BRPI1101419A2 - a forged roll that meets the requirements of the cold rolling industry and a method for producing such a roll - Google Patents

Abstract

A FORGED ROLL MEETING THE REQUIREMENTS OF THE COLD LAMINATION INDUSTRY AND A METHOD FOR PRODUCING SUCH ROLL. This invention generally relates to the field of forged rollers and the production of forged rollers. More particularly the present invention relates to forged rollers for use in the cold rolling industry. The present invention relates to a forged roll for use in the cold rolling industry and a method for producing such a roll. Said forged roll comprises a steel composition and a microstructure comprising: - tempered martensite with a retained austenite rate of less (<) 5% by volume; and - an open eutectic carbide network with eutectic carbides of less than (<) 5% by volume; and wherein the roll exhibits: a hardness between 780-840 HV; and - internal compressive stresses between -300 and -500 MPa in absolute values.

Description

"A FORGED ROLL THAT MEETS THE REQUIREMENTS OF THE COLD LAMINATION INDUSTRY AND A METHOD FOR THE PRODUCTION OF SUCH

ROLL"

Invention field

This invention generally relates to the field of forged rollers and the production of forged rollers. More particularly the present invention relates to forged rollers which satisfy the requirements of and principally being directed for use in the cold rolling industry.

Background

General Background

The general trend for cold rolling development for both ferrous and nonferrous metal industries is to laminate faster, thinner and wider. The current challenge is to do this while achieving perfect control of planing, thickness and surface aspects compatible with high productivity. Therefore, this trend requires the use of advanced lamination technologies that control key lamination parameters.

Some key parameters such as roughness retention and surface aspects can be ensured by working roller chrome plating. This practice is effective and efficient but is becoming more and more questionable and in the near future unacceptable due to environmental constraints.

Forged (2 to 6% Cr) surface-chromed work rollers are usually used in cold rolling processes. The chrome plating of such rollers is applied 2/54

improve wear resistance in terms of surface texture retention which in turn will ensure

* bodies after painting. Deposit Techniques

■ m-

hard electrolytic as chrome plating were initially

*

developed for laminating / tempering box rolling mill applications. In these applications, chromed work rollers exhibit 2 to 8 times longer lifespan than uncoated rollers, mainly because of better roughness retention. The implementation of this technique has been progressively extended to reduction rolling mills.

There are also forged rollers made of high speed steel (HSS) which are made for uncoated use, but there is a need for a roll with low residual internal stresses and there is also a need for an industrial process to produce such a roll which is intended for be used uncoated on a rolling mill while giving roughness retention that is at least equivalent to that of coated rollers.

Specific Background

Rolls produced for use within the cold rolling industry must manage specific processing conditions or operating stresses during use without cracking or being prone to exploding. Exploding a roll may involve worker safety and collateral damage to the rolling mill. Therefore, there is a need for a roll with low residual internal stresses. Prior Art

Examples of the prior art disclosing the development towards uncoated HSS rolls for the purpose of cold rolling:

C. Gaspard, C. Vergne, D. Batazzi, T. Nylen, P.H. Bolt, S. Mui, K.M. Reuver: "Implementation of in-service key parameters of HSS work roll grid dedicated to advanced cold rolling", IST Conference May 3-6, 2010, Pittsburgh, Pa, USA

C. Gaspard, S. Bataille, D. Batazzi, P.Thonus: "Improvement for Advanced Cold Rolling Reduction Mills by Using Semi-HSS and HSS Rolls", Ith International Conference on Steel Rolling (ISIJ), Makuhari, Chiba, Japan, 1998

P.H. Bolt, D. Batazzi, N.P. Belfiore, C. Gaspard, L. Goiset, M. Laugier, O. Lemaire, D. Matthews, T. Nylén, K. Reuver, D. Stocchi, F. Stork, J. Tensen, M. Tornicelli, R. Valle, E. van den Elzen, C. Vergne, IM Williams: "Damage Resistance and Roughness Retention of Work Rolls in Cold Rolling Mills", 5th European Rolling Conference, June 23-25, 2009, London, UK

Other examples of the prior art are shown in the patent publications: JP09003603, JP53077821, JP57047849, JP2002285284, JP2002285285, JP10317102, JP1208437, EP0395477 and JP08158018 which describe cold rolling work rollers to reinforce wear and tear resistance.

However, these prior art parts lack the disclosure of parameters and properties necessary to achieve and enable such an HSS roll that is operative during conditions in a cold rolling mill. Object of the invention

General Object

The general object of the invention is to provide a roller and an industrial process for producing such a roller which is operative during conditions in a cold rolling mill, preferably in an uncoated form. A more specific object is to provide such a roll and process for producing such a roll while maintaining tribological properties such as low friction coefficient, high roughness retention, no fine iron dust pollution at least equivalent to prior art coated rollers and exhibit improved rolling mill performance in terms of higher crack resistance and higher operating safety compared to known rollers.

Partial Problems

The invention still seeks to solve partial problems

in:

-Improve roller surface which gives the roller a higher performance.

-Avoid roll fragmentation accidents

-Avoid non-environmental lamination production processes

-Improve rolling distance or roll life by allowing longer runs per rolling mill campaign.

Summary of the invention

The solution to the problem, partial problems and aspects listed above is a roll according to the invention with improved heat crack resistance and low crack propagation that will reduce rolling mill incident sensitivity while maintaining higher wear resistance.

The present invention provides a forged roll for use in the cold rolling industry and a method for producing such a roll. The roll is preferably uncoated, but may also be coated.

A first aspect of the invention relates to a forged roll comprising a steel composition comprising, in terms of% by weight,

0.8 to less than (<) 1% C, 0.2 to 0.5% Mn, 0.2 to 2.0% Si, 7.0 to 13.0% Cr from 0.6 to 1.6% Mo, more than (>) 1.0 to 3.0% V, the remaining portion of the steel being substantially Fe and possible incidental and / or possibly unavoidable impurities;

and wherein the roller microstructure comprises:

- tempered martensite with a retained austenite rate of less than (<) 5% by volume; and

- an open eutectic carbide network with eutectic carbides of less (<) 5% by volume;

and where the roll displays:

- a hardness between 780 HV to 840 HV; and

- internal compressive stresses between -300 MPa to -500

MPa.

In other embodiments of the invention, the roller of the invention comprises an open eutectic carbide mesh that delimits a eutectic cell-like pattern.

Additional roll varieties comprising any of the following optional, individual or combinable aspects:

A roller wherein the open eutectic carbide mesh of said roller comprises dendritic arms.

A roll wherein the open eutectic carbide web of said roll is formed as substantially insulated portions of eutectic carbide web.

A roll wherein the microstructure of said roll is present at least in the working layer of the roll.

A roll with a steel composition consisting in terms of% by weight;

from 0.8 less than (<) 1% C,

from 0.2 to 0.5% Mn,

from 0.2 to 2.0% Si,

from 7.0 to 13.0% Cr,

from 0.6 to 1.6% Mo,

more than (>) 1.0 to 3.0% of V,

less than (O 0,015% P, and less than (<) 0,015% S, and less than (O 1% Ni less than (O 30 ppm of 02, and less than (O 100 ppm of N2, and less (<) 3 ppm H2 less than (O 2% W, and less (O 1% Nb, and less than (<) 1% Ti, and less than (O 0.5% Ta, and less than (<) 0.5% Zr, the remaining portion of the steel being substantially Fe and possible incidental and / or possibly unavoidable impurities;

The roll according to the invention, wherein the C content in the steel composition is between 0.8 - 0.99% C in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the C content in the steel composition is between 0.85 - 0.9% C in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the Mn content in the steel composition is between 0.4 - 0.5% Mn in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the Si content in the steel composition is between 0.2 - 1.5% Si in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the Si content in the steel composition is between 0.85 - 1.15% Si in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the Cr content in the steel composition is between 7.0 - 11% Cr in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the Cr content in the steel composition is between 7.3 - less than (<) 8.0% Cr in terms of wt% of the total weight of the roll.

The roll according to the invention, wherein the Mo content in the steel composition is between 1.45 - 1.55% Mo in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the Ni content in the steel composition is less than (<) 0.3 Ni in terms of% by weight of the total weight of the roll. The roll according to the invention, wherein the content of V in the steel composition is between 1.3 - 2.1% V in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the content of V in the steel composition is between 1.3 - 1.6% V in terms of% by weight of the total weight of the roll.

A roller according to the invention, wherein the steel composition consists, in terms of% by weight:

the remaining portion of the roll being substantially Fe and possible incidental and / or possibly unavoidable impurities.

