EP1449932A1 - Automatenstahl - Google Patents

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Publication number
EP1449932A1
EP1449932A1 EP02783714A EP02783714A EP1449932A1 EP 1449932 A1 EP1449932 A1 EP 1449932A1 EP 02783714 A EP02783714 A EP 02783714A EP 02783714 A EP02783714 A EP 02783714A EP 1449932 A1 EP1449932 A1 EP 1449932A1
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EP
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Prior art keywords
mass
steel
free cutting
sulfide
cutting steel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP02783714A
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English (en)
French (fr)
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EP1449932A4 (de
EP1449932B1 (de
Inventor
Kiyohito Ishida
Toshiyuki c/o NKK BARS & SHAPES CO. LTD MURAKAMI
Tetsuo c/o NKK BARS & SHAPES CO. LTD SHIRAGA
Katsunari Oikawa
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
National Institute of Advanced Industrial Science and Technology AIST
JFE Bars and Shapes Corp
Original Assignee
National Institute of Advanced Industrial Science and Technology AIST
NKK Bars and Shapes Co Ltd
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Priority claimed from JP2002185496A external-priority patent/JP4295959B2/ja
Priority claimed from JP2002185495A external-priority patent/JP4295958B2/ja
Priority claimed from JP2002185494A external-priority patent/JP3891558B2/ja
Application filed by National Institute of Advanced Industrial Science and Technology AIST, NKK Bars and Shapes Co Ltd filed Critical National Institute of Advanced Industrial Science and Technology AIST
Publication of EP1449932A1 publication Critical patent/EP1449932A1/de
Publication of EP1449932A4 publication Critical patent/EP1449932A4/de
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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
    • 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
    • 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
    • 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
    • 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
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a free cutting steel, particularly, to a low carbon free cutting steel to which lead is not added or in which the lead addition amount is markedly decreased from the conventional level of 0.15 to 0.35 mass %, which is adapted for use as a substitute steel for the conventional low carbon resulfurized and leaded free cutting steel, to a low carbon resulfurized and leaded free cutting steel superior in machinability to the conventional low carbon resulfurized and leaded steel, and to a resulfurized or resulfurized and leaded free cutting steel having an oxygen concentration lower than that in the prior art, low in the surface flaw, and excellent in machinability.
  • Pb lead
  • S sulfur
  • Japanese Patent Disclosure (Kokai) No. 9-25539 discloses a free cutting microalloyed steel without quenching and tempering to which Pb is not added. In this case, Nd is added to the steel for promoting the finely dispersed precipitation of MnS.
  • Japanese Patent Disclosure No. 2000-160284 (hereinafter referred to as “prior art 2”) also discloses a free cutting steel to which Pb is not added. In this case, a large amount of S is added to the steel so as to increase the amount of the sulfide, and the form of the sulfide is controlled by oxygen. Further, Japanese Patent Publication (Kokoku) No.
  • 2-6824 (hereinafter referred to as "prior art 3") discloses a free cutting steel, in which Cr having a reactivity with S to form a compound higher than that of Mn is added to the steel so as to form CrS in place of MnS, thereby improving the free-cutting capability.
  • prior art 1 is directed to a microalloyed steel containing 0.2 to 0.6% of C without quenching and tempering.
  • a special element of Nd is used in prior art. It follows that it is impossible to comply sufficiently with the requirement for the cost reduction. Also, a large amount of S is added to the steel in prior art 2, with the result that the hot ductility of the steel tends to be lowered. Further, prior art 3 necessitates the addition of a large amount reaching 3.5 to 5.9% of costly Cr, resulting in failure to comply sufficiently with the requirement for the cost reduction.
  • formation of a large amount of CrS as in prior art 3 is disadvantageous because the difficulty accompanying the smelting of the material is increased by the presence of a large amount of CrS.
  • Japanese Patent Disclosure No. 1-32302 discloses a free cutting steel, in which a relatively large amount of S is added to the steel so as to increase the amount of the sulfide, and the form of the sulfide is controlled by Te, and the oxygen amount is suppressed to 0.0030% or less so as to decrease the number of alumina clusters, thereby improving the machinability of the free cutting steel. Also, Japanese Patent Disclosure No.
  • prior art 5 discloses a free cutting steel, in which a relatively large amount of S is added to the steel so as to increase the amount of the sulfide, and a free cutting element of Pb is added to the steel so as to improve the machinability of the free cutting steel.
  • Prior art 5 also teaches that the oxygen amount is suppressed to 0.008% or less for preventing the streak flaw caused by the gigantic oxide.
  • the resulfurized and resulfurized and leaded free cutting steels contain in general a large amount of oxygen in order to control the form of the sulfide which is effective for improving the machinability of the free cutting steel.
  • all the oxygen does not dissolve in the sulfide, it is unavoidable for a gigantic oxide to be formed so as to cause the streak flaw, thereby giving rise to a serious defect in the processed article.
  • the oxygen content of steel is suppressed to 0.008% or less in order to avoid generation of the streak flaw.
  • the required amount of oxygen is decreased by increasing the addition amount of S.
