CN101688271B - Maraging steel and maraging steel for metallic belt - Google Patents

Maraging steel and maraging steel for metallic belt Download PDF

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CN101688271B
CN101688271B CN2007800537486A CN200780053748A CN101688271B CN 101688271 B CN101688271 B CN 101688271B CN 2007800537486 A CN2007800537486 A CN 2007800537486A CN 200780053748 A CN200780053748 A CN 200780053748A CN 101688271 B CN101688271 B CN 101688271B
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maraging steel
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CN101688271A (en
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大石胜彦
上原利弘
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Proterial Ltd
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Hitachi Metals Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
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Abstract

A maraging steel for metallic belts which has a composition capable of being reduced in the content of TiN, which serves as a starting point for fatigue failure in a high-cycle-rate region. The composition facilitates nitriding to heighten the surface hardness. The steel has a nitrided surface layer having increased compressive residual stress and hence improved flexural fatigue strength. In the steel, former austenite crystal grains have been reduced in size in order to secure higher strength and higher ductility. The maraging steel contains, in terms of mass%, up to 0.01% C, up to 0.1% Si, up to 0.1% Mn, up to 0.01% P, up to 0.005% S, 17.0-22.0% Ni, 0.1-4.0% Cr, 3.0-7.0% Mo, 7.0-20.0%, excluding 7.0%, Co, up to 0.1% Ti, up to 2.5% Al, up to 0.03% N, up to 0.005% O, and up to 0.01% B (excluding 0), provided that Co/3+Mo+4Al is 8.0-15.0%, with the remainder being Fe and incidental impurities.

Description

Maraging steel and metal strip maraging steel
Technical field
The present invention relates to have the maraging steel of excellent skin fatigue strength, and automobile is with the employed metal strip maraging steel of electrodeless variable-speed motor.
Background technology
Maraging steel generally has the very high tensile strength about 2000MPa, therefore be used to require to have high-intensity parts, such as rocket engine with the electrodeless variable-speed motor of parts, centrifugal separating machine part, aircraft components, motor car engine with various uses such as parts, metal dies.In its representational composition, can enumerate 1 8%Ni-8%Co-5%Mo-0.4%Ti-0.1%Al-bal.Fe.
And maraging steel is to contain in right amount Co, Mo, Ti as strengthening element, can by carrying out ageing treatment, make Ni 3Mo, Ni 3Ti, Fe 2The intermetallic compounds such as Mo are separated out and are obtained high-intensity steel.In addition, particularly use in the employed steel band of parts at the electrodeless variable-speed motor of motor car engine, therefore fatigue strength under the high race way is the characteristic that requires of particularly important, need to make the as much as possible miniaturization of non-metallic inclusion of the TiN that is present in the inside with high-intensity maraging steel etc.In addition, also can effects on surface implement nitriding treatment and form nitride layer, fatigue strength is improved and use.
, propose to have and a kind ofly reduce as the purpose modified alloy with the fatigue strength that solves take non-metallic inclusion as starting point with in the metal strip at the electrodeless variable-speed motor of motor car engine.(for example, with reference to patent documentation 1,2,3).
Patent documentation 1: No. 14056 communiques of special table 2004-5
Patent documentation 2: JP 2001-240943 communique
Patent documentation 3: JP 2002-167652 communique
Above-mentioned spy shows the disclosed alloy of 2004-514056 communique, and the Ti that forms non-metallic inclusion is reduced to below 0.1%.Therefore, favourable on the point of the miniaturization that makes the TiN that consists of the fatigure failure starting point, still, because be the alloy of interpolation that only suppresses to form the element of non-metallic inclusion, so there is the problem that is difficult to carry out nitriding treatment.
In addition, the disclosed alloy of JP 2001-240943 communique also makes Ti reduce, and is therefore favourable on the point of the miniaturization that makes the TiN that consists of the fatigure failure starting point.But, because will suppress very lowly as the Co of one of strengthening element, be difficult to guarantee high tensile strength.In addition, add Si, Mn in order to ensure tensile strength, but therefore can have the possibility of toughness drop.
In addition, the disclosed alloy of JP 2002-167652 communique also makes Ti reduce, and is therefore favourable on the point of the miniaturization that makes the TiN that consists of the fatigure failure starting point.But, realize high strength because actively add C, so the Carbide Precipitation of Cr, Mo etc., it becomes the starting point of fatigure failure, fatigue strength reduces, in addition because the C that actively adds causes the possibility that has the needed weldability of electrodeless variable-speed motor parts to reduce.
