JP2006083448A - Steel for minimum quantity lubrication machining - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide steel for minimum quantity lubrication machining in which machining is carried out while feeding a small quantity of lubricating oil. <P>SOLUTION: The steel for minimum quantity lubrication machining has a chemical composition consisting of 0.30 to 0.46% C, 0.1 to 1.0% Si, 0.2 to 2.0% Mn, ≤0.08% P, 0.01 to 0.12% S, ≤0.010% N, 0.002 to 0.03% Al, 0 to 0.03% Ti and the balance Fe with impurities and satisfying at least either of (Al/N≥2) and (Ti/N≥3) and also has a structure composed of ferrite-pearlite structure of 15 to 65% ferrite fraction. This steel can contain one or more elements selected from at least one group among the following three groups: (1) 0.01 to 0.8% Cr and 0.01 to 0.3% V; (2) 0.005 to 0.05% Nd and 0.005 to 0.1% Nb; (3) 0.0005 to 0.005% B. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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”) has been actively studied. For example, Non-Patent Document 1 to Non-Patent Document 6 relate to an ultra-trace oil lubrication cutting (MQL cutting) technique. A report has been made. Further, Patent Document 1 and Patent Document 2 disclose processing apparatuses suitable for ultra-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, oils, machines, and oil supply systems have been conventionally studied. However, there have been few examples that have been studied on the workpieces to be cut, particularly 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 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 used under a trace oil lubrication cutting condition using a lubricant 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 have made a laboratory melting of free-cutting steel having a chemical composition shown in Table 1, which is conventionally known as free-cutting steel for machine structures, and used for trace oil lubrication cutting, wet cutting and dry cutting. The tool life in each case 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 to 20 times with oil amount 10L / min,
・ Dry cutting: no lubrication,
・ Treatment with a trace amount of oil: Internal lubrication of a highly biodegradable synthetic ester at about 1 cm ³ / hour from a drill oil hole.

  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 is 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. Also, 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 just the hardness at room temperature as in the conventional cutting method. It is also clear that it is not something that can be organized. Furthermore, in the case of deep hole drilling using a thin carbide coating drill, it has become clear that breakage due to an increase in cutting resistance is an important issue, and that the increase in cutting resistance causes tool wear to progress.

  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.

  Therefore, the present inventors first conducted detailed studies 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.

  (A) In the trace oil lubrication cutting method, the cutting resistance when a small diameter drill is used has a correlation with the strength in the vicinity of 200 to 400 ° C., in particular, the 0.2% proof stress in the tensile properties. This is because drilling in the conventional wet cutting method uses a large amount of lubricant (cutting fluid), so the processing temperature is low, whereas in the case of the trace oil lubrication cutting method, there is very little lubricant. Therefore, this is based on the fact that the cooling capacity during processing is reduced.

  (B) Generally, the cutting resistance can be classified into “shear deformation force when generating chips” and “friction force between the tool and the workpiece”. In the case of a micro-oil lubricated cutting method, it is considered that the contribution of frictional force to cutting force is small, so the contribution to cutting force in this processing is dominated by “shear deformation force when generating chips”. From this, in the case of small-diameter drilling by a micro-oil lubricated cutting method, the 0.2% proof stress, which is a measure of plastic deformability, has a large correlation with the cutting resistance, not the breaking strength in the tensile test. It becomes.

  From the above findings (a) and (b), even if the conventionally proposed free-cutting steel is used, if the 0.2% proof stress in the tensile characteristics at 200 to 400 ° C. is increased for some reason, a trace oil lubrication cutting method is used. It will be difficult to apply. Then, in order to obtain the steel material for trace oil lubrication cutting, the present inventors repeated research on the material factor of the steel material affecting the trace oil lubrication machinability. As a result, the following findings (c) to (j) were obtained.

  (C) Some alloying elements added to steel suppress a decrease in strength from normal temperature (room temperature) strength when the temperature increases by several hundred degrees, and even cause an increase in strength from normal temperature strength. . Among alloy elements, N (nitrogen) has the greatest tendency. Therefore, in order to obtain a steel material for trace oil lubrication machinability, it is preferable that N is not present in a solid solution state as much as possible.

  (D) When Ti precipitates as a carbide, it contributes to strengthening and suppresses a decrease in strength in the vicinity of 200 ° C., so that the cutting resistance in the case of trace oil lubrication cutting is increased. Therefore, in order to obtain a steel material for trace oil lubrication cutting, Ti should not be precipitated as carbide. However, since Ti has a large affinity with N and Ti nitride is formed before Ti carbide, Ti may be added from the viewpoint of reducing solid solution N.

