CN114250412A - High strength carburized steel with improved durability - Google Patents
High strength carburized steel with improved durability Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 48
- 239000010959 steel Substances 0.000 title claims abstract description 48
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims abstract description 87
- 239000011651 chromium Substances 0.000 claims abstract description 84
- 239000011572 manganese Substances 0.000 claims abstract description 45
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 31
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 25
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 20
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 18
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 15
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 11
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 11
- 239000010703 silicon Substances 0.000 claims abstract description 9
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims abstract description 8
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims abstract description 6
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims abstract description 6
- 239000011733 molybdenum Substances 0.000 claims abstract description 6
- 239000010955 niobium Substances 0.000 claims description 18
- 239000010936 titanium Substances 0.000 claims description 18
- 229910052758 niobium Inorganic materials 0.000 claims description 10
- 229910052719 titanium Inorganic materials 0.000 claims description 10
- 229910052720 vanadium Inorganic materials 0.000 claims description 10
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 7
- 229910052796 boron Inorganic materials 0.000 claims description 7
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims description 7
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 claims description 7
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 6
- -1 i.e. Inorganic materials 0.000 claims 13
- 238000005255 carburizing Methods 0.000 abstract description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 47
- 230000000052 comparative effect Effects 0.000 description 21
- 229910052742 iron Inorganic materials 0.000 description 21
- 238000005452 bending Methods 0.000 description 18
- 230000000694 effects Effects 0.000 description 18
- 230000001965 increasing effect Effects 0.000 description 13
- 229910001566 austenite Inorganic materials 0.000 description 10
- 238000009826 distribution Methods 0.000 description 10
- 150000001247 metal acetylides Chemical class 0.000 description 9
- 239000011159 matrix material Substances 0.000 description 8
- 230000007797 corrosion Effects 0.000 description 7
- 238000005260 corrosion Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 230000001603 reducing effect Effects 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 6
- 238000011156 evaluation Methods 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- 229910001567 cementite Inorganic materials 0.000 description 5
- 230000002708 enhancing effect Effects 0.000 description 5
- 230000002829 reductive effect Effects 0.000 description 5
- 230000000717 retained effect Effects 0.000 description 5
- 230000003247 decreasing effect Effects 0.000 description 4
- 229910000734 martensite Inorganic materials 0.000 description 4
- 239000002131 composite material Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 230000000087 stabilizing effect Effects 0.000 description 3
- 238000005496 tempering Methods 0.000 description 3
- 229910019819 Cr—Si Inorganic materials 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- 229910017112 Fe—C Inorganic materials 0.000 description 1
- 229910005093 Ni3C Inorganic materials 0.000 description 1
- 229910008071 Si-Ni Inorganic materials 0.000 description 1
- 229910006300 Si—Ni Inorganic materials 0.000 description 1
- 206010062544 Tooth fracture Diseases 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 125000002091 cationic group Chemical group 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 230000006798 recombination Effects 0.000 description 1
- 238000005215 recombination Methods 0.000 description 1
- 239000012779 reinforcing material Substances 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
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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
- C22C38/04—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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- 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
- C23C8/20—Carburising
- C23C8/22—Carburising of ferrous surfaces
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Abstract
The invention discloses a carburizing steel, which comprises the following components in percentage by weight based on the total weight of the carburizing steel: 0.1 wt% or more and 0.3 wt% or less of C (carbon); 2.0 to 2.7 wt% of Cr (chromium); 0.4 wt% or more and 0.7 wt% or less of Si (silicon); 0.3 to 0.7 wt% of Mo (molybdenum); less than 0.6 wt% Mn (manganese); and 0.6 wt% or more and 1.5 wt% or less of Ni (nickel).
Description
Technical Field
The present disclosure relates to a carburized steel, and more particularly, to a high-strength carburized steel for vehicle components having improved durability.
Background
Generally, a gear of a transmission of a vehicle is a member for directly transmitting engine power to a differential system and efficiently transmitting the engine power between two or more shafts according to a driving state of the vehicle, which is simultaneously subjected to bending stress, contact stress, and the like. With the above-described gears, if the durability of the material is insufficient, fatigue fracture (tooth fracture) due to lack of bending fatigue strength and fatigue damage (pitting corrosion) due to lack of contact fatigue strength often occur. Therefore, the above gears require physical properties such as high hardness, strength, toughness, fatigue strength, and fatigue life.
