JPS6030735B2 - Spheroidal graphite cast iron and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spheroidal graphite cast iron and a method for manufacturing the same, and more particularly to a spheroidal graphite cast iron that has a large impact value in cryogenic castles and a method for manufacturing the same.

Metals with a cubic lattice crystal structure are
It has a tendency to become weak. The temperature at which the impact value or impact absorption energy becomes weaker is the temperature at which the impact value or impact absorption energy decreases to a certain value. It is defined as the temperature at which the impact value or the arithmetic average value of the impact absorption energy decreases at , and is called the impact transition temperature. The impact transition temperature depends on the presence or absence of graphite, the shape, size, amount, and distribution of graphite if it is present, the base structure, chemical components, the shape, size, amount, and distribution of inclusions, and the like.

Spheroidal graphite cast iron, whose matrix structure is almost completely ferritic, has a high impact value or impact absorption energy in ductile castles among cast irons, but it has the disadvantage of a high impact transition temperature.

In order to eliminate this drawback, measures such as lowering the Si content and implementing heat treatment have been taken. As a result, a method for producing spheroidal graphite cast iron with a low impact transition temperature comparable to that of black-core malleable cast iron, which has a reputation for having a low impact transition temperature, was developed. However, the spheroidal graphite cast iron produced by these methods also does not have an impact value of more than 1.0k9·m/m at -100qC using a JIS No. 3 impact test piece.
Low-carbon steel, whose base is a mixed structure of ferrite and pearlite, has a much higher impact value or impact absorption energy in a ductile castle than the above-mentioned spheroidal graphite cast iron, but because of its high impact transition temperature, it has a JIS No. 3 impact rating. The impact value of the test piece at -100qo is not necessarily high.

Qiangang has the disadvantage of having a high level of solidification temperature and poor castability due to its low carbon content. Metals with a face-centered cubic lattice crystal structure do not have the property of becoming brittle at low temperatures, so spheroidal graphite cast iron with an austenite matrix structure has been selected as a material for parts that require low-temperature toughness. There were many things.

However, this material is extremely uneconomical since it must contain nearly 20% of expensive nickel. Therefore, based on the results of extensive research on the effects of raw materials, melting methods, inoculation, chemical components, content of impurity elements, release structure, heat treatment conditions, etc. on the impact transition temperature of spheroidal graphite cast iron, The present invention provides a method for producing ferrite-based terrestrial graphite cast iron with a low transition temperature.

An object of the present invention is to provide a ferritic terrestrial graphite cast iron having an impact value of 1.8k9/skin/lump or higher according to a JIS No. 3 impact test piece at -100°C, and a method for producing the same.

In other words, we succeeded in improving the impact value in the three cryogenic castles by using ferrite as the base structure, making it low in Si and Mn, and suppressing the amount of impurity elements that interfere with ferrite formation to below a certain range. be.

Preferably, the sum T of the products of the weight ratios (%) of the impurity elements and their respective coefficients is 5.0 or less. Here, T is expressed by the following formula.
3T=2 r+7Cu+2Ni+5 eaves n+50
0Pb + 50 eaves b + 100 female i + 20 mark B + 100Te
+3$e+50V+20Mo120W+1 platen+50N
+5$+20Ti+200Cd The present invention will be explained in more detail with the following examples.

Table 1 shows the chemical components and allowable amounts of the examples of the present invention and conventional examples, each in weight percent, and also lists the ferritization interference coefficient (the reciprocal of the above-mentioned allowable amount percent). When T is calculated for Examples A and B and the conventional example shown in Table 1, each of them is 2.85 as shown in the table.
1, 4.48 and 6.20. In Examples A and B of Table 1, the base structure is ferrite or a mixed structure of ferrite and some pearlite in the free state, but after heating it to 850°C and changing it to an austenite structure. , the matrix structure was transformed into ferrite by slow cooling.

These microscopic structures are shown in FIGS. 1 and 2. 1st
The figures and FIG. 2 correspond to Examples A and B, respectively, in which spheroidal graphite is distributed in the ferrite matrix structure. FIG. 3 is a diagram showing the relationship between temperature and impact value, and is a so-called impact transition curve diagram.

In the figure, curves A and B correspond to Examples A and B, respectively, and curve Z shows the conventional example of ferritic terrestrial graphite cast iron. As is clear from the figure, curves A and B both have an impact value of 2.0 even at -100qo.
2.2k9 skin/indicates crucian carp, 0.8 in subordinates
It shows much higher values than k9/skin/ground, and in particular, the values at low temperature are all higher than the conventional ones. In the present invention, the C content is set to 3.0 to 4.0% because
If C is too low, shrinkage cavities and chills are likely to occur; conversely, if it is too high, the properties including the impact value of the manufactured spheroidal graphite cast iron will deteriorate. This is because graphite floats up and so-called graphite dross is generated.

