JP3778140B2 - Free-cutting steel - Google Patents

Description

【００４２】
【表２】

【００４３】
表２に示すとおり、No.1〜No.14の発明鋼は、いずれも超硬工具寿命が14.8〜37.Ominと優れた工具寿命が得られ、No.25の従来鉛添加鋼JIS SUM24Lの12.4minに比べて非常に良好な寿命が得られている。切りくず形状に関してもいずれも長さが５mm以下と細かな良好な切りくずが得られている。
【００４４】
これに対し、No.15〜No.23の比較鋼のうち、No.15はＣが範囲外であり、擬ポリゴナルフェライト組織が得られなくなった結果、発明鋼に比べて超硬工具寿命が著しく低下し、切りくず形状も劣化している。No.16は、SiおよびＯが、この発明の範囲外であるため、工具寿命が低下し切りくず形状が劣化している。No.17は、Mnがこの発明の上限より高いため、工具寿命が低下している。No.18は、Mnがこの発明の下限よりも低いため、擬ポリゴナルフェライト組織分率が低下して範囲外となり、工具寿命および切りくず形状が劣化している。No.19は、Ｐが発明の上限より高いため、圧延時に熱間割れが発生したため圧延を中止し、評価不能であった。No.20は、Ｓが発明の上限より高いため、圧延時に熱間割れが発生したため圧延を中止し、評価不能であった。No.21は、Ｓがこの発明の下限より低いため、工具寿命が低下し、切りくず形状が劣化している。No.22は、Nbがこの発明の上限より高いため、工具寿命が低下している。No.23は、Ｏがこの発明の上限より高いため、鋼塊に内部欠絶が発生し圧延不能であったため、評価不能であった。No.24は、鋼記号11の鋼に制御圧延および制御冷却を施さずに製造したところ、擬ポリゴナルフェライト組織分率がこの発明の下限以下となった場合であり、工具寿命が低下し、切りくず形状も劣化している。
【００４５】
【発明の効果】
以上述べたように、この発明によれば、鉛を添加せずとも、圧延のままの状態で、鉛添加快削鋼と同等以上の被削性を有する、鋼材を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a free-cutting steel excellent in machinability such as tool life and chip disposal in cutting.
[0002]
[Prior art]
Conventionally, as free-cutting steel with excellent tool life and chip control during cutting, sulfur free-cutting steel and lead free-cutting steel specified in JIS G4804, or other calcium free-cutting steel and tellurium free-cutting steel Various free cutting steels such as steel, selenium free cutting steel or bismuth free cutting steel have been developed. Among these, lead free-cutting steel is frequently used as free-cutting steel because it has excellent machinability and is economical compared to tellurium, bismuth and the like. However, since lead is harmful to the human body, not only a steel material manufacturing process but also a mechanical part manufacturing process using the lead material requires a large exhaust facility, and there is also a problem in terms of steel recycling. For this reason, conventionally, the development of free-cutting steel having machinability equivalent to that of lead-added steel without adding lead has been desired.
[0003]
In response to the above requirements, for example, in Japanese Patent Laid-Open No. 50-96416, C in steel is present as graphite, and by utilizing the notch lubrication action of this graphite, it is possible to cut without using lead. A method for improving performance is disclosed. However, this method is not necessarily an economical method because heat treatment is indispensable as a pretreatment for graphitizing C in steel.
[0004]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to propose a free-cutting steel that is excellent in machinability while being rolled without using lead.
[0005]
[Means for Solving the Problems]
The inventors diligently studied the composition of a steel material having machinability equivalent to that of lead-added steel without adding lead, and as a result, the area ratio in the structure was 5% for improving machinability. It has been found that it is effective to contain at least% pseudo-polygonal ferrite.
[0006]
Here, pseudopolygonal ferrite is a structure defined by the Japan Iron and Steel Institute Basic Research Group, Bainite Research Committee, which transforms in a low-carbon steel in a shearing manner rather than ferrite and in a diffusive transformation rather than martensite. Organization. That is, in terms of the structure observed with an optical microscope, normal ferrite (polygonal ferrite) has a relatively smooth grain boundary, whereas pseudopolygonal ferrite has a shape with irregularly angular boundaries. Become. Pseudopolygonal ferrite contains more dislocations and higher dislocation density than polygonal ferrite.
