GB2527387A - Bearing steel composition - Google Patents
Bearing steel composition Download PDFInfo
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- GB2527387A GB2527387A GB1500982.2A GB201500982A GB2527387A GB 2527387 A GB2527387 A GB 2527387A GB 201500982 A GB201500982 A GB 201500982A GB 2527387 A GB2527387 A GB 2527387A
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/36—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for balls; for rollers
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/40—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rings; for bearing races
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/30—Parts of ball or roller bearings
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/30—Parts of ball or roller bearings
- F16C33/32—Balls
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/30—Parts of ball or roller bearings
- F16C33/34—Rollers; Needles
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/30—Parts of ball or roller bearings
- F16C33/58—Raceways; Race rings
- F16C33/62—Selection of substances
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/32—Soft annealing, e.g. spheroidising
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2204/00—Metallic materials; Alloys
- F16C2204/60—Ferrous alloys, e.g. steel alloys
- F16C2204/66—High carbon steel, i.e. carbon content above 0.8 wt%, e.g. through-hardenable steel
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2220/00—Shaping
- F16C2220/02—Shaping by casting
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Abstract
A steel which comprises (by weight): 1.2-1.7 % carbon, 3.5-6 % chromium, 4.0-7.0 % molybdenum, 1.0-4.0 % vanadium, 0-1.0 % manganese, 0-0.6 % silicon, 0-0.003 % yttrium, 0-0.25 % nickel, 0 to 0.3 % copper, 0-0.1 % niobium, 0-0.1 % tantalum, 0-0.5 % cobalt, 0-0.5 % tungsten, 0-0.05 % aluminium, up to 200 ppm nitrogen, up to 50 ppm calcium, with the balance being iron and unavoidable impurities. The steel is ingot cast and optionally vacuum arc remelted and/or vacuum induction melted. It is then heated to a temperature in the range 900-1150 0C where it is optionally hot worked, and slow cooled to room temperature over at least 2 hours (and preferably over 24 hours) to form divorced pearlite in the steel. The steel is then formed into a bearing component and hardened by heating to a temperature in the range 1050-1200 0C, quenching to a temperature less than 100 0C and then tempering to give a matrix comprising martensite, optionally with retained austenite, together with carbides and optionally nitrides and/or carbonitrides.
Description
Bearing Steel Comøosition
Technical field
The present invention relates to the field of steels and bearings. More specifically, the present invention relates to a steel alloy composition, a bearing component comprising the steel composition and a method of forming the bearing component.
Backaround
Bearings are devices that permit constrained relative motion between two parts. Rolling element bearings comprise inner and outer raceways and a plurality of rolling elements (balls or rollers) disposed there-between. For long-term reliability and performance, it is important that the various elements have high hardness and resistance to rolling contact fatigue, wear and creep.
Ceramic rolling elements have been considered for use in bearing applications, including highly loaded main shaft aero engines. There are, however, perceived intrinsic limitations associated with the use of ceramic materials in safety critical applications. Powder metallurgy (PM) high speed steels (HSS) offer an alternative for specific, very highly loaded, high temperature aero engine requirements. However, the tooling and equipment required for powder metallurgy are very expensive and there are typically low production volumes.
The high speed steel M62 exhibits high hardness and typically comprises from 1.25 to 1.35 wt.% carbon, from 0.15 to 0.4 wt.% silicon, from 0.15 to 0.4 wt.% manganese, from 3.5 to 4 wt.% chromium, from 10 to 11 wt.% molybdenum, from 1.8 to 2.2 wt.% vanadium, from 5.75 to 6.5 wt.% tungsten and a balance of iron and unavoidable impurities. Rolling elements formed of the high speed steel M62 have been employed in high temperature aero engines.
Such rolling elements may be produced by re-melting and solidification techniques such as, for example, vacuum induction melting (VIM) and vacuum arc refining (VAR). M62 comprises high levels of tungsten. Since tungsten is an expensive element, the cost of M62 is high.
Another known bearing steel comprises 0.97 wt.% C, 0.32 wt.% Si, 0.31 wt.% Mn, 1.43 wt.% Cr, the balance being Fe and any unavoidable impurities. There is also known a commercial through-hardenable steel comprising 0.65 wt.% C, 1.50 wt.% Si, 1.40 wt.% Mn, 1.10 wt.% Cr, 0.25 wt.% Mo, the balance being Fe and any unavoidable impurities.
Many bearing components are produced by a powder metallurgical (PM) process, optionally together with hot isostatic pressing (HIP), particularly for alloys containing carbide-forming elements and an increased carbon content. Sometimes it may be more economical to use ingot casting instead of PM/HIP. However, segregation can occur during ingot casting and this is detrimental to the final mechanical properties of the bearing component, for example resistance to rolling contact fatigue.
It is an objective of the present invention to address or at least mitigate some of the problems associated with prior art or to provide a commercially acceptable alternative thereto.
