CN100519811C - Steel for mechanical parts, method for producing mechanical parts from said steel and mechanical parts obtained by using the steel and method - Google Patents

Steel for mechanical parts, method for producing mechanical parts from said steel and mechanical parts obtained by using the steel and method Download PDF

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CN100519811C
CN100519811C CNB2005800140260A CN200580014026A CN100519811C CN 100519811 C CN100519811 C CN 100519811C CN B2005800140260 A CNB2005800140260 A CN B2005800140260A CN 200580014026 A CN200580014026 A CN 200580014026A CN 100519811 C CN100519811 C CN 100519811C
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steel
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carburizing
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CN1950533A (en
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P·达吉耶
P·迪耶里克
C·皮沙尔
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Ascometal SA
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/04—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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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

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Abstract

The inventive steel for mechanical parts is characterised by the composition thereof expressed in the following percentages by weight: 0.19 % = C = 0.25 %; 1.1 % = Mn = 1.5 %; 0.8 % = Si = 1.,2 %; 0.01 % = S = 0.09 %; traces = P = 0.025 %; traces = Ni = 0.25 %; 1 % = Cr = 1.4 %; 0.10 % = Mo = 0,25 %; traces = Cu = 0.30 %; 0.01 % = Al = 0.045 %; 0.010 % = Nb = 0.045 %; 0.0130 % = N = 0.0300 %; optionally traces = Bi = 0.10 % and/or traces = Pb = 0.12 % and/or traces = Te = 0.015 % and/or traces = Se = 0.030 % and/or traces = Ca = 0.0050 %. The rest being iron and impurities resulting from preparation, a chemical composition being adjusted in such a way that mean values J3m, J11m, J15m et J25m of five Jominy tests are such as alpha = | J11m - J3m x 14/22 - J25m x 8/22 |= 2.5 HRC; and ss = J3m - J15m = 9 HRC. A method for producing a mechanical part from said steel and the thus obtainable mechanical part are also disclosed.

Description

The steel that is used for mechanical part is by the method and the thus obtained mechanical part of described steel production machinery parts
Technical field
The present invention relates to the ferrous metallurgy field, more specifically, relate to the steel that is used for mechanical part such as pinion(gear).
Background technology
The steel that is used for the gear manufacturing must have high-caliber contact resistance fatigability.In most cases, parts by these steel productions carry out the carburizing or carbonitriding processing, described processing is intended to provide enough surface hardness and physical strengths to them, keeps high-caliber core intensity simultaneously, and this is especially owing to the about carbon content of 0.10-0.30% only.The carbon content of cementation zone can be up to about 1%.
Various file descriptions expection made steel by the gear of carburizing.These files comprise US-A-5518685, and wherein the content of Si and Mn remains in the relative low limit (being respectively 0.45-1% and 0.40-0.70%), to prevent the intergranular oxidation in the carburizing operating process.JP-A-4-21757 has described and has been used for the steel that gear is made, and its expection is used plasma body or under reduced pressure by carburizing, carried out shot peening then, and it can have the Si that is higher than aforementioned steel and the content of Mn.They have the character that high-caliber tolerance acts on the surface pressure on the pinion(gear), have increased the time limit of service of pinion(gear) thus.
WO-A-03 012 156 has proposed to be used for the steel of mechanical part such as pinion(gear), and it consists of: 0.12%≤C≤0.30%; 0.8%≤Si≤1.5%; 1.0%≤Mn≤1.6%; 0.4%≤Cr≤1.6%; Mo≤0.30%; Ni≤0.6%; A1≤0.06%; Cu≤0.30%; S≤0.10%; P≤0.03%; Nb≤0.050%.The advantage of this steel is that the operation viscous deformation of parts integral body is minimized, and this is especially owing to the appropriate balance of silicon and manganese content.Carburizing or carbonitriding must preferably carry out under non-oxide condition, and for example under reduced pressure, thereby the relative high-content of silicon and manganese can not cause the problem of intergranular oxidation.
Usually, carburizing or carbonitriding carries out under about 850-930 ℃ temperature.But present trend is to attempt under about 950-1050 ℃ higher temperature (high temperature carburizing or carbonitriding) to carry out this operation.The rising of this processing temperature can make the length of process period reduce under the situation of identical carburized depth, perhaps can under the situation of identical process period of length carburized depth be increased.Therefore the manufacturer can select, so that improve the productivity of equipment or the validity of the raising product that obtains.
