Effect of Heat Input and Annealing Holding Time on Grain Size of Overheating Area in 409L Ferritic Stainless Steel TIG Welded Joint

409L ferritic stainless steel plates were welded by tungsten inert gas arc (TIG) welding under different heat inputs (1 145.5-5 248.0 J·mm^-1), and then the joints were annealed at 830℃ for different holding times (0-13 min). The effect of heat input and annealing holding time on microstructure and grain size of the overheating area of joints was studied by homogeneous design method. The results show that the microstructures of the overheating area of welded joints before and after annealing were both coarse ferrite under different heat inputs, and with the increase of heat input, network ferrite and wisterite were found in the microstructure. The grain size of the overheating area of joints after annealing was almost the same as that before annealing. When the heat input increased from 1 145.5 J·mm^-1 to 5 248.0 J·mm^-1, the grain size of the overheating area increased from 58.64 μm to 160.97 μm. The annealing holding time had little effect on the grain size. The heart input had a nonlinear effect on the grain size of overheating area, and the effect was much larger than that of annealing holding time.