WO2021201178A1 - 快削鋼およびその製造方法 - Google Patents
快削鋼およびその製造方法 Download PDFInfo
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- WO2021201178A1 WO2021201178A1 PCT/JP2021/014049 JP2021014049W WO2021201178A1 WO 2021201178 A1 WO2021201178 A1 WO 2021201178A1 JP 2021014049 W JP2021014049 W JP 2021014049W WO 2021201178 A1 WO2021201178 A1 WO 2021201178A1
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- free
- steel
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- sulfide
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- 229910000915 Free machining steel Inorganic materials 0.000 title claims abstract description 30
- 238000004519 manufacturing process Methods 0.000 title claims description 12
- 238000000034 method Methods 0.000 title description 6
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 38
- 239000010959 steel Substances 0.000 claims abstract description 38
- 150000003568 thioethers Chemical class 0.000 claims abstract 4
- 238000010438 heat treatment Methods 0.000 claims description 20
- 239000000203 mixture Substances 0.000 claims description 20
- 229910052804 chromium Inorganic materials 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 6
- 239000002131 composite material Substances 0.000 abstract description 4
- 238000009826 distribution Methods 0.000 abstract description 4
- 239000002245 particle Substances 0.000 abstract 2
- YIFYMJAOEFVDSH-UHFFFAOYSA-N [Pb].[S].[C] Chemical compound [Pb].[S].[C] YIFYMJAOEFVDSH-UHFFFAOYSA-N 0.000 abstract 1
- 239000000470 constituent Substances 0.000 abstract 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 42
- 238000005520 cutting process Methods 0.000 description 16
- 230000000694 effects Effects 0.000 description 14
- 238000005098 hot rolling Methods 0.000 description 14
- 150000004763 sulfides Chemical class 0.000 description 13
- 239000000463 material Substances 0.000 description 7
- 238000005096 rolling process Methods 0.000 description 7
- 229910052717 sulfur Inorganic materials 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 5
- 229920006395 saturated elastomer Polymers 0.000 description 5
- 229910052787 antimony Inorganic materials 0.000 description 4
- 229910052796 boron Inorganic materials 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 230000001050 lubricating effect Effects 0.000 description 4
- 229910052749 magnesium Inorganic materials 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- 229910052718 tin Inorganic materials 0.000 description 4
- 229910052719 titanium Inorganic materials 0.000 description 4
- 229910052720 vanadium Inorganic materials 0.000 description 4
- 229910052726 zirconium Inorganic materials 0.000 description 4
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 3
- 229910052797 bismuth Inorganic materials 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 238000009749 continuous casting Methods 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000000724 energy-dispersive X-ray spectrum Methods 0.000 description 3
- 229910052711 selenium Inorganic materials 0.000 description 3
- 238000007711 solidification Methods 0.000 description 3
- 239000011593 sulfur Substances 0.000 description 3
- 229910052714 tellurium Inorganic materials 0.000 description 3
- 238000005266 casting Methods 0.000 description 2
- XCAUINMIESBTBL-UHFFFAOYSA-N lead(ii) sulfide Chemical compound [Pb]=S XCAUINMIESBTBL-UHFFFAOYSA-N 0.000 description 2
- 238000005461 lubrication Methods 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 230000002093 peripheral effect Effects 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 230000003746 surface roughness Effects 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 229910000742 Microalloyed steel Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 239000000839 emulsion Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 238000013467 fragmentation Methods 0.000 description 1
- 238000006062 fragmentation reaction Methods 0.000 description 1
- 239000000383 hazardous chemical Substances 0.000 description 1
- 239000000314 lubricant Substances 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D7/00—Modifying the physical properties of iron or steel by deformation
- C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D9/22—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for drills; for milling cutters; for machine cutting tools
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
Definitions
- the present invention relates to free-cutting steel, particularly a steel that is a substitute for free-cutting steel containing sulfur, which is a machinability-improving element, and a trace amount of lead, and is equal to or higher than low-carbon sulfur-lead composite free-cutting steel. It relates to a free-cutting steel having machinability and a method for producing the same.
- Low-carbon sulfur lead free-cutting steel represented by JIS standard SUM24L secures its excellent machinability by adding a large amount of lead (Pb) and sulfur (S) as free-cutting elements.
- lead In steel materials, lead is useful for reducing tool wear and improving chip control during cutting. Therefore, lead is heavily used as an element that greatly improves the machinability of materials, and is used in steel products manufactured by many cutting processes.
- lead is also mentioned as one of them, and its use is required to be restricted.
- Patent Document 1 discloses a Pb-free free-cutting non-tempered steel.
- Patent Document 2 also discloses a Pb-free free-cutting steel.
- Patent Document 3 discloses a free-cutting steel in which Mn-Cr-S-based inclusions are present and machinability is ensured by adding Cr, which is easier to form a compound with S than Mn. ..