Summary of the invention
The object of the invention is to, the metal strip maraging steel that a kind of maraging steel is provided and uses this maraging steel to consist of, it is for reducing the composition of the starting point TiN that consists of the fatigure failure in the high race way, and carry out nitriding treatment easily and improve surface hardness, and the compressive residual stress that makes surface nitride layer increases and bending fatigue strength is improved, and is used in addition the old austenite crystal miniaturization of guaranteeing high intensity, ductility.
The present inventor finds, in order to reduce fatigue strength is improved harmful inclusion TiN, by all suppressing Ti, N very low, Co, Mo are increased, in addition as required, Al is increased, and the value with Co/3+Mo+4Al is limited to proper range again, can remedy thus the strength decreased that causes because of the Ti reduction.Find in addition, in order to improve tensile strength, ductility, fatigue strength, effectively crystal grain miniaturization, and this can solve by the indium addition of B.
In addition, the present inventor also finds, in order to solve the difficulty that reduces the nitriding treatment that brings because of Ti, an amount of interpolation that can be by Cr or add in right amount Cr and Al, the absolute value of the surface compression unrelieved stress that nitrogenize brings is increased, in addition C is suppressed at impurity level guaranteeing weldability, thereby finishes the present invention.
That is, the present invention is a kind of maraging steel, in quality %, below the C:0.01%; Below the Si:0.1%; Below the Mn:0.1%; Below the P:0.01%; Below the S:0.005%; Ni:17.0～22.0%; Cr:0.1～4.0%; Mo:3.0～7.0%; Co: greater than 7.0% but below 20.0%; Below the Ti:0.1%; Below the Al:2.5%; Below the N:0.03%; Below the O:0.005%; B:0.01% is following but do not contain 0%; Co/3+Mo+4Al:8.0～15.0%, surplus are Fe and inevitable impurity.
In the present invention, in order to reach above-mentioned purpose, have following two preferred the composition.Be actively to add Al in the scope of above-mentioned essentially consist this first preferred composition.
That is, maraging steel of the present invention, it is first preferably composed as follows: among above-mentioned composition, make Cr and Al as, Cr:0.1～3.0% take quality %; Al: greater than 0.15% but below 2.5%.This maraging steel, its preferable range of actively adding the composition of Al is, in quality %, below the C:0.008%; Ni: greater than 18.0% but below 22.0%; Mo: greater than 5.0% but below 7.0%; Below the Ti:0.05%; Co/3+Mo+4Al:10.0～15.0%.
More preferably, with quality %, Co: greater than 12.0% but in the maraging steel below 20.0%.
In addition in the present invention, except the composition of aforesaid positive interpolation Al, preferably forming as second, is to adjust to following compositing range: in above-mentioned essentially consist scope, limit Al on one side, slightly how contain Co on one side.
That is, maraging steel of the present invention, it is second preferably composed as follows: among above-mentioned composition, in quality %, make Co, Ti, Al be Co: greater than 10.0% but below 20.0%; Below the Ti:0.05%; Al: be lower than 0.1%; Al+Ti: be lower than 0.1%.
In the present invention, except above-mentioned essentially consist, the first preferred form and the second preferred composition, in quality %, can also contain that Ca:0.01% is following, Mg:0.005% is following more than a kind.
In addition, the present invention is that grain size number is in the maraging steel of the particulate of ASTM No. more than 10.
In addition, the present invention is the metal strip maraging steel of using above-mentioned maraging steel to consist of.
Maraging steel of the present invention, can reduce the TiN that consists of the fatigure failure starting point, can access the high rigidity on the surface behind high strength and the nitriding treatment and large compressive residual stress, if therefore be used to automobile requires high-fatigue strength like this with metal strip with the employed power transmission of electrodeless variable-speed motor parts, then can have long fatigue lifetime etc., can expect significant effect industrial.
Description of drawings
Fig. 1 is the positive electron micrograph that has added the maraging steel surface of Al of the present invention.
Fig. 2 is the electron micrograph on the maraging steel surface of the interpolation that has limited Al of the present invention.
Embodiment
The present invention is based on above-mentioned brand-new discovery and do, below set forth for the effect of each element of the present invention.
In maraging steel of the present invention, the reasons are as follows of following each chemical constitution of scope dictates.Also have, unless special the record, otherwise be quality %.
