EP1700925B1 - High-strength air cooled steel alloy and hot worked product - Google Patents
High-strength air cooled steel alloy and hot worked product Download PDFInfo
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- EP1700925B1 EP1700925B1 EP05101801A EP05101801A EP1700925B1 EP 1700925 B1 EP1700925 B1 EP 1700925B1 EP 05101801 A EP05101801 A EP 05101801A EP 05101801 A EP05101801 A EP 05101801A EP 1700925 B1 EP1700925 B1 EP 1700925B1
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Classifications
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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
- C22C38/18—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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- 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
- C21D9/30—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for crankshafts; for camshafts
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- 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
- C22C38/18—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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- 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
- C22C38/18—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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- 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
- C22C38/60—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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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/24—Nitriding
- C23C8/26—Nitriding of ferrous surfaces
Definitions
- the invention relates to an air cooled steel, and to a forged product manufactured therewith and characterized by a totally ferritic-pearlitic microstructure without bainite and, accordingly, by a high strength, a particularly high fatigue strength, and good machinability
- microalloyed steels in hot-forged products are economically sensible as the pieces require no hardening and tempering.
- a problem with these microsteels is a modest strength, especially a low yield strength, when compared to tempered alloy steels.
- the highest strength microalloyed forging steel is 46MnVS6, having a minimum yield limit of 580 MPa.
- the strength of air cooled microalloyed steels can be improved by increased alloying, for example by adding manganese and/or chromium.
- increased alloying creates a problem as a result of the formation of bainite in the microstructure of steels.
- An objective in such steels is to obtain a totally ferritic-pearlitic microstructure capable of providing the desired properties. Even small amounts of bainite in the microstructure undermine mechanical properties by decreasing yield strength and toughness, especially elongation and reduction of area in tensile test, as well as by degrading machinability.
- bainite An element particularly active with regard to the development of bainite is molybdenum, which in such steels must be considered an impurity and the concentration of which must be often limited to as low as not more than 0,03...0,04 wt-%. Occasionally, in the microstructure is formed not only bainite but also untempered martensite, the effect of which on the above properties is even more deteriorating than that of bainite.
- bainitic steels are a steel as set forth in the published EP application 00850178.5 , which is cooled in air.
- a problem in this case is also a poor and uneven machinability and an increase of alloy content. Since attaining a totally bainitic structure by air cooling without retaining a constant temperature is difficult in practice, in the microstructure usually formed untempered martensite as well. In order to attain even a moderate toughness and machinability, it is generally necessary that the pieces be also annealed for softening hard martensite regions, which increases costs even more.
- an object of the invention is to provide a steel alloy having improved machinability combined with high yield stress and toughness.
- a steel of the invention is characterized by what is set forth in the characterizing clause of claim 1.
- the simultaneous use of silicon alloying and molybdenum alloying results economically a high-strength steel, having a structure which is purely ferritic-pearlitic with neither bainite nor martensite nor drawbacks inflicted thereby.
- chromium concentrations within the range of appr. 0,5 wt-% to appr. 1,5 wt-% enables an improvement in the nitriding properties of steel.
- the chromium concentration is preferably within the range of appr. 0,5 wt-% to appr. 0,8 wt-%.
- the chromium alloying causes development of chromium nitrides in the ferritic diffusion layer of a nitrided surface, thus increasing the layer's hardness.
- 1 wt-% of chromium provides a hardness of about 600 HV ( K-E. Thelning, Steel and its Heat Treatment, Butterworths 1975 pp. 86-87 ). This hardness in the diffusion layer is sufficient even for highly demanding mechanical engineering.
- titanium and vanadium also provide activities similar to that of chromium, thus enhancing the latter's effect.
- the diffusion layer in chromium-alloyed steel has a hardness which is several hundred HV degrees higher, which provides a solid base for an extremely hard compound layer present in the outermost surface. Vanadium and titanium alloying enhances this effect.
- a surface layer nitrided as described is more resistant to a surface pressure without a risk of cracking, which makes it possible to use the steel e.g. for gears and shafts.
- a hard diffusion layer means usually also a greater consolidated layer thickness for improved fatigue strength. This is favourable, for example in nitrided crankshafts.