- Patent Document 1 has a problem that it is hard because the target steel type is a non-microalloyed steel containing C: 0.2% or more, and the manufacturing cost is high because Nd, which is a special element, is used. There is. Further, the technique described in Patent Document 2 has low hot ductility because a large amount of S is added, and cracks occur during continuous casting or hot rolling, which is problematic from the viewpoint of surface properties. On the other hand, in the technique described in Patent Document 3, Cr and S are added by reducing the amount of Mn added, but the amount of Cr added is as high as 3.5% or more, which makes it difficult to reduce the cost and a large amount. Since CrS is generated, there is a manufacturing problem that it is difficult to melt the material in the steelmaking process.
- the present invention has been made to solve the above-mentioned problems, and despite the fact that Pb is not added, the present invention has machinability equal to or higher than that of low-carbon sulfur-lead composite free-cutting steel. It is an object of the present invention to provide free-cutting steel which does not require addition of Nd or a large amount of S or Cr as in Patent Documents 1 to 3 described above, together with a method for producing the same.
- the present invention has been made based on the above findings, and the gist thereof is as follows. 1.
- C By mass% C: less than 0.09%, Mn: 0.50 to 1.50%, S: 0.250 to 0.600%, O: More than 0.0100% and less than 0.0500% and Cr: 0.50 to 1.50% It is composed of the balance Fe and unavoidable impurities, and has a component composition in which the A value defined by the following formula (1) satisfies 6.0 to 18.0.
- Free-cutting steel having a steel structure in which 500 sulfides with a diameter equivalent to a circle of less than 1 ⁇ m are distributed at least 500 pieces / mm 2 and sulfides with a diameter equivalent to a circle of 1 to 5 ⁇ m are distributed at 2000 pieces / mm 2 or more.
- a value 2 ([Mn] + 2 [Cr]) / [S] ⁇ ⁇ ⁇ (1)
- [M] is the content (mass%) of the element in [].
- the component composition is Si: 0.50% or less in mass%, P: 0.10% or less,
- the component composition is Ca: 0.0010% or less in mass%, Se: 0.30% or less, Te: 0.15% or less, Bi: 0.20% or less, Sn: 0.020% or less, Sb: 0.025% or less, B: 0.010% or less, Cu: 0.50% or less, Ni: 0.50% or less, Ti: 0.100% or less, V: 0.20% or less,
- the component composition is Si: 0.50% or less in mass%, P: 0.10% or less,
- the component composition is Ca: 0.0010% or less in mass%, Se: 0.30% or less, Te: 0.15% or less, Bi: 0.20% or less, Sn: 0.020% or less, Sb: 0.025% or less, B: 0.010% or less, Cu: 0.50% or less, Ni: 0.50% or less, Ti: 0.100% or less, V: 0.20% or less,
- C Less than 0.09% C is an important element that has a great influence on the strength and machinability of steel. However, if the content is 0.09% or more, the hardness becomes too high and the machinability deteriorates. Therefore, the C content is set to less than 0.09%. Preferably, it is within the range of 0.07% or less. From the viewpoint of ensuring strength, the C content is preferably 0.01% or more. Further, it is more preferably 0.03% or more.
- Mn 0.50 to 1.50%
- Mn is a sulfide-forming element that is important for improving machinability.
- the Mn content is preferably 0.70% or more.
- the upper limit of the Mn content is set to 1.50%.
- the Mn content is preferably 1.20% or less.
- S 0.250 to 0.600%
- S is a sulfide-forming element effective for improving machinability.
- the content is less than 0.250%, the machinability is not improved because there are few fine sulfides.
- the content exceeds 0.600%, the sulfide becomes too coarse and the number of fine sulfides decreases, so that the machinability is lowered. It also reduces hot workability and ductility, which is an important mechanical property. Therefore, the S content is in the range of 0.250 to 0.600%. Preferably, it is 0.300% or more. Preferably, it is 0.450% or less.
- O More than 0.0100% and 0.0500% or less O is an element that forms oxides and becomes precipitation nuclei of sulfides, and is also an effective element for suppressing elongation of sulfides during hot working such as rolling. By this action, machinability can be improved. However, if the content is 0.0100% or less, the effect of suppressing the elongation of sulfide is not sufficient, and the elongated sulfide remains, and the original effect cannot be expected. Therefore, the content of O is set to more than 0.0100%.
- the upper limit is 0.0500%.
- Cr 0.50 to 1.50% Cr forms sulfide and has the effect of improving machinability by lubricating action during cutting. Further, since the elongation of sulfide during hot working such as rolling is suppressed, the machinability can be improved. However, if the content is less than 0.50%, the formation of sulfide is not sufficient and the elongated sulfide tends to remain, so that the original effect cannot be sufficiently expected. On the other hand, if it is added in excess of 1.50%, in addition to hardening, the sulfide becomes coarse and the effect of suppressing elongation is saturated, and the machinability is rather lowered. Also, adding an excessive amount of alloy cost is economically disadvantageous. Therefore, the Cr content is set to 0.50 to 1.50%. Preferably, it is 0.70% or more. Preferably, it is 1.30% or less.
