JP4788320B2 - Steel material for micro oil lubrication - Google Patents

Description

  The present invention relates to a steel material for trace oil lubrication. More specifically, the present invention relates to a steel material for “trace oil lubrication” which is processed while supplying a small amount of lubricant (cutting fluid) in machining of steel.

  Conventionally, steel materials for cutting have been developed for so-called “wet cutting” using a large amount of lubricant or so-called “dry cutting” using no lubricant.

  However, in recent years, as a new cutting method that not only consumes less energy but is also environmentally friendly, and can improve cutting efficiency and maintain machining accuracy, it is possible to process while supplying a small amount of lubricant. The study of “oil lubrication” (hereinafter also referred to as “micro-lubricating oil cutting”) technology has been actively studied. For example, Non-Patent Document 1 to Non-Patent Document 6 report on micro-oil lubrication cutting (MQL cutting) technology. Has been made. Further, Patent Document 1 and Patent Document 2 disclose processing apparatuses suitable for trace oil lubrication cutting.

  As a typical process to which micro-oil lubrication cutting including these is applied, there is a deep hole process using a small diameter drill having a diameter of 10 mm or less and making a hole having a depth of 10 times or more the drill diameter. Conventionally, such deep hole machining has been carried out using a twist drill made of high-speed tool steel (commonly known as “Hi-S”) or a gun drill in which the cutting edge is brazed with a cemented carbide and using a large amount of lubricant. Sometimes a large amount of lubricating oil is applied and processed at high pressure. However, when using a high-speed twist drill, the cutting speed cannot be increased, and when using a gun drill brazed with a cemented carbide, the feed rate is increased due to the rigid surface of the tool. In all cases, there was a limit to machining efficiency. Further, both of the above-described processing methods use a large amount of lubricating oil, which increases the cost of disposal.

  On the other hand, if a trace oil lubricated cutting is performed using a cemented carbide twist drill, high-speed cutting is possible and the feed amount can be increased. For this reason, highly efficient cutting can be performed, and the problem of disposal of the lubricant can be solved. However, with respect to micro-oil lubrication cutting, tools, oil agents, machines, and oil supply systems have been conventionally studied. However, there have been few examples of materials to be cut, especially steel materials.

  In wet cutting, dry cutting, and trace oil lubricated cutting, it is predicted that the cutting phenomenon will change because of the difference in the state of the lubricant. Therefore, even when using so-called “free-cutting steel”, which is a steel material for cutting developed for conventional wet cutting and dry cutting, there is a possibility that sufficient workability may not be ensured in the case of trace oil lubrication cutting. is there.

  For example, in Patent Document 3, the composition and form of MnS and steel oxide are adjusted, and the tool surface protection and lubrication effect by these inclusions increases the machinability with a carbide tool. “Free-cutting steel for machine structures having excellent properties” is disclosed. However, the cutting of free-cutting steel proposed in Patent Document 3 is a conventional “turning” process performed under the conditions of “speed: 200 m / min, feed: 0.2 mm / rotation, depth: 2 mm”. There is only.

  Further, Patent Document 4 discloses “Bi free-cutting steel” in which chip disposal is improved by adjusting the existence form of bismuth (Bi). The basic idea of the technique proposed in Patent Document 4 is that Bi is a low-melting point inclusion like Pb, so that it melts due to a temperature rise during cutting and enhances the lubricating action on the tool surface. is there. The cutting of free-cutting steel proposed in Patent Document 4 is also “cutting speed: 150 m / min, feed: four levels of 0.05, 0.1, 0.2, 0.3 mm / rev, cutting: It is only the conventional “turning” processing performed under the conditions of “three levels of 0.5, 1.0, and 2.0 mm”.

"Technical trends in MQL cutting" (Ichiro Inasaki, Tribologist, Volume 47, Issue 7 (2002), pages 519-525) "Turning Trends by Compound Mist Method" (Yasuo Suzuki, Tribologist, Vol. 47, No. 7 (2002), pages 526-532) "Trends in machine tools for MQL cutting" (Masayama Hata, Tribologist, Vol. 47, No. 7 (2002), 533-537) "Trends in MQL cutting oil supply system" (by Shigeru Suzuki, Tribologist, Vol. 47, No. 7 (2002), pp. 538-543) "Trends in MQL cutting tools" (Katsuyoshi Kano, Tribologist, Volume 47, Issue 7 (2002), pages 544-549) "Trends in MQL cutting fluids" (Mr. Suda, Tribologist, Vol. 47, No. 7 (2002), 550-556) JP 2002-355735 A Japanese Patent Laid-Open No. 2002-355736 JP 2003-55735 A JP 2000-265243 A

  An object of the present invention is to provide a steel material for trace oil lubrication cutting that is processed while supplying a trace amount of lubricant.

Specifically, it is to provide a steel material excellent in chip disposal that is used under a trace oil lubrication cutting condition using a lubricating oil agent of 200 cm ³ or less per hour.

  In addition to the free-cutting steel proposed in Patent Document 3 and Patent Document 4, the free-cutting steel developed for conventional wet cutting and dry cutting mainly adjusts the form of inclusions in the steel, It utilizes the lubrication action on the tool surface during machining.

