KR20050100701A - A method for processing a steel product, and product produced using said method - Google Patents

Abstract

The invention relates to a method for processing a steel product, in which the steel product is passed between a set of rotating rolls of a rolling mill stand in order to roll the steel product. According to the invention, the rolls of the rolling mill stand have different peripheral velocities such that one roll is a faster moving roll and the other roll is a slower moving roll, and the peripheral velocity of the faster moving roll is at least 5% higher and at most 100% higher than that of the slower moving roll, and the thickness of the steel product is reduced by at most 15% per pass, and the rolling takes place at a maximum temperature of 1350°C. The invention also relates to a steel product produced using the method, and to the use of this steel product.

Description

Manufacturing method of steel products and steel products manufactured thereby {A METHOD FOR PROCESSING A STEEL PRODUCT, AND PRODUCT PRODUCED USING SAID METHOD}

The present invention relates to a method for producing steel products by passing steel between a set of rotating rolls of a rolling mill stand. The rolling and stand is part of a rolling mill device consisting of one or more rolling mill stands.

Rolling is the most basic operation for imparting desired sizes and properties to metals such as steel. Apart from obtaining the desired final geometry of the steel product, the rolling is metallized during and after rolling to obtain structural improvements.

However, conventional rolling, which manufactures wide products in a plane strain compression process that makes significant changes in thickness, is undesirable or impossible in some cases. For example, for heavyweight structures, especially offshore platforms or bridge products, steel sheets with a thickness of 60 to 150 mm are required. Casting steel slabs are made up to a thickness of less than 400 mm and rolling them to 150 mm results in a thickness change of about 60%. Each pass through a conventional rolling mill stand typically changes thickness of 10-30%.

In slab casting, porosity, which is inherent in the casting process, is often formed in the slab. The pores are closed by the pressure generated by rolling the slab several times. However, when forming a very thick plate, the rolling will only close the pores of the outermost layer of the slab and not the pores in the core of the material. However, pores in the core of the material cause major defects in the mechanical properties of the material, in particular the toughness of the plate. In addition, grain refinement occurs only in the outermost layer of the plate. In order to achieve sealing of the pores by pressure and grain refinement in the core of the plate, the degree of rolling through the thick slab must be made high so that the combination of the starting thickness of the slab and the final thickness of the steel product must not allow large thickness reduction.

Equal Channel Angular Extrusion (ECAE), where extreme shear deformation is applied without changing the size of the sample, introduces a large equivalent strain into the product without large thickness reduction under laboratory conditions using small samples. It is possible to do In ECAE, the billet is extruded through a die having two channels of the same cross section that meet at an angle. Under ideal circumstances, the billet is sheared across the cross section of the channel by an amount determined by the angle between the two channels. Since the cross section does not change during processing, it can be repeated, thereby accumulating deformation. However, this laboratory technique cannot be used for industrial production of steel products because of the very high processing forces required and it is not possible to up-scale this process for conventional size flat products.

It is an object of the present invention to provide a method of introducing a large equivalent strain into a steel product without imposing an equal reduction on the product thickness.

It is also an object of the present invention to provide a method for producing steel products in which the properties of the product are improved.

Another object of the present invention is to provide a method for producing a steel product which can obtain grain refinement in the product.

It is another object of the present invention to provide a method for producing continuous cast steel by means of improving the properties of the slab or strip.

It is yet another object of the present invention to provide a method for producing a continuous cast steel slab or strip capable of sealing pores in a casting material.

Another object of the present invention is to provide a steel product with improved mechanical properties produced by this method.

In the context of the present invention, steels are considered to include all iron alloys, for example ultra low carbon steel, low carbon steel, medium to high carbon steel, electric steel and stainless steel. In the context of the present invention, steel products include ingots, slabs, blooms, billets, bars, rods, and strips.

