JP2001073068A - High rigidity steel for machine structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high rigidity steel for a machine structure having a high Young's modulus even in the case of being produced by using an ordinary melting-casting process and moreover having heat-treating characteristics as the important characteristics as a steel material for a machine structure. SOLUTION: This high rigidity steel for a machine structure has a compsn. contg., by weight, 1 to 4% C, 0.01 to 2% Si, 0.1 to 2% Mn, 0.01 to 5% Cr, 5 to 20% V, 0.005 to 0.05% s-Al and 0.005 to 0.05% N, moreover contg., at need, one or >=two kinds selected from Mo, W, Ti, Nb, Zr and Ta, and the balance Fe with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high rigidity steel for a machine structure which can be applied to parts for a mechanical structure, and more particularly to a high rigidity steel for a machine structure having a higher rigidity than ordinary steel which can be produced by a melting method. About steel.

[0002]

2. Description of the Related Art Steel materials are used for many mechanical structural parts. The properties required for the steel material used for the machine structural component include strength, toughness, and rigidity. Extensive research has been conducted on the strength and toughness so far, and significant improvements have been realized by optimizing the alloying elements to be contained and the heat treatment. However, stiffness, that is, Young's modulus is an important factor when designing mechanical parts, and improving the Young's modulus makes it possible to significantly reduce the size of parts. Had not been done enough yet. Against this background, in recent years, there has been a strong demand for the development of high-rigidity steel for machine structures having a high Young's modulus. In particular, for components that move at high speed, such as crankshafts, connecting rods, and piston pins, there is a great advantage in miniaturizing components by improving the Young's modulus, and application of highly rigid materials is expected.

Conventionally, as a material for obtaining this high Young's modulus, 4
A method for producing a steel material having a high Young's modulus by dispersing a boride of an A or 5A element in iron or an iron alloy is disclosed in
No. 88874 and JP-A-7-252609. However, in steel using boride, even if boron and the elements of the 4A and 5A elements are blended in a stoichiometric composition, partially separated boron causes a eutectic reaction with iron,
There was a problem that hot workability was greatly impaired.

Further, Japanese Patent Laid-Open No. Hei 10 (1999) discloses a method of producing a steel material having a high Young's modulus by dispersing 5 to 50 vol% of carbides, borides and complex compounds of elements of Group 4A and 5A in iron or an iron alloy. No. 68048. However, this method involves heating at a high temperature of about 2,000 ° C. in a vacuum to deoxidize and reduce and dissolve and crystallize the compound from the molten metal during solidification. However, there is a problem that it is technically difficult and the cost is high.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a machine which has a high Young's modulus even when manufactured using a normal melting and casting process, and also has a heat treatment property which is an important property as a steel material for machine structure. An object of the present invention is to provide a high-rigidity structural steel.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies on the component composition and the like of high-rigidity steel for mechanical structures, and found that VC has a high Young's modulus and Precipitates at a lower temperature than carbides (has good castability), and if C and V are contained in the steel and a large amount of VC is formed in the steel, a steel having a high Young's modulus can be produced. The present invention has been made based on the finding that a steel having heat treatment properties can be produced by incorporating an appropriate alloying element such as carbon, silicon, manganese, and chromium therein.

That is, in the high rigidity steel for machine structure of the present invention, C: 1 to 4%, Si: 0.01 to 2%, M
n: 0.1 to 2%, Cr: 0.01 to 5%, V: 5-2
0%, s-Al 0.005 to 0.05%, and N: 0.0
0.05-0.05%, and optionally Mo:
0.01 to 5%, W: 0.01 to 5%, Ti: 0.01
-5%, Nb: 0.01-5%, Zr: 0.01-5%
And Ta: one or more selected from 0.01 to 5%, with the balance being Fe and unavoidable impurities.

[0008]

Next, the present invention will be described in detail. First, the components of the high-rigidity steel for machine structure of the present invention and the reason for limiting the content thereof will be described. C: 1 to 4% C is an element to be contained because it forms carbide having a high Young's modulus and partially forms a solid solution in a matrix to enhance heat treatment properties and strength. In order to obtain these effects, it is necessary to contain 1% or more,
If the content exceeds 4%, the steel for machine structural use becomes too hard, so the content is set to 1 to 4%. Also, considering other alloying elements, V / 3.7 + Mo / 15.5 + W /
14.8 + Ti / 3.5 + Nb / 7.2 + Zr / 7.1 + Ta / 1
4.6 ≧ C ≧ V / 4.7 + Mo / 16.5 + W / 15.8 + Ti / 4.5
The range is preferably + Nb / 8.2 + Zr / 8.1 + Ta / 15.6.

