JPS62112753A - High strength cast steel and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the titled steel capable of keeping both superior strength characteristic and high longitudinal modulus of elasticity, by applying a prescribed austemper treatment to cast steel having a specified component compsn. to adjust the quantity of bentonite structure in matrix structure to >=a prescribed value and to adjust hardness to a specified Hv range. CONSTITUTION:Cast steel contg. by weight 0.3-1.0% C, 2.0-4.5% Si, <=0.8% Mn, <=0.05$ P, <=0.05% S and 0.05-1.0% Mo or/and <=2.0% Ni and the balance substantially Fe is treated as follows. Namely, austemper treatment composed of austenitizinig treatment at 880-1,000 deg.C for >=10min and isothermal transformation treatment at 200-500 deg.C for 10min is applied. In this way, graphite in matrix structure of the titled steel is vanished and matrix structure is composed of uniform bentonite structure, the title steel ensuring superior strength characteristic and longitudinal modulus of elasticity is obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a high-strength cast steel and a method for producing the same. Specifically, in the as-cast state, a large amount of ferrite structure and graphite are precipitated in the pearlite matrix mW, resulting in an excellent cast steel. High-strength cast steel that has excellent machinability as well as excellent strength characteristics and a high modulus of longitudinal elasticity by performing a predetermined austempering treatment after machining the cast rough shape material. and its manufacturing method.

[Conventional technology]

In order to ensure excellent strength properties and a high modulus of longitudinal elasticity in iron-based castings, it is necessary to use cast steel with a composition that has a low carbon content.

Since cast steel requires a high melting temperature during casting, there are many manufacturing technology problems such as melting equipment, melting costs, and fire resistance of molds.

However, cast steel has superior mechanical properties;

Since cast steel products can be assembled and used by welding, they have a large degree of freedom in design, and are used as material for a wide range of parts, from large industrial machines to various small parts.

By the way, cast steel is spheroidal graphite cast steel, which has graphite precipitated in a pearlite matrix structure to ensure excellent machinability and vibration damping properties, and has excellent strength properties.

In order to ensure the longitudinal elastic modulus and impact properties, graphite-free cast steel is used, which suppresses the precipitation of graphite in the pearlite matrix structure.

[Problem that the invention seeks to solve]

In view of the current state of the conventional technology as described above, the problem to be solved by the present invention is that among the conventionally commonly used cast steels, spheroidal graphite cast steels have excellent machinability and vibration damping properties. Strength properties.

The impact properties and modulus of longitudinal elasticity are insufficient, and if you try to improve the strength properties using graphite-free cast steel, which has excellent strength properties, modulus of longitudinal elasticity, and impact properties, machinability will be significantly impaired. This means that

Therefore, the technical problem of the present invention is to adjust the composition of cast steel so that a large amount of ferrite structure and graphite can be precipitated in the hacherite base structure in the as-cast state, thereby ensuring excellent machinability. By performing a predetermined austempering treatment after machining cast steel, the graphite in the base structure of high-strength cast steel disappears and the base structure becomes a uniform bainite structure, resulting in excellent strength properties. The goal is to ensure a high longitudinal elastic modulus.

Means for Solving Problem C] In view of the problems in the conventional technology, the means for solving the problem in the conventional technology in the present invention is as follows: C: 0.3 to 1 in weight ratio .0%, Si; 2.0-4
．． 5%+Mn; o, 8% or less, P; 0.05
% or less, S; (1, (15% or less and Mo; 0.05
~1°0% and Ni; at least 1 of 2.0% or less
The balance is essentially Fe, and the amount of bainite structure in the base structure is made to be 40% or more in volume ratio by a predetermined austempering process, and the hardness is Hv27.
A high-strength cast steel characterized by having a tensile strength of 0 to 500, and
In terms of weight ratio, C: 0, 3-1.0%, S i ;
2.0-4.5%, Mn; 0.8% or less, P: 0.05
% or less, S; 0.05% or less and Mo? 0.05-1.0
% and Ni; for cast steel having a composition consisting of at least one of 2.0% or less and the remainder substantially Fe, 8
Austempering treatment for 80~b x 10 minutes or more;
200-b, a method for manufacturing high-strength cast steel characterized by subjecting it to austempering treatment.

