CN101346481A - High-strength steel bolt having excellent resistance for delayed fracture and method for producing the same - Google Patents
High-strength steel bolt having excellent resistance for delayed fracture and method for producing the same Download PDFInfo
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- CN101346481A CN101346481A CNA200680049169XA CN200680049169A CN101346481A CN 101346481 A CN101346481 A CN 101346481A CN A200680049169X A CNA200680049169X A CN A200680049169XA CN 200680049169 A CN200680049169 A CN 200680049169A CN 101346481 A CN101346481 A CN 101346481A
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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
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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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
Abstract
A bolt for use in connection of steel structures and for use as automotive parts and components, and a method for producing the same are disclosed. More specifically, provided is a steel bolt which is capable of achieving high strength simultaneously with an excellent delayed fracture resistance, by appropriate control of the steel microstructure. The bolt has a composition comprising (i) 0.35-0.55 wt% of carbon, 0.05-2.0 wt% of silicon, 0.1-0.8 wt% of manganese, 0.001-0.004 wt% of boron, 0.3-1.5 wt% of chromium, 0.005 wt% and less of oxygen (T.O), 0.015 wt% and less of phosphorous, 0.010 wt% and less of sulfur, and the balance of Fe with inevitable impurities; and further comprising (ii) at least one selected from the group consisting of 0.05-0.5 wt% of vanadium, 0.05-0.5 wt% of niobium, 0.1-0.5 wt% of nickel, 0.1-1.5 wt% of molybdenum and 0.01-0.1 wt% of titanium, wherein the bolt has an internal structure composed of ferrite and tempered martensite, and a content of ferrite in the internal structure is 3 to 10% in terms of an area fraction. The present invention can provide a high-strength bolt which is capable of simultaneously achieving an excellent delayed fracture resistance and a high strength without addition of large amounts of alloying elements, and also exhibits no deterioration of notch toughness. Further, the present invention can provide a method for preparing such a bolt which is simply and conveniently carried out without complicated heat treatment processes.
Description
Technical field
The present invention relates to be used to connect steel construction and as the bolt of trolley part and member, with and manufacture method.More specifically, the present invention relates to following steel bolt: promptly by suitably controlling the microstructure of steel, it can reach high strength and have good resistance for delayed fracture simultaneously.
Background technology
Recently, the development trend of building and structure building turns to the steel construction with excellent safety from skeleton construction.An important factor should considering at the secure context that guarantees steel construction is assembly-assembly interconnection technique.As the example of assembly-assembly method of attachment, can mention that welding is connected with bolt.The bolt connection is compared with welding process and is not needed complicated technology, and advantageously can be by replacing the security that flimsy welding assembly improves steel construction.The high strength that realizes bolt helps reducing bolt quantity of using and the clamping force that increases bolt in assembly-assembly connection, this can therefore shorten the construction time and minimizing simultaneously connects area, thereby increases the security and the soundness of interconnecting piece.Therefore, in order to make up more effective steel construction, carried out multinomial effort recently to obtain to be used to connect the high strength bolt of steel construction.
Conventional bolt designs in the following manner to guarantee bolt strength: steel wire rod is processed into the shape of bolt, thereby then the wire rod of moulding is obtained required intensity through quenching process.Consider productivity, steel wire rod is processed into bolt shape is mainly undertaken by the cold forging method.Therefore, the steel wire rod that is used for bolt processing should have the physical properties that is suitable for cold forging, promptly good cold-heading character (CHQ).Therefore, the most important thing is the toughness of wire rod is reduced to proper level, so just can easily carry out the processing of wire rod in order to obtain required CHQ.
In order to make this steel wire rod, should make the intensity of wire rod low as much as possible with good CHQ.In addition, wire rod is handled through wire drawing and is carried out sizing, reduces intensity through nodularization thermal treatment to take a step forward at processing bolt then.Described nodularization thermal treatment is meant following thermal treatment: by further reduce the intensity of wire rod with the form precipitation carbon of spheroidized carbide, this is the intensity that can increase wire rod owing to carbon sosoloid in wire rod by solution strengthening.As indicated above, after the nodularization thermal treatment wire rod is processed into bolt shape, and with its quenching heat treatment.Yet, cause the toughness of bolt to decrease sharply in the inner martensitic stucture that forms of the bolt that so quenches.Therefore, in order to prevent toughness degradation, bolt process temper owing to the bolt that exists martensitic stucture to cause.The result is, like this Zhi Bei bolt within it portion will have so-called tempered martensite.
Known, add a kind of alloying element, especially carbon is very effective for the reinforcement of the steel with tempered martensite.Yet, adds carbon and cause intensity to begin promptly to increase, thereby the brittle transition temperature (DBTT) that causes cold working difficulty, product sharply increases and the resistance of hydrogen inductive delayed fracture property is significantly reduced from the initial stage (being wire rod) of steel.In addition, shaping is disadvantageous to bolt in the increase of work hardening in processing, thereby produces other softening heat treated demand.
