US20150020926A1 - Steel for nitrocarburizing and nitrocarburized component using the steel as material - Google Patents

Steel for nitrocarburizing and nitrocarburized component using the steel as material Download PDF

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US20150020926A1
US20150020926A1 US14/378,553 US201314378553A US2015020926A1 US 20150020926 A1 US20150020926 A1 US 20150020926A1 US 201314378553 A US201314378553 A US 201314378553A US 2015020926 A1 US2015020926 A1 US 2015020926A1
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nitrocarburizing
steel
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treatment
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Takashi Iwamoto
Keisuke Ando
Kunikazu Tomita
Yasuhiro Omori
Kiyoshi Uwai
Shinji Mitao
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JFE Steel Corp
JFE Bars and Shapes Corp
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JFE Steel Corp
JFE Bars and Shapes Corp
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Assigned to JFE BARS & SHAPES CORPORATION, JFE STEEL CORPORATION reassignment JFE BARS & SHAPES CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ANDO, KEISUKE, IWAMOTO, TAKASHI, MITAO, SHINJI, OMORI, YASUHIRO, TOMITA, KUNIKAZU, UWAI, KIYOSHI
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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
    • C23C8/28—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 more than one element being applied in one step
    • C23C8/30—Carbo-nitriding
    • C23C8/32—Carbo-nitriding of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite

