PURPOSE: To effectively execute continuous heating under non-oxidizing dy specifying air ratio of the reducing gas and heating speed of a steel strip and also executing heating at low temp. range with thin exhaust gas.
CONSTITUTION: At the time of executing heat-treatment to the steel strip W by continuously passing through a preheating zone 3 to the arrow mark direction, fuel is burnt at ≤0.8 the air ratio in a reducing gas generating furnace 8 to generate the reducing gas and to the steel strip W at downstream side to the carrying direction, under condition, in the case of M ≤0.5, u>0 and in the case of 0.5>M≥0.8, u≥55×M+12 (wherein, M: air ratio, (u): heating speed °C/sec), the reducing gas is injected from the plural nozzles 10 in a second heating zone 6 to heat the steel strip W at 300-450°C. Successively, the exhaust gas containing the fuel being not yet burnt in the secondary combustion zone 5 is once extracted to ejector 16, 17 sides and burnt at ≤ about 1.0 the air ratio, and this combustion gas is injected from plural nozzles 22 in a first heating zone 5 to heat the steel strip W at <300°C. By this method, the continuous heating is efficiently executed under non-oxidizing from the room temp. to 450°C and the high quality can be secured.
SUZUKI TOMIO
TOMIMATSU FUMIO
FUKUDA TATSUE
TATEMICHI HIDEO
ODAWARA RYUICHI
