Sulfur-based extreme-pressure agent and metalworking fluid

A sulfur-based extreme-pressure agent comprising a polysulfide (a) represented by the following formula (1) and a sulfurized fat or oil (b) at a weight ratio in the range of 1:0.1 to 1:10,

• R1—Sx—R2 (1)
• wherein R1 and R2 denote an alkyl or alkenyl group having 2 to 24 carbon atoms, and x denotes an integer in the range of 1 to 8, and
• wherein the polysulfide (a) comprises a tertiary polysulfide having the tertiary alkyl or alkenyl group as R1 and R2 and a secondary polysulfide having the secondary alkyl or alkenyl group as R1 and R2, a weight ratio of the tertiary polysulfide to the secondary polysulfide being in the range of 1:0.2 to 1:2,
• wherein a total amount of the tertiary polysulfide and the secondary polysulfide in the sulfur-based extreme-pressure agent is at least 47.5% by weight,
• wherein the secondary polysulfide is bisdecen-2-yl polysulfide,
• wherein the tertiary polysulfide is bis-2,4,4-trimethylpentan-2-yl polysulfide, and
• wherein the sulfurized fat or oil (b) is selected from the group consisting of sulfurized lard, sulfurized recovered vegetable oil, and sulfurized canola oil.