KR101766039B1 - Austenitic heat resistant bolt and method of manufacturing the same - Google Patents
Austenitic heat resistant bolt and method of manufacturing the same Download PDFInfo
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- KR101766039B1 KR101766039B1 KR1020150132068A KR20150132068A KR101766039B1 KR 101766039 B1 KR101766039 B1 KR 101766039B1 KR 1020150132068 A KR1020150132068 A KR 1020150132068A KR 20150132068 A KR20150132068 A KR 20150132068A KR 101766039 B1 KR101766039 B1 KR 101766039B1
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- rolling
- high temperature
- bolt
- tensile strength
- austenite
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- 238000004519 manufacturing process Methods 0.000 title claims description 18
- 238000005096 rolling process Methods 0.000 claims abstract description 41
- 239000011572 manganese Substances 0.000 claims abstract description 35
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 32
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 26
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims abstract description 15
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 15
- 238000005242 forging Methods 0.000 claims abstract description 11
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 10
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 9
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 9
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 9
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 9
- 239000010703 silicon Substances 0.000 claims abstract description 9
- 239000012535 impurity Substances 0.000 claims abstract description 8
- 230000000087 stabilizing effect Effects 0.000 claims abstract description 8
- 238000005097 cold rolling Methods 0.000 claims abstract 2
- 239000000463 material Substances 0.000 claims description 13
- 239000011247 coating layer Substances 0.000 claims description 12
- 238000000034 method Methods 0.000 claims description 12
- CWQXQMHSOZUFJS-UHFFFAOYSA-N molybdenum disulfide Chemical compound S=[Mo]=S CWQXQMHSOZUFJS-UHFFFAOYSA-N 0.000 claims description 12
- 229910052982 molybdenum disulfide Inorganic materials 0.000 claims description 12
- 150000004767 nitrides Chemical class 0.000 claims description 11
- 229910019142 PO4 Inorganic materials 0.000 claims description 9
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 claims description 9
- 239000010452 phosphate Substances 0.000 claims description 9
- 238000010438 heat treatment Methods 0.000 claims description 5
- 239000011248 coating agent Substances 0.000 claims description 4
- 238000000576 coating method Methods 0.000 claims description 4
- 239000012778 molding material Substances 0.000 claims description 4
- 238000004381 surface treatment Methods 0.000 claims description 4
- 239000010410 layer Substances 0.000 claims 2
- 239000011651 chromium Substances 0.000 abstract description 18
- 229910052748 manganese Inorganic materials 0.000 abstract description 15
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 abstract description 8
- 229910052804 chromium Inorganic materials 0.000 abstract description 8
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 abstract description 4
- 229910052750 molybdenum Inorganic materials 0.000 abstract description 4
- 239000011733 molybdenum Substances 0.000 abstract description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 84
- 229910052759 nickel Inorganic materials 0.000 description 29
- 230000000052 comparative effect Effects 0.000 description 21
- 230000006641 stabilisation Effects 0.000 description 16
- 238000011105 stabilization Methods 0.000 description 16
- 230000000694 effects Effects 0.000 description 7
- 229910045601 alloy Inorganic materials 0.000 description 6
- 239000000956 alloy Substances 0.000 description 6
- 230000008569 process Effects 0.000 description 6
- 230000000704 physical effect Effects 0.000 description 4
- 229910000831 Steel Inorganic materials 0.000 description 3
- 238000005266 casting Methods 0.000 description 3
- 230000007797 corrosion Effects 0.000 description 3
- 238000005260 corrosion Methods 0.000 description 3
- 239000010959 steel Substances 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 239000003779 heat-resistant material Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000005482 strain hardening Methods 0.000 description 2
- 229910001182 Mo alloy Inorganic materials 0.000 description 1
- IOVCWXUNBOPUCH-UHFFFAOYSA-M Nitrite anion Chemical compound [O-]N=O IOVCWXUNBOPUCH-UHFFFAOYSA-M 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000010273 cold forging Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000003628 erosive effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Images
