Heat treatment oil

Abstract

Provided is a heat treatment oil which includes a monoester (A) represented by general formula (1) as a base oil and can have both cooling properties and evaporation properties.　(1): R1-COO-R2 (In formula (1), R1 and R2 are each independently a hydrocarbon group optionally having an alkoxy group as a substituent and the total number of carbon atoms of R1 and R2 is 15-30.)

Description

Heat Treatment Oil

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

[0002] Heat treatment processes such as quenching of metal materials are usually performed using a heat treatment liquid to impart a desired hardness to the metal material. Therefore, the heat treatment liquid must have excellent cooling performance to increase the hardness of the metal material. Water is a liquid with extremely excellent cooling capacity, but water-based heat treatment liquids have an excessively high cooling performance, which can cause quench cracking in the metal material and significant quench distortion. For this reason, oil-based heat treatment liquids, i.e., heat treatment oils, are generally used in heat treatment processes such as quenching of metal materials.

[0003] As an index showing the cooling property of heat treatment oil, the quench intensity (H value) calculated from the cooling time from 800°C to 300°C in the cooling curve specified in JIS K2242:2012 is widely used.

[0004] Furthermore, when quenching a heated metal material, if it is immersed in heat treatment oil, the cooling rate is not constant. It typically cools through the following three stages: (1) the first stage (vapor film stage), in which the metal material is enveloped in the vapor of the heat treatment oil; (2) the second stage (boiling stage), in which the vapor film breaks and boiling occurs; and (3) the third stage (convection stage), in which the temperature of the metal material drops below the boiling point of the heat treatment oil and heat is removed by convection. Of these three stages, the second stage (boiling stage) has the greatest cooling rate. Furthermore, if the time until the first stage (the "characteristic number of seconds" in the cooling test in accordance with JIS K2242:2012) is long, the resulting metal material, for example, carbon steel, is likely to have insufficient hardness.

[0005] On the other hand, quenching metal materials improves their hardness, but tempering, in which they are reheated, can be performed to further impart toughness. In this case, quenching oil adheres to the metal material after quenching, so it is common to perform a cleaning process to remove the oil before tempering. However, from the perspective of improving productivity, reduction or omission of the cleaning process has been investigated. For example, Patent Document 1 discloses an invention related to a heat treatment oil containing multiple types of metal soaps, which has good aqueous cleanability after quenching. Patent Document 2 discloses a gas quenching method that uses gas as a coolant instead of heat treatment oil, thereby eliminating the need for a cleaning process. Furthermore, Patent Document 3 discloses an invention related to an apparatus equipped with a reduced-pressure drying chamber for vaporizing the heat treatment oil.

[0006] Japanese Patent Application Laid-Open No. 9-176728 Japanese Patent No. 5817173 International Publication No. 2021 / 240718

[0007] However, even if the heat treatment oil described in Patent Document 1 is used, the cleaning process cannot be completely eliminated, and there remain issues from the perspective of productivity. Next, with the gas quenching method described in Patent Document 2, depending on the cooling gas spray pressure, the H value may be insufficient, resulting in insufficient hardness of the resulting metal material. Furthermore, there is a risk of uneven cooling performance between areas with high and low cooling gas pressure. Furthermore, when using a quenching method using heat treatment oil, switching to a gas quenching method requires the complete replacement of the existing heat treatment equipment. The device described in Patent Document 3 also requires the replacement of the existing heat treatment equipment, and there is a risk of insufficient volatility depending on the heat treatment oil used.

[0008] Therefore, the object of the present invention is to provide a heat treatment oil that can achieve both cooling properties and evaporativity, from the viewpoint of utilizing existing heat treatment equipment while eliminating the need for cleaning treatment after heat treatment.

[0009] The present inventors have found that a heat-treated oil containing a specific monoester as a base oil can solve the above problems, and have completed the present invention.

