WO2016158563A1 - 曲げ加工性に優れた熱処理鋼線 - Google Patents
曲げ加工性に優れた熱処理鋼線 Download PDFInfo
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- WO2016158563A1 WO2016158563A1 PCT/JP2016/058960 JP2016058960W WO2016158563A1 WO 2016158563 A1 WO2016158563 A1 WO 2016158563A1 JP 2016058960 W JP2016058960 W JP 2016058960W WO 2016158563 A1 WO2016158563 A1 WO 2016158563A1
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/02—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for springs
-
- 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
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
-
- 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
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
-
- 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
-
- 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
- C22C38/04—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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
-
- 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
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
-
- 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
-
- 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
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Definitions
- the present invention relates to a heat-treated steel wire, and more particularly to a heat-treated steel wire excellent in bending workability.
- the heat-treated steel wire which is a spring material
- the spring is generally obtained by coiling a heat-treated steel wire obtained by quenching and tempering a wire drawing material. Therefore, the heat-treated steel wire is required to have a bending workability that does not break during coiling.
- the ductility of the heat-treated steel wire decreases as the strength increases, it is difficult to provide a heat-treated steel wire that easily breaks during coiling, has high strength, and has excellent bending workability.
- Patent Document 1 has a predetermined chemical component composition, in particular, the amount of N is controlled to 0.007% or less, the balance is composed of iron and unavoidable impurities, and the extracted residue analysis value after heat treatment is [0 A high-strength heat-treated steel for springs is disclosed in which the V amount (mass%) in the filtrate filtered through a 2 ⁇ m filter ⁇ [the V content in steel (mass%)] ⁇ 0.4.
- TS having a predetermined component composition, a solid solution C amount of 0.15% or less, and a Cr amount contained as a Cr-containing precipitate is 0.10% or less, and is represented by a predetermined formula.
- a high strength spring steel having an excellent brittle fracture resistance and a value of 24.8% or more and a prior austenite grain size of 10 ⁇ m or less is disclosed.
- Patent Document 1 unheated carbide is reduced as much as possible by setting the heating temperature before rolling to 1250 ° C. However, if the heating temperature before rolling is too high, decarburization of the rolled material is likely to occur, so that it is difficult to remove in a subsequent process, and as a result, bending workability may be reduced. Further, in Patent Document 2, there is no temperature condition setting at the time of split rolling and wire rolling, and a coarse Cr-containing precipitate is generated, so that sufficient bending workability may not be obtained.
- the present invention has been made paying attention to the above-described circumstances, and an object of the present invention is to provide a heat-treated steel wire having high strength and excellent bending workability.
- the heat-treated steel wire according to the present invention that has solved the above problems is: C: 0.5 to 0.8%, Si: 1.5 to 2.5%, Mn: 0.5 to 1.5%, P : More than 0%, 0.02% or less, S: more than 0%, 0.02% or less, Cr: 0.3 to less than 0.7%, V: 0.05 to 0.5%, Al: 0% More than 0.01%, N: more than 0%, 0.007% or less, O: more than 0%, 0.004% or less, the balance is made of iron and inevitable impurities, 1.0 ⁇ m filter and 0
- the electrolytic extraction residue analysis was performed using a 4 ⁇ m filter, the [amount of Cr-based carbide substance / electrolytic mass in the 1.0 ⁇ m filter residue] was 1.0% or more and 2.80% or less;
- the [amount of Cr-based carbide substance / electrolytic mass in the 0.4 ⁇ m filter residue] was 0.10% or more.
- the present invention also includes a spring obtained using the above heat-treated steel wire.
- a heat-treated steel wire having a tensile strength of 2100 MPa or more and excellent bending workability can be provided by defining the component composition of the heat-treated steel wire and the amount of Cr-based carbide based on the electrolytic extraction method. Moreover, if the heat-treated steel wire of the present invention is used, a spring having an excellent bending process can be provided.
