The present invention relates to an electric discharge machining oil composition and an electric discharge machining method capable of enhancing machining speed in electric discharge machining. This electric discharge machining oil composition is characterized by including (A) a base oil, and (B) one or more types of petroleum resin selected from hydrogenated products of copolymers of dicyclopentadiene and an aromatic compound and having a softening point of 75 to 185 C. and a mean molecular weight (Mn) of 670 to 3000, wherein the kinematic viscosity of the electric discharge machining oil composition at 40 C. is 1 to 10 mm.sup.2/s. Further, the electric discharge machining method is characterized by employing said electric discharge machining oil composition, and includes interposing the electric discharge machining oil composition between a workpiece and an electrode, and generating an electric discharge between the workpiece and the electrode in this state to machine the workpiece.

A heat-treatment oil composition can make it possible to achieve both high quenching hardness and reduced quenching distortion. A heat-treatment oil composition may include a base oil (A) and a vapor film rupturing agent (B). The heat-treatment oil composition may make it such that, on a cooling curve obtained in accordance with the cooling performance test method in JIS K2242:2012, the time in seconds to 300 C., e.g., the cooling time from 800 to 300 C., is less than 6 seconds. Component (B) may include a petroleum resin.

A heat-treatment oil composition can make it possible to achieve both high quenching hardness and reduced quenching distortion. A heat-treatment oil composition may include a base oil (A) and a vapor film rupturing agent (B). The heat-treatment oil composition may make it such that, on a cooling curve obtained in accordance with the cooling performance test method in JIS K2242:2012, the time in seconds to 300 C., e.g., the cooling time from 800 to 300 C., is less than 6 seconds. Component (B) may include a petroleum resin.

Provided is a heat-treatment oil composition that makes it possible to suppress quenching distortion and distortion variation and to achieve improved quenching hardness. A heat-treatment oil composition that includes a base oil (A) and a vapor film rupturing agent (B). The heat-treatment oil composition makes it such that, on a cooling curve obtained in accordance with the cooling performance test method in HS K2242:2012, the time in seconds to 300 C., e.g., the cooling time from 800 C. to 300 C., is at least 6.5 seconds but less than 10 seconds. Component (B) includes a petroleum resin.

Provided is a heat-treatment oil composition that makes it possible to suppress quenching distortion and distortion variation and to achieve improved quenching hardness. A heat-treatment oil composition that includes a base oil (A) and a vapor film rupturing agent (B). The heat-treatment oil composition makes it such that, on a cooling curve obtained in accordance with the cooling performance test method in HS K2242:2012, the time in seconds to 300 C., e.g., the cooling time from 800 C. to 300 C., is at least 6.5 seconds but less than 10 seconds. Component (B) includes a petroleum resin.