A cold rolled steel flat product for packaging made of a low carbon steel having a thickness of less than 0.49 mm and a method of making. The steel flat product has a martensite-free microstructure and represents a standard grade for packaging with tensile strengths from 300 to 550 MPa, which can be produced from a cold-rolled steel sheet with a carbon content from 0.01% to 0.1% by weight by inductive annealing of the steel sheet and subsequent water cooling for quenching the recrystallization-annealed steel sheet. To achieve flatness of 5 I-units or less, the induction annealed steel sheet is first primarily cooled in the manufacturing process to a take-off temperature at a rate of less than 1000 K/s, with the take-off temperature being below the transformation temperature of 723° C., and thereafter a secondary cooling by water cooling with a water temperature of less than 80° C. at a rate of more than 1000 K/s.

The present invention manufactures a steel sheet for a rotor core for an IPM motor, wherein the steel sheet has a magnetic flux density B.sub.8000 of 1.65 T or more as measured when magnetic field strength is 8000 A/m, and a residual magnetic flux density Br of 0.5 T or more as measured at that time, and optionally, a coercivity Hc of 100 A/m or more as measured after magnetization reaches 8000 A/m. By using the steel sheet manufactured according to the present invention for a rotor core of an IPM motor, it is possible to increase further an output torque in a high-speed rotational range and raise further the maximum rotational speed.

The present invention manufactures a steel sheet for a rotor core for an IPM motor, wherein the steel sheet has a magnetic flux density B.sub.8000 of 1.65 T or more as measured when magnetic field strength is 8000 A/m, and a residual magnetic flux density Br of 0.5 T or more as measured at that time, and optionally, a coercivity Hc of 100 A/m or more as measured after magnetization reaches 8000 A/m. By using the steel sheet manufactured according to the present invention for a rotor core of an IPM motor, it is possible to increase further an output torque in a high-speed rotational range and raise further the maximum rotational speed.

A method for manufacturing a high-strength cold-rolled steel sheet includes a temperature distribution forming step of forming a temperature distribution in a width direction of a steel sheet such that a temperature of the steel sheet increases from an end of the steel sheet in the width direction toward a center part of the steel sheet in the width direction, and a water quenching step of performing water quenching treatment on the steel sheet by immersing, in cooling water, the steel sheet on which the temperature distribution is formed in the width direction.

A method for manufacturing a high-strength cold-rolled steel sheet includes a temperature distribution forming step of forming a temperature distribution in a width direction of a steel sheet such that a temperature of the steel sheet increases from an end of the steel sheet in the width direction toward a center part of the steel sheet in the width direction, and a water quenching step of performing water quenching treatment on the steel sheet by immersing, in cooling water, the steel sheet on which the temperature distribution is formed in the width direction.

A method for manufacturing a metal sheet comprising pinching the metal sheet in rapid quenching between a pair of pinch rolls in the range where the temperature of the metal sheet is from (T.sub.Ms+150) (° C.) to (T.sub.Mf−150) (° C.), wherein the Ms temperature of the metal sheet is T.sub.Ms (° C.) and the Mf temperature thereof is T.sub.Mf (° C.), as well as a rapid quenching unit comprising a pair of pinch rolls capable of use in such a method.

A method for manufacturing a metal sheet comprising pinching the metal sheet in rapid quenching between a pair of pinch rolls in the range where the temperature of the metal sheet is from (T.sub.Ms+150) (° C.) to (T.sub.Mf−150) (° C.), wherein the Ms temperature of the metal sheet is T.sub.Ms (° C.) and the Mf temperature thereof is T.sub.Mf (° C.), as well as a rapid quenching unit comprising a pair of pinch rolls capable of use in such a method.

Provided are a method and apparatus for uniformly controlling the strip temperature of the rapid cooling section of a continuous annealing line. A plurality of sets of cooling nozzle blocks for controlling the strip temperature is installed at the front and back sides of the strip, and is divided into lengthwise flow control nozzle blocks and widthwise flow control nozzle blocks. Strip center temperature meters and widthwise direction temperature meters are installed at the intake and discharge sides of the rapid cooling section. Temperatures obtained using the strip center temperature meters and the width direction temperature meters are used to respectively control the spraying of mist for the lengthwise flow control nozzle blocks and the widthwise flow control nozzle blocks in order to uniformly control the strip temperature and minimize changes in the flatness of the strip. The widthwise temperature meters at the intake and discharge ends of the rapid cooling section of the continuous annealing line are used to detect the temperature. Feedback/feedforward control technique can be used to uniformly control the widthwise temperature of the strip through flow rate control over mist sprayed in the widthwise direction of the rapid cooling section.

Provided are a method and apparatus for uniformly controlling the strip temperature of the rapid cooling section of a continuous annealing line. A plurality of sets of cooling nozzle blocks for controlling the strip temperature is installed at the front and back sides of the strip, and is divided into lengthwise flow control nozzle blocks and widthwise flow control nozzle blocks. Strip center temperature meters and widthwise direction temperature meters are installed at the intake and discharge sides of the rapid cooling section. Temperatures obtained using the strip center temperature meters and the width direction temperature meters are used to respectively control the spraying of mist for the lengthwise flow control nozzle blocks and the widthwise flow control nozzle blocks in order to uniformly control the strip temperature and minimize changes in the flatness of the strip. The widthwise temperature meters at the intake and discharge ends of the rapid cooling section of the continuous annealing line are used to detect the temperature. Feedback/feedforward control technique can be used to uniformly control the widthwise temperature of the strip through flow rate control over mist sprayed in the widthwise direction of the rapid cooling section.

Provided is a hearth roll for supporting and conveying a steel sheet in a continuous annealing furnace, wherein all of a shaft portion and a roil main body are made from one or more ceramic materials, preferably constituted with concentric ceramic layers of different ceramic materials centering on the rotation shaft of the roll. The hearth roll has not only an excellent pickup resistance but also a long roll life free from maintenance for long periods. Also provided is a continuous annealing facility using the hearth roll in at least one of a heating zone, a soaking zone and a cooling zone.