[0010] That is, the present invention provides the following [1] to [9]. [1] A heat-treated oil containing a monoester (A) represented by the following general formula (1) as a base oil. R １ -COO-R ２ ...(1) (wherein, R １ and R ２ are each independently a hydrocarbon group which may have an alkoxy group as a substituent, and R １ and R ２ The total number of carbon atoms in R is 15 to 30. １ is a chain hydrocarbon group having 5 to 20 carbon atoms, and R ２ is a chain hydrocarbon group having 1 to 24 carbon atoms or an alkoxyalkyl group having 1 to 20 carbon atoms. [3] The heat treatment oil according to [1] or [2] above, wherein the content of the monoester (A) is 50 mass% or more based on the total amount of the heat treatment oil. [4] The heat treatment oil according to any one of [1] to [3] above, wherein the flash point is 150°C or higher. [5] The heat treatment oil according to any one of [1] to [4] above, which is used as a quenching oil. [6] A method for producing a metal component, comprising a quenching step of immersing a heated metal component in the heat treatment oil according to any one of [1] to [5] above and cooling the component. [7] The method for producing a metal component according to [6] above, wherein the quenching temperature in the quenching step is 500 to 1400°C. [8] The method for producing a metal component according to [6] or [7] above, comprising a tempering step of reheating the metal component without cleaning it after the quenching step. [9] The method for producing a metal member according to the above [8], wherein the heating temperature in the tempering step is 150 to 650°C.

[0011] According to the present invention, it is possible to provide a heat treatment oil that has both cooling properties and evaporative properties.

[0012] The upper and lower limit values ​​of the numerical ranges described in this specification can be combined in any way. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges "A to D" and "C to B" are also included in the scope of the present invention. Furthermore, the numerical range "lower limit to upper limit" described in this specification means that the range is equal to or greater than the lower limit and equal to or less than the upper limit, unless otherwise specified. Furthermore, in this specification, the numerical values ​​in the examples are numerical values ​​that can be used as upper or lower limit values.

[0013] [Heat Treatment Oil] The heat treatment oil of the present embodiment contains a monoester (A) represented by the following general formula (1) as a base oil: １ -COO-R ２ ...(1) (wherein, R １ and R ２ are each independently a hydrocarbon group which may have an alkoxy group as a substituent, and R １ and R ２ The total number of carbon atoms is 15 to 30.

[0014] As a result of intensive research conducted by the present inventors to solve the above problems, they have found that when a heat treatment oil contains the above specific monoester (A) as a base oil, it ensures cooling properties during heat treatment such as quenching, and also exhibits volatility to such an extent that it can be evaporated during tempering without washing after the heat treatment, making washing after the heat treatment unnecessary.

[0015] The heat-treated oil of this embodiment may consist solely of the monoester (A), but may also contain other components besides the monoester (A) as long as the effects of the present invention are not impaired. When the heat-treated oil of this embodiment contains additives, the total content of the monoester (A) and the additives is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the total amount (100% by mass) of the heat-treated oil. Furthermore, it is usually 100% by mass or less, preferably less than 100% by mass, more preferably 99% by mass or less, and even more preferably 98% by mass or less.

[0016] <Monoester (A)> The heat treatment oil of this embodiment contains a monoester (A) as a base oil. In this embodiment, the monoester (A) is represented by the following general formula (1): R １ -COO-R ２ ...(1) (wherein, R １ and R ２ are each independently a hydrocarbon group which may have an alkoxy group as a substituent, and R １ and R ２ The total number of carbon atoms in R in the above general formula (1) is 15 to 30. １ and R ２ When the total number of carbon atoms in the R group is 15 or more, the cooling property during the heat treatment is good. When the total number of carbon atoms in the R group is 30 or less, the evaporation property of the heat treatment oil is good, and the cleaning treatment after the heat treatment can be omitted, resulting in excellent productivity. １ and R ２ From the viewpoint of the cooling property of the heat treatment oil, the total number of carbon atoms is preferably 18 or more, and more preferably 22 or more, and from the viewpoint of the volatility of the heat treatment oil, the total number of carbon atoms is preferably 30 or less, and more preferably 26 or less, and specifically, is preferably 18 to 30, and more preferably 22 to 26.