  However, as the name suggests, the lubrication effect on the tool surface is already ensured by the oil supply system and the tool. For this reason, the trace oil-lubricated cutting phenomenon is completely different from conventional wet cutting and dry cutting, and improvement in machinability due to the lubrication effect based on inclusions cannot be expected.

  In addition, steel materials for trace oil lubrication cutting have not been developed yet, and Pb free-cutting steel, S free-cutting steel, its combined free-cutting steel, which is subject to wet cutting and dry cutting, and the aforementioned There has never been a detailed study of trace oil lubrication machinability using various conventional free cutting steels such as the free cutting steels proposed in Patent Document 3 and Patent Document 4.

  Therefore, the present inventors first lab-dissolved free-cutting steel having a chemical composition shown in Table 1 conventionally known as free-cutting steel for machine structures, and used trace oil lubrication cutting, wet cutting and dry cutting. The tool life in each case of cutting was compared.

  That is, the ingot of each steel shown in Table 1 was heated to 1250 ° C., subjected to hot forging, and finished at 1000 ° C. or higher to produce a round bar having a diameter of 60 mm. In addition, after finishing, it air-cooled and simulated the manufacturing process of a non-tempered steel material.

  The Vickers hardness (hereinafter referred to as “Hv hardness”) was measured at 8 locations at the R / 2 part (R: radius of the round bar) position in the cross section of each round bar thus obtained. The test force was 98.07N. In Table 1, the average value of the Hv hardness measured at 8 locations for each round bar is also shown.

  As apparent from Table 1, all the round bars have equivalent hardness of about 240 in Hv hardness.

  Therefore, an oil hole having a diameter (D) of 6.0 mm, a total length of 180 mm, a blade length of 130 mm, and a tip angle of 140 ° is obtained by cutting each round bar into a length of 100 mm. Using a cemented carbide coated drill, tool life was compared by applying conventional wet cutting and dry cutting, and a micro oil lubrication cutting, which is a new cutting method, under the following conditions.

・ Rotation speed: 5300 rpm,
-Feed: 0.15 mm / rev,
-Processed hole depth in the longitudinal direction of the test piece: 95 mm (about 16D).
In addition, the lubrication conditions in each cutting method are as follows.

・ Wet cutting: External oil supply with water-soluble emulsion diluted by a factor of 20 with an oil amount of 10 L / min,
・ Dry cutting: No lubrication,
-Trace oil lubrication: Internally feeds synthetic ester with high biodegradability from the drill oil hole at approximately 1 cm ³ / hour.

  The amount of wear on the outer periphery of the drill until 300 holes were drilled under the above conditions was defined as the tool life. However, in the case of conventional wet cutting and dry cutting, the drill broke before drilling 300 holes and became impossible to drill. Therefore, the number of drilled holes until drilling became impossible was defined as the tool life. In all processing tests, a hole having a diameter of 6.05 mm and a depth of 12 mm was processed in advance as a guide hole. Therefore, this guide hole is included in 95 mm as the processing hole depth described above.

  Table 2 shows the tool life measured as described above.

  From Table 2, it can be seen that the trace oil lubrication cutting is remarkably superior in the number of perforations compared to the conventional wet cutting and dry cutting. In the case of micro oil lubricated cutting, the effect of Pb and S which are effective free cutting elements in conventional cutting methods, particularly wet cutting using a water-soluble emulsion, has not been demonstrated. It is suggested that a small amount of oil-lubricated cutting is not simply an extension of the conventional cutting method but is cut by a completely new phenomenon.

  In addition, in the case of micro-oil lubrication cutting, there is a difference in tool life even if the hardness of the work material is the same, so micro-oil lubrication workability is simply the hardness at room temperature as in the conventional cutting method. It cannot be organized by strength.

  As a result of detailed examination, in the case of deep hole drilling using a thin carbide coating drill, in addition to breakage of the drill due to an increase in cutting resistance, the chip becomes large and chipping occurs during machining. It has become clear that the so-called “chip disposal” that makes it difficult to discharge is caused, and that the above two characteristics of cutting resistance and chip disposal determine the tool life.

  As is clear from the above, micro oil lubrication cutting is based on a completely new phenomenon from the conventional cutting method, and therefore it is extremely important to search for free cutting steel for micro oil lubrication cutting. is there.

  Then, the present inventors repeated further detailed research on the trace oil lubrication cutting phenomenon. As a result, the following new findings (a) and (b) were obtained for the controlling factors of trace oil lubrication machinability, particularly cutting resistance and chip disposal.

  (A) In the trace oil lubrication cutting method, the cutting resistance when a small diameter drill is used is generally correlated with the hardness, and increases as the hardness increases. However, the relationship with strength is not a normal tensile strength showing a good correlation with hardness, but has a large correlation with a strength in the vicinity of 200 to 400 ° C., in particular, a 0.2% proof stress in tensile properties.

  (B) On the other hand, the chip processability is good when the chip shape is thin and the mass per chip is small. And as the hardness increases, the chips become smaller and the chip processability becomes better.

