WO2018159617A1 - 切削加工用線材 - Google Patents
切削加工用線材 Download PDFInfo
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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Definitions
- the present invention relates to a cutting wire, and more particularly to a cutting wire that exhibits excellent machinability regardless of conditions.
- steels with improved machinability are generally used as steel for cutting.
- low-carbon sulfur free-cutting steel SUM23, etc. in JIS standards
- low-carbon sulfur composite free-cutting in which lead, which is a free-cutting element, is added in addition to large amounts of Mn sulfide.
- Steel (such as SUM24L in JIS standards) is often used.
- Patent Document 1 proposes a steel having excellent finished surface roughness and small dimensional change, in which the average width and yield ratio of sulfide inclusions in the wire drawing material are defined.
- Patent Documents 2 and 3 propose steels having excellent machinability that define the dispersion state of MnS inclusions, Pb inclusions, and Pb-MnS inclusions.
- Patent Document 4 proposes a free-cutting steel and a manufacturing method in which the range of the surface hardness of the steel is limited with a steel composition to which Nb is added.
- JP 2003-253390 A Japanese Patent No.5954483 Japanese Patent No.5954484 Japanese Unexamined Patent Publication No. 2007-239015
- machinability is improved by optimizing the average width and yield ratio of sulfide inclusions.
- This machinability test to evaluate machinability is performed with a high-speed tool (SKH4).
- the tool material used for cutting is a coating material such as CVD or PVD, cermet and ceramics. And so on. Therefore, when the tool material type is changed, the problem is that the optimization of the average width and yield ratio of sulfide inclusions described in Patent Document 1 may not necessarily contribute to improvement of machinability. It was.
- Patent Document 1 does not mention the lubricant used in the machinability test. Therefore, when the kind of lubricant changed, it turned out that the average width
- Patent Documents 2 and 3 the dispersion state of MnS inclusions, Pb inclusions, and Pb-MnS inclusions is optimized to improve machinability.
- a high-speed tool (SKH4) is used.
- the tool material types are various as described above, when the tool material type is changed, Patent Document 2 and It was found that the method proposed in 3 may not contribute to improvement of machinability. Similarly, it has been found that even when the type of lubricant is changed, the methods proposed in Patent Documents 2 and 3 may not contribute to improvement of machinability.
- Patent Document 4 only machinability evaluation is performed only under specific cutting conditions, and there is a problem that sufficient machinability cannot be obtained when the cutting conditions are different.
- the present invention has been developed in view of the above circumstances, and does not ask a tool material type and a lubricant type, and even when a lubricant is not used, the wire material exhibits excellent machinability.
- the purpose is to provide.
- the inventors have conducted an extensive investigation on the relationship between the component composition of the wire and the machinability. As a result, the tool material type and the lubricant type are not questioned, and no lubricant is used. Even so, the inventors have found a component composition and mechanical properties suitable for exhibiting excellent machinability.
- the present invention is based on the above findings.
- the gist configuration of the present invention is as follows.
- Cutting wire C: 0.001 to 0.150 mass% Si: 0.010 mass% or less, Mn: 0.20 to 2.00% by mass, P: 0.02 to 0.15 mass%, S: 0.20 to 0.50 mass%, N: 0.0300 mass% or less, and O: 0.0050-0.0300 mass%,
- the balance has a component composition consisting of Fe and inevitable impurities,
- the average aspect ratio of the ferrite grains at the 1/4 position of the diameter from the surface of the wire for cutting is more than 2.8, the following expressions (1) and (2) are satisfied: When the average aspect ratio is 2.8 or less, the wire rod for cutting having Vickers hardness satisfying the following formulas (3) and (4).
- the component composition further comprises: Pb: 0.01 to 0.50 mass%, Bi: 0.01 to 0.50 mass%, Ca: 0.01% by mass or less,
- the component composition further comprises: Cr: 3.0% by mass or less, Al: 0.010 mass% or less, Sb: 0.010 mass% or less, Sn: 0.010 mass% or less, Cu: 1.0 mass% or less,
- the component composition further comprises: Nb: 0.050 mass% or less, Ti: 0.050 mass% or less, V: 0.050 mass% or less, Zr: 0.050 mass% or less, W: 0.050 mass% or less, Ta: 0.050 mass% or less, Y: 0.050 mass% or less, 4.
- the cutting wire according to any one of 1 to 3 above, containing 1 or 2 or more selected from the group consisting of Hf: 0.050% by mass or less and B: 0.050% by mass or less.
- the wire rod of the present invention can exhibit excellent machinability without questioning the tool material type and the lubricant type, and even when no lubricant is used.
- C 0.001 to 0.150 mass% C is an element that contributes to improving the strength of steel, and requires 0.001% by mass or more in order to obtain sufficient strength as structural steel. Therefore, the C content is 0.001% by mass or more, preferably 0.01% by mass or more. On the other hand, when the C content exceeds 0.150% by mass, the hardness is excessively increased and the tool life during cutting is reduced. Therefore, the C content is 0.150 mass% or less, preferably 0.13 mass% or less, more preferably 0.10 mass% or less.
- Si 0.010 mass% or less Si in steel combines with oxygen to generate SiO 2 .
- This SiO 2 acts as hard particles in the steel and promotes abrasive wear of the tool during cutting, resulting in reduced tool life. Therefore, the Si content is 0.010% by mass or less, preferably 0.003% by mass or less.
- the lower limit of the Si content is not particularly limited and may be 0, but industrially exceeds 0% by mass.
- Si also has an effect of improving descalability in shot blasting and pickling performed before cold drawing. Therefore, from the viewpoint of obtaining the above effect, the Si content is preferably 0.0005% by mass or more.
