ML08Al线材混晶组织原因分析与改进措施

针对柳钢高线生产的φ6.5 mm ML08Al低碳冷镦钢盘条近表面出现混晶组织的问题，分析了加热工艺、变形工艺及吐丝温度对产生混晶组织的影响，并对相应的温度制度进行了优化。一加热段迅速将钢坯加热至880～920 ℃，二加热段控制在1 080～1 120℃，均热段控制在1 050～1 090 ℃，各段温度控制精度±12 ℃，加热时间不小于95 min，有利于奥氏体晶粒均匀化，大幅度降低钢坯表面与芯部、头部与尾部温差；结合水箱冷却能力及轧机设备能力，预精轧结束后对轧件快速冷却，将入精轧温度由970 ℃降至860 ℃，将轧件冷却至奥氏体未再结晶区轧制，同时利用精轧机组机架间水冷系统，控制终轧温度为990～1 020 ℃，以避免轧件变形过程温度过高导致奥氏体晶粒异常长大；吐丝温度由原先的950 ℃降至830 ℃。采用优化工艺后，获得了晶粒尺寸均匀的F+P组织，改善了ML08Al盘条冷镦性能。

Causes analysis of mixed-grain microstructure of ML08Al wire and its countermeasures

Aiming at the problem of mixed-grain microstructure near the surface ofφ 6.5 mm ML08Al low carbon steel wire coil for cold heading produced by High Speed Wire Mill of Liusteel,the influence of heating process,deformation process and laying temperature on the mixed-grain microstructure were analyzed,and the corresponding temperature schemes were optimized.The billet was heated quickly to 880-920 ℃ in the first heating section,the temperature of the second heating section was controlled to 1 080-1 120 ℃,the temperature of the soaking section was controlled to 1 050-1 090 ℃.The temperature control accuracy of each section reached ±12 ℃,the heating time was assured not less than 95 minutes,which is beneficial to the homogenization of austenite grains,and greatly reduces the temperature difference between the surface and the core,the head and the tail of billet.Combined with the cooling capacity of the water tank and the capacity of the rolling mill,the piece was rapidly cooled at pre-finishing export,the finishing rolling temperature was reduced form 970 ℃ to 860 ℃,and the piece was rolled in austenite non-recrystallization area.At the same time,the water cooling system between the stands of the finishing rolling mill was used to control the finishing rolling temperature at 990-1 020 ℃ to avoid the abnormal growth of austenite grains caused by too high temperature during rolling deformation.The laying temperature was reduced from 950 ℃ to 830 ℃.After the optimization process was adopted,the F+P structure with uniform grain size was obtained,and the cold heading performance of ML08Al wire rod was improved.