  • the required amount of oxygen is decreased by using Nd as a free cutting element.
  • a first object of the present invention is to provide a low carbon free cutting steel to which lead is not added or in which the lead addition amount is markedly lowered from the level in the conventional low carbon resulfurized and leaded free cutting steel, the low carbon free cutting steel being allowed to exhibit a machinability fully comparable to or higher than that in the conventional low carbon resulfurized and leaded free cutting steel without obstructing the cost reduction and without lowering the hot ductility.
  • a second object of the present invention is to provide a low carbon resulfurized and leaded free cutting steel exhibiting a machinability superior to that in the prior art without increasing the lead and sulfur contents from the conventional levels.
  • a third object of the present invention is to provide a resulfurized or resulfurized and leaded free cutting steel exhibiting a machinability superior to that of the conventional steel in spite of the oxygen content lower than that in the conventional steel containing substantially the same amounts of sulfur and lead without obstructing the cost reduction and without lowering the hot ductility, and having a small surface flaw formed in the rolling step, which is derived from the blow-hole generated in the casting step as a result of achieving a low oxygen content.
  • a low carbon free cutting steel containing 0.02 to 0.15 mass % of C, 0.05 to 1.8 mass % of Mn, 0.20 to 0.49 mass % of S, more than 0.01 mass % and not more than 0.03 mass % of O 0.3 to 2.3 mass % of Cr, and the balance consisting of Fe and inevitable impurities, the Cr/S ratio falling within a range of between 2 and 6.
  • a low carbon resulfurized and leaded free cutting steel excellent in machinability containing 0.02 to 0.15 mass % of C, 0.05 to 1.00 mass % of Mn, 0.20 to 0.49 mass % of S, more than 0.008 mass % and not more than 0.030 mass % of O, 0.04 to 0.35 mass % of Pb, 0.3 to 2.3% of Cr, and the balance consisting of Fe and inevitable impurities, the Cr/S ratio falling within a range of between 2 and 6.
  • a resulfurized or resulfurized and leaded free cutting steel small in surface flaw and excellent in machinability said free cutting steel containing 0.16 to 0.49 mass % of S and 0.002 to 0.010 mass % of O wherein the sulfide having an aspect ratio not larger than 5 occupies at least 80% of the sulfides having the major axis of at least 10 ⁇ m.
  • a resulfurized or resulfurized and leaded free cutting steel small in surface flaw and excellent in machinability containing 0.02 to 0.15 mass % of C, 0.05 to 1.8 mass % of Mn, 0.16 to 0.49 mass % of S, 0.002 to 0.010 mass % of O, 0.3 to 2.3% of Cr, and the balance consisting of Fe and inevitable impurities, the Cr/S ratio falling within a range of between 2 and 6.
  • a first free cutting steel is provided by the low carbon free cutting steel according to the first aspect of the present invention, containing 0.02 to 0.15 mass % of C, 0.05 to 1.8 mass % of Mn, 0.20 to 0.49 mass % of S, more than 0.01 mass % and not more than 0.03 mass % of O 0.3 to 2.3% of Cr, and the balance consisting of Fe and inevitable impurities, the Cr/S ratio falling within a range of between 2 and 6.
  • the first free cutting steel of the present invention may further contain not more than 0.1 mass % of Si, 0.01 to 0.12 mass % of P, and not more than 0.01 mass % of Al.
  • the first free cutting steel of the present invention may further contain at least one element selected from the group consisting of 0.0001 to 0.0005 mass % of Ca, 0.01 to 0.03 mass % of Pb, 0.02 to 0.30 mass % of Se, 0.1 to 0.15 mass % of Te, 0.02 to 0.20 mass % of Bi, 0.003 to 0.020 mass % of Sn, 0.004 to 0.010 mass % of B, 0.005 to 0.015 mass % of N, 0.05 to 0.50 mass % of Cu, 0.003 to 0.090 mass % of Ti, 0.005 to 0.200 mass % of V, 0.005 to 0.090 mass % of Zr, and 0.0005 to 0.0080 mass % of Mg.
  • the sulfide having the major axis of at least 10 ⁇ m to occupy at least 90% of all the sulfides. It is also desirable for sulfide having an aspect ratio not larger than 5 to occupy at least 80% of the sulfides having the major axis at least 10 ⁇ m. Further, it is desirable for the particular free cutting steel to have a ferrite-pearlite micro structure with a prior austenite grain diameter exceeding the grain size number 7.
  • the first free cutting steel described above which has been obtained on the basis of the ideas given above, to exhibit a machinability fully comparable to or higher than that exhibited by the conventional low carbon resulfurized and leaded free cutting steel without obstruction the cost reduction and without lowering the hot ductility, even if lead is not added to the free cutting steel or even if the lead addition amount is markedly lowered from the level in the conventional low carbon resulfurized and leaded free cutting steel.
  • Carbon which seriously affects the strength and the machinability of the steel, is an important element.
  • the C content is lower than 0.02 mass %, it is impossible to obtain a sufficient strength of the steel.
