CN101522931A - Steel wire rod for high strength and high toughness spring having excellent cold workability, method for producing the same and method for producing spring by using the same - Google Patents
Steel wire rod for high strength and high toughness spring having excellent cold workability, method for producing the same and method for producing spring by using the same Download PDFInfo
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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
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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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
- C21D9/02—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for springs
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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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- 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
- C22C38/002—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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- 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
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
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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
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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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
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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Abstract
The invention provides a steel wire rod for a high strength and high toughness spring having excellent cold workability, the steel wire rod having a composition comprising: in weight %, C: 0.4 to 0.7%, Si: 1.5 to 3.5%, Mn: 0.3 to 1.0%, Cr: 0.01 to 1.5%, Ni: 0.01 to 1.0%, Cu: 0.01 to 1.0%, B:0.005 to 0.02%, Al:0.1% or less, O: 0,0020% or less, P: 0.02% or less, S: 0.02% or less, N:0.02% or less, remainder Fe, and other unavoidable impurities, having an internal structure formed of ferrite and pearlite, the internal structure in which prior austenite grain size is 8 [mu]m or less.
Description
Technical field
The present invention relates to a kind of high strength and high tenacity steel wire material for spring (steel wire rod) with good cold working quality, produce the method for described steel wire rod, and by using described steel wire rod to produce the method for spring, more specifically, relate to the steel wire material for spring that a kind of high strength has high tenacity simultaneously, described spring is as automobile spiral spring, plate spring, torsion bar and stabilizer, described steel wire rod has good cold-forming property, thereby make and in subsequent disposal, need not to anneal for peeling or scraping, relate to the method for producing described steel wire rod, and use described steel wire rod to produce the method for spring.
Background technology
Recently, the amount of the fossil oil of use, particularly oil fuel increases sharply, and owing to the source of pollution that combustion oil fuel produces, serious atmospheric pollution has appearred in the whole world.In addition, the oil that mammoth tanker not only can take place is revealed, and oil price also rises rapidly.Therefore, for avoiding the harmful effect of oil fuel, from different perspectives the technology that reduces the oil fuel usage quantity is studied.
The automobile that has needs oil fuel.Car manufactures has been carried out multiple trial and has been studied the usage quantity that reduces oil fuel.Just improve the method for automobile fuel efficiency at present in development and application, this is a kind of ordinary method that reduces the oil fuel usage quantity.Also having a kind of method is to improve the efficiency of combustion and the power transmission efficiency of engine.In addition, also having a kind of method is to reduce required energy in the unit distance motion by alleviating tare.
For alleviating tare, a kind of method is to substitute trolley part with having low-gravity lightweight material.But, so far, the superiority of material energy instead of steel product is arranged seldom.Therefore, up to now, still there be the situation of many use product made from steel, and normally attempt improving the fuel efficiency of automobile by alleviating product made from steel weight as trolley part.
When just alleviating the weight of product made from steel,, may cause the fatal problem of vehicle safety aspect owing to the born load of unit weight is determined.Therefore, alleviating component weight can embody after producing the problem with high-strength parts having solved.
Particularly, the automobile spring is that a kind of utmost point need be with the parts of the similar good permanent deformation resistance of high strength.Described permanent deformation resistance is represented spring Level Change and can not recover the resistance of elastic tension set after using the long period.For increasing the permanent deformation resistance of spring, use usually and added the steel wire rod of a large amount of Si as the spring material.Si can increase the yield strength of steel, thereby prevents tension set.
In addition, Si belongs to a kind of element of IV family in the periodictable, and the behavior aspect thermodynamics is similar with C.As mentioned above, also need to improve the intensity of spring, i.e. tensile strength.For improving this intensity, the essential C element that adds.Adding C is easier to.C is by improving the intensity that precipitation strength is improved steel with the alloying element that other added.But when simultaneously adding in alloy with a large amount of Si C, because the thermodynamic behavior of C and Si is similar, C and Si can compete same position, thereby produce the decarburization phenomenon that C removes from alloy.
Spring steel for containing Si has SAE9250.Because Si content is 1.8-2.0 weight % in the spring steel, so the surface decarburization phenomenon that C removes from steel becomes more serious.As a result, the fatigue lifetime of steel is owing to the surface decarburization layer reduces, thereby makes and be difficult to this steel is used for spring.
For solving described problem, the open text No.1999-0048929 of Japanese patent application No.1998-110247 and 1996-176737, korean patent application No.1997-0073576 and Korean Patent discloses high extension spring steel, wherein reduced total body burden of carbon and added Ni and prevented to occur the decarburization part on the surface, the amount that increases Si is more repaired because the carbon amount reduces the reduction of the intensity that produces, and add Mo in addition, thereby make maximum designed toughness increase to 1200Mpa.