- Still another object of the invention is a forged product, which is characterized by what is set forth in the characterizing clause of the independent claim 2.
- the invention relates also to a hot rolled steel bar, which is characterized by what is set forth in the characterizing clause of the independent claim 3.
- Table 1 Chemical composition of test steels and reference steels in weight percentage Steel C Si Mn P S Cr Ni Mo V Ti Als N Ref. 1 0,37 0,60 1,31 0,008 0,034 0,13 0,09 0,02 0,11 0,025 0,018 0,011 Ref.
- Re yield strength [MPa]
- AS elongation [%]
- Z reduction of area [%]
- KCU2 notch impact strength with 2 mm U-notch bar [J/cm2]
- X sum value representing bainite formation [%]
- KCU2 Microstructure Austenite grain size Ref. 1 555 18 48 46 F + P Ref.
- Raising the carbon concentration to higher than 0,4 wt-% increases strength, but the effect on tensile strength is lesser than on yield strength.
- a lower carbon concentration e.g. 0,15...0,25 wt-%, it is possible to establish a higher yield ratio, which is beneficial in some cases.
- the inventive steel has a fatigue strength which is better than that of standard quenched and tempered and micro-alloy steels, as disclosed in the publication EP 0572246B1 .
- the silicon alloying particularly reduces the tendency to bainite formation as evident by comparing a prior known reference alloy (Ref. 2) with test alloys 2...5 of the invention (Tables 1...3), the sum expression thereof giving the value X of higher than 3,3 wt-%.
- Table 2 also shows how the yield strength, elongation, reduction of area and impact strength of a bainite containing reference alloy (Ref. 2) are distinctly weaker than those of test alloys containing more silicon.
- Manganese and chromium increase strength, but add to the risk of bainite formation at high concentrations.
- An alloying element with a particularly powerful strengthening effect and at the same time promoting bainite formation is molybdenum.
- molybdenum alloying together with silicon alloying, has been utilized for increasing strength without drawbacks resulting from bainite.
- the inventive steel tolerates 0,06 wt-% of molybdenum with no problems, but at large dimensions the cooling rate is slower and higher molybdenum concentrations (e.g. 0,1...0,2 wt-%) are possible without a risk of bainite.
- Vanadium is an effective precipitation hardener. Provided that hot working temperatures are not overly high, vanadium is also functional as a grain-size growth inhibitor. At rather high concentrations, higher than 0,3 wt-%, the use of vanadium is uneconomical and, in addition, toughness is reduced by vanadium. For these reasons it is in some cases advisable to omit vanadium completely.
- Nitrogen is an effective hardener, either as such or together with vanadium.
- high concentrations those higher than 0,03...0,04 wt-%, may nevertheless degrade the surface quality of a hot-rolled bar.
- Niobium functions as a precipitation hardener the same way as vanadium.
- Titanium nitrides are capable of withstanding, without dissolving, extremely high temperatures, even higher than 1200 C, which is why a minor addition of titanium is preferred especially in hot forging to inhibit an excessive growth of grain size and to improve toughness.
- Oversized additions of titanium result in a structure developing large primary TiN particles, which precipitate as early as during solidification and which are ineffective in terms of grain growth and which, by functioning as a crack initiator, undermine toughness and fatigue strength.
- they deteriorate machinability especially at higher cutting speeds.
- For the maximum machinability Ti should be kept lower than 0,008 wt-%.
- the inventive steel is highly suitable for such a process by virtue of its minor tendency to bainite formation.
- steels of the invention covers hot-forged products, for example parts of automotive engines, such as crankshafts, connecting rods and pistons.
- such steels are especially applicable for parts of a vehicular chassis, such as suspension arms, steering arms, front axle beams, etc.
- Chromium-alloyed steel in particular, is highly applicable for nitrided components, such as crankshafts, gear wheels and pinions.
- steels of the invention can be used directly in hot rolled condition without forging or heat treatment.
- steels can replace steel bars heat-treated by hardening and tempering.
- Intended applications include vehicular parts and machine components, for example drive shafts, steering components, fasteners, etc.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Heat Treatment Of Steel (AREA)
- Heat Treatments In General, Especially Conveying And Cooling (AREA)
Abstract
Description
- High-strengh air cooled steel alloy, and hot worked product.