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
- F16B35/00—Screw-bolts; Stay-bolts; Screw-threaded studs; Screws; Set screws
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21H—MAKING PARTICULAR METAL OBJECTS BY ROLLING, e.g. SCREWS, WHEELS, RINGS, BARRELS, BALLS
- B21H3/00—Making helical bodies or bodies having parts of helical shape
- B21H3/02—Making helical bodies or bodies having parts of helical shape external screw-threads ; Making dies for thread rolling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
- B21J5/06—Methods for forging, hammering, or pressing; Special equipment or accessories therefor for performing particular operations
- B21J5/12—Forming profiles on internal or external surfaces
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
- B21K1/00—Making machine elements
- B21K1/44—Making machine elements bolts, studs, or the like
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
-
- 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
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- General Engineering & Computer Science (AREA)
- General Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Heat Treatment Of Articles (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
(Ni), nitrogen (N): 0.20% by weight, carbon (C): 0.05-0.15%, silicon (Si): 0.10-1.0%, manganese Of the austenite stabilizing index (F), which is defined by the following formula (1) and contains the iron (Fe) and other unavoidable impurities and is 0.35% by weight, chromium (Cr): 17.5-20.0%, molybdenum ) Is 5.8 to 6.5, and an austenitic heat-resistant bolt which has undergone a cold rolling step forging and a rolling step at a rolling pressure of 45 to 55 kgf / cm 2 is introduced.
F = 0.5 * Mn (wt%) + 0.22 * Ni (wt%) + 1.8 * N (wt%) - -(One)
Description
The present invention relates to an austenitic heat-resistant bolt having a high temperature tensile strength when an austenite stabilization index is set and its range value is satisfied, and a manufacturing method thereof.
The existing heat-resistant bolt material uses a heat-resistant steel material containing a large amount of nickel (Ni) or chromium (Cr) added thereto. Existing materials added with 25% or more of nickel (Ni) have a high tensile strength at a high temperature of about 850 MPa at a temperature of 600 ° C. or more, but a disadvantage in that a large amount of expensive nickel (Ni) In the case of existing materials, the high temperature tensile strength is not high at a high temperature of 600 ° C or higher, and the use thereof is limited.
Accordingly, the present invention reduces the addition of nickel (Ni), which is a high-priced element, and substitutes nickel (Ni) for substitution, sets the formula between these elements, and satisfies the formula, As well.
Also, instead of omitting the heat treatment process in the heat-resistant bolt manufacturing process, a method of manufacturing a heat-resistant bolt having a target value by introducing the rolling pressure at the rolling time is introduced.
It should be understood that the foregoing description of the background art is merely for the purpose of promoting an understanding of the background of the present invention and is not to be construed as an admission that the prior art is known to those skilled in the art.
An object of the present invention is to provide an austenitic heat-resistant bolt having a high temperature tensile strength and a method of manufacturing the same, when the austenite stabilization index is set and the range value is satisfied.
In order to accomplish the above object, the present invention provides a method for manufacturing an austenitic heat-resistant bolt, comprising: 0.05 to 0.15% of carbon (C), 0.10 to 1.0% of silicon (Si) (Fe) and other elements (Fe) are contained in an amount of 0.01 to 9.0%, nickel (Ni) is 5.0 to 8.0%, nitrogen (N) is 0.20 to 0.35%, chromium (Cr) is 17.5 to 20.0%, molybdenum Preparing a wire rod having a composition containing an unavoidable impurity and having an austenite stabilization index (F) defined by the following formula (1) satisfying 5.8 to 6.5; A forging step of forming the wire into a bolt shape in a cold state; And a rolling step in which the workpiece is hardened by making a thread in the shape of a bolt.
F = 0.5 * Mn (wt%) + 0.22 * Ni (wt%) + 1.8 * N (wt%) - -(One)
And a surface treatment step of forming and curing a coating layer composed of phosphate and molybdenum disulfide on the surface of the bolt after the step of rolling.
The rolling step can be rolled at a rolling pressure of 45 to 55 kgf / cm 2.