But, for conventional steel, owing to be to measure by increase Si to improve yield strength and non-deformability aspect alloy designs, therefore Si can take place when continuous casting separate.Because Si separates and to be formed at usually in the middle of the steel wire rod, this is isolating to cause ferritic formation, and this has caused the ununiformity of central microstructure, thereby has produced the performance change of relative broad range and made spring toughness variation.
In addition, because the conventional steel with big stress contains a large amount of alloying elements, so production cost increases.In addition, because the interpolation of a large amount of alloying elements though slowly cool off steel wire rod with relatively low speed when producing steel wire rod, has produced low temperature structure for example bainite and martensitic composite structure.When producing steel wire rod, low temperature structure occurring, may in subsequent processes, have problems.That is owing in conversion, produce internal toughness, so low temperature structure for example bainite or martensite have high rigidity.Described low temperature structure makes that be difficult to that the steel wire bar is carried out peeling or scraping controls this steel wire bar diameter or using this steel wire rod to improve its surface quality before forming spring.Therefore, for carrying out peeling or scraping smoothly, steel wire rod is heat-treated for example softening thermal treatment, this causes the increase of extra production cost and the variation of processability.
In addition, usually,, therefore be difficult to provide simultaneously intensity and toughness because intensity and toughness are two notions that oppose mutually.That is, normally,, must in steel wire rod, form a kind of rigid structure for example martensite or bainite for improving spring strength.But, owing to enbrittle, thus this rigid structure for example martensite or bainite have relatively poor impelling strength.
As mentioned above, spring needs high strength that high permanent deformation resistance and fatigue strength and the high tenacity except that high strength is provided.Up to now, do not develop the spring steel that not only has high strength but also have high tenacity yet.And, owing in the part of spring steel, produce low temperature structure, so spring customization company must soften thermal treatment.
The technical problem of invention
One aspect of the present invention provides a kind of high strength and high tenacity steel wire material for spring, and described steel wire rod has good cold-forming property in subsequent disposal, and a kind of method of producing described steel wire rod is provided.
It is a kind of by using the method for described steel wire rod production high strength and high tenacity spring that one aspect of the present invention also provides.
Technical scheme
According to an aspect of the present invention, a kind of steel wire rod is provided, its composition comprises: in weight %, C:0.4-0.7%, Si:1.5-3.5%, Mn:0.3-1.0%, Cr:0.01-1.5%, Ni:0.01-1.0%, Cu:0.01-1.0%, B:0.005-0.02%, Al:0.1% or still less, O:0.0020% or still less, P:0.02% or still less, S:0.02% or still less, N:0.02% or still less, all the other are Fe, and other unavoidable impurities, described steel wire rod has the internal structure that is formed by ferrite and perlite, and the austenite grain size before in this internal structure is 8 μ m or littler.
In the case, the area fraction sum of bainite and martensitic structure may be less than 1% in the steel wire rod internal structure.
Also can comprise in the V:0.5% of weight % in the composition of steel wire rod or still less or still less with Ti:0.5%.
According to another aspect of the present invention, the high strength that a kind of production has good cold working quality and the method for high tenacity steel wire material for spring are provided, wherein, when the hot rolling composition comprises: in weight %, C:0.4-0.7%, Si:1.5-3.5%, Mn:0.3-1.0%, Cr:0.01-1.5%, Ni:0.01-1.0%, Cu:0.01-1.0%, B:0.005-0.02%, Al:0.1% or still less, O:0.0020% or still less, P:0.02% or still less, S:0.02% or still less, N:0.02% or still less, all the other are Fe, and the blank of other unavoidable impurities is when producing steel wire rod, is 850 ℃ or lower from second milling train of final milling train and the rolling temperature the milling train afterwards.
The composition of steel wire rod also can comprise in the V:0.5% of weight % or still less with Ti:0.5% or still less.
Rolling temperature can be Ar3 or higher.
Rolling steel wire rod can 5 ℃/second rate of cooling begin to cool down to room temperature from 700-850 ℃ temperature.
According to a further aspect of the invention, the high strength and the high tenacity steel wire material for spring that provide a kind of production to have good cold working quality, the composition of described steel wire rod comprises: in weight %, C:0.4-0.7%, Si:1.5-3.5%, Mn:0.3-1.0%, Cr:0.01-1.5%, Ni:0.01-1.0%, Cu:0.01-1.0%, B:0.005-0.02%, Al:0.1% or still less, O:0.0020% or still less, P:0.02% or still less, S:0.02% or still less, N:0.02% or still less, all the other are Fe, and other unavoidable impurities, described steel wire rod has the internal structure that is formed by ferrite and perlite, austenite grain size before in this internal structure is 8 μ m or littler, and described method comprises: steel wire rod is carried out peeling and scraping and need not annealing; Make the steel wire rod austenitizing; The steel wire rod of austenitizing is carried out oil cooling; To carry out tempering through oil cooled steel wire rod; With tempered steel wire rod is cold worked into the spring shape.
