Structure-Properties Relationship of TRIP-assisted Steels by Non-destructive Testing Method

Abstract

This study was conducted on two TRIP-assisted steels (having low temperature (–40℃) high Charpy impact value) designated A (having no Cr and Cu content, VHN=169, UTS=542MPa) and B (having higher Ni, Cr and Cu content, VHN=217, UTS=657MPa).These steels were heattreated under different conditions to investigate correlation between heat treatment, microstructure and different properties. Micro-structural characterizations were carried out by optical microscope and scanning electron microscope after electrolytic etching. Non-destructive electro-chemical and ultrasonic testing on two TRIP-assisted steels were used to find out corrosion and mechanical properties of different alter microstructure phase’s steels. Furthermore, micro-structural studies accompanied by the evaluation of mechanical properties revealed that steels having martensite phases with higher corrosive and hardness value were less sound velocity and also steel’s microstructure having finer grains that was more grain boundary was less corrosion resistance. Steel containing more Cu, Ni and Cr was less corrosive compared to other steels having same processing or microstructure i.e. Rp (B) > Rp (A). The additions of alloying elements, such as Cu, Cr, Mo, Ni, etc. within the rust layer contribute to the improvement of electro-chemical characteristic of TRIP assisted steel. The corrosion current or i corr increases and corrosion resistance or Rp decreases with increasing Cl - ions in solution up to a threshold value beyond which the corrosion rate starts to decrease.