Effect of Deformation Temperature on Anneal-Hardening of Type 304L Stainless Steel

Abstract

The relation between deformation temperature and anneal-hardening of type 304L stainless steel was investigated. Specimens were rolled at several temperatures ranging between -60° and 600°C and subsequently annealed up to 900°C.Amount of anneal-hardening was estimated by measuring the change of mechanical properties.
The results were summarized as follows:
(1) Anneal-hardening occured at 400-500°C before recrystallization when specimens were rolled at a deformation temperature below 600°C and subsequently annealed. Amount of anneal-hardening was increased with falling deformation temperatures. The specimen deformed at 600°C did not show any hardening phenomenon during annealing.
(2) Retrogression phenomenon was observed with the specimen anneal-hardened at 400°C after 38% deformation at -60°C. It was presumed that the mechanism of anneal-hardening of type 304L stainless steel was very similar to that of α-brass in consideration of this retrogression phenomenon.
(3) Sub-boundaries were formed with the specimens anneal-hardened. It seemed that one of the causes of anneal-hardening in this steel was also attributable to a formation of subboundaries.
(4) By measuring magnetic properties of the deformed specimens, it was estimated that Md point of the steel used was about 45°C.
(5) In microstructure of the deformed specimens, many parallel stripes were observed in some of grains. These stripes were increased as the degree of deformation was increased and as the deformation temperature was decreased. It was presumed that this structure was a mixed structure of martensite and strain-marking in the case of specimens deformed at a temperature below Md, whereas it was a strain-marking in the case of specimens deformed at a temperature above Md.