Abstract
Hydrogen induced damage is a dangerous phenomenon affecting the weld quality with regard to construction service life even without visible indication. The determination of diffusible hydrogen in weld metal has been standardized at an international level in ISO 3690:2012. This international standard specifies the sampling and analytical procedure for the determination of diffusible hydrogen in martensitic, bainitic and ferritic steel weld metal which arises from the welding of such steels using arc welding processes with filler metal. In this study, S960QL steel is extensively used in the heavy transport, lifting and mining industry, where mobile or fixed structures have to carry high loads – often in safety critical situations. In order to sustain extreme characteristics of these high strength low alloy steels, it is a must to reduce the manufacturing defects. In the investigations presented in this paper, the influence of arc length on the weld metal hydrogen concentration was studied according to the ISO DIS 3690 in S960QL type steel with submerged arc welding. Measurement of the diffusible hydrogen was carried out by means of carrier gas hot extraction method. The weld seams with different arc length have similar chemical compositions. Maximum hardness values in the range of 410–425 HV1 were measured in the HAZ on both vertical and horizontal rows in welded structure with two mm wire diameter due to recrystallization condition. For four mm wire diameter, the hardness decreasing which is depending on the grain coarsening in the welded samples with two mm was not occurred in the weld seam-HAZ interface. The larger weld pool and the long arc length increased possibility of hydrogen pick-up and absorbing. Because of this reason, the diffusible hydrogen contents in the welded structure increased in accordance with the arc length.
Kurzfassung
Die wasserstoffunterstützte Schädigung ist ein gefährliches Phänomen, das die Schweißnahtqualität bezüglich der Lebensdauer einer Konstruktion sogar ohne visuelle Erkennbarkeit beeinflusst. Die Bestimmung des diffusionsfähigen Wasserstoffs im Schweißgut wurde auf internationalem Niveau in ISO 3690:2012 genormt. Diese internationale Norm spezifiziert die Probenentnahme und die analytische Prozedur, um den diffusionsfähigen Wasserstoff in martensitischem, bainitischem und ferritischem Schweißgut zu bestimmen, der sich beim Lichtbogenschweißen solcher Stähle mit Zusatzwerkstoff einstellt. Der für diesen Beitrag untersuchte Stahl S960QL wird ausgiebig in der Schwerlasttransportindustrie für die Herstellung von Hebezeug und im Bergbau verwendet, wo mobile und feste Strukturen große Lasten aufnehmen müssen, vor allem auch in sicherheitskritischen Anwendungen. Um die extremen Charakteristika dieser hochfesten niedriglegierten Stähle zu erhalten, müssen Herstellungsfehler reduziert werden. In der Studie, die in diesem Beitrag dargestellt wird, wurde der Einfluss der Lichtbogenlänge auf die Wasserstoffkonzentration im Schweißgut eines unterpulvergeschweißten Stahls des Typs S960QL entsprechend der ISO DIS 3690 untersucht. Die Messungen des diffusionsfähigen Wasserstoffs wurden mittels der Trägergas-Heißextraktion durchgeführt. Die Schweißraupen, die mit verschiedenen Lichtbogenlängen hergestellt wurden, haben eine ähnliche chemische Zusammensetzung. Die maximale Härte betrug in beiden, den vertikalen und den horizontalen, Reihen der mit einem Drahtdurchmesser von zwei Millimetern geschweißten Struktur aufgrund der Rekristallisationsbedingungen zwischen 410 und 425 HV1. Für den Drahtdurchmesser von vier Millimetern nahm die Härte ab, weil die in den mit einem Draht von zwei Millimetern Durchmesser geschweißten Schweißproben beobachtete Grobkornbildung an der Schmelzlinie nicht auftrat. Das größere Schweißbad und die längere Lichtbogenlänge konnte die Möglichkeit für eine Wasserstoffaufnahme und Wasserstoffabsorption erhöhen. Aus diesem Grund nahm der diffusionsfähige Wasserstoffgehalt in der geschweißten Struktur mit der Lichtbogenlänge zu.
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