Heat treatment oil

Abstract

To provide a heat treatment oil having excellent thermal stability and with which it is possible to maintain luster for a long period.SOLUTION: A heat treatment oil contains a base oil including a mineral oil (A). The mineral oil (A) has a kinetic viscosity of 100-600 mm2 / s at 40°C. The heat treatment oil has a sulfur component content of 0.10-0.20 mass%, and the content of the mineral oil (A) is greater than 0.5 mass% with respect to the total amount of the base oil.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to heat treatment oil.

Background Art

[0002] Metal materials such as steel materials may be subjected to heat treatments such as quenching, tempering, annealing, and normalizing for the purpose of improving their properties. Among these heat treatments, quenching is a process of immersing a heated metal material in a coolant to transform it into a predetermined quenched structure. By quenching, the metal material becomes very hard and its mechanical strength is improved.

[0003] As a coolant for quenching, a heat treatment oil composition is widely used. In addition to the performance as a coolant, the heat treatment oil composition is also required to have the performance of maintaining the surface gloss of the metal material before quenching even after quenching from the viewpoint of enhancing the commercial value of the metal material after quenching. That is, the heat treatment oil composition is required to have the performance of making the brilliance of the metal material after quenching good.

[0004] For example, in Patent Document 1, at least one of a mineral oil and a synthetic oil having a sulfur content of 300 mass ppm or less and at least one of sulfur and sulfur compounds are blended to adjust the total sulfur content to 3 mass ppm to 1000 mass ppm, and a base oil, and at least one selected from the group consisting of an alkaline earth metal salt of sulfonic acid, an alkaline earth metal salt of phenol, an alkenyl succinic acid derivative, a fatty acid, a fatty acid derivative, a phenolic antioxidant, and an amine antioxidant. By using the heat treatment oil composition thus obtained, it has been proposed to make the brilliance of the metal material after quenching good.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, as a result of investigations by the present inventors, even in the case of heat treatment oils to which these additives were added, there were problems such as poor thermal stability and difficulty in maintaining luster over a long period of time. The present invention has been made in view of the above problems, and an object thereof is to provide a heat treatment oil having excellent thermal stability and capable of maintaining luster over a long period of time.

Means for Solving the Problems

[0007] As a result of intensive investigations by the present inventors, it has been found that a heat treatment oil containing a specific mineral oil can solve the above problems, and the present invention has been completed.

[0008] That is, the present invention provides the following [1] and [2]. [1] A heat treatment oil containing a base oil containing a mineral oil (A), wherein the mineral oil (A) has a kinematic viscosity at 40 ° C of 100 to 600 mm 2 / s and a sulfur content of 0.10 to 0.20 mass%, and the content of the mineral oil (A) is more than 0.5 mass% based on the total amount of the base oil. [2] A method for manufacturing a metal member, which includes a cooling step of immersing a heated metal member in the heat treatment oil of [1] in which the oil temperature is maintained at 120 ° C or higher and cooling it.

Effects of the Invention

[0009] According to the present invention, it is possible to provide a heat treatment oil having excellent thermal stability and capable of maintaining luster over a long period of time.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] The upper and lower limit values of the numerical ranges described in this specification can be arbitrarily combined. For example, when the numerical ranges "A to B" and "C to D" are described, the numerical ranges "A to D" and "C to B" are also included in the scope of the present invention. In addition, the numerical range "lower limit value to upper limit value" described in this specification means, unless otherwise specified, that it is greater than or equal to the lower limit value and less than or equal to the upper limit value. In addition, in this specification, the numerical values of the examples are numerical values that can be used as the upper limit value or the lower limit value.

[0012] [Heat treatment oil] The heat treatment oil of the present embodiment is a heat treatment oil containing a base oil containing mineral oil (A), The mineral oil (A) has a kinematic viscosity at 40 °C of 100 to 600 mm 2 / s, and the sulfur content is 0.10 to 0.20 mass%, The content of the mineral oil (A) is more than 0.5 mass% based on the total amount of the base oil.

[0013] As a result of intensive studies by the present inventors to solve the above problems, it has been found that the sulfur content contained in a specific mineral oil can provide a heat treatment oil having excellent thermal stability and capable of maintaining luster for a long time, and the present invention has been completed.

