Field welding repair method especially for larger and penetrating defects in steel casting with heavy wall thickness

The invention relates to a field welding repair method especially for larger and penetrating defects in a steel casting with heavy wall thickness. The method comprises a pre-welding preparation process, a welding repair process and a post-welding quality inspection process, wherein the welding repair process comprises the steps of (1) preheating; (2) carrying out 1 to 2 layers of backing weld for all positions of a groove by adopting TIG weld, and filling the whole bottom of the groove with solid wire materials; (3) warming up to 220 to 330 DEG C, carrying out constant thermal insulation for 3 to 8 hours, adopting manual arc welding to implement the filler welding for the groove, hammering the welded bead immediately with an air hammer, and ensuring the dense and uniform traces of the hammer; (4) carrying out dehydrogenation heat treatment; (5) carrying out post-welding treatment: carrying out stress annealing at the temperature of 500 to 550 DEG C, then carrying out high tempering at the temperature of 700 to 750 DEG C, and finally, cooling at the speed of 65 to 150 DEG C/h to the room temperature. After welding repair, a welding seam is tested to be good in quality, and have low possibility of cracking again.