Heat treatment oil

Abstract

Provided is a heat treatment oil with which both cooling properties and evaporation properties can be achieved, the heat treatment oil comprising, as a base oil, a polyol ester (A) of a divalent or trivalent polyhydric alcohol having 1-10 carbon atoms and a monovalent fatty acid having 2-12 carbon atoms.

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 and it is usually cooled through the following three stages (1) to (3). (1) Stage 1 (vapor film stage) in which the metal material is enveloped in the vapor of the heat treatment oil. (2) Stage 2 (boiling stage) in which the vapor film breaks and boiling occurs. (3) Stage 3 (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 the three stages, the second boiling stage has the greatest cooling rate. Furthermore, if the time until the first vapor film stage is completed (the "characteristic number of seconds" in the cooling test in accordance with JIS K2242:2012) is long, quenching distortion is likely to occur.

[0005] On the other hand, although quenching metal materials improves their hardness, tempering treatment, in which they are reheated, may be performed to further impart toughness. In this case, since quenching oil adheres to the metal material after quenching, it is common to perform a cleaning treatment to remove the oil before tempering. However, from the perspective of improving productivity, reduction or omission of the cleaning treatment has been investigated. For example, Patent Document 1 discloses an invention relating to a heat treatment oil containing multiple types of metal soaps, which has good aqueous cleanability after quenching, and Patent Document 2 discloses an invention relating 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 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 omitted, and there are still problems in terms of productivity. The device described in Patent Document 2 also requires replacement of existing heat treatment equipment, and there is a risk that the volatility of the heat treatment oil used may be insufficient.

[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 items [1] to

[10] . [1] A heat-treatment oil containing a polyol ester (A) as a base oil, wherein the polyol ester (A) is a polyol ester of a dihydric or trihydric polyhydric alcohol having 1 to 10 carbon atoms and a monohydric fatty acid having 2 to 12 carbon atoms. [2] The heat-treatment oil according to item [1] above, wherein the polyhydric alcohol has 2 to 6 carbon atoms. [3] The heat-treatment oil according to item [1] or [2] above, wherein the fatty acid has 3 to 12 carbon atoms. [4] The heat-treatment oil according to any one of items [1] to [3] above, wherein the content of the polyol ester (A) is 50 mass% or more based on the total amount of the heat-treatment oil. [5] The heat-treatment oil according to any one of items [1] to [4] above, wherein the flash point is 150°C or higher. [6] The heat-treatment oil according to any one of items [1] to [5] above, wherein the heat-treatment oil is used as a quenching oil. [7] 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 [1] to [6] above and cooling it. [8] A method for manufacturing a metal component according to [7] above, wherein the quenching temperature in the quenching step is 500 to 1400°C. [9] A method for manufacturing a metal component according to [7] or [8] above, comprising a tempering step of reheating the metal component without cleaning it after the quenching step.

[10] A method for manufacturing a metal component according to [9] above, wherein the heating temperature in the tempering step is 150 to 600°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 this embodiment is a heat treatment oil containing a polyol ester (A) as a base oil, and the polyol ester (A) is a polyol ester of a divalent or trivalent polyhydric alcohol having 1 to 10 carbon atoms and a monovalent fatty acid having 2 to 12 carbon atoms.

[0014] As a result of intensive research conducted by the present inventors to solve the above-mentioned problems, they have found that when a heat treatment oil contains the above-mentioned specific polyol ester (A) as a base oil, it ensures cooling properties when a heat treatment such as quenching is performed, and at the same time, it exhibits volatility to such an extent that it can be volatilized 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 polyol ester (A), but may also contain other components other than the polyol ester (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 polyol ester (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. In addition, 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] <Polyol Ester (A)> The heat treatment oil of this embodiment contains a polyol ester (A) as a base oil. In this embodiment, the polyol ester (A) is a polyol ester of a dihydric or trihydric polyhydric alcohol having 1 to 10 carbon atoms and a monohydric fatty acid having 2 to 12 carbon atoms. Using a monohydric fatty acid having 2 or more carbon atoms improves the cooling properties of the resulting polyol ester (A) during heat treatment. Furthermore, using a monohydric fatty acid having 12 or less carbon atoms and a dihydric or trihydric polyhydric alcohol improves the volatility of the resulting polyol ester (A), making it possible to omit a cleaning treatment after heat treatment, resulting in excellent productivity. Furthermore, by containing the polyol ester (A), the heat treatment oil of this embodiment has excellent volatility compared to one containing a diester of a dibasic acid and an alcohol.