  (E) 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) Since Mo suppresses the strength decrease in the vicinity of 200 ° C., it increases the cutting resistance in the case of trace oil lubrication cutting. For this reason, it is desirable not to add Mo in order to obtain a steel material for trace oil lubrication machinability.

  (G) Cu and Ni also suppress the strength decrease in the vicinity of 200 ° C. and increase the cutting resistance in the case of trace oil lubrication cutting. For this reason, in order to obtain 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) Pb and Bi, which are conventionally known as free-cutting elements, may be added, but in the case of micro-oil lubricated cutting, the machinability improving effect is hardly recognized. Similarly, low-melting point oxides formed by MnS inclusions, Ca treatment, etc. have almost no cutting effect in the case of trace oil lubrication cutting. Moreover, the influence of inclusions such as sulfides on the improvement effect of 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 tensile properties at high temperatures will be different if the microstructure at normal temperature is different. In particular, when the structure is a ferrite pearlite structure, by optimizing the ferrite content ratio, the strength near 200 ° C, especially the 0.2% proof stress, is greatly reduced. can do.

  (J) Cr is an element that stabilizes cementite and promotes the formation of a pearlite structure to reduce the amount of ferrite, thus increasing the cutting resistance in the case of trace oil-lubricated cutting. For this reason, it is desirable not to add Cr in order to obtain a steel material for trace oil lubrication machinability. However, Cr 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 Cr.

  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: 0.30 to 0.46%, Si: 0.1 to 1.0%, Mn: 0.2 to 2.0%, P: 0.08% or less, S: 0.01 to 0.12%, N: 0.010% or less, Al: 0.002 to 0.03% and Ti: 0 to 0.03%, and at least the following formula (1) or (2 ), And the balance is a chemical composition of Fe and impurities, and the structure is a ferrite pearlite structure having a ferrite ratio of 15 to 65%.
Al / N ≧ 2 (1),
Ti / N ≧ 3 (2),
In addition, the element symbol in (1) Formula and (2) Formula represents content in steel in the mass% of the element.

  (2) In place of part of Fe, in the above-mentioned (1) containing at least one of Cr: 0.01 to 0.8% and V: 0.01 to 0.3% in mass% Steel material for lubrication processing of trace amount of description.

  (3) In place of a part of Fe, (1) or (%) containing one or more of Nd: 0.005 to 0.05% and Nb: 0.005 to 0.1% in mass% (2) The steel material for trace oil lubrication processing according to (2).

  (4) The steel material for trace oil lubrication according to any one of (1) to (3) above, which contains B: 0.0005 to 0.005% by mass% instead of part of Fe.

  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. “Ferrite ratio” means the proportion of ferrite in the “ferrite pearlite structure” and does not include “ferrite” in “pearlite” composed of “cementite” and “ferrite”.

  In addition, it is known that the volume ratio of a certain phase is equal to the area ratio. Therefore, the above-mentioned “ferrite ratio” is obtained by a normal two-dimensional evaluation method such as observation with an optical microscope. What is necessary is just to determine from the ratio of a ferrite.

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 relating to the steel materials for trace oil lubrication processing of (1) to (4) above are referred to as “invention of (1)” to “invention of (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 C: 0.30 to 0.46%
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 0.30%, it is difficult to obtain the above effect. On the other hand, if the C content exceeds 0.46%, the cutting resistance is increased and the amount of tool wear is increased. Therefore, the content of C is set to 0.30 to 0.46%. In addition, preferable content of C is 0.33-0.43%.

Si: 0.1 to 1.0%
Si is an element effective for deoxidation of steel. However, if the content is less than 0.1%, the effect cannot be expected. On the other hand, if Si is contained in excess of 1.0%, the above effect is saturated and the toughness is reduced. Therefore, the Si content is set to 0.1 to 1.0%. The upper limit of the Si content is preferably 0.7%.

Mn: 0.2 to 2.0%
Mn has the effect of increasing strength. In order to obtain this effect with certainty, the Mn content must be 0.2% or more. However, when the content exceeds 2.0%, the ferrite ratio in the structure is lowered, so that workability is lowered, and further, toughness is greatly deteriorated. Therefore, the Mn content is set to 0.2 to 2.0%. The lower limit of the Mn content is preferably 0.5%, and the upper limit is preferably 1.6%.

P: 0.08% or less P reduces toughness. In particular, when the content exceeds 0.08%, the toughness is significantly lowered. Therefore, the content of P is set to 0.08% or less. The P content is preferably 0.03% or less.