[0014] Hereinafter, each component contained in the heat treatment oil of the present embodiment will be described.

[0015] [Base oil] The heat treatment oil of the present embodiment contains a base oil. The base oil contains at least mineral oil (A), but may further contain mineral oil (B) and other base oil components. It is preferable that the total content of the mineral oil (A) and the mineral oil (B) is 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 98% by mass or more. Furthermore, it is particularly preferable that it consists only of the mineral oil (A) or consists only of the mineral oil (A) and the mineral oil (B).

[0016] When the base oil consists only of the mineral oil (A) and the mineral oil (B), the content of the mineral oil (A) is preferably 0.8 to 99.2% by mass based on the total amount of the base oil, and the content of the mineral oil (B) is preferably 0.8 to 99.2% by mass based on the total amount of the base oil.

[0017] In the heat treatment oil of the present embodiment, the content of the base oil is preferably 80.0% by mass or more, more preferably 85.0% by mass or more, still more preferably 87.0% by mass or more based on the total amount of the heat treatment oil.

[0018] <Mineral oil (A)> As the mineral oil (A), one or more selected from mineral oils conventionally used as base oils for lubricating oils can be used, and the kinematic viscosity at 40 ° C is 100 to 600 mm 2 / s and the sulfur content is 0.10 to 0.20% by mass.

[0019] Examples of the mineral oil (A) include atmospheric residue obtained by atmospheric distillation of crude oil such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; distillate oil obtained by vacuum distillation of the atmospheric residue; and the distillate oil. Mineral oils obtained by subjecting the distillate oil to one or more purification treatments such as solvent dewaxing, solvent extraction, hydrofinishing, hydrocracking, deep hydrocracking, solvent deasphalting, catalytic deasphalting, and hydroisomerization deasphalting can be mentioned. As the mineral oil (A), a distillate oil obtained by further vacuum distilling an atmospheric residue obtained by atmospheric distillation of naphthenic crude oil is preferably used, and particularly preferably, a product obtained by further subjecting the distillate oil to solvent refining is preferably used. Further, as the mineral oil (A), it may or may not be hydrotreated within the range where the effects of the present invention are exhibited with respect to the straight-run oil, but those not subjected to hydrotreatment are particularly preferred. By avoiding hydrotreatment of the straight-run oil, a mineral oil can be obtained in which a specific sulfur compound contained in the straight-run oil and capable of forming a suitable sulfide film on the surface of the metal member during heat treatment to improve brightness remains, and thus it is preferably used in the heat treatment oil of the present embodiment. That is, as the mineral oil (A), it is preferably one obtained by subjecting the atmospheric residue obtained by atmospheric distillation of naphthenic base crude oil to solvent refining with respect to the straight-run oil obtained by further vacuum distillation, and not subjected to various hydrotreatments such as hydrofinishing, hydrocracking, deep hydrocracking, and hydroisomerization dewaxing.

[0020] The kinematic viscosity of the mineral oil (A) preferably falls within the following range from the viewpoint of having good cooling performance for the upper limit value, and from the viewpoint of obtaining a heat treatment oil with a high flash point and suppressing the generation of oil fumes for the lower limit value. The kinematic viscosity of the mineral oil (A) at 40 °C should be 100 mm 2 / s or more, preferably 110 mm 2 / s or more, more preferably 120 mm 2 / s or more, and should be 600 mm 2 / s or less, preferably 550 mm 2 / s or less, more preferably 500 mm 2 / s or less. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it should be 100 mm 2 / s to 600 mm 2 / s, preferably 110 mm 2 / s to 550 mm 2 / s, more preferably 120 mm 2 / s to 500 mm 2 / s. The kinematic viscosity of the mineral oil (A) at 100 °C is preferably 3.0 mm 2 / s or more, more preferably 5.0 mm 2 / s or more, still more preferably 7.0 mm 2 / s or more, and also 50.0 mm2 Preferably, it is 40.0 mm / s or less, 2 more preferably, it is 30.0 mm / s or less, 2 even more preferably, it is less. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, 3.0 mm / s 2 to 50.0 mm / s 2 is preferable, and 5.0 mm / s 2 to 40.0 mm / s 2 is more preferable, and 7.0 mm / s 2 to 30.0 mm / s 2 is even more preferable. The kinematic viscosity at 40 °C and the kinematic viscosity at 100 °C can be measured in accordance with JIS K 2283:2000.