C can form carbide with Mo and separate out, and intermetallic compound is reduced also and strength decreased, so need to suppress lowly.In addition, if actively add C, then for example the danger of the desired weldability reduction of electrodeless variable-speed motor parts uprises.From such reason, C is below 0.01%.Be preferably below 0.008%.
The intermetallic compound miniaturization of separating out when Si makes ageing treatment forms intermetallic compound with Ni, is to remedy the element that reduces the strength decreased part of bringing because of Ti.But, because it might make toughness drop, therefore in order to ensure toughness, ductility, need in the present invention to suppress lowly.Surpass 0.1% if add, then toughness, ductility reduce, so Si is below 0.1%.Be used for more positively carrying out the preferable range of guaranteeing of toughness, ductility below 0.05%.
Mn when ageing treatment and Ni form intermetallic compound, be the element that helps age hardening, therefore be to can be used in to remedy the element that reduces the strength decreased that causes because of Ti.But, owing to may make toughness drop, so in order to ensure toughness, ductility, need in the present invention to suppress lowly.Surpass 0.1% if add, then toughness, ductility reduce, so Mn is below 0.1%.The preferable range of guaranteeing that is used for more positively carrying out toughness, ductility is below 0.05%.
P, S form inclusion in old austenite grain boundary segregation, are to make the maraging steel embrittlement, harmful element that fatigue strength is reduced.Therefore, P is below 0.01%, and S is below 0.005%.Preferred P is below 0.005%, and S is in the scope below 0.004%.
Cr when carrying out nitrogenize and the avidity of N strong, be to make the nitrogenize depth as shallow, improve nitrogenize hardness, therefore the element that the compressive residual stress of nitrided surface is increased must add.If but there is not at least effect than 0.1%, on the other hand, surpass 4.0% even add, also can't see effect and further improve, the intensity after the timeliness significantly reduces in addition, so Cr is 0.1～4.0%.Also have, when actively adding Al, the upper limit of Cr is take 3.0% as abundant.
Ni makes stable formation of low C martensitic stucture as the matrix of maraging steel, therefore needs at least 17.0%.But if surpass 22.0%, then the austenite structure stabilization is difficult to occur martensitic transformation, so Ni is 17.0～22.0%.The preferable range of Ni is greater than 18.0% but below 22.0%.
Mo forms Ni when ageing treatment 3Mo, Fe 2The fine intermetallic compound of Mo etc. is the important element that helps precipitation strength.In addition, Mo is being effective element for increasing hardness and compressive residual stress from the surface of nitrogenize.If therefore Mo lacks than 3.0%, then tensile strength is insufficient, on the other hand, if than more than 7.0%, then form easily the thick intermetallic compound take Fe, Mo as principal element, so Mo is 3.0～7.0%.The preferable range of Mo is greater than 5.0% but below 7.0%.
Co does not have large impact to the stability of the martensitic stucture of matrix, the solid solubility of its precipitation forming element by making Mo, Al etc. with the solutionizing treatment temp increases, the solid solubility of Mo, Al under the Precipitation temperature province is reduced, promoting thus to contain the separating out of fine intermetallic compound of Mo, Al, is the important element that helps Precipitation intensity.Therefore from intensity face, toughness face, need a large amount of Co of interpolation.Co is 7.0% when following, and the maraging steel that has reduced Si, Mn, Ti is difficult to obtain sufficient intensity, surpasses 20.0% if add on the other hand, and then stabilization of austenite is difficult to obtain martensitic stucture, is greater than 7.0% but below 20.0% therefore.The scope of preferred Co is greater than 12.0% but below 20.0%.
Also have, during restriction Al, in order to limit the Al that helps intensity, can improve slightly Co.Therefore, making the scope of Co is Co: greater than 10.0% but below 20.0%.
Ti was one of important strengthening element in the maraging steel originally, but formed simultaneously TiN or Ti (C, N) as inclusion, the harmful element that the fatigue strength under the superelevation race way is reduced.Therefore, when paying attention to fatigue strength, Ti need to suppress very lowly as impurity.
In addition, Ti forms thin and stable oxide film easily on the surface, if this oxide film forms, then hinders nitrogenizing reaction, therefore is difficult to obtain the compressive residual stress of sufficient nitrided surface.In order to carry out easily nitrogenize, in order to strengthen the compressive residual stress on the surface after the nitrogenize, Ti needs suppress very lowly as harmful impurity element in addition.