  • the C content exceeds 0.15 mass %, the strength of the steel is rendered excessively high so as to deteriorate the machinability of the steel.
  • the C content is defined in the present invention to fall within a range of between 0.02 mass % and 0.15 mass %.
  • the C content should fall within a range of between 0.02 mass % and 0.10 mass %.
  • Manganese is a sulfide formation element that is important for improving the machinability of the steel.
  • the Mn content is lower than 0.05 mass %, the amount of the sulfide formed is excessively small, resulting in failure to obtain a sufficient machinability.
  • the Mn content exceeds 1.8 mass %, the formed sulfide is much elongated, with the result that the machinability of steel is lowered.
  • the Mn content is defined in the present invention to fall within a range of between 0.05 and 1.8 mass %.
  • the Mn content should be not lower than 0.22 mass % and lower than 0.60 mass %.
  • Sulfur is a sulfide formation element which forms a sulfide effective for improving the machinability of the steel.
  • the S content is lower than 0.20 mass %, the amount of the sulfide formed is excessively small, resulting in failure to obtain a sufficient effect for improving the machinability of the steel.
  • the S content exceeds 0.49 mass %, the hot workability and the ductility of the steel are markedly lowered. Such being the situation, the S content of steel is defined in the present invention to fall within a range of between 0.20 and 0.49 mass %.
  • Oxygen is an element effective for suppressing the elongation of the sulfide in the hot working step such as a rolling step. Therefore, oxygen is an element important for improving the machinability of the steel by suppressing the elongation of the sulfide.
  • the O content is not higher than 0.01 mass %, it is difficult to obtain a sufficient effect of suppressing the elongation of the sulfide. Since the elongated sulfide remains in the steel, it is impossible to obtain a sufficient effect of improving the machinability of the steel.
  • the O addition amount exceeds 0.03 mass %, the effect of suppressing the elongation of the sulfide is saturated.
  • the addition of an excessively large amount of O is disadvantageous in economy.
  • a casting defect such a blow-hole is generated.
  • the O content is defined in the present invention to exceed 0.01 mass % and to be not higher than 0.03 mass %.
  • Chromium is an element effective for suppressing the elongation of the sulfide in the hot working step such as a rolling step. Therefore, Cr is an element important for improving the machinability of the steel by suppressing the elongation of the sulfide.
  • the Cr content is lower than 0.3 mass %, it is difficult to obtain a sufficient effect of suppressing the elongation of the sulfide. Since the elongated sulfide remains in the steel, it is impossible to obtain a sufficient effect of improving the machinability of the steel.
  • the Cr addition amount exceeds 2.3 mass %, the effect of suppressing the elongation of the sulfide is saturated.
  • the Cr content is defined in the present invention to fall within a range of between 0.3 mass % and 2.3 mass %.
  • the Cr content should fall within a range of between 0.3 mass % and 1.5 mass %.
  • the Cr/S ratio is an important index seriously affecting the degree of elongation of the sulfide in the hot working step such as a rolling step. It is possible to obtain a sulfide having a desired degree of elongation, which permits improving the machinability of the steel, by defining the Cr/S ratio appropriately. If the Cr/S ratio is smaller than 2, the sulfide elongated by the formation of MnS is rendered prominent so as to deteriorate the machinability of the steel. On the other hand, if the Cr/S ratio exceeds 6, the effect of suppressing the elongation of the sulfide is saturated. Such being the situation, the Cr/S ratio is defined in the present invention to fall within a range of between 2 and 6. Preferably, the Cr/S ratio should fall within a range of between 2 and 4.
  • the conditions given above are absolutely necessary for the first free cutting steel of the present invention.
  • the other conditions of the first free cutting steel are as follows:
  • Silicon is a deoxidizing element. Since the oxide of Si acts as a nucleus of the sulfide formation, Si promotes the sulfide formation so as to pulverize finely the sulfide, with the result that the tool life is shortened. Such being the situation, where it is desired to further prolong the tool life, it is desirable to define the Si content not to exceed 0.1 mass %. More desirably, the Si content of the steel should not exceed 0.03 mass %.
  • Phosphorus is an element effective for suppressing the formation of the built-up edge in the cutting process step so as to lower the finish surface roughness.
  • the P content is lower than 0.01 mass %, it is difficult to obtain a sufficient effect.
  • the P content exceeds 0.12 mass %, the effect noted above is saturated. Also, the hot workability and the ductility of the steel are markedly lowered.
  • the P content is defined in the present invention to fall within a range of between 0.01 mass % and 0.12 mass %.
  • the P content should fall within a range of between 0.01 mass % and 0.09 mass %.
  • Aluminum is a deoxidizing element like Si. Since the oxide of Al acts as a nucleus of the sulfide formation, Al promotes the sulfide formation so as to pulverize finely the sulfide, with the result that the tool life is shortened. Such being the situation, where it is desired to further prolong the tool life, it is desirable to define the Al content not to exceed 0.01 mass %. More desirably, the Al content of the steel should not exceed 0.003 mass %.