[0017] The monoester (A) is represented by R in the general formula (1). １ is a chain hydrocarbon group having 5 to 20 carbon atoms, and R ２ is preferably a chain hydrocarbon group having 1 to 24 carbon atoms or an alkoxyalkyl group having 1 to 20 carbon atoms. １ is preferably an alkyl group having 5 to 20 carbon atoms, and more preferably an alkyl group having 6 to 18 carbon atoms. ２ is preferably an alkyl group having 1 to 20 carbon atoms or an alkoxyalkyl group having 1 to 20 carbon atoms, and more preferably an alkyl group having 1 to 16 carbon atoms or an alkoxyalkyl group having 1 to 16 carbon atoms.

[0018] In the heat-treated oil of this embodiment, the monoester (A) functions as a base oil. In the heat-treated oil of this embodiment, the content of the monoester (A) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass, based on the total amount (100% by mass) of the heat-treated oil. Note that the content of the monoester (A) may be 100% by mass or less, based on the total amount (100% by mass) of the heat-treated oil.

[0019] (Kinematic Viscosity of Monoester (A)) The kinematic viscosity of the monoester (A) at 40°C is preferably 1.0 mmHg from the viewpoint of achieving both cooling properties and evaporative properties. ２ / s or more 20mm ２ / s or less, more preferably 2.5 mm ２ / s or more 10mm ２ / s or less, more preferably 3.0 mm ２ / s or more 8.5mm ２ In this specification, the kinematic viscosity at 40°C of the monoester (A) means a value measured in accordance with JIS K2283:2000.

[0020] <Method for Producing Monoester (A)> The method for producing the monoester (A) is not particularly limited, and the monoester (A) can be produced, for example, by reacting an alcohol or an alkoxy alcohol with a fatty acid in a combination that results in a predetermined total carbon number, and then performing esterification by a standard method.

[0021] <Base Oil Other Than Monoester (A)> The heat-treated oil of this embodiment may or may not further contain a base oil other than the monoester (A). Examples of the base oil other than the monoester (A) include one or more selected from the group consisting of synthetic oils that do not fall under the category of monoester (A) and mineral oils.

[0022] Examples of synthetic oils that do not fall under the category of monoester (A) include polyvinyl ethers, polyalkylene glycols, copolymers of polyalkylene glycol or its monoether with polyvinyl ether, polyol esters, polyesters, polycarbonates, hydrogenated α-olefin oligomers, alicyclic hydrocarbon compounds, alkylated aromatic hydrocarbon compounds, GTL base oils produced by isomerizing GTL wax (gas-to-liquid wax) produced by the Fischer-Tropsch process, etc. The synthetic oils may be used alone or in combination of two or more.

[0023] From the viewpoint of making it easier to exhibit the effects of the present invention, the content of synthetic oils not corresponding to the monoester (A) is preferably small. Specifically, the content of synthetic oils not corresponding to the monoester (A) is preferably less than 3 parts by mass, more preferably less than 1 part by mass, even more preferably less than 0.1 parts by mass, and still more preferably no synthetic oils not corresponding to the monoester (A) are contained, per 100 parts by mass of the monoester (A).

[0024] Examples of mineral oils include atmospheric residues obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; distillates obtained by vacuum distillation of these atmospheric residues; mineral oils obtained by subjecting the distillates to one or more treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; wax isomerized mineral oil, etc. Note that one mineral oil may be used alone, or two or more mineral oils may be used in combination.

[0025] From the viewpoint of more easily achieving the effects of the present invention, the mineral oil content is preferably low. Mineral oil has a wider molecular weight distribution than the monoester (A) of this embodiment, and therefore contains lower or higher molecular weight components. Low molecular weight components have high volatility, i.e., they evaporate easily, which increases the time (characteristic seconds) until the vapor film stage of the heat-treated oil ends, so a small amount is preferable. Furthermore, high molecular weight components have low volatility, i.e., they are difficult to evaporate, so a small amount is preferable from the viewpoint of improving the volatility of the heat-treated oil. From the above viewpoints, the mineral oil content is preferably less than 10 parts by mass, more preferably less than 1 part by mass, per 100 parts by mass of the monoester (A).