A roller according to the invention, wherein the steel composition consists, in terms of% by weight:

10

15

0.8 - 0.99% C, and

0.4 - 0.5% Mn, and

0.2 - 1.5% Si, and

7.0 - 11% Cr, and

of 0.6 - 1.6% Mo, and

less than (<) 1.0 Ni, and

1.0 - 2.1% of V, and

20

less than (<) 0.015% P, and

less (<) 0.015% S, and

less (<) 30 ppm than 02, and

less (<) 100 ppm N2, and

less (<) 3 ppm H2, and

0.85 - 0.9% C, and

0.4 - 0.5% Mn, and

0.85 - 1.15% Si, and

7.3 - less than (<) 8.0% Cr, and

30

1.45 - 1.55% Mo, and less (<) 0.3 Ni, and 1.3 - 1.6% V and less (<) 0.015% P, and less than (<) 0.015% S, and less (<) 30 ppm 02, and less (<) 100 ppm N2, and less (<) 3 ppm H2, and the remaining portion of the roll being substantially Fe and possible incidental and / or possibly unavoidable impurities.

A roller according to the invention further being configured for use as a cold rolling working roller.

A roller according to the invention further having a weight of over 400 kg.

A roller according to the invention further having a diameter in the range of 215-800 mm.

A further aspect of the invention provides a forged roll produced by a process comprising the steps of:

The. To provide a steel composition comprising by weight 0.8% less than (<) 1% C, 0.2 to 0.5% Mn, 0.2 to 2.0% Si, from 7.0 to 13.0% Cr, from 0.6 to 1.6% Mo, more than (>) 1.0 to 3.0% V,

the remaining portion of the steel being substantially Fe and possible incidental and / or possibly unavoidable impurities; In other embodiments, the composition according to the invention is like any of the compositions or combinations of compositions described above.

B. Fabricate an ingot maintaining a solidification rate greater than 15 ° C / min in the ingot surface layer, equivalent to the roll surface layer, in the solidification range;

ç. Forge the ingot to a roll;

d. Harden the roller by induction heating;

and. Season the roll;

thereby achieving a roller microstructure comprising:

tempered martensite with a retained austenite rate of less (<) 5% by volume; and

- an open eutectic carbide net with eutectic carbides of less (<) 5% by volume;

and where the roll (1) displays:

- a hardness of between 780 HV to 840 HV; and

- internal compressive stresses between -300 MPa to -500 MPa.

Additional roll varieties comprising any of the following individual or combinable optional aspects with respect to the chemical composition or microstructure of the roller mentioned above and further comprising the characteristics of any of the following individual or combinable optional aspects mentioned below.

A further aspect of the invention provides a process for making an unforged roll according to the invention, the process comprising the steps of:

The. To provide a steel composition comprising by weight 0.8% less than (<) 1% C, 0.2 to 0.5% Mn, 0.2 to 2.0% Si, from 7.0 to 13.0% Cr, from 0.6 to 1.6% Mo, more than (>) 1.0 to 3.0% V,

the remaining portion of the steel being substantially Fe and possible incidental and / or possibly unavoidable impurities; In other embodiments the composition according to the invention is like any of the combinations of compositions described above.

B. Fabricate an ingot while maintaining a solidification rate greater than 15 ° C / min in the

ingot work, equivalent to the layer of

roll work in the solidification range;

ç. Forge the ingot to a roll;

d. Harden the roller by induction heating;

and. Temper the roller at a temperature between 450-5300C to reach hardness between 780 HV to 840 HV;

thereby achieving a microstructure of the roller (1) comprising:

tempered martensite with a retained austenite rate of less (<) 5% by volume; and - an open eutectic carbide network with carbides

eutectics of less than (<) 5% by volume; and where the roll (1) displays:

- a hardness of between 780 HV to 840 HV; and

- internal compressive stresses between -300 and -500 MPa.

5th

Additional roll varieties comprising any of the following optional, individual or combinable aspects mentioned below.

A process according to the invention wherein the ingot is manufactured by maintaining a solidification rate in the working layer as well as in the core in the range of 15 ° C / min to 55 ° C / min, or alternatively 17 ° C / min. ° C / min, or alternatively 35 ° C / min - 55 ° C / min, or alternatively 45 ° C / min - 55 ° C / min.

A process according to the invention, wherein the ingot is manufactured by maintaining a solidification rate greater than 35 ° C / min in the working layer or surface of the ingot in the solidification range.

A process according to the invention wherein the solidification range is between 1400-1200 ° C for said ingot.

A process according to the invention, wherein the ingot is manufactured by maintaining a preselected solidification rate in an electro-slag refining furnace (ESR) process by controlling the ampere current supply according to a function. predetermined solidification rate.

A process, wherein the step of forging the ingot to a roll comprises the steps of:

The. Heat the ingot to a temperature of approximately 850-100 ° C or 800-100 ° C, preferably for a period of approximately 6 hours;

B. Forge the ingot at a temperature above about 8000C or above 850 ° C; ç. Repeat steps a-b until the ingot has been formed into a roll of the desired shape and size.

An additional process after the forging step comprising a preliminary heat treatment step applied to the blank of the roll, preferably to a temperature of approximately 700-1100 ° C or between 800 - 900 ° C, which may include the treatment of hydrogen diffusion.

A process further comprising a step-step hardening by progressive induction heating, preferably at a temperature of approximately 900-1150 ° C.

A process in which the tempering roll step comprises the steps of:

d. Heat the roller to approximately 450 - 530 ° C or 450 - 520 ° C, preferably 3 times,

and. Cool the roller between the heating steps with air.

A process further comprising machining the roll to texturize a white layer comprising eutectic carbides.

Additional varieties of the process of the invention comprising any of the following individual or combinable optional aspects with respect to the chemical composition or microstructure of the roller mentioned above and further comprising the characteristics of any of the following individual or combinable optional aspects mentioned below.

A further aspect of the invention provides an ingot of intermediate product in the production of a roll, the ingot comprising a steel composition comprising, in terms of% by weight,

0.8 to less than (<) 1% C, 0.2 to 0.5% Mn, 0.2 to 2.0% Si, 7.0 to 13.0% Cr from 0.6 to 1.6% Mo, more than (>) 1.0 to 3.0% V, the remaining portion of the steel being substantially Fe and possible incidental and / or possibly unavoidable impurities;

and wherein the final roll microstructure resulting from the ingot comprises:

tempered martensite with a retained austenite rate of less (<) 5% by volume; and

- an open eutectic carbide net with eutectic carbides of less (<) 5% by volume.

Additional varieties of the intermediate ingot of the invention comprising any of the following individual or combinable optional aspects with respect to the chemical composition of the aforementioned ingot and further comprising the characteristics of any of the following individual or combinable optional aspects mentioned below.

A further aspect of the invention provides the use of a forged roll according to the invention for cold rolling material which requires a high rolling load.

Other embodiments of the invention provide the use of a cold rolled forged roll of high strength materials such as AHSS steel grades. The use of a forged roller according to the invention for a selection of:

- Cold-rolling reduction laminators for initial and finishing chairs, reversible and non-reversing tinplate chairs, sheets, silicon steel, stainless steel, aluminum and copper; or

- Laminators with lamination box and / or cold rolling temper; or

- Laminator configurations such as 2-High, 4- High and 6-High chairs with textured or non-textured surface.

The use of a forged roller according to the invention as a working roller.

The roller according to the invention is useful in many applications as an uncoated roller. However, in further aspects and embodiments of the invention, the roller may also be provided with a cover selected for any specific chain or application. The cover may, for example, be a chrome overlay. The roller can also be used in warm rolling applications.

Brief Description of the Figures

The invention will be further described by exemplary embodiments wherein:

Figure 1 shows a schematic illustration of a roller according to the invention.

Figure 2 shows a schematic view of the roll production process according to the invention.

Figure 3 shows a schematic illustration of an ingot according to the invention. Figure 4 shows a manufacturing process of an ingot according to the invention.

Figure 5A-B shows a roll grade fused microstructure made using a production process according to the invention. The degree of roll is shown in sectional view of the working layers of the degree of roll.

Figure 6A-B shows a roll grade cast microstructure made using a production process according to the invention. The degree of roll is shown in sectional view of the working layers of the degree of roll.

Figure 7 shows roll grade cast microstructure made using a production process according to the invention, but with the deviation shown when a very low solidification rate is used. The degree of roll is shown in sectional view of the working layers of the degree of roll.

Figure 8 shows a first set of examples of solidification rates for the roll production process according to the invention.

Figure 9 shows a second set of examples of solidification rates for the roll production process according to the invention.

Figures 10A-B show a fused microstructure of an ingot made under laboratory conditions when the production process according to the invention is used.

Figures 11A-B show a fused microstructure of an ingot made under laboratory conditions when the production process according to the invention is used, but with the deviation shown when a very high Mo content is used. Figure 12 shows a schematic view of forging according to the invention.

Figure 13 shows a schematic view of the steps of ingot formation by forging it into a roll according to the invention.

Figure 14 shows a schematic view of progressive induction hardening at different frequencies of the roller according to the invention.

Figure 15A-B shows a surface microstructure of a roll according to a standard degree after surface texturing (EDT texturing).

