Provided is a method capable of producing a plated black heart malleable cast iron member having a plating layer with excellent adhesiveness to a black heart malleable cast iron member, while having less burden on the environment, compared to conventional methods.

The black heart malleable cast iron according to the present embodiment comprises a matrix of ferrite and lump graphite included in the matrix, the black heart malleable cast iron comprising 50 ppm or more and 100 ppm or less of boron, and 65 ppm or more and 200 ppm or less of nitrogen in a mass ratio, wherein a grain size of the matrix is 8.0 or more and 10.0 or less in terms of grain size number, numerically determined by comparison between a metallographic photograph and a standard grain size chart.

The present invention suppresses leakage of combustion gas from a contact surface. A cylinder head (20) is attached to a cylinder block. The surface (26) of the side of the cylinder head (20) that is attached to the cylinder block includes a first region (AH1) and a second region (AH2) that has higher hardness than the first region (AH1).

The present invention suppresses leakage of combustion gas from a contact surface. A cylinder head (20) is attached to a cylinder block. The surface (26) of the side of the cylinder head (20) that is attached to the cylinder block includes a first region (AH1) and a second region (AH2) that has higher hardness than the first region (AH1).

There is provided a centrifugally cast composite roll for rolling having excellent wear resistance and surface deterioration resistance at levels of a high-speed steel cast iron roll and having rolling incident resistance at a level of a high alloy grain cast iron roll. Its outer layer includes chemical components by mass ratio: C: 1.5 to 3.5%; Si: 0.3 to 3.0%; Mn: 0.1 to 3.0%; Ni: 1.0 to 6.0%; Cr: 1.5 to 6.0%; Mo: 0.1 to 2.5%; V: 2.0 to 6.0%; Nb: 0.1 to 3.0%; B: 0.001 to 0.2%; N: 0.005 to 0.070%; and the balance being Fe and inevitable impurities, wherein: a chemical composition of the outer layer satisfies Formula (1) and has 5 to 30% of M.sub.3C carbide by area ratio; an outer layer Shore hardness (A) of a roll surface satisfies Formula (2); and a residual stress (B) of the roll surface satisfies Formula (3),
2×Ni+0.5×Cr+Mo>10.0  (1)
Hs 75≤A≤Hs 85  (2)
100 MPa≤B≤350 MPa  (3).

There is provided a centrifugally cast composite roll for rolling having excellent wear resistance and surface deterioration resistance at levels of a high-speed steel cast iron roll and having rolling incident resistance at a level of a high alloy grain cast iron roll. Its outer layer includes chemical components by mass ratio: C: 1.5 to 3.5%; Si: 0.3 to 3.0%; Mn: 0.1 to 3.0%; Ni: 1.0 to 6.0%; Cr: 1.5 to 6.0%; Mo: 0.1 to 2.5%; V: 2.0 to 6.0%; Nb: 0.1 to 3.0%; B: 0.001 to 0.2%; N: 0.005 to 0.070%; and the balance being Fe and inevitable impurities, wherein: a chemical composition of the outer layer satisfies Formula (1) and has 5 to 30% of M.sub.3C carbide by area ratio; an outer layer Shore hardness (A) of a roll surface satisfies Formula (2); and a residual stress (B) of the roll surface satisfies Formula (3),
2×Ni+0.5×Cr+Mo>10.0  (1)
Hs 75≤A≤Hs 85  (2)
100 MPa≤B≤350 MPa  (3).

A method of manufacturing a cam piece for a continuously variable valve duration and a cam piece manufactured therefrom, and more particularly, to material and heat treatment conditions of a cam piece, may include manufacturing a cam piece by casting; heating the cam piece; maintaining a heating temperature; and salt-bathing the cam piece, in which the cam piece includes 3.2 to 4.2 wt % of carbon (C), 2.2 to 3.4 wt % of silicon (Si), and the balance iron (Fe), and may have a carbon equivalent value of 4.4 to 4.6.

A method of manufacturing a cam piece for a continuously variable valve duration and a cam piece manufactured therefrom, and more particularly, to material and heat treatment conditions of a cam piece, may include manufacturing a cam piece by casting; heating the cam piece; maintaining a heating temperature; and salt-bathing the cam piece, in which the cam piece includes 3.2 to 4.2 wt % of carbon (C), 2.2 to 3.4 wt % of silicon (Si), and the balance iron (Fe), and may have a carbon equivalent value of 4.4 to 4.6.

A ductile iron composition including, by weight: about 3.4% to about 4.0% Si; about 3.0% to about 3.5% C; about 0.5% to about 1.0% Cr; about 0.02% to about 0.05% Mo; up to about 0.01% S; up to about 0.5% Mn; and balance iron and incidental impurities.

The composition has a a ferritic body center cubic microstructure and has a graphite nodule density of greater than 100 per mm.sup.2. A method for forming a ductile iron composition is also disclosed.

Austempered steel for components requiring high strength and high ductility and/or fracture toughness, which has a silicon content of 3.1 weight-% to 4.4 weight-% and a carbon content of 0.4 weight-% to 0.6 weight-%. The microstructure of the austempered steel is ausferritic or superbainitic.