In order to achieve the above object, the present invention provides an austenitic heat-resistant bolt comprising 0.05 to 0.15% of carbon (C), 0.10 to 1.0% of silicon (Si), 7.5 to 9.0% of manganese (Mn) (Fe), and other unavoidable impurities (Fe), and the like. The amount of iron (Fe) and other unavoidable impurities And an austenite stabilization index (F) of 5.8 to 6.5 as defined by the following formula (1) is used as a material, and subjected to a forging step and a rolling step in a cold state, and the rolling pressure is 45 To 55 kgf / cm < 2 >.
F = 0.5 * Mn (wt%) + 0.22 * Ni (wt%) + 1.8 * N (wt%) - -(One)
And a coating layer composed of phosphate and molybdenum disulfide on the surface of the bolt.
The austenitic heat-resistant bolt can have a high temperature tensile strength of 650 MPa or higher at 600 캜 or higher.
The austenitic heat resistant bolts may have a hardness value of 35 to 43 HRC.
According to the austenitic heat-resistant bolt manufacturing method of the above-described steps, the production of a heat-resistant bolt having a tensile strength value of 650 MPa or more at a high temperature of 600 ° C or more while using less expensive nickel (Ni) It is possible to expect an excellent production cost reduction effect.
It is also possible to produce heat resistant bolts with hardness values of 35 ~ 43HRC suitable for bolts by omitting the heat treatment process and adjusting the rolling pressure value.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing crystals of a grain boundary nitride to be deposited according to an embodiment of the present invention. FIG.
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
The austenitic heat-resistant bolt according to the present invention comprises 0.05 to 0.15% of carbon (C), 0.10 to 1.0% of silicon (Si), 7.5 to 9.0% of manganese (Mn) (Fe), and other unavoidable impurities, and having the following formula (1): ???????? (1) ???????? (1) ???????? ), The austenite stabilization index (F) defined as 5.8 to 6.5 is used as a material and subjected to a cold forging step and a rolling step, and the rolling pressure in the rolling step is within 45 to 55 kgf / cm 2 .
F = 0.5 * Mn (wt%) + 0.22 * Ni (wt%) + 1.8 * N (wt%) - -(One)
Hereinafter, the reasons for restricting the constituent conditions of the steel in the steel used for producing the austenitic heat-resistant bolt of the present invention will be described in detail.
Carbon (C): 0.05 to 0.15%
Carbon (C) improves casting and improves casting by adding 0.05% or more of molten metal to chromium (Cr) and process oxide. However, when it is added in excess of 0.15%, it becomes saturated and unnecessary amount is added, so it is limited to the range of 0.05 to 0.15%.
Silicon (Si): 0.10 to 1.0%
Silicon (Si) has an effect on the improvement of high temperature fatigue strength when it is added by 0.10% or more in the austenitic alloy, but it is limited to 0.10 ~ 1.0% due to the formation of harmful phase after casting.
Manganese (Mn): 7.5 to 9.0%
When manganese (Mn) is added as an austenite stabilizing element at 7.5% or more, a dispersoid is formed inside the structure during solidification without additional heat treatment, and exhibits a high temperature tensile strength and fatigue life increase effect. However, when added over 9.0%, ductility and corrosion resistance are lowered, and the range is limited to 7.5 ~ 9.0%.
Nickel (Ni): 5.0 to 8.0%
Nickel (Ni) is an austenite stabilizing element like manganese (Mn), and is a typical element added to improve high-temperature properties in a heat resistant material. Therefore, it maintains the austenite phase at high temperature and has a great influence on increasing the tensile strength and ductility at high temperature. When added less than 5.0%, heat resistance enough to be used as heat-resistant bolts becomes insufficient, and because addition of 8.0% or more causes nickel (Ni) to be very expensive, the production cost is limited to 5.0 ~ 8.0%.
Nitrogen (N): 0.20 to 0.35%
Nitrogen (N) is an austenite stabilizing element such as nickel (Ni) and manganese (Mn), and is a major element for improving high temperature tensile strength and fatigue life. It has a cost lower than nickel (Ni) It is possible to manufacture a heat-resistant material which is economically excellent. When added in an amount of less than 0.20%, the effect of substituting nickel (Ni) at high temperature properties is not obtained. When added in excess of 0.35%, nitrite precipitates due to reaction with chromium (Cr) Respectively.
