JP2000219936A - Free-cutting steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide free-cutting steel small in the variation of machinability and having excellent machinability such as turning workability more than that of the conventional one. SOLUTION: This steel comprises, by weight, 0.05 to 0.8% C, 0.01 to 2.5% Si, 0.1 to 3.5% Mn, 0.001 to 0.2% P, 0.005 to 0.4% S, 0.001 to 0.1% Al, 0.0005 to 0.02% Ca, 0.0005 to 0.01% O, and the balance Fe with inevitable impurities and also contains sulfides of >=5 μm diameter equivalent to a circle contg. 0.1 to 10% Ca by >=5 pieces per 3.3 mm2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a free-cutting steel, and more particularly, to a free-cutting steel having a combination of S and Ca and excellent in machinability such as turning property.

[0002]

2. Description of the Related Art Generally, steel mechanical structural parts used in the automobile industry and the like are roughly worked by plastic working such as forging, and then finished to a desired final shape by cutting. Among them, the turning process is a process applied to most parts. Since the cost of the cutting process is considerably high in the cost of the machine structural parts, the demand for a free-cutting steel having excellent machinability is increasing to reduce the cost.

Conventionally, free cutting steels such as S, Pb, Bi, S
e, Te, and other elements that improve machinability,
There are known those to which Ca is added and those to which Ca and S are added in combination. Japanese Patent Application Laid-Open No. Sho 49-5815 discloses a compound in which Ca and S are added in combination. The free-cutting steel described in this publication is
Mainly non-metallic inclusions composition shown in _{CaO-Al 2 0 3 -SiO 2} 3 ternary phase diagram In the mullite region, Ca
It contains 5 to 15 ppm and 0.04 to 0.1% of S. However, these conventional Ca free-cutting steels containing oxide inclusions and S have large variations in machinability, and it cannot be said that the machinability is sufficient.

Therefore, the present inventor has filed a patent application as Japanese Patent Application No. 9-231075 inventing a Ca free-cutting steel in which the machinability of a conventional Ca free-cutting steel containing oxide inclusions is further improved. In the present invention, C: 0.05-0.8%, Si: 0.
01 to 2.5%, Mn: 0.1 to 3.5%, P: 0.0
01-0.2%, S: 0.005-0.4%, Al:
0.001-0.1%, Ca: 0.0005-0.02
%, O: 0.0005 to 0.01%, N: 0.001 to
0.04%, the balance consists of Fe and inevitable impurities, and the Ca content exceeds 40%. A / (A + B + C), where B is the area ratio of the -40% sulfide to the entire area of the observation field of observation and C is the area ratio of the sulfide having a Ca content of less than 0.3% to the entire area of the observation field of observation. ) ≦ 0.3 and B / (A +
B + C) Free cutting steel excellent in turning workability with ≧ 0.1. This Ca free-cutting steel is made of Ca containing conventional oxide inclusions.
Although the variation in machinability was smaller than that of free-cutting steel, and the machinability was also improved, it was not yet sufficient.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a free-cutting steel which has a small variation in machinability and is more excellent in machinability such as turning workability than the conventional one. is there.

[0006]

In order to solve the above-mentioned problems, the present inventors have developed a free-cutting steel which has less variation in machinability and is more excellent in machinability such as turning property than conventional ones. During the study, when S, Ca, Al and O were each added in an appropriate amount in combination, CaO─Al ₂ O ₃ —SiO ₂ previously crystallized at the time of solidification was used as nuclei (Ca, Mn).
When the sulfide of S is crystallized and uniformly and finely dispersed, the machinability is improved. When the Ca content of the sulfide exceeds 10%, the sulphide becomes hard and the machinability is not improved. The present invention has been made based on the finding that it is necessary to contain 5 or more sulfides having an equivalent circle diameter of 5 μm or more per 3.3 mm ² in order to improve the properties.

