JPS5943816A - Manufacture of spheroidal graphite cast iron parts - Google Patents

Abstract

PURPOSE:To provide high fatigue strength and high wear resistance by forming granular pearlite in spheroidal graphite cast iron contg. specified amounts of C, Si, Mn, P, S, Cu, Sn, Mo and Mg while specifying the granular pearlite formation rate and the carbon content of the matrix, and carrying out working and quenching for surface hardening. CONSTITUTION:The composition of spheroidal graphite cast iron is composed of, by weight, 2.6-4% C, 1.5-3.5% Si, 0.1-1% Mn, <0.15% P, <0.03% S, 0.3- 1.5% Cu or 0.03-1.6% Sn, 0.03-0.1% Mo, 0.025-0.1% Mg and the balance Fe. Granular pealite is formed in the cast iron so as to regulate the granular pearlite formation rate to 35-65% and the carbon content of the matrix to 0.3- 0.65%, and working and quenching for surface hardening are carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing spheroidal graphite cast iron that is excellent in both hardenability and workability.

In the past, many heat treatment methods for spheroidal graphite cast iron parts have been proposed, and Japanese Patent Application Laid-Open No. 56-116853 describes a method for heat treatment of spheroidal graphite cast iron parts.
There is also a special method in which spheroidal graphite cast iron containing 3 to 0.09% by weight of o, o and 3 to 1.5% by weight of CuQ is annealed to make the structure ferrite, and then austempered and shot peened. JP-A-57-19320 discloses a method in which spheroidal graphite cast iron is normalized to pearlite, and then austempered.

By the way, as shown in Fig. 1, spheroidal graphite cast iron A with a ferrite base structure has the problem of poor hardenability because it takes a long time to reach a predetermined hardness during heat treatment, that is, it takes a long time to change to austenite. There is. On the other hand, pearlitized spheroidal graphite cast iron B has a short austenitization time and good hardenability, and even with rapid heating using high frequency etc., a sufficient carbon concentration can be obtained, the hardness depth can be arbitrarily selected, and the surface layer It has the advantage of being able to provide compressive stress that is beneficial for fatigue strength.

However, as shown in Fig. 2, from the viewpoint of workability, the cutting tool wear of spheroidal graphite cast iron B with pearlite base is significantly higher than that of spheroidal graphite cast iron A with ferrite base. There is a problem of being significantly inferior in terms of gender.

The present invention has been made in view of such problems, and includes:
The object of the present invention is to provide a method for manufacturing spheroidal graphite cast iron parts that are excellent in both hardenability and workability, and therefore have high fatigue strength and high wear resistance.

Therefore, in the present invention, C2,6 to 4.0% by weight
, Si 1.5-3.5w M%, MnQ, 1-1.0
Heavy bottle% 1Po, 15% by weight or less, 50.03% by weight or less, Cu O, 3 to 1.5 weight-i < or Sn O, 03 to
1.6% by weight, MOo, 03-0.1% by weight, Mg0.
Spheroidal graphite cast iron consisting of 0.025 to 0.01% by weight and the balance of Fe is processed after being made into granular pearlite with a granular pearlite conversion rate of 35 to 65% and a base carbon content of 0.3 to 0.65%, The basic feature is that the surface is then six-fermented and hardened.

In this case, the reason for limiting the chemical composition of the spheroidal graphite cast iron is as follows.

C: At 2.6% or less, casting defects, especially cavities and chills, occur due to the saturation degree with Si.

If it is 4.0% or more, the saturation level with Si will cause a nest, 70
-Causes defects such as tission (.

Si: 1. If it is less than 5%, castability (rollability) is inhibited due to the saturation degree with C.

If it exceeds 3.5%, the fluidity will improve due to the saturation level with C, but this will lead to stagnation and flotation.

Mn: Mn is necessarily 0 as the amount that enters the solution from any family.
．． At 1% or more, Mn is an element that strongly causes pearlitization and at the same time at 1.0% or more, it inhibits j, l, and +J properties.

If the content is 11': o, is% or more, a large amount of steadite is formed, which impairs toughness.

If S: 0.03% or more, a large amount of Mg is required, resulting in the generation of many inclusions such as oxides.

Cu: If Q is 3 or less, pearlite decomposes during annealing and granular pearlite uniformly distributed throughout the base cannot be obtained. In addition, the fatigue strength and surface pressure resistance properties that are the effects of combined use with MO cannot be obtained.

At 1.5% or more, the above-mentioned effect of the Cu element is saturated,
This will increase costs.

Sn: Sn is used as a substitute element for Cu and is a strong pearlitizing element.

If it is less than 0.03%, granular pearlite uniformly distributed in the matrix cannot be obtained.

If it exceeds 1.6%, it will precipitate at grain boundaries, resulting in a decrease in strength properties. Moreover, the effect becomes saturated and the cost increases.

If Mo: 0.03% or less, the effects (fatigue strength characteristics, surface strength, wear resistance) cannot be obtained by using Cu in combination, and
Hardenability also deteriorates, and a uniform structure cannot be obtained.

