WO2016012860A1

WO2016012860A1 - Annealed cold rolled steel and method for preparing same

Info

Publication number: WO2016012860A1
Application number: PCT/IB2015/001751
Authority: WO
Inventors: Hamid BAYATI; Mansour AL-HARBI
Original assignee: Sabic Global Technologies.B.V.
Priority date: 2014-07-24
Filing date: 2015-07-14
Publication date: 2016-01-28

Abstract

In accordance with the present invention, disclosed herein is a system comprising a first cylindrical coil of cold rolled steel and a second cylindrical coil of cold rolled steel, wherein the second cylindrical coil is positioned concentrically within the hollow bore defined by a first coil inner diameter, and wherein an annular gap is formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil. Also disclosed herein, are processes to anneal cold rolled steel utilizing the disclosed system and exhibiting a reduced carbon footprint.

Description

ANNEALED COLD ROLLED STEEL AND METHOD FOR PREPARING SAME

FIELD OF INVENTION

[0001] This disclosure relates to annealed cold rolled steel and methods for preparing same.

BACKGROUND

[0002] Steel is a metal alloy comprising iron and carbon, which can contribute up to 2.1% of its weight. Carbon, other elements, and inclusions within iron, can act as hardening agents that prevent the movement of dislocations that naturally exist in the iron atom crystal lattices. Varying the amount of alloying elements, their form in steel either as solute elements, or as precipitated phases, retards the movement of those dislocations that make iron ductile and weak, and thus, it controls qualities such as the hardness, ductility, and tensile strength of the resulting steel. Various steel processing steps can also introduce changes in the metal microstructure. For example, when metal is cast, the solidification process results in both macro and micro segregation of the present alloying elements. Often, macro segregation needs to be broken down by mechanical work that in turn can cause the steel to accumulate stresses and increase steel hardness. In contrast, micro segregation cannot be resolved by mechanical work and additional steel treatment is required.

[0003] Annealing is a heat treatment process which is generally performed to reduce hardness, remove residual stresses, improve toughness, restore ductility, and to alter various mechanical, electrical or magnetic properties of the material by refinement of grains in steel microstructure. Annealing can also be performed to homogenize the steel structure to break down micro segregation of the alloying elements in steel and ensure uniform mechanical and electromagnetic properties.

[0004] There are a number of annealing processes commonly used in the steel industry. The general industry practice first requires a tight rewinding of cold rolled steel, to form large coils, before it is transferred for annealing. To achieve a successful outcome of the annealing process, an optimized holding time and temperature, appropriate heating/cooling media, and minimal temperature differences within the structure of heat treated steel are required.

However, the conventional coil setup can prevent heat from efficiently reaching the internal strips or layers of the coil during the annealing process. As a result, these conventional annealing processes are usually slow, highly energy intensive, and can require more than 50 hours to complete. Additionally, the high temperatures and long annealing times required in steel production contribute to already high carbon dioxide emissions by the steel industry (it is estimated that approximately 6.7 % of total world carbon dioxide emission is generated by iron and steel industry).

[0005] Accordingly, there remains a need for an annealed cold rolled steel and methods for preparing same that can provide high quality annealed cold rolled steel while minimizing the total period of time required for a steel heat treatment, reducing carbon footprint, improving cost efficiency, and providing energy consumption savings. This need and other needs are satisfied by the various aspects of the present disclosure.

SUMMARY OF THE INVENTION

[0006] In accordance with the purposes of the invention, as embodied and broadly described herein, the invention provides a system for use in annealing cold rolled steel. The system generally comprises at least a first and second cylindrical coil of cold rolled steel. The first cylindrical coil of cold rolled steel comprises a continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outer most layer defines the outside diameter of the first coil, wherein the inner most layer of the first cylindrical coil defines a hollow bore extending longitudinally through the coil and defining a first coil inner diameter. The second cylindrical coil of cold rolled steel comprises a second continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outermost layer of the second cylindrical coil defines an outside diameter that is smaller than the first coil inner diameter. The second cylindrical coil is positioned concentrically within the hollow bore of the first cylindrical coil such that an annular gap is formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil.

[0007] In further aspects, the invention also relates to a process for annealing cold rolled steel. The process generally comprises providing a system as described above. The system comprises a first cylindrical coil of cold rolled steel comprising a continuous sheet of steel rolled to form a plurality of concentric adjacent layers wherein the outer most layer defines the outside diameter of the first coil, wherein the inner most layer of the coil defines a hollow bore extending longitudinally through the coil and defining a first coil inner diameter; and a second cylindrical coil of cold rolled steel comprising a second continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outermost layer of the second cylindrical coil defines an outside diameter that is smaller than the first coil inner diameter. The second cylindrical coil is positioned concentrically within the hollow bore of the first cylindrical coil such that an annular gap is formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil. According to the process, the first and the second cylindrical coils are heated to a predetermined temperature for a predetermined period of time.

[0008] While aspects of the present invention can be described and claimed in a particular statutory class, such as the system statutory class, this is for convenience only and one of skill in the art will understand that each aspect of the present invention can be described and claimed in any statutory class. Unless otherwise expressly stated, it is no way intended that nay method or aspect set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not specifically state in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including matters of logic with respect to arrangement of steps or operational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.

[0009] Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or can be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects and together with the description serve to explain the principles of the invention.