According to a further aspect of the invention, the high strength that a kind of production has good cold working quality and the method for high tenacity steel wire material for spring are provided, the composition of described steel wire rod comprises: in weight %, C:0.4-0.7%, Si:1.5-3.5%, Mn:0.3-1.0%, Cr:0.01-1.5%, Ni:0.01-1.0%, Cu:0.01-1.0%, B:0.005-0.02%, Al:0.1% or still less, O:0.0020% or still less, P:0.02% or still less, S:0.02% or still less, N:0.02% or still less, all the other are Fe, and other unavoidable impurities, described steel wire rod has the internal structure that is formed by ferrite and perlite, austenite grain size before in this internal structure is 8 μ m or littler, and described method comprises: steel wire rod is carried out peeling and scraping and need not annealing; Steel wire rod is thermally processed into the spring shape; Will be through hot worked spring austenitizing; The steel wire rod of austenitizing is carried out oil cooling; With will carry out tempering through oil cooled spring.
In the case, austenitizing temperature can be 900-1000 ℃.
In addition, tempering temperature can be 350-450 ℃.
Beneficial effect
According to an exemplary of the present invention, high strength, high tenacity spring not only can be provided, and because the good cold-forming property of the steel wire rod that is used to provide spring produced, peeling and scraping processing can be carried out under the heat treated especially situation not carrying out.
Description of drawings
Fig. 1 schemes for the CCT of the ordinary steel wire rod that the example explanation is cooled;
Fig. 2 carries out refrigerative CCT figure for the steel wire rod that the example explanation has small grains after rolling; With
Fig. 3 for example explanation when reduction during from the rolling temperature of second milling train of final milling train and milling train afterwards grain size and with its reverse situation under the figure of grain size.
Embodiment
Hereinafter, will describe embodiment of the present invention in detail.
Normally, tensile strength and impelling strength have reciprocal performance.Therefore, importantly when increasing notched bar impact strength, reduce the reduction of tensile strength values.Correspondingly, the composition of spring steel described below can increase impelling strength when keeping tensile strength high.
Specialize for making described technical conceive, the present inventor is as follows with the composition control of steel wire rod, thereby when use has the steel wire rod production spring of following composition, intensity is provided and improves toughness by the throw out of formation in steel wire rod based on Al, B, V and the Ti of oxygen/carbon/nitrogen, quenching performance when having strengthened thermal treatment by use B improvement quenching performance simultaneously, and strengthened crystal boundary.
Hereinafter, will the component of steel wire rod be described.
C:0.4-0.7 weight %
C is a kind of a kind of fundamental element for providing spring strength to add.When the content of C during,, therefore also can't provide spring steel required intensity because the quenching performance can't be provided less than 0.4 weight %.In addition, when the content of C during, when quenching and during tempering, having formed the twin crystal martensitic structure and in material, produced crackle, thereby significantly reduced fatigue strength greater than 0.7 weight %.In addition, owing to be difficult to provide toughness and the decarburization of control enough for high strength, therefore C content can be limited in the 0.4-0.7 weight % scope owing to the interpolation material that a large amount of Si produced.
Si:1.5-3.5 weight %
Si uses in ferrite, and can improve the intensity and the non-deformability of base mateiral.But when Si content during less than 1.5 weight %, effect is also insufficient.The lower limit of Si content can be 1.5 weight %.When Si content during greater than 3.5 weight %, the effect of improving non-deformability no longer increases, and does not produce other effects.And, in heat treatment process, cause surface decarburization.Therefore, Si content can be limited in the 1.5-3.5 weight % scope.
Mn:0.3-1.0 weight %
When having Mn in the steel, thereby the quenching performance that can improve steel provides intensity.When Mn content during, be difficult to obtain high-strength spring with required intensity and the quenching performance of material less than 0.3 weight %.When Mn content during greater than 1.0 weight %, toughness reduces.Therefore, Mn content can be limited in the 0.3-1.0 weight % scope.
Cr:0.01-1.5 weight %
Cr can be used for providing oxidation-resistance and temperability, prevents surface decarburization, and the quenching performance is provided.But,, be difficult to provide oxidation-resistance, temperability, prevent surface decarburization and quenching performance when Cr content during less than 0.01 weight %.When Cr content during greater than 1.5 weight %, the reduction of non-deformability can cause strength degradation.Therefore, Cr content may be limited in the 0.01-1.5 weight % scope.