Summary
In a first aspect, the present invention provides a steel alloy for a bearing, the alloy having a composition comprising: from 1.2 to 1.7 wt.% carbon from 3.5 to 6 wt.% chromium from 4.0 to 7.0 wt.% molybdenum from 1.0 to 4.0 wt.% vanadium from 0 to 1.0 wt.% manganese from 0 to 0.6 wt.% silicon from 0 to 0.003 wt.% yttrium from 0 to 0.25 wt.% nickel, from 0 to 0.3 wt.% copper, from 0 to 0.1 wt.% niobium, from 0 to 0.1 wt.% tantalum, from 0 to 0.5 wt.% cobalt, from 0 to 0.5 wt.% tungsten, from 0 to 0.05 wt.% aluminium, from 0 to 0.025 wt.% phosphorous, from 0 to 0.015 wt.% sulphur, from 0 to 0.075 wt.% tin, from 0 to 0.075 wt.% antimony, from 0 to 0.075 wt.% selenium, from 0 to 0.04 wt.% arsenic, from 0 to 0.002 wt.% lead, up to 200 ppm nitrogen, up to 15 ppm oxygen, up to 50 ppm calcium, up to 20 ppm boron, up to 30 ppm titanium, the balance iron, together with any unavoidable impurities.
The present invention will now be further described. In the following passages different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other featule or features indicated as being preferred or advantageous.
Once hot-worked, conventional high-carbon steels (e.g. Fe-1C-1.5Cr) typically have a pearlitic structure, and therefore have to be softened prior to fabrication into a bearing component and the final hardening heat-treatment. One way of softening the steel involves a long heat treatment at temperatures where only cementite and ferrite are stable, causing the lamellae of cementite to spheroidise, driven by a reduction in the total amount of cementite/ferrite interfacial area. Such a spheroidising heat treatment can be uneconomical, and may increase the cost of manufacturing the bearing component.
An alternative method of softening certain high-carbon steels, for example Fe-iC-i.5Cr, is to form a so-called divorced pearlite microstructure, in which ferrite and cementite grow from the austenite in a non-cooperative manner, resulting in the formation of a ferritic matrix within which spherical cementite particles are embedded. Such a divorced pearlite structure may be obtained by employing a particularly economical spheroidising heat treatment, i.e. a heat treatment employing relatively low temperatures and/or short heating times. However, many high carbon steels, including M62, are not able to form such a divorced pearlite structure.
Accordingly, they must be softened by employing long, high temperature heat treatment regimes.
The combination of alloying elements in the steel alloy of the present invention means that it is possible to form a divorced pearlite structure without the need for a long spheroidising, annealing heat-treatment. This, in turn, means that the steel alloy can be used to manufacture a bearing component more economically.
In the present invention, the steel alloy composition comprises from 1.2 to 1.7wt.% carbon, preferably from 1.3 to 1.6 wt.% carbon, more preferably from 1.4 to 1.6 wt.% carbon, still more preferably from 1.45 to 1.55 wt.% carbon. In combination with the other alloying elements, this results in the desired final martensitic microstructure, together with one or more carbides (and optional nitrides and/or carbonitrides), and optional retained austenite.
The relatively high carbon content impacts positively on mechanical properties, for example hardness, of bearing components formed from the alloy. In particular, the alloy may exhibit a hardness of at least 66 HRC.
The alloy composition according to the present invention also lends itself to ingot casting, and the resulting bearing steel exhibits a high fraction of relatively fine carbides (and optionally nitrides and/or carbonitrides). This, in turn, has been found to be beneficial in terms of hardness and resistance to rolling contact fatigue, which are important properties in bearing applications. The carbides present in the final microstructure typically include, for example, MC, M6C, M2C or M7C3. These carbides typically contain one or more of Fe, Cr, Mo and V. With a relatively high carbon content, the overall percentage of carbides (and optional nitrides and/or carbonitrides), which are retained during hardening is quite high. This impedes austenite grain growth, which is beneficial since such grain growth can be detrimental to mechanical properties and fatigue.
The steel alloy composition comprises from 3.5 to 6.0 wt.% chromium, preferably from 4.0 to 5.8 wt.% chromium, more preferably from 4.8 to 5.5 wt.% chromium, still more preferably from 5.1 to 5.3wt.% chromium. Chromium acts to increase hardenability. Chromium also provides an improved corrosion resistance property to the steel. Chromium controls the stability of various forms of carbides so that no carbide is allowed to grow excessively, meaning that the steel's properties do not deteriorate during heat treatment.
The steel alloy composition comprises from 4.0 to 7.0 wt.% molybdenum, preferably the from 4.5 to 6.5 wt.% molybdenum, more preferably from 5.0 to 6.0 wt.% molybdenum, still more preferably from 5.2 to 5.8 wt.% molybdenum. Molybdenum acts to avoid austenite grain boundary embrittlement owing to impurities such as, for example, phosphorus. Molybdenum also acts to increase hardenability. Molybdenum is a strong carbide former and may contribute to secondary hardening upon tempering the steel at temperatures typically around 500°C or above. Accordingly, the steel alloy may exhibit high hot-hardness. Molybdenum imparts toughness for heavy service, particularly to overcome peak structural loads, and provides especially heat-resistant alloys.
