As-rolled multi-phase microalloyed steel bars with improved properties
Valjane večfazne mikrolegirane jeklene palice z izboljšanimi lastnostmi

english

1997

volume 31, issue 6

Narodna in univerzitetna knjižnica

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 treatment.

22.07.2011