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Mechanical properties of SMA- and SA-welded joints for quenched and tempered high-strength steel N-A-XTRA 70

  • Vilpas, Martti
  • Tihekari, Hannele
  • Karppi, Risto
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The report gives the test results of mechanical properties of shielded metal arc (SMAW) and submerged arc (SAW) welded joints for quenched and tempered high-strength steel N-A-XTRA 70 (StE 690). The testing procedure comprised conventional hardness, tensile and Charpy-V testing and fracture mechanics. The test results of the joints welded with Ni-Cr-Mo alloyed filler materials (SMAW: E 11018-M, SAW: S3NiCrMo2.5), using arc energies of 17 kJ/cm and 30 kJ/cm and preheat temperature of 170 °C showed that the weld metal strength and toughness properties were close to the base material values. The hardness was found to vary in the range of 278 - 337 HV5 for the weld metals and 295 - 476 HV5 for the heat affected zones of the joints. The hardness values were the highest (max. 476 HV5) close to the top areas of the heat affected zones welded with SMAW. The corresponding measurements from the SAW-joints gave somewhat lower hardness levels (max. 394 ElV5). The weld metals showed reasonably good Charpy-V transition behaviour as compared with the base material. The transition of toughness properties for the fusion boundaries was, however, located at markedly higher temperatures than that of the base material. The results indicate that the arc energy should be kept low (i.e. around 17 kJ/cm) for reasonable impact properties at fusion boundaries of the steel N-A-XTRA 70. In this respect, SAW turned out to be a more favourable welding procedure than SMAW. The fracture toughness testing of the joints showed that the arc energy had no marked effect on the K J-transition behaviour of the weld metals. The testing of the fusion boundaries, however, revealed again that the arc energy should be restricted around 17 kJ/cm to achieve good fracture toughness at fusion boundaries of the steel N-A-XTRA 70. This was found to be the case especially at the lower test temperatures.

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