Effect of Cu Alloying on Strain Capacity of Cu-bearing Pipeline Steels

Abstract

The present study aims to elucidate the effect of Cu alloying on the strain capacity of Cu-bearing pipeline steels. The main emphasis was placed on understanding the effects of Cu content (1.0Cu, 1.5Cu and 2.0Cu) and the existence form of Cu (as-rolled and as-aged steels) on the yield stress/tensile stress ratio (yield ratio), uniform elongation and strain hardening exponent. Experimental results show that the engineering stress-strain curves present continuous yielding behavior for the as-rolled steels but discontinuous yielding for the as-aged steels. For both as-rolled and as-aged steels, increasing Cu content increases the yield ratio with an accompanying decrease of uniform elongation. It was found that the as-rolled 1.0Cu steel has one strain hardening exponent (n value), low yield ratio (0.68), high n value (0.18) and high uniform elongation (17.7%), showing an excellent deformation ability. There are two n values for the other steels (1.0Cu as-aged, 1.5Cu and 2.0Cu as-rolled and as-aged), and their n values increase at low stress but decrease at high stress with increase of Cu content. In contrast to the as-aged steels, the as-rolled steels show better strain capacity.