A method of manufacturing a hot-rolled strip and sheet

 

The invention relates to a method of manufacturing a hot-rolled strips and sheets. The method is carried out at the production plant consisting of continuous casting of slabs with a thickness of from 100 to 180 mm, purifier scale, single or multi - stage rolling device with combined compression mill or without him, the cooling section, the heating furnace and the Steckel mill. Between continuous casting and reheating furnace plastically deform only the extreme surface layer of the slab, pre-cleaned from scale, and this layer recrystallizes during and after the plastic deformation, and then its speed is cooled to a temperature below the point Andr3transformation and can stand up to the completion of the structural transformation of recrystallized fine-grained austenite in the ferrite/pearlite. The method allows to process steel with a higher content of copper, aluminum and nitrogen in the absence of cracks or delamination. 4 C. p. F.-ly, 2 Il.

The invention relates to a method of manufacturing a hot-rolled strip and sheet production plant consisting of continuous casting of slabs with a thickness of the second under the name of FFM (Flexible Flat Mill) production installation for the manufacture of hot-rolled strips and sheets slab thickness 100-180 mm is transported from the continuous casting with roller conveyor directly to the heating furnace, is loaded into the furnace in a hot condition, heats up and after exit from the heating furnace rolled into one - or multi-stage Steckel mill in the band or in one or more sheets.

Usually the temperature of the slab at the outlet of the continuous casting is from 1000 to 1150oWith and decreases during transport to the heating furnace by the conveyor. Hot load in the heating furnace is at a temperature of from 750 to 950oC. In the heating furnace, the slab is uniformly heated by the thickness, width and height to a temperature 1050-1280oWith depending on the material.

Hot download characteristically, before the first plastic deformation in the rolling mill on the thickness of the slab does not occur or occurs only to a small extent the structural transformation of the austenite - ferrite/pearlite in surface area if the temperature of the outer surface when transporting the slab from continuous casting to the heating furnace falls below the temperature structural transformations or falls only slightly and briefly. Occurring during solidification of the slab coarse primary austenite remains to plastic deformation in rolling is hnologie heating.

How hot load compared to how cold boot saves energy and time during the heating process.

Describes how hot load paid off for steels with copper content less than 0.3%. At a higher content of copper in steel copper released during the formation of scale in the heating furnace, is deposited on the grain boundaries of primary austenite. Depending on the copper content, heating temperature and scaling these deposits copper on the grain boundaries can during plastic deformation in the rolling mill to cause delamination of the material in the appearance of the mesh cracks.

In EP 0686702 A1 to resolve this problems also for casting and rolling of thin slabs proposed to cool the outer surface of the thin slabs with a thickness of 40-70 mm in the cooling section, located behind the continuous casting, to a temperature below the temperature AG3so that in the surface region of a depth of at least 2 mm is at least 70% of the structural transformation of austenite into ferrite/pearlite with the new orientation of the grain boundaries of austenite after re-heating in a furnace roller hearth. The average rate is these transformations of the material.

It was established that in General, when the rolling of blooms, rolled billets and slabs specific chemical composition of cracks or delamination can occur if a hot load in the heating furnace is used as the direct link between continuous casting and rolling mill.

In JP 59-189001 for rolling billets of carbon steels containing 5-100 parts per thousand boron, 0.03 to 0.15% of sulfur, and 0.5 to 2.0% silicon, to avoid the occurrence of cracks in the material during rolling also suggested that rapid cooling at the surface layer in the area between the continuous casting and reheating furnace.

In EP 0587150 A1 as the causes of cracks in the material during rolling relieved aluminum steels containing 0,008-0,030% N and 0.03 to 0.25% Pb, indicated the deposition of aluminum nitride during hot load. To prevent deposition of aluminum nitride, it is recommended that rapid cooling at the surface layer of the blooms with the structural transformation into bainite region. Rapid cooling is performed on the area between the continuous casting and reheating furnace.

In the US 5634512 as the cause of cracking in the blooms, rolling just EMA hot load. Also proposed rapid cooling at the surface layer of a thickness of at least 10 mm to a temperature of 400oWith subsequent szamotulska 900oWith thanks to the warmth emanating from the core. Installation for rapid cooling is between continuous casting and reheating furnace. Provided by the management and regulation of the cooling unit depending on the material.