The durability of carburized steel for vehicle components used as a countermeasure to this is improved by 1) increasing the high-hardness carbide fraction by increasing Cr, and 2) increasing the matrix structure strength and softening resistance by increasing Si.
However, when the content of Cr/Si is increased, the pitting initiation time point causing surface damage by carbide and hardness increasing effect is improved, but there is a tendency that crack propagation and bending strength are significantly reduced due to the matrix structure toughness reducing effect caused by Cr/Si.
The matter described in the background is for background to aid in understanding the present disclosure and may include matter not previously known to those of skill in the art to which the present disclosure pertains.
Disclosure of Invention
The present disclosure is intended to solve the above-mentioned problems, and an object of the present disclosure is to provide a case hardening steel capable of simultaneously ensuring bending strength and pitting corrosion resistance.
A high strength carburized steel according to one aspect of the present disclosure includes, based on the total wt% of the carburized steel: 0.1 wt% or more and 0.3 wt% or less of C (carbon); 2.0 to 2.7 wt% of Cr (chromium); 0.4 wt% or more and 0.7 wt% or less of Si (silicon); 0.3 to 0.7 wt% of Mo (molybdenum); less than 0.6 wt% Mn (manganese); and 0.6 wt% or more and 1.5 wt% or less of Ni (nickel).
The content of Si (silicon) may be 0.6 wt% or more and 0.7 wt% or less.
The Ni (nickel) content may be 0.6 wt% or more and 1.0 wt% or less.
The Mn (manganese) content may be 0.1 wt% or more and 0.5 wt% or less.
The carburized steel may further contain one or more of Ti (titanium), V (vanadium), and Nb (niobium).
The sum of the contents of Ti (titanium), V (vanadium), and Nb (niobium) may be 1.0 wt% or less with respect to the total wt%.
The carburized steel may further contain 1 to 30ppm of B (boron).
In the case of the case hardening steel according to the present disclosure, the value of the following formula may be 0.2 or more,
([Ni]+0.3[Mn])/([Cr]+3[Si])，
wherein [ Ni ], [ Mn ], [ Cr ], [ Si ] represent the wt% of Ni, Mn, Cr, Si, respectively.
A carburized steel according to another aspect of the present disclosure, comprising, based on total wt% of the carburized steel: 0.1 wt% or more and 0.3 wt% or less of C (carbon); 2.0 to 2.7 wt% of Cr (chromium); 0.4 wt% or more and 0.7 wt% or less of Si (silicon); 0.3 to 0.7 wt% of Mo (molybdenum); less than 0.6 wt% Mn (manganese); 0.6 wt% or more and 1.5 wt% or less of Ni (nickel); 1.0 wt% or less of the sum of Ti (titanium), V (vanadium) and Nb (niobium); and 1 to 30ppm of B (boron). The value of the following formula is 0.2 or more, ([ Ni ] +0.3[ Mn ])/([ Cr ] +3[ Si ]), wherein [ Ni ], [ Mn ], [ Cr ], [ Si ] represent the wt% of Ni, Mn, Cr, Si, respectively.
The content of Si (silicon) may be 0.6 wt% or more and 0.7 wt% or less.
The Ni (nickel) content may be 0.6 wt% or more and 1.0 wt% or less.
The Mn (manganese) content may be 0.1 wt% or more and 0.5 wt% or less.
The carburized hardness is 780Hv or more, and the bending strength may be 3,000MPa or more.
The high strength carburized steel according to the present disclosure may improve bending strength by 10% or more and improve carburized layer hardness by 20Hv or more, compared to conventional steels, thereby achieving durability.
In general, conventional high-durability carburized steel is improved in strength and durability by increasing the content of Cr-Si, in which case strong brittleness (Cr, Fe) is generated due to the toughness-reducing effect of Si7C3And a base carbide, and therefore the overall material tends to be brittle. The present disclosure optimizes the Ni/Mn content also in a relatively low Cr/Si range based on the ratio of (Ni +0.3Mn)/(Cr +3Si) to ensure toughness of the matrix structure, thereby inhibiting the diffusion of fatigue cracks to ensure both strength and toughness.
