Hello all an thanks in advance for help on this one.Heres the deal,stair stringer made of 1/2 plate an 3/4 plate.Each stringer is about 11 feet.The 2 thickness are joined together to make a channel.The leg of the home made channel is 3/4.The face is 1/2.Width of said channel is about 2 feet an the legs are 4 inches.The legs are double beveled at about 30 degrees on one side .That said side connects to the 1/2 plate to make up the channel.During welding 2 stringers are back to back an clamped off to help from bowing.Welds are jumped around until fully welded.Problem-when releasing clamps after cooling period legs look out of square with face.I feel its more of the 1/2 face plate bowing an making the leg look out.Question-How would one go about heat srinking or applying heat to straight them back to pre weld form.There not out by much but enough to notice.Also they are made of mild steel.All opinions welcome.Thanks.