JP6801542B2 - Mechanical steel and its cutting method - Google Patents

Description

The present invention relates to a mechanical structural steel having excellent impact characteristics and intermittent machinability, and a cutting method thereof.

In recent years, as the strength of steel has increased, the decrease in machinability has become a problem. The main parts of an automobile manufactured from machine structural steel, such as gears, CVTs, crankshafts, connecting rods, and CVJs, are manufactured by cutting machine structural steel. It is known that the cost related to cutting accounts for a large part of the cost of manufacturing parts, and there is an increasing need for steel that does not shorten the tool life in order to reduce the manufacturing cost. This tendency is particularly noticeable for parts including intermittent cutting such as gear gear cutting and end milling, which have high tool costs.

Conventionally, in order to improve the tool life, there is a method of adding Pb or S as an alloy component to the steel material to be cut, but Pb has a problem in terms of environmental load, and S has an impact value or the like when the addition amount is increased. There is a problem of deteriorating the mechanical properties of. Further, a method of softening the oxide in the steel by adding Ca and adhering to the tool surface during cutting, that is, a method of protecting the tool with a so-called bellague is also utilized as needed. However, the utilization of Bellag is not generally used due to many restrictions on cutting conditions and components.

Against this background, free-cutting steel with a new composition for the purpose of improving the tool life during intermittent cutting and intermittent cutting methods are disclosed. For example, Patent Document 1 defines the composition of the machine structural steel in a predetermined range, and the contact time and non-contact time between the tool and the machine structural steel in a predetermined range, at a cutting speed of 50 m / min or more. A method for cutting machine structural steel having an excellent tool life in intermittent cutting is disclosed, which comprises forming a protective film mainly composed of oxide on the tool surface by cutting.

In intermittent cutting, the tool does not continuously contact the work material, so the new surface of the steel material attached to the tool is exposed to air and rapidly oxidizes, which may cause oxidative wear. Patent Document 2 discloses an invention in which Al is added to the machine structural steel to be cut to suppress oxidative wear of the tool during intermittent cutting. According to Patent Document 2, since Al in the steel material adhering to the tool is more easily oxidized than Fe, Al suppresses oxidative wear of the tool during intermittent cutting.

These techniques are different from the conventional techniques for controlling the second phase of steel by utilizing Pb, S, etc. to improve machinability. In other words, it is a technology that controls the interface during cutting by optimizing the combination of steel materials and cutting conditions to suppress tool wear, and is extremely useful as a technology for improving machinability during intermittent cutting of high-strength machine structural steel. Is important to.

Japanese Unexamined Patent Publication No. 2008-36769 Japanese Unexamined Patent Publication No. 2010-24549

The above-mentioned conventional technique has the following problems.
In Patent Document 1, it is essential that the steel material contains a predetermined amount of S and Al in order to generate a protective film that is effective in suppressing tool wear. However, since S may deteriorate the mechanical properties of steel as described above, its addition to high-strength steel is limited. Further, the addition of Al tends to generate hard non-metal inclusions such as Al ₂ O ₃ , which may reduce mechanical properties such as fatigue strength. Hard inclusions are known to cause absorptive wear of the tool, which may be accelerated depending on the cutting conditions.

The mechanical structural steel described in Patent Document 2 is required to contain 0.06 to 0.5% by mass of Al. This amount of Al is relatively large for mechanical structural steel, and therefore, as described above, hard non-metal inclusions are likely to be generated, which may cause a decrease in fatigue strength and an increase in abrasive wear of a tool.

As described above, the conventional technique is not always suitable as a technique for improving the machinability while maintaining the mechanical properties of the steel material. In addition, in order to control the interface between the steel material and the tool during cutting and improve the tool life, it is considered important to control not only the steel material but also the tool side, but no technical improvement from the tool side has been proposed. ..

The present invention has been devised in view of the above-mentioned problems, and an object of the present invention is to provide a mechanical structural steel having excellent mechanical properties and a tool life during intermittent cutting and a cutting method thereof.