[0011] FIGURE 1 shows a schematic representation of the disclosed system.

[0012] FIGURE 2 shows a schematic steel phase diagram as a function of temperature, iron weight percent, and carbon weight percent.

[0013] FIGURE 3 shows a schematic of various steel heat treatments.

[0014] FIGURE 4 shows a schematic representation of annealing heat treatment steps applied to cold rolled steel.

DETAILED DESCRIPTION

[0015] The present invention can be understood more readily by reference to the following detailed description of the invention.

[0016] Before the present compounds, compositions, articles, systems, devices, and/or methods are disclosed and described, it is to be understood that they are not limited to specific synthetic methods unless otherwise specified, or to particular reagents unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, exemplary methods and materials are now described.

[0017] Moreover, it is to be understood that unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; and the number or type of aspects described in the specification.

[0018] All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.

A. DEFINITIONS

[0019] It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. As used in the specification and in the claims, the term "comprising" can include the aspects "consisting of and "consisting essentially of." Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined herein.

[0020] As used in the specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a layer" includes the presence of two or more layers.

[0021] As used herein, the term "combination" is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0022] As used herein, the terms "about" and "at or about" mean that the amount or value in question can be the value designated some other value approximately or about the same. It is generally understood, as used herein, that it is the nominal value indicated up to a ±10% variation unless otherwise indicated or inferred. The term is intended to convey that similar values can promote equivalent results or effects recited in the claims. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is "about" or "approximate" whether or not expressly stated to be such. It is understood that where "about" is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise. [0023] Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent 'about,' it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as "about" that particular value in addition to the value itself. For example, if the value "10" is disclosed, then "about 10" is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

[0024] The terms "first," "second," "first part," "second part," and the like, where used herein, do not denote any order, quantity, or importance, and are used to distinguish one element from another, unless specifically stated otherwise.

[0025] As used herein, the terms "optional" or "optionally" means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

[0026] References in the specification and concluding claims to parts by weight of a particular element or component in a composition or article, denotes the weight relationship between the element or component and any other elements or components in the composition or article for which a part by weight is expressed. Thus, in a compound containing 2 parts by weight of component X and 5 parts by weight component Y, X and Y are present at a weight ratio of 2:5, and are present in such ratio regardless of whether additional components are contained in the compound.

[0027] A weight percent ("wt %") of a component, unless specifically stated to the contrary, is based on the total weight of the formulation or composition in which the component is included. For example if a particular element or component in a composition or article is said to have 8% by weight, it is understood that this percentage is relative to a total compositional percentage of 100% by weight.

[0028] As used herein, the term or phrase "effective," "effective amount," or "conditions effective to" refers to such amount or condition that is capable of performing the function or property for which an effective amount is expressed. As will be pointed out below, the exact amount or particular condition required will vary from one aspect to another, depending on recognized variables such as the materials employed and the processing conditions observed. However, it should be understood that an appropriate effective amount will be readily determined by one of ordinary skill in the art using only routine experimentation.

[0029] As used herein, the term "rolling" refers to a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness and to make the thickness uniform.

[0030] As used herein, the term "cold rolled steel" refers to a metal formed during a process in which a steel ingot is cooled to a temperature below recrystallization temperature of the metal and is forged or rolled into sheets or other shapes. In some aspects, the temperature below the recrystallization temperature of the metal can be a room temperature. In other aspects, cold rolling of the steel results in an increase of the steel strength via strain hardening of up to 20 %. In certain aspects, cold rolling of the steel improves the steel surface finish and enables the steel to hold tighter tolerances. For example and without limitation, common cold-rolled steel products include sheets, strips, bars, and rods. In some aspects, these products can be smaller than similar products produced by processes other than cold rolling. In certain aspects, processing of the cold rolling shapes requires a series of shaping operations, for example and without limitation, sizing, breakdown, roughening, semi- roughening, semi-finishing, and finishing. In some aspects, exemplary uses for cold rolled steel include but are not limited to metal furniture, desks, filing cabinets, shelves, tables, chairs, motorcycle exhaust pipes, computer cabinets and hardware, home appliances and components, shelving, lighting fixtures, hinges, tubing, steel drums, lawn mowers, electronic housing, lighting fixtures, water heaters, metal containers, and a variety of construction related products.

[0031] As used herein, the term "hot rolled steel" refers to a metal formed during a process in which a steel ingot is kept at a temperature above recrystallization temperature of the metal and is forged or rolled into sheets or other shapes. In some aspects, the metal grains can deform during hot rolling processing. In other aspects, after the deformation the grains can recrystallize. Recrystallization of grains can result in an equiaxed micro structure that can prevent the metal from work hardening. As one of ordinary skill in the art will appreciate, equiaxial grains of equal axial length can have more planes on which to slip and thus can have higher strength and ductility. In certain aspects, the starting material can be large pieces of metal, including exemplary semi-finished casting products, slabs, blooms, or billets. In some aspects, high quality hot rolled steel can have a surface that is covered in mill scale (an oxide forming at high-temperatures). In certain aspects, this oxide layer can be removed via pickling or the smooth clean surface process, which can reveal a smooth surface. In other aspects, hot rolling is used to produce sheet metal or simple cross sections, such as rail tracks. Other exemplary uses for the hot rolled metal include, but are not limited to, truck frames, automotive wheels, pipes and other tubular articles, water heaters, agriculture equipment, strappings, stampings, compressor shells, railcar components, wheel rims, metal buildings, railroad-hopper cars, doors, shelving, discs, guard rails, and automotive clutch plates.