In addition, because the inherent nature of tempered martensite be distributed with Fe base precipitation in its crystal boundary, and the matrix of lath martensite is also responsive to sedimentary distribution.When this tempered martensite is applied to heavily stressed (high strength) steel members such as bolt, tempered martensite depend on its environment for use be exposed to heavily stressed in.Thisly heavily stressedly help hydrogen migration and a large amount of hydrogen is also accumulated in the throw out, therefore produce the situation that is easy to occur delayed fracture.The result is that the application that makes tempered martensite be used to make high strength component is restricted.
As indicated above, bolt strength and resistance for delayed fracture are mutual exclusive physical propertiess, so exploitation has the intensity of needs simultaneously and the bolt of resistance for delayed fracture is very important.The exploitation expection that has the bolt of high strength and good resistance for delayed fracture simultaneously can provide following multiple advantage.Aspect steel construction, bolt connects with being welded to connect to compare and does not need complicated technology.And with regard to replacing flimsy welding assembly, bolt connects provides following advantage: can strengthen clamping force by bolt to assembly is fixing, and because the interconnecting piece area reduces the security that increases steel construction; Used bolt quantity reduces used steel amount in the assembly connection owing to reducing, and shortens the construction time; In the weight that promotes to alleviate parts aspect the parts of automobile and the member; And, can realize the variation design and the compactness of automobile assembling equipment owing to alleviate the feasibility of component weight.
The routine techniques that improves resistance for delayed fracture can comprise: 1) suppress the corrosion of steel, 2) infiltration of hydrogen in steel minimized, 3) reduction can cause the concentration of the diffusible hydrogen of delayed fracture, 4) use has the steel of high critical diffusible hydrogen content, 5) tensile stress is minimized, 6) reduce stress concentration, 7) dwindle austenite grain boundary size or the like.For reaching this purpose, carried out highly alloyedly, perhaps mainly used surperficial coating or the electro-plating method prevent that external hydrogen from infiltrating.In addition, also have method to form the precipitation that to capture diffusible hydrogen or control steel microstructure, and the phosphorus (P) that causes described austenite grain boundary embrittlement and the content of sulphur (S) are minimized by in steel, adding element-specific.
As one for improving the technology that resistance for delayed fracture is developed, the open text of the Japanese Patent of publication No. 2003-321743 discloses a kind of method that is used to produce the high-strength bolt with excellent resistance for delayed fracture.According to this patent, described high-strength bolt has the tempered martensite single phase structure of following composition: the carbon (C) that is no more than 0.35wt%, be no more than the silicon (Si) of 0.50wt%, the molybdenum (Mo) of the manganese of 0.1-2.0wt% (Mn) and 0.05-0.6wt%, also have one or more to be selected from the niobium (Nb) that is no more than 0.08wt% in addition, be no more than the vanadium (V) of 0.15wt% and be no more than the metal of the tungsten (W) of 1.5wt%, one or more are selected from copper (Cu), nickel (Ni), the metal of chromium (Cr) and boron (B), the Fe of surplus and unavoidable impurities wherein satisfy 0.5≤(C/12)/{ (Ti/48)+(Mo/96)+(Nb/93)+(V/51)+(W/192) }≤5.Yet the shortcoming of this Japanese Patent is: in order to obtain alloying element and the tempering temperature height that resistance for delayed fracture has added mass expensive, thereby its application in actual production is had difficulties.
In addition, the open text of the Japanese Patent of the flat 7-173531 of publication No. discloses a kind of method that is used to produce bainite+martensite dual-phase steel, this method is the steel thermoforming by the aluminium (Al) of the niobium (Nb) of the chromium (Cr) of the manganese (Mn) of the silicon (Si) that makes the carbon (C) that consists of 0.05-0.3wt%, 0.05-2.0wt%, 0.3-5.0wt%, 1.0-3.0wt%, 0.01-0.5wt% and 0.01-0.06wt%, and cool off described steel continuously with critical cooling rate or higher speed, so that proeutectoid ferrite can not precipitate.Yet because a large amount of heat treatment steps, the application of this method in actual production also has difficulties.