- The invention relates to an air cooled steel, and to a forged product manufactured therewith and characterized by a totally ferritic-pearlitic microstructure without bainite and, accordingly, by a high strength, a particularly high fatigue strength, and good machinability
- The use of air cooled microalloyed steels in hot-forged products is economically sensible as the pieces require no hardening and tempering. However, a problem with these microsteels is a modest strength, especially a low yield strength, when compared to tempered alloy steels. For example, in EN 10267:1998 standard, the highest strength microalloyed forging steel is 46MnVS6, having a minimum yield limit of 580 MPa. In practice, however, the most popular grade is 38MnVS6, having an Re = 520 N/mm2.
- The strength of air cooled microalloyed steels can be improved by increased alloying, for example by adding manganese and/or chromium. However, increased alloying creates a problem as a result of the formation of bainite in the microstructure of steels. An objective in such steels is to obtain a totally ferritic-pearlitic microstructure capable of providing the desired properties. Even small amounts of bainite in the microstructure undermine mechanical properties by decreasing yield strength and toughness, especially elongation and reduction of area in tensile test, as well as by degrading machinability. An element particularly active with regard to the development of bainite is molybdenum, which in such steels must be considered an impurity and the concentration of which must be often limited to as low as not more than 0,03...0,04 wt-%. Occasionally, in the microstructure is formed not only bainite but also untempered martensite, the effect of which on the above properties is even more deteriorating than that of bainite.
- Since, in addition to molybdenum, there are also other effective alloying elements, the tendency to bainite formation can be practically demonstrated by the following summation in wt-%:
- One way of upgrading the strength of air cooled forging steels is to subject them to such intensive alloying that their microstructure becomes completely or at least substantially bainitic. An example of such steels is described in the publication
US 5820706 . Instead of direct, simple air cooling, a problem in this technique is maintaining the temperature range of bainite formation, which hampers the forging process and brings forth one more source of process error. Moreover, there are problems regarding the machinability of such steels, especially because from retained austenite they can also easily develop small amounts of hard untempered martensite in addition to bainite. Generally, especially with forged products of considerable thickness, it is also necessary to increase the alloy content of such steels, thus resulting in high manufacturing costs. - Another example of bainitic steels is a steel as set forth in the published
EP application 00850178.5 - It is known that a fatigue strength higher than conventional can be achieved in microalloyed steels rich in silicon. A steel like this is disclosed in the publication
EP 0572246B1 . A problem here is a low yield strength which is also typical of microalloyed steels in general.EP 0572246B1 is the closest prior art document. - The bainite formation in conventional microalloyed steels rich in manganese is sometimes discouraged by decelerating their post-forging cooling by providing for example a tunnel around the cooling line. However, this represents an extra cost and, at the same time, another source of error in the manufacturing process.
- It is obvious in light of the above that, by finding a steel alloying based way of precluding bainite formation, the strength of microalloyed steels can be enhanced without disrupting the properties. Thus, it is economically feasible to achieve simultaneously high yield strength, good toughness and good machinability.
- In part making usually the greatest individual cost is machining. It is well known that a fine grain size deteriorates machinability of steel. Therefore, a prior austenite grain size coarser than 10 ASTM (greater than about 10 µm in grain diameter) in the material of workpiece is advantageous. Therefore, an object of the invention is to provide a steel alloy having improved machinability combined with high yield stress and toughness.
- In order to accomplish the objectives of the invention, a steel of the invention is characterized by what is set forth in the characterizing clause of claim 1.
- With respect to the inventive steel, the simultaneous use of silicon alloying and molybdenum alloying results economically a high-strength steel, having a structure which is purely ferritic-pearlitic with neither bainite nor martensite nor drawbacks inflicted thereby.
- Further, the use of chromium concentrations within the range of appr. 0,5 wt-% to appr. 1,5 wt-% enables an improvement in the nitriding properties of steel. The chromium concentration is preferably within the range of appr. 0,5 wt-% to appr. 0,8 wt-%.
