JPH0688123A - Production of spheroidal graphite cast iron and spheroidal graphite cast iron - Google Patents

Abstract

PURPOSE:To provide the material for parts for specification in a cold district by forming spheroidal graphite cast iron incorporated with a specified amt. of Sn and subjected to heat treatment. CONSTITUTION:Cast iron is added with, by weight, 0.02 to 0.06% Sn and is subjecte to heat treatment. In this way, the spheroidal graphite cast iron having a structure in which ferrite having 5mum width and <=25mum length lies in a large quantity of pearlitic matrix as well as the area ratio of ferrite excluding graphite occupying in the matrix is regulated to <=10% is formed. Furthermore, its Brinell hardness HB is regulated to >=240 and its impact absorbing energy at -60 deg.C is regulated to >=25J/cm<2> in a test piece free from a Charpy notch.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing spheroidal graphite cast iron and spheroidal graphite cast iron, and more particularly to a method for producing spheroidal graphite cast iron which is effectively used as a large strength component and spheroidal graphite cast iron.

[0002]

2. Description of the Related Art Conventionally, spheroidal graphite cast iron having high strength and hardness and excellent toughness has been used for undercarriage parts such as carriers of drive parts of caterpillars for construction machines and spring brackets of trucks. Especially, since these construction machines may be used in cold regions,
A high impact value is required for the spheroidal graphite cast iron used for these parts. Therefore, these suspension parts have conventionally been subjected to a very special heat treatment to lower the impact transition temperature.

[0003]

However, the above-mentioned conventional method for producing spheroidal graphite cast iron has the following problems. That is, in the conventional method for producing spheroidal graphite cast iron, a very special heat treatment is required to achieve the required impact value, at which time very delicate control is required, the production efficiency is low, and as a result, the product There was a problem that the manufacturing cost was high. In particular, when the product to be manufactured is a large product of a certain size or more, it becomes extremely difficult to uniformize the structure of each part of the component by heat treatment to achieve the required properties, and there is a problem that the structure and properties become uneven. It was In that case, even if it is possible to obtain a uniform structure by repeating the process of austenitizing the entire body, cooling it in a furnace, and normalizing it many times, it is difficult to industrially apply such a method and in any case. However, there is a problem that it causes an increase in production cost. Therefore, the present invention has been made in view of the above problems of the prior art, and it is possible to manufacture spheroidal graphite cast iron that has high strength and impact value and can be applied as a component material for cold district specifications extremely efficiently and at low cost. An object of the present invention is to provide a spheroidal graphite cast iron that can be produced and a spheroidal graphite cast iron with good characteristics obtained by such a method.

[0004]

[Means for Solving the Problems] In order to achieve the above objects, the present inventors investigated the effect of Sn on pearlite formation and impact value at various cooling rates, and attempted improvement by heat treatment. As a result, they have found that a spheroidal graphite cast iron having a high strength and a high impact value can be produced by subjecting the spheroidal graphite cast iron containing a certain amount of Sn to an appropriate heat treatment, and have thus created the present invention. That is, the method for producing spheroidal graphite cast iron of the present invention is characterized in that Sn is added in an amount of 0.02% by weight or more and 0.06% by weight or less and heat treatment is performed. Process or A ₁ eutectoid heat treatment quenching after cooling in a furnace to a temperature not rotate the lower range of the A ₁ eutectoid transformation temperature range after holding at a temperature greater than A ₁ eutectoid transformation temperature in the above the present invention It is effective to carry out a treatment of holding at a temperature higher than the transformation temperature, quenching to room temperature, then holding at a temperature not higher than the A ₁ eutectoid transformation temperature and then quenching. This is because by doing so, a necessary amount of fine ferrite is dispersed in a large amount of pearlite matrix. Further, Sn is 0.02% by weight or more,
If less than 0.02% by weight, the structure tends to become ferritic, and the effect of heat treatment becomes insufficient, and sufficient hardness cannot be obtained.
This is because if the content exceeds 100% by weight, the impact value will be low and the application as a cold region component will be limited.

The spheroidal graphite cast iron of the present invention is a mixed structure of spheroidal graphite, pearlite and ferrite, and the main matrix structure is pearlite. In the ferrite having a width of 5 μm and a length of 25 μm or less, or branched ferrite, The main branch has a width of 5 μm and a length of 25 μm or less, and the ferrite area ratio excluding graphite in the matrix is 1
It is characterized by having a structure of 0% or less. Here, the size of the ferrite is set to a width of 5 μm and a length of 25 μm or less because if the size of the ferrite exceeds it, a fine structure cannot be obtained and the strength, particularly the hardness, becomes insufficient. . The reason why the ferrite area ratio is 10% or less is that if the ferrite area ratio exceeds it, the hardness is still insufficient.

