JP3063379B2 - Super free-cutting steel with excellent hot workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates not only to machinability but also to machinability.
The present invention relates to a super free-cutting steel excellent in hot workability.

[0002]

2. Description of the Related Art Ultra-free-cutting steel having good machinability is widely used as a material for components requiring high precision, such as OA equipment, household electric equipment, cameras and watches. And in such super free cutting steel, in order to improve its machinability,
Generally, free-cutting elements such as Pb, Se, and Te are added.

[0003] However, these free-cutting elements have a drawback that they have a wide hot embrittlement region, are easily cracked when the steel material temperature is lowered during slab rolling, and are liable to generate surface flaws during working. In order to correct such defects, conventionally, measures such as raising the soaking temperature or increasing the temperature during rolling by reducing the amount of cooling water during rolling have been adopted to prevent the occurrence of cracks and surface flaws. ing. However, in these means, a new problem arises in that a large amount of fuel is consumed in order to increase the soaking temperature, resulting in an increase in cost, and a high steel material temperature resulting in a shortened life of the rolling roll.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and an object of the present invention is to provide excellent hot workability and prevent surface flaws from being generated during processing. An object of the present invention is to provide a small amount of super free cutting steel.

[0005]

The ultra-free-cutting steel of the present invention, which has achieved the above-mentioned objects, is C: 0.2% or less, Si: 0.4% or less.
% Or less, Mn: 0.7 to 1.5%, P: 0.01 to 0.
2%, S: 0.1 to 0.4%, O: 0.01 to 0.03
%, Al: less than 0.002%, Pb: 0.01 to 0.4
9%, B: 0.0005 to 0.0035%, N: 0.0
The present invention has a gist in that it contains 0.3 to 0.03% and the balance is Fe and unavoidable impurities.

[0006]

The present invention is constructed as described above.
By strictly defining the general alloy composition range of ultra-free-cutting steel and adding an appropriate amount of B, hot workability is reduced by Pb (including Se and Te in some cases) which is a free-cutting element. It has been found that the above-mentioned disadvantages can be suppressed and excellent hot workability can be ensured. Next, the reason for adding the alloy component and the reason for limiting the composition range in the present invention will be described.

C: 0.2% or less C is an element necessary for securing strength, but if contained in a large amount, machinability, which is important as a free-cutting steel, deteriorates.
The upper limit was 0.2%. Si: 0.4% or less Si is added for the purpose of deoxidizing a steel material. However, when added in a large amount, sulfide is extremely reduced and machinability is reduced, so the upper limit was made 0.4%.

Mn: 0.7-1.5% Mn is added for improving hot workability. If it is less than 0.7%, its effect is not exhibited, and surface flaws are easily generated during hot rolling. . On the other hand, if added excessively, the strength becomes too high and adversely affects the machinability, so the content should be 1.5% or less. P: 0.01 to 0.2% P is an element that improves the finished surface of steel, and the amount of P added is 0.
If it is less than 01%, the improvement effect is not exhibited. On the other hand, even if it exceeds 0.2%, the effect is saturated.

S: 0.1 to 0.4% S must be added in an amount of 0.1% or more in order to improve machinability. However, excessive addition of S deteriorates cold forgeability. %. O: 0.01 to 0.03% When the O content is less than 0.01%, MnS is extended by rolling to reduce the machinability, and when added in excess of 0.03%, plastic deformation is caused. The performance decreases and the machinability decreases.

Al: less than 0.002% Al is likely to combine with oxygen in steel to form Al ₂ O ₃ -based inclusions, shorten tool life, and cause sulfides to precipitate on austenite grain boundaries to reduce surface roughness. Cracks are easily generated.
Should be less than 002%. Pb: 0.01 to 0.49% Pb is a machinability improving element, but it is necessary to contain 0.01% or more in order to exert its effect. However, if it is contained excessively, it has a significant adverse effect on hot workability and the effect of improving machinability is saturated, so that 0.49%
Should be:

B: 0.0005-0.0035% Pb, Se and Te form a low melting point eutectic compound,
It causes grain boundary embrittlement and easily causes grain boundary cracking,
B exerts an effect of suppressing the precipitation and growth of these compounds at the grain boundaries. To achieve these effects,
Although it is necessary to contain 0.0005% or more,
Even if the content exceeds 0.0035%, the effect is saturated.