The present inventors have conducted intensive research to solve the above problems, and considered that it is important to control both the steel material side and the tool side in order to control the steel material / tool interface during cutting and improve the tool life. Therefore, we focused on the lubrication mechanism of the steel / tool interface, which is considered to have a large effect on the tool life, and conducted basic research using steel materials to which various alloying elements were added and various tool materials. As a result, the following findings were obtained.

(A) When a steel material containing a relatively large amount of an element to which O is bonded more easily than Fe is intermittently cut as a solid solution element, an oxide film mainly composed of the element is formed on the tool. This effect is more remarkable as the surface roughness of the tool material is smaller. When the surface roughness becomes large, the adhesion of Fe becomes intense and the oxide film is not formed.

(B) When a steel material containing a relatively large amount of Al is intermittently cut using a tool material having a relatively small surface roughness, the tool life is greatly deteriorated. When the tool surface was observed in detail by SEM, a lot of adhesion of Fe was observed in addition to oxides. Al-based oxides such as alumina have a high melting point, maintain hardness at the high temperature interface during cutting, and are not easily sheared. Therefore, it is considered that the unevenness of the Al oxide adhering to the interface during cutting promotes the adhesion of Fe and induces the adhesion wear of the tool. In Patent Document 2, addition of Al is preferable for suppressing oxidative wear. However, in order to suppress adhesive wear, the amount of addition should be limited. In oxidative wear, the tool coating gradually wears, but in adhesive wear, the coating wears rapidly with peeling. Therefore, it is more important to suppress adhesive wear from the viewpoint of improving tool life. The finding that the amount of Al added should be limited is a result that could not be predicted from the conventional findings.

(C) When a steel material containing a relatively large amount of Si is intermittently cut while limiting the amount of Al added to a certain range using a tool material having a relatively small surface roughness, an oxide mainly composed of Si oxide is produced. Formed on the tool. In this case, the tool life is dramatically improved. When the surface of the Si oxide on the tool is observed in detail by SEM, it is very smooth, so it is considered that this oxide softened at a high temperature during cutting and gave a lubricating effect. Here, the oxide mainly composed of Si oxide is an oxide having the largest atomic ratio of Si among the metal elements contained in the oxide.

As described above, the present inventors can generate an oxide mainly composed of Si oxide on the tool during intermittent cutting of the steel material by optimizing the steel material component and the surface roughness of the tool. It was found that the lubrication effect protects the tool and improves the tool life. Specifically, it is a completely new finding that the amount of Al added, which has been conventionally considered to be preferable, is reduced in the present invention, and Si is added as an element having a lubricating action.

Furthermore, it was found that the impact characteristics, which are important characteristics of machine structural steel, can be improved by adding an appropriate amount of Ti, Nb and / or V.

That is, the machine structural steel and the cutting method thereof according to the present invention are as follows.
(1)
By mass%
C: 0.30 to 0.72%,
Si: 0.73 to 1.40%,
Mn: 0.46 to 0.80 %,
Cr: 0.065 to 0.65%,
P: 0.001 to 0.045%,
S: 0.001 to 0.023%,
N: 0.0036 to 0.0100%,
Al: contains less than 0.001 to 0.026%, further,
Ti: 0 to 0.500%,
Nb: 0 to 0.500%,
V: 0 to 0.110 %
Containing any one or more of the above, the balance is composed of Fe and unavoidable impurities, 0 <[Ti%] + [Nb%] + [V%] ≤ 0.500, and 42.5 <66. A steel for machine structural use, which satisfies [Si%] -3 [Mn%] -5 [Cr%] <90.9.
Here, [Ti%], [Nb%], [V%], [Si%], [Mn%] and [Cr%] are the masses of Ti, Nb, V, Si, Mn and Cr, respectively. Represents%.
(2)
The mechanical structural steel is further increased by mass%.
B: 0.0003 to 0.0050%
The steel for machine structure according to (1), which is characterized by containing.
(3)
The mechanical structural steel is further increased by mass%.
Mo: 0.01-0.30%,
Ni: 0.05-1.0%,
and,
Cu: 0.05-1.0%
The mechanical structural steel according to any one of (1) and (2), which comprises one or more selected from the group consisting of.
(4)
A method for obtaining a raw material by intermittently cutting the mechanical structural steel according to any one of (1) to (3), wherein the outermost surface is ceramically coated by PVD or CVD, and the surface roughness thereof is reduced. A method for cutting steel for machine structural use, which comprises using a tool having a Ra of 0.80 μm or less.