But, high temperature carburizing or carbonitriding operational applications are being appearred during to the known steel described many problems.The first, high temperature may cause controlling insufficient crystal grain to be increased, and its mechanical property to parts is harmful.The second, quench after the carburizing or carbonitriding, parts stand distortion in quenching process.These may require parts by mechanical workout again, perhaps cause it to be abandoned under extreme case.When quenching on the parts that just carried out over carburizing or carbonitriding operation under high temperature and improper temperature, these problems are particularly serious.
Summary of the invention
The objective of the invention is that especially the high temperature carburizing of pinion(gear) or the metallargist of carbonitriding provide a kind of steel in order to carry out mechanical part, described steel has overcome the problems referred to above, the physical strength that keep to need simultaneously, and its also with normal temps under the carburizing carried out compatible with the carbonitriding operation.
For this reason, theme of the present invention is the steel that is used for mechanical part, it is characterized in that it consists of, by weight percentage:
-0.19％≤C≤0.25％；
-1.1％≤Mn≤1.5％；
-0.8％≤Si≤1.2％；
-0.01％≤S≤0.09％；
-trace≤P≤0.025%;
-trace≤Ni≤0.25%;
-1％≤Cr≤1.4％；
-0.10％≤Mo≤0.25％；
-trace≤Cu≤0.30%;
-0.010％≤Al≤0.045％；
-0.010％≤Nb≤0.045％；
-0.0130％≤N≤0.0300％；
-randomly, trace≤Bi≤0.10% and/or trace≤Pb≤0.12% and/or trace≤Te≤0.015% and/or trace≤Se≤0.030% and/or trace≤Ca≤0.0050%; Surplus is an iron and by the impurity that production operation produces, and regulates the mean value J that this chemical constitution makes five Jominy tests 3m, J 11mJ 15mAnd J 25mFor:
α=| J 11m-J 3m* 14/22-J 25m* 8/22|≤2.5HRC; With
β＝J 3m-J 15m≤9HRC。
Preferably, regulating it forms feasible
β＝J 3m-J 15m≤8HRC。
Preferably, it consists of:
-0.19％≤C≤0.25％；
-1.2％≤Mn≤1.5％；
-0.85％≤Si≤1.2％；
-0.01％≤S≤0.09％；
-trace≤P≤0.025%;
-0.08％≤Ni≤0.25％；
-1.1％≤Cr≤1.4％；
-0.10％≤Mo≤0.25％；
-0.06％≤Cu≤0.30％；
-0.010％≤Al≤0.045％；
-0.015％≤Nb≤0.045％；
-0.0130％≤N≤0.0300％；
Randomly, trace≤Bi≤0.07% and/or trace≤Pb≤0.12% and/or trace≤Te≤0.010% and/or trace≤Se≤0.020% and/or trace≤Ca≤0.045%, surplus is iron and the impurity that produced by production operation.
Optimally, it consists of:
-0.20％≤C≤0.25％；
-1.21％≤Mn≤1.45％；
-0.85％≤Si≤1.10％；
-0.01％≤S≤0.08％；
-trace≤P≤0.020%;
-0.08％≤Ni≤0.20％；
-1.10％≤Cr≤1.40％；
-0.11％≤Mo≤0.25％；
-0.08％≤Cu≤0.30％；
-0.010％≤Al≤0.035％；
-0.025％≤Nb≤0.040％；
-0.0130％≤N≤0.0220％；
Randomly, trace≤Bi≤0.07% and/or trace≤Pb≤0.12% and/or trace≤Te≤0.010% and/or trace≤Se≤0.020% and/or trace≤Ca≤0.045%, surplus is iron and the impurity that produced by production operation.
Theme of the present invention also is a kind of method that is used for by the steel production machinery parts of carburizing or carbonitriding, it is characterized in that using the steel of the above-mentioned type to be used for this purpose, it is carried out machining operations, and hardening step is carried out in carburizing operation or carbonitriding operation then.
This carburizing or carbonitriding preferably carries out under 950-1050 ℃ temperature.
Theme of the present invention also is the steel mechanical part, as geared parts, it is characterized in that these parts obtain by aforesaid method.
Should be appreciated that the present invention is based on the adjusting of the content range of main alloy element, and the aluminium, niobium and the nitrogen that exist content clearly to limit simultaneously.