  As described above, in the case of trace oil lubrication cutting, the hardness of the steel material has an effect that contradicts two characteristics of cutting resistance and chip disposal. For this reason, even if the conventionally proposed free-cutting steel is used, it is difficult to apply it to the trace oil lubrication cutting method.

  Therefore, in order to obtain a steel material for micro oil-lubricated cutting, the present inventors have further conducted various studies on the material factors of the steel material affecting the micro oil-lubricated cutting property. As a result, the following findings (c) to (j) were obtained.

  (C) Among alloy elements added to steel, phosphorus (P) and tin (Sn) are effective in improving chip disposal and reducing cutting resistance. That is, P and Sn are segregated at the grain boundaries of the steel structure in a range where the content is small, so that the deformation resistance in the shear deformation region during chip generation is reduced compared to other solid solution strengthening elements and precipitation strengthening elements. Has an effect. Furthermore, since the chips are easily broken by the embrittlement effect due to the grain boundary segregation of P and Sn, the chips are reduced regardless of the change in cutting resistance. However, if the contents of P and Sn are excessive, these elements are present not only in the grain boundaries but also in the grains, resulting in an increase in hardness, resulting in an increase in cutting resistance. End up. Therefore, in order to achieve both improvement in chip disposal and reduction in cutting resistance, it is necessary to optimize the contents of P and Sn.

  (D) Titanium (Ti) contributes to strengthening when precipitated as a carbide, and suppresses a decrease in strength in the vicinity of 200 ° C., and therefore increases cutting resistance in the case of trace oil lubrication cutting. However, since Ti has a large affinity with nitrogen (N) and Ti nitride is formed before Ti carbide, Ti may be added up to an amount that can reduce solid solution N.

  (E) Vanadium (V) also precipitates as a carbide like Ti, and suppresses a decrease in strength in the vicinity of 200 ° C., thus increasing the cutting resistance in the case of trace oil lubrication cutting. For this reason, it is desirable not to add V in order to obtain a steel material for trace oil lubrication machinability. However, V is an element indispensable for ensuring the strength of the non-tempered steel material. For this reason, when using a non-tempered steel material as a steel material for trace oil lubrication cutting, you may add V.

  (F) Molybdenum (Mo) increases the cutting resistance in the case of trace oil-lubricated cutting because it suppresses strength reduction near 200 ° C. For this reason, it is desirable not to add Mo in order to obtain a steel material for trace oil lubrication machinability.

  (G) Copper (Cu) and nickel (Ni) also suppress a decrease in strength in the vicinity of 200 ° C. and increase cutting resistance in the case of trace oil lubrication cutting. For this reason, in order to make a steel material for trace oil lubrication cutting, it is desirable not to add Cu and Ni, but to suppress the level to be mixed as an impurity during melting.

  (H) For trace oil lubrication cutting, even if lead (Pb) and bismuth (Bi), which are conventionally known as free cutting elements, are added, almost no improvement effect on machinability is observed. Similarly, low-melting point oxides formed by Ca treatment or the like have almost no machinability improving effect in the case of trace oil lubrication cutting. Further, although the amount of sulfide contributes to the machinability improvement effect, the influence of the sulfide form on the improvement effect of the trace oil lubrication machinability is small. This is because a trace amount of lubricant is already present in the case of the trace oil lubrication cutting method.

  (I) Even if the steel materials have the same chemical composition, the shear deformation behavior at the time of chip generation also differs if the microstructure at room temperature is different. In particular, when the structure is a ferrite / pearlite structure, by optimizing the ratio of the amount of ferrite, the cutting resistance is reduced and the chip disposal is improved, so that it is possible to improve trace oil lubrication machinability.

  The present invention has been completed based on the above findings.

  The gist of the present invention resides in the steel materials for trace oil lubrication processing shown in the following (1) to (4).

  (1) By mass%, C: 0.33-0.45%, Si: 0.1-1.2%, Mn: 0.5-2.0%, S: 0.01-0.12% N: 0.010% or less, Al: 0.002-0.03%, Cr: 0.01-0.5% and P: more than 0.03% and containing 0.08% or less, the balance Has a chemical composition of Fe and impurities, and consists of a ferrite pearlite structure having a ferrite ratio of 15 to 55%.

(2) By mass%, C: 0.33-0.45%, Si: 0.1-1.2%, Mn: 0.5-2.0%, S: 0.01-0.12% N: 0.010% or less, Al: 0.002-0.03%, Cr: 0.01-0.5%, P: 0.08% or less and Sn: 0.25% or less, The value of fn1 represented by the following formula (1) satisfies 0.03 to 0.08, and the balance has a chemical composition of Fe and impurities, and consists of a ferrite pearlite structure having a ferrite ratio of 15 to 55%. A steel material for lubrication of trace oil, characterized by
fn1 = P + (Sn / 3.8) (1).
In addition, the element symbol in (1) Formula represents the content in steel in the mass% of the element.

  (3) The steel material for trace oil lubrication according to the above (1) or (2), which contains V: 0.3% or less in mass% instead of part of Fe.