One or more of these objects is a method of manufacturing a continuous cast steel product that passes steel through a pair of rotating rolls of a rolling mill stand for rolling, wherein the rolls of the rolling mill stand are one roll is a high speed moving roll and the other roll is As a slow moving roll having different peripheral velocities, the high speed moving roll has at least 5% and up to 100% faster than the low speed moving roll, and the thickness of the steel product is reduced to 15% at each pass, Rolling is achieved by a process that takes place at a temperature of up to 1350 ° C.

It has been found that with rolls provided at different speeds, shear occurs in the steel product and occurs throughout the thickness of the product. It has been found that this requires a speed difference of at least 5%. Shear seals the pores in the continuous casting material to a significant extent. This does not require a large change in thickness, a thickness change of up to 15% is sufficient. Preferably, this thickness reduction is at most 8%, more preferably at most 5%. This is because the thickness of the steel product at the start of the process does not cause significant reduction in the thickness direction since the thickness is substantially maintained in the production of the steel product.

In addition, the rolling according to the invention results in grain refinement throughout the thickness of the rolled material, which gives advantages to the mechanical properties of the slab or strip. In particular, the strength of the material increases. The effect of small grain size is well known.

It is preferable that rolling is performed at high temperature. However, the maximum temperature is limited to 1350 ° C. to avoid the formation of low melt oxides on the surface of the steel product produced. Higher temperatures make the rolling movement more smooth.

The preparation according to the invention will yield a rolled sheet with a small lateral spread.

 The circumferential speed of the high speed moving roll is preferably at most 50%, more preferably at most 20% than the low speed moving roll. If the speed difference is high, there is a significant sleeping loss between the roll and the steel product which results in uneven shearing.

According to an embodiment, the rolling mill is designed such that the rolls have different diameters. This can achieve a desired speed difference at the main speed.

According to another embodiment, the rolls have different rotational speeds. It can also achieve a desired difference in rotational speed.

The combination of rolls with different diameters and different rotational speeds can be measured in two to obtain the desired circumferential speed difference of the rolls.

According to the method of the invention, the steel product is introduced between the rolls at an angle of 5 to 45 degrees perpendicular to the plane through the central axis of the roll. Introducing the steel product at an angle between the rolls makes it easier for the roll to grab the steel product, keeping the change in thickness as small as possible. In addition, experiments have shown that if steel products are introduced at an angle between the rolls, they have improved linearity after rolling the steel products. The steel product is preferably supplied at an angle of 10 to 25 °, more preferably at an angle of 15 to 25 °, and the steel product exits the rolling mill with a good level of linearity. The effect also depends on the reduction in size of the steel product, the shape of the steel product and the alloy and temperature.

For this purpose, after the first rolling is performed, this machining operation is preferably repeated one or more times. For example, very good grain refinement is obtained by carrying out the machining operation according to the present invention three times. However, the number of machining operations is performed in accordance with the thickness of the steel product, the circumferential speed difference of the rolls, and the desired grain refinement. During each machining operation the steel product is introduced between the rolls at an angle of 5 to 45 degrees, preferably at an angle of 10 to 25 degrees, more preferably at an angle of 15 to 25 degrees.

If the machining operation according to the invention is repeated several times, according to the embodiment the steel product can be passed through a rolling mill stand in the opposite direction for each pass. The steel product then changes direction after each rolling operation and always passes through the same rolling mill stand. In this case, the roll is rotated in the opposite direction with respect to each pass. Also in each case the steel product is introduced at an angle between the rolls.

According to another embodiment, the steel product is continuously passed through two or more rolling mill stands. This method is well suited for strip materials in such a way that the desired machining operation is very fast.

According to a preferred embodiment of the invention, the rolling is carried out through a steel product having at least a skin layer substantially austenite structure, preferably a steel product having substantially austenite texture throughout. Typical minimum temperature ranges are from 900 ° C. for ultra low carbon steels to 800-870 ° C. for low carbon steels (based on chemical composition, of course) and 723 ° C. for steels with 0.8% carbon. In all cases, the maximum temperature is 1350 ° C. In the case of rolling austenitic stainless steel, the rolling is always performed in the austenitic structure.