Desired effects is two kinds basically.The first, the content of main alloy element selects expection to obtain not have the Jominy curve of fairly obvious flex point.This condition can make and obtain minimum distortion in the hardening step process.In this respect, as already mentioned, at high temperature the carburizing or carbonitriding that carries out especially needs.
Be noted that the Jominy curve of the steel that uses conventional criteria test generation can characterize the hardenability of steel.It is to produce by the hardness of measuring cylindrical test block along one of its generating apparatus, and this test block has used the aqueous jet of spraying the one end to quench.Locating to measure hardness from the several of injected end apart from x (in mm), and corresponding value representation is J xJ XmBe meant at distance x place and measure the mean value that obtains in 5 tests of hardness.
As disclosed among the file EP-A-0 890 653 (reader can obtain further details with reference to this document), the applicant proves, in order to produce the distortion that significantly reduces in the hardening step process after the carburizing or carbonitriding operation, the composition that produces the steel of the Jominy curve that does not have flex point is favourable.J on duty 11m, J 3m, J 25mAnd J 15mWhen satisfying following the relation, produce this Jominy curve that does not have flex point:
-α＝|J 11m-J 3m×14/22-J 25m×8/22|≤2.5HRC；
-β=J 3m-J 15m≤ 9HRC or preferred≤8HRC.
Therefore regulate the composition of steel of the present invention, thereby also produce this relation in this case.
Also regulate this composition, especially the combination owing to aluminium, niobium and the nitrogen of determining content exists, thereby makes grain-size keep Be Controlled, even at high temperature carry out under the situation of carburizing or carbonitriding operation.
At last, described steel is formed the use that is necessary for parts certainly provides desired mechanical characteristics.The standard of monitoring more specifically comprises carburized depth when being 550HV (be normally defined measured hardness the degree of depth), (it must be low as far as possible for the surface of carburized component and the hardness deviation between the core, so that the minimizing deformation in the quenching process), and core hardness (it must be high, so that parts are the stress in the operation response process effectively, and therefore have favorable durability and fatigue resistance).
Description of drawings
By reading following description, and will understand the present invention better with reference to the accompanying drawings, accompanying drawing is represented the Jominy curve of four kinds of reference steel and three kinds of steel of the present invention.
Embodiment
Steel of the present invention is mainly used in produces mechanical part such as the teeth parts that stand high-level stress, and this mechanical part is expected under about 850-930 ℃ the normal temps and carries out carburizing or carbonitriding (preferably under low pressure or in non-oxidizing atmosphere, oxidized to prevent most of oxidizable element) under about 950-1050 ℃ the temperature.These parts must have high antifatigue, high strength, and slight deformation only in the hardening step process after thermal treatment such as carburizing or carbonitriding.It has following composition (all per-cents all are weight percents).
Its carbon content is 0.19-0.25%.It is normal that these content are made steel for gear.And this scope makes it possible to regulate the content of other element, and this makes the Jominy curve can produce desired shape.Proved further that by the core hardness that after quenching, can obtain 0.19% minimum content is appropriate.Greater than 0.25% o'clock, then exist hardness too high so that can not keep the risk of the desired machinability of steel.Preferable range is 0.20-0.25%.
Its manganese content is 1.1-1.5%.Proved that by obtain desirable Jominy curve in conjunction with other constituent content this minimum value is appropriate.Greater than 1.5% o'clock, then there is the risk that segregation occurs and zonal structure in the annealing operation process, occurs.And so high-content will cause the refractory coating excessive corrosion of steel teeming ladle in the production operation process.It is undesirable further limiting this content range, may be extremely difficult because obtain desirable accurate steel grade at steelworks.Preferable range is 1.2-1.5%, preferred 1.21-1.45%.
Its silicone content is 0.8-1.2%.In this scope, can obtain desirable Jominy curve shape in conjunction with other constituent content.Core hardness by producing expectation and proved that by the hardness deviation between limiting surface and the core after carburizing or carbonitriding 0.8% minimum value is appropriate.Greater than 1.2% o'clock, then there is the risk that excessive segregation occurs, though because only segregation a little of silicon itself tends to strengthen other elements segregation.The risk of oxidation increases in the carburizing or carbonitriding process in addition.Preferable range is 0.85-1.20%, preferred 0.85-1.10%.