That is, in the free-cutting steel of the present invention,
C: 0.05-0.8%, Si: 0.01-2.5%,
Mn: 0.1-3.5%, P: 0.001-0.2%,
S: 0.005 to 0.4%, Al: 0.001 to 0.1
%, Ca: 0.0005 to 0.02%, O: 0.000%
5% to 0.01%, and if necessary, Pb: ≦
0.4%, Bi: ≦ 0.4%, Se: ≦ 0.5%, and Te: 0.1% or more.
The balance consists of Fe and inevitable impurities, and 0.1 to
It is to contain 5 or more sulfides having a circle equivalent diameter of 5 μm or more containing 10% of Ca per 3.3 mm ² .

[0008] In the free-cutting steel of the present invention, C:
0.05-0.8%, Si: 0.01-2.5%, M
n: 0.1 to 3.5%, P: 0.001 to 0.2%,
S: 0.005 to 0.4%, Al: 0.001 to 0.1
%, Ca: 0.0005 to 0.02%, O: 0.000%
5% to 0.01%, Cr: ≦ 3.5%, M
o: ≦ 2.0%, Cu: ≦ 2.0%, Ni: ≦ 4.0%
And B: 0.0003-0.01% group and N
b: ≦ 0.2%, Ti: ≦ 0.2%, V: ≦ 0.5%,
Contains one or more of one or two of the groups of Ta: ≦ 0.5% and Zr: 0.5%, and if necessary, Pb: ≦ 0.4%, Bi: ≦ 0. 4%, Se: ≦ 0.5
% And Te: one or more members of the group of 0.1%, the balance being Fe and unavoidable impurities, and containing 0.1 to 10% of Ca and having a circle equivalent diameter of 5 μm or more. 5 or more per 3.3 mm ² . The “equivalent circle diameter” in the present invention is the diameter of a circle assuming a circle having the same area as the cross-sectional area.

[0009]

Next, the composition of the free-cutting steel according to the present invention, sulfide C
The reason why the content and the size of a are specified as described above will be described. C: 0.05 to 0.8% C is an element to be contained in order to secure strength.
If it is less than 0.05%, the required strength cannot be ensured, and if it exceeds 0.8%, the toughness and machinability decrease, so the content is made 0.05 to 0.8%.

Si: 0.01 to 2.5% Si is an element contained as a deoxidizing agent at the time of steel making, and is contained in order to improve hardenability. When the content exceeds 2.5%, ductility is reduced and cracks are easily generated during plastic working. Therefore, the content is set to 0.01 to 2.5%. Mn: 0.1 to 3.5% Mn is a sulfide-forming element. If it is less than 0.1%, a required amount of sulfide cannot be obtained, and if it exceeds 3.5%, the hardness of steel is increased. To reduce the machinability.
1 to 3.5%.

P: 0.001 to 0.2% P is an element useful for improving machinability, especially the quality of the finished surface. If less than 0.001%, the effect cannot be obtained. If it exceeds 2%, the toughness is significantly reduced, so the content is made 0.001 to 0.2%. S: 0.005 to 0.4% S is an element to be contained in order to improve machinability, and if less than 0.005%, machinability is not improved,
If it exceeds 0.4%, the toughness significantly decreases, so the content is made 0.005 to 0.4%.

Al: 0.001 to 0.1% Al is an element added for deoxidizing.
If it is less than 01%, the effect cannot be obtained. If it exceeds 0.1%, hard alumina clusters are formed and the machinability of the steel is reduced. I do. Ca: 0.0005 to 0.02% Ca is an element contained in sulfide to form a protective film of a cutting tool. If less than 0.0005%, the effect cannot be obtained. If the content exceeds 0.02%, an excessive amount forms CaS having a high melting point and causes a great obstacle such as nozzle closing in the casting process, so the content is made 0.0005 to 0.02%.

