High Temperature Steel
Molybdenum has been the key element to develop ferritic steels with good creep strength for service temperatures up to 530 °C.
Products and components made of high temperature steels include
- seamless tubes for water boilers and superheaters, boiler drums,collectors, pumps and pressure vessels for elevated temperature service
- heavy steam turbine shafts with the diameter exceeding 2 meters, weighing more than
100 mt.
Fig 1: The creep rupture strength of 1%CrMoV steel improves with Mo content up to 0.7% Mo. (Base composition 0.3%C,1%Cr,0.3%V)
Molybdenum in solid solution is very efficient in reducing the creep rate of steel at elevated temperatures. Molybdenum slows the coagulation of carbides during high temperature service. The best results in terms of elevated temperature strength are obtained in quenched and tempered condition with an upper bainitic microstructure.
The family of Mo, CrMo and CrMoV steels continues to be the materials of choice for the worldwide installations of power plants, oil refineries and petrochemical plants.
| DIN - EN | ASTM/ASME | % Alloy content | |||
|---|---|---|---|---|---|
| C | Cr | Mo | V | ||
| Mo and CrMo Steel | |||||
| 15Mo3 | 0.15 | 0.3 | |||
| 13CrMo45 | T2/P2 | 0.13 | 1 | 0.4 | |
| 10CrMo910 | T22/P22 | 0.1 | 2.25 | 1 | |
| MoV Steel | |||||
| 14MoV63 | 0.14 | 0.6 | 0.3 | ||
| 21CrMoV511 | 0.21 | 1.25 | 1 | 0.3 | |
| 9% CrMo Steel | |||||
| X12CrMo9 1 | 0.12 | 9 | 1 | ||
| 12% CrMoV Steel | |||||
| X20CrMoV121 | 0.2 | 12 | 1 | 0.3 | |
Table 1: Standard High Temperature structural steels
In recent years, worldwide efforts to increase efficiency in power plants have created a demand for steels that can withstand higher pressure and higher service temperatures. A promising development is grade P/T91 – X10CrMoVNb9-1, which is a modification of the existing 9% Cr 1% Mo grade with additions of vanadium and niobium (columbium).