Definitions

  • This disclosure relates to steel for nitrocarburizing and nitrocarburized components using the steel as material.
  • the disclosure relates to steel for nitrocarburizing that has excellent fatigue properties after nitrocarburizing and is suitable for use in automobiles and construction equipment and to nitrocarburized components using the steel as a material.
  • Carburizing treatment carbon is caused to infiltrate and diffuse into a high-temperature austenite region, yielding a deep hardening depth. Carburizing treatment is thus useful to improve fatigue strength.
  • Induction quench hardening is a process of quenching a surface part by high frequency induction heating and, like carburizing treatment, causes degradation of dimensional accuracy.
  • Nitriding treatment is a process to harden a surface by causing nitrogen to infiltrate and diffuse into a high-temperature region at or below the Ac 1 critical point.
  • the treatment is long, taking 50 to 100 hours, and requires removal of a brittle compound layer on the surface after treatment.
  • nitrocarburizing treatment has been developed for nitriding at approximately the same treatment temperature as nitriding treatment yet in a short time.
  • nitrocarburizing treatment has become commonly used on machine structural components and the like.
  • nitrogen and carbon are simultaneously caused to infiltrate and diffuse into a temperature region at 500° C. to 600° C. to harden the surface, making it possible to reduce the treatment time to half or less that of conventional nitriding treatment.
  • nitrocarburizing treatment is performed at a temperature at or below the critical point of steel, thus causing the core hardness not to increase and yielding nitrocarburized material with poorer fatigue strength than carburized material.
  • JP 2002-69572 A discloses cogging steel that contains 0.5% to 2% of Cu by hot forging and then air cooling the steel to provide a ferrite-based microstructure with solute Cu, precipitating the Cu during nitrocarburizing treatment at 580° C. for 120 minutes and, furthermore, concurrently precipitation-hardening Ti, V and Nb carbonitrides to yield a steel that, after the nitrocarburizing treatment, has excellent bending fatigue properties.
  • JP 2010-163671 A discloses steel for nitrocarburizing having dispersed therein Ti—Mo carbides and carbides including at least one element selected from the group consisting of Nb, V and W.
  • the nitrocarburizing steel recited in JP 5-59488 A and JP 7-138701 A improves bending fatigue strength through precipitation-hardening of Cu and the like, the resulting workability cannot be considered sufficient.
  • the nitrocarburizing steel recited in JP 2002-69572 A has a high production cost.
  • the steel for nitrocarburizing recited in JP 2010-163671 A has the problem of high production cost due to the inclusion of a relatively large amount of Ti and Mo.
  • a steel for nitrocarburizing comprising, in, mass %, C: 0.01% or more and less than 0.10%, Si: 1.0% or less, Mn: 0.5% to 3.0%, Cr: 0.30% to 3.0%, Mo: 0.005% to 0.4%, V: 0.02% to 0.5%, Nb: 0.003% to 0.15%, Al: 0.005% to 0.2%, S: 0.06% or less, P: 0.02% or less, B: 0.0003% to 0.01%, and the balance being Fe and incidental impurities, and including a microstructure with a bainite area ratio exceeding 50% before nitrocarburizing.
  • FIG. 1 is a schematic diagram illustrating the manufacturing process to manufacture a nitrocarburized component using steel for nitrocarburizing.
  • the microstructure before nitrocarburizing has a bainite area ratio exceeding 50%
  • the microstructure after nitrocarburizing has V and Nb precipitates dispersed in a bainite phase.
  • a matrix phase before nitrocarburizing is a bainite-based microstructure with a bainite area ratio exceeding 50%
  • formation of V and Nb precipitates in the matrix phase is drastically inhibited compared to a ferrite-pearlite microstructure.
  • formation of the V and Nb precipitates before nitrocarburizing and consequent increased hardness of the steel can be prevented, thereby improving workability of cutting generally performed before nitrocarburizing.
  • nitrocarburizing treatment causes the surface part to be nitrided and simultaneously age precipitates the V and Nb precipitates in the core bainite phase other than the nitrided surface part, thereby increasing the core hardness. Both the fatigue properties and the strength after nitrocarburizing therefore dramatically improve.
  • the “microstructure with a bainite area ratio exceeding 50%” contemplated herein refers to the area ratio of the bainite microstructure (phase) exceeding 50% under cross-sectional microstructure observation (microstructure observation with a 200 ⁇ optical microscope).
  • the area ratio of the bainite phase preferably exceeds 60% and even more preferably exceeds 80%.
  • the V and Nb precipitates in the bainite phase are preferably a dispersion of fine precipitates having a grain size of less than 10 nm.
  • 500 or more of the V and Nb precipitates with the grain size of less than 10 nm preferably exist per 1 ⁇ m 2 .
  • Carbon (C) is added for bainite phase formation and to ensure strength.
  • the amount of C added is less than 0.01%, the amount of bainite formed decreases, as does the amount of V and Nb precipitates, thus making it difficult to ensure strength.