If Ti is than more than 0.1%, then the reduction at TiN or Ti (C, N) can not get sufficient effect, in addition owing to forming stable oxide film on the surface easily, so Ti is below 0.1%.Be preferably below 0.05%, more preferably below 0.01%.
Al has following 2 kinds of the situation of the situation of positive interpolation and restriction in situation of the present invention.
If actively add Al, the intensity of maraging steel is improved.Therefore, when paying attention to intensity, can actively add Al.Al content during for positive the interpolation is set forth.
Al is a small amount of interpolation for deoxidation usually, but originally forms intermetallic compound with Ni when ageing treatment, is to help the element strengthened.With in the maraging steel, preferably the interpolation by Al remedies intensity at the metal strip of the present invention that has reduced Si, Mn, Ti.In addition, in the maraging steel that has reduced Ti, obtain good nitride layer in order to carry out nitriding treatment easily, also need the interpolation of Al.A can not get the sufficient strengthening effect from ageing treatment 0.15% when following, if on the other hand than more than 2.5%, then forms in a large number AlN, Al 2O 3Inclusion and fatigue strength is reduced forms thin and stable oxide film on the surface, hinder nitrogenizing reaction, so Al is greater than 0.15% but below 2.5%.Also have, if actively add Al, then exist the maraging steel surfaceness that the situation of some chaps is arranged.Preferred upper limit when therefore, actively adding Al is 1.5%.
If the content of restriction Al then can make the non-metallic inclusion in the maraging steel reduce.In addition, make easily because the roughness on the maraging steel surface that Al causes keeps smooth, therefore in the starting point that reduces fatigure failure, when paying attention to fatigue strength, can adopt the method for restriction Al.Preferred content during for restriction Al is set forth.
Al is combined with oxygen, nitrogen and is formed non-metallic inclusion, and fatigue strength is reduced, and reduces to get low getting final product when paying attention to fatigue strength.If Al adds more than 0.1%, then form easily AlN, Al 2O 3Inclusion has the situation that fatigue strength is reduced, and therefore also Al can be limited in to be lower than 0.1%.The preferable range of Al is below 0.05%.
In addition, Al, Ti all are the elements that form non-metallic inclusion, and therefore the total amount with Al+Ti suppresses lowly, and fatigue strength is improved effectively, and therefore making Al+Ti is below 0.1%.The preferable range of Al+Ti is below 0.07%.
Co, Mo and Ti all are the main strengthening elements in the maraging steel, and Al also is the element that helps the ageing strengthening of maraging steel in addition.If suppress Ti low, then need to make the addition of Co, Mo to increase, to remedy the reduction part from the intensity of Ti, perhaps when actively adding Al, except Co, Mo, also need to remedy reduction part from the intensity of Ti by the addition that increases Al.But this each element is different to the help of strengthening, and is respectively from the reinforced portion of Mo 1/3 and 4 times from the reinforced portion of Co and Al.
Therefore, can put in order according to Co/3+Mo+4Al from the reinforcement of Co, Mo, Al.In quality %, if the value of Co/3+Mo+4Al is less than 8.0%, then intensity is insufficient, and on the other hand, if it is too high to surpass 15.0% intensity, toughness might reduce, so Co/3+Mo+4Al is 8.0～15.0%.The scope of preferred Co/3+Mo+4Al is 10.0～15.0%.
N is combined with Ti and is formed the inclusion of TiN or Ti (C, N), the impurity element that the fatigue strength under the superelevation race way is reduced.In containing the maraging steel of Ti, in order to prevent the formation of thick TiN or Ti (C, N), need to suppress N and make it significantly to reduce.But in the maraging steel that contains hardly Ti, the N that sneaks into owing to common vacuum fusion measures its detrimentally affect seldom, is below 0.03% therefore.Be preferably below 0.01%, more preferably below 0.005%.
O forms oxide based inclusion, is the impurity element that toughness, fatigue strength are reduced, and therefore is limited in below 0.005%.Be preferably below 0.003%.
Old austenite crystal miniaturization when B makes and carries out solutionizing after the cold working and process helps to strengthen, and is the element with the effect that suppresses surperficial tangerine peel, must add.If B lacks than 0.01%, then toughness drop, so B is (not contain 0%) below 0.01%.Be preferably below 0.005% and (do not contain 0%).Can more positively make the lower of preferred B of old austenite crystal miniaturization be limited to 0.0002%, be limited to 0.0003% under preferred.
