CN101128611A - Non-tempered steel soft nitrided component - Google Patents

Non-tempered steel soft nitrided component Download PDF

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Publication number
CN101128611A
CN101128611A CN200680005930.XA CN200680005930A CN101128611A CN 101128611 A CN101128611 A CN 101128611A CN 200680005930 A CN200680005930 A CN 200680005930A CN 101128611 A CN101128611 A CN 101128611A
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bainite
ferrite
steel
nitride
tufftride
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CN100545289C (en
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佐野直幸
松本齐
中谷贵行
镰田芳彦
天野政树
浅井铁也
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Honda Motor Co Ltd
Nippon Steel Corp
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Honda Motor Co Ltd
Sumitomo Metal Industries 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/30—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for crankshafts; for camshafts
    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • 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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
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Abstract

This invention provides a non-tempered steel soft nitrided component that, even when soft nitriding is carried out in such a state that tempering is omitted, has high fatigue strength and excellent bending correction properties. The soft nitrided component is characterized in that it is produced by soft-nitriding a machinical component of a non-tempered steel characterized by comprising by mass C: 0.30 to 0.45%, Si: 0.1 to 0.5%, Mn: 0.6 to 1.0%, Ti: 0.005 to 0.1%, and N: 0.015 to 0.030% with the balance consisting of Fe and impurities and having a mixed texture comprising bainite and ferrite or a mixed texture comprising bainite, ferrite, and pearlite, the bainite fraction in the mixed texture being 5 to 90%, and that the texture of the diffusion layer in the mixed texture is such that the size of a rod-like nitride, in the longitudinal direction, present within ferrite grains in the diffusion layer is not more than 20 [mu]m. The steel as a material to be subjected to this soft nitriding treatment may contain one or more of Nb: 0.001 to 0.1%, Mo: 0.01 to 1.0%, Cu: 0.01 to 1.0%, Ni: 0.01 to 1.0%, B: 0.001 to 0.005%, S: 0.01 to 0.1%, and Ca: 0.0001 to 0.005%.

Description

Non-tempered steel soft nitrided component
Technical field
The present invention relates to non-hardened and tempered steel is implemented the mechanical component that tufftride is handled.Relate in detail the bent axle (crankshaft) of automobile, industrial machine and building machinery etc. and connecting rod (connecting rod) etc. have been implemented the mechanical component that tufftride is handled.
Background technology
In the past, the mechanical component such as crankshaft-and-connecting-rod of automobile, industrial machine and building machinery etc., be by methods such as heat forged after carrying out hot-work, implement modifier treatment (quenching, tempering, normalizing, annealing) again and make.Bring homogenizing of tissue and miniaturization by modifier treatment.After the modifier treatment, mainly implement tufftride and handle for the purpose that improves fatigue strength.
Strain takes place owing to implement the tufftride meeting of processing.Because this strain infringement size of component precision, so implementing to carry out detorsion after tufftride is handled more.Therefore, just need detorsion and high-fatigue strength excellent equally the part after tufftride is handled.
Above-mentioned what is called " excellent detorsion ", the meaning are until reaching very big bending deflection amount, and the surface of part does not have crackle to enter yet.
In the manufacturing of mechanical component,, should require particularly strong in recent years in order to cut down manufacturing cost and energy-conservation and modifier treatment is omitted in expectation.
But, if omit modifier treatment, the inhomogeneous tissue that generates when then remaining in hot-work easily, in addition, the adding of the former material hot-work begins before, pine for growing up and the crystal grain of thickization also can directly remain in the goods, causes the mechanical properties reduction of goods.Therefore, can after hot-work, implement normalizing treatment usually to address this problem.When after hot-work, not implementing normalizing treatment, the situation of thickization of crystal grain is arranged, become the thermal distortion tissue part residual inhomogeneous tissue in ground.Therefore in the material that has omitted normalizing treatment, handle and also can not get the fatigue strength expected even implement tufftride.
In addition as above-mentioned, the bent corrective excellence of part request rate after tufftride handled, but when omitting modifier treatment, because above-mentioned texture of coarse crystal is or/and heterogeneity tissue, the detorsion of the part after the tufftride processing is significantly inferior mostly.
Therefore, though expectation develop with cutting down cost and energy-conservation be purpose when omitting modifier treatment, after tufftride is handled, still have the mechanical component of high-fatigue strength and excellent detorsion.
Below, choose " normalizing " as the typical example among the modifier treatment and describe.Under the situation of omitting normalizing treatment, the tufftride that still can access the part that has " detorsion " that high-fatigue strength and the excellent people draw after tufftride is handled is handled the method with non-hardened and tempered steel, and several motions are arranged up to now.They are divided into following two kinds.
(1), and under this state, avoids the method (for example with reference to patent documentation 1～4) of thickization of the tissue that heat forged brings as far as possible with the same ferrite and the perlite of remaining of the micro organization of steel with quenched and tempered steel.
(2) make the micro organization of steel become the method (for example with reference to patent documentation 5～9) of bainite.
In patent documentation 1, " a kind of nitriding steel; the content of its alloying element is in quality %; be made of C:0.15～0.40%, Si≤0.50%, Mn:0.20～1.50%, Cr:0.05～0.50%, surplus Fe and unavoidable impurities; the tissue after the hot-work comes down to the ferritic-pearlitic tissue; the ferrite area occupation ratio is more than 30% is that the ferrite grain size number is the granularity more than No. 5, and pearlitic mean sizes is that 50 μ m are following " disclosed.Even this steel is recorded and narrated to omitting normalizing treatment, fatigue strength behind the nitriding treatment and detorsion are still excellent.
In patent documentation 2, " a kind of nitriding treatment part; be that steel is carried out the nitriding treatment part that nitriding treatment forms; contain C:0.15～0.40% as alloying constituent in quality %; below the Si:50%; Mn:0.20～1.50%; Cr:0.05～0.50% is disclosed, surplus is made of Fe and unavoidable impurities, and described steel is under thermal process status, has the mixed structure that constitutes by ferrite and perlite, the mean sizes of described ferritic crystal grain is below the 50 μ m, the mean sizes of described pearlitic crystal grain is below the 50 μ m, the average hardening depth that described nitriding treatment brings is more than the 0.3mm, and the change of described hardening depth is in 0.1mm ".And even this part is recited as the omission heat forged and is carried out nitriding treatment, its fatigue strength and detorsion are still excellent.
