HEAT TREATMENT OIL COMPOSITION

Abstract

A heat treatment oil composition is provided that is capable of reducing the fluctuation in cooling capability among components subjected to mass quenching while retaining a cooling capability equivalent to the No. 1 oil of Class 2 of JIS K2242:2012 in a heat treatment of a metal material, such as quenching, and is capable of suppressing deterioration in cooling capability thereof with the lapse of time under repetition of the heat treatment. The heat treatment oil composition contains (A) a base oil and (B) at least one selected from a petroleum resin and/or a derivative of a petroleum resin, and has a characteristic time obtained from a cooling curve obtained according to the cooling capability test method of JIS K2242:2012 of 1.00 second or less and a 300 C. number of second, which is a cooling time from 800 C. to 300 C. in the cooling curve, of 6.00 seconds or more and 14.50 seconds or less.

Claims

1. A heat treatment oil composition, comprising: (A) a base oil; and (B) at least one selected from the group consisting of a petroleum resin, a derivative of a petroleum resin, and a mixture thereof, wherein the heat treatment oil composition has a characteristic time obtained from a cooling curve obtained according to the cooling capability test method of JIS K2242:2012 of 1.00 second or less, and a 300 C. number of second, which is a cooling time from 800 C. to 300 C. in the cooling curve, of 6.00 seconds or more and 14.50 seconds or less.

2. The heat treatment oil composition according to claim 1, wherein the petroleum resin, the derivative of a petroleum resin, or both, has a softening point measured by the ring and ball method of JIS K2207:2006 of 40 C. or more.

3. The heat treatment oil composition according to claim 2, wherein the petroleum resin, the derivative of a petroleum resin, or both, has a softening point measured by the ring and ball method of JIS K2207:2006 of 60 C. or more and 150 C. or less.

4. The heat treatment oil composition according to claim 1, wherein the base oil as the component (A) has a 40 C. kinetic viscosity of from 40 to 500 mm.sup.2/s.

5. The heat treatment oil composition according to claim 1, comprising: from 10 to 99.9% by mass of the base oil; and from 0.1 to 90% by mass of the petroleum resin, the derivative of a petroleum resin, or both, based on a total mass of the heat treatment oil composition.

6. The heat treatment oil composition according to claim 1, wherein the heat treatment oil composition has a 100 C. kinetic viscosity of from 10 to 30 mm.sup.2/s.

Description

DESCRIPTION OF EMBODIMENTS

[0032] Embodiments of the present invention will be described below. The heat treatment oil composition of the embodiment contains (A) a base oil and (B) at least one selected from a petroleum resin and/or a derivative of a petroleum resin, and has a characteristic time obtained from a cooling curve obtained according to the cooling capability test method of JIS K2242:2012 of 1.00 second or less and a 300 C. number of second, which is a cooling time from 800 C. to 300 C. in the cooling curve, of 6.00 seconds or more and 14.50 seconds or less.

[(A) Base Oil]

[0033] Examples of the base oil as the component (A) include a mineral oil and/or a synthetic oil.

[0034] Examples of the mineral oil include a paraffin-based mineral oil, an intermediate-based mineral oil, and a naphthene-based mineral oil, which are obtained by an ordinary refining method, such as solvent refining and hydrogenation refining; and a wax isomerized oil, which is produced through isomerization of wax, such as was produced by the Fischer-Tropsch process or the like (gas-to-liquid wax), and mineral oil wax.

[0035] Examples of the synthetic oil include a hydrocarbon synthetic oil and an ether synthetic oil. Examples of the hydrocarbon synthetic oil include an alkylbenzene and an alkylnaphthalene. Examples of the ether synthetic oil include a polyoxyalkylene glycol and a polyphenyl ether.

[0036] The base oil as the component (A) may be a single component system using one of the mineral oils and the synthetic oils described above, or may be a mixed system obtained by mixing two or more of the mineral oils, mixing two or more of the synthetic oils, or mixing one or two or more each of the mineral oils and the synthetic oils.