  • any of Ca, Pb, Se, Te, Bi, Sn, B, N, Cu, Ti, V, Zr and Mg is used in the case where it is important to improve the machinability of the steel.
  • the addition amount of each of these elements is smaller than the lower limit noted above, the effect of improving the machinability of the steel cannot be obtained.
  • the addition amount of each of these elements exceeds the upper limit noted above, the effect of improving the machinability of the steel is saturated. Also, the addition of an excessively large amount of each of these elements is disadvantageous in economy.
  • these elements should be added such that Ca falls within a range of between 0.0001 and 0.0005 mass %, Pb falls within a range of between 0.01 and 0.03 mass %, Se falls within a range of between 0.02 and 0.30 mass %, Te falls within a range of between 0.1 and 0.15 mass %, Bi falls within a range of between 0.02 and 0.20 mass %, Sn falls within a range of between 0.003 and 0.020 mass %, B falls within a range of between 0.004 and 0.010 mass %, N falls within a range of between 0.005 and 0.015 mass %, Cu falls within a range of between 0.05 and 0.50 mass %, Ti falls within a range of between 0.003 and 0.090 mass %, V falls within a range of between 0.005 and 0.200 mass %, Zr falls within a range of between 0.005 and 0.090 mass %, and Mg falls within a range of between 0.0005 and 0.00
  • the micro structure of the first free cutting steel is a ferrite ⁇ pearlite-based structure.
  • Concerning the machinability of the steel it is advantageous for the prior austenite grain size to be large. However, a satisfactory machinability can be maintained even in the case of fine grains.
  • the sulfide it is advantageous for the sulfide to grow into a large body.
  • the major axis of the sulfide it is desirable for the major axis of the sulfide to be at least 10 ⁇ m. It is also desirable for the sulfide having the major axis of at least 10 ⁇ m to occupy at least 90% of all the sulfides.
  • the aspect ratio of the sulfide is represented by L/d, where "L” denotes the major axis and “d” denotes the minor axis of the sulfide, as shown in FIG. 1.
  • L denotes the major axis
  • d denotes the minor axis of the sulfide
  • a second free cutting steel is provided by the low carbon free cutting steel according to the second aspect of the present invention, containing 0.02 to 0.15 mass % of C, 0.05 to 1.00 mass % of Mn, 0.20 to 0.49 mass % of S, more than 0.008 mass % and not more than 0.030 mass% of O, 0.04 to 0.35 mass % of Pb, 0.3 to 2.3% of Cr, and the balance consisting of Fe and inevitable impurities, the Cr/S ratio falling within a range of between 2 and 6.
  • the second free cutting steel of the present invention may further contain not more than 0.1 mass % of Si, 0.01 to 0.12 mass % of P, and not more than 0.01 mass % of Al.
  • the second free cutting steel of the present invention may further contain at least one element selected from the group consisting of 0.0001 to 0.0005 mass % of Ca, 0.02 to 0.30 mass % of Se, 0.1 to 0.15 mass % of Te, 0.02 to 0.20 mass % of Bi, 0.003 to 0.020 mass % of Sn, 0.004 to 0.010 mass % of B, 0.005 to 0.015 mass % of N, 0.05 to 0.50 mass % of Cu, 0.003 to 0.090 mass % of Ti, 0.005 to 0.200 mass % of V, 0.005 to 0.090 mass % of Zr, and 0.0005 to 0.0080 mass % of Mg.
  • the second free cutting steel of the present invention which has been achieved on the basis of the ideas given above, exhibits a machinability superior to that exhibited in the past without increasing the lead amount and the sulfur amount from the levels in the prior art.
  • the C content is defined in the present invention to fall within a range of between 0.02 mass % and 0.15 mass %.
  • the C content should fall within a range of between 0.02 mass % and 0.10 mass %.
  • Manganese is an element important for improving the machinability of the steel.
  • the Mn content is lower than 0.05 mass %, the amount of the sulfide formed is excessively small, resulting in failure to obtain a sufficient machinability.
  • the Mn content exceeds 1.00 mass %, the formed sulfide is much elongated, with the result that the machinability of steel is lowered.
  • the Mn content is defined in the present invention to fall within a range of between 0.05 and 1.00 mass %.
  • the Mn content should be not lower than 0.22 mass % and lower than 0.60 mass %.
  • the S content of the steel is defined in the present invention to fall within a range of between 0.20 and 0.49 mass %.
  • Oxygen is an element effective for suppressing the elongation of the sulfide in the hot working step such as a rolling step. Therefore, oxygen is an element important for improving the machinability of the steel by suppressing the elongation of the sulfide.
  • the O content is not higher than 0.008 mass %, it is difficult to obtain a sufficient effect of suppressing the elongation of the sulfide. Since the elongated sulfide remains in the steel, it is impossible to obtain a sufficient effect of improving the machinability of the steel.
  • the O addition amount exceeds 0.030 mass %, the effect of suppressing the elongation of the sulfide is saturated.
  • the addition of an excessively large amount of O is disadvantageous in economy.
  • a casting defect such a blow-hole is generated.