[0021] As the mineral oil (A), from the viewpoint of selecting a mineral oil containing the specific sulfur compound described above, %C by ring analysis (n-d-M method) N is preferably 29.0 to 47.0, more preferably 30.0 to 45.0, and even more preferably 32.0 to 43.0. Similarly, as the mineral oil (A), %C by ring analysis (n-d-M method) A is preferably 5.0 to 25.0, more preferably 8.0 to 22.0, and even more preferably 11.0 to 20.0. In this specification, the ring analysis (n-d-M method) is carried out in accordance with ASTM D 3238-95.

[0022] In the heat treatment oil of this embodiment, the content of the mineral oil (A) needs to be more than 0.5% by mass based on the total amount (100% by mass) of the base oil, preferably 0.7 to 100% by mass, more preferably 0.8 to 100% by mass, and even more preferably 0.9 to 100% by mass.

[0023] As described above, the mineral oil (A) used in this embodiment has a sulfur content of 0.10 to 0.20% by mass based on the total amount of the mineral oil (A), and the sulfur content indicates a value measured in accordance with the wavelength dispersive X-ray fluorescence method of JIS K 2541-7:2013. The sulfur content of the mineral oil (A) is preferably 0.11 to 0.17% by mass.

[0024] <Mineral oil (B)> In addition to the above-mentioned mineral oil (A), the base oil may further contain mineral oil (B). As the mineral oil (B), one or more selected from mineral oils conventionally used as base oils for lubricating oils can be used, but it is necessary that the sulfur content in the total amount of the mineral oil (B) is 100 mass ppm or less. If the sulfur content exceeds 100 mass ppm, sulfur compounds contained in the mineral oil may sulfide and discolor the surface of the metal member during heat treatment.

[0025] Examples of the mineral oil (B) include atmospheric residue obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; distillate oil obtained by vacuum distillation of the atmospheric residue; and mineral oil obtained by subjecting the distillate oil to one or more purification treatments such as solvent deasphalting, solvent extraction, hydrofinishing, hydrocracking, deep hydrocracking, solvent dewaxing, catalytic dewaxing, and hydroisomerization dewaxing.

[0026] <Other base oil components> The base oil may contain other base oil components other than the above-mentioned mineral oil (A) and mineral oil (B). The other base oil components are not particularly limited as long as they do not correspond to the above-mentioned mineral oil (A) or mineral oil (B). For example, atmospheric residue obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; distillate oil obtained by vacuum distillation of the atmospheric residue; and mineral oil obtained by subjecting the distillate oil to one or more purification treatments such as solvent deasphalting, solvent extraction, hydrofinishing, hydrocracking, deep hydrocracking, solvent dewaxing, catalytic dewaxing, and hydroisomerization dewaxing can be mentioned, and various synthetic oils can also be used.

[0027] <Sulfur-containing synthetic additive> The heat treatment oil of this embodiment may contain a sulfur-containing synthetic additive. However, from the perspective of improving the thermal stability of the heat treatment oil and suppressing the deterioration of brightness due to the generation of sludge, its content is preferably less than 100 ppm by mass based on the total amount of the heat treatment oil, and more preferably less than 10 ppm by mass. Examples of the above sulfur-containing synthetic additives include sulfides and sulfones. Therefore, in the heat treatment oil of this embodiment, the total content of sulfides and sulfones is preferably less than 100 ppm by mass based on the total amount of the heat treatment oil, and more preferably less than 10 ppm by mass.

[0028] <Additive> If desired, the heat treatment oil of this embodiment may further contain additives commonly used in heat treatment oils. Examples of such additives include steam film breakers, brightness improvers, antioxidants, and detergents, and one or more selected from these can be used. That is, the heat treatment oil of this embodiment may be a heat treatment oil containing one or more selected from steam film breakers, brightness improvers, antioxidants, and detergents in addition to the above base oil, or may be a heat treatment oil consisting only of the above base oil and one or more additives selected from steam film breakers, brightness improvers, antioxidants, and detergents.