If it exceeds 0.1%, double carbides are formed, which improves wear resistance, but increases the fatigue strength properties most necessary for gears, etc. [11
decreases to

Mg: Mg is an essential element for desulfurizing and deoxidizing the molten metal and making the graphite spheroidal.

If it is less than 0.025%, this effect will be insufficient and spheroidization will not occur, making it difficult to obtain tough spheroidal graphite cast iron.

At 0.10% or more, spheroidization is sufficiently achieved.

However, sulfides and oxides (Mg
cavities) remain in the molten metal and cause a decrease in toughness.

In the present invention, the structure of the spheroidal graphite cast iron material having the above-mentioned chemical composition is adjusted by a granular pearlite treatment, so that the granular pearlite conversion rate ranges from 35 to 65 and the base carbon content is from 0.3 to 0.65%. It becomes granular pearlite.

This granular pearlite treatment has good hardenability and workability (
This is done in order to simultaneously impart both machinability and machinability. Specifically, it is heated at a temperature of 850 to 1000°C for 0.5 hours or more, then air cooled, and then heated to a temperature of 670 to 760°C for 0.5 It can be carried out by a two-step heat treatment of heating for ~8.0 hours and then cooling with air or water (slow cooling is possible).

The first heat treatment described above is to simultaneously decompose the chill and turn it into granular pearlite.In order to uniformly distribute the granular pearlite, air cooling is necessary, and gradual cooling (furnace cooling) cannot achieve uniform distribution. . Furthermore, if the temperature is below 850°C, the chill cannot be decomposed, and if it is above 1000°C, the crystal grains will become coarse, which is not preferable. In order to effectively decompose the chill, it is necessary to continue heating for 0.5 hours or more. If cooling after heating is performed by slow cooling, impurities will crystallize at grain boundaries during austenitization treatment, causing embrittlement.

The second stage heat treatment reduces the granular pearlite conversion rate to 35-65%.
This is done to control the situation. Granular perlite 35
% or less, the workability is good, but it is not preferable because it takes a long time to achieve the carbon concentration necessary to obtain sufficient hardenability. On the other hand, when it is 65% or more, the opposite tendency occurs, that is, the hardenability improves, but the workability tends to deteriorate.

As for the temperature condition, if the temperature is 670° C. or lower, it becomes difficult to form granular pearlite, and it takes a long time to obtain the necessary granulation, which is not preferable. Further, at temperatures above 760° C., graphitization progresses rapidly and 35% or more of granular pearlite is not suspended. Processing time is required to be at least 0.5 hours, and if it is longer than 8 hours, productivity will deteriorate and costs will increase. The cooling method is preferably air cooling or water cooling for the purpose of shortening operating time and uniformly distributing granular pearlite in the base.

After the above-mentioned granular pearlite treatment, the treated spheroidal graphite cast iron parts are subjected to necessary pre-shaping. For example, in the case of gears, machining (shaving machining) is performed until a lapping allowance and a grinding allowance remain.

After the above-mentioned processing, surface hardening quenching (local quenching) is performed. This surface hardening and quenching process is performed by locally heating at a temperature of 850 to 1000°C for 3 seconds or more using a frequency etc., then quenching with oil, salt, etc., cooling to a specified temperature, and then heating in an electric furnace. 60 minutes in an electric furnace.
This is done by maintaining a predetermined temperature for a period of seconds or more and then cooling by air or water cooling.

This hardening is intended to generate compressive residual stress at least on the surface and inside of the part to improve wear resistance.
The surface layer is made of bainite or martensite, and the inside is made of granular pearlite by primary heat treatment (granular pearlite treatment).

The predetermined temperature to be maintained in the electric furnace is selected depending on the target load on the parts. For high load gears and shafts, the temperature range is 220 to 390°C, and the surface layer is made of bainitic material, while for low load gears and shafts, the temperature range is 130 to 220°C, which is marten. The site gon' be.

As mentioned above, if the base structure of the spheroidal graphite cast iron parts is granular pearlite, as shown by C in Figure 1, the austenitization time will be close to that of pearlite B, so it will be easy to use. At the same time, as shown by C in FIG. 2, it is possible to obtain almost the same good workability as ferrite material A.

After the primary and secondary heat treatment according to the present invention, stress concentration areas, such as tooth bottoms in gears and corner areas in shafts, are subjected to shot peening or roll processing to create high lf shrinkage residual stress. The fatigue strength characteristics may be further improved.

Next, examples of the present invention will be shown.

〔Example〕

CSi Mn P S Cu Mo M
g wood stock 3B92.760.250.02 0.011
0.760.080.043 Comparison material 3.682.770
．． 400.0180.013 - - 0.036 920 was produced by casting a spheroidal graphite cast iron material having the above chemical composition in a high-frequency atmospheric melting furnace, and then subjected to chill decomposition in an electric furnace for the purpose of ensuring machinability and hardenability. ℃X 2.
After heating with OHr, furnace cooling was avoided and air cooling was used to prevent impurities from precipitating at grain boundaries.

