| Budget Amount *help |
¥16,120,000 (Direct Cost: ¥12,400,000、Indirect Cost: ¥3,720,000)
Fiscal Year 2017: ¥5,200,000 (Direct Cost: ¥4,000,000、Indirect Cost: ¥1,200,000)
Fiscal Year 2016: ¥6,500,000 (Direct Cost: ¥5,000,000、Indirect Cost: ¥1,500,000)
Fiscal Year 2015: ¥4,420,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥1,020,000)
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| Outline of Final Research Achievements |
1.6-2.0 GPa-class ultra-high strength steel bars were fabricated through multi-pass warm caliber rolling for (0.2-0.6)%C-2%Si-1%Cr-1%Mo steels (mass%), and were warm formed into JIS M12 hexagon head bolts, and then their mechanical properties were investigated. The developed bolts consist of ultrafine grained structures and were demonstrated to be more ductile and tougher,compared to the conventionally quenched and tempered bolts at ultra-high tensile strength of 1.6-2.0 GPa. There was a linear relationship between shear strength and tensile strength. Friction tensile tests for joints using the developed bolts demonstrated that slip coefficient for the ultra-high-strength bolts were greater or equal to the ordinary high-strength bolts. No significant stress relaxation was observed in the bolted joints. Furthermore, the bolted joints using the ultra-high strength bolts were also observed to have high fracture resistance.
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