EP1964939B1 - Acier de decolletage a faible teneur en carbone resulfure ayant une excellente aptitude a l'usinage - Google Patents

Acier de decolletage a faible teneur en carbone resulfure ayant une excellente aptitude a l'usinage Download PDF

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EP1964939B1
EP1964939B1 EP06811670.6A EP06811670A EP1964939B1 EP 1964939 B1 EP1964939 B1 EP 1964939B1 EP 06811670 A EP06811670 A EP 06811670A EP 1964939 B1 EP1964939 B1 EP 1964939B1
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content
percent
carbon
nitrogen
mass
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EP1964939A4 (fr
EP1964939A1 (fr
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Koichi Sakamoto
Atsuhiko Yoshida
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Kobe Steel Ltd
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Kobe Steel Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • B22D11/114—Treating the molten metal by using agitating or vibrating means
    • B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
    • 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
    • C22C38/02—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
    • 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
    • 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
    • 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

Definitions

  • the present invention relates to low-carbon resulfurized free-machining steels which are free of harmful lead (Pb) and exhibit good finished surface roughness.
  • Low-carbon resulfurized free-machining steels are widely used as steels for hydraulic parts of gear box units of automobiles, as well as for small parts, such as screws and printer shafts, which do not require strength so high.
  • lead-sulfur free-machining steels comprising the low-carbon resulfurized free-machining steels combined with lead (Pb) are used.
  • Lead (Pb) contained in free-machining steels is an element vary effective for improving machinability, but is harmful to the human body.
  • lead-containing free-machining steels have some problems typically in fume of lead upon ingot making and chip disposability. Accordingly, free-machining steels exhibiting good machinability without adding lead (Pb) (lead-free) are demanded.
  • Patent Document 1 discloses a technique for improving the machinability (finished surface roughness and chip disposability) by controlling the size of sulfide inclusions.
  • Patent Document 2 teaches that the oxygen content in steel must be appropriately controlled in order to control the size of sulfide inclusions.
  • Patent Document 3 proposes a technique for improving the machinability by specifying the ratio of manganese (Mn) to sulfur (S) and by controlling the free oxygen content immediately before casting.
  • lead-free steels should have good productivity in addition to satisfactory machinability. From this viewpoint, they must be produced by a continuous casting process, be free typically from surface defects and be capable of easily being rolled.
  • the continuous casting process isbelieved to be disadvantageous for improving the machinability of steels. It is, therefore, also important to produce free-machining steels excellent in machinability with good productivity by a continuous casting process.
  • Patent Document 8 discloses a technique for providing a free-machining steel excellent in machinability (finished surface roughness) by the continuous casting process. This technique indicates that a free-machining steel excellent in machinability can be obtained in good yield according to a continuous casting process, by incorporating a relatively large amount of oxygen of 100 to 300 ppm to a steel and incorporating nitrogen (N) thereto in a larger amount than those of conventional equivalents. By satisfying this, built-up edges can be suppressed, which built-up edges occur in a tool surface upon machining.
  • an object of the present invention as defined in the present claim 1 is to provide a low-carbon resulfurized free-machining steel which exhibits good machinability typified by finished surface roughness, even being free from lead, and can be produced with good productivity by a continuous casting process while suppressing blow holes.
  • the present invention has been accomplished to achieve the above obj ect and provides a low-carbon resulfurized free-machining steel excellent in machinability, containing:
  • the low-carbon resulfurized free-machining steels according to the present invention preferably have a chemical composition in which (1) the content of soluble nitrogen is 0.002% to 0.02% and (2) the total content of at least one selected from the group consisting of Ti, Cr, Nb, V, and Zr is 0.02% or less (exclusive of 0%).
  • the low-carbon resulfurized free-machining steels according to the present invention have further improved properties.
  • the steels are preferably produced by subjecting to electromagnetic stirring in which a magnetic field of 100 to 500 gausses is applied during casting. The resulting steels have better surface quality.
  • the present invention controls the contents of carbon, manganese, and nitrogen in steel so as to satisfy a specific relational expression. By satisfying this, low-carbon resulfurized free-machining steels good in finished surface roughness can be produced with good productivity while suppressing blow holes even according to a continuous casting process.