- the present inventors have studied from various angles in order to suppress breakage during coiling of a high-strength heat-treated steel wire, in particular to improve the toughness of the heat-treated steel wire and improve the bending workability. It was found that the frequency of coiling breakage occurring during coiling of the heat-treated steel wire tends to increase as the strength of the heat-treated steel wire increases. As a result of examining the cause in detail, it was found that the frequency of coiling breakage was related not only to the strength of the heat-treated steel wire but also to the precipitation amount of Cr-based carbide. And it discovered that coiling breakage could be suppressed even if it was high intensity
- the amount of Cr-based carbides in the surface layer of the heat-treated steel wire was examined by measuring the amount of electrolytic extraction residue of the heat-treated steel wire that was broken during coiling and the heat-treated steel wire that was not broken.
- electrolytic extraction residue it is possible to analyze the properties of carbide on the surface layer of the heat-treated steel wire, which is the starting point of coiling breakage, and it is possible to perform appropriate evaluation for a larger inspection volume compared to the observation of the structure with an electron microscope It becomes.
- the amount of Cr-based carbide obtained from the heat-treated steel wire with breakage was smaller than that of the heat-treated steel wire without breakage. Therefore, as a result of repeated research on the relationship between the amount of Cr-based carbides and breakage of heat-treated steel wire, if the ratio of electrolytic mass and residual mass is within the following predetermined range, toughness is improved and excellent bending workability is obtained. I understood it.
- Cr-based carbides include not only Cr carbides but also Cr carbonitrides, composite carbides with carbide-generating elements such as V, and composite carbonitrides.
- the present inventors have found that a heat-treated steel wire having high strength and excellent bending workability can be provided by appropriately controlling the Cr-based carbide and the component composition.
- the reason why the Cr-based carbide and the component composition are specified will be described in detail.
- the residue amount / electrolytic mass of the 1.0 ⁇ m filter is 1.0% or more, preferably 1.20% or more, more preferably 1.40% or more.
- the residue amount / electrolytic mass of the 0.4 ⁇ m filter is preferably 0.01% or more, more preferably 0.02% or more.
- C is an element effective for improving the strength of the heat-treated steel wire.
- the C content is 0.5% or more, preferably 0.55% or more, more preferably 0.6% or more.
- the strength is improved with an increase in the C content, but if the added amount is excessive, a large amount of coarse cementite is precipitated, which adversely affects the bending workability of the heat-treated steel wire. Therefore, the C content is 0.8% or less, preferably 0.75% or less, and more preferably 0.7% or less.
- Si is an element effective for deoxidizing steel and improving the strength of heat-treated steel wire.
- the Si content is 1.5% or more, preferably 1.55% or more, more preferably 1.6% or more.
- the Si content is 2.5% or less, preferably 2.4% or less, and more preferably 2.3% or less.
- Mn 0.5 to 1.5%
- Mn increases hardenability and contributes to improved spring strength.
- the Mn content is 0.5% or more, preferably 0.6% or more, more preferably 0.7% or more.
- the Mn content is 1.5% or less, preferably 1.4% or less, more preferably 1.3% or less.
- P over 0%, 0.02% or less
- P segregates at the prior austenite grain boundaries and embrittles the structure, so that the fatigue characteristics are reduced. Therefore, the P content is 0.02% or less, preferably 0.018% or less. The smaller the P content, the better. However, it is difficult to make it zero, and about 0.003% may be contained as an inevitable impurity.
- S more than 0%, 0.02% or less
- S segregates at the prior austenite grain boundaries and embrittles the structure, so that fatigue characteristics are reduced. Therefore, the S content is 0.02% or less, preferably 0.015% or less. The smaller the S content, the better. However, it is difficult to make it zero, and about 0.003% may be contained as an inevitable impurity.
- Cr 0.3 to less than 0.7%
- Cr has the effect of reducing the activity of C and preventing decarburization during rolling and heat treatment.
- the Cr content is 0.3% or more, preferably 0.35% or more, and more preferably 0.4% or more.
- the Cr content is less than 0.7%, preferably 0.68% or less, more preferably 0.65% or less.
