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球狀黑鉛鑄鐵 製造에 있어서 절대 필요한 조건의 하나로 볼 수 있는 脫黃問題와 高溫熔解, 및 加炭量을 調節하기 爲해서 3 Ton Herould type are 式 電氣爐에서 鋼屑과 低炭素鋼 古鐵만을 裝入하고 加炭劑로서는 木炭만을 使用하였을 時 이 때 溶湯의 加炭과 脫炭 現狀이 操業時間에 따라 最高 加炭量 3.8∼4.0% 까지 加炭되었다가 脫炭되는 現狀을 고찰하고 이때 製造된 球狀黑鉛鑄鐵의 化學成分에 따라 그 物現的 性質의 變化에 對해 調査하였다.
The mechanical properties of ductile east iron can be significantly improved by austempering, isothermal transformation in the temperature range from Ar" to Ar' point flollowing austenitization. Fracture experiments were performed on 0.24 % Mo-0.5 % Cu alloyed ductile cast irons which were austenized for 1.5 hr at 900℃ and austempered for 2 hr in the temperature range from 280℃ to 415℃. Fracture toughness values higher than K_(IC) 80 MPa m^(½) were obtained with the bainite ductile irons which were austempered in the range of 365 to 385℃, and then values of yield strength, elongation and hardness were in the ranges of 810 to 880 MPa, 8.8 to 10.4 % and 270 to 310 H_B, respectively.
The fracture properties of ductile cast iron (DCI) can be significantly improved by austempering, isothermal transformation in the temperature range from Ar$quot; to Ar' point following austenitization. According to the results of experiment, when a 0.27%Mo-1.08%Ni alloyed DCI was austenitized for 1.5hr at 900 ℃ and austempered for 2hr at temperature range from 280 to 415℃, as the austempering temperature was increased, strength and hardness decreased, while ductility increased. Also, the fracture toughness values K_IC obtained were over about 80 MPa m^(½) when yield strength, elongation and hardness were the ranges of 750 to 850 MPa, 5 to 8% and 270 to 330 H_B respectively. The homogeneous bainitic microstructure of the austempered ductile iron (ADI) was obtained by the austempering temperature range of 340 to 385 ℃, and its SEM fractography showed a fibrous structure of dimple pattern, and it had the high fracture toughness.
The fatigue crack growth behaviors of the base metal, the heat affected zone and the weld metal in AISI 304 stainless steel weldment were studied. The effects of the rolling direction, the content of δ-ferrite, sensitization and solution heat treatment were also investigated. The fatigue crack growth rates in the weld increased in the order of the weld metal, the base metal and the heat affected zone. But was found independent of the rolling direction. Sensitized specimens showed low fatigue crack growth rate in low ΔK region, however, intergranular facets were observed on the fatigue fracture surface. The fatigue crack growth rates of the base metal, the heat affected zone and the we1d metal were decreased with the solution heat treatment. The content of δ-ferrite up to 10.1% did not influence the fatigue crack growth rate with an exception of the specimens with 7.8% which showed a decreased crack growth rate.
주철법랑제조에 Glossy Ground Coat의 여러시유조건에 의하는 영향과 소지금속에 함유되어 있는 탄소형태에 따르는 영향을 검토하기 위하여 밀착성 측정, 내열충격성 측정, 발포현상 및 소지금속에 대한 조직을 관찰하였다. 본 연구로서 Ground Coat는 소지금속과 Cover Coat와의 밀착력 향상 역활보다 발포억제를 보다 더 주역활로 하고 있다는 것을 알게되었으며, 또한 소지금속의 조성, 특히 결합탄소와 유리탄소함량에 따라 법랑화에 큰 영향을 미친다는 것을 알 수 있었다. In order to examine the effects attendant upon varing conditions of glossy ground coat as well as upon the type of carbon contained in the base metal in manufacturing the ceramic coating on cast iron. I have measured the adherence of the wet-process cast iron enamels and the resistance of the thermal shocking, observed the blistering phenomena and surveyed the base with a microscope. This study showed that the ground coat played a main role more in forbidding the blistering than increasing the adherence between the base metal and the cover coat and that the adherence was affected strongly by the composition of the base metal, especially by the ratio of combined carbon and free carbon.
3˝칠드볼 생산시 금형온도를 변화시켜 볼표면이 美麗한 溫度인 170℃∼250℃의 溫度區間을 찾고 이 溫度 범위 내에서 化學成分을 變化시켜 칠의 깊이, 表面硬度 및 內部 수축공의 變化를 관찰하였다. 耐충격, 耐마모용의 最適化學成分은 C3.4∼4%이고 Si 0.6% 였으며 볼 내부에 발생하는 shrinkage cavity는 칠의 깊이가 깊어짐에 따라 中心 가까이 位置함을 규명할 수 있었다. This research aims to find out the temperature range of the chilled ball metal mold, 170℃∼250℃ for sound surface in chilled ball casting, and to observe the depth of chill, surface hardness and Shrinkage cavity situation in ball according to chemical composition variety within this temperature range, the optimum chemical composition range for wear found to be C 3.4∼4.0%, Si 0.6% shrinkage cavity in ball has a tendency to situate at center of ball when the chill depth is deep.
One aspect of the properties of austempered ductile iron (ADI) which should be exploited further in promoting engineering applications is their fracture toughness. In this study ductile irons with various Si content were austempered and the relationship among austempering temperatures, quantity of retained austenite and fracture characteristics was investigated. As Si content increases from 2.28% to 3.0%, the precipitation of carbide during bainite transformation is suppressed, and the fracture toughness and the amount of the retained austenite is increased. The high Si content limits the formation of martensite in the structure and minimizes segregation of other elements at cell boundaries. But in the excessive Si content (3.3%) showed the formation of islands of free ferrite in the bainitic structures and it decreased the fracture characteristics.