[0007]
This pseudo-polygonal ferrite has the effect of facilitating shear deformation of steel materials when chips are generated during cutting. Therefore, chip generation is facilitated, cutting resistance is reduced, tool life and chip processability, etc. It has the effect | action which improves machinability. The remaining structure other than the pseudopolygonal ferrite may be any structure such as ferrite or pearlite, and need not be specified.
[0008]
That is, the gist of the present invention is as follows.
(1) C: less than 0.15 mass%, Si: less than 0.1 mass%, Mn: 0.1 to 4.0 mass%, S: 0.05 to 0.5 mass%, P: 0.2 mass% or less, Nb: 0.1 mass% or less, and O: 0.0015 A free-cutting steel containing ˜0.050 mass%, the balance being Fe and unavoidable impurities, and the structure containing pseudopolygonal ferrite in an area ratio of 5% or more.
[0009]
(2) In the above (1), Cu: 2.0 mass% or less, Ni: 2.0 mass% or less, Cr: 3.0 mass% or less, and Mo: 2.0 mass% or less Free-cutting steel characterized by
[0010]
(3) In the above (1) or (2), the free cutting steel further contains any one or two of W: 0.1 mass% or less and V: 0.5 mass% or less.
[0011]
(4) In the above (1), (2) or (3), Te: 0.2 mass% or less, Se: 0.2 mass% or less, Sn: 0.3 mass% or less, Zr: 0.2 mass% or less, Ca: 0.02 mass % Or less, REM: 0.03 mass% or less, Bi: 0.3 mass% or less, Sb: 0.2 mass% or less, Co: 0.1 mass% or less, N: 0.04 mass% or less Free-cutting steel characterized by
[0012]
(5) In any one of the above (1) to (4), Mg: 0.02 mass% or less, Hf: 0.1 mass% or less, and Al: 1.0 mass% or less Free-cutting steel characterized by
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, the reason why the component composition of the free cutting steel of the present invention is limited to the above range will be described.
C: Less than 0.15 mass% C is added to ensure strength. However, when 0.15 mass% or more is added, a pseudo-polygonal ferrite structure cannot be obtained, and tool wear at the time of cutting increases and machinability decreases, so the amount is limited to less than 0.15 mass%. Furthermore, in order to secure a pseudo-polygonal ferrite structure, it is preferable that the content be less than 0.10 mass%.
[0014]
Si: Less than 0.1 mass%
Si is an element effective for deoxidation, but if it is added in an amount of 0.1 mass% or more, the tool life is reduced, so it is necessary to limit it to less than 0.1 mass%. More preferably, it is less than 0.05 mass%.
[0015]
Mn: 0.1-4.0mass%
Mn combines with S or O to produce MnS or MnS-MnO composite inclusions, thereby improving the machinability. Moreover, since hardenability is improved, it is effective in ensuring strength. For this purpose, it is added at 0.1 mass% or more. On the other hand, if it exceeds 4.0 mass%, the strength is excessively increased and the machinability is lowered, so that it is limited to the range of 0.1 to 4.0 mass%. In addition, a suitable range is 0.5-2.0 mass%. More preferably, it is 1.0-2.0 mass%.
[0016]
S: 0.05-0.5mass%
S combines with Mn in steel and exists as MnS, or combines with S and O as MnS-MnO composite inclusions, and becomes a stress concentration source during cutting, making it easy to cut chips and machinability. Add to improve. However, if it is less than 0.05 mass%, the effect of addition is poor. On the other hand, if it exceeds 0.5 mass%, the hot workability is lowered, so it is limited to the range of 0.05 mass% to 0.5 mass%. In addition, a suitable range is 0.1-4 mass%.
[0017]
P: 0.2 mass% or less P is preferably added in an amount of 0.05 mass% or more in order to facilitate the propagation of cracks in the generated chips, thereby significantly improving chip disposal. However, if added over 0.2 mass%, the hot workability is lowered, so the range is limited to 0.2 mass% or less. More preferably, it is 0.1 mass% or less.
