Yûnoshin Imai and Hikotarô Imai
This paper describes the results of mechanical tests on several series of low-carbon (0.05 ∼ 0.08%), low-alloy (0.3 ∼ 0.5% Mo) steels containing boron (0.003%), tested in a normalized condition. The max. stresses and yield stresses are improved markedly by addition of boron, that is the former is raised from 40 kg/mm2 to 60 kg/mm2, and the latter, from 20 kg/mm2 to 40 ∼ 50 kg/mm2. In spite of such a remarkable increase of its strength, the toughness and ductility are not affected so much, only the elongation is decreased from 40% to the degree of 25 ∼ 27% and indicated local contractions distinctly. The desirable effects, mentioned above, are obtained only when the steels are deoxidized and denitrogenized with the required amount of Ti (0.05 ∼ 0.2%) or Al (0.1 ∼ 0.2%), prior to the addition of brone. The addition of Mn or Cr, to the degree of 1.0%, to these steels is very effective, and the max. stress and the yield stress are increased remarkably. Also, an increase of carbon-cotents up to the degree of 0.15% is very effective, similar to Mn or Cr-addition, but an increase of carbon-content results in a sharp decrease of toughness and ductility. Therefore, it is desirable that the carbon-content of these types of steels is limited under 0.2%.
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