[0026] <Additives> The heat treatment oil of this embodiment may optionally contain additives commonly used in heat treatment oils. Examples of additives include glitter improvers, antioxidants, and coolability improvers. One type of additive may be used alone, or two or more types may be used in combination.

[0027] (Brilliance improver) When the heat treatment oil of this embodiment contains a brilliance improver, the brilliance of the appearance can be improved. Examples of brilliance improvers include fats and oils; complete esters of alkyl succinic acid and alkyl succinimides and derivatives thereof; complete esters of alkenyl succinic acid, alkenyl succinimides and derivatives thereof; substituted hydroxyaromatic carboxylic acid esters (complete esters) and derivatives thereof. Specific examples include polybutenyl succinimide, polyisobutenyl succinimide, pentadecenyl succinic acid, etc. These brilliance improvers may be used alone or in combination of two or more. The content of the brilliance improver is preferably 0.1% by mass to 5.0% by mass, more preferably 0.3% by mass to 3.0% by mass, and even more preferably 0.4% by mass to 2.5% by mass, based on the total amount of the heat treatment oil.

[0028] (Antioxidant) Examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, etc. Examples of the phenol-based antioxidant include 2,6-di-tert-butyl-paracresol, 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). monocyclic phenols such as propionate; and 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), and 4,4'-butylidenebis(3-methyl-6-tert-butylphenol). Examples of the amine-based antioxidant include diphenylamine-based antioxidants and naphthylamine-based antioxidants. Examples of diphenylamine antioxidants include alkylated diphenylamines having an alkyl group having 3 to 20 carbon atoms, and specific examples thereof include diphenylamine, monooctyldiphenylamine, monononyldiphenylamine, 4,4'-dibutyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-dioctyldiphenylamine, 4,4'-dinonyldiphenylamine, tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, and tetranonyldiphenylamine.Examples of naphthylamine antioxidants include alkyl-substituted phenyl-α-naphthylamines having 3 to 20 carbon atoms, such as 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 0.02% by mass to 3.0% by mass, and even more preferably 0.05% by mass to 2.0% by mass, based on the total mass of the heat treatment oil.

[0029] (Cooling Improver) Examples of the cooling improver include imide-based dispersants such as boron-containing alkenyl succinimides, and mono- or di-carboxylic acid amides such as fatty acids or succinic acid. These cooling improvers may be used alone or in combination of two or more. The content of the cooling improver is preferably 0.05% by mass to 5.0% by mass, more preferably 0.1% by mass to 3.0% by mass, and even more preferably 0.3% by mass to 2.0% by mass, based on the total amount of the heat treatment oil.

[0030] Furthermore, from the viewpoint of the volatility of the heat treatment oil, the content of the vapor film breaker in the heat treatment oil of this embodiment is preferably less than 3 mass%, more preferably less than 1 mass%, even more preferably less than 0.1 mass%, even more preferably less than 0.01 mass%, and even more preferably no vapor film breaker is contained, based on the total amount of the heat treatment oil.

[0031] [Physical properties of heat-treated oil] <Flash point> The heat-treated oil of this embodiment is not particularly limited in terms of its properties, but the flash point is preferably 130°C or higher, more preferably 140°C or higher, even more preferably 150°C or higher, and even more preferably 160°C or higher. In this specification, the flash point of the monoester (A) refers to the value measured by the Cleveland Open C.O.C. method in accordance with K2265-4:2007. <40°C kinematic viscosity> The 40°C kinematic viscosity of the heat-treated oil of this embodiment is preferably 1.0 mm from the viewpoint of achieving both cooling properties and evaporability. ２ / s or more 20mm ２ / s or less, more preferably 2.5 mm ２ / s or more 10mm ２ / s or less, more preferably 3.0 mm ２ / s or more 9.0mm ２ In this specification, the kinematic viscosity at 40°C of the monoester (A) means a value measured in accordance with JIS K2283:2000.

