아공석보통탄소강 (亞共析普通炭素鋼) 에 있어서 반복가열냉각처리에 의한 입상화에 미치는 고온가공소입의 영향 = The effect of hot work-quenching on spheroidizing by thermal cycling in Hypo-Eutectoid carbon steel

국문 초록 (Abstract)

炭素含有量이 0.3%인 亞共析普通炭素鋼을 高溫加工燒入處理後反復加熱冷却處理하였을때 pearlite의 粒狀化(sph), 및 ferrite 粒內에 析出하는 fine spherical Cementite의 數(No/100μ²)를 中心으로, 또 定常加熱의 影響, pearlite 形狀, 冷却速度 및 加工度等을 單純反復加熱冷却處理時의 結果와 比較檢討하였으며 同時에 機械約性質變化도 調査하였든바 다음과 같은 結論을 얻었다.
(1) 高溫加工燒入後 反復加熱冷却處理를 하였을때가 高溫加工燒入後定常加熱時 보다 粒狀化가 促進되었으며, 反復加熱冷却處理效果에 미치는 高溫加工燒入의 影響은 顯著하였다.
(2) 單純反復加熱冷却處理한 境遇는 200cycle을 分岐點으로하여 그 以下에서는 核生成過程에 해당하고 그 以上에서는 核成長過程에 해당하지만 高溫加工燒入後 反復熱加冷却處理한 境遇는 100cycle이 分岐點이 되었고 다같이 300cycle까지는 微少하나마 核生成이 倂行되고 있었다.
(3) 高溫加工燒入後 反復 加熱冷却處理한 境遇에 있어서 高溫에서의 加工度가 클수록 또 cycle 數 및 冷却速度가 增加할수록 粒狀化가 促進되었다.
(4) 反復加熱冷却處理에 있어서는 試料의 組織이 粗大 pearlite-微細 pearlite-martensite順으로 粒狀化를 促進시켰다.
(5) 全體約으로 反復加熱冷却處理時 cycle數의 增加에 따라 引張强度 및 硬度値가 減少한 것으로 보아 靭性이 增加하였음을 알 수 있다. 引張强度와 硬度値는 高溫加工燒入後反復加熱冷却處理할 때가 單純反復加熱冷却處理할 때보다 더 減少하였다. 따라서 靭性이 增加된 것으로 期待된다.

다국어 초록 (Multilingual Abstract)

Then Hypo-eutectoid carbon steel, containing 0.3% of carbon, was treated by repeated thermal cycling after hot work-quenching. The results of simple repeated thermal cycling treatment and that of repeated thermal cycling treatment after hot work-quenching were compared and discussed mainly in point of the spheroidization rate (sph) of pearlite and number of fine spherical cementite (NO/100u²) deposited in ferrite particles. Consequently the shape of pearlite, the cooling velocity and the effect of working degree and steady heating were examined, and also the mechanical properties were surveyed.
The results are as follows
(1) Repeated thermal cycling treatment after hot work-quenching accelerated the spherical tendency than steady heating treatment after hot work-quenching and the effect of hot work-quenching on the repeated thermal cycling.
(2) The thermal peak of the simple thermal cycling treatment was 200 cycles and the cycles less than this peak deserves the nucleation process and that more than this peak comes under the growth process of nucleus.
The thermal peak of thermal cycling treatment after hot work-quenching, however, was 100 cycles and both treatment showed that the nucleation takes place, until 300 cycles, even it is a very small amount.
(3) When the repeated thermal cycling treated after hot work-quenching spheroidization rate was promoted in proportion to the increase of working degree at high temperature, the number of cycles, and the cooling velocity.
(4) In the case of repeated thermal cycling treatment the structure of sample accelerated the spherical tendency in order of coarse pearlite-fine pearlite-martensite.
(5) On the whole, it could be understood that the toughness was increased in contrast with decrease of tensile strength and hardness of the material, according to the number of cycling in the case of repeated thermal cycling. Tensile strength and hardness in the case of repeated thermal cycling treatment after hot work-quenching were decreased than those of simple repeated thermal cycling treatment. Consequently, it is anticipated that the toughness would be increased.