TW200302872A - Low-carbon free cutting steel - Google Patents

Abstract

The invention provides a low-carbon resulfurized free cutting steel containing no lead and at least comparable in machinability to the conventional leaded free cutting steels; the steel consists of, by mass percent, C: 0.05 - 0.19%, Mn: 0.4 - 2.0%, S: 0.21 - 1.0%, Ti: 0.03 - 0.30%, Si: not more than 1.0%, P: 0.001 - 0.3%, Al: not more than 0.2%, O (oxygen): 0.0010 - 0.050% and N: 0.0001 - 0.0200%, with the balance being Fe and impurities; the contents of Ti and S satisfies the relation (1) given below, the atomic ratio between Mn and S satisfies the relation (2) given below, and the MnS contained in the steel includes Ti sulfide and/or Ti carbosulfide therein: (1) Ti (% by mass)/S (% by mass) < 1, (2) Mn/S ≤ 1; the steel may further contain, in addition to the above components, one or more elements selected from the group consisting of Se, Te, Bi, Sn, Zr, Ca, Mg and rare earth elements and/or the group consisting of Cu, Ni, Cr, Mo, V and Nb.

Description

200302872 (1) Description of the invention [Technical field to which the invention belongs] The present invention relates to a free-cutting steel that is lead-free and superior to conventional free-cutting steel, and composite free-cutting steel with lead and other free-cutting elements. Low-carbon free-cutting steel with machinability and hot workability. [Previous technology] Conventionally, in order to improve the productivity of soft small parts when extremely high strength is not required, steels with excellent machinability are used, so-called free-cutting steels. The best-known free-cutting steels are sulfur free-cutting steel with a large amount of S to modify machinability, lead free-cutting steel with Pb, and composite free-cutting steel containing S and Pb. Especially free-cutting steel with Pb has excellent chip cutting performance, which helps to extend the tool life. To improve machinability, free-cutting steels containing Te (tellurium) and Bi (bismuth) are available. These have been widely used in various mechanical parts including automotive parts, computer peripheral equipment parts, electromechanical equipment parts, molds and so on. In recent years, with the improvement of cutting machine performance, the cutting work rate has increased. However, the steel used as the material of the above parts is still expected to improve its machinability during high-speed cutting. The machinability of steel, along with the machinability that is helpful to extend the life of the tool, and the chip breakability, that is, chip handling, are valued. This chip handling is indispensable for the automation of processing lines and is necessary for productivity improvement. Lead free-cutting steel and composite free-cutting steel with lead and other machinability improving elements are already the best of the above-mentioned machinability. However, lead-containing steels must have large exhaust equipment in the manufacturing process. In addition, the call for the prohibition of lead in environmental protection is high, and -6- (2) (2) 200302872 free-cutting steel without lead is highly anticipated. In response to the above-mentioned expectations, there are proposals to replace lead free-cutting steel, increase the S content in low-carbon sulfur free-cutting steel, and increase the amount of Mn S in the steel to improve machinability. However, an increase in the S content deteriorates the hot workability of the steel. In addition, when high-speed free-cutting steel is called high-speed cutting at a cutting speed of more than 150 meters per minute, it also lacks the extension effect of tool life, and must not match the machinability of lead free-cutting steel. Japanese Patent Laid-Open No. 2000- 3 1 97 5 3 discloses that low-carbon and sulfur-free free-cutting steels containing more than 0.4% of S, more MnS, and no Pb are added. Although the steel can be seen to have improved tool life to some extent, this effect is small during high-speed cutting. In addition, the chip has no improvement in chip handling, which is an important factor in tool life and machinability, and its performance is similar to that of the conventional sulfur free-cutting steel. JP-A-Sho 50-209 1 7 discloses that it contains C0.5%. Below, sulfur free-cutting steel with S0.3 to 0.75% and TiO.l to 0.5% with Ti content not exceeding S content. This steel is mainly made of iron sulfide, and Ti is added to solid-solve Ti and Mn in the iron sulfide to improve the machinability. However, the C content of this steel is more than 0.24% as described in the actual examples. In this bulletin, there is no record about controlling the composition and morphology of sulfides in low-carbon steels with C 0.19% or less to obtain exceptional machinability. In addition, although iron sulfide with a proper amount of solid solution Ti and Mn is mainly used to improve the machinability, compared with the low-carbon free-cutting steel and composite free-cutting steel of the present invention described later, the machinability is still insufficient. Furthermore, the steel disclosed in the aforementioned publication is difficult to control due to the composition of the iron sulfide and insufficient hot workability, and it is difficult to manufacture continuous casting equipment and the like, which is not practical. -7- (3) 200302872 Japanese Patent Publication No. 09- 5 3 1 47 revealed that C: 0.01 to 0.2%,