[0037] The base oil as the component (A) preferably has a 40 C. kinetic viscosity of 40 mm.sup.2/s or more and 500 mm.sup.2/s or less, more preferably 50 mm.sup.2/s or more and 350 mm.sup.2/s or less, and further preferably 60 mm.sup.2/s or more and 200 mm.sup.2/s or less.

[0038] When the 40 C. kinetic viscosity of the base oil as the component (A) is in the range, the essential cooling capability based on the component (A) can be easily ensured to control the characteristic time and the 300 C. number of second to the ranges described later.

[0039] In the case where the base oil as the component (A) is a base oil containing two or more base oils mixed, the mixed base oil preferably has a kinetic viscosity that satisfies the aforementioned range.

[0040] In the embodiment, the kinetic viscosity of the base oil and the heat treatment oil composition can be measured according to JIS K2283:2000.

[0041] The content ratio of the base oil as the component (A) based on the total amount of the heat treatment oil composition is preferably from 10 to 99.9% by mass, more preferably from 50 to 98% by mass, and further preferably from 80 to 95% by mass.

[0042] When the content ratio of the component (A) is 80% by mass or more, the essential cooling capability based on the component (A) can be ensured, and when the content ratio of the component (A) is less than 100% by mass, the amount of the petroleum resin and/or the derivative of a petroleum resin as the component (B) used can be ensured to facilitate the effect based on the component (B) described later.

[(B) Petroleum Resin and/or Derivative of Petroleum Resin]

[0043] The heat treatment oil composition of the embodiment contains (B) at least one of a petroleum resin and/or a derivative of a petroleum resin. The petroleum resin and/or the derivative of a petroleum resin as the component (B) has a function of a vapor blanket breaking agent.

[0044] The use of the petroleum resin and/or the derivative of a petroleum resin as a vapor blanket breaking agent can shorten the vapor blanket stage, and the cooling capability of the heat treatment composition can be easily equivalent to the No. 1 oil of Class 2 of JIS K2242:2012.

[0045] The use of the petroleum resin and/or the derivative of a petroleum resin can shorten the vapor blanket stage, and thus the vapor blanket stage and the boiling stage can be suppressed from being mixedly present on the surface of the metal material. Accordingly, the use of the petroleum resin and/or the derivative of a petroleum resin can suppress the fluctuation in cooling capability (i.e., the fluctuation in hardness and distortion) among components subjected to mass quenching from being formed. In the case where the component has a complex shape, the use of the petroleum resin and/or the derivative of a petroleum resin can suppress the fluctuation in cooling capability among portions of the component, and thus the distortion of the component can be suppressed.

[0046] Furthermore, in the case where the heat treatment of the metal material is performed repeatedly, the use of the petroleum resin and/or the derivative of a petroleum resin can suppress the deterioration in cooling capability of the heat treatment oil composition with the lapse of time. Specifically, in the case where the heat treatment of the metal material is performed repeatedly, the increase with the lapse of time of the number of second (characteristic time) until reaching the temperature where the vapor blanket stage ends and the decrease with the lapse of time of the kinetic viscosity can be suppressed. Accordingly, the use of the petroleum resin and/or the derivative of a petroleum resin can prolong the lifetime of the heat treatment oil composition.

[0047] The petroleum resin and/or the derivative of a petroleum resin can shorten the characteristic time in the initial stage of the heat treatment.

[0048] It is considered that the petroleum resin and/or the derivative of a petroleum resin can exhibit the aforementioned effects due to the thermoplastic characteristics of the petroleum resin and/or the derivative of a petroleum resin and the excellent solubility thereof in the base oil.