- the balance contains Fe and unavoidable impurities, or further contains optional components described later.
- the above components, or further optional components described later are composed of the remaining Fe and unavoidable impurities.
- the A value defined by the following formula (1) is 6.0 to 18.0.
- a value 2 ([Mn] + 2 [Cr]) / [S] ⁇ ⁇ ⁇ (1)
- [M] is the content (mass%) of the element in []. That is, the A value is an important index that influences the miniaturization of Mn-Cr-S sulfide during hot working such as rolling, and by limiting this A value, machinability can be improved. can.
- the A value is set to 6.0 to 18.0.
- it is 6.5 or more.
- it is 17.0 or less.
- the optional contained components will be described.
- the following components can be contained, if necessary.
- Si 0.50% or less
- Si is a deoxidizing element, and the oxide of Si acts as a sulfide formation nucleus, promotes the formation of sulfide, refines the sulfide, and improves the life of the cutting tool. Therefore, if it is desired to further extend the tool life, it may be contained in steel. However, if it is added in excess of 0.50%, the oxide will become large and the number will decrease, so that it will not be effective as a nucleation nuclei of sulfide, and in addition, it will induce abrasive wear due to the hard oxide and the tool life will be shortened. It causes deterioration. Therefore, the Si content should be 0.50% or less. Preferably, it is 0.03% or less. In addition, in order to exhibit the above-mentioned action by Si, it is preferably contained in an amount of 0.001% or more.
- P 0.10% or less
- P is an element effective in reducing the roughness of the finished surface by suppressing the formation of landmarks during cutting. From this viewpoint, P is preferably contained in an amount of 0.01% or more. However, if the content exceeds 0.10%, the material becomes hard and the machinability is lowered, and the hot workability and ductility are remarkably lowered. Therefore, the P content is preferably 0.10% or less. More preferably, it is 0.08% or less.
- Al 0.010% or less
- Al is a deoxidizing element like Si and may be contained.
- Al produces Al 2 O 3 in steel, but since this oxide is hard, so-called abrasive wear deteriorates the life of the cutting tool, so it is necessary to avoid excessive Al content. ..
- the amount of Al added is 0.010% or less. More preferably, it is 0.005% or less. From the viewpoint of exhibiting the deoxidizing effect of Al, it is preferable that Al is contained in an amount of 0.001% or more.
- N 0.0150% or less N forms a nitride with Cr and the like, and the nitride decomposes due to the temperature rise during cutting to form an oxide film called bellague on the tool surface. Since the bellag has an effect of protecting the tool surface and thus improves the tool life, N may be contained. In order to effectively exhibit this effect, it is preferable that N is contained in an amount of 0.0050% or more. On the other hand, if it is added in excess of 0.0150%, the effect of Belag is saturated and the material is hardened, so that the tool life is shortened. Therefore, the N content is preferably 0.0150% or less. More preferably, it is 0.0060% or more. More preferably, it is 0.0120% or less.
- the following components can be further contained, if necessary.
- Ca, Se, Te, Bi, Sn, Sb, B, Cu, Ni, Ti, V, Zr, Mg are all covered. Since it has an action of improving machinability, it may be added when machinability is important.
- the amount of these elements added is Ca: less than 0.0001%, Se: less than 0.02%, Te: less than 0.10%, Bi: less than 0.02%, Sn: less than 0.003%, Sb: less than 0.003%, B: less than 0.003%, Cu: less than 0.05%, Ni: less than 0.50%, Ti: less than 0.003%, V: less than 0.005%, Zr: less than 0.005%, Mg: less than 0.0005% is sufficient Since no effect can be obtained, Ca: 0.0001% or more, Se: 0.02% or more, Te: 0.10% or more, Bi: 0.02% or more, Sn: 0.003% or more, Sb: 0.003% or more, B: 0.003% or more, respectively. , Cu: 0.05% or more, Ni: 0.05% or more, Ti: 0.003% or more, V: 0.005% or more, Zr: 0.005% or more, Mg: 0.0005% or more.
- the contents of these elements are Ca: 0.0010% or less, Se: 0.30% or less, Te: 0.15% or less, Bi: 0.20% or less, Sn: 0.020% or less, Sb: 0.025% or less, B: 0.010%, respectively.
- Step structure Distribution of 500 pieces / mm 2 or more of sulfides with a diameter equivalent to a circle of less than 1 ⁇ m, and 2000 pieces / mm 2 or more of sulfides with a diameter equivalent to a circle of 1 to 5 ⁇ m. It is advantageous to promote the lubricating action between the tool and the work material during cutting. In order to ensure the machinability of free-cutting steel by fine dispersion of sulfides, sulfides with a circle-equivalent diameter of less than 1 ⁇ m and a circle-equivalent diameter of 1 to 5 ⁇ m are dispersed in a certain amount or more in the steel structure. There is a need.