- V 0.05 to 0.5%
- V has the effect
- secondary precipitation hardening occurs during high-temperature treatment such as nitriding treatment, which contributes to improvement of spring strength.
- the V content is 0.05% or more, preferably 0.10% or more, more preferably 0.15% or more.
- the V content is 0.5% or less, preferably 0.45% or less, more preferably 0.40% or less.
- Al more than 0%, 0.01% or less
- Al forms inclusions of Al 2 O 3 and AlN in the steel. These inclusions significantly reduce the fatigue life of the spring. Therefore, the Al content is 0.01% or less, preferably 0.005% or less.
- N more than 0%, 0.007% or less
- N combines with Al to form AlN inclusions.
- AlN inclusions significantly reduce the fatigue life of the spring. Therefore, the N content is 0.007% or less, preferably 0.006% or less, more preferably 0.005% or less.
- O more than 0%, 0.004% or less
- the O content is 0.004% or less, preferably 0.003% or less.
- the basic components of the heat-treated steel wire of the present invention are as described above, and the balance is substantially iron.
- inevitable impurities such as Ca and Na, which are inevitably mixed in depending on the situation of materials such as iron raw materials (including scrap), auxiliary materials, and manufacturing equipment, are contained in the steel.
- the steel material of the present invention may further contain at least Ni or B as necessary, and the characteristics of the heat-treated steel wire can be further improved according to the kind and content of the element to be contained.
- the reason for setting a preferable range when these elements are contained is as follows.
- Ni more than 0%, 0.3% or less
- the Ni content is preferably 0.05% or more, more preferably 0.07% or more, and further preferably 0.1% or more.
- the Ni content is preferably 0.3% or less, more preferably 0.27% or less, and still more preferably 0.2% or less.
- B more than 0%, 0.01% or less
- B has an effect of improving hardenability and cleaning austenite grain boundaries, and improves toughness.
- the B content is preferably 0.001% or more, more preferably 0.0015% or more, and further preferably 0.002% or more.
- the B content is preferably 0.01% or less, more preferably 0.008% or less, and still more preferably 0.006% or less.
- the manufacturing method of the heat-treated steel wire of the present invention is not particularly limited, and known manufacturing conditions can be adopted.
- a steel piece obtained by melting and rolling a steel having the above chemical composition is processed into a wire having a diameter of about 5.0 to 8.0 mm by hot rolling, wound into a coil shape, and cooled.
- the steel wire rod (hereinafter, sometimes referred to as “rolled wire rod”) is subjected to a skin removing process to remove surface flaws and decarburized parts without heat treatment or the like.
- the wire is drawn to a desired wire diameter, for example, about 3 to 4 mm in the case of a valve spring.
- the drawn wire thus obtained is then subjected to quenching and tempering treatment called oil temper to obtain a heat-treated steel wire.
- Various springs such as valve springs and clutch springs can be obtained by processing the heat-treated steel wire thus obtained into a spring shape.
- the cooling start temperature after winding at the time of wire rod rolling In order to control the precipitation size and number of Cr-based carbides in the heat-treated steel wire, in addition to the heating temperature at the time of ingot rolling, the cooling start temperature after winding at the time of wire rod rolling, the rolling temperature control such as the cooling rate, etc. It is necessary to control the heat treatment conditions of the patenting treatment in the secondary processing and the quenching / tempering treatment after the wire drawing treatment.
- the ingot is subjected to split rolling to produce a billet of a predetermined size.
- the upper limit of the heating temperature is not particularly limited because the Cr-based carbide can be dissolved as the billet is heated to a higher temperature.
- the upper limit of the heating temperature is 1250 ° C. or less, preferably in consideration of the heat resistance temperature and heating cost of the heating furnace. It is 1240 degrees C or less, More preferably, it is 1230 degrees C or less.
- the temperature at which the rolled wire rod is placed on the cooling conveyor that is, the rolling coiling temperature is 750 ° C. or higher, preferably 780 ° C. or higher, more preferably 800 ° C. or higher. 950 ° C. or lower, preferably 920 ° C. or lower, more preferably 900 ° C. or lower.