S: 0.01 to 0.12%
S has the effect | action which forms MnS in steel and improves machinability. The effect is to reduce the shear deformation resistance by becoming the starting point of deformation in the chip shear region rather than lubrication with the tool. 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 added, MnS coarsens and the amount thereof increases, so that the anisotropy of toughness becomes remarkable and 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 an element having an important meaning in the present invention. That is, even if it dissolves in ferrite, N ages and precipitates at around 200 ° C. to increase the strength, and the cutting resistance in the case of trace oil lubrication cutting is increased regardless of the normal temperature hardness (strength) of the steel material. For this reason, in order to make a steel material for trace oil lubrication machinability, it is preferable to reduce the N content as much as possible. Therefore, the N content is set to 0.010% or less. A more preferable N content is 0.008% or less. The N content is very preferably 0.006% or less.

Al: 0.002 to 0.03%
Al is an element effective for deoxidation of steel and forms an oxide in the steel. Moreover, it has the effect of forming nitrides and reducing the solute 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.

Ti: 0 to 0.03%
The addition of Ti is optional. If added, it has the action of forming nitrides and reducing the solid solution N and suppressing the cutting resistance from increasing. In order to obtain this effect with certainty, Ti is preferably contained in an amount of 0.005% or more. However, if a large amount of Ti is included, the amount of hard nitride may increase and cause tool damage, and when Ti carbide is formed to increase not only normal temperature strength but also high temperature strength, in the case of trace oil lubrication cutting In some cases, the cutting resistance of the steel increases and the machinability decreases. In particular, when the Ti content exceeds 0.03%, tool damage becomes significant, and the machinability in the case of trace oil lubrication cutting also becomes significant. Therefore, the content of Ti is set to 0 to 0.03%.

Al / N: 2 or more or / and Ti / N: 3 or more In order to suppress the increase in cutting resistance due to aging precipitation of solid solution N at around 200 ° C. It is preferable to fix solute N as a nitride with Ti. For this purpose, at least the value of “Al / N” needs to be 2 or more, or the value of “Ti / N” needs to be 3 or more. Therefore, it was decided to satisfy either of the above formulas (1) or (2).

  From the above, the chemical composition of the steel material for micro-oil lubrication processing according to the invention of (1) above contains elements from C to Ti within the above range, and at least the above formula (1) or (2) One of the above was satisfied, and the balance was defined as consisting of Fe and impurities.

  In addition to the above-described component elements, the steel material for micro-oil lubrication processing according to the present invention includes, as necessary, one or more elements selected from at least one of the first to third groups described below. May be added as an optional additive element.

  Hereinafter, the optional additive element will be described.

First group: Cr: 0.01 to 0.8% and V: 0.01 to 0.3%
Cr has the effect | action which raises the intensity | strength of steel materials. In order to reliably obtain this effect, the Cr content is preferably 0.01% or more. However, if its content exceeds 0.8%, the ferrite ratio in the structure is greatly reduced, resulting in a decrease in workability and a large deterioration in toughness. Therefore, the Cr content when added is preferably 0.01 to 0.8%. In addition, from the viewpoint of trace oil lubrication machinability, the upper limit of the Cr content is preferably 0.55%.

  V, like Cr, has the 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, increasing the cutting resistance in the case of trace oil lubrication cutting. Therefore, when V is added, the content of V is preferably 0.01 to 0.3%.

  In addition, said Cr and V can be added only in any 1 type or 2 types of composite.

Second group: Nd: 0.005 to 0.05% and Nb: 0.005 to 0.1%
Nd finely disperses MnS that forms ferrite nuclei, ensures the ferrite rate in the ferrite pearlite structure, and has an action of reducing cutting resistance in the case of trace oil lubrication cutting. In order to reliably obtain this effect, the Nd content is preferably 0.005% or more. However, if Nd exceeds 0.05%, not only the above effect is saturated, but also the hot workability is significantly reduced. Therefore, the content of Nd when added is preferably 0.005 to 0.05%.

Nb
Similarly to Nd, Nb also has the effect of securing the ferrite rate in the ferrite pearlite structure and reducing the cutting resistance in the case of trace oil lubrication cutting. Nb also has the effect of increasing the toughness by making the crystal grains fine. In order to reliably obtain such an effect, it is preferable that Nb has a content of 0.005% or more. However, if its content exceeds 0.1%, coarse and hard Nb carbonitrides remain undissolved and the machinability deteriorates. Therefore, the content of Nb when added is preferably 0.005 to 0.1%.

  In addition, said Nd and Nb can be added only by any 1 type or 2 types of composite.