- Mn 0.20 to 2.00% by mass
- Mn is an element having an effect of improving machinability by combining with S to form a sulfide. In order to acquire the said effect, it is necessary to add 0.20 mass% or more. Therefore, the Mn content is 0.20% by mass or more, preferably 0.60% by mass or more, more preferably 0.80% by mass or more. On the other hand, excessive addition of Mn causes an increase in hardness due to solid solution strengthening, and reduces the tool life during cutting. Therefore, the Mn content is 2.00% by mass or less, preferably 1.80% by mass or less, more preferably 1.60% by mass or less.
- P 0.02-0.15 mass%
- P is an element having an effect of improving machinability.
- 0.02 mass% or more needs to be added. Therefore, the P content is 0.02% by mass or more, preferably 0.03% by mass or more.
- the machinability improving effect is saturated. Therefore, the P content is 0.15% by mass or less, preferably 0.14% by mass or less, more preferably 0.13% by mass or less.
- S 0.20 to 0.50 mass%
- S is an element that exists as sulfide inclusions and is effective in improving machinability. In order to obtain this effect, addition of 0.20% by mass or more is necessary. Therefore, the S content is 0.20% by mass or more, preferably 0.25% by mass or more, more preferably 0.30% by mass or more. On the other hand, addition exceeding 0.50 mass% reduces the hot workability of steel. Therefore, the S content is 0.50 mass% or less, preferably 0.45 mass% or less, more preferably 0.43 mass% or less.
- N 0.0300% by mass or less
- N is an element having an effect of improving the surface roughness after cutting.
- the N content is 0.0300 mass% or less, preferably 0.0200 mass% or less, more preferably 0.0180 mass% or less.
- the lower limit of the N content is not particularly limited and may be 0, but industrially exceeds 0% by mass.
- the N content is preferably 0.002% by mass or more, and more preferably 0.004% by mass or more.
- O 0.0050 to 0.0300 mass%
- O is an element having an effect of improving machinability through an effect of coarsening sulfide inclusions.
- the O content is 0.0050% by mass or more, preferably 0.0100% by mass or more.
- the O content is 0.0300 mass% or less, preferably 0.0250 mass% or less, more preferably 0.0200 mass% or less.
- the cutting wire in one embodiment of the present invention includes the above-described elements, and the remainder has a component composition composed of Fe and inevitable impurities.
- the above component composition is optionally further Pb: 0.01 to 0.50 mass%, Bi: 0.01 to 0.50 mass%, Ca: 0.01% by mass or less, Se: 0.1 mass% or less, and Te: 1 or 2 or more selected from the group consisting of 0.1 mass% or less can be contained.
- Pb 0.01 to 0.50 mass%
- Pb is an element having an effect of refining chips at the time of cutting, and the chip disposability can be further improved by addition.
- Pb content shall be 0.01 mass% or more.
- the Pb content is 0.50% by mass or less, preferably 0.30% by mass or less, more preferably 0.10% by mass or less.
- Bi 0.01 to 0.50 mass%
- Bi is an element having an effect of refining chips at the time of cutting, and the chip disposability can be further improved by addition.
- Bi content shall be 0.01 mass% or more.
- the Bi content is set to 0.50% by mass or less, preferably 0.30% by mass or less, more preferably 0.10% by mass or less.
- Ca 0.01% by mass or less
- Ca is an element having an effect of refining chips at the time of cutting, and can further improve chip treatability by addition. However, even if these elements are added excessively, the effect of improving chip disposal is saturated. Therefore, from the viewpoint of suppressing an increase in alloy cost, the Ca content is set to 0.01% by mass or less, preferably 0.008% by mass or less, and more preferably 0.007% by mass or less.
- the lower limit of the Ca content is not particularly limited, but is preferably 0.0010% by mass or more, more preferably 0.003% by mass or more, and further preferably 0.005% by mass or more.
- Se 0.1% by mass or less Se, like Pb, is an element that has an effect of refining chips during cutting, and can further improve chip treatability by addition. However, even if these elements are added excessively, the effect of improving chip disposal is saturated. Therefore, from the viewpoint of suppressing an increase in alloy cost, the Se content is set to 0.1% by mass or less, preferably 0.008% by mass or less, and more preferably 0.007% by mass or less.
- the lower limit of the Se content is not particularly limited, but is preferably 0.0010% by mass or more, more preferably 0.003% by mass or more, and further preferably 0.005% by mass or more.
- Te 0.1% by mass or less Te, like Pb, is an element having an effect of refining chips at the time of cutting, and can further improve chip treatability by addition. However, even if these elements are added excessively, the effect of improving chip disposal is saturated. Therefore, from the viewpoint of suppressing an increase in alloy cost, the Te content is set to 0.1% by mass or less, preferably 0.008% by mass or less, and more preferably 0.007% by mass or less.
- the lower limit of the Te content is not particularly limited, but is preferably 0.0010% by mass or more, more preferably 0.003% by mass or more, and further preferably 0.005% by mass or more.
- the component composition further optionally, Cr: 3.0% by mass or less, Al: 0.010 mass% or less, Sb: 0.010 mass% or less, Sn: 0.010 mass% or less, Cu: 1.0 mass% or less, One or more selected from the group consisting of Ni: 1.0 mass% or less and Mo: 1.0 mass% or less can be contained.
- Cr, Al, Sb, Sn, Cu, Ni, and Mo are elements that affect the scale properties or corrosion resistance after rolling, and can be arbitrarily added.