[0017] (Polyhydric Alcohol) In this embodiment, the polyhydric alcohol is an alcohol component constituting the polyol ester (A), and may be dihydric or trihydric and have 1 to 10 carbon atoms. The polyhydric alcohol may be linear, branched, or cyclic, and may be saturated or unsaturated, but linear or branched alcohols are preferred, and linear or branched and saturated alcohols are more preferred. Furthermore, the polyhydric alcohol preferably has 2 to 8 carbon atoms, more preferably has 2 to 6 carbon atoms, and even more preferably has 3 to 6 carbon atoms.

[0018] Specific examples of the polyhydric alcohol include dihydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, 2-methyl-1,3-propanediol, pentanediol, neopentyl glycol, hexanediol, 2-ethyl-2-methyl-1,3-propanediol, heptanediol, 2-methyl-2-propyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, octanediol, nonanediol, and decanediol; and trihydric alcohols such as glycerin, trimethylolethane, ditrimethylolethane, and trimethylolpropane. Among these, it is more preferable to use at least one selected from neopentyl glycol and glycerin, from the viewpoint of achieving both cooling properties and evaporative properties. The polyhydric alcohols may be used alone or in combination of two or more.

[0019] (Fatty Acid) In the present embodiment, the monovalent fatty acid having 2 to 12 carbon atoms is an acid component constituting the polyol ester (A). The monovalent fatty acid preferably has 3 to 12 carbon atoms, more preferably has 5 to 12 carbon atoms, and even more preferably has 5 to 10 carbon atoms.

[0020] The fatty acids constituting the polyol ester (A) may be used singly or in combination of two or more. The fatty acids may be linear saturated fatty acids, linear unsaturated fatty acids, branched saturated fatty acids, or branched unsaturated fatty acids. Therefore, the fatty acids may be one or more selected from linear saturated fatty acids, linear unsaturated fatty acids, branched saturated fatty acids, and branched unsaturated fatty acids, and are preferably one or more selected from linear saturated fatty acids and branched saturated fatty acids.

[0021] Specific examples of the straight-chain saturated fatty acid include acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, etc. These may be used alone or in combination of two or more.

[0022] Specific examples of branched saturated fatty acids include 2-ethylhexanoic acid, isodecanoic acid, 2-methyldecanoic acid, etc. Among these, 2-ethylhexanoic acid is preferred.

[0023] In the heat treatment oil of this embodiment, the polyol ester (A) functions as base oil.In the heat treatment oil of this embodiment, the content of the polyol ester (A) is preferably 50 mass% or more, more preferably 70 mass% or more, even more preferably 80 mass% or more, even more preferably 90 mass% or more, even more preferably 95 mass% or more, and even more preferably 100 mass% based on the total amount (100 mass%) of the heat treatment oil.In addition, the content of the polyol ester (A) may be 100 mass% or less based on the total amount (100 mass%) of the heat treatment oil.

[0024] The polyol ester (A) may be a partial ester or a complete ester, but preferably contains a complete ester from the viewpoint of improving evaporative properties and cooling properties, etc. In this embodiment, the content of the complete ester in the polyol ester (A) is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass.

[0025] (Kinematic Viscosity of Polyol Ester (A)) The kinematic viscosity of the polyol ester (A) at 40°C is preferably 1.0 mmHg or less from the viewpoint of achieving both cooling properties and evaporative properties. ２ / s or more 40mm ２ / s or less, more preferably 1.0 mm ２ / s or more 30mm ２ / s or less, more preferably 2.5 mm ２ / s or more 30mm ２ / s or less, particularly preferably 2.5 mm ２ / s or more 25mm ２ In this specification, the kinematic viscosity at 40°C of the polyol ester (A) means a value measured in accordance with JIS K2283:2000.

[0026] <Method for producing polyol ester (A)> The method for producing the polyol ester (A) is not particularly limited, and the polyol ester (A) can be produced, for example, by combining and reacting the polyhydric alcohol with a monohydric fatty acid, and then esterifying the resulting mixture by a standard method.

[0027] <Base Oil Other Than Polyol Ester (A)> The heat treatment oil of this embodiment may or may not further contain a base oil other than the polyol ester (A). Examples of the base oil other than the polyol ester (A) include one or more selected from the group consisting of synthetic oils that do not fall under the category of polyol ester (A) and mineral oils.

[0028] Examples of synthetic oils that do not fall under the category of polyol ester (A) include polyvinyl ethers, polyalkylene glycols, copolymers of polyalkylene glycol or its monoether with polyvinyl ether, monoesters, polyol esters, polyol esters that do not fall under the category of polyol ester (A): 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.

[0029] From the viewpoint of making it easier to exhibit the effects of the present invention, the content of synthetic oils that do not fall under the category of polyol ester (A) is preferably small. Specifically, the content of synthetic oils that do not fall under the category of polyol ester (A) is preferably less than 40 parts by mass, more preferably less than 10 parts by mass, even more preferably less than 1 part by mass, per 100 parts by mass of polyol ester (A), and even more preferably no synthetic oils that do not fall under the category of polyol ester (A).