Further, the carburizing performance can be significantly improved by reducing the contents of Cr and Si, so that the carburizing heat treatment can be achieved only by gas carburizing without applying a preheating treatment, thus saving costs such as heat treatment costs.
Further, the present disclosure is not achieved by Cr carbides having high hardness as in conventional steels, but the contents of Ni and Mn may be controlled by Cr having a low content, thereby securing toughness of a matrix structure and improving strength and hardness, particularly suppressing the propagation of fatigue cracks, thereby remarkably improving durability.
Therefore, the fatigue life can be improved to reduce surface pitting caused by fatigue fracture, thereby suppressing an increase in transmission noise.
Drawings
FIG. 1 shows hardness, Fe according to Cr content3C. High temperature (Cr, Fe)7C3And (4) carbide distribution.
FIG. 2 shows impact toughness, Fe, as a function of Si content3C. High temperature (Cr, Fe)7C3And (4) carbide distribution.
Fig. 3 shows the distribution of bulk retained austenite according to the Ni content, and fig. 4A and 4B are texture pictures showing the distribution of bulk retained austenite.
FIG. 5 shows Fe according to the content of Mo3C and high temperature (Mo, Ni, Fe) complex carbide distribution.
Fig. 6A to 6F show pitting generation amount evaluation result images under severe conditions.
Fig. 7A to 7C show pitting generation amount evaluation result images in the flat condition (flat conditions).
Fig. 8A shows a microstructure according to comparative example 8, fig. 8B shows a microstructure according to example 1, and fig. 8C shows a microstructure according to example 8.
Detailed Description
For a fuller understanding of the present disclosure, its operating advantages, and the objects obtained by its implementation, reference should be made to the accompanying drawings, which illustrate exemplary embodiments of the disclosure and to the contents thereof.
In describing exemplary embodiments of the present disclosure, descriptions or duplicate descriptions of known technologies that can unnecessarily obscure the subject matter of the present disclosure will be reduced or omitted.
An object of the present disclosure is to provide a case hardening steel capable of simultaneously securing a bending strength and a pitting corrosion resistance strength exceeding the conventional limits as a case hardening steel for vehicle parts manufactured by subjecting a steel material to a carburizing heat treatment, quenching, tempering, or the like.
To this end, a carburized steel according to an exemplary embodiment of the present disclosure includes 0.1 wt% or more and 0.3 wt% or less of C (carbon), 2.0 wt% or more and 2.7 wt% or less of Cr (chromium), 0.4 wt% or more of Si (silicon), 0.3 wt% or more and 0.7 wt% or less of Mo (molybdenum), less than 0.6 wt% of Mn (manganese), 0.6 wt% or more and 1.5 wt% or less of Ni (nickel), 1.0 wt% or less of Ti (titanium) + V (vanadium) + Nb (niobium), and 1 to 30ppm of B (boron) with respect to 100 wt% (wt%) of the total component, and may include the balance of Fe (iron) and impurities; further, since the value of ([ Ni ] +0.3[ Mn ])/([ Cr ] +3[ Si ]) satisfies 0.2 or more, no network carbide is formed in the carburized layer; the carburized steel has a carburization hardness (Hv) of 780Hv or more and a bending strength of 3,000MPa or more.
Here, [ Ni ], [ Mn ], [ Cr ], [ Si ] denote the wt% of Ni, Mn, Cr, Si, respectively.
That is, this relates to a new Cr-Si-Ni carburized steel component system that can improve pitting corrosion resistance and bending strength by increasing toughness, as compared to conventional high-durability high Cr-Si carburized steels.
In the prior art, there is a carburized steel component system having improved durability compared to conventional materials by securing substantial toughness using Mn and increasing the content of Cr — Si that is advantageous for controlling carbides.
However, since the prior art is highly likely to excessively lower toughness by the Si content of 2% at the maximum, the present disclosure utilizes a method of increasing Ni having better effect than Mn, rather than optimizing the Si content of lowering the toughness of the material in a low range, thereby improving the toughness of the matrix structure, thus realizing a method of utilizing the effect of controlling the formation of Cr — Si carbide, thereby securing durability.
Hereinafter, each component and content will be described in more detail with reference to fig. 1 to 5.