  • the bainite phase becomes harder, thereby reducing the mechanical workability. Accordingly, the amount of C added is 0.01% or more and less than 0.10%. C preferably 0.03% or more and less than 0.10%.
  • Silicon (Si) is added for its usefulness in deoxidizing and bainite phase formation. Adding an amount of Si exceeding 1.0%, however, deteriorates mechanical workability and cold-rolling workability due to solid solution hardening of ferrite and bainite phases. Accordingly, the amount of Si added is 1.0% or less. The amount is preferably 0.5% or less and more preferably 0.3% or less. Note that for Si to contribute effectively to deoxidation, the amount of Si added is preferably 0.01% or more.
  • Chromium (Cr) is added for its usefulness in bainite phase formation.
  • the amount of Cr added is less than 0.30%, the amount of bainite phase formed decreases, and V and Nb precipitates are formed, causing the hardness before nitrocarburizing to increase and the amount of V and Nb precipitates formed after nitrocarburizing treatment to decrease. In turn, this lowers the hardness after nitrocarburizing and makes it difficult to ensure strength.
  • adding an amount of Cr exceeding 3.0% deteriorates mechanical workability and cold-rolling workability. Accordingly, the amount of Cr added is 0.30% to 3.0%.
  • the amount is preferably 0.5% or more and 2.0% or less, and more preferably 0.5% or more and 1.5% or less.
  • Vanadium (V) forms fine precipitates along with Nb due to the rise in temperature during nitrocarburizing and is therefore an important element to increase core hardness and improve strength.
  • An added amount of V less than 0.02% does not satisfactorily achieve these effects.
  • adding an amount of V exceeding 0.5% causes the precipitates to coarsen. Accordingly, the amount of V added is 0.02% to 0.5%.
  • the amount is preferably 0.03% or more and 0.3% or less, and more preferably 0.03% or more and 0.25% or less.
  • Niobium (Nb) forms fine precipitates along with V due to the rise in temperature during nitrocarburizing and is therefore an extremely effective element to increase core hardness and improve fatigue strength.
  • An added amount of Nb less than 0.003% does not satisfactorily achieve these effects.
  • adding an amount of Nb exceeding 0.15% causes the precipitates to coarsen. Accordingly, the amount of Nb added is 0.003% to 0.15%.
  • the amount is preferably 0.02% or more and 0.12% or less.
  • Molybdenum (Mo) causes fine V and Nb precipitates to form and is effective in improving the strength of the nitrocarburized material. Mo is therefore an important element. Mo is also useful for bainite phase formation. To improve strength, 0.005% or more is added, but since Mo is an expensive element, adding more than 0.4% leads to increased component cost. Accordingly, the amount of Mo added is 0.005% to 0.4%. The amount is preferably 0.01% to 0.3% and more preferably 0.04% to 0.2%.
  • Aluminum (Al) is a useful element to improve surface hardness and effective hardened case depth after nitrocarburizing and is therefore intentionally added. Al also yields a finer microstructure by inhibiting the growth of austenite grains during hot forging and is thus a useful element to improve toughness. Therefore, 0.005% or more is added. On the other hand, including over 0.2% does not increase this effect, but rather causes the disadvantage of higher component cost. Accordingly, the amount of Al added is 0.005% to 0.2%. The amount is preferably over 0.020% and 0.1% or less, and more preferably over 0.020% and 0.040% or less.
  • S Sulfur
  • S forms MnS in the steel and is a useful element to improve the machinability by cutting. Including over 0.06%, however, lessens toughness. Accordingly, the amount of S added is 0.06% or less. The amount is preferably 0.04% or less. Note that for S to achieve the effect of improving machinability by cutting, the amount of S added is preferably 0.002% or more.
  • Phosphorus (P) exists in a segregated manner at austenite grain boundaries and lowers the grain boundary strength, thereby lowering strength and toughness. Accordingly, the P content is preferably kept as low as possible, but a content of up to 0.02% is tolerable. The P content is therefore 0,02% or less. Note that setting the content of P to less than 0.001% requires a high cost. Therefore, it suffices in industrial terms to reduce the content of P to 0.001%.
  • B Boron
  • B be present in the steel as a solute.
  • solute N is present in the steel, however, the B in the steel is consumed by formation of BN. B does not contribute to improved quench hardenability when existing in the steel as BN. Accordingly, when solute N exists in the steel, B is preferably added in an amount greater than that consumed by formation of BN, and the amounts of B (% B) and of N (% N) in the steel preferably satisfy formula (1) below.
  • one or more selected from the group of Pb ⁇ 0.2% and Bi ⁇ 0.02% may be added. Note that the desired effects achieved are not diminished regardless of whether these elements are added and regardless of their content.
  • the balance other than the above added elements consists of Fe and incidental impurities.
  • Ti not only adversely affects strengthening by precipitation of V and Nb, but also lowers the core hardness and therefore is not to be included insofar as possible.
