JP2636008B2 - High strength and high wear resistant ductile cast iron material and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ductile cast iron material having excellent strength and abrasion resistance used for sprockets, gears, cams, guides, and the like, and a preferable production method thereof.

(Conventional technology and problems) Conventionally, when ductile cast iron is used for members that require wear resistance and strength, high-strength ductile cast iron such as FCD60 is subjected to bright quenching or induction hardening to improve wear resistance. The one given was used.

However, since the strength is not sufficient, the thickness of the member is increased to reduce the stress acting on the member. For this reason, the weight is increased, which hinders the weight reduction.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a ductile cast iron material having both wear resistance and high strength, and a suitable method for producing the same.

(Means for Solving the Problems) The ductile cast iron material of the present invention made in order to achieve the above object has a chemical composition of C: 3.0 to 3.8% by weight, Ni: 0.2 to 0.4% Si: 2.4 to 3.0% by weight. %, Cu: 0.4 to 0.6% Mn: 0.2 to 0.4%, Nb: 0.05 to 0.10% P: 0.04% or less, Mg: 0.03 to 0.06% The balance consists essentially of Fe, and the base structure consists of bainite and retained austenite This is the configuration of the invention.

Further, the preferred production method is that, after heating the ductile cast iron of the chemical composition to an austenitizing temperature, 225 to 2
An object of the present invention is to quench in a salt bath kept at 75 ° C. to make the base structure a mixed structure of a bainite structure and a retained austenite structure.

(Example) First, the reasons for limiting the components of the ductile cast iron material of the present invention will be described. The unit is% by weight.

C: 3.0-3.8% Si: 2.4-3.0% C and Si are the same as the components of ordinary ductile cast iron, taking into account the prevention of chill, prevention of dross generation, securing of molten metal flowability, and prevention of embrittlement of materials. It is regulated in the above range.

Mn: 0.2 to 0.4% Mn is added for improving hardenability. If it is less than 0.2%, the effect is too small, and it is difficult to form a benite structure up to the center of the casting by austempering heat treatment described below.

On the other hand, if it exceeds 0.4%, segregation is apt to occur at the grain boundaries, and a large amount of retained austenite is generated, resulting in a decrease in proof stress.

P: 0.04% or less Since P causes material embrittlement, it is desirable that P is as small as possible.
Keep it below 04%. The content of S is preferably as small as possible in order to suppress the formation of spheroidal graphite, and is preferably kept to 0.02% or less.

Ni: 0.2 to 0.4% Cu: 0.4 to 0.6% Both Ni and Cu contribute to the improvement of hardenability, but Ni is expensive, so the economics of using Ni alone are inferior. Is partially bainite and hardened. Since the cast iron material of the present invention has high hardness, it is roughly worked before casting and before heat treatment. However, if bainite is present in the structure at this time, working becomes difficult. Therefore, Ni and Cu are added in combination. If the content of Ni is less than 0.2% and Cu is less than 0.4%, the effect of improving hardenability is too small. On the other hand, if the content of Ni exceeds 0.4% and Cu is more than 0.6%, the hardenability becomes excessive, leading to deterioration of strength and casting. The hardness at the time of release becomes too large, and processing becomes difficult.

Nb: 0.05 to 0.10% Nb combines with C to generate fine carbides, contributes to an increase in hardness after heat treatment, and contributes to an improvement in wear resistance. 0.
If it is less than 05%, there is almost no such effect, while if it exceeds 0.10%, the amount of carbide becomes excessive and it becomes brittle.

Mg: 0.03-0.06% Mg is added to spheroidize graphite. The amount added is in the usual range.

The ductile cast iron material of the present invention is substantially formed of Fe in addition to the above alloy components.

The ductile cast iron material of the present invention can be obtained by casting a ductile cast iron melt of the above-described components and subjecting the obtained casting to the following austempering heat treatment.

First, the casting in the as-cast state is subjected to roughing as necessary, and then heated to 880 to 950 ° C., and 0.5 to 1 per 25.4 mm of the wall thickness.
Austenite is maintained by holding the time. If the temperature is lower than 880 ° C., austenite is not completely formed, and ferrite and pearlite remain in the structure, resulting in insufficient strength. Meanwhile, 950 ° C
If it exceeds, the crystal grains become coarse and the strength is reduced. If the holding time is less than 0.5 hour, the central part of the casting may not be austenitized, while if it exceeds 1 hour, the crystal grains become extremely coarse.

The austenitized casting is then put into a salt bath maintained at 225 to 275 ° C. and quenched, and the quenching is performed at a rate of 0.
Hold for 5 to 2 hours. As a result, the base structure is mainly composed of lower bainite, and the strength of 140 kgf / mm ² or more is secured and the wear resistance is improved. If the salt bath temperature is lower than 225 ° C., martensitic transformation occurs, making it difficult to secure elongation of 2.5% or more, resulting in insufficient toughness. On the other hand, it tends to occur exceeds the low hardness of the upper bainite to 275 ° C., the H _B 400 or more hardness and thus wear resistance of the difficult to secure. Also,
If the holding time is less than 0.5 hour, the formation of bainite is insufficient and it is difficult to secure a strength of 140 kgf / mm ² or more.

 Next, a specific embodiment will be described.

Production Example of a Drive Sprocket with a Single Weight of 2.5 kg (1) Ductile cast iron having the chemical composition shown in Table 1 below was melted and poured into a mold at 1380 ° C. to obtain a sprocket material casting.

(2) After roughly casting the sprocket material casting, it was subjected to the following heat treatment and air-cooled.

・ Example 1 Austenitization: 900 ° C. × 1Hr Bainite: 250 ° C. × 1Hr ・ Example 2 Austenitization: 900 ° C. × 1Hr Bainite: 275 ° C. × 1Hr (3) Mechanical properties and bainite of the obtained product casting The results of the determination are shown in Table 2.

From Table 2, it was confirmed that the ductile cast iron material according to the example had excellent strength and hardness.

(Effects of the Invention) As described above, according to the present invention, by using ductile cast iron having a specific composition and performing a predetermined heat treatment,
In the base structure consisting of bainite and retained austenite
Nb carbide was produced, and the ductile cast iron material was able to have both high strength and high wear resistance. As a result, it is possible to reduce the thickness and weight of the ductile iron casting requiring both properties.

Claims (2)

(57) [Claims] 1. Chemical composition in weight%: C: 3.0-3.8%, Ni: 0.2-0.4% Si: 2.4-3.0%, Cu: 0.4-0.6% Mn: 0.2-0.4%, Nb: 0.05-0.10% P: 0.04% or less, Mg: 0.03 to 0.06% A high-strength and wear-resistant ductile cast iron material characterized by the fact that the balance is substantially Fe and the base structure is composed of bainite and retained austenite. 2. Chemical composition in weight%: C: 3.0-3.8%, Ni: 0.2-0.4% Si: 2.4-3.0%, Cu: 0.4-0.6% Mn: 0.2-0.4%, Nb: 0.05-0.10% P: 0.04% or less, Mg: 0.03 to 0.06% balance After heating ductile cast iron substantially consisting of Fe to an austenitizing temperature, it was quenched in a salt bath maintained at 225 to 275 ° C. to transform the base structure into a bainite structure and A method for producing a high-strength and wear-resistant ductile cast iron material having a retained austenite structure.