In the case where the range of 0.20 to 0.35% is not satisfied, as shown in FIG. 1, grain boundary nitride is formed, resulting in deterioration of high-temperature properties.
Chromium (Cr): 17.5 to 20.0%
Cr (Cr) is a component contributing to oxidation resistance, and its cost is about 10 to 30% of nickel (Ni) compared to nickel (Ni). The addition of more than 17.5% improves the fatigue life and physical properties similar to that of nickel (Ni) by complementing the reduction of nickel (Ni) content. When added more than 20.0%, the base structure becomes ferrite instead of austenite. Respectively.
Molybdenum (Mo): 0.01 to 0.60%
Molybdenum (Mo) increases the temper softening resistance of the material when it is added by 0.01% or more and is limited to the range of 0.01 ~ 0.60% because the effect is saturated when it is added over 0.60%.
As described above, manganese (Mn), nickel (Ni), and nitrogen (N), which serve as the austenite stabilizing elements, basically maintain the base structure at a high temperature as austenite, thereby increasing the high temperature strength and fatigue life. In particular, manganese (Mn) and nitrogen (N) substitute for reduced nickel (Ni) contributes to an excellent increase in high temperature properties.
Accordingly, it is important to control the amount of manganese (Mn), nickel (Ni), and nitrogen (N) added in combination in the physical properties of the austenitic heat-resistant bolts. When the amount of the complex addition is small, the physical properties at high temperature are lowered, and when it is exceeded, the ductility and the corrosion resistance are lowered and the brittleness due to the precipitation of nitride with chromium (Cr) occurs.
Therefore, an austenitic stabilization index relation was established in consideration of the effect of manganese (Mn), nickel (Ni), and nitrogen (N) elements on austenite stabilization and economical efficiency, and the index range for obtaining optimum properties was limited to 5.8 to 6.5 Respectively. The austenite stabilization index relation is as follows.
Austenite stabilization index (F) = 0.5 * Mn (wt%) + 0.22 * Ni (wt%) + 1.8 * N (wt%
Since the austenite stabilizing index (F) contributes to stabilize the austenite structure of each of the elements of Mn, Ni and N, the three elements constitute the austenite stabilization index formula. Further, the numbers of the elements of Mn, Ni and N contributing to the stabilization of the austenite structure were varied, and the numbers of 0.22, 0.5 and 1.8 were multiplied by the weight% of the elements.
In one embodiment according to the present invention, the volume fraction of the austenite structure having an excellent high temperature tensile strength is preferably limited to 30 to 70%. When the volume fraction of the austenite structure is less than 30%, the tensile strength is lowered and it is difficult to produce the desired heat-resistant bolt with high tensile strength. When the volume fraction of the austenite structure exceeds 70%, the yield strength tends to decrease Therefore, the range of the volume fraction is set as described above.
The crystal size of the nitride-based nitride in which the alloy component and nitrogen (N) meet and precipitate is limited to a size ranging from 60 to 70 μm in particle size as shown in FIG. Precipitation of grain boundary nitrides causes the action of an alloy component and nitrogen (N), so formation of a nitride-based nitride having a grain size of 60 탆 or more is necessarily inevitable.
However, when the grain size of the precipitated nitride is more than 70 μm, the physical properties at high temperature are deteriorated, which makes it difficult to produce a heat resistant bolt having a good tensile strength at a high temperature.
The forging and rolling operations proceed cold and in this process the screw outer diameter, effective diameter and length of the bolt are adjusted. The reason why the work progresses in the cold is that it has advantages in that the material is saved and the mechanical properties are better than those in the hot case. This is also true for the properties of the present invention which produce bolts.
The machined bolt can greatly improve the tensile strength of the bolt by end rolling. When the rolling pressure is insufficient, it is difficult to secure the hardness value of the desired bolt because the work hardening becomes insufficient. When the rolling pressure is higher than necessary, It is difficult to secure the desired hardness value of the bolt.
