Fine Grain Size and High Hardness Cast Steel Alloys Products and Method of Making the Same

Abstract

High hardness cast steel alloy products and methods of making the same are provided. The methods includes preparing a molten mass consisting essentially of, by weight %, about 0.05% to about 3.0% C, about 0.005% to about 1.0% Si, about 0.01% to about 1.0% Mn, about 0.01% to about 0.3% Nb, about 0.01% to about 0.3% Ni, about 0.04% to about 1.0% Mo, about 1% to about 16.0% Cr and a balance essentially iron, incidental elements and impurities, at a temperature ranging from about 1400° C. to about 1700° C.; and forming the cast steel alloy product from the molten mass.

Description

FIELD OF THE INVENTION

The present disclosure generally relates to steel alloys, particularly fine grain size and high-hardness steel alloys used for making cast products, including grinding balls and methods for producing the same.

BACKGROUND OF THE INVENTION

Steel alloys are widely used, e.g., in the construction, automotive and aerospace industries, among others, due to high tensile strength and other factors. Various high strength steel alloys have been proposed in the past that have characteristic properties in terms of weight, strength, castability, resistance to corrosion, cost, etc. Improvements in steel alloys remain desirable.

SUMMARY OF THE INVENTION

Fine grain sizes, high-hardness steel alloy products, and methods of making them are provided. In one embodiment, the method may include preparing a molten mass consisting essentially of, by weight %, about 0.05% to about 3% C, about 0.5% to about 1.0% Si, about 0.01% to about 1.0% Mn, about 0.01% to about 0.9% Nb, about 0.01% to about 0.9% Ni, about 0.04% to about 1.0% Mo, about 1% to about 16% Cr and a balance essentially iron, incidental elements and impurities, at a temperature ranging from about 1400° C. to about 1700° C.; and forming the steel alloy product from the molten mass.

In one embodiment, preparing a molten mass may comprises: heating a material consisting essentially of about 0.05% to about 3% C, about 0.5% to about 1.0% Si, about 0.01% to about 1.0% Mn, and a balance essentially iron, incidental elements and impurities, to a temperature within a range of about 1400° C. to about 1700° C.; allowing the material to begin cooling once the material reaches a peak temperature within the range; adding about 0.01% to about 0.9% Nb with about 0.04% to about 1.0% Mn, after adding the Nb; and, after adding the Mn to form the molten mass. As can be appreciated, the temperature when Nb is added may be above 1200° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned features and objects of the present disclosure will become more apparent with reference to the following description taken in conjunction with the accompanying reports:

FIG. 1 is the SGS report ASTM 14 is the finest we report per the attached is what we observed at 500×. Steel microscopic photograph according to an embodiment of the present disclosure.

FIG. 2 is a cast steel ball per SGS testing lab report with the surface-to-core hardness at 63 HRC.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following detailed description includes representative examples utilizing numerous features and teachings, both separately and in combination. It describes numerous embodiments of high-hardness steel and the methods used to make it. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the claims. Therefore, combinations of features disclosed in the following detailed description and incorporated documents may not be necessary to practice the teachings in the broadest sense and are instead taught merely to describe particularly representative examples of the present teachings.

For the description of alloy compositions that follow, all references to percentages are by weight percent (wt %) unless otherwise indicated. When referring to any numerical range of values herein, such ranges are understood to include each and every number and/or fraction between the stated range minimum and maximum. A range of about 0.5 wt % to about 3.0% Carbon, for example, would expressly include all intermediate values of about 0.05, 0.06, 0.07, all the way up to and including 0.99, 1%, 2% and 3.0% C. The same applies to all other elemental ranges set forth below, including those incorporated by reference below.

According to an embodiment of the present disclosure, the high-hardness steel alloy comprise the following components:

C: About 0.05% to about 3%.

Carbon (C) greatly affects the strength of the steel. It also influences the quantity and shape. Therefore, the content of carbon is preferably about 3.0 wt %/

Si: About 0.5% to about 1.0%.

Silicon (Si) contributes to the improved strength of steel.

Mn: About 0.01% to about 1.0%.

