JP2647325B2 - Graphite free-cutting steel with excellent cold forgeability - Google Patents

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 containing graphite as a main free-cutting element, and more particularly to a free-cutting steel excellent in cold forgeability.

[0002]

2. Description of the Related Art Graphite is known to exhibit excellent lubricity due to weak interlayer bonding force, and is widely used as a lubricant. For example, they are used for self-lubricating friction parts such as sliding bearings, seal materials, current collecting brushes, and self-lubricating plastics. Graphite in cast iron is used as free-cutting precipitate.

[0003] Lead, bismuth, MnS, Ca-based oxides and the like are well known as free-cutting precipitates for improving the machinability of steel.
3, vol. 30 (1966), 279 and No. 1
2, vol. 52 (1988) and 1285, it was first reported in 1966 that the dispersibility of graphite in ferrite ground improved the machinability of steel. Since then, a number of research reports have been made on the effects of graphite on machinability, and further on practical application, see JP-B-54-30.
No. 366 discloses a graphite free-cutting steel excellent in cold forgeability.

[0004] However, graphite free-cutting steel based on these findings minimizes free-cutting elements that impair cold forgeability, and therefore has a disadvantage in terms of finished surface roughness, which is a characteristic required for free-cutting steel. There's a problem. Due to this drawback, it has not yet been manufactured and sold on an industrial scale. The development of a graphite free-cutting steel having both the properties of cold forgeability and finished surface roughness has been strongly desired by the industry.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention has newly found a method for improving cold forgeability without sacrificing the machinability of graphite free-cutting steel. Provide graphite free-cutting steel with excellent properties.

[0006]

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems, and the gist of the present invention is that the chemical component value is expressed by weight%.
As indications: (1) C: 0.20 to 1.0%, Si: 0.55 to 1.
2%, Mn: 0.3 to 1.0%, P: 0.02% or less,
S: 0.025 to 0.035% , the balance being iron and
Graphite having an average cross-sectional area of ² to 15 μm ² , which is composed of unavoidable impurities,
Graphite free-cutting steel excellent in cold forgeability, characterized by having 1.0%. (2) C: 0.20-1.0%, Si: 0.55-1.
2%, Mn: 0.3 to 1.0%, P: 0.02% or less,
S: containing from 0.025 to 0.035%, further, P
One or two of b and Bi are contained in an amount of 0.05 to 0.35%, the balance being iron and unavoidable impurities, and the ferrite matrix has an average sectional area of ^{2 to} 15 μm ^2.
Graphite free-cutting steel excellent in cold forgeability, characterized by having a graphite content of 0.20 to 1.0%. (3) C: 0.20-1.0%, Si: 0.55-1.
2%, Mn: 0.3 to 1.0%, P: 0.02% or less,
S: 0.025 to 0.035% , and T
One or two of e and Se are contained in an amount of 0.002 to 0.02%, the balance being iron and unavoidable impurities, and the ferrite matrix has an average sectional area of 2 to 15 μm.
^2. A graphite free-cutting steel excellent in cold forgeability, characterized by having 0.20 to 1.0% of graphite of No. ² . (4) C: 0.20-1.0%, Si: 0.55-1.
2%, Mn: 0.3 to 1.0%, P: 0.02% or less,
S: 0.025-0.035%, B: 0.001-0.
004%, N: 0.002-0.01% , balance
Which is composed of iron and unavoidable impurities, and has 0.20 to 1.0% of graphite having an average sectional area of ² to 15 μm ^{2 in} a ferrite matrix. Cutting steel. (5) C: 0.20-1.0%, Si: 0.55-1.
2%, Mn: 0.3 to 1.0%, P: 0.02% or less,
S: 0.025-0.035%, B: 0.001-0.
004%, N: 0.002 to 0.01%.
In addition, one or two of Pb and Bi are 0.05 to 0.35
%, The balance being iron and unavoidable impurities, and in the ferrite matrix, the average cross-sectional area: 2-1.
A graphite free-cutting steel excellent in cold forgeability, comprising 0.20 to 1.0% of graphite of 5 μm ² . (6) C: 0.20-1.0%, Si: 0.55-1.
2%, Mn: 0.3 to 1.0%, P: 0.02% or less,
S: 0.025-0.035%, B: 0.001-0.
004%, N: 0.002 to 0.01%, and one or two of Te and Se are added in an amount of 0.002 to 0.02%.
2%, with the balance being iron and unavoidable impurities and having an average cross-sectional area of 2 to 1 in the ferrite matrix.
It is a graphite free-cutting steel excellent in cold forgeability, characterized by having 0.20% to 1.0% of graphite of 5 μm ² . That is, as a result of various studies, the present inventors first clarified the cause of the poor finished surface roughness of the currently proposed graphite free-cutting steel having excellent cold forgeability. By the graphitization, the microstructure of the steel changes from a two-phase structure of ferrite and pearlite to one phase of ferrite in which graphite is dispersed. As a result, it has been found that the finished surface roughness is particularly poor because the cutting tool and the ferrite adhere to each other and further grow to form the constituent cutting edge. Thus, it was found that adhesion and formation of the cutting edge should be suppressed in order to improve the finished surface roughness.