N: 0.003 to 0.03% A part of the work material is work hardened during the cutting, and agglomerated on the tool edge is called a component edge. When the content is less than 0.003%, the amount of the formed cutting edge is excessively increased, and as a result, the unevenness of the tool cutting edge is eliminated, and the tool cutting edge is transferred to the surface after cutting, and the finished surface roughness becomes rough. On the other hand, as the content of N increases, the amount of the formed cutting edge decreases, but if the content exceeds 0.03%, the surface flaw increases. The ultra-free-cutting steel of the present invention contains the above elements as basic components, and the balance consists of Fe and unavoidable impurities. From the viewpoint of improving the machinability, the degree to which the hot workability is not reduced is considered. To
One or two elements selected from the group consisting of Se and Te can be contained. Each content when these elements are contained is as follows.

Se: 0.01 to 0.1% As described above, Se is an element for improving machinability, but in order to exhibit its effect, it is necessary to contain 0.01% or more. However, if it is contained excessively, the mechanical strength as a steel material becomes unsatisfactory and the effect of improving machinability is saturated, so the content should be 0.1% or less.

Te: 0.01 to 0.1% Te is a machinability improving element like Se, but it is necessary to contain 0.01% or more in order to exert its effect. However, Te is an expensive element, and if it is contained excessively, it significantly affects hot workability and saturates the machinability improving effect, so it should be 0.1% or less.

The ultra-free-cutting steel of the present invention may be manufactured according to a conventional method, and the manufacturing method is not particularly limited. For example, a steel material that satisfies the above requirements is manufactured by a continuous casting method or an ingot casting method, the obtained slab or steel ingot is soaked, then rolled to a steel slab, and then heat-treated again to obtain a wire or a bar. By rolling, free-cutting steel with few surface defects can be obtained.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and any design changes in the spirit of the present invention will be described below. It is included in the range.

[0017]

EXAMPLE A trial steel having the chemical composition shown in Table 1 (inventive steel) and Tables 2 and 3 (comparative steel) was melted and cast, and after being lumped, the diameter was 9 mm.
It was rolled into a coil of mmφ and cold-drawn until it finally became a steel bar having a diameter of 8 mmφ. For these steels, the presence or absence of surface flaws was investigated for machinability. The results are shown in Tables 1 to 3. In addition, the presence or absence of surface flaws was determined by inspecting the surface flaws of the obtained bar material using a magnetic flaw detector. The surface quality index was set to 28 (Table 2), and the surface quality of other steels was shown as an absolute value. The surface quality index was calculated as follows.

<Surface quality index> Surface quality index = {[Pass rate (%) of prototype steels other than No. 28]-[N
o.28 pass rate (%)]} / [No.28 pass rate (%)] × 5 On the other hand, the machinability is determined by cutting a specified number of test pieces using an automatic lathe. Of the finished surface was evaluated, and No. 1 having the worst finished surface roughness was evaluated. 15 (Table 2)
Was set as the machinability index 1, and the surface quality of other steels was shown as a relative value. The machinability index was calculated as follows. <Machinability index> Machinability index = [Roughness of finished surface of No.15 (μm)] / [N
Finished surface roughness of prototype steel other than o.15 (μm)]

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

[0022]

According to the present invention, an ultra-free-cutting steel excellent in hot workability and having few surface flaws at the time of working can be obtained.

Continuation of front page (56) References JP-A-1-298138 (JP, A) JP-A-64-55365 (JP, A) JP-A-4-52266 (JP, A) JP-A-2-73950 (JP) JP-A-62-196361 (JP, A) JP-A-63-241113 (JP, A) JP-A-1-188622 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) C22C 38/00 301 C22C 38/60

Claims (2)

(57) [Claims] 1. C: 0.2% or less (meaning by weight%, the same applies hereinafter), Si: 0.4% or less, Mn: 0.7 to 1.5
%, P: 0.01 to 0.2%, S: 0.1 to 0.4%,
O: 0.01 to 0.03%, Al: less than 0.002%,
Pb: 0.01-0.49%, B: 0.0005-0.
An ultra-free-cutting steel excellent in hot workability, characterized by containing 0035% and N: 0.003 to 0.03%, respectively, and the balance being Fe and unavoidable impurities. 2. In addition, 1 selected from the group consisting of Se: 0.01 to 0.1% and Te: 0.01 to 0.1%.
The ultra-free-cutting steel according to claim 1, wherein the steel contains one or two kinds.