Effect of Isothermal Ageing on Microstructure and Mechanical Behavior of 0.5Cr-0.5Mo-0.2V Low Alloy Steel

Abstract

Cr-Mo-V based low alloy steels are widely used in thermal power plants because of their

ability to withstand elevated temperature and high pressure under continuous operation. With

ferrite-pearlite and/or ferrite-bainite microstructures, these steels find their applications in

boiler tubes, pressure vessels and steam turbines. Being cost effective is one of the important

factors, which draws attention of many industrialists towards low alloyed steels over highly

alloyed steels with austenitic matrix. In this work, the microstructure and mechanical

properties degradation of low alloy steel sample were analyzed. Investigated material was in

service for 35 years. During its service life, it was exposed to high temperature and pressure

resulting in properties to undergo changes. To figure out these evident changes, sample was

solutionized and tempered for different ageing times under laboratory conditions. Changes in

the morphology of the steel microstructure such as pearlite decomposition, carbide

precipitation and spheroidisation etc. could be observed. Due to its coherent relation with

microstructure, mechanical properties were also found to have undergone variations. In order

to investigate the behavior of this steel after its exposition to different environments, hardness

and tensile tests were conducted. Microstructural evolution of the sample was observed using

SEM. TEM analysis was done to figure out the nature of carbides formed during

experimentation. Experiments revealed the improvement in mechanical properties of the steel

in the initial hours of its service due to the phenomenon of secondary precipitation. But, after

reaching its peak condition (over-ageing) deterioration in the properties started.

Cite this Article

Ranjana Kumari, Goutam Das. Effect of

Isothermal Ageing on Microstructure and

Mechanical Behavior of 0.5Cr-0.5Mo-

0.2V Low Alloy Steel. Journal of

Materials & Metallurgical Engineering.

2015. 5(3): 7–14p.