  • the amount of Ti is preferably less than 0.010% and more preferably less than 0.005%.
  • FIG. 1 is a schematic diagram illustrating the manufacturing process of manufacturing a nitrocarburized component using steel for nitrocarburizing according to the present invention.
  • S 1 indicates a manufacturing process of a steel bar as a material
  • S 2 indicates a transportation process
  • S 3 indicates the process of finishing the product (nitrocarburized component).
  • a steel ingot is hot rolled into a steel bar and shipped after quality inspection.
  • the steel bar is transported (S 2 ), and during the process (S 3 ) of finishing the product (nitrocarburized component), the steel bar is cut to predetermined dimensions and subjected to hot forging or cold forging.
  • nitrocarburizing treatment is performed, yielding the final product.
  • hot rolling material may be directly cut into a predetermined shape by lathe turning, drill boring or the like, with nitrocarburizing treatment then being performed to yield the final product.
  • nitrocarburizing treatment then being performed to yield the final product.
  • cold straightening may be performed afterwards.
  • Coating treatment such as painting or plating, may also be applied to the final product. Preferable manufacturing conditions will now be described.
  • the rolling heating temperature is preferably 950° C. to 1250° C. This range is adopted to cause carbides remaining after melting to be present as a solute during hot rolling, so as not to diminish forgeability due to formation of fine precipitates in the rolling material (the steel bar which is the material for the hot forging component).
  • the rolling heating temperature is less than 950° C., it becomes difficult for the carbides remaining after melting to form a solute.
  • a temperature exceeding 1250° C. facilitates coarsening of the crystal grains, thus reducing forgeability.
  • the rolling heating temperature is preferably 950° C. to 1250° C.
  • the rolling finishing temperature is preferably 800° C. or more. This temperature is adopted because at a rolling finishing temperature of less than 800° C., a ferrite phase forms. Particularly when the next process is nitrocarburizing after cold forging or cutting, such a ferrite phase is disadvantageous to obtain a bainite phase with an area ratio exceeding 50% of the matrix phase after nitrocarburizing. Moreover, at a rolling finishing temperature of less than 800° C., the rolling load increases, which degrades the out-of-roundness of the rolling material. Accordingly, the rolling finishing temperature is preferably 800° C. or more.
  • the cooling rate after rolling In the precipitation temperature range of fine precipitates of 700° C. to 550° C., it is preferable to cool the steel bar faster than the critical cooling rate at which fine precipitates are produced (0.5° C./s).
  • the resulting steel bar is then used as material that is forged and shaped into components by cutting and the like.
  • Nitrocarburizing treatment is then performed.
  • the temperature for nitrocarburizing treatment is preferably 550° C. to 700° C. to yield fine precipitates including V and Nb, and the treatment time is preferably 10 minutes or more. This range is adopted because at less than 550° C., insufficient precipitates are obtained, whereas over 700° C., the temperature enters the austenite region, making nitrocarburizing difficult.
  • a more preferable range is 550° C. to 630° C.
  • the treatment time is 10 minutes or more to obtain a sufficient amount of V and Nb precipitates.
  • the hot forging is preferably performed with the heating temperature during hot forging at 950° C. to 1250° C., with the forging finishing temperature at 800° C. or more and the cooling rate after forging exceeding 0.5° C./s for the bainite phase to exceed 50% in area ratio of the matrix phase after nitrocarburizing and in order to prevent formation of fine precipitates from the standpoints of cold straightening and workability of cutting after hot forging.
  • Steel samples with the composition shown in Table 1 were obtained by steelmaking in a 150 kg vacuum melting furnace, then rolling by heating at 1150° C., finishing at 970° C., and subsequently cooling to room temperature at a cooling rate of 0.9° C./s to prepare steel bars with o 50 mm.
  • No. 17 is a conventional material, JIS SCr420.
  • P was not intentionally added to any of the steel samples in Table 1. Accordingly, the content of P in Table 1 indicates the amount mixed in as an incidental impurity.
  • Ti was added to steel samples No. 14 and No. 15 but not intentionally added to steel samples No. 1 to 13 and No. 16 to 17 in Table 1. Accordingly, the content of Ti in steel samples No. 1 to 13 and No. 16 to 17 in Table 1 indicates the amount mixed in as an incidental impurity.
  • Hardness was measured by testing the hardness of the core using a Vickers hardness tester, with a test force of 100 g.
  • gas nitrocarburizing treatment was further applied to the hot forging material, and for steel sample No. 17, gas carburizing treatment was applied to the hot forging material.
  • the gas carburizing treatment was performed by carburizing at 930° C. for 3 h, then oil quenching after retaining at 850° C. for 40 minutes and, furthermore, tempering at 170° C. for 1 h.
