| 摘要 |
PROBLEM TO BE SOLVED: To obtain a heat-treatment oil which is useful in metal hardening, can impart sufficient hardness even to a poorly hardenable steel material and is lowly flammable by selecting a heat treatment oil having a specified 5% evaporation temperature and a specified kinematic viscosity at 40 deg.C. SOLUTION: This oil has a 5% evaporation temperature of 290-310 deg.C and a kinematic viscosity of 12-30mm<2> /s at 40 deg.C and desirably has a flash point of 170 deg.C or above and an aniline point of 40-130 deg.C and a density of 0.70-0.95g/cm<3> at 15 deg.C. In order to further improve the ability to harden a metal, it may further contain 0.01-20wt.% at least either a polyolefin or a product of hydrogenation thereof having a number-average molecular weight of 1,200-4,000 or an asphalt having a penetration (at 25 deg.C) of 0-300, a softening point of 30-150 deg.C and a density (at 15 deg.C) of 1.0g/cm<3> or above. It may further contain known additives. The starting oil of the heat treatment oil is at least one mineral or synthetic oil. |