In addition, the open text of the Korean Patent of publication No. 2000-0033852 discloses a kind of method that is used to prepare high-strength bolt, and described bolt is basic organization with ferrite and tempered martensite dual phase steel and comprises: (i) manganese of the silicon of the carbon of 0.4-0.6wt%, 2.0-4.0wt%, 0.2-0.8wt%; The nitrogen of the chromium of 0.25-0.8wt%, the phosphorus that is no more than 0.01wt%, the sulphur that is no more than 0.01wt%, 0.005-0.01wt% and be no more than the oxygen of 0.005wt%; The randomly (ii) at least a vanadium of following element: 0.05-0.2wt%, the niobium of 0.05-0.2wt%, the nickel of 0.3-2.0wt%, the boron of 0.001-0.003wt%, molybdenum, titanium, copper and the cobalt of 0.01-0.5wt% of being selected from.Yet because low quenching temperature causes existing residual spheroidized carbide in bolt, this Korean Patent has the problem about the notch toughness deterioration.
Summary of the invention
Technical problem
Therefore, The present invention be directed to the problems referred to above and make, and an object of the present invention is to provide and a kind ofly need not to add a large amount of alloying elements and can not only have good delayed fracture resistance but also have high strength but also do not have the high-strength bolt of notch toughness degradation phenomena.
Another object of the present invention provides a kind of like this method for preparing above-mentioned bolt, and this method can simply and easily be carried out, and does not need the complicated heat treatment step.
Technical scheme
According to an aspect of the present invention, above-mentioned and other purposes can realize by a kind of high-strength bolt that contains following component is provided: contain boron, the 0.3-1.5wt% of manganese, the 0.001-0.004wt% of silicon, the 0.1-0.8wt% of carbon, the 0.05-2.0wt% of (i) 0.35-0.55wt% chromium, be no more than 0.005wt% oxygen (T.O), be no more than 0.015wt% phosphorus, be no more than the sulphur of 0.010wt%, the Fe of surplus and unavoidable impurities; And contain the (ii) at least a vanadium of following element: 0.05-0.5wt%, the niobium of 0.05-0.5wt%, the nickel of 0.1-0.5wt%, the molybdenum of 0.1-1.5wt% and the titanium of 0.01-0.1wt% of being selected from, wherein said bolt has the interior tissue of being made up of ferrite and tempered martensite, and ferritic content is counted 3-10% by area fraction in the described interior tissue.
At this moment, the amount of carbide preferably is no more than 10% by area fraction in described interior tissue.In addition, described carbide preferably has the equivalent circle diameter (Heywood diameter) that is up to 5.
According to a further aspect in the invention, a kind of method that is used to prepare the high-strength bolt with excellent resistance for delayed fracture is provided, it comprises: with a kind of bolt shape wire rod---its composition comprise boron, the 0.3-1.5wt% of manganese, the 0.001-0.004wt% of silicon, the 0.1-0.8wt% of carbon, the 0.05-2.0wt% of (i) 0.35-0.55wt% chromium, be no more than 0.005wt% oxygen (T.O), be no more than 0.015wt% phosphorus, be no more than the sulphur of 0.010wt%, the Fe of surplus and unavoidable impurities; And comprise the element of the titanium of the molybdenum of nickel, 0.1-1.5wt% of niobium, the 0.1-0.5wt% of vanadium, the 0.05-0.5wt% of the (ii) at least a 0.05-0.5wt% of being selected from and 0.01-0.1wt%---be heated to temperature, then cooling (quenching) fast above Ae3+80 ℃; Heat described refrigerative wire rod to Ae3-10 ℃ to Ae3+10 ℃ temperature, then cooling fast (quenching again); With the tempering under 450 ℃ or higher temperature of the described wire rod that quenches again.
Beneficial effect
As indicated above, the present invention can provide a kind of and need not to add that a large amount of alloying elements can have good resistance for delayed fracture and high strength simultaneously but also the high-strength bolt that do not have the notch toughness degradation phenomena.
And the present invention can provide a kind of like this method for preparing this bolt, and this method can simply and easily be carried out, and does not need the complicated heat treatment step.
Implement best mode of the present invention
Hereinafter the present invention will be described in more detail.
For solving the problem that routine techniques faced, the present inventor, draws as drawing a conclusion in conjunction with to bolt with superior strength and resistance for delayed fracture and the conscientiously experiment for preparing its method through various extensive and deep research and experiment.
Promptly, compare with conventional martensite single phase structure, when in described steel, forming the duplex structure of ferrite and tempered martensite coexistence, the mark of ferrite in interior tissue is limited in specified level, cause ferrite to disperse equably and distribute, this then stoped the infiltration of hydrogen atom in original austenite grain boundary, thereby strengthen resistance for delayed fracture.And ferrite is compared relative softer with tempered martensite, thereby and therefore when crack propagation takes place, form passivation effect and disturb crack propagation in crack tip, come to guarantee effectively resistance for delayed fracture thus.In addition, by hydrogen capture the delayed fracture that causes can by make thick carbide for example the amount of iron carbide (Fe), chromium carbide (Cr) etc. minimize and prevent.And, when by remaining carbide being disperseed and when being distributed to meticulousr size a large amount of meticulous hydrogen capture site being provided, can improving resistance for delayed fracture effectively.And in order to obtain to help improving the structure and the distribution of carbides of resistance for delayed fracture, control steel composition to following OK range is important.
