Abstract: In accordance with the invention, an insulating box (32) is applied to the depending portion (28) of the center plate (24) of a railway freight car. This box is provided with external insulation (27) and a cooling medium such as air or water is passed through a conduit (56) into the box to maintain the temperature of the hardened portion of the bowl sufficiently low that no transformation or softening takes place during stress relief. After stress relieving the box is removed and the cooling medium turned off. The hardness and strength of the center plate has not decreased sufficiently to require rehardening, and it is not necessary to rotate the car into another position to attach the center plate, or to reharden the center plate.