  • FIG. 1 is a graph showing how the finished surface roughness (maximum height of irregularities Rz) varies depending on the left-hand value of Expression (1) and on the presence or absence of a magnetic field.
  • the finished surface roughness of a free-machining steel varies significantly depending on generation, size, shape and uniformity of built-up edges.
  • Generation of built-up edges is a phenomenon that part of a work attaches to a surface of a tool and actually behaves as part (cutting edge) of the tool. It may adversely affect the finished surface roughness of a work material.
  • the built-up edges generate only under specific conditions, but free-machining steels are generally cut in the art under such conditions as to induce the built-up edges.
  • the built-up edges are believed to provide fatal defects due to variation in their size.
  • the built-up edges play a role to protect the edge of a tool to thereby prolong the lifetime of the tool. All factors considered, therefore, it is not advantageous to remove such a built-up edge fully, and the built-up edges must be stably formed with uniformized sizes and shapes.
  • MnS inclusions are known to be useful as sites for forming fine cracks. Not all MnS inclusions but large-sized (wide) spherical MnS inclusions act as fine-crack-forming sites. Such MnS inclusions elongate in the primary and secondary shear zones, but if they become too thin as thin as matrix, they do not work as fine-crack-forming sites. Accordingly, a work (steel to be cut) must comprise large-sized spherical MnS inclusions before cutting.
  • Oxygen (total oxygen) in steel affects the size and sphericity of MnS inclusions (for example, Patent Document 2), and it is believed that the size (diameter) of sulfides increases with an increasing oxygen content of steel. Consequently, the oxygen content of steel must be increased to some extent in order to make MnS inclusions larger and more spherical.
  • the manganese content and sulfur content must be higher than those in conventional free-machining steels, such as Japanese Industrial Standards (JIS) SUM 23 steel and SUM 24L steel, so as to increase MnS inclusions working as fine-crack-forming sites.
  • soluble nitrogen in steel also significantly affects the formation of fine cracks and that free-machining steels good in machinability can be realized by appropriately adjusting the content of soluble nitrogen.
  • the temperatures in the primary and secondary shear zones significantly vary from a position to another.
  • the deformation resistance varies depending on temperatures at individual positions when the soluble nitrogen is present in a certain amount.
  • the difference (variation) in deformation resistance causes fine-crack-forming sites. Accordingly, a certain level or more of the soluble nitrogen can be effectively ensured by controlling the total amount of Ti, Cr, Nb, V, Zr, to a specific level or less. This is because these components work to fix the soluble nitrogen, namely, they work to form nitrides.
  • the present inventors have found that built-up edges can be stably formed with uniformized sizes and shapes, for example, by the two phenomena, namely, (1) makingMnS inclusions become larger and spherical, and (2) increasing soluble nitrogen.
  • the resulting steels have dramatically improved finished surface roughness in forming process and thereby exhibit properties as good as lead-free-machining steels.
  • the free-machining steels according to the present invention must have appropriately specified chemical compositions.
  • the reasons for specifying the contents of basic components C, Si, Mn, P, S, Al, O, and N are as follows.
  • Carbon (C) is an essential element to ensure the strength of steel, and, if added to a specific amount or more, acts to improve the finished surface roughness.
  • the carbon content must be 0.02% or more to exhibit these activities .
  • An excessively high content thereof may shorten the lifetime of a tool upon cutting to thereby deteriorate the machinability, and may induce defects due to carbon monoxide (CO) gas upon casting.
  • the carbon content is preferably 0.15% or less.
  • Preferred lower and upper limits of the carbon content are 0.05% and 0.12%, respectively.
  • Silicon (Si) is an element effective for ensuring the strength of steel as a result of solid-solution strengthening, but it basically acts as a deoxidizing agent to form silicon dioxide (SiO 2 ).
  • the silicon dioxide SiO 2 serves to form MnO-SiO 2 -MnS inclusions. If the silicon content exceeds 0.003%, the SiO 2 content in the inclusions becomes too high to ensure a necessary oxygen content in MnS inclusions. Thus, the finished surface roughness deteriorates. From these viewpoints, the silicon content must be 0.003% or less.
  • Manganese (Mn) acts to improve hardenability, to enhance the formation of the bainite, and to improve the machinability. It is an element effective for ensuring the strength of steel. Further, it combines with sulfur to form MnS and combines with oxygen to form MnO to thereby form MnO-MnS composite inclusions. Thus, it acts to improve the machinability. To exhibit these actions, the manganese content must be 0.6% or more, but if it exceeds 3%, the strength increases excessively to deteriorate the machinability. Preferred lower and upper limits of the manganese content are 1% and 2%, respectively.
