Influence of Mechanical Processing and Heat Treatment on Microstructure Evolution in Nickel Free High Nitrogen Austenitic Stainless Steels.

Abstract

A series of nickel free high nitrogen austenitic stainless steels were processed by various mechanical processing and heat treatment conditions to study the evolution of microstructure at every stage of processing. About eleven steels varying in composition, especially in terms of carbon contents, were processed through forging, rolling, solution annealing, cold rolling and warm rolling etc. The microstructure at every stage of processing was studied. The hot rolled condition, hot rolled and cold rolled condition gave deformation induced fragmented grain structure. The high carbon steels in the hot rolled conditions showed banding and grain boundary carbo-nitride precipitation. There were also intragranular carbide prcipitation in some of the high carbon steels.The solution treated microstructure in all steels showed extensive annealing twins and the lattice parameter increased with carbon and nitrogen contents. Cold rolling followed by solution treatment lead to development of slip lines in the fully austenitic matrix due to strain hardening of the matrix. The 600°C warm rolled condition showed grain boundary carbide precipitation.

Influence of Thermal and Mechanical Processing on Room Temperature Mechanical Properties of Nickel Free High Nitrogen Austenitic Stainless Steels.

“…The microstructures of the low carbon steels 17) , corresponded close to those reported by Efimenko et al 18) and Andreev et al…”

“…The ductility values of higher carbon steels M4 and M8 are significantly lowered, due to the formation of lamellar precipitates that formed during cooling the hot rolled steels. 17) The precipitation of lamellar nitrides in high carbon steels M4 and M8 was confirmed by mi- croscopy and XRD studies. 17) Though, the steel 3/1 had significant C content, along with high nitrogen, there was no precipitation of any kind detected in the XRD analysis.…”

“…17) The precipitation of lamellar nitrides in high carbon steels M4 and M8 was confirmed by mi- croscopy and XRD studies. 17) Though, the steel 3/1 had significant C content, along with high nitrogen, there was no precipitation of any kind detected in the XRD analysis. This contradicts the data of Ikegami et al, 16) according to whom grain boundary and lamellar carbides should precipitate.…”

“…The microstructures corresponding to the various processing conditions presented earlier 17) can be referred to the properties presented here.…”

“…The steels studied by Ikegami had 2% Mo, 0.2% V which are strong carbide formers and 2 to 4% Ni. The presence of Ni in those steels could enhance formation of lamellar precipitates, due to positive interaction between Ni and N. The high carbon steel 2/1, evaluated in the as-hot forged condition, showed lamellar nitride precipitates in isolated regions 17) and the mechanical properties exhibited lower ductility than in the solution annealed condition.…”