[0029] (Steam film breaker) Examples of steam film breakers include ethylene-α-olefin copolymers such as ethylene-propylene copolymers (the carbon number of α-olefin is 3 to 20); hydrogenated products of the ethylene-α-olefin copolymers; α-olefin polymers having 5 to 20 carbon atoms such as 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene; hydrogenated products of the α-olefin polymers; olefin polymers having 3 or 4 carbon atoms such as polypropylene, polybutene, and polyisobutylene; hydrogenated products of the olefin polymers; high molecular compounds such as polymethacrylate, polyacrylate, polystyrene, and petroleum resin; asphalt, etc. These steam film breakers may be used individually or in combination of two or more kinds. The number average molecular weight (Mn) of the steam film breaker is preferably usually 800 to 100,000. The number average molecular weight (Mn) of the steam film breaker is a value in terms of polystyrene measured using gel permeation chromatography (GPC). The content of the steam film breaker is preferably 0.5% by mass to 18% by mass, more preferably 1.0% by mass to 16% by mass, still more preferably 2.0% by mass to 15% by mass based on the total amount of the heat treatment oil.

[0030] (Brightness improver) Examples of the brightness improver include fats and oils; fatty acids of fats and oils; alkyl succinic acids such as alkyl succinimide; alkenyl succinic acids such as alkenyl succinimide; substituted hydroxyaromatic carboxylic acid ester derivatives and the like. These brightness improvers may be used individually or in combination of two or more kinds. The content of the brightness improver is preferably 0.1% by mass to 5.0% by mass, more preferably 0.3% by mass to 3.0% by mass, still more preferably 0.4% by mass to 2.0% by mass based on the total amount of the heat treatment oil.

[0031] (Antioxidant) Examples of the antioxidant include phenolic antioxidants and amine antioxidants. Examples of phenolic antioxidants include monocyclic phenols such as 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-4-hydroxymethylphenol, 2,6-di-tert-butylphenol, 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-butyl-4-(N,N-dimethylaminomethyl)phenol, 2,6-di-tert-amyl-4-methylphenol, and n-octadecyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate; polycyclic phenols such as 4,4'-methylenebis(2,6-di-tert-butylphenol), 4,4'-isopropylidenebis(2,6-di-tert-butylphenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-bis(2,6-di-tert-butylphenol), 4,4'-bis(2-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 2,2'-thiobis(4-methyl-6-tert-butylphenol), and 4,4'-thiobis(3-methyl-6-tert-butylphenol); and the like. Examples of amine antioxidants include diphenylamine-based antioxidants and naphthylamine-based antioxidants. Examples of diphenylamine-based antioxidants include alkylated diphenylamines having an alkyl group with 3 to 20 carbon atoms, specifically, diphenylamine, monooctyldiphenylamine, monononyldiphenylamine, 4,4'-dibutyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-dioctyldiphenylamine, 4,4'-dinonyldiphenylamine, tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, and tetranonyldiphenylamine. Examples of naphthylamine-based antioxidants include alkyl-substituted phenyl-α-naphthylamines having 3 to 20 carbon atoms, and specifically include α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine, and nonylphenyl-α-naphthylamine. These antioxidants may be used alone or in combination of two or more. The content of the antioxidant is preferably 0.01% by mass to 5.0% by mass, more preferably 0.05% by mass to 3.0% by mass, and still more preferably 0.1% by mass to 2.0% by mass based on the total amount of the heat treatment oil.

[0032] (Detergent-dispersant) As the detergent-dispersant, for example, one or more selected from the group consisting of metal detergents and ashless dispersants can be used. Examples of the metal detergent include metal sulfonate, metal salicylate, and metal phenate. Examples of the metal constituting the metal detergent include alkali metals such as sodium and potassium, and alkaline earth metals such as magnesium, calcium, and barium. Examples of the ashless dispersant include alkenyl succinimides, boron-containing alkenyl succinimides, benzylamines, boron-containing benzylamines, succinic esters, and monovalent or divalent carboxylic acid amides represented by fatty acids or succinic acid. These detergent-dispersants may be used alone or in combination of two or more. The content of the detergent-dispersant is 0.01% by mass to 5.0% by mass based on the total amount of the heat treatment oil.