Manganese (Mn) is a solution-enhancing element that contributes to increases hardenability. Consequently, a Mn amount is set at about 0.01% or more. Thus, a Mn amount is set to about 1.0% or less. In one embodiment, this further increases its stability.

In one embodiment, the components of the steel are as stated above, and the remainder is substantially iron, incidental impurities and elements. In another embodiment, the steel may further include one or more of the following:

Al: About 0.001% to about 0.1%.

Addition of Aluminum (Al) is optional. When added, Al has a deoxidizing effect. Like Si.

P: About 0.15% or Less.

Phosphorus (P) is very effective in serving as a solution enhancing element. When the P content exceeds about 0.15%, due to segregation of grain boundary. Therefore, the amount of P is preferably at about 0.15% or less. In one embodiment, a P amount is preferably at about 0.05% or less and yet preferably about 0.015% or less. In one embodiment, P is included in the steel alloy as an inevitable impurity.

S: About 0.1% or Less.

Sulfur(S) forms sulfide inclusions such as MnS, thereby causes cracking and impairs workability. It also deteriorates toughness by grain boundary embrittlement. Thus, the content is preferably about 0.1% or less, and preferably at about 0.03 or less, and more preferably at about 0.003% or less. In one embodiment, S is included in the steel alloy as an inevitable impurity.

Cu: About 0.05% or Less and/or Ni: About 1% or Less.

Both elements are effective at increasing the strength of steel, suppressive decarburization in heating and contributing to improved durability. In order to exhibit the effect, a Cu amount is preferably about 0.01% or more and yet preferably about 0.1% or more. Also, a Ni amount is preferably about 0.01% or more and yet preferably about 0.1% or more. Consequently, a Cu amount is preferably about 0.05% or less, and Ni is preferably about 1% or less. In one embodiment, a Cu amount is preferably about 0.08% or less and still yet preferably about 0.5% or less,

Ca: About 0.1% or Less.

Calcium (Ca) may be optionally added. Ca contributes to the shape control of sulfides and oxides. To exert these effects, Ca is preferably added by about 0.0001% or more. However, if Ca amount is excessive, toughness is deteriorated reversely. Thus, the Ca content is preferably about 0.1% or less, and yet preferably about 0.007% or less, and still yet preferably about 0.005% or less.

Sn: About 1% or Less.

Tin (Sn) has the effect of raising the mechanical strength or improving the material quality, so an amount of about 0.001% or more may be added. However, excessive addition causes the formability to deteriorate. Thus, the Sn content is preferably about 1% or less, and yet preferably about 0.5% or less, and still yet preferably about 0.005% or less.

In one embodiment, at least one element selected from a group of Cr: about 16% or less, Mo: about 2.0% or less, Ni: about 0.2% or less, Nb: about 0.5% or less.

Cr: About 18% or Less.

Chromium (Cr) added to enhance the hardenability and increase the strength of steel. Furthermore, Cr improves the corrosion resistance of steel. To exert these effects, Cr is preferably added at about 16% or more and yet preferably about 10%.

Mo: About 1.0% or Less.

Molybdenum (Mo) added to enhance the hardenability and increase the strength of steel. If P is included in the steel alloy, Mo has the effect of reducing segregation of P on the grain boundary and suppressing deterioration of toughness. Additionally, Mo forms carbide that contributes to miniaturization of the structure and improve toughness. To exhibit these effects, a Mo amount of about 0.05% or more may be added, and preferably 0.15% or more. However, if excessive Mo is added toughness deteriorates. Consequently, a preferably Mo amount of about 0.2% or less may be added. In one embodiment, a Mo amount is yet preferably about 0.4% or less and still yet preferably about 0.2% or less.

Nb: About 0.5% or Less, and Ni about 1.0% or Less.

