Source: https://patents.justia.com/patent/7641742
Timestamp: 2020-07-03 21:09:36
Document Index: 715334847

Matched Legal Cases: ['§ 371', 'Application No. 2004', 'Application No. 2002', 'Application No. 2002', 'Application No. 2002', 'Application No. 2002', 'Application No. 2002', 'Application No. 2002', 'Application No. 2002', 'Application No. 2003', 'Application No. 200410008248', 'Application No. 05703409']

US Patent for Rolling bearing and heat treatment method for steel Patent (Patent # 7,641,742 issued January 5, 2010) - Justia Patents Search
Justia Patents With Working, Machining, Cutting, Or Post-carburizing And Post-nitriding Heating Or QuenchingUS Patent for Rolling bearing and heat treatment method for steel Patent (Patent # 7,641,742)
Rolling bearing and heat treatment method for steel
Jan 11, 2005 - NTN Corporation
This application is the U.S. National Phase under 35 U.S.C. § 371 of International Application No. PCT/1P2005/000170, filed on Jan. 11, 2005, which in turn claims the benefit of Japanese Application No. 2004-007568, filed on Jan. 15, 2004, the disclosures of which Applications are incorporated by reference herein.
A heat treatment method for steel according to the present invention is used for a part formed of a steel containing 0.8-1.5 wt % of carbon, 0.4-1.2 wt % of Si, 0.8-1.5 wt % of Mn, and 0.5-1.8 wt % of Cr, and having a position exhibiting HRC50 in a hardenability test (JISG0561) apart from a quenched end by at least 12.7 mm. In this method, the part formed of the steel is carbonitrided or nitrided at 810-950° C., and subsequently cooled to a temperature range lower than a transformation point A1 of the steel product, and subsequently heated again to a quenching temperature range not lower than the transformation point A1 and lower than a temperature used for the carbonitriding or nitriding, to be quenched.
An example of the present invention will now be described. A rolling bearing part evaluated in the present example was the one made of a steel containing 1.0 wt % of C, 0.5 wt % of Si, 1.0 wt % of Mn, and 1.0 wt % of Cr, the steel being subjected to a heat treatment method shown in FIG. 1A or 1B. A heat treatment method shown in FIG. 1A is a method for quenching twice, in which primary quenching and secondary quenching are performed, while a heat treatment method shown in FIG. 1B is a method including the steps of heating to a carbonitriding temperature A, cooling to a temperature lower than a transformation point A1 without quenching, and subsequently heating again to a quenching temperature B equal to or above transformation point A1 and lower than the carbonitriding temperature, for quenching. In any case, carbonitriding temperature A falls within a temperature range of 810-950° C., and the final quenching temperature B is 750-810° C. If nitriding is performed instead of carbonitriding, the same heating temperatures are used. As shown in FIGS. 1A and 1B, oil quenching is performed as quenching, and tempering is performed at 180° C. after oil cooling.
In order to examine a rolling fatigue life and material property of the part fabricated with the steel according to the example of the present invention, hardness after the heat treatment, a rolling fatigue test using a cylindrical test piece, a static pressure breaking strength, and a rate of dimensional change over time were measured. As a comparative example, a part which uses the conventional steel and to which the similar heat treatment was applied was also tested. In the following, a bearing steel of type 2 (JISSUJ2) subjected to the heat treatment in FIG. 1A is represented as a material A (a comparative example). The above-described steel, which contains 1.0% of C, 0.5% of Si, 1.0% of Mn, and 1.0% of Cr, is subjected to the heat treatment in FIG. 1A to be represented as a material B (an example of the present invention). Furthermore, material B processed by lowering the secondary quenching temperature shown in FIG. 1A to 780° C. is represented as a material BL (an example of the present invention). An austenite crystal grain size was 12 in both of materials A and B, while 13 in material BL.