- Being a major nitride producer, the chromium alloying causes development of chromium nitrides in the ferritic diffusion layer of a nitrided surface, thus increasing the layer's hardness. For example, 1 wt-% of chromium provides a hardness of about 600 HV (K-E. Thelning, Steel and its Heat Treatment, Butterworths 1975 pp. 86-87). This hardness in the diffusion layer is sufficient even for highly demanding mechanical engineering. As nitride producers, titanium and vanadium also provide activities similar to that of chromium, thus enhancing the latter's effect.
- Compared with unalloyed steel or steel with no alloying elements capable of forming nitrides, the diffusion layer in chromium-alloyed steel has a hardness which is several hundred HV degrees higher, which provides a solid base for an extremely hard compound layer present in the outermost surface. Vanadium and titanium alloying enhances this effect. A surface layer nitrided as described is more resistant to a surface pressure without a risk of cracking, which makes it possible to use the steel e.g. for gears and shafts. A hard diffusion layer means usually also a greater consolidated layer thickness for improved fatigue strength. This is favourable, for example in nitrided crankshafts.
- On the other hand, an excessively high chromium concentration reduces the toughness of forged ferritic-pearlitic steel, which is why it is advisable to retain the concentration at less than 1,5 wt-% and in certain cases at less than 1 wt-%.
- Still another object of the invention is a forged product, which is characterized by what is set forth in the characterizing clause of the independent claim 2.
- The invention relates also to a hot rolled steel bar, which is characterized by what is set forth in the characterizing clause of the independent claim 3.
- The following table illustrates mechanical properties and microstructures measured for test steel alloys of the invention as well as corresponding properties in standard reference steels.
Table 1. Chemical composition of test steels and reference steels in weight percentage Steel C Si Mn P S Cr Ni Mo V Ti Als N Ref. 1 0,37 0,60 1,31 0,008 0,034 0,13 0,09 0,02 0,11 0,025 0,018 0,011 Ref. 2 0,39 0,55 1,44 0,007 0,037 0,22 0,17 0,04 0,09 0,020 0,021 0,016 Test 1 0,35 1,49 1,57 0,017 0,057 0,18 0,11 0,03 0,12 0,023 0,024 0,014 Test 2 0,36 1,26 1,08 0,010 0,059 0,20 0,14 0,03 0,12 0,014 0,016 0,011 Test 3 0,35 1,46 1,39 0,020 0,059 0,26 0,13 0,06 0,13 0,004 0,007 0,014 Test 4 0,36 1,43 1,33 0,017 0,056 0,27 0,11 0,06 0,16 0,010 0,009 0,021 Test 5 0,36 1,47 1,34 0,017 0,055 0,27 0,11 0,06 0,22 0,010 0,010 0,028 Table 2. Mechanical properties and microstructure in test steels and reference steels. Bar diameter 20 mm. Heat treatment 1200 C air cooling. Legends: Re = yield strength [MPa]; AS = elongation [%]; Z = reduction of area [%]; KCU2 = notch impact strength with 2 mm U-notch bar [J/cm2]; X = sum value representing bainite formation [%], microstructures: F = ferrite, P = pearlite, B = bainite Steel Re A5 Z KCU2 X Microstructure Austenite grain size Ref. 1 580 16 50 72 2,94 F + P Ref. 2 682 8 10 12 3,47 F + P + B Test 1 717 15 45 50 3,58 F + P ASTM 6 (50 µm) Test 2 651 15 42 39 2,65 F + P ASTM 4 (100 µm) Test 3 658 10 20 38 3,47 F+ P Test 4 735 14 30 40 3,34 F + P Test 5 820 13 27 19 3,36 F + P Table 3. Mechanical properties and microstructure in test steels and reference steels. Bar diameter 60 mm. Heat treatment 1200 C air cooling. Legends: Re = yield strength [MPa]; AS = elongation [%]; Z = reduction of area [%]; KCU2 = notch impact strength with 2 mm U-notch bar [J/cm2]; X = sum value representing bainite formation [%], microstructures: F = ferrite, P = pearlite, B = bainite Steel Re A5 Z KCU2 Microstructure Austenite grain size Ref. 1 555 18 48 46 F + P Ref. 2 591 14 34 12 F + P Test 1 647 15 42 19 F + P ASTM 4 (100 µm) Test 2 598 15 42 F + P ASTM 4 (100 µm) Test 3 665 16 38 27 F + P Test 4 695 13 34 20 F + P Test 5 744 13 33 15 F + P - As indicated by the tables, there is no bainite present in test alloys regardless of high alloying rate and molybdenum concentrations. In test alloys, the sum value representing bainite formation is as high as 3,58 without the presence of bainite.