[0032] <Volatility> The volatility of the heat treatment oil of this embodiment can be evaluated by the method described in the Examples below. <Coolability> The coolability of the heat treatment oil of this embodiment can be evaluated by the quench intensity (H value) by the method described in the Examples below. The H value can be calculated from the cooling time from 800°C to 300°C in the cooling curve specified in JIS K2242:2012. The H value of the heat treatment oil of this embodiment is preferably 0.100 cm －１ More preferably, 0.105 cm －１ More preferably, 0.110 cm －１ More preferably, 0.120 cm －１ That's all.

[0033] <Characteristic seconds> The heat treatment oil of this embodiment can be evaluated for its characteristic seconds by the method described in the Examples below. From the viewpoint of shortening the time in the vapor film stage and suppressing quenching distortion, the characteristic seconds is preferably 10 seconds or less, more preferably 8.0 seconds or less, even more preferably 7.0 seconds or less, still more preferably 5.5 seconds or less, and even more preferably 4.5 seconds or less.

[0034] [Method for Manufacturing Metal Components] The method for manufacturing a metal component of this embodiment includes a quenching step in which a heated metal component is immersed in the heat treatment oil and cooled. The quenching temperature in the quenching step is preferably 400 to 1500°C, more preferably 500 to 1400°C, and even more preferably 600 to 1200°C. Furthermore, the method for manufacturing a metal component of this embodiment preferably includes a tempering step in which the metal component is reheated after the quenching step without being cleaned. By subjecting the quenched metal component to the tempering step as is in this manner, the cleaning step can be omitted, improving productivity. Furthermore, the heat treatment oil of this embodiment has excellent volatility, particularly under the temperature conditions of the tempering step, and can therefore evaporate from the metal component during the tempering step. The heating temperature in the tempering step can be appropriately set depending on the desired hardness and toughness of the metal component, but is, for example, approximately 150 to 600°C.

[0035] [Uses of Heat Treatment Oil] The heat treatment oil of this embodiment can be used for heat treatments such as quenching, tempering, annealing, and normalizing. Furthermore, since the heat treatment oil of this embodiment has excellent cooling properties and evaporativity, the heat treatment oil of this embodiment can be suitably used in heat treatments that do not require cleaning of metal members after the heat treatment, and can be particularly suitably used as a quenching oil that does not require cleaning of metal members after quenching.

[0036] The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0037] [Methods for Measuring Physical Properties] The methods for measuring physical properties were as follows: (1) Kinematic viscosity at 40°C: Measured in accordance with JIS K2283:2000.

[0038] <Measurement of Flash Point> The flash point was measured by the Cleveland Open Cup method (C.O.C. method) in accordance with JIS K2265-4:2007.

[0039] [Examples 1 to 10 and Comparative Examples 1 to 5] Using heat-treated oils containing the following components in the amounts shown in Table 1, the flash point and kinematic viscosity at 40°C were measured, and the volatility, characteristic seconds, and H value were also evaluated.

[0040] <Base oil> Monoester (A'1): butyl hexanoate (R １ and R ２ Total carbon number of: 10) Monoester (A'2): methyl laurate (R １ and R ２ Total carbon number: 13) Monoester (A1): butyl laurate (R １ and R ２ Total carbon number: 16) Monoester (A2): isopropyl myristate (R １ and R ２ Total carbon number: 17) Monoester (A3): isononyl isononanoate (R １ and R ２ Total carbon number: 18) Monoester (A4): 2-ethylhexyl laurate (R １ and R ２ Total carbon number: 18) Monoester (A5): methyl oleate (R １ and R ２ Total carbon number: 19) Monoester (A6): butyl oleate (R １ and R ２ Total carbon number: 22) Monoester (A7): 2-ethylhexanoic acid cetyl ester (R １ and R ２ Total carbon number: 24) Monoester (A8): 2-ethylhexyl palmitate (R １ and R ２ Total carbon number: 24) Monoester (A9): 2-butoxyethyl oleate (R １ and R ２ Total carbon number: 24) Monoester (A10): 2-ethylhexyl oleate (R １ and R ２Total carbon number: 26) Monoester (A'3): Tridecyl stearate (R １ and R ２ Total carbon number: 31) Air: 5 kg / cm instead of heat treatment oil ２ Air is injected at