O: 0.0005% to 0.01% O is an oxide (CaO, Al ₂ ) serving as a nucleus for crystallization of sulfide.
O _3, etc.).
If it is less than 0005%, a large amount of Ca sulfide having a high melting point is generated to lower the pouring property, and if it exceeds 0.01%, a large amount of hard oxide is generated to lower the machinability,
Since all Ca forms an oxide and no sulfide is generated, its content is 0.0005 to 0.5.
01%. Preferably it is 0.001-0.004%.

The free-cutting steel of the present invention further comprises Cr, Mo, Cu, Ni, B, Nb, Ti, V, Ta,
One or more of Zr, Pb, Bi, Se and Te may be contained, and the reason for limiting these as described above will be described. Cr: ≦ 3.5% Cr is an element effective for improving hardenability, but if it exceeds 3.5%, it is disadvantageous in cost.
Further, since cracks occur frequently during hot working, the content is set to 3.5% or less.

Mo: ≦ 2.0% Mo is an element effective for improving the hardenability similarly to Cr, but if it exceeds 2.0%, it is disadvantageous in terms of cost, and also has poor machinability. The content is 2.0% or less, since the content is lowered and cracks occur frequently during hot working. Cu: ≦ 2.0% Cu is an element that densifies the structure and improves the strength. However, if it exceeds 2.0%, the hot workability is reduced and the machinability is also reduced. To 2.0% or less.

Ni: ≦ 4.0% Ni is an element effective for improving the hardenability similarly to Cr, but if it exceeds 4.0%, it is disadvantageous in terms of cost and also has poor machinability. Therefore, the content is set to 4.0% or less. B: 0.0003 to 0.01% B is an element contained for improving the hardenability. If B is less than 0.0003%, the effect cannot be obtained. It is coarsened and cracks frequently occur during hot working.
0003 to 0.01%.

Nb: ≦ 0.2% Nb is an effective element for preventing the crystal grains from becoming coarse at high temperatures, but the effect is saturated even if it exceeds 0.2%. The content is set to 0.2% or less. Ti: ≦ 0.2% Ti is an element that is combined with N to form TiN and contained in order to further enhance the hardenability improving effect of B.
If it exceeds 0.2%, TiN becomes excessive, and as a result, cracks frequently occur during hot working.
The following is assumed.

V: ≦ 0.5% V is an element that is contained in order to form carbonitrides by combining with C and N to refine crystal grains and improve toughness. The effect is saturated even if it is contained beyond 0.5%, so the content is made 0.5% or less. Ta: ≦ 0.5% Ta is an element effective for refining crystal grains and improving toughness, but the effect is saturated even if it exceeds 0.5%. 0.5% or less.

Zr: ≤0.5% Zr has a property similar to that of Ta, and is an element contained to refine crystal grains and improve toughness.
The effect is saturated even if the content exceeds 0.5%, so the content is set to 0.5% or less. Pb: ≦ 0.4% Pb is a well-known element for improving machinability,
It exists alone or in a form such that it adheres to the outer periphery of the sulfide in steel, and itself has an effect on machinability. However, when the content exceeds 0.4%, the solubility in steel is exceeded, and because of its large specific gravity, the excess alone agglomerates and precipitates to become defects in the steel. The following is assumed.

Bi: ≦ 0.4% Bi has similar properties to Pb and is a well-known element for improving machinability. However, if it exceeds 0.4%, it will exceed the solubility in steel. In addition, since the excess is agglomerated and precipitated by itself due to its large specific gravity and becomes a defect in the steel, its content is made 0.4% or less. Se: ≦ 0.5% Se is a well-known element for improving machinability. However, if it exceeds 0.5%, hot workability is reduced and cracks occur frequently. 0.5% or less. Te: ≦ 0.1% Te is a well-known element for improving machinability. However, if it exceeds 0.5%, hot workability is reduced and cracks occur frequently. 0.5% or less.