[0033] [Physical properties of heat treatment oil] <Sulfur content> The heat treatment oil of this embodiment preferably has a sulfur content of 5 mass ppm to 2,000 mass ppm, more preferably 8 mass ppm to 800 mass ppm, and still more preferably 10 mass ppm to 500 mass ppm based on the total amount of the heat treatment oil composition.

[0034] <Kinematic viscosity at 40°C> For the heat treatment oil of this embodiment, the kinematic viscosity at 40°C is set according to the desired oil temperature during heat treatment such as quenching. Heat treatment oils are classified into cold oils used at low oil temperatures, hot oils used at high oil temperatures, and semi-hot oils used at intermediate oil temperatures. Cold oils are classified into Type 1 of JIS K2242:2012, and semi-hot oils and hot oils are classified into Type 2 of JIS K2242:2012. When the heat treatment oil of this embodiment is used as a cold oil, the kinematic viscosity at 40°C is preferably 5 mm 2 / s or more and less than 40 mm 2 / s. When the heat treatment oil of this embodiment is used as a semi-hot oil or a hot oil, the kinematic viscosity at 40°C is more preferably 40 mm 2 / s or more and 500 mm 2 / s or less.

[0035] [Method for manufacturing heat treatment oil] The method for manufacturing the heat treatment oil of this embodiment is not particularly limited. In the method for manufacturing the heat treatment oil of this embodiment, only the mineral oil (A) satisfying the above-mentioned kinematic viscosity at 40°C and sulfur content may be used as the heat treatment oil as it is, or a manufacturing method having a step of mixing the mineral oil (A) with one or more selected from the group consisting of the above-mentioned mineral oil (B), other base oil components, and additives may also be used.

[0036] [Uses of heat treatment oil] The heat treatment oil of this embodiment can be used during heat treatment such as quenching of metal materials, so that the metallic luster of the metal materials after heat treatment such as quenching can be made excellent. For example, it can be suitably used as a heat treatment oil composition when performing heat treatment such as quenching on various alloy steels such as carbon steel, nickel-manganese steel, chromium-molybdenum steel, and manganese steel. Therefore, the present invention provides a heat treatment method for metal members, which uses the heat treatment oil of this embodiment during heat treatment such as quenching of metal materials. At this time, when the heat treatment is a high-temperature quenching treatment, the oil temperature of the heat treatment oil is preferably set to 120°C or higher, more preferably 170°C to 250°C.

[0037] [Method for manufacturing metal members] The method for manufacturing a metal member of this embodiment performs a high-temperature quenching treatment including a cooling step of immersing a heated metal member in the above heat treatment oil having an oil temperature maintained at 120°C or higher and cooling it. It is more preferable to maintain the oil temperature in the above cooling step at 170°C to 250°C.

[0038] [One aspect of the present invention provided] According to one aspect of the present invention, the following [1] to [7] are provided. [1] A heat treatment oil containing a base oil containing mineral oil (A), wherein the mineral oil (A) has a kinematic viscosity at 40°C of 100 to 600 mm 2 / s and a sulfur content of 0.10 to 0.20% by mass, and the content of the mineral oil (A) is more than 0.5% by mass based on the total amount of the base oil. [2] The heat treatment oil according to [1], wherein %C by n-d-M ring analysis of the mineral oil (A) A is 5.0 to 25.0. [3] The heat treatment oil according to [1] or [2], containing 0.7 to 100% by mass of the mineral oil (A) based on the total amount of the base oil. [4] The heat treatment oil according to any one of [1] to [3], wherein the blending amount of the sulfur-containing synthetic additive is less than 100 ppm by mass based on the total amount of the heat treatment oil. [5] The heat treatment oil according to any one of [1] to [4], wherein the base oil further contains a mineral oil (B) having a sulfur content of 100 mass ppm or less. [6] The content of the mineral oil (A) is 0.8 to 99.2% by mass based on the total amount of the base oil, The heat treatment oil according to [5], wherein the content of the mineral oil (B) is 0.8 to 99.2% by mass based on the total amount of the base oil. [7] A method for manufacturing a metal member, including a cooling step of immersing a heated metal member in the heat treatment oil according to any one of [1] to [6] having an oil temperature maintained at 120°C or higher and cooling it, and performing a high-temperature quenching treatment.