In patent documentation 3, disclose that " a kind of tufftride is handled with steel etc.; it contains C:0.20～0.60% in weight %; Si:0.05～1.0%; Mn:0.3～1.0%; below the P:0.05%; S:0.005～0.10%, below the Cr:0.3%, below the Al:0.08%, below the Ti:0.03%, N:0.008～0.020%, below the Ca:0.005%, below the Pb:0.30%, below the Cu:0.30%, below the Ni:0.30%, below the Mo:0.30%, below the V:0.20%, below the Nb:0.05%, and satisfy 221C (%)+99.5Mn (%)+52.5Cr (%)-304Ti (%)+577N (%)+25 〉=150, surplus is the chemical constitution of Fe and unavoidable impurities, tissue is made of ferrite and perlite, and its ferrite branch rate is more than 10% ".
In this patent documentation 3, be recited as, if fatigue strength is showed as the regression equation that contains element, and its factor is more than specific size, and tissue is made of ferrite and perlite, this ferrite branch rate is more than 10%, even then omit normalizing treatment, still can access the nitriding treatment part of fatigue strength and detorsion excellence.
In patent documentation 4, disclose " a kind of nitrogenize is with steel etc.; its in weight % contain C:0.30～0.43%, Si:0.05～0.40%, Mn:0.20～0.60%, below the P:0.08%, below the S:0.10%, below the sol.Al:0.010%; Ti:0.013% is following, Ca:0.0030% is following, Pb:0.20% is following and N:0.010～0.030%; surplus is made of Fe and impurity; the Cr in the impurity is below 0.10%, and V is below 0.01% ".
In patent documentation 4, be recited as, implement nitriding treatment,, also can access the goods of fatigue strength and detorsion excellence by making the hardness gradient smoothness in the nitride layer even omit normalizing treatment.
In patent documentation 5, a kind of " high-fatigue strength structural steel, it contains, and C:0.1～0.35%, Si:0.05～0.35%, Mn:0.6～1.50%, P:0.01% are following, S:0.015% is following, Cr:1.1～2.0%, Mo:0.5～1.0%, V:0.03～0.13%, B:0.0005～0.0030%, Ti:0.01～0.04%, Al:0.01～0.04%, surplus: Fe and unavoidable impurities " disclosed.
In patent documentation 5, Cr is effective on raising hardenability and nitrogenize hardening, thereby V makes the carbide miniaturization of separating out effective on raising fatigue strength.At this, the nitrogenize hardening that Cr brings is because based on being separating out of Cr nitride, so the raising of fatigue strength here is based on the precipitation strength that Cr and V bring.But, in this patent documentation 5, will become bainite structure in case heat once again and cool off for the steel of manufacturing, this steel belongs to the category of quenched and tempered steel.
In patent documentation 6, disclose " a kind of tufftride is handled with non-hardened and tempered steel etc.; its contain C:0.1～0.3% in quality % and do not contain 0.3%, Si:0.01～1.0%, Mn:1.5～3.0%, Cr:0.01～0.5%, Mo:0.1～1.0%, sour solvable Al:0.01～0.045%, N:0.005～0.025%, surplus is made of Fe and unavoidable impurities ".
In this patent documentation 6, think to have steel by the bainite structure that obtains under the effect from the hot processing temperature to the air cooling, its obdurability excellence, and implementing to have excellent detorsion after tufftride is handled.At this, the infringement machinability for the hardness that does not make bainite is really up to the mark, C concentration is defined as and is lower than 0.3%, and in order to ensure the hardenability of the steel that is used to generate bainite, Mn concentration is defined as more than 1.5%.In addition, add 0.01～0.05% Cr, separate out intensity and the hardness increase of real face nitride layer by what the Cr nitride brought.That is, in this patent documentation 6, why detorsion is enhanced by bainite structure, be because bainite is compared with the ferritic-pearlitic tissue, its toughness is higher under same hardness, and is for this reason, really up to the mark and make C concentration be lower than 0.3% as the above-mentioned hardness that does not make bainite.But, when C concentration is lower than 0.3%, lest the wear resistant deficiency.Wear resistant also is an important factors in the mechanical component of crankshaft-and-connecting-rod etc.
In patent documentation 7, " a kind of tufftride processing steel; it contains C:0.05～0.30% in weight %; below the Si:1.20%; Mn:0.60～1.30%; Cr:0.70～1.50%; below the Al:0.10% is disclosed, N:0.006～0.020%, V:0.05～0.20%, Mo:0～1.00%, B:0～0.0050%, S:0～0.060%, Pb:0～0.20%, Ca:0～0.010%, and 0.60≤C+0.1Si+0.2Mn+0.25Cr+1.65V≤1.35, in addition, 0.60≤C+0.1Si+0.2Mn+0.25Cr+1.65V+0.55Mo+8B≤1.35, surplus is made of Fe and unavoidable impurities, cooling off after the hot rolling or after the heat forged, do not heat-treat, thereby becoming core hardness is Hv200～300, is organized as the mixed structure that bainite or ferrite branch rate are lower than 80% ' ferrite+bainite ' ".
In the invention of this patent documentation 7, the thought of employing is also the same with patent documentation 5, is utilize that Cr and V bring separate out intensity and realize the raising of fatigue strength.But, the same with patent documentation 6, because being defined as, C concentration is lower than 0.3%, so can not get rid of the mystery aspect wear resistant.
In patent documentation 8, " a kind of tufftride processing steel; be in weight %; contain C:0.15～0.40%; below the Si:1.20%; Mn:0.60～1.80%; Cr:0.20～2.00% is disclosed, Al:0.02～0.10%, N:0.006～0.020%, V:0.05～0.20%, the steel that surplus is made of Fe and unavoidable impurities, and employing has 0.60≤C+0.1Si+0.2Mn+0.25Cr+1.65V≤1.35 and reaches, 0.25Cr+2V the steel of≤0.85 condition, after hot rolling or heat forged, cool off, do not heat-treat, thereby have core hardness is Hv200～300, be organized as the mixed structure of ' ferrite+perlite ' or ' bainite branch rate is lower than ferrite+perlite (+bainite) of 20% ', by being implemented tufftride, it handles, it has high surface hardness and dark hardening depth, thereby has lower thermal treatment emergent property ".