FIG. 1 shows hardness, Fe according to Cr content3C. High temperature (Cr, Fe)7C3And (4) distribution of composite carbides. Cr is an alloying element that is generally added to ensure hardenability of the material, but ranges are optimized in the present disclosure to determine the type and formation temperature of precipitated carbides, as well as hardenability. According to the disclosure, as carbides influenced by Cr contentThree types: fe3C/(Fe,Cr)3C/(Fe,Cr)7C3。
1)Fe3C: the carbide is the most basic carbide in the Fe-C component system formed at the temperature below A1 (730 ℃). In the case of martensite, Fe is intentionally suppressed by optimizing the heat treatment, particularly the tempering condition, in order to achieve high strength3The precipitation of C thereby supersaturates C, but in many parts the supersaturated C combines with Fe due to heat generated during use to form Fe3C, thereby lowering the strength of the matrix structure, so that Si-delayed Fe is generally added in many cases3And C is precipitated.
2)(Fe,Cr)3C: when the content of Cr having a higher affinity for C than Fe is increased, (Fe, Cr) is formed3C, carbide of carbon. (Fe, Cr)3C is precipitated in a region of 800℃ or more higher than a1 temperature, thereby ensuring stability even during the carburizing heat treatment, and also reducing available carbon contained in the matrix structure, thereby suppressing additional formation of Fe during use3C。
3)(Fe,Cr)7C3: when Cr is further increased, (Fe, Cr) is formed7C3And not (Fe, Cr)3C。(Fe,Cr)7C3Transition carbides formed at high temperatures but classified as unstable, and C is used excessively in precipitation, thereby further reducing strength.
If Cr is added less than 2.0%, the present disclosure may not sufficiently form stable (Fe, Cr) at high temperature during carburization3C-based carbides.
As a result, Fe is formed during use3The total amount of C exceeds 1% and rapid softening occurs, so the lower limit of Cr in the present disclosure is 2.0%.
In contrast, if more than 2.7% of Cr is added, the carbide formation due to Cr is very activated to form (Fe, Cr) having instability and strong brittleness in spite of the high temperature of 900 ℃ or more7C3To reduce the amount of available carbon and thereby reduce the surface hardness enhancing effect. Thus, in this disclosure, up to CrThe limit is 2.7%.
Next, FIG. 2 shows impact toughness, Fe, according to Si content3C. High temperature (Fe, Cr)7C3And (4) carbide distribution.
As is well known, Si is a complex of Fe and Si3An element having a cationic solubility (cation solubility) of C cementite of 0. That is, Fe may not be formed around Si element3C, due to this effect, most of the martensite containing Si is very effective in suppressing the formation of Fe during use3C, and the hardness is reduced. However, when less than 0.4% Si is added, Fe3The content of C cannot be effectively suppressed to less than 1% to be disadvantageous in securing hardness, so the lower limit of Si in the present disclosure is 0.4%.
Another effect of Si is to increase the reactivity (activity) of C upon addition, thereby suppressing Fe3C, but promotes another form of carbide forming reaction. It has been demonstrated that in the component system according to the present disclosure, to suppress Fe3C, Si is added, but when the Si content exceeds 0.7%, an unstable high temperature (Fe, Cr) is formed due to a recombination with Cr7C3Thereby reducing the amount of usable carbon, and thus is rather disadvantageous for ensuring hardness, and even if Ni is added, toughness tends not to be sufficiently ensured.
Therefore, the upper limit of Si in the present disclosure is 0.7%, and more preferably 0.6 wt% or more and 0.7 wt% or less.
Next, fig. 3 shows the distribution of bulk retained austenite according to the Ni content, and fig. 4A and 4B are structure pictures showing the distribution of bulk retained austenite.
In the present disclosure, Ni is an important element for achieving the expected reduction in the propagation speed of fatigue cracks due to the reinforcing material toughness. In particular, since Cr/Si has a greater effect of reducing the toughness of the matrix structure than Ni, in order to achieve the effect of enhancing the toughness by Ni, it is necessary to optimize the Ni/Mn content in consideration of the synergistic effect of Ni and Mn which has the same effect although the relative effect and content are small, on the basis of the Cr/Si content.
The toughness-reducing effect is required to consider the effects of Cr and Si at the same time, and it can be confirmed that the present disclosure can ensure the effect of sufficiently enhancing toughness only when 0.2 or more is satisfied according to the evaluation results based on (Ni +0.3Mn)/(Cr +3 Si).
