Hot work tool material and method for manufacturing hot work tool
Provided are a hot work tool material having an annealed structure effective for producing a finer quenched and tempered structure when made into a hot work tool, and a method for manufacturing a hot work tool. A hot work tool material which has an annealed structure and which is used upon being quenched and tempered, wherein the hot work tool material has a composition that can be adjusted to a martensite structure by the aforementioned quenching, and ferrite grains in a cross-section of the annealed structure of the hot work tool material have, in an oversize cumulative distribution based on the cross-sectional area of the ferrite grains, a grain diameter distribution such that the grain diameter is 25 μm or less as a circle equivalent diameter when the cumulative cross-sectional area is 90% of the total cross-sectional area. In addition, a method for manufacturing a hot work tool in which quenching and tempering is performed on the aforementioned hot work tool material.
1. A hot work tool material having an annealed structure and a composition consisting of, by mass %:
C: 0.30% to 0.50%,
Si: not greater than 2.00%,
Mn: not greater than 1.50%,
P: not greater than 0.0500%,
S: not greater than 0.0500%,
Cr: 3.00% to 6.00%,
one or both of Mo and W in an expression of (Mo+½ W): 0.50% to 3.50%,
V: 0.10% to 1.50%,
Ni: 0% to 1.00%,
Co: 0% to 1.00%,
Nb: 0% to 0.30%, and
the balance of Fe and impurities,
wherein the annealed structure comprises ferrite grains in a cross-sectional structure, the ferrite grains having, in an oversize cumulative distribution based on a cross-sectional area of the ferrite grains, a grain diameter distribution such that the grain diameter is not greater than 25 μm as a circle equivalent diameter when the cumulative cross-sectional area is 90% of the total cross-sectional area.
2. A method for manufacturing a hot work tool, comprising quenching and tempering the hot work tool material according to claim 1 .
3. The method according to claim 2 , wherein a prior austenite grain size number in the structure of the hot work tool after the quenching and tempering is not less than No. 9 as a grain size number pursuant to JIS-G-0551.