Therefore the steel of this patent documentation 8 because C concentration is 0.15～0.40%, predicts that wear resistant improves.But for this steel, the thought that is adopted is also the same with the invention of patent documentation 7, is to utilize the raising that intensity realizes fatigue strength of separating out that Cr and V bring.
In patent documentation 9, disclose " a kind of non-modified nitrogenize forging parts; it contains C:0.15～0.35%, Mn:1.00～3.00%, Cr:0～0.15%, V:0～0.02%, Cu:0.50～1.50%, more than 4 times of Ni:Cu content; the content of B, N and Ti with by Bsol=B-(11/14) Bsol of N-(14/48) Ti} definition counts 0.0010～0.0030%, and surplus is made of Fe and unavoidable impurities ".
In this patent documentation 9, think " as the nitrogenize steel is the ferrite subject organization, or under such situation of difficult, the single phase structure of martensite or bainite is more more preferred than ferrite+pearlitic structure ".At this, though avoided the precipitation strength that Cr and V bring, the substitute is utilize that Cu brings separate out this thought of intensity.In addition,, must make Mn concentration, to become the monophasic non-hardened and tempered steel of bainite more than 1.0% in order to obtain the bainite single phase structure.
On the other hand, method about the tufftride treatment condition, disclosed the soft-nitriding treatment method (with reference to patent documentation 11) of the erosion resistance that is used in soft-nitriding treatment method (with reference to patent documentation 10) that time of forming compound layer shortens, improves compound layer in the past and improved soft-nitriding treatment method (with reference to patent documentation 12) for the resistance of beating trace, the soft-nitriding treatment method that still is used to improve fatigue strength and detorsion is not studied.
For example disclosed soft-nitriding treatment method is in patent documentation 12, by handle the quench treatment that the back reheat arrives austenitic temperature territory and chilling in tufftride, make diffusion layer and mother metal matrix formation of martensite, it is carried out the such thermal treatment of tempering again, thereby improve the wear resistant of mechanical component and for the resistance of beating trace.Yet tufftride processing itself only thinks that carrying out gas soft nitriding in standard temperature (570～580 ℃) handles.
[patent documentation 1] spy opens flat 9-291339 communique
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[patent documentation 6] spy opens the 2000-309846 communique
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[patent documentation 9] spy opens the 2000-160287 communique
[patent documentation 10] spy opens the 2003-253420 communique
[patent documentation 11] spy opens the 2002-302756 communique
[patent documentation 12] spy opens flat 11-269631 communique
As above-mentioned, known by applying flexibly tufftride that bainite obtains becoming after tufftride is handled the part of fatigue strength and detorsion excellence and handled method with non-hardened and tempered steel.Yet the intensity of bringing by the interpolation alloying element of separating out improves fatigue strength, can make the detorsion reduction on the other hand.That is, make high fatigue strength and excellent detorsion and to deposit this problem still unresolved.
In addition, in order to comply with the more requirement of high strength of part in recent years, and require to have the fatigue strength that is higher than up to now, and the non-hardened and tempered steel used of the also excellent soft nitrided component of detorsion.But, in the technology of above-mentioned existing " separating out the bainiteization of intensity and tissue ", may not tackle such requirement.
Summary of the invention
In view of this situation, present inventors' a part, at first, finished the following is the invention of purpose, even promptly provide a kind of when under the state that has omitted modifier treatment, implementing tufftride and handling, steel is used in the non-modified tufftride processing that still becomes the part of the detorsion with high-fatigue strength and excellence, and applies for as PCT/JP2004/012327.Will being intended to of this invention, " be a kind of tufftride processing non-hardened and tempered steel; wherein; contain C:0.30～0.45%, Si:0.1～0.5%, Mn:0.6～1.0%, Ti:0.005～0.1% and N:0.015～0.030% in quality %; surplus is made of Fe and unavoidable impurities; and have mixed structure that constitutes by bainite and ferrite or the mixed structure that constitutes by bainite, ferrite and perlite, the bainite branch rate in its mixed structure is 5～90% ".Also have, this steel also can contain among the following element more than a kind: Nb:0.003～0.1%, Mo:0.01～1.0%, Cu:0.01～1.0%, Ni:0.01～1.0%, B:0.001～0.005%, S:0.01～0.1% and Ca:0.0001～0.005%.
The object of the present invention is to provide a kind of mechanical component, it is handled with on the basis of steel in this non-modified tufftride, even when under the state that has omitted modifier treatment, implementing the tufftride processing, still have the high-fatigue strength and the excellent detorsion that are further improved.
Present inventors still proceed research after the application of PCT/JP2004/012327.Notice that consequently by working hard on the speed of cooling when tufftride is handled, can further make the fatigue strength and the detorsion raising of the part after tufftride is handled, further the result of research obtains following conclusion repeatedly.
(a) in the zone of the diffusion layer after tufftride is handled among the observed precipitate, iron-nitride only generates in the process of cooling that tufftride is handled, and it generates movement and relies on very much cooling conditions.
(b) the main iron-nitride that is created on diffusion layer is bar-shaped γ '-Fe 4N and discoideus α "-Fe 16N 2
(c) whether these iron-nitrides in the diffusion layer generate, and the fatigue strength and the detorsion of the mechanical component that tufftride was handled have a significant impact.Particularly as bar-shaped γ '-Fe 4N separate out can ambassador fatigue strength reduction low.
(d) adjust the form that exists of nitrogen in the ferrite crystal grain in the diffusion layer, promptly, the nitrogen that imports when not making nitriding treatment is separated out as iron-nitride, but as far as possible as oversaturated solid solution nitrogen, realizing ferritic reinforcement, thereby can make the part after tufftride is handled have excellent fatigue strength and detorsion.
The present invention is based on above-mentioned discovery and finish.
Main idea of the present invention is present in the following non-modified soft nitrided component.
(1) a kind of non-hardened and tempered steel that will have following feature carries out the soft nitrided component that tufftride is handled, this non-hardened and tempered steel contains C:0.30～0.45% in quality %, Si:0.1～0.5%, Mn:0.6～1.0%, Ti:0.005～0.1% and N:0.010～0.030%, surplus is made of Fe and unavoidable impurities, and has the mixed structure that constitutes by bainite and ferrite or by bainite, the mixed structure that ferrite and perlite constitute, bainite branch rate in its mixed structure is 5～90%, in this soft nitrided component, the length direction that is present in the γ ' nitride in the ferrite crystal grain of its diffusion layer is of a size of below the 20 μ m.
