WO2023075660A1

WO2023075660A1 - Flat wire and method for production thereof

Info

Publication number: WO2023075660A1
Application number: PCT/SE2022/050964
Authority: WO
Inventors: Oskar FORSMAN; Ola HELMFRIDSSON
Original assignee: Suzuki Garphyttan Ab
Priority date: 2021-10-28
Filing date: 2022-10-21
Publication date: 2023-05-04
Also published as: SE2151318A1; SE545660C2; EP4423305A1; CN118103541A

Abstract

A flat wire (3) and a saw blade (1) obtainable from the flat wire (3) are disclosed. The flat wire (3) is made of a steel comprising 0.45 - 0.70 wt.-% of C, 1.2 - 2.5 wt.-% of Si, 0.2 - 1.1 wt.-% of Mn, 0.5 - 1.4 wt.-% of Cr, 0.05 - 0.40 wt.-% of V, 0.05 - 0.40 wt.-% of Mo, 0.05 - 0.40 wt.-% of W, optionally up to 0.4 wt-% of Ni, optionally up to 0.003 wt.-% of Ti, optionally up to 0.05 wt.-% of Nb, balance Fe and unavoidable impurities.

Description

FLAT WIRE AND METHOD FOR PRODUCTION THEREOF

TECHNICAL FIELD

The present disclosure in general relates to a flat wire made of a steel. The present disclosure further relates in general to a method for producing such a flat wire. The present disclosure further relates in general to the use of the flat wire as well as to a method for producing a saw blade. The present disclosure also relates in general to a saw blade.

BACKGROUND

A band saw blade, such as for cutting wood or metal, needs to have a high strength in order to withstand the forces to which it is subjected during use. Moreover, the material of the band saw blades also needs to have sufficient ductility to allow it to be bent over and tensioned over two rotating rolls of a band saw device without a risk for fracture, at the same time as the material should have high fatigue resistance to ensure that the tension in the band saw blade can be maintained throughout one or more sawing operations. Moreover, the material of the band saw blades should be easy to weld and enable strong weld joints such that they can be made into continuous band saw blades. Furthermore, the teeth of the band saw blade need to have a sufficient strength for the material to be cut by the band saw blade without causing a risk brittle failure of the teeth during use. Band saw blades may, depending on the intended material to be cut by the saw blade and/or the configuration of the band saw device used, typically have a thickness of about 0.1 to 2 mm and a width of about 2 - 50 mm. Band saw blades are often made from carbon steels, due to high performance to cost ratio of such steels.

The saw blades may be manufactured from a steel sheet, having a desired thickness, and slit into the desired width of the saw blade. In other words, the saw blades are often made by slitting into steel strips. Such a slitting may in some cases result in inferior edges which in turn requires planing or grinding to obtain sufficient quality for further processing. Such a planing or grinding step adds to the manufacturing costs. The steel strips are generally provided in rolls to the manufacturer of the band saw blade, who thereafter form the teeth along a longitudinal edge of the steel strip by cutting or punching of the material. In some cases, the teeth of band saw blade may also be subjected to a hardening step. Thereafter, the steel strip with the formed teeth is cut into desired lengths of the band saw blade and the short edges are thereafter welded to form a continuous band saw blade. Manufacturing band saw blades by slitting of a steel sheet has the disadvantage of the length of the steel strip being limited by the length of the steel sheet. Increasing the length of the material from which the band saw blade is to be made would reduce the manufacturing costs for the manufacturer of the band saw blade. For example, it would reduce the down time caused by changing the roll of material comprising the steel strip in which the teeth of the band saw blade is to be cut.

Furthermore, it may reduce the material which, after cutting to desired length of the band saw blade, is left over and therefore should be recycled.

SUMMARY

The object of the present invention is to provide a steel product from which saw blades of high quality may be produced in a cost-effective manner.

The object is achieved by the subject-matter of the appended independent claim(s). Embodiments are defined by the dependent claims.

The present disclosure provides a flat wire of a steel having the following composition, in percent by weight (wt-%):

C 0.45 - 0.70,

Si 1.2 - 2.5,

Mn 0.2 - 1.1,

Cr 0.5 - 1.4,

V 0.05 - 0.40,

Mo 0.05 - 0.40,

W 0.05 - 0.40,

Ni optionally up to 0.4,

Ti optionally up to 0.003,

Nb optionally up to 0.05, balance Fe and unavoidable impurities.

The flat wire according to the present disclosure has an excellent combination of properties making it suitable for production of saw blades, in particular band saw blades. More specifically, the flat wire has very high strength, high fatigue resistance as well as high ductility. Moreover, the flat wire has excellent hardenability, which in turn for example enables teeth of a saw blade to be hardened to a high hardness. Also, the flat wire has good weldability, thereby enabling production of continuous saw blades, if desired.

