抄録
The yield point and the tensile strength of steels worked at elevated temperatures (about 300°C) are higher than those of steels worked at room temperature or of steels annealed at various temperatures after cold working. It can be considered that strengthening of steel by warm working is attributed to the strengthening of α-iron in steel; the dislocation density of α-iron worked at elevated temperatures is higher than that of α-iron cold worked or annealed after cold working because of the multiplication of dislocations due to dynamic strain aging in warm working. 0.02% C α-iron warm worked, cold worked and annealed after cold working is studied, respectively, by means of transmission microscopy and the hardness test.
The results obtained are as follows:
(1) Both the low temperature annealing effect after cold working and the warm working contribute mostly to the strengthening of 0.02% C α-iron in the same way as for other steels, so that the strengthening mechanism of 0.02% C α-iron is considered to be the same as that of other steels.
(2) The strength of the warm-worked steel is higher than that of the steel annealed at various temperatures for various times after cold working.
(3) The dislocation density of α-iron worked at 300°C is higher than that of α-iron worked at other temperatures and annealed after cold working. The dislocation density of α-iron corresponds to the hardness of α-iron.
(4) The mechanism of strengthening α-iron by warm working is based on the increase of the dislocation density by multiplication of dislocations due to dynamic strain aging.