[0032] As used herein, the terms "pickling" or "pickling bath" can be used

interchangeably, and refer to a metal surface treatment used to remove impurities, such as stains, inorganic contaminants, rust or scale from ferrous metals, copper,

and aluminum alloys. In some aspects, pickling can be used to descale or clean steel in various steelmaking processes.

[0033] As used herein, the term "carbon footprint" refers to the total amount of greenhouse gases produced to directly and indirectly support human activities, usually expressed in equivalent tons of carbon dioxide (C0₂). In some aspects, a carbon footprint is calculated annually or for a given time period of a year.

[0034] It is understood that the compositions disclosed herein have certain functions. Disclosed herein are certain structural requirements for performing the disclosed functions and it is understood that there are a variety of structures that can perform the same function that are related to the disclosed structures, and that these structures will typically achieve the same result.

B. SYSTEM

[0035] As briefly described above, the present disclosure provides, in one aspect, a system comprising: a) a first cylindrical coil of cold rolled steel comprising a continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outer most layer defines the outside diameter of the first coil, wherein the inner most layer of the first cylindrical coil defines a hollow bore extending longitudinally through the coil and defining a first coil inner diameter; and b) a second cylindrical coil of cold rolled steel comprising a second continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outermost layer of the second cylindrical coil defines an outside diameter that is smaller than the first coil inner diameter; wherein the second cylindrical coil is positioned concentrically within the hollow bore of the first cylindrical coil; and wherein an annular gap is formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil. FIGURE 1 depicts an exemplary schematic representation of the system.

[0036] In one aspect, the relative dimensions of the first and second coils can be such that the annular gap formed there between are characterized by a distance between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil of greater than 0 cm to about 25 cm, including exemplary values of about 1 cm, about 2 cm, about 3 cm, about 4 cm, about 5 cm, about 6 cm, about 7 cm, about 8 cm, about 9 cm, about 10 cm, about 11 cm, about 12 cm, about 13 cm, about 14 cm, about 15 cm, about 16 cm, about 17 cm, about 18 cm, about 19 cm, about 20 cm, about 21 cm, about 22 cm, about 23 cm, and about 24 cm. In still further aspect, the annular gap can be characterized by a distance between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil in any range derived from any two of the above listed exemplary values. For example and without limitation, the annular gap can be characterized by a distance between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil of about 5 cm to about 15 cm, or about 1 cm to about 20 cm.

[0037] In still further aspects, the relative size and dimensions of the first and second coils can also be such that the overall system fits within the interior volume of conventional annealing furnace equipment. As one of ordinary skill in the art will appreciate, this will eliminate any need to redesign or customize existing annealing furnace equipment. For example, in one aspect, the first coil outer diameter is substantially similar to the outer diameter of a conventional cold rolled steel coil and thus can fit within conventional cold rolled steel annealing equipment.

[0038] The first and second cylindrical coils can comprise any desired combined total weight. For example, the combined total weight can be at least 2 metric tons, at least 3 metric tons, at least 4 metric tons, at least 5 metric tons, at least 6 metric tons, at least 7 metric tons, at least 8 metric tons, at least 9 metric tons, at least 10 metric tons, at least 1 1 metric tons, at least 12 metric tons, at least 13 metric tons, at least 14 metric tons, at least 15 metric tons, at least 16 metric tons, at least 17 metric tons, at least 18 metric tons, at least 19 metric tons, at least 20 metric tons, at least 21 metric tons, at least 22 metric tons, at least 23 metric tons, at least 24 metric tons, and at least 25 metric tons.

[0039] In another aspect, the annular gap formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil can comprise air, nitrogen, hydrogen, or any combination thereof. In another aspect, the annular gap can comprise air. In yet another aspect, the annular gap can comprise nitrogen. In still another aspect, the annular gap can comprise a mixture of air and nitrogen. In a further aspect, the annular gap can comprise hydrogen. In a yet further aspect, the annular gap can comprise a mixture of nitrogen and hydrogen. In a still further aspect, the annular gap can comprise a mixture of air and hydrogen. In a further aspect, the annular gap does not comprise oxygen based gases. In certain aspects, the annular gap can further comprise a noble gas. For example and without limitation, the noble gas can be selected from a group consisting of helium, neon, argon, krypton, xenon, or any combination thereof.

[0040] In one aspect, the system comprised of the first and second cylindrical coils can be present in a heated environment. The heated environment can be of a heat sufficient to anneal the first and second cylindrical coils. In one aspect, the heated environment is suitable to heat the first and the second cylindrical coils to at least 600 °C, at least about 650 °C, at least about 700 °C, at least about 750 °C, at least about 800 °C, at least about 850 °C, at least about 900 °C, at least about 950 °C, at least about 1 ,000 °C, at least about 1 ,050 °C, at least about 1,100 °C, at least about 1,150 °C, at least about 1,200 °C, at least about 1,250 °C, at least about 1,300 °C, at least about 1,350 °C, at least about 1,400 °C, at least about 1,450 °C, at least about 1,500 °C, at least about 1,550 °C, at least about 1 ,600 °C, at least about 1 ,650 °C, at least about 1 ,700 °C, at least about 1,750 °C, at least about 1,800 °C, at least about 1,850 °C, at least about 1 ,900 °C, at least about 1,950 °C, and at least about 2,000 °C. In still further aspects, the heated environment is suitable to heat the first and the second cylindrical coils to any temperature in any range derived from any two of the above listed exemplary values.

