Heat treating oil composition

Abstract

A heat-treatment oil composition contains (A) a first base oil with a kinematic viscosity at 40 degrees C. in a range of 5 mm.sup.2/s to 60 mm.sup.2/s in an amount of 50 mass % to 95 mass % of a total amount of the composition, (B) a second base oil with a kinematic viscosity at 40 degrees C. of 300 mm.sup.2/s or more in an amount of 5 mass % to 50 mass %, and (C) an alpha-olefin copolymer. The heat-treatment oil composition according to the invention can reduce distortion unevenness and hardness unevenness accompanying mass-quenching.

Claims

1. A heat-treatment oil composition, comprising: a mixed base oil comprising (A) a first base oil with a kinematic viscosity at 40 C. in a range of 5 mm.sup.2/s to 60 mm.sup.2/s in an amount of 50 mass % to 95 mass % of a total amount of the mixed base oil, and (B) a second base oil with a kinematic viscosity at 40 C. of 300 mm.sup.2/s or more in an amount of 5 mass % to 50 mass % of the total amount of the mixed base oil; and (C) an alpha-olefin copolymer having a mass average molecular weight in a range of 1000 to 5000 in an amount of 8 mass % or more of a total amount of the composition, wherein the composition has a characteristic time of one second or less and a maximum cooling rate at a boiling stage of 400 C./s or less according to a cooling performance test of JIS K 2242.

2. The heat-treatment oil composition according to claim 1, wherein the alpha-olefin copolymer comprises an ethylene-alpha-olefin copolymer.

3. The heat-treatment oil composition according to claim 1, wherein the alpha-olefin copolymer is in a range of 8 mass % to 30 mass % of the total amount of the composition.

4. The heat-treatment oil composition according to claim 1, wherein the composition has a maximum cooling rate of 311 C./s or less at a boiling stage.

5. The heat-treatment oil composition according to claim 1, wherein the composition has a 300 C.-reached time of from 8 seconds to 12 seconds according to a cooling performance test of JIS K 2242.

6. The heat-treatment oil composition according to claim 1, wherein the alpha-olefin copolymer is in a range of 8 mass % to 20 mass % of the total amount of the composition.

Description

DESCRIPTION OF EMBODIMENT(S)

(1) A heat-treatment oil composition according to an exemplary embodiment of the invention (hereinafter, also referred to as the present composition) contains a mixed base oil of (A) a predetermined low-viscosity base oil and (B) a predetermined high-viscosity base oil, and is further blended with (C) an alpha-olefin copolymer. The exemplary embodiment of the invention will be described below in detail.

(2) The low-viscosity base oil as the component (A) has a kinematic viscosity at 40 degrees C. of 5 mm.sup.2/s to 60 mm.sup.2/s. An oil with a kinematic viscosity at 40 degrees C. less than 5 mm.sup.2/s has a high volatility and thus is not suitable as the base oil of the present composition. On the other hand, when an oil with a kinematic viscosity at 40 degrees C. more than 60 mm.sup.2/s is used, a quenched object cannot be provided with a sufficient hardness. In view of the above, a preferable kinematic viscosity at 40 degrees C. is set in a range of 5 mm.sup.2/s to 35 mm.sup.2/s.

(3) The high-viscosity base oil as the component (B) has a kinematic viscosity at 40 degrees C. of 300 mm.sup.2/s or more. When the kinematic viscosity at 40 degrees C. is less than 300 mm.sup.2/s, the cooling performance is excessively enhanced at the boiling stage and thus cannot exhibit an effect in reducing quenching distortion. On the other hand, when the kinematic viscosity at 40 degrees C. is excessively high, the cooling performance becomes unfavorable. In view of the above, a preferable kinematic viscosity is set in a range of 400 mm.sup.2/s to 1000 mm.sup.2/s.

(4) According to the exemplary embodiment, a mixed base oil of the low-viscosity base oil (i.e., the component (A)) in an amount of 50 mass % to 95 mass % and the high-viscosity base oil (i.e., the component (B)) in an amount of 5 mass % to 50 mass % is used as the base oil so that the composition can efficiently exhibit the above effects.

(5) As a low-viscosity base oil and a high-viscosity base oil according to the exemplary embodiment, mineral oil and synthetic oil are usable. Examples of the mineral oil are fractions of paraffin mineral oil, naphthene mineral oil and aromatic mineral oil, which may be prepared by any purification methods such as solvent purification, hydrorefining and hydrocracking. Examples of the synthetic oil are alkylbenzenes, alkylnaphthalenes, alpha-olefin oligomers and hindered ester oil.