Niobium (Nb) and Nickel (Ni) may be added to improve the strength of steel by forming precipitates of carbide and nitride and suppressing recrystallization. To exhibit these effects, a Ni amount of about 0.01% or more may be added, and yet preferably about 0.35% or more may be added, a Nb amount of about 0.01% or more may be added, and yet preferably about 0.03%. However, if these elements are excessively added and grain boundary frequency increases excessively. Thus, a preferably Ni amount of about 0.4% or less may be added, a preferably Nb amount of about 0.3% or less. In one embodiment, the Nb added may be in any form, such as Niobium pentoxide, Niobium dioxide, Niobium oxide, and/or in other forms/compounds.

As can be appreciated, other elements may be added to those described above, including but not limited to Mg, Zr, Sb, Se, B, W, Co, rare earth metals (REM), and/or others, and any of the elements described in the presented disclosure may have different weight % ranges, as disclosed in one or more of the following references: U.S. Pat. Nos. 6,962,631, 8,133,330, 6,632,296, 5,372,654, U.S. Patent Publication No. 2013/0037180A1, U.S. Patent Publication No. 20130022490A1, U.S. Patent Publication No. 2012/0325364A1, U.S. Patent Publication No. 2012/0305144A1, U.S. Patent Publication No. 2012/0152411a1, U.S. Patent Publication No. 2012/0141829A1, U.S. Pat. Nos. 8,460,800, 8,444,743, 6,855,218, 6,364,968, U.S. Patent Publication No. 2013/0133792A1, U.S. Patent Publication No. 2013/0048151A1, U.S. Patent Publication No. 2012/0288397A1, U.S. Pat. No. 2012/0186707A1, U.S. Patent No. 20120175028a1, US20120118438a1, US20110198002a1, U.S. Patent No. 20100218857a1, US20080286504a1, U.S. Pat. Nos. 7,833,363b2, 7,485,195b2, 6,589,369, 6,221,179, U.S. Patent Publication No. 2013/0133786A1, U.S. Patent Publication No. 2012/0012231A1, U.S. Patent Publication No. 2011/0162762A1, U.S. Patent Publication No. 2012/0009434A1, U.S. Patent Publication No. 2011/0146852A1, U.S. Patent Publication No. 2011/0048589A1, U.S. Patent Publication No. 2011/0030854A1, U.S. Patent Publication No. 2005/0150580A1, U.S. Patent Publication No. 2004/0069382A1, U.S. Pat. Nos. 7,960,035, 7,082,992, 5,601,667, 5,454,883, U.S. Patent Publication No. 2012/0247619A1, U.S. Patent Publication No. 2010/0159276A1, U.S. Patent Publication No. 2009/0014095A1, U.S. Pat. Nos. 8,449,700, 8,177,924, 5,746,842, U.S. Patent Publication No. 2006/0065329A1, U.S. Pat. Nos. 7,458,426, 7,225,868, 7,503,304, 6,652,670, 6,544,354, 6,319,338, U.S. Patent Publication No. 2007/0122554A1, U.S. Pat. No. 6,866,725, U.S. Patent No. 2011/0091348A1, U.S. Patent Publication No. 2003/0196731A1, U.S. Patent Publication No. 2009/0277547A1, U.S. Patent Publication No. 2007/0122251A1, U.S. Patent Publication No. 2012/0195785A1, U.S. Pat. Nos. 6,217,678, 8,257,647, U.S. Patent Publication No. 2011/0132503A1, U.S. Pat. No. 7,754,344, U.S. Pat. No. 2001/0027831A1, U.S. Patent Publication No. 2009/0025835A1, U.S. Pat. Nos. 8,389,128, 4,582,536, U.S. Patent Publication No. 2010/0089504A1, U.S. Patent Publication No. 2011/0300404, U.S. Patent Publication No. 2010/0213407, U.S. Patent Publication No. 2009/0293993, U.S. Pat. Nos. 4,084,965, 7,986,598, 7,737,066, and Japanese Patent Nos. JP-A-55 157226, JP-A-10242004 and JP-A-2000-119710, U.S. Pat. Nos. 4,906,435, 4,294,613, 4,279,647, 4,299,621, 4,265,660, 3,841,866, 3,833,360, European Patent No. EP0020792A1, European Patent No. EP0022134A1, European Patent No. EP0020792B1, European Patent No. EP0020793B1, European Patent No. EP0022134B1, European Patent No. EP0018425A1, European Patent No. EP0294371A1, European Patent No. EP0020793A1, European Patent No. EP0018425B1, European Patent No. EP0294371B1, and PCT Application No. PCT/HU1986/000072 These references are all incorporated herein by reference in their entirety. As can be appreciated, the weight percentages for these additional elements disclosed in any of these references is incorporated herein by reference. In one embodiment, alternative weight percentages of C, Si, Mn, P, S, Cu, Sn, V, Nb, Al, Ni, Cr, Mo and Ca disclosed in these references are likewise incorporated herein by reference.