Further, the spheroidal graphite cast iron of the present invention has a Brunel hardness of HB240 or more and an impact absorption energy at -60 ° C. of 2 in a Charpy notched test piece.
It is characterized by being 5 J / cm ² or more. Here, the Brunel hardness of HB240 or more means that the Brunel hardness is H.
This is because if it is less than B240, the hardness is insufficient and it is not particularly suitable for practical use as an underbody part or the like. Further, the reason why the impact absorption energy at −60 ° C. is 25 J / cm ² or more in a Charpy notch-less test piece is that it is not suitable for practical use as a machine part especially for cold district specifications when it is less than 25 J / cm ² .

[0007]

Function In spheroidal graphite cast iron, it is generally known that Sn lowers the impact value and raises the transition temperature. On the other hand, Sn is an element having a tenfold stronger pearlite conversion ability than Mn, Cu, etc., and even if the cooling rate after casting is slow, a pearlite base sufficient for the FCD700 and 800 specifications can be obtained. According to the present invention, the characteristics of Sn in the spheroidal graphite cast iron are positively utilized, and the spheroidal graphite cast iron is manufactured by adding Sn and heat-treating it. By acting as a stabilizing element and controlling the amount of ferrite in the structure, it is possible to obtain a structure in which fine ferrite is uniformly dispersed in the matrix. As a result, a structure in which fine ferrite is scattered in a large amount of pearlite, and high hardness and a sufficient impact value can be achieved. Furthermore, according to the present invention, by adding Sn and performing heat treatment, the transformation temperature of each portion of the structure in the heat treatment process can be made uniform, the difference in transformation temperature between the respective portions of the structure is reduced, and the hardenability is improved. As a result, a large pearlite phase with poor inter-layer mechanical properties, which is usually inferior in mechanical properties, is not generated even for large and difficult heat-treated castings, and since uniform quenching occurs, no particularly embrittled portions occur after heat treatment, and in cold regions. It is possible to obtain a material having a low temperature impact value improved as a whole component.

[0008]

EXAMPLES Next, examples of the present invention will be described. Example 1 Commercially available steel scraps, factory return scraps, ferroalloys, and the like were mixed with appropriate amounts of Mn and Cu in order to adjust the hardness to Sn of 0.03% and melted to obtain Fe-Si-5.5% Mg. Fe-50% Si was inoculated after spheroidizing by the sandwich method and cast into a plate body 2 having a three-dimensional shape capable of containing a sphere 1 having a diameter of 50 mm as shown in FIG. 1 using a CO ₂ mold. . 5 ° C after casting
The inside of the furnace was cooled at a cooling rate of / min. Example 2 In the same manner as in Example 1 except for the above, after casting, the inside of the furnace was cooled at a cooling rate of 2 ° C./min. Example 3 In the same manner as in Example 1 except for the above, the heat treatment of the heat cycle shown in FIG. 2 was performed on the cast material after casting. Example 4 In the same manner as in Example 1 except for the above, the heat treatment of the heat cycle shown in FIG. 3 was performed on the cast material after casting. Comparative Example 1 The same as in Example 2 except that the addition amount of Sn was 0.015%.
As a result, spheroidal graphite cast iron was cast. Comparative Example 2 In the same manner as in Example 2, except that the addition amount of Sn was 0, spheroidal graphite cast iron was cast. Comparative Example 3 As shown in FIG. 4, the plate body 4 having a three-dimensional shape that cannot include the sphere 1 having a diameter of 50 mm was the same as in Example 3 except Sn.
Was cast with the addition amount of 0 being 0. With respect to the spheroidal graphite cast iron obtained by the above comparative examples, the Brunel hardness and impact absorption energy at −60 ° C. were investigated using a Charpy notched test piece. The results are shown in Table 1. Further, the microstructure of the spheroidal graphite cast iron obtained in each of the examples and comparative examples was observed. The results are shown in FIGS.

[0009]

[Table 1] It was confirmed that each of the examples and comparative examples shown in Table 1 had a Brunel hardness of HB240 or higher.