[0041] In other aspect, the heated environment is suitable to heat the first and the second cylindrical coils to a temperature in the range of from about 600 °C to about 1,100 °C, including exemplary values of about 610 °C, about 620 °C, about 630 °C, about 640 °C, about 650 °C, about 660 °C, about 670 °C, about 680 °C, about 690 °C, about 700 °C, about 710 °C, about 720 °C, about 730 °C, about 740 °C, about 750 °C, about 760 °C, about 770 °C, about 780 °C, about 790 °C, about 800 °C, about 810 °C, about 820 °C, about 830 °C, about 840 °C, about 850 °C, about 860 °C, about 870 °C, about 880 °C, about 890 °C, about 900 °C, about 910 °C, about 920 °C, about 930 °C, about 940 °C, about 950 °C, about 960 °C, about 970 °C, about 980 °C, about 990 °C, about 1,000 °C, about 1,010 °C, about 1,020 °C, about 1 ,030 °C, about 1,040 °C, about 1,050 °C about 1 ,060 °C, about 1 ,070 °C, about 1,080 °C, and about 1 ,090 °C. In still further aspects, the heated environment is suitable to heat the first and second cylindrical coils to any temperature in any range derived from any two of the above listed exemplary values. For example, the heated environment is suitable to heat the first and second cylindrical coils to a temperature in the range of about 600 °C to about 900 °C, or about 700 °C to about 1,100 °C.

C. PROCESSES

[0042] Also disclosed herein is a process for annealing cold rolled steel. The process generally comprises providing a system as described herein, comprising i) a first cylindrical coil of cold rolled steel comprising a continuous sheet of steel rolled to form a plurality of concentric adjacent layers wherein the outer most layer defines the outside diameter of the first coil, wherein the inner most layer of the coil defines a hollow bore extending

longitudinally through the coil and defining a first coil inner diameter; and ii) a second cylindrical coil of cold rolled steel comprising a second continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outermost layer of the second cylindrical coil defines an outside diameter that is smaller than the first coil inner diameter, wherein the second cylindrical coil is positioned concentrically within the hollow bore of the first cylindrical coil; and wherein an annular gap is formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil. The first and the second cylindrical coils are then heated to a predetermined temperature for a predetermined period of time.

[0043] In one aspect, the heating step is sufficient to anneal the first and second cylindrical coils of cold rolled steel. Annealing is a heat treatment process which is generally performed to reduce hardness, remove residual stress, improve toughness, restore ductility, and to alter various mechanical electrical or magnetic properties of material by refinement of grains in microstructure. There are a number of annealing processes which can be applied to steel.

[0044] As briefly discussed above, steel is an alloy of iron with carbon. FIGURE 2 shows an equilibrium diagram for carbon dissolved in a solid solution of iron. Understanding the carbon-iron diagram is particularly important when a specific heat treatment condition is required. The diagram shows iron and carbon combined to form Fe-Fe₃C with a maximum carbon concentration of about 6.67% C. The steel portion of the equilibrium diagram is defined by carbon present in the range from about 0.008 wt% to about 2.14 wt.% and the eutectoid (E), the hypoeutectoid (A), and the hypereutectoid (B) regions. Carbon is an interstitial impurity in various iron phases. It can form a solid solution with a-iron (a- ferrite), γ-iron (γ-austenite) and δ-iron. The maximum solubility of carbon in ferrite is about 0.022%, wherein the maximum solubility of carbon in austenite is about 2.1 1%.

[0045] Various annealing heat treatments are shown on FIGURE 3 as a function of an annealing temperature and an amount of carbon present in steel. In certain aspects, the annealing process described herein can comprise a process annealing. The process annealing is a commonly used heat treatment which is designed to treat work-hardened steel of a low carbon content (<0.25% C) and soften steel sufficiently enough to undergo further cold working without fracturing of steel. In some aspects, it can be achieved by changing the size, shape, and redistribution of the grains in microstructure of steel. In further aspects, such microstructural changes are carried out in consecutive stages of recovery, recrystallization and grain growth. In certain aspects, the process annealing, also known as an intermediate or a subcritical annealing, and is carried out in the ferritic range of steel at any temperatures below steel's austenitizing temperature until any residual stresses have been removed from the lattice structure.

[0046] In other aspects, the annealing process can comprise a normalization annealing process. The normalization annealing process can be applied to ferrous alloys to give the material a uniform fined grained structure and make it less brittle. In some aspects, the normalization annealing process is applied to steel having less than 0.4 % carbon to transform austenite into ferrite, pearlite and sorbite. In certain aspects, the normalization annealing process requires heating steel to 20-50 °C above steel's critical point. In some aspects, the normalization annealing eliminates columnar grains and dendritic segregation that can occur during casting. Yet, in further aspects, the normalization annealing can improve machinability of a component and provide dimensional stability if the component is subjected to further heat treatment process.

