Flux for electroslag welding and electroslag welding method

A flux suitable for electroslag welding used for electroslag welding, the flux comprising:

• a basic oxide;
• an amphoteric oxide;
• an acidic oxide;
• a fluoride;
• and
• at least one selected from the group consisting of BaO, FeO, MgO, MoO3, V2O5, P2O5, ZrO2, TiO2, and B2O3,
• wherein the basic oxide comprises CaO in a range of from 5.1 to 30.0 mass % with respect to a total flux mass, the CaO being present in 30 mass % or more with respect to a total basic oxide mass,
• wherein the acidic oxide comprises SiO2 in a range of 17 mass % or less with respect to the total flux mass, the SiO2 being present in a range of 80 mass % or more with respect to a total acidic oxide mass,
• wherein the fluoride comprises CaF2 in a range of from 35 to 73 mass % with respect to the total flux mass, the CaF2 being present in 80 mass % or more with respect to a total fluoride mass, and
• wherein a value calculated by relation (1) is in a range of from 5 to 56:
• (2×[CaF2]+[CaO])/[SiO2] (1),
• wherein [CaO] is a content of the CaO, [SiO2] is a content of the SiO2, and [CaF2] is a content of the CaF2, each by mass % with respect to the total flux mass.