The steel alloy composition comprises from 1.0 to 4.0 wt.% vanadium, preferably from 1.5 to 3.5 wt.% vanadium, more preferably from 1.8 to 3.2 wt.% vanadium, still more preferably from 2.1 to 2.4 wt.% vanadium. In combination with the other alloying elements, especially carbon, this results in the desired microstructure and mechanical properties, particularly hardness. The vanadium and carbon form vanadium carbides and optionally cabonitrides.
Vanadium carbides and carbonitrides are very hard and incredibly stable compared with other types of carbides and carbonitrides that are common in tool steels.
Manganese is an optional alloying element but its presence may be beneficial to prevent hot-shortness of the steel. The steel alloy composition may therefore comprise up to 1.0 wt.% manganese, preferably from 0.2 to 0.8 wt.% manganese, more preferably from 0.3 to 0.5 wt.% manganese, still more preferably from 0.35 to 0.41 wt.% manganese.
Silicon is an optional alloying element but its presence may be beneficial as a deoxidizer.
Silicon may also act to increase strength and hardness, in particular hardness in the martensite-tempered condition. Higher levels of silicon may increase the risk of over-heating the steel during hardening (austenitisation). For these reasons, the steel alloy composition may comprise up to 0.6 wt.% silicon, preferably from 0.1 to 0.5 wt.% silicon, more preferably from 0.2 to 0.4 wt.% silicon, still more preferably from 0.31 to 0.37 wt.% silicon.
Yttrium is an optional alloying element but its presence may be beneficial in that it is believed to act to fragment the primary carbides and may yield better properties in terms of wear resistance, hardenability and rolling contact fatigue life. For these reasons, the steel alloy composition may comprise up to 0.003 wt.% yttrium, for example from 0.001 and 0.003 wt.% yttrium, preferably from 0.001 and 0.002 wt.% yttrium.
The steel alloy may optionally comprise from 0 to 0.3 wt.% copper, for example from 0.01 to 0.1 wt.% copper. The steel alloy may optionally comprise from 0 to 0.25 wt.% nickel, for example from 0.01 to 0.1 wt.% nickel. The presence of copper and/or nickel may be as a result of melting steel scrap to form the alloy. Nickel may act to increase hardenability and impact strength.
The steel alloy may be tungsten-free. This means that the alloy contains «= 0.01 wt.% tungsten, preferably 0 wt.% tungsten. Alternatively, the steel alloy may optionally comprise up to 0.5 wt.% tungsten, for example from 0.01 to 0.1 wt.% tungsten. While tungsten is preferably kept to a minimum in view of costs, small levels of tungsten may serve to avoid carbide coarsening during prolonged tempering.
The steel alloy may be cobalt-free. This means that the alloy contains «= 0.01 wt.% cobalt, preferably 0 wt.% cobalt. Alternatively, the steel alloy may optionally comprise up to 0.5 wt.% cobalt, for example from 0.01 to 0.1 wt.% cobalt. While cobalt is preferably kept to a minimum in view of costs, small levels of cobalt may serve to improve the hardness of the final product.
To reduce costs, the alloy composition preferably does not contain deliberate additions of cobalt or tungsten.
The steel alloy may optionally comprise from 0 to 0.05 wt.% aluminium, for example from 0.01 to 0.05 wt.% aluminium. Aluminium may be used as a deoxidizer. Aluminium, together with nitrogen, if present, may also act to control the prior austenite grain size in the alloy via the formation of aluminium nitrides.
In some embodiments, nitrogen may be added such that the steel alloy comprises from 50 to ppm nitrogen, preferably from 75 to 100 ppm nitrogen. The presence of nitrogen may be beneficial for promoting the formation of complex regular M2C carbides during ingot casting. The complex regular M2C carbides can be easily broken up during, for example, hot working, so this can be beneficial. In other embodiments, there is no deliberate addition of nitrogen. Nevertheless, the alloy may necessarily still comprise at up to least 50 ppm nitrogen due to exposure to the atmosphere during melting.
In one preferred embodiment, the steel alloy composition comprises from 1.3 to 1.6 wt.% carbon, from 4 to 5.8 wt% chromium, from 4.5 to 6.5 wt.% molybdenum, from 1.5 to 3.5 wt.% vanadium, from 0.2 to 0.8 wt.% manganese, from 0.1 to 0.5 wt.% silicon, and the balance iron and any unavoidable impurities. Such an alloy may exhibit particularly high hardness following heat treatment without requiring an expensive spheroidising-annealing heat treatment process prior to hardening.
In a further preferred embodiment, the steel alloy composition comprises from 1.4 to 1.6 wt.% carbon, from 4.8 to 5.5 wt.% chromium, from 5 to 6 wt.% molybdenum, from 1.8 to 3.2 wt.% vanadium, from 0.3 to 0.5 wt% manganese, from 0.2 to 0.4 wt.% silicon, and the balance iron and any unavoidable impurities. Such an alloy may exhibit particularly high hardness following heat treatment without requiring an expensive spheroidising-annealing heat treatment process prior to hardening.