Common to describe the known solutions is that the true causes, processes, or mechanisms, which lead to cracking and delamination of the material when using hot load in the process of "continuous casting - heating/equalizing furnace and rolling mill", still clearly not explained. It was mentioned that there is a combination of several reasons. In General, in the known solutions offers rapid cooling at the surface layer of the casting below the temperature structural transformations with subsequent release due to heat emanating from the core. About the danger of partial reduction of the surface temperature to below the martensite transformation is said in all the above-mentioned patents, which shows the tee time.

Device for rapid cooling is known from the prior art solutions offered between the continuous casting and heating or leveling oven. Partial transformation at the surface layer in the ferrite/pearlite is connected with the grinding of grain and the new orientation of the grain boundaries of austenite after re-heating, as seen in Fig.1b and 2 line level equipment.

Studies have also shown that for steels containing more than 0.3% copper, 0.02 to 0.05% of Al and 0.008 at 0.020% N and having a ratio of copper/Nickel more than 3, despite the rapid cooling at the surface layer of the slab with partial structural transformation after the continuous casting and before it is loaded into the heating furnace, and the subsequent rolling of the slab into strips of any fracture or delamination of the material.

The task of the invention consists in the combination installation for the production of strips or sheets of the above type can be processed steel with a higher content of si, Al and N in the absence of these shortcomings.

According to the invention between continuous casting and reheating furnace plastically deform only at poornathrayeesa, and then his multi-stage cooled to a temperature below the point AG3transformation and can stand up to the completion of the structural transformation of recrystallized fine-grained austenite in the ferrite/pearlite.

This means that before loading of slab reheating furnace it passes through the deformation of the surface layer, consisting of a purifier scale, single or multi - stage rolling device, combined with compression mill or without him, and controlled cooling section. In the purifier scale the outer surface is completely cleaned from scale.

In a preferred embodiment of the invention provides that the slab is plastically deform with the General compression 5-15% and optimized with respect to diameter ratio of Id/hmthe gap between the rollers constituting less than 0.8. The rolling speed matches the speed of the casting. By optimizing the diameter of the rolls and the proposed compression ratio of the gap between the rollers, is equal to the ratio of the length at which the pressure is to the average height of the car, set so that according to another characteristic of the invention, the thickness of the surface region due to the choice of compression and coefficien remains almost not deformed.

Due to the deformation of the surface region is molded material in the gap between the rollers of the respective stands of the rolling device is partially or fully dynamically recrystallized depending on the conditions of plastic deformation. After leaving the gap between the rollers of the respective rolling mill stand of the site there is a partial or full static recrystallization of deformed extreme surface layer of the steel. The temperature change at the surface layer shown in Fig.1A by the dashed line. Due to the dynamic and static recrystallization is grinding grains at the surface layer (compare Fig.1b, dashed line), i.e. coarse-grained primary austenite transforms into laminated fine-grained structure.

In order to avoid grain growth at the surface layer due to the still high temperature from 850 to 1050oAfter graduating from recrystalization its multi-cooled in the cooling section. When this temperature falls below the temperature AG3transformation, resulting recrystallized and crushed in the rolling grains at the surface layer significantly faster, sravnenie the ACLs to the invention, the intensity of cooling, provided in the cooling section, consisting of several groups of nozzles, controlled and regulated so that the temperature of the outer surface of the slab does not reach the education bainite and does not fall below the threshold of martensitic transformation for the corresponding material.

Multi-stage cooling at the surface layer is carried out until, until 100% conversion of recrystallized and refined grains in the ferrite/pearlite. For this purpose, the control and regulating system for regulating the pressure of the environment in groups of nozzles of the cooling section, depending on the thickness of the slab and the speed of the wheels, the average temperature at the surface layer during curing temperature and cooling time required for 100% structural transformations, as well as the initial temperature of education bainite and the starting temperature of martensitic transformation of the material.

Thanks to the operations of plastic deformation at the surface layer and its speed cooling below the temperature AG3transformations carried out before loading the slab heating furnace, a much more Pelkosenniemi operations when re-heating due to the structural transformation is complete, the new orientation of the grain boundaries of austenite with much smaller grains.

With a complete new orientation of the grain boundaries of austenite with much smaller grains during hot load described in the operating plant can be processed steel with a copper content of more than 0.3%, and additives of Al and N, and with the ratio of copper/Nickel more than 3.