Si: 0.10 to 0.60 ° /. , Mη: 0.5 to 1.75 ° /. , P: 0.005 to 0.15%, S: 0.15 to 0.40%, O (oxygen): 0.001 to 0.010%, Ti: 0.0005 to 0.020%, N: 0.003 to 0.03%, with super hard work

Free-cutting steel with excellent machinability. If the composition is in this range, the tool life can be improved to some extent, but because the upper limit of the amount of Ti is less than 0.02%, not only the tool life cannot be sufficient, but also the excellent chip handleability that attaches importance to the tool life cannot be ensured. Japanese Patent Application Laid-Open No. 2001-107182, as disclosed in 152281, 152282, and 1 5 228 3, the main components are C: less than 0.05%, Μκ 0.1 to 4.0%, S: more than 0.1 5 to 0.5%, Cr: Less than 0.5%, Ti: 0.003 to 0.3 ° /. : B: 0.003 to 0.004% steel. This steel is a free-cutting steel that segregates B around sulfides to improve chip handling, and makes C less than 0.05% to improve machinability. However, since C is less than 0.05%, the chipping surface is deteriorated during cutting, and sufficient machinability cannot be obtained.

JP 2001-294976 discloses that C: 0.02 to 0.15%, Mn: 0.3 to 1.8%, S: 0.2 to 0.5%, and at least one of Ti: 0.1 to 0.6% and 0.1 to 0.6%, and Ti + Free-cutting steel with Zr in the range of 0.3 to 0.6% and (Ti + Zr) / S in the range of 1.1 to 1.5. This steel has the above-mentioned composition, and generates sulfides of Ti and Zr with high deformation resistance by heating and the like, and improves mechanical anisotropy and machinability. However, for sulfide with high deformation resistance, it is difficult to obtain a quasi-slip effect of sulfide during cutting. The cutting resistance is high and the effect of improving machinability is limited. -8- (4) (4) 200302872 [Summary of the Invention] Problems to be Solved by the Invention The subject of the present invention is to provide lead-free (Pb) -free steel with current lead free-cutting steel and lead-containing and other machinability improving elements. It is a low-carbon and sulfur free-cutting steel with a combination of cutting properties above free-cutting steel and excellent hot workability. Means for Solving the Problems The present inventors have studied the relationship between the shape of the medium and the machinability due to the addition of Ti in order to improve the machinability of low-carbon sulfur free-cutting steel that does not substantially contain Pb. As a result, the following new knowledge was obtained. ① The C content should be 0.05 to 0.19%. ② In the steel with the above C content, the atomic ratio of Mη and S satisfies the conditions of Mn / S-1, and when Ti is contained in a range not exceeding the S content (mass%)

Most of the sulfides are not Ti sulfide or iron sulfide, but Mn S.

③ As in the composition range of ② above, Ti is hardly dissolved in MnS, and Mn · Ti sulfide, that is, no (Mn, Ti) S is formed. Therefore, MnS exists in a phase different from Ti sulfide and Ti carbon sulfide. Most Ti-based media (sulfides, carbon sulfides) exist in the form contained in M n S. c

④ In the form of ③ above, steels with MnS and Ti-based media are excellent in machinability under high-speed cutting. That is, for example, at a high-speed rotation of 100 m / min or more, Mn S adheres to the surface of the tool and forms a hard layered TiN. Because of the protection of TiN for tools, compared with the current JIS (5) (5) 200302872 SUM22L to 24L composite free-cutting steel with the best machinability, it can also have far better tool life. Moreover, if Ti is added within the above-mentioned predetermined range, fine sulfides are formed, and the number is increased. These sulfides become a stress concentration source during cutting, which promotes the propagation of cracks. Compared with current sulfur free-cutting steel and composite free-cutting steel with Pb, it also has excellent chip handling properties. Furthermore, there is no problem with the hot workability of the steel. 'It does not have any trouble when it is manufactured by continuous casting equipment and the like, and it is practical. The present invention is based on the above-mentioned findings, and also explores the effects of components other than the alloy components in detail. The gist is the free-cutting steel of (1) to (4) below. (1) It is characterized by C: 0.05 to 0.19, Mn: 0.4 to 2.0%, S: 0.21 to 1.0%, T i: 0.03 to 0.30%, Si : 1.0% or less, p: 0.000 to 0.3 ° / 〇, A1: 0.2% or less, 〇 (oxygen): 0.0010 to 0.05 0% and N: 0.000 1 to 0.0200%, the balance is

Fe and impurities; the content of Ti and s satisfies the following formula ①, the atomic ratio of Mη and S satisfies the following formula ②, and the steel contains Mn S containing Ti sulfide or / and Ti carbon sulfide Carbon free-cutting steel.