In ferritic terrestrial graphite cast iron, Si increases the impact transition temperature as its content increases, so the upper limit was set at 2.3%.

As the Si content decreases, free cementite is generated in an unrusted state. Free cementite is
Although graphitization can be achieved by heating in the austenite region, the generation of free cementite is undesirable because the shock transition temperature increases due to the formation of irregularities on the surface of spheroidal graphite. Therefore, the lower limit of Si content is set to 1.
It was set at 5%. When the content of Mn increases, free cementite is generated.

Although this free cementite is graphitized by heating in an austenite castle, it is accompanied by the same disadvantages as in the case of low Si, so it needs to be 0.20 or less. Since P is an element that increases the impact transition temperature, it must be contained in an amount of 0.025% or less in order to produce spheroidal graphite cast iron having toughness at low temperatures by the method according to the present invention.

Sulfur is an element that inhibits the spheroidization of graphite, so when producing spheroidal graphite cast iron, the content must be reduced to 0.0.
It is normal to set it to 15% or less.

In the spheroidal graphite cast iron manufactured by the method according to the present invention, 4Mg is set to 0.030 to 0.060% because it is better to have less 4Mg as long as graphite is sufficiently spheroidized. During the production of ferritic terrestrial graphite cast iron, there are a number of elements that interfere with ferritization by crystallizing out free cementite or by stabilizing pearlite.

Interfering elements that are problematic in relation to the present invention include Cr, Cu,
Ni, Sn, Pb, Sb, Bi, B, Te, Se, V,
These are Mo, W, Zn, N, As, Ti, and Cd. The degree to which ferrite formation is obstructed varies depending on the element, and it is meaningless to regulate the overall content by the algebraic sum of the content of each interfering element. Therefore, the content of each interfering element and the ferrite formation of each element are The content of the interfering elements was regulated so that the sum of the products with the coefficients corresponding to the degree of interference did not exceed 5.0. Even if the total sum exceeds 5.0 and free cementite crystallizes, or even if the area ratio of pearlite in the free state increases, the base structure can be converted to ferrite by performing the above heat treatment. Si content is 1.5
% or less, it is not preferable because it causes unevenness on the surface of the spherical graphite. Since the spheroidal graphite cast iron of the present invention and the method for manufacturing the same have the configuration and operation as described above, it can achieve the following effects.

'1' The impact value at -100qo is over 1.8k9/me, which is 3 to 4 times higher than conventional products, making it extremely reliable as a material for vehicle parts, construction equipment, and structures in extremely cold regions. Highly sexual.

■ It also has high reliability as a shock-resistant material in low-temperature castles, such as refrigeration equipment parts for areas other than cold regions and piping equipment parts for LMG.

t3' Like the secondary spheroidal graphite cast iron, it is possible to cast complex parts without requiring any major or medium changes in manufacturing methods.

{4- Since it is not necessary to contain an expensive nickel element to impart low-temperature integrity, it can be used not only for mass production but also as an economical means of production.

[Brief explanation of the drawing]

FIGS. 1 and 2 are photographs showing microscopic structures in examples of the present invention, and FIG. 3 is a diagram showing the relationship between temperature and impact value. Uto - Figure 2 Figure 3

Claims (1)

[Claims] 1. C3.0-4.0%, Si1.5-2.3 in weight ratio
%, Mn 0.20% or less, P 0.025% or less, S0.
015% or less, Mg 0.030-0.060% balance Fe
and some impurities, and the weight ratio (%) of the impurity elements is
) and each coefficient T = 200r + 70u
+2Ni+50Sm+500Pb+500Sb+100
0Bi+200B+100Te+33Se+50V+2
0Mo+20W+10Zn+50Al+50As+20
Spheroidal graphite cast iron whose Ti+200Cd is 5.0 or less, whose base structure consists of ferrite, and which has a large impact value at low temperatures. 2 C3.0-4.0%, Si1.5-2.3 in weight ratio
%, Mn 0.20% or less, P 0.025% or less S0.0
Contains 15% or less, Mg0.030-0.060% balance Fe and some impurities, weight ratio (%) of the impurity elements
and the sum of products of each coefficient T=200r+7Cu+
2Ni+50Sm+500Pb+500Sb+1000
Bi+200B+100Te+33Se+50V+20
Mo+20W+10Zn+50Al+50As+20T
A method for producing spheroidal graphite cast iron having i+200Cd of 5.0 or less, a base structure consisting of ferrite, and having a large impact value at low temperatures, the base structure comprising ferrite or a mixed structure of ferrite and some pearlite. Spheroidal graphite comprising heating as-cast spheroidal graphite cast iron to form an austenite base structure, and then slowly cooling or holding at an arbitrary temperature between 670 and 780°C to transform the base structure into ferrite. How to make cast iron.