METHOD FOR HEAT TREATING LONGER-LENGTH PRODUCT, METHOD FOR MANUFACTURING LONGER-LENGTH PRODUCT, AND HEAT TREATMENT FURNACE USED FOR SAID METHOD

Provided is a method for heat treating longer-length products, in which a cylindrical batch-type heat treatment furnace with opposite ends thereof being enclosed and with the inner space thereof being divided into a plurality of heating zones along a longitudinal direction is used, and a longer-length product to be heat treated is heat treated, wherein the heat treatment furnace is configured so that, endmost heating zones each is divided into a plurality of divisions each having a length shorter than that of each of heating zones other than the endmost heating zones; and a heat source is disposed in each of divisions and other heating zones, and the heat treating method includes a series of steps of: (Step 1) in advance, determining the heating output pattern of each heat source in each division of endmost heating zones based on the measurement result of actual temperature in the end portion of the product to be heat treated at the time of heating and (Step 2) controlling the heating output of individual heat source, at the time of heat treatment for the product to be heat treated, based on the heating output pattern of each heat source determined in step 1 and further the measurement result of in-furnace temperatures of each division of endmost heating zones and each of other heating zones. By using this heat treating method, even in the heat treatment furnace having no heat source on both end walls thereof, the product to be heat treated can be heated uniformly throughout the overall length of the product to be heat treated with high accuracy.