Claims

1. A method of manufacturing a hot-rolled strip and sheet manufacturing plant consisting of continuous casting of slabs with a thickness of from 100 to 180 mm, purifier scale, single or multi - stage rolling device with combined compression mill or without a plot cooling, reheating furnaces and Steckel mill, characterized in that between the continuous casting and reheating furnace plastically deform only the extreme surface layer of the slab, purified prior to this scale, and during and after the plastic deformation of this layer recrystallizes, after which its multi-stage cooled to a temperature below the point Andr3transformation and can stand up to the completion of the structural transformation of recrystallized fine-grained austenite in the ferrite/pearlite.

2. The method according to p. 1, characterized in that the slab of plastic the gap between the rollers constituting less than 0.8.

3. The method according to any of the p. 1 or 2, characterized in that the thickness of the plastically deformed surface region due to the choice of compression ratio and the gap between the rollers is a maximum of one quarter of the thickness of the slab.

4. The method according to any of the p. 1 or 3, characterized in that neintensivnostju cooling cooling section, consisting of several groups of nozzles, controlled and regulated in such a way that the surface temperature of the slab does not reach the education bainite and does not fall below the threshold of martensitic transformation for the corresponding material.

5. The method according to any of the p. 1 or 4, characterized in that the control and regulating system for regulating the pressure of the environment in groups of nozzles of the cooling section depending on the respective thickness of the slab and casting speed, the average temperature at the surface layer during curing temperature and cooling time required for 100% structural transformations, as well as the initial temperature of education bainite and the starting temperature of martensitic transformation.

 

Same patents:

The invention relates to a method for producing a high-strength steel strip and device for its implementation

The invention relates to the manufacture of steel strip for parts made deep hood or hood with thinning
The invention relates to the technology of production of cold-rolled strips of sverkhnizkochastotnye steels for the automotive industry, with a hardening effect during drying of the paint coating (EXT-effect)

The invention relates to the field of metallurgy, in particular to the production of the rolled strip from sverhskorostey steel (IF-steel) for further forging used in the automotive industry

The invention relates to the production of steel strip or sheet for deep drawing in the manufacture of cans

The invention relates to the field of metallurgy, namely, rolling and heat treatment of steel, and can be used in the production of cold-rolled galvanized tape used to protect electrical cables

The invention relates to sheets of very high-strength welded low-alloy steel and the method of production of steel sheets

The invention relates to metallurgy, and more specifically to a technology of manufacturing of hot-rolled strips of sverhskorostey steel with high exhaust properties for cold forming

The invention relates to the processing of metals by pressure, in particular the production of broadband hot-rolled carbon steel of ordinary quality and quality

The invention relates to a process of continuous casting - rolling steel strip

The invention relates to a method for producing a high-strength steel strip and device for its implementation

The invention relates to the manufacture of rolled profiled metal products, with a partially or fully polygonal cross section by continuous casting in the casting wheel groove and the subsequent continuous rolling by using the sequence consisting of at least three pairs of rolling rollers, provided with a peripheral groove located symmetrically in relation to the profiled this product and installed alternately in vertical and horizontal position

The invention relates to the metallurgical industry, in particular to equipment for the production of flat products, including the production of continuous cast flat blanks, hot and cold rolling of ferrous and/or nonferrous metals, bimetallic and polymetallic compositions, which enables within a single process with the greatest efficiency to use one set of equipment for production of continuously cast and hot rolled strips and strips, cold rolled coils, strips, plates and maps, including high-precision production of special alloys and bimetals, trimetallic and polymetals different compositions methods of cold rolling

The invention relates to the field of rolling after continuous casting of steel

The invention relates to the field of rolling continuously cast billets

The invention relates to the production of steel strip or sheet for deep drawing in the manufacture of cans

The invention relates to the manufacture of thin stainless steel strips by direct solidification of liquid steel in the form of a strip with a thickness that is less than or equal to 8 mm

The invention relates to the production of textured electrical strip steel with high magnetic characteristics

FIELD: rolled stock production, possibly rolling merchant bars and rods of continuously cast carbon (standard and high-quality) steel, low alloy, alloy, roll-bearing and spring steels.

SUBSTANCE: method comprises steps of heating steel continuously cast billet until austenite temperature; further multi-pass hot rolling while providing normalized temperature of rolling termination period; performing multi-pass rolling at temperature 860-1000 C of rolling termination period and at total elongation value γ selected according to kinds of steel. Invention provides complete treatment of axial zone of billet, lowered liquation of chemical elements along cross section and length of bar, regular contour of bar cross section.

EFFECT: enhanced quality, less loss of yield.

4 ex, 1 tbl

Up!