Furthermore, by means of the flat wire according to the present disclosure, it is possible to produce saw blades in a more cost-effective manner in comparison to, for example, the conventional method of producing saw blades from steel strips obtained by slitting. This is primarily due to the possibility of enabling a longer longitudinal extension (i.e. longer length) of a flat wire compared to a steel strip slitted from a steel sheet. Typically, the flat wire may be at least 5 times longer or even 10 times longer than a slitted steel strip conventionally used for producing saw blades. Furthermore, the flat wire according to the present disclosure may, when producing saw blades thereof, increase the material yield by reduced need for edge treatment and decreased amount of scrap due to setup and left over material after finished cutting. In addition to reduced manufacturing cost this is positive from environmental perspective.

The flat wire may be a flat rolled wire. By producing the flat wire by rolling to the final dimension, a very high width to thickness ratio may be achieved in a cost-effective manner. Preferably, the flat wire may be a flat cold rolled wire.

The flat wire may suitably have a width to thickness ratio of at least 3:1, preferably at least 5:1. Thereby, the flat wire has a dimension which is suitable for production of a large variety of products, such as saw blades, knives, retaining rings or wave springs.

Moreover, the flat wire may have a thickness of from 0.1 mm to 2 mm. Preferably, the flat wire may have a thickness from 0.3 mm to 1.6 mm. Thereby, the flat wire has a thickness making it highly suitable for production of, for example, band saw blades.

The present disclosure further provides a method for producing the flat wire described above. The method comprises: casting a steel having the above specified composition, optionally heat treating the cast material, hot rolling the cast material to a wire rod, optionally patenting the wire rod at a temperature of at least 900 °C, preferably at least 930 °C, optionally cold drawing the wire rod to a wire having an intermediate dimension, optionally heat treating and/or patenting the wire having an intermediate dimension, and cold drawing or cold rolling to desired final dimension of the flat wire.

The flat wire described above is particularly useful in the manufacture of a saw blade, in particular in the manufacture of a band saw blade.

The present disclosure also provides a method for producing a saw blade, such a band saw blade.

Said method comprises: removing material along a longitudinal edge of the above-described flat wire so as to form saw teeth along said longitudinal edge of the flat wire, thereby obtaining the saw blade, and optionally hardening the formed saw teeth.

The present disclosure further provides a saw blade of a steel, said steel having the following composition, in percent by weight (wt.-%):

C 0.45 - 0.70,

Si 1.2 - 2.5,

Mn 0.2 - 1.1,

Cr 0.5 - 1.4,

V 0.05 - 0.40,

Mo 0.05 - 0.40,

W 0.05 - 0.40,

Ni optionally up to 0.4,

Ti optionally up to 0.003,

Nb optionally up to 0.05, balance Fe and unavoidable impurities.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 illustrates a side view of a part of an example of a saw blade,

Fig. 2 schematically illustrates a cross sectional view of a first exemplifying embodiment of the flat wire according to the present disclosure, and Fig. 3 schematically illustrates a cross sectional view of a second exemplifying embodiment of the flat wire according to the present disclosure.

DETAILED DESCRIPTION

The invention will be described in more detail below with reference to exemplifying embodiments and the accompanying drawings. The invention is however not limited to the exemplifying embodiments discussed and/or shown in the drawings, but may be varied within the scope of the appended claims. Furthermore, the drawings shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate the invention or features thereof.

When ranges are disclosed in the present disclosure, such ranges include the end values of the range, unless explicitly disclosed otherwise. Similarly, when an open range is disclosed, the open range also include the single end value of the open range, unless explicitly disclosed otherwise.

A flat wire is in the present disclosure considered to mean a wire with at least two parallel longitudinal surfaces and which has a width to thickness ratio of at least 2:1. The width and thickness, respectively are here considered to correspond to (in a cross-sectional view of the flat wire) the greatest extension of the width and thickness, respectively. Such a flat wire may have a substantially rectangular or trapezoidal cross section, with naturally rounded, purposively rounded or sharp corners and/or edges. Naturally rounded corners and/or edges are in the present disclosure considered to mean corners and/or edges obtaining a curvature as a result of the manufacturing process when no active measures have been taken in order to control the shape of such corners and/or edges.