- Sb and Sn have an effect of improving descaling properties in shot blasting and pickling performed before cold drawing, and can be arbitrarily added. However, even if Sb and Sn are added in an amount exceeding 0.010% by mass, the effect of improving the descaling property is saturated. Therefore, Sb content and Sn content are 0.010 mass% or less, preferably 0.009 mass% or less. In addition, when adding Sb and Sn, it is preferable that Sb content and Sn content shall be 0.003 mass% or more, and it is more preferable to set it as 0.005 mass% or more.
- Cr, Al, Cu, Ni, and Mo are elements having an effect of improving the corrosion resistance, and can be arbitrarily added.
- excessive addition of Cr, Al, Cu, Ni, and Mo leads to solid solution strengthening of the steel and reduces the tool life during cutting through an increase in hardness. Therefore, the upper limit of Cr content is 3.0% by mass, the upper limit of Al content is 0.010% by mass, and the upper limit of Cu, Ni and Mo content is 1.0% by mass.
- Cr, Al, Cu, Ni, and Mo are preferably added at 0.001% by mass or more.
- the component composition further optionally, Nb: 0.050 mass% or less, Ti: 0.050 mass% or less, V: 0.050 mass% or less, Zr: 0.050 mass% or less, W: 0.050 mass% or less, Ta: 0.050 mass% or less, Y: 0.050 mass% or less, 1 or 2 or more selected from the group which consists of Hf: 0.050 mass% or less and B: 0.050 mass% or less can be contained.
- Nb, Ti, V, Zr, W, Ta, Y, and Hf have the effect of forming fine precipitates and improving the strength of the wire.
- B has the effect
- Nb, Ti, V, Zr, W, Ta, Y, Hf, and B are added, the fatigue strength can be improved.
- Nb, Ti, V, Zr, W, Ta, Y, Hf and B are preferably added at 0.0001% by mass or more. However, for any component, excessive addition exceeding 0.050% by mass lowers the hot workability of the steel, so the upper limit is preferably 0.050% by mass.
- the component composition of the wire in one embodiment of the present invention includes each of the above elements, the remaining Fe and unavoidable impurities, and preferably comprises the above each element, the remaining Fe and unavoidable impurities.
- the cutting wire of the present invention satisfies the following formulas (1) and (2) when the average aspect ratio of the ferrite grains at a 1/4 position of the diameter from the surface of the cutting wire is more than 2.8.
- the average aspect ratio is 2.8 or less, it is necessary to have Vickers hardness that satisfies the following expressions (3) and (4).
- the average aspect ratio, H ave , and H ⁇ can be obtained by the following procedure.
- Average aspect ratio A cross section including the central axis of the wire and parallel to the longitudinal direction of the wire is mirror-polished and then subjected to nital etching. Next, the ferrite grains at a position 1/4 of the diameter of the wire from the surface of the wire are observed with an optical microscope, and the maximum ferret diameter and the minimum ferret diameter are obtained for 100 ferrite grains by image analysis. For the 100 ferrite grains, the aspect ratio of each ferrite grain defined as the maximum ferret diameter / minimum ferret diameter is calculated, and the average value of the obtained values is taken as the average aspect ratio.
- ⁇ H ave Vickers hardness at a position of a depth of 1/4 of the diameter of the wire from the surface of the wire is measured at 100 points under a load of 0.1 kgf, and the average value of the obtained Vickers hardness is H ave .
- the distance between adjacent impressions shall be 0.3 mm or more.
- the radius is 1/4 of the diameter in the cross section orthogonal to the longitudinal direction of the wire, and the center is aligned with the center of the wire cross section. Vickers hardness may be measured every 3.6 °.
- Have may be referred to as average hardness.
- H ⁇ H ⁇ It is H sigma, the standard deviation of the Vickers hardness of 100 points measured in the H ave the same way.
- H ⁇ may be referred to as a standard deviation of hardness.
- the hardness of the wire is the most important factor on the work side (wire) that affects the tool life when cutting the wire.
- the hardness of the wire is controlled to be low, and the variation in hardness, in particular, the variation in hardness in the circumferential direction is suppressed, which improves the machinability of the wire, specifically the tool material type. It is extremely important to realize excellent machinability regardless of the type of lubricant.
- the machinability of the wire is affected not only by the Vickers hardness but also by the aspect ratio of the ferrite grains. That is, the main structure of low-carbon free-cutting steel is ferrite. At the time of cutting, a very large stress acts on the contact portion between the steel and the tool, and the steel is forcibly deformed greatly, and as a result, it is broken and cut off. As shown in FIG. 1, the aspect ratio of the ferrite grains affects machinability through the influence on the resistance to load stress. That is, it is considered that as the aspect ratio of the ferrite grain is larger, the structure is more easily broken, and as a result, the machinability is improved.
- the same machinability was obtained when the average aspect ratio of the ferrite grains (hereinafter sometimes simply referred to as the average aspect ratio) exceeds 2.8 and when the average aspect ratio is 2.8 or less.
- the H ave and scope of the H sigma to obtain is found different.
- the necessary ranges of H ave and H ⁇ will be described for each case.
- the average aspect ratio of ferrite grains is 1.3 or more.
- the upper limit value of the average hardness H ave of the wire is set to 350 (HV).
- a more preferred upper limit is 300 (HV). This is because the average Vickers hardness affects the average cutting resistance, and when Have exceeds the above upper limit value, the tool life is reduced.
- the upper limit value of the standard deviation H sigma to 30 HV. That is, even if the average hardness value satisfies the above conditions, if the hardness varies in the circumferential direction, the cutting of the soft part and the hard part is repeated. It has been found that this soft-hard repeated cutting is a major factor that reduces the tool life. That is, as a result of repeated soft-hard cutting, the cutting tool is intermittently loaded, resulting in accelerated tool wear. Therefore, to limit the upper limit of the standard deviation H sigma hardness which is an index of the hardness variation in 30 (HV). A more preferred upper limit is 20 (HV). If the H sigma between 100 points 30 (HV) or less, a soft - intermittent load applied to the cutting tool due to the repeated cutting of hard is reduced.
