Effects of carbon and niobium on microstructure and properties for Ti bearing steels

Abstract

The objective of the study described here is to elucidate the effect of carbon and niobium on the microstructure, precipitation behaviour, and mechanical properties of 0?09C-0?11Ti (%) steel and 0?05C-0?025Nb-0?11Ti (%) steel under ultra fast cooling condition. The strengthening mechanisms are also discussed. The ferrite grains size and the size of precipitates in Ti and Nb-Ti steels were measured respectively. The mechanical properties obtained in Ti steel were similar to Nb-Ti steel with yield stress .700 MPa, elongation .20%, and good low temperature impact toughness. The study underscores that addition of higher carbon content by 0?04% under controlled rolling and ultra fast cooling conditions, we can achieve similar strength in the absence of micro-alloying element, niobium.

Microalloyed steels

“…As pointed out by Ji et al, 130 these highly alloyed steels detailed above achieved their yield strength at a relatively high cost. The recent approach of Ji et al 130 22 a four caps formed on sides of cuboid core with probability that there are also caps on top and bottom faces and b cruciform particle with four arms nucleating and growing from core 21 a Ti-Nb particles in 0.01%Ti, showing smaller Nb rich spheroids and b EELS spectrum collected from centre of ,20 nm Nb rich spheroid showing niobium, carbon nitrogen and titanium edges 119 Baker Microalloyed steels…”

“…As pointed out by Ji et al , 130 these highly alloyed steels detailed above achieved their yield strength at a relatively high cost. The recent approach of Ji et al − 1 compared two laboratory steels of compositions based on 0.09C–0.11Ti and 0.05C–0.025Nb–0.11Ti.…”

“…As pointed out by Ji et al , 130 these highly alloyed steels detailed above achieved their yield strength at a relatively high cost. The recent approach of Ji et al − 1 compared two laboratory steels of compositions based on 0.09C–0.11Ti and 0.05C–0.025Nb–0.11Ti. Both steels reached σ y values of >700 MPa with >20% elongation and good toughness; it should be pointed out that one steel was without a niobium addition.…”

“…Some of the more recent works, which lead to the gradual raising of the yield strength by controlled rolling MA steels, was summarised by Ji et al 130 Campos et al 131,132 developed yield stress of 530–608 MPa respectively using nominal chemical compositions of 0.12C–0.057Nb–0.049Ti and 0.11C–0.04Nb–0.11Ti. In addition, the precipitation behaviour in a 0.07C–0.086Nb–0.047Ti steel was investigated by Charleux et al , 133 who obtained σ y levels of 650 MPa in a plate.…”

Titanium microalloyed steels

“…Smith et al, 223 who investigated Mn-Mo-Nb steels, were among the first to develop AF microstructures in line pipe steels.More recently, AF microstructures formed in titanium steels have been studied extensively. [252][253][254][255][256][257][258] Acicular ferrite, also referred to as intragranular ferrite (IGF), has been recognized as a separate phase in steels for over 40 years, initially in arc welded deposits of low alloy steels, to be discussed later,where it was most commonly present due the transformation of austenite, during cooling at intermediate transformation temperatures of 650 to 500°C. 216 AF has been found to improve HAZ toughness 259,260 and is also observed in wrought steels which have been deliberately inoculated with non-metallic inclusions.…”