- Sulfide with a circular equivalent diameter of less than 1 ⁇ m is mainly effective for lubrication between the tool and the work material. Further, a sulfide having a circle-equivalent diameter of 1 to 5 ⁇ m is effective not only for the above-mentioned lubrication effect but also for chip fragmentation. Therefore, the number of sulfides with a circle-equivalent diameter of less than 1 ⁇ m is 500 pieces / mm 2 or more, and the number of sulfides with a circle-equivalent diameter of 1 to 5 ⁇ m is 2000 pieces / mm 2 or more.
- a rectangular slab having the above-mentioned composition and having a side length of 250 mm or more perpendicular to the longitudinal direction is rolled at a heating temperature of 1120 ° C. or higher and a surface reduction rate of 60% or higher to billet.
- the billet is hot-worked at a heating temperature of 1050 ° C. or higher and a surface reduction rate of 75% or higher.
- the length of one side in the cross section of the slab shall be 250 mm or more. More preferably, it is 300 mm or more.
- the upper limit of the length of one side in the cross section of the slab does not need to be particularly regulated, but from the viewpoint of feasibility of hot rolling following casting, the length is preferably 600 mm or less.
- Heating temperature of slabs 1120 ° C or higher
- the slabs are hot-rolled to form billets, but the heating temperature during this hot rolling must be 1120 ° C or higher. If the heating temperature is less than 1120 ° C., the coarse sulfide crystallized during cooling-solidification in the casting stage does not dissolve in solid solution, and the coarse sulfide remains even after the billet is formed. As a result, the sulfide remains coarse even after the subsequent hot working, and the desired fine sulfide distribution state cannot be obtained. Therefore, the heating temperature when hot rolling the slabs into billets is 1120 ° C or higher, preferably 1150 ° C or higher.
- the upper limit of the heating temperature of the slab does not need to be particularly regulated, but from the viewpoint of suppressing scale loss, the heating temperature is preferably 1300 ° C. or lower, more preferably 1250 ° C. or lower.
- the surface reduction ratio (%) of hot rolling is such that the cross-sectional area of the slab before hot rolling is S0 in the cross section perpendicular to the hot rolling direction, and the hot rolling direction of the billet manufactured by hot rolling.
- S1 be the cross-sectional area of the cross section perpendicular to, and the following formula 100 ⁇ (S0-S1) / S0 Can be obtained by.
- Heating temperature 1050 ° C or higher
- the heating temperature when hot-working billets into steel bars or wires is an important factor. If the heating temperature is less than 1050 ° C., the sulfide is not finely dispersed, so that the lubricating action during cutting is reduced. As a result, the tool wear is increased and the tool life is shortened. Therefore, the heating temperature of the billet is set to 1050 ° C. or higher. More preferably, it is 1080 ° C. or higher. Although it is not necessary to regulate the upper limit, it is preferable to set the temperature to 1250 ° C. or lower from the viewpoint of suppressing the decrease in yield due to scale loss.
- the surface reduction rate for hot working is also an important factor for the miniaturization of sulfides. If the surface reduction rate is less than 75%, the sulfide is not sufficiently refined, so the lower limit of the surface reduction rate is set to 75%. More preferably, it is 80% or more.
- the surface reduction rate of hot working is S1 for the cross-sectional area of the billet before hot rolling, which is perpendicular to the hot working direction, and the hot working direction (stretching) of the steel bar or wire rod manufactured by hot working.
- S2 be the cross-sectional area of the cross section perpendicular to the direction), and the following equation 100 ⁇ (S1-S2) / S1 Can be obtained by.
- the steel having the chemical composition shown in Table 1 was made into a rectangular slab having a cross section perpendicular to the longitudinal direction with the dimensions shown in Table 2-1 and Table 2-2 by a continuous casting machine.
- the obtained slabs were rolled into steel bars under the production conditions shown in Table 2-1 and Table 2-2.
- the steel of the present invention and the comparative steel were subjected to the following tests. That is, the slabs are hot-rolled at the heating temperature and surface reduction rate shown in Tables 2-1 and 2-2, and the long piece dimensions and short piece dimensions are as shown in Tables 2-1 and 2-2. It was a square billet.
- the obtained billets were heated at the heating temperatures shown in Tables 2-1 and 2-2 and hot-rolled to obtain steel bars having the diameters shown in Tables 2-1 and 2-2.
- the obtained steel bars (steel of the present invention and comparative steel) were subjected to the tests shown below.
- a test piece was collected from a cross section parallel to the rolling direction of the obtained steel bar, and the 1/4 position in the radial direction from the peripheral surface of the cross section was observed with a scanning electron microscope (SEM). , The circle-equivalent diameter and number density of sulfide in steel were investigated.
- the composition of the precipitate was analyzed by Energy Dispersive X-ray spectrum (EDX), and the obtained SEM image of the precipitate confirmed to be sulfide by EDX is imaged. The analysis was performed and binarization was performed to obtain the equivalent circle diameter and the number density.