As noted above, the steel alloy compositions according to the present invention may also optionally include one or more of the following elements: from 0 to 0.25 wt.% nickel (for example 0.01 to 0.2 wt.% nickel) from 0 to 0.3 wt.% copper (for example 0.01 to 0.2 wt.% copper) from 0 to 0.1 wt.% cobalt (for example 0.01 to 0.05 wt.% cobalt) from 0 to 0.1 wt.% tungsten (for example 0.01 to 0.05 wt.% tungsten) from 0 to 0.05 wt.% aluminium (for example 0.01 to 0.03 wt.% aluminium) from 0 to 0.1 wt.% niobium (for example 0.01 to 0.05 wt.% niobium) from 0 to 0.1 wt.% tantalum (for example 0.01 to 0.05 wt.% tantalum) from 0 to 0.02 wt.% nitrogen (for example 50 to 200 ppm nitrogen) It will be appreciated that the steel alloy referred to herein may contain unavoidable impurities, although, in total, these are unlikely to exceed 0.3 wt.% of the composition.
Preferably, the alloys contain unavoidable impurities in an amount of not more than 0.2 wt.% of the composition, more preferably not more than 0.1 wt.% of the composition. In particular, the steel alloy compositions may also include one or more impurity elements. A non-exhaustive list of impurities includes, for example:
B
from 0 to 0.025 wt.% phosphorous from 0 to 0.015 wt.% sulphur from 0 to 0.04 wt.% arsenic from 0 to 0.075 wt.% tin from 0 to 0.075 wt.% antimony from 0 to 0.075 wt.% selenium from 0 to 0.002 wt.% lead from 0 to 0.002 wt.% boron from 0 to 0.003 wt.% titanium The steel alloy compositions according to the present invention preferably comprise little or no sulphur, for example from 0 to 0.015 wt.% sulphur.
The steel alloy compositions according to the present invention preferably comprise little or no phosphorous, for example from 0 to 0.025 wt.% phosphorous.
The steel alloy compositions according to the present invention preferably comprise «= 15 ppm oxygen. Oxygen may be present as an impurity. The steel composition preferably comprises «= 30 ppm titanium. Titanium may be present as an impurity. The steel composition preferably comprises «= 20 ppm boron. Boron may be present as an impurity at, for example, 1-5 ppm.
With regard to any phosphorous and sulphur and oxygen, the content of these three elements is preferably kept to a minimum.
The steel alloy compositions preferably comprise «= 50 ppm calcium, more preferably «= 30 ppm calcium. Calcium may be present as an impurity but may also be added intentionally in very small amounts, for example 1-3 ppm, in calcium-treated steel ingots.
The steel alloy composition may consist essentially of the recited elements. It will therefore be appreciated that in addition to those elements that are mandatory other non-specified elements may be present in the composition provided that the essential characteristics of the composition are not materially affected by theil presence.
Following an initial heat treatment, the steel alloy may exhibit a divorced pearlite microstructure. Such a microstructure results in the steel alloy being able to exhibit a high hardness after hardening, for example a hardness of 60 HRC or more, typically 65 HRC or more. Accordingly, the steel alloy may be effectively used in high load environments such as, for example, aerospace bearings. Advantageously, the alloy may achieve such a high hardness without containing high levels of high cost elements such as cobalt and tungsten.
In one embodiment of the present invention, powder metallurgy (PM) is not employed in the processing of the steel alloy. Instead, the steel alloy compositions according to the present invention lend themselves to ingot casting.
The steel alloy composition according to the present invention achieves desired targets in terms of improved hardness and strength via the increased levels of carbide forming elements and carbon, but is fine-tuned such that the PM route is not necessary. As such, fine carbides can be obtained in the final bearing steel structure using melts that were ingot cast, for example, without the need for very fast cooling rates during solidification. As a result of the fine carbides, the produced bearing steel structures yield better performance in terms of resistance to rolling contact fatigue, for example.
The steel alloy composition, when combined with a hot-working schedule, ensures that the structure in the as hot-worked condition is almost fully spheroidised, without the need for a dedicated annealing cycle afterwards. This greatly contributes to cost reduction. This is because a dedicated annealing cycle is known to have an impact on the final cost of the bearing product, since annealing is typically carried out at high temperatures for very long soaking times.
According to another aspect of the present invention, there is provided a bearing component, comprising a steel alloy as herein described. Examples of bearing components where the steel can be used include a rolling element (e.g. ball, cylinder or tapered rolling element), an inner ring, a sprag and an outer ring. The bearing component could also be part of a linear bearing such as ball and roller screws. The present invention also provides a bearing comprising a bearing component as herein described.
In a further aspect the present invention provides a method for manufacturing a steel alloy, the method comprising: (I) providing a steel alloy as herein described; and (ii) ingot casting the steel alloy.