After air cooling, the mixture was heated from 720±10°C to 750°C in an electric furnace prepared in advance to reduce the post-treatment time. After the workpiece reached room temperature, surface scale was removed by blasting and finishing was performed. Next, high-frequency heating was performed at 890°C for about 15 seconds to heat the prepared 26
Approximately 2. It was immersed in oHr to form bainite. After the treatment was completed, it was washed with warm water at about 80°C.

1. The microstructures of the test piece according to the present invention after finishing processing and after bainiticization are shown in FIGS. 3 and 4, respectively.

The method of the present invention is advantageously applied to the manufacture of differential gear cases 3.4 for FF and FR in which ring gears 1 and 2 are integrally formed, respectively, as shown in Fig. 5"6 and 6, respectively. be able to.

In this case, the 7 rungs 5.6 that form the ring gears 1 and 2 are formed integrally with the gear case 3.4, and the outer 1 part of the 7 rungs where the gears are machined is shaved and then localized. What is necessary is to give it a hardened finish. In this case, it is preferable that the local hardening be an austempering process, and for the ring gear 1°2 that receives a high load, a shot peening process is performed after the hardening to further improve the fatigue strength.

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram showing the difference in hardenability due to the difference in the matrix structure of spheroidal graphite cast iron, and Fig. 2 is a characteristic diagram showing the difference in workability due to the difference in the matrix structure of spheroidal graphite cast iron. The structure of the test piece after the secondary heat treatment and the austempering treatment is shown in the micrographs substituted for drawings at a magnification of (×400), No. 5.
6 and 6 are sectional views of an allencial gear case for a vehicle, in which a ring gear is integrally formed, showing an example of application of the method of the present invention. Patent applicant: Toyo Kogyo Co., Ltd. Agent
Person: Patent attorney Seihaku, 2 people, Fig. 1, Fig. 20, number of cases, (Higashi, Police 3, Fig. 5, Fig. 6, Procedural amendments October 12, 1980, Commissioner of the Patent Office, Tono 1, Indication of the case, 1982) Patent Application No. 155647 2,
Title of the invention: Process for manufacturing spheroidal graphite cast iron parts 3 Relationship with the case of the person making the amendment Patent applicant 4, agent 5 arrested 2 orders #2 2 (voluntary) 7. Contents of the amendment In the Showa 1 book, the following: I will correct the part. A1 Detailed Description of the Invention Column (1) Page 3, line 10, page 5, line 6, r1.6J is corrected to ro, 16J. (2) On page 11, line 6, the words "differential gear case" will be corrected to "differential gear case." As per column 111 of the previous claim. Claims r(1) C2, 6-40% by weight, Sil, 5-3.
5% by weight, Mn 0.1 to 1.0% by weight, Po, 15% by weight or less, 50.03% by weight or less, CuQ, 3 to 1.5% by weight, or Sn o, 3 to 0.16% by weight, Mo O
Spheroidal graphite cast iron consisting of 0.03 to 0.1% by weight, 0.025 to 0.1% by weight of Mg, and the balance of Fe has a granular pearlite ratio of 35 to 65% and a base carbon content of 03 to 0.65. A method for manufacturing spheroidal graphite cast iron parts, which is characterized in that the parts are made into granular pearlite, processed, and then surface hardened and quenched. ” Procedural amendment (spontaneous) October 18, 1980 Patent Office Palace 1, case indication 1981 Patent Application No. 1556472,
Title of the invention: Method for manufacturing spheroidal graphite cast iron parts 3. Relationship with the case of the person making the amendment. Patent applicant 4: Scope of claims in the attorney's specification. 7. Details of the amendments are as shown in the attached sheet. Claims r (11C2, 6-40% by weight, Sil, 5-3.5% by weight, MnQ, 1-1.0% by weight, PO, 15i% by weight
[F, 30.03% or less, Cu 03-15% by weight
or Sn o, o 3-0.16% by weight, Mo o, o
3-0.1% by weight, Mg 0.025-0.1% by weight
, Spheroidal graphite cast iron consisting of Fe remainder is transformed into granular pearlite with a granular pearlite conversion rate of 35 to 65% and a base carbon content of 0.3 to 0.65, processed, and then surface hardened and quenched. A method for manufacturing spheroidal graphite cast iron parts characterized by: ”

Claims (1)

[Claims] is lc2.6-4.0 small amount%, Sil, 5-3.5 market weight%, Mn 0.1-1.0 weight 1%, P 0.15
Weight <12 or less, 5O903 weight 1i% or less, Cu 0
．． 3-1.5 YJ amount 'Io or SnO, 03-1.
6! i%, Mo o, o 3-0. I Llt[, Mg
After spheroidal graphite cast iron consisting of 0.025~O, L weight@% and the balance of Fe is made into granular pearlite so that the granular pearlite conversion rate is 35~65% and the base carbon content is 0.3~0.65%. A method for producing spheroidal graphite cast iron parts, characterized in that the parts are processed and then surface hardened and quenched.