Fig. 15 C-D shows a surface microstructure of a roller according to the invention after surface texturing (EDT texturing).

Figure 16 A-D shows detrimental defects in a roll generated during the manufacture of low chromium content and high molybdenum content rolls.

Figure 17A shows one embodiment of a microstructure according to the invention with an open eutectic network.

Figure 17B shows an example of a microstructure with a closed eutectic network in which the eutectic carbs 200 form a closed eutectic network with clearly separated eutectic cells 212.

Figure 18 shows an example depicting the microstructure of a roller surface according to the invention after Electric Discharge Texturing.

Figure 19 shows the microstructure of the roll at a depth of 4 mm on the roll surface after hardening and induction hardening of the roll. Detailed Description

Introduction

The invention generally relates to a forged roll 1 which preferably has a weight of over 400 kg, or, as in embodiments for common applications, for example, a weight of over 1000 kg. The roll according to the invention is produced according to a forged roll production method which in its general stages is known per se, but is specifically adapted according to the inventive concept of being able to produce a roll according to the invention. the invention.

The invention is primarily directed to rollers weighing between 400 kg and 10000 kg. The roll according to the invention has a diameter 2 typically of more than 200 mm and, for example, between 215-800 mm, and a length of cylinder 8 typically between 1-3 meters and a maximum length of typically approximately 6 meters including the necks 10. Roll 1 has a working layer 4 which corresponds to a portion of the outer layer and is typically in the range of 20 mm to 120 mm in diameter, dependent upon the application of the specific roller and / or dependent on the diameter of the total roller. 2. Commonly, outer diameter 1/6 part 6 of roll 2 is referred to as working layer 4 of roll 1, see Figure 1. External 1/6 part 6 of diameter 2 of ingot 34 is also referred to as working layer 4 of ingot 34 in the text.

There are special problems and challenges involved in making large forged rollers due to the internal stresses involved when these large roll pieces are formed. A roll with a smaller diameter would not need the same treatment because then the internal stresses would be lower and those rolls would not be as likely to explode during hardening.

The production process of roll 12 according to the invention is crucial for manufacturing a roll 1 of this size according to the invention. Improved mechanical properties such as low residual internal tensions of the roller of the invention result from the production process of roller 12. In order to achieve the low level of residual internal tensions of the resulting roller, the thermal gradient induced internal stresses and allotropic transformations have to be minimized. at all stages of the production processes through casting, forging, heat treatment and machining. The microstructure of roll 1 according to the invention comprises tempered martensite with a retained austenite rate of less than 5% by volume due to the roll production process and due to the chemical composition according to the invention.

The roller production process according to the invention comprises a selection of the following basic steps schematically shown in the flow diagram of the

Fig 2: 14. Providing a steel composition 16. Fabricating an ingot 34 18. Forging said ingot 34 to a roll 1 20. Preliminary heat treatment of said roll 1 22. Rough machining of said roll 1 24. Induction hardening said roll 1 26. Tempering heat treatment of said roll 1 28. Machining said roll 1

Intermediate products are obtained after the respective steps. Specific control parameters as well as a chemical composition of the roll are selected to produce a roll according to the invention.

Roller production process

The present invention relates to a forged roll (1) produced by a process comprising the steps of:

The. Providing a steel composition comprising, in terms of% by weight,

from 0.8 less than (<) 1% C,

from 0.2 to 0.5% Mn,

from 0.2 to 2.0% Si,

from 7.0 to 13.0% Cr,

from 0.6 to 1.6% Mo,

more than (>) 1.0 to 3.0% of V,

the remaining portion of the steel being substantially Fe and possible incidental and / or possibly unavoidable impurities;

B. Fabricate an ingot by maintaining a solidification rate greater than 15 ° C / min in the working layer of the ingot in the solidification range;

ç. Forge the ingot to a roll;

d. Harden the roller by induction heating;

and. Season the roll;

thereby achieving a microstructure of the roller (1) comprising:

tempered martensite with a retained austenite rate of less (<) 5% by volume; and

- an open eutectic carbide net with eutectic carbides of less (<) 5% by volume;

and where the roll (1) displays:

- a hardness of more than 780 HV; and - internal compressive stresses of less than -500 MPa in absolute values.

Wherein the chemical composition provided according to the invention used in combination with the process steps described according to the invention gives the roller according to the invention the desired properties in the microstructure of the roller according to the invention.

A process of making a forged roll according to the invention comprises the following steps:

Step 14: Provide a steel composition. In one embodiment of the invention the steel composition comprises an alloy comprising or consisting of the following constituents indicated by weight% as listed in Table 1. In Table 1, the impact of the constituents and the inventive roll effect that is achieved by the selected constituents and Specific ranges are explained.

Table 1

Elements of the Chemical Composition Alloy according to the embodiments of the present invention% by weight. Range impact according to the invention C 0.8 - 0.99 Carbon is the most important and influential alloy element in steel. In addition to carbon, however, any unalloyed steel will contain silicon, manganese, phosphorus and sulfur, which occur unintentionally during fabrication. Adding additional alloying elements to achieve special effects and intentional increase in manganese and silicon content results in alloy steel. With increasing C content, steel strength and hardness increase, but its ductility, forgeability, weldability and machinability (using cutting machine tools) are reduced. In the invention the level of C is less than 1% to avoid the formation of very large closed eutectic carbide net. Mn 0.2 - 0.5 Manganese deoxide. Compounds with sulfur to form Mn sulfide, thereby reducing the undesirable effect of iron sulfide. This is of particular importance in free cut steel; reduces the risk of network smallness. Mn very markedly reduces the critical cooling rate, thereby increasing the hardness. Strength and yield point are increased by the addition of Mn, and furthermore Mn favorably affects forgeability and weldability and markedly increases temper penetration depth. In the invention Mn is kept below 0.5% to avoid excessive brittleness. Si 0.2 -2.0 Silicon is contained in all steel in the same way as manganese, since iron ores incorporate an amount of it according to its composition. In steel production by itself, silicon is absorbed in the melting of refractory kiln coatings. But only those steels are called silicon steels that have Si content>> 0.40%. Si is not a metal, but a metalloid as it is, for example, phosphorus and sulfur. Si deoxides. Because of the significant reduction in electrical conductivity, coercive field strength and low voltage loss, Si is used in steels for electrical grade sheets. As a result, in the invention, very high level of Si influences the eddy current response during roll inspection leading to possible false reading and needs to be kept below 1.5% S <0.015 Sulfur produces the most pronounced segregation of all elements. that accompany the steel. Iron sulphide leads to small net or hot brittleness, as low melting sulfide eutectics surround the grains in a reticular manner, so that only a slight cohesion of the latter occurs and during hot formation of the sulphides. Grain boundaries tend to break. This is further increased by the action of oxygen. As sulfur has a considerable affinity for manganese, it is combined in the form of Mn sulfide, since this is the least dangerous of all existing inclusions, being present distributed in point form in the steel. The toughness in the transverse direction is significantly reduced by S. To be kept at the lowest level. P <0.015 Phosphorus is usually considered as a steel parasite, as P produces pronounced primary segregation in fusion solidification and the possibility of secondary solid state segregation due to pronounced gamma phase restriction. As a result of the relatively low diffusion rate in both alpha and gamma crystal, the segregation that has occurred can only be corrected with difficulty. According to the invention, P is to be kept at the lowest level, preferably <0.015 W%. Cr 7.0 - 13.0 Chromium gives oil and air hardenable steels. By reducing the critical cooling rate required for martensite formation, it increases hardness, thereby improving its susceptibility to hardening and tempering. Notch toughness is reduced, however, but ductility suffers only very slightly. The tensile strength of steel increases by 80-100 N / mm2 by 1% Cr. Cr is a carbide former. Their carbides increase cutting capacity and wear resistance. High temperature resistance property is promoted by chrome. The element restricts the gamma phase and thus extends the ferrite range.

With a Cr content greater than 13%, extended eutectic carbides tend to be formed.

With a Cr content of less than 7%, the hardness level remains too low for cold rolling application due to a deficit in secondary hardening mechanisms.

Mo

0.6 - 1.6 Molybdenum is usually bonded together with other elements. Reducing the critical cooling rate improves hardness. Mo significantly reduces temper brittleness and promotes the formation of fine grains. Increase in resistance and yield point. Pronounced carbide former; Fast steel cutting properties are improved in this way. Very severe restriction of the gamma phase. Increased high temperature resistance. With increased Mo content, forging is reduced. As a result, its content is kept below 1.6% to prevent harmful formation of delta ferrite.

Ni

<1.0

Nickel steel produces a significant increase in notch toughness, even in the low temperature range, and is therefore alloyed to increase toughness in heat-treatable cemented steels and sub-zero toughness. Ni is not a carbide former.