Although the flat wire according to the present disclosure primarily has been developed for use in the manufacture of band saw blades, it may also be used when producing other types of saw blades, such as saw blades for jig saws or fret saws. A saw blade produced from the flat wire according to the present disclosure may be a continuous saw blade, or may be a saw blade having two opposing free longitudinal ends. The flat wire may also be used for other purposes, such as in the production of blades (such as knives, razor blades, doctor blades), chain links, retaining rings, washers, bearings, piston rings, reinforcement, or springs (such as wave springs). The flat wire according to the present disclosure is a flat wire of a steel having the following composition, in percent by weight (wt.-%):

C 0.45 - 0.70,

Si 1.2 - 2.5,

Mn 0.2 - 1.1,

Cr 0.5 - 1.4,

V 0.05 - 0.40,

Mo 0.05 - 0.40,

W 0.05 - 0.40,

Ni optionally up to 0.4,

Ti optionally up to 0.003,

Nb optionally up to 0.05, balance Fe and unavoidable impurities.

In the following, the importance of the different alloying elements of the steel will be briefly discussed. Upper and lower limits of the individual elements of the composition can be freely combined within the broadest limits set out in the claims.

Carbon (C) is an element greatly affecting the strength of the steel. More specifically, the strength increases with increasing carbon content. In order to achieve sufficient strength, the steel of the flat wire comprises at least 0.45 wt.-% carbon. Suitably, the steel comprises at least 0.50 wt.-% C. Preferably, carbon is present in an amount of at least 0.58 wt.-%. However, too high contents of carbon may negatively affect the ductility of the flat wire. Moreover, too high contents of carbon may also result in a risk of formation of coarse cementite precipitates in the steel, which in turn could negatively affect the toughness. The carbon content should therefore not exceed 0.70 wt.-%.

Suitably, the steel comprises 0.65 wt.-% or less of carbon.

Silicon (Si) is an effective deoxidizing element in the steel production. Alloying with silicon also increases the strength as well as the obtainable hardness of the material. Therefore, the steel comprises at least 1.2 wt.-% Si. Silicon may preferably be present in an amount of at least 1.70 wt.-%, more preferably at least 2.10 wt.-%, in order to achieve a high strength and excellent hardenability. However, the silicon content should not exceed 2.5 wt.-% since higher contents may cause the steel to harden too much such that it becomes brittle. Preferably, silicon is present in an amount of 2.40 wt.-% or less. Manganese (Mn) is also an effective deoxidizing element. Furthermore, it may be used for the purpose of immobilization of sulfur in the steel by formation of manganese sulfides. Alloying with manganese may also improve the hardenability of the material, and therefore also the hardness. The manganese content of the steel is therefore at least 0.2 wt.-%. Preferably, manganese is present in an amount of at least 0.30 wt.-%. Too high contents of manganese may however lead to risk of embrittlement. Therefore, manganese is present in an amount of at most 1.1 wt.-%. Preferably, manganese is present in an amount of 0.70 wt.-% or less.

Chromium (Cr) is added in order to improve the hardenability as well as resistance to tempering softening. Therefore, chromium is added in an amount of at least 0.5 wt.-%, preferably at least 1.10 wt.-%. Chromium also has a positive effect on hardness and depth of hardened surface layer in case the flat wire (or a product produced therefrom) is subjected to surface hardening by nitridation. However, too high contents of chromium may lead to increased alloying costs without further improving the properties. Rather, too high chromium contents may lead to the flat wire becoming brittle. Therefore, the chromium content is 1.40 wt.-% or less.

Vanadium (V) has the beneficial effect of being able to suppress coarsening of austenite grains during the manufacturing process of the flat wire by forming nitrides, carbides and/or carbonitrides. Vanadium can also contribute to hardening at a tempering temperature of the steel. Moreover, vanadium also contributes to increased surface hardness as well as depth of hardened surface layer if the flat wire is subjected to nitriding as a surface hardening process. Therefore, vanadium is present in an amount of at least 0.05 wt.-%. Vanadium may suitably be present in an amount of at least 0.10 wt.-%. However, in case too much vanadium is added, there is a risk of formation of coarse inclusions which in practice cannot be dissolved during the manufacturing process since these can be formed also over the austenitization temperature of the steel. Such coarse inclusions may reduce the toughness and there may be an increased risk for cracking during production of the flat wire, for example during the final cold processing step(s). Therefore, the amount of vanadium is limited to 0.40 wt.% or less. Preferably, vanadium is present in an amount of 0.25 wt.-% or less.

