Spheroidal graphite cast iron having excellent strength and toughness and its production method
AssigneeHitachi Metals, Ltd.
InventorsLin Wang, Masahide Kawabata, Kentaro Fukumoto
Life of this patent
Estimating the term…
Abstract
A spheroidal graphite cast iron having (a) a composition comprising by mass 3.4-4% of C, 1.9-2.8% of Si, 0.02-0.06% of Mg, 0.2-1% of Mn, 0.2-2% of Cu, 0-0.1% of Sn, 0.85-3% of (Mn+Cu+10×Sn), 0.05% or less of P, and 0.02% or less of S, the balance being Fe and inevitable impurities, and (b) a duplex matrix structure comprising by area 2-40% of fine ferrite phases and 60-98% of fine pearlite phases, the maximum length of the ferrite phases being 300 μm or less, and (c) the pearlite phases being formed around graphite particles dispersed in the duplex matrix structure.
Claims5
A spheroidal graphite cast iron having excellent strength and toughness, which has
- (a) a composition comprising by mass 3.4-4% of C, 1.9-2.8% of Si, 0.02-0.06% of Mg, 0.2-1% of Mn, 0.2-2% of Cu, 0.85-3% of (Mn+Cu), 0.05% or less of P, and 0.02% or less of S, the balance being Fe and inevitable impurities, wherein Sn is not present in the composition;
- and
- (b) a duplex matrix structure comprising by area 2-40% of fine ferrite phases and 60-98% of fine pearlite phases, the maximum length of said ferrite phases being 300 μm or less;
- and
- (c) said pearlite phases being formed around graphite particles dispersed in said duplex matrix structure.
A method for producing a spheroidal graphite cast iron having excellent strength and toughness comprising the steps of
- (1) casting and solidifying a melt having a composition comprising by mass 3.4-4% of C, 1.9-2.8% of Si, 0.02-0.06% of Mg, 0.2-1% of Mn, 0.2-2% of Cu, 0.85-3% of (Mn+Cu), 0.05% or less of P, and 0.02% or less of S, the balance being Fe and inevitable impurities, wherein Sn is not present in the composition;
- and
- (2) conducting a heat treatment comprising a step (i) of holding the resultant casting at a temperature at which an entire matrix of the casting is austenized, to form fine austenite crystal grains, which are transformed to pearlite crystal grains by cooling, and a step (ii) of cooling the casting at a cooling rate of forming fine ferrite phases in a predetermined temperature range within a temperature span in which eutectoid transformation occurs, thereby forming a duplex matrix structure comprising by area 2-40% of fine ferrite phases and 60-98% of fine pearlite phases, the maximum length of said ferrite phases being 300 μm or less, and said pearlite phases being formed around graphite particles dispersed in said duplex matrix structure.
Dependencies are inferred from the claim text.