JPH0153328B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing as-cast pearlitic pseudo-spheroidal graphite cast iron. More specifically, the present invention relates to a method for stably obtaining pseudo-spheroidal graphite cast iron in an as-cast state, the entire base structure of which is composed of almost only a fine pearlite structure. It has been known for a long time that spheroidal graphite cast iron can be obtained in the as-cast state with a pearlite base structure.
There is a method using Mn. However, since Mn is both a pearlitizing element and a cementitizing element, there are problems such as precipitation of a cementite structure, resulting in locally increased hardness and brittleness. Precipitation of this cementite structure can be prevented by increasing the Si content, but the pearlitic terrestrial graphite cast iron obtained by this method is easily affected by the cooling rate in the casting mold, and has a thin wall thickness. In areas where the cooling rate is high, a base structure rich in pearlite is obtained, but in areas where the cooling rate is low, such as in thick-walled areas, a pearlite base structure containing a large amount of ferrite is obtained, making it difficult to transform the overall structure of the casting into pearlite. Can not. In order to solve the above problem, a method has been proposed in which Ni is used as a pearlitization promoting element (see Japanese Patent Application Laid-open No. 134720/1983), but even in this method, a large amount of ferrite structure is precipitated, and the entire base structure is cannot be converted into pearlite. In view of the above points, the present invention aims to provide a method for preventing the precipitation of harmful cementite structures and stably producing pseudo-spheroidal graphite cast iron whose base structure is pearlite, regardless of the cooling rate during casting. It is. That is, in the present invention, C2.80~4.00%, Si1.50~
2.90%, Mn0.1~0.8%, S0~0.05%, P0~0.1%,
Cu, Sn, and Sb are added to the pseudospheroidal graphite cast iron source melt, the remainder of which is essentially Fe, to increase the content of these elements (values in the final molten metal, the same applies hereinafter) to Cu0.2~
Adjust to 0.8%, Sn0.05~0.25%, Sb0.01~0.1%,
The present invention then relates to a method for producing as-cast pearlite earth pseudospheroidal graphite cast iron, which is characterized by subjecting it to pseudospheroidization treatment and inoculation. In the present invention, by adjusting the contents of the three elements Cu, Sn, and Sb to the above-mentioned specific range, a base structure that does not contain harmful cementite structure can be created, regardless of the thickness of the casting. Pseudo-spheroidal graphite cast iron consisting only of fine pearlite, for example, 95% or more pearlite, can be obtained as-cast. Note that the method of the present invention can be equally applied to spheroidal graphite cast iron. In the present invention, it is important to adjust the contents of the three elements within the above range, and the intended purpose cannot be achieved by adjusting only one or two of the three elements. However
If the content of Cu, Sn or Sb is less than the above range, it is difficult to transform the base structure into pearlite almost completely. If the Cu content exceeds the above range, it is disadvantageous in terms of cost. If the Sn content exceeds the above range, precipitation of cementite etc. will be observed, and properties such as workability will be greatly impaired. If the Sb content exceeds the above range, the time for cementite to precipitate increases, and it becomes difficult to stably obtain pseudo-spheroidal graphite cast iron. The pseudospheroidal graphite cast iron obtained by the method of the present invention does not contain any harmful structures such as cementite, and the base structure consists almost exclusively of pearlite, so it has good mechanical properties such as hardness, tensile strength, and wear resistance. All are excellent. For example hardness (Hv)
is about 200 to 270, and the tensile strength is about 30 to 45 Kg/ ^mm2 . In addition, the pseudospheroidal graphite cast iron obtained by the method of the present invention exhibits excellent castability, and has the same eutectic expansion and external sink as gray cast iron. Therefore, even when applied to cast parts with large wall thickness fluctuations, A desired casting without sink marks, cavities, etc. can be obtained without special provision of a riser, blind riser, etc. Therefore, it is particularly useful for manufacturing engine cylinder blocks. In the casting of cylinder blocks, the inner surface of the bore is a slow-cooling area. Therefore, in the conventional method, the matrix structure on the inner surface of the bore easily turned into ferrite, and it was not possible to transform the matrix structure of the entire block into pearlite. However, in the present invention, Since the base structure of the entire block can be made into pearlite without being affected by the cooling rate, it is extremely advantageous for casting cylinder blocks. Moreover, the excellent wear resistance of cast iron makes it possible to make the cylinder block linerless. In addition, it has higher tensile strength than gray cast iron, and has better castability than conventional spheroidal graphite cast iron, so problems such as cracking of the cylinder block can be avoided, and it can also be made thinner and easier to cast.
It is possible to reduce the weight. As described above, the present invention is suitably applied to the casting of cylinder blocks, but it is not limited to this example, but can also be applied to the manufacture of cast parts that require particularly high wear resistance, such as drum brakes and disc brakes. be done. In the present invention, the pseudo-spheroidal graphite cast iron source water used is one that can make graphite pseudo-spheroidal, and has a C2.80~
4.00%, Si1.50~2.90%, Mn0.1~0.8%, S0~
The composition used is 0.05%, P0 to 0.1%, and the remainder substantially Fe. As mentioned above, the content of Mn, which is generally used as a pearlitizing element, needs to be 0.8% or less. In the present invention, the production method for pseudo-spheroidal graphite cast iron can be carried out in the same manner as the conventional method for producing pseudo-spheroidal graphite cast iron, except that the above-mentioned three elements are added to the pseudo-spheroidal graphite cast iron source bath to adjust the content. After adjusting the components, pseudo-spheroidization treatment is performed in a ladle using Ca alloy, Ce alloy, Mg alloy, etc., followed by inoculation and casting. Next, the method of the present invention will be explained with reference to Examples and Comparative Examples. Examples and Comparative Examples 1 to 2 Cu, Sn, and Sb were added to the pseudo-spheroidal graphite cast iron base melt in a low frequency furnace to adjust the composition, and then tapped, and 0.8% of Ca-Mg-RE-Si alloy was added in a ladle. Then, 0.3% Fe-Si inoculation was performed, and the metal was poured into a mold to cast two types of test pieces with different thicknesses. The final composition of the molten metal is shown in Table 1. Surface hardness, tensile strength,
The presence or absence of cementite precipitation and the content of pearlite structure in the matrix structure were investigated. The content of pearlite structure was determined using an image analysis device manufactured by Shimadzu Corporation. The results are shown in Table 2.

【table】

【table】

Claims (1)

[Claims] 1 C2.80~4.00%, Si1.50~2.90%, Mn0.1~0.8
%, S0 ~ 0.05%, P0 ~ 0.1%, the balance is essentially Fe
Cu, Sn and Sb are added to the pseudo-spheroidal graphite cast iron source water.
The contents of these elements (values in the final molten metal) are increased by adding Cu0.2 to 0.8%, Sn0.05 to 0.25%, and Sb0.01.
A method for producing as-cast pearlite earth pseudospheroidal graphite cast iron, which is characterized by adjusting the concentration to ~0.1%, followed by pseudospheroidization treatment and inoculation.