JPH03122250A - Iron-base alloy having high vibration-absorbing property and its production - Google Patents

Abstract

PURPOSE:To provide an iron-base alloy having superior vibration-absorbing property and excellent in toughness and machinability by specifying the shape of graphite in a cast iron consisting of a two-phase mixed structure of bainite and austenite. CONSTITUTION:This iron-base alloy contains bell-shaped (discoid, in three dimensions) and/or fibrous (thick tape-shaped, in three dimensions) graphite prepared by applying plastic working to spheroidal graphite or malleable cast iron and has a matrix structure consisting of the above two-phase mixed structure. In order to obtain this alloy, a stock for plastic working which is composed of a material consisting of matrix structure free from or containing primary cementite and spheroidal graphite or a material consisting of primary cementite and matrix structure is as cast state is cast. This stock is heated up to a temp. capable of plastic working, and heating which doubles as the decomposition of primary cemntite in the case of a stock containing primary cementite and decomposition are performed. This heated stock is subjected to temporary cooling, to reheating, and to rolling and/or forging or is directly subjected to rolling and/or forging without temporary cooling. The resulting plastic-worked stock is subjected to austempering treatment after temporary cooling or is directly subjected to austempering treatment without temporary cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an iron-based alloy that has high vibration absorption properties, is tough and has good machinability, and a method for manufacturing the same.

[Conventional technology]

Cast iron is widely used in industry as a structural member. For example, in automobiles, large amounts of flaky graphite cast iron are used for engine blocks, and spheroidal graphite cast iron is used for drive parts and suspension parts.

The functions required of materials for these application fields include vibration absorption performance for higher-grade products, toughness for safety and weight reduction, and machinability for improved productivity.

Among these, the vibration absorption performance of cast iron is determined by the graphite structure area ratio (
In terms of three dimensions, the influence of volume ratio) and its form are significant.

In other words, the larger the area ratio of graphite, the better the vibration absorption performance.
Regarding the shape of graphite, flaky is the most preferable, followed by vermicular, lumpy, and spherical.

In recent years, a technology has been developed that improves the toughness of spheroidal graphite cast iron by austempering cast iron to make the matrix structure a two-phase mixed structure of bainite and austenite.
It is known as a5t Iron (abbreviated as ADI).

Cast iron having this two-phase mixed structure of bainite and austenite has already been reported in Japanese Patent Application No. 54-60888 and in Japanese Patent Publication No. 1987-1988 as having better vibration absorption performance than pearlite and/or ferrite base cast iron with the same graphite form.
It is disclosed as Publication No. 1-60140.

[Problem to be solved by the invention]

However, all of the above-disclosed graphite materials have flaky or semi-spherical graphite shapes, and cannot be used as drive parts or suspension parts because of poor strength, especially fatigue strength.

Although ADI has significantly superior toughness and vibration absorption performance compared to spheroidal graphite cast iron, which has the same graphite form, ADI is significantly inferior in machinability, so it has to be machined into the shape of the part in advance and then subjected to austempering treatment. There are problems with accuracy and product cost.

The present invention has extremely excellent vibration absorption performance, and also has strong toughness and
The purpose of the present invention is to provide an iron-based alloy with excellent machinability and a method for producing the same.

[Means to solve the problem]

As a result of various studies on iron-based alloys with excellent vibration absorption performance, toughness, and machinability in which graphite exists in the structure, and methods for manufacturing the same, the present inventors discovered that the structure has a spindle shape (three-dimensionally circular). Iron-based alloys that have graphite in the form of plates (plate-like) and/or fibers (three-dimensionally thick tape) and whose base structure is bainite or a two-phase mixed structure of bainite and austenite meet these requirements. We found that the material satisfies the above requirements, and established a series of manufacturing methods from casting materials to plastic working and final heat treatment.

That is, the first invention of the present application has bell-shaped and/or fibrous graphite obtained by plastically working spheroidal graphite cast iron or malleable cast iron, and the matrix structure is a two-phase mixed structure of bainite and austenite. It is characterized by consisting of.

Next, the second invention of the present application is as follows: (a) In the cast state, a material consisting of a matrix structure that does not contain primary cementite and spheroidal graphite, or a material that contains primary cementite and consists of a matrix structure and spheroidal graphite, or a material that contains primary cementite and consists of a matrix structure and spheroidal graphite; a casting process for producing a material for plastic working consisting of a matrix structure, (b) heating the casting material to a temperature at which plastic working is possible;
For materials containing primary cementite, a heating and decomposition step that also decomposes the primary cementite; (c) The heating material is once cooled and reheated to be rolled and/or forged, or immediately rolled and/or forged without being cooled. or a plastic working process of forging; (d) an austempering process in which the material is cooled once and then reheated to perform austempering treatment, or an austempering process is performed immediately without cooling; This is a method for producing a highly vibration-absorbing iron-based alloy that is strong and has excellent machinability, and is characterized by comprising the steps from ) to (d).

