Dies and molds steels are essential materials in the manufacturing industry of engineering products. These materials are usually machined in the hardened condition and therefore, can be problematic to transform them in chips. Calcium treatment can be a viable alternative to increase machinability without compromising the main properties of the steel. The present work investigates the machinability of the calcium treated mold steel, AISI P20 UF, and compares it to the non-treated version of the same material, AISI P20, in slot milling tests with triple coated (TiN, TiCN and Al2O3) cemented carbide tools. A consolidated method that minimizes the number of tests needed for the determination of the extended Taylor's equation coefficients was used and the power consumption was measured during the machining experiments. SEM was used for the exploration of the wear of the used tool and its mechanism. The results showed that the calcium treated steel presented a considerably higher tool life, and although the treatment did not affect the power consumption directly, indirectly it reduced it because of the positive reduction of the tool wear rate allowing the power to be kept at lower levels for more extended periods. Attrition (adhesion) and abrasion were the primary tool wear mechanisms observed when machining the non-treated steel and attrition for the calcium treated material. In this latter case, because of the longer tool lives, chippings of the cutting edge were also present.