The composition used in the method preferably corresponds to the composition of the final article produced. However, while the weight percentage of most of the elements will remain essentially constant, any nitrogen content may decrease slightly, perhaps due to degassing.
The method may optionally further comprise one or both of the following steps: (iH) vacuum arc remelting the steel alloy; and/or (iv) vacuum induction melting the steel alloy.
The steel alloy according to the present invention lends itself to ingot casting processes.
The alloy composition has been found to reduce segregation during casting, which results in better uniformity and fineness in the steel structure. This, in turn, leads to better resistance to rolling contact fatigue. Further refinement of the microstructure may be achieved via additional processing such as vacuum arc remelting (VAR) and/or vacuum induction melting (VIM-VAR) the steel alloy the steel alloy. Such processes may help in further refining the primary carbides. Additionally, the VAR process may reduce the sulphur content.
In a further aspect, the present invention provides a method of forming a bearing component as described herein, the method comprising: (I) manufacturing a steel alloy using the method described hereinabove; (II) heating the composition at a temperature of from 900 to 1150°C and then cooling the composition to achieve a microstructure comprising divorced pearlite; (Ill) forming the composition into the shape of a bearing component; and (IV) subjecting the formed bearing component to a hardening heat treatment.
The temperature of step (II) is preferably from 950 to 1100°C, more preferably from 1050 to 1100°C. Such temperatures are typically above a temperature at which all the ferrite is dissolved, and the alloy is typically maintained at such temperatures for a sufficient time to form austenite and an amount of undissolved carbides. Step (II) may further comprise hot-working the steel before cooling the composition.
In between Step (I) and Step (II), the method may further comprise the step of holding the composition at this temperature for at least 12 hours, preferably at least 24 hours, in a so-called soaking step.
Step (II) preferably involves slow cooling of the composition to room temperature. Such slow cooling may result in the divorced pearlite formation occurring. The cooling may take at least 2 hours, more preferably at least 12 hours and more preferably at least 24 hours.
Step (Ill) may rely on any conventional forming technique to make the bearing component, for example an inner ring, outer ring or rolling element.
Step (IV) may preferably comprise: (A) heating the alloy at a temperature of from 1050 to 1200°C to at least partially austenitise the composition; (B) quenching the alloy to a temperature of less than 100°C; and (C) carrying out a tempering heat-treatment.
In step (A), the composition is at least partially austenitised, preferably completely austenitised, with some retained undissolved carbides. This is achieved by heating the alloy composition at a temperature of from 1050 to 1200°C, preferably from 1100 to 1160°C, more preferably from 1120 to 1140°C, and most preferably about 1130°C. The composition may be maintained in this temperature regime for up to about 10 minutes.
The method may further comprise a vacuum hardening pre-heating step prior to step (IV).
The pre-heating step may comprise, for example: heating to a temperature of from 550 to 650°C (typically about 600°C) and then equalising; then heating to a temperature of from 750 to 850 °C (typically about 800°C) and then equalising; then heating to a temperature of from 1050 to 1100°C (typically about 1080°C).
Heating to a temperature of from 1050 to 1100°C is typically carried out at a rate of from ito 10°C per minute, more typically about 5°C per minute. The steel alloy is typically cleaned and degreased prior to the pre-heating step. The pre-heating step may be carried out using a conventional furnace. The steel alloy is preferably inserted into the furnace at a temperature of 250°C or less. The pre-heating step may increase the hardness of the steel alloy, which may be advantageous when the steel alloy is used in a bearing component.
Step (B) preferably comprises gas quenching using, for example nitrogen gas, with pressure of from 6 to 8 bar. The quenching is preferably carried out to a temperature of from 40 to 50°C. The cooling rate during quenching is sufficiently fast such that the formation of grain boundary carbides may be prevented.
Step (C) may advantageously keep the reduced austenite content of the steel alloy to a minimum. Step (C) preferably comprises: tempering the alloy at a temperature of from 500 to 600°C for at least 1 hour; and cooling the alloy to a temperature of less than -100°C.
Tempering may preferably be carried out in a vacuum or inert atmosphere. The tempering is preferably carried out for from 1 to 3 hours. Longer tempering times may be employed. The tempering is preferably carried out at a temperature of from 530°C to 580°C, more preferably about 530°C. The alloy is preferably quenched to a temperature of from -220 to -150°C, preferably about -196°C, in between the tempers. The quenching may be carried out using, for example, liquid nitrogen. When fast cooling is carried out, for example by the use of liquid nitrogen, the alloy is preferably cooled more slowly to room temperature prior to fast coo Ii n g.
Step (C) is preferably carried out from 2 to 4 times, more preferably 3 or 4 times.
The steel alloy according to the present invention preferably has a final microstructure (i.e. after Step (IV)) comprising tempered martensite together with one or more carbides and optionally nitrides and/or carbonitrides. In particular, the microstructure preferably exhibits a high fraction of fine carbides specifically for optimum performance in demanding bearing applications. The microstructure may contain a small amount of retained austenite.
