Apparatus for continuous annealing of strip and method for continuous annealing of same
The present invention relates to an apparatus for continuous annealing of a strip, capable of manufacturing a high-strength and highly ductile cold-rolled steel sheet having both excellent strength and ductility, and to a method for continuous annealing of a strip. The continuous annealing apparatus, according to the present invention, is capable of continuous annealing by cooling after heating, and then reheating, unlike an existing continuous annealing apparatus which heats only once and then cools or provides an overaging treatment. As a result, the continuous annealing apparatus, according to the present invention, can preliminarily render a homogeneous texture or control the texture as desired, and then perform another reheating heat treatment to stabilize the texture or control the shape thereof to a desired state. Also, provided is a continuous annealing apparatus and a continuous annealing method using the apparatus, the continuous annealing apparatus also capable of manufacturing high-strength steel having excellent processability and strength by using a low alloy, and capable of manufacturing a zinc-plated strip having excellent plated surfaces by controlling the thickness of elements and oxides enriched on the surface of the strip.
1. An apparatus for continuous annealing of a cold-rolled steel strip comprising:
a first heating zone configured to heat a cold-rolled steel strip to a first heating temperature to form a first heated steel strip:
a first cooling or constant temperature maintaining zone configured to receive and cool the first heated steel strip to a first cooling temperature to form a first cooled steel strip, wherein the first cooling or constant temperature maintaining zone is provided with at least one cooling device selected from a cooling device using a gas, a cooling device using a gas and mist and a cooling device using a gas, mist and water, and wherein the first cooling or constant temperature maintaining zone comprises: at least one gas and steam exhaust device provided therein to generate negative pressure in the first cooling or constant temperature maintaining zone;
a second heating and soaking zone configured to receive and heat the first cooled steel strip to a second heating temperature to form a second heated steel strip arid soak the second heated steel strip at the second heating temperature to form a second soaked steel strip, wherein the second heating temperature is higher than the first heating temperature;
a second cooling zone configured to receive and cool the second soaked steel strip to a second cooling temperature to form a second cooled steel strip;
an overaging or constant temperature maintaining zone configured to receive and overage the second cooled steel strip to form an overaged steel strip; and
a final cooling zone configured to receive and cool the overaged steel strip to a room temperature;
wherein the first cooling or constant temperature maintaining zone is provided with a pair of tension control rolls, one of which is installed at entrance of the first cooling or constant temperature maintaining zone and the other one of which is installed at exit thereof;
wherein the first cooling or constant temperature maintaining zone is further provided with a pair of hollow cooling rolls installed under the at least one cooling device, a coolant being circulated through the hollow cooling rolls and a steel strip cooled by the at least one cooling device passing through a gap between the pair of hollow cooling rolls.
2. The apparatus of claim 1 , wherein the first cooling or constant tempera lure maintaining zone is further provided with a movable water cooling bath installed under the pair of hollow cooling rolls, a steel strip having passed the gap passing through the movable water cooling bath.