Molybdenum (Mo) is added to improve the hardenability and forms carbides in the steel during production of the flat wire. Molybdenum forms carbides at lower temperatures compared to Ti and Nb. Therefore, carbides of molybdenum can, if desired, be dissolved during a possible heat treatment (such as prior to hot rolling). This may in turn facilitate subsequent processing steps during the manufacturing process. However, molybdenum can also precipitate during subsequent processing steps of the production of the flat wire due to the formation temperature of such carbides. These precipitated carbides in turn improve the resistance to temper softening and contributes to the strength of the flat wire. Therefore, it is possible to obtain high strength without softening even after high temperature tempering or other heat treatment, such as during hardening by nitration, that may be needed or desired for producing various products of the flat wire. Molybdenum is therefore present in an amount of at least 0.05 wt.-%. Molybdenum also has the advantage of not forming nitrides, which is in contrast to vanadium. However, in case too much molybdenum is added to the steel, there is a risk of formation of too large (coarse) carbides. Presence of coarse carbides is undesirable since it may lead to risk for cracking or breaking during the production of the flat wire. Furthermore, the formation of such coarse carbides (or too much of said carbides) leads to a reduction of the carbon content which is available for contributing to the strength of the flat wire. Moreover, too high contents of molybdenum may suppress formation of a martensite structure during the production and is therefore undesirable. Therefore, the molybdenum content is 0.40 wt.-% or less. Preferably, the steel comprises 0.25 wt.-% or less molybdenum.

Tungsten (W) is added to improve hardenability and forms carbides in the steel during production of the flat wire. Similarly to molybdenum, tungsten forms carbides at lower temperatures compared to Ti and Nb, and the carbides of tungsten can therefore, if desired, be dissolved during a possible heat treatment (such as prior to hot rolling). However, tungsten can also precipitate during subsequent processing steps. These precipitated carbides in turn improve the resistance to temper softening and contributes to the strength of the flat wire. Tungsten is therefore present in an amount of at least 0.05 wt.-%. Like molybdenum, tungsten has the advantage of not forming nitrides in the steel. However, in case too much tungsten is added to the steel, there is a risk of formation of coarse carbides which can lead to cracking during the production of the flat wire as well as to a reduction of the carbon content which is available for contributing to the strength of the flat wire. Therefore, the tungsten content is 0.40 wt.-% or less. Preferably, the tungsten content is 0.25 wt.-% or less.

Nickel (Ni) may be added in an amount of up to 0.4 wt.-%, if desired. Nickel may improve the ductility and could also improve the hardenability. However, nickel may also increase the residual austenite which inter alia may lead to a loss of uniformity of the microstructure in the flat wire. This may in turn lead to difficulties in the production of the flat wire. Therefore, the amount of nickel may suitably be less than 0.05 wt-%, in which case the steel is considered to be free from any additions of nickel.

Titanium (Ti) is an efficient deoxidation element, and a nitride- and sulfide-forming element, and may be added in small amounts for taking care of oxygen, nitrogen and sulfur in the steel melt. However, if present in too large amounts, it may form hard oxides and nitrides, which in turn may lower the fatigue resistance of the flat wire. Therefore, titanium may be present only up to 0.003 wt.-%, if added.

Niobium (Nb) is able to form nitrides, carbides and carbonitrides. Nitrides of niobium are formed at higher temperatures than those of vanadium. Therefore, by alloying with niobium, the amount of vanadium nitrides and vanadium carbonitrides can be reduced leaving more vanadium available for achieving beneficial properties. Niobium may also be used for the purpose of suppressing the austenite grain size. However, niobium increases the alloying costs and, if present in a too large amount, may also risk formation of coarse inclusions and lower the toughness. Therefore, niobium may be present only up to 0.05 wt.-% if added.

As mentioned above, the remaining part (the balance) of the steel constitutes iron and unavoidable impurities. Unavoidable impurities is in the present disclosure considered to mean impurities resulting from the raw material used and/or the manufacturing process for producing the chemical composition of the flat wire. Examples of unavoidable impurities include, but is not limited to, phosphorus (P), sulfur (S), copper (Cu) and aluminum (Al). Preferably, the steel comprises maximally 0.020 wt.-%, more preferably maximally 0.015 wt.-%, of P. Moreover, the steel preferably comprises maximally 0.030 wt.-%, more preferably maximally 0.025 wt.-%, of S. The Cu content is preferably maximally 0.05 wt.-%, more preferably maximally 0.02 wt.-%. Moreover, the Al content is preferably max 0.01 wt.-%, more preferably max 0.005 wt.-%. The steel may further be allowed to comprise oxygen (O) as an unavoidable impurity in an amount of up to 25 ppm. Yet another example of an unavoidable impurity is nitrogen (N), which should be limited to at most 0.007 wt.%. If the unavoidable impurities are within the ranges specified above, these are not considered to substantially affect the properties of the steel.