- the average cooling rate from the start of cooling after placing the conveyor to the end temperature range of pearlite transformation is 1.0 ° C./second or more, preferably 2 ° C. / Sec or more and 6 ° C./sec or less, preferably 5 ° C./sec or less, more preferably 4 ° C./sec or less.
- the average cooling rate from less than 600 ° C. to 300 ° C. is 2.0 ° C./second or more, preferably 3 ° C./second or more, Or less, preferably 7 ° C./second or less.
- the cooling rate control can be performed by appropriately combining, for example, rolling line speed, conveyor speed, blower cooling, cover cooling, and the like.
- the said temperature can be measured with the radiation thermometer provided in the several places on a conveyor.
- the heating temperature during patenting is 850 ° C. or higher, preferably 860 ° C. or higher, more preferably 870 ° C. or higher.
- the heating temperature is set to 900 ° C. or lower, preferably 890 ° C.
- the holding time at the heating temperature is 10 seconds or longer, preferably 15 seconds or longer, more preferably 20 seconds or longer, 60 seconds or shorter, preferably 55 seconds or shorter, more preferably 50 seconds or shorter.
- the average cooling rate is 1.0 ° C./second or more, preferably 2.0 ° C./second or more, and is 6 ° C./second or less, preferably 5 ° C./second or less.
- the heating temperature during quenching is 850 ° C. or higher, preferably 860 ° C. or higher, more preferably 870 ° C. or higher in order to suppress coarse undissolved Cr-based carbides due to insufficient heating.
- the heating temperature is 950 ° C. or lower, preferably 940 ° C. or lower, and more preferably 930 ° C. or lower from the viewpoint of suppressing the remaining austenite crystal grains from coarsening and lowering toughness.
- the holding time is 5 seconds or more, preferably 10 seconds or more, more preferably 15 seconds or more, and 50 seconds or less, preferably 45 seconds or less, more preferably 40 seconds or less.
- Quenching may be performed with heated oil after holding for a predetermined time, for example, oil of about 50 to 60 ° C.
- Tempering after quenching may be adjusted as appropriate so that the tensile strength is 2100 MPa or more. However, when the tempering temperature is too high or the heating and holding temperature is too long, the residual amount of coarse Cr-based carbide increases, and the bending workability decreases. For example, tempering has a heating temperature of 350 ° C. or more and 450 ° C. or less, and a holding time at the heating temperature of 50 seconds or more and 200 seconds or less.
- the heat-treated steel wire of the present invention exhibits excellent fatigue characteristics as shown in the examples below.
- the heat-treated steel wire of the present invention can be processed into a desired coil diameter, free height, and number of turns to produce various springs such as a valve spring, a clutch spring, an engine spring, and a transmission spring.
- the heat-treated steel wire may be subjected to various known treatments such as nitriding treatment and vacuum carburizing treatment as necessary when processing.
- a steel ingot having a chemical composition shown in Table 1 was melted in a small vacuum melting furnace, heated at 1200 ° C. simulating the lump temperature, and forged to produce a ⁇ 155 mm steel piece. After this steel slab was hot-rolled, the mounting temperature, the average cooling rate I up to 600 ° C. after the mounting, and the average cooling rate II up to 300 ° C. were controlled as shown in Table 2, and the wire diameter ⁇ 8 A rolled wire rod of 0.0 mm was produced. After removing the surface decarburized layer, wrinkles and the like by cutting this rolled wire, it is subjected to a patenting treatment under the conditions shown in Table 2 to form a pearlite structure, and then cold-drawn so that the wire diameter becomes 4.0 mm. Wire processed.
- the tensile strength, drawing, the amount of Cr-based carbide based on the electrolytic extraction method, and the bending workability were measured as follows and listed in Table 3.
- the metal Fe of the matrix phase is electrolyzed to obtain Cr-based carbides in the steel of the electrolytic solution, and other carbides other than Cr-based carbides, carbonitrides, nitrides, etc., having a mesh diameter of 1.0 ⁇ m, and Two-stage filtration using a 0.4 ⁇ m filter [Advantech Toyo Co., Ltd. membrane filter] was performed and collected as an extraction residue on each filter.
