합금에서는 주로 slipped martensite 미세구조가 형성된 반면에 수냉한 Zr-0.8Sn-0.4V 합금에서는 twinned martensite 미세구조가 관찰하였다. 수냉한 Zr-0.8Sn 합금에서 V의 첨가향이 증가함에 따라 slipped martensite에서 twinned martensite 미세구조로의 천이는 M(sub)s 온도의 감소에 기인한 것으로 생각된다. The effects of Fe and V content on the characteristics of $\beta$ to $\alpha$ phase transformation for Zr-0.8Sn alloys were studied by optical and transmission electron microscopy. With increasing V content, $\beta{\rightarrow}\alpha+\beta$ transformation temperature decreased, thus allowing the width of $\alpha$-lath to be fine air-cooled Zr-0.8Sn-xV alloys. The width of $\alpha$-lath, however, was slightly increased with Fe content. While the $\beta$ to $\alpha$ transformed microstructures of water-quenched Zr-0.8Sn, Zr-0.8Sn-0.1Fe, Zr-0.8Sn-0.2Fe, Zr-0.8Sn-0.4Fe, Zr-0.8Sn-0.1V and Zr-0.8Sn-0.2V were mainly slipped martensite, that of water-quenched Zr-0.8Sn-0.4V was predominantly twinned martensite. The transition of slipped martensite to twinned martensite in Zr-0.8Sn-Xv was thought to be due to the decrease of $M_S$ temperature.

마르텐사이트와 오스테나이트의 2상 혼합조직을 갖는 고 Mn 오스테나이트 스테인리스강의 감쇠능

황태현 ( Tae Hyun Hwang ),강창룡 ( Chang Yong Kang ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.9

Abstract: The damping capacity of high manganese austenitic stainless steel with a two phase mixed structure of deformation-induced martensite and reversed austenite was studied. Reversed austenite with an ultra-fine grain size of less than 0.2 μm was obtained by reversion treatment. The two phase structure of deformation-induced martensite and reversed austenite was obtained by annealing treatment at a range of 500-700℃ and various times in cold rolled high manganese austenitic stainless steel. The damping capacity increased with an increasing annealing temperature and time. In high manganese stainless steel with the two phase mixed structure of martensite and austenite, the damping capacity decreased with an increasing volume fraction of deformation-induced martensite. Thus, the damping capacity was strongly affected by deformation-induced martensite. The results confirmed that austenitic stainless steel with a good combination of strength and damping capacity was obtained from the two phase mixed structure of austenite and martensite.

Fe-26Mn-2Al 합금의 진동 감쇠능 및 강도에 미치는 결정립 크기의 영향

김재환(J. W. Kim),이도훈(D. H. Lee),강창룡(C. Y. Kang) 한국동력기계공학회 2005 한국동력기계공학회 학술대회 논문집 Vol.- No.-

The effect of grain size on the damping capacity and strength of Fe-26Mn-2Al alloy studied in this paper has been investigated after changing the microstructure by cold rolling and changing grain size. The results obtained from this study as follows : 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. 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. In case of tensile strength, it influenced on both ε and α' martensite. With increasing the grain size in Fe-26Mn-2Al alloy, strength and elongation was decreased while damping capacity was increased due to increasing the volume fraction of ε martensite by decrement in stability of austenite phase. While tensile strength was linearly increased with increasing the degree of rolling due to transforming austenite to martensite by working, elongation was dramatically decreased at early stage but slowly decreased with increasing the degree of cold rolling.

Fe-28Mn-2Al-3Si 합금의 진동 감쇠능에 관한 연구

권민기(M. K. Kwon),박영태(Y. T. Park),조덕호(D. H. Cho),강창룡(C. Y. Kang) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-

The effect of the damping capacity of Fe-28Mn-2Al-3Si alloy has been investigated after changing the microstructure by cold rolling. Microstructures in Fe-28Mn-2Al-3Si at room temperature consist of a large quantity of austenite and small quantities of ε and α' martensites. And ε and α' martensites were increased by increasing the degree of cold rolling. With increasing the grain size, the volume fraction of martensite was increased which transformed from the austenite by the cold rolling. Damping capacity was linearly increased with increasing the degree of rolling due to transforming austenite to martensite by deformation. Damping capacity is strongly affected by ε martensite than α' martensite making by deformation induced martensite.