  • the O content is defined in the present invention to exceed 0.008 mass % and to be not higher than 0.03 mass %.
  • Lead is an element important for improving the machinability of the steel.
  • the Pb content of the steel is lower than 0.04 mass %, it is impossible to obtain a sufficient effect of improving the machinability of the steel.
  • the effect of improving the machinability of the steel is saturated.
  • the hot workability of the steel is markedly lowered.
  • the Pb content of the steel is defined in the present invention to fall within a range of between 0.04 mass % and 0.35 mass %.
  • the Cr content is lower than 0.3 mass %, it is difficult to obtain a sufficient effect of suppressing the elongation of the sulfide, as described previously in conjunction with the first free-cutting steel of the present invention. Since the elongated sulfide remains in the steel, it is impossible to obtain a sufficient effect of improving the machinability of the steel. On the other hand, even if the Cr addition amount exceeds 2.3 mass %, the effect of suppressing the elongation of the sulfide is saturated. It follows that the addition of an excessively large amount of Cr is disadvantageous in economy. Under the circumstances, the Cr content is defined in the present invention to fall within a range of between 0.3 mass % and 2.3 mass %. Preferably, the Cr content should fall within a range of between 0.3 mass % and 1.4 mass %.
  • the Cr/S ratio is important in the second free cutting steel as in the first free cutting steel. If the Cr/S ratio is smaller than 2, the sulfide elongated by the formation of MnS is rendered prominent so as to deteriorate the machinability of the steel. On the other hand, if the Cr/S ratio exceeds 6, the effect of suppressing the elongation of the sulfide is saturated. Such being the situation, the Cr/S ratio is defined in the present invention to fall within a range of between 2 and 6. Preferably, the Cr/S ratio should fall within a range of between 2 and 4.
  • Si shortens the tool life. Such being the situation, where it is desired to further prolong the tool life, it is desirable to define the Si content not to exceed 0.1 mass % as in the first free cutting steel of the present invention. More desirably, the Si content of the steel should not exceed 0.03 mass %.
  • the P content is defined in the present invention to fall within a range of between 0.01 mass % and 0.12 mass %.
  • the P content should fall within a range of between 0.01 mass % and 0.09 mass %.
  • Aluminum shortens the tool life as described previously in conjunction with the first free cutting steel. Therefore, where it is desired to further prolong the tool life, it is desirable to define the Al content not to exceed 0.01 mass %. More desirably, the Al content of the steel should not exceed 0.003 mass %.
  • any of Ca, Se, Te, Bi, Sn, B, N, Cu, Ti, V, Zr and Mg is used in the case where it is important to improve the machinability of the steel.
  • the addition amount of each of these elements is smaller than the lower limit noted above, the effect of improving the machinability of the steel cannot be obtained.
  • the addition amount of each of these elements exceeds the upper limit noted above, the effect of improving the machinability of the steel is saturated. Also, the addition of an excessively large amount of each of these elements is disadvantageous in economy.
  • these elements should be added such that Ca falls within a range of between 0.0001 and 0.0005 mass %, Se falls within a range of between 0.02 and 0.30 mass %, Te falls within a range of between 0.1 and 0.15 mass %, Bi falls within a range of between 0.02 and 0.20 mass %, Sn falls within a range of between 0.003 and 0.020 mass %, B falls within a range of between 0.004 and 0.010 mass %, N falls within a range of between 0.005 and 0.015 mass %, Cu falls within a range of between 0.05 and 0.50 mass %, Ti falls within a range of between 0.003 and 0.090 mass %, V falls within a range of between 0.005 and 0.200 mass %, Zr falls within a range of between 0.005 and 0.090 mass %, and Mg falls within a range of between 0.0005 and 0.0080 mass %.
  • the micro structure of the second free cutting steel is a ferrite ⁇ pearlite-based structure like the micro structure of the first free cutting steel described previously.
  • Concerning the machinability of the steel it is advantageous for the prior austenite grain size to be large. However, a satisfactory machinability can be maintained even in the case of fine grains.
  • the third free cutting steel of the present invention is a resulfurized or resulfurized and leaded free cutting steel small according to the third aspect of the present invention, the free cutting steel containing 0.16 to 0.49 mass % of S and 0.002 to 0.010% of O.
  • the sulfide having an aspect ratio not larger than 5 occupies at least 80% of the sulfides having the major axis of at least 10 ⁇ m.
  • the specific free cutting steel which permits realizing the particular sulfide and which defines the carbon content affecting the machinability of the free cutting steel, contains 0.02 to 0.15 mass % of C, 0.05 to 1.8 mass % of Mn, 0.16 to 0.49 mass % of S, 0.002 to 0.010 mass % of O 0.3 to 2.3% of Cr, and the balance consisting of Fe and inevitable impurities, the Cr/S ratio falling within a range of between 2 and 6.
  • the third free cutting steel of the present invention may further contain not more than 0.1 mass % of Si, 0.04 to 0.12 mass % of P, and not more than 0.01 mass % of Al.