Si: 0.01 to 2% Since Si has a deoxidizing effect when smelting steel, it also forms a solid solution in ferrite to increase hardness and increase strength.
It is an element to be included for that purpose. To obtain these effects, it is necessary to contain 0.01% or more.
If it exceeds 2%, the hardness increases more than necessary and the machinability decreases, so the content is made 0.01 to 2%.

Mn: 0.1 to 2% Mn is an element that is mainly contained in the matrix to increase the hardenability of the matrix and to improve the heat treatment properties. To obtain this effect, 0.1
However, when the content exceeds 2%, the hardness is hardly reduced even by annealing or normalizing treatment, and the workability is impaired.
And

Cr: 0.01 to 5% Cr is an element to be added for enhancing the hardenability of the matrix and improving the heat treatment property, like Mn. In order to obtain this effect, the content must be 0.01% or more. However, if it exceeds 5%, the hardness is hardly reduced even by annealing or normalizing treatment, and workability is impaired. The amount is 0.1-5%.

V: 5 to 20% V combines with C to form VC having a high Young's modulus,
Since it is dispersed in steel and contributes to high rigidity, it is an element contained for that purpose. This VC is equal to other Nb, Ti, Z
Unlike carbides such as r, it has a low crystallization temperature and can be uniformly and finely dispersed in a matrix. For this reason, high rigidity can be achieved without significantly lowering manufacturability such as castability and hot workability. For these reasons, in the present invention, high rigidity is mainly achieved by VC, and in order to obtain such an effect, it is necessary to contain 5% or more. Since the workability decreases and the cost increases, the content is set to 5 to 20%. Preferably, it is 7 to 13%.

S-Al: 0.005 to 0.05% s-Al is an element added to perform deoxidation during steelmaking. In order to obtain this effect, the content must be 0.005% or more. However, if the content exceeds 0.05%, the effect of deoxidation is saturated and the castability and hot workability are impaired. , The content of which is 0.005 to 0.05%.

N: 0.005 to 0.05% N forms a nitride having a high Young's modulus similarly to C and is effective for increasing the rigidity, so N is an element to be contained for that purpose. In order to obtain this effect, the content must be 0.005% or more. However, if the content exceeds 0.05%, castability is remarkably reduced due to crystallization of a large amount of nitride. 0.005 to 0.05%.

Mo: 0.01 to 5%, W: 0.01 to 5
%, Ti: 0.01 to 5%, Nb: 0.01 to 5%, Z
r: 0.01 to 5%, Ta: 0.01 to 5% Mo, like Cr, enhances the hardenability of the matrix and improves the heat treatment properties, and is an element to be contained for that purpose. In order to obtain these effects, it is necessary to contain 0.01% or more. However, if it exceeds 5%, carbides having a low Young's modulus are formed, and an unnecessary increase in hardness is performed without increasing the Young's modulus. Therefore, the content is set to 0.01 to 5%.

W, Ti, Nb, Zr and Ta, like V, form carbides having a high Young's modulus and contribute to higher rigidity, and are elements to be contained for that purpose. In order to obtain this function and effect, it is necessary to contain 0.01% or more, but since these carbides have a higher crystallization temperature than VC, a large amount of crystallization temperature is high when they are contained in excess of 5%. Since carbides are formed and castability is remarkably reduced, the content is set to 0.01 to 5%.

The high-rigidity steel for machine structural use according to the present invention contains P: 0.03% or less, S: 003% or less, Cu:
0.30% or less, Ni: 0.20% or less, Co: 0.3
0% or less, O: 0.003% or less is preferable.

Next, a method for producing the high-rigidity steel for machine structure of the present invention and a heat treatment method will be described. The production of high-rigidity steel for machine structures according to the present invention can be carried out in the atmosphere, particularly without heating at a high temperature, by the same smelting method as that of ordinary steel, and the casting method is also sand mold, Can be cast into ingots using ordinary molds such as water-cooled copper molds,
Further, it can be carried out by ordinary bulk forging or rolling, hot forging or rolling.

The method for heat-treating high-rigidity steel for mechanical structures according to the present invention varies depending on the composition of the components, the application, the size, etc., but annealing is performed at a temperature of about 800 to 900 ° C. for about 0.5.
It can be performed by heating and cooling in a furnace for up to 2 hours. Normalization can be performed by air cooling after heating and holding. Furthermore, quenching is about 800-9
It can be carried out by heating at a temperature of 00 ° C. for about 10 minutes to 1 hour and then cooling with water or oil. Further, the tempering can be performed by heating to a temperature of about 500 to 700 ° C. for 20 minutes to 1 hour and then air cooling.