[0007] One way to prevent adhesion is to insert a lubricant at the interface between the ferrite phase and the tool. As a specific method, Pb,
It has been clarified that it is effective to form a film such as Bi, MnS, MnTe, and MnSe. Next, the S, Pb, Bi, Te, Se contents and the dimensions of graphite which do not impair the cold forgeability of the duplex stainless steel of graphite and ferrite were clarified, and both the characteristics of the cold forgeability and the finished surface roughness were determined. The present invention has been achieved as a result of the successful provision at the same time.

The reasons for defining the scope of the steel of the present invention as described above will be described below. Regarding item (1), C is an indispensable element for producing graphite, and from the viewpoint of securing a certain amount of graphite effective for tool life, its lower limit is set to 0.1.
Limited to 2%. The upper limit is set to 1% or less in order to prevent a decrease in workability during hot rolling or hot forging and generation of surface scratches.

[0009] Si is an essential element because it has a small bonding force with carbon atoms in steel and is one of the powerful elements that promotes graphitization. Although quenching and long-time annealing treatment are required for graphitization, it is necessary to add Si to shorten the annealing time for cost reduction, and the lower limit is 0.55%. Must be limited. The reason for limiting the upper limit to 1.2% is to ensure workability during hot forging.

Mn requires an amount obtained by adding an amount necessary for fixing and dispersing sulfur in steel as MnS and an amount necessary for securing solid strength by dissolving it in a matrix, and the lower limit is 0. 0.3%. If the amount of Mn increases, machinability is impaired, so the upper limit was set to 1.0%. Since P is present in the steel as a phosphorus compound precipitated at the grain boundaries and as P dissolved in ferrite, the machinability is improved and the hot workability is significantly impaired.
2%.

S bonds with Mn and exists as MnS inclusions. When the amount of MnS inclusions in steel increases, tool and MnS
The chance of contact with inclusions increases, and the MnS inclusions plastically deform on the tool rake face to form a coating. as a result,
Adhesion is suppressed because the chance of contact between the ferrite and the tool is reduced. In order to suppress the adhesion, the lower limit of S needs to be 0.025%. The upper limit is set to 0.035% from the viewpoint of cold workability.

[0012] The amount of graphite and the average cross-sectional area are determined by tool life and finish.
It is the most important factor that governs surface roughness. C in steel
Since almost the entire amount is graphitized, the amount of graphite is almost equal to the C content.
equal. Therefore, the reason for limiting the amount of graphite was described in the section of C%.
The reason is exactly the same. Larger average cross-sectional area of graphite
And the cold workability decreases, the upper limit is 15 μm ^Two
Is limited to When the average cross-sectional area of graphite becomes extremely small
The effect of free-cutting elements is lost in steels of this composition.
And the lower limit is 2 μm^TwoIt is necessary to

Next, the reasons for limiting the components in item (2) of the present invention will be described. C, Si, Mn, P, S and graphite are exactly the same as item (1). Pb and Bi are elements that remarkably improve the finished surface roughness because they have an action of suppressing adhesion at the interface between the tool and the work material. However, if the content is less than 0.05%, the effect is small, and 0.35% If the ratio exceeds the limit, the cold and hot workability deteriorates. Therefore, the upper limit is set to 0.35% and the lower limit is set to 0.05%.

Regarding the reasons for limiting the components in the item (3) of the present invention, C, Si, Mn, P, S and graphite are exactly the same as the item (1). Te and Se are elements that remarkably improve the finished surface roughness because they have the effect of suppressing adhesion at the interface between the tool and the work material. However, if less than 0.002%, the effect is small, and 0.02%. If the ratio exceeds 1, the cold and hot workability deteriorates. Therefore, the upper limit was made 0.02% and the lower limit was made 0.002%.

Regarding the reasons for limiting the components in the item (4) of the present invention, C, Si, Mn, P, S and graphite are exactly the same as those in the item (1). B and N produce BN which shortens the time of graphitizing annealing. In order to obtain a sufficient shortening effect, 0.001% or more of B must be added.
If the B content exceeds 0.004%, the shortening effect is saturated, so the upper limit was made 0.004%. N is 0.001
0.004% The amount required to convert B into BN, that is, 0.
002 to 0.01%.

As to the reasons for limiting the components in the item (5) of the present invention, C, Si, Mn, P, S and graphite are exactly the same as in the item (1). B and N are the same as the item (4), and Pb and Bi are the same as the item (2). As to the reasons for limiting the components in the item (6) of the present invention, C, S
i, Mn, P, S, and graphite are exactly the same as in the item (1). B and N are the same as the item (4), and Te and Se are the same as the item (3).

Here, means for producing the steel of the present invention will be described. The steel of the present invention can be easily produced by ordinary steel making and rolling processes. This is a method in which the steel is quenched immediately after the end of rolling, and then annealed in a heating furnace for a long time. Next, the effects of the present invention will be described more specifically with reference to examples.