Ti (mass) / s (mass./〇) &lt; 1 ......... ①

Mi n / S ^ l ......... ② (2) It is characterized in that in addition to the components of (1) above, it is further selected from

Se: 0.001 to 0.01%, Te: 0.001 to 0.01%, Bi: 0.0 〇5 g 0.3%, Sn: 0.00 5 to 〇3%, Ca: 〇. Ο Ο Ο 5 to 〇. 〇 1%, Mg: 0.0 0 0 5 to 0.01% and rare earth elements: 0 or 0 to 5 to 0.01% of the group or two or more kinds, which meet the above formulas ① and ② of low-carbon and sulfur free-cutting steel -10- (6 ) (6) 200302872 (3) It is characterized in that in addition to the component (I) above, it is selected from the group consisting of Cu: 0.0 1 to 1.0%, Ni: 0.0 1 to 2.0% 'Cr: 〇. 〇1 to 2.5%,

Mo: 0.01 to 1.0%, V: 0,005 to 0.5%, and Nb: 0.00 5 to 0.1%. One or two or more groups, which satisfy the above-mentioned formulas ① and ② of low-carbon and sulfur free-cutting steel. (4) It is characterized in that in addition to the components of (1) above, it also contains S: 0.001 to 0.01%, Te: 0.001 to 0.01%, Bi: 0.005 to 0.3%, Sn: 0.005 to 0.3%, and Ca: 0.0005. To 0.01%, Mg: 0.0005 to 0.01% and rare earth elements: 0.0005 to 0.01% of one or two or more groups, and selected from Cu: 0.01 to 1.0%, Ni: 0.01 to 2.0 ° /. , Cr: 0.0 1 to 2.5%, Mo: 0.01 to 1.0%, V: 0.005 to 0.5%, and Nb: 0.005 to 0.1% of one or more of the groups, which satisfy the above-mentioned low-carbon formulas ① and ② Sulfur free-cutting steel. The Si content of the free-cutting steels (1) to (4) above should preferably be less than 0.1% by mass. Embodiment of the invention

1 · MnS containing Ti sulfide or / and Ti carbon sulfide A major feature of the present invention is that it contains "Mn n S containing Ti sulfide or / and Ti carbon sulfide". Butanite can be dissolved in MnS in a trace amount as (Mn, Ti) S, and Ti dissolved in MnS is in a trace amount. The sulfide is essentially MnS. On the other hand, there is warfare and this] VlnS is significantly different, 甶 TiS or -11-(7) 200302872

Ti4C2S2 is the chemical formula of Ti sulfide or Ti carbon sulfide. These are mostly separated from MnS, and exist in MnS. The existence of the sulfide in the above form can be confirmed by surface analysis and quantitative analysis by cutting the micro-EPMA (electron beam microanalyzer), EDX (energy dispersive X-analyzer) from the steel. Figure 1 is the result of EPA analysis of sulfide of No. 3 steel in Table 1 below. (A) is a medium, and (b) to (d) show the presence of Ti, Mn, and S. From these figures, it can be seen that Ti sulfides or Ti carbon sulfides are present in the vicinity of the compounds, exist in the form of surrounding MnS, and the like, and have various coexistence states. Together with such one of the MnS, Ti sulfide or / and Ti carbon-sulfur phase separation and existence, and a sulfide in a sulfide accounted for 50% of the area ratio of MnS, in the present invention is defined as "Ti-containing sulfur bucket And MnS of Ti carbon sulfide ". The total area ratio of Ti sulfide and Ti carbon sulfide contained in a MnS can be confirmed by the above EPMA or EDX. In addition, the steel "MnS containing Ti sulfide or / and Ti carbon sulfide" can also be confirmed, and its number can be measured. The majority measured in the visual field is converted to the number of square millimeters, and the average value is more than 10 per square millimeter. When cutting steel containing Ti sulfide and / or Ti carbon sulfide, soft Mn S has a pseudo slipperiness of the contact surface between the material being cut and the tool, forming TiN on the surface of the tool to protect the tool. That is to say, the surface of the tool that is in contact with the material being cut together with MnS has Ti sulfide in the test piece rays as the surface quality. The sulfur formation rate is not in the same or / composition. Cut, -12- (8) (8) 200302872