  • Phosphorus acts to improve the finished surface roughness . It also acts to significantly improve the chip disposability by facilitating crack propagation in chip. To exhibit these advantages, the phosphorus content must be 0.02% or more. An excessively high phosphorus content, however, deteriorates the hot workability, and the phosphorus content must be 0.2% or less. Preferred lower and upper limits of the phosphorus content are 0.05% and 0.15%, respectively.
  • S is an element which combines with manganese in steel to form manganese sulfide (MnS), thereby acts as a stress concentrator upon cutting. Thus, chips are partitioned to thereby improve the machinability. To exhibit these actions, the sulfur content must be 0.35% or more. If the sulfur content is excessively high exceeding 1%, the hot workability may deteriorate. Accordingly, a preferred upper limit of the sulfur content is 0.8%.
  • Total aluminum 0.003% or less (exclusive of 0%)
  • Aluminum (Al) is an element useful for ensuring the strength of steel as a result of solid-solution strengthening and for deoxidization. It also acts as a strong deoxidizing agent to form an oxide (Al 2 O 3 ).
  • the oxide Al 2 O 3 constitutes MnO-Al 2 O 3 -MnS inclusions. If the aluminum content exceeds 0.003% the Al 2 O 3 content of the inclusions becomes too high to ensure a necessary oxygen content in MnS inclusions to thereby adversely affect the finished surface roughness.
  • the aluminum content is 0.003% or less and more preferably 0.001% or less.
  • Oxygen (O) combines with manganese (Mn) to form manganese oxide (MnO) .
  • the MnO contains a large amount of sulfur to thereby constitute MnO-MnS composite inclusions.
  • the MnO-MnS composite inclusions are resistant to elongation upon rolling, are present as relatively spherical inclusions and thereby act as stress concentrator zones upon cutting. Accordingly, oxygen is positively added to the steel. If the oxygen content is less than 0.008%, these actions are insufficient, but if it exceeds 0.03%, internal defects caused by carbon monoxide gas may occur in steel ingots. Accordingly, the oxygen content (total oxygen content) must be within the range of 0.008% to 0.03%.
  • MnO manganese oxide
  • MnO-MnS composite inclusions act as nuclei so as to precipitate MnS inclusions during solidification.
  • the resulting billet (ingot prepared as a result of continuous casting) contains MnO-MnS composite inclusions mainly comprising MnS. The billet then undergoes heating, blooming, and wire rod rolling or bar mill rolling.
  • the MnO-MnS composite inclusions mainly comprising MnS are more resistant to elongation in the blooming, wire rod rolling or bar mill rolling, and they constitute large-sized spherical MnS inclusions in final products such as wire steels and bar steels.
  • the lower limit of oxygen (total oxygen) is set in view of these mechanisms in which the oxygen content is preferably high.
  • the upper limit of oxygen content is also set in actuality. The reasons of this will be explained below.
  • Oxygen (total oxygen) comprises oxygen in the form of oxides, and soluble oxygen (free oxygen) dissolved in molten steel.
  • the oxygen in the form of oxides namely, oxygen inMnO is very useful.
  • the N 2 gas also causes blow holes.
  • blow holes mainly comprise CO (gas) and N 2 (gas).
  • a feature (concept) of the present invention is that the free oxygen (O) and nitrogen (N) contents are set highest within such ranges that the CO (gas) and N 2 (gas) do not form blow holes.
  • the formation of blow holes in steel can also be improved by carrying out electromagnetic stirring, in addition to setting the chemical composition of steel. This is because blow holes, if formed, can be eliminated from the steel by electromagnetic stirring carried out in a mold in continuous casting.
  • the present inventors made investigations to determine which affects the free oxygen (O) content and have found that the manganese content [Mn] and the sulfur content [S] mainly affect the free oxygen (O) content. Accordingly, the amount of CO (gas) can be controlled by [C], [Mn], and [S], and the amount of CO (gas)+N 2 (gas) can be determined according to Expression (1), wherein the nitrogen content [N] is added to these parameters. Thus, blow holes can be controlled. The detail of this will be described later.
  • the free oxygen (O) content in molten steel is preferably controlled to about 0.0050% or less from the viewpoint of preventing internal defects caused by CO gas, while it varies depending on the carbon and nitrogen contents [C] and [N] or electromagnetic stirring conditions.
  • Preferred lower and upper limits of the oxygen content (total oxygen content) of steel are 0.01% and 0.03%, respectively.
  • Nitrogen (N) is an element affecting the amount of built-up edges, and the content thereof affects the finished surface roughness. If the nitrogen content is less than 0.007%, excessively large amounts of built-up edges occur to thereby adversely affect the finished surface roughness. Nitrogen is liable to segregate in dislocations in the matrix. It segregates in dislocations during cutting to thereby make the matrix brittle and facilitate crack propagation. Thus, nitrogen serves to improve chip breakability (chip disposability). However, an excessively high nitrogen content exceeding 0.03% causes bubbles (blow holes) upon casting, which may often become internal and surface defects of the resulting ingot. The nitrogen content must therefore be controlled to 0.03% or less. Preferred lower and upper limits of the nitrogen content are 0.005% and 0.025%, respectively.
