Abstract
The equilibrium solubilities of C and N decrease sharply between 721°C and room temperature, although equilibrium is rarely approached during the cooling cycles employed industrially. The resulting supersaturated ferrite is thus susceptible to the precipitation of C and N during storage and subsequent processing. Such ‘quench aging’ effects are evaluated for three typical post-hot rolling cooling rates employed in the processing of low C steel wire rod. The investigation was carried out on steels containing 32 ppm N (low N) and 102 ppm N (high N); these were heated to 900°C, cooled at 8,3, or 1·5 K S−l, and then aged at room or freezer temperatures for periods of between 1 h and 532 days. The specimens subjected to the fastest cooling rate exhibited considerable quench aging effects, as did industrially processed specimens that had been cooled in the mill and aged for several weeks at room temperature. It is shown that the high N steel is more susceptible to quench aging than the low N material. The implications regarding the occurrence of breaks during wire drawing are discussed.
MST/3175
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