Analysis and improvement of grain boundary oxidation during annealing process of ER69-3 wire rod
ER69-3 is representative brand of 70 kg grade welding wire steel for construction machinery.After hot rolled wire rod is annealed at 720 ℃ for 3.5 h,welding wire surface processed by mechanical descaling,drawing,copper plating and other processes appears blackening.There are many crack defects on blackened welding wire surface,and correspond-ing annealed wire rod has obvious grain boundary oxidation.Through single variable test one by one,it is confirmed that grain boundary oxidation of annealed wire rod is mainly due to high setting of annealing temperature.At 720 ℃,oxygen in oxide scale diffuses from grain boundary to matrix,resulting in grain boundary oxidation.By reducing annealing tempera-ture to 670 ℃ or removing oxide scale by pickling and then annealing at 720 ℃,martensite and bainite structures can be e-liminated after annealing,and grain boundary oxidation of annealed wire rod is almost avoided,which solves problem of blackening on welding wire surface during annealing process of wire rod.
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