(2) a kind of non-hardened and tempered steel that will have following feature carries out the soft nitrided component that tufftride is handled, this non-hardened and tempered steel contains C:0.30～0.45% in quality %, Si:0.1～0.5%, Mn:0.6～1.0%, Ti:0.005～0.1% and N:0.010～0.030%, and contain from the element more than a kind of following first groups of elements selection, and among the element more than a kind from second groups of elements, selected one or two, surplus is made of Fe and unavoidable impurities, and has the mixed structure that constitutes by bainite and ferrite or by bainite, the mixed structure that ferrite and perlite constitute, bainite branch rate in its mixed structure is 5～90%, in this soft nitrided component, the length direction that is present in the γ ' nitride in the ferrite crystal grain of its diffusion layer is of a size of below the 20 μ m.
First groups of elements:
Nb：0.001～0.1％、
Mo：0.01～1.0％、
Cu：0.01～1.0％、
Ni:0.01～1.0%, and
B：0.001～0.005％。
Second groups of elements:
S:0.01～0.1% and
Ca：0.0001～0.005％。
Also have, so-called " diffusion layer " here is by JIS G562 definition, removes the compound layer among the upper layer of the part that tufftride handled and is considered to the layer that nitrogen, carbon etc. spread.In addition, so-called " γ ' nitride " is described γ '-Fe 4N.
According to the present invention, be former material with non-hardened and tempered steel, can access the high-intensity soft nitrided component of fatigue strength and detorsion excellence.Therefore, can cut down part manufacturing cost.
Description of drawings
Fig. 1 is that the tufftride used as the former material of soft nitrided component of the present invention is handled the representational photo of organizing with " bainite+ferrite+perlite " mixed structure of non-hardened and tempered steel.
Fig. 2 is the SEM image that is dispersed with the old austenite crystal of bainite ferrite.
Fig. 3 is the tissue that is dispersed with the thick diffusion layer of γ ' nitride when (being represented by arrow).
Embodiment
Below, each important document of the present invention is described.Also have, " % " express meaning of the content of each element is " quality % ".
(A) chemical constitution
C：0.30～0.45％
C is used to obtain the necessary element of " bainite+ferrite " or " bainite+ferrite+perlite " mixed structure.The content of needs more than 0.30% in order to ensure the wear resistant of austenitic stabilization and material.On the other hand, if surpass 0.45%, then hardenability excessively improves, and causes deleterious martensitic generation easily.Therefore, the proper range of C content is 0.30～0.45%.
Si：0.1～0.5％
Si adds in steel making working procedure as reductor, but because also help ferritic solution strengthening, so need the content more than 0.1%.On the other hand, if Si content surpasses 0.5%, the thermal distortion impedance that then can improve steel makes toughness and machinability deterioration.Therefore, the proper range of Si content is 0.1～0.5%.
Mn：0.6～1.0％
Mn is the same with Si to be added in steel making working procedure as reductor.In addition, still be used to make stabilization of austenite and the necessary element of mixed structure or " bainite+ferrite+perlite " mixed structure that obtains " bainite+ferrite ".In addition, Mn combines with S in the steel and forms MnS, and the effect of improving machinability is also arranged.
In above-mentioned mixed structure, bainite divides the rate must be more than 5%.And, generate such hardenability in order to ensure the bainite structure that makes this minute rate, and need the content of the Mn more than 0.6%.On the other hand, if the content of Mn surpasses 1.0%, then hardenability excessively improves and causes deleterious martensitic generation easily.Therefore the proper range of Mn content is 0.6～1.0%.
Ti：0.005～0.1％
Ti is that thickization of crystal grain pinning (pinning) particle that is used to be used in when suppressing hot-work forms necessary element.As the pinning particle nitride, carbide, the carbonitride of Ti are arranged,, need Ti that content more than 0.005% is arranged for the pinning particle that makes sufficient distribution density generates.On the other hand, do not exhaust the N in the steel that helps to increase strength of parent for the Fe nitride, Ti content need be suppressed at below 0.1%.For above reason, the proper range of Ti content is 0.005～0.1%.More preferably 0.01～0.05%.
N：0.010～0.030％
The interpolation of N is to be used to make stabilization of austenite and mixed structure or " bainite+ferrite+perlite " mixed structure of obtaining " bainite+ferrite ", for the pinning particle that is configured for suppressing thickization of crystal grain with in order to help solution strengthening as solid solution nitrogen to increase strength of parent.At this,, then need to contain more than 0.010% if consider the part that is consumed as the pinning particle.On the other hand, if N surpasses 0.030%, then meeting generates air blister defect and damages material in ingot casting.Therefore, the proper range of the content of N is 0.010～0.030%.Preferably 0.015～0.030%, more preferably 0.015～0.025%.
Handling with one of non-hardened and tempered steel as the employed tufftride of the former material of soft nitrided component of the present invention, is except above-mentioned element, the steel that surplus is made of Fe and unavoidable impurities.
Handle another that use non-hardened and tempered steel as the employed tufftride of the former material of soft nitrided component of the present invention, be except above-mentioned element, also contain among element of selecting from above-mentioned first groups of elements more than a kind and the element of from second groups of elements, selecting more than a kind one or both, the steel that surplus is made of Fe and impurity.
Belong to first group element, promptly Nb, Mo, Cu, Ni and B have this common action effect of intensity that improves steel of the present invention.The action effect separately and the qualification of content be the reasons are as follows.
Nb：0.001～0.1％
Nb is the element that can utilize aspect the pin that is used to form thickization of crystal grain when being used to suppress hot-work is decided particle.In addition, become fine carbonitride in its cooling after finishing hot-work and separate out, also effective on the intensity of raising mother metal.The content of needs more than 0.001% in order to obtain such effect.On the other hand, it also is saturated that its content surpasses 0.1% effect, can form the residual carbonitride of thick fusing during this external steel-making and makes the quality badness of steel billet.Therefore, when adding Nb, can make its content is 0.001～0.1%.Preferred content is 0.003～0.1%, more preferably 0.005～0.1%, most preferably 0.005～0.05%.
