Free-cutting copper alloy casting, and method for producing free-cutting copper alloy casting

A free-cutting copper alloy casting comprising:

• 75.5 mass % to 77.8 mass % of Cu;
• 3.1 mass % to 3.4 mass % of Si;
• 0.10 mass % to 0.27 mass % of Sn;
• 0.06 mass % to 0.13 mass % of P;
• 0.024 mass % to 0.15 mass % of Pb;
• and
• a balance including Zn and inevitable impurities,
• wherein a total amount of Fe, Mn, Co, and Cr as the inevitable impurities is lower than 0.08 mass %,
• when a Cu content is represented by [Cu] mass %, a Si content is represented by [Si] mass %, a Sn content is represented by [Sn] mass %, a P content is represented by [P] mass %, and a Pb content is represented by [Pb] mass %, the relations of
• 76.6≤f1=[Cu]+0.8×[Si]−8.5×[Sn]+[P]+0.5×[Pb]≤79.6 and
• 61.4≤f2=[Cu]−4.4×[Si]−0.8×[Sn]−[P]+0.5×[Pb]≤62.6
• are satisfied,
• in constituent phases of metallographic structure, when an area ratio of α phase is represented by (α)%, an area ratio of β phase is represented by (β)%, an area ratio of γ phase is represented by (γ)%, an area ratio of κ phase is represented by (κ)%, and an area ratio of μ phase is represented by (μ)%, the relations of
• 30≤(κ)≤56,
• 0≤(γ)≤1.2,
• (β)=0,
• 0≤(μ)≤1.0,
• 98.0≤f3=(α)+(κ),
• 99.5≤f4=(α)+(κ)+(γ)+(μ),
• 0≤f5=(γ)+(μ)≤1.5, and
• 32≤f6=(κ)+6×(γ)1/2+0.5×(μ)≤58
• are satisfied,
• the length of the long side of γ phase is 40 μm or less,
• the length of the long side of μ phase is 15 μm or less, and
• κ phase is present in α phase.

A free-cutting copper alloy casting comprising:

• 75.0 mass % to 78.5 mass % of Cu;
• 2.95 mass % to 3.55 mass % of Si;
• 0.07 mass % to 0.28 mass % of Sn;
• 0.06 mass % to 0.14 mass % of P;
• 0.022 mass % to 0.20 mass % of Pb;
• and
• a balance including Zn and inevitable impurities,
• wherein a total amount of Fe, Mn, Co, and Cr as the inevitable impurities is lower than 0.08 mass %,
• wherein when a Cu content is represented by [Cu] mass %, a Si content is represented by [Si] mass %, a Sn content is represented by [Sn] mass %, a P content is represented by [P] mass %, and a Pb content is represented by [Pb] mass %, the relations of
• 76.2≤f1=[Cu]+0.8×[Si]−8.5×[Sn]+[P]+0.5×[Pb]≤80.3 and
• 61.2≤f2=[Cu]−4.4×[Si]−0.8×[Sn]−[P]+0.5×[Pb]62.8
• are satisfied,
• in constituent phases of metallographic structure, when an area ratio of α phase is represented by (α)%, an area ratio of β phase is represented by (β)%, an area ratio of γ phase is represented by (γ)%, an area ratio of κ phase is represented by (κ)%, and an area ratio of μ phase is represented by (μ)%, the relations of
• 25≤(κ)≤65,
• 0≤(γ)≤2.0,
• 0≤(β)≤0.3,
• 0≤(μ)≤2.0,
• 96.5≤f3=(α)+(κ),
• 99.2≤f4=(α)+(κ)+(γ)+(μ),
• 0≤f5=(γ)+(μ)≤3.0, and
• 29≤f6=(κ)+6×(γ)1/2+0.5×(μ)≤66
• are satisfied,
• the length of the long side of γ phase is 40 μm or less,
• the length of the long side of μ phase is 25 μm or less, and
• κ phase is present in α phase;
• wherein an amount of Sn in κ phase is 0.08 mass % to 0.40 mass %, and
• an amount of P in κ phase is 0.07 mass % to 0.22 mass %.

A free-cutting copper alloy casting comprising:

• 75.0 mass % to 78.5 mass % of Cu;
• 2.95 mass % to 3.55 mass % of Si;
• 0.07 mass % to 0.28 mass % of Sn;
• 0.06 mass % to 0.14 mass % of P;
• 0.022 mass % to 0.20 mass % of Pb;
• and
• a balance including Zn and inevitable impurities,
• wherein a total amount of Fe, Mn, Co, and Cr as the inevitable impurities is lower than 0.08 mass %,
• wherein when a Cu content is represented by [Cu] mass %, a Si content is represented by [Si] mass %, a Sn content is represented by [Sn] mass %, a P content is represented by [P] mass %, and a Pb content is represented by [Pb] mass %, the relations of
• 76.2≤f1=[Cu]+0.8×[Si]−8.5×[Sn]+[P]+0.5×[Pb]≤80.3 and
• 61.2≤f2=[Cu]−4.4×[Si]−0.8×[Sn]−[P]+0.5×[Pb]62.8
• are satisfied,
• in constituent phases of metallographic structure, when an area ratio of α phase is represented by (α)%, an area ratio of β phase is represented by (β)%, an area ratio of γ phase is represented by (γ)%, an area ratio of κ phase is represented by (κ)%, and an area ratio of μ phase is represented by (μ)%, the relations of
• 25≤(κ)≤65,
• 0≤(γ)≤2.0,
• 0≤(β)≤0.3,
• 0≤(μ)≤2.0,
• 96.5≤f3=(α)+(κ),
• 99.2≤f4=(α)+(κ)+(γ)+(μ),
• 0≤f5=(γ)+(μ)≤3.0, and
• 29≤f6=(κ)+6×(γ)1/2+0.5×(μ)≤66
• are satisfied,
• the length of the long side of γ phase is 50 μm or less,
• the length of the long side of μ phase is 25 μm or less, and
• κ phase is present in α phase;
• wherein a Charpy impact test value is 23 J/cm2 to 60 J/cm2, and
• a creep strain after holding the casting at 150° C. for 100 hours in a state where a load corresponding to 0.2% proof stress at room temperature is applied is 0.4% or lower.

