With the demand for the increasingly large capacity of machines and equipment, structural dimensions are growing large, and design stress is becoming higher eventually. This naturally necessitates the use of high-strength steel possessing high tensile strength and high toughness.
Although mild steel is generally adopted for welded structures, it needs an exceedingly large gauge to give sufficient strength and involves difficulties in building up welded structures. In this report an examination was conducted on the effects of intensity of restraint, restraint stress, and the groove shape influencing delayed cracks during manual are welding on 80 kg/mm2 high-strength steel. A summary of the results of this research is as follows.
(1) It was clarified in single bevel groove and H-type restraint cracking tests that the values of critical intensity of restraint KCr for preventing weld cracks at various preheat temperatures were as follows:
KCr≅1700 kg/mm.mm for 50°C preheating
KCr≅1900 kg/mm.mm for 100°C preheating
KCr≅2500 kg/mm.mm for 150°C preheating
Regarding the parcentage of weld cracks in welds, the single bevel groove was nigher than the Y-slit groove in the above value, and materials of high carbon equivalent were also high in the abovo value.
(2) Root crack-preventive preheat temperatures for the Y-slit groove (PHY) and single bevel groove (PHK) may be determined respectively by the following equations:
PHy≅(1.33Pw-0.38)×103(°C)
PHK≅(2.03Pw-0.55)×103(°C)
PW=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B+H/60+/40×103