The form of the sulfide of the free-cutting steel of the present invention will be described. Generally, the main component of sulfide contained in steel is M
Although it is nS, a part of Mn is replaced by Ca by the addition of Ca. In this MnS, part of Mn is Ca
The properties change depending on the degree of substitution. Sulfide with Ca in the range of 0.1 to 10% forms a film for protecting the tool at the time of cutting, but when it is less than 0.1% of the entire sulfide, the effect of containing Ca is poor and the tool is poor. Since the protective film is not formed, the effect of improving the tool life cannot be obtained, and if it exceeds 10%, CaS having a high melting point becomes excessive and the tool protective film is not formed, and the productivity is deteriorated.

In addition, sulfides having an equivalent circle diameter of 5 μm or more are used.
When there are no more than 5 pieces per 3 mm ^{2, the} tool protection film formed is small in amount, so that the entire surface of the tool is not completely covered, and the tool life improvement effect is small. Therefore, in the present invention, it is assumed that the sulfide component contains 0.1 to 10% of Ca, the size thereof is 5 μm or more, and the density is 5 or more per 3.3 mm ^2. To identify.

The free-cutting steel of the present invention can be produced in the same manner as a conventional free-cutting steel containing Ca, and can be produced by either an ingot ingot ingot casting method or a continuous casting method. In addition, the free-cutting steel of the present invention can be used for all applications conventionally known as free-cutting steel applications, such as machine structural parts that are subjected to roughing by plastic working such as forging and then cutting. it can.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

EXAMPLE A steel of Examples and Comparative Examples of the present invention having the component compositions shown in Table 1 below was used in a 5-ton arc furnace or 150 kg.
It was melted in a high-frequency vacuum induction furnace, cast while investigating pouring properties, and the ingot obtained by casting was rolled or forged into a round bar having a diameter of 90 mm. In addition to investigating the hot workability of this round bar, the presence or absence of internal defects was tested, and the results are shown in Table 3 below.

The above-mentioned pouring properties were evaluated as poor when the casting nozzle was blocked by the precipitation of the high melting point material during casting and the casting could not be continued with 10% of the entire casting amount, and the others were good. . Further, the hot workability was evaluated as poor when the amount of defects caused by surface flaws after hot rolling or hot forging exceeded 5% of the total amount of rolling or forging, and the others were regarded as good. In addition, the internal defects were obtained by heating a rolled or forged round bar at 500 ° C. for 30 minutes, cooling, and visually observing Pb,
Exudation of Bi was observed (perspiration test). Those with abnormalities were regarded as having, and the others were regarded as having no.

[0026]

[Table 1]

Thereafter, the above-mentioned round bar having a diameter of 90 mm was inserted into the
After normalizing at 870 ° C, test specimen for impact test,
A sample for testing machinability and a sample for evaluating sulfides were cut out, and the following impact test, tool life test and evaluation of sulfides were performed using these test pieces or samples. It is described in Table 3. The impact test was performed using JIS No. 3 test pieces according to JIS Z 2242.
Was performed according to

In the tool life test, a cutting test was performed under the conditions shown in Table 2 below. The tool life time obtained in this test was set to 1 as the tool life time of No. 1 of the comparative example, and each tool life time ratio was calculated and set as each tool life ratio. In addition, the evaluation of sulfide was carried out by using the above sample as a microscope sample and visually checking the sample in 3.3 mm ² (3 times with a microscope of 100 times).
The number of sulfides having a circle equivalent diameter of 5 μm or more (equivalent to about 0 visual field) was investigated, and the components of five sulfides arbitrarily selected from each sample were analyzed.
The number of sulfides in the range was determined.

[0029]

[Table 2]

[0030]

[Table 3]

From these results, the free-cutting steel of the present invention has a turning tool life of 6.3 to 310 times that of No. 1 of the comparative example, while the free-cutting steel of the comparative example has a life of 0.2 to 310 times. It was 99 times. In addition, the free-cutting steel of the present invention had good pouring properties, hot workability, internal quality and toughness, while those of the comparative examples showed turning tool life, pouring properties and hot working properties. There were drawbacks in either workability, internal quality or toughness.