V

> 1-3

Vanadium refines the primary grain and thus the foundry structure. Pronounced carbide former, thus providing a hardness level compatible with the cold rolling process, increased wear resistance, high shear capacity and high temperature resistance. It is therefore primarily used as an additional high speed alloying element, hot forming and creep resistant steels. Significant improvement in temper retention, reduced overheat sensitivity. V restricts the gamma phase and changes the Curie point at elevated temperatures. With a V content of less than 1%, the hardness level remains very low compared to the cold rolling process. With a V content of more than 3%, the rectifiability of steel becomes prohibitive for the cold rolling process. W 0.0 - 2.0 Tungsten is a very pronounced carbide former (its carbides are very hard) and restricts the gamma phase. Improves toughness and prevents grain growth. W increases high temperature resistance and temper retention as well as high temperature wear resistance (red heat) and thus cutting capacity. It is therefore primarily bonded to high speed and hot forming tool steels as well as creep and ultra-hard steel resistant steels. Ti 0.0 - 1.0 Titanium because of its very strong affinity for oxygen, nitrogen, sulfur and carbon, Ti has pronounced deoxidation, pronounced denitrification and pronounced carbide forming action. Widely used as carbide former. It also has grain refining properties. Ti restricts the gamma phase very sharply. At high concentration, it leads to precipitation processes and is added to permanent magnet alloys because of the high coercive field strength. Ti increases creep resistance through the formation of special nitrides. Finally, Ti has a pronounced tendency to segregation and folding. Nb 0.0 - 0.5 Niobium (Nb) and Tantalum (Ta) occur Ta 0.0 - 0.5 almost exclusively together and are very difficult to separate from each other, so they are usually used together. Very pronounced carbide formers, thus bonded in particular as chemical resistant steel stabilizers. Both elements are ferrite forming and thus reduce the gamma phase. Due to the increase in high temperature resistance and creep rupture resistance due to Nb. Zr 0.0 - 0.5 Zirconium is a carbide former; metallurgical use as an alloying element for deoxidation, denitration and desulfurization as it leaves minimal deoxidation products behind. Zr additions to free-cutting steels carrying completely deoxidized sulfur have a favorable effect on sulphide formation and thus the prevention of mesh smallness. Increases the life of heating conductive materials and produces gamma phase restriction.

and optionally further comprising H2, N2, O2, Al, Cu, each in amounts less than 0.4 wt%; and wherein the remaining portion of the steel composition is substantially Fe, apart from incidental elements and possibly unavoidable impurities.

In one embodiment of the invention, the steel composition comprises, by weight%, from 0.8 to less than (<) 1% C, from 0.2 to 0.5% Mn,

0.2 to 2.0% Si, 7.0 to 13.0% Cr, 0.6 to 1.6% Mo, more than (>) 1.0 to 3.0% Cr V, wherein the remaining portion of the steel is substantially Fe, apart from incidental elements and possibly unavoidable impurities.

In different embodiments and embodiments of the invention, the composition comprises or consists of a combination or selection of constituents (% by weight) according to the following examples. In some examples, the aforementioned embodiment is combined with, substituted by or restricted by variants below amounts of constituents.

A roll with a steel composition consisting in terms of% by weight;

from 0.8 less than (<) 1% C,

from 0.2 to 0.5% Mn,

from 0.2 to 2.0% Si,

from 7.0 to 13.0% Cr,

from 0.6 to 1.6% Mo,

more than (>) 1.0 to 3.0% of V,

less than (O 0.015% P, and less than (O 0.015% S, and less than (O 1% Ni less than (<) 30 ppm O2, and less than (<) 100 ppm N2), and less than (<) 3 ppm H2 less (<) 2% W, and less (<) 1% Nb, and less (<) 1% Ti, and less (<) 0.5 % Ta, and less than (<) 0.5% Zr,

the remaining portion of the steel being substantially Fe and possible incidental and / or possibly unavoidable impurities;

The roll according to the invention, wherein the C content in the steel composition is between 0.8 - 0.99% C in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the C content in the steel composition is between 0.85 - 0.9% C in terms of% by weight of the total weight of the roll. The roll according to the invention, wherein the Mn content in the steel composition is between 0.4 - 0.5% Mn in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the Si content in the steel composition is between 0.2 - 1.5% Si in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the Si content in the steel composition is between 0.85 - 1.15% Si in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the Cr content in the steel composition is between 7.0 - 11% Cr in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the Cr content in the steel composition is between 7.3 - less than (<) 8.0% Cr in terms of wt% of the total weight of the roll.

The roll according to the invention, wherein the Mo content in the steel composition is between 1.45 - 1.55% Mo in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the Ni content in the steel composition is less than (<) 0.3 Ni in terms of% by weight of the total weight of the roll.

The roll according to the invention, wherein the content of

V in the steel composition is between 1.3 - 2.1% V in terms of% by weight of total roll weight.

The roll according to the invention, wherein the content of

V in the steel composition is between 1.3 - 1.6% V in terms of% by weight of total roll weight.

A roller according to the invention, wherein the steel composition consists, in terms of% by weight:

0.8 - 0.99% C, and

0.4 - 0.5% Mn, and 0.2 - 1.5% Si, and 7.0 - 11% Cr, and 0.6 - 1.6% Mo, and less than (O 1.0 Ni, and 1.0 - 2.1% V, and less than (O 0.015% P, and less (<) 0.015% s, and less than (<) 30 O 2 ppm, and less than (O 100 ppm N 2, and less than

the remaining portion of the roll being substantially Fe and possible incidental and / or possibly unavoidable impurities.

A roller according to the invention, wherein the steel composition consists, in terms of% by weight: of 0.85 - 0.9% of C, and of 0.4 - 0.5% of Mn, and of 0.85 - 1.15% Si, and 7.3 - less than (<) 8.0% Cr, and 1.45 - 1.55% Mo, and less than (<) 0, 3 of Ni, and 1.3 - 1, 6% V and less (<) 0.015% P, and less (<) 0.015% S, and less (<) 30 ppm O2, and less than (<) 100 ppm N 2, and less than (<) 3 ppm H 2, and the remaining portion of the roll being substantially Fe and possible incidental and / or possibly unavoidable impurities. Step 16: Fabricate 16 of a Cylindrical Ingot 34

In a typical application of the invention, an intermediate product, ingot 34 produced according to the method of the invention preferably has a diameter 32 of between 450 and 1100 mm, length 30 to 6 meters and weight between 400 and 30000 kg, see figure 3. The method of making an ingot 34 according to the invention involves the use of a technique that allows rapid cooling during the manufacture of the ingot 34. For example, the ingot 34 may be produced using different ingot forming techniques. Suitable manufacturing techniques are those that are capable of being controlled to achieve and maintain a specific minimum solidification rate.

According to embodiments of the invention, the average solidification rate is controlled to be above 15 ° C / min on the surface and preferably also above 10 ° C / min on the core during ingot formation. Preferably, this solidification rate is maintained while controlling the cooling of the ingot material in the solidification range which may, for example, be between 1400 ° C to 1200 ° C. In other embodiments of the invention, the average solidification rate is controlled to be greater than 35 ° C / min in the working layer in the solidification range.

From a practical point of view it is generally difficult to achieve very high solidification rates when the invention is implemented. Additional embodiments of the invention comprise the average solidification rate in the working layer as well as in the core is controlled to be in the range of 15 ° C / min to 55 ° C / min, or alternatively 35 ° C / min - 55 ° C / min, or alternatively 45 ° C / min - 55 ° C / min.

Techniques that are used in the invention to control the process with respect to solidification parameters according to the invention are, for example, different types of electroslag refining furnace (ESR), for example melt ESR melting techniques. movable mold or ESR plating or spray forming etc.

An ingot made using a solidification rate and a chemical composition as described in any of the above embodiments according to the invention has the following characteristics:

-Very thin dendritic macrostructure.

-Uniformity of chemistry.

-Lack of macro segregations and dark lode in the intermediate layers.

-No minor segregations.

Furthermore, an ingot made using a process according to the invention has the following advantages over the rolled product:

Elimination of the "orange skin" effect (consists of the appearance of dendrite patterns due to the difference in wear of the interdendritic area).

- No problems with pin hole.

- Very bright surface finish.

-Homogeneity of texture obtained by texturing.

-Lack of marks related to heterogeneity

of the structure.

In one embodiment of the invention an electro-slag refining furnace (ESR) is used to manufacture the ingot 34 according to the invention, for a schematic view see figure 4.

Electro-slag refining furnace (ESR) is capable of melting approximately 300-1100 kg / h, and comprises an electrode clamp 36, a stinger 38, an electrode 40, a cooling jacket outlet 42, an cooling jacket 50 to cool water. In the ESR, the ingot is formed by melting the electrode 40 and thus different layers are formed in the ingot material 48 such as a slag reservoir 44, which is located next to the electrode, and a molten metal reservoir 46.