According to a second preferred embodiment, the rolling is carried out through a steel product having at least the surface layer substantially austenite-ferrite biphasic tissue, preferably a steel product having substantially the entire austenite-ferrite biphasic tissue. . Typical temperature ranges are from 723 ° C. to 800-870 ° C. for low carbon steels. Increasing the carbon content to reduce to a vacancy point of about 723 ° C. for steel with 0.8% carbon lowers the temperature range.

According to a third embodiment of the invention, the rolling is carried out through a steel product having a ferrite structure substantially at least in the surface layer, preferably a steel product having a ferrite structure substantially throughout. For low carbon steels with a carbon content of at least 0.02%, the maximum temperature is about 723 ° C., for steels with low carbon content such as ultra low carbon steels it is about 850 ° C. These temperatures are bounded by the ferrite, ferrite-austenite, and austenite zones, depending on the composition of the steel and the heat treatment history of the steel. Phase transformation does not occur immediately, and when the critical temperature is exceeded, the transformation steel has a surface layer of a different phase compared to the central layer of the steel product.

According to another embodiment of the invention, the rolling is carried out at a temperature between 0 ° C and 720 ° C. This includes the cold rolling of ferritic steel products as well as the rolling of steels having martensitic or austenitic stainless steel textures.

The method processed or carried out by a rolling operation can be carried out using a rolling mill having substantially the same circumferential speed. In this way, for example, exactly the desired thickness or flatness can be imparted to the product.

According to yet another embodiment, the product is produced according to a method comprising the following steps of a steel product.

Continuous casting of steel strands;

Selectively heating and / or temperature equalizing the steel strand between a casting machine and a rolling device;

Optionally rolling the steel product in one or more rolling mill stands of the rolling apparatus with rolls having substantially the same circumferential speed;

Optionally accelerated cooling after the final rolling step;

Selectively cutting the steel product into slabs or coils before and after rolling;

Optionally winding the steel product;

-Cooling the steel product

The most commonly used method for producing steel slabs is to continuously cast steel strands and cut them into steel slabs having a thickness between 200 and 400 mm. After casting, these slabs are typically cooled to ambient temperature before they are introduced into the furnace of a hot strip mill. In some cases, the slab may be introduced into the furnace until it is warmed or hot from the casting (referred to as "melt charge" or "direct charge", respectively).

The thickness of the continuous cast strand is preferably less than 150 mm, more preferably less than 100 mm and even more preferably less than 80 mm for thin slab casting.

The casting strand may be cut by the cutting device after casting. Thus, the obtained slab can be stored during post-treatment and cooled or immediately treated. In the former case, the slab may require reheating before rolling, while in the latter case the slab may require homogenization. After finish rolling, the rolled product is cooled using accelerated cooling and can be optionally wound up. In the case where the cast strand is not cut into slabs but is immediately processed by continuous, infinite or semi-infinite rolling, the rolled product will be cut off after the rolling process, ie before the selective winding. The rolling according to the invention can be carried out at any position between the casting step and the final cooling step or subsequent steps.

Accelerated cooling may be performed before cooling the steel product. After the finishing process, the steel product is cooled or cooled to ambient temperature.

According to another embodiment of the present invention, the thickness of the continuous cast strand is preferably less than 20 mm, more preferably less than 10 mm, even more preferably less than 5 mm.

