JPS5910988B2 - 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 having a mixed structure of austenite and paynite, and a method for manufacturing the same (a method having heat treatment and cooling steps corresponding to %).

Spheroidal graphite cast iron with a basic structure of this type and its mechanical properties are suitable, apart from its normal use, as a structural material.

This material includes refined steel that has hitherto been used exclusively for crankshafts for automobile motors, segment shafts and pistons for fluid power steering devices, traction coupling journals for LKW-articulated clutches, and flexible shaft heads for automobile deflection shafts. It is suitable as a structural material for clutch bodies for trailer clutches, etc.

Among spheroidal graphite cast irons, those having a complete payinite structure as a highly hard and wear-resistant material are known from ancient times and have been used.

In this case, generally 920-950℃ is used when manufacturing castings.
The austenitizing impregnation [held for 2 to 5 minutes, which ensures that the matrix has an almost uniform overall carbon content, or in some cases decomposes the redebrit present after casting.

After austenitization, the casting is completely rapidly cooled, and the austenite is pearlized before reaching the isothermal payinite transformation degree.
Preventing damage.

Casting until the paynight reaction ends? It is maintained at that temperature, and then cooled to room temperature as usual.
ie-βerei) 6 Omi (1978) Bi 4, 73-80
page〕.

Another type of cast iron, known as spheroidal graphite cast iron, which has a full paynitic structure, uses an alloyed cast iron as a starting material and, in direct connection with the cooling step that follows the casting process, the thickness of the casting is adjusted to the desired amount of nickel, molybdenum, and copper. In some cases, a payinite reaction occurs due to chromium and manganese (German Published Application No. 1808515).

According to DE-A-2334992, conventional amounts of carbon, silicon, phosphorus, sulfur and magnesium, 0.10-0.26% molybdenum and 0.3%
Low alloy spheroidal graphite cast irons containing ~1.4% manganese are known.

The resulting castings are heated to an austenitizing temperature of 900 DEG C. and then kept in a 300 DEG C. bath for 2 hours before being cooled for 10 minutes to 4 hours.

In this method, an austenite-bainite structure is formed, so that an elongation rate of 10% and a hardness of 270 to 300 HB can be obtained.

Furthermore, JP-A-53-48015 describes nodular cast iron having a microscopic structure consisting of at least 5% by volume of retained austenite in addition to spheroidal graphite, with the remainder being mainly paynite.

This cast iron was intended to be used in metal mechanical parts for transmission by friction, and was intended to improve the major drawbacks of such metal mechanical parts up to that time: high wear and low frictional resistance. .

Furthermore, since such cast iron has high hardness, heat treatment is usually performed after machining.

In addition to iron, the typical composition of cast iron is, for example, 2.4
%C, 1.5%Si, 0.5%Kite, 0.05%P and 0
．． 1% S (all percentages by weight).

The object of the present invention is to improve a spheroidal graphite cast iron having a mixed austenite-bainite structure and a method for producing the same without impairing the material's advantageous value for use.

The purpose is to use less than 0.3% manganese and 0.2% molybdenum.
~0.8%, copper 0.1-1.5%, silicon 2.0-3.
This is achieved by the present invention, which relates to spheroidal graphite cast iron consisting essentially of 0% carbon, 2.5 to 3.9% carbon, 3% or less nickel, and the remainder substantially iron.

This spheroidal graphite cast iron is suitable for forming an austenite-bainite structure, and when forming it, the casting material having the above composition is heated to 800 to 860°C, preferably 820 to 830°C.
heating to the austenitizing temperature of °C for 10 to 60 minutes;
Preferably hold the flatness for 10-25 minutes, then
Rapidly cool to 350-400°C, preferably about 375°C within minutes, and keep at this temperature for about 5-60 minutes, preferably 20-200°C.
Hold for 5 minutes.

After that, it is cooled down to room temperature. In the above composition of this spheroidal graphite cast iron, the manganese content is 0.01 to 0. 2
5%, molybdenum content 0.25-0.4%, copper content 0.4-0.6%, silicon content 2.2%.
~2.6%, carbon content 2.5-37% and even 30
~3.2 is preferable.

Next, the reasons for limiting the above composition will be explained.

The content of carbon and silicon is within the same range as that of generally known spheroidal graphite cast iron, and the reason for the limitation is also the same as that well known, so a complete explanation will be omitted.

Manganese content'to. Less than 3%, preferably 0.0
The reason for setting it at 1 to 0.25% is that if the content of manganese is too high, it will cause damage to the cast structure (at least when the wall thickness is small).
This is because carbide is generated.

In the present invention, heat treatment can be performed at a temperature approximately 100° C. lower than when carbide is generated and must be melted.

From this point of view, the lower the manganese content, the better in theory, but in reality it is impossible to completely remove all manganese, and it is okay to contain manganese to the extent that carbide is not produced. .

Further, manganese in the above-mentioned range f 3n has the effect of increasing the strength of cast iron.

The content of molybdenum is 0.2 to 0.8%, preferably 0.8%.
It is 25-0.4%.

Molybdenum inhibits the growth of paynite, especially when the wall thickness is 20
It is known that stabilization is promoted when the value is larger than rrrIn.

However, if the amount of molybdenum is too large, carbide is generated, so the upper limit of the amount of molybdenum has conventionally been set at 0.2%.

In the present invention, the amount of molyptene 'k0. It is now possible to increase the rate to more than 2%.

As a result, the desirable growth of a bainitic-austenitic structure is also possible in the case of small wall thicknesses, which was normally only possible with a 2-4% nickel content.

Molyptene has the unique effect of preventing the formation of pearlite.

This effect is much greater than that of nickel, so adding a small amount of molybdenum can largely save the normally required nickel, reducing costs despite the high cost of molybdenum.

