Fracture toughness analysis and process improvement of YG1600 ultra-high strength stainless steel
For the φ300 mm YG1600 ultra-high strength stainless steel produced by double vacuum smelting and forging process,it was found that the fracture toughness index was on the low side during the mechanical property test.The micro-structure of sample with low fracture toughness index was analyzed by metallographic microscope and scanning electron mi-croscope.The results showed that there were microscopic cracks in the plane along the cracking direction of fracture toughness sample.The cracks were along the boundary of the martensite lath.The length of the martensite lath was not uniformly distributed between 20-80 μm,which was the reason to cause low fracture toughness of the bar.After a se-ries of process analysis and process simulation,the original production process was adjusted.The vacuum arc remelt-ing speed was reduced from 4.85-5.2 kg/min to 3.8-4.15 kg/min;the last fire heating temperature of forging was re-duced from 1 100-1 130 ℃ to 1 060-1 100 ℃;the last fire forging ratio was increased from 2.25-2.77 to 3.36-4.Through the adjustments above,the fracture toughness of YG1600 ultra-high strength steel increased by 30-40 MPa·m1/2.
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