Ni:0.01-1.0 weight %
One kind of Ni is for improving the element that quenching performance and toughness are added.When Ni content during less than 0.01 weight %, it is insufficient to improve quenching performance and flexible effect.When Ni content during,, so reduce fatigue lifetime because the amount of residual austenite increases greater than 1.0 weight %.And,, can cause the rapid increase of production cost because the price of Ni is higher.Therefore, Ni content can be limited in the 0.01-1.0 weight % scope.
Cu:0.01-1.0 weight %
Adding Cu can be used for preventing surface decarburization and improves erosion resistance.Decarburized layer can significantly reduce to be processed the fatigue lifetime of spring afterwards.When Cu content during, prevent surface decarburization and improve the effect of erosion resistance not remarkable less than 0.01 weight %.And when Cu content during greater than 1.0 weight %, in the operation of rolling owing to embrittlement produces defective.
B:0.005-0.02 weight %
Add B and have the closely knit effect of rust that makes in surface formation, increase erosion resistance, and increase grain-boundary strength by improving hardening capacity.When B content during,, therefore can not provide spring steel required intensity because the quenching performance can't be provided less than 0.005 weight %.When B content during, thereby fatigue property had disadvantageous effect based on the throw out alligatoring of carbonitride greater than 0.02 weight %.
O:0.0020 weight % or still less
When O content during, form coarse-grained non-metallic inclusion, thereby sharply reduced fatigue lifetime based on oxide compound greater than 0.0020 weight %.Contain 0.0020 weight % or O still less in the therefore preferred steel.
Al:0.1 weight % or still less
Interpolation Al can make grain size refine and improve toughness.
When Al content during greater than 0.1 weight %, the sedimentary amount based on oxide compound that is produced increases, alligatoring simultaneously, thus fatigue property is had adverse influence.
P and S: 0.02 weight % or still less respectively does for oneself
The content of P and S all is limited in 0.02 weight or still less.Because P isolates from crystal boundary and P can reduce toughness, so the upper limit of P content can be restricted to 0.02 weight %.Because S has lower fusing point, can isolate from crystal boundary, and toughness is reduced, form milk sap, and the spring performance is had adverse influence.
N:0.02 weight % or still less
N easy and B effect formation BN and reduction quenching performance.Therefore, it is relatively good to reduce N content as far as possible.But, consider technical load, N content can be restricted to 0.02 weight % or still less.
Only by using described composition can obtain promising result.
But the intensity of steel and toughness can be improved by the favourable composition that adds V and Ti steel extremely as described below.
V:0.005-0.5 weight % or still less, Ti:0.005-0.5 weight % or still less
V and Ti are the elements more favourable for the composition of spring steel, and V and Ti can form carbide or nitride by adding individually or compoundly, and make precipitation hardening, thereby improve the spring performance.V and Ti content are limited in respectively in 0.005-0.5 weight % and the 0.005-0.5 weight % scope.When content reduces, owing to reduce, therefore control crystal boundary and improve the spring performance that for example the effect of fatigue property and permanent deformation resistance is insufficient based on the precipitation of the carbide of V and Ti and nitride.When content was higher, production cost sharply increased and by using described throw out not produce to improve other effects of spring performance.And the amount that is insoluble to the thick alloy carbide of base mateiral when the thermal treatment austenite increases and the formation non-metallic inclusion, thereby has reduced the effect of fatigue property and reinforced deposition.
When the steel wire rod that has the above composition by use is produced spring, can obtain to have superior strength and flexible spring.
But, as mentioned above, when control is formed with the improvement spring strength, when the cooling steel wire rod, easily forming low temperature structure, this makes the hardness of steel wire rod also increase.Correspondingly, because the cold-forming property variation though use the steel wire rod with described composition, also can not provide good cold-forming property by using conventional production method.
The result that the reason of described problem generation is studied is, use the conventional spring steel of forming, although carry out relatively slow cooling, the cooling curve on the figure of CCT shown in Fig. 1 can not pass ferrite and perlitic range, but directly enters bainite and martensitic range.Therefore, what can learn is to have produced a large amount of low temperature structure for example bainite or martensite.
Thereby, have the people and think that can make it pass the making of perlite or ferrite zone by the rate of cooling that slows down produce low temperature structure.But the present inventor's a result of study is that rate of cooling should be passed ferrite or the perlitic range on the CCT figure less than the cooling curves that 3 ℃ of/second spring steels that routine is formed---comprise composition of the present invention---.But the at present normally used cooling power that is used to cool off the device of steel wire rod is 5 ℃/second or littler.Very difficult accurately controlled chilling speed is extremely less than 3 ℃/second.Therefore, do not wish to produce steel wire rod with good cold working quality by the rate of cooling that slows down.