The adhesion of Ti carbon sulfide, and the friction temperature during cutting increases, and these Ti sulfides react with N (nitrogen) in the ambient gas to form a layered hard TiN with a thickness of several micrometers to several tens of micrometers. Its existence can be confirmed on the surface of the tool after the carbon-based dirt (oil content) is removed by Ai * splatter, etc., and analyzed by AES (Auger Electron Spectroscopy) 'ΕΡΜΑ. It can be known from the above method that the surface area of the layered TiN film is about 10 to 80% of the contact area between the material being cut and the tool. The remaining part may have MnS, Fe attached, or the original surface of the tool without attachments. . The hard TiN film formed on the surface of the tool in this way has a large protection effect on the tool, improves the abrasion resistance of the tool, and extends its life. The tool life improvement effect is far greater than sulfur free-cutting steel and Pb-containing composite free-cutting steel. Except for "MnS containing Ti sulfide or / and Ti carbon sulfide" in the steel of the present invention, MnS, Ti sulfide, and Ti carbon sulfide exist in a fine medium. That is, the significant number of all media becomes the stress concentration point in cutting generated during cutting, which helps to propagate cracks and also improves chip breakability. By adjusting the composition of the steel as described above, "MnS containing Ti sulfide and / or Ti carbon sulfide" can be present in the steel. In order to make the MnS stable, it is suitable to heat it at a sufficiently high temperature above 1000 ° C after casting, keep it fully forged, or perform normal heat treatment at the same high temperature. 2. Reasons for Limiting Chemical Composition The reasons for limiting the chemical composition in the present invention will be described below. In addition, the% of the component content refers to% by mass. -13- (9) (9) 200302872 C: 0 0.5 to 0.19% C is an important element that has a great influence on the machinability of steel. For steels where the machinability is important, the strength of the steel will increase when the C content exceeds 0.1 9%, and the machinability will deteriorate. However, when the C content is less than 0.05%, the steel material is too soft, and cracks occur during cutting. On the contrary, the tool wear is promoted and the chip handleability is deteriorated. Therefore, C is limited to the range of 0.05 to 0.19%. For better machinability, the more appropriate range of C amount is 0.0 5 to 0.17%.

Mn: 0.40 to 2.0% · Mn and S are important elements that form sulfur compound-based media and greatly affect machinability. When it is less than 0.40%, the absolute amount of sulfide is insufficient, and the desired machinability cannot be achieved. If it exceeds 2.0%, the strength of the steel increases, the cutting resistance increases, and the tool life decreases. In addition, the reduction of cutting resistance, the improvement of tool life, the improvement of cutting brush handling, and the improvement of hot workability are also important in relation to the amount of S. That is, the amount must satisfy the relationship of the atomic ratio Mn / S-1. In order to achieve these properties, the Mη content is preferably 0.6 to 1.8. φ S: 0.2 1 to 1.0% S is a necessary additive element for forming sulfides and carbon sulfides together with Mn or Ti, which can improve cutting and machinability. In particular, the machinability improvement effect of MnS is more-it increases with the amount of production. However, if it is less than 0.21%, a sufficient amount of sulfide-based medium shall not be used, and the machinability shall not be as intended. Generally, when the S content exceeds 0.35%, the hot workability of the steel is deteriorated, S segregation occurs in the central portion of the steel block, and fracture during forging occurs. However, if the composition stipulated in the present invention is maintained, the disadvantages of jealousy can be eliminated, and the upper limit of the S content can be increased to 1.0%. Considering -14- (10) 200302872 yield at the time of manufacture, a preferable upper limit of the S content is 0.7 ο%.

Ti: 0.03 to 0.30%

Ti together with S and C forms Ti sulfide or Ti carbon sulfide, and the form contained in Mn S exists to improve the machinability and heat addition of steel. Therefore, it is an important essential element in the steel of the present invention. Ti is a more sulfide than Mη, and since it exists in a state of being contained in Mn S, a sufficient improvement effect can be obtained. The effect is insufficient at less than 0.0 3%. On the other hand, if T i exceeds 0.3 0%, there will be more hard τ i sulfide or Ti carbon sulfide, the cutting resistance will increase, and the machinability will deteriorate. A more preferable Ti limit is 0.10%.

