JPH05125480A - Spheroidal graphite cast iron with high - Google Patents

Abstract

PURPOSE:To provide a spheroidal graphite cast iron excellent in tensile strength and elongation in an as-cast state. CONSTITUTION:The spheroidal graphite cast iron has a chemical composition where 2.6-3.3%, by weight, C, 3.7-4.5% Si, 0.2-0.7% Mn, <=0.06% P, <=0.01% S, and 0.03-0.06% Mg are contained as essential components and 0.07-0.15% Cr, 0.2-0.5% Cu, or 0.2-0.5% (Cr+Cu) (where Cr is <=0.13%) is added to the above components and the balance consists essentially of Fe. Further, this spheroidal graphite cast iron combines high strength with high toughness and has >=60kg/mm<2> tensile strength and >=10% elongation in the as-cast state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to as-cast spheroidal graphite cast iron excellent in strength and toughness.

[0002]

2. Description of the Related Art Ductile cast iron has excellent mechanical strength such as tensile strength comparable to that of steel.
It is well known that the tendency of products made of malleable cast iron, forged steel, etc., such as automobile members and civil engineering construction members, to be converted to ductile cast iron has been accelerated from the viewpoint of economy and quality. ..

For example, as an automobile member, FCD40
(Tensile strength: 41-43kg / mm ² , elongation: 19-28%), FC
D60 (tensile strength: 67-85kg / mm ² , elongation: 2.2-7.3
%), FCD70 (tensile strength: 76 to 95 kg / mm ² , elongation:
2.1 to 5.5%) is applied to each member as appropriate. The F
CD40 is annealed to a perfect ferrite structure, FCD60 is generally as-cast to obtain a pearlite structure, and FCD70 is annealed to obtain a sorbitic pearlite structure.

[0004]

The FCD 40 has high toughness but low strength, and the FCDs 60 and 70 both have high strength but low toughness. However, some parts require high strength and high toughness, and it is proposed that the composition is changed in addition to the above-mentioned tough spheroidal graphite cast iron, but these are heat-treated such as annealing, normalizing cast products. Had been given.

However, such heat treatment has a drawback that the product price is increased accordingly. Therefore, many attempts have been made to obtain high strength and high toughness by as-casting, but as long as it does not reach the range that satisfies the JIS standard, the tensile strength is 60 kg / mm ² or more and the elongation is as-cast. No spheroidal graphite cast iron having high strength and high toughness of 10% or more was obtained. In view of the above, it is an object of the present invention to provide as-cast high-strength, high-toughness spheroidal graphite cast iron at low cost.

[0006]

Means for Solving the Problems The features of the present invention taken to achieve the above object are that the chemical composition is% by weight, C: 2.6 to 3.3%, Si: 3.7 to 4.5.
%, Mn: 0.2 to 0.7%, P: 0.06% or less, S
: 0.01% or less, Mg: 0.03 to 0.06% as a basic composition, and Cr: 0.07 to 0.15% (claim 1), or Cu: 0.2 to 0.5% (claim 2), or Cr + Cu:
0.2 to 0.5%, but Cr is added with 0.13% or less (claim 3), and the balance consists essentially of Fe, and as-cast has a tensile strength of 60 kg / mm ² or more and an elongation of 10% or more. It is a point that the spheroidal graphite cast iron has high strength and high toughness.

[0007]

EXAMPLES Examples of the present invention will be described below. The basic composition of the present invention is C: 2.6 to 3.3%, Si: 3.7 to 4.5.
%, Mn: 0.2 to 0.7%, P: 0.06% or less, S
: 0.01% or less, Mg: 0.03 to 0.06%, which is low C and high S as compared with the conventional FCD 40, 60, 70, etc.
i, low P, trace amount of Cr: 0.07 to 0.15 in order to maintain the toughness of the ferrite composition with an area ratio of 90% or more
%, Or Cu: 0.2 to 0.5%, or Cr + Cu: 0.2 to
0.5% (however, Cr is 0.13% or less) is added. The balance is substantially Fe.