Also having a kind of method is to make the perlite leading edge shown in Fig. 1---promptly use a small amount of time (transverse axis of CCT figure is the time)---to moving to left, so that cooling curve is under higher relatively cooling temperature can fully pass perlite or ferrite zone.CCT figure in the case as shown in Figure 2.
Usually, the shape of CCT figure depends on composition.But the present inventor's a result of study is to verify that the shape of CCT figure can be come controlled by the control grain size, although the composition of steel wire rod is constant.
That is, in producing the ordinary method of steel wire rod, before the cooling in the steel wire rod internal structure austenitic grain size be about 12 μ m.The shape of CCT figure in the case as shown in fig. 1.But a kind of important condition of the present invention is, austenitic grain size is controlled to be 8 μ m before cooling or more hour, what CCT figure had is shaped as: perlite and ferrite zone are obviously to moving to left, and promptly the direction to the short period moves, as shown in Figure 2.Ferrite or pearlitic crystal grain transform at crystal boundary.When austenite grain size (AGS) was more tiny before transforming, ferrite or perlite transform required grain boundary interfaces to be increased fast, and this makes the ferrite or the pearlitic amount that are transformed increase.
Therefore, under the situation that does not change composition, because hardness is not high under higher relatively cooling temperature, therefore for producing the steel wire rod with good cold working quality, importantly the AGS before the controlled chilling is 8 μ m or littler.Therefore, steel wire rod of the present invention has favourable composition, wherein internal structure form by ferrite and perlite and internal structure in before austenite grain size be 8 μ m or littler.
And, being preferably, low temperature structure for example bainite and martensite does not form as far as possible.Because can form low temperature structure to a certain degree inevitably, its amount can be less than 1% of entire structure face integration rate.
Can use several different methods to control AGS.That is, AGS depends on amount and speed and the hot rolled temperature that transforms in the course of hot rolling to a great extent.By the control hot-rolled condition, static recrystallization, dynamic recrystallization, half dynamic recrystallization and grain growing can take place.When material processed for example the cross section of hot rolled steel wire rod be circle and roll speed when higher, be difficult to change amount and the speed that transforms.Therefore, recrystallization behavior and grain growing behavior can be controlled by the control hot-rolled temperature.
For obtaining tiny crystal grain by the control hot-rolled temperature, normally used a kind of method is, when being rolled, keeps the temperature of whole finish rolling workshop section lower simultaneously, thus suppress recrystallization and make austenite crystal be shaped as pancake shape and tiny.But, in the case,, there is load on the equipment owing in whole finish rolling process, milling train is increased load, thereby to watt consumption with have disadvantageous effect equipment life.
But according to the present invention, as shown in Figure 3,---its milling train after final milling train contains second milling train and one---in fact has influence to AGS though be rolled rolling workshop section in whole rolling workshop section.When the rolling temperature with milling train remained on 750-850 ℃, AGS can be controlled at 8 μ m or littler.Among Fig. 3, square marks represents to produce with the conventional mode of production situation of steel wire rod, and wherein represents temperature profile, and ■ represents the variation of AGS.Similarly, circular mark represents to produce with the mode of production of the present invention the situation of steel wire rod, and wherein zero represents temperature profile, ● the variation of expression AGS.As shown in Figure 3, under the mode of production of the present invention, when keeping when the rolling temperature of second milling train of final milling train and next milling train is 850 ℃, AGS is finally less than 5 μ m.Under the conventional mode of production, be 950 ℃ or higher from the rolling temperature of second milling train of final milling train and milling train afterwards, the grain size in the steel wire rod of being produced is shown as 12 μ m or bigger.Because half dynamic recrystallization occurs in the first half of the operation of rolling, so the not very big change of the grain size of steel wire rod.On the other hand, at the latter half of the operation of rolling, particularly from second milling train of final milling train and next milling train, because the static recrystallization of steel wire rod takes place, therefore the recrystallization behavior is slowed down and the grain growing delay, thereby by the rolling effect that obtains crystal grain thinning.
Therefore, importantly keeping from the rolling temperature of second milling train of final milling train and next milling train is 850 ℃ or lower.
But, when final rolling temperature is Ar3 or when lower, before by rolling refined austenite austenite/ferritic conversion can take place, thereby form coarse ferrite.Therefore, final rolling temperature can be greater than Ar3.
Ar3 depends on the composition of steel wire rod.The Ar3 of relevant steel wire rod of the present invention is confirmed as about 740 ℃.
In the process of producing steel wire rod, except that controlling from the temperature of second milling train of final milling train and next milling train, other are similar with the ordinary methods of producing steel wire rod.That is, those skilled in the art can easily produce steel wire material for spring through reheat, breaking down, finish rolling and cooling blank by using multiple known technology, wherein need to control the temperature of two or more final milling trains.
