SZ-Steel, which refers to sub-zero temperatures, is a family of steel that has proven to retain properties for safer and more reliable performances in temperatures down to -40°C and below. The impact toughness of the steel is a key factor in creating reliable solutions in cold climates, especially in applications where a high-strength steel would be the best design solution. The family of SZ-Steel from Ovako has been optimized to allow the impact strength required at high strength levels and low temperature applications. 

Ovako R&D delivers for the future

To gain and maintain toughness you have to take into account a number of parameters such as structure, grain size, impurities and alloying. For a steel to be designated a SZ-Steel we have to secure our control of all these parameters. We are aiming even higher, however. We are moving to better measure and understand the fracture in order to really define whether it is ductile or brittle. To achieve this we measure the total impact fracture process. What we then see is something that looks very similar to tensile testing, although we are actually measuring when the fracture shifts from ductile behavior to more brittle behavior.

Figure 1. Curve showing transition from brittle to ductile fracture with increasing temperature.

SZ-Steel combined with IQ-Steel®

In conventional steels there are non-metallic inclusions elongated in the rolling direction of the steel. At standard, the sampling of material for mechanical testing is along the rolling direction, the direction least influenced by these inclusions. When the sampling is instead carried out transverse to the rolling direction, the properties will show a different behavior, a negative difference with much lower values. If we combine the SZ-Steel with an IQ-Steel® treatment we can minimize the influence of these nonmetallic inclusions as the IQ-Steel has fewer and much more uniform inclusions. The result can be seen in figure 2.

Figure 2. Impact strength of Ovako 277L and IQ-Steel version Ovako 277Q. The blue upper line is impact strength in the longitudinal direction for both versions.