Analysis of the amount of input heat during welding and its influence on structure and toughness of high strengthened micro-alloyed steels

Abstract

Compared to the low-carbon and low-alloyed constructive steels, application of high strengthened steels has significant advantages. Those advantages are contained in reducing the mass of construction, increasing the carrying capacity and working period, increasing the anti-corrosive protection and attaining the good properties of welded joint. But it is not that easy to accomplish these characteristics in high strengthened micro-alloyed steels because of following difficulties:- increase of strength is usually followed by decrease of plasticity,- increase of strength causes decrease of impact toughness, which increases tendency to brittle fracture,- increase of strength steels decreases the ratio between yield limit and tensile strength, which leads to decreasing of dependability of welded assembly. The purpose of this paper was to determine optimum regime of thermo-mechanical treatment for certain amount of input heat during welding, what should contribute in achievement of quality appliance of welded assembly. The tested material was high strengthened micro-alloyed steel with all its properties, such as resistance and deformation, toughness, macroscopic, microscopic and submicroscopic changes in material.

Primena čelika visoke čvrstoće ima znatne prednosti u odnosu na obične niskougljenične i niskolegirane konstrukcione čelike. Prednosti se ogledaju u smanjenju mase konstrukcije, povećanju nosivosti i veka trajanja, povećanju antikorozivne zaštite i postizanju dobrih karakteristika zavarenog spoja. Međutim, postizanje navedenih svojstava kod mikrolegiranih čelika visoke čvrstoće nije tako jednostavno zato što: - povećanje čvrstoće obično prati smanjenje plastičnosti; - povećanje čvrstoće izaziva smanjenje udarne žilavosti, a time i povećanje sklonosti ka krtom lomu; - sa povećanjem čvrstoće čelika smanjuje se odnos granice tečenja i zatezne čvrstoće, što dovodi do smanjenja pouzdanosti zavarene konstrukcije. Cilj ovoga rada je bio da se na mikrolegiranom čeliku visoke čvrstoće na osnovu ispitivanja svojstava otpornosti i deformacije, karakteristika žilavosti, praćenja makroskopskih, mikroskopskih i submikroskopskih promena u materijalu utvrdi optimalni režim termomehaničke obrade za određenu količinu unesene toplote pri zavarivanju, što bi doprinelo da se postigne odgovarajući kvalitet za primenu zavarene konstrukcije.