621 KB25 KB200020242014Aydin, Hakanštevilka:1letnik:48str. 15-22COBISSID:1030314ISSN:1580-2949URN:URN:NBN:SI:doc-8JIIS8KLenInštitut za kovinske materiale in tehnologijeMateriali in tehnologijebainitbainitefriction-stir weldingjeklo X80microhardnessmikrotrdotatorno vrtilno varjenjeX80 steelRelationship between a bainitic structure and the hardness in the weld zone of the friction-stir welded X80 API-grade pipe-line steel| Odvisnost med bainitno mikrostrukturo in trdoto v področju zvara pri torno vrtilnem varjenju jekla X80 API za cevovode|The present study focuses on the morphology of the weld zone, especially on the quantitative microstructural characterization of bainitic structures, and the relationship between post-weld bainitic structures and the hardness at the weld zone of the friction-stir welded X80 API-grade pipe-line steel. The employed rotating and traverse speeds of the polycrystalline cubic boron nitride tool during the friction-stir welding process were 350 r/min and 12.7 cm/min (5 inch per minute), respectively. A microstructural analysis of the weld was carried out using optical microscopy, orientation imaging microscopy and transmission electron microscopy, and the hardness variation was also mapped across the weld-plate cross section. The frictional heat and plastic flow during friction-stir welding create a granular bainitic structure (the stir zone), a lath-like upper bainitic structure (the hard zone) and a recrystallized equiaxed polygonal ferritic structure (the heat-affected zone) in the weld zone. The maximum hardness was observed in the classical upper bainitic microstructure in the hard zone. The minimum hardness was found in the heat-affected zone. A good correlation between the post-weld bainitic structures and the hardness in the weld zone was obtained; the hardness increases almost linearly with the decreasing bainite-lath and packet sizesŠtudija obravnava morfologijo področja zvara, posebno kvantitativno karakterizacijo bainitne mikrostrukture in odvisnost med bainitno strukturo po varjenju in trdoto zvara pri torno vrtilnem varjenju X80 API jekla za cevovode. Uporabljene hitrosti rotacije in prečne hitrosti orodja iz kubičnega bor nitrida med torno vrtilnim varjenjem so bile 350 r/min in 12,7 cm/min (5 inčev na minuto). Mikrostruktura zvara je bila pregledana s svetlobnim mikroskopom, z mikroskopijo usmerjenosti slik in s presevno elektronsko mikroskopijo. Prikazano je spreminjanje trdote po prečnem prerezu zvara. Toplota zaradi trenja in plastični tok materiala med torno vrtilnim varjenjem povzročita nastanek zrnate bainitne strukture (cona mešanja), latasti zgornji bainit (trda cona) in rekristalizirano poligonalno feritno strukturo (toplotno vplivana cona) v zvaru. Najvišja trdota je bila opažena v navadni mikrostrukturi gornjega bainita v trdi coni. Najnižja trdota je bila vtoplotno vplivani coni. Ugotovljena je bila dobra korelacija med bainitno strukturo zvara in trdoto v coni zvara: trdota narašča skoraj linearno z manjšanjem bainitnih lat in velikostjo bainitnega sestavaTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaInštitut za kovinske materiale in tehnologije