Influence of diffusible hydrogen on brittle fracture resistibility of metal in heat-affected zone of high-strength carbon steel
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Abstract
Abstract
Influence of diffusible hydrogen on the change of brittle fracture resistibility and mode of HAZ metal of welded joints on high-strength steels with 0,58% and 0,65% carbon content has been studied. Methods of simulation of thermal cycle of welding, saturation of model samples by hydrogen and their subsequent testing at bending were used to determine the influence of dif- fusible hydrogen on stress intensity factor К1С of HAZ metal. Metal microstructure in HAZ overheated zone and model sample fractures after testing were studied. It is shown that high-strength carbon steels and their joints have high susceptibility to embrittlement in the presence of hydrogen. Metal structural condition plays an essen- tial role here. Optimum structure of HAZ metal is bainitic- martensitic one at more than 1 ratio of structural components. At saturation of joints by diffusion hydrogen occurring in welding, their brittle fracture susceptibility increases. To lower metal embrittlement, it is necessary to apply special welding processes, at which hydrogen saturation of deposited metal is minimum (less than 0,2 ml/100g) or techniques, allowing removal of diffusible hydrogen from the metal after welding.
Streszczenie
W artykule zaprezentowano wyniki badań poświęconych opisaniu wływu wodoru dyfundującego na kruche pękanie w SWC złączy spawanych wysokowytrzymałej stali o stężeniu masowym węgla 0.58% oraz 0,65%. Do określenia współczynnika intensywności naprężeń KIC w SWC użyto metod symulacji cyklu termicznego spa- wania z możliwością nasycania wodorem SWC. Przebadano mikrostrukturę przełomów w obszarze przegrzania w SWC próbek z symulatora cykli cieplnych spawania. Otrzymane wyniki wskazują, że złącza spawane stali o wysokiej wytrzymałości wykazują wysoką skłonność do pęknięć wodorowych. Właściwości struktury materiału odgrywają pod tym względem znaczącą rolę. Za optymalną strukturę w SWC uznaną bainityczno-martenzytyczną. Nasycenie złączy wodorem znacząco zwiększa ich skłonność do kruchego pękania. W celu obniżenia kruchości metalu w SWC koniecznym jest stosowanie niskowodorowych procesów spawania, w których nasycenie wodorem jest poniżej 0,2 ml/100g stopiwa lub technik pozwalających obniżenie stężenia wodoru po spawaniu w obszarze złącza.
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