[0047] In yet another aspect, the annealing process can comprise a spheroidizing annealing that is applicable to steels having more than 0.8% carbon. Parts are heated to temperatures of 650-720 °C (below Ferrite-Austenite line (Al), or below the Austenite- Cementite line, FIGURE 2) and hold at this temperature for a period time sufficient to ensure that the microstructural changes are completed. In one aspect, during spheroidizing annealing process cementite phase is transformed to the form of small globules (spheroids) dispersed throughout the ferrite matrix. In certain aspects, the spheroidizing annealing is performed on steel parts that have been work hardened to allow further machining such as coil rolling or wire drawing. In some aspects, shperoidization annealing can also improve steel resistance to abrasion. In certain aspects, the resulting product has improved ductility and toughness with reduced hardness and strength. In some aspects, spheroidizing annealing can be carried out under a protective (endothermic) atmosphere to prevent oxidation and decarburization.

[0048] In certain aspects, the annealing process described herein can comprise full annealing. In one aspect, the full annealing comprises heating carbon steel to about 40 °C above Al and A3 lines (FIGURE 3). In certain aspects, heating to these temperatures can ensure transformation of the ferrite phase into austenite phase. In other aspects, the cementite phase can continue to exist if carbon content is greater than about 0.77%. Fully annealed steel is soft and ductile with no internal stresses, which is often necessary for cost-effective forming.

[0049] In certain aspects, the annealing process described herein can comprise isothermal annealing. In one aspect, isothermal annealing can be performed to produce a pearlite structure, which is a suitable microstructure for cutting and wiredrawing. In some aspects, isothermal annealing can be applied to high alloy steels after hot rolling and cooling, to transform any detrimental structures which may have formed.

[0050] The changes in the steel microstructure take place once steel is heated up to the required holding temperature, annealing temperature, and hold for sufficient time to ensure the microstructural changes are completed. These processes are followed by cooling the steel to room temperature. In some aspects, the annealing heat treatments described herein, commonly occurs in three steps: i) heating; ii) soaking; and iii) cooling. These three steps are shown in FIGURE 4. To achieve a successful and desirable outcome of the annealing process an optimized holding time and temperature, appropriate heating/cooling media, and minimum temperature differences within structure of heat treated steel are required.

[0051] In one aspect, the furnace used for annealing process can be any furnace capable accommodating the three steps of annealing for a selected shape and size of steel. In certain aspects, batch annealing furnaces (BAF) can be used to anneal the system comprising a) a first cylindrical coil of cold rolled steel comprising a continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outer most layer defines the outside diameter of the first coil, the inner most layer of the first cylindrical coil defines a hollow bore extending longitudinally through the coil and defining a first coil inner diameter; and b) a second cylindrical coil of cold rolled steel comprising a second continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outermost layer of the second cylindrical coil defines an outside diameter that is smaller than the first coil inner diameter, wherein the second cylindrical coil is positioned concentrically with the hollow bore of the first cylindrical coil; and wherein an annular gap is formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer layer of the second cylindrical coil. In some aspects, the batch annealing furnace can comprise a single-stack batch annealing furnace. In other aspects, the batch annealing furnace can comprise a multi-stack batch annealing furnace.

[0052] In one aspect, the multi-stack batch annealing furnace can be used. In one aspect, the multi-stack batch annealing furnace can comprise about eight batteries, wherein each battery comprises four bases, and wherein each base comprises four stacks comprising two systems each. In one aspect, the heat source in the multi-stack batch annealing furnace is an electrical heating. In another aspect, the heat media in the multi-stack batch annealing furnace is hydrogen gas.

[0053] In one aspect, the single-stack batch annealing furnace can be used. In one aspect, the single-stack batch annealing furnace is a HICON bell type furnace. In one aspect, the single-stack batch annealing comprises heating about 4 to 6 systems comprising: a) a first cylindrical coil of cold rolled steel comprising a continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the inner most layer of the first cylindrical coil defines a hollow bore extending longitudinally through the coil and defining a first coil inner diameter; and b) a second cylindrical coil of cold rolled steel comprising a second continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outermost layer of the second cylindrical coil defines an outer diameter that is smaller than the first coil inner diameter, wherein the second cylindrical coil is positioned concentrically with the hollow bore of the first cylindrical coil; and wherein an annular gap is formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer layer of the second cylindrical coil, can be present in a heated environment. In another aspect, the stack of the systems is covered with an inner cover. In one aspect, the space between the inner cover and the bell type furnace is heated by a heat source. In one aspect, the heat source is a natural gas. In another aspect, the natural gas is fired into the space between the inner cover and the bell type furnace without contacting the steel systems. In one aspect, burners are located tangentially around the circumference of the furnace.

[0054] In one aspect, to ensure substantially uniform heat distribution inside of the each system in the stack and to prevent an oxidation of the first and second cylindrical coils in the system, a heat media can be circulated inside the cover. In one aspect, the heat media can comprise one or more of hydrogen, nitrogen, air, or any combination thereof. In another aspect, the heat media is hydrogen. In yet another aspect, the heat media is a mixture of hydrogen and nitrogen, wherein the relative amount of each gas in the mixture can be determined by one of ordinary skill in the art. In one aspect, the heat media is circulated by a fan located at the base of the BAF. In another aspect, the fan used to circulate the heat media has a size substantially identical to the second coil inner diameter. In yet another aspect, the fan used to circulate the heat media has a size of at least about 5 % larger than the second coil inner diameter, including exemplary values of at least 10% larger, at least 20 % larger, at least 30 % larger, at least 40 % larger, and at least 50 % larger.