- the mass difference before and after electrolysis of the heat-treated steel wire was defined as electrolytic mass.
- Each filter residue mass was divided by the electrolytic mass to determine the Cr-based carbide content (%).
- the bending workability was evaluated by self-winding. Each of the heat-treated steel wires obtained was subjected to 1000 turns of its own diameter, and the superiority or inferiority of the bending workability was judged by the number of breakage. When the number of breakage was less than 5 in the self-winding winding 1000, it was evaluated that the bending workability was excellent, and the case where the number of breakage was 5 or more was evaluated as poor bending workability.
- Test No. Examples 1 to 10 are examples that satisfy the requirements defined in the present invention. In these, the component composition and Cr-based carbide were controlled, and they had high strength and excellent bending workability.
- Test No. 11 and 12 are examples in which the heating temperature before the block rolling was low. Therefore, Cr-based carbides could not be sufficiently dissolved, and a large amount of Cr-based carbides remained in the 0.4 ⁇ m filter residue, resulting in poor bending workability.
- Test No. 13 is an example in which the conveyor placement temperature at the end of wire rod rolling, that is, the cooling start temperature was high. Therefore, a supercooled structure was generated, and the evaluation was stopped because a disconnection occurred in the shaving process.
- Test No. No. 14 is an example in which the average cooling rate I from the start of cooling during wire rod rolling to 600 ° C. was slow. Therefore, the growth of Cr-based carbides progressed, and a lot of coarse Cr-based carbides remained in the 0.4 ⁇ m filter residue after quenching and tempering, and the bending workability was poor.
- Test No. No. 15 is an example in which the average cooling rate II up to 300 ° C. was slow.
- the growth of Cr-based carbides progressed, and a large amount of coarse Cr-based carbides remained in the 1.0 ⁇ m filter residue after quenching and tempering, and bending workability was poor.
- Test No. 16 is an example in which the heating temperature during the patenting process was low.
- the Cr carbide remaining after the patenting treatment remained after the quenching and tempering treatment, so that a large amount of Cr carbide remained in the 1.0 ⁇ m filter residue, and the bending workability was poor.
- Test No. 17 is an example in which the heating and holding time of the patenting process was short. In this example, the evaluation was stopped because an incomplete structure was formed and the wire was disconnected during wire drawing.
- Test No. 18 is an example in which the average cooling rate during the patenting process was slow.
- the growth of Cr carbide progressed, and after quenching and tempering, a large amount of Cr carbide remained in the 0.4 ⁇ m filter residue, and the bending workability was poor.
- Test No. 19 is an example in which the heating temperature during quenching was low.
- coarse undissolved Cr-based carbides were generated and the toughness decreased.
- a large amount of Cr-based carbide remained in the 1.0 ⁇ m filter residue and the 0.4 mm filter residue, and the bending workability was poor.
- Test No. No. 20 is an example in which the heating and holding time during quenching was short.
- a large amount of Cr carbide remained in the 1.0 ⁇ m filter residue and the 0.4 mm filter residue, and the bending workability was inferior.
- Test No. No. 21 is an example in which the tempering temperature is high and the holding time is short. In this example, a large amount of Cr-based carbide remained in the 1.0 mm filter residue, and the bending workability was poor.
- Test No. No. 22 is an example in which the heating and holding time for tempering was long. In this example, a large amount of Cr-based carbide remained in the 1.0 mm filter residue, and the bending workability was poor.
- Test No. No. 23 is an example having a high C content and a high tempering temperature.
- coarse undissolved Cr-based carbides were generated and the toughness decreased. Further, a large amount of Cr-based carbide remained in the 1.0 ⁇ m filter residue and the 0.4 mm filter residue, and the bending workability was poor.
- Test No. 24 is an example in which the Si content was high and the tempering temperature was high.
