HEAT TREATMENT METHOD FOR THICK STEEL PLATE IN DIRECT FIRED ROLLER-HEARTH TYPE CONTINUOUS HEAT TREATMENT FURNACE AND RADIANT-TUBE ROLLER-HEARTH TYPE CONTINUOUS HEAT TREATMENT FURNACE

摘要

PROBLEM TO BE SOLVED: To provide a heat treatment method for thick steel plate which can obtain material characteristics less in variation and enhances productivity.;SOLUTION: In the heat treatment method using a direct fired roller-hearth type continuous heat treatment furnace or a radiant-tube roller-hearth type continuous heat treatment furnace, the heat treatment is applied to a plane steel thick plate in the heat treatment temperature range of 300-450C. In the heat treatment temperature range, the aimed heat treatment temperature range of Ts_min to Ts_max (C) is set based on the temperature fluctuation range permissible in the material quality. As for this aimed heat treatment temperature range, the setting temperature range in the continuous heat treatment furnace is regurated so that the lower-limit temperature TG_min (C) is defined as the upper-limit temperature +10C or higher in the aimed heat treatment temperature range, and the upper-limit temperature TG_max (C) is defined as Ts_min to Ts_max (C) in the aimed heat treatment temperature range, and is lower than the temperature preset by specific formula according to the plate thickness (t)mm of the thick steel plate, and thus, the heat treatment is perfoermed by setting the furnace temperature TG (C) in the continuous heat treatment furnace within this setting temperature range.;COPYRIGHT: (C)2011,JPO&INPIT