The structural characteristics of the iron-based alloy of the present invention include bell-shaped and/or fibrous graphite obtained by m-type processing, and the base structure is a two-phase mixed structure of paynite or austenite. It is configured.

It has long been known that cast iron can be plastically worked (e.g. IE, Piwowarsky U.
ndA, Wittmoser: Gevarztes/
Gusseisen, Verlag W.

Girardet, 1949), and it is also known that this plastically worked cast iron has excellent vibration absorption properties (for example, for valves, Nippon Tanaka, Bulletin of the Japan Institute of Metals, 16, 1).
977.71). As a result of examining the relationship between the shape of graphite in cast iron subjected to plastic working and vibration absorption performance, the inventor found that effective vibration absorption performance improved when the average value of the long sleeve/short axis of graphite deformed by plastic working was 4 or more. I gained some knowledge. The results are shown in FIG. Furthermore, when the average values of the long sleeve/short axis of graphite were at the same level, the results showed that the greater the number of graphite particles, the better the suction performance.

The results are shown in FIG.

In the case of cast iron subjected to plastic working, it is preferable to set the Si content low for the purpose of reducing deformation resistance and reducing defects such as edge cracks. In the case of low-St cast iron, the number of crystallized graphite particles is small, usually less than 150 particles/mm'', and there are cases where the expected vibration absorption performance is not satisfied.Also, the Si content affects machinability. A low concentration of graphite grains has an advantageous effect, but a low graphite particle concentration has a disadvantageous effect.
Alternatively, by using a quenching mold to create a structure of spotted iron or white cast iron containing spheroidal and/or lumpy graphite, this is graphitized in the next thermal decomposition process, usually 250 pieces/
It is possible to obtain graphite with a particle size of 100 mm or more.The faster the primary cementite is cooled, the faster the decomposition rate and the more graphite grains are produced. It is preferable to use financial aid, etc.

Primary cementite crystallized during the casting process is heated at a heating temperature of 85
It starts to decompose around 0°C, and from 950°C to 10°00°C.
It rapidly decomposes into graphite and austenite in the heating temperature range of . At this time, the shape of graphite that has been treated with a spheroidizing element such as Mg in the previous process of melting and casting becomes more spherical, and the shape of graphite that is not subjected to this treatment is a block-like shape similar to that seen in malleable cast iron. However, plastic working is of course possible for both.

The suitable plastic working temperature for the alloy of the present invention is in the range of 900-1000°C. Therefore, starting the plastic working process immediately from the previous process is advantageous in terms of energy costs. However, depending on the shape of the part, it may be overall advantageous to cool the part once, machine it into a shape that is easy to plastically process, and then reheat and enter the plastic forming process.

The austempering quenching temperature of the alloy of the present invention is 850
A range of 900°C is suitable. Therefore, energy consumption can be reduced by quenching to the austempering temperature immediately after the plastic working step. Note that in the case of parts with complex shapes, temperature unevenness may occur locally during plastic working.

In that case, it is sufficient to quench the material after once eliminating temperature unevenness in a soaking furnace, and the energy consumption can be reduced. Also,
It may be reheated and austempered.

It is already known that the austempering temperature greatly affects the mechanical properties of ADI and the amount of retained austenite (γ11).

In the alloy of the present invention, the influence of the austempering temperature on the matrix structure is exactly the same as that of ADI, and therefore the tendency of mechanical properties is also similar to that of ADI.

Therefore, it is necessary to perform austempering treatment according to the required functions of the applied parts. That is, 35
Austempering temperatures of 0-400°C are applied. Note that the material treated at an austempering temperature of 350 to 400° C. has a large amount of TII in the bainite structure and has high vibration absorption performance, but the machinability is slightly reduced. When the austempering temperature is set to 400 to 450°C, the γR amount is significantly reduced, and the machinability is further improved. As the austempering temperature becomes lower than 350°C, the base structure becomes dominated by lower bainite, the hardness increases and the toughness decreases, so this is particularly applicable when wear resistance is required. If extreme wear resistance is required, it is possible to meet this requirement by cooling the base to 190° C. or lower and making the base martensite. The time required for the above austempering treatment is 1 to 2 hours.

[Effect]

Because the deformed graphite in the structure of the plastically processed material is aligned in the same direction, it has mechanical properties that are more than 3 times as high in tensile strength and 5 times as high in elongation compared to flaky graphite cast iron materials that have the same vibration absorption performance. It has the characteristics of a strong material.