- coarse undissolved Cr-based carbides were generated and the toughness decreased. Further, a large amount of Cr carbide remained in the 1.0 mm filter residue, and the bending workability was inferior.
- Test No. 25 is an example in which the Cr content was high.
- the growth of Cr carbide progressed, and after quenching and tempering, a large amount of Cr carbide remained in the 1.0 ⁇ m filter residue and 0.4 mm filter residue, and the bending workability was poor.
- Test No. 26 is an example in which the V content was large.
- the growth of Cr carbide progressed, and after quenching and tempering, a large amount of Cr carbide remained in the 0.4 ⁇ m filter residue, and the bending workability was poor.
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Abstract
Description
(a)Ni:0%超、0.3%以下
(b)B:0%超、0.01%以下
1.0μmフィルターと0.4μmフィルターを用いて電解抽出残渣分析をしたとき、[1.0μmフィルター残渣中のCr系炭化物質量/電解質量](以下、「1.0μmフィルターの残渣量/電解質量」ということがある):1.0%以上、2.80%以下
且つ
上記1.0μmフィルターで得られたろ液を残渣分析したとき、
[0.4μmフィルター残渣中のCr系炭化物質量/電解質量](以下、「0.4μmフィルターの残渣量/電解質量」ということがある):0.10%以下
1.0μmを超えるCr系炭化物はコイリング折損を誘発する原因となり、高強度熱処理鋼線の曲げ加工性を大幅に低下させる。そのため1.0μmフィルターの残渣量/電解質量は2.80%以下、好ましくは2.70%以下、より好ましくは2.60%以下である。一方、Cr系炭化物は熱処理鋼線の強度を向上させる役割もあるため、Cr系炭化物が少なすぎると熱処理鋼線の強度が不足する。1.0μmフィルターの残渣量/電解質量は1.0%以上、好ましくは1.20%以上、より好ましくは1.40%以上である。
0.4μmを超えるCr系炭化物の析出量が増加すると、熱処理鋼線の靭延性が低下して曲げ加工性が低下する。したがって0.4μmを超えるCr系炭化物は少ないほどよい。0.4μmフィルターの残渣量/電解質量は0.10%以下、好ましくは0.08%以下、より好ましくは0.06%以下である。一方、0.4μm以下のCr系炭化物は少ないほど靭延性に優れるが、Cr系炭化物を低減させるために熱処理時の加熱温度が高すぎる場合や加熱保持時間が長すぎる場合は、旧γ結晶粒度の粗大化が進み靭延性を更に低下させることがある。したがって0.4μmフィルターの残渣量/電解質量は好ましくは0.01%以上、より好ましくは0.02%以上である。
Cは、熱処理鋼線の強度向上に有効な元素である。このような効果を有効に発揮させるには、C含有量は0.5%以上、好ましくは0.55%以上、より好ましくは0.6%以上である。C含有量の増加に伴って強度は向上するが、添加量が過剰になると粗大セメンタイトを多量に析出し、熱処理鋼線の曲げ加工性に悪影響を及ぼす。そのためC含有量は0.8%以下、好ましくは0.75%以下、より好ましくは0.7%以下である。
Siは、鋼の脱酸、および熱処理鋼線の強度向上に有効な元素である。このような効果を有効に発揮させるには、Si含有量は1.5%以上、好ましくは1.55%以上、より好ましくは1.6%以上である。一方、Si含有量が過剰になると、材料を硬化させるだけでなく、靭延性の低下や、表面の脱炭量が増加してばねの疲労特性を低下させることがある。そのためSi含有量は2.5%以下、好ましくは2.4%以下、より好ましくは2.3%以下である。