  • the core hardness and surface hardness were measured.
  • the surface hardness was measured at a position 0.02 mm from the surface, and the effective hardened case depth was measured as the depth from the surface at a hardness of HV 400.
  • Samples for transmission electron microscopy observation were created from the cores of the nitrocarburized material and the carburized material by Twin-jet electropolishing. Precipitates were observed in the resulting samples using a transmission electron microscope with an acceleration voltage of 200 kV. Furthermore, the composition of the observed precipitates was calculated with an energy-dispersive X-ray spectrometer (EDX).
  • EDX energy-dispersive X-ray spectrometer
  • Notched test pieces R: 10 mm, depth: 2 mm were used as test pieces.
  • the notched test pieces were collected from the hot forging material, and after performing the above-described nitrocarburizing treatment or carburizing treatment, the collected test pieces were used in the Charpy impact test.
  • Notched test pieces (notch R: 1.0 mm; notch diameter: 8 mm; stress concentration factor: 1.8) were used as test pieces. The test pieces were collected from the hot forging material and, after the above-described nitrocarburizing treatment or carburizing treatment, were used in the fatigue test.
  • Table 2 shows the test results. No. 1 to 6 are our examples, No. 7 to 17 are comparative examples, and No. 18 is a conventional example provided by JIS SCr420 steel.
  • nitrocarburized materials No. 1 to 6 have better fatigue strength than the material resulting from carburizing, quenching, and tempering the conventional example (No. 18).
  • the material before nitrocarburizing treatment in No. 1 to 6 hot forging material
  • the results of transmission electron microscopy observation and of testing the precipitate composition by EDX confirm that the nitrocarburized materials No. 1 to 6 contain 500 or more fine precipitates, including V and Nb, with a grain size of less than 10 nm dispersed per 1 ⁇ m 2 in the bainite phase. Based on these results, it can be concluded that our nitrocarburized material exhibits a high fatigue strength due to strengthening by precipitation based on the above fine precipitates.
  • comparative examples No. 7 to 17 have a chemical composition or a resulting microstructure that are outside of our scope and thus have worse fatigue strength or drill workability.
  • No. 7 has low fatigue strength as compared to our examples due to the slow cooling rate after hot forging.
  • the results of transmission electron microscopy observation showed no dispersion of fine precipitates with a grain size of less than 10 nm, whereas course precipitates with a grain size greatly exceeding 10 nm were observed. Based on these results, the coarseness of such resulting precipitates can be considered the cause of the reduction in fatigue strength.
  • No. 8 includes a high amount of C, outside of our range. The hardness of the bainite phase therefore increases, reducing drill workability.
  • No. 9 includes high amounts of Si and Mn, outside of our range.
  • the hardness of the hot forging material is therefore high, reducing the drill workability to approximately 1 ⁇ 5 that of conventional material.
  • No. 10 includes a low amount of Mn, outside of our range.
  • a ferrite-pearlite microstructure thus forms before nitrocarburizing (after hot forging), lowering the area ratio of the bainite phase and forming V and Nb precipitates in the microstructure.
  • the hardness before nitrocarburizing thus increases, reducing the drill workability.
  • No. 11 includes a low amount of Cr, outside of our range.
  • a ferrite-pearlite microstructure thus forms before nitrocarburizing (after hot forging), lowering the area ratio of the bainite phase and forming V and Nb precipitates in the microstructure.
  • the hardness before nitrocarburizing thus increases, reducing the drill workability.
  • No. 12 includes a low amount of Mo, outside of our range. Therefore, few fine precipitates exist after the nitrocarburizing treatment, and the resulting core hardness is insufficient. The fatigue strength is therefore lower than the conventional example.
  • No. 13 includes low amounts of V and Nb, outside of our range. Therefore, few fine precipitates exist after the nitrocarburizing treatment, and the resulting core hardness is insufficient. The fatigue strength is therefore lower than the conventional material.
  • No. 14 includes a low amount of Nb, outside of our range. Therefore, few fine precipitates exist after the nitrocarburizing treatment, and the resulting core hardness is insufficient. The fatigue strength is therefore lower than the conventional material.
  • Ti was added to No. 15 and No. 16, thus yielding few precipitates including V and Nb after the nitrocarburizing treatment.
  • the resulting core hardness is therefore insufficient, and the fatigue strength is lower than the conventional material. Furthermore, the impact value is low.
  • No. 17 includes a low amount of Al, outside of our range.
  • the surface hardness after the nitrocarburizing treatment and the effective hardened case depth are therefore insufficient, resulting in a lower fatigue strength than the conventional material.