  (4) The trace amount oil according to any one of (1) to (3) above, which contains, in mass%, B: 0.005% or less and Ti: 0.03% or less instead of part of Fe Steel material for lubrication.

  Here, the above-mentioned “ferrite-pearlite structure” means that a portion exceeding 95% of the whole is composed of a mixed structure of ferrite and pearlite. The “ferrite ratio” means the ratio of ferrite in the “ferrite / pearlite structure” and does not include “ferrite” in “pearlite” composed of “cementite” and “ferrite”.

  The above-mentioned “ferrite ratio” refers to the ratio of ferrite obtained by a normal two-dimensional evaluation method such as observation with an optical microscope, that is, the area ratio.

Specifically, “trace oil lubrication” indicates that the amount of lubricant (cutting fluid) to be used is 200 cm ³ or less per hour.

  Hereinafter, the inventions related to the steel materials for micro oil lubrication processing of the above (1) to (4) are referred to as “present invention (1)” to “present invention (4)”, respectively. Also, it may be collectively referred to as “the present invention”.

  The steel material for trace oil lubrication processing of the present invention can be used for trace oil lubrication cutting. The micro-oil lubricated cutting method is a technique that not only consumes less energy but is also environmentally friendly, and can increase cutting efficiency and maintain machining accuracy. For this reason, protection of global environment and cost reduction can be aimed at by using the steel material for trace oil lubrication processing of the present invention.

  Hereinafter, each requirement of the present invention will be described in detail. In addition, "%" display of the content of each element means "mass%".

(A) Chemical composition of steel material C: 0.33 to 0.45%
C is an element essential for increasing the hardness (strength) of steel and imparting a desired high hardness to machine structural parts. C also has an effect of optimizing the ferrite rate described later, which affects the workability in the case of micro oil lubrication cutting. However, if the content is less than 0.33%, it is difficult to obtain the above effect. On the other hand, when the content of C exceeds 0.45%, the cutting resistance is increased, and the amount of tool wear is increased. Therefore, the content of C is set to 0.33 to 0.45%. The C content is preferably 0.35 to 0.42%.

Si: 0.1-1.2%
Si is an element that increases the strength. However, if the content is less than 0.1%, the effect cannot be expected. On the other hand, when the Si content exceeds 1.2%, the hardness increases, and particularly, the solid solution dissolves in soft ferrite to increase the shear deformation resistance, resulting in an increase in cutting resistance. Therefore, the Si content is set to 0.1 to 1.2%. The upper limit of Si content is preferably 0.7%.

Mn: 0.5 to 2.0%
Mn has the effect of increasing strength. In order to reliably obtain this effect, the Mn content must be 0.5% or more. However, if the content exceeds 2.0%, the ratio of ferrite in the structure decreases and the hardness increases, so that the cutting resistance increases. Therefore, the Mn content is set to 0.5 to 2.0%. The lower limit of the Mn content is preferably 0.65%, and the upper limit is preferably 1.6%.

S: 0.01 to 0.12%
S has the effect | action which forms MnS in steel and improves machinability. The effect is not to lubricate with the tool but to reduce the shear deformation resistance by becoming the starting point of deformation in the chip shear region. However, if the content is less than 0.01%, it is difficult to obtain the above effect. On the other hand, when a large amount of S is contained, MnS becomes coarse and the amount thereof increases, so that anisotropy of toughness becomes remarkable, and further, the toughness itself deteriorates. In particular, when the S content exceeds 0.12%, the deterioration of toughness becomes significant. Therefore, the content of S is set to 0.01 to 0.12%. In addition, it is preferable that content of S shall be 0.03-0.10%.

N: 0.010% or less N is dissolved in ferrite, but near 200 ° C., the strength is increased by aging precipitation. For this reason, in the case of trace oil lubricated cutting, the cutting resistance is increased regardless of the hardness at room temperature, so that the N content is preferably as small as possible. Therefore, the N content is set to 0.010% or less. In addition, the more preferable content of N as a steel material for trace oil lubrication cutting is 0.008% or less.

Al: 0.002 to 0.03%
Al is an element having a deoxidizing action of steel. Moreover, there exists an effect which suppresses cutting resistance by forming the nitride and reducing the solid solution N. However, if the content is less than 0.002%, the effect of addition is poor. On the other hand, if a large amount of Al is contained, the amount of hard oxide may increase, resulting in tool damage. In particular, if the Al content exceeds 0.03%, tool damage becomes significant. Therefore, the content of Al is set to 0.002 to 0.03% or less.

Cr: 0.01 to 0.5%
Cr has the effect | action which raises the intensity | strength of steel materials. This effect is obtained when the Cr content is 0.01% or more. In order to ensure the strength of the steel material, the Cr content is preferably 0.05% or more. On the other hand, if the Cr content exceeds 0.5%, the ratio of ferrite in the structure is greatly reduced, so that the workability is lowered and the toughness is greatly deteriorated. Therefore, the Cr content is set to 0.01 to 0.5%. In addition, it is preferable that the upper limit of Cr content shall be 0.3%.