Si: 1.0% or less

Si is a deoxidizing element that can adjust the amount of oxygen in steel. However, when the amount exceeds 1.0 ° / 0, the hot workability of the steel is deteriorated, and the cutting resistance is increased due to the ferrite solution strengthening, and the machinability is deteriorated. Therefore, although the Si content is 1.0%, it is controlled to be less than 0.1 ° /. For the better. The content of Si should be more than 0.001%, but it is essentially 0 (zero)%. As described later, the amount of oxygen in the steel is adjusted to an appropriate range to reduce the machinability. P: 0.00 1 to 0.3% When P exceeds 0.3%, it promotes segregation of the steel ingots and heat addition. Therefore, the upper limit of the content is 0.3%. On the other hand, due to the element of the P-based machinability effect, in order to obtain the effect 'lower limit, the content of p is from 0.001 to 0.15%. A1: 0.2% or less, within the workability. Easy to shape Machinability On the one hand, if the upper limit of the solid content in the sulfur content of the material is deoxidized, then, if it can, the workability can be improved. -15- (11) (11) 200302872 A1 is used as a powerful deoxidizing element, and can be contained to 0.2%. However, the oxide formed by deoxidation is hard, and if the A1 content exceeds 0.2%, a large amount of hard oxide is formed, and the machinability is deteriorated. The preferred value is 0 · 1 ° /. the following. When Si can be sufficiently deoxidized, A1 need not be added, and its content can be substantially 0 (zero)%. 〇 (Oxygen): 0.0010 to 0.05% When the appropriate amount of oxygen is contained in the steel, the oxygen is dissolved in MnS to prevent compression and delay the extension of MnS and reduce the anisotropy of mechanical properties. It also helps to improve machinability and hot workability, and effectively prevents segregation of S. Therefore, it should be more than 0.00 10% oxygen. However, if it exceeds 0.05%, there are disadvantages that the refractory is damaged during melting. Therefore, the upper limit is 0.05%. In order to properly obtain the above-mentioned effects, a preferred range is from 0.05 to 0.02%. N: 0.0001 to 0.0200% N can form hard nitrides along with Ti and these nitrides can make the grains finer. This effect is exhibited when the N content is more than 0.001%. If these nitrides are present in a large amount, the machinability will be deteriorated, and the wear of the cutting tool will be increased. In order to protect the tool by forming TiN on the surface of the tool during the cutting of the steel of the present invention, Machinability does not deteriorate. However, if the amount of N exceeds 0.0 2 0 0%, the effect is low. In order to obtain a longer tool life, it is preferable that it is not more than 0.015%. In order to extend the tool life more, it can be set below 0.0 100%. One of the steels of the present invention, the rest of which is Fe and impurities in addition to the above components. The other system of the present invention, in addition to the above components, contains the following first group of elements -16- (12) (12) 200302872 Prime or / And steel of one or more elements of the second group. The first group element is composed of Se, Te, Bi, Sn, Ca, Mg, and rare earth elements. These can further improve the machinability of steel. The second group of elements is made of Cu, Ni, Cr, Mo, V, and Nb, which can improve the mechanical properties of steel.

Se: 0.001 to 0.01%, Te: 0.001 to 〇 · 0 1 〇 / 〇

Se and Te, together with Mn, form Mn (S, Se) or Mn (S 'Te), elements that improve machinability. If each is less than 0.01%, the effect will be inferior. On the other hand, if both S e and T e exceed 0.0 1%, the effect will not only be saturated, but it will be uneconomical and the hot workability will deteriorate.

Bi: 0.005 to 0.3%, Sn: 0.005 to 0.3% B i and S η are low-melting-point metal media, which exhibits a lubricating effect during cutting and improves machinability. This effect is remarkable when each is 0.00 5% or more. However, if the contents exceed 0.3% each, not only the effect is saturated, but the hot workability is also deteriorated.

Ca: 0.0005 to 0.01%, Mg: 0.0005 to 0.01%

Ca and Mg have a high affinity for S and oxygen in steel, and simultaneously dissolve in MnS with the formation of sulfides or oxides. Ca and Mg exist as (Mn, Ca) S, (Mn, Mg) S. In addition, since these oxides serve as growth nuclei and Mn S crystallizes, there is an effect of controlling the extension of MnS. In this way, Ca and Mg can be added to control the morphology of sulfide to improve machinability if necessary. In order to achieve this effect, Ca and M g should each contain more than 0.05%. However, if it exceeds 0.0 1 ° / 〇, the effect is saturated. In addition, the addition yields of C a and M g are both low. To increase the content, a large amount of effort is needed:], and the manufacturing cost is not good. Therefore, the upper limit of the content -17- (13) (13) 200302872 is each 0.01%. Rare earth elements: 0. 005 to 0. 0%. Rare earth elements are classified as lanthanide element groups. When it is added, it is usually a reticulated metal, etc., which is the main component. The content of the rare earth element in the present invention is expressed by the total content of one or more elements of the rare earth element. Rare earth elements, together with S and oxygen, form sulfides or oxides while controlling the morphology of sulfides to improve machinability. In order to achieve this effect, it should contain more than 0.000 5%. However, if the content exceeds 0.001%, not only the effect is saturated, but because Ca and Mg 'are added at low yields, it is not economical to contain a large amount. Cu: 0.0 1 to 1.0%

Cu can improve the hardenability of steel. In order to obtain the effect, it should preferably contain more than 0.00%. However, if the content exceeds 1.0%, the hot workability of the steel is deteriorated and the machinability is reduced.

Ni: 0.01 to 2.0%

Ni has the effect of improving the strength of steel by solid solution strengthening, and the effect of improving hardenability and toughness. To achieve this effect, the content should be above 0.01%. However, if it exceeds 2.0%, machinability and hot workability deteriorate.

Cr: 0.0 1 to 2.5%

Cr has the effect of improving the hardenability of steel. In order to obtain this effect, 0.01% or more should be contained, and more than 2.5%, the machinability deteriorates.