- the average aspect ratio of the ferrite grains is 2.8 or less
- the average aspect ratio of the ferrite grains is more than 2.8 ( Compared to the case of FIG. 1A, the structure is less likely to be destroyed during cutting. Therefore, when the average aspect ratio of the ferrite grains is 2.8 or less, in order to ensure machinability, the values of H ave and H ⁇ need to be in a lower range than in the case of exceeding 2.8. There is. Therefore, when the average aspect ratio of the ferrite grains is 2.8 or less, the upper limit value of the average hardness Have of the wire is set to 250 (HV). A more preferred upper limit is 200 (HV). This is because the average hardness affects the average cutting resistance, and when the upper limit is exceeded, the tool life is reduced.
- the upper limit value of the standard deviation H ⁇ of the hardness is limited to 25 (HV). A more preferred upper limit is 15 (HV). If the H ⁇ is 25 (HV) or less, the intermittent load applied to the cutting tool due to repeated soft-hard cutting is reduced.
- the average hardness and hardness variation of the wire on the work side affects the tool life during cutting, regardless of the type of cutting tool or lubricant. In other words, it is possible to obtain excellent machinability regardless of the type of cutting tool or the type of lubricant by accurately regulating the average hardness and the initial deviation of the wire. That is, if the average hardness and hardness variation of the wire satisfy the above conditions, excellent machinability can be obtained regardless of the type of cutting tool or lubricant.
- the diameter of the wire rod for cutting according to the present invention is not particularly limited and may be any value, but is preferably 20 mm or less, and preferably 16 mm or less.
- shape of the wire for cutting according to the present invention is not particularly limited, and can be any shape.
- the cross section perpendicular to the longitudinal direction may be circular, and the cross section perpendicular to the longitudinal direction may be square.
- the microstructure of the wire in the present invention is not particularly limited, and can be an arbitrary structure.
- the wire preferably has a microstructure containing ferrite, and more preferably has a microstructure containing ferrite and pearlite.
- the wire for cutting according to the present invention is not particularly limited and can be produced by any method.
- the wire may be a hot-rolled wire that has not been drawn (undrawn wire), or cold-rolled into a hot-rolled wire (round bar). It may be a wire drawing material subjected to wire drawing. The average aspect of the ferrite grains tends to be larger in the wire drawing material than in the undrawn material.
- preferable manufacturing conditions will be described by taking the case of an undrawn wire and a drawn wire as an example.
- an undrawn wire in the case of an undrawn wire, that is, a wire that has been hot-rolled, the steel having the above-mentioned predetermined component composition is melted to form a material, and the material is hot-rolled and formed into a wire Thus, a wire can be manufactured. At that time, in order to obtain an undrawn wire material having Vickers hardness that satisfies the above conditions, it is effective to control the cooling rate after the hot rolling.
- the average cooling rate in the temperature range of 500 ° C to 300 ° C is 0.7 ° C / s or less. That is, by setting the average cooling rate to 0.7 ° C./s or less, spheroidization of cementite in the cooling process is promoted, pearlite, which is the original hard portion, is softened, and the hardness difference from the parent phase ferrite is reduced. . As a result, the average hardness of the wire decreases and the variation in hardness also decreases.
- the average cooling rate is preferably 0.5 ° C./s or less, and more preferably 0.4 ° C./s or less.
- the lower limit of the average cooling rate is not particularly limited, but is preferably 0.1 ° C./s or more from the viewpoint of productivity.
- the cooling conditions in the temperature range below 300 ° C. are not particularly limited, and may be, for example, allowed to cool.
- a wire drawing material In the case of a wire drawing material, first, the steel of the above-mentioned predetermined composition is melted to make a material, and the material is hot-rolled to form a round bar or a wire. Next, the wire rod can be produced by subjecting a round bar or wire rod obtained by hot rolling to wire drawing. At that time, in order to obtain a wire drawing material having Vickers hardness satisfying the above conditions, it is effective to control both the cooling rate after the hot rolling and the area reduction rate at the time of wire drawing.
- the average cooling rate in the temperature range of 500 ° C. to 300 ° C. is 0.7 ° C./s or less in the manufacturing process of the drawn wire. That is, by setting the average cooling rate to 0.7 ° C./s or less, spheroidization of cementite in the cooling process is promoted, pearlite, which is the original hard portion, is softened, and the hardness difference from the parent phase ferrite is reduced. . As a result, the average hardness of the wire decreases and the variation in hardness also decreases.
- the average cooling rate is preferably 0.5 ° C./s or less, and more preferably 0.4 ° C./s or less.
- the lower limit of the average cooling rate is not particularly limited, but is preferably 0.1 ° C./s or more from the viewpoint of productivity.
- a preferred area reduction is 50% or less, more preferably 40% or less.
- Example 1 Steels having the component compositions shown in Tables 1 and 2 were melted and formed into wire rods by hot rolling.
- the cross-sectional shape of the wire was a circle having a diameter of 12 mm.
- Tables 3 and 4 show the average cooling rate in the temperature range of 500 to 300 ° C. after the hot rolling in this manufacturing process. In this example, no wire drawing was performed. Therefore, the area reduction rate at the time of wire drawing is 0.
- each of the obtained wire rods was subjected to a machinability test by peripheral turning under various conditions to evaluate tool life, surface roughness after cutting, and chip disposal.
- the following five conditions were changed as parameters.
- Tables 5 to 10 to be described later numbers assigned to the respective conditions are shown.