  • the ratio [Mn]/[S] is an important factor affecting, for example, cracking during hot working. If the manganese content is insufficient relative to the sulfur content, namely, [Mn]/[S] is less than 3, FeS often forms, and this causes hot crack. When the ratio [Mn]/[S] is within the range of 3 to 4, the manganese content is sufficient relative to the sulfur content, which prevents the formation of FeS to thereby prevent hot crack. If the ratio [Mn]/[S] exceeds 4, this effect is saturated and the free oxygen (O) content decreases to thereby adversely affect the finished surface roughness. The free oxygen content varies depending on [Mn] and [S].
  • blow holes may form.
  • the left-hand value is preferably 1.1 or less and more preferably 0.9 or less.
  • the local pressure mainly comprises the total of the atmospheric pressure, molten steel static pressure, and (interfacial energy between liquid and gas) / (diameter of bubble) .
  • the bubbles often form in the vicinity of menisci in which the molten steel static pressure is low.
  • the gas (bubbles) comprises CO (gas) and N 2 (gas). If the gas (bubbles) floats due to difference in density and escapes from the molten steel to the atmosphere, it does not remain as blow holes in the billet. However, if it is engulfed, for example, by solidified crystals, it remains as blow holes and as defects in the billet.
  • Expression (2) will be examined provided that a reaction proceeds from the right to the left.
  • the equilibrium constant K CO in Expression (2) is given by the activity coefficient of carbon (f C ), the carbon content [C], the activity factor of oxygen (f O ), the oxygen content [O], and the CO partial pressure (P CO ).
  • the equilibrium constant is determined according to Expression (4), in which T represents the absolute temperature.
  • the carbon content [C] and the oxygen content [O] refer to contents after microsegregation and are determined according to the Sheil Equation as in Expressions (5) and (6).
  • C C 0 and C O 0 represent the initial carbon content [C] and oxygen content [O] of molten steel before casting, respectively; and C C L and C O L represent the carbon content [C] and oxygen content [O] of the liquid phase during solidification where a solid phase and a liquid phase are coexistent.
  • the C C L and C O L represent the contents after enrichment due to microsegregation.
  • the CO partial pressure (P CO ) can be represented by Expression (7).
  • "f" represents the fraction of solid phase; and k C and k O represent the equilibrium distribution coefficients of carbon and oxygen, respectively.
  • the equilibrium constant K N2 in Expression (8) can be represented by Expression (9), and the equilibrium constant can be represented by Expression (10).
  • the nitrogen content [N] of the molten steel after microsegregation can be represented by Expression (11), and by substituting this into Expression (9), the N 2 partial pressure (P N2 ) can be represented by Expression (12) .
  • Blow holes are formed when the total sum (P CO + P N2 ) of the partial pressures represented by Expressions (7) and (12) thus estimated exceeds the total of the external pressure (atmospheric pressure), molten steel static pressure, and (interfacial energy between liquid and gas) / (diameter of bubble), as represented by following Expression (13): P g ⁇ P a + ⁇ Lgh + 2 ⁇ / r
  • the present inventors examined how the occurrence frequency of blow holes varies depending on the total of partial pressures (P CO + P N2 ) calculated according to the above-mentioned method of calculation having these physical meanings. As a result, they have found that blow holes occur when the total of partial pressures (P CO + P N2 ) exceeds 1.2 atm.
  • the present inventors made an attempt to convert the total of partial pressures (P CO + P N2 ) into an index.
  • the carbon and nitrogen contents [C] and [N] can be easily determined by on-line analyses, but the free oxygen content must be determined using a free-oxygen analyzer. It may be accompanied by a large error in some determination procedures.
  • the present inventors examined what affects the free oxygen content [O] and have found that the manganese content [Mn] and the sulfur content [S] affect the free oxygen content [O]. This is also apparent from the fact that oxygen forms MnO-MnS oxide-sulfide inclusions in molten steel. This shows that the formation of blow holes can be indicated by a relational expression among [C], [Mn], [S], and [N].
  • the manganese and sulfur contents [Mn] and [S] have a relation in which the ratio [Mn]/[S] is 3 to 4.
  • the formation of blow holes can be schematically expressed by the relational expression among [C], [Mn], and [N].
  • FIG. 1 shows that the threshold of the total of partial pressures is about 1.2 in view of the formation of surface defects and the finished surface roughness.
  • the low-carbon resulfurized free-machining steels according to the present invention comprise the above-mentioned components with the remainder basically being iron. However, they can further comprise trace components in addition to these components, and those further comprising such trace components are also included within the scope of the present invention.
  • the low-carbon resulfurized free-machining steels according to the present invention comprise inevitable impurities such as Cu, Sn, and Ni, and these inevitable impurities are accepted within ranges not adversely affecting the advantages of the present invention.
