The crack defects can be greatly reduced and eliminated by improving the main key process methods in the manufacture of c12a alloy steel valve castings.
(1) The prerequisite for the charge is to use pure iron, plus the smelted return material and pure element metal block, which is the basis for reducing the content of oxidized inclusions, s and P.
(2) The smelting method adopts medium frequency induction furnace roughing + AOD refining, which is an effective method to control chemical composition, spheroidizing inclusions, improve grain size and reduce the contents of [n], [O] and [H].
(3) The heat treatment method of valve castings adopts (1080 ± 14) ℃ normalizing + (1050 ± 14) ℃ normalizing + (760 ± 10) ℃ tempering. It is discharged from the furnace below 500 ℃ and air cooled to room temperature, which can ensure the requirements of metallographic structure and mechanical properties and prevent cold cracks of products.
(4) FCAW flux cored wire arc welding is used for defect repair welding of valve castings, and f 1.2mm deposited metal: e91t1-b9m is used for flux cored wire, which eliminates the defects such as microcracks, pores and slag inclusion in the repair welding area. Annealing at (730 ± 10) ℃ immediately after welding, holding time ≥ 4h, stress removal and dehydrogenation treatment.