CN101287850B - Steel for high intensity spring and heat-treating steel line for high intensity spring - Google Patents
Steel for high intensity spring and heat-treating steel line for high intensity spring Download PDFInfo
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- CN101287850B CN101287850B CN2006800012411A CN200680001241A CN101287850B CN 101287850 B CN101287850 B CN 101287850B CN 2006800012411 A CN2006800012411 A CN 2006800012411A CN 200680001241 A CN200680001241 A CN 200680001241A CN 101287850 B CN101287850 B CN 101287850B
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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
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing 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
- C22C38/04—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
Abstract
A heat-treated steel wire for springs which is coiled by cold working, can combine sufficient atmospheric strength with suitability for coiling, and has a tensile strength of 2,000 MPa or higher; and a spring-use steel for use in producing the steel wire therefrom. The heat-treated steel wire for high-strength springs is characterized by containing, in terms of mass%, 0.5-0.9% C, 1.0-3.0% Si, 0.1-1.5% Mn, 1.0-2.5% Cr, 0.15-1.0%, excluding 0.15% and 1.0%, V, and less than 0.005% Al, having a nitrogen content reduced to 0.007% or lower, further containing one or both of 0.001-0.01%, excluding 0.01%, Nb and 0.001-0.005%, excluding 0.005%, Ti, and having a tensile strength of 2,000 MPa or higher; It is further characterized in that in a microscopic examination concerning cementite carbide spheres and alloy carbide spheres, the proportion of that area in the surface being examined which is occupied by these spheres having a diameter of 0.2 [mu]m or larger in terms of equivalent-circle diameter is 7% or lower and the population of the spheres having a diameter of 0.2 [mu]m or larger in terms of equivalent-circle diameter is 1 or less per [mu]<2>;, and that the former austenite grain size number is not smaller than 10 and the residual austenite content is 5 mass% or lower.
Description
Technical field
Spring steel that the present invention relates under cold conditions, reel, have high strength and high tenacity and spring thermal treatment steel wire.
Background technology
Be accompanied by lightweight, the high performance of automobile, spring is high strength also, and tensile strength is used to spring above the high-strength steel of 1500MPa after the thermal treatment.In recent years, also always demand tensile strength surpass the steel wire of 1900MPa.This is because when making spring, even because stress-removal is annealed and heating such as nitriding treatment causes softeningly a little, still can guarantee the cause as the no problem material hardness of spring.
In addition, well-known, handle by nitriding treatment, shot peening, surface hardness improves, and the fatigue durability of spring raises extraordinarily, but weakens characteristic about the elastic force of spring, be not to determine that by surface hardness the intensity or the hardness of spring starting material inside have a significant impact.Therefore, can to keep very high the composition adjustment be important to inner hardness.
As its method, there is invention (for example opening clear 57-32353 communique) to point out, by adding elements such as V, Nb, Mo, the fine carbide of be created on solid solution in the quenching, in tempering, separating out with reference to the spy, limit moving of dislocation thus, make anti-elastic force weaken characteristic and improve.
On the other hand, in the manufacture method of steel disk spring, have: the austenitic area that will be heated to steel reel the hot rolling that carries out Q-tempering then around and the high strength steel wire of in advance steel having been implemented Q-tempering carry out cold coiling that cold conditions reels around.Cold coiling around in, but can use rapid heating and refrigerative oil tempering processings fast, high frequency processing etc. when making steel wire, so can reduce the original austenite particle diameter of spring material, its result can make the spring of fracture characteristics excellence.And the equipment such as process furnace on the spring production line can be oversimplified, so for spring manufacturer, have the advantage of bringing equipment cost attenuating etc., coldization of spring develops recently.For pendulum spring, though compare with valve spring, wire rod uses thick steel wire, owing to above-mentioned advantage, also importing cold coiling around.
But, when cold coiling increases around the intensity of spring steel line, cold coiling around the time to lose, can not be configured as the situation of spring shape also many.Up to now, because intensity and processibility can not have concurrently, therefore industrially have to adopt the method for the Q-tempering that can be described as after disadvantageous heating is reeled and reeled etc. to have intensity and processibility concurrently.
In addition, high-intensity thermal treatment steel wire is carried out cold coiling around processing, carry out the occasion that intensity is guaranteed in nitrogenize, can think that the so-called alloying elements such as V, Nb that in steel heavy addition can be separated out fine carbide are effective.But when the heavy addition alloying element, adding when quenching pines for can not solid solution, grow thickly, becomes the so-called carbide that do not dissolve, and becomes the reason of losing when reeling under the cold conditions.Therefore, also can see not dissolving the technology that carbide is paid close attention to.
Also have following invention (for example opening the 2002-180198 communique) with reference to the spy: by not only controlling such alloying element,, also be controlled at the cementite that exists in the steel is the carbide at center morely, seeks performance and improves.
Summary of the invention
Problem of the present invention is, is provided at the tensile strength of reeling under the cold conditions, can have sufficient atmosphere intensity and coiling processibility concurrently and is the above spring of 2000MPa with the thermal treatment steel wire be used for the spring steel of this steel wire.
Present inventors find, by the unheeded up to now N of control, even add the generation that alloying element also can suppress not dissolve carbide, can guarantee toughness and processibility, thereby develop the spring that has high strength and coiling concurrently thermal treatment steel wire.That is, main idea of the present invention is as follows.
(1) a kind of high-strength spring steel, it is characterized in that: contain: surpass below 0.15%～1.0%, below the Al:0.005% in quality % C:0.5～0.9%, Si:1.0～3.0%, Mn:0.1～1.5%, Cr:1.0～2.5%, V, N is limited in below 0.007%, and containing among Nb:0.001%～less than 0.01%, the Ti:0.001%～less than 0.005% a kind or 2 kinds, its surplus is made up of Fe and unavoidable impurities.
(2) according to (1) described high-strength spring steel, it is characterized in that: further contain in a kind in quality % W:0.05%～0.5%, Mo:0.05%～0.5% or 2 kinds.
(3), it is characterized in that according to (1) or (2) described high-strength spring steel: further contain in quality % Ni:0.05%～3.0%, Cu:0.05%～0.5%, Co:0.05%～3.0%, B:0.0005%～0.006% more than a kind or 2 kinds.
(4) according to each the described high-strength spring steel in (1)～(3), it is characterized in that: further contain in quality % Te:0.0002%～0.01%, Sb:0.0002%～0.01%, Mg:0.0001%～0.0005%, Zr:0.0001%～0.0005%, Ca:0.0002%～0.01%, Hf:0.0002%～0.01% more than a kind or 2 kinds.
(5) a kind of heat-treatment steel for high-strength spring line, it is characterized in that: have each the described composition of steel in above-mentioned (1)～(4), tensile strength is more than the 2000MPa, and about carburizing system globular carbide and the alloy system globular carbide that occupies on the microsection surface, satisfy circle quite the footpath be that the occupied area rate of the above carbide of 0.2 μ m is 7% below, circle quite the footpath be that the density that exists of the carbide more than the 0.2 μ m is 1/μ m
2Below, and the original austenite grains degree number is more than No. 10, residual austenite is below the 15 quality %.
Description of drawings
Fig. 1 adds the figure of the effect (relation of tempering temperature and Charpy impact value) of Nb when being explanation attenuating N.
(a) is that the photo of sweep electron microscope to the observation example of not dissolving carbide adopted in expression among Fig. 2, (b) being that the expression alloy system does not dissolve the figure of the X ray ultimate analysis example of carbide X, (c) is that the expression carburizing system does not dissolve the figure of the X ray ultimate analysis example of carbide Y.
Embodiment
The present inventor is in order to obtain high strength, by the regulation chemical ingredients and by the carbide shape in the thermal treatment control steel, invents out the steel wire of having guaranteed to be enough to make the coiling characteristic of spring.
Its details is as follows.At first, just limiting high-strength spring describes with the chemical ingredients of steel and the reason of composition range.