The austenitic heat-resisting bolt according to the present invention is characterized in that a phosphate coating layer is formed on the surface of the intermediate member which has been subjected to the forging step and the rolling step, and molybdenum disulfide is coated on the coating layer.
A coating layer of a phosphate is formed on the surface of the bolt to increase the corrosion resistance and the coating layer is coated with molybdenum disulfide (MoS2), whereby the wear resistance is improved.
The austenitic heat-resistant bolt according to the present invention is characterized by having a high temperature tensile strength of 650 MPa or higher at 600 캜 or higher.
Since the present invention is for manufacturing a heat resistant bolt capable of fastening high temperature parts of an automobile engine, a high temperature tensile strength at 600 DEG C or more, which can withstand the inside of the engine, is required. In addition, bolts having a tensile strength of 650 MPa or less are required to have a tensile strength of 650 MPa or more since it is difficult to perform the fastening function.
The austenitic heat-resistant bolt according to the present invention is characterized by having a hardness value of 35 to 43 HRC.
Since the bolts have a constant hardness value or more, the thread formed on the surface of the bolt is maintained and functions as a bolt, so that the austenitic heat-resistant bolt according to the present invention has a hardness value of 35 to 43 HRC.
The method for manufacturing an austenitic heat-resistant bolt according to the present invention is characterized in that it comprises 0.05 to 0.15% of carbon (C), 0.10 to 1.0% of silicon (Si), 7.5 to 9.0% of manganese (Mn) (Fe), and other unavoidable impurities, and having a composition represented by the following formula (1): ???????? R 1 -O- (F) of 5.8 to 6.5 as defined in (1) above; A forging step of forming a wire material in a bolt shape in a cold state to produce a molding material; And a rolling step of producing an intermediate member by working and hardening while forming threads on the surface of the molding material.
F = 0.5 * Mn (wt%) + 0.22 * Ni (wt%) + 1.8 * N (wt%) - -(One)
The austenitic heat-resistant bolts produced by the present invention are produced as an intermediate grade material of a 25% Ni-based alloy and a Cr-Mo alloy, and are prepared by adding 5.0 to 8.0% of nickel (Ni) It is very economical because it saves more than 30%, and it has high tensile strength at over 600 ℃ and it is excellent in heat resistance bolts.
The method of manufacturing an austenitic heat-resistant bolt according to the present invention further includes a surface treatment step of forming a phosphate coating layer on the surface of the intermediate member and coating molybdenum disulfide on the coating layer after the step of rolling.
After the step of rolling, as described above, a coating layer of phosphate is formed on the surface of the intermediate member, molybdenum disulfide (MoS2) is coated on the coating layer, and the coating is cured. By coating a phosphate film and molybdenum disulfide (MoS2) on the surface of the intermediate member, an effect of improving the erosion resistance and the wear resistance can be obtained. The surface treatment process proceeds at about 150 DEG C for about 30 minutes.
The rolling step is characterized in that the rolling is carried out at a rolling pressure of 45 to 55 kgf / cm < 2 >.
As described above, since the influence of the pressure at the rolling time on the hardness value of the bolt is large, it is important to control the pressure at the time of rolling. If the rolling pressure is less than 45 kgf / ㎠, it is difficult to secure the hardness value of the desired bolt because the work hardening is insufficient. If the rolling pressure exceeds 55 kgf / ㎠, the processing heat is generated in the working process, It is hard to secure. Therefore, the range of rolling pressure was set to 45 ~ 55kgf / ㎠.
Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.
(Indicators)
(kgf / cm2)
(HRC)
(MPa)
As a result of the high temperature tensile strength test, the high temperature tensile strength value at the temperature of 600 ° C. of the present Example was higher than that of the presently used 25% Ni-based alloy and the conventional example 2 < / RTI > alloy.
In the case of Conventional Example 1, the austenite stabilization index satisfies the range of 5.8 to 6.5, but element components such as chromium (Cr), nickel (Ni), manganese (Mn) and nitrogen (N) (N) is not added at all, and the weight percentage of nickel (Ni), which is expensive, is 25%, which is expensive to manufacture. Thus, it is economical to aim at the present invention in the beginning, The distance from the manufacturing of the heat resistant bolt having the strength and the hardness becomes far apart.