The ESR also comprises a starter plate 52 which is water cooled 54, see Figure 4. The ESR technique may require a starter ingot (electrode 40) obtained by a conventional casting process to be melted to form a Ingot 48 according to the invention. Re-melting using ESR is carefully controlled to achieve the average solidification rate according to embodiments of the invention, for example, an average solidification rate greater than 15 ° C / min in the working layer and also in the core. ingot during ingot formation.

Electrode 40 is in the ESR process thus heated by an electric current, for example, a high ampere current to melt the electrode steel to form an ingot according to the invention. The high ampere current of electrode 40 is carefully controlled to control the melting rate and it also affects the cooling rate and thus the rate of solidification. The rate of solidification depends on the amperage of the current fed to the electrode according to a predetermined function. Basically, the higher the current amperage, the higher the power supplied to melt electrode 40 (see Ohm's law). The higher the power supplied, the higher the slag temperature and the lower the solidification rate.

By maintaining the correct melt rate and slag temperature, directional solidification can be achieved with a solidification rate according to the invention in the core and working layer while cooling the ingot at certain intervals. For example, in one embodiment, a solidification rate which on average is greater than 15 ° C / min in both the core and ingot working layer while cooling the ingot in the solidification range from 1400 ° C to 1200 ° C.

According to the invention and as a consequence of the combination of the steel composition and the inventive concept process, the eutectic carbide content in the ingot is held below 5% by volume. This gives good rectifiability of the resulting roll. Roll grindability is important since during use of the final roll grinding is an important procedure to achieve proper roll roughness in relation to the cold rolling process. It is known that a concentration of eutectic carbides greater than 5% gives unsatisfactory grindability of such a roll.

In addition, another effect of the low eutectic carbide content is a low tendency of the roller to form dust during rolling operation. In contrast, dust formation can be generated on rollers having high carbide concentrations, which is negative for laminated products as well as the working environment in the rolling mill.

It is especially important to control the rate of solidification when the ingot is made from compositions comprising high Cr levels (e.g., 7-13%). High segregation that is obtained if the rate of solidification is too slow produces defects in high chrome ingots.

A solidification rate greater than 15 ° C / min during the solidification interval when the ingot is made gives a low segregation rate resulting in a eutectic carbide content of less than 5% by volume.

The present invention will be more readily understood by reference to the following examples. However, these examples are intended to illustrate embodiment variants of the ingot forming step of the invention and are not to be construed to limit the scope of the invention.

Comparative Examples

Example 1 demonstrates the effect that the method of the invention has on the microstructure of roll 1 according to the invention. Example 2 is a comparative example. Examples are realized during the production of full scale roll prototypes. The experiments show the important variation of the eutectic carbide distribution and the shape of the ingot after casting depending on the solidification rate used, see examples 1 and 2 below and table 2. The eutectic carbide distribution and the shape of the mesh Ingot view is remained on the final roll after forging and quenching according to the invention. Example 1

This example shows the effect on the microstructure in the roll according to the invention when a solidification rate greater than 15 ° C / min is used during ingot formation 34 according to the invention.

Figures 5A-B show an example of a LINGOTE 1 microstructure according to the invention that is made using a process with an average solidification rate of 50 ° C / min (at 90 mm ingot depth) at the same time. where the ingot is cooled from 1400 ° C to 12000C. The eutectic cells in the LINGOTE Example 1 according to the invention are small (940,942), Figure 5B shows the fragmented network with an open eutectic network. See also figure 8 for the different solidification ranges in the different parts of the ingot during solidification showing the core temperature rate 82, the average radius 84, 90 mm 86, 50 mm 88, 30 mm 90 and surface 92. Figure 5B is an enlargement of figure 5A. See also table 2.

Figures 6A-B show an example of a LINGOTE 2 microstructure according to the invention that is made using a process with an average solidification rate of 18 ° C / min (at 90 mm ingot depth) at the same time. where the ingot is cooled from 14000C to 1200 ° C. Figure 6 shows the eutectic cells in the LINGOTE 2 example according to the invention, and they are small, see, for example, the cross-sectional distance 1024. See also Figure 9 for the different solidification ranges in the different parts of the ingot. during solidification 80, showing the core temperature rate 100, the average radius 102, 90 mm 104, 50 mm 106, 30 mm 108 an> 36/54

surface 110. Figure 6B is an enlargement of Figure 6A. See also table 2.

Conclusion

The method according to the invention ensures the absence

segregation in the middle radius of the ingot. The absence of medium radius segregation (or 5/6 of the inner diameter of the cylindrical roller) ensures the integrity of the roller during the hardening process. A solidification rate greater than 15 ° C / min in the working layers thus generates a thinner microstructure which, as explained above, is better in terms of grinding and dust pollution, see Figures 5A-B and Figure 6A-B. .

Example 2

This example shows the effect of using a solidification rate of less than 15 ° C / min during TEST 1 ingot formation.

Figures 7A-C show an example of a TEST 1 ingot microstructure that is made using a process with a solidification rate of less than 15 (indeed even less than 10) ° C / min while cooling the ingot in the solidification range from 1400 0C to 1200 0C. Comparative TEST 1 ingot cells 700 in Figure 7A-C are larger in size, see, for example, cross-section 708 which has a cross-section length 708 which is greater than the largest cross-section at, for example, the Ingot 1 in Example 1 according to the invention. TEST 1 ingot also shows shrinkage porosities 704. Coarse conglomerate eutectic netting 702 can also be seen in Figure 1A-C. See also Table 2. Figure 7B-C is an enlargement of Figure 7A.

Conclusion:

A solidification rate of less than 15 ° C / min within

of the solidification range gives high carbide segregation and a thick carbide mesh 7 02 the average radius of the TEST 1 ingot structure and also porosities 704, see figure 7A-C. High carbide segregation and a coarse carbide net make a blank blank roll or a finished roll made by a fragile TEST 1 ingot and thus likely to explode during induction hardening (a white blank roll) or in the rolling mill. cold rolling (finished roll). Example 2 also shows that a rate of

solidification below 15 ° C / min also causes the size of the eutectic cell structure to be larger and thicker compared to when an ingot is made using solidification rates greater than 15 ° C / min as according to the invention.

A solidification rate greater than 15 ° C / min during the solidification interval when the ingot is made gives a low segregation rate resulting in a eutectic carbide content of less than 5% by volume. Table 2

Average solidification rate * C Ifti Si Cr Md Ni V Effect on segregation / eutectic carbide formation Effect on microstructure LINGOTE 1 50 ° C / min 0.8 0.5 1.0 7.2 1.4 < 1 1.8 Low segregation rate + control over eutectic carbides see Figure 5A-B LINGOTE 2 18 ° C / min 0.8 0.5 1.0 7.2 1.4 <1 1.8 Low segregation rate + control on eutectic carbs See Figure 6A-B TEST 1 <15 ° C / min 0.8 0.5 1.0 7.2 1.4 <1 1.8 High segregation rate - No control over eutectic carbs See Figure 7A-C

Table 2 shows experimental data for testing ingots with different average solidification rate (*) while cooling the ingot from 14000C to 1200 ° C at 90 mm depth of the ingot.

Comparative Examples

Example 3 demonstrates, for example, the effect that the method of the invention and the chemical composition of the ingot has on the microstructure of the ingot and thus also on the roll of the invention. Example 4 is a comparative example. Examples 3 and 4 show the microstructure of ingots produced by laboratory experimentation with controlled solidification device and controlled cooling rates.

The shape of the eutectic carbide mesh in the ingot is affected depending on the chemical composition used, see also table 3.

20 Example 3

This example shows a LINGOTE 1 microstructure produced according to the method of the invention by laboratory experimentation with controlled solidification device and controlled cooling rates greater than 15 ° C / min in the solidification range. When a chemical composition comprising 1.4% Mo is used according to the invention, an open eutectic carbide system 750 is achieved in the ingot structure, see Figure 10A-B. See also table 3. This open eutectic carbide system 750 as seen on roll 1 according to the invention is characterized as a dendrite pattern and the eutectic carbide structures 752 are not forming closed eutectic carbide network (as in the example 4, TEST 2), but instead forms dendrite arms in a net, see Figure IOA-B which shows an illustration of the microstructure of a 1.4% Mo ingot that is produced according to the process of invention. This open eutectic carbide system according to the invention makes the roll easier to grind compared to rolls made using quantities higher than 1.6% Mo.

Example 4

A TEST 2 ingot is made using a process of the invention and a composition wherein the main constituents are in accordance with the above embodiments, but with the difference that the chemical composition differs from the invention with respect to the amount of Mo. This TEST 2 ingot is produced according to the method of the invention by laboratory experimentation with controlled solidification device and controlled cooling rates greater than ° C / min in the solidification range. In TEST 2 the amount of Mo is 2.77%, see also table 3. Using a chemical composition comprising 2.77% Mo in the process of the invention to produce an ingot makes the eutectic ingot carbide system formed in a closed eutectic carbide cell, see Figure 11Ab, and eutectic carbides 852 form substantially isolated portions 850, such as islands or segregated cell structures in Figure IlA-B showing the microstructure of TEST 2. The white areas in Figure IlA-B represent a matrix; mainly iron, black is secondary carbides.