Casting strands having a cast microstructure may be cut by a cutting device after casting. Thus, the obtained slab can be stored during post-treatment and cooled or immediately treated. In the former case, the slab may require reheating before rolling or may be used as a final product. In the latter case, the slab may require homogenization. One defect of strip-cast steel products is that the final product has a large cast microstructure because the strip hardly rolls. Thus, the mechanical properties of the final product are relatively low, which limits the use of the final product and does not conflict with standard or recent thin slab methods of products obtained through conventional thick slabs. During the rolling process according to the invention, the microstructures are transformed from the cast structure to the processed microstructures without substantial thickness reduction, thereby significantly improving the final properties of the steel product. After finish rolling, the rolled product may be cooled using accelerated cooling and optionally wound up. After the finishing process, the steel product is cooled or cooled to ambient temperature. In the case where the cast strand is not cut into slabs but is immediately processed by continuous, infinite or semi-infinite rolling, the rolled product will be cut off after the rolling process, ie before the selective winding. After finish rolling, the rolled product can be cooled using accelerated cooling. After the finishing process, the steel product is cooled or cooled to ambient temperature. Again, the rolling according to the invention can be carried out at any position between the casting step and the final cooling step or subsequent steps.

Further advantages are obtained if the steel product treated according to the two embodiments described above is stainless steel.

In the context of the present invention, stainless steel includes both ferritic, austenitic-ferritic two-phase steels, and austenitic stainless steels. These steels are commonly applied in applications where the corrosion resistance of corrosion resistant non-alloyed or low alloyed steels is insufficient. The combination of corrosion resistance, high strength and good ductility is combined with two-phase stainless steels in applications where the formability of ferrite and austenitic stainless steels is insufficient. A typical example of ferritic stainless steel according to EN 10088 (1995) is X2CrNi1201.4003 (410) X6Cr14-1.4016 (430), a typical example of austenitic stainless steel is X5CrNiMo17-12-2 1.4401 (316) X5CrNi18-10-1.4301 (304 )to be. These steels are commonly used as general purpose stainless steel for plates, strips, semi-bars, rods, rods, and as structural steel for buildings, pipelines, kitchen utensils, pump elements and valves and the like.

The thickness of the slab or strip is reduced to at most 15%, preferably at most 8%, more preferably at most 5% per pass. Since shear and grain refinement are caused by the circumferential speed difference between the rolls, a thickness reduction of the material for obtaining grain refinement is not required. Thickness reduction is mainly required for the roll to catch the material. This requires only minor thickness changes in the case of thin continuous cast steel slabs, strip mainly materials and strip materials. If the reduction is small, a thick slab or strip remains after each pass. The applicability of continuous casting slabs and strip materials is increased. In addition to the method according to the invention, good mechanical properties can be imparted to steel products. Since the process according to the invention can be used to impart good properties to relatively thin steel products, good mechanical properties and industrial applications are expected for thick continuous cast plates and strip materials.

In the production of high-strength steel strips microalloyed with one or more of Nb, V, Ti or B (these steel grades are commonly referred to as HSLA-steels (high strength, low alloy)), hot according to the known law of work heat treatment rolling Strip mills have the problem of producing strips of very thick thickness. The continuous casting slab used to initiate the rolling process has a fixed thickness between 200 and 350 mm, for example 225 mm thickness. The rolling mill is also typically divided into roughing sections, and the slab is rolled in a number of passes, for example five passes, to a selected thickness, for example 36 mm. This transfer bar thickness is a fixed thickness in a given hot strip mill, with a deviation of this fixed value being minimal. The deviation of this value by increasing its value is obtained in the rolling force or torque in the finishing mill exceeding the operating limit, which results in loss in the rolling mill or inadequate change in shape or product appearance. Reducing the thickness of the transfer bar results from rolling forces or torques in rough mills that exceed operating limits. However, the fixed value of the transfer bar causes a problem because it is obtained with a different reduction value, for example for a thick strip of 18 mm or a thin strip of 4 mm. In the first case, the total reduction in the finishing mill is 50%, and in the second case it is 89%. This has a great reaction to the development of the microstructure of the steel after or during hot rolling because the processing heat treatment conditions are completely different with other recrystallization of modified austenite or different precipitation movements of micro-alloy elements. Therefore, it affects the phase transformation during the cooling after rolling. In an embodiment of the present invention, the degree of deformation of the steel product can be increased without increasing the transfer bar thickness or the degree of deformation can remain unchanged while the final thickness of the steel product is increased.