- EDX Energy Dispersive X-ray spectrum
- the machinability was evaluated by an outer peripheral turning test.
- BNC-34C5 manufactured by Citizen Machinery was used as the cutting machine
- Carbide EX 35-bit TNGG160404R-N manufactured by Hitachi Tool was used as the turning tip
- DTGNR2020 manufactured by Kyocera was used as the holder.
- As the lubricant a 15-fold diluted emulsion of Yushiroken FGE1010 manufactured by Yushiro Chemical Industry Co., Ltd. was used.
- the cutting conditions were a cutting speed of 120 m / min, a feed rate of 0.05 mm / rev, a depth of cut of 2.0 mm, and a machining length of 10 m.
- the machinability was evaluated by the flank wear Vb of the tool after the cutting test for a length of 10 m was completed.
- the flank wear Vb after the completion of the cutting test was 200 ⁇ m or less, it was rated as “ ⁇ ”, and when the flank wear was more than 200 ⁇ m, it was rated as “x”.
- Table 2-1 and Table 2-2 show the test results of the invention steel and the comparative steel. As is clear from Table 2-1 and Table 2-2, the steel of the present invention has good machinability with respect to the comparative steel.
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Abstract
Description
(i)Mn、CrおよびSの適量添加ならびに2(Mn+2Cr)/Sの比の適正化により、適量の硫化物の組成がMn-Cr-Sの複合系となる。この複合系組成の硫化物は、熱間加工により微細化することができる。
1.質量%で、
C:0.09%未満、
Mn:0.50~1.50%、
S:0.250~0.600%、
O:0.0100%超0.0500%以下および
Cr:0.50~1.50%
を含有し、残部Feおよび不可避的不純物からなり、下記式(1)で定められるA値が6.0~18.0を満足する成分組成を有し、
円相当径で1μm未満の硫化物が500個/mm2以上、円相当径で1~5μmの硫化物が2000個/mm2以上分布してなる鋼組織を有する快削鋼。
記
A値=2([Mn]+2[Cr])/[S] ・・・(1)
但し、[M]は[ ]内の元素の含有量(質量%)
Si:0.50%以下、
P:0.10%以下、
Al:0.010%以下および
N:0.0150%以下
から選ばれる1種または2種以上を含有する前記1に記載の快削鋼。
Ca:0.0010%以下、
Se:0.30%以下、
Te:0.15%以下、
Bi:0.20%以下、
Sn:0.020%以下、
Sb:0.025%以下、
B:0.010%以下、
Cu:0.50%以下、
Ni:0.50%以下、
Ti:0.100%以下、
V:0.20%以下、
Zr:0.050%以下および
Mg:0.0050%以下
から選ばれる1種または2種以上を含有する前記1または2に記載の快削鋼。
C:0.09%未満、
Mn:0.50~1.50%、
S:0.250~0.600%、
O:0.0100%超0.0500%以下および
Cr:0.50~1.50%
を含有し、残部Feおよび不可避的不純物からなり、下記式(1)で定められるA値が6.0~18.0を満足する成分組成を有し、長手方向と垂直な断面の一辺の長さが250mm以上である矩形の鋳片を、加熱温度1120℃以上、減面率60%以上にて圧延してビレットとし、該ビレットを加熱温度:1050℃以上、減面率75%以上にて熱間加工する快削鋼の製造方法。
記
A値=2([Mn]+2[Cr])/[S] ・・・(1)
但し、[M]は[ ]内の元素の含有量(質量%)
Si:0.50%以下、
P:0.10%以下、
Al:0.010%以下および
N:0.0150%以下
から選ばれる1種または2種以上を含有する前記4に記載の快削鋼の製造方法。
Ca:0.0010%以下、