Hereinafter, will steel composition, structure and the precipitate distribution of preferred bolt provided by the present invention be described in further detail.
Steel is formed
Carbon (C): 0.35-0.55wt%
Carbon (C) is a kind of element for guaranteeing that product strength adds.Yet if carbon content surpasses 0.55wt%, so a large amount of membranaceous carbide are deposited in austenite grain boundary unfriendly, thereby reduce the resistance to hydrogen inductive delayed fracture property.On the other hand, if carbon content is lower than 0.35wt%, bolt will be difficult to obtain enough tensile strength by quenching and tempering heat treatment so.Therefore, carbon content is preferably in the scope of 0.35-0.55wt%.
Silicon (Si): 0.05-2.0wt%
Silicon (Si) is a kind of element that can be used for steel-deoxidizing and can guarantee required hardness of steel effectively.Yet, if silicone content surpasses 2.0wt%, when carrying out that steel wire rod is processed into the cold forging of bolt shape work hardening takes place apace so, thereby causes processing characteristics relatively poor.On the other hand, if silicone content is lower than 0.05wt%, then be difficult to guarantee required bolt strength.Therefore, silicone content preferably is limited in the scope of 0.05-2.0wt%.
Manganese (Mn): 0.1-0.8wt%
Manganese (Mn) is a kind of by forming in matrix structure that substitutional solid solution provides the solution strengthening effect and being of great use element for the feature of Hi-tensile bolt.Manganese content is preferably in the scope of 0.1-0.8wt%.Or rather, if add manganese amount surpass 0.8wt%, so since the structure inhomogeneity that the manganese segregation causes to the adverse effect of bolt properties greater than the solution strengthening effect.Steel is responsive to macrosegregation and microsegregation in process of setting, and this depends on segregation mechanisms.Because the spread coefficient of manganese is lower relatively than other metal, the manganese segregation promotes the formation of segregation zone, and consequently: the raising of hardening capacity becomes the main cause that produces low temperature tissue (core martensite).On the other hand, be no more than 0.1wt%, be difficult to obtain the improvement of required stress relaxation so by solution strengthening, though the manganese segregation does not have influence substantially to the segregation zone if add the amount of manganese.In other words, if manganese content is no more than 0.1%, owing to weak solution strengthening effect, the raising of hardening capacity and permanent deformation resistance is insufficient so.On the other hand, surpass 0.8% if add the amount of manganese, so because the formation of the segregation zone that hardening capacity that the part increases in the steel casting and manganese segregation cause causes the anisotropy of serious structure, promptly because the inhomogeneity of structure causes the deterioration of bolt characteristic.
Boron (B): 0.001-0.004wt%
Boron (B) mainly is to be added into as a kind of grain-boundary strengthening element in the present invention, to improve hardening capacity and resistance for delayed fracture.The lower limit of boron content is 0.0010wt% preferably.If boron content is lower than 0.0010wt%, grain boundary segregation, the raising deficiency of grain-boundary strength and hardening capacity take place during so owing to thermal treatment.On the other hand, if boron content surpasses 0.004wt%, the saturated and boron nitride of the boron effect of adding is at grain boundary precipitate so, thereby reduces grain-boundary strength.
Chromium (Cr): 0.3-1.5wt%
Chromium (Cr) is a kind of element that improves hardening capacity in quenching and tempering heat treatment effectively.If chromium content is lower than 0.3wt%, in quenching and tempering heat treatment, be difficult to guarantee enough hardening capacity so.Therefore, need be arranged on the scope that is not less than 0.3wt% to chromium content.In addition, according to the inventor's result of study, have been found that the increase of the hardening capacity that chromium itself is produced is small, increase shows significant lifting effect to hardening capacity and add chromium and boron simultaneously, and this shows that it is necessary adding chromium.On the other hand, if chromium content surpasses 1.5wt%, can disadvantageously form membranaceous carbide in steel inside so.This is because the known membranaceous carbide that exists at austenite grain boundary can reduce the resistance to hydrogen inductive delayed fracture property.
Oxygen (T.O): be no more than 0.005wt%
Analyse oxygen (O) by total oxygen (T.O) score, and oxygen level is limited in being no more than in the scope of 0.005wt%.This is that the oxide-base non-metallic inclusion can cause the deterioration of fatigue lifetime so because if oxygen level surpasses 0.005wt%.