- In reference alloy 2 of the prior art, as expected, bainite is present at the rate of X = 3,47 wt-%. It is further noted that, as a result of bainite, the elongation, reduction of area and impact ductility of said reference alloy are lower than those of the inventive steels. Because of the absence of bainite it is also clear that the inventive steel is better than the reference steels in terms of machinability.
- Raising the carbon concentration to higher than 0,4 wt-% increases strength, but the effect on tensile strength is lesser than on yield strength. On the other hand, at a lower carbon concentration, e.g. 0,15...0,25 wt-%, it is possible to establish a higher yield ratio, which is beneficial in some cases.
- By virtue of silicon alloying, the inventive steel has a fatigue strength which is better than that of standard quenched and tempered and micro-alloy steels, as disclosed in the publication
EP 0572246B1 . - In a steel of this invention, the silicon alloying particularly reduces the tendency to bainite formation as evident by comparing a prior known reference alloy (Ref. 2) with test alloys 2...5 of the invention (Tables 1...3), the sum expression thereof giving the value X of higher than 3,3 wt-%. Table 2 also shows how the yield strength, elongation, reduction of area and impact strength of a bainite containing reference alloy (Ref. 2) are distinctly weaker than those of test alloys containing more silicon.
- Manganese and chromium increase strength, but add to the risk of bainite formation at high concentrations.
- An alloying element with a particularly powerful strengthening effect and at the same time promoting bainite formation is molybdenum. In a steel of the invention, molybdenum alloying, together with silicon alloying, has been utilized for increasing strength without drawbacks resulting from bainite. At small dimensions (20 mm), the inventive steel tolerates 0,06 wt-% of molybdenum with no problems, but at large dimensions the cooling rate is slower and higher molybdenum concentrations (e.g. 0,1...0,2 wt-%) are possible without a risk of bainite.
- Vanadium is an effective precipitation hardener. Provided that hot working temperatures are not overly high, vanadium is also functional as a grain-size growth inhibitor. At rather high concentrations, higher than 0,3 wt-%, the use of vanadium is uneconomical and, in addition, toughness is reduced by vanadium. For these reasons it is in some cases advisable to omit vanadium completely.
- Nitrogen is an effective hardener, either as such or together with vanadium. On the other hand, high concentrations, those higher than 0,03...0,04 wt-%, may nevertheless degrade the surface quality of a hot-rolled bar.
- Niobium functions as a precipitation hardener the same way as vanadium.
- Titanium nitrides are capable of withstanding, without dissolving, extremely high temperatures, even higher than 1200 C, which is why a minor addition of titanium is preferred especially in hot forging to inhibit an excessive growth of grain size and to improve toughness. Oversized additions of titanium, however, result in a structure developing large primary TiN particles, which precipitate as early as during solidification and which are ineffective in terms of grain growth and which, by functioning as a crack initiator, undermine toughness and fatigue strength. Moreover, they deteriorate machinability especially at higher cutting speeds. For the maximum machinability Ti should be kept lower than 0,008 wt-%.
- Strength can be enhanced in hot forging by accelerating the cooling rate of the forged product in flowing air, in water-air mist or in some other flowing gas. The inventive steel is highly suitable for such a process by virtue of its minor tendency to bainite formation.
- The range of application for steels of the invention covers hot-forged products, for example parts of automotive engines, such as crankshafts, connecting rods and pistons.
- In addition, such steels are especially applicable for parts of a vehicular chassis, such as suspension arms, steering arms, front axle beams, etc.
- Chromium-alloyed steel, in particular, is highly applicable for nitrided components, such as crankshafts, gear wheels and pinions.
- In addition, steels of the invention can be used directly in hot rolled condition without forging or heat treatment. Thus, such steels can replace steel bars heat-treated by hardening and tempering. Intended applications include vehicular parts and machine components, for example drive shafts, steering components, fasteners, etc.