The alloys described herein have at least one of the following benefits: (a) high hardness, (b) corrosion resistance, and (c) decreased grain sizes, even without any heat treatments. According to an embodiment of the present disclosure, the above features may be achieved by the following manufacturing method.

Initially, scrap steel comprising C, Si, and Mn with a chemical composition within the above-specified ranges may be liquefied via an electric arc furnace at a temperature of about 1400° C. or higher. In one embodiment, the scrap steel may be heated to a temperature of about 1500° C. or higher, and still preferably about 1600° C. or higher, but may be less than about 1700° C. and may yet preferably be less than about 2400° C. After verifying temperature and preliminary composition through testing, the heat may be tapped and the scrap steel sent to a furnace, such as a Ladle Metallurgy Furnace (LMF). The LMF is a refining station in which chemical composition will be adjusted by adding rare earth components and controlling temperature.

In one embodiment, the maximum temperature may be maintained for a predetermined period, for example, 10 to 15 minutes, then it may be allowed to cool down at a rate of about 0.4° C./min or more. During the cooling phase, Nb may be then added within the above-specified range. In one embodiment, Nb may combine with carbon and/or nitrogen to form NbC and/or NbN, which may contribute to the formation of ultra-fine grain steel. Next, during the cooling phase, Mo and Ni may be added within the above-specified range. In one embodiment, Mo and Ni may combine with carbon and/or nitrogen to form MoC, MoN, and/or TiN, which may contribute to inhibiting grain growth, grain migration and strengthening of the steel. Next, during the cooling phase, C. In one embodiment, Cr and Ni may combine with carbon and/or nitrogen to form carbon and/or nitrogen which may strengthen the steel.

Temperature may be adjusted in preparation for casting. When proper chemical composition and temperature are reached, the heated liquid steel may be sent to the continuous caster. The liquid metal may be continually poured into a tundish and then air cooled.

In one embodiment, wrought or cast products may be made from the steel alloy of the present disclosure. As used herein, “wrought product” refers to any wrought product as that term is understood in the art, including, but not limited to, rolled products such as extrusions, including rod and bar, and the like. The wrought product may be utilized in numerous industries, including automotive, aerospace, construction, etc. Furthermore, the inventive alloy may be used as a casting alloy, as that term is understood in the art, where a shape is produced.

As can be appreciated, the addition of Nb during the cooling cycle (and at a high temperature of about 1300° C. or higher, and preferably at a temperature of about 1500° C. or higher, and yet preferably about 1600° C. or higher) prevents oxidation, resulting in improved utilization of these expensive additives. As such, less amounts of these expensive elements may be utilized to form high-hardness steel alloys according to the teachings of the present disclosure. In one embodiment, the weight percentage of Nb is less than 1% of the steel alloy (with the remaining weight percentage being the scrap steel).

As can be appreciated, the present disclosure's microstructure of the steel alloy may be controlled by the composition and production process. The microstructure may provide a mechanism for increased corrosion resistance and may contribute to superior mechanical properties of high hardness with high-temperature brittle fracture resistance. These material properties lead to longer service life in corrosive environments.

The microstructure of the steel alloy of the present disclosure exhibits a unique structure at the atomic scale, generally resembling a matrix structure with generally uniform grain structure. Artisans would appreciate that the steel alloy of the present disclosure is substantially free of microgalvanic cells, the driving force behind corrosion. As used herein, the term “substantially free” means having no significant amount of that component in the steel all. The steel alloy's “ultra fine microstructure” effect lends superior hardness, toughness, and corrosion resistance.