When the content of Ni exceeds 1.5%, bulk austenite begins to exist at room temperature due to the strong austenite stabilizing effect of Ni, thereby decreasing the fraction of martensite formed at the time of heat treatment, thus improving toughness, but causing an adverse effect of decreasing strength. Therefore, the upper limit of Ni in the present disclosure is 1.5%.
Further, Ni is a toughness-enhancing improving element and a hardenability-improving element, and when the content of Ni is less than 0.6%, the toughness is reduced, resulting in an increase in the propagation speed of fatigue cracks and a reduction in fatigue life.
Therefore, the Ni content is required to be 0.6 wt% or more and 1.5 wt% or less, and more preferably 0.6 wt% or more and 1.0 wt% or less.
Next, FIG. 5 shows Fe according to the content of Mo3Distribution of C and high temperature (Mo, Ni, Fe) complex carbides. The (Mo, Ni, Fe) composite carbide may be (Mo, Ni, Fe)2C or (Mo, Ni, Fe)6C carbide.
Mo is a suppression of Fe at tempering by high affinity with C3C forms and causes micronization to enhance homogeneity. In addition, Mo also serves to delay the movement of the potential to enhance the strength and toughness of the material. However, when less than 0.3% of Mo is added, Fe is hardly suppressed3C and does not cause an effect of micronization, thereby not achieving a hardness enhancing effect, so the lower limit of Mo in the present disclosure is 0.3%.
On the other hand, when Mo exceeds 0.7%, Mo reacts with Ni and forms (Mo, Ni, Fe) -based composite carbides at high temperatures, reducing the amount of available carbon, so that a phenomenon occurs in which the surface hardness is again decreased.
Therefore, the upper limit of Mo in the present disclosure is 0.7%.
It is well known that Mn is an austenite stabilizing element capable of enhancing toughness, similar to Ni, although its effect is about 1/3 level. In addition, Mn has the effect of hardenability and toughness similar to those of Ni, but because of the austenite stabilizing effect caused by Ni already sufficiently contained, when the content of Mn exceeds 0.6%, a phenomenon occurs in which the martensite fraction decreases while bulk austenite is stabilized at room temperature, resulting in a decrease in hardness.
Therefore, the upper limit of Mn in the present disclosure is 0.6%, and more preferably 0.1 wt% or more and 0.5 wt% or less.
Nb/Ti/V is an alloy element having a large strength improvement effect by forming MC-based carbide at high temperature to miniaturize grain boundaries and enhance precipitation. However, since Nb/Ti/V is formed at a higher temperature than Cr carbide, when Nb/Ti/V is excessively added, there is a tendency to decrease the amount of Cr carbide required for improving durability, which is desired by the present disclosure. Therefore, the total of Nb/Ti/V is limited to 1% or less.
It is known that B (boron) is an element that effectively suppresses ferrite formation during cooling to improve hardenability even in a small amount. However, due to the property that B is preferentially located in grain boundaries, the grain boundaries are weakened when B is excessively added, and thus the content of B in the present disclosure is limited to 1 to 30 ppm.
Hereinafter, test examples and experimental results by examples and comparative examples within the composition range according to the present disclosure will be described.
The test examples are shown in table 1 below.
TABLE 1
It can be seen that examples 1 to 10 all satisfy the target values of the carburized hardness and the bending strength when the value of (Ni +0.3Mn)/(Cr +3Si) is 0.2 or more, and examples 1 and 8 can be referred to as best examples when the carburized hardness and the bending strength are determined comprehensively.
Further, embodiment 6 is an example in which Mo is added in embodiment 1, and embodiment 7 is an example in which Mn is decreased in embodiment 1.
Next, example 9 is an example of applying the upper limit value of Ni based on example 8, and example 10 is an example of applying the upper limit value of most components.
On the other hand, comparative example 1 shows a result of low carburized hardness because Mo is smaller than that of example 1, and comparative example 2 shows a result of low carburized hardness because Mo is larger than that of example 1.
It can be seen that Mn of comparative example 3 is greater than Mn of example 1, thus showing the result that carburized hardness and bending strength are small, Ni of comparative example 4 is less than Ni of example 1 and the value of (Ni +0.3Mn)/(Cr +3Si) is less than 0.2, thus showing the result that bending strength is small.