- Insert material 1 CVD coated carbide 2: PVD coated carbide 3: Cermet (TiN) 4: Ceramic (Al 2 O 3 )
- Feeding speed 1 0.05 mm / rev 2: 0.2 mm / rev
- Lubricant 1 Water-insoluble cutting oil 2: Water-soluble cutting oil (emulsion, 10% dilution)
- flank average wear width Vb The tool life was evaluated based on the flank average wear width Vb of the tool after cutting a 10 m length of wire.
- the flank average wear width refers not to the wear width at the boundary wear portion (flank boundary wear width) but to the wear width at the average wear portion as shown in FIG.
- the evaluation results are shown in Tables 5 and 6.
- the flank average abrasion width Vb is 250 micrometers or less, it can be said that it is excellent in a tool life. Therefore, in Table 5, when the flank average wear width Vb is 250 ⁇ m or less, a “ ⁇ ” symbol indicating that the pass is acceptable, and when the flank average wear width Vb is more than 250 ⁇ m, A “ ⁇ ” symbol indicating a pass was shown.
- the surface roughness after cutting was determined by measuring the 10-point average roughness Rz (JIS B 0601) using a stylus type roughness meter for a range of 10 mm in length immediately after cutting the wire over a length of 1 m. And evaluated based on the results. The reference length in the measurement was 4 mm. The evaluation results are shown in Tables 7 and 8. If the ten-point average roughness Rz is 25 ⁇ m or less, it can be said that good quality parts can be manufactured.
- Chip disposal The chip disposability was evaluated based on the chip shape in the cutting section from 0.9 m to 1 m when the wire was cut over a length of 1 m. The evaluation results are shown in Tables 9 and 10. In addition, it can be said that the chips are finely divided and excellent in chip disposal. Therefore, in Tables 9 and 10, when the chip length is 1.5 mm or less, the symbol “ ⁇ ” indicating the best condition is passed when one or more chips are not generated. The symbol “ ⁇ ” indicating that when one or more rolls of chips were generated, the symbol “ ⁇ ” indicating failure was indicated.
- Example 2 A wire rod was produced under the same conditions as in Example 1 except that the wire drawing was performed after hot rolling.
- Tables 11 and 12 show the average cooling rate in the temperature range of 500 to 300 ° C. after hot rolling and the area reduction rate in wire drawing in this manufacturing process.
Abstract
Description
C :0.001~0.150質量%、
Si:0.010質量%以下、
Mn:0.20~2.00質量%、
P :0.02~0.15質量%、
S :0.20~0.50質量%、
N :0.0300質量%以下、および
O :0.0050~0.0300質量%を含み、
残部がFeおよび不可避的不純物からなる成分組成を有し、
前記切削加工用線材の表面から直径の1/4位置におけるフェライト粒の平均アスペクト比が2.8超の場合、下記(1)および(2)式を満足し、
前記平均アスペクト比が2.8以下の場合、下記(3)および(4)式を満足する、ビッカース硬さを有する、切削加工用線材。
Have≦350 …(1)
Hσ≦30 …(2)
Have≦250 …(3)
Hσ≦20 …(4)
ここで、
Have:表面から直径の1/4位置におけるビッカース硬さの周方向の平均値
Hσ:表面から直径の1/4位置における100点のビッカース硬さの標準偏差
