A heavy thick (100mm) 100kgf/mm
2 class high tensile strength steel plate (H-T100) and the submerged-arc welding (SAW) consumables have been developed. The developed HT100 steel plate has uniform mechanical properties in the through-thickness direction, and has good weldability comparable to that of 80kgf/mm
2 class high tensile strength steel plate (HT80) against hydrogen cracking and bearing rather high heat input of 60kJ/cm. The developed SAW consumables has been certified the weld metal has good resistance for cold cracking due to the ultra low hydrogen content in addition to good toughness and has good workability even in applying a narrow gap welding.
The characteristics of HT100 steel plate and its welded joints obtained are as follows:
(1) The newly developed HT100 steel plate whose chemistry consists of. 13%C-0.12%Si-0.87%Mn-2.97%Ni-Cr-Mo-V-B, has been successfully manufactured by using the low-temperature-quenching and tempering process.
(2) The pre-heat temperature for preventing weld cracking was 100°C, which was evaluated by an oblique Y-groove cracking test. The maximum hardness on HAZ was lower than 400 in Vickers hardness. These results prove that the weldability of the HT100 steel plate is same that of HT80 steel plate.
(3) By the addition of optimum amount of carbonate, fluoride and MgO into agglomerated flux hydrogen content in the weld metal can be decreased in ultra low level and oxygen content can be adjusted in the optimum range. The slag detouchability is also improved so good as to use in a narrow gap welding.
(4) The tensile strength of weld joint was 101kgf/mm
2 for the weld heat input of
47kJ/cm and 100kgf/mm
2 for 60kJ/cm, respectively. An absorbed energy of Charpy test at -12°C notched in a fusion line was 11.1kgf m for 47kJ/ cm welding and 7.1kgf·m for 60kJ/cm, respectively. The Charpy test results show that these welded joints are safety enough against brittle fracture in spite of adoption of rather high heat input welding.
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