Se:0.30%以下、
Te:0.15%以下、
Bi:0.20%以下、
Sn:0.020%以下、
Sb:0.025%以下、
B:0.010%以下、
Cu:0.50%以下、
Ni:0.50%以下、
Ti:0.100%以下、
V:0.20%以下、
Zr:0.050%以下および
Mg:0.0050%以下
から選ばれる1種または2種以上を含有する前記4または5に記載の快削鋼の製造方法。
Cは、鋼の強度および被削性に大きな影響を及ぼす重要な元素である。しかし、その含有量が0.09%以上であると、硬質化し強度が高くなりすぎて、被削性が劣化する。従って、C含有量は、0.09%未満とする。好ましくは、0.07%以下の範囲内とする。なお、強度を確保する観点からは、C含有量を0.01%以上とすることが好ましい。さらには0.03%以上とすることがより好ましい。
Mnは、被削性の向上に重要な硫化物形成元素である。しかし、その含有量が0.50%未満では、硫化物量が少ないために十分な被削性が得られないので、下限を0.50%とする。Mn含有量は好ましくは、0.70%以上とする。一方、その含有量が1.50%を超えると、硫化物が粗大化することに加え、長く伸長して被削性が低下する。また、機械的性質が低下するので、Mn含有量の上限値は1.50%とする。Mn含有量は、好ましくは、1.20%以下とする。
Sは、被削性の向上に有効な硫化物形成元素である。しかし、その含有量が0.250%未満では微細な硫化物が少ないために被削性が向上しない。一方、その含有量が0.600%を超えると、硫化物が粗大化しすぎて、微細な硫化物の個数が減るため、被削性が低下する。また、熱間加工性ならびに重要な機械的特性である延性が低下する。従って、S含有量は、0.250~0.600%の範囲内とする。好ましくは、0.300%以上である。好ましくは、0.450%以下である。
Oは、酸化物を形成し、硫化物の析出核となることに加え、圧延等の熱間加工時における硫化物の伸長を抑制するのに有効な元素であり、この作用により被削性を向上させることができる。しかし、その含有量が0.0100%以下では、硫化物の伸長の抑制効果が十分ではなく、伸長した硫化物が残存して、本来の効果が期待できない。従って、Oの含有量は、0.0100%超とする。一方、0.0500%を超えて添加しても硫化物の伸長抑制効果が飽和することに加え、硬質な酸化物系介在物の量が多くなるため、および、過剰な量の添加は経済的に不利であるため、上限を0.0500%とする。
Crは、硫化物を形成し、切削時の潤滑作用により被削性を向上させる作用を有する。また、圧延等の熱間加工時における硫化物の伸長を抑制させるため、被削性を向上させることができる。しかし、その含有量が0.50%未満では、硫化物の生成が充分でなく、伸長した硫化物が残存しやすくなるため、本来の効果が充分に期待できない。一方、1.50%を超えて添加すると、硬質化することに加え、硫化物が粗大になり、かつ伸長を抑制する効果が飽和し、かえって被削性が低下する。また、過剰な量の合金コストの添加は経済的に不利である。従って、Cr含有量は、0.50~1.50%とする。好ましくは、0.70%以上である。好ましくは、1.30%以下である。
ここで、以上の成分組成において、次式(1)にて定義されるA値が6.0~18.0であることが肝要である。
A値=2([Mn]+2[Cr])/[S] ・・・(1)
但し、[M]は[ ]内の元素の含有量(質量%)
すなわち、A値は、圧延等の熱間加工時におけるMn-Cr-S系硫化物の微細化を左右する重要な指標で、このA値を限定することにより、被削性を向上させることができる。しかし、A値が6.0未満であると、Mn-S単独の硫化物が生成し、粗大な硫化物となりやすく、被削性が劣化する。一方、A値が18.0を超えると、硫化物を微細化する効果が飽和することに加え、硫黄に対して硫化物形成元素が多くなりすぎ、硫化物が粗大になる。従って、A値は6.0~18.0とする。好ましくは、6.5以上である。好ましくは、17.0以下である。
Si:0.50%以下、
P:0.10%以下、
Al:0.010%以下および
N:0.0150%以下
から選ばれる1種または2種以上
Siは、脱酸元素であり、また、Siの酸化物は硫化物の生成核として作用し、硫化物の生成を促進し硫化物を微細化し、切削工具寿命を向上させる作用を有することから、工具寿命を更に延ばしたい場合は、鋼に含有されていてもよい。ただし、0.50%を超えての添加は、酸化物が大きくなり、数も少なくなるため、硫化物の生成核としての効果がなくなることに加え、硬質な酸化物によるアブレイシブ摩耗を誘発し工具寿命の劣化を招く。そのため、Siの含有量は0.50%以下とする。好ましくは、0.03%以下とする。なお、Siによる上記の作用を発現させるためには、0.001%以上含有されていることが好ましい。
Pは、切削加工時に構成刃先の生成を抑制することにより、仕上げ面粗さを低減させるのに有効な元素である。この観点から、Pは0.01%以上含有されることが好ましい。ただし、その含有率が0.10%を超えると、材質が硬質化するため被削性を低下させるとともに、熱間加工性および延性を著しく低下させる。従って、P含有量は、0.10%以下とすることが好ましい。より好ましくは、0.08%以下とする。
