Abstract:
An experimental study has been made of the effect of heat treatment (hardening followed by tempering) on the mechanical properties of martensitic grade of stainless steel X22Cr13-Mo-V used in steam turbine applications.
The present investigation was carried out in the form of material/product appraisal. It was observed that hardness in the as quenched condition was a function of the hardening temperature & ranged from 460 to 530 HV30. Tempering lead to a decrease in the as quenched hardness, the magnitude of the decrease being small on varying both, the tempering temperature (660°C & 685°C) & period (90 min to 270 min). Microstructure in the as tempered condition retained the accicularity observed in the quenched condition.
The material behaviour, from the point of view of inclusion rating, was acceptable except for the presence of chunky refractory/slag materials.
Tensile properties in the tempered condition were a function of the quenching temperature as well as tempering temperature & time. The inconsistencies observed in
the mechanical properties data could be satisfactory observed/resolved by plotting the mechanical properties as a function of dependent variables and through using the best fit method. Overall the PS ranged from 700-870 MPa, UTS from 800-1000 MPa, %EL from 14 to 23 and %RA from 60-73.
Impact toughness improved with tempering temperatures and with tempering periods. However, at the lower of the two hardening temperatures, the toughness in the as tempered condition showed a more distinctive tendency towards improvement, both with tempering temperature & periods.
Through the above mentioned exercise a correlation is sought to be established between structure and properties. This proved helpful in arriving at understanding of, the material's behaviour for the specified application.