Next, individual consideration will be made. Comparative Example No. 6, which has a higher S content than the free-cutting steel of the present invention, is inferior in pouring properties, hot workability and impact value. In addition, No. 7 of Comparative Example in which the Al content was smaller than that of the free-cutting steel of the present invention had a tool life ratio of 3.1 and was inferior in machinability. Also, No. 8 of the comparative example having a large content thereof has a tool life ratio of 0.8 and is inferior in machinability.

No. 1 of Comparative Example having a Ca content lower than that of the free-cutting steel of the present invention has a tool life ratio of 1.0 and is inferior in machinability. Further, Comparative Example No. 9 in which the Ca content is larger than the free-cutting steel of the present invention has good machinability but poor pouring properties. In Comparative Example No. 10 having an O content lower than that of the free-cutting steel of the present invention, the pouring property was inferior, the tool life ratio was 2.3, and the machinability was inferior. Also, No. 11 of Comparative Example in which the O content is higher than that of the free-cutting steel of the present invention has a tool life ratio of 1.5 and is poor in machinability.

No. 12, No. 13 and No. 13 of Comparative Examples in which Cr, Mo, S, Ti, Bi or Te are higher than the free-cutting steel of the present invention.
No. 15 is inferior in hot workability, and No. 12 in Comparative Example, which contains more Ti, is inferior in machinability. Also,
No. 16 and No. 17 of Comparative Examples not containing 5 or more sulfides having a circle equivalent diameter of 5 μm or more containing 0.1 to 10% of Ca per 3.3 mm ² had a tool life ratio of 2.1. 1.2
And the machinability is inferior.

[0035]

The free-cutting steel according to the present invention, having the above-described configuration, has an excellent effect that the machinability is small and the machinability is higher than that of the conventional steel.

Claims (8)