Phosphorus (P): be no more than 0.015wt%
Phosphorus (P) content is limited in being no more than in the scope of 0.015wt%.Phosphorus is because its segregation in crystal boundary is to cause toughness deterioration and resistance for delayed fracture main reasons for decrease.Therefore, the upper limit of phosphorus content is limited in being no more than the scope of 0.015wt%.
Sulphur (S): be no more than 0.010wt%
Sulphur (S) is a kind of lower boiling element, and participates in grain boundary segregation, thereby causes the flexible deterioration, and by forming sulfide resistance for delayed fracture and stress relaxation property list is revealed bad side effect.Therefore, the upper limit of sulphur content preferably is limited in 0.010wt%.
Except adding above-mentioned moiety, preferably also add the element that one or more are selected from vanadium (V), niobium (Nb), molybdenum (Mo) and nickel (Ni) with the amount of following qualification.
Vanadium (V): 0.05-0.5wt%
Vanadium (V) is a kind of by forming the element that precipitation improves resistance for delayed fracture and softening resistance, and content of vanadium is limited in the scope of 0.05-0.5wt%.If content of vanadium is no more than 0.05wt%, then the minimizing that vanadium base precipitation distributes in the matrix can cause vanadium can not give full play to effect as the capture site of non-diffusible hydrogen, therefore is difficult to obtain the improvement of resistance for delayed fracture.In addition, also be difficult to obtain required precipitation strength effect, so the raising of softening resistance is inadequate.On the other hand, if content of vanadium surpasses 0.5wt%, throw out is in state of saturation to the raising of resistance for delayed fracture and softening resistance so.In addition, the thick alloy carbide of increasing amount is not dissolved in the matrix in austenitic thermal treatment, but becomes non-metallic inclusion, thereby causes the deterioration of fatigue property.
Niobium (Nb): 0.05-0.5wt%
Similar with vanadium, niobium (Nb) also is a kind of by forming the element that throw out improves resistance for delayed fracture and softening resistance, and content of niobium is limited in the scope of 0.05-0.5wt%.If content of niobium is no more than 0.05wt%, then the minimizing that niobium base precipitation distributes in the matrix can cause niobium can not give full play to effect as the capture site of non-diffusible hydrogen, therefore is difficult to obtain the improvement of resistance for delayed fracture.In addition, also be difficult to obtain required precipitation strength effect, therefore the lifting effect to softening resistance is insufficient.On the other hand, if content of niobium surpasses 0.5wt%, throw out is in state of saturation to the lifting of resistance for delayed fracture and softening resistance so.In addition, the thick alloy carbide of increasing amount is not dissolved in the matrix in austenitic thermal treatment, but becomes non-metallic inclusion, thereby causes the deterioration of fatigue property.
Nickel (Ni): 0.1-0.5wt%
Nickel (Ni) thus be a kind of element that infiltration that nickel enriched layer suppresses external hydrogen improves resistance for delayed fracture that when steel is heat-treated, forms on its surface.If nickel content is no more than 0.1wt%, owing to be not completed into the surface enrichment layer of nickel, be difficult to obtain the lifting of required resistance for delayed fracture so, and the cold shaping performance does not improve in the cold working of bolt.On the other hand, if nickel content surpasses 0.5wt%, the risk that the increase of remaining austenite amount may cause impelling strength to reduce.
Molybdenum (Mo): 0.1-1.5wt%
Molybdenum (Mo) content is limited in the scope of 0.1-1.5wt%.This is because be no more than the carbide that the molybdenum of 0.1wt% can cause being difficult to be formed for improving softening resistance or resistance for delayed fracture, and the realization of this effect is to generate cementite by suppress cementite growth and inhibition on the turn in drawing process from εTan Huawu.On the other hand, the amount of the molybdenum of adding surpasses 1.5wt% can improve softening resistance efficiently, but is easy to generate low temperature tissue (for example martensite and bainite) when making wire rod.
Titanium (Ti): 0.01-0.1wt%
When boron formed boron nitride, the improvement of hardening capacity reduced significantly.Titanium (Ti) is a kind of useful element in the present invention.Or rather, thus titanium replaces boron to combine the formation of inhibition boron nitride with nitrogen.The content of titanium is limited in the scope of 0.01-0.1wt%.If titanium content is no more than 0.01wt%, titanium is insufficient to the effect of improving of erosion resistance so, is difficult to form the titanium nitride of inhibition boron nitride formation to improve the hardening capacity of boron.On the other hand, if titanium content surpasses 0.1wt%, the increase effect of titanium is saturated so, and the thick titanium base nitride that forms has disadvantageous effect to fatigue property.
