22 KB1172 KB21 KB199219991997Drobnjak, DjordjeKoprivica, A.letnik:315 straništevilka:6str. 533-537ISSN:1318-0010COBISSID:71338URN:URN:NBN:SI:doc-X5V2SFSZenInštitut za kovinske materiale in tehnologijeŽelezarna JeseniceŽelezarna RavneŽelezarna ŠtoreKovine zlitine tehnologijefazejeklamehanske lastnostimikrolegiranjemikrolegirano jeklopalicestrukturaAs-rolled multi-phase microalloyed steel bars with improved properties| Valjane večfazne mikrolegirane jeklene palice z izboljšanimi lastnostmi|A series of experimental steels, based on a 0.3 C, 1.5 Mn, 0.1 V composition, with and without 0.01% Ti addition, was made by laboratory and full scale casting, and fabricated into 22 mmdia bars by full-scale hot-rolling. Multi phase Polygonal Ferrite-Pearlite-Non Polygonal Ferrite (PF-P-NPF) structures with varying amount of NPF are obtained in as-rolled bars. Acicular Ferrite (AF) and classical Bainite Sheaves (BS) are found to be dominant NPF morphologies in steels with a low (<30%) and a high (>40%) fraction of NPF, respectively. In Ti-bearing PF-P-AF steels, the PF-grain and P-colony size control, obtained through fine TiN particles, which also provide preferential sites for intragranular nucleation of AF, a tensile strength of 800/850 MPa and 900/950 MPa in 0.2 and 0.3 C steels was obtained, while maintaining the room temperature CVN impact energy at a level of 65/75 J and 40/50 J, respectively. A high fraction of grain boundary nucleated BS is promoted by increasing the content of Cr, Mo or Mn above the base level. The main effect of introducing BS into structure is a drop in impact toughness. Even so, in some BS dominated steels (notably Cr treated) an impact energy of 30/35 J is maintained at a tensile strength level of 1050/1100 MPa. These results have provided a bases for the development of as-rolled medium carbon mycroalloyed engineering bars, that achieve satisfactory properties in the as-rolled conditions without the need for subsequent heat treatmentVrsta eksperimentalnih jekel z osnovno sestavo 0.3 C, 1.5 Mn in 0.1 V z ali brez dodatka 0.01% Ti je bila izdelana z laboratorijskim in industrijskim ulivanjem ter industrijsko izvaljana v 22 mm palice. Dosežene so večfazne poligonalni ferit-perlitne - poligonalni ferit (PF-P-NPF) mikrostrukture z različnim deležem NPF. Acikularni ferit (AF) in klasični bajnitni snopi (BS) so prevladujoče MPF morfologije v jeklih z majhnim (<30%) in velikim (>40%) deležem MPF. V PF-P-AF jeklih z dodatkom Ti, kjer je dosežena kontrola velikost zrn PF in P kolonij z izlički TiN, ki so tudi prednostna mesta za intergranularno nukleacijo AF, je bila dosežena pri 0.2 in 0.3 C jeklih natezna trdnost 800/850 in 900/950 MPa. Pri tem je ostala CVN udarna energija pri temperaturi ambienta 65/75 oz. 40/50 J. Velik delež BS z nukleacijo na kristalnih mejah se doseže z dodatkom Cr, Mo ali Mn nad osnovno vsebnostjo. Glavna posledica prisotnosti BS v mikrostrukturi je zmanjšanje udarne žilavosti. Vendar je bila tudi v nekaterih jeklih s prevladujočo BS (predvsem z dodatkom Cr) ohranjena udarna energija 300/335 J pri trdnosti 1050/1100 MPa. Ti rezultati so bili osnova za razvoj srednje ogljičnih konstrukcijskih jekel, ki imajo v valjnem stanju dobre lastnosti brez dodatne tooplotne obdelaveTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of Slovenia