A steel sheet having a specified chemical composition and a tensile strength of 1,320 MPa or more, and methods for producing the steel sheet. The steel sheet has a specified microstructure including martensite and bainite, the total area fraction of the martensite and the bainite being 95% or more and 100% or less, the balance being one or more selected from ferrite and retained austenite. The forumulae [% Ti]+[% Nb]>0.007 and [% Ti]?[% Nb].sup.2?7.5?10.sup.?6 are satisfied in the chemical composition.

A casting mold including a copper plate and a plurality of optical fibers, having a plurality of temperature measuring points for the copper plate while casting. Molten metal is cast into the mold along an axis of, the optical fibers built-in the plate. A method for detecting temperature distribution of a molten metal in a casting mold having at least one copper plate, including determining by calculation or measurement an ideal molten flow of the metal, building-in a plurality of optical fibers into the copper plate based on flow, arranging the optical fibers inside at least the upper part of the copper plate, receiving the measurements of temperatures, and comparing the measurements of temperatures with a calculated/measured distribution of an ideal molten flow.

The primary object of the present invention is to provide a mold for continuous casting including a temperature detection unit which can detect the temperature of a copper plate of the mold with high precision, and can be easily inserted into and pulled out of the copper plate. The present invention includes: a main body; and a temperature detection unit which is inserted in an insertion hole in the main body, and detects temperature inside the mold. The temperature detection unit includes: an FBG sensor inserted in a protection tube which can be deformed in a radial direction; and a support member which supports the FBG sensor along the longitudinal direction. At a temperature detection point, the protection tube in which the FBG sensor is inserted is held between a stretched member in the support member and an inner surface of the insertion hole.

Mould provided with a detection system of the level a liquid metal within a crystallizer of the mould in which the detection system is based on the transmission of at least one detection signal transmitted towards the crystallizer and a phase of reception of at least one received measuring signal dependent on the transmitted detection signal and mould and continuous casting machine provided with said mould.

A system of detection of a temperature of a crystallizer or a level of liquid metal in the crystallizer has a sensor positioned within a mould of the crystallizer. The sensor has a case, a closing cover positioned at a detection face of the case, a plurality of ultrasonic elements arranged in vertically spaced relation to a length of the case, and a plurality of attenuation elements positioned sideways with respect to the closing cover. The plurality of ultrasonic elements include a first ultrasonic element, a second ultrasonic element and a third ultrasonic element positioned in orthogonal relation to the length of the sensor. The plurality of ultrasonic elements transmit and receive ultrasonic waves.