  • the third free cutting steel of the present invention may further contain at least one element selected from the group consisting of 0.0001 to 0.0090 mass % of Ca, 0.01 to 0.40 mass % of Pb, 0.02 to 0.30 mass % of Se, 0.03 to 0.15 mass % of Te, 0.02 to 0.20 mass % of Bi, 0.003 to 0.020 mass % of Sn, 0.004 to 0.010 mass % of B, 0.005 to 0.015 mass % of N, 0.05 to 0.50 mass % of Cu, 0.003 to 0.090 mass % of Ti, 0.005 to 0.200 mass % of V, 0.005 to 0.090 mass % of Zr, and 0.0005 to 0.0080 mass % of Mg.
  • the third free cutting steel described above which has been obtained on the basis of the ideas given above, to exhibit a machinability fully comparable to or higher than that exhibited by the conventional steel containing substantially the same amounts of sulfur and lead without obstructing the cost reduction and without lowering the hot ductility in spite of the oxygen content lower than that in the conventional steel. Also, since it is possible to lower the oxygen concentration, it is possible to suppress the surface flaw in the rolling step, which is derived from the blow-hole generated in the casting step.
  • Sulfur is a sulfide formation element which forms a sulfide effective for improving the machinability of the steel.
  • the S content is lower than 0.16 mass %, the amount of the sulfide formed is excessively small, resulting in failure to obtain a sufficient effect for improving the machinability of the steel.
  • the S content exceeds 0.49 mass %, the hot workability and the ductility of the steel are markedly lowered. Such being the situation, the S content of steel is defined in the present invention to fall within a range of between 0.16 and 0.49 mass %.
  • Oxygen is an element effective for suppressing the elongation of the sulfide in the hot working step such as a rolling step. Therefore, oxygen is an element important for improving the machinability of the steel by suppressing the elongation of the sulfide.
  • the O content is not higher than 0.002 mass %, it is difficult to obtain a sufficient effect of suppressing the elongation of the sulfide. Since the elongated sulfide remains in the steel, it is impossible to obtain a sufficient effect of improving the machinability of the steel.
  • O permits generating the blow-hole in the casting step, and the surface flaw is derived from the blow-hole. Therefore, an excessively high O content is harmful.
  • the O content exceeds 0.010 mass %, a large number of blow-holes are generated and, thus, the surface flaw tends to be increased in the rolling step. In addition, the improvement in the effect of suppressing the elongation of the sulfide is small. Under the circumstances, the O content is defined in the present invention to fall within a range of between 0.002 mass % and 0.010 mass %.
  • the sulfide it is advantageous for the sulfide to be large and to be formed like a spindle. Therefore, it is necessary for the sulfide having an aspect ratio of 5 or less to occupy at least 80% of the sulfides having the major axis of 10 ⁇ m or more.
  • the C content is defined in the present invention to fall within a range of between 0.02 mass % and 0.15 mass %.
  • the C content should fall within a range of between 0.02 mass % and 0.10 mass %.
  • the Mn content is lower than 0.05 mass %, the amount of the sulfide formed is excessively small, resulting in failure to obtain a sufficient machinability, as in the first free cutting steel described previously.
  • the Mn content exceeds 1.8 mass %, the formed sulfide is much elongated, with the result that the machinability of the steel is lowered.
  • the Mn content is defined in the present invention to fall within a range of between 0.05 and 1.8 mass %.
  • the Mn content should be not lower than 0.22 mass % and lower than 0.60 mass %.
  • the Cr content is lower than 0.3 mass %, it is difficult to obtain a sufficient effect of suppressing the elongation of the sulfide, as in the first free cutting steel described previously. Since the elongated sulfide remains in the steel, it is impossible to obtain a sufficient effect of improving the machinability of the steel. On the other hand, even if the Cr addition amount exceeds 2.3 mass %, the effect of suppressing the elongation of the sulfide is saturated. It follows that the addition of an excessively large amount of Cr is disadvantageous in economy. Under the circumstances, the Cr content is defined in the present invention to fall within a range of between 0.3 mass % and 2.3 mass %. Preferably, the Cr content should fall within a range of between 0.3 mass % and 1.5 mass %.
  • the Cr/S ratio is important in the third free cutting steel as in the first and second free cutting steels. If the Cr/S ratio is smaller than 2, the sulfide elongated by the formation of MnS is rendered prominent so as to deteriorate the machinability of the steel. On the other hand, if the Cr/S ratio exceeds 6, the effect of suppressing the elongation of the sulfide is saturated. Such being the situation, the Cr/S ratio is defined in the present invention to fall within a range of between 2 and 6. Preferably, the Cr/S ratio should fall within a range of between 2 and 4.
  • the other conditions of the third free cutting steel are as follows:
  • Si shortens the tool life. Therefore, where it is desired to further prolong the tool life, it is desirable to define the Si content not to exceed 0.1 mass %. More desirably, the Si content of the steel should not exceed 0.03 mass %.
  • the P content is lower than 0.04 mass %, it is difficult to produce effectively the effect of suppressing the formation of the built-up edge in the cutting process step, resulting in failure to obtain a sufficient effect of lowering the finish surface roughness.