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  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Heat Treatment Of Steel (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Heat Treatment Of Articles (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
US14/378,553 2012-02-15 2013-02-15 Steel for nitrocarburizing and nitrocarburized component using the steel as material Abandoned US20150020926A1 (en)

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JP2012-031031 2012-02-15
JP2012031031 2012-02-15
PCT/JP2013/000838 WO2013121794A1 (fr) 2012-02-15 2013-02-15 Acier à nitruration modérée et matière d'acier utilisant un composant à nitruration modérée

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EP (1) EP2816128B1 (fr)
JP (1) JP5449626B1 (fr)
KR (1) KR20140129081A (fr)
CN (1) CN104114733A (fr)
MY (1) MY177826A (fr)
WO (1) WO2013121794A1 (fr)

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US20160175241A1 (en) * 2013-08-05 2016-06-23 Polichem Sa Composition for skin anti-ageing treatment
US20170096719A1 (en) * 2014-03-18 2017-04-06 Innomaq 21, Sociedad Limitada Extremely high conductivity low cost steel
US20210350557A1 (en) * 2020-05-11 2021-11-11 The Boeing Company Rapid effective case depth measurement of a metal component using physical surface conditioning
US11242593B2 (en) 2016-11-30 2022-02-08 Jfe Steel Corporation Steel for nitrocarburizing, and component
WO2024003593A1 (fr) * 2022-06-28 2024-01-04 Arcelormittal Pièce forgée en acier et son procédé de fabrication
US11959177B2 (en) 2015-03-24 2024-04-16 Jfe Steel Corporation Steel for nitrocarburizing and nitrocarburized component, and methods of producing same

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JP5767594B2 (ja) * 2012-02-15 2015-08-19 Ｊｆｅ条鋼株式会社 窒化用鋼材およびこれを用いた窒化部材
JP6225965B2 (ja) * 2014-09-05 2017-11-08 Ｊｆｅスチール株式会社 軟窒化用鋼および部品ならびにこれらの製造方法
JP6431456B2 (ja) * 2014-09-05 2018-11-28 Ｊｆｅスチール株式会社 軟窒化用鋼および部品ならびにこれらの製造方法
CN104975160A (zh) * 2015-06-18 2015-10-14 柳州科尔特锻造机械有限公司 一种主、从动锥齿轮热处理方法
JP6477614B2 (ja) * 2016-06-30 2019-03-06 Ｊｆｅスチール株式会社 軟窒化用鋼および部品ならびにこれらの製造方法

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Publication number Priority date Publication date Assignee Title
US20160175241A1 (en) * 2013-08-05 2016-06-23 Polichem Sa Composition for skin anti-ageing treatment
US20170096719A1 (en) * 2014-03-18 2017-04-06 Innomaq 21, Sociedad Limitada Extremely high conductivity low cost steel
US11421290B2 (en) * 2014-03-18 2022-08-23 Innomaq 21, Sociedad Limitada Extremely high conductivity low cost steel
US11959177B2 (en) 2015-03-24 2024-04-16 Jfe Steel Corporation Steel for nitrocarburizing and nitrocarburized component, and methods of producing same
US11242593B2 (en) 2016-11-30 2022-02-08 Jfe Steel Corporation Steel for nitrocarburizing, and component
US20210350557A1 (en) * 2020-05-11 2021-11-11 The Boeing Company Rapid effective case depth measurement of a metal component using physical surface conditioning
US11625844B2 (en) * 2020-05-11 2023-04-11 The Boeing Company Rapid effective case depth measurement of a metal component using physical surface conditioning
WO2024003593A1 (fr) * 2022-06-28 2024-01-04 Arcelormittal Pièce forgée en acier et son procédé de fabrication

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JP5449626B1 (ja) 2014-03-19
JPWO2013121794A1 (ja) 2015-05-11
CN104114733A (zh) 2014-10-22
KR20140129081A (ko) 2014-11-06
EP2816128A1 (fr) 2014-12-24
EP2816128A4 (fr) 2015-05-20
MY177826A (en) 2020-09-23
EP2816128B1 (fr) 2019-02-06
WO2013121794A1 (fr) 2013-08-22
WO2013121794A8 (fr) 2014-07-17

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