Next, it can be seen that Ni of comparative example 5 is larger than Ni of example 1 and thus shows a result that carburized hardness is small, Cr of comparative example 6 is larger than Cr of example 1 and a value of (Ni +0.3Mn)/(Cr +3Si) is less than 0.2 and thus shows a result that bending strength is small, Si of comparative example 7 is larger than Si of example 1 and (Ni +0.3Mn)/(Cr +3Si) is less than 0.2 and thus shows a result that bending strength is small.
Further, Ni of comparative example 8 is smaller than Ni of example 1 and the value of (Ni +0.3Mn)/(Cr +3Si) is smaller than 0.2, thus showing a result of small bending strength, Cr of comparative example 9 is smaller than Cr of example 1, thus showing a result of small carburized hardness and bending strength, and comparative example 10 adopts the upper limit value of most components and Ni is larger than Ni of example 1, showing a result of small carburized hardness.
Fig. 6A to 6F show pitting generation amount evaluation result images under severe conditions, in which fig. 6A shows the results of example 1, fig. 6B shows the results of example 2, fig. 6C shows the results of comparative example 4, fig. 6D shows the results of comparative example 5, fig. 6E shows the results of comparative example 6, and fig. 6F shows the results of comparative example 8.
Test method the planetary gear assembly evaluation apparatus may be used to test the sun gear, the pinion gear, and the carrier and apply 400Nm of torque to the carrier to drive the planetary gear formed of the carburized steel of the present disclosure at a speed of 4,000RPM based on the sun gear for 24 hours and then disassemble the planetary gear and confirm the pitting generation state of the gear surface.
As can be seen from the results, it was visually confirmed that the pitting corrosion generation amounts of comparative examples 4, 5, 6, 8 were larger than those of examples 1 and 2.
Further, fig. 7A to 7C show pitting generation amount evaluation result images in a flat condition, in which fig. 7A shows the results of example 1, fig. 7B shows the results of example 2, and fig. 7C shows the results of comparative example 8.
Here, the flat condition means a level lower than the severe condition in fig. 6A to 6F, and it is possible to drive the planetary gear formed of the carburized steel of the present disclosure at a speed of 3,000RPM based on the sun gear for 24 hours by applying a torque of 300Nm to the carrier by the same test method as the severe condition and then disassemble the planetary gear, and confirm the pitting corrosion generation state of the gear surface.
As can be seen from the results, it was visually confirmed that the amount of pitting corrosion generation of comparative example 8 was larger than that of examples 1 and 2.
As described above, the exemplary embodiments of the present disclosure may improve bending strength by 10% or more and improve carburized layer hardness by 20Hv or more, compared to conventional steel, thereby achieving durability.
Fig. 8A shows a microstructure according to comparative example 8, fig. 8B shows a microstructure according to example 1, and fig. 8C shows a microstructure according to example 8.
FIG. 8A shows a 2.4Cr-0.7Si-0.08Ni steel in comparative example 8, and bulk retained austenite can be confirmed; FIG. 8B shows the 2.0Cr-0.6Si-0.7Ni steel in example 1, and it can be seen that Fe3The size and fraction of C is reduced by the increase of Ni.
Further, FIG. 8C shows 2.7Cr-0.7Si-1.0Ni in example 8Steel, and it was confirmed that Fe was increased due to Cr + Ni3C is suppressed at grain boundaries, and (Cr, Fe)7C3Formed into a number of particles.
As described above, the present disclosure has been described with reference to the exemplary drawings, but the present disclosure is not limited to the described exemplary embodiments, and it will be apparent to those skilled in the art that various modifications and changes may be made to the present disclosure without departing from the spirit and scope of the present disclosure. Accordingly, these modified examples or changed examples fall within the claims of the present disclosure, and the scope of the present disclosure should be construed based on the appended claims.
Claims (11)
1. A carburized steel comprising, based on the total wt% of the carburized steel:
0.1 to 0.3 wt% of C (carbon);
2.0 to 2.7 wt% of Cr (chromium);
0.4 to 0.7 wt% of Si, i.e., silicon;
0.3 to 0.7 wt% of Mo, i.e., molybdenum;
less than 0.6 wt% Mn, i.e., manganese; and
0.6 to 1.5 wt% of Ni, i.e., nickel.