For the cross section, the strain is a characteristic of the final product. For example, steel billets rolled into cross sections, such as H-sections, often have portions that are not subjected to almost any rolling, where no grain refinement occurs. The steel billet has a gauge between 200 and 400 mm, for example a 230 mm or 310 mm gauge. They are rolled in the slab / bloom / billet stages after reheating at temperatures up to 1350 ° C. Finish rolling is usually performed at a temperature where the steel is austenite, with a flange thickness in the range of 10 to 150 mm. In a non-limiting example, typical steel grades used in these sections are CMn- and HSLA-steels. The method according to the invention results in a finer grain size of the billet because of the higher degree of strain in the billet, and also reduces the pore size of the billet to obtain excellent fracture toughness.

It can be clearly seen from the results of the basic investigation that properties such as strength, toughness and corrosion resistance can be improved by reducing the grain size. Steel is being developed with very fine grain size by controlling crystal structure. These steels not only provide high tensile strength compared to conventional steels, but also provide improved toughness, durability and corrosion resistance. This technique is implemented by increasing the rolling force and torque to very high values by cold rolling in a hot strip mill and imposing a very large thickness reduction. However, the proposed solution for obtaining ultrafine ferrite crystals relies on grain refinement by normal rolling (ie planar deformation compression) at low temperature rolling, and requires a very powerful rolling mill. In the process according to the invention, sufficient crystal reduction can be achieved by accumulation of deformation of the steel without significantly reducing the thickness. The average grain size of the steel product obtained is less than 5 μm, preferably less than 2 μm, more preferably less than 1 μm. According to another embodiment of the present invention, the properties of a composite phase steel are unexpectedly improved by the accumulation of strain in the steel without a loss in thickness. When steel products are rolled in an austenitic state and continuously accelerated cooled, a large degree of accumulated strain is caused by the very fine ferrite crystals combined with the very finely dispersed microcrystalline second phase consisting of bainite or martensite. Be perverted. Small amounts of carbide may also be present. The ferrite content of this steel product is at least 60%, preferably at least 70%, more preferably at least 80%. The average grain size of the steel product obtained is less than 5 μm, preferably less than 2 μm, more preferably less than 1 μm.

In conventional steel plates, for example carbon-manganese or HSLA-steel, the starting point is a continuous cast slab having a thickness of 200 to 350 mm. These slabs are reheated in a reheat furnace to a temperature of 1000 to 1350 ° C. After reheating, these slabs are rolled to 20 to 200 mm, preferably 40 to 150 mm and shielded and held at that temperature instead of cooling. During this holding period at high temperatures, crystal growth occurs which deteriorates the mechanical properties of the final product. In common knowledge, large grain sizes reduce the ductility and toughness of steel products. In addition, the yield strength is decreased by increasing the grain size. Therefore, crystal growth during maintenance should be avoided. However, the use of accelerated cooling has the drawback of increasing the temperature difference between the center portion of the slab and the surface portion of the slab. This temperature difference adversely affects the homogeneity of the final microstructure of the slab.

In many cases, the plates are subjected to heat treatment during product manufacture. This can be, for example, a normalization treatment in which the slab is reheated to an austenite zone and cooled by air or tempering anneal or stress relief anneal to reduce the value of internal stress. Another example of heat treatment is spheroidisation treatment in which the expanded carbide is transformed into constituent particles. These carbides may be iron carbides (ie cementite) or other metal carbides such as chromium carbides. This form of annealing is often used in steels with carbon contents greater than 0.8%. Unfortunately, most of these heat treatments, in particular spheroidization, require a long time, which decarburizes the surface of the strip and adversely affects its properties.