It has already been mentioned that the machinability of ADI is significantly inferior, but since the graphite of the present invention is bell-shaped and/or fibrous, chips are separated very easily during machining, and the casting properties seen in ADI are also excellent. The pool of residual austenite caused by the segregation of alloying elements during casting is difficult to generate when the casting material is cast iron or white cast iron, and the segregation is dispersed by plastic working, so the present invention Since it does not form in alloys, it has machinability equal to or better than ordinary spheroidal graphite cast iron, and does not reduce machining productivity.

〔Example〕

(Example 1) The casting material was made from pig iron and steel scraps, the chemical components were adjusted by preparation, and the material was melted in a high frequency electric furnace. Melting temperature is 148
It is 0°C. The graphite was spheroidized by a sandwich method in a ladle, and Fe-3i-Mg (5) was used as the spheroidizing agent, and 0.045% of Mg was added. Inoculation is Fe-
8i (75) was used and 0.15% was added locally at 5iffi.

The molten metal was poured into three types of molds at 1380°C.

The chemical composition of the obtained casting material is shown in Table 1, and the type of mold and the structure of the casting material are shown in Table 2.

The heating temperature before plastic working, which also serves as decomposition of primary cementite, was 980°C for each sample group. After the temperature of the center of the sample is raised to 980°C, for samples with primary cementite, it is necessary to hold the sample for a period of time for this to completely decompose, but for the samples of Group B shown in Table 2, the holding time is 4 hours. For Group C samples, 2 hours was sufficient. Samples in group A without primary cementite were subjected to plastic working immediately after heating.

Plastic working was performed by forging or rolling.

Forging was performed at two levels of reduction ratios of 50% and 75% in Group A, Group B, and Group C, and rolling was performed at a reduction ratio of 75% in Group A and Group C.

After plastic working, each sample was placed in a salt bath at 375°C and subjected to austempering treatment. Input temperature is 890℃ to 91℃
It is between 0°C. The retention time in the salt bath was 2 for each sample.
It took time and thought. After austempering, each sample was cooled in water and used as a material for measuring each characteristic.

Specimens for vibration absorption performance, tensile properties, amount of retained austenite, and structure observation were cut from the material and used for measurements.

Cutting performance was evaluated using a high-speed steel drill with a diameter of 10 mm, cutting speed of 14 m/min, and feed rate of 0.3 mm/rev.
This was done by measuring the torque generated during machining. The inventor has already conducted a test under the same conditions and found that the torque of FCD60 equivalent material is 60 kgf-cm, whereas A which was austempered at 375°C
The torque of DI material is as large as 100 kgf-cm, and the life of the drill is shortened to about 1/4.

The above series of results are shown in Table 3.

From Table 3, the logarithmic damping ratios of the present invention shown by Al-A3, B1, B2, C1 to C3 are equal to or higher than the logarithmic damping ratio of flake graphite cast iron (FCIO), and have excellent vibration absorption performance. I know what you're doing.

In addition, the tensile strength is 9 (3 to 108 kgf/mm" elongation is 6.5 to 9.0%), making it an excellent strong member. And the torque during drilling is 45%.
~59kgf-cm, which is the same or lower than normal spheroidal graphite cast iron, and the small torque of 00kgf-cm when machining the ADI material mentioned above.
It is extremely small compared to cm, making it possible to increase machining efficiency and extend the tool life of the drill.

(Example 2) The casting material was made from pig iron and steel scraps, the chemical components were adjusted using a preparation, and the material was melted in a high-frequency electric furnace. Melting temperature is 147
It is 0°C. The graphite was spheroidized by a sandwich method in a ladle, and Fe-8i-Mg (5) was used as the spheroidizing agent, and 0.050% of Mg was added. Inoculation is Fe
5i (75) was used, and 0.20% Si was added locally.

The molten metal was poured into two types of molds at 1370°C.

The chemical composition of the obtained casting material is shown in Table 4, and the type of mold and the structure of the casting material are shown in Table 5.

The heating temperature before plastic working was 980℃ for each sample group.
And so. For the samples of group D, plastic working was performed immediately after the center part was heated to 980°C. In group E, in order to also decompose the primary cementite, plastic working was performed after holding for 2 hours.

Plastic working was performed by forging or rolling.

For forging, the reduction rate is 40% for both Group D and Group E.
The rolling was carried out at two levels: and 70%, and rolling was carried out at a rolling reduction rate of 75% for both Group D and Group E.

After plastic working, each sample was placed in a salt bath at 375°C and subjected to austempering treatment. Input temperature is 890℃ to 91℃
It is between 0°C. The retention time in the salt bath was 2 hours for each sample. After austempering, each sample was cooled in water and used as a material for measuring each characteristic.