Mo: 0.01 to 1.0%

Mo has the effect of miniaturizing the microstructure of steel 'and improving its toughness. To achieve this effect, the content should be above 0.01%. However, if it exceeds 1.0 ° / °, the effect is saturated and the manufacturing cost of steel increases. -18- (14) 200302872 V: 0.00 5 to 0.5%, Nb: 0.00 5 to 0.1% V and Nb precipitate into fine nitrides and carbonitrides, strength. In order to achieve this effect, the content should be 0.00 5% each. If V exceeds 0.5% and Nb exceeds 0.1%, the above-mentioned effect forms excessive nitrides and carbides, and the machinability deteriorates. 3. About ① and ②

The reason why the Ti content and the S content must satisfy the formula (1) is as follows.

Ti forms Ti sulfide or Ti together with C and S as described above. This tendency is as large as the tendency of Mn sulfide formation. Effect of Ti With Ti-based media, TiN is formed on the surface of the tool during cutting to achieve longevity. On the other hand, Ti sulfide and Ti carbon sulfide are hard media with large deformation resistance. Therefore, under the composition where the Ti content is higher than the S content, the amount decreases, and Ti sulfide and Ti carbon sulfide become the main body, which has a pseudo-lubricating effect of non-sulfide between the material to be cut and suddenly rises. Increasing cutting resistance not only shortens the life of the tool, but also causes defects such as vibration of the material being cut. If the above formula (1) is satisfied, "Ti (mass%) / S" is adjusted to be less than 1, and Ti sulfide and Ti carbon sulfide do not become the main body of sulfide, that is, MnS. At this time, the cutting resistance generated when the Ti sulfocarbon sulfide becomes the main sulfide as described above can increase tool life and chip handling. The reason why the atomic ratio of Mn to S must satisfy the formula (2) is as follows. S is an element that can cause fracture during hot forging. If the dimension is higher than steel, but saturated, and carbon sulfide: As mentioned above, increase the cutting resistance of the tool during the cutting of MnS and MnS. ) Sulfide 5: Compounds, Ti, etc. are absent, and the atomic ratio is -19- (15) (15) 200302872 M η / S — 1 ', then S crystallizes as M η sulfide, which does not cause adverse effects on hot workability. .

When Mn / S is less than 1, if the Ti and S contents are adjusted so as not to satisfy the above-mentioned formula (1), Ti-based sulfides are formed, and hot workability can also be improved. However, at this time, the above-mentioned cutting resistance increases, resulting in a lack of shortened tool life and the like. Furthermore, when Mn / S is less than 1, if the Ti content does not exceed the s content, which satisfies the above formula ① but not ②, the main body of the medium is sulfide in which Mn S and TiS are more solid-dissolved with F e S . Since these sulfides have a solid solution of F e S in many cases, the hot workability of the steel is deteriorated, and it is difficult to control the operating conditions during manufacturing such as continuous casting. [Embodiment] _ Example The test steels with the composition of Tables 1 and 2 were cast by a high-frequency induction furnace to produce steel blocks of 22 mm in diameter and 150 kg in diameter. In order to stably generate "MnS containing Ti sulfide or / and Ti carbon sulfide", these ingots are heated at a temperature of up to 1 200 ° c for more than 2 hours, and finally forged at more than 1 000 ° C, air-cooled (AC) A round rod with a diameter of 65 mm was obtained. Keep the round bar at 95 ° C for 1 hour for air cooling (AC) normalization. 200302872 6)

