A steel sheet has a composition containing, by mass %, C: 0.04% to 0.20%, Si: 0.6% to 1.5%, Mn: 1.0% to 3.0%, P: 0.10% or less, S: 0.030% or less, Al: 0.10% or less, N: 0.010% or less, one, two, or all of Ti, Nb, and V in an amount of 0.01% to 1.0% each, and the balance being Fe and inevitable impurities, a microstructure including, in terms of area ratio, 50% or more of ferrite, in which an average grain diameter at a position located 50 m from a surface of the steel sheet in a thickness direction is 3000(tensile strength TS (MPa)).sup.0.85 m or less, C precipitates having a grain diameter of less than 20 nm formed in steel is 0.010 mass % or more, and a amount of precipitated Fe is 0.03 mass % to 1.0 mass %, and a roughness Ra of 3.0 m or less.

The subject matter of this invention is a heat distribution management device in a treatment device of wires in movement on a means of transport, said means of transport being able to be traversed by a flow of heat at or through the of orifices, characterized in that the device comprises at least one means of sealing by coverage of at least one part of the orifices of the means of transport, said means of sealing being independent of the means of transport.

The present disclosure provides assemblies, systems and methods for a single-step process for selective heat treatment of metals. More particularly, the present disclosure provides assemblies, systems and methods for a single-step process for selective heat treatment of metals using a coil-in-furnace configuration. A hybrid modeling-test approach can be used in the design process to improve or optimize the process parameters to achieve location specific and improved/optimal microstructure and residual stress to enhance the part performance. It is also noted that performing the selective heat treatment in a single step can reduce the cycle time significantly. Moreover, large thermal gradients can be avoided in the part as different volumes of the part are heated to their desired temperature simultaneously.

The present disclosure provides assemblies, systems and methods for a single-step process for selective heat treatment of metals. More particularly, the present disclosure provides assemblies, systems and methods for a single-step process for selective heat treatment of metals using a coil-in-furnace configuration. A hybrid modeling-test approach can be used in the design process to improve or optimize the process parameters to achieve location specific and improved/optimal microstructure and residual stress to enhance the part performance. It is also noted that performing the selective heat treatment in a single step can reduce the cycle time significantly. Moreover, large thermal gradients can be avoided in the part as different volumes of the part are heated to their desired temperature simultaneously.

A continuous annealing apparatus includes: a pre-treatment device to prepare a strip unwound from a coil; a heating device to heat the strip prepared by the pre-treatment device; a heat holding device to isothermally maintain the strip heated by the heating device; a first cooling device to cool the strip heat-maintained by the heat holding device; an annealing device including a first annealing device for annealing the strip, which, is cooled by the first cooling device, for a first time, and a second annealing device for winding the strip, which is cooled by the first cooling device, into a coil and then unwinding the coil into the strip again after annealing for a second time; a second cooling device to cool the strip annealed by the first annealing device or the second annealing device; and a post-treatment device to wind the strip cooled by the second cooling device into the coil.

Disclosed is a method for continuous thermal treatment of a steel strip. The strip passes through consecutive thermal treatment chambers, is quickly cooled in at least one of the chambers by spraying liquid onto the strip, or by spraying a fluid made up of gas and liquid or spraying a combination of gas and liquid forming a mist. After quick cooling, a protective metal layer is deposited on the strip by dip coating. The cooling fluid strips iron oxides or other alloy elements contained in the steel to be treated, minimizing oxidation and reducing the oxides on the strip. Spray pressure and distance are chosen to facilitate the stripping property and the mechanical action of the sprayed fluid, reducing the layer of oxides on the strip. The temperature of the strip at the end of the cooling step is the temperature necessary for carrying out the desired treatment cycle.

Disclosed is a method for continuous thermal treatment of a steel strip. The strip passes through consecutive thermal treatment chambers, is quickly cooled in at least one of the chambers by spraying liquid onto the strip, or by spraying a fluid made up of gas and liquid or spraying a combination of gas and liquid forming a mist. After quick cooling, a protective metal layer is deposited on the strip by dip coating. The cooling fluid strips iron oxides or other alloy elements contained in the steel to be treated, minimizing oxidation and reducing the oxides on the strip. Spray pressure and distance are chosen to facilitate the stripping property and the mechanical action of the sprayed fluid, reducing the layer of oxides on the strip. The temperature of the strip at the end of the cooling step is the temperature necessary for carrying out the desired treatment cycle.

The present invention provides a method for manufacturing a cold-rolled or zinc-plated dual-phase steel plate over 980 MPa. After being subjected to hot rolling, coiling, bundling, and online heat preservation, a slab is directly sent to a cold rolling and continuous annealing process, or a cold rolling, continuous annealing, and zinc plating process, so as to obtain a cold-rolled or zinc-plated dual-phase steel plate, wherein the coiling temperature is controlled to be over 450? C. The online thermal preservation means that after uncoiling of each hot-rolled coil, an independent and airtight thermal preservation cover is closed, and the hot-rolled coil with the closed thermal preservation cover is transferred to coil rolling by means of a steel coil conveying chain or a traveling car; the thermal preservation temperature for the hot-rolled coil in the thermal preservation cover is over 450? C., and the thermal preservation duration is less than 20 hours. According to the present disclosure, by means of the design of a thermal preservation process with or without a heat source after hot rolling and coiling, the manufacturing problems such as edge cracks and sharp fluctuation in thickness after cold rolling are solved, and good cold rolling manufacturability is achieved.

The present invention provides a method for manufacturing a cold-rolled or zinc-plated dual-phase steel plate over 980 MPa. After being subjected to hot rolling, coiling, bundling, and online heat preservation, a slab is directly sent to a cold rolling and continuous annealing process, or a cold rolling, continuous annealing, and zinc plating process, so as to obtain a cold-rolled or zinc-plated dual-phase steel plate, wherein the coiling temperature is controlled to be over 450? C. The online thermal preservation means that after uncoiling of each hot-rolled coil, an independent and airtight thermal preservation cover is closed, and the hot-rolled coil with the closed thermal preservation cover is transferred to coil rolling by means of a steel coil conveying chain or a traveling car; the thermal preservation temperature for the hot-rolled coil in the thermal preservation cover is over 450? C., and the thermal preservation duration is less than 20 hours. According to the present disclosure, by means of the design of a thermal preservation process with or without a heat source after hot rolling and coiling, the manufacturing problems such as edge cracks and sharp fluctuation in thickness after cold rolling are solved, and good cold rolling manufacturability is achieved.

Disclosed is a method for continuous thermal treatment of a steel strip. The strip passes through consecutive thermal treatment chambers, is quickly cooled in at least one of the chambers by spraying liquid onto the strip, or by spraying a fluid made up of gas and liquid or spraying a combination of gas and liquid forming a mist. After quick cooling, a protective metal layer is deposited on the strip by dip coating. The cooling fluid strips iron oxides or other alloy elements contained in the steel to be treated, minimizing oxidation and reducing the oxides on the strip. Spray pressure and distance are chosen to facilitate the stripping property and the mechanical action of the sprayed fluid, reducing the layer of oxides on the strip. The temperature of the strip at the end of the cooling step is the temperature necessary for carrying out the desired treatment cycle.