When the addition of nickel (Ni), which is expensive as in Conventional Example 2, is not taken into consideration at all to lower the manufacturing cost, it can be confirmed that the high temperature tensile strength value at 600 캜 as well as the hardness has a value far below the numerical value of the present invention .
As shown in Table 1, when the range of the austenite stabilization index (F) and the rolling pressure exceeds the range of the index indicated in the present invention or falls below the range of the index, it can not satisfy the desired hardness and high temperature tensile strength Can be confirmed.
Comparative Examples 1 to 2, Comparative Examples 5 to 6, Comparative Examples 9 to 10, and Comparative Examples 13 to 14 show examples in which the range of rolling pressure is satisfactory but the range of the austenite stabilization index (F) is not satisfied. As a result, it can be confirmed that the high temperature tensile strength and hardness values do not satisfy 650 (MPa) and 35 to 43 (HRC).
Comparative Examples 3 to 4 and Comparative Examples 7 to 8 show examples in which the range of the austenite stabilization index (F) is satisfied, but the range of the precursor pressure is not satisfied. As a result, it can be confirmed that the high temperature tensile strength and hardness values do not satisfy 650 (MPa) and 35 to 43 (HRC).
Comparative Examples 11 to 12 show examples in which the austenite stabilization index (F) and the range of the warp pressures are not satisfied. As a result, it can be confirmed that the high temperature tensile strength and hardness values do not satisfy 650 (MPa) and 35 to 43 (HRC).
While the present invention has been particularly shown and described with reference to specific embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims It will be apparent to those of ordinary skill in the art.
Claims (7)
(Ni), nitrogen (N): 0.20% by weight, carbon (C): 0.05-0.15%, silicon (Si): 0.10-1.0%, manganese (1), and the balance iron (Fe) and other unavoidable impurities, and the austenite stabilizing index (1) as defined by the following formula (1) F) of 5.8 to 6.5 is used as a material and subjected to a cold rolling step forging and a rolling step at a rolling pressure of 45 to 55 kgf / cm < 2 >, and the grain boundary nitride present in the grain has a grain size of 60 to 70 탆, and a volume fraction of the austenite structure is 30 to 70%.
F = 0.5 * Mn (wt%) + 0.22 * Ni (wt%) + 1.8 * N (wt%) - -(One)
Wherein a phosphate film layer is formed on the surface of the intermediate member subjected to the forging step and the rolling step, and molybdenum disulfide is coated on the coat layer.
Wherein the intermediate member subjected to the forging step and the rolling step has a high temperature tensile strength of 650 MPa or more at 600 DEG C or more.
Wherein the intermediate member subjected to the forging step and the rolling step has a hardness value of 35 to 43 HRC.
(Ni), nitrogen (N): 0.20% by weight, carbon (C): 0.05-0.15%, silicon (Si): 0.10-1.0%, manganese (1), and the balance iron (Fe) and other unavoidable impurities, and the austenite stabilizing index (1) as defined by the following formula (1) F) of 5.8 to 6.5, the grain boundary nitrides existing in the grain have a grain size of 60 to 70 mu m, and a volume fraction of the austenite structure is 30 to 70%;
A forging step of forming a wire material in a bolt shape in a cold state to produce a molding material;
A rolling step of producing an intermediate material having a high temperature tensile strength of 650 MPa or more and a hardness value of 35 to 43 HRC at 600 DEG C or higher by rolling the surface of the molding material at a rolling pressure of 45 to 55 kgf / And
And a surface treatment step of forming a phosphate coating layer on the surface of the intermediate member and coating molybdenum disulfide on the coating layer.
F = 0.5 * Mn (wt%) + 0.22 * Ni (wt%) + 1.8 * N (wt%) - -(One)
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| KR101974815B1 (en) * | 2017-11-28 | 2019-05-07 | 포항공과대학교 산학협력단 | Austenitic steel excellent in high temperature strength using reduction of chromium content |
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