Mo：0.01～1.0％
Mo improves the hardenability of steel and helps high strength, and on toughness improves also effective elements.In addition, if add mixed structure or " bainite+ferrite+perlite " mixed structure that Mo then is easy to obtain " bainite+ferrite ".In order to obtain such effect, need the content more than 0.01%.On the other hand, if the content of Mo surpasses 1.0%,,, make detorsion and toughness deterioration after tufftride is handled so promote martensitic generation then because hardenability excessively improves.Therefore, when adding Mo, can make its content is 0.01～1.0%.Preferred content is 0.05～0.6%.
Cu：0.01～1.0％、Ni：0.01～1.0％
When adding Cu, expect the increase of the bainite branch rate that its solution strengthening and stabilization of austenite bring.Therefore Cu is contained more than 0.01%.
For Cu and Ni, the effect of the precipitation strength that does not have carbonitride to form to bring is separated out and can be helped precipitation strength but timeliness takes place in ferrite Cu.But when replacing temperature (about 580 ℃) that general tufftride handles and treatment time (about a few hours) by ageing treatment, needing the content of Cu in order to make the separating out generation of sufficient Cu is more than 1.0%., in soft nitrided component of the present invention, tufftride does not need to expect the age hardening effect of Cu when handling.In addition, because the fusing point of Cu is 1085 ℃ very low, thus long in the process of setting in steel making working procedure as the remaining time of liquid phase, therefore, at the grain boundary segregation of steel and bring out thermal crack.In order to eliminate this drawback, in steel of the present invention, make Cu content on be limited to more than 1.0%.Also have, during heavy addition Cu, preferably add Ni in order to prevent above-mentioned drawback.
Ni is also the same with Cu to be austenite stabilizer element because in solution strengthening and on the bainite branch rate of guaranteeing to expect effectively, so preferably contain more than 0.01%.On the other hand, it also is saturated that content surpasses 1.0% its effect, just increases former material cost, so is limited to 1.0% on it.Also have, with Cu and time spent, in order to realize preventing the effect of described thermal crack really, the Ni that preferably contains is more than 1/2 of content of Cu.
B：0.001～0.005％
B improves the hardenability of steel, promotes the mixed structure of " bainite+ferrite " or the generation of " bainite+ferrite+perlite " mixed structure.0.001% this effect of above content clearly manifests.On the other hand, if the content of B surpasses 0.005%, then the toughness of steel is impaired.Therefore, when adding B, can make its content is 0.001～0.005%.
Second group element is S and Ca, and they can improve the tufftride of using as the former material of soft nitrided component of the present invention and handle the machinability of using non-hardened and tempered steel.The qualification of content separately be the reasons are as follows.
S：0.01～0.1％、Ca：0.0001～0.005％。
S and Ca are the elements that makes the machinability raising of steel.If add then machinability further improves, therefore add any one or two kinds as required.Yet if excessively add, the segregation defective in the steel billet takes place, and makes the hot workability deterioration, so the scope of S content is advisable with 0.01～0.1%, and the scope of Ca content is advisable with 0.0001～0.005%.The preferred lower limit of Ca is 0.001%.
Except that the element of the above, to handle with also having impurity in the non-hardened and tempered steel in the tufftride of using as the former material of soft nitrided component of the present invention, it does not painstakingly add.But, increase in order not cause in the steel making working procedure futile cost, about the allowance of impurity such as following.
P is because encourage embrittlement of grain boundaries at grain boundary segregation, so preferably below 0.05%.
Al as reductor by adding when the melting.Al can remain in the steel as aluminium oxide particles, combines with N in addition and forms AlN.Aluminum oxide is the oxide based inclusion of high rigidity, can shorten the life-span of employed instrument in the machining.AlN separates out near surface when tufftride is handled, and promotes the growth of surface compound layer and significantly improves upper layer hardness, thereby make the detorsion deterioration.In addition, because of AlN solid solution under hot processing temperature,, almost do not having effect aspect the miniaturization of crystal grain so can't expect to decide the function of particle as pin.Therefore, the content of preferred Al is low.But, make the minimum meeting of lower limit of Al content produce the restriction in the deoxidation step and cause cost to increase, therefore preferred Al content is below 0.05% of detorsion that does not hinder steel of the present invention.
Cr and V do not add in steel of the present invention yet.They all are impurity, and its content is few more good more.Its reason such as above-mentioned is the hardness that nitride is separated out significantly improve the near surface layer of steel owing to Cr and V, the infringement detorsion.If do not damage effect of the present invention, and the purity of the former material of the strand manufacturing process of the method beyond consideration refining cost and the blast furnace-converter method, then allow Cr to reach 0.15% as impurity, V reaches 0.02%.Also have, more preferably Cr is below 0.1%.
(B) tissue of the former material of soft nitrided component of the present invention
The tissue of handling with non-hardened and tempered steel as the employed tufftride of the former material of soft nitrided component of the present invention is bainite and ferritic mixed structure, perhaps bainite and ferrite and perlite mixed structure.And the bainite branch rate in these mixed structure is 5～90%.
As above-mentioned, if utilize bainitic transformation, then can avoid martensitic generation, and can access than the fine tissue of thick pearlite colony (pearlite colony).This bainite structure is made of bamboo foliate ferrite (bainite ferrite) and carbide as shown in Figure 1.This bainite ferrite is dispersed in the inside of old austenite crystal, than little from the first ferrite (polygon ferrite) of analysing of old austenite grain boundary expansion.Promptly, this bainite is " in a pearlite colony; form leaf of bamboo shape but be dispersed with the tissue of finer ferrite (bainite ferrite) ", this is dispersed with the pearlite colony of bainite ferrite if compare with the situation of the pearlite colony completely that does not contain this bainite ferrite, then its lamellated (lamellar) tissue disorder.
Fig. 2 is the SEM image that is dispersed with the old austenite crystal of bainite ferrite.As indicated in this figure, the lamellated lamellar structure that is not marshalling that organizes of the ferrite/cementite in pearlite colony all confirms confusion everywhere.Such tissue is compared with the tissue that pearlitic transformation integrally takes place old austenite crystal, its intensity reduces, but the viscous deformation at the crackle front end in the warpage of crackle and the bainite ferrite takes place, and is therefore on the progress impedance this point of crackle, more excellent than thick pearlite colony.
That is,,, still can highly guarantee the crack propagation impedance even grain structure has some thickization by sneaking into bainite structure.For this reason, Yi Shi bulk area rate meter and need containing more than 5%.At this, organized whole is also harmless as bainite structure, but in bainite branch rate surpasses 90% tissue, the situation of reality be martensitic sneak into inevitable.Because martensite makes the detorsion deterioration, machinability is worsened, so it is sneaked into not for preferred.Therefore the bainite branch rate in the mixed structure is 5～90%.Preferred bainite branch rate is 10～80%.Tissue beyond the bainite comes down to ferrite or ferrite and perlite.