In the present invention, can contain that Ca:0.01% is following, Mg:0.005% is following more than a kind.
Maraging steel of the present invention can be by vacuum induction melting or after the vacuum induction melting, and ingot casting is made in the melting of carrying out again in the vacuum atmosphere of vacuum arc remelting or esr etc.But, even carry out melting in these vacuum atmospheres, eliminate non-metallic inclusion fully and still have technical difficulty.
In the situation of the present invention, exist with intensity to rise to purpose and the situation of actively adding Al, therefore thick like this and Al of thick matter of the 25 μ m of surpassing is for example arranged 2O 3The danger that inclusion forms, and Al 2O 3The danger of gatheringization.Al 2O 3Inclusion is hard, high-melting-point, even for example also can be out of shape hardly in thermoplasticity processing.Therefore, for example it can make on roller when cold rolling flaw occurs, and has to make metal strip with the possibility that the surface imperfection of maraging steel produces, and therefore, can make Al 2O 3Inclusion becomes the complex inclusion of oxide compound with other, thereby reduces hardness, reduces fusing point.In addition, the preferred element that can prevent gathering that meanwhile adds is to prevent inclusion defects.
As for making Al 2O 3Inclusion becomes the effective element of complex inclusion, can enumerate Si, Mn, Ca, Mg, but in the present invention, Si, Mn will control addition as the element that toughness and ductility are reduced.Therefore by adding Si, Mn more than a kind of Ca, Mg in addition, can make Al 2O 3Inclusion becomes complex inclusion.In addition, Ca, Mg also have the Al of preventing 2O 3The effect of inclusion gatheringization.Therefore in the present invention, contain below the Ca:0.01%, scratch also and contain below the Mg:0.005%.
Also have, in order positively to obtain the effect of this Ca and Mg, Ca is take 0.001% as lower limit, and Mg gets final product take 0.0001% as lower limit.
Beyond the explanation element, be Fe and inevitable impurity more than.
Also have, if following element in following scope, then also can add for the purpose of deoxidation, desulfurization etc.
Zr≤0.01％
Maraging steel of the present invention; after the cold working more than 10%; suitable temperature with the correspondence composition; for example the temperature about 780～1000 ℃ is carried out solution treatment; can make thus old austenite crystal (at this; in the situation of maraging steel, so-called crystal grain refers to old austenite crystal) grain refined is to more than the ASTM No.10.
In maraging steel of the present invention, can expect following effect by making the crystal grain grain refined: can stablize and improve hardness, tensile strength, fatigue strength, impelling strength etc., in steel band, can make surperficial tangerine peel slight etc.
Maraging steel of the present invention contains Al as above-mentioned in the scope below 2.5%.
In maraging steel of the present invention, brand-new discovery is according to the content of Al, can produce the so distinctive phenomenon of shape chap on maraging steel surface.Its reason is presumably because the high Al of spread coefficient through pyroprocessing and this atmosphere of solutionizing thermal treatment etc., causes in surface densification, and surface oxidation occurs thus.
If the surface shape chap, when then for example maraging steel of the present invention being used metal strip for automobile with the employed power transmission of electrodeless variable-speed motor, the danger of the fatigure failure of low circulation side uprises.Therefore, it is smooth that the surface shape that as much as possible Al is caused keeps.
Particularly actively adding in the maraging steel of Al, in order to make having an even surface of maraging steel, the surface etching that can enumerate by mechanical grinding and chemical makes the method that has an even surface, but under the state of the former material of maraging steel, importantly do one's utmost to suppress the surface densification of Al.
In the former material before cold working, think that the formed zone of oxidation in former material surface is removed, the Al densified layer on surface also is removed, and therefore, particularly the solutionizing carried out in the cold working is processed atmosphere and is adjusted into that Al is difficult to be combined with said oxygen and nitrogen and the atmosphere that becomes oxide compound and oxide compound gets final product.For example, vacuum atmosphere, nitrogen atmosphere, Ar atmosphere etc. get final product.Wherein, from productive viewpoint, preferably can process continuously nitrogen atmosphere, the Ar atmosphere of cold rolling material.Because hydrogen is cheap, therefore particularly preferably use hydrogen.
