Analysis of dynamic and impact loads influence on welded steel structures made of super duplex stainless steel

[S. Perković]

106 str.

Tehničke nauke – Mašinsko inženjerstvo - Tehnologija materijala, mehanika loma / Technical Sciences – Mechanical Engineering - Materials science, Fracture Mechanics

Tema ove doktorske disertacije je analiza mogućnosti upotrebe superdupleks nerđajućeg čelika S32750 za zavarene konstrukcije koje tokom eksploatacije mogu biti izložene niskim temperaturama do -80 ℃, kao i uticaj udarnog i promenljivog opterećenja na zavarene spojeve i na njihov integritet i vek. Za jednu vrstu dodatnog materijala i postupak zavarivanja koji su primenjeni na spajanje ploča dupleks čelika S32750, ispitan je dobijeni zavareni spoj analizom mikrostrukture i makrostrukture, hemijskog sastava i mehaničkih karakteristika, uključujući ispitivanja i detaljnu analizu ponašanja pri udarnom i promenljivom opterećenju, za tri zone spoja OM, MŠ i ZUT. Pri tome su poređeni rezultati analiza i razmatran je uticaj zavarenog spoja na integritet i vek cele konstrukcije u odnosu na osnovni metal, kao i ponašanje tog spoja kada je izložen udarnom i promenljivom opterećenju. Ovim istraživanjem se pored slike o ponašanju super dupleks čelika S32750 dobija slika o ponašanju zavarenog spoja i to pored standardne sobne temperature (+20℃) i na spektru niskih temperatura -80 ℃, -60 ℃ i -40 ℃. Ovim se proširuju dosadašnja istraživanja koja su uglavnom tretirala upotrebu ovog tipa čelika, ali na visokim temperaturama. Na osnovu prikazanih analiza su uočene pojave kojima se potvrđuje izbor super dupleks čelika S32750 kao odgovarajućeg za njegove osnovne namene, a uz to se potvrđuje i izbor dodatnog materijala, metoda i parametara zavarivanja kao pogodnih za ovaj čelik. Osim navedenog dobijeni su i rezultati koji upućuju na ograničenja upotrebe zavarenih konstrukcija od čelika S32750, kao što je radna temperatura iznad -50 ℃. Dodatne ograničenja su u vezi integriteta i veka, u oba slučaja zbog zavarenih spojeva, odnosno heterogenosti mikrostrukture ZUT i MŠ i njihovih svojstava otpornosti na nastanak i rast prslina.

The topic of this doctoral dissertation is the analysis of the possibility of using superduplex stainless steel S32750 for welded constructions that may be exposed to low temperatures up to -80 ℃ during operation, as well as the impact of impact and variable loads on welded joints on their integrity and life. For one type of additional material and welding procedure applied to the joining of S32750 duplex steel plates, the obtained welded joint was tested by analysing microstructure and macrostructure, chemical composition and mechanical characteristics, including tests and detailed analysis of the behaviour under impact and variable loading, for three joint zones BM, WM and HAZ. In doing so, the results of the analyses were compared and the influence of the welded joint on the integrity and life of the entire structure in relation to the base metal was considered, as well as the behaviour of that joint when exposed to impact and variable loads. With this research, in addition to the view of the behaviour of the super duplex steel S32750, a view of the behaviour of the welded joint is obtained at the standard room temperature (+20℃) and at the spectrum of low temperatures -80 ℃, -60 ℃ and -40 ℃. This expands previous research that mostly dealt with the use of this type of steel, but at high temperatures. Based on the presented analyses, phenomena were observed that confirm the choice of super duplex steel S32750 as appropriate for its basic purposes, and also confirm the choice of additional material, methods and welding parameters as suitable for this steel. In addition to the above, results were also obtained that point to the limitations of the use of welded structures made of S32750 steel, such as the operating temperature above -50 ℃. Additional limitations are related to integrity and life, in both cases due to welded joints, i.e. the heterogeneity of the microstructure of HAZ and WM and their properties of resistance to the initiation and growth of cracks

Super dupleks čelik S32750, zavareni spojevi, udarno i ciklično opterećenje, integritet i vek konstrukcije, udarna žilavost, energije nastanka i rasta prsline.

Super duplex steel S32750, welded joints, impact and cyclic loading, structural integrity and life, impact toughness, energy for crack initiation and growth

621.791.052:669.15:539.42(043.3)

Tekst