According to the present invention, it is possible to provide a mechanical structural steel having excellent tool life and impact characteristics at the time of intermittent cutting such as gear cutting and end mills, and a cutting method thereof.

It is a figure which shows the relationship between the hardness (HV) and machinability (tool life [m]) of the steel of the invention example and the comparative example.

The reason for limiting the composition of the steel of the present invention will be described. Hereinafter,% means mass%.

(C: 0.30 to 0.72%)
C is an element added to ensure the strength of steel. If the amount of C added is less than 0.30%, sufficient strength cannot be obtained when the final processed product is used in a ferrite pearlite structure or when it is hardened or tempered, while 0. If it is more than 72%, the hardness of the cutting material increases, the machinability deteriorates, and the toughness of the steel part decreases. Therefore, the amount of C is set to 0.30% to 0.72%. The preferred amount of C is 0.40% to 0.60%.

(Si: 0.73 to 1.40%)
Si is the most important element in the present invention. Si is required to cause a chemical reaction with oxygen in the atmosphere on the tool surface during intermittent cutting to generate an oxide mainly composed of Si oxide on the tool. If the addition amount of Si is less than 0.73%, the addition effect cannot be sufficiently obtained, while if it exceeds 1.40%, the toughness of the steel is lowered and hard inclusions are formed in the steel. , The machinability is reduced. Therefore, the amount of Si is set to 0.73% to 1.40%. The preferred amount of Si is 0.80% to 1.20%.

(Mn: 0.40 to 1.0%)
Mn is a solid solution strengthening element of steel, and is an element necessary for ensuring hardenability when parts are hardened and tempered for use. Further, it has an effect of improving machinability by combining with S in the steel material to generate MnS-based sulfide. However, when the Mn content is less than 0.40%, S in the steel material combines with Fe to generate FeS, and the steel becomes brittle. On the other hand, when the Mn content exceeds 1.0%, the hardness of the substrate increases and the workability decreases. Further, it inhibits the formation of oxides mainly composed of Si on the tool surface during cutting. Therefore, the Mn content is set to 0.40 to 1.0%. It is preferably 0.46 to 0.80%.

(Cr: 0.065 to 0.65%)
Cr is a solid solution strengthening element of steel, and when a part is hardened and tempered before use, it improves hardenability and imparts tempering softening resistance to improve fatigue strength after quenching. If the Cr content is less than 0.065%, these effects cannot be obtained. When the Cr content exceeds 0.65%, Cr carbides are generated and the steel becomes embrittled. Further, it inhibits the formation of oxides mainly composed of Si on the tool surface during cutting. Therefore, the amount of Cr is set to 0.065 to 0.65%. It is preferably 0.10 to 0.30%.

(P: 0.001 to 0.045%)
P is an unavoidable impurity. Since P segregates at the austenite grain boundaries and causes grain boundary cracks during hot working, it is desirable to reduce the amount of P to 0.045% or less. It is desirable to reduce P as much as possible, but limiting the amount of P to less than 0.001% is excessively costly. Therefore, the range of P amount is 0.001 to 0.045%.

(S: 0.001 to 0.023%)
S combines with Mn to form MnS. MnS has an effect of improving machinability, but in order to obtain the effect, it is necessary to add 0.001% or more of S. On the other hand, when the S content exceeds 0.023%, the toughness and fatigue strength are lowered. Therefore, the S content is set to 0.001 to 0.023%. It is preferably 0.005 to 0.016%.