Maraging steel of the present invention contains Ti hardly, this Ti can form the stable oxide film with the possibility that hinders nitrogenize on the surface, therefore can easily carry out the various nitriding treatment such as common gas nitriding, gas soft nitriding, nitrosulphurizing, ion nitriding, salt-bath nitriding.In addition, use in the maraging steel at the metal strip that does not contain Ti, absolute value about the compressive residual stress of the nitride layer of easy reduction, utilization has Cr, the Al of effect of the absolute value of the compressive residual stress that improves nitrogenize hardness and nitride layer, also can improve the absolute value of the compressive residual stress of nitride layer.
In addition, the maraging steel of adjusting in the chemical composition range of above-mentioned the present invention regulation is formed for example band shape below the 0.5mm, as the steel band of metal strip with maraging steel, if metal strip is carried out nitriding treatment with the steel band of maraging steel with suitable condition, then can form nitride hardly, and can form on the surface thin nitride layer about 20～40 μ m, and can give the surface with large compressive residual stress, can expect the raising of fatigue characteristic.
Also have, the high method of compressive residual stress on surface is considered to favourable to fatigue characteristic, and its control can be by the suitable thickness of adjusting nitride layer.
Metal strip maraging steel of the present invention has high-tensile, high-fatigue strength, carries out easily nitrogenize, therefore is suitable for the electrodeless variable-speed metal strip of motor car engine.
Embodiment
Illustrate in greater detail the present invention by following embodiment.
Melt maraging steel of the present invention and comparative steel with the vacuum induction melting furnace, make the ingot casting of 10kg, behind the enforcement homogenizing anneal, carry out forge hot.By hot rolling, steel band that the about 0.3mm of cold rolling making is thick, become the maraging steel that metal strip is used again., carry out solutionizing with 820～900 ℃ and process thereafter, carry out ageing treatment with 490 ℃ again after, under 450～470 ℃, carry out tufftride with the such condition of the nitrogenize degree of depth 20～40 μ m.
Also have, solutionizing is processed and is implemented in nitrogen atmosphere.The electron micrograph of the steel strip surface that the 0.3mm of No.6 of the present invention and No.15 is thick is presented among Fig. 1 and Fig. 2.Fig. 1 is the maraging steel that actively is added with Al, and the surface has some thick, but because carrying out solutionizing in nitrogen atmosphere processes, so the such surface imperfection of starting point to consisting of fracture unconfirmed.
Fig. 2 is the maraging steel of restriction Al, and surface shape is smooth as can be known.
The chemical constitution that shows maraging steel No.1 of the present invention～8 (actively adding Al), steel No.11～16 (restriction Al), existing steel and comparative steel No.21～22 in the table 1.At this, comparative steel No.21 is the existing steel that contains Ti, and comparative steel No.22 is the maraging steel that does not contain Ti and do not add Cr, Al.Any one maraging steel is all adjusted to C the scope below 0.01%, to prevent the reduction of weldability.In addition, the positive No.5 that adds Al, the No.6 of steel of the present invention are added with Mg.Mg content No.5 is 10ppm, and No.6 is 6ppm.In addition, the No.15, the No.16 that control the steel of the present invention of Al of the present invention have also added Mg.Mg content No.15 is 7ppm, and No.16 is 12ppm.
Also have, in table, do not show, but in the cross section of above-mentioned steel of the present invention and comparative steel, in 1000 times the visual field, at random for 10 visuals field, use electron microscope and x-ray analysis equipment, carry out observation, the analysis of microinclusions.Consequently, in removing whole test film of comparative steel No.21, do not observe above the TiN of 3 μ m and the inclusion of Ti (C, N).
In addition, steel No.1 of the present invention, No.6, No.15 for having implemented fatigue test described later carry out cross-section with electron microscope to 10 visuals field with 1000 times, but do not observe Al 2O 3Inclusion.
In addition, be displayed in Table 2 the unrelieved stress on the surface behind inside hardness, surface hardness and the nitriding treatment behind old austinite grain size after each test portion timeliness, tensile strength, the nitriding treatment.At this, the symbol of the unrelieved stress in the table 2 ,+expression stretches, and-expression compression all is compressive residual stress.In addition, among the steel of the present invention, No.1,6,15 and existing steel No.21, the comparative steel No.22 fatigue test results after with 480 ℃ of timeliness be presented in the table 3.
