焊条电弧焊焊补铸铁件焊区硬度控制

Controlling of hardness of cast iron joint by manual arc welding

采用微合金化灰铸铁同质电焊条和直流电焊机,研究了焊接电流和预热温度对焊补区组织和硬度的影响规律.结果表明,焊接电流和预热温度对焊补区组织和硬度均有显著的影响.在焊接电流一定的情况下,预热温度越高,接头温度分布越均匀,冷速越缓慢,越有利于形成灰口组织;在预热温度一定的情况下,随着焊接电流的增大,焊接热输入增大,焊区冷却速率减小,容易获得无白口的灰口组织.采用小电流打底、大电流连续焊补工艺,可有效地控制焊补区组织和硬度,获得机械加工性能优良的同质焊缝.

Repairing of casting defect for iron casting has great economic significance.The relationship between welding parameters and joint microstructure along with hardness is investigated by micro-alloyed gray cast iron homogenous electrodes and DC welding machine.The results show that the welding parameters have significant effects on joint microstructure and hardness.Keeping the welding current constant,the higher the preheating temperature is,the more uniform the temperature distribution is and slower the cooling rate of joint is,the much easier gray cast iron microstructure forms.Keeping the preheat temperature constant,with the increase of welding current,welding heat input increases and the cooling rate of joint decreases,which is easy to form gray cast iron microstructure with non-chilled phase.The welding parameters should be controlled in the upper right zone of welding current-preheat temperature-microstructure type diagram.By strictly controlling of welding current and preheat temperature,and using small current to make a rendering combined with high-current continuous welding process,the microstructure and hardness of joint can be effectively controlled,obtaining the homogenous weld with excellent machinability.