Group 3: B: 0.0005 to 0.005%
B is a delayed fracture associated with intergranular cracking that occurs after quenching when strengthening the grain boundaries and applying a quenching treatment to the steel material having the “ferrite pearlite structure” according to the present invention after machining. Has the effect of suppressing In order to reliably obtain this effect, it is preferable that B has a content of 0.0005% or more. However, even if B is contained in an amount exceeding 0.005%, the above effect is saturated, and the cost is increased. Therefore, when B is added, the B content is preferably 0.0005 to 0.005%.

  From the above, the chemical composition of the steel material for micro-oil lubrication processing according to the invention of (2) is replaced with a part of Fe of the steel of the invention of (1) for the purpose of increasing the strength of the steel material. , Cr: 0.01 to 0.8% and V: 0.01 to 0.3%.

  In addition, the chemical composition of the steel material for micro-oil lubrication processing according to the invention of (3) described above is for the purpose of ensuring the ferrite rate in the ferrite pearlite structure and reducing cutting resistance. Instead of a part of Fe of the steel of the invention, it was defined to contain one or more of Nd: 0.005 to 0.05% and Nb: 0.005 to 0.1%.

  Furthermore, the chemical composition of the steel for micro-oil lubrication processing according to the invention of (4) suppresses delayed fracture due to grain boundary cracking that occurs after quenching when performing quenching after machining such as cutting. As an object, it was defined that B: 0.0005 to 0.005% was contained instead of a part of Fe of the steel of any one of the inventions (1) to (3).

  In addition, Mo is not 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 a decrease in strength in the vicinity of 200 ° C. and increases the cutting resistance in the case of trace oil-lubricated cutting.

  Similarly, Cu and Ni are not added to the steel material for trace oil lubrication processing according to the present invention. This is also because Cu or Ni suppresses the strength decrease in the vicinity of 200 ° C. and increases the cutting resistance in the case of trace oil lubrication cutting as described in the previous finding (g). 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 no cutting effect is reduced by reducing the cutting resistance, it is not necessary to add these elements in the steel material for trace oil lubrication processing according to the present invention intended for trace oil lubrication cutting. In addition, the steel material for trace oil lubrication processing according to the present invention may contain Pb, Bi, Ca, Te, and Se. The upper limits in that case are 0.25%, 0.10%, 0.05%, 0.05% and 0.5%, respectively.

  Note that the content of O (oxygen) as an impurity mixed in the steel does not have to be specified, but in order to ensure good toughness, the content is preferably 0.015% or less. Preferably, 0.010% or less is more 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 of the present invention needs to have a ferrite pearlite structure with a ferrite ratio of 15 to 65%.

  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, if the ferrite ratio exceeds 65%, 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, thereby increasing the cutting resistance in the case of trace oil lubrication cutting. May end up.

  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 65%.

  More preferably, the structure of the steel for micro-oil lubrication processing of the present invention is composed of a ferrite pearlite structure having a ferrite ratio of 20 to 45%.

  As already described, the term “ferrite pearlite structure” as used in the present invention refers to a structure in which more than 95% of the whole is composed of a mixed structure of ferrite and pearlite. The “ferrite ratio” refers to the ratio of ferrite in the “ferrite pearlite structure” and does not include “ferrite” in “pearlite” composed of “cementite” and “ferrite”.

  In addition, it is known that the volume ratio of a certain phase is equal to the area ratio. Therefore, the above-mentioned “ferrite ratio” is obtained by a normal two-dimensional evaluation method such as observation with an optical microscope. As already described, it may be determined from the ratio of ferrite.

  In addition, examples of the structure other than the “ferrite pearlite structure” in the steel material for micro-oil lubrication processing of the present invention can include the third phase such as bainite and martensite, but the third phase is 5% or less. As long as it is done, 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 is defined in a “ferrite pearlite structure” in which a portion exceeding 95% of the whole is composed of a mixed structure of ferrite and pearlite. 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” referred to in the present invention means that the amount of lubricant (cutting fluid) used is 200 cm ³ or less per hour, but in 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.

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

  Steels A1 to A24 and B1 to B7 having chemical compositions shown in Tables 3 and 4 were melted using a 150 kg vacuum melting furnace. Steels A1 to A24 in Tables 3 and 4 are steels of the present invention examples whose chemical compositions are within the range defined by the present invention. On the other hand, steels B1 to B7 in Table 4 are steels of comparative examples that deviate from the conditions defined in the present invention.

  Subsequently, these steel ingots were heated to 1250 ° C. and 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.

  Each round bar thus obtained was examined for structure, mechanical properties and trace oil lubrication machinability.

