Sensitization induced deterioration in fracture toughness of 304LN austenitic stainless steel

Abstract

The aim of this report is to examine the influence of sensitization on the mechanical properties of AISI grade 304LN stainless steel with special emphasis on its fracture toughness. A series of stainless steel samples has been sensitized by holding these at 1023K for different time periods ranging from 1 to 100 h followed by water quenching. The degree of sensitization (DOS) for each type of the varyingly heat treated samples has been measured by electrochemical potentiodynamic reactivation test. The microstructures of these samples have been characterized by optical, SEM, and XRD analyses together with measurements of their hardness and tensile properties. The fracture toughness of the samples has been measured by ball indentation technique and the results are validated by conducting conventional J-integral tests. It is revealed for the first time that fracture toughness and ductility of AISI 304LN stainless steel deteriorate significantly with increased DOS while their tensile strength values remain almost unaltered. The results have been critically discussed in terms of the depletion of solid solution strengtheners, nature of grain boundary precipitations and strain induced martensite formation with increasing DOS of the 304LN stainless steel.