C: be the element that the fundamental strength to steel has a significant impact, the past just is defined as 0.5～0.9% in order to obtain full intensity.When less than 0.5%, can not obtain full intensity.Especially,, also need the C more than 0.5% in order to ensure sufficient spring strength in the occasion of having omitted the nitrogenize that is used to improve the spring performance.Surpassing at 0.9% o'clock, owing to become hypereutectoid in fact, thick cementite is separated out in a large number, therefore toughness is significantly reduced.This makes the coiling characteristic reduce simultaneously.And, also in close relations with microstructure, carbide quantity is few when less than 0.5%, so distribution of carbides, the area occupation ratio of the zone of lacking than other parts (calling " carbide rarefied zone " in the following text) increases easily partly, is not easy to obtain full intensity and toughness or coiling (ductility).Therefore, carbon is preferably more than 0.55%, and the viewpoint that balances each other from intensity-coiling is more preferably more than 0.6%.
On the other hand, in the many occasions of C amount, the carbide of alloy system, carburizing system adds the tendency of pining for existing the solid solution difficulty when quenching, and in short occasion of the high occasion of heat treated Heating temperature, heat-up time, the insufficient situation of intensity and coiling is also many.And, do not dissolve carbide and influence the carbide rarefied zone yet, when carbide was not dissolved in the formation of the C in the steel, essence C reduced in the matrix, and therefore as described above, carbide rarefied zone area occupation ratio also can increase.Know that in addition when the C amount increased, the morphology of martensite during tempering is general lath martensite, and was relative therewith in medium carbon steel,, can make its form become lenticular martensite in the many occasions of C amount.Found that of research and development, the distribution of carbides of the tempered martensite that the lenticular martensite tempering is generated and is compared the distribution of carbides of lath martensite tempered occasion, and carbide density is low.Therefore, because by increasing the C amount, lenticular martensite, do not dissolve carbide and increase, thus also sometimes the carbide rarefied zone increase.So carbon is preferably below 0.7%, more preferably below 0.65%, the carbide rarefied zone is reduced.
Si: be intensity, hardness and the necessary element of anti-weakening property of elastic force in order to ensure spring, in less occasion, necessary strength and anti-weakening property of elastic force deficiency, so lower limit is defined as 1.0%.And Si has the carbonization system precipitate nodularization of crystal boundary, the effect of refinement, by adding, have the effect in the occupied area rate of crystal boundary that reduces grain boundary precipitate on one's own initiative.But, when heavy addition too, not only make hardened material, and embrittlement take place.Therefore, in order to prevent the embrittlement behind the Q-tempering, the upper limit is defined as 3.0%.In addition, Si is the element that also helps anti-temper softening, in order to make high-strength wire material, preferably adds in large quantities in a way.Specifically, preferably add more than 2%.On the other hand, in order to obtain stable coiling, be preferably below 2.6%.
Mn: in deoxidation and with MnS form fixed simultaneously, improve hardening capacity, can fully obtain the hardness after the thermal treatment, therefore be used mostly with the S in the steel.In order to ensure its stability, lower limit is defined as 0.1%.And for the embrittlement that prevents to cause owing to Mn, the upper limit is defined as 2.0%.In addition, have concurrently, be preferably 0.3%～1% in order to make intensity and coiling.In addition, make the preferential occasion of coiling, it is effective being defined as below 1.0%.
Cr: be to improving hardening capacity and anti-temper softening (temper softening drag) effective elements.And, be in such nitriding treatment that nearest high strength valve spring is seen, not only to guarantee tempered-hardness, to increasing also effective elements of surface hardness after the nitrogenize and case depth thereof.But, when addition for a long time, not only cause cost to increase, and make the cementite alligatoring of being seen behind the Q-tempering.In addition, also has the effect that makes alloy system carbide stabilization, alligatoring.Its result is because therefore the wire rod embrittlement also has the drawback of losing easily when reeling.Therefore, adding the occasion of Cr, if be not more than 0.1%, its DeGrain then.In addition, embrittlement is become significant 2.5% as the upper limit.But, in the present invention,, therefore can add a large amount of Cr, so be defined as obtaining easily high-intensity addition owing to control carbide very fine by regulation N.In addition, in the occasion of carrying out nitriding treatment, when having added Cr, can deepen the hardened layer that produces by nitrogenize.Therefore, preferably add more than 1.1%, and then the nitrogenize of unexistent high-strength spring is in the past preferably added more than 1.2% in order to be suitable for.
Cr hinder cementite by the dissolving that adds thermogenesis, particularly increase when reaching C＞0.55% when the C amount, suppress Cr and measure the generation that can suppress thick carbide, have intensity and coiling easily concurrently.Therefore, preferably its addition is below 2.0%, more preferably below 1.7% about.
V: owing to 2 precipitation-hardenings of hardened etc. take place in carbide precipitate when the tempering, the sclerosis on the top layer in the time of therefore can being used for sclerosis, the nitrogenize of the steel wire under tempering temperature.In addition, has the effect that suppresses the alligatoring of austenite particle diameter owing to the generation of nitride, carbide, carbonitride, therefore preferred the interpolation.But the nitride of V, carbide, carbonitride also generate more than the austenitizing temperature A3 of steel point up to now, therefore in the inadequate occasion of its solid solution, easily as not dissolving carbide (nitride) and residual.This does not dissolve carbide, not only becomes the reason of losing when spring is reeled, and causes " waste of V ", and the anti-temper softening that V brought of interpolation and the effect of improving of 2 precipitation-hardenings are lowered, and the performance of spring is reduced.Therefore, present industrial being preferably below 0.15%.But, in the present invention,, can be suppressed at nitride, carbide, the carbonitride of the above V of generation of austenitizing temperature A3 point by control N amount, but therefore heavy addition V correspondingly, the V addition is defined as above 0.15% and below 1.0%.Its addition is 0.15% when following, improve nitride layer hardness, increase nitride layer the effect of interpolation V of the degree of depth etc. less, can not guarantee the above sufficient fatigue durability of existing steel.And its addition surpasses at 1.0% o'clock, generates thick not solid solution inclusion, and toughness is reduced, and is simultaneously the same with Mo, generates cold tissue easily, becomes the reason of fracture of wire when cracking with wire drawing easily.So, industrial carry out easily stable operation 1.0% as the upper limit.
The nitride of V, carbide, carbonitride are at the austenitizing temperature A of steel
3Also can generate more than the point, therefore in the inadequate occasion of its solid solution, residual with the form of not dissolving carbide (nitride) easily.So, the ability of the industrial control nitrogen amount of consideration realistic situation, industrial being preferably below 0.5% is more preferably below 0.4%.
On the other hand, because in the surface hardening undertaken by nitrogenize is handled, the temperature more than the reheat to 300 ℃, therefore softening for the sclerosis on the top layer that suppresses to be undertaken, inner hardness by nitrogenize, need addition to surpass 0.15%, preferably add more than 0.2%.
Al: be deoxidant element, influence the generation of oxide compound.Particularly in the high strength valve spring, with Al
2O
3For the hardening oxidation thing at center becomes the fracture starting point easily, therefore need be avoided it.So it is very important strictly to control the Al amount.Particularly surpass the such occasion of 2100MPa as thermal treatment steel wire tensile strength, for the fluctuation that makes fatigue strength is lowered, must strict controlled oxidation thing generting element.In the present invention, be defined as below the Al:0.005%.This is owing to generate with Al easily when surpassing 0.005%
2O
3Therefore be the oxide compound of main body, produce and result from the losing of oxide compound, thereby can not guarantee the cause of sufficient fatigue strength and quality stability.In addition, requiring the occasion of high-fatigue strength, be preferably below 0.003%.
In the present invention, the control of N is very big main points, and the present invention has stipulated strict limits value, i.e. N≤0.007%.This is because pay close attention to the cause of the effect of N again for spring steel.The effect of control N and the regulation reason among the present invention are described below.In steel, N has following influence: 1) exist with solid solution N form in ferrite, by moving of dislocation in the inhibition ferrite, make the ferrite sclerosis; 2) generate nitride with alloying elements such as Ti, Nb, V, Al, B, influence steel performance, its mechanism etc. are narrated in the back; 3) influencing iron such as cementite is the behavior of separating out of carbide, and steel performance is exerted an influence.