[0049] The petroleum resin is a resin that is obtained through polymerization or copolymerization of one kind or two or more kinds of an unsaturated compound selected from an aliphatic olefin compound and an aliphatic diolefin compound having a number of carbon atoms of from 4 to 10 obtained as a by-product in the production of an olefin, such as ethylene, through thermal cracking of a petroleum product, such as naphtha, and an aromatic compound having a number of carbon atoms of 8 or more and having an olefinic unsaturated bond. The petroleum resin can be roughly classified, for example, into an aliphatic petroleum resin obtained through polymerization of an aliphatic olefin compound or an aliphatic diolefin compound, an aromatic petroleum resin obtained through polymerization of an aromatic compound having an olefinic unsaturated bond, and an aliphatic-aromatic copolymerized petroleum resin obtained through copolymerization of an aliphatic olefin compound or an aliphatic diolefin compound and an aromatic compound having an olefinic unsaturated bond.

[0050] Examples of the aliphatic olefin compound having a number of carbon atoms of from 4 to 10 include butene, pentene, hexene, and heptene. Examples of the aliphatic diolefin compound having a number of carbon atoms of from 4 to 10 include butadiene, pentadiene, isoprene, cyclopentadiene, dicyclopentadiene, and methylpentadiene. Examples of the aromatic compound having a number of carbon atoms of 8 or more and having an olefinic unsaturated bond include styrene, -methylstyrene, -methylstyrene, vinyltoluene, vinylxylene, indene, methylindene, and ethylindene.

[0051] The raw material compound of the petroleum resin may not be entirely a by-product in the production of an olefin through thermal cracking of a petroleum product, such as naphtha, and a chemically synthesized unsaturated compound may also be used. Examples thereof include a dicyclopentadiene petroleum resin obtained through polymerization of cyclopentadiene or dicyclopentadiene, and a dicyclopentadiene-styrene petroleum resin obtained through copolymerization of cyclopentadiene or dicyclopentadiene and styrene.

[0052] Examples of the derivative of a petroleum resin include a hydrogenated petroleum resin obtained by adding hydrogen atoms to the aforementioned petroleum resin. Examples of the derivative of a petroleum resin also include an acid-modified petroleum resin obtained through modification of the petroleum resin with an acidic functional group represented by a carboxylic acid, and a compound obtained through reaction modification of the acid-modified petroleum resin with a compound, such as an alcohol, an amine, an alkali metal, and an alkaline earth metal.

[0053] The acid-modified petroleum resin can be roughly classified into a carboxylic acid-modified petroleum resin and an acid anhydride-modified petroleum resin obtained through modification of the petroleum resin with an unsaturated carboxylic acid and an unsaturated carboxylic acid anhydride. Examples of the unsaturated carboxylic acid include an unsaturated monocarboxylic acid, such as acrylic acid and methacrylic acid; an unsaturated polybasic carboxylic acid, such as maleic acid, fumaric acid, itaconic acid, and citraconic acid; and a partial ester compound of an unsaturated polybasic carboxylic acid, such as monomethyl maleate and monoethyl fumarate, and examples of the unsaturated carboxylic acid anhydride include an unsaturated polybasic carboxylic acid anhydride, such as maleic anhydride and itaconic anhydride.

[0054] The petroleum resin or the derivative of a petroleum resin is preferably an aliphatic-aromatic copolymerized petroleum resin or a hydrogenated aliphatic-aromatic copolymerized petroleum resin since the characteristic time tends to be decreased.

[0055] The number average molecular weight of the petroleum resin or the derivative of a petroleum resin is preferably from 200 to 5,000, more preferably from 250 to 2,500, and further preferably from 300 to 1,500, from the standpoint of easily exhibiting the effect of the embodiment.

[0056] The petroleum resin and/or the derivative of a petroleum resin preferably has a softening point measured by the ring and ball method of JIS K2207:2006 of 40 C. or more, more preferably 60 C. or more and 150 C. or less, further preferably 80 C. or more and 140 C. or less, and still further preferably 85 C. or more and 130 C. or less.