The microtexture of steel
The microtexture of bolt will be discussed in the present invention, and it is to comprise ferrite and martensitic polyphase structure.Preferably, ferrite is homodisperse and distribution.As indicated above, this is because ferrite can stop hydrogen atom to penetrate in the original austenite grain boundary, thereby strengthens resistance for delayed fracture; And ferrite is compared relative softer with tempered martensite, therefore can disturb crack propagation by the passivation effect by crack tip when crack propagation takes place, thereby guarantee resistance for delayed fracture effectively.In order to obtain homodisperse ferrite, ferritic area fraction preferably is limited in the scope of 3-10%.If ferritic area fraction is no more than 3%, then be difficult to obtain the raising of resistance for delayed fracture by the adding ferrite.On the other hand,, can't obtain ferritic homodisperse so, and, be difficult to the intensity that reaches required because bolt tensile strength excessively reduces if ferritic area fraction surpasses 10%.
Sedimentary distribution
As indicated above, the wire rod that is used to make bolt is processed into bolt shape then through nodularization thermal treatment.Make carbon deposition increasing the intensity of wire rod because the heat treated process of nodularization is the form by carbide, thus after the nodularization heat treatment process a large amount of thick distribution of carbides in wire rod.Particularly, the composition of bolt of design according to the present invention can form the carbide of iron and chromium, and they can provide the hydrogen capture site, thereby reduces resistance for delayed fracture.Therefore, before entering the bolt processing stage, need to reduce as far as possible the content of carbide.The condition that realizes this target is as follows.
Need be controlled at the area ratio of carbide in 10% the scope of being no more than.Surpass 10% if carbide is pressed area ratio, then carbide can cause the reduction of resistance for delayed fracture and the reduction of notch toughness.Therefore, the area ratio of carbide is preferably in being no more than 10% scope.
In addition, need also to guarantee that the diameter of the residual carbide of removal is not no more than 5.Or rather, under same carbide area ratio, the quantity of the meticulous more then hydrogen of the size of carbide capture site is many more, and these sites are meticulous more, thereby can reduce the dividing potential drop of accumulation hydrogen.Therefore, need to keep the carbide size below 5.
Hereinafter, will a kind of method with high-strength bolt of excellent resistance for delayed fracture provided by the invention that is used to prepare be described in more detail.
The preparation of high-strength bolt
In order to prepare high-strength bolt, need quench, quench again and tempering (so-called Q-Q '-T) handle, and be processed into the shape of bolt having steel wire rod that above-mentioned preferred steel forms.
Quenching that (Q) handle is in order to make carbide such as iron carbide and chromium carbide form the solid solution attitudes, thereby the area ratio of control carbide is to being no more than 10%, and forms meticulous carbide.In this step, the solid solution temperature of carbide will be not less than Ae3+80 ℃.If the Heating temperature of steel wire rod is no more than Ae3+80 ℃, then can causes carbide not to be dissolved in fully in the matrix structure of bolt, thereby occur being detained relevant problem with thick carbide.Bolt is heated to after above specified temperature dissolves inner carbide again, with its fast cooling to prevent the redeposition of carbide.
Afterwards, in order to obtain uniform ferritic phase, wire rod is carried out the Ya Wenre processing at austenite and ferrite+austenitic two-phase zone, then cooling (Q ') fast.Heating temperature is preferably in Ae3+10 ℃ to Ae3-10 ℃ scope.If Heating temperature surpasses Ae3+10 ℃, so ferritic ratio can reduce, the raising of passing through ferritic homodisperse/distribution acquisition resistance for delayed fracture that therefore is difficult to think as the present invention.On the other hand, if Heating temperature is no more than Ae3-10 ℃, then ferritic ratio is excessively increased, thereby is difficult to form ferritic uniform distribution and produces the risk that bolt tensile strength reduces.
Subsequently, carry out tempering heat treatment (T) to guarantee the toughness of bolt.Thermal treatment with bolt of steel constituent of the present invention should because be lower than the temperature tempering meeting generation temper embrittlement of above-mentioned scope, and the problem relevant with membranaceous carbide precipitation occur implementing above under 450 ℃ the temperature in austenite grain boundary.On the other hand, if carrying out temper above under 500 ℃ the temperature, the tensile strength of bolt can be not enough.Therefore, suitable tempering temperature is in 450 ℃-500 ℃ scope.
Embodiment
Now the present invention is described in more detail by the reference the following examples.These embodiment only for explaining that the present invention provides, should not be interpreted as the restriction to the scope and spirit of the present invention.
Embodiment
The band steel that will have listed composition of steel in the table 1 hereinafter carries out homogenizing thermal treatment 48 hours under 1200 ℃, carry out hot rolling then.It is 80% that the hot rolling draft is set, and finishing temperature is set is 950 ℃.Then carry out the steel wire rod of air cooling after the hot rolling with preparation diameter 13mm.
In table 1, invention material 1 and 2 representatives are satisfied the band steel that steel that the present invention limits forms and are formed, and contrast material 1 represent the band steel composition outside the composition that the present invention limits.