(N: 0.0036 to 0.0100%)
N combines with Al and V in steel to form carbonitride, suppresses grain growth by pinning the austenite grain boundaries, and has the function of refining the structure that transforms from austenite. It is necessary to add 0.0036% or more in order to obtain. On the other hand, if it is excessively added in excess of 0.0100%, the ductility in a high temperature range of 1000 ° C. or higher decreases, which causes a decrease in yield during continuous casting and rolling. Therefore, the amount of N needs to be 0.0036 to 0.0100%. A suitable range for the amount of N is 0.0040 to 0.0080%.

(Al: 0.001 to less than 0.040%)
Al is an element effective for deoxidizing steel, and it is necessary to add 0.001% or more to obtain the effect. However, when steel with an Al content of 0.040% or more is intermittently cut, an oxide mainly composed of Al oxide is formed on the tool surface, and this oxide promotes iron adhesion, resulting in tool adhesion wear. Will promote. Therefore, the amount of Al is set to less than 0.001 to 0.040%, and the upper limit is preferably set to less than 0.026%.

(Contains any one or more of Ti: 0 to 0.500%, Nb: 0 to 0.500%, V: 0 to 0.500%)
Ti, Nb and V form fine carbides, nitrides and / or carbonitrides with C and / or N to suppress grain growth and abnormal grain growth during heating in the austenite temperature range. Contributes to fine homogenization of the structure and improves impact characteristics. In order to obtain this effect, one or more Ti, Nb and V are added in the range of 0 to 0.500%, respectively. If it exceeds 0.500% in either case, hard carbides are generated and the machinability is lowered, so the upper limit is 0.500%. Preferred addition amounts of Ti, Nb and V are 0.020 to 0.200%, 0.010 to 0.150% and 0.050 to 0.300%, respectively.

(0 <[Ti%] + [Nb%] + [V%] ≤ 0.500)
In order to suppress crystal grain growth and abnormal grain growth during heating in the austenite temperature range by Ti, Nb and V, one or more of Ti, Nb and V are contained, and the total content thereof is 0 <[. It is necessary to satisfy [Ti%] + [Nb%] + [V%]. The preferable range of [Ti%] + [Nb%] + [V%] is 0.003 to 0.500, and more preferably 0.010 to 0.300.

(42.5 <66 [Si%] -3 [Mn%] -5 [Cr%] <90.9) ... Equation (1)
In order to dramatically improve the tool life by forming an oxide mainly composed of Si oxide on the tool when intermittent cutting is performed using a tool material with a relatively small surface roughness, Si in steel , Mn and Cr by mass% ([Si%], [Mn%] and [Cr%]) need to satisfy the above formula (1).

This limitation is defined as follows. That is, steel materials having various components are intermittently cut, and the amount of tool wear and the composition of oxides formed on the tool are investigated by an energy dispersive X-ray spectrometer (EDS) attached to a scanning electron microscope (SEM). did. As a result, when comparing steel materials with the same hardness level, it is effective to generate an oxide mainly composed of Si oxide on the tool in order to reduce the amount of tool wear and improve the tool life. It turned out that there was. Oxides mainly composed of Si oxide have a low melting point and soften due to heat generation during cutting to provide lubricity, which contributes to excellent tool life. Further, the ratio of Si in the oxide can be predicted by the formula of 66 [Si%] -3 [Mn%] -5 [Cr%] in the component range of the present invention, and the lower limit value of this formula is 42.5. If there is, it has been experimentally clarified that an oxide mainly composed of Si oxide is generated on the tool and contributes to an excellent tool life. Here, [Si%], [Mn%], and [Cr%] represent the mass% of Si, Mn, and Cr, respectively. Therefore, the lower limit of this equation is set to 42.5. Regarding the upper limit value, since the maximum value of 66 [Si%] -3 [Mn%] -5 [Cr%] is 90.875 within the scope of the claims of the present invention, the second decimal place is rounded off to 90. It was set to 9.