In spring steel, owing to adopt the alloying element of C and Si, V and so on to guarantee intensity, so the hardening effect of solid solution N and little.On the other hand,,, can make to add Ministry of worker's embrittlement, the coiling processing characteristics is reduced by suppressing the distortion that suppresses to add the Ministry of worker of moving of dislocation in the occasion of the cold working of considering spring (processing of reeling).
In addition, in the regulation element in (1) of the summary of the invention, V at high temperature generates precipitate in steel.Its chemical ingredients is followed cooling at high temperature based on nitride, little by little changes its form to carbonitride, carbide.Therefore, the nitride that generates at high temperature becomes the nuclear of separating out of V carbide easily.This generates easily undissolved carbide when the heating of lead bath quenching (patenting), quenching process, and then it becomes nuclear, so its size is grown up easily.And from the viewpoint of cementite, such high-strength spring from its desired strength, is to carry out tempering under 300～500 ℃ the condition in tempering temperature.The iron that spring steel generates when being tempering by its distinctive composition is that carbide is ε-carbide, θ-carbide (so-called cementite Fe
3C), its metamorphosis complexity.Therefore, the mechanical propertiess such as ductility to steel exert an influence.N also influences its carbide and generates, and I haven't seen you for ages makes ductility and toughness raising 350～500 ℃ under for the N amount.In the present invention, in order to reduce the hazardous property of such N, the N amount is limited to N≤0.007%.
In addition, as described later, trace adds Ti and Nb wantonly a kind or 2 kinds.If originally the N amount was suppressed at below 0.003%, wantonly a kind or 2 kinds that does not then add Ti and Nb can obtain good performance, still industrial stably be controlled to be 0.003% unfavorable to manufacturing cost when following.Therefore, just micro-wantonly a kind or 2 kinds of adding Ti and Nb.When adding Ti or Nb, these elements at high temperature generate nitride, and solid solution N is reduced, and therefore can access and the same effect of situation that reduces the N addition.So, can increase the addition upper limit of N.But when the N amount surpassed 0.007%, the nitride growing amount of V, Nb or Ti increased, its result is not dissolved carbide and is increased, and hard inclusions things such as TiN increase, therefore toughness reduces, fatigue durability and coiling reduction, so the ceiling restriction of N amount is 0.007%.
That is, in the occasion of wantonly a kind or 2 kinds that add Ti and Nb, if the N amount is too much or Ti or Nb are too much, then still can generate the nitride of Ti or Nb, it is harmful to become on the contrary, so the addition of Ti or Nb still needs trace.So the upper limit of N amount is preferably below 0.005%, more preferably below 0.004%.By so critically controlling N, when suppressing the ferrite embrittlement, suppress the generation of V based nitride, thereby suppress not dissolve the generation of carbide and grow up.In addition, be the form of carbide by control iron, can improve toughness.That is, when N surpassed 0.007%, the V based nitride generated easily, did not dissolve carbide and generated morely, caused the steel embrittlement sometimes according to the form of ferrite, carbide.
Like this, even in the occasion of adding Ti or Nb, if the easiness of consideration thermal treatment etc. also is preferably below 0.005%.In addition, about the lower limit of N amount, though preferred few, in steel making working procedure etc., from atmosphere, sneak into easily, therefore consider to be preferably manufacturing cost and the easness in the denitrogenation operation more than 0.0015%.
Nb: generate nitride, carbide, carbonitride, with the V ratio, its nitride produces under higher temperature.Therefore, consume N in the steel, can suppress the generation of V based nitride by generate the Nb nitride in when cooling.Its result can suppress the generation that carbide is not dissolved in V system, therefore can guarantee anti-temper softening and processibility.
In addition, be that carbonitride suppresses the alligatoring of austenite particle diameter except can be used for by Nb, the sclerosis on the top layer in the time of can also being used for sclerosis, the nitrogenize of the steel wire under tempering temperature.But, when its addition is too much, be that the not dissolving carbide of nuclear is residual easily with the Nb based nitride, therefore must avoid the interpolation of volume.Specifically, during Nb addition less than 0.001%, almost can't see the effect of interpolation.And the volume more than 0.01% is added, and can cause generating thick not solid solution inclusion, and toughness is descended, and is simultaneously the same with Mo, is easy to generate cold tissue, becomes the reason of broken string when cracking with wire drawing easily.So, be defined as industrial stable operation and be easy to less than 0.01%.
Fig. 1 is the result that the material of the chemical ingredients shown in the his-and-hers watches 1 is measured impact value, is that expression adopts the method for embodiment described later to carry out the figure of the impact value measurement result of heat treated Sample A and B.As shown in Figure 1 as can be known, add the steel of a little Nb control N, can obtain high impact value on the whole.
Table 1
In the present invention, add the occasion of Ti, its addition is more than 0.001%, less than 0.005%.Ti is a deoxidant element, also is nitride, sulfide generting element simultaneously, therefore influences the generation of oxide compound and nitride, sulfide.So, when adding, volume generates hardening oxidation thing, nitride easily, if therefore add inadvertently, then generate hard carbide, and fatigue durability is reduced.The same with Al, particularly for high-strength spring, compared with the safe range of stress of spring itself, the wave stability of fatigue strength is reduced, and in the Ti amount for a long time, the fracture incidence of inclusion of resulting from increases, therefore need its amount of control, be defined as less than 0.005%.
On the other hand, Ti at high temperature generates TiN in molten liquid steel, so have the effect of lowering the sol.N in the molten liquid steel.In the present invention, N suppresses the generation of V based nitride by restriction, and then suppresses V system and do not dissolve growing up of carbide, and this is the main points of technology.So,, then can suppress the V based nitride and be growing up of carbonitride with its V that serve as nuclear grow when the cooling if under the V based nitride generates temperature more than the temperature, consume N.That is,, make in fact and reduce, therefore reduce the generation temperature of V based nitride, and then can suppress V system and do not dissolve carbide with V bonded N amount by adding Ti.
Therefore, be the viewpoint that generates of dissolved carbon nitride and oxide compound not from Ti, the volume of Ti is added and be avoided, and the interpolation of trace can reduce the V based nitride and generate temperature, therefore can lower and not dissolve carbide.Its addition is more than 0.001%, does not consume the effect of N when less than 0.001%, does not also suppress the effect that carbide is not dissolved in V system, can't see the effect that processibility is improved.But the Ti addition is preferably below 0.003%.
Steel of the present invention as basal component, and then can add the composition of the character that is used to improve steel with above-mentioned composition.That is,, further add a kind or 2 kinds among W, the Mo in the occasion of strengthening anti-temper softening.W not only makes hardening capacity improve, and also generates carbide in steel, plays the effect that improves intensity, and is effective to giving anti-temper softening.Therefore, do one's utmost to add comparatively ideal.W compares with Ti, Nb etc., generates carbide at low temperature, therefore is not easy to generate not dissolve carbide.In addition, by precipitation-hardening, can give anti-temper softening.That is, in nitrogenize, stress-removal annealing, inner hardness is reduced greatly.Its addition is 0.05% when following, can't see effect, be 0.5% to produce thick carbide when above, on the contrary might damage mechanical properties such as ductility, so the addition of W is defined as 0.05%～0.5%.In addition, the easiness of consideration thermal treatment etc. etc. are preferably 0.1%～0.4%.Particularly in order to avoid the drawback of the cold tissue of mistake etc. after just rolling, and obtain anti-temper softening to greatest extent, further preferably add more than 0.15%.
Mo: hardening capacity is improved, and under the temperature about tempering, nitriding temperature, Mo separates out with the carbide form simultaneously, therefore can give anti-temper softening.So, not softening even through thermal treatments such as tempering at high temperature, the annealing of eliminating the stress that in technology, produces and nitriding treatment yet, can bring into play high strength.The reduction that this can suppress the inner hardness of nitrogenize rear spring makes the set of heating handle (hot setting), stress-removal annealing easily, and the fatigue characteristic of final spring are improved.That is the tempering temperature high temperatureization in the time of, can making control intensity.The high temperatureization of this tempering temperature is favourable to the occupied area rate at crystal boundary that reduces grain boundary carbide.That is, make membranaceous grain boundary carbide nodularization of separating out, have the effect that lowers the grain boundary area rate by tempering at high temperature.In addition, to generate Mo mutually independently with cementite in steel be carbide to Mo.Particularly compare with V etc., it is low that it separates out temperature, therefore has the effect that suppresses the carbide alligatoring.Its addition is 0.05% when following, can't see effect.But its addition generated cold tissue in the softening thermal treatment before rolling, drawing etc. for a long time easily, became the reason of crackle and the broken string when hot candied easily.That is, preferably when wire drawing, make steel form the ferrite-pearlite tissue by the lead bath quenching processing in advance and carry out afterwards wire drawing.