Table 1
| C | Si | Mn | Cr | Mo | V | Al | Ti | B | Cu | Ae 3(℃) | |
| Invention material 1 | 0.404 | 0.204 | 0.701 | 1.2 | 0.297 | 0.09 8 | 0.032 | 0.02 | 0.0022 | - | 810 |
| Invention material 2 | 0.346 | 0.204 | 0.704 | 1.21 | 0.297 | 0.1 | 0.03 | 0.02 | 0.0021 | 0.098 | 810 |
| Contrast material 1 | 0.350 | 0.200 | 0.8 | 1.2 | 0.200 | - | 0.03 | - | - | - | 820 |
In order to estimate mechanical property (tensile strength and elongation) and delayed fracture property, so collecting sample in the Rolled Steel material along rolling direction.
As hereinafter describing in the table 2, above-mentioned different steel are heat-treated by two kinds of methods respectively.First method is in order to estimate the physical property of steel when the interior tissue of steel bolt is the tempered martensite single phase structure, carry out successively as follows: heat-treated steel is 40 minutes under 900 ℃ quenching temperature, cool off fast afterwards, then with the described steel of the tempering temperature thermal treatment that provides in the table 2 90 minutes (so-called Q-T handles).Second method is in order to obtain the uniform distribution of ferritic phase after quenching heat treatment, carry out successively as follows: with the heat-treated steel of quenching temperature again that provides in the table 2 40 minutes, cool off fast afterwards, then with the tempering temperature heat-treated steel that provides in the table 2 90 minutes (so-called Q-Q '-T handles).Difference between first heat treating method and second heat treating method is that the interior tissue of steel is tempered martensite single phase structure or ferrite (area fraction is no more than 10%)+tempered martensite polyphase structure.Suppose promptly to use same Q-Q '-T method preparation, comparative example 3 carries out being no more than under Ae3+80 ℃ the quenching temperature, the quenching conditions of this discontented unabridged version invention, and also do not meet and be suitable for steel constituent of the present invention.
Assessment result by the made bolt physical property of aforesaid method provides in the table 2 hereinafter.
Hereinafter the assessment of the resistance for delayed fracture in the table 2 is by using conventional constant loading method (the constant load method) realization of using of institute in this area.The resistance for delayed fracture that this appraisal procedure is measured is the following time: promptly take place fracture institute's time spent according to used stress or under specified stress.As for employed proof stress in the delayed fracture test, then determine based on notched tensile strength.
Use constant loaded type delayed fracture tester to carry out the test of delayed fracture.Preparation is used for the sample of delayed fracture test: sample diameter 6mm, notch diameter 4mm, the sample of breach root radius 0.1mm.Normal pressure solution (atmosphere solution) NaCl+CH of preparation sample
3CHOOH (pH 2) solution, and under room temperature (25 ℃ ± 5 ℃), be used for test.
Critical delayed fracture strength is meant following tensile strength: promptly under identical stress ratio (loading stress/notched tensile strength), breach through not taking place until rupturing in the band steel sample more than 150 hours.By the breach sample is carried out tension test, calculate the value of notch strength (sectional area of maximum load/barbed portion).Be used for determining that the minimum number of test specimens of critical delayed fracture strength is 15.
Table 2
From table 2, can confirm, compare with 2 with comparative example 1 respectively with 2, show identical or bigger tensile strength and elongation according to embodiments of the invention 1.
And, can compare than the about 100MPa of exceeding of embodiment 2-4 according to the delayed fracture strength of embodiments of the invention 1-1 by the results verification of table 2, even the tensile strength between them is identical.
In other words, even use identical member, the steel that the inventive method generates has more excellent resistance for delayed fracture, guarantees to have tensile strength and the elongation suitable with traditional Q-T method simultaneously.
By the tensile strength of embodiment 1 and 2 and the tensile strength that is widely used as the contrast material (comparative example 3 and embodiment 4) of resistance for delayed fracture steel are usually compared, embodiment 1 and 2 result demonstrate better tensile strength than the result of conventional contrast material as can be seen.
And, consider that embodiment 1 and 2 demonstrates the good elongation values that never is inferior to comparative example 3 and embodiment 4 so if the elongation that material can stably show above 13% is enough.
Equally, as shown in table 2 can the conclusive evidence: embodiments of the invention 1 and 2 show tensile strength and the elongation that is equal to or higher than conventional contrast material (comparative example 3 and embodiment 4); And its delayed fracture resistance strength ratio comparative example 3 the about 400Mpa of height, comparison is than the about 100Mpa of the height of embodiment 3.This steel of representing embodiment 1 and 2 shows more excellent resistance for delayed fracture value than conventional delayed fracture resistance steel.