It is effective to improve the characteristics by containing one or more selected elements from the following elements in addition to the above basic components as the steel component.

(B: 0.0003 to 0.0050%)
B is an optional component that can be added as needed. B dissolved in austenite has the effect of greatly enhancing the hardenability of steel in a small amount. Therefore, B is effective for obtaining a martensite structure when quenching is performed after cutting. In order to obtain this effect, 0.0003% or more of B may be added in the present invention. On the other hand, even if it is added in excess of 0.0050%, the effect is saturated. Therefore, when B is added, the amount of B is set in the range of 0.0003 to 0.0050% or less. A suitable range for the amount of B is 0.0010 to 0.0025%. When B is added, it is preferable to add an appropriate amount of Ti and Al for fixing N at the same time in order to stably secure the solid solution B.

(Mo: 0.01 to 0.30%, Ni: 0.05 to 1.0%, and Cu: one or two of 0.05 to 1.0%)
Mo, Ni, and Cu are all solid solution strengthening elements. In order to obtain this effect, Mo may be added in an amount of 0.01% or more, and Ni and Cu may be added in an amount of 0.05% or more, respectively, as long as the excellent properties of the steel of the present invention are not impaired. When Mo exceeds 0.30%, hardenability becomes high, bainite or island-like martensite is formed, and processability decreases. Therefore, the Mo content is 0.30% or less, preferably 0.20% or less. If both Ni and Cu exceed 1.0%, as with Mo, the hardenability becomes too high, bainite or island-shaped martensite is formed, and the workability is lowered. Therefore, the upper limit of the contents of Ni and Cu is set to 1.0% or less.

The composition of the mechanical structural steel used in the present invention is as described above, and the balance is Fe and unavoidable impurities. Depending on the conditions of raw materials, materials, manufacturing equipment, etc., unavoidable impurities (for example, As, Co, etc.) are mixed in the steel, but it is permissible as long as it does not impair the excellent properties of the present invention.

The cutting hardness of the steel of the present invention is preferably in the range of 150 to 260 HV. If it is less than 150 HV, the roughness of the machined surface after cutting may become large, while if it exceeds 260 HV, it may be too hard and cutting may become difficult. However, the effect of the tool protective film of the present invention is not affected by the hardness and can be obtained in a wide range of hardness. In order to adjust the hardness to a preferable range, heat treatment such as annealing or spheroidizing annealing may be performed before the cutting step.

It is generally known that mainite and martensite are contained in the structure to reduce machinability. Therefore, the structure of the mechanical structural steel of the present invention at the time of cutting is preferably a ferrite-pearlite structure. However, the effect of the tool protective film of the present invention is not affected by the structure and can be obtained by any structure.

In order to obtain the tool life improving effect of the present invention, it is necessary to cut the machine structural steel having the above-mentioned components under predetermined conditions.

The most important point in the present invention is that an oxide mainly composed of Si oxide is formed on the tool during cutting. In order for such oxides to be formed, oxygen must be supplied to the contact interface between the steel material and the tool, which are subject to high temperature and high pressure. In the case of so-called intermittent cutting in which the tool and the steel material repeatedly contact and non-contact during cutting, such as gear cutting and end mills, oxygen enters from the atmosphere during the non-contact. This oxygen contributes to the oxide formation reaction. On the other hand, in the case of continuous cutting in which the tool and the steel material are in constant contact during cutting, such as turning, oxygen is not supplied from the atmosphere, so that most of the tools do not form oxides. For this reason, the present invention limits the cutting method to intermittent cutting.