The invention will now be described further, by way of example, with reference to the following non-limiting figures, in which: Figure 1 are SEM micrographs showing the decomposition and fragmentation of the M2C-type of carbides for a steel according to the present invention.
Figure 2 is a SEM micrograph showing an example of the achieved divorced pearlite structure in the as hot-rolled condition for a steel according to the present invention.
Figure 3 is an optical light micrograph showing the initial microstructure of the steel from the
Examples.
Figure 4 is an optical light micrograph shows the steel microstructure from the Examples after hot-working (hot flat-rolling).
Examples
Two ingots based on Fe -1.49 C -5.17 Cr -0.38 Mn -0.34 Si -5.56 Mo -2.26 V (wt%) were ingot-cast. Each ingot had the dimensions 7.5 x lOx 50cm, roughly. The specific chemical composition is provided below in Table 1, in weight %, with the balance being iron (84.593) and any unavoidable impurities.
Table 1: Chemical Composition of Steel Alloy (Present Invention) C Cr Mo V 1.493 5.17 5.56 2.261 Mn Si Cu Ni 0.38 0.34 0.001 0.02 W Co Ca Al <0.007 <0.002 0.0002 0.041 Ti Se Nb Ta <0.001 0.023 0.013 <0.001 B Pb Sb As <0.0002 0.012 0.017 0.012 Si N P 5 <0.007 0.008 0.012 0.003 The ingots were heated under vacuum to approximately 1100°C, then soaked at this temperature for about 24 hours. After soaking, the furnace was switched off, while maintaining vacuum, allowing the ingots inside the furnace to cool down slowly.
As can be seen in Figure 1, this heat treatment step caused the decomposition and fragmentation of the M2C-type carbides. The refinement of the carbide structure was a beneficial outcome as it leads to a finer structure, which exhibits, after hardening and tempering, improved hardness and strength. Coarser carbides would not be favourable from a fatigue stand point.
The ingots were subsequently flat, hot-rolled. This treatment, in combination with the steel's novel chemical composition, enabled the formation of a divorced pearlite structure in the as-rolled condition. This is particularly interesting as it renders a time-consuming and expensive spheroidising-annealing (full annealing) heat treatment process, which is typically applied prior to hardening, unnecessary. An example of the achieved divorced pearlite structure in the as hot-rolled condition is presented in Figure 2.
From the as hot-rolled steel segments, 7 mm long and 4 mm diameter dilatometer specimens were machined and subsequently hardened and, if applicable, tempered using a Bähr-Thermoanalyse (now TA Instruments) D1L805 AID push-rod type dilatometer.
Various hardening (austenitising) temperatures were tried, including, for example, austenitising at approximately 1020°C soaking for about 20 mm at temperature. The highest measured hardness value, which is the most critical material property that controls the resistance to rolling contact fatigue, was approximately 66 HRC (converted according to ASTM E140-07, section Xlii).
Even though the measured 66 HRC hardness is believed to be very good for a steel material that is tungsten-and cobalt-free, and also not processed via a powder metallurgy (PM) route, the hardness would increase further to 67 HRC or more when cryogenic treatments are applied in between the temper steps.
Further Examples
Steel samples were prepared according to the chemical composition in Table 1 and with the hardening conditions (heat-treatments) varied as follows: Material 1: T-L direction, hot rolled condition, 1020°C, 560°C triple tempering; Material 2: T-L direction, annealed condition, 1020°C, 560°C triple tempering; Material 3: T-L direction, hot rolled condition, 1020°C, 540°C triple tempering; Material 4: L-T direction, hot rolled condition, 1020°C, 560°C triple tempering; Material 5: L-T direction, annealed condition, 1020°C, 560°C triple tempering; Material 6: L-T direction, hot rolled condition, 1020°C, 540°C triple tempering.
The directions may be understood as follows. A rolled sheet has three dimensions including a short transverse direction (the thickness of the sheet). The longitudinal direction (LD) is the rolling direction and the transverse direction lies across the width of the rolled sheet. A 1-L strip has the longest dimension along the transverse direction. An L-T strip has a longest direction along the longitudinal direction.
The strips were subjected to impact testing with the results shown in Table 2 below.