Alは、Siと同様に脱酸元素であり含有されていてもよい。Alは鋼中でAl2O3を生成するが、この酸化物は硬質であるため、いわゆるアブレイシブ摩耗によって切削工具寿命を劣化させることから、Alを過剰に含有されることを回避する必要がある。この意味からは、Al添加量を0.010%以下とすることが好ましい。より好ましくは、0.005%以下とする。なお、Alによる脱酸効果を発現させる観点からは、Alは0.001%以上含有させることが好ましい。
Nは、Cr等と窒化物を形成し、切削加工中の温度上昇により窒化物が分解することで、工具表面にベラーグと呼ばれる酸化物被膜を形成する。ベラーグは、工具表面を保護する作用があるため、工具寿命を向上させることから、Nを含有させてもよい。この作用を有効に発現させるためには、Nは0.0050%以上含有させることが好ましい。一方、0.0150%を超えて添加すると、ベラーグの効果が飽和することに加え、材質が硬質化するため、工具寿命が短くなる。そのため、Nの含有量は、0.0150%以下とすることが好ましい。より好ましくは、0.0060%以上である。より好ましくは、0.0120%以下である。
Ca:0.0010%以下、
Se:0.30%以下、
Te:0.15%以下、
Bi:0.20%以下、
Sn:0.020%以下、
Sb:0.025%以下、
B:0.010%以下、
Cu:0.50%以下、
Ni:0.50%以下、
Ti:0.100%以下、
V:0.20%以下、
Zr:0.050%以下および
Mg:0.0050%以下
から選ばれる1種または2種以上
Ca、Se、Te、Bi、Sn、Sb、B、Cu、Ni、Ti、V、Zr、Mgは、何れも被削性を向上させる作用を有するため、被削性が重視される場合に添加されてもよい。被削性の向上を目的としてこれら元素を含有させる場合、その添加量が、Ca:0.0001%未満、Se:0.02%未満、Te:0.10%未満、Bi:0.02%未満、Sn:0.003%未満、Sb:0.003%未満、B:0.003%未満、Cu:0.05%未満、Ni:0.50%未満、Ti:0.003%未満、V:0.005%未満、Zr:0.005%未満、Mg:0.0005%未満では十分な効果が得られないので、それぞれ、Ca:0.0001%以上、Se:0.02%以上、Te:0.10%以上、Bi:0.02%以上、Sn:0.003%以上、Sb:0.003%以上、B:0.003%以上、Cu:0.05%以上、Ni:0.05%以上、Ti:0.003%以上、V:0.005%以上、Zr:0.005%以上、Mg:0.0005%以上とすることが好ましい。
円相当径で1μm未満の硫化物が500個/mm2以上、円相当径で1~5μmの硫化物が2000個/mm2以上分布
快削鋼の組織に関しては、硫化物が微細分散していることが、切削加工時の工具と被削材の間の潤滑作用を促進するのに有利である。硫化物の微細分散により快削鋼の被削性を確保するためには、鋼組織中に、円相当径1μm未満と円相当径で1~5μmの硫化物が一定量以上に分散している必要がある。円相当径1μm未満の硫化物は主に工具と被削材との間の潤滑に有効である。また、円相当径1~5μmの硫化物は、前記の潤滑効果だけでなく、切りくずの分断性にも有効である。そのため、円相当径で1μm未満の硫化物の個数が500個/mm2以上、円相当径で1~5μmの硫化物が2000個/mm2以上とする。
すなわち、上記した成分組成を有し、長手方向と垂直な断面の一辺の長さが250mm以上である矩形の鋳片を、加熱温度1120℃以上、減面率60%以上にて圧延してビレットとし、該ビレットを加熱温度:1050℃以上、減面率75%以上にて熱間加工する。
長手方向と垂直な断面の一辺の長さが250mm以上の矩形断面
まず、前記成分組成に調整された溶鋼を、鋳造して鋳片とするが、鋳片としては、長手方向と垂直な断面の一辺の長さが250mm以上である矩形の鋳片を用いる。
該鋳片は、連続鋳造法や造塊法によって矩形断面の鋳片として製造する。その際、矩形断面の一辺の長さが250mmより小さいと、鋳片凝固時に硫化物粒のサイズが大きくなる。そのため、引き続き鋼片圧延でビレットとした後も粗大な硫化物が残存するため、最終的な熱間加工された後の硫化物の微細化に不利となる。そのため、鋳片の断面における一辺の長さは250mm以上とする。より好ましくは300mm以上とする。なお、鋳片の断面における一辺の長さについて、上限は特に規制する必要はないが、鋳造に続く熱間圧延の実現性の観点から、上記長さは600mm以下とすることが好ましい。
鋳片の加熱温度:1120℃以上
鋳片は、熱間圧延されてビレットとされるが、この熱間圧延の際の加熱温度は1120℃以上とする必要がある。加熱温度が1120℃未満では、鋳造段階において冷却-凝固する際に晶出した粗大な硫化物が固溶せず、ビレットとなった後も粗大な硫化物が残存することとなる。その結果、引き続く熱間加工後も硫化物が粗大なままで、所望の微細な硫化物の分布状態が得られない。そのため、鋳片をビレットへ熱間圧延する際の加熱温度は1120℃以上、好ましくは1150℃以上とする。なお、鋳片の加熱温度について、上限は特に規制する必要はないが、スケールロス抑制の観点から、加熱温度は1300℃以下、より好ましくは1250℃以下とすることが好ましい。
