JPS62270752A - Free-cutting steel excellent in property of nitriding - Google Patents

Abstract

PURPOSE:To obtain a free-cutting steel excellent in machinability and having superior properties owing to the property of nitriding including soft nitriding and carbonitriding, by specifying a composition consisting of C, Si, Mn, Cr, V, S, Pb, Bi, Se, Te, and Fe. CONSTITUTION:The free-cutting steel excellent in property of nitriding has a composition consisting of, by weight, <=0.15% C, <=0.15% Si, 0.3-1.5% Mn, 0.2-3.0% Cr and/or 0.05-0.4% V, and the balance Fe with impurities and further containing one or more kinds among 0.03-0.35% S, 0.05-0.3% Pb, 0.02-0.2% Bi, 0.03-0.3% Se, and 0.01-0.1% Te and further containing, if necessary, one or more kinds among 0.05-0.5% Mo, 0.01-0.2% Nb, and 0.01-0.2% Ta. On application of this steel, high-efficiency and high-accuracy machining is enabled and also it is made possible to increase wear resistance at the parts surface to a great degree by means of nitriding treatment. Further, in the above steel, it is desirable that Mn/S>=4 is satisfied and the amounts of P and Al among the impurities are regulated to <=0.10% and <=0.01%, respectively.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention is directed to nitriding treatment (soft nitriding treatment, carbonitriding treatment -
Regarding free-cutting steel with excellent mechanical properties and machinability, it can be used as a material for telecommunication equipment parts, precision machinery parts, machine tool parts, agricultural machinery parts, automobile parts, bicycle parts, etc. This invention relates to a free-cutting steel that has excellent nitriding properties and machinability.

(Prior art) Conventionally, free-cutting steels used for the above-mentioned applications include sulfur and sulfur composite free-cutting steels, which are established as JIS SUMII~43, as well as P, S, and Pb.
Free-cutting steel with composite additions (for example, Daido Steel Co., Ltd. standards: 5F02F, 3F).

4F), free-cutting steel with composite addition of S, Pb, and Te (
For example, there is Daido Steel Co., Ltd. standard: 5FC3FT).

(Problems to be Solved by the Invention) As mentioned above, conventional free-cutting steels have been applied in a wide range of fields, and their machinability has deteriorated significantly.

Although it has an extremely excellent feature of being able to significantly extend the life of cutting tools such as drills, it cannot be said that its nitriding properties are very good, so it has excellent machinability. There was also a demand for a free-cutting steel that was not only highly nitridable, but also had sufficient nitriding properties.

(Purpose of the Invention) This invention was made in view of the above-mentioned conventional demands, and it not only has excellent machinability but also excellent nitriding properties including soft nitriding and carbonitriding. The purpose is to provide free-cutting steel.

[Structure of the Invention] (Means for Solving the Problems) The free-cutting steel having excellent nitriding properties according to the present invention has, in weight%,
C: 0.15% or less, Si: O, 15% or less, Mn: 0
．． 3-1.5%, and Cr2 0.2-3.0%, V:
0.03-0.35% of 0.05-0.4%, Pb:0
．． 05-0.3%, Bi: 0.02-0.2%, S
One or more types selected from e: 0.03 to 0.3%, Te: 0.01 to 0.1%, M as necessary
o: 0.05-0.5%, Nb: 0.01-0.2%,
Ta: One or more selected from 0.01 to 0.2%, the balance being Fe and impurities, more preferably an S content of 0.03 to 0.
．． 35%, M n /S≧4, and more preferably P:0.
10% or less, AfL: 0.01% or less, and the zero content is more preferably 50 to 200 ppm in order to improve machinability. It is something.

Next, the reason for limiting the composition range (weight %) of the free-cutting steel according to the present invention, which has excellent not only machinability but also excellent nitriding properties, will be explained.

r , ^ IC, O / 11ζC is an effective element for ensuring the mechanical strength of various parts such as precision machine parts, telecommunication machine parts, automobile parts, bicycle parts, etc. However, if it is contained in large amounts, Since the hardness increases and the workability before nitriding decreases, cutting workability, forging workability, etc. when manufacturing one part are reduced, so the upper limit is set at 0.15%.

Sj: 0.15% or less If Si is contained in a large amount, machinability is reduced, so the upper limit is set to 0.15%.

Mn: 0.3 to 1.5% Mn combines with S to form sulfide MnS and is an effective element for improving rigidity, so it is contained in an amount of 0.3% or more. However, if it is contained in a large amount, it will actually reduce machinability and cold workability, so the upper limit is set at 1.5%.

Cr: 0.2 to 3.0%, V: 0.05 to 0.4% Cr and V improve the nitriding properties of this type of free-cutting steel. It has the effect of deepening the hardened layer, and is an effective element for improving surface hardness, wear resistance, and strength through nitriding treatment, so in order to obtain such effects,
Cr should be at least 0.2% - and ■ should be at least 0.05%.

However, if it is too large, it will actually deteriorate the toughness and reduce the workability before nitriding treatment, so the content of Cr is 3.0% or less.

■ should be 0.4% or less.

S: 0.03-0.35%, Pb: 0.05-0.3%
, Bi: 0.02-0.2%, Se: 0.03-0.3
%, Te: One or more selected from 0.01 to 0.1% S, Pb, Bi, Se, and Te are all effective elements for improving the stiffness of steel. , S
is 0.03% or more, pb is O, OS% or more, and Bi is 0.03% or more.
02% or more, Se 0.03% or more, Te 0.01%
One or more selected from the above may be included. However, if it is contained in a large amount, it will impair the manufacturability, hot workability, or toughness of steel, so S should be 0.3596 or less, P
b is 0.3% or less, Bi is 0.2% or less, Se is 0.3
% or less, and Te is 0.1% or less. When S is included as an element for improving machinability, the S content is set to 0.
It is desirable to adjust the components as necessary so that Mn/S is in the range of 0.03 to 0.35%, but S is 4 or more.
0.615% as an impurity element when not containing
It is preferable to do the following.