[Claims] 1. C: 0.05-% by weight (the same applies hereinafter)
0.8%, Si: 0.01 to 2.5%, Mn: 0.1 to
3.5%, P: 0.001 to 0.2%, S: 0.005
-0.4%, Al: 0.001-0.1%, Ca: 0.
0005-0.02%, O: 0.0005-0.01%
And the balance consists of Fe and unavoidable impurities, and contains at least 5 sulfides having an equivalent circle diameter of 5 μm or more per 3.3 mm ² containing 0.1 to 10% of Ca. Free cutting steel. 2. C: 0.05-0.8%, Si: 0.0
1 to 2.5%, Mn: 0.1 to 3.5%, P: 0.00
1 to 0.2%, S: 0.005 to 0.4%, Al: 0.
001-0.1%, Ca: 0.0005-0.02%,
O: 0.0005-0.01%, Cr:
≦ 3.5%, Mo: ≦ 2.0%, Cu: ≦ 2.0%, N
i: ≦ 4.0% and B: one or more of 0.0003 to 0.01%, the balance being Fe and unavoidable impurities, and 0.1 to 10% of Ca A free-cutting steel characterized in that it contains 5 or more sulfides having an equivalent circle diameter of 5 μm or more per 3.3 mm ² . 3. C: 0.05-0.8%, Si: 0.0
1 to 2.5%, Mn: 0.1 to 3.5%, P: 0.00
1 to 0.2%, S: 0.005 to 0.4%, Al: 0.
001-0.1%, Ca: 0.0005-0.02%,
O: 0.0005 to 0.01%, and further Nb:
≦ 0.2%, Ti: ≦ 0.2%, V: ≦ 0.5%, T
a: ≦ 0.5% and Zr: a circle containing one or more of 0.5%, the balance being Fe and unavoidable impurities, and containing 0.1 to 10% Ca A free-cutting steel containing at least 5 sulfides having an equivalent diameter of 5 μm or more per 3.3 mm ² . 4. C: 0.05-0.8%, Si: 0.0
1 to 2.5%, Mn: 0.1 to 3.5%, P: 0.00
1 to 0.2%, S: 0.005 to 0.4%, Al: 0.
001-0.1%, Ca: 0.0005-0.02%,
O: 0.0005-0.01%, Cr:
≦ 3.5%, Mo: ≦ 2.0%, Cu: ≦ 2.0%, N
i: ≦ 4.0% and B: one or more of 0.0003 to 0.01%, and Nb: ≦ 0.
2%, Ti: ≦ 0.2%, V: ≦ 0.5%, Ta: ≦
0.5% and Zr: one or more of 0.5%, the balance being Fe and an unavoidable impurity part, and a circle-equivalent diameter of 5 μm containing 0.1 to 10% of Ca.
free-cutting steel characterized by containing m or more sulfide 3.3 mm ² per 5 or more. 5. C: 0.05-0.8%, Si: 0.0
1 to 2.5%, Mn: 0.1 to 3.5%, P: 0.00
1 to 0.2%, S: 0.005 to 0.4%, Al: 0.
001-0.1%, Ca: 0.0005-0.02%,
O: 0.0005 to 0.01%, and Pb:
≦ 0.4%, Bi: ≦ 0.4%, Se: ≦ 0.5%, and Te: One or more of 0.1%, with the balance being Fe and unavoidable impurities And 0.
A free-cutting steel characterized by containing 5 or more sulfides having a circle equivalent diameter of 5 μm or more containing 1 to 10% of Ca per 3.3 mm ² . 6. C: 0.05-0.8%, Si: 0.0
1 to 2.5%, Mn: 0.1 to 3.5%, P: 0.00
1 to 0.2%, S: 0.005 to 0.4%, Al: 0.
001-0.1%, Ca: 0.0005-0.02%,
O: 0.0005-0.01%, Cr:
≦ 3.5%, Mo: ≦ 2.0%, Cu: ≦ 2.0%, N
i: ≦ 4.0% and B: one or more of 0.0003 to 0.01%, and Pb: ≦ 0.
4%, Bi: ≦ 0.4%, Se: ≦ 0.5% and T
e: contains one or more of 0.1%, the balance being Fe and inevitable impurities, and 0.1 to 1
A free-cutting steel characterized by containing at least 5 sulfides having a circle equivalent diameter of 5 μm or more containing 0% Ca per 3.3 mm ² . 7. C: 0.05-0.8%, Si: 0.0
1 to 2.5%, Mn: 0.1 to 3.5%, P: 0.00
1 to 0.2%, S: 0.005 to 0.4%, Al: 0.
001-0.1%, Ca: 0.0005-0.02%,
O: 0.0005 to 0.01%, and further Nb:
≦ 0.2%, Ti: ≦ 0.2%, V: ≦ 0.5%, T
a: ≦ 0.5% and Zr: contain one or more of 0.5%, Pb: ≦ 0.4%, Bi: ≦
0.4%, one or more of Se: ≦ 0.5% and Te: 0.1%, the balance being Fe and inevitable impurities, and 0.1 to 10% A free-cutting steel characterized in that it contains 5 or more sulfides containing Ca and having an equivalent circle diameter of 5 μm or more per 3.3 mm ² . 8. C: 0.05-0.8%, Si: 0.0
1 to 2.5%, Mn: 0.1 to 3.5%, P: 0.00
1 to 0.2%, S: 0.005 to 0.4%, Al: 0.
001-0.1%, Ca: 0.0005-0.02%,
O: 0.0005-0.01%, Cr:
≦ 3.5%, Mo: ≦ 2.0%, Cu: ≦ 2.0%, N
i: ≦ 4.0% and B: one or more of 0.0003 to 0.01%, and Nb: ≦ 0.
2%, Ti: ≦ 0.2%, V: ≦ 0.5%, Ta: ≦
One or more of 0.5% and Zr: 0.5% are contained, and Pb: ≤ 0.4%, Bi: ≤
0.4%, one or more of Se: ≦ 0.5% and Te: 0.1%, the balance being Fe and inevitable impurities, and 0.1 to 10% A free-cutting steel characterized in that it contains 5 or more sulfides containing Ca and having an equivalent circle diameter of 5 μm or more per 3.3 mm ² .