Pb:0.01~0.50質量%、
Bi:0.01~0.50質量%、
Ca:0.01質量%以下、
Se:0.1質量%以下、および
Te: 0.1質量%以下
からなる群より選択される1または2以上を含有する、上記1に記載の切削加工用線材。
Cr: 3.0質量%以下、
Al:0.010質量%以下、
Sb:0.010質量%以下、
Sn:0.010質量%以下、
Cu:1.0質量%以下、
Ni:1.0質量%以下、および
Mo:1.0質量%以下
からなる群より選択される1または2以上を含有する、上記1または2に記載の切削加工用線材。
Nb:0.050質量%以下、
Ti:0.050質量%以下、
V :0.050質量%以下、
Zr:0.050質量%以下、
W :0.050質量%以下、
Ta:0.050質量%以下、
Y :0.050質量%以下、
Hf:0.050質量%以下、および
B :0.050質量%以下
からなる群より選択される1または2以上を含有する、上記1~3のいずれか一項に記載の切削加工用線材。
まず、本発明において、切削加工用線材(以下、単に「線材」という場合がある)の成分組成を上記した範囲に限定した理由について詳しく説明する。
Cは、鋼の強度向上に資する元素であり、構造用鋼として十分な強度を得るため0.001質量%以上を必要とする。そのため、C含有量は0.001質量%以上、好ましくは0.01質量%以上とする。一方、C含有量が0.150質量%を超えると、硬度が過度に上昇し、切削加工時の工具寿命が低下する。そのため、C含有量は0.150質量%以下、好ましくは0.13質量%以下、より好ましくは0.10質量%以下とする。
鋼中のSiは、酸素と結合してSiO2を生成する。このSiO2は、鋼中で硬質粒子として働き、切削における工具のアブレシブ摩耗を促進し、その結果、工具寿命を低下させる。そのため、Si含有量を0.010質量%以下、好ましくは0.003質量%以下とする。一方、Si含有量の下限は特に限定されず、0であってもよいが、工業的には0質量%超である。また、Siは、冷間伸線前に施されるショットブラストおよび酸洗における脱スケール性の向上効果を有する。そのため、前記効果を得るという観点からは、Si含有量を0.0005質量%以上とすることが好ましい。
Mnは、Sと結合し硫化物を形成することで、被削性を向上させる効果を有する元素である。前記効果を得るために0.20質量%以上添加する必要がある。そのため、Mn含有量は0.20質量%以上、好ましくは0.60質量%以上、より好ましくは0.80質量%以上とする。一方、Mnの過剰な添加は、固溶強化による硬度の上昇を招き、切削加工時の工具寿命を低下させる。そのため、Mn含有量は2.00質量%以下、好ましくは1.80質量%以下、より好ましくは1.60質量%以下とする。
Pは、被削性を向上させる効果を有する元素である。前記効果を得るためには0.02質量%以上の添加が必要である。そのため、P含有量は0.02質量%以上、好ましくは0.03質量%以上とする。一方、0.15質量%を超えて添加しても、被削性向上効果は飽和する。そのため、P含有量は0.15質量%以下、好ましくは0.14質量%以下、より好ましくは0.13質量%以下とする。
Sは、硫化物系介在物として存在し、被削性の向上に有効な元素である。この効果を得るためには0.20質量%以上の添加が必要である。そのため、S含有量は0.20質量%以上、好ましくは0.25質量%以上、より好ましくは0.30質量%以上とする。一方、0.50質量%を超える添加は、鋼の熱間加工性を低下させる。そのため、S含有量は0.50質量%以下、好ましくは0.45質量%以下、より好ましくは0.43質量%以下とする。
Nは、切削後の表面粗さを向上させる効果がを有する元素であるある。しかし、過度の添加は鋼材の硬度上昇を招き、切削時の工具寿命を低下させる。そのため、N含有量は0.0300質量%以下、好ましくは0.0200質量%以下、より好ましくは0.0180質量%以下とする。一方、N含有量の下限は特に限定されず、0であってもよいが工業的には0質量%超である。N含有量は、0.002質量%以上とすることが好ましく、0.004質量%以上とすることがより好ましい。
Oは、硫化物系介在物を粗大化させる効果を通じ、被削性を向上させる効果を有する元素である。前記効果を得るためには、Oを0.0050質量%以上で含有させる必要がある。そのため、O含有量は0.0050質量%以上、好ましくは0.0100質量%以上とする。一方、過度の添加は鋼材の靱性低下を招き、構造部材の早期破壊を引き起こす。そのため、O含有量は0.0300質量%以下、好ましくは0.0250質量%以下、より好ましくは0.0200質量%以下とする。
Pb:0.01~0.50質量%、
Bi:0.01~0.50質量%、
Ca:0.01質量%以下、
Se:0.1質量%以下、および
Te: 0.1質量%以下
からなる群より選択される1または2以上を含有することができる。
Pbは、切削時の切屑を微細化する効果を有する元素であり、添加により切屑処理性をさらに向上させることができる。Pbを添加する場合、前記効果を得るために、Pb含有量を0.01質量%以上とする。一方、過度に添加しても切屑処理性の向上効果は飽和する。そのため、合金コスト上昇を抑えるという観点からは、Pb含有量を0.50質量%以下、好ましくは0.30質量%以下、より好ましくは0.10質量%以下とする。
Biは、Pbと同様に、切削時の切屑を微細化する効果を有する元素であり、添加により切屑処理性をさらに向上させることができる。Biを添加する場合、前記効果を得るために、Bi含有量を0.01質量%以上とする。一方、過度に添加しても切屑処理性の向上効果は飽和する。そのため、合金コスト上昇を抑えるという観点からは、Bi含有量を0.50質量%以下、好ましくは0.30質量%以下、より好ましくは0.10質量%以下とする。
Caは、Pbと同様に、切削時の切屑を微細化する効果を有する元素であり、添加により切屑処理性をさらに向上させることができる。しかし、これらの元素を過度に添加しても切屑処理性の向上効果は飽和する。そのため、合金コスト上昇を抑えるという観点からは、Ca含有量を0.01質量%以下、好ましくは0.008質量%以下、より好ましくは0.007質量%以下とする。一方、Ca含有量の下限は特に限定されないが、0.0010質量%以上とすることが好ましく、0.003質量%以上とすることがより好ましく、0.005質量%以上とすることがさらに好ましい。
