이진영
2008-06-18 14:32:31
2
653
Head를 Normalizing할 경우, Normalizing의 열변형이 S.R.(Stress Relief)의 열변형보다 많기 때문에 개선변형을 최소화하기 위해 Normalizing한 후에 final cutting을 하라고 하던데 어떠한 이유와 원리에서 Normalizing이 S.R.보다 열변형이 큰 것인가요?
In addition to above good answer, here is some more information.
1. Deformation by heat treatment
The most common deformations of CS fabrication are normally come from quenching (rapid cooling) or welding (local heat input and faster cooling than that of S.R or normalizing). However the deformation effects by the following normalizing or S.R is not much critical if it is not a precision component (i.e., required fine machining or fixing/assembly) when fully supported during heat treatment.
; Normalizing of CS : @ 1750F (950C) ~ 1830F (1000C) followed furnace cooling (very slow cooling) up to 800F (427C)
; S.R of CS : @ 1100F (593C) ~ 1200F (650C) followed air cooling (slow cooling)
Theoretically when the structure is fully supported during heat treatment and extremely slow-cooled, the deformation may be nil. The deformations by two heat treatments may not expected much different because the deformation effect with very slow cooling may mostly compensate for the likelihood of cooling contraction from higher temperature.
2. Oxidation
The surface of welding preparation or machined will be oxidized (rusted) because the initiation temperature of CS oxidation is about 1000F (538C) at high temperature. The oxidized surfaces after heat treatment should be oxides-free before welding or fixing/assembly.
3. Conclusion (the best work sequence)
; Welding Parts : recommended to do the weld preparation after heat treatment.
; Machining Parts : should be machined after heat treatment.
1. Deformation by heat treatment
The most common deformations of CS fabrication are normally come from quenching (rapid cooling) or welding (local heat input and faster cooling than that of S.R or normalizing). However the deformation effects by the following normalizing or S.R is not much critical if it is not a precision component (i.e., required fine machining or fixing/assembly) when fully supported during heat treatment.
; Normalizing of CS : @ 1750F (950C) ~ 1830F (1000C) followed furnace cooling (very slow cooling) up to 800F (427C)
; S.R of CS : @ 1100F (593C) ~ 1200F (650C) followed air cooling (slow cooling)
Theoretically when the structure is fully supported during heat treatment and extremely slow-cooled, the deformation may be nil. The deformations by two heat treatments may not expected much different because the deformation effect with very slow cooling may mostly compensate for the likelihood of cooling contraction from higher temperature.
2. Oxidation
The surface of welding preparation or machined will be oxidized (rusted) because the initiation temperature of CS oxidation is about 1000F (538C) at high temperature. The oxidized surfaces after heat treatment should be oxides-free before welding or fixing/assembly.
3. Conclusion (the best work sequence)
; Welding Parts : recommended to do the weld preparation after heat treatment.
; Machining Parts : should be machined after heat treatment.
공지사항
이진영님의 글
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Head를 Normalizing할 경우, Normalizing의 열변형이 S.R.(Stress Relief)의 열변형보다 많기 때문에 개선변형을 최소화하기 위해 Normalizing한 후에 final cutting을 하라고 하던데 어떠한 이유와 원리에서 Normalizing이 S.R.보다 열변형이 큰 것인가요?
----------------- [답 변] -------------------
노멀라이징 온도와 S.R 처리 온도 및 온도 유지 조건이 다르죠...
S.R은 보통 500도 전후지만, 노멀라이징은 보통 변태점 이상에서 처리합니다.
성형(주조 등등)후 노멀라이징 혹은 S.R을 했을 경우 변형이 많이 발생했다면 결국 내부 잔류 응력이 많이 완화 되었음을 의미합니다.
또한 노멀라이징과 잔류응력 열처리는 기본 목적이 다르지만,
잔류 응력 제거 목적으로만, 노멀라이징이 잔류 응력 제거가 효과적입니다.
일반적으로 강재의 인장 강도는 500도 정도에서 상온의 절반 이하로 떨어짐니다. 이것을 이용해서 잔류응력 처리를 합니다. 하지만 완전히 없어지지는 않구, 대략 인장강도의 30% 정도는 남습니다.
만약 용접구조물을 노멀라이징 처리를 한다면 무척 비싸지겠죠...
결국 처리 비용과 목적에 따라 방법이 결정된다고 할 수 있습니다.