Examples

[0039] The present invention will be specifically described by the following examples, but the present invention is not limited to the following examples. In addition, each component used in the examples and comparative examples and various properties of the obtained heat treatment oil were measured by the following methods.

[0040] [Kinematic viscosity at 40°C and 100°C] The kinematic viscosity at 40°C and 100°C of various mineral oils and heat treatment oils were measured or calculated in accordance with JIS K 2283:2000.

[0041] [Sulfur content] When the sulfur content of the mineral oil (A), mineral oil (B), other mineral oils used in each example and each comparative example, and the heat treatment oil prepared in each example and each comparative example was less than 0.05% by mass (500 mass ppm), it was measured in accordance with the ultraviolet fluorescence method of JIS K 2541-6:2013. When it was 0.05% by mass (500 mass ppm) or more, it was measured in accordance with the wavelength-dispersive fluorescent X-ray method of JIS K 2541-7:2013.

[0042] [Examples 1 to 8, and Comparative Examples 1 to 9] The following components were added in the contents shown in Tables 1 to 2 and mixed well to obtain a heat treatment oil. Details of each component used in Examples 1 to 8 and Comparative Examples 1 to 9 are as shown below.

[0043] <Mineral oil (A)> · Mineral oil A1 (obtained by solvent extraction of the lubricating oil fraction obtained by vacuum distillation of naphthenic base crude oil. Kinematic viscosity at 40 °C: 137.3 mm 2 / s, kinematic viscosity at 100 °C: 10.02 mm 2 / s, sulfur content: 0.12 mass%, naphthene content (%C N ): 41.5, aromatic content (%C A ): 13.1) · Mineral oil A2 (obtained by solvent extraction of the lubricating oil fraction obtained by vacuum distillation of naphthenic base crude oil. Kinematic viscosity at 40 °C: 316.2 mm 2 / s, kinematic viscosity at 100 °C: 16.52 mm 2 / s, sulfur content: 0.14 mass%, naphthene content (%C N ): 36.0, aromatic content (%C A ): 15.5) · Mineral oil A3 (obtained by solvent extraction of the lubricating oil fraction obtained by vacuum distillation of naphthenic base crude oil. Kinematic viscosity at 40 °C: 480.8 mm 2 / s, kinematic viscosity at 100 °C: 22.19 mm 2 / s, sulfur content: 0.16 mass%, naphthene content (%C N ): 33.7, aromatic content (%C A ): 14.4) <Mineral oil (B)> · Mineral oil B1 (obtained by mixing the dewaxed oil obtained by solvent dewaxing of the vacuum distillation residue oil with the lubricating oil fraction obtained by atmospheric distillation and vacuum distillation of intermediate base crude oil, and then performing hydrocracking. Kinematic viscosity at 40 °C: 408.8 mm 2 / s, kinematic viscosity at 100 °C: 30.88 mm 2 / s, sulfur content: less than 100 mass ppm, naphthene content (%C N ): 27.0, aromatic content (%C A ): 0.0) · Mineral oil B2 (obtained by hydrocracking the lubricating oil fraction obtained by atmospheric distillation and vacuum distillation of intermediate base crude oil. Kinematic viscosity at 40 °C: 89.41 mm 2 / s, kinematic viscosity at 100 °C: 10.70 mm 2 / s, sulfur content: less than 100 mass ppm, naphthene content (%C N ): 25.5, aromatic content (%C A ): 3.7) · Mineral oil B3 (obtained by mixing the deasphalted oil obtained by solvent deasphalting the vacuum residue oil with the lubricating oil fraction obtained by atmospheric distillation and vacuum distillation of intermediate-base crude oil, and subjecting it to hydrocracking. Kinematic viscosity at 40 °C: 441.6 mm 2 / s, kinematic viscosity at 100 °C: 32.07 mm 2 / s, sulfur content: 96 mass ppm, naphthene content (%C N ): 25.1, aromatic content (%C A ): 3.6) <Other mineral oils> · Mineral oil C1 (obtained by subjecting the vacuum residue oil obtained by atmospheric distillation and vacuum distillation of intermediate-base crude oil to solvent extraction and then hydrofinishing with respect to the deasphalted oil obtained by solvent deasphalting. Kinematic viscosity at 40 °C: 495.8 mm 2 / s, kinematic viscosity at 100 °C: 31.79 mm 2 / s, sulfur content: 1.18 mass%, naphthene content (%C N ): 23.3, aromatic content (%C A ): 7.0) · Mineral oil C2 (obtained by subjecting the vacuum residue oil obtained by atmospheric distillation and vacuum distillation of intermediate-base crude oil to solvent extraction and then hydrofinishing with respect to the deasphalted oil obtained by solvent deasphalting. Kinematic viscosity at 40 °C: 479.5 mm 2 / s, kinematic viscosity at 100 °C: 31.65 mm 2 / s, sulfur content: 0.47 mass%, naphthene content (%C N ): 23.6, aromatic content (%C A ): 5.8) · Mineral oil C3 (obtained by subjecting the lubricating oil fraction obtained by atmospheric distillation and vacuum distillation of intermediate-base crude oil to solvent extraction and then hydrofinishing. Kinematic viscosity at 40 °C: 20.10 mm 2 / s, kinematic viscosity at 100 °C: 4.070 mm 2 / s, sulfur content: 1000 mass ppm, naphthene content (%C N ): 28.2, aromatic content (%C A ): 4.9) · Mineral oil C4 (obtained by subjecting the lubricating oil fraction obtained by atmospheric distillation and vacuum distillation of intermediate-base crude oil to solvent extraction and then hydrofinishing. Kinematic viscosity at 40 °C: 102.5 mm 2 / s, kinematic viscosity at 100 °C: 11.300 mm 2 / s, sulfur content: 5300 mass ppm, naphthene content (%C N ): 24.1, aromatic content (%C A ): 7.0) · Mineral oil C5 (obtained by subjecting a naphthene-based crude oil to vacuum distillation and then performing solvent extraction on the resulting lubricating oil fraction. Kinematic viscosity at 40°C: 27.13 mm 2 / s, kinematic viscosity at 100°C: 4.158 mm 2 / s, sulfur content: 700 mass ppm, naphthene content (%C N ): 47.3, aromatic content (%C A ): 10.2)