[Effect]

Hereinafter, the effects of the present invention will be explained.

In the present invention, by configuring the above-mentioned means to solve the problems of the conventional technology, in the as-cast state, a large amount of ferrite structure and graphite are precipitated in the pearlite base structure, thereby increasing the hardness. At the same time, the base structure of high-strength cast steel is improved by performing a prescribed austempering treatment after machining the cast steel, and by performing the prescribed austempering treatment after machining the cast steel. By eliminating the graphite inside and making the base U weave a uniform bainite structure, it is possible to ensure excellent strength characteristics and a high modulus of longitudinal elasticity.

Further, in the present invention, it is desirable that the hardness of the high-strength cast steel in the as-cast state be HV280 or less, and if the hardness is higher than this, it is not preferable because machinability will be significantly deteriorated.

The reason for limiting the range of the amount of each alloy component added to the cast steel used in the high-strength cast steel and the method for producing the same of the present invention will be explained below.

In the following description, the amount of each alloy component added is expressed in percent by weight.

First, C is effective for precipitating graphite in the pearlite matrix structure of high-strength cast steel in the as-cast state, but 0.3%
If it is less than 1.0%, the effect will not be sufficient, whereas if it is added in excess of 1.0%, it will ensure that graphite in the pearlite base structure precipitated in the as-cast state will disappear during austempering treatment. Since graphite remains even after austempering and deteriorates the strength characteristics of high-strength cast steel, it is set at 0.3 to 1.0%.

In addition, like C, St is effective for precipitating graphite in the pearlite matrix structure of high-strength cast steel in the as-cast state, but if it is less than 2.0%, it may not be possible to precipitate graphite in the as-cast state. In addition, since it also reduces the ability to form ferrite structures, the amount of ferrite structures decreases and machinability deteriorates. On the other hand, when added in excess of 4.5%, it reduces the toughness of high-strength cast steel. 2.0~
It was set at 4.5%.

Furthermore, if Mn is added in an amount exceeding 0.8%, the toughness of the high-strength cast steel that has been cast is reduced, so the Mn content is set to 0°8% or less.

Further, both P and S have the same effect as Mn, and if added in an amount exceeding 0.05%, the toughness of the high-strength cast steel that has been cast is reduced, so the content was set to 0.05% or less.

In addition, Mo is effective because it strengthens the matrix structure and improves the hardenability of high-strength cast steel, but 0.05%
If it is less than 0.05%, the effect will be sufficient; on the other hand, if it is added in excess of 1.0%, it will not only significantly deteriorate the castability of high-strength cast steel but also reduce the toughness of the cast high-strength cast steel. ~1.0%.

Further, although Ni is effective because it strengthens the matrix weave, if it is added in excess of 2.0%, the castability of high-strength castings and steels will be significantly deteriorated, so it is set at 2.0% or less.

Next, conditions for austempering treatment after machining a rough section of high-strength cast steel in an as-cast state will be described.

In the method for producing high-strength cast steel of the present invention, the austempering treatment conditions are set to 880 to 10.
00℃ x 10 minutes or more, constant temperature transformation treatment condition 200~50
The reason why the content is 0tXIO or more is that the amount of bainite structure in the base structure after austempering using this high-strength cast steel is 40% or more in volume ratio, and the balance is a mixed structure with austenite structure, and the austempering process is performed. The hardness of high-strength cast steel is Hv270-500.
This is for the purpose of

In the high-strength cast steel of the present invention, the amount of bainite structure in the base structure is set to 40% or more by volume because
This is because if the amount of bainite structure is smaller than this, excellent strength characteristics as a high-strength cast steel cannot be ensured.

In addition, the hardness of austempered high-strength cast steel is important to ensure excellent strength properties, but if Hv is less than 270, the effect of improving the strength properties is not sufficient;
If it exceeds Hv500, the toughness of austempered high-strength cast steel will be significantly reduced.
And so.

Next, the reason for limiting the austempering conditions will be explained.

In the austempering process of the present invention, the austempering temperature is set at 880 to 1000°C because if the temperature is lower than 880°C, the graphite precipitated in the as-cast state cannot be reliably eliminated by the austempering process. Moreover, if the temperature exceeds 100° C., the crystal grains of the high-strength cast steel will become significantly coarser and the strength characteristics will deteriorate.