Since the cutting interface is in a harsh environment of high temperature and high pressure, the tool is required to have wear resistance and heat resistance. Therefore, at present, coating tools with improved wear resistance and heat resistance are mainly used by applying ceramic coating by CVD or PVD to base tool materials such as high-speed steel, cemented carbide, and cermet. .. Although uncoated solid high-speed steel tools and cemented carbide tools are still used, it is desirable to cut the steel of the present invention with coated tools. This is because by using a coating tool, Fe adhesion to the tool is significantly suppressed and Si oxide is stably formed. The coating _{TiN, TiAlN, AlCrN, Al 2} O 3, TiC, although various ceramic such as TiCN is used in a single layer or multi-layer, the effect of the present invention is the type of coating, particularly limited in thickness and manufacturing method However, the range currently used in industry can be widely applied.

In order to form an oxide film on the tool, it is important to reduce the surface roughness of the tool material. This is because when the surface roughness becomes large, Fe violently adheres to the unevenness of the tool, and the oxide film is not formed. In order to stably form the oxide film, the tool surface roughness needs to be Ra 0.80 μm or less, preferably 0.40 μm or less, and more preferably 0.10 μm or less. Such surface roughness can be achieved, for example, by polishing the tool material after coating or before and after coating.

In the present invention, it is important that oxygen in the atmosphere is supplied to the cutting interface, so that the cutting is preferably performed dry. However, the present invention is not particularly limited by the lubrication method because it has a certain effect even when a water-soluble or water-insoluble cutting oil is used.

Next, an example of the present invention will be described. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is described in this one condition example. It is not limited. In the present invention, various conditions can be adopted as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

The steels having the composition shown in Table 1 were melted by a vacuum melting method, cast into a 180 kg ingot, and hot forged into a 65φ steel bar. Numbers 1 to 16 are invention examples, and numbers 17 to 27 are comparative examples. Nos. 21 to 23 are shown as comparative examples because the chemical composition of the steel material is within the range of the present invention, but the tool surface roughness Ra is out of the range or the tool is not ceramic-coated.

As a normalizing treatment, the steel bar was held at 950 ° C. for 1 hour and then air-cooled. Subsequently, a sample was cut out so that an intermediate position between the center of the circle and the surface could be observed on a circular cross section perpendicular to the length direction of the steel bar, embedded in resin, polished, and then the Vickers hardness at the same position was measured. After the nital corrosion, the same position was observed with an optical microscope. The results of hardness measurement are shown in Table 1. The structure of the steel materials used in this test was a ferrite-pearlite structure. The ferrite-pearlite structure referred to here also includes those having a ferrite area ratio of 15% or less and most of which is pearlite. A cutting test was performed on a 40 × 40 × 250 mm square test piece cut out from a steel bar after normalizing with a dance tool (fly tool) assuming gear gear cutting (hobbing). The cutter used in the hobbing process at the time of manufacturing actual parts has a plurality of cutting edges. On the other hand, the dance tool of this embodiment is a cutter having only one hobbing cutting edge. It has been confirmed that the cutting results of the cutter with multiple cutting edges and the dance tool have a good correspondence. For this reason, the dance tool is used as a substitute test for hobbing. The test method by cutting the dance tool is described in detail in, for example, "TOYOTA Technical Review Vol.52 No.2 Dec.2002 P78". Table 2 shows the test conditions.

The surface roughness of the tool before the cutting test was measured with a stylus type roughness meter. Then, every time the test piece was cut by 0.5 m, the maximum rake face wear depth (maximum crater wear depth) of the tool was measured with a stylus type roughness meter. When the amount of wear became 70 μm or more, it was judged that the tool life was reached, and the cutting distance up to that point was taken as the tool life, and the test was completed. In addition, for the purpose of investigating the composition of the produced oxide, a tool cut only 0.5 m was prepared separately. The rake face of the tool was observed by SEM, and the composition of the oxide film was analyzed by EDS. The ratio (at%) of Si among the metal elements contained in the oxide was determined and shown in Table 1.