Table 2: Impact Test Results Number Dimension Absorbed Energy I J Info Material_1 ________________________ ________________________ ________________________ 11 5mm x 10 mm x 55 mm 3.1 150 kpcm pendulum 12 5mm x 10mm x 55mm 32 150 kpcm pendulum 13 5mm x 10mm x 55mm 3.0 150 kpcm pendulum 14 5mm x 10mm x 55mm 2.8 150 kpcm pendulum 5mm x 10mm x 55mm 3.0 150 kpcm pendulum ______________________ Average 3.0 _______________________ Material_2 __________________________ __________________________ __________________________ 21 5mm x 10 mm x 55 mm 32 150 kpcm pendulum 22 5mm x 10mm x 55 mm 32 150 kpcm pendulum 23 5mm x 10 mm x 55 mm 3.5 150 kpcm pendulum 24 5mm x 10 mm x 55 mm 22 150 kpcm pendulum 5mm x 10mm x 55mm 3.1 150 kpcm pendulum ______________________ Average 3.0 _______________________ Material_3 ________________________ ________________________ ________________________ 31 5mm x 10 mm x 55 mm 34 150 kpcm pendulum 32 5mm x 10mm x 55mm 2.7 150 kpcm pendulum 33 5mm x 10 mm x 55 mm 3.3 150 kpcm pendulum 34 5mm x 10mm x 55mm 3.4 150 kpcm pendulum 5mm x 10 mm x 55 mm 34 150 kpcm pendulum ______________________ Average 3.2 _______________________ Material_4 __________________________ __________________________ __________________________ 41 5mm x 10 mm x 55 mm 42 150 kpcm pendulum 42 5mm x 10 mm x 55 mm 4.1 150 kpcm pendulum 43 5mm x 10 mm x 55 mm 4.6 150 kpcm pendulum 44 5mm x 10 mm x 55 mm 44 150 kpcm pendulum 5mm x 10 mm x 55 mm 4.3 150 kpcm pendulum _____________________ Average 4.3 _____________________ Material_5 __________________________ __________________________ __________________________ 51 5mm x 10 mm x 55 mm 3.5 150 kpcm pendulum 52 5mm x 10 mm x 55 mm 4.5 150 kpcm pendulum 53 5mm x 10 mm x 55 mm 4.9 150 kpcm pendulum 54 5mm x 10mm x 55mm 42 150 kpcm pendulum 5mm x 10mm x 55mm 34 150 kpcm pendulum _____________________ Average 4.1 _____________________ Material_6 __________________________ __________________________ __________________________ 61 5mm x 10 mm x 55mm 3.6 150 kpcm pendulum 62 5mm x 10mm x 55mm 3.5 150 kpcm pendulum 63 5mm x 10mm x 55mm 34 150 kpcm pendulum 64 5mm x 10 mm x 55 mm 3.5 150 kpcm pendulum 5mm x 10mm x 55mm 3.5 150 kpcm pendulum _____________________ Average 3.5 _____________________ Figure 4 shows the steel structure after hot-working (hot flat-rolling). From this figure, it is clear that the microstructure was almost fully annealed after the hot flat-rolling process (the measured HV1O hardness was 297±0 [5 measurements]). Consequently, a dedicated annealing cycle was not necessary. The fineness of the hot-worked (annealed) structure can be compared with the initial microstructure shown in Figure 3.
A calculated equilibrium phase diagram for the current steel composition (at 1.5 wt% C) shows the presence of several types of carbides (MC/M4C3+M2C+M7C3), along with the austenite during the hot-working stage of the steel. Without wishing to be bound by theory, it is believed that the competition for solute elements between the various types of carbides does not allow either to grow excessively large, which otherwise would negatively impact performance. Owing to the alloying of the steel with significant amounts of strong carbide forming elements, the structure possesses significant volume fractions of carbides.
As will be appreciated, the matrix phase properties can be tailored by modifying the alloy bulk carbon content and/or the austenitisation temperature. It follows that for applications which require, for example, high dimensional stability, or more strength, or both, it may be necessary to deep-freeze the hardened structures to sub-zero temperatures to reduce the retained austenite content.
The resulting hardened and tempered microstructures containing fine dispersions of numerous carbides will provide high yield and tensile strength, and also hardness properties, that are beneficial for improving resistance to rolling contact fatigue and surface wear.
The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the ad, and remain within the scope of the appended claims and their equivalents.
Claims (16)
- Claims: 1. A steel alloy for a bearing, the alloy having a composition comprising: from 1.2 to 1.7 wt.% carbon from 3.5 toO wt.% chromium from 4.0 to 7.0 wt.% molybdenum from 1.0 to 4.0 wt.% vanadium from 0 to 1.0 wt.% manganese from 0 to 0.6 wt.% silicon from 0 to 0.003 wt.% yttrium from 0 to 0.25 wt.% nickel, from 0 to 0.3 wt.% copper, from 0 to 0.1 wt.% niobium, from 0 to 0.1 wt.% tantalum, from 0 to 0.5 wt.% cobalt, from 0 to 0.5 wt.% tungsten, from 0 to 0.05 wt.% aluminium, from 0 to 0.025 wt.% phosphorous, from 0 to 0.015 wt.% sulphur, from 0 to 0.075 wt.% tin, from 0 to 0.075 wt.% antimony, from 0 to 0.075 wt.% selenium, from 0 to 0.04 wt.% arsenic, from 0 to 0.002 wt.% lead, up to 200 ppm nitrogen, up to 15 ppm oxygen, up to 50 ppm calcium, up to 20 ppm boron, up to 30 ppm titanium, the balance iron, together with any unavoidable impurities.
- 2. The steel alloy of claim 1, comprising from 1.3 to 1.6 wt.% carbon, preferably from 1.4 to 1.6 wt.% carbon, more preferably from 1.45 to 1.55 wt.% carbon.