Seは、Pbと同様に、切削時の切屑を微細化する効果を有する元素であり、添加により切屑処理性をさらに向上させることができる。しかし、これらの元素を過度に添加しても切屑処理性の向上効果は飽和する。そのため、合金コスト上昇を抑えるという観点からは、Se含有量を0.1質量%以下、好ましくは0.008質量%以下、より好ましくは0.007質量%以下とする。一方、Se含有量の下限は特に限定されないが、0.0010質量%以上とすることが好ましく、0.003質量%以上とすることがより好ましく、0.005質量%以上とすることがさらに好ましい。
Teは、Pbと同様に、切削時の切屑を微細化する効果を有する元素であり、添加により切屑処理性をさらに向上させることができる。しかし、これらの元素を過度に添加しても切屑処理性の向上効果は飽和する。そのため、合金コスト上昇を抑えるという観点からは、Te含有量を0.1質量%以下、好ましくは0.008質量%以下、より好ましくは0.007質量%以下とする。一方、Te含有量の下限は特に限定されないが、0.0010質量%以上とすることが好ましく、0.003質量%以上とすることがより好ましく、0.005質量%以上とすることがさらに好ましい。
Cr:3.0質量%以下、
Al:0.010質量%以下、
Sb:0.010質量%以下、
Sn:0.010質量%以下、
Cu:1.0質量%以下、
Ni:1.0質量%以下、および
Mo:1.0質量%以下
からなる群より選択される1または2以上を含有することができる。
Nb:0.050質量%以下、
Ti:0.050質量%以下、
V :0.050質量%以下、
Zr:0.050質量%以下、
W :0.050質量%以下、
Ta:0.050質量%以下、
Y :0.050質量%以下、
Hf:0.050質量%以下、および
B :0.050質量%以下
からなる群より選択される1または2以上を含有することができる。
本発明の切削加工用線材は、該切削加工用線材の表面から直径の1/4位置におけるフェライト粒の平均アスペクト比が2.8超の場合、下記(1)および(2)式を満足し、前記平均アスペクト比が2.8以下の場合、下記(3)および(4)式を満足する、ビッカース硬さを有する必要がある。
Have≦350 …(1)
Hσ≦30 …(2)
Have≦250 …(3)
Hσ≦20 …(4)
線材の中心軸を含み、該線材の長手方向に平行な断面を鏡面研磨後、ナイタールエッチングを施す。次いで、線材の表面から該線材の直径の1/4の深さの位置におけるフェライト粒を光学顕微鏡にて観察し、画像解析によりフェライト粒100個について最大フェレ径および最小フェレ径を求める。前記100個のフェライト粒について、最大フェレ径/最小フェレ径として定義される個々のフェライト粒のアスペクト比を算出し、得られた値の平均値を平均アスペクト比とする。
線材の表面から該線材の直径の1/4の深さの位置におけるビッカース硬さを、荷重0.1kgfの条件で、100点で測定し、得られたビッカース硬さの平均値をHaveとする。前記ビッカース硬さの測定で形成される圧痕については、隣接する圧痕間の距離を0.3 mm以上とする。また、線材の周方向に満遍なくビッカース硬度測定を行うには、線材の長手方向に直交する断面内の直径の1/4を半径とし、中心を線材断面中心と一致させた円上で、中心との角度3.6°毎にビッカース硬度測定を行えばよい。以下、Haveを平均硬度という場合がある。
Hσは、上記Haveと同様方法で測定された100点のビッカース硬さの標準偏差である。以下、Hσを硬度の標準偏差という場合がある。
フェライト粒の平均アスペクト比が2.8超の場合、線材の上記平均硬度Haveの上限値を350(HV)とする。より好ましい上限値は300(HV)である。なぜなら、平均ビッカース硬さは平均切削抵抗に影響し、Haveが上記上限値を上回る場合、工具の寿命が低下するためである。
フェライト粒の平均アスペクト比が2.8以下の場合、図1(b)に示したように、フェライト粒の平均アスペクト比が2.8超の場合(図1(a)の場合)に比べ、切削時に組織が破壊されにくい。そのため、フェライト粒の平均アスペクト比が2.8以下の場合は、被削性を確保するためには、2.8超の場合に比べ、HaveおよびHσの値をより低い範囲とする必要がある。したがって、フェライト粒の平均アスペクト比が2.8以下の場合、線材の上記平均硬度Haveの上限値を250(HV)とする。より好ましい上限値は200(HV)である。なぜなら、平均硬度は平均切削抵抗に影響し、上記上限値を上回る場合、工具の寿命が低下するためである。
本発明の切削加工用線材の直径は特に限定されず、任意の値とすることができるが、20mm以下とすることが好ましく、16mm以下とすることが好ましい。
また、本発明の切削加工用線材の形状は特に限定されず、任意の形状とすることができる。例えば、長手方向に垂直な断面における断面が円形であってもよく、また、長手方向に垂直な断面が四角形であってもよい。
本発明における線材のミクロ組織は特に限定されず、任意の組織とすることができる。通常、前記線材は、フェライトを含むミクロ組織を有することが好ましく、フェライトおよびパーライトを含むミクロ組織を有することがより好ましい。
本発明の切削加工用線材は、特に限定されることなく、任意の方法で製造することができる。前記線材は、熱間圧延まま(as hot-rolled)で伸線加工が施されていない線材(未伸線材)であってもよく、また、熱間圧延された線材(丸棒)に冷間で伸線加工が施された伸線材であってもよい。伸線材は未伸線材と比較して、フェライト粒の平均アスペクトが大きくなりやすい。以下、未伸線材と伸線材の場合を例として、好適な製造条件について説明する。
未伸線材、すなわち、熱間圧延ままの線材の場合、上記した所定の成分組成の鋼を溶製して素材とし、前記素材に熱間圧延を施して線材に成形することにより線材を製造することができる。その際、上記条件を満たすビッカース硬さを備える未伸線材を得るためには、前記熱間圧延後の冷却速度を制御することが有効である。
具体的には、熱間圧延後の冷却過程において、500℃~300℃の温度範囲における平均冷却速度を0.7℃/s以下とする。すなわち、前記平均冷却速度を0.7℃/s以下とすることにより、前記冷却過程におけるセメンタイトの球状化が促進され、元々の硬質部であるパーライトが軟質化し、母相フェライトとの硬度差が低減する。そしてその結果、線材の平均硬度が低下するとともに、硬度のばらつきも減少する。前記平均冷却速度は、0.5℃/s以下とすることが好ましく、0.4℃/s以下とすることがより好ましい。一方、前記平均冷却速度の下限は特に限定されないが、生産性の観点からは0.1℃/s以上とすることが好ましい。また、300℃未満の温度域における冷却条件は特に限定されず、例えば、放冷すればよい。