Its sulphur content is 0.01-0.09%, has proved that by producing suitable machining property minimum value is appropriate.Greater than 0.09% o'clock, then there is the excessively risk of reduction of hot forging property.Preferable range is 0.01-0.08%.
Phosphorus content is a trace to 0.025%.Usually, existing standard often needs the maximum phosphorus content of this grade.In addition, when surpassing this value, then exist and the interactional risk of niobium, this makes the steel of Steel Bloom or steel ingot form become fragile in thermoforming and/or continuous casting process.Phosphorus content preferably at the most 0.020%.
Its nickel content is trace to 0.25%.Having a mind to will unnecessarily increase the metal cost with this element that high level is introduced.In practice, be enough from the unearned nickel content of the raw-material fusing of casting, do not need to have a mind to add.Preferable range is 0.08-0.20%.
Its chromium content is 1.00-1.40%.In this scope,, can produce the Jominy curve shape of expectation in conjunction with the content of other element.And 1.00% minimum content can produce high-caliber core hardness.Greater than 1.40% o'clock, the production operation cost will unnecessarily increase.Preferable range is 1.10-1.40%.
Its molybdenum content is 0.10-0.25%.In this scope,, can produce the Jominy curve shape and the core hardness of expectation in conjunction with the content of other element.Preferable range is 0.11-0.25%.
Its copper content is trace to 0.30%.Still in this case, with the same, keep the content that is produced after the starting material fusion usually fully and simply at nickel.Greater than 0.30% o'clock, will damage the ductility and the core intensity of parts.Preferable range is 0.06-0.30%, and preferred 0.08-0.30% is to optimize the Jominy curve shape and the hardness afterwards of quenching.
Its aluminium, niobium and nitrogen content must be controlled in the limit of accuracy.These elements can cause the fineness control of metal grain when interacting.This fineness is desirable, and purpose is in order to cause the high strength of carburizing or carbonitriding layer, distortion dispersive minimizing in high fatigue resistance and the quenching process.And it also is important for the Jominy curve shape that produces expectation.In the context of the present invention, the control grain-size is more importantly, because steel must at high temperature stand the carburizing or carbonitriding operation, and the excessive increase of grain-size does not take place.
Described crystal grain control utilizes the nitride of aluminium and/or niobium and separating out of carbonitride to carry out basically.In order to produce this control, therefore need a large amount of these two kinds of elements that exist, and apparently higher than the nitrogen content of the content that carries out under normal operation usually being produced after the production operation.
Aluminium content is necessary for 0.010-0.045%.Except its above-mentioned crystal grain control action kou, the deoxidation of this element control steel and the cleanliness factor of oxide inclusion thereof.Less than 0.010% o'clock, from above angle, it acts on deficiency.Greater than 0.045% o'clock, there is insufficient risk in the cleanliness factor of oxide inclusion for the application of main expection.Preferable range is 0.010-0.035%.
Content of niobium is necessary for 0.010-0.045%.Less than 0.010% o'clock, the effect of crystal grain control is deficiency, especially for the aluminium of minimum content.Greater than 0.045% o'clock, then in the continuous casting process of steel, exist and fissured risk occurs, when the interaction with phosphorus especially if possible took place, this was as discussed above.Preferable range is 0.015-0.045%, preferred 0.015-0.040%.
In conjunction with the content of described aluminium and niobium, nitrogen content is necessary for 0.0130-0.0300% (130-300ppm), thereby the expectation that realizes grain-size and Jominy curve shape is regulated.Preferable range is 0.0130-0.0220%.
If desired, but Xiang Gangzhong adds known one or more elements usually, to improve its machinability: especially lead, tellurium, selenium, calcium, bismuth.Maximum level is 0.10% for Bi, is preferably 0.07%, is 0.12% for Pb, is 0.015% for Te, is preferably 0.010%, is 0.030% for Se, is preferably 0.020%, is 0.0050% for Ca, is preferably 0.0045%.
Other element is usually to be present in those elements in the steel as the impurity that is produced by production operation, and they are not to have a mind to add.Especially must guarantee that titanium content is no more than 0.005%.Because steel of the present invention is rich in nitrogen very much, exceeding this content will have the risk that forms thick titanium nitride and/or titanium carbonitride (these materials can be seen by microscope), and this will reduce fatigue resistance and damage machinability.And titanium is thus with capturing nitrogen, and then nitrogen will no longer can be used in control crystal grain.