  • the P content exceeds 0.12 mass %, the effect noted above is saturated. Also, the hot workability and the ductility of the steel are markedly lowered. Such being the situation, the P content is defined in the present invention to fall within a range of between 0.04 mass % and 0.12 mass %.
  • the Al content of the steel should not exceed 0.003 mass %.
  • any of Ca, Pb, Se, Te, Bi, Sn, B, N, Cu, Ti, V, Zr and Mg is used in the case where it is important to improve the machinability of the steel.
  • the addition amount of each of these elements is smaller than the lower limit noted above, the effect of improving the machinability of the steel cannot be obtained.
  • the addition amount of each of these elements exceeds the upper limit noted above, the effect of improving the machinability of the steel is saturated. Also, the addition of an excessively large amount of each of these elements is disadvantageous in economy.
  • these elements should be added such that Ca falls within a range of between 0.0001 and 0.0090 mass %, Pb falls within a range of between 0.01 and 0.40 mass %, Se falls within a range of between 0.02 and 0.30 mass %, Te falls within a range of between 0.03 and 0.15 mass %, Bi falls within a range of between 0.02 and 0.20 mass %, Sn falls within a range of between 0.003 and 0.020 mass %, B falls within a range of between 0.004 and 0.010 mass %, N falls within a range of between 0.005 and 0.015 mass %, Cu falls within a range of between 0.05 and 0.50 mass %, Ti falls within a range of between 0.003 and 0.090 mass %, V falls within a range of between 0.005 and 0.200 mass %, Zr falls within a range of between 0.005 and 0.090 mass %, and Mg falls within a range of between 0.0005 and 0.00
  • the micro structure of the third free cutting steel is a ferrite ⁇ pearlite-based structure like the first and second free cutting steels.
  • Concerning the machinability of the steel it is advantageous for the prior austenite grain size to be large. However, a satisfactory machinability can be maintained even in the case of fine grains. In view of the mechanical properties of the article, it is desirable for the grains to be fine such that the grain size exceeds the grain size number 7.
  • the manufacturing method of each of the first to third free cutting steels of the present invention is not particularly limited. It is possible to carry out the casting and the hot rolling under the ordinary conditions.
  • the subsequent heat treatment is not particularly limited, either. For example, it is possible to employ the ordinary normalizing.
  • the first Example is directed to Examples of the first free cutting steel.
  • the major axis L length in the rolling direction
  • the minor axis d thickness or length in a direction perpendicular to the rolling direction
  • FIG. 2 is a graph showing the relationship between the life of the turning tool (SKH4), which is taken up as a typical characteristic value, and the life of the drilling tool.
  • the Mn content exceeded the upper limit specified in the present invention in sample No. 7 for the Comparative Example.
  • the Cr content was lower than the lower limit specified in the present invention in sample No. 9 for the Comparative Example.
  • the O content was insufficient in sample No. 10 for the Comparative Example.
  • the Cr/S ratio was lower than the lower limit specified in the present invention in sample No. 11 for the Comparative Example.
  • the aspect ratio of the sulfide was rendered large in each of these steel samples of the Comparative Example and, thus, these steel samples were rendered inferior to the steel samples of the present invention in the machinability.
  • the S content of the steel sample No. 8 for the Comparative Example was lower than the lower limit specified in the present invention. Therefore, the steel sample No. 8 noted above was insufficient in the total amount of the sulfide effective for improving the machinability of the steel, with the result that the steel sample No. 8 was inferior in the machinability of the steel to the steel samples of the present invention.
  • the second Example is directed to the second free cutting steel of the present invention.
  • Cast under the conditions equal to those for the first Example were steel samples Nos. 21 to 26 for the present invention each having the chemical composition falling within the range specified for the second free cutting steel of the present invention as shown in Table 4, steel samples Nos. 27 to 31 for the Comparative Example each having a chemical composition failing to fall within the range specified for the second free cutting steel of the present invention, and a steel sample No. 32 for the reference Example directed to a low carbon resulfurized and leaded free cutting steel.
  • the cast steel samples were subjected to a hot rolling and, then, to a normalizing under the conditions equal to those for the first Example.
  • Table 5 shows the results of the test. As apparent from Table 5, it was confirmed that any of the steel samples Nos. 21 to 26 for the present invention had satisfactory characteristics, compared with the steel sample No. 32 for the reference Example directed to a low carbon resulfurized and leaded free cutting steel.
  • the Mn content of the steel sample No. 27 for the Comparative Example exceeded the upper limit specified in the present invention.
  • the Cr content of the steel sample No. 29 for the Comparative Example was lower than the lower limit specified in the present invention.
  • the Cr/S ratio in the steel sample No. 30 for the Comparative Example was lower than the lower limit specified in the present invention.
  • the O content of the steel sample No. 31 for the Comparative Example was insufficient.
  • the aspect ratio of the sulfide was rendered large in each of these steel samples for the Comparative Example and, thus, the machinability of each of these steel samples for the Comparative Example was found to be inferior to that of any of the steel samples for the present invention.
  • the third Example is directed to the third free cutting steel of the present invention.