The rolling according to the invention can be carried out at low temperatures between 0 and 720 ° C. The particular benefit from this rolling is that it can be carried out at low temperatures (cold rolling), thus disrupting the production of undesirable particles. By breaking up these undesirable particles, the final properties of the steel product are improved. Shear resulting from breaking up undesirable particles in steel products can result in improved toughness, for example with metal carbides such as cementite or chromium carbides. Particle splitting also affects the heat treatment reaction of steel products. The difference between the heating and cooling periods can be employed to obtain an overall improved or improved product through the heat treatment step, i.e., spheroidizing annealing.

The process according to the invention can be treated by heat treatment of steel products. Examples of these heat treatments are known soaking treatments, stress relief annealing treatments, temper annealing treatments or spheroidizing annealing treatments.

In the context of the present invention, steel products comprise steel in which one or both surfaces of the steel to be rolled are covered with one or more layers prior to rolling according to the invention. Combinations of steel products coated with one or both surfaces with one or more metal layers are commonly referred to as clad plates or strips. In the manufacture of clad plates, there are three choices for the clad metal to be bonded to the steel substrate: exposed joint, rolled joint and weld lamination. One of the important factors affecting the quality of the clad is the adhesion quality between the substrate and the clad layer. This is a problem that in conventional rolling, the clad plate is produced by roll bonding because the stress state at the interface between the substrate and the clad layer or clad layer is only compression. According to an embodiment of the invention, the surface of the rolled steel product is covered with one or more layers before rolling. The coating layer may be a metal, preferably steel or stainless steel of different composition, titanium, nickel, copper, aluminum or alloys thereof. This makes it possible to produce laminate materials such as, for example, known clad materials for use in pipes and pipelines, chemical plants, power plants, vessels, pressure vessels.

The invention also relates to an improved metal plate or strip produced by continuous casting, in addition to the method according to the first aspect of the invention, the pores in the core of the plate or strip have a maximum size of less than 200 μm, preferably Has less than 100 μm, more preferably less than 20 μm, even more preferably less than 10 μm. As a result of continuous casting, continuous casting plate and strip materials always have pores considerably larger than 200 μm. Standard rolling operations do not seal these pores in the core to some extent or at all. The rolling operation according to the invention makes it possible to provide continuous casting plates and strips with very small pores.

The present invention also relates to an improved metal plate or strip produced by continuous casting, in addition to the method according to the first aspect of the invention, after the recrystallization the metal plate or strip is substantially uniform over the entire thickness. It has a degree of crystallinity. As a result of the rolling operation according to the present invention, all sheared crystals (including those in the core) will be recrystallized over the entire thickness of the continuous cast plate and strip material.

The invention also has a thickness between 10 and 300 mm, preferably between 20 and 160 mm, for example 60 mm, for example for use in buildings, bridges, earth mobile devices, pipelines, offshore structures and the like. A steel product produced according to the invention.

The invention also relates to steel billets produced according to the invention, for example for use as starting materials for the production of steel sections, for example H-sections.

The steel products produced according to the invention have a starting point of steel ingots, and the pores in the core of the steel products have a maximum size of less than 200 μm, preferably less than 100 μm, more preferably less than 20 μm, even more preferably 10 μm. In addition to having less than, the pores in the core of the plate or strip of the steel product produced by continuous casting and treated according to the invention have a maximum size of less than 200 μm, preferably less than 100 μm, more preferably less than 20 μm. More preferably less than 10 μm.

The invention also relates to steel strips produced according to the invention for use in parts of automobiles, transportation equipment, piling, buildings, structures, for example, and pipes, chemical plants, power plants, vessels, pressure vessels and the like. Regarding clad steel products and steel strips for use, the steel is an HSLA-steel comprising at least one of niobium, titanium, vanadium or boron, or the steel is at least partially stabilized with at least one of titanium, niobium or boron Ultra low carbon steel.