[0030] 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.

[0031] From the viewpoint of making it easier to exert the effects of the present invention, the content of mineral oil is preferably small. Mineral oil has a wider molecular weight distribution than the polyol ester (A) of this embodiment, and therefore contains low molecular weight components. Low molecular weight components are highly volatile and therefore easily evaporate. As a result, the time (characteristic seconds) until the vapor film stage of the heat treatment oil ends becomes longer, so a small content is preferable. From the above viewpoint, the content of mineral oil is preferably less than 10 parts by mass, more preferably less than 1 part by mass, even more preferably less than 0.1 parts by mass, and even more preferably no mineral oil, per 100 parts by mass of polyol ester (A).

[0032] <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.

[0033] (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.

[0034] (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.

[0035] (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.

[0036] 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.

[0037] [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 polyol ester (A) refers to the value measured by the Cleveland Open Cup method (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 40mm ２ / s or less, more preferably 2.5 mm ２ / s or more 30mm ２ / s or less, more preferably 3.0 mm ２ / s or more 20mm ２ In this specification, the kinematic viscosity at 40°C of the polyol ester (A) means a value measured in accordance with JIS K2283:2000.

[0038] <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 0.095 cm －１ More preferably, 0.100 cm －１ More preferably, 0.105 cm －１ More preferably, 0.110 cm －１ More preferably, 0.120 cm or more －１ That's all.

[0039] <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 6.0 seconds or less, and even more preferably 5.0 seconds or less.

[0040] [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.

[0041] [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.

[0042] The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0043] [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.

[0044] <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.

[0045] [Examples 1 to 4 and Comparative Examples 1 to 6] 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.

[0046] <Base oil> Polyol ester (A1): complete ester of neopentyl glycol and 2-ethylhexanoic acid Polyol ester (A2): complete ester of glycerin and acetic acid (purity of complete ester: 95% by mass or more) Polyol ester (A3): complete ester of glycerin and propionic acid (purity of complete ester: 95% by mass or more) Polyol ester (A4): complete ester of glycerin and 2-ethylhexanoic acid (purity of complete ester: 95% by mass or more) Polyol ester (A'1): complete ester of glycerin and oleic acid (purity of complete ester: 95% by mass or more) Polyol ester (A'2): complete ester of pentaerythritol and fatty acid having 5 to 10 carbon atoms (purity of complete ester: 95% by mass or more) Dibasic acid ester 1: ditridecyl adipate Dibasic acid ester 2: bis(2-ethylhexyl) dodecanedioate Dibasic acid ester 3: bis(2-ethylhexyl) sebacate Monoester: butyl hexanoate

[0047] [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.

[0048] [Evaluation of Cooling Ability] According to 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 calculated from the time required to reach the characteristic temperature. In addition, the H value was calculated by the Osaka University cooling ability evaluation method using the time required to reach the characteristic temperature from 800°C to 300°C on the created cooling curve.

[0049] The compositions and evaluation results of the heat-treated oils of Examples 1 to 4 and Comparative Examples 1 to 6 are shown in Table 1.

[0050]

[0051] As shown in Table 1, the heat-treated oils of Examples 1 to 4, which used a polyol ester (A) of a dihydric or trihydric polyhydric alcohol having 1 to 10 carbon atoms and a monohydric fatty acid having 2 to 12 carbon atoms as a base oil, had excellent volatility, a relatively short characteristic time, and a relatively high H value. In contrast, the heat-treated oil of Comparative Example 1, which used a polyol ester (A'1) of a polyhydric alcohol and a fatty acid having 18 carbon atoms as a base oil, the heat-treated oil of Comparative Example 2, which used a polyol ester (A'2) of a tetrahydric polyhydric alcohol and a fatty acid, and the heat-treated oils of Comparative Examples 3 to 5, which used dibasic acid esters, had low volatility and required cleaning after heat treatment. Furthermore, the heat-treated oil of Comparative Example 6, which used a monoester as a base oil, had a long characteristic time and a low H value.

Claims

1. A heat-treated oil containing, as a base oil, a polyol ester (A) of a dihydric or trihydric polyhydric alcohol having 1 to 10 carbon atoms and a monohydric fatty acid having 2 to 12 carbon atoms.

2. The heat treatment oil according to claim 1, wherein the polyhydric alcohol has 2 to 6 carbon atoms.

3. Heat-treated oil according to claim 1 or 2, wherein the fatty acid has 3 to 12 carbon atoms.

4. A heat treatment oil described in any one of claims 1 to 3, wherein the content of the polyol ester (A) is 50 mass% or more based on the total amount of the heat treatment oil.

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

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

7. 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 6 and cooling it.

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

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

10. The method for manufacturing a metal part according to claim 9, wherein the heating temperature in the tempering step is 150 to 600°C.

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