Mo: 0, 05~0.5%, Nb: 0.01~
0.2%, Ta: 0.01 NO, 2% Mo, Nb, and Ta are all effective elements for further increasing strength and toughness. In order to obtain the desired effect, if necessary, Mo should be added to 0.05% or more, and Nb should be added to 0.
．． It is also good to contain Ta at 0.01% or more, but if it is contained in a large amount, the toughness will be reduced, so even if it is included, MO is 0.5%.
Hereinafter, it is preferable that Nb be 0.2% or less and Ta be 0.2% or less.

P: 0.10% or less If P is contained in a large amount, it reduces toughness, so it is desirable that the upper limit is 0.10%.

Al: 0.01% or less If AI is contained in a large amount, machinability is reduced, so it is desirable to set the upper limit to 0.01%.

0 2 50 to 200 ppm If the O content is too low, machinability may be reduced, so it is desirable to set the lower limit to 50 ppm, if necessary.

However, if the 0 content is too large, the solubility may be lowered, so it is desirable to set the upper limit to 200 ppm as necessary, and it is particularly desirable to set the content to about 70 to 180 ppm.

(Example and Comparative Example) 50 kg of each steel having the chemical composition shown in Table 1 was melted in an induction melting furnace, then formed into ingots, and after blooming and product rolling, cutting test pieces were taken. It was subjected to a cutting test under the conditions shown below. In this cutting test, cutting speed V=5
The drill life at 0 m/min was investigated. The results are also shown in Table 1, and 570℃ x 5
Hardness H after soft nitriding
The effective hardened layer depth at which v550 or more was obtained was measured. The results are also shown in Table 1.

Table 2 As shown in Table 1, 1 Invention steel No. 1-a to No. 6
-c are comparative steel Nos. 1 to 6, each of which has a corresponding tool life (drill life) at a cutting speed of 50 m/min.
Although it is rather superior compared to nitrocarburizing, the effective hardening layer depth at which Hv550 can be obtained after soft nitriding is large;
It is clear that the nitriding property is extremely excellent. It was also confirmed that in order to improve machinability, it is more desirable to regulate the amounts of St and Al and also adjust the zero content.

[Effects of the Invention] As explained above, the free-cutting steel according to the present invention contains, in weight percent, C: 0.15% or less, Si2: 0.15% or less,
Mn: 0, 3-1, 5%, and Cr:
0, 2-3, 0%, V: 0.05-0.4%, and S: 0.03-0.
．． 35%, Pb: 0.05-0.3%, Bi: 0.02
~0.2%, Se: 0.03~0.3%, Te: 0.0
One or more types selected from 1 to 0.1%,
Mo: 0, 05-0.5%, Nb as necessary
:0.01-0.2%, Ta:0.01-0.2%, and the balance is Fe and impurities, so it has extremely excellent machinability. Not only does it have excellent nitriding properties, including soft nitriding and immersion nitriding, and the free-cutting steel of the present invention can be used for parts for telecommunication equipment, parts for precision vEIa machines,
When used as materials for machine tool parts, agricultural machinery parts, automobile parts, bicycle parts, etc., these cutting processes can be performed more efficiently and with high precision, making it possible to cut carbide parts, high-speed tool molds, etc. It is possible to significantly extend tool life and improve dimensional accuracy.

In addition to reducing tool costs and the frequency of tool replacement, nitriding allows for a greater effective hardened layer depth than conventional free-cutting steel, which improves the surface of parts. This brings about the remarkable effect that it is possible to significantly improve the wear resistance and fatigue strength of.

Claims (1)

[Claims] (1) In weight%, C: 0.15% or less, Si: 0.15% or less, Mn: 0.3 to 1.5%, and Cr: 0.2 to 3.0. %, V: 0.05-0.4
%, further S: 0.03-0.35%, Pb: 0.05-0.3%, Bi: 0.02-0.2%, Se
: 0.03 to 0.3%, Te: 0.01 to 0.1%, and the balance is Fe and impurities. Steel cutting. (2) S content is 0.03 to 0.35% and Mn/S
≧4. A free-cutting steel with excellent nitriding properties according to claim (1). (3) Claims (1) or (2) characterized in that P: 0.10% or less in impurities
Free-cutting steel with excellent nitriding properties as described in Section 1. (4) Claims (1) to (3) characterized in that Al in impurities is 0.01% or less.
) Free-cutting steel with excellent nitriding properties. (5) In weight%, C: 0.15% or less, Si: 0.15% or less, Mn: 0.3 to 1.5%, and Cr: 0.2 to 3.0%, V: 0. 05-0.4
%, further selected from Mo: 0.05-0.5%, Nb: 0.01-0.2%, Ta: 0.01-0.2% One or more types, S: 0.03 to 0.35%, Pb: 0.05
~0.3%, Bi:0.02~0.2%, Se:0.0
A free-cutting steel with excellent nitriding properties, characterized by comprising one or more selected from 3% to 0.3%, Te: 0.01% to 0.1%, and the remainder Fe and impurities. (6) S content is 0.03 to 0.35% and Mn/S
≧4. A free-cutting steel with excellent nitriding properties according to claim (5). (7) Claim (5) or (6) characterized in that P: 0.10% or less in impurities
Free-cutting steel with excellent nitriding properties as described in Section 1. (8) Claims (5) to (7) characterized in that Al in impurities is 0.01% or less.
) Free-cutting steel with excellent nitriding properties.