The reasons for limiting the above composition will be described below.
Note that Mn, S, and Mg have no special features as compared with ordinary ductile cast iron, and therefore the description of the reason for limitation is omitted. C
If less than 2.6%, the tendency of chilling becomes strong, and even if the Si content is increased to 4% or more, high elongation cannot be obtained. On the other hand, if the C content exceeds 3.3% and the Si content exceeds 4%, the precipitation of graphite increases and high tensile strength cannot be obtained. For the above reasons, C is limited to 2.6 to 3.3%.

In Si, if C is around 3% and Si is less than 3.7%, pearlite is often precipitated and high elongation cannot be obtained. On the other hand, if the Si content exceeds 4.5%, the elongation decreases due to the precipitation of silicoferrite. From the above reasons, Si
Limited to 4.5%. When P exceeds 0.06%, the elongation drops sharply, so P was limited to 0.06% or less.

In the above basic composition of the present invention, Cr is
If it is less than 0.07%, high tensile strength cannot be obtained, and if it exceeds 0.15%, high elongation cannot be obtained. Therefore, Cr is limited to 0.07 to 0.15%. In the above basic composition of the present invention, Cu is 0.
If it is less than 2%, high tensile strength cannot be obtained, and if it exceeds 0.5%, high elongation cannot be obtained. Therefore, Cu is limited to 0.2 to 0.5%.

In the above basic composition of the present invention, Cr + Cu has a high tensile strength below 0.2% and a high elongation above 0.5%, as in the case of adding Cr and Cu alone. Cr + Cu 0.2 to 0.5% (however,
Cr was limited to 0.13% or less). Table 1 and Table 2 below
The present invention and the comparative example cast iron are shown in FIG.

[0012]

[Table 1]

[0013]

[Table 2]

In the above Tables 1 and 2, Claims 1 to 3
Specimen No. of spheroidal graphite cast iron described in is as follows,
Others are comparative sample materials. Claim 1 No. 2,3,4,9,10,11,13,14,15,23,24 Claim 2 No. 18,19,20 Claim 3 No. 27,28,30,32,33 , 34,35,37,38,39 All of these are as-cast and have tensile strength of 60 kg / mm ² or more and elongation of 10% or more, and have high strength and high toughness. It is understood that there is.

The test materials of the comparative examples showed the as-cast mechanical properties except for No. 42 which was annealed.

[0016]

The spheroidal graphite cast iron of the present invention has a tensile strength of 60 kg / mm ² or more and an elongation of 10% or more as cast.
Since it has high strength and high toughness mechanical strength, it does not require heat treatment and can be manufactured at low cost. Therefore, it can be used as a member for automobiles, a member for civil engineering construction, etc., which requires high strength and toughness.

Claims (3)

[Claims] 1. The chemical composition is% by weight, C: 2.6-3.3%, Si: 3.7-4.5%, Mn:
0.2-0.7%, P: 0.06% or less, S: 0.01% or less, Mg:
0.03 to 0.06%, Cr: 0.07 to 0.15% The balance consists essentially of Fe, and as cast, has a tensile strength of 60 kg.
/ mm ² or more, elongation is 10% or more, a tough spheroidal graphite cast iron. 2. The chemical composition is% by weight, C: 2.6 to 3.3%, Si: 3.7 to 4.5%, Mn:
0.2-0.7%, P: 0.06% or less, S: 0.01% or less, Mg:
0.03 to 0.06%, Cu: 0.2 to 0.5% The balance consists essentially of Fe, and the tensile strength after casting is 60 kg.
/ mm ² or more, elongation is 10% or more, a tough spheroidal graphite cast iron. 3. The chemical composition is% by weight, C: 2.6 to 3.3%, Si: 3.7 to 4.5%, Mn:
0.2-0.7%, P: 0.06% or less, S: 0.01% or less, Mg:
0.03 to 0.06%, Cr + Cu: 0.2 to 0.5% (however, Cr is 0.13% or less) The balance consists essentially of Fe, and the tensile strength after casting is 60 kg.
/ mm ² or more, elongation is 10% or more, a tough spheroidal graphite cast iron.