Mnは、鋼の脱酸、鋼中SをMnSとして固定することに加えて、焼入れ性を高めてばね強度の向上に貢献する。このような効果を有効に発揮させるには、Mn含有量は0.5%以上、好ましくは0.6%以上、より好ましくは0.7%以上である。一方、Mn含有量が過剰になると、焼入れ性が過度に向上するため、マルテンサイト、ベイナイト等の過冷組織が生成しやすくなる。そのため、Mn含有量は1.5%以下、好ましくは1.4%以下、より好ましくは1.3%以下である。
Pは旧オーステナイト粒界に偏析し、組織を脆化させるため疲労特性が低下する。そのためP含有量は、0.02%以下、好ましくは0.018%以下である。P含有量は少ないほど好ましいが、ゼロとするのは製造上困難であり、0.003%程度は不可避不純物として含有することがある。
Sは旧オーステナイト粒界に偏析し、組織を脆化させるため疲労特性が低下する。そのためS含有量は、0.02%以下、好ましくは0.015%以下である。S含有量は少ないほど好ましいが、ゼロとするのは製造上困難であり、0.003%程度は不可避不純物として含有することがある。
Crは、焼入れ性を向上させて、ばね強度を向上させることに加え、Cの活量を低下させて圧延時や熱処理時の脱炭を防止する効果がある。このような効果を有効に発揮させるにはCr含有量は、0.3%以上、好ましくは0.35%以上、より好ましくは0.4%以上である。一方、Crが増加すると鋼中のCr系炭化物が増加するだけでなく、粗大なCr系炭化物が生じて熱処理鋼線の曲げ加工性を悪化させる。そのためCr含有量は0.7%未満、好ましくは0.68%以下、より好ましくは0.65%以下である。
Vは、熱間圧延、および焼入れ焼戻し処理において結晶粒を微細化する作用があり、靭延性を向上させる。また、窒化処理などの高温処理時に2次析出硬化を起こしてばねの強度の向上に寄与する。これらの効果を発揮させるためには、V含有量は0.05%以上、好ましくは0.10%以上、より好ましくは0.15%以上である。一方、V含有量が多いと、CrとVの複合炭化物が増加して熱処理鋼線の曲げ加工性を低下させる。そのためV含有量は0.5%以下、好ましくは0.45%以下、より好ましくは0.40%以下である。
Alは、鋼中でAl2O3やAlNの介在物を形成する。これらの介在物はばねの疲労寿命を著しく低下させる。そのためAl含有量は0.01%以下、好ましくは0.005%以下である。
NはAlと結合してAlNの介在物を形成する。AlN介在物はばねの疲労寿命を著しく低下させる。そのためN含有量は0.007%以下、好ましくは0.006%以下、より好ましくは0.005%以下である。
Oを過剰に含有すると粗大な非金属介在物を生成して疲労強度を低下させる。そのためO含有量は0.004%以下、好ましくは0.003%以下である。
Niは、熱間圧延時の脱炭を抑制する他、熱処理鋼線の靭延性を向上させる効果がある。このような効果を有効に発揮させるにはNi含有量は、好ましくは0.05%以上、より好ましくは0.07%以上、更に好ましくは0.1%以上である。一方、Ni含有量が多いとコスト面で劣るだけでなく、焼入れ性が過度に向上するため、圧延時にマルテンサイト、ベイナイト等の過冷組織が生成しやすくなる。そのため、Ni含有量は好ましくは0.3%以下、より好ましくは0.27%以下、更に好ましくは0.2%以下である。
Bは、焼入れ性の向上とオーステナイト結晶粒界の清浄化作用があり、靭延性を向上させる。この様な効果を有効に発揮させるには、B含有量は好ましくは0.001%以上、より好ましくは0.0015%以上、更に好ましくは0.002%以上である。一方、Bを過剰に含有させるとFeとBの複合化合物が析出し、熱間圧延時の割れを引き起こす危険がある。また、焼入れ性が過度に向上するため、マルテンサイト、ベイナイト等の過冷組織が生成しやすくなる。そのため、B含有量は好ましくは0.01%以下、より好ましくは0.008%以下、更に好ましくは0.006%以下である。
オートグラフ(島津製作所製)にて評価間距離を200mm、ひずみ速度20mm/minとして引張り試験を行い引張強度、およびオートグラフで測定を行い、破面形状から絞りを測定した。絞りが45.0%以上であれば靭延性に優れると判定した。