The dimensions of the flat wire may be selected depending on the intended use of the flat wire. For most of the intended uses of the flat wire, the flat wire should have a width to thickness ratio of at least 3:1, preferably a width to thickness ration of at least 5:1. In case the flat wire is to be used for the production of saw blades, it may suitably have a width to thickness ratio of equal to or above 8:1, preferably equal to or above 10:1. Thereby, teeth may easily be formed in the flat wire by removal of material along a longitudinal edge of the flat wire without jeopardizing mechanical properties in the remaining part of the flat wire. This may be especially useful in the case of band saw blades, since such saw blades are, during use, tensioned over two rotating rolls and run thereover during multiple sawing operations. Furthermore, the flat wire may suitably have a thickness of from 0.1 - 2 mm depending on the intended use thereof, although other thicknesses are also plausible. Preferably, the flat wire may have a thickness of from 0.3 mm to 1.6 mm. Thereby, it is particularly suitable for production of band saw blades intended for cutting for example wood or metal. Naturally, the thickness as well as the width to thickness ratio is typically essentially constant over the longitudinal length of the flat wire. The flat wire may typically have a length after the production thereof of at least 1 km, or at least 5 km. It may however thereafter be cut into various lengths, and the length of the flat wire does therefore not limit the scope of the present disclosure. If compared to slitted steel strips conventionally used for production of for example saw blades, the flat wire according to the present disclosure may typically be at least 5 times longer or at least 10 times longer than such a slitted strip.

The flat wire according to the present disclosure has a tensile strength of at least 1700 MPa in the as rolled or drawn condition, and may easily be hardened to a tensile strength of 2000 MPa or more (for example by hardening with oil quenching), in general to a tensile strength of 2100 MPa or more. The flat wire according to the present disclosure may be hardened to a tensile strength of up to 2400 MPa, if desired. Moreover, it has a good ductility with an elongation to fracture of at least 5 % even if hardened to a tensile strength of more than 2000 MPa. It may also be surface hardened to at least 800 HV, or even 900 HV or above, using nitriding.

Compared to carbon steels commonly used in the production of saw blades, the steel according to the present disclosure can be made harder, has good resistance to temper softening, has higher fatigue resistance and higher tensile strength. Furthermore, if hardened to the same target tensile strength, the steel of the present disclosure may have a higher elongation to fracture than carbon steels. Thus, the present steel has an excellent combination of properties making it suitable for use in the manufacture of saw blades (as well as other products).

The present disclosure further relates to a method for producing the above-described flat wire. The method comprises casting a steel having the above specified composition. The steel may for example be continuously cast into a bloom or a billet. The cast material may optionally be subjected to a heat treatment at a temperature of at least 1100 °C for the purpose of at least partially dissolving carbides formed during the casting step. This may in turn facilitate the subsequent processing steps. The cast material is thereafter hot rolled to a wire rod. The wire rod may for example have a diameter of from 5 mm to 20 mm, but is not limited thereto. The wire rod may optionally be subjected to patenting at a temperature of at least 900 °C, preferably at least 930 °C. The purpose of such a patenting step is to form austenite and then perform a controlled rapid cooling and holding at a desired temperature for the purpose of obtaining a desired microstructure. If desired, the wire rod may optionally be cold drawn to a wire having an intermediate dimension. An intermediate dimension is here considered to be a dimension smaller than the wire rod, but a dimension that has a cross-sectional area greater than the cross-sectional area of the final flat wire. The wire having an intermediate dimension may suitably have a circular or elliptic cross section. Cold drawing may be performed at a temperature of at most 200 °C, preferably at a temperature of 100 °C or less. Moreover, the wire having an intermediate dimension may optionally be subjected to a heat treatment, such as tempering or annealing, and/or patenting for the purpose of facilitating the subsequent step for obtaining the final dimension of the flat wire. Thereafter, the wire rod (or where applicable the wire having an intermediate dimension) is subjected to cold drawing or cold rolling to desired final dimension of the flat wire. Said step may be performed at a temperature of at most 200 °C, preferably at a temperature of 100 °C or less. By means of said step, the flat wire obtains the desired width to thickness ratio as well as the desired cross-sectional shape.