Claims (3)
- An air cooled steel alloy characterized in that, in hot-worked condition, it has a ferritic-pearlitic microstructure, austenite grain size coarser than ASTM 10 (coarser than 10 µm), having the following alloying element contents:
C 0,15...0,6 percent by weight Si 1,25...2,0 percent by weight Mn 0,5...1,6 percent by weight S 0...0,2 percent by weight Cr 0...1,5 percent by weight Mo 0,04...0,10 percent by weight Al 0...0,1 percent by weight V 0,04...0,2 percent by weight N 0,12...0,04 percent by weight Nb 0...0,1 percent by weight Ti 0...0,05 percent by weight. - A forged product made of an air cooled steel alloy characterized in that, in hot-worked condition, it has a ferritic-pearlitic microstructure as well as a high yield and fatigue strength, and that it has austenite grain size coarser than ASTM 10 (coarser than 10 µm) and the steel alloy having the following alloying element contents:
C 0,15...0,6 percent by weight Si 1,25...2,0 percent by weight Mn 0,5...1,6 percent by weight S 0...0,2 percent by weight Cr 0...1,5 percent by weight Mo 0,04...0,10 percent by weight Al 0...0,1 percent by weight V 0,04...0,2 percent by weight N 0,012...0,04 percent by weight Nb 0...0,1 percent by weight Ti 0...0,05 percent by weight - A hot-rolled steel bar made of an air cooled steel alloy characterized in that it has a ferritic-pearlitic microstructure, austenite grain size coarser than ASTM 10 (coarser than 10 µm) as well as a high yield and fatigue strength, that the alloy has the following alloying element contents:
C 0,15...0,6 percent by weight Si 1,25...2,0 percent by weight Mn 0,5...1,6 percent by weight S 0 ...0,2 percent by weight Cr 0 ...1,5 percent by weight Mo 0,04...0,10 percent by weight Al 0...0,1 percent by weight V 0,04...0,2 percent by weight N 0,012...0,04 percent by weight Nb 0...0,1 percent by weight Ti 0...0,05 percent by weight,
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT05101801T ATE442464T1 (en) | 2005-03-09 | 2005-03-09 | HIGH-STRENGTH AIR-COOLED STEEL AND RESULTING HOT-FORMED PRODUCT. |
DE602005016522T DE602005016522D1 (en) | 2005-03-09 | 2005-03-09 | High-strength air-cooled steel and resulting thermoformed product. |
EP05101801A EP1700925B1 (en) | 2005-03-09 | 2005-03-09 | High-strength air cooled steel alloy and hot worked product |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP05101801A EP1700925B1 (en) | 2005-03-09 | 2005-03-09 | High-strength air cooled steel alloy and hot worked product |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1700925A1 EP1700925A1 (en) | 2006-09-13 |
EP1700925B1 true EP1700925B1 (en) | 2009-09-09 |
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EP05101801A Not-in-force EP1700925B1 (en) | 2005-03-09 | 2005-03-09 | High-strength air cooled steel alloy and hot worked product |
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EP (1) | EP1700925B1 (en) |
AT (1) | ATE442464T1 (en) |
DE (1) | DE602005016522D1 (en) |
Cited By (1)
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---|---|---|---|---|
CN110343962A (en) * | 2019-07-26 | 2019-10-18 | 马鞍山钢铁股份有限公司 | A kind of 700Mpa grades or more hot-rolled ribbed high tensile reinforcement steel and its production method |
Families Citing this family (10)
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IT1398688B1 (en) * | 2009-06-12 | 2013-03-08 | F A C E M S P A | PROCEDURE FOR THE PRODUCTION OF A CEMENTATION STEEL PIECE, BASED ON HOT MOLDING FOLLOWED BY CONDITIONED COOLING AND SUB-CRITICAL ANNEALING, AND ITS RELATIVE SYSTEM |