[0044] The above raw materials were thoroughly mixed in the blending amounts (mass %) shown in Tables 1 to 2, and heat treatment oils of Examples 1 to 8 and Comparative Examples 1 to 9 were prepared respectively, and the following glow property evaluation and thermal stability evaluation were performed.

[0045] <Glow property evaluation> With reference to "Influence of Oxygen in the Heat Treatment Oil Tank on Glow Property (Discharge Tribo Review, No. 31, pp. 1963 - 1966, issued on September 30, 2008)", the glow property of the steel material after quenching was evaluated. Specifically, a dumbbell-shaped steel material S45C (diameter: 16 mm, length: 30 mm, hardness H RC : 16) and a cylindrical steel material SUJ2 (diameter: 10 mm, length: 30 mm, hardness H RC : 15) were combined to form a test piece. Specifically, using a SUS303 wire, the dumbbell-shaped steel material S45C and the cylindrical steel material SUJ2 were tied at the central part to bind the dumbbell-shaped steel material S45C and the cylindrical steel material SUJ2 (see Figure 1). Then, the test piece was heated in a furnace with a mixed gas atmosphere of nitrogen and hydrogen, and after that, the test piece was put into the heat treatment oil composition for quenching, and a quenching test was conducted. The conditions of the quenching test were as follows.

[0046] (Hot oil assumed test) Furnace temperature: 850°C Holding time of the test piece in the furnace: 40 minutes after the furnace temperature reaches 850°C Temperature of the heat treatment oil: 120°C Immersion time of the test piece in the heat treatment oil (quenching time): 10 minutes