The measurement items and the offshore determination method were the same as in Example 1.

A series of these results are shown in Table 6.

From Table 6, the logarithmic damping rate of the present invention shown by DI-B3 and El-B3 is equal to or higher than that of flake graphite cast iron (FCIO), and has excellent vibration absorption performance. I understand. In addition, the tensile strength is 97-106 kg
17mm” and elongation of 6.9 to 11.0%, making it an excellent strong material.The torque during drilling is 42 to 60 kgf-cm, which is equal to or lower than ordinary spheroidal graphite cast iron. This torque is extremely small compared to the 00 kgf-cm torque for machining ADI materials mentioned above, and it is possible to increase machining efficiency and extend the tool life of the drill.

(Example 3) The casting material was made from pig iron and steel scraps, the chemical components were adjusted by preparation, and the material was melted in a high frequency electric furnace. B in the ladle when pouring hot water
0.01% of i was added. The molten metal is 20mm wide and 25mm long.
It was cast into a 0 mm green sand mold at 1420°C. The structure of the obtained casting material is white cast iron, and the chemical composition is as shown in Table 7.

The heating temperature was 980° C. and the holding time was 6 hours for heating before plastic working, which also serves as decomposition of primary cementite.

Plastic working was performed by forging or rolling. The rolling reduction ratio was 70% in both cases.

After plastic working, each sample was placed in a salt bath at 375°C and subjected to austempering treatment. The charging temperature is 890°C to 9
It is between 10°C. The retention time in the salt bath was 2 for each sample.
The time was set as °. After austempering, each sample was cooled in water and used as a material for measuring each characteristic.

The measurement items and measurement method are the same as in Examples 1 and 2. A series of these results are shown in Table 8.

From Table 8, the logarithmic attenuation rate of the present invention indicated by Fl and F2 is:
It can be seen that the logarithmic damping rate is equal to or higher than that of flake graphite cast iron (FCIO), and has excellent vibration absorption performance. Also, tensile strength 101~1'03 kg 17mm
”, has an elongation of 7.5 to 7.7%, which makes it an excellent strong material.The torque during drilling is 46 to 48 kgf-cm, which is equal to or lower than ordinary spheroidal graphite cast iron. The torque is extremely small compared to the aforementioned ADI material machining torque OO kgr-cm, which increases machining efficiency and extends the tool life of the drill.

〔Effect of the invention〕

As detailed above, the alloy of the present invention has excellent vibration absorption performance because the graphite morphology is bell-shaped and/or fibrous, and the deformed graphite in the structure has the same stretching direction, so it has excellent vibration absorption performance. Compared to flaky graphite cast iron, it has extremely superior properties as a strong member in terms of tensile strength, and it also has excellent machinability that is equivalent to or better than normal spheroidal graphite cast iron, as chips are separated very easily during machining. It has high processing productivity and is an extremely useful alloy in industry.

The logarithmic attenuation rate is plotted on the axis, and the graphite shape is plotted on the horizontal axis (indicated by the average value of the ratio of the long axis/short axis of the spindle shape and/or fibrous graphite observed under a microscope). Note that the diagonal line in the figure indicates the logarithmic attenuation rate of flake graphite cast iron (FCIO).

FIG. 2 shows the vibration absorption performance of the iron-based alloy of the present invention, with the vertical axis representing the logarithmic damping rate and the horizontal axis representing the number of graphites per unit area observed under a microscope. Note that the graphite shape has a long axis/short axis ratio of about 8.

[Brief explanation of drawings]

Claims (2)

[Claims] (1) Spheroidal graphite cast iron or malleable cast iron has bell-shaped and/or fibrous graphite formed by plastic working, and the matrix structure is composed of a two-phase mixed structure of bainite and austenite. A highly vibration-absorbing iron-based alloy that is strong and has excellent machinability. (2) (a) In the cast state, a material consisting of a matrix structure and spheroidal graphite that does not contain primary cementite, a material that contains primary cementite and a matrix structure and spheroidal graphite, or a material that consists of primary cementite and a matrix structure. a casting process for producing a plastically processed material; (b) a heating and decomposition process in which the casting material is heated to a temperature that allows plastic processing, and in the case of a material containing primary cementite, the primary cementite is also decomposed; (c) the heated material A plastic working step in which the material is once cooled and then reheated and then rolled and/or forged, or immediately rolled and/or forged without being cooled, (d) the plastic worked material is once cooled and reheated to undergo austempering treatment. or an austempering process in which the austempering process is performed immediately without cooling. Method for manufacturing base alloys.