[0018]
Nb: 0.1 mass% or less
Nb promotes the formation of a pseudo-polygonal ferrite structure and improves the machinability. It is also effective for securing the strength, and can be added for this purpose. However, when added excessively, the component cost increases and the strength increases excessively, leading to a decrease in machinability, so the content is limited to a range of 0.1 mass% or less. More preferably, the addition is 0.08 mass% or less. In order to make the pseudopolygonal ferrite structure 5% or more in terms of area ratio, Nb is preferably 0.004 mass% or more.
[0019]
O: 0.0015 to 0.050 mass%
O combines with S together with Mn to form MnS-MnO complex inclusions. MnS-MnO composite inclusions are larger in steel than MnS single inclusions, and MnS-MnO composite inclusions are difficult to stretch during hot rolling and exist in a relatively spherical shape. It acts as a stress concentration source during cutting and has the effect of improving machinability. For this purpose, it is added positively, but if it is added less than 0.0015 mass%, the effect is small, while if it exceeds 0.050 mass%, internal shortage will occur in the steel soul, so 0.0015 mass% or more The range was limited to 0.050 mass% or less. More preferably, it is 0.0050 mass% or more and 0.030 mass% or less.
[0020]
In the present invention, in addition to the basic components described above, by adding or restricting the addition of a predetermined chemical component, the machinability can be further improved or the strength can be adjusted.
First, in order to increase strength or improve hardenability, Cu: 2.0 mass% or less, Ni: 2.0 mass% or less, Cr: 3.0 mass% or less and Mo: 2.0 mass% or less, one or more It is advantageous to add
[0021]
Cu: 2.0 mass% or less
Cu is effective in improving hardenability and ensuring strength. However, if added over 2.0 mass%, the strength is increased, the machinability is lowered, and the cost is increased. Therefore, the amount is limited to 2.0 mass% or less. More preferably, it is 1.0 mass% or less.
[0022]
Ni: 2.0 mass% or less
Ni can be added to ensure strength by improving hardenability. However, even if added excessively, it is expensive and the strength is increased and the machinability is lowered. Therefore, the amount is limited to 2.0 mass% or less. More preferably, it is 1.0 mass% or less.
[0023]
Cr: 3.0 mass% or less
Cr can be added because it improves hardenability and is effective in securing strength. However, if added over 3.0 mass%, the strength is increased, the machinability is lowered, and the component cost is increased, so the addition is made 3.0 mass% or less. More preferably, it is 1.5 mass% or less.
[0024]
Mo: 2.0 mass% or less
Mo can be added to ensure strength. However, when added excessively, it is expensive, and the strength is excessively increased and the machinability is lowered. Therefore, the amount is limited to 2.0 mass% or less. More preferably, it is 1.0 mass% or less.
[0025]
Next, in order to improve the strength, any one or two of W: 0.1 mass% or less and V: 0.5 mass% or less can be added.
W: 0.1 mass% or less W has an effect of improving strength by solid solution, but if added over 0.1 mass%, the machinability deteriorates, so 0.1 mass% or less is added. More preferably, it is 0.05 mass% or less. In addition, in order to improve intensity | strength by W, it is preferable to add 0.01 mass% or more.
[0026]
V: 0.5 mass% or less V has the effect of improving strength by precipitation strengthening with V (C, N), but if added over 0.5 mass%, the machinability decreases, so addition of 0.5 mass% or less And More preferably, it is 0.4 mass% or less. In addition, in order to improve intensity | strength by V, it is preferable to add 0.01 mass% or more.
[0027]
In order to further improve machinability, Te: 0.2 mass% or less, Se: 0.2 mass% or less, Sn: 0.3 mass% or less, Zr: 0.2 mass% or less, Ca: 0.02 mass% or less, REM : 0.03 mass% or less, Bi: 0.3 mass% or less, Sb: 0.2 mass% or less, Co: 0.1 mass% or less, N: 0.04 mass% or less, or one or more of them can be contained.
[0028]
Te: 0.2 mass% or less, Se: 0.2 mass% or less
Te and Se combine with Mn to form MnTe and MnSe, respectively, which act as a chip breaker, thereby improving machinability. However, if the addition exceeds 0.2 mass%, the effect is saturated and the cost of ingredients is increased. Therefore, the addition is 0.2 mass% or less. More preferably, it is 0.1 mass% or less respectively. In order to improve machinability with Te and Se, it is preferable to add 0.005 mass% or more respectively.