  • Cast under the conditions equal to those for the first Example were steel samples Nos. 41 to 46 for the present invention each having the chemical composition falling within the range specified for the third free cutting steel of the present invention as shown in Table 6, steel samples Nos. 47 to 51 for the Comparative Example each having a chemical composition failing to fall within the range specified for the third free cutting steel of the present invention, and a steel sample No. 52 for the reference Example directed to JIS SUM23L.
  • the cast steel samples were subjected to a hot rolling and, then, to a normalizing under the conditions equal to those for the first Example.
  • Table 7 shows the results of the test.
  • each of steel samples Nos. 41 to 44 included in the steel samples of the present invention was found to have satisfactory characteristics, compared with the steel sample No. 52 for the reference Example directed to JIS SUM23L.
  • the steel sample No. 45 for the present invention which is equal in the S content to and a half in the O content of the steel sample No. 52 for the reference Example directed to JIS SUM23L, was found to be substantially equal in the machinability to the steel sample No. 52 (JIS SUM23L).
  • a surface flaw was scarcely found in the steel sample No. 45 for the present invention.
  • the steel sample No. 46 for the present invention which had a S content equal to that of the steel sample No.
  • the Mn content of the steel sample No. 47 for the Comparative Example exceeded the upper limited specified in the present invention.
  • the Cr content of the steel sample No. 49 for the Comparative Example was lower than the lower limit specified in the present invention.
  • the Cr/S ratio of the steel sample 51 for the Comparative Example was lower than the lower limit specified in the present invention.
  • the sulfide in each of these steel samples for the Comparative Examples had a large aspect ratio and, thus, each of these steel samples was found to be inferior in machinability to any of the steel samples of the present invention.
  • the S content of the steel sample No. 48 for the Comparative Example was lower than the lower limit specified in the present invention. Therefore, the steel sample No.
  • the Comparative Example 48 for the Comparative Example was insufficient in the total amount of the sulfides effective for improving the machinability of the steel and, thus, was also inferior in the machinability to any of the steel samples of the present invention. Still further, the O content of the steel sample No. 50 for the Comparative Example was lower than the lower limit specified in the present invention and, thus, the steel sample No. 50 was inferior in the machinability to any of the steel samples of the present invention.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
EP02783714A 2001-11-30 2002-11-29 Automatenstahl Expired - Fee Related EP1449932B1 (de)

Applications Claiming Priority (9)

Application Number Priority Date Filing Date Title
JP2001366695 2001-11-30
JP2001366695 2001-11-30
JP2002185496 2002-06-26
JP2002185494 2002-06-26
JP2002185495 2002-06-26
JP2002185496A JP4295959B2 (ja) 2002-06-26 2002-06-26 表面疵の少ない被削性に優れた硫黄および硫黄複合快削鋼
JP2002185495A JP4295958B2 (ja) 2002-06-26 2002-06-26 被削性に優れた低炭素硫黄複合快削鋼
JP2002185494A JP3891558B2 (ja) 2001-11-30 2002-06-26 低炭素快削鋼
PCT/JP2002/012559 WO2003046240A1 (fr) 2001-11-30 2002-11-29 Acier de decolletage

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EP1449932A1 true EP1449932A1 (de) 2004-08-25
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WO (1) WO2003046240A1 (de)

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EP2789710A4 (de) * 2012-08-06 2015-05-20 Closed Joint Stock Company Omutninsk Metallurg Plant Automatenstahl mit wismut

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TWI391500B (zh) * 2008-08-06 2013-04-01 Posco 環保無鉛之快削鋼及其製作方法
CN102965577A (zh) * 2012-11-26 2013-03-13 湖南华菱湘潭钢铁有限公司 一种易切削钢
CN103741077A (zh) * 2013-12-24 2014-04-23 中兴能源装备股份有限公司 一种钢材
JP6927444B1 (ja) * 2019-12-23 2021-09-01 Ｊｆｅスチール株式会社 快削鋼およびその製造方法
TWI717990B (zh) * 2019-12-23 2021-02-01 日商杰富意鋼鐵股份有限公司 快削鋼及其製造方法
US20230108640A1 (en) * 2020-03-31 2023-04-06 Jfe Steel Corporation Free-cutting steel and method of producing same
CN112095051B (zh) * 2020-11-02 2021-02-02 北京科技大学 镁钙碲复合处理的易切削钢及其制备方法和应用
CN112795851B (zh) * 2020-12-29 2022-02-25 钢铁研究总院 一种低成本低合金半硬磁合金及其制备方法

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EP2789710A4 (de) * 2012-08-06 2015-05-20 Closed Joint Stock Company Omutninsk Metallurg Plant Automatenstahl mit wismut

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TW200300799A (en) 2003-06-16
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CN1276985C (zh) 2006-09-27
TW583315B (en) 2004-04-11
KR20040060996A (ko) 2004-07-06
WO2003046240A1 (fr) 2003-06-05
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EP1449932B1 (de) 2007-09-12
DE60222460D1 (de) 2007-10-25

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