[0047] Regarding the test piece after quenching, focusing on "brightness", "coloring at the end", and "coloring at the contact part", the brightness was evaluated based on the following criteria. Also, based on the evaluation results of "brightness", "coloring at the end", and "coloring at the contact part", the brightness of the test piece was comprehensively evaluated according to the following criteria. (Brightness) An appearance sample with a predetermined coloring was prepared and visually compared and evaluated with the color of the test piece after quenching. The degree of coloring of the appearance sample is indicated by the numerical values shown below. 0: No coloring at all. 1: Slight coloring. 2: Coloring in blackish brown to black. (Coloring at the end) The end of the test piece (refer to Figure 1) was visually observed and evaluated according to the following criteria. 0: No coloring or almost no coloring. 1: Slight coloring is recognized. 2: Coloring in blackish brown to black is recognized. (Coloring at the contact part) The test piece (the contact part between the dumbbell-shaped steel material and the cylindrical steel material, refer to Figure 1) was visually observed and evaluated according to the following criteria. 0: No coloring or almost no coloring. 1: Slight coloring is recognized. 2: Coloring in blackish brown to black is recognized.

[0048] (Comprehensive evaluation of brightness) Using the evaluation results of "brightness", "coloring at the end", and "coloring at the contact part", a comprehensive evaluation was conducted based on the following criteria. Evaluation S: The sum of the evaluation results of "brightness", "coloring at the end", and "coloring at the contact part" is 0 Evaluation A: The sum of the evaluation results of "brightness", "coloring at the end", and "coloring at the contact part" is 1 Evaluation B: The sum of the evaluation results of "brightness", "coloring at the end", and "coloring at the contact part" is 2 Evaluation C: The sum of the evaluation results of "brightness", "coloring at the end", and "coloring at the contact part" is 3 or more However, when the evaluation result of any one of "brightness", "coloring at the end", and "coloring at the contact part" is 2 or more, the evaluation was set as C. The heat treatment oil composition with evaluation S has extremely excellent brightness. The heat treatment oil composition with evaluation A has excellent brightness. On the other hand, the heat treatment oil composition with evaluation B has slightly inferior brightness. The heat treatment oil composition with evaluation C has inferior brightness.

[0049] <Heat stability evaluation> In accordance with the JIS-2540 heat stability test, the sample oil after 96 hours at 175°C was visually confirmed, and the presence or absence of sludge was evaluated according to the following criteria. Evaluation A: No sludge in the sample oil Evaluation F: Sludge present in the sample oil

[0050]

Table 1

[0051]

Table 2

[0052] As can be seen from Tables 1 to 2, it can be seen that the lubricating oil compositions of Examples 1 to 8 that satisfy all the configurations of the present invention are excellent in brightness and heat stability. On the other hand, it can be seen that the lubricating oil compositions of Comparative Examples 1 to 9 are inferior to the lubricating oil compositions of Examples 1 to 8 in terms of brightness and heat stability.

Claims

1. A heat treatment oil containing a base oil containing mineral oil (A) or mineral oils (A) and (B), The mineral oil (A) has a kinematic viscosity at 40 °C of 100 to 600 mm ２ / s and a sulfur content of 0.10 to 0.20% by mass, wherein the sulfur content of the mineral oil (B) is 100 mass ppm or less, the content of the mineral oil (A) exceeds 0.5 mass% based on the total amount of the base oil, the total content of the mineral oils (A) and (B) is 80 mass% or more based on the total amount of the base oil, the content of the base oil in the heat treatment oil is 80 mass% or more based on the total amount of the heat treatment oil, and when a sulfur-containing synthetic additive is blended, the blending amount is less than 100 mass ppm based on the total amount of the heat treatment oil.

2. % C by n-d-M ring analysis of the mineral oil (A) Ａ The heat treatment oil according to claim 1, wherein Ａ is 5.0 to 25.

0.

3. The heat treatment oil according to claim 1 or 2, wherein the mineral oil (A) is contained in an amount of 0.7 to 100 mass% based on the total amount of the base oil.

4. The heat treatment oil according to any one of claims 1 to 3, wherein the content of the mineral oil (A) is 0.8 to 99.2 mass% based on the total amount of the base oil, and the content of the mineral oil (B) is 0.8 to 99.2 mass% based on the total amount of the base oil.

5. A method for manufacturing a metal member, including a cooling step of immersing a heated metal member in the heat treatment oil according to any one of claims 1 to 4, in which the oil temperature is maintained at 120°C or higher, for cooling, thereby performing a high-temperature quenching treatment.

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