JP5716640B2 (en) * | 2011-11-21 | 2015-05-13 | 新日鐵住金株式会社 | Rolled steel bar for hot forging |
CN102560248A (en) * | 2012-01-31 | 2012-07-11 | 首钢总公司 | Method for producing bolt steel |
WO2019177034A1 (en) * | 2018-03-13 | 2019-09-19 | 日本製鉄株式会社 | Steel material |
JP6525115B1 (en) * | 2018-06-27 | 2019-06-05 | 日本製鉄株式会社 | Nitriding bars and machine parts |
WO2020090816A1 (en) * | 2018-10-29 | 2020-05-07 | 日本製鉄株式会社 | Raw blank for nitrided component, and nitrided component |
JP7270420B2 (en) * | 2019-03-13 | 2023-05-10 | 株式会社神戸製鋼所 | Hot forged non-heat treated parts, manufacturing method thereof, and steel materials for hot forged non-heat treated parts |
CN110819892A (en) * | 2019-10-14 | 2020-02-21 | 长沙东鑫环保材料有限责任公司 | Niobium-nitrogen-containing microalloyed HRB400E steel bar and production method thereof |
CN111663076A (en) * | 2020-05-29 | 2020-09-15 | 江苏联峰实业有限公司 | Automobile steel with high plasticity and high strength |
FR3119445A1 (en) | 2021-02-03 | 2022-08-05 | Adam Pyrométrie | "RAKU" electric ceramic kiln on domestic power supply |
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DE3434744A1 (en) * | 1984-09-21 | 1986-04-03 | M.A.N.-B & W Diesel GmbH, 8900 Augsburg | Process for producing hot-rolled bars |
DE4017973A1 (en) * | 1989-06-09 | 1990-12-13 | Thyssen Edelstahlwerke Ag | Precipitation hardenable ferritic pearlitic steel |
DE4137240A1 (en) * | 1991-11-13 | 1993-05-19 | Thyssen Edelstahlwerke Ag | AFP steel used for prodn. of large forged tools - has low sulphur content and uniformly high tensile strength through tempering |
FI922461A (en) * | 1992-05-29 | 1993-11-30 | Imatra Steel Oy Ab | SMIDESSTYCKE OCH DESS FRAMSTAELLNINGSFOERFARANDE |
FI95050C (en) * | 1992-05-29 | 1995-12-11 | Imatra Steel Oy Ab | Forging piece and its manufacturing process |
JP3261552B2 (en) * | 1993-10-05 | 2002-03-04 | 新日本製鐵株式会社 | Manufacturing method of non-heat treated steel with excellent fatigue properties |
JPH09111340A (en) * | 1995-08-11 | 1997-04-28 | Sumitomo Metal Ind Ltd | High strength and low yield ratio steel for reinforcing bar and its production |
FR2744733B1 (en) | 1996-02-08 | 1998-04-24 | Ascometal Sa | STEEL FOR MANUFACTURING FORGED PART AND METHOD FOR MANUFACTURING FORGED PART |
JP3543581B2 (en) * | 1996-12-20 | 2004-07-14 | 住友金属工業株式会社 | Ferrite / pearlite non-heat treated steel |
JPH10235447A (en) * | 1997-02-25 | 1998-09-08 | Daido Steel Co Ltd | Manufacture of ferrite plus pearlite type non-heattreated steel forged product having high toughness and high yield strength |
JP3485805B2 (en) * | 1997-09-18 | 2004-01-13 | 株式会社神戸製鋼所 | Hot forged non-heat treated steel having high fatigue limit ratio and method for producing the same |
JP3489434B2 (en) * | 1998-04-10 | 2004-01-19 | 住友金属工業株式会社 | High-strength free-cut non-heat treated steel |
SE515624C2 (en) | 1999-11-02 | 2001-09-10 | Ovako Steel Ab | Air-curing low- to medium-carbon steel for improved heat treatment |
-
2005
- 2005-03-09 AT AT05101801T patent/ATE442464T1/en not_active IP Right Cessation
- 2005-03-09 DE DE602005016522T patent/DE602005016522D1/en active Active
- 2005-03-09 EP EP05101801A patent/EP1700925B1/en not_active Not-in-force
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN110343962A (en) * | 2019-07-26 | 2019-10-18 | 马鞍山钢铁股份有限公司 | A kind of 700Mpa grades or more hot-rolled ribbed high tensile reinforcement steel and its production method |
Also Published As
Publication number | Publication date |
---|---|
EP1700925A1 (en) | 2006-09-13 |
ATE442464T1 (en) | 2009-09-15 |
DE602005016522D1 (en) | 2009-10-22 |
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