Method for manufacturing a hot press-formed member

摘要

A method of producing a hot press-formed member having good corrosion resistance comprises subjecting a zinc-based plated steel sheet to heat treatment by heating to a temperature region of 600-750° C. at a rate of temperature increase up to 600° C. of at most 50° C. per second followed by cooling to 550° C. or below to form a steel blank which has a zinc oxide layer in its uppermost surface portion and below it a zinc-iron alloy phase having an Fe content of at least 25 mass %. This steel blank is heated to a temperature of at least its Ac3 point, then press formed immediately at a temperature of at least its Ac3 point, and then rapidly cooled. The hot press-formed member has a surface region with zinc oxide and iron-zinc solid solution phases and not containing an intermetallic compound phase or a pure zinc phase.

主权项

1. A method for manufacturing a hot press-formed member characterized by
subjecting a zinc-based plated steel sheet to heat treatment which includes a first heating step in which the steel sheet is heated in an oxygen-containing atmosphere to a temperature region of at least 600° C. to at most 750° C. at an average rate of temperature increase up to 600° C. of at most 50° C. per second and a first cooling step in which the steel sheet which was heated in the first heating step is cooled to 550° C. or below, thereby forming a steel blank having on the surface of the steel sheet a zinc oxide layer constituting an uppermost layer and below it a zinc-iron alloy phase having an Fe content of at least 25 mass %, and heating the steel blank in a second heating step to a temperature of at least the Ac3 point of the steel constituting the sheet, and carrying out a hot press forming step on the heated steel blank by starting press forming when the temperature of the steel blank is at least the Ac3 point and rapidly cooling the press-formed member, thereby obtaining a hot press-formed member having a surface region which has a zinc oxide layer and an iron-zinc solid solution phase and which does not contain an intermetallic compound phase or a pure zinc phase.