[0055] In one aspect, the first and the second cylindrical coils are heated to a

predetermined temperature of at least 600 °C, at least about 650 °C, at least about 700 °C, at least about 750 °C, at least about 800 °C, at least about 850 °C, at least about 900 °C, at least about 950 °C, at least about 1,000 °C, at least about 1 ,050 °C, at least about 1,100 °C, at least about 1 ,150 °C, at least about 1,200 °C, at least about 1,250 °C, at least about 1,300 °C, at least about 1,350 °C, at least about 1,400 °C, at least about 1,450 °C, at least about 1 ,500 °C, at least about 1,550 °C, at least about 1 ,600 °C, at least about 1 ,650 °C, at least about 1 ,700 °C, at least about 1,750 °C, at least about 1,800 °C, at least about 1,850 °C, at least about 1 ,900 °C, at least about 1 ,950 °C, and at least about 2,000 °C. In still further aspects, the first and the second cylindrical coils are heated to a predetermined temperature in any range derived from any two of the above listed exemplary values.

[0056] In one aspect, the first and the second cylindrical coils are heated to a

predetermined temperature in the range from at least about 600 °C to about 1,100 °C, including exemplary values of about 610 °C, about 620 °C, about 630 °C, about 640 °C, about 650 °C, about 660 °C, about 670 °C, about 680 °C, about 690 °C, about 700 °C, about 710 °C, about 720 °C, about 730 °C, about 740 °C, about 750 °C, about 760 °C, about 770 °C, about 780 °C, about 790 °C, about 800 °C, about 810 °C, about 820 °C, about 830 °C, about 840 °C, about 850 °C, about 860 °C, about 870 °C, about 880 °C, about 890 °C, about 900 °C, about 910 °C, about 920 °C, about 930 °C, about 940 °C, about 950 °C, about 960 °C, about 970 °C, about 980 °C, about 990 °C, about 1,000 °C, about 1,010 °C, about 1,020 °C, about 1,030 °C, about 1,040 °C, about 1,050 °C about 1,060 °C, about 1,070 °C, about 1,080 °C, and about 1,090 °C. In still further aspects, the first and the second cylindrical coils are heated to a predetermined temperature in any range derived from any two of the above listed exemplary values. For example, the first and second cylindrical coils are heated to a temperature in the range of about 600 °C to about 900 °C, or about 700 °C to about 1,100 °C.

[0057] In one aspect, the first and the second cylindrical coils are heated to a

predetermined temperature for a predetermined period of time sufficient to anneal the first and second cylindrical coils. In one aspect, the predetermined period is time is about 5 to about 20 hours, including exemplary values of about 5.5 hours, about 6 hours, about 6.5 hours, about 7 hours, about 7.5 hours, about 8 hours, about 8.5 hours, about 9 hours, about 9.5 hours, about 10 hours, about 10.5 hours, about 11 hours, about 1 1.5 hours, about 12 hours, about 12.5 hours, about 13 hours, about 13.5 hours, about 14 hours, about 14.5 hours, about 15 hours, about 15.5 hours, about 16 hours, about 16.5 hours, about 17 hours, about 17.5 hours, about 18 hours, about 18.5 hours, about 19 hours, and about 19.5. In still further aspects, the predetermined period of time is in any range derived from any two of the above listed exemplary values. In one aspect, after the system is heated as described above, the heated system is cooled back to a second predetermined temperature. In one aspect, to cool the heated system, the heating bell furnace can be replaced by a cooling bell. In another aspect, the cooling process can comprise, air cooling, water flashing, chilled water cooling, or any combination thereof. [0058] In one aspect, the heating of the system to the predetermined temperature for the predetermined period of time and cooling to the second predetermined temperature is performed in a total period of time in the range of from less than about 45 hours to about 10 hours, including exemplary values of less than about 44 hours, about 43 hours, about 42 hours, about 41 hours, about 40 hours, about 39 hours, less than about 38 hours, less than about 37 hours, less than about 36 hours, less than about 35 hours, less than about 34 hours, less than about 33 hours, less than about 32 hours, less than about 31 hours, less than less than about 30 hours, less than about 29 hours, less than about 28 hours, less than about 27 hours, less than about 26 hours, less than about 25 hours, less than about 24 hours, less than about 23 hours, less than about 22 hours, less than about 21 hours, less than about 20 hours, less than about 19 hours, less than about 18 hours, less than about 17 hours, less than about 16 hours, less than about 15 hours, less than about 14 hours, less than about 13 hours, less than about 12 hours, and less than about 11 hours. In still further aspects, the total period of time is in any range derived from any two of the above listed exemplary values.

[0059] The steel industry is known in the art to be one of the industrial emitters of carbon dioxide. Conventional steel making technologies are typically energy intensive, where large quantities of fuel are used to provide the needed energy to heat as well as to promote the chemical reactions necessary to produce high quality steel. It is estimated that between 4 and 7 % of the anthopogenic carbon dioxide emissions are actually originated from the steel industry. It is also estimated that the conventional annealing processes require about 1.086 GJ per ton of annealed steel of a direct energy that is defined by the energy use to perform the annealing process. The conventional annealing processes also results in direct emission of about 0.049 ton C0₂ per ton of annealed steel.

