Method for producing steel strip for tin plate and tin-free steel plate in various temper grades

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the accompanying drawings.
First, the conventional method for the adjustment of temper grade in steel strip for tin plate will be described with reference to FIG.
1.
Conventionally, steel strip to be used as the material for production of tin plate has been produced, as illustrated in FIG.
1, by first adjusting the composition of the starting material steels and the hot rolling conditions to selectively obtain soft and hard cold rolled steel strip and subjecting the soft cold rolled steel strip to box annealing to obtain temper grades T-1 through T-3 and the hard cold rolled steel strip to continuous annealing to obtain temper grades T-4 through T-6, temper grades T-1 through T-6 being as defined in Japanese Industrial Standard G 3303.
In FIG.
1, A denotes an electric cleaning unit, B a box annealing furnace, C a coil cooling unit, D a continuous annealing line, E a temper rolling mill, F a coil preparation line and G an electric tin-plate line or tin-free steel line.
The fact that adjustment of the composition of the starting material is carried out in the steelmaking stage results in an increase in the total number of lots involved in the steelmaking operation, and poses a serious obstacle to the improvement of productivity through use of large converters and continuous casting.
Moreover, it is exceedingly difficult to adjust the composition of the starting material for the steel strip to within their respectively prescribed ranges and, further, the addition of alloying elements increases the production cost of the steel strip.
In the method according to the present invention, the drawbacks of the conventional method for the manufacture of steel strip for use in the production of surface-treated plate, such as tin plate, are eliminated, the number of types of such steel strip can be reduced to one type and high-quality steel strip for use in the production of surface-treated plate can be produced inexpensively, efficiently and continuously by subjecting this single type of cold rolled steel strip for all temper grades to continuous annealing and then obtaining the various temper grades by controlling strip hardness through the adjustment of the reduction rate during temper rolling, at the same time, incorporating into the same line the steps for inspection and fine adjustment