The content of nickel is 3.0% or less.

Nickel prevents the formation of pearlite and has a stabilizing effect on austenite, especially when it is contained in a cast product after heat treatment at 30 to 40%.

Although the nickel content depends on the wall thickness, the above-mentioned effect reaches saturation at a factor of 3.0, and if it exceeds that, the cost will only increase.

The average nickel content is 1.0-1.5% for castings with wall thicknesses of about 100 mm or less.

Copper content is 0. 1-1.5%, preferably 04-0
．． It is 6%.

Copper has the effect of stabilizing the paynitic-austenite structure at high temperatures, but if the content is too small, this effect will not be sufficient, and if the content is too thick, undesirable phases will be formed between the structures.

Example 1 Cast iron having the following chemical composition was prepared according to a conventional method.

0 375% P 0.02%Si
Section 2.65 S (0.01%Mn
0.18% Mg 0.04% Ni
1.35% MoO. 35%C
uO. 80% This cast iron was heated at 820°C for 20 minutes, then rapidly cooled to 375°C within 2 minutes, held at this level for 20 minutes, fc, and then cooled to room width.

The physical properties of this cast iron were as follows.

Yield strength 61 6N/rnA ultimate strength
8 9 2 N/Fna elongation
148% Brinell hardness 2 6 9 KpAnjt'゛7th grade'' 80 ft lbs (chamber 1n
) Impact strength 48.5 ft lbs (-40°F/-40°C) Example 2 Cast iron having the following chemical composition was prepared in the same manner as in Example 1. Created.

C388% po. oio%Si
2.61% SO. 007 Section Mn 0
．． 22% Mg 0.042% Ni 1.
47%Mo 0.35%Cu
O. 76% CrO. 03% All of this cast iron was heat treated in the same manner as in Example 1 and then cooled.

This cast iron had the following physical properties. yield strength
6 4 0N/m method ultimate strength 9
8 3 NAnA elongation 13.9% Brinell hardness 298 Kp/2yj The advantage obtained by the present invention is that, compared to the state of the art, the consumption required for heat treatment is significantly lower.

Moreover, this can be achieved without impairing the good material properties of spheroidal graphite cast iron, which has an entirely austenite-bainite structure.

The micrograph shows a polished surface of the spheroidal graphite cast iron according to the present invention in which a paynitic-austenite structure with internally added spherolite was present.

t: (7) In photo J, the black round parts indicate graphite nodules, the dark needle-shaped parts indicate paynite, and the bright structural components indicate austenite.

The present invention described above can be summarized as follows.

Spheroidal graphite cast iron with austenite-bainite mixed structure produced by corresponding heat treatment and cooling,
Shows suitable material values for use.

In order to reduce the consumption required for its production, spheroidal graphite cast iron is added to a pond of normal amounts of carbon, silicon, phosphorus, sulfur, and magnesium at 0-0.3% (excluding 0% and 0.3%K). ) contains manganese.

Claims (1)

[Claims] 1 Spheroidal graphite cast iron having a mixed structure of austenite and paynite, less than 0.3% manganese, 0.2 to 0.8% molypten, 0.1 to 1.5% copper, 2 silicon
．． 0-3.0%, carbon 2.5-3.9%, nickel 3%
Spheroidal graphite cast iron characterized in that the following and the remainder essentially consist of iron. 2. Spheroidal graphite cast iron according to claim 1, wherein the manganese content is 0.01 to 0.25%. 3. Spheroidal graphite cast iron according to claim 1 or 2, characterized in that the content of molybdenum is 0.25 to 0.4%. 4. Spheroidal graphite cast iron according to any one of claims 1 to 3, characterized in that the copper content is 0.4 to 0.6%. 5. Spheroidal graphite cast iron according to any one of claims 1 to 4, characterized in that the silicon content is 2.2 to 2.6%. 6. Spheroidal graphite cast iron according to any one of claims 1 to 5, characterized in that the carbon content is 3.0 to 3.2%. γ Manganese less than 0.3%, molybdenum 0.2-0.8
All spheroidal graphite cast iron materials consisting of 0.1 to 1.5% copper, 2.0 to 3.0% silicon, 2.5 to 3.9% carbon, 3% or less nickel, and the balance substantially iron. It is heat-treated at 800-860°C for 10-60 minutes to austenitize, then rapidly cooled to 350-400°C within 2 minutes, and the degree of flatness is approximately 5
A method for producing spheroidal graphite cast iron characterized by holding for ~60 minutes. 8 Austenitization at 820-830℃ 10-25
8. The method for producing spheroidal graphite cast iron according to claim 7, characterized in that the process is carried out for 1 minute, then rapidly cooled to about 375°C, and further maintained at this temperature for 20 to 25 minutes. 9. The method for producing spheroidal graphite cast iron according to claim γ or 8, characterized in that the spheroidal graphite cast iron material contains 0.01 to 0.25% manganese. 10. The method for producing spheroidal graphite cast iron according to any one of claims 7 to 9, wherein the total molyptene content is 0525 to 0.4% in the spheroidal graphite cast iron material. . 11 Claims 7 to 1, characterized in that the spheroidal graphite cast iron material contains 0.4 to 0.6% copper.
The method for producing spheroidal graphite cast iron according to any one of item 0. 12 Claims 7 to 1, characterized in that the spheroidal graphite cast iron material has a total silicon content of 2.2 to 2.6%
The method for producing spheroidal graphite cast iron according to any one of Item 1. 13 Claims 7 to 12, characterized in that the spheroidal graphite cast iron material has a total carbon content of 3.0 to 3.2%.
A method for producing spheroidal graphite cast iron according to any one of item n or 1.