In the Charpy impact test, a cylindrical material having a diameter of 25 mm was cut out from the steel bar after the above-mentioned normalizing treatment so that the central axis was perpendicular to the forging direction of the steel bar. Next, each columnar material is held for 1 hour under a temperature condition of 850 ° C., then oil-quenched to cool it to 60 ° C., further held for 30 minutes under a temperature condition of 550 ° C., and then water-cooled. went. Then, each tempered columnar material was machined to prepare a Charpy test piece specified in JIS Z 2202, and a Charpy impact test at room temperature was carried out by a method specified in JIS Z 2242. At that time, the absorbed energy per unit area (J / cm ² ) was adopted as the evaluation index.

Items that do not meet the conditions of the present invention in Table 1 are underlined. In addition. It is widely known that the tool life is affected by the hardness of the steel material at the time of cutting, and the larger the hardness, the shorter the tool life. Therefore, we decided to compare and evaluate the length of tool life with steel materials of the same hardness level. FIG. 1 shows the relationship between the hardness (HV) and machinability (tool life [m]) of the steels of the invention example and the comparative example.

Since the steels of Nos. 17 and 18 have an insufficient amount of Si added and do not satisfy the formula (1), the tool life is shorter than that of the steel material having the same hardness level in the invention example.
Since the steel numbers 19 and 20 have an excessive amount of Al added, the tool life is shorter than that of the steel material having the same hardness level in the invention example.
Nos. 21 and 22 have a large tool surface roughness, so that an oxide film is not formed and the tool life is shorter than that of the steel material having the same hardness level in the invention. From these examples, the influence of Ra of the tool is clear.
In No. 23, since the tool is not coated, no oxide film is formed and the tool life is shorter than that of the steel material having the same hardness level in the invention.
No. 24 has a small absorbed energy in the Charpy test because none of Ti, Nb and V is added.
No. 25 has a shorter tool life than the steel material having the same hardness level in the invention example because the amount of Ti added is excessive.
No. 26 has a shorter tool life than the steel material having the same hardness level in the invention example because the amount of Nb added is excessive.
No. 27 has a shorter tool life than the steel material having the same hardness level in the invention example because the amount of V added is excessive.
Nos. 1 to 16 have a long tool life and sufficiently absorbed energy because the component composition, the formula (1), and the tool surface roughness are within the range of the present invention.

The present invention provides a mechanical structural steel having excellent tool life during intermittent cutting in a member manufacturing process and impact characteristics of a final member.

Claims (4)

By mass%
C: 0.30 to 0.72%,
Si: 0.73 to 1.40%,
Mn: 0.46 to 0.80 %,
Cr: 0.065 to 0.65%,
P: 0.001 to 0.045%,
S: 0.001 to 0.023%,
N: 0.0036 to 0.0100%,
Al: contain less than from 0.001 to 0.026 percent, further,
Ti: 0 to 0.500%,
Nb: 0 to 0.500%,
V: 0 to 0.110 %
Containing any one or more of the above, the balance is composed of Fe and unavoidable impurities, 0 <[Ti%] + [Nb%] + [V%] ≤ 0.500, and 42.5 <66. A steel for machine structural use, which satisfies [Si%] -3 [Mn%] -5 [Cr%] <90.9.
Here, [Ti%], [Nb%], [V%], [Si%], [Mn%] and [Cr%] are the masses of Ti, Nb, V, Si, Mn and Cr, respectively. Represents%. The mechanical structural steel is further increased by mass%.
B: 0.0003 to 0.0050%
The steel for machine structure according to claim 1, wherein the steel contains. The mechanical structural steel is further increased by mass%.
Mo: 0.01-0.30%,
Ni: 0.05-1.0%,
and,
Cu: 0.05-1.0%
The steel for machine structural use according to any one of claims 1 or 2, wherein it contains one kind or two or more kinds selected from the group consisting of. The method for obtaining a raw material by intermittently cutting the mechanical structural steel according to any one of claims 1 to 3, wherein the outermost surface is ceramically coated by PVD or CVD, and the surface roughness thereof is Ra0. A method for cutting steel for machine structural use, which comprises using a tool having a length of 80 μm or less.

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