The invention will be described with reference to the preferred embodiments.

Experiments were carried out using slabs of titanium stabilized ultra low carbon steel, carbon-manganese steel and niobium microalloy HSLA-steel.

The slab was introduced with an angle change of 5 ° to 45 °. The temperature of the slab when introduced into the rolling apparatus was about 1000 ° C. Two rolls were driven at a speed of 5 revolutions per minute.

After rolling, the slab had some curved surface which was very dependent on the angle of introduction. The linearity of the slab after rolling can be determined by the angle of introduction, and the optimum angle of introduction will depend on the rolling reduction of the slab, the shape and temperature of the material and alloy. For the rolled steel slab in the above embodiment, the optimum introduction angle is about 20 degrees.

A shear angle of 20 ° was measured in the steel slab rolled according to the above-described example. Using this measurement and the slab size reduction, the equivalent strain can be calculated according to the following equation (1).

It is possible that this equation represents a deformation in one size, and was described in 1997 by R. H. Wagner and J. L. Known in the book "Fundamentals of metal forming" by Chennut, John Willy & Sons.

Therefore, in the slab rolled according to the embodiment, the equivalent strain is the following formula (2).

In the case of rolling with an ordinary rolling mill, shearing does not occur across the thickness of the plate, and the equivalent stress follows the equation (3).

(Machining over the entire thickness of steel products based on uniform stress)

Thus, the rolling using the process according to the invention obtains 3 to 4 times more equivalent strain than conventional rolling without any difference in circumferential speed. Higher equivalent strain means less porosity in the slab, greater recrystallization, and therefore larger grain refinement, and broader secondary phase particle (component particle) breakdown in the slab. These effects are generally known by those skilled in the art. The rolling according to the invention thus obtains the properties of the material greatly improved as a result of the use of the method according to the invention.

Claims (32)