Typical prior art carbon steels. These carbides are strong, yet brittle-immovable at the grain boundaries.

In contrast, the steel alloy of the present disclosure may (according to one embodiment) form a matrix that is substantially free of carbide, and up to three times as strong as conventional steel. The steel alloy of the present disclosure is also substantially stronger and tougher than conventional steel.

In one embodiment, the steel alloy may generally have an average grain size of at least ASTM #14, i.e. less than 10 micrometers, contributing to increased hardness. This higher hardness may occur due to an increased bonding surface than conventional carbon steel.

The steel alloys discussed above, particularly fine grain size and high-hardness steel alloys are useful for making cast products, including grinding balls.

Cast steel alloy grinding balls for the cement, mining, and coal firing industries are useful for 24 months because the coarse grain size in grinding balls leads to reduced strength, lower toughness, increased ductility, and a higher susceptibility to distortion during heat treatment, making it less desirable for applications requiring high mechanical properties and dimensional stability; essentially, a coarse grain structure makes the steel weaker and less resistant to cracking compared to a fine-grained structure due to fewer grain boundaries to impede dislocation movement.

Larger grains have fewer grain boundaries, which are obstacles for dislocation movement, resulting in a lower yield strength and reduced overall strength of the steel.

When grinding balls have low hardness, the primary problem is excessive wear and tear, leading to a significantly reduced lifespan, increased grinding media consumption, and ultimately decreased efficiency in the milling process due to the balls rapidly losing their ability to grind the material effectively; this can result in higher operating costs and potential production disruptions requiring frequent ball replacements.

Soft balls wear down quickly when impacting against the material being ground, leading to a faster rate of particle size increase and a decline in grinding performance.

As the balls wear down, more energy is needed to achieve the desired particle size due to the reduced grinding force exerted by the softer balls.

If the hardness of the balls is inconsistent, some areas of the mill might experience less grinding action compared to others, resulting in uneven particle size distribution.

When grinding balls deform excessively, it leads to several problems including reduced grinding efficiency, increased wear and tear on the balls, uneven grinding results, potential contamination of the material being ground, and a higher risk of ball breakage due to the stress caused by excessive deformation, especially if the material being ground is particularly hard or abrasive; this can significantly impact the overall productivity and cost of the grinding process.

When a ball deforms significantly upon impact with the material, it absorbs a large portion of the kinetic energy, reducing the force available for actual grinding.

Excessive deformation leads to increased surface wear on the ball, causing it to degrade and lose its spherical shape faster, resulting in shorter lifespan.

Deformed balls may not effectively contact the material at all points, leading to inconsistent particle size distribution in the final product.

Spherical balls are advantageous for grinding because they offer a high level of efficiency due to their smooth tendency to roll and cascade, causing consistent impact and abrasion on the material being ground, leading to a more even particle size distribution and better overall grinding performance compared to irregularly shaped grinding media.

The spherical shape allows for optimal rolling and cascading action within the mill, maximizing the contact between the balls and the ground material.

The uniform shape and size of spherical balls ensures consistent grinding action and mixing, Impact from spherical balls results in a more even particle size distribution in the final cement.

Reduced wear and tear smooth surface minimizes friction and wear on the mill lining, leading to longer equipment lifespan.

The high surface area contact between the balls and the material increases the rate of particle size reduction among other effects due to the high hardness of 63 HRC from surface to core and fine grain size of ASTM 14 and other factors. Various high-hardness steel alloys have been proposed in the past that have characteristic properties in terms of grain size, hardness, castability, cost, etc. Improvements in steel alloys remain desirable.

EXAMPLE

The present invention is hereunder explained more specifically in reference to the following example, but the present invention is not limited by the following example by its very nature, and it is a matter of course that the present invention may be appropriately modified with the range conforming to the aforementioned, and those modifications are included in the technological scope of the present invention.