To utilize embodiment that the present invention is described now.Accompanying drawing is depicted as the Jominy curve of four kinds of steel, and the composition of described four kinds of steel is listed in table 1.Steel A, B, C and D are reference steel.Steel E, F and G are steel of the present invention.
Table 1: the composition of sample
Steel C％ Mn％ Si％ S％ P％ Ni％ Cr％ Mo％ Cu％ Al％ Ti％ Nb％ N％
A (reference) 0.236 0.888 0.224 0.015 0.011 0.011 1.194 0.014 0.010 0.021 Trace Trace 0.0124
B (reference) 0.195 1.188 0.069 0.023 0.012 0.208 1.228 0.096 0.162 0.021 Trace 0.030 0.0179
C (reference) 0.192 1.205 0.845 0.029 0.014 0.080 0.995 0.099 0.110 0.025 Trace 0.011 0.0110
D (reference) 0.245 1.215 0.840 0.035 0.012 0.085 0.980 0.103 0.098 0.035 Trace 0.012 0.0090
E (the present invention) 0.230 1.287 0.920 0.018 0.017 0.201 1.269 0.200 0.211 0.032 Trace 0.025 0.0174
F (the present invention) 0.201 1.453 1.191 0.041 0.014 0.139 1.381 0.246 0.122 0.031 0.002 0.038 0.0243
G (the present invention) 0.241 1.254 0.852 0.015 0.010 0.189 1.121 0.111 0.109 0.012 Trace 0.016 0.0141
For sample A, value α equals 8.7 as defined above, and value β equals 19.1 as defined above.Therefore they are higher than the maximum value of requirement of the present invention far away.Can find out that the Jominy curve has very significantly flex point.
For sample B, α equals 2.38, and β equals 11.1.Therefore the requirement of the discontented unabridged version invention of β, and Jominy curve also has tangible flex point, though this ladle is contained in niobium and nitrogen in the aforesaid limits.The fundamental cause of this situation is its silicone content deficiency.
For sample C, α equals 3.38, and β equals 10.7.Not in the limit of regulation, the Jominy curve has tangible flex point for α and β.Cr and Mo just are lower than required minimum value, especially the nitrogen content deficiency.
For sample D, α equals 2.845, and β equals 9.5, and it is again outside prescribed limit.Because Cr and nitrogen contain quantity not sufficient, the Jominy curve has tangible flex point.
But for sample E according to the present invention, α equals 0.41, and β equals 2.7.Required condition is met, and can find out, the Jominy curve almost is linearly, does not have flex point.
In an identical manner, for sample F according to the present invention, α equals 0.23, and β equals 3.7.In this case, its Jominy curve also almost is linearly, does not have flex point.
In an identical manner, for sample G according to the present invention, α equals 0.83, and β equals 6.6.Its Jominy curve almost is linearly, does not have obvious flex point.
Steel A, B and the character of E in cementation process in the table 1 under normal temperature conditions and under the high temperature, have also been studied.
Carburizing under the normal temps (930 ℃) operates in low pressure and uses under the conditions of similarity of cylindrical sample and carry out, to give 0.75% carbon content at carburized surface.After these carburizings operation, then in gas phase media, (be in this case in nitrogen, but for example can use the nitrogen/hydrogen mixture that comprises 10% hydrogen), at two kinds of different pressure conditions: carry out hardening step under 5 crust and 20 cling to.Therefore expection obtains the surface hardness of 700-800HV and the carburized depth (that is to say the degree of depth when hardness is 550HV) of 0.50mm.The result provides in table 2 (in test under 5 crust) and table 3 (test under 20 crust).
Table 2: the carburizing character when under 5 crust, quenching in the gas phase media
Steel Surface hardness HV Carburized depth (mm) The core hardness HV of carburized zone outside
A (reference) 760 0.35 263
B (reference) 760 0.50 408
E (the present invention) 780 0.48 426
Table 3: the carburizing character when under 20 crust, quenching in the gas phase media
Steel Surface hardness HV Carburized depth (mm) The core hardness HV of carburized zone outside
A (reference) 780 0.45 318
B (reference) 720 0.55 423
C (reference) 738 0.53 408
E (the present invention) 750 0.55 524
These test specifications, reference steel A can not easily obtain the carburized depth expected.This is because it lacks hardenability.
These three kinds of steel of reference steel B and C and steel E of the present invention all can produce the carburized depth of expection under the normal temperature conditions of carburizing.