Cooling can 5 ℃/second or littler speed begin and finish from 700-850 ℃ temperature in room temperature.
, can to the steel wire rod by described method produced carry out peeling, scraping, austenitizing processing, oil cooling after tempering, and be cold worked into the spring shape or be thermally processed into the spring shape and need not in subsequent disposal, to soften thermal treatment thereafter.On the other hand, the temperature of steel wire rod at 850-1000 ℃ can be thermally processed into the spring shape, carry out austenitizing processing, oil cooling, and tempering, thereby make spring.
The roughly temperature range of spring production method is identical with conventional spring working condition.Just, the characteristics of spring production method of the present invention are not carry out softening thermal treatment.
Therefore, peeling condition, scraping condition, austenitizing temperature, oil cooling temperature, and quenching temperature is all based on conventional spring working condition.
But austenitizing carries out to prevent that recrystallization from producing coarse grain 900-1000 ℃ temperature.That is, when austenitizing temperature is lower than 900 ℃, because temperature is hanged down and produce proeutectoid ferrite in process of cooling.When temperature is higher than 1000 ℃, cause decarburization and grain growing.After the austenitizing, finish quenching by quick cooling.
Spring through quenching has high strength.But,, can carry out tempering subsequently because martensitic structure is helpless to improve toughness.Become tempered martensite by the tempering internal structure by martensite.
Tempering temperature can be 350-45O ℃.When tempering temperature was lower than 350 ℃, the effect of tempered martensite was insufficient, thereby made spring toughness variation.When tempering temperature was higher than 450 ℃, martensite may be converted into more pyritous structure.Therefore, tempering temperature can be 350-450 ℃.
Embodiment
Hereinafter, will be described in detail invention example of the present invention.Just the present invention is not limited to described invention example.And those skilled in the art will recognize that be, under the situation that does not depart from principle of the present invention and purport, can these examples be changed, scope of the present invention limits by claims, and equivalent way.
(embodiment)
Have the steel of forming shown in the following table 1 by casting and produce blank and under condition shown in the table 2, this blank is carried out hot rolling, thereby make steel wire rod.To be processed into the spring shape through the hot rolled steel wire rod, 950 ℃ of thermal treatments, oil cooling, and under 390 and 420 ℃ tempering temperature as shown in table 3, heat-treat, thereby make sample.
When being processed into the spring shape, with reference to table 2,, therefore it is carried out peeling, scraping and is processed into the spring shape because invention example 1-6 has good cold-forming property, need not to carry out other softening thermal treatment.But, because case of comparative examples lacks cold-forming property, therefore directly carry out peeling and scraping, worry to destroy material.Therefore, case of comparative examples was softened thermal treatment 120-180 minute at 500-700 ℃, peeling, scraping, and be processed into spring.
For detecting the cold-forming property of the steel wire rod that under condition shown in the table 2, makes, carried out tension test.The sample of tension test makes by taking a sample along rolling direction and being processed into the ASTM-Sub size.Dop speed (cross head speed) with 2mm/min is carried out tension test.Detailed value is shown in Table 2.
Table 1
| C | Si | Mn | Ni | Cr | V | Ti | Cu | B | P | S | Al | N | O | |
| Case of comparative examples 1 | 0.55 | 3.0 | 0.5 | 0.25 | 0.7 | 0.05 | - | 0.1 | 0.001 | 0.01 | 0.03 | 0.001 | 50 | 16 |
| Case of comparative examples 2 | 0.55 | 2.2 | 0.5 | 0.25 | 0.7 | 0.20 | - | 0.1 | - | 0.008 | 0.008 | 0.01 | 49 | 16 |
| Case of comparative examples 3 | 0.50 | 2.2 | 0.7 | 0.30 | 1.0 | 0.20 | 0.07 | 0.3 | 0.03 | 0.009 | 0.007 | 0.06 | 55 | 14 |
| Case of comparative examples 4 | 0.6 | 1.4 | 0.6 | - | 0.5 | - | - | - | - | 0.03 | 0.01 | 0.07 | 48 | 19 |
| Example 1 of the present invention | 0.45 | 2.9 | 0.7 | 0.5 | 1.2 | 0.4 | 0.3 | 0.3 | 0.006 | 0.008 | 0.009 | 0.03 | 49 | 15 |
| Example 2 of the present invention | 0.49 | 3.1 | 0.6 | 0.3 | 0.4 | 0.2 | 0.4 | 0.5 | 0.001 | 0.012 | 0.008 | 0.02 | 59 | 13 |
| Example 3 of the present invention | 0.55 | 2.6 | 0.7 | 0.1 | 0.6 | 0.4 | 0.2 | 0.8 | 0.008 | 0.009 | 0.015 | 0.05 | 53 | 11 |
| Example 4 of the present invention | 0.59 | 2.6 | 0.4 | 0.7 | 1.2 | 0.2 | 0.4 | 0.5 | 0.014 | 0.015 | 0.009 | 0.06 | 52 | 13 |
| Example 5 of the present invention | 0.64 | 1.9 | 0.8 | 0.5 | 1.3 | 0.3 | 0.4 | 0.1 | 0.017 | 0.018 | 0.015 | 0.04 | 48 | 10 |
| Example 6 of the present invention | 0.69 | 1.6 | 0.9 | 0.8 | 0.9 | 0.2 | 0.09 | 0.4 | 0.007 | 0.005 | 0.016 | 0.07 | 49 | 12 |
Wherein except that the content of N and O was represented with ppm, the content of each element was all represented with weight %.
