Showing papers on "Microalloyed steel published in 1983"

Austenite grain coarsening in microalloyed steels

Abstract: A uniform, fine-grain structure is essential in steels, particularly for strip and plate, that are to meet demands for high strength and toughness. To produce such microstructures, every step of the high-temperature processing of the steel must be carefully controlled, beginning with grain coarsening that occurs during reheating for slab rolling. Extremely coarse or nonuniform grain structures in the reheated slab are difficult to refine by subsequent hot working. Accordingly, the grain-coarsening behavior of laboratory heats of C-Mn-Si base steels and of such steels with additions of Al, V, Ti, or Nb was examined to understand the principles governing the behavior of this class of steels. The grain-coarsening temperature (the temperature at which abnormal or discontinuous growth occurs) varies with the type and concentration of the microalloy addition; an approximate relation is presented. Generally the grain-coarsening temperature increases with, but is lower than, the temperature required for complete dissolution of the microalloy carbide or nitride present. Thus, steels containing the very insoluble TiN coarsen at much higher temperatures than steels containing the more soluble VCN. These results agree qualitatively with predictions of models of grain-boundary pinning by precipitate particles.

Role of Annealing Twins for Grain Refinement in Controlled Rolling of Low Carbon Microalloyed Steel

Abstract: A 0.1%C-1.35%Mn-0.03%Nb steel was hot rolled in a single pass up to 83% reduction in thickness at a temperature between 790°C and 1 050°C and the deformation state of austenite was examined metallographically in detail. It was found that annealing twins were formed abundantly in the austenite during heating before rolling, or during recrystallization in a high temperature. Rolling at a temperature below the recrystallization temperature of austenite resulted in a severe deformation of these annealing twins. At the same time, a heavy local deformation was introduced into the regions near boundaries of these annealing twins, and also near austenite grain boundaries. Such a local concentration of deformation was found to enhance the formation of ferrite nuclei in these regions during the subsequent ferrite-pearlite transformation. It was suggested that this effect was most essential in the grain refinement of control-rolled steel.

Process for making fine-grain weldable steel sheet for large-diameter pipes

Abstract: Microalloyed steel containing, among other ingredients, at least 0.02% niobium, between 0.005 and 0.01% nitrogen, and titanium in a proportion equaling about 3.5 to 4 times that of nitrogen is continuously cast into a slab which is heated to a temperature between about 1120° and 1160° C. whereby titanium nitride precipitates in particles ranging between about 0.06 and 0.2μ. The slab is thermomechanically treated at this temperature and after intermediate cooling in several hot-rolling stages, with an initial deformation of at least 55%; after final rolling, the slab is cooled in water at a rate of at least 10° C. per second to a temperature of about 500° to 550° C. Niobium, which goes into solution at the elevated initial temperature, forms NbC precipitates during the subsequent treatment; this has a hardening and grain-refining effect.

Microalloyed Hot Rolled Bars for Hot Forging Applications

Abstract: Energy conservation and cost savings can be realized by elimination of the heat treatment of forgings by the use of hot rolled microalloyed steel bars.