抄録
High strength steel can be produced by the straightening process in the warm-working temperature range. In this investigation, in addition to mechanical properties of straightening steel, the deformation mechanism of high carbon steel in the warm-working temperature range is discussed.
The results are as follows:
(1) As for as-rolled steel, 0.2% proof stress and tensile strength of warm-worked steel are 50% and 10% higher than those of cold-worked steel.
(2) As for 60% cold-drawn steel, the strength of cold-worked steel considerably decreases, while the strength of warm-worked steel increased. The 0.2% proof stress is 150∼170 kg/mm2 and the tensile strength is 170∼190 kg/mm2. The strength difference by both treatments is about 40∼50 kg/mm2 in 0.2% proof stress and 15∼20 kg/mm2 in tensile strength. The effect of low temperature annealing is recognized, but less than the warm-working effect. Moreover, the relaxation value is especially excellent and elongation is enough.
(3) The activation energy in the warm-working temperature range is about 20 kcal/mol, which is obtained from the strain rate variation in the compressional test. This value is equal to the activation energy of carbon and nitrogen diffusion in ferrite, therefore, it is reasonable to consider that the flow stress increase of high carbon steel depends on the diffusion of C and N. With this activation energy, the authors calculated the moderate warm-working temperature for straightening, and obtained good agreement with the experimental temperature range.
(4) It was shown that even in the as-rolled specimen 2/3 of the strength increase is due to the increase of work-hardening and 1/3 due to the decrease of the Bauschinger effect.
Therefore, for the cold drawn wire, the variation in strength during straightening mainly results in the softening due to the Bauschinger effect.