[0057] When the softening point of the petroleum resin and/or the derivative of a petroleum resin is 40 C. or more, the fluctuation in cooling capability (i.e., the fluctuation in hardness and distortion) among components subjected to mass quenching can be prevented from being formed, and simultaneously in the case where the component has a complex shape, the fluctuation in cooling capability among portions of the component can be prevented from being formed, and thus the distortion of the component can be suppressed.

[0058] Furthermore, when the softening point of the petroleum resin and/or the derivative of a petroleum resin is 40 C. or more, the deterioration in cooling capability with the lapse of time (i.e., the increase of the characteristic time with the lapse of time and the decrease of the kinetic viscosity with the lapse of time) in the case where the heat treatment of the metal material is performed repeatedly can be suppressed, and simultaneously the characteristic time in the initial stage of the heat treatment can be decreased. Accordingly, when the softening point of the petroleum resin and/or the derivative of a petroleum resin is 40 C. or more, the cooling capability of the heat treatment oil composition can be retained not only in the initial stage but also after the repeated use, and the fluctuation in cooling capability among components subjected to mass quenching and the distortion of the component can be suppressed over a prolonged period of time.

[0059] When the softening point of the petroleum resin and/or the derivative of a petroleum resin is 150 C. or less, stickiness on the surface of the processed material, such as the metal material, having been cooled with the heat treatment oil composition can be suppressed.

[0060] The softening point of the petroleum resin and/or the derivative of a petroleum resin can be controlled by the polymerization degree of the petroleum resin, the modification component therefore, and the modification degree thereof.

[0061] In the case where two or more kinds of materials are used as the petroleum resin and/or the derivative of a petroleum resin, all the materials preferably have a softening point within the aforementioned range.

[0062] The content ratio of the petroleum resin and/or the derivative of a petroleum resin as the component (B) based on the total amount of the heat treatment oil composition is preferably from 0.1 to 90% by mass, more preferably from 2 to 50% by mass, and further preferably from 5 to 20% by mass.

[0063] When the content ratio of the component (B) is 0.1% by mass or more, the effect based on the component (B) described above can be easily obtained. When the content ratio of the component (B) is 90% by mass or less, the amount of the base oil being the component (A) used, which secures the essential cooling capability, can be ensured to impart the cooling capability to the heat treatment oil composition.

[0064] The total content of the component (A) and the component (B) is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 100% by mass, based on the total amount of the heat treatment oil composition.

[0065] The heat treatment oil composition may contain an additional vapor blanket breaking agent other than the petroleum resin and/or the derivative of a petroleum resin, in such a range that does not impair the effect of the embodiment. Examples of the additional vapor blanket breaking agent include a terpene resin, a derivative of a terpene resin, rosin, and a derivative of rosin.

[(C) Additives]

[0066] The heat treatment oil composition of the embodiment may contain an additive, such as an antioxidant and a cooling capability improver.

[0067] The content ratios of the antioxidant, the cooling capability improver, and the like each are preferably 10% by mass or less, and more preferably from 0.01 to 5% by mass based on the total amount of the heat treatment oil composition.

[Properties of Heat Treatment Oil Composition]

[0068] The heat treatment oil composition of the embodiment necessarily has a characteristic time obtained from a cooling curve obtained according to the cooling capability test method of JIS K2242:2012 of 1.00 second or less.

[0069] When the characteristic time of the heat treatment oil composition exceeds 1.00 second, it is difficult to reduce the fluctuation in cooling capability among components subjected to mass quenching, and it is difficult to suppress the distortion of the component.

[0070] The characteristic time of the heat treatment oil composition is preferably 0.95 second or less, and more preferably 0.90 second or less.

[0071] The characteristic time can be more specifically calculated by the following procedures (1) and (2).

[0072] (1) According to the cooling capability test method of JIS K2242:2012, a silver specimen heated to 810 C. is placed in the heat treatment oil composition, and a cooling curve is obtained with the x-axis for the time and the y-axis for the temperature on the surface of the silver specimen.