(C) manufacture method of the former material of soft nitrided component of the present invention
Handle the tissue of using non-hardened and tempered steel as the employed tufftride of the former material of soft nitrided component of the present invention, for example can obtain by method shown below.
Former material as heat forged, preparation to ingot bar carried out the rolling steel billet of piecemeal, to the continuous casting material carried out the rolling steel billet of piecemeal etc. or to they carried out the hot rolled bar steel any one can, but former material will have the chemical composition range of regulation.These heat forged are 1100～1250 ℃ with the Heating temperature of former material.Cooling after the heat forged can be put cold in atmosphere, or uses the pressure cooling of fan.In addition, for example also can be quickly cooled near the eutectoid transformation temperature, slowly cool off, also can be cooled to immediately about 500～300 ℃ after the heat forged, and under this temperature, keep to promote bainitic transformation 700～500 ℃ scope.Continuous cooling transformation diagram (CCT graphic representation) is made in being adjusted at of speed of cooling in advance, tries to achieve the speed of cooling scope by the bainitic transformation zone, adjusts to the speed of cooling scope of trying to achieve and gets final product.
(D) tissue of the diffusion layer of soft nitrided component of the present invention
In the diffusion layer of soft nitrided component of the present invention, the length direction that is present in the bar-shaped γ ' nitride in the ferrite crystal grain is of a size of below the 20 μ m.
As above-mentioned, the oversaturated nitrogen that is solid-solubilized in the diffusion layer is separated out as γ ' nitride, if the γ ' nitride of separating out is grown up greatly and solid solution nitrogen is reduced, then the intensity of ferrite crystal grain reduces, and causes the reduction of fatigue strength.In addition, γ ' nitride is bar-shaped form, grows up in the mode of extending in ferrite crystal grain from the ferrite crystal boundary, and is therefore if γ ' nitride becomes to look big, then can be with the distributions in the cross-section ferrite crystal grain.Because the solid solution nitrogen concentration significantly reduces near γ ' nitride, so intensity also reduces, therefore, if elongated γ ' nitride disperses in the mode in the cross-section ferrite crystal grain, the crackle that then invades in the ferrite crystal grain will be propagated at γ ' nitride/ferrite interface more easily, and the crack progress impedance reduces.That is, owing to separating out of γ ' nitride, except the average intensity reduction of ferrite crystal grain self, the crack propagation impedance of locality also reduces near γ ' nitride, so fatigure failure becomes easy.Therefore to suppress separating out and growing up of γ ' nitride.
Be based on following reason below the size block of the length direction of bar-shaped γ ' nitride is decided to be 20 μ m.Particle diameter as the ferrite crystal grain of the non-hardened and tempered steel of the former material of soft nitrided component of the present invention is about 10～50 μ m.Therefore, in order in ferrite crystal grain, to link to the bar-shaped γ ' nitride of growing up to grain from the ferrite crystal boundary, and avoid just what a thick such situation of the cross-section ferrite crystal grain of γ ' nitride, need the length of bar-shaped γ ' nitride is suppressed at below 1/2 of ferrite particle diameter, thus, the size block that will be present in the length direction of the bar-shaped γ ' nitride in the ferrite crystal grain of diffusion layer is decided to be below the 20 μ m.Be preferably below the 10 μ m, more preferably below the 5 μ m.
(E) be used to obtain the method for the diffusion layer of soft nitrided component of the present invention
In tufftride is handled, can adopt gas soft nitriding processing, salt bath tufftride to handle (tufftride processing), ion nitriding etc.Can both form compound layer (nitride layer) and the diffusion layer under it about thick 20 μ m in heterogeneity on the surface of goods according to any method.But, adopt any tufftride to handle, all need to suppress separating out and growing up of γ ' nitride, the size of length direction that makes γ ' nitride is below 20 μ m.For this reason, need to plan to the refrigerating work procedure of room temperature in the soaking temperature of handling from tufftride.Below, about the refrigerating work procedure of tufftride processing soaking temperature, set forth gas soft nitriding for example and handle.
To obtain mechanical component in order handling, for example to carry out the processing to a few hours in tens of minutes with 550～620 ℃ soaking temperature in 1: 1 blended atmosphere at RX gas and ammonia by gas soft nitriding.If soaking temperature is low excessively, then the growth of surface compound layer is slow, and the diffusion intrusion of nitrogen in former material steel is also slow, thereby can not get sufficient sclerization.On the other hand, if soaking temperature is too high, the problem of the dimensional change (distortion) of the part in the refrigerating work procedure appears then.Therefore, soaking temperature is preferably 550～620 ℃, and preferred soaking temperature is 580～600 ℃ a scope.According to the hold-time under the soaking temperature (treatment time), the amount that the thickness of surface compound layer and diffusion invade the nitrogen in the steel is determined.The effect that improves from the fatigue strength that can access expectation, and the viewpoint of the production efficiency of industry sets out, and the hold-time can be 30 minutes～3 hours, is preferably 1 hour～2 hours.
Under the soaking maintaining condition that tufftride is handled, nitrogen that diffusion is invaded and Fe only form compound layer on the surface, separating out of Fe nitride do not taken place in diffusion layer region, are in solid solution condition among the Fe of nitrogen in parent phase.Thereafter, in the process of cooling after soaking keeps, if speed of cooling is little, then the nitrogen of diffusion layer region can solid solution in parent phase, the diffusion of γ ' nitride, grows up.On the other hand, if strengthen speed of cooling, then the hypersaturated state solid solution takes place in the nitrogen of diffusion layer region in parent phase, and γ ' nitride is separated out, growing up is suppressed.Yet, even strengthen speed of cooling, if the temperature with 100～200 ℃ keeps for a long time after cooling, then as the α of metastable phase " nitride still can separate out; in addition,, this α then if under this temperature, keep for a long time " nitride is phase-changed into γ ' nitride.When such nitride was separated out, fatigue strength reduced.Particularly γ ' nitride makes the effect of fatigue strength reduction obvious.