For the quenchant under 5 crust, the deviation delta HV between surface hardness and the core hardness is very suitable for reference steel B and steel E of the present invention (Δ HV equals 352 and 354 respectively), and more much lower than reference steel A (Δ HV=497).But for the quenchant under 20 crust, Δ HV compares steel E of the present invention (Δ HV equals 297,330 and 226 respectively) significant adverse for reference steel B and C.The result is that these hardness deviations produce unrelieved stresss, and this causes deforming when carburized component quenches under stringent condition, but this unrelieved stress the application of the invention steel and minimizing.
At last, steel E of the present invention produces the core hardness of highest level.Therefore, for the geared parts that in operating process, stands high-level stress, and seek high-caliber mechanical property (especially under cementation zone and) in the high-level hardness at core place for this geared parts, it is bigger than the stress that parts stand in operating process, in order to guarantee the high-level fatigue resistance in the operating process, steel of the present invention is suitable for the high-level fatigue resistance in the operating process most under given car-burization condition.
The carburizing test is also being carried out on the cylindrical sample of above-mentioned reference steel A and D and steel E of the present invention under the high temperature (980 ℃).In this case, carburized surface has 0.75% carbon content again.In both cases, seek the carburized depth of 0.50mm under the surface hardness of 700-800HV and the 550HV hardness.Quenching after the carburizing in gas phase media (nitrogen) is carried out under the pressure of 20 crust for steel A and D, only carries out under 1.5 crust for steel E.The result lists in table 4.The evaluation of grain-size also provides according to the ASTM standard.
Table 4: the carburizing character when 20 crust (steel A and C) and 1.5 crust (steel E) quench down in gas phase media
Steel Surface hardness HV Carburized depth (mm) The core hardness HV of carburized zone outside Grain-size ASTM in the cementation zone The grain-size ASTM that cementation zone is outer
A (reference) 740 0.50 312 7/9 8/9
D (reference) 735 0.59 461 7/8 8/9
E (the present invention) 740 0.70 500 8/9 9/10
For the operation of the carburizing under 930 ℃ normal temps, two kinds of surface hardnesses that steel can obtain to expect.
The present invention can produce obvious ratio with reference to the bigger carburized depth of A, though quench under much stricter condition with reference to A, known this can increase carburized depth, and wherein all others are identical.
Hardness deviation between surface and the core is compared to reference to A and D (Δ HV equals 240 for E respectively, equals 428 for A, equals 274 for D) obviously littler for the present invention.Above-mentionedly also further be reinforced in this case about the advantage aspect the distortion in the quenching process after the carburizing under normal temps.
It is higher that core hardness is compared to reference steel for the present invention, though the pressure of quenchant is much lower.Result aspect the fatigue resistance raising in the aforesaid operations process of also finding in this case under normal temps, to quench.
At last, in cemented zone and outside the cemented zone, the steel capital of the present invention has than reference steel A and the thinner ASTM grain-size of D.Therefore, it is not easy to the risk that grain-size increases in the cementation process under the high temperature more.This is very important advantage, because the increase of grain-size has very injurious effects to the fatigue resistance at place, tusk bottom and the intensity of carburized component on the carburized component.Therefore steel of the present invention is suitable for producing at high temperature fully by the geared parts of carburizing or carbonitriding (or need any other parts of the suitable character), and this brings all economical advantage, and the validity of sacrifice mems by any way not.
Other carburizing test is also under low pressure carried out on reference steel A and steel E of the present invention.
For after be the low-pressure carburization operation that 20 crust carry out on steel A under 930 ℃ of gas quenching down, need 72 minutes carburizing, be the expection carburized depth of 0.50mm to produce for HV=550.Use steel E of the present invention, for after be the down low-pressure carburizations under 930 ℃ of gas quenchings (with for the identical gas of steel A) of 1.5 crust, it is the identical carburized depth of 0.50mm that 30 minutes carburizing is enough to produce for HV=550.
For the low-pressure carburization that carries out on reference steel A under 980 ℃ the high temperature, the gas quenching under carburizing that needs 30 minutes and 20 crust is the expection carburized depth of 0.50mm to produce for HV=550.980 ℃ are enough to produce for HV=550 for steel E of the present invention with the following 20 minutes carburizing time of low pressure is the identical carburized depth of 0.5mm, and gas quenching is only carrying out under 1.5 pressure that cling to.Certainly, the quenching gas that is used for steel A and E is identical.