But, Mo is an element of greatly giving hardening capacity, when therefore addition increases, time till pearlitic transformation finishes is elongated, during rolling postcooling, generated cold tissue easily in the lead bath quenching operation, the reason that breaks when becoming wire drawing does not perhaps have broken string but the occasion that exists as internal fissure, and the characteristic that can make end article is deterioration greatly.Surpass at 0.5% o'clock at Mo, it is big that hardening capacity becomes, and is difficult to form the ferrite-pearlite tissue industrial, thus with it as the upper limit.For the generation that in manufacturing processes such as rolling, wire drawing, suppresses to reduce the martensitic stucture under the processibility, industrial stable and easily be rolled and hot candied, be preferably below 0.4% more preferably about 0.2%.
In addition, W and Mo are compared with V, the Nb, the Ti that have the effect of strengthening anti-temper softening equally, V, Nb, Ti are as described above, generate nitride, and with its serve as nuclear carbide is grown up, relative with it, W and Mo generate nitride hardly, can strengthen softening resistance after the influence ground that not measured by N adds.That is, though V, Nb, Ti can strengthen softening resistance, for fear of not dissolving carbide and strengthening softening resistance and when adding, addition is restricted naturally.Therefore, do not generating the occasion of not dissolving carbide and needing high softening resistance, do not generate nitride, and the interpolation of carbide precipitate, the W that plays the precipitation strength element or Mo at a lower temperature be extremely effective.In addition, in order to have intensity and processibility concurrently, in the occasion that can not obtain the optimum balance of softening resistance and processibility by the control carbide, in order to guarantee intensity by matrix strengthening, add among Ni, Cu, Co, the B more than a kind or 2 kinds.
Ni: hardening capacity is improved, by thermal treatment high strength stably.In addition, the ductility of matrix is improved, make the coiling raising.But, through Q-tempering residual austenite is increased, so spring shaping back deterioration aspect anti-weakening property of elastic force and material homogeneity.Its addition is 0.05% when following, can't see the effect that high strength and ductility improve.On the other hand, preferred heavy addition Ni, when it is 3.0% when above, the drawback that residual austenite is increased becomes significantly, and while hardening capacity and ductile raising effect are saturated, become unfavorable at aspects such as costs.
Cu:, can prevent decarburization by adding Cu.Decarburized layer reduces fatigue lifetime after spring processing, therefore must make great efforts to reduce as far as possible.In addition, the occasion in that Decarburized layer deepens removes the top layer by the processing that strips off the skin that is called as " stripping off the skin ".In addition, equally also has the effect that the solidity to corrosion of making improves with Ni.By suppressing Decarburized layer, can improve spring fatigue lifetime, omit the operation that strips off the skin.The inhibition decarburization effect of Cu and to improve corrosion proof effect be 0.05% can bring into play when above as described later, even add Ni, when above 0.5% the time, also becomes the reason of rolling defect easily owing to embrittlement.Therefore, its lower limit is defined as 0.05%, the upper limit is defined as 0.5%.Adds Cu and damage mechanical properties under the room temperature hardly, but the Cu addition surpasses 0.3% occasion, can make the hot ductility deterioration, therefore when rolling sometimes the surface at steel billet crack.Therefore, prevent the Ni addition of the crackle when rolling, be preferably [Cu%]＜[Ni%] corresponding to the addition of Cu.When Cu is scope below 0.3%, can not produce rolling defect, need be not purpose restriction Ni addition therefore to prevent rolling defect.
Co: hardening capacity is descended, but hot strength is improved.In addition, owing to hinder the generation of carbide, therefore has the effect of the generation of the thick carbide that suppresses to become problem in the present invention.Therefore, can suppress to comprise the alligatoring of the carbide of cementite.So, the preferred interpolation.In the occasion of adding, when being that 0.05% its effect when following is little.When but volume was added, the hardness of ferritic phase increased, and ductility is reduced, so its upper limit was defined as 3.0%.Industrial be promptly can obtain stable performance below 0.5%.
B: be the element that improves hardening capacity, and have the effect that purifies austenite grain boundary.By adding B, reduce elements such as flexible P, S at grain boundary segregation innoxious thereby can make, and fracture characteristics is improved.At this moment, when B combined generation BN with N, its effect disappeared.Its addition, with its effect become tangible 0.0005% be defined as lower limit, with effect saturated 0.0060% as the upper limit.But, even generate a little BN, just making its embrittlement, therefore must fully be careful, do not generate BN.Therefore, be preferably below 0.003%, further preferably by the fixing N freely of nitride generting elements such as Ti, Nb, and to make B be 0.0010%～0.0020%, effectively.
These Ni, Cu, Co and B, mainly effective to the reinforcement of the ferritic phase of matrix.In order to have intensity and processibility concurrently, in the time can not obtaining the optimum balance of softening resistance and processibility, guarantee the occasion of intensity by matrix strengthening by the control carbide, they are effective elements.
And then, in the occasion that requires further high performance and stable performanceization, as the element of control oxide morphology, add among Te, Sb, Mg, Zr, Ca, the Hf more than a kind or 2 kinds.
Te: have the effect that makes the MnS nodularization.Its DeGrain when less than 0.0002%; Reduce surpassing the toughness to make matrix at 0.01% o'clock, produce thermal crack, the drawback of fatigue durability reduction etc. is become significantly, so the upper limit is defined as 0.01%.
Sb: have the effect that makes the MnS nodularization, its DeGrain when less than 0.0002%; Reduce surpassing the toughness to make matrix at 0.01% o'clock, produce thermal crack, the drawback of fatigue durability reduction etc. is become significantly, so the upper limit is defined as 0.01%.
Mg: generate oxide compound in generate the high molten liquid steel of temperature than MnS, this oxide compound is when generating MnS Already in the molten liquid steel.Therefore, the nuclear of separating out of MnS can be used as, the distribution of MnS can be controlled thus.In addition, distribute about its number, Mg is that oxide compound is that oxide compound is distributed in the molten steel imperceptibly more morely than the Si, the Al that see in existing steel, is that oxide compound is MnS dispersion imperceptibly in steel of nuclear with Mg therefore.Therefore, even identical S content, according to the difference that has or not of Mg, MnS distributes also different, and the MnS particle diameter becomes finer when adding them.Even trace adds, also can fully obtain its effect, if add Mg, then MnS refinement.But, when surpassing 0.0005%, except easy generation hardening oxidation thing, also begin to generate the MgS sulfides, cause the reduction of fatigue strength and the reduction of coiling.Therefore, the addition of Mg is defined as 0.0001%～0.0005%.Being used for the occasion of high-strength spring, be preferably below 0.0003%.Though these elements are micro-,, therefore can add about 0.0001% owing to use the Mg series refractory material mostly.In addition, select auxiliary material, use the less auxiliary material of Mg content, can control the Mg addition by strictness.
Zr: be oxide compound and sulfide generting element.Because dispersion oxide imperceptibly in spring steel is therefore the same with Mg, become the nuclear of separating out of MnS.Thus, fatigue durability is improved, increase ductility, make the coiling raising.When less than 0.0001%, can't see its effect, in addition, add even surpass 0.0005% ground, owing to encourage the generation of hardening oxidation thing,, also be easy to generate the problem of oxide compound of resulting from even therefore sulfide disperses imperceptibly.In addition, when volume is added, except oxide compound, also generate nitride, sulfide such as ZrN, ZrS, thereby produce the problem on making and the tired wear properties of spring is reduced, therefore be defined as below 0.0005%.And, being used for the occasion of high-strength spring, this addition is preferably below 0.0003%.Though these elements are micro-,, can control by strict auxiliary material, the accurate control refractory materials etc. selected.
