K_han NACT(normalizing + Accelerated colling + Tempering)의 조건으로
만드는 plate와 Quenching and tempering(QT)로 만드는 plate에 대하여
알고 싶습니다.
Job spec에는 QT재질 사용시에는 tempering 온도가 630도 이상이어야합니다.
그런데, spec상의 화학 성분 조건과 그외 사항들을 만족시키기 위해서
Mill maker에서는 NACT의 조건으로 plate를 생산한다고 합니다.
그래서 client측은 NACT조건의 재질과 QT재질을 동일한 것으로 간주되니 열처리 온도를 630도 이상으로 맞춰야 한다고 하고, Mill에서는 610도까지 밖에 못해준다고 합니다.
여기서 질문입니다.
NACT조건으로 만드는 plate를 QT재질과 동일한 것으로 간주하는것이
맞는 겁니까?
NACT와 QT의 구별을 정확히 하고 싶습니다.
여러분의 도움을 구합니다.
만드는 plate와 Quenching and tempering(QT)로 만드는 plate에 대하여
알고 싶습니다.
Job spec에는 QT재질 사용시에는 tempering 온도가 630도 이상이어야합니다.
그런데, spec상의 화학 성분 조건과 그외 사항들을 만족시키기 위해서
Mill maker에서는 NACT의 조건으로 plate를 생산한다고 합니다.
그래서 client측은 NACT조건의 재질과 QT재질을 동일한 것으로 간주되니 열처리 온도를 630도 이상으로 맞춰야 한다고 하고, Mill에서는 610도까지 밖에 못해준다고 합니다.
여기서 질문입니다.
NACT조건으로 만드는 plate를 QT재질과 동일한 것으로 간주하는것이
맞는 겁니까?
NACT와 QT의 구별을 정확히 하고 싶습니다.
여러분의 도움을 구합니다.
I believe your company had a mistake which was not considered the Job spec requirements before you purchased the materials.
1. Summary of the Situation
(1) Job Spec : Tempering Temperature (TT) of QT steel : min. 630C
: PWHT Temperature (PT) should be at least 20C less than TT.
(2) For Example - ASTM A387: 5.1 Minimum tempering temperatures shall be as follows:
Grade Temperature, °F [°C]
2, 12, and 11 : 1150 [620]
22, 22L, 21, 21L, and 9 : 1250 [675]
5 : 1300 [705]
(3) Mill maker’s Proposal : TT should be max. 610C on NACT.
(4) Minimum PWHT temperatures
For Example ; ASME Sec. VIII-D1 : Minimum PWHT temperatures shall be as follows:
P. No. Temperature, °F [°C]
4 : 1200 [660]
5A : 1250 [675]
In P No. 4 material, if you follow the requirements in ASME (PT = min. 660C) and Job spec (PT < TT - 20C), the TT should be 680C and above.
2. NACT vs. QT (AC = Q)
The benefit of NACT may be to get the better toughness than QT at the same strength. The strength is controlled by AC (Q) and T without remarkable difference between two processes.
3. Key of Dilemma in the Position of Mill Maker
; The higher TT (> 610C) will increase the impact toughness, but reduce the strength (TS at atmospheric and hot). When the mill maker applies the TT (>610C), the strength at atmospheric and design temperature (hot) after PWHT (with three or four cycles) may be decreased (probably less than MSTS-minimum specified tensile strength) due to Hollomon parameter effect and temper embrittlement. In general, the most critical issue for QT and NACT of Cr-Mo steels may be the mechanical properties (i.e., 1st-tensile strength and 2nd-step cooling test).
4. Question
(1) “Does not apply to normalized and tempered (NT) or quenched and tempered (QT) materials” : I cannot make sense it. Please give/show me the full sentence/paragraph.
5. Case Study -2007
[Situation]
; Hydrotreating Reactor (2.25Cr-1Mo) with heavy wall in one of the largest refinery plants in Amenrica.
; Materials Supplier : Japan mill maker
; Q-T steel : TT = min. 630C
; PWHT : min. 675C
[Action] The materials were accepted by several metallurgists (including myself) after evaluated all requirements, such as, chemical composition (heat & product), mechanical test (room TS, design TS, impact, creep, etc.), step cooling test, heat treatment procedures, grain size, hardness, all NDE procedures, WPS & PQR, experience, etc.
6. Recommendation
(1) The mill maker’s support is the most important. You may have to obtain all technical data (see section 5 above) from the mill maker in order to get the approval of the spec deviation.
(2) Please keep a sound metallurgist in your side before you discuss with your client.
(3) You may have to open more detail information (i.e., material, thickness, applicable code, job spec, industry, fabrication schedule, operating/design conditions, etc.) for the effective problem solving.
Good luck.
1. Summary of the Situation
(1) Job Spec : Tempering Temperature (TT) of QT steel : min. 630C
: PWHT Temperature (PT) should be at least 20C less than TT.