[0018]

EXAMPLES Tables 1 and 2 show the chemical composition of the test steel, the average sectional area of graphite, the cutting performance, the cold workability and the surface condition after hot working. The average cross-sectional area of graphite is 1 in the steel rolling direction.
It was determined by dividing the total cross-sectional area of graphite contained in a square mm by the total number of graphite. The cross-sectional area of each graphite was 20
0 using an optical microscope.

[0019]

[Table 1]

[0020]

[Table 2]

The cutting test method is as follows. Cutting method: Turning by lathe, Cutting condition: V = 130m /
min, d = 2.0 mm, f = 0.15 mm / rev, tool shape: (−6, −6,6,6,15,15,0.8), tool material type: Al ₂ O ₃ —TiCN— A cemented carbide tool coated with TiC by CVD, lubricating oil: 71 / min. The finished surface roughness was measured by a contact type roughness meter.

The forgeability was evaluated by a cold upsetting test. The test conditions are as follows. Test piece shape: 20mmφ
× 30 mmh, compression ratio: 6 steps in steps of 5% from 40 to 65%, number of test repetitions: 10, the maximum compression ratio at which the crack occurrence ratio is less than 50% is defined as the limit compression ratio, and the cooling value is determined by the value. The quality of the forging property was determined. The cold forgeability of the graphite steel of the present invention is remarkably superior to that of the graphite steel-free carbon steel for machine structural use S55C equivalent (K, L), and the finished surface roughness is equivalent. The comparative graphite free-cutting steel (M, N, P) is inferior to the graphite free-cutting steel of the present invention in either cold forgeability or finished surface rust after hot working.

[0023]

As is clear from the above embodiments, according to the present invention, it is possible to provide a graphite ultra-free-cutting steel having remarkably excellent cold forgeability and cut surface roughness. The effect is extremely remarkable.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-63651 (JP, A) JP-A-49-103817 (JP, A) JP-B-54-11773 (JP, B2) JP-B-54- 5367 (JP, B2)

Claims (6)

(57) [Claims] As claimed in claim 1 the weight percentage, C: 0.20~1.0%, Si: 0.55~1.2%,
Mn: 0.3-1.0%, P: 0.02% or less, S:
0.025-0.035% , the balance being iron
Graphite having an average cross-sectional area of ² to 15 μm ^{2 in} a ferrite matrix.
Graphite free-cutting steel excellent in cold forgeability, characterized by having 0%. 2. C: 0.20 to 1.0%, Si: 0.55 to 1.2%, expressed as% by weight .
Mn: 0.3-1.0%, P: 0.02% or less, S:
0.025-0.035% , and Pb, B
one or two i contain from 0.05 to 0.35%, residual
Characterized in that the portion is made of iron and unavoidable impurities, and has 0.20 to 1.0% of graphite having an average cross-sectional area of ² to 15 μm ^{2 in} a ferrite matrix. Free cutting steel. 3. As % by weight, C: 0.20 to 1.0%, Si: 0.55 to 1.2%,
Mn: 0.3-1.0%, P: 0.02% or less, S:
0.025-0.035% , and further, Te, S
e contains one or two of 0.002 to 0.02%,
A graphite excellent in cold forgeability, characterized in that the balance consists of iron and unavoidable impurities, and that the ferrite matrix has 0.20 to 1.0% of graphite having an average sectional area of ² to 15 m2. Free cutting steel. 4. C .: 0.20 to 1.0%, Si: 0.55 to 1.2%, expressed as% by weight .
Mn: 0.3-1.0%, P: 0.02% or less, S:
0.025 to 0.035%, B: 0.001 to 0.00
4%, N: 0.002-0.01% , the balance being iron
And it becomes unavoidable impurities, and, in the ferrite matrix, the average cross-sectional area: graphite 2 to 15 [mu] m ² 0.2
Graphite free-cutting steel excellent in cold forgeability, characterized by having 0 to 1.0%. 5. The method of claim 2 , wherein C: 0.20 to 1.0%, Si: 0.55 to 1.2%,
Mn: 0.3-1.0%, P: 0.02% or less, S:
0.025 to 0.035%, B: 0.001 to 0.00
4%, N: 0.002 to 0.01% ,
One or two of Pb and Bi are contained in an amount of 0.05 to 0.35%, the balance being iron and unavoidable impurities, and the ferrite matrix has an average sectional area of 2 to 15 μm.
^2. A graphite free-cutting steel excellent in cold forgeability, characterized by having 0.20 to 1.0% of graphite of No. ² . As claimed in claim 6 weight percentage, C: 0.20~1.0%, Si: 0.55~1.2%,
Mn: 0.3-1.0%, P: 0.02% or less, S:
0.025 to 0.035%, B: 0.001 to 0.00
4%, N: 0.002 to 0.01% ,
0.002 to 0.02% of one or two of Te and Se
Contain, the balance being iron and unavoidable impurities, and
Average cross-sectional area in ferrite matrix: 2 to 15μ
Excellent graphite cutting steel cold forgeability, characterized in that it has a 0.20 to 1.0% graphite m ^2.