抄録
Precipitation characteristics of Nb(C, N) in the austenite phase of low carbon-high manganese steels have been investigated kinetically.
It has been demonstrated that the precipitation behavior in austenite can be followed by a two-step aging treatment: Steels which had been solution-treated at 1250°C were precipitation-treated at temperature between 840 and 1020°C for various periods and then quenched to 540°C in ferrite region and subsequently aged for 900 min.
Age-hardenability of ferrite is reduced by the first step precipitation-treatment in austenite because of the decrease of the driving force for precipitation in ferrite. It has been recognized that the precipitation of Nb(C, N) in austenite ca nbe estimated by such reduced age-hardenability of ferrite.
The rate of precipitation of Nb(C, N) in austenite increases with Nb content and is largest at about 980°C because the time to reach a certain fraction of Nb(C, N) is shortest at this temperature when plotted against the precipitation temperature.
Precipitation of Nb(C, N) is rate-controlled by the diffusion of Nb in austenite but not by that of C or N.
The rate of precipitation Nb(C, N) is accelerated markedly by hot working in austenite and the acceleration is larger at lower hot working temperature. But the precipitation of Nb(C, N) does not take place during hot working at any temperature investigated.