Table 2
Wherein low temperature structure branch rate is represented area branch rate, and steel wire rod intensity is represented tensile strength.And, in fact keep identical until the temperature of final milling train from the 4th milling train of final milling train.
Table 3
As can be known from Table 2, when rate of cooling is 3 ℃/second and 5 ℃/second, in case of comparative examples 1-4, wherein form and the rolling temperature of milling train all outside the institute of the present invention range of definition, demonstrate very high low temperature structure branch rate greater than 2%.Consequently, the intensity of steel wire rod is far above the intensity of example 1-6 of the present invention.On the other hand, for example 1-6 of the present invention, low temperature structure divides rate less than 1%, and this belongs to the cold worked scope that is suitable for.Playing the result is that the intensity of steel wire rod is comparatively favourable, less than 1000MPa.Just when rate of cooling is 7 ℃/second, even in example of the present invention, also detect low temperature structure branch rate greater than 1% and the tensile strength of steel wire rod higher relatively, greater than 1000MPa.The difference of case of comparative examples and example of the present invention is caused by the AGS before the cooling.In the case of comparative examples, make that the AGS before that room temperature AGS can be detected is 12 μ m or bigger.On the other hand, for example of the present invention, AGS before is 6 μ m or littler, is different from case of comparative examples.
In addition, known from table 3, for satisfying the example of the present invention that the present invention forms, its tensile strength is 2000MPa or bigger, and this is a gratifying value.For case of comparative examples 1-4, its tensile strength is unsatisfactory especially.Described advantageous effects is by causing forming of steel of the present invention.That is, in the steel of the present invention's definition was formed, the amount that reduces the Si that is added reduced the surface decarburization effect, and compound interpolation B, V and Ti remedy because the loss of strength that the minimizing of Si causes.Add B, V and Ti and be for, by in quenching process by throw out V (C for example, N) and Ti (C, N) grain refining of carrying out is used for reducing intensity and flexible reduces, with increase quenching characteristics and grain-boundary strengthening effect by B, and improve intensity by the precipitation strength that causes in the drawing process.
Claims (11)
1. a high strength and high tenacity steel wire material for spring with good cold working quality, described steel wire rod is formed and is comprised: in weight %, C:0.4-0.7%, Si:1.5-3.5%, Mn:0.3-1.0%, Cr:0.01-1.5%, Ni:0.01-1.0%, Cu:0.01-1.0%, B:0.005-0.02%, Al:0.1% or still less, O:0.0020% or still less, P:0.02% or still less, S:0.02% or still less, N:0.02% or still less, all the other are Fe, and other unavoidable impurities, described steel wire rod has the internal structure that is formed by ferrite and perlite, and the austenite grain size before in this internal structure is 8 μ m or littler.
2. the steel wire rod of claim 1, wherein in the steel wire rod internal structure face integration rate sum of bainite and martensitic structure less than 1%.
3. claim 1 or 2 steel wire rod, wherein the composition of steel wire rod also comprises: in weight %, V:0.5% or still less or still less with Ti:0.5%.
4. a production has the high strength of good cold working quality and the method for high tenacity steel wire material for spring, wherein, when the hot rolling composition comprises: in weight %, C:0.4-0.7%, Si:1.5-3.5%, Mn:0.3-1.0%, Cr:0.01-1.5%, Ni:0.01-1.0%, Cu:0.01-1.0%, B:0.005-0.02%, Al:0.1% or still less, O:0.0020% or still less, P:0.02% or still less, S:0.02% or still less, N:0.02% or still less, all the other are Fe, and the blank of other unavoidable impurities is when producing steel wire rod, is 850 ℃ or lower from the rolling temperature of second milling train of final milling train and milling train afterwards.
5. the method for claim 4, wherein the composition of steel wire rod also comprises: in weight %, V:0.5% or still less or still less with Ti:0.5%.
6. claim 4 or 5 method, wherein rolling temperature is Ar3 or higher.