In the present invention, in addition to the above elements from C to Cr,
(1) P: more than 0.03% and 0.08% or less (in the case of the present invention (1)),
Or
(2) P and Sn satisfying P: 0.08% or less and Sn: 0.25% or less, and satisfying a value of fn1 represented by the formula (1) of 0.03 to 0.08 (present invention) (In the case of (2)),
Need to be included. This will be described below.

  P is an important element in the present invention. That is, P segregates at the grain boundary and has an action of reducing deformation resistance in the shear deformation region at the time of chip generation. Further, since the chips are easily divided by the embrittlement effect due to the grain boundary segregation of P, P also has an effect of improving the chip processability.

  In particular, when P is contained in an amount exceeding 0.03%, the above-described effects become remarkable. However, even if the P content exceeds 0.08%, the amount of P segregated at the grain boundaries is saturated, and the amount of P dissolved in the crystal grains such as ferrite increases, so the hardness increases. With this, cutting resistance also increases. Therefore, in order to achieve both improvement in chip disposal and reduction in cutting resistance, in the present invention (1), the P content is more than 0.03% and 0.08% or less. In addition, in this invention (1), in order to ensure the effect | action of P mentioned above stably, it is preferable that the content shall be 0.035 to 0.065%.

  In the present invention (1), the effect of P, which is more than 0.03% and 0.08% or less in content, is P: 0.08% or less and Sn: 0.25% or less. This can also be achieved by including a composite of P and Sn satisfying the fn1 value represented by the formula (0.03) to 0.08.

  Sn is an important element in the present invention. That is, Sn segregates at the grain boundary like P, and has the effect of reducing the deformation resistance in the shear deformation region during chip formation. Further, since the chips are easily broken by the embrittlement effect due to the grain boundary segregation of Sn, Sn also has an effect of improving the chip processability.

  In the case of the present invention (2) containing a composite of P and Sn, the above-mentioned effects are remarkable if the value of fn1 represented by the above formula (1) is 0.03 or more. However, the amount of P and Sn that segregates at the grain boundaries is saturated even if P and Sn are included in a composite with Pn exceeding 0.08 in the value of fn1, and the solid solution of P and Sn dissolved in the crystal grains such as ferrite As the amount increases, the hardness increases and the cutting resistance also increases. However, even if the value of fn1 represented by the above formula (1) is 0.03 to 0.08, when the P content exceeds 0.08%, it is hardened in the crystal grains such as ferrite. The amount of dissolved P increases to increase the hardness, and this causes an increase in cutting resistance. Further, even when the Sn content exceeds 0.25%, the amount of Sn dissolved in the crystal grains such as ferrite is increased, the hardness is increased, and the cutting resistance is increased at the same time. Therefore, in order to achieve both improvement in chip disposal and reduction in cutting resistance, the present invention (2) contains P: 0.08% or less and Sn: 0.25% or less. ) The value of fn1 represented by the formula satisfies 0.03 to 0.08. In the present invention (2), in order to stably secure the above-mentioned combined action of P and Sn, P: 0.065% or less and Sn: 0.2% or less, The represented value of fn1 is preferably 0.04 to 0.075.

  From the above, the chemical composition of the steel material for micro-oil lubrication processing according to the present invention (1) includes elements from C to Cr in the above-described range, and P: more than 0.03% and 0.08% The following were included, and the remainder was defined as consisting of Fe and impurities.

  Further, the chemical composition of the steel material for micro-oil lubrication processing according to the present invention (2) includes elements from C to Cr in the above-described range, and P: 0.08% or less and Sn: 0.25% or less. It was specified that the value of fn1 represented by the formula (1) satisfies 0.03 to 0.08, and the balance is composed of Fe and impurities.

In addition, in the steel material for trace oil lubrication processing according to the present invention, if necessary, instead of a part of Fe,
First group: V: 0.3% or less,
Second group: B: 0.005% or less and Ti: 0.03% or less,
And at least one group of elements. That is, at least one element of the first group and the second group may be contained as an optional additive element instead of a part of Fe.

  Hereinafter, the above optional additive elements will be described.

First group: V: 0.3% or less V has an effect of increasing the strength of the steel material. In order to reliably obtain this effect, it is preferable that V is a content of 0.01% or more. However, if its content exceeds 0.3%, the strength becomes excessively high and the softening resistance against high temperature strength increases, so that the cutting resistance also increases, and the machinability in the case of trace oil lubrication cutting decreases. Therefore, when V is contained, the upper limit of the content is set to 0.3%. In addition, when V is contained, the content of V is preferably 0.01 to 0.3%.

Second group: B: 0.005% or less and Ti: 0.03% or less B strengthens the grain boundary and performs machining such as cutting on the steel material having the “ferrite / pearlite structure” in the present invention. In the case where the quenching treatment is performed after this, it has the effect of suppressing delayed fracture due to the grain boundary cracking that occurs after quenching. In order to reliably obtain this effect, the B content is preferably 0.0005% or more. However, even if B is contained in an amount exceeding 0.005%, the above effect is saturated and grain boundary segregation of P is suppressed, so that the above-described effect of P is reduced. Therefore, when B is contained, the upper limit of the content is set to 0.005%. When B is included, the B content is preferably 0.0005 to 0.005%.