[0020]

Next, an embodiment of the present invention will be described. The steels of the present invention and comparative examples having the component compositions shown in Table 1 below were melted in a high frequency induction furnace, cast into a mold, and ingot into a 50 kg ingot. Comparative Examples Nos. 9 and 11 to 15 solidified in the crucible (with an estimated melting point of 2000 ° C. or higher) and could not be cast. This ingot is 1100 ° C
After forging to φ25mm with (No. 7 and 8 of Comparative Example
Cracks occurred during forging, and the following test pieces could not be prepared. ), Annealing at 850 ° C. for 60 minutes and furnace cooling. A test piece for measuring hardness was cut out from the annealed round bar, and the hardness was measured by Vickers hardness. The results are shown in Table 2 below.

[0021]

[Table 1]

The annealed round bar is 850
Quenching by heating at 30 ° C for 30 minutes and then cooling with water.
After heating at 0 ° C. for 60 minutes, tempering was performed by air cooling. 2mm thick from the center of the quenched and tempered round bar
Cut out a test piece of width 8mm x length 60mm, JIS
The Young's modulus was measured based on Z2280. Further, the hardness of the test piece was measured by Vickers hardness. The results are shown in Table 2 below. In the steels of the present invention and comparative examples, P: 0.03% or less, S: 003% or less, Cu: 0.30% or less, Ni: 0.20% or less, and C as impurities.
o: 0.30% or less and O: 0.003% or less.

[0023]

[Table 2]

From the above results, the sample of the present invention had an annealing hardness of 286 to 324 in HV and a quenching and tempering hardness of 306 to 342 in HV. The Young's modulus was 219 to 268 GPa. On the other hand, in the case of Comparative Example No. 1 in which the C content was lower than that of the present invention, the annealing hardness, quenching and tempering hardness and Young's modulus were lower than those of the present invention. Comparative Examples No. 2 and No. 3 in which the C content or the Si content is higher than the present invention have a Young's modulus equal to or lower than that of the present invention, although the annealing hardness and the quenching and tempering hardness are high. I was

Comparative Examples No. 4 and No. 5 having a higher Mn content or Cr content than the present invention have the same Young's modulus as those of the present invention, but have a high annealing hardness, and There was a problem with the sharpness. Comparative example in which V content is lower than the present invention
The sample of No. 6 had a considerably lower Young's modulus than that of the example of the present invention, and was not a highly rigid steel. In the case of Comparative Example No. 7 in which the V content was higher than that of the present invention, the VC amount was too large, so that the hot workability was reduced and cracks occurred during hot forging.

Comparative Example No. 8 in which the Al content is lower than that of the present invention
In the case of No. 1, casting defects due to poor deoxidation were recognized, and hot workability was deteriorated, and cracks occurred during hot forging. Comparative Example No. 9 having a higher N content than the present invention
N crystallized and solidified in the crucible due to reduced castability. In the case of Comparative Example No. 10 in which the Mo content is higher than that of the present invention, the Young's modulus is similar to that of the present invention, but the annealing hardness is high and there is a problem in machinability.

Comparative Examples Nos. 11 to 15 having higher contents of W, Ti, Nb, Zr and Ta than the present invention produced a large amount of crystallized substances, and were solidified in the crucible due to reduced castability. C
Comparative Example No. 16, which has a lower content than the present invention and does not contain V or the like and corresponds to JIS S45C, has a considerably lower quench and temper hardness than that of the present invention, and also has a Young's modulus lower by about 10 to 20%. Has become.

[0028]

The high-rigidity steel for machine structure of the present invention has the following excellent effects by adopting the above-mentioned composition. (1) The Young's modulus and quenching and tempering hardness are sufficiently high, and the annealing hardness is such that it can be machine-cut. (2) Heat treatment such as quenching and tempering and annealing can be performed. (3) It can be manufactured by ordinary melting and casting methods without requiring special melting and casting. (4) Since hot forging can be performed, molding can be easily performed.

Claims (2)

[Claims] C. 1 to 4% by weight (hereinafter the same),
Si: 0.01 to 2%, Mn: 0.1 to 2%, Cr:
0.01-5%, V: 5-20%, s-Al: 0.00
High rigidity steel for machine structures containing 5 to 0.05% and N: 0.005 to 0.05%, the balance being Fe and unavoidable impurities. 2. C: 1-4%, Si: 0.01-2%,
Mn: 0.1-2%, Cr: 0.01-5%, V: 5-
20%, s-Al: 0.005 to 0.05% and N:
0.005 to 0.05%, and Mo: 0.01
-5%, W: 0.01-5%, Ti: 0.01-5%,
Nb: 0.01 to 5%, Zr: 0.01 to 5%, and T
a: High rigidity steel for machine structures containing one or more selected from 0.01 to 5%, the balance being Fe and unavoidable impurities.