[0041] <Additives> Ca salicylate: calcium salicylate (calcium atom content: 8.0 mass%, base number (perchloric acid method): 225 mg KOH / g, density: 1.051 g / cm ３ Na sulfonate: sodium sulfonate (sodium atom content: 3.4 mass%, density: 1.02 g / cm ３ )

[0042] [Evaluation of Volatility] Evaluation was performed using a Tg-DTA apparatus according to JIS K0129:2005. 5.0 mg of sample oil was weighed and placed in the sample measurement location of the heating furnace. The heating furnace was closed, and while flowing nitrogen at 200 mL / min, the temperature was raised to 200°C at 25°C / min, and after reaching 200°C, the temperature was maintained for 2 hours. Thereafter, the mass of the residual oil after the maintenance was measured, and the ratio (mass%) to the mass before the maintenance was calculated.

[0043] [Evaluation of Cooling Ability] In accordance with the cooling ability test method specified in JIS K 2242:2012, a cooling curve was created by recording the temperature change from 800°C for 60 seconds, and the characteristic number of seconds was determined from the time it took to reach the characteristic temperature. In addition, the H value was determined by the Osaka University cooling capacity evaluation method using the time from 800°C to 300°C on the created cooling curve. However, in Comparative Example 5, in which air was used as the coolant, air at 25°C was blown at 5 kg / cm. ２ The cooling curve was created.

[0044] The compositions and evaluation results of the heat-treated oils of Examples 1 to 10 and Comparative Examples 1 to 5 are shown in Table 1.

[0045]

[0046] As shown in Table 1, R １ and R ２The heat-treated oils of Examples 1 to 10, which used as the base oil monoester (A) having a total carbon number of 15 to 30, were excellent in volatility, had a relatively short characteristic time, and also had a relatively high H value. In contrast, the heat-treated oil of Comparative Example 1, which used mineral oil as the base oil, and the heat-treated oil of R １ and R ２ The heat-treated oil of Comparative Example 4, which used the monoester (A'3) having a total carbon number of 31, had low volatility and required washing after the heat treatment. １ and R ２ The heat-treated oils of Comparative Examples 2 and 3, which used monoesters (A'1) and (A'2) having a total carbon number of 10 to 13, had long characteristic seconds and relatively low H values. Comparative Example 5, which used air as the coolant, also had a low H value.

Claims

1. A heat-treated oil containing a monoester (A) represented by the following general formula (1) as a base oil. １ -COO-R ２ ...(1) (wherein, R １ and R ２ are each independently a hydrocarbon group which may have an alkoxy group as a substituent, and R １ and R ２ The total number of carbon atoms is 15 to 30.

2. In the general formula (1), R １ is a chain hydrocarbon group having 5 to 20 carbon atoms, and R ２ The heat treatment oil according to claim 1, wherein is a chain hydrocarbon group having 1 to 24 carbon atoms or an alkoxyalkyl group having 1 to 20 carbon atoms.

3. A heat treatment oil as described in claim 1 or 2, wherein the content of the monoester (A) is 50 mass% or more based on the total amount of the heat treatment oil.

4. A heat-treated oil according to any one of claims 1 to 3, having a flash point of 150°C or higher.

5. The heat treatment oil according to any one of claims 1 to 4, which is used as a quenching oil.

6. A method for manufacturing a metal component, comprising a quenching step of immersing a heated metal component in the heat treatment oil according to any one of claims 1 to 5 and cooling it.

7. The method for manufacturing a metal part according to claim 6, wherein the quenching temperature in the quenching step is 500 to 1400°C.

8. A method for manufacturing a metal component according to claim 6 or 7, further comprising a tempering step of reheating the metal component without cleaning it after the quenching step.

9. The method for manufacturing a metal part according to claim 8, wherein the heating temperature in the tempering step is 150 to 650°C.

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