  When B is contained, Ti must be contained at the same time. That is, Ti has the effect of forming nitrides and reducing the solute N, and suppresses the formation of B nitrides (BN) in boron steel, so that the effect of B described above can be sufficiently exerted. In order to surely obtain such an effect, Ti is preferably contained in a content of 0.005% or more. However, if a large amount of Ti is contained, the amount of hard nitride may increase and cause tool damage. If excessive Ti content forms carbides, this increases strength and increases cutting resistance. The machinability in the case of trace oil lubrication cutting is reduced. Therefore, when Ti is contained, the upper limit of the content is set to 0.03%. In addition, when Ti is contained, the content of Ti is preferably 0.005 to 0.03%.

  For the above reasons, the chemical composition of the steel material for micro oil lubrication processing according to the present invention (3) is replaced with a part of Fe of the steel material for micro oil lubrication processing of the present invention (1) or the present invention (2), V: Specified to contain 0.3% or less.

  Moreover, the chemical composition of the steel material for trace oil lubrication processing according to the present invention (4) is replaced with a part of Fe of the steel material for trace oil lubrication processing according to any one of the present invention (1) to the present invention (3). B: 0.005% or less and Ti: 0.03% or less.

  In addition, Mo is not actively added to the steel material for trace oil lubrication processing according to the present invention. This is because, as described in the previous finding (f), Mo suppresses the strength decrease in the vicinity of 200 ° C. and increases the cutting resistance, leading to a decrease in machinability in the case of trace oil lubrication cutting. .

  Similarly, Cu and Ni are not positively added to the steel for micro-oil lubrication processing according to the present invention. As described in the previous knowledge (g), Cu and Ni suppress the strength reduction near 200 ° C. and increase the cutting resistance in the case of trace oil-lubricated cutting. This is because the machinability is reduced. In addition, Cu and Ni may be mixed as an impurity element at the time of melting, and within this range, it is sufficiently acceptable even in the case of trace oil lubrication cutting. Specifically, even if both Cu and Ni are contained up to 0.15%, they do not greatly affect the workability in the case of trace oil lubrication cutting.

  As described in Knowledge (h), in addition to Pb and Bi, which have been well known as free-cutting elements, Ca, Te, Se, etc., which can control the form of MnS, Since there is no cutting effect improvement effect by reducing the cutting resistance, these elements are not positively added to the steel for micro oil lubrication processing according to the present invention for micro oil lubrication cutting. . Pb exceeds 0.25%, Bi exceeds 0.10%, Ca exceeds 0.05%, Te exceeds 0.05%, Se contains more than 0.5% Then, although hot workability is deteriorated, any element can be acceptable as long as it is an impurity amount because it does not affect the machinability if it is not more than the above value.

  In addition, about O (oxygen) as an impurity mixed in steel, the content is not specified in particular, but in order to ensure good toughness, the content is preferably 0.015% or less. It is preferable.

  Steel having the above-described chemical composition can be melted by, for example, a converter or an electric furnace. For the production of the steel ingot, any means of “ingot-making method” or “continuous casting method” injected into the mold may be used.

(B) Structure of steel material The steel material for trace oil lubrication processing according to the present invention needs to have a ferrite-pearlite structure with a ferrite ratio of 15 to 55%.

  Ferrite is a soft phase. For this reason, it deforms preferentially in the case of trace oil-lubricated cutting to reduce the deformation resistance during the cutting process, thereby contributing to the reduction of the cutting resistance. However, if the ferrite ratio is less than 15%, the above effect cannot be obtained sufficiently. On the other hand, when the ferrite ratio exceeds 55%, it becomes difficult to ensure the strength as a steel material, and the soft structure becomes excessive, and the ductility as the steel material increases, resulting in high cutting resistance in the case of trace oil lubrication cutting. In addition, chip disposal may be reduced.

  For the reasons described above, the steel for micro-oil lubrication processing according to the present invention is composed of a ferrite pearlite structure having a ferrite ratio of 15 to 55%.

  It is more preferable that the structure of the steel material for trace oil lubrication processing of the present invention is composed of a ferrite pearlite structure having a ferrite ratio of 20 to 50%.

  As described above, the term “ferrite / pearlite structure” in the present invention refers to a structure in which 95% of the whole is composed of a mixed structure of ferrite and pearlite. “Ferrite ratio” refers to the proportion of ferrite in the “ferrite / pearlite structure”, and does not include “ferrite” in “pearlite” composed of “cementite” and “ferrite”.

  In addition, as described above, the above-mentioned “ferrite ratio” refers to the ratio of ferrite, that is, the area ratio obtained by a normal two-dimensional evaluation method such as observation with an optical microscope.

