热变形工艺对SAE8620H齿轮钢带状组织的影响

Effect of hot deformation process on banded structure of SAE8620H gear steel

对比研究了截面规格为300 mm×340 mm的SAE8620H齿轮钢连铸坯不同部位、变形量、变形方向、变形终了温度、变形后冷却方式等参数对其带状组织的影响。结果表明,连铸坯心部热变形试棒带状明显,带较宽;热变形后冷速对带状组织影响最为关键,适当快冷可抑制碳元素的偏析,掩盖合金元素的带状偏析而得到较轻的带状组织;提高热变形终了温度,铁素体-珠光体晶粒尺寸增大,带状组织有增强的趋势;变形量<27%时,变形组织不形成交替的元素偏析带,即使完全退火缓慢冷却也不形成带状组织;带状组织形成与铸坯的拉坯方向无关,无论沿拉坯方向变形还是垂直拉坯方向变形,带状组织均沿变形方向形成。

Effects of the hot deformation,deformation direction,final deformation temperature,cooling rate after deformation on banded structure of SAE8620H gear steel continuous casting( CC) billet with size of 300 mm × 340 mm were comparatively studied. The results show that the sampling position of the CC billet have a great effect on banded structure,the banded structure of the test sample from the billet core displays more serious,at the same time the width of band is more broad. The cooling rate after hot deformation plays a pivotal role on banded structure,proper quick cooling can inhibit the segregation of carbon,as well as banding structure. When increasing the final deformation temperature,the grain size of ferrite-pearlite increases and the banded structure has a increasing tendency. When the deformation is less than 27%,deformation microstructure does not form alternating elements segregation band,also not form banded structure even if slow cooling during full annealing. The formation of banding structure has nothing to do with casting direction of billet,no matter along or vertical the casting direction,banding structure are formed along the deformation direction.