Some embodiments of the disclosure provide a method for homogeneously controlling a transverse temperature during laminar cooling of a hot-rolled strip. In an embodiment, a mathematical model of middle convexity cooling in a water volume is established by designing different types of middle convexity water cooling heat transfer coefficient curves. Process procedures and equipment parameters of the hot-rolled strip during the laminar cooling are considered to restore the actual situation on site. Through finite element calculation, an optimal middle convexity water cooling heat transfer coefficient curve is obtained. Process parameters corresponding to middle convexity water volume distribution during the laminar cooling (a water flow density) are further obtained to guide a water volume control process.

Provided is a hot press-formed member having excellent crack propagation resistance and ductility. The hot press-formed member includes: a base steel sheet and a zinc or zinc alloy plating layer on at least one surface of the base steel sheet. The base steel sheet contains, by wt %, carbon (C): 0.08-0.30%, silicon (Si): 0.01-2.0%, manganese (Mn): 3.1-8.0%, aluminum (Al): 0.001-0.5%, phosphorus (P): 0.001-0.05%, sulfur (S): 0.0001-0.02%, nitrogen (N): 0.02% or less, and a balance of iron (Fe) and other impurities. The hot press-formed member comprises 1-30 area % of retained austenite as a microstructure, and a Mn(wt %)/Zn(wt %) content ratio in an oxide layer of 0.5-1.2 m in a thickness direction from a surface layer of the plating layer is 0.1 or more.

Provided is a hot press-formed member having excellent crack propagation resistance and ductility. The hot press-formed member includes: a base steel sheet and a zinc or zinc alloy plating layer on at least one surface of the base steel sheet. The base steel sheet contains, by wt %, carbon (C): 0.08-0.30%, silicon (Si): 0.01-2.0%, manganese (Mn): 3.1-8.0%, aluminum (Al): 0.001-0.5%, phosphorus (P): 0.001-0.05%, sulfur (S): 0.0001-0.02%, nitrogen (N): 0.02% or less, and a balance of iron (Fe) and other impurities. The hot press-formed member comprises 1-30 area % of retained austenite as a microstructure, and a Mn(wt %)/Zn(wt %) content ratio in an oxide layer of 0.5-1.2 m in a thickness direction from a surface layer of the plating layer is 0.1 or more.

A cooling device cooling an undersurface of a hot rolled steel sheet that is being transported on transport rolls after finish rolling of a hot rolling step includes: width divided cooling zones that are a plurality of cooling zones into which a whole cooling zone is divided in a sheet width direction; divided cooling sections that are a plurality of cooling zones into which each of the width divided cooling zones is divided in the rolling direction; a water nozzle spraying cooling water over each of undersurfaces of the divided cooling sections; a switching mechanism switching the cooling water between impinging and not impinging on the divided cooling sections; a width direction thermometer measuring a temperature distribution in the sheet width direction; and a controller controlling operation of the switching mechanism.

A cooling device cooling an undersurface of a hot rolled steel sheet that is being transported on transport rolls after finish rolling of a hot rolling step includes: width divided cooling zones that are a plurality of cooling zones into which a whole cooling zone is divided in a sheet width direction; divided cooling sections that are a plurality of cooling zones into which each of the width divided cooling zones is divided in the rolling direction; a water nozzle spraying cooling water over each of undersurfaces of the divided cooling sections; a switching mechanism switching the cooling water between impinging and not impinging on the divided cooling sections; a width direction thermometer measuring a temperature distribution in the sheet width direction; and a controller controlling operation of the switching mechanism.

A cooling bar (1) for cooling rolled material (5) being moved in a transport direction (3) and in particular for reducing temperature differences in the temperature of the rolled material (5) transversely to the direction of transport (3). The cooling bar (1) has several full jet nozzles (11) by means of which a coolant beam of a coolant with an approximately constant jet diameter can be distributed to the rolling stock (5) in the direction of distribution (15). A cooling device has at least two cooling bars (1) of that type. The cooling bars extend transversely to a transport direction, one behind the other. Each cooling bar has a respective different pattern of jet nozzles and selection of applicable pattern of jet nozzles in their respective bars selectively cools the rolled material transversely to the transport direction.

Provided is a hot press-formed member having excellent crack propagation resistance and ductility. The hot press-formed member includes: a base steel sheet and a zinc or zinc alloy plating layer on at least one surface of the base steel sheet. The base steel sheet contains, by wt %, carbon (C): 0.08-0.30%, silicon (Si): 0.01-2.0%, manganese (Mn): 3.1-8.0%, aluminum (Al): 0.001-0.5%, phosphorus (P): 0.001-0.05%, sulfur (S): 0.0001-0.02%, nitrogen (N): 0.02% or less, and a balance of iron (Fe) and other impurities. The hot press-formed member comprises 1-30 area % of retained austenite as a microstructure, and a Mn(wt %)/Zn(wt %) content ratio in an oxide layer of 0.5-1.2 m in a thickness direction from a surface layer of the plating layer is 0.1 or more.

Provided is a hot press-formed member having excellent crack propagation resistance and ductility. The hot press-formed member includes: a base steel sheet and a zinc or zinc alloy plating layer on at least one surface of the base steel sheet. The base steel sheet contains, by wt %, carbon (C): 0.08-0.30%, silicon (Si): 0.01-2.0%, manganese (Mn): 3.1-8.0%, aluminum (Al): 0.001-0.5%, phosphorus (P): 0.001-0.05%, sulfur (S): 0.0001-0.02%, nitrogen (N): 0.02% or less, and a balance of iron (Fe) and other impurities. The hot press-formed member comprises 1-30 area % of retained austenite as a microstructure, and a Mn(wt %)/Zn(wt %) content ratio in an oxide layer of 0.5-1.2 m in a thickness direction from a surface layer of the plating layer is 0.1 or more.

A steel strip processing system is provided that includes a plurality of microstructure sensors that measure the phase fraction in a steel strip at desired locations in a processing furnace. A process control system includes a plurality of control loops for receiving the outputs of the microstructure sensors to determine the amount of heating and cooling required to achieve a desired phase fraction at the desired locations in the processing furnace. One or more energy systems that receive the output of the process control system to coordinate the heating or cooling of the desired locations to achieve the desired phase fraction.

A steel strip processing system is provided that includes a plurality of microstructure sensors that measure the phase fraction in a steel strip at desired locations in a processing furnace. A process control system includes a plurality of control loops for receiving the outputs of the microstructure sensors to determine the amount of heating and cooling required to achieve a desired phase fraction at the desired locations in the processing furnace. One or more energy systems that receive the output of the process control system to coordinate the heating or cooling of the desired locations to achieve the desired phase fraction.