(6) As each of the low-viscosity base oil and the high-viscosity base oil for the present composition, any one of the above mineral oils or a combination of two or more thereof may be used or, alternatively, any one of the above synthetic oils or a combination of two or more thereof may be used. Further alternatively, a combination of one or more of the above mineral oils and one or more of the above synthetic oils may be used. The present composition further contains another base oil in addition to the above mixed base oil as long as the effects of the invention are not hampered.

(7) According to the exemplary embodiment, (C) the alpha-olefin copolymer is further blended to the above mixed base oil. By blending the component (C), the vapor blanket stage in the quenching process can be controlled to significantly reduce distortion unevenness and hardness unevenness accompanying mass-quenching. Even though being known as a vapor-blanket-rupturing agent, substances such as polyolefins (i.e., homopolymers of polybutene and the like) and polymethacrylate, which are not alpha-olefin copolymers, are not suitable as the component (C) because the composition cannot sufficiently exhibit the above effects.

(8) The component (C) is preferably an ethylene-alpha-olefin copolymer. The mass average molecular weight of the component (C) is preferably in a range of 1000 to 5000 in terms of the effects of the invention. The blending amount of the component (C) in the present composition is preferably in a range of 0.1 mass % to 30 mass %, more preferably in a range of 1 mass % to 20 mass %, and further preferably in a range of 3 mass % to 10 mass %. As long as the blending amount is in the above range, the component (C) suitably exhibits a vapor-blanket-rupturing effect to reduce distortion unevenness and/or hardness unevenness among the materials subjected to mass-quenching. Further, the kinematic viscosity of the present composition is also suitably adjusted, so that the present composition can favorably function as a heat-treatment oil composition.

(9) Preferably, the characteristic time (sec) (vapor blanket duration) of the present composition according to a cooling performance test (JIS K 2242) is one second or less and the maximum cooling rate of the present composition at the boiling stage is 400 degrees C./s or less.

(10) Specifically, when the vapor blanket duration is shortened and the maximum cooling rate is lowered, the vapor blanket can be ruptured with less unevenness and thus distortion unevenness and/or hardness unevenness can be reduced irrespective of the shape of materials or components to be quenched.

(11) Further, the 300-degrees-C-reached time (sec) of the present composition according to the cooling performance test (JIS K 2242) is preferably in a range of 8 seconds to 12 seconds. The 300-degrees-C-reached time stands for a cooling time (sec) required for reduction from 800 degrees C. to 300 degrees C. according to the cooling performance test (JIS K 2242). When the 300-degrees-C-reached time is less than eight seconds, hardness provided by quenching may be excessively high. On the other hand, when the 300-degrees-C-reached time exceeds 12 seconds, hardness provided by quenching may be insufficient.

(12) The present composition preferably has a kinematic viscosity at 100 degrees C. in a range of 5 mm.sup.2/s to 50 mm.sup.2/s. As long as the kinematic viscosity at 100 degrees C. is 5 mm.sup.2/s or more, the hardness is prevented from becoming excessively high and inflammability can be favorably lowered. On the other hand, as long as the kinematic viscosity at 100 degrees C. is 50 mm.sup.2/s or less, a sufficient hardness can be provided and detergency is favorably less deteriorative. In view of the above, the kinematic viscosity at 100 degrees C. of the present composition is father preferably in a range of 8 mm.sup.2/s to 35 mm.sup.2/s.

(13) The present composition may be added with additives typically used for a heat-treatment oil such as an antioxidant, a detergent dispersant and a brightness improver as needed as long as an object of the invention can be achieved.

(14) As the antioxidant, known phenolic antioxidant and amine antioxidant are usable. Examples of the phenolic antioxidant include monophenolic antioxidants such as 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol and 2,4,6-tri-tert-butylphenol, and polyphenolic antioxidants such as 4,4-methylenebis(2,6-di-tert-butylphenol) and 4,4-isopropylidenebis(2,6-di-tert-butylphenol). Examples of the amine antioxidant include diphenylamine, monooctyl diphenylamine and monononyl diphenylamine. The blending amount of the antioxidant is approximately in a range of 0.01 mass % to 5 mass % of the total amount of the composition in terms of an antioxidant effect and economic balance.