This shows that steel E of the present invention can both reduce carburizing time down at normal carburizing temperature (930 ℃) and high temperature (980 ℃), and this can reduce carburizing cost (amount of carburizing gas, carburizing time ...), and can improve the productivity of producing carburized component.
Steel of the present invention is because its controlled hardenability can also reduce the pressure of quenching gas, to produce identical carburized depth, this can further reduce or eliminate the distortion in the carburized component, and can obtain to save and simplify by the technical elements of gas quenching parts in the chamber of gas quenching furnace.
Under low pressure and high temperature (980 ℃), also there be not the shock strength sample (size: L=55mm of otch, carry out carburizing on the cross section 10 * 10mm), on reference steel A, carrying out before the gas quenching under the pressure of 20 crust on the one hand, on steel E of the present invention, carry out on the other hand, but under the pressure of 1.5 crust only, carry out before the gas quenching in this case.The carburized depth of expectation is identical, because the type of quenching gas is identical.Then, ruptured by at room temperature impacting by the sample of carburizing and quenching by this way.Energy result during the fracture that obtains by this way is respectively:
-for reference steel A, 19 joules,
-for steel E of the present invention, 29 joules.
Simultaneously, the shock strength sample of reference steel A is in low pressure and normal temps (930 ℃) carburizing down, to obtain identical carburized depth as above.They are quenched under the pressure of 20 crust with identical gas then.As above at room temperature make these sample breakage then, the energy the during fracture that obtains by this way is 17 joules, that is to say that the steel E of the present invention that is compared to carburizing at high temperature is much smaller.
This shows, though the core hardness of the sample of reference steel A (312HV) is lower than steel E of the present invention (500HV), for identical final carburized depth, the toughness of the steel E of carburizing at high temperature is higher than the reference steel A of carburizing under high temperature or normal temps.That is to say, the high temperature carburizing operation of using steel of the present invention to expect to produce specific carburized depth and the toughness of using reference steel to compare can not to damage the carburized component of producing by this steel, wherein this reference steel also under high temperature or normal carburizing temperature carburizing to obtain identical carburized depth.The difference of core hardness aspect is not disadvantageous in this regard between two kinds of steel.This shows that also steel of the present invention is particularly suitable for the carburizing under the high temperature, compares with the known steel of carburizing under normal temps or high temperature, and steel of the present invention reduces carburizing time, boosts productivity and reduces the carburizing cost.The use character (as toughness) that these parts obtained is compared with reference steel and is without prejudice.
Under these conditions, also in low pressure and high temperature (980 ℃) carburizing down, pericardium is drawn together the U-shaped otch of widening to tired crooked (fatigue-flexion) sample of steel E of the present invention therein.Be the gas quenching under 1.5 bar pressures only after the carburizing, expection carburized depth and quenching gas type are all with identical at the test of shock strength sample.In an identical manner, carrying out the gas carburizing under 930 ℃ the normal carburizing temperature on the steel A according to prior art, to obtain as above identical carburized depth, the gas cementation of carrying out on the crooked sample of fatigue is identical with steel E's.After carburizing, they are carried out oil quenching operation, with the hardness and the intensity of the tired crooked aspect that improves steel A.Then to two batch samples of the steel E of carburizing in this way and A at 4 points relatively in the safe range of stress of fatigue aspect crooked, wherein these samples widens the U-shaped otch at the center according to the zone of the crooked applying load of fatigue.Every kind of steel A and E to carburizing and quenching in the above conditions carry out tired crooked test up to 1,000 ten thousand circulations.
Under these conditions, the safe range of stress under 1,000 ten thousand circulations is the 1405MPa of steel E of the present invention, and steel A only is 1165MPa.
This shows, use steel of the present invention to expect that the high temperature carburizing operation of the specific carburized depth of acquisition can't damage the intensity of tired crooked aspect, on the contrary, compare with the normal carburizing operation of on the steel in prior art under the normal carburizing temperature, carrying out, it is very favorable on the contrary, the steel of wherein said prior art by carburizing to the identical degree of depth and at oil quenching, to improve the intensity of its tired crooked aspect.
What should replenish in this is that these tired crooked tests are intended to simulate wheel tooth bottom, gear mechanism that uses in the motor vehicle gearbox or geared parts.This also shows, steel of the present invention is particularly suitable for high temperature carburizing, with under normal temps the known steel of carburizing compare, steel of the present invention reduces carburizing time, boosts productivity, reduces the carburizing cost, and do not damage the use properties of utilizing parts to obtain, as the intensity of the tired crooked aspect of the wheel tooth carburizing bottom of pinion(gear) or gear mechanism.

