Development of SCM440 hot rolled large coil for cold heading standard parts
The production technology,process control and quality of SCM440 hot rolled coil for high grade cold heading standard parts were introduced.In the steelmaking process,the converter smelting,LF+RH refining,and continuous cast-ing processes should be strictly controlled to ensure the chemical composition and purity of steel.Water cooling was adopted in the rolling process to maintain the coiling temperature at 840-870 ℃.Meanwhile,the cooling speed of the rolled coil was controlled below 2℃/s through the adjustments in insulation cover opening/closing and fan air volume.According to the testing,the hot rolled structure of φ26 mm SCM440 hot rolled large coil was bainite+perlite+ferrite with a grain fine-ness number of 9-10.Additionally,the ratio of total decarburization layer was ≤1％,and the pass rate for 1/2 cold forging was 100％.The results indicated that SCM440 large coil could fully meet the processing requirements of grade 12.9 cold heading steel.
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