In preparing an exemplary inventive alloy composition to illustrate the improvement in mechanical properties, scarp steel (with a composition provided in Table 1) is heated to a temperature of about 1628° C. The molten scrap steel is then allowed to cool to a temperature of about 1621° C. in an LMF, then Nb with a chemical composition provided in Table 1 are added with a chemical composition provided in Table 1 are added to the molten steel alloy at a temperature of about 1611° C. The batch is then allowed to air cool for 2 days slowly.

TABLE 1
Element Composition (wt %)
C       2.11
Si      0.49
Mn      0.35
P       0.025
S       0.028
Cu      0.04
Nb      0.30
Al      0.02
Ni      0.31
Cr      9.95
Mo      0.11

Some samples of the exemplary inventive steel alloy was tested for mechanical properties, including hardness, toughness, and breakage.

The results show the exemplary inventive steel alloy having a hardness at 63 HRC from the surface to the core.

As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be “a little above” or “a little below” the endpoint. The degree of flexibility of this term can be dictated by the particular variable and would be within the knowledge of those skilled in the art to determine based on experience and the associated description herein. Further, as used herein, the term “substantially” or “substantial” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking, the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained.

Any patents, publications, or other references mentioned therein are hereby incorporated by reference. In addition, as to each term used, it should be understood that unless its utilization in this application is inconsistent with such interpretation, common dictionary definitions should be understood as incorporated for each term and all definitions, alternative terms, and synonyms such as contained in at least one of a standard technical dictionary recognized by artisans, incorporated herein by reference.

Finally, all references listed in the Information Disclosure Statement of other information statement filed with the application are hereby appended and hereby incorporated by reference; however, as to each of the above, to the extent that such information or statements incorporated by reference might be considered inconsistent with the patenting of this/these invention(s), such statements are expressly not to be considered as made by the applicants.

It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Such modifications are to be considered as included within the following claims unless the claims, by their language, expressly state otherwise. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Claims

1. A method of making a cast steel alloy product, the method comprises:

preparing a molten mass comprising, by weight %, about 0.05% to about 3.0% C, about 0.005% to about 1.0% Si, about 0.01% to about 1.0% Mn, about 0.01% to about 0.3% Nb, about 0.01% to about 0.3% Ni, about 0.04% to about 1.0% Mo, about 1% to about 16.0% Cr, and a balance essentially iron, incidental elements and impurities, at a temperature within a range of about 1400° C. to about 1700° C.;

slowly air cooling the molten mass for two days; and

forming the cast steel alloy product from the molten mass.

2. The method of claim 1, wherein the cast steel alloy product generally has an average grain size of less than 10 micrometers.

3. The method of claim 1, wherein the cast steel alloy product has 63 HRC without heat treatment.

4. The method of claim 1, wherein the molten mass further consists of at least one of about 0.001% to about 0.1% Al, about 0.15% or less P, about 0.1% or less S, about 0.01% or less Cu, about 1% or less Ni, about 0.1% or less Ca.

5. The method of claim 1, wherein preparing the molten mass comprises:

heating a material consisting essentially of about 0.05% to about 3.0% C, about 0.005% to about 1.0% Si, about 0.01% to about 1.0% Mn, and a balance essentially iron, incidental elements and impurities, to a temperature within a range of about 1400° C. to about 1700° C.;

allowing the material to begin cooling once the material reaches a peak temperature within the range;

adding about 0.01% to about 0.3% Nb to the heated material while still hot; and

adding about 1% to about 16.0% Cr with about 0.01% to about 1.0% Ni, after adding the Mo and Nb, to form the molten mass.

6. The method of claim 1, wherein the cast steel alloy product has ASTM 16 grain size.

7. A high hardness cast steel alloy product comprising a high hardness of 63 HRC from surface to core and a microstructure with an ASTM grain size of 14.

8. The high hardness cast steel alloy product of claim 7 comprising,

by weight % of about 0.05% to about 3.0% C, about 0.005% to about 1.0% Si, about 0.01% to about 1.0% Mn, about 0.01% to about 0.3% Nb, about 0.01% to about 0.5% Ni, about 0.04% to about 1.0% Mo, about 1% to about 10.0% Cr, about 0.01% to about 0.1% Cu, and a balance essentially iron, incidental elements and impurities.