(15) Examples of the detergent dispersant include an ashless dispersant and a metal detergent. Examples of the ashless dispersant include alkenyl succinimides, boron-containing alkenyl succinimides, benzylamines, boron-containing benzylamines, succinates, and amides of mono- or di-carboxylic acid typified by aliphatic or succinic acid. Examples of the metal detergent include neutral metal sulfonates, neutral metal phenates, neutral metal salicylates, neutral metal phosphonates, basic sulfonates, basic phenates, basic salicylates, overbased sulfonates, overbased salicylates and overbased phosphonates. The above substances as the detergent dispersant are effective in dispersing sludge generated when the heat-treatment oil composition is repeatedly used, and the metal detergent also functions as a neutralizer for deteriorated acid. The blending amount of the detergent dispersant is approximately in a range of 0.01 mass % to 5 mass % of the total amount of the composition in terms of efficiency and economic balance.

(16) Examples of the brightness improver include known fat, oil and oil fatty acid, alkenyl succinimide, and substituted hydroxy aromatic carboxylic acid ester derivative.

EXAMPLES

(17) Next, the invention will be described in further detail with reference to Examples, which by no means limit the invention. Specifically, two types of materials were subjected to a heat treatment (mass-quenching) using a sample oil, and distortion unevenness and hardness unevenness of each material was evaluated.

Example 1 and Comparatives 1 to 6

(18) Sample Oil

(19) Table 1 shows components and properties of the sample oil used for each of Example and Comparatives.

(20) TABLE-US-00001 TABLE 1 Ex. 1 Comp. 1 Comp. 2 Comp. 3 Comp. 4 Comp. 5 Comp. 6 Base Oil.sup.1) A: 40 C. Kinematic Viscosity 15 mm.sup.2/s 94 25 (mass %) B: 40 C. Kinematic Viscosity 20 mm.sup.2/s 25 100 C: 40 C. Kinematic Viscosity 45 mm.sup.2/s 80 D: 40 C. Kinematic Viscosity 90 mm.sup.2/s 49 E: 40 C. Kinematic Viscosity 420 mm.sup.2/s 68 40 90 72 F: 40 C. Kinematic Viscosity 490 mm.sup.2/s 10 10 10 Additives -olefin copolymer.sup.2) 8 6 (mass %) Detergent Dispersant etc. 2 1 1 6 3 Properties Characteristic Time (sec) 0.84 1.57 1.57 2.03 4.46 0.78 2.13 Maximum Cooling Rate ( C./s) 311 287 486 787 338 446 381 300 C.-reached Time (sec) 11.2 10.8 11.3 5.4 8.8 15.9 9.3 Test Temperature at Quenching ( C.) 130 130 130 80 80 160 130 Conditions Kinematic Viscosity at Quenching (mm.sup.2/s) 8.448 13.210 8.949 5.617 6.350 8.084 7.525 .sup.1)The base oil F is categorized into Group I but the other base oils are categorized into Group II. .sup.2)LUCANT (Mw 3500) manufactured by Mitsui Chemicals, Inc was used.
Evaluation Method

(21) Materials to be evaluated (shown below) were subjected to a heat treatment (mass-quenching) under predetermined conditions, and distortion unevenness and hardness unevenness were evaluated. An evaluation method was the same as one described in connection with Example of JP-A-2007-9238.

(22) (1) Materials to be Evaluated and Heat-treatment Conditions

(23) 1) Counter drive gear (module 2.45)

(24) See Example 1-1 and Comparatives 1-1 to 6-1 in Table 2 for results of the use of the sample oils of Example 1 and Comparatives 1 to 6, respectively.

(25) Material: SCr420

(26) Heat-treatment conditions: carburizing process: 950 degrees C.48 minutes, Cp=1.1 mass % dispersing process: 930 degrees C.36 minutes, Cp=0.8 mass % soaking process: 850 degrees C.20 minutes, Cp=0.8 mass %

(27) Oil-quenching conditions:

(28) oil temperatures shown below, cooling time 4 minutes, stirring 20 cm/sec Example 1 and Comparatives 1, 2 and 6: oil temperature 130 degrees C. Comparatives 3 and 4: oil temperature 80 degrees C. Comparative 5: oil temperature 160 degrees C.

(29) Incidentally, the oil temperatures were regulated so that the sample oils exhibit a practical kinematic viscosity.