凝固時に晶出した硫化物粒のサイズは大きいため、鋼片圧延である程度サイズを小さくしておく必要がある。熱間圧延での減面率が少ないと、硫化物粒が大きいままビレットとなる。そのため、引き続きビレットを棒鋼や線材へ熱間加工する際の加熱時-圧延時に、硫化物粒を微細化させることが困難である。そのため、鋳片からビレットへ60%以上の減面率にて熱間圧延することとする。
100×(S0-S1)/S0
によって求めることができる。
加熱温度:1050℃以上
ビレットを棒鋼あるいは線材へと熱間加工する際の加熱温度は重要な因子である。加熱温度が1050℃未満では、硫化物が微細分散しないため、切削加工時の潤滑作用が少なくなる。その結果、工具摩耗が大きくなるため、工具寿命もが短くなる。従って、ビレットの加熱温度は1050℃以上とする。より好ましくは1080℃以上である。なお、上限は特に規制する必要はないが、スケールロスによる歩留まり低下抑制の観点から1250℃以下とすることが好ましい。
ビレットを棒鋼あるいは線材へと熱間加工する際の減面率も硫化物の微細化のため重要な因子である。この減面率が75%未満では、硫化物の微細化が十分でないため、減面率の下限を75%とした。より好ましくは80%以上とする。ここで、熱間加工の減面率は、熱間圧延前のビレットの、熱間加工方向に垂直な断面の断面積をS1、熱間加工により製造した棒鋼あるいは線材の熱間加工方向(延伸方向)に垂直な断面の断面積をS2として、次式
100×(S1-S2)/S1
によって求めることができる。
表1に示す化学組成の鋼を、連続鋳造機にて長手方向と垂直な断面が表2-1および表2-2に示す寸法の矩形形状の鋳片とした。得られた鋳片を表2-1および表2-2に示す製造条件にて棒鋼に圧延した。本発明鋼および比較鋼について以下のような試験に供した。すなわち、鋳片を、表2-1および表2-2に示す加熱温度、減面率にて熱間圧延を行い、長片寸法および短片寸法が表2-1および表2-2に示すとおりの角ビレットとした。得られたビレットを表2-1および表2-2に示す加熱温度にて加熱し、熱間圧延して表2-1および表2-2に示す直径の棒鋼とした。得られた棒鋼(本発明鋼および比較鋼)を、以下に示す試験に供した。
Claims (6)
- 質量%で、
C:0.09%未満、
Mn:0.50~1.50%、
S:0.250~0.600%、
O:0.0100%超0.0500%以下および
Cr:0.50~1.50%
を含有し、残部Feおよび不可避的不純物からなり、下記式(1)で定められるA値が6.0~18.0を満足する成分組成を有し、
円相当径で1μm未満の硫化物が500個/mm2以上、円相当径で1~5μmの硫化物が2000個/mm2以上分布してなる鋼組織を有する快削鋼。
記
A値=2([Mn]+2[Cr])/[S] ・・・(1)
但し、[M]は[ ]内の元素の含有量(質量%) - 前記成分組成は、さらに、質量%で
Si:0.50%以下、
P:0.10%以下、
Al:0.010%以下および
N:0.0150%以下
から選ばれる1種または2種以上を含有する請求項1に記載の快削鋼。 - 前記成分組成は、さらに、質量%で
Ca:0.0010%以下、
Se:0.30%以下、
Te:0.15%以下、
Bi:0.20%以下、
Sn:0.020%以下、
Sb:0.025%以下、
B:0.010%以下、
Cu:0.50%以下、
Ni:0.50%以下、
Ti:0.100%以下、
V:0.20%以下、
Zr:0.050%以下および
Mg:0.0050%以下
から選ばれる1種または2種以上を含有する請求項1または2に記載の快削鋼。 - 質量%で、
C:0.09%未満、
Mn:0.50~1.50%、
S:0.250~0.600%、
O:0.010%超0.050%以下および
Cr:0.50~1.50%
を含有し、残部Feおよび不可避的不純物からなり、下記式(1)で定められるA値が6.0~18.0を満足する成分組成を有し、長手方向と垂直な断面の一辺の長さが250mm以上である矩形の鋳片を、加熱温度1120℃以上、減面率60%以上にて圧延してビレットとし、該ビレットを加熱温度:1050℃以上、減面率75%以上にて熱間加工する快削鋼の製造方法。
記
A値=2([Mn]+2[Cr])/[S] ・・・(1)
但し、[M]は[ ]内の元素の含有量(質量%) - 前記成分組成は、さらに、質量%で
Si:0.50%以下、
P:0.10%以下、
Al:0.010%以下および
N:0.0150%以下
から選ばれる1種または2種以上を含有する請求項4に記載の快削鋼の製造方法。 - 前記成分組成は、さらに、質量%で
Ca:0.0010%以下、
Se:0.30%以下、
Te:0.15%以下、
Bi:0.20%以下、
Sn:0.020%以下、
Sb:0.025%以下、
B:0.010%以下、
Cu:0.50%以下、
Ni:0.50%以下、
Ti:0.100%以下、
V:0.20%以下、
Zr:0.050%以下および
Mg:0.0050%以下
から選ばれる1種または2種以上を含有する請求項4または5に記載の快削鋼の製造方法。
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