A method of manufacturing a free-cutting copper alloy casting, the free-cutting copper alloy casting comprising:

• 75.0 mass % to 78.5 mass % of Cu;
• 2.95 mass % to 3.55 mass % of Si;
• 0.07 mass % to 0.28 mass % of Sn;
• 0.06 mass % to 0.14 mass % of P;
• 0.022 mass % to 0.20 mass % of Pb;
• and
• a balance including Zn and inevitable impurities,
• wherein a total amount of Fe, Mn, Co and Cr as the inevitable impurities is lower than 0.09 mass %,
• wherein when a Cu content is represented by [Cu] mass %, a Si content is represented by [Si] mass %, a Sn content is represented by [Sn] mass %, a P content is represented by [P] mass %, and a Pb content is represented by [Pb] mass %, the relations of,
• 76.2≤f1=[Cu]+0.8×[Si]−8.5×[Sn]+[P]+0.5×[Pb]≤80.3 and
• 61.2≤f2=[Cu]−4.4×[Si]−0.8×[Sn]−[P]+0.5×[Pb]62.8
• are satisfied,
• in constituent phases of metallographic structure, when an area ratio of α phase is represented by (α)%, an area ratio of β phase is represented by (β)%, an area ratio of γ phase is represented by (γ)%, an area ratio of κ phase is represented by (κ)%, and an area ratio of μ phase is represented by (μ)%, the relations of
• 25≤(κ)≤65,
• 0≤(γ)≤2.0,
• 0≤(β)≤0.3,
• 0≤(μ)≤2.0,
• 96.5≤f3=(α)+(κ),
• 99.2≤f4=(α)+(κ)+(γ)+(μ),
• 0≤f5=(γ)+(μ)≤3.0, and
• 29≤f6=(κ)+6×(γ)1/2+0.5×(μ)≤66
• are satisfied,
• the length of the long side of γ phase is 40 μm or less,
• the length of the long side of μ phase is 25 μm or less, and
• κ phase is present in α phase:
• the method comprising:
• a melting and casting step,
• wherein the copper alloy casting is cooled in a temperature range from 575° C. to 510° C. at an average cooling rate of 0.1° C./min to 2.5° C./min and subsequently is cooled in a temperature range from 470° C. to 380° C. at an average cooling rate of higher than 2.5° C./min and lower than 500° C./min in the process of cooling after the casting.

A method of manufacturing a free-cutting copper alloy casting, the free-cutting copper alloy casting comprising:

• 75.0 mass % to 78.5 mass % of Cu;
• 2.95 mass % to 3.55 mass % of Si;
• 0.07 mass % to 0.28 mass % of Sn;
• 0.06 mass % to 0.14 mass % of P;
• 0.022 mass % to 0.20 mass % of Pb;
• and
• a balance including Zn and inevitable impurities,
• wherein a total amount of Fe, Mn, Co and Cr as the inevitable impurities is lower than 0.08 mass %,
• wherein when a Cu content is represented by [Cu] mass %, a Si content is represented by [Si] mass %, a Sn content is represented by [Sn] mass %, a P content is represented by [P] mass %, and a Pb content is represented by [Pb] mass %, the relations of
• 76.2≤f1=[Cu]+0.8×[Si]−8.5×[Sn]+[P]+0.5×[Pb]≤80.3 and
• 61.2≤f2=[Cu]−4.4×[Si]−0.8×[Sn]−[P]+0.5×[Pb]≤62.8
• are satisfied,
• in constituent phases of metallographic structure, when an area ratio of α phase is represented by (α)%, an area ratio of β phase is represented by (β)%, an area ratio of γ phase is represented by (γ)%, an area ratio of κ phase is represented by (κ)%, and an area ratio of μ phase is represented by (μ)%, the relations of
• 25≤(κ)≤65,
• 0≤(γ)≤2.0,
• 0≤(β)≤0.3,
• 0≤(μ)≤2.0,
• 96.5≤f3=(α)+(κ),
• 99.2≤f4=(α)+(κ)+(γ)+(μ),
• 0≤f5=(γ)+(μ)≤3.0, and
• 29≤f6=(κ)+6×(γ)1/2+0.5×(μ)≤66
• are satisfied,
• the length of the long side of γ phase is 40 μm or less,
• the length of the long side of μ phase is 25 μm or less, and
• κ phase is present in α phase;
• the method comprising:
• a melting and casting step;
• and
• a heat treatment step that is performed after the melting and casting step,
• wherein in the melting and casting step, a casting is cooled to lower than 380° C. or to a normal temperature,
• in the heat treatment step, (i) the casting is held at a temperature of 510° C. to 575° C. for 20 minutes to 8 hours or (ii) the casting is heated under the condition where a maximum reaching temperature is 620° C. to 550° C. and is cooled in a temperature range from 575° C. to 510° C. at an average cooling rate of 0.1° C./min to 2.5° C./min, and
• subsequently the casting is cooled in a temperature range from 470° C. to 380° C. at an average cooling rate of higher than 2.5° C./min and lower than 500° C./min.