As mentioned above, cold drawing or cold rolling may be used to obtain the final dimension of the flat wire. According to a preferred embodiment, cold rolling is utilized. Thereby, a high width to thickness ratio may be achieved without the need for intermediate heat treatments. In contrast, cold drawing may sometimes require a plurality of cold drawing steps separated by an intermediate heat treatment if high width to thickness ratios, such as for example about 10:1 are desired. This is believed to be due to some deformation hardening during such a cold drawing step, which may limit the reduction degree possible for each cold drawing step. Moreover, the steel tends to be sensitive to for example surface defects or uneven distribution of lubricant during final cold drawing, at least when drawn to finer dimensions. Therefore, there may in some situations be a risk of brittle failure during final cold drawing to desired final dimension of the flat wire. The present inventors have however surprisingly found that the issue of deformation hardening during the final cold deformation step is however not as pronounced for the steel according to the present disclosure if using cold rolling to desired final dimension of the flat wire. The reason therefore is not completely understood, but could possibly be associated with the difference in pattern of deformation distribution within the steel during cold rolling compared to during cold drawing. Moreover, there is a considerably lower risk for possible surface defects affecting the ability to cold deform the steel to desired final dimension of the flat wire. Therefore, for reasons of process economy, cold rolling to final dimension of the flat wire is preferred. It should here be noted that it is naturally also possible to perform a heat treatment between two cold rolling passes, if desired, although this is typically not needed for the herein described steel. The flat wire according to the present disclosure may thereafter be used in the production of various types of products. As previously mentioned, the flat wire is especially useful in the manufacture of a saw blade, such as a band saw blade. The present disclosure therefore also provides a method for producing a saw blade, such as a band saw blade, comprising removing material along a longitudinal edge of the flat wire described above so as to form saw teeth along said longitudinal edge, thereby obtaining the saw blade. Said removal of material may be performed according to any previously known method therefore and will therefore not be further described in the present disclosure. The teeth of the saw blade may thereafter suitably be hardened. Examples of suitable hardening process include oil quenching and nitriding. The flat wire may, either before or after the formation of the teeth, be cut into a desired length of the saw blade. For reasons of process economy, cutting to desired length is usually performed after formation of the teeth. Moreover, said cutting may be performed either before or after the optional hardening of the teeth. If seeking to obtain a continuous saw blade, the longitudinal ends of the saw blade, after it is cut to desired length, are welded to each other. One example of a suitably method therefore is butt welding.

The saw blade produced from the herein described flat wire is especially advantageous for cutting wood. Such a saw blade may also be used for cutting metal, such as pure metals or alloys based on aluminum, copper or zinc. Moreover, such a saw blade may also be used for cutting other materials, such as graphite, fiberglass, or plastics. Furthermore, a saw blade produced from the herein described flat wire is also believed to be a suitable candidate for cutting food products.

Furthermore, in accordance with the present disclosure, a saw blade (such as a band saw blade) is provided. The saw blade comprises or consists of a steel having the following composition (in percent by weight):

C 0.45 - 0.70, preferably 0.50 - 0.70, more preferably 0.58 - 0.65;

Si 1.2 - 2.5, preferably 1.70-2.50, more preferably 2.10 - 2.40;

Mn 0.2 - 1.1, preferably 0.30 - 0.70;

Cr 0.5 - 1.4, preferably 1.10 - 1.40;

V 0.05 - 0.40, preferably 0.05 - 0.25, more preferably 0.10-0.25;

Mo 0.05 - 0.40, preferably 0.05 - 0.25;

W 0.05 - 0.40, preferably 0.05 - 0.25;

Ni optionally up to 0.4;

Ti optionally up to 0.003;

Nb optionally up to 0.05, preferably 0.004 - 0.040; balance Fe and unavoidable impurities. Figure 1 illustrates a side view of a part of an example of a saw blade 1, such as a band saw blade. The saw blade 1 has a longitudinal extension, as illustrated by the arrow Lb, in the running direction of the saw blade during a cutting operation. The saw blade 1 also has a width Wb and a thickness (not visible in the figure), the thickness being perpendicular to the width and to the longitudinal extension. The saw blade 1 further comprises a plurality of teeth 2 arranged along one of the longitudinal edges of the saw blade.

Figure 2 schematically illustrates a cross sectional view of a first exemplifying embodiment of the flat wire 3 according to the present disclosure. The flat wire 3 has a width W and a thickness T. The flat wire 3 shown has a substantially rectangular cross section with rounded corners 4. The flat wire comprises two parallel longitudinal surfaces 5 extending in a width direction of the flat wire 3, and two parallel longitudinal surfaces 6 extending in the thickness direction. In other words, the flat wire 3 shown has a substantially rectangular cross section. The flat wire 2 further comprises rounded corners 4 connecting the respective longitudinal surfaces 5, 6. The rounded corners 4 may have a purposively selected radius of curvature r4. Alternatively, the corners 4 may be sharp corners, or be naturally rounded corners.

Figure 3 schematically illustrates a cross sectional view of a second exemplifying embodiment of a flat wire 3 according to the present disclosure. In contrast to the flat wire according to the first exemplifying embodiment shown in Figure 2, the flat wire 3 shown in Figure 3 has a trapezoidal cross section. The two parallel longitudinal surface 5 thus have different extensions in the width direction of the flat wire 3. The width W of the flat wire 3 is in the present disclosure considered to mean the greatest width extension, as shown in the figure and here represented by the width of the horizontal lower surface. The flat wire 3 further comprises a first inclined longitudinal surface 7a , inclined at an angle a in relation to a plane 8 perpendicular to the parallel longitudinal surfaces 5. The first inclined longitudinal surface 7a, via a respective corner 4, connects the parallel longitudinal surfaces 5. A second inclined longitudinal surface 7b is arranged opposite the first inclined longitudinal surface 7a and connecting the parallel longitudinal surfaces 5 via respective corners 4. The second longitudinal surface 7b may be mirrored to the first longitudinal surface 7a. In other words, the second longitudinal surface 7b may be inclined at angle, in relation to a plane perpendicular to the parallel longitudinal surfaces 5, of the same size but opposite sign to a. Alternatively, the second inclined longitudinal surface 7b may be inclined at an angle different than -a . Experimental results