Test Piece φ12 × L12, R480 Number of Tests Conducted 10 Counterpart Piece φ20 Roller Product (SUJ2) Contact Surface Pressure 4.16 GPa Loading Rate 20400 rpm Lubricant Oil Turbine VG68: oiled by forced circulation
Life (Number of Loading Cycles)
Material L10 (×104 times) L50 (×104 times) L10 ratio
Material A 4290 8259 1.0 (Comparative Example) Material B 5206 9325 1.2 (Example of the Present Invention) Material BL 6341 10520 1.5 (Example of the Present Invention)
Number of Static Pressure Static Pressure Tests Breaking Strength Breaking Steel Conducted (kgf) Strength Ratio
Material A (Comparative 5 3900 1.00 Example) Material B (Example of 5 3765 0.97 the Present Invention) Material BL (Example of 5 4150 1.04 the Present Invention)
Table 4 shows the measurement results of rate of dimensional change over time, the results being obtained at a holding temperature of 120° C., after a holding time of 500 hours. In addition to the rate of dimensional change over time, Table 4 also shows surface hardness, and an amount of residual austenite at a position 0.1 mm deep from the surface. Although the present embodiment has a larger amount of residual austenite, the rates of dimensional change over time of materials B and BL, each serving as an example of the present invention, are restricted to a rate not more than one-third of that of material A serving as a comparative example.
Number Surface Rate of Rate of of Tests Hard- Amount of Dimensional Dimensional Con- ness Residual γ Change Change Steel ducted (HRC) (%) (×10−5) Rate*)
Material A 2 63.2 15.3 22 1.0 (Compar- ative Example) Material B 2 63.4 17.6 6.5 0.3 (Example of the Present Invention) Material BL 2 63 15.6 5.5 0.3 (Example of the Present Invention) *)A lower rate is superior.
TABLE 5 Rolling Fatigue Test Conditions under Lubrication with Foreign Substance Mixed Thereinto
Load Fr = 17.64 kN Contact Surface Pressure Pmax = 2.6 GPa Number of Revolutions 2000 rpm Lubrication Turbine VG56: oiled by oil bath Amount of Foreign Substance 1 g/1000 cc Foreign Substance Grain Diameter: 100-180 μm, Hardness: Hv800
Life Test Results under Lubrication with Foreign Substance Mixed Thereinto
Steel L10 life (h) L10 ratio
Material A (Comparative Example) 119.9 1.0 Material B 111.1 0.9 (Example of the Present Invention) Material BL 143.8 1.2 (Example of the Present Invention)
Jominy Value Quenching at 800° C. Quenching at 780° C.° C.
(Distance Between Surface Surface Chemical Position Exhibiting Layer Crystal Layer Crystal Composition HRC50 and Quenched Hardness Grain Size Hardness Grain Size
No. C Si Mn Cr End) (mm) (HV) Number (HV) Number Note
1 1.0 0.5 1.0 1.0 23 750 12 720 13 Examples of 2 0.8 0.5 1.1 0.6 15 735 12 705 13 the Present 3 1.2 1.0 0.8 1.5 38 770 12 730 13 Invention 4 1.0 0.5 0.8 1.0 17 740 11 710 13 15 0.8 0.4 1.1 0.8 12.7 740 11 715 13 16 1.0 0.8 0.4 0.8 10 670 11 610 13 Comparative 5 1.0 0.2 0.3 1.4 8 650 11 600 13 Examples 6 0.8 0.3 0.5 0.5 5 620 12 580 13 Note (i) A Jominy value is a value estimated from chemical components (calculated with a crystal grain size number of 10). (ii) Surface layer hardness is a value actually measured in a test piece having a wall thickness of 15 mm (a ring having an outside diameter of 85 mm, an inside diameter of 55 mm, a width of 30).
In the heat treatment method for the steel described above, a quenching temperature range, which is equal to or higher than transformation point A1 and lower than a carbonitriding or nitriding temperature, can be set to 750-810° C.
carbonitriding or nitriding at 810-950° C. a part formed of a steel containing 0.8-1.5 wt % of carbon, 0.4-1.2 wt % of Si, 0.8-1.5 wt % of Mn, and 0.5-1.8 wt % of Cr, the steel having a position exhibiting HRC50 in a hardenability test (JISG0561) apart from a quenched end by at least 12.7 mm;
2. The heat treatment method for steel according to claim 1, wherein the quenching temperature range not lower than said transformation point A1 and lower than the temperature used for said carbonitriding or nitriding is 750-810° C.
3. The heat treatment method for steel according to claim 1, wherein the temperature used for tempering the quenched part a first time is 180° C.
4. The heat treatment method for steel according to claim 1, wherein the temperature used for tempering the part a second time is 180° C.
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Patent number: 7641742
Patent Publication Number: 20070169850
Inventors: Chikara Ohki (Kuwana), Kohei Fujita (Kuwana)
Application Number: 10/586,299
Current U.S. Class: With Working, Machining, Cutting, Or Post-carburizing And Post-nitriding Heating Or Quenching (148/219); With Post-nitriding Heat Or Quenching (148/232)