7. claim 4 or 5 method, wherein rolling steel wire rod begins to cool down to room temperature with 5 ℃/second the rate of cooling temperature from 700-850 ℃.
8. a production has the high strength of good cold working quality and the method for high tenacity steel wire material for spring, described steel wire rod is formed and is comprised: in weight %, C:0.4-0.7%, Si:1.5-3.5%, Mn:0.3-1.0%, Cr:0.01-1.5%, Ni:0.01-1.0%, Cu:0.01-1.0%, B:0.005-0.02%, Al:0.1% or still less, O:0.0020% or still less, P:0.02% or still less, S:0.02% or still less, N:0.02% or still less, all the other are Fe, and other unavoidable impurities, described steel wire rod has the internal structure that is formed by ferrite and perlite, austenite grain size before in this internal structure is 8 μ m or littler, and this method comprises:
Steel wire rod is carried out peeling and scraping and need not annealing;
Make the steel wire rod austenitizing;
The steel wire rod of austenitizing is carried out oil cooling;
To carry out tempering through oil cooled steel wire rod; With
Tempered steel wire rod is cold worked into the spring shape.
9. a production has the high strength of good cold working quality and the method for high tenacity steel wire material for spring, described steel wire rod is formed and is comprised: in weight %, C:0.4-0.7%, Si:1.5-3.5%, Mn:0.3-1.0%, Cr:0.01-1.5%, Ni:0.01-1.0%, Cu:0.01-1.0%, B:0.005-0.02%, Al:0.1% or still less, O:0.0020% or still less, P:0.02% or still less, S:0.02% or still less, N:0.02% or still less, all the other are Fe, and other unavoidable impurities, described steel wire rod has the internal structure that is formed by ferrite and perlite, austenite grain size before in this internal structure is 8 μ m or littler, and this method comprises:
Steel wire rod is carried out peeling and scraping and need not annealing;
Steel wire rod is thermally processed into the spring shape;
Will be through hot worked spring austenitizing;
To carry out oil cooling through the spring of austenitizing; With
To carry out tempering through oil cooled spring.
10. claim 8 or 9 method, wherein austenitizing temperature is 900-1000 ℃.
11. the method for claim 8 or 9, wherein tempering temperature is 350-450 ℃.
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| Application Number | Priority Date | Filing Date | Title |
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| KR10-2006-0098940 | 2006-10-11 | ||
| KR1020060098940A KR100797327B1 (en) | 2006-10-11 | 2006-10-11 | Steel wire rod for high strength and high toughness spring having excellent cold workability, method for producing the same and method for producing spring by using the same |
| KR1020060098940 | 2006-10-11 | ||
| KR1020070101347A KR20090036272A (en) | 2007-10-09 | 2007-10-09 | Steel wire rod for high strength and high toughness spring having excellent cold workability, method for producing the same and method for producing spring by using the same |
| KR10-2007-0101347 | 2007-10-09 | ||
| KR1020070101347 | 2007-10-09 | ||
| PCT/KR2007/004924 WO2008044859A1 (en) | 2006-10-11 | 2007-10-10 | Steel wire rod for high strength and high toughness spring having excellent cold workability, method for producing the same and method for producing spring by using the same |
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| CN101522931A true CN101522931A (en) | 2009-09-02 |
| CN101522931B CN101522931B (en) | 2011-03-02 |
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Cited By (8)
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| CN102575312A (en) * | 2009-11-03 | 2012-07-11 | Posco公司 | Wire rod for drawing having excellent drawability, super-high-strength steel wire and manufacturing method thereof |
| CN103025904A (en) * | 2010-08-04 | 2013-04-03 | 日本发条株式会社 | Spring and manufacture method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| KR101053305B1 (en) * | 2008-12-09 | 2011-08-01 | 주식회사 포스코 | Low decarburized wire and its manufacturing method |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000239797A (en) * | 1998-12-21 | 2000-09-05 | Kobe Steel Ltd | Steel for spring excellent in workability and production of steel wire for spring |
| KR100368530B1 (en) * | 1998-12-21 | 2003-01-24 | 가부시키가이샤 고베 세이코쇼 | Spring Steel Superior in Workability |
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| CN103025904A (en) * | 2010-08-04 | 2013-04-03 | 日本发条株式会社 | Spring and manufacture method thereof |
| CN103025904B (en) * | 2010-08-04 | 2015-04-01 | 日本发条株式会社 | Spring and manufacture method thereof |
| CN104884656A (en) * | 2012-12-27 | 2015-09-02 | Posco公司 | High strength steel sheet having excellent cryogenic temperature toughness and low yield ratio properties, and method for manufacturing same |
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| KR100797327B1 (en) | 2008-01-22 |
| CN101522931B (en) | 2011-03-02 |
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