For example,, use the Zr series refractory material mostly, therefore can add about 1ppm the molten liquid steel about 200t in the place with the situation of molten liquid steel Long contact time such as ladle, tundish, sprue gate.And, consider these situations, add auxiliary material and make that being no more than specialized range gets final product.The analytical procedure of Zr in the steel is the part sampling 2g of influence that never is subjected to the top layer oxide skin of determination object steel, adopt handle sample with the same method of JIS G 1237-1997 annex 3 after, can measure by ICP.Set and make the lubber-line of ICP be suitable for micro-Zr this moment.
Ca: be oxide compound and sulfide generting element.For spring steel, can be by making the MnS nodularization, suppress length as the MnS of the fracture starting point of fatigue etc., make it innoxious.Its effect is not obvious when less than 0.0002%, and when surpassing the interpolation of 0.01% ground, qualification rate variation not only, and generation oxide compound and CaS sulfides, on making, go wrong, make the tired wear properties of spring to descend, therefore be defined as below 0.01%, its addition is preferably below 0.001%.
Hf: be the oxide compound generting element, become the nuclear of separating out of MnS.Therefore, by fine dispersion, Hf is oxide compound and sulfide generting element.Because dispersion oxide imperceptibly in spring steel is therefore the same with Mg, become the nuclear of separating out of MnS.Thus, fatigue durability is improved, increase ductility, make the coiling raising.Its effect is not obvious when less than 0.0002%, and when surpassing the interpolation of 0.01% ground, qualification rate variation not only, and generate oxide compound, nitride and sulfide such as ZrN, ZrS, on making, go wrong, make the tired wear properties of spring to descend, therefore be defined as below 0.01%, its addition is preferably below 0.003%.
Below, what other composition was described preferably contains scope.
About P, S,, need restriction though in the scope that the present invention asks for protection, do not stipulated.P makes hardening of steel, and produces segregation, makes material embrittlement.Particularly, cause the reduction of impact value, owing to the intrusion of hydrogen causes delayed fracture etc. at the P of austenite grain boundary segregation.Therefore, content is less for well.Therefore, P is preferably the embrittlement tendency and becomes significant below 0.015%.And, surpass the such high-intensity occasion of 2150MPa in the tensile strength of thermal treatment steel wire, be preferably less than 0.01%.
S is also the same with P, makes the steel embrittlement when existing in steel.Can do one's utmost to reduce the influence of S by the effect of Mn, but because MnS also presents the form of inclusion, so fracture characteristics reduces.Especially high-strength steel also can produce fracture owing to the MnS of trace, therefore wishes to do one's utmost to reduce S.Be preferably its detrimentally affect and become significant below 0.015%.And, surpass the such high-intensity occasion of 2150MPa in the tensile strength of thermal treatment steel wire, be preferably less than 0.01%.
Add up to oxygen amount (t-O) to be defined as 0.0002～0.01%.In steel, exist through deoxidation step and the oxide compound that produces and solid solution oxygen.But, add up to the many occasions of oxygen amount (t-O) at this, mean that oxide based inclusion is many.If the size of oxide based inclusion is little, then do not influence the performance of spring, but if the big oxide compound of size exists in a large number, then the performance to spring has a significant impact.When the oxygen amount exists above 0.01%, the performance of spring is significantly reduced, so its upper limit is preferably 0.01%.In addition, oxygen is advisable less, even but less than 0.0002%, its effect is also saturated, and is therefore that less than 0.0002% is comparatively desirable as lower limit.The easness of the deoxidation step in the consideration practicality etc. wishes to be adjusted into 0.0005%～0.005%.
In the present invention, preferred tensile strength is more than the 2000MPa.If the tensile strength height, the tendency that then exists the fatigue characteristic of spring to improve.In addition, even implementing surface-treated occasion such as nitrogenize, if the fundamental strength height of steel wire then also can access higher fatigue characteristic and anti-elastic force weakens characteristic.On the other hand, when intensity was high, it is difficult that coiling decline, the manufacturing of spring become.Therefore, not only improve intensity, it also is important giving the ductility that can reel simultaneously.
Consider that from the viewpoint tired, that elastic force weakens etc. the intensity of steel wire is necessary, TS 〉=2000MPa is defined as lower limit with tensile strength.And then be suitable for the occasion of high-intensity spring, and wish further high intensity, be preferably more than the 2200MPa, in order to be applicable to more high-intensity spring, preferably in the scope of not damaging coiling, carry out high strength to 2250, more than the 2300MPa.
For not dissolving carbide, in order to obtain high strength, add C and other Mn, Ti, so-called alloying elements such as V, Nb, but among these elements, heavy addition forms the occasion of the element of nitride, carbide, carbonitride, and it is residual easily not dissolve carbide.Do not dissolve carbide be generally spherical, have alloying element and be a main body with cementite be the not dissolving carbide of main body.
Fig. 2 expresses typical observation example.Fig. 2 (a) is the observation example of not dissolving carbide that adopts sweep electron microscope to obtain, and (b) is the X ray ultimate analysis example that alloy system does not dissolve carbide X, (c) represents the X ray ultimate analysis example that carburizing system does not dissolve carbide Y.Observe example according to these, in steel, can see 2 kinds of the acicular structure of matrix and globular structures.Know that usually steel forms martensitic acicular structure by quenching, and generates carbide by tempering, has intensity and toughness thus concurrently.But, in the present invention, as Fig. 2 (a) X, Y, not necessarily be acicular structure sometimes, residual also morely globular structure.This globular structure is undissolved carbide, and its distribution has a significant impact the performance of spring steel line.Therefore, here the said carbide that do not dissolve, be meant above-mentioned alloy has not just generated the so-called alloy system globular carbide (X) of nitride, carbide, carbonitride, also comprises with Fe carbide (cementite) being the carburizing system globular carbide (Y) of principal constituent.
Fig. 2 (b), (c) express to adopt and are installed in the analysis example that the EDX on the SEM obtains.The carbide of alloying element systems such as V, Nb is only paid close attention in invention in the past, and the one example is Fig. 2 (b), it is characterized in that the Fe peak value is less in the carbide, alloys peak (this routine occasion is V) is bigger.This alloy system carbide (X), strictly become with the situation of the double carbide (so-called carbonitride) of nitride in the majority, therefore, carbide, nitride and the spherical precipitate of compound alloy system thereof of these alloy systems is generically and collectively referred to as the alloy system globular carbide here.
In the present invention, be not existing alloying element be globular carbide, find out like that shown in Fig. 2 (c) circle is the following Fe of footpath 3 μ m quite
3C and solid solution therein a little alloying element so-called carburizing system carbide to separate out form also very important.As the present invention, in high strength and the two occasion that has concurrently of processibility of reaching more than the existing steel wire, the carburizing system globular carbide below 3 μ m for a long time, processibility is damaged greatly.Below with so spherical and such shown in Fig. 2 (c) be that the carbide of principal constituent is designated as the carburizing system globular carbide with Fe and C.
Moreover these results adopt the extraction replica method under the transmission type microscope, also can obtain same analytical results.Can think that these globular carbide are to handle in oil tempering, do not have abundant solid solution in the high-frequency quenching temper process, the nodularization and the carbide of growing up or having dwindled in the Q-tempering operation.The carbide of this size not only to intensity and toughness not contribution fully, makes its deterioration by Q-tempering on the contrary.That is, because fixing C in the steel, simple consumption should become the C that is added in the source of intensity, and alligatoring, becomes stress raiser, therefore makes the mechanical properties reduction of steel wire.
Therefore, about alloy system globular carbide and the carburizing system globular carbide that occupies, increase following regulation on the microsection surface, in order to get rid of the drawback that is caused by them, following restriction is important.
The circle quite occupied area rate of the carbide more than the 0.2 μ m of footpath is below 7%;
The circle quite density that exists of the carbide more than the 0.2 μ m of footpath is 1/μ m
2Below.