伸線材の場合、まず、上記した所定の成分組成の鋼を溶製して素材とし、前記素材に熱間圧延を施して丸棒または線材に成形する。次いで、熱間圧延で得られた丸棒または線材に伸線加工を施すことにより、伸線材を製造することができる。その際、上記条件を満たすビッカース硬さを備える伸線材を得るためには、前記熱間圧延後の冷却速度と、伸線加工時の減面率の両者を制御することが有効である。
伸線材の製造においても、未伸線材の場合と同様に、熱間圧延後の冷却過程において、500℃~300℃の温度範囲における平均冷却速度を0.7℃/s以下とする。すなわち、前記平均冷却速度を0.7℃/s以下とすることにより、前記冷却過程におけるセメンタイトの球状化が促進され、元々の硬質部であるパーライトが軟質化し、母相フェライトとの硬度差が低減する。そしてその結果、線材の平均硬度が低下するとともに、硬度のばらつきも減少する。前記平均冷却速度は、0.5℃/s以下とすることが好ましく、0.4℃/s以下とすることがより好ましい。一方、前記平均冷却速度の下限は特に限定されないが、生産性の観点からは0.1℃/s以上とすることが好ましい。
さらに、伸線加工時の減面率60%以下とすることにより、硬度の過度な上昇が抑制され、伸線材の平均硬度を所定範囲内にすることができる。好ましい減面率は50%以下であり、より好ましくは40%以下である。
表1、2に示す成分組成を有する鋼を溶製し、熱間圧延によって線材に成形した。前記線材の断面形状は、直径12 mmの円とした。この製造工程での、熱間圧延後の500~300℃の温度範囲における平均冷却速度を表3、4に示す。なお、本実施例においては、伸線加工は行わなかった。したがって、伸線加工時の減面率は0である。
1:CVDコーテッド超硬
2:PVDコーテッド超硬
3:サーメット(TiN)
4:セラミック(Al2O3)
1:50 m/min
2:200 m/min
1:0.05 mm/rev
2:0.2 mm/rev
1:0.2 mm
2:1 mm
1:不水溶性切削油
2:水溶性切削油(エマルション、10%希釈)
工具寿命は、線材の長さ10 mを切削した後の工具における逃げ面平均摩耗幅Vbに基づいて評価した。ここで、逃げ面平均摩耗幅とは、図2に示すように、境界摩耗部における摩耗幅(逃げ面境界摩耗幅)ではなく、平均摩耗部における摩耗幅を指す。評価結果を表5、6に示す。なお、前記逃げ面平均摩耗幅Vbが250μm以下であれば工具寿命に優れるといえる。そこで、表5においては、前記逃げ面平均摩耗幅Vbが250μm以下であった場合、合格であることを示す「○」記号を、前記逃げ面平均摩耗幅Vbが250μm超であった場合、不合格であることを示す「▼」記号を示した。
切削後面粗さは、線材を長さ1mにわたって切削した後、切削終了直前の長さ10mmの範囲について、触針式粗さ計を用いて十点平均粗さRz(JIS B 0601)を測定し、その結果に基づいて評価した。前記測定における基準長さは4 mmとした。評価結果を表7、8に示す。なお、前記十点平均粗さRzが25μm以下であれば良品質な部品製造が可能といえる。そこで、表7、8においては、前記十点平均粗さRzが25μm以下であった場合、合格であることを示す「○」記号を、前記十点平均粗さRzが25μm超であった場合、不合格であることを示す「▼」記号を示した。
切屑処理性は、線材を長さ1mにわたって切削した際の、0.9 mから1mまでの切削区間における切屑形態に基づいて評価した。評価結果を表9、10に示す。なお、切屑が微細に分断されており、切屑の処理性に優れるといえる。そこで、表9、10においては、切屑長さが1.5mm以下であった場合、最も良好であることを示す「◎」記号を、1巻以上の切屑が生成していなかった場合、合格であることを示す「○」記号を、1巻以上の切屑が生成していた場合、不合格であることを示す「▼」記号を示した。
熱間圧延後に伸線加工を行った点以外は上記実施例1と同様の条件で線材を製造した。この製造工程での、熱間圧延後の500~300℃の温度範囲における平均冷却速度と、伸線加工における減面率を表11、12に示す。
Claims (4)
- 切削加工用線材であって、
C :0.001~0.150質量%、
Si:0.010質量%以下、
Mn:0.20~2.00質量%、
P :0.02~0.15質量%、
S :0.20~0.50質量%、
N :0.0300質量%以下、および
O :0.0050~0.0300質量%を含み、
残部がFeおよび不可避的不純物からなる成分組成を有し、
前記切削加工用線材の表面から直径の1/4位置におけるフェライト粒の平均アスペクト比が2.8超の場合、下記(1)および(2)式を満足し、
前記平均アスペクト比が2.8以下の場合、下記(3)および(4)式を満足する、ビッカース硬さを有する、切削加工用線材。
Have≦350 …(1)
Hσ≦30 …(2)
Have≦250 …(3)
Hσ≦20 …(4)
ここで、
Have:表面から直径の1/4位置におけるビッカース硬さの周方向の平均値
Hσ:表面から直径の1/4位置における100点のビッカース硬さの標準偏差 - 前記成分組成が、さらに、
Pb:0.01~0.50質量%、
Bi:0.01~0.50質量%、
Ca:0.01質量%以下、
Se:0.1質量%以下、および
Te: 0.1質量%以下
からなる群より選択される1または2以上を含有する、請求項1に記載の切削加工用線材。 - 前記成分組成が、さらに、
Cr:3.0質量%以下、
Al:0.010質量%以下、
Sb:0.010質量%以下、
Sn:0.010質量%以下、
Cu:1.0質量%以下、
Ni:1.0質量%以下、および
Mo:1.0質量%以下
からなる群より選択される1または2以上を含有する、請求項1または2に記載の切削加工用線材。 - 前記成分組成が、さらに、
Nb:0.050質量%以下、
Ti:0.050質量%以下、
V :0.050質量%以下、
Zr:0.050質量%以下、
W :0.050質量%以下、
Ta:0.050質量%以下、
Y :0.050質量%以下、
Hf:0.050質量%以下、および
B :0.050質量%以下
からなる群より選択される1または2以上を含有する、請求項1~3のいずれか一項に記載の切削加工用線材。
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