[0060] In one aspect, the process described herein provides a more energy efficient solution to reduce carbon footprint as compared to conventional annealing processes. In one aspect, the described process for annealing exhibits a reduced carbon footprint relative to that of a conventional annealing process, wherein a substantially identical amount of cold rolled steel present as a singular coil of cold rolled steel is heated to the same predetermined temperature. In one aspect, the reduced carbon footprint is at least about a 5 % reduced carbon footprint, at least about a 10 % reduced carbon footprint, at least about a 10 % reduced carbon footprint, at least about a 15 % reduced carbon footprint, at least about a 20 % reduced carbon footprint, at least about a 25 % reduced carbon footprint, at least about a 30 % reduced carbon footprint, and at least about a 35 % reduced carbon footprint. In still further aspects, the reduced carbon footprint is in any range derived from any two of the above listed exemplary values.

[0061] In certain aspects, the reduced carbon footprint can be quantified by a reduction in C0₂ emissions resulting from the firing of the furnace used to heat the steel. In other aspects, the reduced carbon footprint can be quantified by a reduction in C0₂ emission resulting from decreased amount of heat media circulated inside of the furnace. In various aspects, the reduced carbon footprint can be quantified by a reduction in C0₂ emission resulting from waste heat recovery.

[0062] In some aspects of this invention, after annealing process is completed and the system is cooled down to the second predetermined temperature, the system can be transferred for further processing. In one aspect, the system can be dismantled to remove the second cylindrical coil from the hollow bore of the first cylindrical coil to produce a separate first second cylindrical coil. In yet another aspect, the separate first and second cylindrical coils can be uncoiled to form a first uncoiled continuous sheet of steel and a second uncoiled continuous sheet of steel. In a further aspect, the first and the second uncoiled continuous sheets of steel can be welded to form a third uncoiled continuous sheet of steel. In a yet another aspect, the third uncoiled continuous sheet of steel can be rolled to form a third coil having a plurality of concentric adjacent layers and wherein the inner and outer diameter of the third coil can be defined by one of ordinary skill in the art.

D. ASPECTS

[0063] In various aspects, the present invention pertains to and includes at least the following aspects.

[0064] Aspect 1 : A system, comprising: a) a first cylindrical coil of cold rolled steel comprising a continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outer most layer defines the outside diameter of the first coil, wherein the inner most layer of the first cylindrical coil defines a hollow bore extending longitudinally through the coil and defining a first coil inner diameter; and b) a second cylindrical coil of cold rolled steel comprising a second continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outermost layer of the second cylindrical coil defines an outside diameter that is smaller than the first coil inner diameter; wherein the second cylindrical coil is positioned concentrically within the hollow bore of the first cylindrical coil; and wherein an annular gap is formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil.

[0065] Aspect 2: The system of Aspect 1, wherein the annular gap is characterized by a distance between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil of about 5 cm to about 15 cm.

[0066] Aspect 3: The system of any one of Aspects 1-2, wherein the first and second cylindrical coils comprise a combined total weight of at least about 18 metric tons.

[0067] Aspect 4: The system of any one of Aspects 1-3, wherein the first and second coils are present in a heated environment.

[0068] Aspect 5: The system of any one of Aspects 1-4, wherein the heated environment is suitable to anneal the first and second cylindrical coils.

[0069] Aspect 6: The system of any one of Aspects 1-5, wherein the heated environment is suitable to heat the first and second cylindrical coils to a temperature in the range of from about 600 °C to about 900 °C.

[0070] Aspect 7: A process comprising: a) providing a system comprising: i) a first cylindrical coil of cold rolled steel comprising a continuous sheet of steel rolled to form a plurality of concentric adjacent layers wherein the outer most layer defines the outside diameter of the first coil, wherein the inner most layer of the coil defines a hollow bore extending longitudinally through the coil and defining a first coil inner diameter; and ii) a second cylindrical coil of cold rolled steel comprising a second continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outermost layer of the second cylindrical coil defines an outside diameter that is smaller than the first coil inner diameter, wherein the second cylindrical coil is positioned concentrically within the hollow bore of the first cylindrical coil; and wherein an annular gap is formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil; and b) heating the first and the second cylindrical coils to a predetermined temperature for a predetermined period of time. [0071] Aspect 8: The process of Aspect 7, wherein the heating step is sufficient to anneal the first and second cylindrical coils of cold rolled steel.

[0072] Aspect 9: The process of any one of Aspects 7-8, wherein the annular gap is characterized by a distance between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil of about 5 cm to about 15 cm.

[0073] Aspect 10: The process of any one of Aspects 7-9, wherein the first and second cylindrical coils comprise a combined total weight of at least about 18 metric tons.

[0074] Aspect 1 1 : The process of any one of Aspects 7-10, wherein the first and the second cylindrical coils are heated to a predetermined temperature of at least about 700 °C.

[0075] Aspect 12: The process of any one of Aspects 7-1 1, wherein the first and the second cylindrical coils are heated to a predetermined temperature in the range from at least about 700 °C to about 1 100 °C.

