Abstract: Generation of cavitation jet in air on a surface of a work roll provides a higher cleaning force than squirting of only high pressure fluid, so that sticking substances on the surface of the work roll are reliably removable. When a distance between a cleaning nozzle and the surface of the work roll and pressure of the high pressure fluid are controlled within a predetermined range, sticking substances are efficiently removable while roughness of the surface of the work roll is maintained.

Abstract: Generation of cavitation jet in air on a surface of a work roll provides a higher cleaning force than squirting of only high pressure fluid, so that sticking substances on the surface of the work roll are reliably removable. When a distance between a cleaning nozzle and the surface of the work roll and pressure of the high pressure fluid are controlled within a predetermined range, sticking substances are efficiently removable while roughness of the surface of the work roll is maintained.

Abstract: The oxide film thickness of the steel material surface (dH2O+do2) is made to become 15 nm or less where post-treatment after water-cooling is not needed by suitably setting the conditions of the water-cooling start temperature (Ti), water-cooling end temperature (To), steel material thickness (d), concentration of solute oxygen in the cooling water (Do), and cooling rate (CR) in the equation of dH2O+do2=7.98×10?4(Ti?To)dDo+{5.50×10?3(Ti2?To2)?6.51(Ti?To)}/CR.

Abstract: The oxide film thickness of the steel material surface (dH2O+do2) is made to become 15 nm or less where post-treatment after water-cooling is not needed by suitably setting the conditions of the water-cooling start temperature (Ti), water-cooling end temperature (To), steel material thickness (d), concentration of solute oxygen in the cooling water (Do), and cooling rate (CR) in the equation of dH2O+do2=7.98×10?4(Ti?To)dDo+{5.50×10?3(Ti2?To2)?6.51 (Ti?To)}/CR.

Abstract: The present invention provides a cooling apparatus having sufficient cooling ability in the cooling process of a continuous annealing facility and capable of minimizing the strip temperature difference in the width direction caused by the high speed blowing of the gas and preventing the strip from fluttering by making the most of the holding rolls, wherein the continuous annealing facility a plurality of nozzles for blowing gas protruding from a surface of a cooling chamber installed in the continuous annealing facility so as to keep the tips of the nozzles 50 to 100 mm distant from the surface of the steel strip and the cooling chamber is disposed so that the maximum width of the steel strip (Wmax:mm) and the distance (H:mm) from the surface of the cooling chamber to the steel strip satisfy the expression (1) below: 6<Wmax/H<13??(1)

Abstract: The present invention provides a cooling apparatus having sufficient cooling ability in the cooling process of a continuous annealing facility and capable of minimizing the strip temperature difference in the width direction caused by the high speed blowing of the gas and preventing the strip from fluttering by making the most of the holding rolls, wherein the continuous annealing facility a plurality of nozzles for blowing gas protruding from a surface of a cooling chamber installed in the continuous annealing facility so as to keep the tips of the nozzles 50 to 100 mm distant from the surface of the steel strip and the cooling chamber is disposed so that the maximum width of the steel strip (Wmax:mm) and the distance (H:mm) from the surface of the cooling chamber to the steel strip satisfy the expression (1) below:

Abstract: In a method of continuously annealing steel strip comprising a heating step (A), a soaking step (B), a primary cooling step (C) including a rapid cooling step at least in a second half thereof, an overaging step (D), and a final cooling step (E), inert atmosphere gas containing H.sub.2 gas in the concentration of 30-60% is employed as cooling gas for use in the rapid cooling step, the blowoff temperature of the cooling gas is 30.degree.-150.degree. C., and the blowoff speed of the cooling gas is 100-150 m/sec. The primary cooling method in continuously annealing steel strip provides the primary cooling step (C) including the rapid cooling step which can be carried out with a high efficiency and a low cost.