In order to prove conclusively the result of the tension test that depends on multiple quenching temperature, use the steel that has with the steely composition of embodiments of the invention 1 class to make bolt, carry out tension test then.The result who so obtains provides in following table 3.
Table 3
Can prove conclusively from table 3, the temperature that is heated to 870 ℃ when steel is quenched is compared with the quenching temperature that is heated to 900 ℃, and the elongation that obtains is obviously lower.In order to support this result, observed the effect of undissolved iron (Fe) and chromium (Cr) carbide in quenching heat treatment, with reference to Fig. 1 and 2.
Should remove fully in follow-up quenching process by iron and chromium carbide that nodularization thermal treatment produces.Yet, when having the carbide of iron and chromium, itself in addition after quenching, do not dissolve yet, as shown in Figure 1, these carbide are considered to fissured point of beginning.For fear of this phenomenon, in quenching process, must assurance raise quenching temperature fully to dissolve carbide fully, as shown in Figure 2.After carbide dissolved fully, the elongation of bolt recovered.
Though the preferred embodiment of the invention is disclosed for the purpose of illustration, it will be apparent to those skilled in the art that under the situation that does not depart from the disclosed the scope and spirit of the present invention of appended claims, multiple improvement, replenish and replace and allow.
Claims (4)
1. high-strength bolt with good resistance for delayed fracture, contain:
(i) Fe and the unavoidable impurities of the chromium of the boron of the manganese of the silicon of the carbon of 0.35-0.55wt%, 0.05-2.0wt%, 0.1-0.8wt%, 0.001-0.004wt%, 0.3-1.5wt%, the oxygen (T.O) that is no more than 0.005wt%, the phosphorus that is no more than 0.015wt%, the sulphur that is no more than 0.010wt% and surplus; And
Also contain:
The (ii) at least a vanadium of following element: 0.05-0.5wt%, the niobium of 0.05-0.5wt%, the nickel of 0.1-0.5wt%, the molybdenum of 0.1-1.5wt% and the titanium of 0.01-0.1wt% of being selected from,
Wherein said bolt has the interior tissue of being made up of the tempered martensite of the ferrite of 3-10% and 90-97% by area fraction.
2. according to the bolt of claim 1, wherein the amount of carbide in described interior tissue is no more than 10% by area fraction.
3. according to the bolt of claim 1 or 2, wherein said carbide has the equivalent circle diameter that is up to 5.
4. method for preparing the bolt with good resistance for delayed fracture comprises:
Wire rod with a kind of bolt shape---its composition comprises the Fe and the unavoidable impurities of the carbon of (i) 0.35-0.55wt%, the silicon of 0.05-2.0wt%, the manganese of 0.1-0.8wt%, the boron of 0.001-0.004wt%, the chromium of 0.3-1.5wt%, the oxygen (T.O) that is no more than 0.005wt%, the phosphorus that is no more than 0.015wt%, the sulphur that is no more than 0.010wt% and surplus; And contain the (ii) at least a vanadium of following element: 0.05-0.5wt%, the niobium of 0.05-0.5wt%, the nickel of 0.1-0.5wt%, the molybdenum of 0.1-1.5wt% and the titanium of 0.01-0.1wt% of being selected from---be heated to temperature, then cooling (quenching) fast above Ae3+80 ℃;
Heat described refrigerative wire rod to Ae3-10 ℃ to Ae3+10 ℃ temperature, then cooling fast (quenching again); And
Heat the described wire rod that quenches again to the temperature that is not less than 450 ℃.
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| Application Number | Priority Date | Filing Date | Title |
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| KR1020050130106A KR100723186B1 (en) | 2005-12-26 | 2005-12-26 | High-strength steel bolt having excellent resistance for delayed fracture and method for producing the same |
| KR10-2005-0130106 | 2005-12-26 | ||
| KR1020050130106 | 2005-12-26 | ||
| PCT/KR2006/005457 WO2007074984A1 (en) | 2005-12-26 | 2006-12-14 | High-strength steel bolt having excellent resistance for delayed fracture and method for producing the same |
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| CN101346481A true CN101346481A (en) | 2009-01-14 |
| CN101346481B CN101346481B (en) | 2011-10-12 |
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| Country | Link |
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| JP (1) | JP5281413B2 (en) |
| KR (1) | KR100723186B1 (en) |
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Also Published As
| Publication number | Publication date |
|---|---|
| WO2007074984A1 (en) | 2007-07-05 |
| JP5281413B2 (en) | 2013-09-04 |
| JP2009521600A (en) | 2009-06-04 |
| WO2007074984A9 (en) | 2010-07-08 |
| CN101346481B (en) | 2011-10-12 |
| KR100723186B1 (en) | 2007-05-29 |
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