2. Carburized steel according to claim 1 further comprising one or more of Ti, i.e., titanium, V, i.e., vanadium, and Nb, i.e., niobium.
3. Carburized steel according to claim 2, wherein the sum of Ti, i.e., titanium, V, i.e., vanadium, and Nb, i.e., niobium, is 1.0 wt% or less with respect to the total wt% of the carburized steel.
4. Carburized steel according to claim 1 further comprising 1 to 30ppm of B, boron.
5. A carburized steel according to claim 1, wherein a value of the following formula is 0.2 or more,
([Ni]+0.3[Mn])/([Cr]+3[Si])，
wherein [ Ni ], [ Mn ], [ Cr ], [ Si ] represent the wt% of Ni, Mn, Cr, Si, respectively.
6. A carburized steel comprising, based on the total wt% of the carburized steel:
0.1 to 0.3 wt% of C (carbon);
2.0 to 2.7 wt% of Cr, namely chromium, and 0.4 to 0.7 wt% of Si, namely silicon;
0.3 to 0.7 wt% of Mo, i.e., molybdenum;
less than 0.6 wt% Mn, i.e., manganese; 0.6 to 1.5 wt% of Ni, i.e., nickel;
less than 1.0 wt% Ti, i.e. titanium, V, i.e. the sum of vanadium and Nb, i.e. niobium; and
1 to 30ppm of B, i.e. boron,
wherein the value of the following formula satisfies 0.2 or more,
([Ni]+0.3[Mn])/([Cr]+3[Si])，
wherein [ Ni ], [ Mn ], [ Cr ], [ Si ] represent the wt% of Ni, Mn, Cr, Si, respectively.
7. The carburized steel according to claim 1 or 6, wherein the Si is silicon in an amount of 0.6 wt% or more and 0.7 wt% or less.
8. The carburized steel according to claim 1 or 6, wherein the Ni is nickel in an amount of 0.6 wt% or more and 1.0 wt% or less.
9. Carburized steel according to claim 1 or 6, wherein the Mn content is 0.1 wt% or more and 0.5 wt% or less.
10. The carburized steel of claim 1 or 6, wherein the carburized steel has a carburized hardness of 780Hv or more.
11. The carburized steel of claim 1 or 6, wherein the carburized steel has a flexural strength of 3,000MPa or more.
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| KR1020200123021A KR20220040153A (en) | 2020-09-23 | 2020-09-23 | Carburizing steel improved durability |
| KR10-2020-0123021 | 2020-09-23 |
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|---|---|---|---|---|
| JP2001329338A (en) * | 2000-05-17 | 2001-11-27 | Sanyo Special Steel Co Ltd | Case hardening steel excellent in bending strength |
| CN102317490A (en) * | 2009-03-30 | 2012-01-11 | 新日本制铁株式会社 | Carburized steel part |
| CN104024444A (en) * | 2011-11-01 | 2014-09-03 | 新日铁住金株式会社 | Method for producing steel part |
| CN106048456A (en) * | 2015-04-14 | 2016-10-26 | 现代自动车株式会社 | Carburized alloy steel having improved durability and method of manufacturing the same |
| CN106065455A (en) * | 2015-04-20 | 2016-11-02 | 现代自动车株式会社 | There is carburizing alloy steel and the manufacture method thereof of the durability of improvement |
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| KR20160069595A (en) | 2014-12-08 | 2016-06-17 | 현대자동차주식회사 | Carburizing alloy steel having superior durability and the method of manufacturing the same |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2001329338A (en) * | 2000-05-17 | 2001-11-27 | Sanyo Special Steel Co Ltd | Case hardening steel excellent in bending strength |
| CN102317490A (en) * | 2009-03-30 | 2012-01-11 | 新日本制铁株式会社 | Carburized steel part |
| CN104024444A (en) * | 2011-11-01 | 2014-09-03 | 新日铁住金株式会社 | Method for producing steel part |
| CN106048456A (en) * | 2015-04-14 | 2016-10-26 | 现代自动车株式会社 | Carburized alloy steel having improved durability and method of manufacturing the same |
| CN106065455A (en) * | 2015-04-20 | 2016-11-02 | 现代自动车株式会社 | There is carburizing alloy steel and the manufacture method thereof of the durability of improvement |
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