A flat wire according to the present disclosure was produced and compared with two flat wires having the same dimension and produced from commercially available steels, Ref 1 and Ref 2. These reference steel materials were selected since they may be processed into flat wires and hardened to obtain a tensile strength above 2000 N/mm².

The flat wire according to the present disclosure was prepared from a steel having a composition comprising about 0.62 wt.-% C, about 2.2 wt.-% Si, about 0.55 wt.-% Mn, about 1.1 wt.-% Cr, about 0.16 wt.-% V, about 0.1 wt.-% Mo, about 0.15 wt.-% W and less than 10 ppm Ti. No additions of Ni and/or Nb were made to the composition. Furthermore, the content of unavoidable impurities were below the maximum allowable content thereof specified above.

The first reference material, Ref 1, is a CrSi steel comprising 0.50-0.70 wt.-% C, 1.35-1.60 wt.-% Si, 0.40-0.80 wt.-% Mn, max 0.025 wt.-% P, max 0.020 wt.-% S, 0.50-0.80 wt.-% Cr, and 0.05-0.20 wt.- % V. The second reference material, Ref 2, is a carbon steel comprising 0.80-0.95 wt.-% C, 0.10-0.30 wt.-% Si, 0.30-0.60 wt.-% Mn, max 0.025 wt.-% P, and max 0.020 wt.-% S.

Flat wires with a width of 6.35 mm and a thickness of 0.63 mm were produced of the three compositions described above by drawing of wire rods followed by cold-rolling to final dimension. Hardening of the respective flat wires were then made for the purpose of obtaining a target tensile strength of 2100 N/mm². In other words, parameters of the hardening was purposively selected for each of the flat wires so as to obtain the target tensile strength. Said target tensile strength was selected since it was believed to be a suitable tensile strength for saw blade applications. The same furnace was used for hardening of the three different flat wires.

Tensile testing according to ISO 6892 was performed on samples of the respective flat wires, and the test results are presented in Table 1 as an average of six samples from each wire. Table 1

From the test results given above it can be seen that, although all three materials may be hardened so as to achieve a tensile strength of about 2100 N/mm², the flat wire according to the present invention has a considerably higher elongation under these conditions. More specifically, the flat wire has an elongation which is about 170 % of the elongation of Ref 1 and about 162 % of the elongation of Ref 2.

The combination of the ability to achieve a high tensile strength while still having a high elongation is particularly advantageous for example when the flat wire is to be used in saw blade applications since it allows for a relatively large deformation before possible fracture of the saw blade. Furthermore, it improves the possibility for setting of the teeth of the saw blade to a desired angle due to the higher formability.

Furthermore, tests were performed for the purpose of investigating the obtainable width to thickness ratio before cracking during final cold rolling, for the three steels described above. For the purpose of these tests, patented wire rods were investigated before cold rolling with regard to prior austenite grain size, tensile strength, and ratio of area reduction at fracture (measured at the neck) during tensile testing. The tested wire rods were each patented at a temperature substantially corresponding to the temperature of the perlite nose for the respective steel composition. Tensile testing was performed according to ISO 6892. Ratio of area reduction is the difference between the area of original cross section and the minimum final area divided by the area of the original cross section. Prior austenite grain size number was determined according to ASTM E 112. The results are specified in Table 2 together with the obtained crack upper limit of width to thickness ratio achieved during cold rolling. Cold rolling was performed without any intermediate heat treatment of the steel between different cold rolling passes. The crack upper limit was determined based on when the cold rolling resulted in crack failure during cold rolling. Table 2

It can be seen from the results in Table 2 that the steel according to the present disclosure has a higher prior austenite grain size number, and thus a smaller prior austenite grain size, compared to the reference steels Ref 1 and Ref 2. This is a result of the composition of the herein described steel, which limits the size of the austenite grains during production. A smaller prior austenite grain size number has a beneficial effect on the crack upper limit of width to thickness ratio.

Moreover, it can be seen that the steel according to the present disclosure has a significantly higher ratio of area reduction compared to Ref 2 and substantially corresponding to the ratio of area reduction of Ref 1. A higher ratio of area reduction indicates a higher ductility. Therefore, a higher ratio of area reduction, at a certain tensile strength, may typically be an indication of a greater ability for cold deformation. Here it can be noted that the steel according to the present disclosure has a higher tensile strength that Ref 1 after patenting.

