The fracture behaviour of S960 steel in different conditions, i.e as-delivered, cold strained, cold strained and artificially aged, has been studied using small-scale fracture mechanics and Charpy V testing as well as tests on large-scale U-beams and cold-formed rectangular hollow sections. At room temperature and -40 deg C, fracture resistance testing indicated overall ductile behaviour. Regarding brittle fracture, the T0 reference temperature for the as-received material was around -50 deg C. Artificial ageing alone increased this temperature only slightly, but cold-straining and artificial ageing together raised T0 (and T28J) by almost 50 deg C. For the strength level studied, the FITNET correlation between T0 and T28J leads to severely un-conservative KJC estimates, indicating that KJC needs to be measured directly. T0 estimates based on fracture mechanics tests using small-scale 3-point bend specimens were clearly conservative in relation to the large-scale U-beam behaviour due to different constraints. Shear fracture occurred in the U-beam tests as a result of the small plate thickness; however, this led to only a 10 % decrease in the load-bearing capacity from the theoretical maximum load. Quasi-static bending tests on welded fatigue-cracked cold-formed rectangular hollow sections at -40 deg C showed good agreement with nonlinear FEA calculations using the J-integral approach. Both large-scale test variants showed that brittle cleavage fracture will not become the dominant fracture mode in the welded beam constructions studied, provided the service temperature does not fall below -50 deg C.
|Title of host publication||Proceedings|
|Subtitle of host publication||2nd International Conference Super-High Strength Steels (SHSS), Peschiera del Garda, 17-20 October 2010|
|Place of Publication||Milano|
|Publisher||Associazione Italiana di Metallurgia AIM|
|Number of pages||14|
|Publication status||Published - 2010|
|MoE publication type||B3 Non-refereed article in conference proceedings|
Nevasmaa, P., Karjalainen-Roikonen, P., Laukkanen, A., Nykänen, T., Ameri, A., Björk, T., Limnell, T., & Kuoppala, J. (2010). Fracture characteristics of new ultra-high-strength steel with yield strengths 900-960 MPa. In Proceedings: 2nd International Conference Super-High Strength Steels (SHSS), Peschiera del Garda, 17-20 October 2010 Associazione Italiana di Metallurgia AIM.