Fatigue test has rotoflector, Compression and Expansion, the various mechanical load patterns of spiral, still since with maraging steel of the present invention as band, so be fit to the evaluation method of load stress in bending.Therefore, in repeated bending fatigue test, if apply that existing maraging steel can rupture so heavily stressed the time and do not rupture, then show to have high-fatigue strength.Therefore, with mean stress 537MPa, when maximum stress 1016MPa applies repeated stress, be implemented into the fracture number of occurrence and reach 10 7
[table 1]
(quality %)
Steel No. C Si Mn P S Cr Ni Mo Co Ti Al
1 0.006 0.01 0.02 0.003 0.001 1.1 18.7 5.5 16.1 0.005 0.22
2 0.007 0.02 0.03 0.004 0.002 1.6 18.6 5.4 16.3 0.007 0.26
3 0.004 0.02 0.01 0.003 0.001 0.9 18.8 5.6 12.9 0.009 1.10
4 0.005 0.01 0.03 0.004 0.002 1.2 18.5 5.3 14.2 0.011 0.86
5 0.003 0.01 0.01 0.003 0.001 0.1 18.9 4.9 12.6 0.010 0.87
6 0.003 0.01 0.01 0.003 0.001 0.1 18.7 6.4 9.2 0.006 1.01
7 0.003 0.01 0.01 0.002 0.001 0.6 18.9 5.5 12.7 0.007 0.52
8 0.004 0.02 0.01 0.003 0.002 0.4 18.7 6.4 9.3 0.009 0.59
11 0.004 0.02 0.01 0.002 0.002 1.6 18.6 5.4 16.2 0.011 0.03
12 0.006 0.01 0.03 0.003 0.001 1.3 18.5 5.6 17.8 0.013 0.02
13 0.005 0.03 0.02 0.002 0.002 2.6 18.9 5.7 16.6 0.009 0.05
14 0.003 0.02 0.02 0.003 0.001 2.2 18.7 5.2 15.9 0.012 0.04
15 0.003 0.01 0.01 0.003 0.001 1.0 19.3 5.1 12.8 0.007 0.03
16 0.004 0.01 0.02 0.002 0.001 1.1 18.9 5.9 10.4 0.010 0.03
21 0.004 0.02 0.02 0.002 0.001 - 18.7 4.9 9.2 0.470 0.09
22 0.006 0.03 0.02 0.004 0.002 - 17.9 5.1 15.8 0.008 0.03
Steel No. N O B Surplus Co/3+Mo+4Al Al+Ti Reference
1 0.0008 0.0010 0.0012 Fe and inevitable impurity 11.7 0.225 Steel of the present invention
2 0.0010 0.0012 0.0014 Fe and inevitable impurity 11.9 0.267 Steel of the present invention
3 0.0007 0.0009 0.0018 Fe and inevitable impurity 14.3 1.109 Steel of the present invention
4 0.0013 0.0015 0.0011 Fe and inevitable impurity 13.5 0.871 Steel of the present invention
5 0.0005 0.0009 0.0011 Fe and inevitable impurity 12.6 0.880 Steel of the present invention
6 0.0006 0.0008 0.0007 Fe and inevitable impurity 13.5 1.016 Steel of the present invention
7 0.0009 0.0006 0.0006 Fe and inevitable impurity 11.8 0.527 Steel of the present invention
8 0.0011 0.0009 0.0008 Fe and inevitable impurity 11.9 0.599 Steel of the present invention
11 0.0009 0.0011 0.0013 Fe and inevitable impurity 10.9 0.041 Steel of the present invention
12 0.0012 0.0008 0.0011 Fe and inevitable impurity 11.6 0.033 Steel of the present invention
13 0.0008 0.0006 0.0010 Fe and inevitable impurity 11.4 0.059 Steel of the present invention
14 0.0011 0.0012 0.0014 Fe and inevitable impurity 10.7 0.052 Steel of the present invention
15 0.0006 0.0018 0.0015 Fe and inevitable impurity 9.5 0.037 Steel of the present invention
10 0.0005 0.0009 0.0012 Fe and inevitable impurity 9.5 0.040 Steel of the present invention
21 0.0008 0.0007 - Fe and inevitable impurity 8.3 0.479 Conventional example
22 0.0012 0.0011 - Fe and inevitable impurity 10.5 0.038 Comparative example
(notes): "-" expression is not added.