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5 9 rNl inch § 6e ooe Li 9i ST inch £ s Vi h: R -22- (18) (18) 200302872 (1) Investigation of the composition of the medium The above forged and stretched material is equivalent to Df / 4 (Df series forged and stretched material (Diameter) part of the microscopic observation test piece was cut from the longitudinal section direction, after honing, EPMA and EDX for surface analysis and quantitative analysis. As a result, in the steels No. 1 to No. 29, it was confirmed that MnS containing Ti sulfide or / Ti carbon sulfide contained 10 or more per square millimeter on average. (2) Examination of machinability · The forged round bar was cut out to 60 mm and used for cutting test. However, if the hot workability is inferior to that caused by cracking during forging, it is then maintained at 950 ° C for 1 hour to be normalized. After air cooling (AC), it is cut to 60 mm 0 as the test material. The machinability test was performed using a JIS P-type superhard tool without TiN coating. Cutting is dry (no lubricant). The conditions are cutting rate: 150 m / min, movement: 0.10 mm / rev, cutting depth: 2 mm. After 30 minutes of spinning under the above conditions, the cutting tool is measured. The average side wear (VB). For a test material with an average side wear amount of 200 ”microns or more within 30 minutes, the average side wear amount at that time-(VB) was measured. The time taken for the average side wear amount (VB) to reach 100 μm was used as the tool life. The index is evaluated. In the test, the abrasion resistance is excellent, and the wear is very slow. If the test material is insufficient, the time of the average side wear (VB) of 100 micrometers is calculated from the regression of the turning time-tool wear curve. Representatives of more than 0 discharged chips are calculated after weighing -23- (19) (19) 200302872 per unit weight for evaluation. (3) Evaluation of hot workability The evaluation of hot workability is as follows That is, in order to simulate the manufacturing conditions using continuous casting equipment, a 150-kilogram steel block was manufactured in the same manner as above, with the diameter of the Di / 8 (Di-based steel block diameter) position near the surface as the center, and the diameter taken from the height of the steel block Ten-millimeter high-temperature tensile test pieces with a length of 130 mm. These are directly heated at a fixed interval of 10 mm to 1 250 ° C, and after holding for 5 minutes, they are cooled to 1 at a cooling rate of 10 ° C / sec. 1 00 ° C, rewarranty After 10 seconds, at a strain rate of 1 "s for the tensile test. At this time, the shrinkage of the fractured portion was measured to evaluate the hot workability. The above test results are shown in Tables 3 and 4. The second graph shows the relationship between chip processing and tool life. The third graph shows the relationship between shrinkage in the thermal tensile test and tool life. -24- (20) 200302872 Table 3 Steel No. Shrinkage (%) Tool wear after 30 minutes (micron) VB = 100 micron arrival time (minutes) Chip handling (number / g) 1 65.8 21 179 * 15 2 55.2 35 110 12 3 54.8 32 1 81 * 16 4 56.9 35 117 17 5 58.8 29 119 21 6 52.7 38 109 15 7 56.7 35 1 16 14 8 55.8 41 101 18 9 57.7 44 94 13 10 61.0 42 1 08 12 11 57.8 38 111 11 12 63.2 34 121 15 13 61.5 39 96 14 14 60.6 39 94 13 15 52.1 27 128 23 16 56.9 25 1 56 11 17 52.0 26 135 13 18 59.7 29 1 39 19 19 53.4 24 155 16 20 55.9 28 130 17 21 52.1 42 1 02, 15 22 50.4 35 113 15 23 63.6 44 91 14 24 65.8 38 97 13 25 54.9 45 90 18 26 58.8 40 93 17 27 53.8 39 95 14 28 57.6 36 1 02 14 29 54.3 39 90 18 + Table Due to insufficient test materials. Calculated from the tool wear curve regression -25- (21) 200302872 Table 4 Steel No. Shrinkage (%) Tool wear after 30 minutes (microns) VB = 100 micron Chip handling remarks Reach time (number / G) (minutes) 30 47.8 97 36 9 31 49.6 99 30 8 32 55.4 1 65 17 1 33 51.8 210 (20 minutes 9 6 34 45.4 68 72 10 35 54.4 90 39 2 36 64.2 72 69 15 37 52.8 93 36 12 38 67.9 89 38 14 39 57.5 1 04 29 7 40 65.3 138 20 5 41 5.1 39 1 02 5 Cracking during forging 42 4.3 48 61 9 Cracking during forging 43 65.7 205 (20 minutes) 8 10 44 13.6 103 28 18 Cracking during forging 45 52.0 245 (1 5 minutes) 7 13 46 55.3 205 (20 minutes) 9 17 47 54.7 275 (15 minutes ) 6 10 -26- (22) (22) 200302872 Table 2 steel No. 30 and 3 1 series composite free-cutting steel, steel No. 3 series sulfur free-cutting steel, which is currently the best machinability steel (equivalent Based on JIS SUM23L or SUM 23). As can be seen from Tables 3, 4 and 2, the steel of the present invention has an extremely excellent tool wear suppressing effect compared with these. In addition, the steels of the present invention of steel Nos. 1 to 29 have no cracks at the time of forging, and the continuous high temperature tensile test to simulate actual manufacturing shrinkage is performed by continuous forging equipment and the like, as shown in Table 3. Cutting steel and sulfur free cutting steel are equal or more, without any problems in practice. On the other hand, if any one of the steel Nos. 30 to 47 exceeds the requirements of the present invention, at least one of the hot rolling, tool life, and chip handling properties is inferior to the steel of the present invention. However, Steel Nos. 41 and 42 have poor hot workability because Mη and S do not satisfy the above formula (2). EFFECT OF THE INVENTION The free-cutting steel of the present invention does not only contain Pb, but has better machinability than any one of conventional lead free-cutting steel and composite free-cutting steel. The steel is also excellent in hot workability and can be manufactured at low cost by the continuous casting method. Therefore, it is suitable for the material of various mechanical parts. [Brief Description of the Drawings] Figure 1 is the result of epma analysis of MηS containing Ti sulfide and / or Ti carbon sulfide observed in the steel of the present invention. Fig. 2 is a graph showing the relationship between chip handleability and tool life of the steel of the present invention (steel No. 0.1 to 2 9) and the comparative steel (steel No. 0.3 to 4 7). -27- (23) 200302872 The third figure is the relationship between shrinkage and tool life in the heat ductility test of the steel of the present invention (steel No. 1 to 29) and the comparative steel (steel No. 3 0 to 47) 鹞