After steel is carried out Q-tempering, carry out cold coiling around occasion, do not dissolve globular carbide influence its coiling characteristic, promptly influence up to the fracture till curved characteristic.In order to obtain high strength, not only added C usually, also volume is added alloying elements such as Cr, V, but exists intensity too high in the past, and the deformability deficiency makes the drawback of coiling deterioration in characteristics., its reason can be thought the factor of separating out thick carbide in the steel.
These steel interalloy system and carburizing system carbide, by observing to implement corrosion such as picric acid burn into electrolytic corrosion through the sample of mirror ultrafinish, but detailed observation evaluations such as its size, need observe with the high magnification more than 3000 times by sweep electron microscope, at this alloy system globular carbide and carburizing system globular carbide as object, its circle quite footpath is more than the 0.2 μ m.Usually, the carbide in the steel is indispensable to intensity, the anti-temper softening of guaranteeing steel, but its effective particle diameter is below the 0.1 μ m, and when surpassing 1 μ m on the contrary, the not contribution of refinement to intensity and austenite particle diameter only can make the deformation characteristic deterioration.But this importance is not recognized so in the prior art, just pays close attention to the alloy carbide of V, Nb etc., thinks that 3 μ m following carbide, particularly carburizing system globular carbide in the suitable footpath of circle is harmless.
This alloy system and carburizing system carbide, be that the sample through mirror ultrafinish is carried out electrolytic corrosion, observe 10 more than the visual field with sweep electron microscope with 10000 times, the extreme deterioration of processibility when the occupied area rate of globular carbide surpasses 7% is so be decided to be the upper limit with it.
In addition, in the present invention, as the circle of object quite the footpath be the alloy system more than the 0.2 μ m and the occasion of carburizing system globular carbide, size not only, quantity is also referred to as very big factor.Therefore, the two has stipulated protection scope of the present invention to consider this.That is, the quantity that is the globular carbide more than the 0.2 μ m when the suitable footpath of circle is very many, surpasses 1/μ m in the lip-deep density that exists of microsection
2The time, the deterioration of coiling characteristic becomes significantly, therefore with 1/μ m
2As the upper limit.On the other hand, when the size of carbide surpassed 3 μ m, the influence of size was bigger, therefore wished not have to surpass the carbide of 3 μ m.
The original austenite grains degree number is defined as the reasons are as follows more than No. 10: be in the steel wire of matrix with the tempered martensite, original austenite particle diameter and carbide have a significant impact the essential property of steel wire in the lump.That is, original austenite particle diameter hour fatigue characteristic and coiling excellence.But even the austenite particle diameter is little, if above-mentioned carbide contains more than regulation in a large number, then its effect is also little.Usually, in order to reduce the austenite particle diameter, the Heating temperature that reduces when quenching is effectively, but the above-mentioned globular carbide that do not dissolve is increased.Therefore, make that to become the steel wire that carbide amount and original austenite particle diameter average out be important.At this, satisfy the occasion of afore mentioned rules about carbide, when No. 10, original austenite particle diameter less than, can not obtain sufficient fatigue characteristic and coiling, so the original austenite particle diameter number is defined as more than No. 10.
In addition, in order to be applicable to high-strength spring, crystal grain is thinner comparatively desirable, is No. 11 and then is more than No. 12 by making it, and can have high strength and coiling concurrently.
Residual austenite is defined as following the reasons are as follows of 15 quality %: near the zone that residual austenite remains in segregation portion, original austenite crystal boundary, clipped by subgrain.Residual austenite is owing to processing is brought out phase transformation and become martensite, if bring out phase transformation when spring is shaped, then the partial high rigidity of generation district in the material is certain to make the coiling reduction as spring.In addition, nearest spring, carry out surface strengthening by the shot peening and the processing viscous deformation such as (seting) of halting, but in occasion with the manufacturing process that comprises a plurality of operations that apply viscous deformation in this wise, the martensite of phase transformation is brought out in the processing of stage generation in early days, the breaking strain amount is lowered, and the fracture characteristics of the spring in processibility and the use is reduced.In addition, in the occasion that industrial inevitable distortion such as knocking defective is introduced into, in coiling, lose easily.In addition, in thermal treatments such as nitrogenize and stress-removal annealing, residual austenite is slowly decomposed, and mechanical properties variation, intensity are reduced, and causes drawbacks such as coiling property reduction.Therefore, by doing one's utmost to reduce residual austenite, suppressing the martensitic generation that phase transformation is brought out in processing, processibility is improved.Particularly, when residual austenite surpassed 15% (quality %), the susceptibility of knocking defective etc. raise, reel and other operation in lose easily, therefore be restricted to below 15%.
Different according to alloying element additions such as C, Mn and heat-treat condition, remained austenite content also changes.Therefore, not only composition design, enriching of thermal treatment bar also is important.
Martensite generates temperature (beginning temperature Ms point, finishing temperature Mf point) when becoming low temperature, just not can not generate martensite, easy residual residual austenite if do not reach quite low temperature when quenching.Industrial quenching makes water or oil, and the inhibition of residual austenite needs the thermal treatment control of height.Particularly, heat-eliminating medium is remained on low temperature, also do one's utmost to keep low temperature after the cooling, guarantee that the control of long time to martensitic transformation etc. is necessary.Industrial, on tinuous production, handle, so the temperature of heat-eliminating medium is easy to rise near 100 ℃, but preferably maintains below 60 ℃, and then the low temperature below 40 ℃ more preferably.In addition, in order fully to promote in heat-eliminating medium, to keep martensitic transformation more than 1 second, guarantee that the cooled hold-time is also very important.
In addition, except regulation to these carbide etc., the tissue that should avoid the distribution of carbide to lack than other parts.Particularly, in lenticular martensite and tempered martensite thereof, the distribution of carbide is lacked than other part, produces the ununiformity of microstructure, therefore fatigue strength and processibility is caused bad influence.
Embodiment
Assessment item:
In order to estimate the suitability of the present invention to spring, as assessment item, illustrate tensile strength, annealing after hardness, impact value and the relative reduction in area of in tension test, measuring.Tensile strength is directly connected to the weather resistance of spring, and intensity is high more, represents that its weather resistance is high more.
In addition, when measuring tensile strength, the relative reduction in area of Ce Dinging is to represent the viscous deformation behavior of material simultaneously, is the evaluation index of the processibility (coiling characteristic) of spring.This relative reduction in area is big more, and expression can be processed more easily, if but usually intensity uprise, then relative reduction in area reduces.Know from the example of existing steel, in the evaluation under this line footpath, when relative reduction in area surpasses 30%, in the mass production of industry, be not easy to occur obstacle for other line footpath.Starting material for the φ 13mm that makes carry out the Q-tempering processing, so that tensile strength approximately surpasses 2200MPa, then, No. 22019 test pieces make test piece according to JIS Z, test according to JIS Z 2241, calculate tensile strength from its crushing load.
In addition, in recent years, for the high strength of spring, the situation of hardening treatment of the top layer being implemented nitrogenize is more.Nitrogenize is in nitrogen atmosphere spring to be heated to 400～500 ℃, is incubated about several minutes～1 hour, makes case-hardening thus.At this moment, the inside of not invading nitrogen is heated, and therefore is annealed, softens.It is important suppressing this softening, therefore will simulate hardness after the annealing of nitrogenize as the assessment item of anti-softening shape.
In addition, in order to estimate raw-material processibility and anti-fracture characteristics, with Charpy impact value as assessment item.It has been generally acknowledged that the material that impact value is good comprises that the anti-fracture characteristics of fatigue characteristic is also good.In addition, its processibility of crisp material is also relatively poor, thinks that therefore high its processibility of material of toughness is also excellent.In the present embodiment, measured the Charpy impact value of having implemented with the same heat treated material of the sample of measuring the tensile strength behind the Q-tempering.Charpy impact value also is subjected to the influence of austenite particle diameter, has therefore also measured same raw-material austenite particle diameter.Summer is the U type breach that processes 2mm on the material by the so-called half-size scale (5 * 10mm cross section) of the thermal treatment raw material preparing of φ 13mm than impacting test piece.