Cr系炭化物の電解抽出残渣分析を行った。まず、熱処理鋼線表面のスケールをサンドペーパーで除去した後、アセトンで洗浄処理を行った。得られたサンプルを電解液である10質量%アセチルアセトン含有エタノール溶液中に浸漬させ、熱処理鋼線表層からの電解質量が0.4~0.5g程度となった後、試験片を取り出した。その後、母相の金属Feを電気分解して電解液の鋼中のCr系炭化物、およびその他微量に存在するCr系炭化物以外の炭化物、炭窒化物、窒化物などをメッシュ直径1.0μm、および0.4μmのフィルター[アドバンテック東洋(株)製メンブランフィルター]を使用した2段階のろ過を行って各フィルター上に抽出残渣として採取した。熱処理鋼線の電解前後の質量差を電解質量とした。各フィルター残渣質量を電解質量で除してCr系炭化物質量(%)を求めた。具体的には電解液を1.0μmフィルターでろ過した後、得られたろ液を0.4μmフィルターでろ過した。電解抽出残渣分析をしたとき、[1.0μmフィルターの残渣量/電解質量]が1.0%以上、2.80%以下であり、且つ、上記1.0μmフィルターで得られたろ液を残渣分析したとき、[0.4μmフィルターの残渣量/電解質量]が0.10%以下の場合を合格とした。
曲げ加工性は自径巻きで評価を行った。得られた各熱処理鋼線で1000巻の自径巻を行い折損回数で曲げ加工性の優劣を判断した。自径巻1000巻中、折損回数が5回未満の場合を曲げ加工性に優れると評価し、折損回数が5回以上の場合を曲げ加工性が悪いと評価した。
Claims (3)
- 質量%で、
C :0.5~0.8%、
Si:1.5~2.5%、
Mn:0.5~1.5%、
P :0%超、0.02%以下、
S :0%超、0.02%以下、
Cr:0.3~0.7%未満、
V :0.05~0.5%、
Al:0%超、0.01%以下、
N :0%超、0.007%以下、
O :0%超、0.004%以下を含有し、
残部が鉄および不可避不純物からなり、
1.0μmフィルターと0.4μmフィルターを用いて電解抽出残渣分析をしたとき、[1.0μmフィルター残渣中のCr系炭化物質量/電解質量]が1.0%以上、2.80%以下であり、且つ、
前記1.0μmフィルターで得られたろ液を残渣分析したとき、
[0.4μmフィルター残渣中のCr系炭化物質量/電解質量]が0.10%以下である曲げ加工性に優れた熱処理鋼線。 - 更に、質量%で、以下の(a)、(b)の少なくとも1つを含有する請求項1に記載の熱処理鋼線。
(a)Ni:0%超、0.3%以下
(b)B:0%超、0.01%以下 - 請求項1または2に記載の熱処理鋼線を用いて得られるばね。
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CN201680020050.3A CN107406952A (zh) | 2015-03-31 | 2016-03-22 | 弯曲加工性优异的热处理钢线 |
US15/562,084 US20180087124A1 (en) | 2015-03-31 | 2016-03-22 | Heat-treated steel wire having excellent bendability |
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BRPI0607042B1 (pt) * | 2006-11-09 | 2014-08-19 | Nippon Steel & Sumitomo Metal Corp | Aço para mola de alta resistência |
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2016
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- 2016-03-22 US US15/562,084 patent/US20180087124A1/en not_active Abandoned
- 2016-03-22 CN CN201680020050.3A patent/CN107406952A/zh active Pending
- 2016-03-22 WO PCT/JP2016/058960 patent/WO2016158563A1/ja active Application Filing
- 2016-03-22 KR KR1020177026619A patent/KR20170118217A/ko not_active Application Discontinuation
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JP2016191100A (ja) | 2016-11-10 |
KR20170118217A (ko) | 2017-10-24 |
EP3279358A4 (en) | 2018-08-15 |
CN107406952A (zh) | 2017-11-28 |
EP3279358A1 (en) | 2018-02-07 |
US20180087124A1 (en) | 2018-03-29 |
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