ISO/TR 15608 Material Group 6.4: Steels such as material X10CrMoVNb9-1 with
7,0 % ≤ Cr < 12,5 %, 0,7 < Mo ≤ 1,2 % and V ≤ 0,35 %;
High-temperature martensitic steels above 7% Cr in CrMo steels leads to a group of steels containing martensite. This microstructure introduces a new element of structural hardening. Martensite is characterized by a high dislocation density and a fine lath structure stabilized. This structural hardening is responsible for the large increase in the high creep-rupture strength of e.g. X10CrMoVNb9-1. Further improvements, especially of the creep strength, have been achieved by alloying with vanadium, niobium, tungsten and boron. The modified 9 % Cr steel X10CrMoVNb9-1 (T91 & P91) is now used in power plants all over the world, both in new plants and in refurbishment work of high-pressure/high-temperature piping systems. Subsequently, new steel grades like X11CrMoWVNb9-1-1 (T911 & P911), developed based on T91 & P91. These grades represent the current state of development for creep-resistant ferritic steels.
Weldability of chromium-molybdenum alloyed steels ISO/TR 15608 Material Group 6.4 such as X10CrMoVNb9-1
The chromium-molybdenum alloyed heat-resistant steels are generally welded with a preheating suitable for the steel grade and wall thickness in question e.g. 150 -300 °C. The working temperature should not reach 350°C. After welding, these steels generally have to be annealed e.g. 730 – 760 °C. Before the necessary tempering annealing (740 – 760°C), intermediate cooling to room temperature is required in order to achieve complete martensite transformation.
The filler metals used are essentially alloyed grades of the same type. Only under these conditions can the welded joint be expected to have the same creep rupture strength as the base material.
As the welding technology has a significant influence on the achievable toughness properties in the weld metal, the use of multi-layer technology, i.e. low layer thickness, is recommended in order to achieve a high proportion of tempered weld metal structure and thus an improved toughness level.
Typical materials in group 6.4
| Name/Grade | Number | Standard | Product | Remarks/Trade Marks |
|---|---|---|---|---|
| X10CrMoVNb9-1 X10CrMoVNb9-1 X10CrMoVNb9-1 X10CrMoVNb9-1 F91 T91 WP91 P91 F91 FP91 91, Cl. 2 | 1.4903 1.4903 1.4903 1.4903 K90901 K90901 K90901 K90901 K90901 K90901 K90901 | EN 10028-2 EN 10216-2 EN 10222-2 EN 10253-2 ASTM A-182 ASTM A-213 ASTM A-234 ASTM A-335 ASTM A-336 ASTM A-369 ASTM A-387 | Plate Smls. tube Forgings Fittings Forging Smls. tube Fitting Smls. pipe Forging Forged pipe Plate | EN 13445-2 & EN 13480-2 EN 13445-2 & EN 13480-2 EN 13445-2 & EN 13480-2 EN 13445-2 & EN 13480-2 ASME BPVC ASME BPVC ASME BPVC ASME BPVC ASME BPVC ASME BPVC ASME BPVC |
| X10CrWMoVNb9-2 X10CrWMoVNb9-2 F92 T92 WP92 P92 F92 FP92 92 | 1.4901 1.4901 K92460 K92460 K92460 K92460 K92460 K92460 K92460 | EN 10216-2 EN 10253-2 ASTM A-182 ASTM A-213 ASTM A-234 ASTM A-335 ASTM A-336 ASTM A-369 ASTM A-1017 | Smls. tube Fittings Forging Smls. tube Fitting Smls. pipe Forging Forged pipe Plate | EN 13445-2 & EN 13480-2 EN 13445-2 & EN 13480-2 ASME BPVC ASME BPVC ASME BPVC ASME BPVC ASME BPVC ASME BPVC ASME BPVC |
| 91 | K91560 | ASTM A-691 | Fusion welded pipe | ASME BPVC |
| X11CrMoWVNb9-1-1 X11CrMoWVNb9-1-1 P911 | 1.4905 1.4905 – | EN 10216-2 EN 10302 – | Smls. tube – – | EN 13445-2 & EN 13480-2 EN 13445-2 & EN 13480-2 – |
| X20CrMoV11-1 X20CrMoV11-1 X20CrMoV11-1 | 1.4922 1.4922 1.4922 | EN 10216-22 EN 10222-2 EN 10253-2 | Smls. tube Forging Fitting | EN 13445-2 & EN 13480-2 EN 13445-2 & EN 13480-2 EN 13445-2 & EN 13480-2 |
| X22CrMoV12-1 | 1.4923 | EN 10269 | Fasteners | EN 13445-2 & EN 13480-2 |
| GX23CrMoV12-1 C12A 12A C91 | 1.4931 J84090 J84090 J84090 | EN 10213 ASTM A-213 ASTM A-356 ASTM A-1091 | Casting Casting Casting Casting | EN 13445-2 & EN 13480-2 ASME BPVC ASME BPVC ASME BPVC |