[table 2]
Figure G2007800537486D00121
(notes): remained on surface stress is whole compressive residual stresses
[table 3]
Steel No. Breaks (inferior) repeatedly Reference
1 10 7(not fracture) Steel of the present invention
6 10 7(not fracture) Steel of the present invention
15 346900 Steel of the present invention
21 340500 Existing steel
(notes) fatigue test is with maximum stress 1016MPa, and mean stress 537MPa implements.
As shown in Table 2, use the metal strip maraging steel of maraging steel of the present invention, the tensile strength after the timeliness all more than 1700MPa, has sufficient intensity as the metal strip purposes.Particularly actively be added with the maraging steel of Al, the tensile strength after the timeliness is more than the 1900MPa.In addition, after nitrogenize, still have high inside hardness, surface hardness and large surface compression unrelieved stress, compare with the existing steel No.21 that contains Ti, also have as can be known equal above characteristic.
In addition, the invention steel is under the effect of adding B, and old austinite grain size maintains the above particulate of ASTMNo.10.
On the other hand, do not add Ti and do not add the comparative steel No.22 of Cr, Al, the tensile strength after the timeliness, surface hardness and surface compression unrelieved stress are lower than the present invention steel.In addition because do not contain B, so obtain yet slightly thick result of crystal grain.
In addition, as shown in Table 3, the fatigue test results after steel No.1 of the present invention, 6 timeliness is that breaks surpass 10 repeatedly 7Inferior.In addition we know, steel No.15 of the present invention also has the more excellent fatigue characteristic than existing steel No.21.Steel of the present invention such as above-mentioned and existing steel are compared in addition, and Nitriding Characteristics is excellent, therefore can expect the further raising of fatigue characteristic by nitriding treatment.
So, use the metal strip maraging steel of maraging steel of the present invention, can reach than existing martensitic aging and much higher fatigue strength.
Utilize possibility on the industry
Maraging steel of the present invention can for the metal strip that uses, therefore can be applicable to automobile requires to have high-tensile, high-fatigue strength like this with employed power transmission metal strips such as electrodeless variable-speed motors parts under harsh condition.

Claims (14)

1. a maraging steel is characterized in that, in quality %, below the C:0.01%; Below the Si:0.1%; Below the Mn:0.1%; Below the P:0.01%; Below the S:0.005%; Ni:17.0～22.0%; Cr:0.1～4.0%; Mo:3.0～7.0%; Co: greater than 10.0% but below 20.0%; Below the Ti:0.1%; Below the Al:2.5%; Below the N:0.03%; Below the O:0.005%; B:0.01% is following but do not contain 0%; Mg:0.005% is following but do not contain 0%; Co/3+Mo+4Al:8.0～15.0%, surplus are Fe and inevitable impurity.
2. maraging steel according to claim 1, wherein, in quality %, Cr:0.1～3.0%; Al: greater than 0.15% but below 2.5%.
3. maraging steel according to claim 1 and 2, wherein, in quality %, below the C:0.008%; Ni: greater than 18.0% but below 22.0%; Mo: greater than 5.0% but below 7.0%; Below the Ti:0.05%; Co/3+Mo+4Al:10.0～15.0%.
4. maraging steel according to claim 1 and 2, wherein, in quality %, Co: greater than 12.0% but below 20.0%.
5. maraging steel according to claim 3, wherein, in quality %, Co: greater than 12.0% but below 20.0%.
6. maraging steel according to claim 1 is in quality %, below the Ti:0.05%; Al: be lower than 0.1%; Al+Ti: be lower than 0.1%.
7. according to claim 1, each described maraging steel in 2,5 or 6, it is characterized in that, in quality %, contain below the Ca:0.01%.
8. maraging steel according to claim 3 is characterized in that, in quality %, contains below the Ca:0.01%.
9. maraging steel according to claim 4 is characterized in that, in quality %, contains below the Ca:0.01%.
10. according to claim 1, each described maraging steel in 2,5,6,8 or 9, it is characterized in that grain size number is counted particulate more than 10 with ASTM No..
11. maraging steel according to claim 3 is characterized in that, grain size number is counted particulate more than 10 with ASTM No..
12. maraging steel according to claim 4 is characterized in that, grain size number is counted particulate more than 10 with ASTM No..
13. maraging steel according to claim 7 is characterized in that, grain size number is counted particulate more than 10 with ASTM No..
14. a metal strip maraging steel is characterized in that, each described maraging steel forms in the right to use requirement 1～13.
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