[0029]
Ca: 0.02 mass% or less, REM: 0.03 mass% or less, Zr: 0.2 mass% or less
Ca, REM and Zr form a sulfide together with MnS, which improves the machinability by acting as a chip breaker. However, even if Ca: 0.02 mass%, REM: 0.03 mass%, and Zr: 0.2 mass% are added, the effect is saturated and the component cost is increased. More preferably, they are Ca: 0.01 mass% or less, REM: 0.015 mass% or less, and Zr: 0.1 mass% or less.
[0030]
Bi: 0.3 mass% or less
Bi, like Pb, can be added for this purpose because it improves machinability by melting, lubrication and embrittlement during cutting. However, even if added over 0.3 mass%, not only the effect is saturated, but also the component cost increases, so the range is limited to 0.3 mass% or less. More preferably, it is 0.2 mass% or less. In addition, in order to improve machinability by Bi, it is preferable to add 0.001 mass% or more.
[0031]
Sn: 0.3 mass% or less, Sb: 0.2 mass% or less, and Co: 0.1 mass% or less
Sn, Sb and Co are elements that improve machinability by the embrittlement effect. However, Sn: 0.3mass%, Sb: 0.2mass% and Co: Even if added over 0.1mass%, the effect is saturated and the cost is increased, which is economically disadvantageous. Limit to the range. More preferably, they are Sn: 0.15 mass% or less, Sb: 0.1 mass% or less, and Co: 0.05 mass% or less.
[0032]
N: 0.04 mass% or less N has an effect of embrittlement of chips at the time of cutting, and thus has an effect of improving chip disposal and tool life. However, when added over 0.04 mass%, internal defects and surface defects of the steel ingot are generated, so 0.04 mass% or less is added. The addition is preferably 0.02 mass% or less.
[0033]
Al: 1.0 mass% or less, Mg: 0.02 mass% or less, and Hf: 0.1 mass% or less
Al, Mg, and Hf can be added because they are deoxidizing elements and become a stress concentration source and have an effect of improving machinability. However, if added excessively, the effect is saturated and the component cost increases, so the amount added is limited to the above range. More preferably, Al: 0.05 mass% or less, Mg: 0.01 mass% or less, and Hf: 0.05 mass% or less.
[0034]
Cu, Ni, Cr, Sn, Zr, Ca, REM, Sb, Co, N, Mg, Hf, and Al, all of which have the above-described effects due to the addition of a small amount, especially lower limit There is no need to provide.
[0035]
In the present invention, Pb is basically not added for the purpose, but this does not mean that it cannot be technically added. That is, if only the free-cutting property is considered, the addition is not hindered. However, even in this case, it is preferable to suppress the addition amount to about 0.25 mass% or less from the viewpoint of environmental hygiene.
[0036]
In the present invention, it is important that the pseudo-polygonal ferrite contained in the structure is 5% or more in area ratio. This is because the pseudo-polygonal ferrite has the effect of facilitating the shear deformation of the steel material when generating chips during cutting, which facilitates chip generation, resulting in reduced cutting resistance and tool life. Or it is because it has the effect | action which improves machinability, such as chip disposal.
[0037]
In order to improve machinability, it is necessary that pseudopolygonal ferrite be present in an area ratio of 5% or more, more preferably 10 mass% or more.
[0038]
Below, the manufacturing method of the free-cutting steel of this invention is demonstrated.
First, regarding the production of the raw material, after melting in a conventionally known converter or electric furnace or the like, it is made into a slab or bloom by a continuous casting method or an agglomeration / separation method. Subsequently, it is made into a predetermined shape by hot rolling. At the time of hot rolling, in order to obtain a pseudopolygonal ferrite structure of 5% or more, controlled rolling with a finish rolling of 960 ° C. or lower and / or water cooling after completion of rolling (cooling rate of 5 to 80 ° C./s) It is effective to perform controlled cooling for cooling. Then, after forming into a predetermined part shape, it is set as a machine part. In some cases, nitriding or carburizing treatment is performed to obtain a product.