[0073] (2) In the cooling curve, the number of second until reaching the temperature (characteristic temperature) where the vapor blanket stage of the heat treatment oil composition ends is calculated by the tangent crossover method, and the number of second is designated as the characteristic time.

[0074] In the procedure (1), the time interval of measurement is preferably 1/100 second.

[0075] The heat treatment oil composition of the embodiment necessarily has a 300 C. number of second, which is a cooling time from 800 C. to 300 C. in a cooling curve obtained according to the cooling capability test method of JIS K2242:2012, of 6.00 seconds or more and 14.50 seconds or less.

[0076] When the 300 C. number of second of the heat treatment oil composition deviates from the range, it is difficult to make the cooling capability of the heat treatment oil composition equivalent to the No. 1 oil of Class 2 of JIS K2242:2012.

[0077] The 300 C. number of second of the heat treatment oil composition is preferably from 6.50 to 13.50 seconds, and more preferably from 7.00 to 12.50 seconds.

[0078] For making the characteristic time and the 300 C. number of second of the heat treatment oil composition within the aforementioned ranges, it is preferred to make the content and the 40 C. kinetic viscosity of the component (A) and the content, the softening point, and the number average molecular weight of the component (B) within the aforementioned ranges.

[0079] The heat treatment oil composition of the embodiment preferably has a 100 C. kinetic viscosity of from 10 to 30 mm.sup.2/s, and more preferably from 15 to 20 mm.sup.2/s.

EXAMPLES

[0080] The present invention will be described more specifically with reference to examples below, but the present invention is not limited to the examples. [0081] A. Evaluations and Measurements [0082] A-1. Hardness and Distortion

[0083] As a material for evaluating quenching, a case hardened steel having a cylindrical shape (outer diameter: 85 mm, height: 44 mm, thickness: 4 mm, material: SCM415) was subjected to a heat treatment or the like under the following conditions, and was further evaluated for the following items.

<Conditions for Heat Treatment, etc.>

[0084] Heat treatment condition: carburizing process: 930 C.150 min, CP (carbon potential): 1.1% by mass

[0085] Diffusion process: 930 C.60 min, CP (carbon potential): 0.8% by mass

[0086] Soaking process: 850 C.20 min, CP (carbon potential): 0.8% by mass

[0087] Oil cooling condition: oil temperature: 120 C., oil cooling time: 10 min, agitation: 20 Hz

[0088] Tempering condition: 180 C.60 min

[0089] Placing mode: sword hanger type, quenched: 8 pieces (4 pieces2)

<Evaluation Items>

[0090] Average ellipticity (mm)

[0091] Ellipticity 3 (mm)

[0092] Average taper distortion (mm)

[0093] Taper distortion 3 (mm)

[0094] Average internal hardness (1.5 mm inside quenched material, HV)

[0095] Average effective hardened layer depth (mm)

A-2. Initial Cooling Capability

[0096] According to the cooling capability test method defined in JIS K2242:2012, a silver specimen heated to 810 C. was placed in the heat treatment oil composition, a cooling curve of the silver specimen was obtained, and the characteristic time and the 300 C. number of second below were calculated. The temperature of the heat treatment oil composition before placing the silver specimen therein was 120 C. in all Examples 1-1 to 1-9, Comparative Example 1, Example 2, and Comparative Examples 2-1 and 2-2.

<Characteristic Time>

[0097] In the cooling curve, according to JIS K2242:2012, the temperature (characteristic temperature) where the vapor blanket stage of the heat treatment oil composition ended was calculated, and the number of second until reaching the temperature was designated as the characteristic time.

<300 C. Number of Second>

[0098] In the cooling curve, the cooling time from 800 C. to 300 C. was designated as the 300 C. number of second.

A-3. Temporal Stability of Cooling Capability

[0099] The result in the item A-2 above was designated as the result before the repeated quenching deterioration test. The repeated quenching deterioration test was then performed under the following condition. After performing the repeated quenching deterioration test, the same test and evaluation as in the item A-2 were performed to obtain a result, which was designated as the result after the repeated quenching deterioration test. The change rate before and after the test was calculated by the following expression (2).

