Spheroidal graphite cast iron, cast article and automobile structure part made thereof, and method for producing spheroidal graphite cast iron article
A spheroidal graphite cast iron meeting N (5-) ≥250, N (5-20) /N (5-) ≥0.6, and N (30-) /N (5-) ≤0.2, wherein N (5-) represents the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 5 μm or more, N (5-20) represents the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 5 μm or more and less than 20 μm, and N (30-) represents the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 30 μm or more, among graphite particles observed in an arbitrary cross section of at least 1 mm 2 .
1 . A method for producing a cast article of spheroidal graphite cast iron meeting the following conditions:
N (5-) ≥250,
N (5-20) /N (5-) ≥0.6, and
N (30-) /N (5-) ≤0.2,
wherein N (5-) , N (5-20) , and N (30-) are the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 5 μm or more, the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 5 μm or more and less than 20 μm, and the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 30 μm or more, respectively, among graphite particles observed in an arbitrary cross section of at least 1 mm 2 ; comprising
pouring a melt into a gas-permeable casting mold by gravity-casting,
pressing a surface of the melt in the gas-permeable casting mold by a gas at a pressure of 1-100 kPa, before said melt starts eutectic solidification; and
solidifying said melt while supplying said gas into said casting mold,
wherein said method meets
0< dt pE /dt E ≤1/2,
wherein dt E represents a time period from the start of eutectic solidification of said melt to the completion of the eutectic solidification, and dt pE represents a time period from the start of eutectic solidification of said melt to the completion of said pressing.
2 . The method for producing a cast article according to claim 1 , wherein said pressure is 10-50 kPa.
3 . The method for producing a cast article according to claim 1 , wherein said gas-permeable casting mold is a green sand mold, a shell mold, or a self-hardening mold, constituted by sand particles.
4 . The method for producing a cast article according to claim 1 , wherein the spheroidal graphite cast iron has a composition comprising by mass 2-4.5% of C, 0.8-2.26% of Si, and 0.010-0.080% of Mg, the balance being Fe and inevitable impurity elements and optionally one or more of S, P, Mn, Cu, Cr, Ni, Mo, W,
wherein said graphite particles meet N (2-5) ≥100, wherein N (2-5) represents the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 2 μm or more and less than 5 μm,
wherein said graphite particles meet D max ≥50.4 μm, wherein D max represents the maximum equivalent-circle diameter of graphite particles, and
wherein said graphite particles meet −0.15≤[N (5-10) -N (15-20) ]/N (5-10) ≤0.25, wherein N (5-10) represents the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 5 μm or more and less than 10 μm, and N (15-20) represents the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 15 μm or more and less than 20 μm.
5 . The method for producing a cast article according to claim 1 , wherein said method meets 0<dt pE /dt E ≤1/4.
6 . The method for producing a cast article according to claim 1 , wherein said method meets 1/4≤dt pE /dt E ≤1/2.
7 . The method for producing a cast article according to claim 1 , wherein said method meets 1/4≤dt pE /dt E <1/2.
8 . The method for producing a cast article according to claim 1 , wherein the gas is supplied to monotonically increase the pressing pressure from the start.
9 . A method for producing a cast article of spheroidal graphite cast iron meeting the following conditions:
N (5-) ≥250,
N (5-20) /N (5-) ≥0.6, and
N (30-) /N (5-) ≤0.2,
wherein N (5-) , N (5-20) , and N (30-) are the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 5 μm or more, the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 5 μm or more and less than 20 μm, and the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 30 μm or more, respectively, among graphite particles observed in an arbitrary cross section of at least 1 mm 2 ; comprising
pouring a melt into a gas-permeable casting mold by gravity-casting,
pressing a surface of the melt in the gas-permeable casting mold by a gas at a pressure of 1-100 kPa, before said melt starts eutectic solidification; and
solidifying said melt while supplying said gas into said casting mold,
wherein said method meets
0< dt pE /dt E ≤1/1.9,
wherein dt E represents a time period from the start of eutectic solidification of said melt to the completion of the eutectic solidification, and dt pE represents a time period from the start of eutectic solidification of said melt to the completion of said pressing.
10 . The method for producing a cast article according to claim 9 , wherein said pressure is 10-50 kPa.
11 . The method for producing a cast article according to claim 9 , wherein said gas-permeable casting mold is a green sand mold, a shell mold, or a self-hardening mold, constituted by sand particles.
12 . The method for producing a cast article according to claim 9 , wherein the spheroidal graphite cast iron has a composition comprising by mass 2-4.5% of C, 0.8-2.26% of Si, and 0.010-0.080% of Mg, the balance being Fe and inevitable impurity elements and optionally one or more of S, P, Mn, Cu, Cr, Ni, Mo, W,
wherein said graphite particles meet N (2-5) ≥100, wherein N (2-5) represents the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 2 μm or more and less than 5 μm,
wherein said graphite particles meet D max ≥50.4 μm, wherein D max represents the maximum equivalent-circle diameter of graphite particles, and
wherein said graphite particles meet −0.15≤[N (5-10) -N (15-20) ]/N (5-10) ≤0.25, wherein N (5-10) represents the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 5 μm or more and less than 10 μm, and N (15-20) represents the number (/mm 2 ) of graphite particles having equivalent-circle diameters of 15 μm or more and less than 20 μm.
13 . The method for producing a cast article according to claim 9 , wherein the gas is supplied to monotonically increase the pressing pressure from the start.