[0076] Aspect 13: The process of any one of Aspects 7-12, wherein after the system is heated for the predetermined period of time the heated system is cooled back to a second predetermined temperature.

[0077] Aspect 14: The process of any one of Aspects 7-13, wherein heating the system to the predetermined temperature for the predetermined time and cooling to the second predetermined temperature is performed in a total period of time less than 45 hours.

[0078] Aspect 15: The process of any one of Aspects 7-14, wherein the heating is performed in the presence of a heat media.

[0079] Aspect 16: The process of any one of Aspects 7-15, wherein the heat media comprises hydrogen, nitrogen, or a combination thereof.

[0080] Aspect 17: The process of any one of Aspects 7-16, wherein the process exhibits a reduced carbon footprint relative to that of a conventional annealing process wherein a substantially identical amount of cold rolled steel present as a singular coil of cold rolled steel is heated to the same predetermined temperature.

[0081] Aspect 18: The process of any one of Aspects 7-17, wherein the reduced carbon footprint is at least a 20% reduced carbon footprint. [0082] Aspect 19: The process of any one of Aspects 7-18, wherein the reduced carbon footprint can be quantified by a reduction in C0₂ emissions resulting from the firing of the furnace used to heat the steel.

[0083] Aspect 20: An annealed cold rolled steel produced by the process of any one of Aspects 7-19.

[0084] Without further elaboration, it is believed that one skilled in the art can, using the description herein, utilize the present invention. The following examples are included to provide addition guidance to those skilled in the art of practicing the claimed invention. The examples provided are merely representative of the work and contribute to the teaching of the present invention. Accordingly, these examples are not intended to limit the invention in any manner.

Claims

CLAIMS s claimed is:

A system, comprising:

a) a first cylindrical coil of cold rolled steel comprising a continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outer most layer defines the outside diameter of the first coil, wherein the inner most layer of the first cylindrical coil defines a hollow bore extending longitudinally through the coil and defining a first coil inner diameter; and

b) a second cylindrical coil of cold rolled steel comprising a second

continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outermost layer of the second cylindrical coil defines an outside diameter that is smaller than the first coil inner diameter;

wherein the second cylindrical coil is positioned concentrically within the hollow bore of the first cylindrical coil; and

wherein an annular gap is formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil.

The system of claim 1, wherein the annular gap is characterized by a distance between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil of about 5 cm to about 15 cm.

The system of claim 1 , wherein the first and second cylindrical coils comprise a combined total weight of at least about 18 metric tons.

The system of claim 2, wherein the first and second coils are present in a heated environment.

The system of claim 4, wherein the heated environment is suitable to anneal the first and second cylindrical coils.

The system of claim 5, wherein the heated environment is suitable to heat the first and second cylindrical coils to a temperature in the range of from about 600 °C to about 900 °C.

A process comprising:

a) providing a system comprising: i. a first cylindrical coil of cold rolled steel comprising a continuous sheet of steel rolled to form a plurality of concentric adjacent layers wherein the outer most layer defines the outside diameter of the first coil, wherein the inner most layer of the coil defines a hollow bore extending longitudinally through the coil and defining a first coil inner diameter; and

ii. a second cylindrical coil of cold rolled steel comprising a second continuous sheet of steel rolled to form a plurality of concentric adjacent layers, wherein the outermost layer of the second cylindrical coil defines an outside diameter that is smaller than the first coil inner diameter,

wherein an annular gap is formed around the second cylindrical coil between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil; and

b) heating the first and the second cylindrical coils to a predetermined

temperature for a predetermined period of time.

8. The process of claim 7, wherein the heating step is sufficient to anneal the first and second cylindrical coils of cold rolled steel.

9. The process of claim 7, wherein the annular gap is characterized by a distance

between the inner most layer of the first cylindrical coil and the outer most layer of the second cylindrical coil of about 5 cm to about 15 cm.

10. The process of claim 7, wherein the first and second cylindrical coils comprise a

combined total weight of at least about 18 metric tons.

11. The process of claim 7, wherein the first and the second cylindrical coils are heated to a predetermined temperature of at least about 700 °C.

12. The process of claim 7, wherein the first and the second cylindrical coils are heated to a predetermined temperature in the range from at least about 700 °C to about 1100 °C.

13. The process of claim 7, wherein after the system is heated for the predetermined

period of time the heated system is cooled back to a second predetermined

temperature.

14. The process of claim 13, wherein heating the system to the predetermined temperature for the predetermined time and cooling to the second predetermined temperature is performed in a total period of time less than 45 hours.

15. The process of claim 7, wherein the heating is performed in the presence of a heat media.

16. The process of claim 15, wherein the heat media comprises hydrogen, nitrogen, or a combination thereof.

17. The process of any of claims 7-16, wherein the process exhibits a reduced carbon footprint relative to that of a conventional annealing process wherein a substantially identical amount of cold rolled steel present as a singular coil of cold rolled steel is heated to the same predetermined temperature.

18. The process of claim 17, wherein the reduced carbon footprint is at least a 20%

reduced carbon footprint.

19. The process of claim 17, wherein the reduced carbon footprint can be quantified by a reduction in C0₂ emissions resulting from the firing of the furnace used to heat the steel.

20. An annealed cold rolled steel produced by the process of any one of claims 7-19.