- 3. The steel alloy of claim 1 or claim 2, comprising from 4.0 to 5.8 wt.% chromium, preferably from 4.8 to 5.5 wt.% chromium, more preferably from 5.1 to 5.3 wt.% chromium.
- 4. The steel alloy of any preceding claim, comprising from 4.5 to 6.5 wt.% molybdenum, preferably from 5 toS wt.% molybdenum, more preferably from 5.2 to 5.8 wt.% molybdenum.
- 5. The steel alloy of any preceding claim, comprising from 1.5 to 3.5 wt.% vanadium, preferably from 1.8 to 3.0 wt.% vanadium, even more preferably from 2.1 to 2.4 wt.% vanadium.
- 6. The steel alloy of any preceding claim, comprising from 0.2 to 0.8 wt.% manganese, preferably from 0.3 to 0.5 wt.% manganese, more preferably from 0.35 to 0.41 wt.% manganese.
- 7. The steel alloy of any preceding claim, comprising from 0.1 to 0.5 wt.% silicon, preferably from 0.2 to 0.4 wt.% silicon, more preferably from 0.31 to 0.37 wt.% silicon.
- 8. The steel alloy of any preceding claim, comprising from 50 to 150 ppm nitrogen, preferably from 75 to 125 ppm nitrogen.
- 9. The steel alloy of any preceding claim, wherein the composition is Co-free and/or W-free.
- 10. The steel alloy of any preceding claim, comprising from 1.3 to 1.6 wt.% carbon, from 4.0 to 5.8 wt.% chromium, from 4.5 to 6.5 wt.% molybdenum, from 1.5 to 3.5 wt.% vanadium, from 0.2 to 0.8 wt.% manganese, and from 0.1 to 0.5 wt.% silicon.
- 11. The steel alloy of any preceding claim, having a microstructure comprising: (a) a matrix comprising martensite and optionally retained austenite, together with carbides and optionally nitrides and/or carbonitrides; or (b) divorced pearlite.
- 12. A bearing component made from a steel alloy composition as defined in any preceding claim.
- 13. The bearing component as claimed in claim 12, which is a rolling element, inner ring, or outer ring for a bearing.
- 14. A bearing comprising a bearing component as defined in claim 12 or claim 13.
- 15. A method of manufacturing a steel alloy comprising: (i) providing a steel alloy as defined in any one of claims ito 10; and (ii) ingot casting the steel alloy; and (iii) optionally vacuum arc remelting the steel alloy; and/or (iv) optionally vacuum induction melting the steel alloy.
- 16. A method of forming a bearing component, the method comprising: (I) manufacturing a steel alloy using the method as defined in claim 15; (II) heating the composition at a temperature of from 900 to 1150°C and then cooling the composition to achieve a microstructure comprising divorced pearlite; (Ill) forming the composition into the shape of a bearing component; and (IV) subjecting the formed component to a hardening heat treatment.
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RU2643772C1 (en) * | 2017-06-01 | 2018-02-05 | Юлия Алексеевна Щепочкина | Wear resistant alloy on base of iron |
WO2018103080A1 (en) * | 2016-12-09 | 2018-06-14 | 张康 | High-carbon chromium bearing steel heat treatment process |
CN110629105A (en) * | 2019-10-25 | 2019-12-31 | 安徽信息工程学院 | Ceramic quenched and tempered steel and preparation method thereof |
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CN118109753B (en) * | 2024-04-19 | 2024-07-26 | 辽宁材料实验室 | Low-arsenic long-service-life bearing steel and short-process preparation method |
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JPH11302777A (en) * | 1998-04-17 | 1999-11-02 | Nippon Steel Corp | Work roll for cold rolling |
JPH11310825A (en) * | 1998-04-28 | 1999-11-09 | Nippon Steel Corp | Manufacture of work roll for cold rolling |
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DE968681C (en) * | 1937-04-01 | 1958-03-20 | Eisen & Stahlind Ag | High-speed steel |
US3295966A (en) * | 1964-04-30 | 1967-01-03 | Crucible Steel Co America | Versatile low-alloy tool steel |
JPH08199311A (en) * | 1995-01-20 | 1996-08-06 | Nippon Steel Corp | High seizuring resistant roll material for hot rolling |
JPH11302777A (en) * | 1998-04-17 | 1999-11-02 | Nippon Steel Corp | Work roll for cold rolling |
JPH11310825A (en) * | 1998-04-28 | 1999-11-09 | Nippon Steel Corp | Manufacture of work roll for cold rolling |
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WO2018103080A1 (en) * | 2016-12-09 | 2018-06-14 | 张康 | High-carbon chromium bearing steel heat treatment process |
RU2643772C1 (en) * | 2017-06-01 | 2018-02-05 | Юлия Алексеевна Щепочкина | Wear resistant alloy on base of iron |
CN110629105A (en) * | 2019-10-25 | 2019-12-31 | 安徽信息工程学院 | Ceramic quenched and tempered steel and preparation method thereof |
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