Excessive addition of alloying elements in TEST 2 leads to the formation of a thick carbide net joined to carbide segregation. See also table 3.

Table 3

Average solidification rate * C Mn Si Cr Mo Ni V Effect on the microstructure TEST 2 18 ° C / min 0.8 0, 6 1.11 7.19 2, 77 <1 0.44 Figure 11 A-B. Shows a closed eutectic carbide mesh LINGOTE 1 18 ° C / min 0.8 0.5 1.0 7.2 1.4 <1 1.8 Figure 10 A-B. Shows an open eutectic carbide net.

Table 3 shows experimental data for ingot testing with different average solidification rate (*) while cooling the ingot from 1400 ° C to 1200 ° C. The constituents except Mo are within the ranges as described above.

Step 18: Forging Said Ingot 34 to a Roll 1 In a typical application of the invention, the ingot 34 made in accordance with the previous step of the invention is then forged. In one embodiment of the invention the ingot 34 is hot pressed forged using a process known per se to simultaneously reduce the cross-sectional area and change shape by passing it between a hammer and an anvil to form the ingot to a roll 1 of 1. according to the invention. The ingot is heated in a dedicated furnace, see Figure 12 for a schematic view of the forging step.

Forging step 18 according to the invention includes the following steps, see figure 12;

- Preheat 56 of ingot 34 for approximately 6 h to a temperature of between 800-12000C or between 850-10000C. Preheating step 56 involves heating ingot 34 from the surface and all the way to the ingot core. The temperature during forging is set within the range 800-1200 ° C or between 850-1100 ° C since a temperature higher than 1200 ° C leads to defects in the ingot structure due to roll burning. The reasons for maintaining the ingot temperature within the indicated temperature range is that a temperature below 8000C leads to cracking in the ingot. As ingot 34 is cooled, it becomes stronger and less ductile which can induce cracking if deformation continues.

After preheating (step 56) of ingot 1, it is forged (step 60) using a forging ratio of 1.35-2.0. Forging step 60 and preheating step 56 are repeated, this forging cycle commonly being called a heater 58. A heater 58 is repeated as many times as necessary to form a roll according to the invention, see figure 12 .

In one embodiment the roll 1 according to the invention is forged using 3-6 heaters 58 to forge the ingot into a blank of the roll. A roll blank is a roll that is shaped like a roll, but still with a roll that lacks the final treatments to make a roll usable in the rolling mill.

In another embodiment, ingot 34 is forged in various heaters 58, see Figure 13 for a schematic view of forging a roll:

a) first, ingot 34 is set in the cross-sectional area on a few or 1-2 heaters 58,

b) a roller neck is made in a heater,

c) The other neck of the roller is forged in the next heater.

Forging a steel composition according to the invention is more difficult to do because of the high alloy content according to the invention than compared to standard steel grades of the forging example.

During forging, the diameter 32 of ingot 34 is reduced by 30-50% while forging in a roll 1 according to the invention. For example, a roll 1 according to the invention preferably has a diameter 2 between 250-800 mm, see Figure 1 and an ingot 34 according to the invention preferably has a diameter 32 between 400-1000 mm or between 450-100 mm. 1100 mm.

It is important that ingot 34 has the desired eutectic carbide microstructure formed during the process of manufacturing ingot 34 during solidification step 80. It is shown that ingots 34 with 43/54

Eutectic carbide microstructure according to the invention with eutectic carbide amounts of less than 5% by volume are possible for forging using hot press forging techniques. Using an ingot formed by another process, for example with a solidification rate of less than 15 ° C / min, causes these large rollers to be blown up during induction hardening or in the rolling mill.

Step 20: Preliminary heat treatment of said roll 1 In the manufacturing process of the invention, the roll is

treated with a preliminary heat treatment step. In one embodiment of the invention, the roller is heated to between 700 ° C-100 ° C during preliminary heat treatment according to the invention in an oven and then the roller is kept at that temperature for a certain time until a satisfactory diffusion of hydrogen has occurred. Preliminary heat treatment (normalization and spheroidal annealing) is performed in order to improve the machinability of the roll.

Step 22: Thinning Machining 22 of Said Roll

In the manufacturing process of the invention the roll is treated by a roughing machining step 22. The roughing machining 22 of the formed roll 1 according to the invention means removing the outer layer of the forged roll. In one embodiment of the invention, the outer layer is removed during roughing machining. The roll is called a black blank before being treated by rough machining. By removing the oxidizing layer from the surface of the roll the black blank roll is then transformed to a white blank. Step 24: Induction hardening of said roller 1 In the manufacturing process of the invention the roller is treated by induction hardening. During induction hardening of the roller the hard surface of the roller is formed. See Figure 14 for a schematic view of the induction hardening step.

In one embodiment of the invention the roller is slowly moved downwards while an electric current or voltage frequency between 50-1000 Hz is applied through the inductor arrangement 70 during the induction hardening step. Roll 1 is cooled using water cooling 72 after the heating step, see figure 14. The hard surface formed is also called working layer 4 of the roll and is approximately 1/6 (see figure 1, number 6). 1. The surface of the roller cylinder is heated rapidly when lowered through a series of inductors comprising electric coils carrying in an extinguishing box. Rapid induction heating heat penetration and immediate quenching using water produce a defined layer of uniform hardness of the roller surface. Both necks and roll core remain at low temperatures throughout the process. During induction hardening frequencies typically between 50-1000 Hz are applied to the surface of roll 1 and a selected frequency from the bottom of this range gives a deeper working layer 4 of roll 1. Other factors affecting the depth of the layer 1 formed work is the space between inductors 70 (if multiple inductors are used). Also the space or distance between inductor 70 and roll 1 affects the depth of the formed working layer 4. The induction hardening step 24 according to the invention could be single frequency, double frequency or more frequency / s.

The roller according to the invention explodes using conventional hardening techniques and induction heating is the most suitable technique for hardening the roller according to the invention. The cooling of roller 1 during induction hardening 24 is accomplished by high flow of cold water.

In one embodiment of the invention induction hardening 34 is done by double induction hardening and cooling of roll 1 after induction hardening 24 is done by high water flow which has a temperature of 40 ° C and is conveyed in a stream. approximately 300 m3 / h and the roll is moved downward at a speed of 0.3 mm to 1 mm / s.

In one embodiment, the induction hardening step 24 takes between 0.5-2 h.

Step 26: Quenching This Roll

In the manufacturing process of the invention roll 1 is tempered. The purpose of the tempering step is to reduce the brittleness of the roll and to adjust the hardness level. Quenching step 26 is a crucial step during roll formation because it decreases internal stresses. During the quenching stage the roller reaches its final microstructure by diffusion and secondary carbide precipitation. Air cooling is applied between the heating and quenching steps. The rolls are preferably tempered 3 times at 450-530 ° C. The hardening step causes the roll to obtain the required hardness level greater than 780 HV or between 780-840 HV. Precise control of time and temperature during the quenching process is critical to achieving a well balanced microstructure metal, for example, tempered martensite so that the roll made according to the process of the invention after quenching comprises a quenched martensite at a rate retained austenite of less than 5% by volume.

Step 28: Machining That Roll

In the manufacturing process of the invention, the roll is preferably treated by a machining step 28 before use in the rolling mill. For example, in the rolling mill a specific surface treatment application of the roll is carried out by grinding and other surface treatments to obtain the desired roughness and related friction on the surface of the roll. Examples of roller surface treatments are, for example: Laser Beam Texturing (LBT), Electron Beam Texturing (EBT) or Electric Discharge Texturing (EDT).

In one embodiment, the roller is treated by grinding and surface treatment by Electric Discharge Texturing (EDT). Figures 15A-B show the microstructure of the surface of a roller comprising a low chromium composition after Electric Discharge Texturing. Figures 15 C-D show the microstructure of the roller surface according to the invention after Electric Discharge Texturing. Just below the white layer 300 in the 15D layer there is the re-austenitized layer and a thinner softened zone, since this grade has a high tempering temperature. It is also noted that within the white layer on the 15 D ribbon, the eutectic carbs 302 were not affected by the electric arc energy. For comparison, these types of carbides are not present in the roller described in Figure 15 A-B. The roller according to the invention has better properties and performance than a standard grade roller (see Figure 15A-B) due to the presence of hard eutectic carbides in the white layer.

Figure 18 shows a more schematic figure of Figure 15D, depicting the microstructure of a roller surface according to the invention wherein newly formed eutectic carbides 302 formed by re-melting are present within the white layer 304. Also Previously formed eutectic carbs 300 are shown in figure 18. The surface of the roller in figure 18 illustrates what the surface looks like after Electric Discharge Texturing according to the invention. The scale 306 represents 5 μπι.

