EFFECT OF CARBON ON THE COLD-WORKED STATE AND ANNEALING BEHAVIOR OF 218WT-PERCENT-CR-8WT-PERCENT-NI AUSTENITIC STAINLESS-STEELS

The influence of carbon on the work hardening, formation and reversion of deformation induced martensite and on the recrystallization of two austenitic stainless steels 18%Cr-8%Ni type were studied with the hel p of different microstructural analysis techniques. Two steels were se lected: the first an AISI 304L with low carbon (%C = 0.021) content an d the second an AISI 304 with higher carbon (%C = 0.065) content. Both steels were heat treated to obtain two different initial conditions: one with the carbon completely in solid solution (after a solution ann ealing treatment at 1100 degrees C) and the other with practically all the carbon in the precipitated form, as (Cr, Fe)(23)C-6 (after a prec ipitation treatment at 750 degrees C). The material having higher carb on content, both in solid solution and precipitated, presented in both cases higher strain hardening, smaller tendency to form strain induce d martensite and higher resistance to recrystallization. Carbon in sol id solution, as compared to the precipitated condition, led to a mater ial with a higher tendency to strain hardening, less susceptibility to martensite formation and more resistance to recrystallization. Nuclea tion of recrystallization preferably occurred in the vicinity of grain boundaries. Based on the results of the kinetics of recrystallization and intergranular corrosion tests it was concluded that the usually r ecommended annealing temperatures (1000 to 1120 degrees C) are sometim es unnecessarily high.