In the present invention, in order to suppress separating out of γ ' nitride, resultful method is that soaking temperature is not increased to more than 1.0 ℃/second to 200 ℃ the speed of cooling that γ ' nitride separates out can not take place, and more preferably makes speed of cooling more than 1.5 ℃/second.In addition, when adopting oil quenching, make the oil temperature below 100 ℃, and use the oil groove of the big thermal capacity that heat radiation with mechanical component can fully take place, perhaps once deduct the counting etc. of part of processing, do not make long-time (more than 30 minutes) in the refrigerating work procedure of part after tufftride is handled to remain on 100～200 ℃ temperature range therefrom, note this point guarantee on the high-fatigue strength also very important.
During from soaking temperature cool to room temperature that gas soft nitriding is handled, reduce, generally adopt the speed of cooling oil cooling littler (oil quenching) than water-cooled in order to make quenching strain.In addition, the oil temperature of refrigerant is changed, use the different various heat-treated oils of proterties.In addition, in the gas soft nitriding of industry is handled, for the reason in operating efficiency and the security, directly to oil groove, do not carry out oil quenching from the processing atmosphere of meeting RX gas and ammonia, and be handled thing to be pulled out to the space that is full of by other rare gas elementes mostly, and then in oil groove, carry out oil quenching from satisfying the process furnace of handling atmosphere quickly.
Carry out the refrigerating work procedure in the soaking temperature of handling from such gas soft nitriding, for example, if handled thing is pulled out to another space from 580 ℃ processing atmosphere, then remain in 100 ℃ the oil groove and carry out oil cooling, then in diffusion layer, confirm γ ' nitride and α " nitride.It is the reasons are as follows.
1) handled thing before oil cooling by conveyance to other spatial stages, the temperature of handled thing is reduced to about 400 ℃ from 580 ℃, because speed of cooling at this moment is little, so cause separating out of γ ' nitride.
2) handled thing be immersed in for a long time 100 ℃ oil groove during, the α of metastable phase " nitride and then cause separating out of above-mentioned γ ' nitride.
Thereby, even when carrying out such process of cooling, also must strengthen handled thing and before oil cooling, be arrived the speed of cooling of another space under this stage by conveyance, be immersed in for a long time in the pyritous oil groove to avoid handled thing.
[embodiment 1]
Explain the present invention by the following examples.
Behind the steel 180kg with the chemical ingredients shown in the vacuum melting stove melting table 1, steel billet is heated to 1200 ℃, can be lower than that 1000 ℃ state carries out heat forged and the pole that becomes diameter 50mm with the steel temperature.Cooling after the heat forged is by cold the carrying out of putting in atmosphere.Extract the test film that test film, sublevel pole pliability test sheet and plane fatigue-bending test that microstructure observation uses are used from this pole.
[table 1] is for the chemical constitution (mass%) of examination steel
No. C Si Mn Ti N Nb Mo Cu Ni S Ca B Cr V Bainite divides rate
Example of the present invention 1 0.38 0.15 0.80 0.010 0.020 -- -- -- -- -- -- -- -- -- 7％
2 0.35 0.14 0.79 0.011 0.018 0.011 0.20 -- -- -- -- -- -- -- 42％
3 0.32 0.20 0.82 0.018 0.021 -- -- 0.28 0.17 -- -- -- -- -- 20％
4 0.38 0.16 0.85 0.022 0.028 0.007 0.25 -- -- 0.052 0.0012 0.0031 -- -- 65％
5 0.40 0.20 0.84 0.007 0.017 -- 0.16 -- -- 0.082 0.0015 -- -- -- 15％
6 0.41 0.21 0.80 0.011 0.018 -- 0.18 -- -- -- -- -- 0.10 0.015 60％
Comparative example 7 0.38 0.27 0.50 0.006 0.011 -- -- -- -- 0.046 -- -- 0.10 -- 0％
8 0.42 0.14 0.91 -- 0.010 -- -- -- -- -- -- -- 0.51 0.12 22％
9 0.36 0.20 1.10 0.012 0.018 0.040 0.95 -- -- 0.050 -- -- 0.20 0.01 ＞90％
"--" expression is not the element that adds intentionally in the table, is illustrated in below the common composition analysis precision.
Each element such as following: Ti:＜0.002%, Nb:＜0.001%, Mo:＜0.01%, Cu:＜0.01%, Ni:＜0.01%, S:＜0.01%, Ca:＜0.001%, B:＜0.001%, Cr:0.05%, V:＜0.01%.
The test film that microstructure observation uses cuts off its part, with the micro organization under the observation by light microscope heat forged state of 200 times of multiplying powers, measures bainite and divides rate (area occupation ratio).The zone that is defined as bainite is, surrounds the zone that has bamboo foliate bainite ferrite with the successive closed curve, and calculate according to the area occupation ratio with respect to whole visuals field area in this zone.The bainite branch rate merging of each steel grade is displayed in Table 1.The steel of No.7 is not seen bainite in ferrite and pearlitic tissue.In addition, the steel bainite branch rate of No.9 surpasses 90%, and generates martensite.The test film that the surplus of the test film that microstructure observation uses is used with the plain bending fatigue test carries out tufftride to be handled, with the micro organization of scanning electron microscope (SEM) observation diffusion layer, and the size of investigation γ ' nitride.The size of γ ' nitride is the size of the length direction of the longest viewed γ ' nitride when taking 10 visuals field with 1000 times multiplying power.
Sublevel pole pliability test sheet is that the central part diameter is thicker than two ends, the shape of section difference that wide 10mm is arranged, is 15mm at the diameter of centre portion, and the diameter of main part is 10mm, and the part turning of section difference is the curvature of 2mm in addition.Sublevel pole test film is carried out to the part additional strain instrument of this curvature, carrying out the detorsion test according to the main points of three-point bending after tufftride handles.Detorsion is to the central part applying load time, and the punching press stroke that reaches broken string according to strain gage is estimated.The punching press stroke reaches 3mm, and strain gage ruptures not yet, and to be judged to be detorsion good.
The plain bending fatigue test piece is the neck (recess diameter 20mm) that is processed with tapering on the columned main body of diameter 44mm.This test film is carried out after tufftride handles, and the head side of restraint test sheet is opposing to carry out the plain bending fatigue test thus by the end load repeated load of side.