In addition, spring is about the φ of thinner diameter 4mm, with relatively shorter time end thermal treatment.Therefore know, do not dissolve carbide residual easily, processibility is reduced.Thereby, in example of the present invention, also carry out lead bath quenching-wire drawing, be made into φ 4mm, should heat-treat by the wire drawing material, measure the distribution and the austenite particle diameter of its carbide.Usually,, do not dissolve the trend that carbide increases, must carry out comprehensive evaluation according to the balance of the two but exist if Heating temperature is low, the time is short then the austenite particle diameter diminishes.Its result shows on tensile strength and the unit elongation, therefore with this two as evaluation object.The thin footpath material that φ 5mm is following, its sectional area is less, so the viscous deformation behavior, its unit elongation more presents evident difference than relative reduction in area.
The details of the heat-treat condition of evaluating material etc. is described below.
Tension test according to the test piece of JIS standard making parallel zone φ 6mm, is measured its tensile strength and unit elongation.About remained austenite content, behind Q-tempering, carry out mirror ultrafinish, measure with X ray.And, about the hardness after the annealing, after thermal treatment, carry out mirror ultrafinish, measures 3 be the Vickers' hardness of 1/2 position of radius apart from the surface, its mean value is as the hardness after annealing.
About raw-material manufacture method (line-bar), example 16 of the present invention is with after 2 tons the vacuum melting furnace melting, by rolling making steel billet.At this moment, in example, keep certain hour at the high temperature more than 1200 ℃.Any then occasion all becomes φ 13mm by billet rolling.
In other embodiments, after the melting of 16kg vacuum melting furnace, forge into φ 13mm * 600mm, heat-treat then by forging.Keep certain hour at the high temperature more than 1200 ℃ this moment too, heat-treats then to reach the intensity of regulation.
About heat treating method, in the making of estimating test piece, there is not the special occasion of recording and narrating, through behind the 1200 ℃ * 15 minutes → air cooling, put in the lead bath groove that is heated to 650 ℃ after 10 minutes 950 ℃ of heating, again after heating in 950 ℃ * 10 minutes, put in 60 ℃ the oil groove and quench, then, example of the present invention has been regulated tempering temperature, so that tensile strength surpasses 2200MPa.Tensile strength, relative reduction in area and Charpy impact value after this thermal treatment have been measured.
This tempering temperature, different and different according to chemical ingredients, but in the present invention, carried out thermal treatment corresponding to chemical ingredients, so that tensile strength becomes more than the 2200MPa.On the other hand, about comparative example, only carried out thermal treatment in order to be in harmonious proportion tensile strength.In addition, by carrying out 400 ℃ * 20 minutes annealing of blank nitriding, and measure its hardness, estimated softening resistance.
In addition,, do not having the special occasion of recording and narrating, behind 1200 ℃ * 15 minutes → air cooling, be made into φ 10mm, putting in the lead bath groove that is heated to 650 ℃ after 10 minutes 950 ℃ of heating by machining about the φ 4mm wire rod of carbide evaluation usefulness.And then with its by the thin footpathization of wire drawing to φ 4mm, in the oil groove of 60 ℃ of 950 ℃ * 5 minutes heating back inputs, quench again, then, regulated tempering temperature so that tensile strength above 2200MPa.In addition, by middle village formula rotating bending test, the duty cycle number of times can be surpassed 10
7Stress as fatigue strength.
Table 2
Table 3
Table 4
Table 5
Table 6
Table 7
Table 8
Table 9
Table 2～table 9 is expressed the steel of the present invention of the occasion of handling and the chemical ingredients of comparative steel under φ 4mm, carburizing system carbide rarefied zone area occupation ratio, the occupied area rate of alloy system/carburizing system globular carbide, circle quite directly is that the carburizing system globular carbide of 0.2～3 μ m exists density, there is density in the carburizing system globular carbide that circle quite directly surpasses 3 μ m, the maximum oxide particle diameter, original austenite grains degree number, remained austenite content (quality %), the tensile strength that its result obtains, hardness after the annealing, impact value and the relative reduction in area by stretching test measurement.That is, the chemical ingredients of table 2 and table 3 expression example No.1～25, the chemical ingredients of table 4 and table 5 expression example No.26～51, the chemical ingredients of table 6 expression comparative example No.52～77.And table 7 and table 8 are represented the characteristic that wire drawing (through drawing) and nothing hot candied (without drawing) are arranged of example No.1～25 and example No.26～51 respectively.In addition, table 9 expression comparative example No.52～77 has wire drawing and does not have hot candied characteristic.
Below, comparative example is described.
In example, even heat-treated wood without wire drawing, softening resistance after its impact value and the annealing, tensile properties etc. are all brought into play good performance, in addition, heat-treated wood after wire drawing, tensile properties and distribution of carbides etc. are included in the scope of regulation, therefore can obtain good performance.But following comparative example owing to depart from regulation, therefore fails to bring into play sufficient performance.
Comparative example 52,53 is situations that Ti and Nb do not contain and since heavy addition V, Cr, therefore generating with the nitride is the not dissolving carbide of nuclear, so the relative reduction in area in the tension test, the unit elongation after the wire drawing are low, processibility is reduced.
Comparative example 54,55, though added Ti and Nb, N is too much, generating with the nitride is the not dissolving carbide of nuclear, so the relative reduction in area in the tension test, the unit elongation after the wire drawing are low, processibility is reduced.
Comparative example 56～59 is to have added Ti, fixed N with the TiN form, but too much because of the Ti addition, obviously has the example by the drawback due to the TiN.Therefore, inclusion distributes and increases, its result, and relative reduction in area, the unit elongation after the wire drawing in the tension test are low, and processibility is reduced.
Particularly comparative example 57, are because the Heating temperature when reduce quenching has caused generating a lot of situation of not dissolving carbide of quantity.
Comparative example 60～62nd has added the example of Nb, because its addition is too much, can see that therefore not dissolve carbide a lot, and relative reduction in area, the unit elongation after the wire drawing in the tension test are low, and processibility is reduced.Comparative example 63,64 is because Al is too much, so oxide compound becomes big, the fatigue characteristic reduction.
Comparative example the 65, the 66th, the situation that the V addition is very few, the hardness after the annealing of blank nitriding is low at this moment, and the tendency that exists the original austenite particle diameter to become thick, and fatigue characteristic reduce.In addition, in the nitrogenize of reality, compare with the example of the V that adds specified amount, surface hardness is low, even the perhaps nitridation time of identical time, the nitrogenize degree of depth also shoals etc., and difference appears in the performance behind the nitriding treatment.
In the comparative example 67,68, the Cr addition is very few, and the hardness after the annealing of blank nitriding is low, and the perhaps cementation zone attenuation during nitriding treatment reduces fatigue characteristic.
Comparative example 69～71st, cooling temperature height and cooling time when quenching are the situation of short period of time, remained austenite content increases, the therefore hardness deficiency after the annealing, simultaneously in the practicality a little the use defective around, owing to bring out phase transformation and embrittlement, therefore reduce processibility.
Comparative example the 72, the 73rd, the too high example of Heating temperature when quenching, original austenite particle diameter become big, the impact value step-down, fatigue characteristic descend.
Comparative example 74～77th, C or Si have reduced the tensile strength after the annealing than the situation that specified amount lacks, and are the examples that can not guarantee fatigue strength therefore.
Utilizability on the industry
Steel of the present invention, by reducing carburizing system and the occupied area rate of the globular carbide of alloy system of cold coiling in the spring steel line, having density, austenite particle diameter, remained austenite content, can be more than the 2000MPa with the intensity high strength, guarantee simultaneously coiling property, can make the spring of high strength and fracture characteristics excellence.
In the present application the expression number range " more than " and " following " include given figure.
Claims (5)
1. high-strength spring steel, it is characterized in that: contain: surpass below 0.15%～1.0%, below the Al:0.005% in quality % C:0.5%～0.9%, Si:1.0%～3.0%, Mn:0.1%～1.5%, Cr:1.0%～2.5%, V, N is limited in below 0.007%, and contain Nb:0.001%～0.007%, contain Ti:0.001%～less than 0.005% selectively, its surplus is made up of Fe and unavoidable impurities.
2. high-strength spring steel according to claim 1 is characterized in that: further contain in a kind in quality % W:0.05%～0.5%, Mo:0.05%～0.5% or 2 kinds.
