ISO/TR 15608 Material Group 3.2: Quenched and tempered (QT) fine-grain high strength steels with a specific minimum yield strength ReH > 690 N/mm2.
What is the quenched and tempering (QT) process of high strength steels?
Quenching and tempering is a heat-treatment method for high strength low alloy steel. Quenching and tempering consists of a two-stage heat-treatment process.
Stage 1 includes hardening, in which the plate is austenitised to approximately 900°C and then quickly cooled. The material is water-quenched in a quench unit, in which the plate is clamped to avoid warpage.
Stage 2 consists of tempering the material to obtain the desired material properties. Quenching and tempering achieves an extremely fine-grained and homogeneous microstructure. Quenched and tempered steel is characterised by high strength and good ductility.
Weldability of high strength steels ISO/TR 15608 Material Group 3.2
The high-strength tempered materials are generally weldable. However, certain requirements must be met during welding with regard to heat input and controlled cooling in the heat-affected zone and the use of hydrogen-reduced weld metal
When welding high strength steels, it should be noticed that that a tempering effect occurs due to the heat input during welding, which influences the properties of the base material. The temperature-time cycles during welding have a significant effect on the mechanical properties of a welded joint and the heat effect zones. It is understood, that the t8/5-time is sufficient to describe the temperature-time characteristics. t8/5 is the cooling time from 800°C to 500°C and describes the cooling conditions of an individual weld pass for the weld metal and the corresponding heat affected zone (HAZ). t8/5 depends on the heat input during welding, the plate temperature (or interpass temperature), the shape factor (geometry) and on plate thickness if two dimensional heat flow occurs which is generally the case for thin plates. To achieve satisfactory weld metal properties the welding parameters must be limited with increasing yield strength. For example acceptable properties for an P960QL steel are normally obtained with cooling times between 5 s and 20 s. For lower cooling times the hardness of the heat affected zone may exceed limiting values with the risk of introducing cracks.
The hydrogen content of the consumables H2 has a significant influence on the preheating temperature. In order to reduce the risk of hydrogen-induced cracking the preheating temperature must be increased with growing hydrogen content.
Flame straightening of high strength steels ISO/TR 15608 Material Group 3.2
The maximum recommended temperatures for flame straightening is usually 550°C for quenched and tempered steels.
Quenched and tempered (QT) fine-grain steels with a specific minimum yield strength 460 < ReH ≤ 690 N/mm2: see Group 3.1
Typical materials in group 3.2
| Name / Grade | Number | Standard | Product | Remarks |
|---|---|---|---|---|
| S700MC | 1.8974 | EN 10149-2 | Plate | for cold forming |
| S900MC | 1.8798 | EN 10149-2 | Plate | for cold forming |
| S690MC | 1.8799 | EN 10149-2 | Plate | for cold forming |
| S890Q | 1.8940 | EN 10025-6 | Plate | structural steels |
| S890QL | 1.8983 | EN 10025-6 | Plate | structural steels |
| S890QL1 | 1.8925 | EN 10025-6 | Plate | structural steels |
| S960Q | 1.8941 | EN 10025-6 | Plate | structural steels |
| S960QL | 1.8933 | EN 10025-6 | Plate | structural steels |
| A, Cl. 1 A, Cl. 2 A, Cl. 3 | K12521 K12521 K12521 | ASTM A-533 ASTM A-533 ASTM A-533 | Plate Plate Plate | ASME BPVC ASME BPVC ASME BPVC |
| J100 | K12521 | ASTM A-672 | Fusion welded pipe | ASME BPVC |
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