  • the low-carbon resulfurized free-machining steels according to the present invention preferably have (1) a content of soluble nitrogen of 0.002% to 0.02% and/or (2) a total content of at least one selected from the group consisting of Ti, Cr, Nb, V, Zr, and B of 0.02% or less (exclusive of 0 percent), according to necessity.
  • a content of soluble nitrogen 0.002% to 0.02% and/or (2) a total content of at least one selected from the group consisting of Ti, Cr, Nb, V, Zr, and B of 0.02% or less (exclusive of 0 percent), according to necessity.
  • soluble nitrogen in steel affects the formation of fine cracks, and free-machining steels with good machinability can be realized by appropriately controlling the content of the soluble nitrogen.
  • the content of soluble nitrogen in steel is preferably controlled to 0.002% or more. If it exceeds 0.02%, however, surface defects may increase.
  • these elements combine with nitrogen to form nitrides, and if the contents thereof are excessively high, the content of soluble nitrogen becomes too small below the necessary content of soluble nitrogen. From this viewpoint, the total content of these elements is preferably controlled to 0.02% or less.
  • the low-carbon resulfurized free-machining steels according to the present invention are basically produced by a continuous casting process. They can be specifically produced, for example, according to the following procedure. Initially, carbon is blown down to a carbon content of 0.04% or less in a converter so as to make molten steel have a high free oxygen content (soluble oxygen content). The free oxygen content herein is preferably 500 ppm or more. Next, alloys such as Fe-Mn alloy and Fe-S alloy are added upon tapping. These alloys contain silicon and aluminum as impurities . By adding these alloys to high-oxygen molten steel upon tapping from the converter, silicon and aluminum are oxidized to form SiO 2 and Al 2 O 3 .
  • electromagnetic stirring is preferably carried out, in which a predetermined magnetic field is applied to the steels upon casting.
  • the electromagnetic stirring is carried out from the viewpoint of reducing blow holes to thereby prevent defects and to provide good surface quality.
  • the production of steels in combination with the electromagnetic stirring is very useful for making MnS inclusions large-sized and spherical and for preventing the formation of blow holes.
  • the magnetic field to be applied in the electromagnetic stirring preferably has an intensity of about 100 to about 500 gausses. If the intensity of the magnetic field is less than 100 gausses, the effect of electromagnetic stirring may not be exhibited. In contrast, if it exceeds 500 gausses, the molten steel in a continuous casting mold may flow at an excessively high rate, and the steel may involve a mold powder and make casting difficult.
  • a series of molten steels having varying contents of, for example, Si, Mn, S, Al, and N were made using a 3-ton induction furnace, a 100-ton converter, and molten steel refining facilities including a pouring ladle.
  • the silicon and aluminum contents were adjusted by varying the silicon and aluminum contents in Fe-Mn alloys and Fe-S alloys to be added, respectively.
  • the free oxygen contents in the resulting molten steels were determined immediately before casting into a predetermined mold using a free oxygen probe (the product of Heraeus Electro-Nite under the trade name of "HYOP 10A-C150”), and they were defined as the free oxygen contents.
  • the molten steels were subjected to continuous casting using a (bloom-type) mold having a sectional size of 300 mm wide and 430 mm long.
  • a (bloom-type) mold having a sectional size of 300 mm wide and 430 mm long.
  • they were cast in the 3-ton induction furnace using a cast-iron mold having a sectional size of 300 mm wide and 430 mm long which had been designed to achieve a cooling rate as in bloomed billets.
  • a magnetic field was applied to the mold during casting so as to carry out electromagnetic stirring.
  • the resulting billets and ingots were heated at 1250°C for one hour, subjected to blooming to a sectional size of 155 mm wide and 155 mm long, rolled to a diameter of 25 mm, subjected to acid pickling to yield cold finished steel bars having a diameter of 22 mm, and subjected to cutting tests.
  • the rolling herein was conducted at 1000°C and the rolled steels were cooled forcedly at an average cooling rate from 800°C to 500°C of about 1.5°C per second.
  • the temperatures of steels were determined using a radiation pyrometer.
  • the steels were measured on content of soluble nitrogen and subjected to cutting tests under the following conditions.
  • the finished surface and surface defects of the steels after cutting tests were evaluated according to the following criteria.
  • the content of soluble nitrogen was determined as the difference between the total nitrogen and the nitrogen in compound.
  • the total nitrogen was determined according to a method using a conductivity of an inert gas heat of fusion, and the nitrogen in compound was determined by dissolving and extracting a sample with a methanol solution containing 10% of acetylacetone and 1% of tetramethylammonium chloride, collecting nitrogen through a 1- ⁇ m filter and determining nitrogen using an indophenol-absorptiometer.
  • samples not satisfying at least one of the requirements specified in the present invention are poor in at least one of the properties.
  • FIG. 1 shows how the finished surface roughness (maximumheight of irregularities Rz) varies depending on the left-hand value of Expression (1) and on the presence or absence of a magnetic field.