A roll 1 according to the invention made by the process described above

A typical roll according to the invention has a diameter of between 215 and 800 mm or between 250-700 mm, the total length including the necks is up to 6 meters, where the cylinder length is between 1-3 meters. Typical roll weight is between 400 and 10000 kg. The microstructure of a roller according to one embodiment of the invention is characterized by comprising tempered martensite with a retained austenite rate of less than 5% by volume, and wherein the roller comprises an open eutectic carbide network of less than 5% by volume. eutectic carbides; and roller (1) exhibits a hardness between 780 and 840 HV; and internal compressive stresses between -300 and -500 MPa. These roll properties are due to the roll production process of the invention and also due to the chemical composition of the roll according to the chemical composition of the invention.

The roll according to the invention is intended for use in a cold strip mill which requires rollers withstanding high pressures. The roller according to the invention is intended for use in the cold strip rolling mill as a working roller and is suitable in any chair in the rolling process and is suitable in rolling mills from 2Hi to 6Hi and can have surface roughness from 0,3-0,5 μιη which is required on the finishing chairs to a roughness of 1,5-2,5 μιη which is required on the initial chairs.

The present invention will be more readily understood by reference to the following examples. However, these examples are intended to illustrate the roller properties of the invention and are not to be construed as limiting the scope of the invention.

In table 4 different rollers are compared with the roll according to the invention. All rolls comprise Mn in amounts between 0.2-0.5 wt%.

Two examples of the invention

ROLL 1 according to the invention in table 4 is made using the process according to the invention, using a solidification rate greater than 15 ° C / min in the working layer during the solidification interval and also using induction heating. using a frequency of 50-250 HZ and quenching 3 times at 450-530 ° C.

ROLL 2 according to the invention in table 4 is made using the process according to the invention using a solidification rate of 18 ° C / min in the working layer for 10 minutes.

Roll C Cr Mo V Average Hardness Level (HV) Secondary Hardening Peak Test Comments 4 0, 6 5 1.1 0.25 700 No To soften the working roll in cold rolling application TEST 5 0, 8 10 1.1 0.25 730 Slightly To soften the back seat- Convenient on front seat TEST 6 0.7 5 2 0.5 750 Slightly Unable to produce. Rejection due to high temperature delta ferrite formation during forging heat. See Figure 16 A-D showing detrimental defects 502 in a roll generated during the manufacture of low chromium content rollers. Harmful defects 502 are, for example, porosities and contraction. TEST 7 0.9 8 2 2 820 Abruptly Adapted for cold rolling (required for

solidification range and also using induction heating using a frequency of 50-250 HZ and tempering 3 times; first at 490 ° C, then at 490 ° C and at the last quench at 480 ° C. Figure 19 shows the microstructure of a roll after quenching and induction hardening, tested at 4 mm depth from the surface of ROLL 2. Microstructure 1034 with open eutectic net and eutectic carbs 1032 of the roll is also shown in figure 19

Table 4 aluminum rolling) ROLL 1 0.9 8 1.5 1.45 800 Abruptly Adapted for cold rolling and easier to grind compared to TEST 7, for example. ROLL 2 0.87 OO Γ— 1.5 1.5 800 Abruptly Adapted for cold rolling and easier to grind compared to TEST 7, for example.

The Mn content for the rolls in table 4 are all within the range 0.4-0.5, the Si content for the rolls in table 4 are all within the range 0.2-2.0, Ni is always below 1%. Roller Applications

Applications where the rollers are suitable are: Aluminum Industry:

4Hi Single Chairs Without Reversible Laminator Steel Industry:

single chair 4 Hi reversible

4 and 5 tandem 4 Hi chairs for plates in continuous and discontinuous process

4 and 5 tandem 4 Hi chairs for sheet

flanders

6 Hi Tandem Rolling Mill for Roll Usage

The forged roll according to the invention is suitable for use, for example, as a working roll or intermediate roll in cold rolling mills or in, for example;

- Cold-rolling reduction laminators for initial and finishing chairs, reversible and non-reversing tinplate chairs, sheets, silicon steel, aluminum or copper.

- Cold rolling tempering and / or laminating box laminators;

- Laminator configurations such as 2-High, 4- High and 6-High chairs with textured or non-textured surface.

- Cold rolling of steel grades AHSS.

Roll surface

Surface texture

One problem with known rollers is that the surface texture becomes warm during roll use. Surface texture is important because it ensures the coefficient of friction to prevent slippage and / or derailment of the strip. It also determines the texture of the strip surface that gives the crucial surface properties for deep drawing and painting of the laminated strip. The rollers according to the invention exhibit an increased ability to maintain their surface texture due to a white layer of the roll and wherein the white layer comprises hard eutectic carbides such as M7C3. At the work layer; The microstructure of the roll of the invention after final heat treatment consists of tempered martensite with a retained austenite rate of less than 5% by volume and carbides such as MC and M2C (M = metal, C = carbon) finely and evenly distributed in the matrix. This type of microstructure has been shown to be important in maintaining the texture of the roller surface.

Roughness Transfer

Roll surface roughness transfer changes during roll use. The rollers according to the invention exhibit an increased ability to keep the roughness transfer constant during rolling which is important for the life of the roll. This is due to the special claimed composition and also due to the production method used when making the rollers.

Free Programming Rolling Mill

One problem when using rollers is that dirt that fuses on the surface of the roll leads to a track on the strip. In the working layer, the inventive roller has a strong surface because the roller microstructure of the invention comprises tempered martensite with a retained austenite rate of less than 5% by volume and finely and homogeneously distributed carbides like MC and M2C in the matrix, where M indicates metal and C indicates carbon. This special microstructure increases the possibilities for free program lamination.

Fragmentation

Another problem with known rollers is that crack propagation within the rollers is governed by the cumulative stresses induced by the rolling operation and the residual internal stress field of the roll. A roll in service is subjected to a complex set of stresses. The roller according to the invention shows a low level of residual internal stresses and thus a better resistance to shredding and this makes the incident rate in the rolling mill low.

The mechanical strength of the roll of the invention is better compared to a roll with the same alloy composition as the roll of the invention, but made using another production method. The mechanical strength of the roller according to the invention is due to the open eutectic mesh formed in the working layer of the roller. This open eutectic net is formed during the cooling step in the roll production process. A solidification rate of more than 15 ° C / min during the cooling step when the ingot is made is crucial for the formation of the open mesh that is present in the rollers according to the invention.

Also, the accumulation of various tempering treatments at high temperature after hardening, for example between 450-5300 ° C during roll production, induces a significant relaxation of internal roll stresses. Internal stresses are minimized using differential heating of the outer layer. The tempering penetration depth of the roller according to the invention can be controlled between 20 and 120 mm in the diameter measured from the roller surface and inwards. The internal compressive stresses of the roll of the invention are preferably between -300 and -500 MPa in absolute value or, for example, less than -400 MPa.

Roller microstructure

Figure 17A shows a schematic view of an exemplary roller microstructure according to the invention. Figure 17A shows dendrite arms 210, comprising eutectic carbs forming eutectic cell structures 204 by forming an open carbide network. The open eutectic net comprising dendrite arms 210 forming eutectic cells 204, which can be seen in figure 17A, is formed in the process due to the specific chemical composition according to the invention. Scale 208 represents 100 pm.

In one embodiment of the invention, the roller microstructure of the invention comprises an open eutectic mesh that is only spread over a grain or two grains of the cell structures.

In comparison, Figure 17B shows a closed eutectic net in which the eutectic carbs 200 form a closed eutectic net with clearly separated eutectic cells 212. This type of net is undesirable in the roll according to the invention due to the brittleness of the roll as it comprises. type of microstructure. The scale 214 represents 100 μπι.

The invention has been explained by different embodiments within the scope of the appended claims.

