The Formation and Decomposition of Cu-C Pairs in Quench-aged Fe-C-Cu Alloys.

The formation and decomposition of Cu–C pairs in alpha-irons have been discussed in quench-aged Fe–C–Cu alloys which are five kinds of cold-drawn low carbon steel wires of 0.65 mm diameter containing copper from 0.00 to 0.55 mass%. These specimens were heated at 973 K for 600 s in argon gas, quenched into 273 K, and then isothermal-aged in an oil bath of 423 K. These were taken out from the oil bath at a suitable time during ageing for the measurement of electrical resistivity at 77 and 273 K. The difference from Matthiessen's rule (DMR) during ageing is obtained from the electrical resistivity at both measuring temperatures. The following results are obtained. (1) The electrical resistivity for all specimens decreases during ageing. However, DMR during ageing increase for the specimens except 0.00 mass% Cu specimen. The more the Cu content, the bigger the increment. (2) The behaviour above mentioned can be explained by the formation of Cu–C quasi-pairs within a very short time during quenching and by their decomposition during ageing. (3) The quasi-pairs may be formed by trapping of diffusing carbon atoms into the second nearest octahedral interstices around substitutional Cu atoms by an elastic interaction not by a chemical one. (4) The existence of Cu–C quasi-pairs are also suggested from the comparison of micro Vickers hardness of these alloys with the decarburized ones at just after quenched stage.