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Claims (3)

  1. Acier de décolletage resulfuré à faible teneur en carbone présentant une excellente aptitude à l'usinage, comprenant:
    0,02 à 0,15 pourcent en masse de carbone (C);
    0,003 pourcent en masse ou moins (sauf 0 pourcent) de silicium (Si);
    0,6 à 3 pourcent en masse de manganèse (Mn);
    0,02 à 0,2 pourcent en masse de phosphore (P);
    0,35 à 1 pourcent en masse de soufre (S);
    0,003 pourcent en masse ou moins (sauf 0 pourcent en masse) d'aluminium (Al);
    0,008 à 0,03 pourcent en masse d'oxygène (O); et
    0,007 à 0,03 pourcent en masse d'azote (N), et facultativement une teneur totale en au moins un élément sélectionné parmi le groupe consistant en du Ti, Cr, Nb, V et Zr de 0,02 pourcent en masse ou moins; le reste étant constitué de fer et d'inévitables impuretés, dans lequel le rapport [Mn] / [S] de la teneur en manganèse [Mn] sur la teneur en soufre [S] se situe dans l'intervalle de 3 à 4, et
    dans lequel la teneur en carbone [C], la teneur en manganèse [Mn] et la teneur en azote [N] satisfont à l'expression (1) suivante: 10 C × Mn − 0,94 + 1226 N 2 ≤ 1,2
    Figure imgb0016
     dans laquelle [C], [Mn] et [N] représentent respectivement les teneurs sur base de pourcent en masse du carbone, du manganèse et de l'azote.
  2. Acier de décolletage resulfuré à faible teneur en carbone selon la revendication 1, dans lequel la teneur en azote soluble va de 0,002 à 0,02 pourcent en masse.
  3. Acier de décolletage resulfuré à faible teneur en carbone selon la revendication 1 ou 2, comme produit ayant subi une agitation électromagnétique dans laquelle un champ magnétique de 100 à 500 gauss est appliqué pendant le coulage.
EP06811670.6A 2005-12-16 2006-10-12 Acier de decolletage a faible teneur en carbone resulfure ayant une excellente aptitude a l'usinage Not-in-force EP1964939B1 (fr)