(2) For Example - ASTM A387: 5.1 Minimum tempering temperatures shall be as follows:
Grade Temperature, °F [°C]
2, 12, and 11 : 1150 [620]
22, 22L, 21, 21L, and 9 : 1250 [675]
5 : 1300 [705]
(3) Mill maker’s Proposal : TT should be max. 610C on NACT.
(4) Minimum PWHT temperatures
For Example ; ASME Sec. VIII-D1 : Minimum PWHT temperatures shall be as follows:
P. No. Temperature, °F [°C]
4 : 1200 [660]
5A : 1250 [675]
In P No. 4 material, if you follow the requirements in ASME (PT = min. 660C) and Job spec (PT < TT - 20C), the TT should be 680C and above.
2. NACT vs. QT (AC = Q)
The benefit of NACT may be to get the better toughness than QT at the same strength. The strength is controlled by AC (Q) and T without remarkable difference between two processes.
3. Key of Dilemma in the Position of Mill Maker
; The higher TT (> 610C) will increase the impact toughness, but reduce the strength (TS at atmospheric and hot). When the mill maker applies the TT (>610C), the strength at atmospheric and design temperature (hot) after PWHT (with three or four cycles) may be decreased (probably less than MSTS-minimum specified tensile strength) due to Hollomon parameter effect and temper embrittlement. In general, the most critical issue for QT and NACT of Cr-Mo steels may be the mechanical properties (i.e., 1st-tensile strength and 2nd-step cooling test).
4. Question
(1) “Does not apply to normalized and tempered (NT) or quenched and tempered (QT) materials” : I cannot make sense it. Please give/show me the full sentence/paragraph.
5. Case Study -2007
[Situation]
; Hydrotreating Reactor (2.25Cr-1Mo) with heavy wall in one of the largest refinery plants in Amenrica.
; Materials Supplier : Japan mill maker
; Q-T steel : TT = min. 630C
; PWHT : min. 675C
[Action] The materials were accepted by several metallurgists (including myself) after evaluated all requirements, such as, chemical composition (heat & product), mechanical test (room TS, design TS, impact, creep, etc.), step cooling test, heat treatment procedures, grain size, hardness, all NDE procedures, WPS & PQR, experience, etc.
6. Recommendation
(1) The mill maker’s support is the most important. You may have to obtain all technical data (see section 5 above) from the mill maker in order to get the approval of the spec deviation.
(2) Please keep a sound metallurgist in your side before you discuss with your client.
(3) You may have to open more detail information (i.e., material, thickness, applicable code, job spec, industry, fabrication schedule, operating/design conditions, etc.) for the effective problem solving.
Good luck.
Jop spec상의 조항은 아래와 같습니다.
"Does not apply to normalized and tempered (NT) or quenched and tempered (QT) materials.
Post weld heat treatment temperature of such materials shall not exceed the tempering temperature of
the base material less 20 degC and shall be such that the mechanical properties are not less than minimum specified.”
본 조항이 적용될 경우 Tempering Temperature는 PWHT Temperature 보다 최소 20 degC 높은 630 degC 이상이 되어야 한다고 client는 주장하고
있습니다.
client를 설득할 backdata나 기타 다른 사항들이 있으면 알려주시기
바랍니다.
이문제로 인해서, 잘못하면 발주 해놓은 plate전량을 못쓰게 될지도 모르겠습니다.
"Does not apply to normalized and tempered (NT) or quenched and tempered (QT) materials.
Post weld heat treatment temperature of such materials shall not exceed the tempering temperature of
the base material less 20 degC and shall be such that the mechanical properties are not less than minimum specified.”
본 조항이 적용될 경우 Tempering Temperature는 PWHT Temperature 보다 최소 20 degC 높은 630 degC 이상이 되어야 한다고 client는 주장하고
있습니다.
client를 설득할 backdata나 기타 다른 사항들이 있으면 알려주시기
바랍니다.
이문제로 인해서, 잘못하면 발주 해놓은 plate전량을 못쓰게 될지도 모르겠습니다.
공지사항
최종적으로 얻어지는 결과는 비슷할 것 같지만, 기계적 특성이나 금속학적인 조직의 차이점이 있지요.
NACT를 온도를 높여서 열처리를 하게 되면, 결국 입자의 성장이 우려되고, 그렇게 되면 기계적 특성의 저하가 발생하기에 적용이 어렵다고 Mill에서 주장하는 것으로 이해합니다.
이번 기회에 TMCP강의 제조법과 기존의 Rolled강재 그리고 QT강재와의 비교 자료를 참고하시어 공부해 보세요
Web에서도 TCMP를 기준으로 찾으면 많은 자료를 찾을 수 있으니, 참고자료는 어렵지 않게 구하실 수 있을 것으로 기대합니다.