[(value after testvalue before test)/value before test]100 (2)

<Test Condition>

[0100] Test piece: SUS316

[0101] Quenching temperature: 850 C.

[0102] Oil amount: 400 mL

[0103] Oil temperature: 170 C.

[0104] Number of times of quenching: 400

A-4. Kinetic Viscosity

[0105] According to JIS K2283:2000, the heat treatment oil composition was measured for the 100 C. kinetic viscosity before and after the repeated quenching deterioration test of the item A-3.

B. Preparation and Evaluation of Heat Treatment Oil Compositions

Examples 1-1 to 1-9 and Comparative Example 1

[0106] Heat treatment oil compositions having the compositions shown in Table 1 were prepared and evaluated and measured according to the items A-2 and A-4 above. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Example Example Example Example Example Example Example Example Example Comparative 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 Example 1 Base oil 1 85 85 85 85 85 85 85 85 85 100 (% by mass) Vapor Material petroleum petroleum petroleum petroleum petroleum petroleum petroleum petroleum petroleum blanket 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 breaking Content ratio 15 15 15 15 15 15 15 15 15 agent (% by mass) Total 100 100 100 100 100 100 100 100 100 100 100 C. kinetic viscosity 18.37 18.46 17.92 16.17 17.29 15.14 16.33 16.41 18.38 10.89 (mm.sup.2/s) Cooling Characteristic 0.47 0.99 0.81 0.72 0.57 0.92 0.58 0.69 0.52 2.10 capability time (sec) 300 C. 10.00 10.91 10.22 10.11 11.55 10.13 10.75 10.81 10.27 11.45 number of second (sec)

[0107] The materials shown in Table 1 are as follows.

[0108] Base oil 1: mineral oil, 40 C. kinetic viscosity: 90 mm.sup.2/s

[0109] Petroleum 1-1: partially hydrogenated aliphatic-aromatic copolymerized petroleum resin, softening point: 110 C., number average molecular weight: 760

[0110] Petroleum 1-2: aliphatic petroleum resin, softening point: 99 C., number average molecular weight: 1,300

[0111] Petroleum 1-3: aliphatic-aromatic cop olymerized petroleum resin, softening point: 103 C., number average molecular weight: 900

[0112] Petroleum 1-4: hydrogenated aliphatic petroleum resin, softening point: 105 C., number average molecular weight: 400

[0113] Petroleum 1-5: hydrogenated aliphatic petroleum resin, softening point: 125 C., number average molecular weight: 430

[0114] Petroleum 1-6: hydrogenated aliphatic petroleum resin, softening point: 87 C., number average molecular weight: 370

[0115] Petroleum 1-7: hydrogenated aliphatic petroleum resin, softening point: 103 C., number average molecular weight: 410

[0116] Petroleum 1-8: partially hydrogenated aromatic modified petroleum resin, softening point: 102 C., number average molecular weight: 500

[0117] Petroleum 1-9: aliphatic petroleum resin, softening point: 124 C., number average molecular weight: 430

[0118] As is clear from the results in Table 1, it is confirmed that the heat treatment oil compositions of Examples 1-1 to 1-9 each have a short 300 C. number of second, and thus have a cooling capability equivalent to the No. 1 oil of Class 2 of JIS K2242:2012.

[0119] It is also confirmed that the heat treatment oil compositions of Examples 1-1 to 1-9 each have a short characteristic time. Accordingly, it is understood that the suppression of the fluctuation in cooling capability among components subjected to mass quenching and the suppression of the distortion of the component can be expected by the use of the heat treatment oil compositions of Examples 1-1 to 1-9.

