Abstract
The effects of carbon, niobium and manganese on the precipitation behavior of Nb in deformed austenite were investigated in a series of micro-alloyed steels. The steels were hot rolled in a five pass schedule on laboratory scale mills to define the effect of holding time at 950°C prior to forth pass on the rolling load, tensile properties and quantitatively analyzed soluble Nb( Sol. Nb).
The increase in amount of C and Nb accelerates the precipitation of Nb and tensile strength (TS) decreases with the decrease of Sol. Nb. These results indicates that in the specified rolling conditions TS of the steel with lower C or Nb content is larger than that with higher C or Nb content.
It is found that soluble Nb increases the rolling load. Therefore, the precipitation behavior of Nb can be estimated by the change in the rolling load.
The addition of Mn retards the precipitation of Nb and therefore enhances the strength of the Nb treated steel.
The observed decrease of Sol. Nb with the holding time is larger than that estimated by the decrease of rolling load. This result suggests that the growth of Nb precipitates takes place mainly during cooling subsequent to hot rolling.