Most importantly, it can been seen from the test results specified in Table 2 that the steel according to the present disclosure demonstrated a considerably higher crack upper limit of width to thickness ratio compared to the reference materials, Ref 1 and Ref 2. This demonstrates that the chemical composition of the herein described steel is highly suitable for production of flat wires having a high width to thickness ratio by cold rolling.

For the steel according to the present disclosure, Inv., a wire rod not subjected to a patenting step was also investigated by tensile testing in the same way as described above. A tensile strength of 1253 MPa and a ratio of area reduction of 59% was obtained. This may indicate that a similar crack upper limit of width to thickness ratio during final cold rolling, i.e. about 20, can be obtained also in case of omitting a patenting step prior to final cold rolling.

Claims

1. A flat wire (3) made of a steel having the following composition, in percent by weight (wt.- %):

C 0.45 - 0.70,

Si 1.2 - 2.5,

Mn 0.2 - 1.1,

Cr 0.5 - 1.4,

V 0.05 - 0.40,

Mo 0.05 - 0.40,

W 0.05 - 0.40,

Ni optionally up to 0.4,

Ti optionally up to 0.003,

Nb optionally up to 0.05, balance Fe and unavoidable impurities.

2. The flat wire (3) according to claim 1, wherein the flat wire is a flat rolled wire.

3. The flat wire (3) according to any one of the preceding claims, wherein the flat wire has a width to thickness ratio of at least 3:1, preferably at least 5:1.

4. The flat wire (3) according to any one of the preceding claims, having a thickness of from 0.1 mm to 2 mm, preferably from 0.3 mm to 1.6 mm.

5. The flat wire (3) according to any one of the preceding claims, wherein the steel comprises 0.50 - 0.70 wt.-% C; preferably 0.58 - 0.65 wt.-% C.

6. The flat wire (3) according to any one of the preceding claims, wherein the steel comprises 1.70 - 2.50 wt.-% Si, preferably 2.10 - 2.40 wt.-% Si.

7. The flat wire (3) according to any one of the preceding claims, wherein the steel comprises 0.30 - 0.70 wt.-% Mn.

8. The flat wire (3) according to any one of the preceding claims, wherein the steel comprises 0.05 - 0.25 wt.-% V, preferably 0.10 - 0.25 wt.% V.

9. The flat wire (3) according to any one of the preceding claims, wherein the steel comprises 0.05 - 0.25 wt.-% Mo.

10. The flat wire (3) according to any one of the preceding claims, wherein the steel comprises 0.05 - 0.25 wt.-% W.

11. The flat wire (3) according to any one of the preceding claims, wherein the steel comprises 1.10 - 1.40 wt.-% Cr.

12. The flat wire (3) according to any one of the preceding claims, wherein the steel comprises 0.004 - 0.040 wt.-% Nb.

13. The flat wire (3) according to any one of the preceding claims, wherein the unavoidable impurities P, S, Cu and Al in the composition of the steel are limited to:

P max 0.020 wt.-%, preferably max 0.015 wt.-%,

S max 0.030 wt.-%, preferably max 0.025 wt.-%,

Cu max 0.05 wt.-%, preferably max 0.02 wt.-%, and

Al max 0.01 wt.-%, preferably max 0.005 wt.-%.

14. A method for producing the flat wire (3) according to any one of the preceding claims, the method comprising: casting a steel having the composition, optionally heat treating the cast material, hot rolling the cast material to a wire rod, optionally patenting the wire rod at a temperature of at least 900 °C, preferably at least 930 °C, optionally cold drawing the wire rod to a wire having an intermediate dimension, optionally heat treating and/or patenting the wire having an intermediate dimension, and cold drawing or cold rolling to desired final dimension of the flat wire (3).

15. Use of the flat wire (3) according to any one of claims 1 to 12 in the manufacture of a saw blade (1), preferably in the manufacture of a band saw blade. Method of producing a saw blade (1), such as a band saw blade, the method comprising: removing material along a longitudinal edge of a flat wire (3) according to any one of claims 1 to 12 so as to form saw teeth (2) along said longitudinal edge of the flat wire (3), thereby obtaining the saw blade (1), and optionally hardening the formed teeth (2). A saw blade (1) of a steel, said steel having the following composition, in percent by weight (wt.-%):

C 0.45 - 0.70,

Si 1.2 - 2.5,

Mn 0.2 - 1.1,

Cr 0.5 - 1.4,

V 0.05 - 0.40,

Mo 0.05 - 0.40,

W 0.05 - 0.40,

Ni optionally up to 0.4,

Ti optionally up to 0.003,

Nb optionally up to 0.05, balance Fe and unavoidable impurities.