In addition, in the austempering process in the method of the present invention, the austempering process time is 10 minutes or more because
This is because if the time is shorter than this, the austempering of the cast steel will be incomplete, and a uniform bainite structure cannot be obtained, resulting in a decrease in the strength characteristics of the high-strength cast steel.

Next, in the austempering treatment in the method of the present invention, the isothermal transformation treatment temperature is set at 200 to 500°C.
If the temperature is lower than 00℃, the hardness will exceed HV500 and the toughness of the high-strength cast steel will be reduced.If it exceeds 500℃, the structure of the austempered high-strength cast steel will not only become rough, but also the hardness will exceed HV270. This is because the strength characteristics of high-strength cast steel are lowered.

In addition, in the austempering process according to the present invention, the isothermal transformation treatment time is set to 10 minutes or more because if the time is shorter than this, the bainitic structure of the base structure will be insufficient, causing martensitic transformation during the cooling process, and the austempering process will occur. This is because it reduces the toughness of high-strength cast steel.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings.

First, in terms of weight ratio, Fe -0.5%G -2.5%
Si-0,5%Mn-0,008%P-0.007%
S-〇, high strength cast steel made of 2% Mo, JIS standard A
It was cast into the shape of a No. Y block.

FIG. 1 shows a microscopic photograph of the metal structure of the high-strength cast steel cast in this way in an as-cast state.

As is clear from Figure 1, the as-cast structure of this high-strength cast steel not only has a large amount of ferrite structure and graphite in the pearlite base structure, but also has a low hardness of HV230, which is an excellent structure. It is understood that this provides evidence of machinability.

Next, the high-strength cast steel cast as described above is
375 after austenite ratio treatment at 950°C x 5.5 hours
Austemper treatment consisting of constant temperature transformation treatment at ℃×1 hour was carried out.

FIG. 2 shows a microscopic photograph of the metal structure of the high-strength cast steel in the state after such austempering treatment.

As is clear from FIG. 2, the structure of the high-strength cast steel subjected to the above-described austempering treatment has a uniform base structure of bainite structure, and it is understood that graphite has been reliably eliminated.

Table 1 shows the properties of the high strength cast steel produced in this manner.

Excellent tensile strength as evident from Table 1.

It is understood that it has high fatigue strength, elongation (toughness), and high modulus of longitudinal elasticity.

As is clear from Table 1 and above, according to the high-strength cast steel and the manufacturing method thereof according to the present invention, by adjusting the composition of the cast steel, it becomes barley in the as-cast state.

In addition to ensuring excellent machinability by precipitating a large amount of ferrite 1-M1 weave and graphite in the base structure, high strength is achieved by performing a predetermined austenburizing treatment after machining the cast steel. By eliminating graphite in the matrix structure of cast steel and making the matrix structure a uniform bainite structure, there is an advantage that excellent strength characteristics and a high modulus of longitudinal elasticity can be ensured.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a microscopic photograph of the metal structure of the material of the present invention in an as-cast state. FIG. 2 is a diagram showing a microscopic photograph of the metal structure of the material of the present invention in a state after austempering treatment.

Claims (1)

[Claims] 1. Weight ratio: C: 0.3 to 1.0%, Si: 2.0
~4.5%, Mn: 0.8% or less, P: 0.05% or less, S: 0.05% or less, Mo: 0.05-1.0%, and Ni: 2.0% or less. It has a composition of at least one type, the remainder of which is essentially Fe, and is characterized by having a bainite structure content in the base structure of 40% or more in terms of volume ratio through a predetermined austempering treatment, and a hardness of Hv270 to 500. High strength cast steel. 2. Weight ratio: C: 0.3-1.0%, Si: 2.0
~4.5%, Mn: 0.8% or less, P: 0.05% or less, S: 0.05% or less, Mo: 0.05-1.0%, and Ni: 2.0% or less. 880 to 880 for cast steel having at least one composition, the remainder substantially consisting of Fe.
A method for manufacturing high-strength cast steel, characterized by performing an austempering treatment consisting of an austenitization treatment at 1000°C for 10 minutes or more and a constant temperature transformation treatment at 200 to 500°C for 10 minutes or more.