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용접 열영향부 미세조직 및 재질 예측 모델링 : III. 석출물 - Free 저합금강의 초기 오스테나이트 결정립크기의 영향을 고려한 용접 열영향부 오스테나이트 결정립성장 예측 모델
엄상호,문준오,정홍철,이종봉,이창희,Uhm, Sang-Ho,Moon, Joon-Oh,Jeong, Hong-Chul,Lee, Jong-Bong,Lee, Chang-Hee 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.4
The austenite grain growth model in low alloyed steel HAZ without precipitates was proposed by analyzing isothermal grain growth behavior. Steels used in this study were designed to investigate the effect of alloying elements. Meanwhile, a systematic procedure was proposed to prevent inappropriate neglect of initial grain size (D0) and misreading both time exponent and activation energy for isothermal grain growth. It was found that the time exponent was almost constant, irrespectively of temperature and alloying elements, and activation energy increased with the addition of alloying elements. From quantification of the effect of alloying elements on the activation energy, an isothermal grain growth model was presented. Finally, combining with the additivity rule, the austenite grain size in the CGHAZ was predicted.
김새암 ( Sea Arm Kim ),이상우 ( Sang Woo Lee ) 한국열처리공학회 2003 熱處理工學會誌 Vol.16 No.2
N/A As a research for developing fine-grained high strength low carbon steels, the effects of austenitization temperature and hot deformation on microstructure was investigated in 0.15 wt% carbon steels with microalloying elements such as Nb and Ti. When the steels were reheated at 1250℃, Nb containing steel showed very coarse austenite grain size of 200㎛ whereas Nb-Ti steel did fine one of 70㎛ because Ti carbonitrides could suppress the austenite grain growth. In case of 50% reduction at 850℃, the austenite grains in the Nb steel partially recrystallized while those in the Nb-Ti steel fully recrystallized probably due to finer prior austenite grains. For the Nb-Ti steel, ferrite grain size was not sensitively changed with austenitization temperature and compression strain and, severe deformation of 80% reduction was not essentially necessary to refine ferrite grains to about 3㎛ which could be obtained through lighter deformation of 40% reduction.
Behavior and Mechanism of Void Welding Under Thermal Mechanical Coupling
Fei Chen,Xitao Wang,Huiqin Chen,Shue Dang 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7
Shrinkage cavity, microporosity, blowhole and the likes are the typical void defects in ingot. Only through reasonable hightemperature deformation and heat preservation process can the void defects be closed and welded to ensure the high qualityof forgings. However, there are few researches on the welding behavior of voids, and the understanding of the void weldingmechanism is still insufficient. In order to further study the welding behavior of void and explore the welding mechanism,the welding process of void and microstructure evolution around void under thermal mechanical coupling were studied byphysical simulation. The results show that heating temperature, holding time, plastic deformation play an important role invoid welding. The void welding degree increases with the increase of heating temperature, holding time and plastic deformation. Besides, there are three main welding mechanisms for void defects, including the volume of microvoids decreasesdue to vacancy diffusion, the void welding mechanism caused by the austenite-ferrite transformation at lower temperaturesand the void welding mechanism caused by recrystallization and grain growth of austenite grains at higher temperatures.
Moon, Joonoh,Lee, Jongbong,Lee, Changhee Elsevier 2007 Materials science & engineering. properties, micro Vol.459 No.1
<P><B>Abstract</B></P><P>A model to predict the austenite grain size in a Ti-microalloyed steel weld heat affected zone (HAZ) was developed. Grain boundary mobility for the austenite grain growth was expressed as a function of aging temperature and alloying elements. By analyzing isothermal austenite grain growth behavior, the Zener coefficient of cubic TiN particle was measured. From quantification of the effect of grain boundary pinning by TiN particle and alloying elements on the grain boundary mobility, an isothermal grain growth model of Ti-microalloyed steel is presented. The predicted austenite grain sizes from the proposed model were in agreement with the experimental results. Finally, combining with the additivity rule, a general austenite grain growth model during the continuous welding thermal cycle was developed.</P>