  In addition, examples of the structure other than the “ferrite / pearlite structure” in the steel material for micro-oil lubrication processing according to the present invention include the third phase such as bainite and martensite. The third phase is 5% or less. As long as there is, there is no substantial effect on the machinability in the case of micro oil lubrication cutting. Therefore, in the present invention, as described above, the ferrite ratio in the “ferrite / pearlite structure” in which the portion exceeding 95% of the whole is composed of a mixed structure of ferrite and pearlite is defined. That is, the above-mentioned “ferrite ratio” more specifically means {“ferrite” / (“ferrite” + “pearlite” + “third phase”)} × 100 (%).

  In addition, the predetermined structure can be obtained by non-tempering treatment, that is, even after cooling after the final hot working, and after the hot working, heat treatment such as “normalizing” and “normalizing-tempering” is performed. Can also be obtained. From the viewpoint of cost, it is preferable to use a non-tempering treatment in which a predetermined structure is obtained without performing heat treatment. This non-tempering treatment is advantageous in terms of cost because it does not require heat treatment, and is advantageous in terms of delivery because the process can be simplified.

The “trace oil lubrication” as used in the present invention means that the amount of lubricant (cutting fluid) used is 200 cm ³ or less per hour, but in the actual processing of steel materials, the amount of lubricant is 1 It is often carried out at about 50 cm ³ or less per hour. As a method for applying the lubricant, a method in which the lubricant is made into a mist, mixed with air and sprayed is generally used. In some cases, mist-like water may also be mixed. In the present invention, the form of the lubricant at the time of application is not particularly limited, and the effect can be secured if the amount of the lubricant alone is 200 cm ³ or less per hour. In particular, the steel material of the present invention is suitable for trace oil lubrication processing of internal oil supply such as internal oil supply from a drill oil hole.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1]
Steels A1 to A12, steels B1 to B6, and steels C1 to C3 having chemical compositions shown in Table 3 were melted using a 150 kg vacuum melting furnace. Steels A1 to A12 in Table 3 are steels whose chemical compositions are within the range defined by the present invention. On the other hand, steels B1 to B6 and steels C1 to C3 are steels of comparative examples whose chemical compositions deviate from the conditions defined in the present invention. For steel containing a composite of P and Sn, the value of fn1 represented by the formula (1) is also shown in Table 3.

  Subsequently, the ingot of these steels was heated to 1250 ° C. and then hot-worked (hot forging) to finish at 1000 ° C. or higher was performed to produce a round bar having a diameter of 60 mm. In addition, after the hot forging, the manufacturing process of the non-tempered steel material was simulated by air cooling.

  For each round bar thus obtained, the structure and trace oil lubricity machinability were investigated.

  The specimen was cut in parallel to the forging axis around a position 15 mm from the surface of the round bar (position of half the radius of the round bar, hereinafter referred to as “R / 2 part position”). After the cut surface (longitudinal section of the round bar) was mirror-polished and corroded with nital, the ferrite ratio (area ratio) at the R / 2 part position was observed with an optical microscope having a magnification of 400 times. Measurements and organization (phase) were identified.

  Micro oil lubrication cutting performance is obtained by cutting each of the above round bars into a length of 100 mm as a test piece, having a diameter (D) of 5.57 mm, a total length of 180 mm, a blade length of 130 mm, and a tip angle of Using a cemented carbide drill with a 140 ° oil hole, cutting at a depth of 90 mm was performed under the following conditions, and trace oil lubrication machinability was evaluated based on the measured value of cutting resistance (thrust force) and chip disposal. As for chip disposal, a large number of chips generated at the time of cutting resistance measurement were collected, the thickness of the chips was measured for 10 pieces with a micrometer, and the smaller the average value, the better the chip disposal. It was determined that In all the processing tests, a hole having a diameter of 5.60 mm and a depth of 10 mm was processed in advance as a guide hole. Therefore, this guide hole is included in 90 mm as the processing hole depth described above.

・ Rotation speed: 5718 rpm,
-Feed: 0.25mm / rev,
-Processing hole depth in the longitudinal direction of the test piece: 90 mm (about 16D),
Lubrication condition: Synthetic ester with high biodegradability is sprayed by mixing it with air from the drill oil hole with internal oil at a rate of about 1.0 cm ³ / hour.

  Table 4 summarizes the results of the various surveys described above. Moreover, the relationship between cutting resistance and chip disposal is shown in FIG. In FIG. 1, “●”, “◯”, and “Δ” are the results of investigations relating to the present invention examples of test numbers 1 to 12 using steels A1 to A12, and tests using steels B1 to B6, respectively. It is the investigation result which concerns on the comparative example of the test number 19-21 using the investigation result which concerns on the comparative example of the numbers 13-18, and steel C1-C3.

  As is apparent from Table 4 and FIG. 1, the chemical composition of the steel is within the range defined by the present invention, and the structure is cut in the case of test numbers 1 to 12 of the present invention example that satisfies the requirements of the present invention. The chip thickness, which is the standard for resistance (thrust force) and chip disposal, is small, the balance between cutting resistance and chip disposal is good, and the trace oil lubrication machinability is excellent.

  On the other hand, the comparative examples of test numbers 13 to 21 all have a low balance between cutting resistance and chip disposal.

