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Welding handbook 16.0 Post-weld heat treatment

16.0 Post-weld heat treatment
©SSAB

Welding creates residual stresses in a structure’s The drawbacks associated with the PWHT of a
joint and its surrounding area. In certain types of structure are that:
steels, these stresses can be reduced by applying a 4 The mechanical properties in the HAZ and other
post-weld heat treatment (PWHT). parts of the parent metals can be reduced.
4 The PWHT increases the production cost
Strenx 700-Strenx 960, Hardox HiTuf and Hardox substantially since a separate operation is
HiTemp can be subjected to PWHT. However, the added to the manufacturing process.
treatment is rarely applied to these steel grades 4 New residual stresses can be encountered in the
because, in most cases, the properties of the welded stucture if the PWHT is performed without
structures make it unnecessary and there are following the recommendations from SSAB.
drawbacks associated with this operation.
Strenx 1100-Strenx 1300 and all Hardox grades,
The principal advantages of a PWHT in welded except Hardox HiTuf and Hardox HiTemp, should
structures of Strenx 700-Strenx 960, Hardox HiTuf not be exposed to a PWHT. Doing so will impair the
and Hardox HiTemp are:
mechanical properties in the unaffected parent metal.
4 Lowered levels of residual stresses can further
increase the ductile behavior of the structure. The PWHT is performed by first heating the welded
4 Chip producing machining of a component is structure with a specified heating rate. Once the
facilitated since a lower level of residual stresses holding temperature is reached, it is maintained
promotes less distortion in the structure. for a certain period of time. As a final step, the
4 A reduction of the residual stresses in a structure can temperature is reduced with a specified cooling rate
improve its fatigue properties. More information on until ambient temperature is reached. This process
this matter is found in chapter 8. is normally carried out in a furnace, but other
techniques, such as placing electric heating mats on
4 Lowered hardness values in the joint are possible. the welded structure, may be applied.
This, together with decreased levels of residual
stresses, can diminish the risk for stress corrosion Recommended procedures for PWHT of structures
cracking in the joint. This issue is relevant if the in Strenx 700-Strenx 960, Hardox HiTuf and
structure is subjected to certain types of corrosive Hardox HiTemp are according to table 16.1.
environments.

Steel grade Holding temperature Heating and cooling rate Holding time Suitable time at the holding
[ºC] [ºC/h] temperature
[h]
Strenx 700 550-580 ºC 100 2 min/mm of single plate 1-6
thickness*, min 1 h
Strenx 900 520-550 ºC -”- -”- -”-
Strenx 960 520-550 ºC -”- -”- -”-
Hardox HiTuf 510-530 ºC -”- -”- -”-
Hardox HiTemp 450-480 ºC -”- -”- -”-

* A definition of the term single plate thickness can be found in chapter 4.
Table 16.1: Recommended parameters for PWHT of welded structures in different Hardox and Strenx grades.
The holding temperatures are preferably measured on the actual structures.
This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications. 99
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.