(30) Tempering conditions: 130 degrees C.90 minutes

(31) 2) Differential drive pinion gear (module 2.36)

(32) See Example 1-2 and Comparatives 1-2 to 6-2 in Table 3 for results of the use of the sample oils of Example 1 and Comparatives 1 to 6, respectively.

(33) Material: SCM420

(34) Heat-treatment conditions: carburizing process: 950 degrees C.150 minutes, Cp=1.1 mass % dispersing process: 930 degrees C.60 minutes, Cp=0.8 mass % soaking process: 850 degrees C.60 minutes, Cp=0.8 mass %

(35) Oil-quenching conditions and tempering conditions were the same as the conditions of 1).

(36) (2) Evaluation Items

(37) Difference between maximum and minimum values of torsion angle error (m)

(38) Torsion angle error 3 (m)

(39) Tooth-flank hardness (internal hardness, HV) (according to JIS Z 2244)

(40) Difference between maximum and minimum values of tooth-flank hardness

(41) Effective carburized depth (mm)(according to JIS G 0557)

(42) Effective carburized depth 3(mm)

(43) A reduction in a torsion angle error leads to an improvement in the accuracy of a component to be manufactured (a gear according to Examples). For instance, when the accuracy of a gear is improved, vibration and noise accompanying the engagement of the gear can be reduced and thus a quiet transmission can be manufactured. For a bearing, quiet operation and elongated lifetime can be achieved. When quenching accuracy is improved, the machining tolerance of a non-quenched component can be increased and thus the component can be more easily machined. When the unevenness of tooth-flank hardness and unevenness of effective carburized depth are reduced, it is not necessary to excessively increase the hardness so that the minimum value can fall within a desired range and thus a component can be efficiently and economically manufactured. A reduction in hardness unevenness results in an improvement in component lifetime (e.g., fatigue).

(44) TABLE-US-00002 TABLE 2 Ex. 1-1 Comp. 1-1 Comp. 2-1 Comp. 3-1 Comp. 4-1 Comp. 5-1 Comp. 6-1 Evaluation Difference between 11.7 20.4 17.5 36.5 15.2 20.7 29.4 Items Max and Min Torsion Angle Errors (m) Torsion Angle Error 3 (m) 14.4 28.0 23.0 42.9 22.1 26.1 35.1 Tooth-flank Hardness (HV) 323 315 320 385 364 312 330 Difference between 15 27 13 18 29 14 20 Max and Min Tooth-flank Hardnesses (HV) Effective Carburized Depth (mm) 0.72 0.60 0.70 0.83 0.80 0.65 0.71 Effective Carburized Depth 3 (mm) 0.15 0.15 0.10 0.05 0.08 0.15 0.07

(45) TABLE-US-00003 TABLE 3 Ex. 1-2 Comp. 1-2 Comp. 2-2 Comp. 3-2 Comp. 4-2 Comp. 5-2 Comp. 6-2 Evaluation Difference between 6.0 1.5 17.3 21.9 25.2 14.4 8.5 Items Max and Min Torsion Angle Errors (m) Torsion Angle Error 3 (m) 25.1 28.9 31.3 40.6 45.3 54.4 36.0 Tooth-flank Hardness (HV) 318 308 332 426 394 331 352 Difference between 4 3 14 38 25 43 24 Max and Min Tooth-flank Hardnesses (HV) Effective Carburized Depth (mm) 1.04 0.90 1.05 1.43 1.34 1.06 1.10 Effective Carburized Depth 3 (mm) 0.06 0.10 0.18 0.50 0.24 0.22 0.23
Evaluation Results

(46) As shown in Tables 2 and 3, when mass-quenching is performed using the sample oil satisfying the conditions according to the invention (Example 1), distortion unevenness and hardness unevenness are reduced (Examples 1-1 and 1-2). It is also found that the sample oil can be favorably used for materials in different shapes.

(47) In contrast, it can be understood from Comparatives that the distortion unevenness and hardness unevenness accompanying mass-quenching cannot be reduced unless all the conditions (i.e., the viscosity ranges of the low-viscosity base oil and the high-viscosity base oil, the mixing ratio of the low-viscosity base oil and the high-viscosity base oil, and blending of the alpha-olefin copolymer) are satisfied.

(48) It should be noted that the characteristic time (sec) is one second or less and the maximum cooling rate is 400 degrees C./s or less in each of Examples 1-1 and 1-2.