  In addition, among the comparative examples, the balance between the cutting resistance and chip disposal in the case of test numbers 19 to 21 using steels C1 to C3 represented by “Δ” in FIG. 1 is further lowered. This is because the content of V (test number 19 using steel C1), the content of C and P (test number 20 using steel C2), the content of C, P and Ti, and the ferrite in the ferrite-pearlite structure This is because the rate (test number 21 using steel C3) is out of the definition of the present invention.

[Example 2]
The fact that the steel material for micro-oil lubrication processing according to the present invention has an effect when used under micro-oil lubrication cutting conditions was verified by taking lathe turning as an example of a conventional cutting method.

  That is, using a round bar of steel A2 and steel B2 to B4 made in [Example 1] with a diameter of 60 mm as a test material, turning was performed under the following conditions using a P-type carbide tool, and the cutting resistance (main Component force), a number of chips were collected in the same manner as in [Example 1], the thickness of the chips was measured for 10 pieces with a micrometer, and the chip thickness was calculated from the average value. And the influence of the P content on cutting resistance and chip disposal was investigated.

・ Cutting speed: 100 mm / min,
-Feed: 0.10 mm / rev,
・ Incision amount: 1.5 mm,
・ Lubrication condition: no lubrication.

  The reason why the feed is set to 0.10 mm / rev, which is about ½ in this turning process, in contrast to the feed of 0.25 mm / rev in the case of trace oil lubrication cutting in [Example 1], This is because the number of cutting edges in drilling is two, and the feed per blade is substantially halved.

  Table 5 and Table 6, FIG. 2 and FIG. 3 show the above-mentioned investigation results together with the investigation results in the case of trace oil lubrication cutting in [Example 1]. “Change rate” in Table 5, Table 6, FIG. 2 and FIG. 3 are all expressed as a ratio to the value of steel B2 having a P content of 0.012%. Further, “●” and “◯” in FIG. 2 and FIG. 3 represent the result in the case of micro oil-lubricated cutting and the result in the case of unlubricated turning, respectively.

  From Table 5 and FIG. 2, there is almost no effect of the P content in the case of non-lubricated turning on the rate of change in cutting resistance, but in the case of trace oil-lubricated cutting, P is The tendency for cutting resistance to become low clearly is recognized by containing.

  Further, from Table 6 and FIG. 3, even in the case of the thickness of the chip, in the case of the trace oil lubrication cutting compared with the case of the non-lubricated turning, the chip can be effectively removed by containing P. It is clear that it is getting thinner.

  From the above, it has become clear that the steel material for trace oil lubrication processing according to the present invention has an effect when used under trace oil lubrication cutting conditions.

  The steel material for trace oil lubrication processing of the present invention can be used for trace oil lubrication cutting. The micro-oil lubricated cutting method is a technique that not only consumes less energy but is also environmentally friendly, and can increase cutting efficiency and maintain machining accuracy. For this reason, protection of global environment and cost reduction can be aimed at by using the steel material for trace oil lubrication processing of the present invention.

It is a figure which shows the relationship between the cutting resistance in the case of the trace oil lubricated cutting investigated in [Example 1], and chip disposal property. P content affecting the rate of change in cutting resistance in the case of micro oil lubricated cutting investigated in [Example 1] and in the case of non-lubricated turning as an example of the conventional cutting method investigated in [Example 2] It is a figure which compares and shows the influence of these. The effect of P on the rate of change in chip thickness in the case of micro-oil lubricated cutting investigated in [Example 1] and in the case of non-lubricated turning as an example of the conventional cutting method investigated in [Example 2] It is a figure which compares and shows the influence of content.

Claims (4)

  In mass%, C: 0.33-0.45%, Si: 0.1-1.2%, Mn: 0.5-2.0%, S: 0.01-0.12%, N: 0.010% or less, Al: 0.002 to 0.03%, Cr: 0.01 to 0.5% and P: more than 0.03% and 0.08% or less, with the balance being Fe and A steel material for lubricating a trace amount of oil having a chemical composition of impurities and comprising a ferrite pearlite structure having a ferrite ratio of 15 to 55%. In mass%, C: 0.33-0.45%, Si: 0.1-1.2%, Mn: 0.5-2.0%, S: 0.01-0.12%, N: 0.010% or less, Al: 0.002 to 0.03%, Cr: 0.01 to 0.5%, P: 0.08% or less, and Sn: 0.25% or less. ) The value of fn1 represented by the formula satisfies 0.03 to 0.08, the remainder has a chemical composition of Fe and impurities, and consists of a ferrite pearlite structure with a ferrite ratio of 15 to 55%. Steel material for micro oil lubrication.
fn1 = P + (Sn / 3.8) (1)
In addition, the element symbol in (1) Formula represents the content in steel in the mass% of the element.   The steel material for trace oil lubrication according to claim 1 or 2, which contains V: 0.3% or less in mass% instead of part of Fe. The steel material for micro-oil lubrication processing according to any one of claims 1 to 3, which contains B: 0.005% or less and Ti: 0.03% or less in mass% instead of a part of Fe.

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