Claims (10)

1, be used for the steel of mechanical part, it is characterized in that, it consists of, by weight percentage:
-0.19％≤C≤0.25％；
-1.1％≤Mn≤1.5％；
-0.8％≤Si≤1.2％；
-0.01％≤S≤0.09％；
-trace≤P≤0.025%;
-trace≤Ni≤0.25%;
-1％≤Cr≤1.4％；
-0.10％≤Mo≤0.25％；
-trace≤Cu≤0.30%;
-0.010％≤Al≤0.045％；
-0.010％≤Nb≤0.045％；
-0.0130％≤N≤0.0300％；
-randomly, trace≤Bi≤0.10% and/or trace≤Pb≤0.12% and/or trace≤Te≤0.015% and/or trace≤Se≤0.030% and/or trace≤Ca≤0.0050%;
Surplus is an iron and by the impurity that production operation produces, and regulates the mean value J that this chemical constitution makes five Jominy tests 3m, J 11m, J 15mAnd J 25mFor:
α=| J 11m-J 3m* 14/22-J 25m* 8/22|≤2.5HRC; With
β＝J 3m-J 15m≤9HRC。
2, according to the steel that is used for mechanical part of claim 1, it is characterized in that, regulate it and form feasible
β＝J 3m-J 15m≤8HRC。
3, according to the steel that is used for mechanical part of claim 1 or 2, it is characterized in that it consists of:
-0.19％≤C≤0.25％；
-1.2％≤Mn≤1.5％；
-0.85％≤Si≤1.2％；
-0.01％≤S≤0.09％；
-trace≤P≤0.025%;
-0.08％≤Ni≤0.25％；
-1.1％≤Cr≤1.4％；
-0.10％≤Mo≤0.25％；
-0.06％≤Cu≤0.30％；
-0.010％≤Al≤0.045％；
-0.015％≤Nb≤0.045％；
-0.0130％≤N≤0.0300％；
-randomly, and trace≤Bi≤0.07% and/or trace≤Pb≤0.12% and/or trace≤Te≤0.010% and/or trace≤Se≤0.020% and/or trace≤Ca≤0.0045%, surplus is iron and the impurity that produced by production operation.
4, according to the steel that is used for mechanical part of claim 3, it is characterized in that, its be made into into
-0.20％≤C≤0.25％；
-1.21％≤Mn≤1.45％；
-0.85％≤Si≤1.10％；
-0.01％≤S≤0.08％；
-trace≤P≤0.020%;
-0.08％≤Ni≤0.20％；
-1.10％≤Cr≤1.40％；
-0.11％≤Mo≤0.25％；
-0.08％≤Cu≤0.30％；
-0.010％≤Al≤0.035％；
-0.025％≤Nb≤0.040％；
-0.0130％≤N≤0.0220％；
-randomly, and trace≤Bi≤0.07% and/or trace≤Pb≤0.12% and/or trace≤Te≤0.010% and/or trace≤Se≤0.020% and/or trace≤Ca≤0.0045%, surplus is iron and the impurity that produced by production operation.
5, a kind of method that is used for by the steel production machinery parts of carburizing is characterized in that using according to each steel among the claim 1-4 being used for this purpose, and it is carried out machining operations, and hardening step is carried out in the carburizing operation then.
According to the method for claim 5, it is characterized in that 6, described carburizing is carried out under 950-1050 ℃ temperature.
7, a kind of method that is used for by the steel production machinery parts of carbonitriding is characterized in that using according to each steel among the claim 1-4 being used for this purpose, and it is carried out machining operations, and hardening step is carried out in the carbonitriding operation then.
According to the method for claim 7, it is characterized in that 8, described carbonitriding is carried out under 950-1050 ℃ temperature.
9, the steel mechanical part is characterized in that, it is by obtaining according to each method among the claim 5-8.
According to the mechanical part of claim 9, it is characterized in that 10, it is a geared parts.
CNB2005800140260A 2004-03-24 2005-03-21 Steel for mechanical parts, method for producing mechanical parts from said steel and mechanical parts obtained by using the steel and method Expired - Fee Related CN100519811C (en)

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