HOT-DIE NI-BASED ALLOY, HOT-FORGING DIE EMPLOYING SAME, AND FORGED-PRODUCT MANUFACTURING METHOD
Provided are a Ni-based alloy for hot die having a high high-temperature compressive strength and a good oxidation resistance and being capable of suppressing the deterioration in the working environment and the shape deterioration, a hot forging die using the Ni-based alloy for hot die, and a method for manufacturing a forged product using the hot forging die. The present invention provides a hot forging die comprising a Ni-based alloy for hot die comprising, in mass %, W: 7.0 to 15.0%, Mo: 2.5 to 11.0%, Al: 5.0 to 7.5%, Cr: 0.5 to 7.5%, and the balance of Ni with inevitable impurities, wherein at least 80% of a surface area of the Ni-based alloy for hot die is covered with an aluminum oxide layer. In addition to the composition, the Ni-based alloy for hot die may further comprise 7.0% or less of Ta and may further comprise one or two or more elements selected from Zr: 0.5% or less, Hf: 0.5% or less, rare-earth elements: 0.2% or less, Y: 0.2% or less, and Mg: 0.03% or less.
1 . A hot forging die comprising a Ni-based alloy for hot die comprising, in mass %, W: 7.0 to 15.0%, Mo: 2.5 to 11.0%, Al: 5.0 to 7.5%, Cr: 0.5 to 7.5%, and the balance of Ni with inevitable impurities, wherein at least 80% of a surface area of the Ni-based alloy for hot die is covered with an aluminum oxide layer.
2 . The hot forging die according to claim 1 , wherein the Ni-based alloy for hot die further comprises, in mass %, one or two or more elements selected from Zr: 0.5% or less, Hf: 0.5% or less, rare-earth elements: 0.2% or less, Y: 0.2% or less, and Mg: 0.03% or less.
3 . The hot forging die according to claim 1 , wherein the Ni-based alloy for hot die further comprises, in mass %, Ta: 7.0% or less.
4 . The hot forging die according to claim 2 , wherein the Ni-based alloy for hot die further comprises, in mass %, one or two elements selected from Ti and Nb in a total amount of 3.5% or less, and a total content of Ta, Ti, and Nb is 1.0 to 7.0%.
5 . The hot forging die according to claim 1 , wherein the Ni-based alloy for hot die further comprises, in mass %, Co: 15.0% or less.
6 . The hot forging die according to claim 1 , wherein the Ni-based alloy for hot die further comprises, in mass %, one or two elements selected from C: 0.25% or less and B: 0.05% or less.
7 . The hot forging die according to claim 1 , wherein the hot forging die has a covering layer of an antioxidant on at least one of a die surface or a side surface of the hot forging die.
8 . A Ni-based alloy for hot die comprising, in mass %, W: 7.0 to 15.0%, Mo:
2 . 5 to 11.0%, Al: 5.0 to 7.5%, Cr: 0.5 to 7.5%, Ta: 0 to 7.0%, Co: 0 to 15.0%, and the balance of Ni with inevitable impurities.
9 . A Ni-based alloy for hot die, wherein the Ni-based alloy for hot die according to claim 8 further comprises, in mass %, one or two or more elements selected from Zr: 0.5% or less, Hf: 0.5% or less, rare-earth elements: 0.2% or less, Y: 0.2% or less, and Mg:
0 . 03% or less.
10 . A Ni-based alloy for hot die, wherein the Ni-based alloy for hot die according to claim 8 further comprises, in mass %, one or two elements selected from Ti and Nb in a total amount of 3.5% or less, and a total content of Ta, Ti, and Nb is 1.0 to 7.0%.
11 . The Ni-based alloy for hot die according to claim 8 , wherein 0.2% compressive strength at a test temperature of 1000° C. and a strain rate of 10 −3 /sec is 500 MPa or more.
12 . The Ni-based alloy for hot die according to claim 8 , wherein 0.2% compressive strength at a test temperature of 1100° C. and a strain rate of 10 −3 /sec is 300 MPa or more.
13 . A method for manufacturing a forged product, comprising:
a first step of heating a material for forging, and
a second step of hot forging the material for forging heated in the first step by using the hot forging die according to claim 1 .
14 . The method for manufacturing a forged product according to claim 13 , wherein the second step is performed by heating the hot forging die to 1000° C. or more.
15 . The method for manufacturing a forged product according to claim 14 , wherein a Ni-based alloy for hot die is pre-heated in the air to 1000° C. or more to form an aluminum oxide layer on 80% or more of a surface area of the Ni-based alloy for hot die, before the step of heating the hot forging die to 1000° C. or more.