Example 2 and Comparative Examples 2-1 and 2-2

[0120] Heat treatment oil compositions having the compositions shown in Table 2 were prepared and evaluated and measured according to the items A-1 to A-4 above. The 100 C. kinetic viscosity of the item A-4 was measured before and after the repeated quenching deterioration test of the item A-3. The results are shown in Table 2.

TABLE-US-00002 TABLE 2 Comparative Comparative Example 2 Example 2-1 Example 2-2 Base oil Base oil 2-1 90 (% by mass) Base oil 2-2 91 Base oil 2-3 99.25 Vapor blanket Petroleum resin 2 10 breaking agent -Olefin copolymer 8 (% by mass) Antioxidant 1 0.75 Total 100 100 100 Hardness and Average ellipticity (mm) 0.120 0.170 0.197 distortion Ellipticity 3 (mm) 0.142 0.174 0.240 Average taper distortion (mm) 0.078 0.069 0.093 Taper distortion 3 (mm) 0.040 0.035 0.058 Average internal hardness (HV) 346 322 328 Average effective hardened layer 0.94 0.91 0.85 depth (mm) Cooling Before test 100 C. kinetic viscosity (mm.sup.2/s) 18.00 17.41 18.5 capability Characteristic time (sec) 0.86 0.53 1.58 300 C. number of second (sec) 10.73 11.08 10.76 After test 100 C. kinetic viscosity (mm.sup.2/s) 17.2 10.96 18.52 Characteristic time (sec) 0.90 1.07 1.52 300 C. number of second (sec) 11.00 10.12 13.81 Change 100 C. kinetic viscosity 4.4 37.0 0.1 rate before Characteristic time 4.7 101.9 3.8 and after 300 C. number of second 2.5 8.7 28.3 test (%)

[0121] The materials shown in Table 2 are as follows.

[0122] Base oil 2-1: mineral oil, 40 C. kinetic viscosity: 120 mm.sup.2/s

[0123] Base oil 2-2: mineral oil, 40 C. kinetic viscosity: 60 mm.sup.2/s

[0124] Base oil 2-3: mineral oil, 40 C. kinetic viscosity: 200 mm.sup.2/s

[0125] Petroleum resin 2: partially hydrogenated aliphatic-aromatic copolymerized petroleum resin, softening point: 110 C., number average molecular weight: 760

[0126] -Olefin copolymer: -olefin copolymer, 100 C. kinetic viscosity: 2,000 mm.sup.2/s

[0127] As is clear from the results in Table 2, it is confirmed that the heat treatment oil composition of Example 2 has a short 300 C. number of second, and thus has a cooling capability equivalent to the No. 1 oil of Class 2 of JIS K2242:2012. It is also confirmed that the heat treatment oil composition of Example 2 has small values for the ellipticity 3 and the taper distortion 3, and thus can suppress the fluctuation in distortion in mass quenching. It is further confirmed that the heat treatment oil composition of Example 2 can suppress the deterioration of the capability (i.e., the increase of the characteristic time, the increase of the 300 C. number of second, and the decrease of the kinetic viscosity) with the lapse of time in the repeated heat treatment.

[0128] Furthermore, it is confirmed that the heat treatment oil composition of Example 2 shows good values for the characteristic time and the 300 C. number of second in the initial stage, and thus can retain the good capability over a prolonged period of time, i.e., in the initial stage and after the repeated use.

INDUSTRIAL APPLICABILITY

[0129] The heat treatment oil composition of the embodiment is capable of reducing the fluctuation in cooling capability among components subjected to mass quenching while retaining a cooling capability equivalent to the No. 1 oil of Class 2 of JIS K2242:2012, and is capable of suppressing deterioration in cooling capability thereof with the lapse of time under repetition of the heat treatment of the metal material. Therefore, the heat treatment oil composition of the embodiment is favorably used as a heat treatment oil for heat treatments, such as quenching, annealing, and tempering, of an alloy steel, such as a carbon steel, a nickel-manganese steel, a chromium-molybdenum steel, and a manganese steel, and particularly favorably used as a heat treatment oil for quenching.