Claims (40)

1. Forged roller (1), characterized in that it comprises a steel composition comprising, by weight%, from 0,8 to less than (<) 1% C, from 0,2 to 0,5 % Mn, from 0.2 to 2.0% Si, from 7.0 to 13.0% Cr, from 0.6 to 1.6% Mo, more than (>) 1.0 to 3 0% V, the remaining portion of the steel being substantially Fe and possible incidental and / or possibly unavoidable impurities; and wherein the microstructure of the roll (1) comprises: - tempered martensite with a retained austenite rate of less than (<) 5% by volume; and - an open eutectic carbide network with eutectic carbides of less than (<) 5% by volume; and wherein the roll (1) exhibits: a hardness of between 780 and 840 HV; and - internal compressive stresses between -300 and -500 MPa. Roller according to the preceding claim, characterized in that the open eutectic carbide mesh delimits a cell-like pattern of eutectic cells. Roller according to one of the preceding claims, characterized in that the open eutectic carbide mesh comprises dendritic arms. Roll according to one of the preceding claims, characterized in that the microstructure is present in at least one working layer of the roll. Roll according to one of the preceding claims, characterized in that it has a steel composition consisting in terms of% by weight; 0.8 to less than (<) 1% C, 0.2 to 0.5% Mn, 0.2 to 2.0% Si, 7.0 to 13.0% Cr , from 0,6 to 1,6% Mo, more than (>) 1,0 to 3,0% V, less than (<) 0,015% P, and less than (<) 0,015% S, and less than (<) 1% Ni less than (<) 30 ppm O2, and less than (<) 100 ppm N2, and less than (<) 3 ppm H2 less (<) 2% W , and less than (<) 1% Nb, and less than (<) 1% Ti, and less than {<) 0.5% Ta, and less than (<) 0.5% Zr, remaining portion of the steel being substantially Fe and possible incidental and / or possibly unavoidable impurities. Roll according to one of the preceding claims, characterized in that the C content in the steel composition is between 0.8 - 0.99% C in terms of% by weight of the total weight of the roll. Roll according to any one of the preceding claims, characterized in that the C content in the steel composition is between 0.85-0.9% C in terms of% by weight of the total weight of the roll. Roll according to one of the preceding claims, characterized in that the content of Mn in the steel composition is between 0.4 - 0.5% Mn in terms of% by weight of the total weight of the roll. Roll according to one of the preceding claims, characterized in that the Si content in the steel composition is between 0.2 - 1.5% Si in terms of% by weight of the total weight of the roll. Roll according to one of the preceding claims, characterized in that the Si content in the steel composition is between 0.85 - 1.15% Si in terms of% by weight of the total weight of the roll. Roll according to one of the preceding claims, characterized in that the Cr content in the steel composition is between 7.0 - 11% Cr in terms of% by weight of the total weight of the roll. Roll according to any of the preceding claims, characterized in that the Cr content in the steel composition is between 7.3 - less than (<) 8.0% Cr in terms of weight% by weight. roll total. Roll according to one of the preceding claims, characterized in that the Mo content in the steel composition is between 1.45 - 1.55% Mo in terms of% by weight of the total weight of the roll. Roll according to any one of the preceding claims, characterized in that the Ni content in the steel composition is less than (<) 0.3 Ni in terms of% by weight of the total weight of the roll. Roll according to one of the preceding claims, characterized in that the content of V in the steel composition is between 1.3 - 2.1% V in terms of% by weight of the total weight of the roll. Roll according to one of the preceding claims, characterized in that the content of V in the steel composition is between 1.3 - 1.6% V in terms of% by weight of the total weight of the roll. Roll according to one of the preceding claims, characterized in that the steel composition consists, in terms of% by weight: 0.8 - 0.99% C, and 0.4 - 0.5. % Mn, and 0.2 - 1.5% Si, and 7.0 - 11% Cr, and 0.6 - 1.6% Mo, and less (<) 1.0 Ni, and 1.0 - 2.1% V, and less (<) 0.015% P, and less (<) 0.015% S, and less (<) 30 ppm than 02, and less than (<) 100 ppm N 2, and less than (<) 3 ppm H 2, and the remaining portion of the roll being substantially Fe and possible incidental and / or possibly unavoidable impurities. Roll according to one of the preceding claims, characterized in that the steel composition consists, in terms of% by weight: of 0.85 - 0.9% of C, and of 0.4 - 0.5. % Mn, and 0.85 - 1.15% Si, and 7.3 - less than (<) 8.0% Cr, and 1.45 - 1.55% Mo, and less (<) 0.3 Ni, and 1.3 - 1.6% V and less (<) 0.015% P, and less (<) 0.015% S, and less than (<) 30 ppm of O 2, and less (<) 100 ppm N 2, and less than (<) 3 ppm H 2, and the remaining portion of the roll being substantially Fe and possible incidental and / or possibly unavoidable impurities. Roll according to one of the preceding claims, characterized in that it is additionally configured for use as a cold rolling working roll. Roll according to one of the preceding claims, characterized in that it additionally has a weight of more than 400 kg. Roll according to one of the preceding claims, characterized in that it further has a diameter in the range 215-800 mm. 22. Process for making an unforged roll, characterized in that the process comprises the steps of: a. To provide a steel composition comprising by weight 0.8% less than (<) 1% C, 0.2 to 0.5% Mn, 0.2 to 2.0% Si, 7.0 to 13.0% Cr, 0.6 to 1.6% Mo, more than (>) 1.0 to 3.0% V, the remaining portion of the steel being substantially Fe and possible incidental and / or possibly unavoidable impurities; B. Fabricate an ingot while maintaining a solidification rate greater than 150C / min in the working layer of the ingot in the solidification range; ç. Forge the ingot to a roll; d. Harden the roller by induction heating; and. Temper the roller at a temperature between 450-5300C to achieve hardness between 780 to 840 HV; thereby achieving a microstructure of the roll (1) comprising: - tempered martensite with a retained austenite rate of less than (<) 5% by volume; and - an open eutectic carbide network with eutectic carbides of less than (<) 5% by volume; and wherein the roll (1) exhibits: a hardness of between 780 and 840 HV; and - internal compressive stresses between -300 and -500 MPa. Process according to Claim 22, characterized in that the ingot is manufactured by maintaining a solidification rate in the working layer as well as in the core in the range of 15 ° C / min to SS0CZmin, or alternatively 17 ° C / min. 50 ° C / min, or alternatively 35 ° C / min - 55 ° C / min, or alternatively 45 ° C / min - 55 ° C / min. Process according to any one of claims 22-23, characterized in that the ingot is manufactured by maintaining a solidification rate of greater than 35 ° C / min in the working layer of the ingot in the solidification range. Process according to any one of claims 22-24, characterized in that the solidification range is between 1400 ~ 1200 ° C for said ingot. Process according to any one of claims 22-25, characterized in that the ingot is manufactured by maintaining a preselected solidification rate in an electro-slag refining furnace (ESR) technique process controlling the supply of ampere current according to a predetermined function of the solidification rate. Process according to any one of claims 22-26, characterized in that the step of forging the ingot to a roll comprises the steps of: a. Heat the ingot to a temperature of 800 - 1200 ° C or 850 - 100 ° C, preferably for a period of approximately 6 hours; B. Forge the ingot at a temperature above 800 ° C or above 850 ° C; ç. Repeat steps a-b until the ingot has been formed into a roll that has the desired shape and size. Process according to any one of claims 22-27, characterized in that further after the forging step it comprises a preliminary heat treatment step, preferably up to a temperature of between 700 - 100 ° C or between 800 - 900 ° C. , which may include hydrogen diffusion treatment. A process according to any one of claims 22-29, characterized in that the step of tempering the roll comprises the steps of: a. Heat the roll to approximately 450 - 530 ° C, preferably 3 times, b. Cool the roller between the heating steps with air. Process according to any one of claims 22-29, characterized in that it further comprises machining the roller to texture a white layer comprising eutectic carbides. Process according to any one of claims 30, characterized in that said eutectic carbides in the white layer are selected from M7C3. Process according to any one of claims 22-31, characterized in that it further comprises the features of any of claims 1-21. Ingot of an intermediate product in the production of a roll according to any of the preceding claims 1-32, characterized in that the ingot comprises a steel composition comprising, in terms of weight%, of 0.8 to less than (<) 1% C, 0.2 to 0.5% Mn, 0.2 to 2.0% Si, 7.0 to 13.0% Cr, 0.6 to 1 , 6% Mo, more than (>) 1.0 to 3.0% V, the remaining portion of the steel being substantially Fe and possible incidental and / or possibly unavoidable impurities; and wherein the final roll microstructure resulting from the ingot comprises: - tempered martensite with a retained austenite rate of less than (<) 5% by volume; and - an open eutectic carbide net with eutectic carbides of less than {<) 5% by volume. Intermediate ingot according to claim 33, characterized in that it further comprises the features of any of claims 1-32. Use of a roller according to any of claims 1-21, characterized in that it is for cold rolling material which requires a high rolling load. Use of a roller according to any one of claims 1-21, characterized in that it is for cold rolling of high strength materials such as AHSS steel levels. Use of a roller according to any one of claims 1-21, characterized in that it is for a selection of: - cold rolling reduction laminators for front and finishing chairs, reversible and non-reversible chair for sheet- tinplate, sheet metal, silicon steel, stainless steel, aluminum and copper; or - laminating box and / or cold rolling temper laminators; or - laminator configurations such as 2-High, 4- High and β-High chairs with textured or non-textured surface. Use of a roller according to any of claims 1-21, characterized in that it is like a working roller. Roll, roll produced by a process, process for producing a roll and / or use of a roll according to any of the preceding claims, characterized in that the roll is not covered. Roll, roll produced by a process, process for producing a roll and / or use of a roll according to any of the preceding claims, characterized in that the roll is coated with a selectable coating, for example a coating of chrome.