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JP2005363816A JP4203068B2 (ja) 2005-12-16 2005-12-16 被削性に優れた低炭素硫黄快削鋼
PCT/JP2006/320373 WO2007069386A1 (fr) 2005-12-16 2006-10-12 Acier de decolletage soufre a faible teneur en carbone ayant une excellente aptitude a la decoupe

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EP1964939A1 EP1964939A1 (fr) 2008-09-03
EP1964939A4 EP1964939A4 (fr) 2009-11-18
EP1964939B1 true EP1964939B1 (fr) 2018-05-16

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CN (1) CN101331242A (fr)
TW (1) TWI326714B (fr)
WO (1) WO2007069386A1 (fr)

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JP2009106967A (ja) * 2007-10-30 2009-05-21 Sumitomo Metal Ind Ltd 鋼の連続鋳造方法
KR101253806B1 (ko) * 2009-07-01 2013-04-12 주식회사 포스코 피삭성이 우수한 고유황 쾌삭강 및 그 제조방법
HUP1300336A2 (en) * 2013-05-27 2014-11-28 Astra Mining Hungary Kft Method for production of steel microalloyed with super clean sulfur and controlled sulfur addition affecting metalurgical characteristics
CN104451458B (zh) * 2014-12-01 2016-09-28 杭州钢铁集团公司 一种易切削钢及其生产方法和在制造钥匙中的应用
CN115386800B (zh) * 2022-08-30 2023-10-20 鞍钢股份有限公司 一种低碳高锰硫环保型易切削钢及其制造方法

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JP2922105B2 (ja) * 1993-12-21 1999-07-19 新日本製鐵株式会社 被削性の優れた低炭硫黄系快削鋼
JPH10158781A (ja) * 1996-12-02 1998-06-16 Kobe Steel Ltd 超硬工具寿命に優れた快削鋼
JP3687370B2 (ja) * 1998-11-25 2005-08-24 住友金属工業株式会社 快削鋼
KR100708430B1 (ko) * 2002-11-15 2007-04-18 신닛뽄세이테쯔 카부시키카이샤 피삭성이 우수한 강과 그 제조 방법
JP4034700B2 (ja) * 2003-06-30 2008-01-16 株式会社神戸製鋼所 被削性に優れた高ｓ快削鋼の製造方法及び高ｓ快削鋼
JP4441360B2 (ja) * 2003-12-01 2010-03-31 株式会社神戸製鋼所 仕上面粗さに優れた低炭素複合快削鋼材

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US20090169414A1 (en) 2009-07-02
TWI326714B (en) 2010-07-01
US20120121454A1 (en) 2012-05-17
KR101033073B1 (ko) 2011-05-06
JP2007162119A (ja) 2007-06-28
CN101331242A (zh) 2008-12-24
WO2007069386A1 (fr) 2007-06-21
JP4203068B2 (ja) 2008-12-24
EP1964939A4 (fr) 2009-11-18
EP1964939A1 (fr) 2008-09-03
TW200738892A (en) 2007-10-16
KR20080068750A (ko) 2008-07-23

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