As shown in Table 1, in each of the examples, the impact absorption energy at −60 ° C. is 25 J / cm ² or more in the Charpy notch-less test piece.
On the other hand, in Comparative Examples 1 and 2, the impact absorption energy at −60 ° C. is 10 to 14 J / cm ² in the Charpy notched test piece. Further, in Comparative Example 3, the impact absorption energy at −60 ° C. was 25 J / cm ² in the test piece without Charpy notch as in each Example.
As described above, this comparative example 3 has a sphere 1 with a diameter of 50 mm.
It was found to be cast as a plate having a three-dimensional shape that cannot contain, and it is understood that the required characteristics can be obtained for such small articles without adding Sn. See also FIG.
As can be seen from FIG. 9, each of the samples obtained in the respective examples has a structure in which fine ferrite is dispersed in pearlite with a close layer spacing, that is, a mixed structure of spheroidal graphite, pearlite and ferrite, which is the main matrix. The organization is perlite. Ferrite has a width of 5 μm and a length of 2
The size is 5 μm or less, and particularly in a branched ferrite, the main branch has a width of 5 μm and a length of 25 μm or less. The ferrite area ratio excluding graphite in the matrix is 10% or less.

[0011]

As described above, according to the method for producing spheroidal graphite cast iron and the spheroidal graphite cast iron of the present invention, spheroidal graphite is obtained by adding Sn in an amount of 0.02 wt% or more and 0.06 wt% or less and subjecting it to heat treatment. The main matrix structure is a mixed structure of pearlite, pearlite, and ferrite, and the main matrix structure is pearlite. The structure is such that ferrite has a width of 5 μm and a length of 25 μm or less, and the ferrite area ratio excluding graphite in the matrix is 10% or less. A spheroidal graphite cast iron having a Brunel hardness of HB240 or more and an impact absorption energy at -60 ° C of 25 in a specimen without Charpy notch.
By using spheroidal graphite cast iron with J / cm ² or more,
The spheroidal graphite cast iron, which has high strength and impact value and can be applied as a component material for cold district specifications, can be manufactured extremely efficiently at low cost.

[Brief description of drawings]

FIG. 1 is a perspective view showing a form of a cast product obtained by carrying out the present invention.

FIG. 2 is a diagram showing a heat cycle according to an embodiment of the present invention.

FIG. 3 is a diagram showing a heat cycle according to another embodiment of the present invention.

FIG. 4 is a perspective view showing a form of a cast product of a comparative example with respect to the embodiment of the present invention.

FIG. 5 is a photograph of the structure of a cast product according to an example of the present invention.

FIG. 6 is a structural photograph of a cast product of another example of the present invention.

FIG. 7 is a photograph of the structure of a cast product of another example of the present invention.

FIG. 8 is a photograph of the structure of a cast product according to another embodiment of the present invention.

[Explanation of symbols]

 1 sphere 2, 4 plate

Claims (6)

[Claims] 1. A method for producing spheroidal graphite cast iron, which comprises adding Sn in an amount of 0.02% by weight or more and 0.06% by weight or less and performing heat treatment. 2. A method for producing a spheroidal graphite cast iron product having a three-dimensional shape as an outer shape capable of including a sphere having a diameter of 50 mm in at least a part thereof, wherein Sn is 0.02% by weight or more and 0.1.
A method for producing a spheroidal graphite cast iron product, which comprises adding 06% by weight or less and performing heat treatment. 3. adding Sn 0.02 wt% or more 0.06 wt% or less, not rotate the lower range of the A ₁ eutectoid transformation temperature range after holding at a temperature greater than A ₁ eutectoid transformation temperature Temperature A method for manufacturing spheroidal graphite cast iron, which comprises subjecting a spheroidal graphite cast iron to a heat treatment in which the temperature is lowered in a furnace and then rapidly cooled. 4. Sn is added in an amount of 0.02% by weight or more and 0.06% by weight or less, held at a temperature higher than the A ₁ eutectoid transformation temperature, and then rapidly cooled to room temperature, and thereafter, at a temperature lower than the A ₁ eutectoid transformation temperature. A method for manufacturing spheroidal graphite cast iron, characterized by performing a heat treatment of quenching after holding at the temperature. 5. A mixed structure of spheroidal graphite, pearlite and ferrite, the main matrix structure of which is pearlite, and the main branch of ferrite having a width of 5 μm and a length of 25 μm or less or a branched ferrite has a width of 0. ．
A spheroidal graphite cast iron characterized by having a structure having a size of 05 μm and a length of 0.25 μm or less and having a ferrite area ratio excluding graphite in the matrix of 10% or less. 6. The spheroidal graphite cast iron according to claim 4, wherein the Brunel hardness is HB240 or more and the impact absorption energy at −60 ° C. is 25 J / cm ² or more in a Charpy notched test piece. Spheroidal graphite cast iron.