  The surface of each round bar is mirror-polished in parallel with the longitudinal direction of forging and includes a position 15 mm from the surface (position of 1/2 radius, hereinafter referred to as “R / 2 part position”). Then, after corroding with the nital, the ferrite ratio (area ratio) was measured at the R / 2 part position and the structure (phase) was identified with an optical microscope having a magnification of 400 times.

  The mechanical properties were obtained by collecting a tensile test piece of JIS14A from the R / 2 part position of each round bar and conducting a tensile test at room temperature and 200 ° C. The ratio was evaluated by the ratio of 0.2% proof stress at ℃ (hereinafter referred to as “high temperature yield ratio”).

  Micro oil lubrication cutting performance is obtained by cutting each of the above-mentioned round bars into a length of 100 mm as a test piece, 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 Using a cemented carbide drill with a 140 ° oil hole, cutting was conducted under the following conditions.

・ Rotation speed: 5300 rpm,
-Feed: 0.15 mm / rev,
-Processing hole depth in the longitudinal direction of the test piece: 95 mm (about 16D),
Lubrication condition: Synthetic ester with high biodegradability is applied at a rate of about 1.0 cm ³ / hour from the drill oil hole with internal lubrication.

  In addition, micro oil lubrication cutting performance is evaluated based on the measured value of cutting resistance (thrust force) and tool life when micro oil lubricated cutting is performed under the above conditions. The tool life is that the drill breaks before 700 holes are drilled. Evaluation was made based on the number of drilled holes until drilling was not possible. In addition, when 700 holes could be drilled without breaking, the tool life was considered good. In this processing test, a hole having a diameter of 6.05 mm and a depth of 12 mm is processed in advance as a guide hole. Therefore, this guide hole is included in 95 mm as the processing hole depth described above.

  Table 5 summarizes the results of the various surveys described above. In Table 5, the tensile strength at room temperature was expressed as “TS (RT)”, and the 0.2% proof stress at 200 ° C. was expressed as “YP (200 ° C.)”. In addition, a “◯” mark in the “tool life” column indicates that 700 holes could be drilled without breakage and that the tool life was good. The “third phase” in Table 5 refers to a structure other than the “ferrite pearlite structure” as described above.

  As is apparent from Table 5, the chemical composition of the steel is within the range defined by the present invention, and the structure is also the test numbers 1 to 24 of the present invention examples that satisfy the requirements of the present invention. It is 0.53 or less, cutting resistance (thrust force) is small, tool life is good, and trace oil lubrication machinability is excellent.

  On the other hand, the comparative examples of test numbers 25 to 31 all have a high high-temperature yield ratio, the cutting resistance (thrust force) is a high value exceeding 1000 N, and the drill breaks before 700 holes are drilled. It is clear that the tool life is also short and inferior in trace oil lubricity.

  In addition, in the case of test number 25 using steel B1 in which the content of S is lower than the lower limit specified in the present invention, the high temperature yield ratio is 0.55 which is only slightly higher than the present invention examples of test numbers 1 to 24. The reason why the oil-lubricated machinability is low in spite of the fact is that there is little MnS that is the starting point of deformation in the chip shear region, and the shear deformation resistance is large.

  Further, in the case of test number 28 using steel B4 in which the C content exceeds the upper limit specified in the present invention, the high temperature yield ratio is 0.55 which is only slightly higher than the present invention examples of test numbers 1 to 24. Nevertheless, the reason why the trace oil lubricity machinability is low is that the 0.2% proof stress itself at 200 ° C. is high because the strength itself is increased by the C increase.

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.

Claims (4)

In mass%, C: 0.30 to 0.46%, Si: 0.1 to 1.0%, Mn: 0.2 to 2.0%, P: 0.08% or less, S: 0.01 -0.12%, N: 0.010% or less, Al: 0.002-0.03% and Ti: 0-0.03%, and at least of the following formula (1) or (2) A trace oil lubrication steel material characterized by satisfying any of the above, with the balance being the chemical composition of Fe and impurities, and the structure comprising a ferrite pearlite structure having a ferrite ratio of 15 to 65%.
Al / N ≧ 2 (1)
Ti / N ≧ 3 (2)
In addition, the element symbol in (1) Formula and (2) Formula represents content in steel in the mass% of the element.   The trace amount oil of Claim 1 which replaces with a part of Fe and contains 1 or more types in Cr: 0.01-0.8% and V: 0.01-0.3% by the mass%. Steel material for lubrication.   It replaces with a part of Fe, and contains 1 or more types of Nd: 0.005-0.05% and Nb: 0.005-0.1% by the mass%. Steel material for micro oil lubrication. The steel material for trace oil lubrication processing according to any one of claims 1 to 3, which contains B: 0.0005 to 0.005% in mass% instead of a part of Fe.