In a method of manufacturing a steel product passing between a pair of rotating rolls of a rolling mill stand for rolling, The roll of the rolling mill stand is one roll is a high speed moving roll, the other roll has a different circumferential speed as a low speed moving roll, The circumferential speed of the high speed moving roll is at least 5% and at most 100% higher than the low speed moving roll, The thickness of the steel product is reduced by up to 15% per pass, Said rolling is carried out at a temperature of up to 1350 ° C. The method of claim 1, Wherein the thickness of the steel product is reduced to a maximum of 8% per pass, preferably at a maximum of 5% per pass. The method according to claim 1 or 2, The circumferential speed of the high speed moving roll is up to 50%, preferably up to 20% than the low speed moving roll. The method according to any one of claims 1 to 3, And said rolling mill is designed in such a way that said rolls have different diameters. The method according to any one of claims 1 to 4, Said rolls having different rotational speeds. The method according to any one of claims 1 to 5, The steel product is introduced between the rolls at an angle of between 5 and 45 degrees, preferably between 10 and 25 degrees, more preferably between 15 and 25 degrees with respect to the perpendicular of the plane passing through the central axis of the roll. Steel product manufacturing method. The method according to any one of claims 1 to 6, Wherein said rolling operation is repeated one or more times after rolling is performed once. The method of claim 7, wherein Said steel product passes said rolling mill stand in opposite directions per each pass. The method of claim 7, wherein Wherein said steel product passes continuously through at least two rolling mill stands. The method according to any one of claims 1 to 9, 10. A method for producing a steel product, characterized in that the rolling operation according to any one of claims 1 to 9 is performed by a rolling operation in which the roll is performed using a rolling mill having substantially the same circumferential speed. The method according to any one of claims 1 to 10, Wherein said rolling is carried out on a steel product having at least the surface layer substantially austenite structure, preferably on a steel product having substantially austenite structure throughout. The method according to any one of claims 1 to 10, The rolling is carried out on a steel product having at least the surface layer substantially of the austenite-ferrite two-phase structure, preferably on the steel product having the austenite-ferrite two-phase structure substantially throughout. . The method according to any one of claims 1 to 10, Said rolling is carried out on a steel product having at least a surface layer substantially ferritic on a steel product, preferably a steel product having ferritic structure substantially throughout. The method according to any one of claims 1 to 10, Wherein said rolling is carried out while the temperature of the steel product is higher than 0 ° C. and lower than 720 ° C. The method of claim 14, Wherein said rolling is carried out on a steel product having a substantially martensite structure. Continuous casting of steel strands; Selectively heating and / or temperature equalizing the steel strand between a casting machine and a rolling device; Optionally rolling the steel product in one or more rolling mill stands of the rolling apparatus with rolls having substantially the same circumferential speed; Optionally accelerated cooling after the final rolling step; Selectively cutting the steel product into slabs or coils before or after rolling; Optionally winding the steel product; -Cooling the steel product In the steel product manufacturing method comprising a, The steel product manufacturing method according to any one of claims 1 to 10, wherein the steel product is carried out between the strand casting step and the accelerated cooling step or the winding step or the cooling step, or after the cooling step. The method of claim 16, The thickness of the cast strand is less than 150 mm, preferably less than 100 mm, more preferably less than 80 mm. The method of claim 16, The thickness of the cast strand is less than 20 mm, preferably less than 10 mm, more preferably less than 5 mm. The method according to any one of claims 16 to 18, The steel product manufacturing method, characterized in that the stainless steel product. The method according to any one of claims 16 to 19, The rolling is carried out on steel products having substantially austenite structures, The steel is accelerated cooled in a subsequent process, Steel products essentially comprise ferrite, bainite and / or martensite, The ferrite content after cooling is at least 60%, preferably 70% or more, more preferably 80% or more. The method according to any one of claims 16 to 20, A method for producing steel products, characterized in that the average grain size of the steel product is less than 5 μm, preferably less than 2 μm, more preferably less than 1 μm. The method according to any one of claims 1 to 21, Wherein said steel product is subjected to a heat treatment of a soaking treatment, a complete annealing, a stress relief annealing or a spheroidizing annealing treatment before or after the rolling step. The method according to any one of claims 1 to 21, The surface of the steel product to be rolled is coated with at least one layer before rolling. The method of claim 23, wherein Said coating layer is a metal, preferably steel or stainless steel of different composition, titanium, nickel, copper, aluminum or an alloy thereof. Claim 1 to claim 1 having a thickness of between 10 and 300 mm, preferably between 20 and 160 mm, for example 60 mm, for use in buildings, bridges, earthmoving installations, pipelines, shipbuilding and offshore structures. Steel products manufactured according to the method of any one of 24. The steel product produced according to the method of claim 1, wherein the steel product is a steel billet. Steel section, such as an H-section, made using the billet according to claim 26. A steel product made according to the method of any one of claims 1 to 24, wherein The starting point is the river ingot, A steel product characterized in that the pores in the core of the steel product have a maximum size of less than 200 μm, preferably less than 100 μm, more preferably less than 20 μm, even more preferably less than 10 μm. The pores in the core of the plate, strip or billet produced by continuous casting using the method of any one of claims 1 to 10 have a maximum size of less than 200 μm, preferably less than 100 μm, more preferably 20 Steel plate, strip or billet characterized in that less than 10 μm, more preferably less than 10 μm. A steel strip manufactured according to the method of any one of claims 16 to 21 and used as part of automobiles, transportation equipment, piling, buildings, structures. Clad steel prepared according to claim 23 or 24 and used in pipes, chemical plants, power plants, vessels, pressure vessels. A steel strip made according to any of claims 16, 17, 18 or 21, The steel strip is characterized in that it is an HSLA-steel comprising at least one of niobium, titanium, vanadium or boron or an ultra low carbon steel which is at least partially stabilized or preferably has at least one of titanium, niobium or boron.