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 fr om 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 ti me during ageing for the measurement of electrical resistivity at 77 a nd 273 K. The difference from Matthiessen's rule (DMR) during ageing i s obtained from the electrical resistivity at both measuring temperatu res. The following results are obtained. (1) The electrical resistivit y for all specimens decreases during ageing. However, DMR during agein g increase for the specimens except 0.00 mass% Cu specimen. The more t he Cu content, the bigger the increment. (2) The behaviour above menti oned can be explained by the formation of Cu-C quasi-pairs within a ve ry short time during quenching and by their decomposition during agein g. (3) The quasi-pairs may be formed by trapping of diffusing carbon a toms into the second nearest octahedral interstices around substitutio nal 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 o f micro Vickers hardness of these alloys with the decarburized ones at just after quenched stage.