日本金属学会誌

J. Japan Inst. Metals, Vol. 34, No. 11 (1970),
pp. 1168-1172

The Effect of Cold Work on Temper Brittleness in Steel

Tomoo Suzuki1

1Research Laboratory of Precision Machinery and Electronics, Tokyo Institute of Technology, Tokyo

Abstract:

The effect of cold work and subsequent heat-treatment on temper brittleness was investigated using a commercial steel of SCr 1. The results obtained were as follows:
(1) After cold reduction the maximum absorbed energy of fracture was lowered. The severer cold reduction, the lower becomes the transition temperature. The transition temperature of the embrittled material was lowered more markedly than that of the unembritted one by cold reduction.
(2) The maximum energy of fracture and the transition temperature were improved by retempering after cold work. Without greatly affecting the prior conditions the impact transition curve was dependent on the degree of reduction and the final heat-treatment, i.e. slow cooling or rapid cooling. The transition temperature of the embrittled material followed by severe cold reduction approached that of the unembrittled material without cold reduction.
(3) Temper-embrittlement could be interpreted in terms of grain boundary segregation of phosphorus, i.e. the formation of an atomosphere or a cluster, which was easily broken up by the cold deformation. It was concluded that the embrittled treatment after cold work was to cause a redistribution of solute atom to the site of many imperfections in the grain created by plastic deformation. Then the grain boundary segregation making the steel more brittle was decreased.
(4) Because the transition temperature of the unembrittled material was lowered by cold reduction and subsequent heat treatment, it seemed likely that the segregation at grain boundary occurred slightly during holding at the temperature 650°C or cooling into water. This showed that the water-cooled material was not the best condition for impact toughness.


(Received 1970/8/27)

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