3. high-strength spring steel according to claim 1 and 2 is characterized in that: further contain in quality % Ni:0.05%～3.0%, Cu:0.05%～0.5%, Co:0.05%～3.0%, B:0.0005%～0.006% more than a kind or 2 kinds.
4. according to each the described high-strength spring steel in the claim 1～3, it is characterized in that: further contain in quality % Te:0.0002%～0.01%, Sb:0.0002%～0.01%, Mg:0.0001%～0.0005%, Zr:0.0001%～0.0005%, Ca:0.0002%～0.01%, Hf:0.0002%～0.01% more than a kind or 2 kinds.
5. heat-treatment steel for high-strength spring line, it is characterized in that: have each the described composition of steel in the claim 1～4, tensile strength is more than the 2000MPa, and about carburizing system globular carbide and the alloy system globular carbide that occupies on the microsection surface, satisfy circle quite the footpath be that the occupied area rate of the above carbide of 0.2 μ m is 7% below, circle quite the footpath be that the density that exists of the carbide more than the 0.2 μ m is 1/μ m
2Below, and the original austenite grains degree number is more than No. 10, residual austenite is below the 15 quality %.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/JP2006/322784 WO2008056428A1 (en) | 2006-11-09 | 2006-11-09 | Steel for high-strength spring and heat-treated steel wire for high-strength spring |
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| Publication Number | Publication Date |
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| CN101287850A CN101287850A (en) | 2008-10-15 |
| CN101287850B true CN101287850B (en) | 2011-04-27 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN2006800012411A Active CN101287850B (en) | 2006-11-09 | 2006-11-09 | Steel for high intensity spring and heat-treating steel line for high intensity spring |
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| Country | Link |
|---|---|
| EP (1) | EP2058411B1 (en) |
| KR (1) | KR100968938B1 (en) |
| CN (1) | CN101287850B (en) |
| BR (1) | BRPI0607042B1 (en) |
| WO (1) | WO2008056428A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US8734600B2 (en) * | 2009-07-09 | 2014-05-27 | Nippon Steel & Sumitomo Metal Corporation | High strength steel wire for spring |
| KR101253813B1 (en) * | 2009-09-08 | 2013-04-12 | 주식회사 포스코 | Steel without spheroidizing heat treatment and method for manufacturing the same |
| KR101603485B1 (en) * | 2011-08-18 | 2016-03-14 | 신닛테츠스미킨 카부시키카이샤 | Spring steel and spring |
| CN104060175B (en) * | 2014-05-27 | 2017-01-11 | 安徽红桥金属制造有限公司 | Spring and production method thereof |
| RU2578276C1 (en) * | 2014-12-22 | 2016-03-27 | Юлия Алексеевна Щепочкина | Steel |
| CN104630650A (en) * | 2015-02-06 | 2015-05-20 | 铜陵百荣新型材料铸件有限公司 | Low-temperature-resistant high-strength spring steel and preparation method thereof |
| CN105316591A (en) * | 2015-03-14 | 2016-02-10 | 洛阳辰祥机械科技有限公司 | Preparation method for high-performance spring |
| CN104745953B (en) * | 2015-03-31 | 2017-01-11 | 马鞍山市兴隆铸造有限公司 | Marine side plate low-carbon chromium alloy material and preparation method thereof |
| JP6453138B2 (en) * | 2015-03-31 | 2019-01-16 | 株式会社神戸製鋼所 | Heat-treated steel wire with excellent bending workability |
| CN105088090A (en) * | 2015-08-28 | 2015-11-25 | 宝山钢铁股份有限公司 | Armor plate with tensile strength being 2000 MPa and manufacturing method thereof |
| JP6461360B2 (en) | 2015-09-04 | 2019-01-30 | 新日鐵住金株式会社 | Spring steel wire and spring |
| KR101745192B1 (en) | 2015-12-04 | 2017-06-09 | 현대자동차주식회사 | Ultra high strength spring steel |
| KR101745196B1 (en) | 2015-12-07 | 2017-06-09 | 현대자동차주식회사 | Ultra high strength spring steel |
| KR101776491B1 (en) * | 2016-04-15 | 2017-09-20 | 현대자동차주식회사 | High strength spring steel having excellent corrosion resistance |
| KR101776490B1 (en) | 2016-04-15 | 2017-09-08 | 현대자동차주식회사 | High strength spring steel having excellent corrosion resistance |
| CN105886930B (en) * | 2016-04-26 | 2017-12-26 | 宝山钢铁股份有限公司 | A kind of high-strength corrosion-resistant spring steel and its manufacture method |
| CN114555849B (en) * | 2019-10-16 | 2022-11-01 | 日本制铁株式会社 | Steel wire |
| DE112021001166T5 (en) * | 2020-02-21 | 2022-12-08 | Nippon Steel Corporation | STEEL WIRE |
| US20230340631A1 (en) * | 2020-09-23 | 2023-10-26 | Arcelormittal | Steel for leaf springs of automobiles and a method of manufacturing of a leaf thereof |
| CN113265590A (en) * | 2021-06-08 | 2021-08-17 | 江苏通工金属科技有限公司 | High-strength antirust alloy spring steel wire and forming process thereof |
| CN113930680B (en) * | 2021-09-29 | 2023-03-17 | 武汉钢铁有限公司 | Low-temperature-resistant high-strength spring flat steel and production method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CA2057190C (en) * | 1991-02-22 | 1996-04-16 | Tsuyoshi Abe | High strength spring steel |
| JP3403913B2 (en) * | 1997-03-12 | 2003-05-06 | 新日本製鐵株式会社 | High strength spring steel |
| JP3577411B2 (en) * | 1997-05-12 | 2004-10-13 | 新日本製鐵株式会社 | High toughness spring steel |
| JP3595901B2 (en) * | 1998-10-01 | 2004-12-02 | 鈴木金属工業株式会社 | High strength steel wire for spring and manufacturing method thereof |
| JP4464524B2 (en) * | 2000-04-05 | 2010-05-19 | 新日本製鐵株式会社 | Spring steel excellent in hydrogen fatigue resistance and method for producing the same |
| WO2002050327A1 (en) * | 2000-12-20 | 2002-06-27 | Nippon Steel Corporation | High-strength spring steel and spring steel wire |
| WO2002050328A1 (en) * | 2000-12-20 | 2002-06-27 | Kabushiki Kaisha Kobe Seiko Sho | Steel wire rod for hard drawn spring, drawn wire rod for hard drawn spring and hard drawn spring, and method for producing hard drawn spring |
| JP3851095B2 (en) * | 2001-02-07 | 2006-11-29 | 新日本製鐵株式会社 | Heat-treated steel wire for high-strength springs |
| EP2465963B1 (en) * | 2004-11-30 | 2015-10-07 | Nippon Steel & Sumitomo Metal Corporation | High strength spring steel and steel wire |
| JP4476863B2 (en) * | 2005-04-11 | 2010-06-09 | 株式会社神戸製鋼所 | Steel wire for cold forming springs with excellent corrosion resistance |
| JP4478072B2 (en) * | 2005-06-09 | 2010-06-09 | 新日本製鐵株式会社 | High strength spring steel |
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- 2006-11-09 WO PCT/JP2006/322784 patent/WO2008056428A1/en active Application Filing
- 2006-11-09 CN CN2006800012411A patent/CN101287850B/en active Active
- 2006-11-09 EP EP06823432.7A patent/EP2058411B1/en active Active
- 2006-11-09 KR KR1020077011280A patent/KR100968938B1/en active IP Right Grant
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Also Published As
| Publication number | Publication date |
|---|---|
| WO2008056428A1 (en) | 2008-05-15 |
| EP2058411A1 (en) | 2009-05-13 |
| EP2058411A4 (en) | 2010-01-13 |
| CN101287850A (en) | 2008-10-15 |
| KR100968938B1 (en) | 2010-07-14 |
| BRPI0607042A2 (en) | 2009-08-04 |
| EP2058411B1 (en) | 2014-02-19 |
| BRPI0607042B1 (en) | 2014-08-19 |
| KR20080057205A (en) | 2008-06-24 |
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