In tufftride is handled, use RX gas: the gas soft nitriding under the atmosphere of ammonia=1: 1 is handled.Soaking temperature is 600 ℃, and the hold-time under the soaking temperature is 2 hours.Be through with the experiment slice of equal thermal treatment by conveyance quickly to being separated with adjustment doors (shutter) with equal hot cell and being adjusted in another chamber of nitrogen atmosphere, afterwards, be inserted in the oil groove of the bottom that is installed in this another chamber and carry out oil cooling.At this moment, make from conveyance to another chamber to change to the time of inserting oil groove, thereby the degree of separating out, growing up of γ ' nitride is changed.The oily temperature of oil groove is 80～150 ℃ the interior specified temperature of scope, and the test film time in the oil groove that is maintained at is 10～90 minutes interior specified time of scope behind the oil cooling.Be under the state of nitrogen atmosphere in whole stove, utilize point to be welded in the Pt-Rh thermopair on the surface of the test film that the plain bending fatigue test uses, measure the speed of cooling of carrying out the refrigerative refrigerating work procedure from soaking temperature.This be because, atmosphere (the RX gas of handling at the gas soft nitriding of reality: ammonia=1: 1), have the damage problem of thermopair.When measuring, test film is changed to the time of inserting oil groove, for the arrival temperature of at this moment test film with reach synthermal speed of cooling and noted and measure to another chamber from equal hot cell by conveyance.
In table 2, show about size, fatigue strength and the detorsion end of the γ ' nitride of each steel grade.In remarks column, the maintenance hundred after merging has shown the speed of cooling from the refrigerating work procedure of the soaking temperature of gas soft nitriding processing and comprised oil cooling remains on the time more than 100 ℃.
[table 2] each evaluation result for size, fatigue strength and the detorsion of the γ ' nitride of examination steel
For the examination steel The size of γ ' nitride [μ m] Fatigue strength [MPa] Detorsion * [mm] Remarks
Average cooling rate [℃/second] from soaking temperature to 200 ℃ Hold-time more than 100 ℃ [minute]
Example of the present invention 1 5.2 570 5.5 2 10
2 3.5 660 3.9 2 10
3 4 620 4.7 2 10
4 3.6 630 3.8 2 10
5 5.3 570 5.4 2 10
6 3.8 660 3.2 2 10
1 11.5 550 6.1 1.2 20
2 8.8 600 4.5 1.2 20
3 9.2 580 5.1 1.2 20
4 9.4 590 4.2 1.2 20
5 10.7 550 6 1.2 20
6 9 610 3.7 1.2 20
1 7.8 560 5.8 1.8 15
2 6.2 650 3.9 1.8 15
3 6.7 600 4.8 1.8 15
4 6.8 610 4 1.8 15
5 7.6 560 5.6 1.8 15
6 6.4 650 3.3 1.8 15
Comparative example 7 8.2 510 4.5 1.8 15
8 7.3 600 1.7 1.8 15
9 4.2 650 1.2 1.8 15
1 27.0 490 6.5 0.8 60
2 23.5 520 5.6 0.8 60
3 26.0 510 5.9 0.8 60
4 22.0 515 5.7 0.8 60
5 27.5 480 6.6 0.8 60
6 25.5 530 5.6 0.8 60
1 35.0 450 7.1 0.4 15
2 28.5 490 6.8 0.4 15
3 30.0 480 6.6 0.4 15
4 24.5 485 6.4 0.4 15
5 33.5 450 6.9 0.4 15
6 30.5 500 6 0.4 15
7 32.0 430 8.1 0.4 15
8 29.5 500 6.1 0.4 15
9 25.5 510 5.8 0.4 15
*The value that be pressed into path increment (mm) of strain agent when broken string.
It is good for being judged as detorsion more than the 3mm.
Show as table 2, in the present invention, can access the fatigue strength that is categorized as the standard of high-intensity category as omitting normalizing type: equal with 550MPa, perhaps high-fatigue strength more than it and good detorsion (more than the crooked stroke 3mm).
On the other hand, because the speed of cooling under the gas soft nitriding processing is little, so surpass under the such situation of 20 μ m in the size of γ ' nitride, fatigue strength reduces equally.The representational tissue that in Fig. 3, has shown the diffusion layer when being dispersed with γ ' nitride.At this, among the figure shown in the arrow is thick especially γ ' nitride.
In addition, if break away from the present invention,, still have fatigue strength and reduce, perhaps the result of detorsion difference even then the size of γ ' nitride is below 20 μ m as the chemical ingredients and the micro organization of the non-hardened and tempered steel of former material.
[the altogether upper possibility of utilizing of industry]
As above, according to the present invention, take non-hardened and tempered steel as former material, can access the high-intensity soft nitrided component of fatigue strength and detorsion excellence. Therefore, can cut down the part cost of manufacture.

Claims (2)

1. soft nitrided component, be that following non-hardened and tempered steel is carried out the soft nitrided component that tufftride is handled, this non-hardened and tempered steel contains C:0.30～0.45% in quality %, Si:0.1～0.5%, Mn:0.6～1.0%, Ti:0.005～0.1% and N:0.010～0.030%, surplus is made of Fe and impurity, and, this non-hardened and tempered steel has the mixed structure that is made of bainite and ferrite or by bainite, the mixed structure that ferrite and perlite constitute, bainite branch rate in its mixed structure is 5～90%, this soft nitrided component is characterised in that, the length direction that is present in the γ ' nitride in the ferrite crystal grain of its diffusion layer is of a size of below the 20 μ m.
2. soft nitrided component, be that following non-hardened and tempered steel is carried out the soft nitrided component that tufftride is handled, this non-hardened and tempered steel contains C:0.30～0.45% in quality %, Si:0.1～0.5%, Mn:0.6～1.0%, Ti:0.005～0.1% and N:0.010～0.030%, and contain from the element more than a kind of following first groups of elements selection, and in the element more than a kind from second groups of elements, selected one or two, surplus is made of Fe and impurity, and, this non-hardened and tempered steel has the mixed structure that is made of bainite and ferrite or by bainite, the mixed structure that ferrite and perlite constitute, bainite branch rate in its mixed structure is 5～90%, this soft nitrided component is characterised in that, the length direction that is present in the γ ' nitride in the ferrite crystal grain of its diffusion layer is of a size of below the 20 μ m
First groups of elements:
Nb：0.001～0.1％、
Mo：0.01～1.0％、
Cu：0.01～1.0％、
Ni:0.01～1.0%, and
B：0.001～0.005％，
Second groups of elements:
S:0.01～0.1% and
Ca：0.0001～0.005％。
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