Studies on nickel-manganese managing steels

Abstract

The kinetics of precipitations and mechanism of hardening have been studied in four Ni-Mn-Co-Mo maraging steels containing 7-11% Ni, 4-14% Mn, 4% Mo and 6-7% Co at a temperature range of 450°C-550°C. The age-hardening characteristics were studied by hardness measurements. X-ray diffraction and optical and electro-microscopy. X-ray diffraction and other studies showed that steels containing 5% Mn with 18-21% Ni were either completely or partially austenitic. Alloy with 11% Ni-4.5% Mn-4.5% Mo with 7% Co was completely martensitic and showed better maraging properties. Precipitations of h-Fe3Mo3C, Fe2Mo and Ni3Mo have been detected during ageing. Maraging results from ordering and precipitation reaction in the above mentioned temperature range of Ni3Mo type phase along with Fe2Mo. This paper deals with the structural transformations and precipitation reactions during ageing in 18 Ni-8 Co-4 Mo type maraging steels where nickel was partially replaced by manganese in varying amounts. Results of X-ray diffraction and metallographic studies along with some mechanical properties have been reported in the present paper. (Dr. J.K. Mukherjee, Scientist and Dr. T. Banerjee, Scientist-in-charge, National Metallurgical Laboratory, Jamshedpur)