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Claims (1)

(1) (1) 200302872 Pickup and patent application scope 1. A low carbon sulfur free-cutting steel, characterized by mass%, containing C: 0.05 to 0.19, Mn: 0.4 to 2.0%, S: 0 .2 1 to 1.0%, Ti: 0.03 to 0.30%, S i: 1 · 0% or less, P: 0 · 0 0 1 to 0.3%, A1: 0.2% or less, 0 (oxygen): 0.0010 to 0 · 0 5 0% and N: 0.0001 to 0.002 0 0%, the balance is made of Fe and impurities, the content of Ti and s satisfies the following formula ①, and the atomic ratio of Mη and S satisfies the following formula ② And contains MnS, which contains Ti sulfide or Ti carbon sulfide: Ti (mass) / S (mass%) &lt; 1 • · * »·· · · · Mn / S ^ 1 .... ..... ② 2. A low-carbon sulfur free-cutting steel, characterized by mass%, containing C: 0.05 to 0.19, Μη: 0.4 to 2.0%, S: 0.21 to 1.0%, T i: 0 〇3 to 0.3 0%, Si: 1 · 〇% or less, p: 〇. 〇〇1 to 0.3%, A1: 〇 · 2% or less, 〇 (oxygen): 0.0010 to 0.05 0%, and N: 0.0001 To 0.0200%, and selected from Se: 0.001 to 0.01%, Te: 0.001 to 0.01%, Bi: 0.005 to 0.3%, Sn : 0.005 to 0.3%, Ca: 0.0005 to 0.01%, and Mg: 0.0005 to 0.01. /. And rare earth elements: one or two or more groups of 0.0005 to 0.01%, the balance is made of Fe and impurities, and the content of Ti and S satisfies the following formula ① The atomic ratio of η and S satisfies the following formula ② It also contains Mn S, which contains T 丨 sulfide or / and Ti carbon sulfide: butyl i (mass) / S (mass%) &lt; 1 ......... ① Mn / S ^ 1 ......... Φ 3. —A kind of low-carbon sulfur free-cutting steel 'whose range is: in terms of quality %% ten' containing -29- (2) (2) 200302872 C: 0.05 to 0.19 , Mη: 0.4 to 2.0%, S: 0.21 to 10% 'Ti: 0.03 to 0.30%, Si: 1.0% or less, P: 0 · 〇〇1 affected by 0.3%, A1: 0.2% or less, 0 (oxygen): 0.0010 to 0.050% and N: 0.0001 to 0.0200 ° /. , And selected from Cu: 0.01 to 1.0 ° / c Nl: 0 · 0 1 to 2 · 0%, C r: 0. 0 to 2.5%, Μ: 0.0 1 to .0% 'V: 0.00 5 to 0.5% and Nb: 0.005 to 0.1% of one or two or more groups, and the balance is made of Fe and impurities. The content of Ti and S satisfies the following formula ①, and the atomic ratio of Mη and S The following ② formula contains MnS ′, which contains Ti sulfide or Ti carbon sulfide: Ti (mass) / S (mass%) &lt; 1 ......... ① Mn / S ^ 1 ......... ② 4. A low-carbon sulfur free-cutting steel characterized by: 'mass%' with C: 0.05 to 0.19, Mn: 0.4 to 2.0%, S: 0.21 to 'T i: 0.0 3 to 0.3 0%, S i: 1.0% or less, P: 0.0 0 1 to 0.3%, A1: 0.2% or less, 〇 (oxygen): 0.0010 to 0 05 0❶ / ° and N: 0.0 00 1 to 0.0 2 00%, and selected from Se: 0.001 to 0.01% J Te: 0.001 to 0.01%, Bi: 0.005 to 0.3% 'Sn: 0.005 to 0.3%, Ca: 0.0005 to 0.01%, Mg: 0.0005 To 0.001 ° /. And rare earth elements: 0.0005 to 0.01% of one or two or more groups and selected from Cu: 0.01 to 1.0%, Ni: 0.01 to 2.0%, Cr: 0.01 to 2.5%, Mo: 0.01 to 1.0%, V: 0.00 5 to 0.5% and Nb: 0.0 0 5 to 0.1% of one or two or more groups, the balance is made of Fe and impurities, and the content of Ti and S satisfies the following formula (1), and the atom of 5 The ratio satisfies the following formula: 叵 contains Mn n, which contains T i fti.L t dagger or / and T i private ash-30- (3) (3) 200302872 Sulfide: Ti (mass) / S (Mass%) &lt; 1 ......... ① Mn / S ^ 1 ......... ② 5. If the low carbon of any one of the scope of patent applications 1 to 4 1 质量 ％。 Sulfur free-cutting steel, in which the si content is less than 0.1% by mass. quail -31-