[0039]
【Example】
Steels having the chemical composition shown in Table 1 were melted in a converter, made into a bloom by continuous casting, hot rolled into a 150 mm square billet, and further rolled into a 30 mmφ steel bar. In the steel bar rolling, controlled rolling or controlled cooling was performed. The machinability of the steel bar thus obtained was investigated. The results are shown in Table 2.
[0040]
Here, the machinability test was performed by a peripheral turning test using a cemented carbide tool (PlO) under conditions of cutting speed: 200 m / min, feed: 0.25 mm / rev., Depth of cut: 2.Omm, and no lubrication. . The tool life evaluation was evaluated by the total cutting time until the carbide flank wear reached 0.2 mm.
[0041]
[Table 1]

[0042]
[Table 2]

[0043]
As shown in Table 2, the invention steels of No. 1 to No. 14 all have a carbide tool life of 14.8 to 37.Omin. Compared to 12.4min, very good life is obtained. As for the chip shape, good fine chips as small as 5 mm or less were obtained.
[0044]
On the other hand, among the comparative steels of No.15 to No.23, C is out of range for No.15, and the pseudopolygonal ferrite structure can no longer be obtained. The chip shape is significantly lowered and the chip shape is also deteriorated. In No. 16, since Si and O are outside the scope of the present invention, the tool life is reduced and the chip shape is deteriorated. No. 17 has a lower tool life because Mn is higher than the upper limit of the present invention. In No. 18, since Mn is lower than the lower limit of the present invention, the pseudo-polygonal ferrite structure fraction falls and falls outside the range, and the tool life and chip shape are deteriorated. In No. 19, since P was higher than the upper limit of the invention, hot cracking occurred during rolling, so rolling was stopped and evaluation was impossible. In No. 20, since S was higher than the upper limit of the invention, hot cracking occurred during rolling, so rolling was stopped and evaluation was impossible. In No. 21, since S is lower than the lower limit of the present invention, the tool life is reduced and the chip shape is deteriorated. No. 22 has a lower tool life because Nb is higher than the upper limit of the present invention. No. 23 was not able to be evaluated because O was higher than the upper limit of the present invention, and the steel ingot was internally broken and could not be rolled. No.24 was manufactured without subjecting the steel of steel symbol 11 to controlled rolling and controlled cooling, and the pseudopolygonal ferrite structure fraction was below the lower limit of the present invention, and the tool life decreased. The chip shape has also deteriorated.
[0045]
【The invention's effect】
As described above, according to the present invention, a steel material having machinability equivalent to or higher than that of a lead-added free-cutting steel can be obtained in the state of rolling without adding lead.

Claims (5)

C: Less than 0.15 mass%,
Si: less than 0.1 mass%
Mn: 0.1-4.0mass%,
S: 0.05-0.5 mass%,
P: 0.2 mass% or less,
Nb: 0.1 mass% or less and O: 0.0015 to 0.050 mass%
A free-cutting steel characterized in that the balance is made of Fe and inevitable impurities, and the structure contains pseudopolygonal ferrite in an area ratio of 5% or more. In Claim 1, Cu: 2.0mass% or less, Ni: 2.0mass% or less, Cr: 3.0mass% or less and Mo: 2.0mass% or less are contained 1 type or 2 types or more, It is characterized by the above-mentioned. Free-cutting steel. The free-cutting steel according to claim 1 or 2, further comprising any one or two of W: 0.1 mass% or less and V: 0.5 mass% or less. In Claim 1, 2, or 3, Furthermore, Te: 0.2 mass% or less, Se: 0.2 mass% or less, Sn: 0.3 mass% or less, Zr: 0.2 mass% or less, Ca: 0.02 mass% or less, REM: 0.03 mass% A free-cutting steel characterized by containing one or more of Bi: 0.3 mass% or less, Sb: 0.2 mass% or less, Co: 0.1 mass% or less, and N: 0.04 mass% or less. The free cutting according to any one of claims 1 to 4, further comprising any one or more of Mg: 0.02 mass% or less, Hf: 0.1 mass% or less, and Al: 1.0 mass% or less. steel.