Fe-Mn 계 합금에서 비부피 차를 이용한 ε 마르텐사이트의 부피분율 측정

지광구 ( Ji Gwang Gu ),한준현 ( Han Jun Hyeon ),장우양 ( Jang U Yang ) 한국열처리공학회 2003 熱處理工學會誌 Vol.16 No.4

N/A In this work, a new way of measuring the volume fraction of E martensite in Fe-based alloys has been proposed. Since the specific volume of ε martensite, depending on alloy composition, is smaller than that of austenite i.e γ phase, volume expansion takes place during ε→γ reverse transformation. As the amount of the volume expansion is proportional to the product of specific volume difference times the volume fraction of ε martensite, the volume fraction of ε martensite can be calculated by measuring the volume expansion and the specific volume difference. Such a relationship was confirmed in Fe-21 Mn and Fe-32Mn-6Si alloys which undergo γ→ε martensitic transformation on cooling and by cold rolling, respectively. It was also found that the former has isotropic E martensite while the latter has anisotropic E martensite.

Isothermal Phase Transformations and Stability of Retained Austenite during Quenching and Partitioning Process for 0.15C Steel

진종원,박철호,강남현 대한용접접합학회 2017 대한용접·접합학회지 Vol.35 No.1

The microstructure and dilatation for 0.15C steels were investigated to define the phase transformation during the quenching and partitioning (Q&P) process. For the one step Q&P dilatation, the isothermal martensite/ bainite transformation occurred because the holding temperature was between Ms and Mf. The isothermally transformed martensite/bainite and the athermally transformed martensite were produced by a loss of retained austenite. As the holding time increased, new martensite-start (Ms) temperature produced from the final quenching process decreased due to the carbon partitioning from the martensite to the retained austenite. This was the direct evidence of increment for the retained austenite stability. For the two step Q&P dilatation, the isothermal bainitic transformation occurred because the partitioning temperature was larger than the Ms and new Ms. The partitioning at 400℃ indicated the short incubation period for the bainite transformation than the 350℃ partitioning because the partitioning at 400℃ should acquire the larger thermal driving force for carbon partitioning than the 350℃ partitioning. A quick drop of Ms and short period of bainite incubation for the 400℃ partitioning steel were also the direct evidence of significant effects of carbon partitioning on the stability of retained austenite.

Isothermal Phase Transformations and Stability of Retained Austenite during Quenching and Partitioning Process for 0.15C Steel

Jong-Won Jin,Chulho Park,Namhyun Kang 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.1

The microstructure and dilatation for 0.15C steels were investigated to define the phase transformation during the quenching and partitioning (Q&P) process. For the one step Q&P dilatation, the isothermal martensite/bainite transformation occurred because the holding temperature was between Ms and Mf. The isothermally transformed martensite/bainite and the athermally transformed martensite were produced by a loss of retained austenite. As the holding time increased, new martensite-start (Ms) temperature produced from the final quenching process decreased due to the carbon partitioning from the martensite to the retained austenite. This was the direct evidence of increment for the retained austenite stability. For the two step Q&P dilatation, the isothermal bainitic transformation occurred because the partitioning temperature was larger than the Ms and new Ms. The partitioning at 400℃ indicated the short incubation period for the bainite transformation than the 350℃ partitioning because the partitioning at 400℃ should acquire the larger thermal driving force for carbon partitioning than the 350℃ partitioning. A quick drop of Ms and short period of bainite incubation for the 400℃ partitioning steel were also the direct evidence of significant effects of carbon partitioning on the stability of retained austenite.