Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
  • B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
  • B21J1/06—Heating or cooling methods or arrangements specially adapted for performing forging or pressing operations
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
  • B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
  • B21J1/003—Selecting material
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/06—Surface hardening
  • C21D1/09—Surface hardening by direct application of electrical or wave energy; by particle radiation
  • C21D1/10—Surface hardening by direct application of electrical or wave energy; by particle radiation by electric induction
• • 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
  • C21D9/30—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for crankshafts; for camshafts
• • 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
  • C22C38/06—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
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • 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
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • C—CHEMISTRY; METALLURGY
  • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/002—Bainite
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/004—Dispersions; Precipitations
• • 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
• • 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
  • Y02P10/25—Process efficiency

Definitions

• the present invention relates to a non-heat treated steel material for hot forging that is processed into machine parts such as automobiles and industrial machines without being subjected to a tempering treatment after hot forging, and a hot work using the same.
• the present invention relates to a forged non-tempered product and a method for producing the same, and is particularly hot forged, has a high strength and a high durability ratio without being tempered, and can be induction hardened.
• Patent Document 1 has a strength and low temperature toughness that are higher than those of conventional tempered materials while still being hot forged, using a steel material to which Si is added in excess of 1.0% and a large amount of S, V, and N are added. It is described that hot forged non-tempered steel was obtained. However, there is no description regarding the fatigue strength and durability ratio of this non-heat treated steel.
• Non-heat treated steel for induction hardening There have been some reports on non-heat treated steel for induction hardening.
• the invention described in Patent Document 2 prevents a decrease in surface layer hardness and surface hardened layer depth due to generation of residual ferrite after induction hardening by setting the structure before induction hardening to a bainite ratio of 75% or more. It is an invention.
• the non-heat treated steel for induction hardening described in Patent Document 2 has no description regarding fatigue strength and durability ratio, and these characteristics are not considered at all.
• the invention described in Patent Document 3 is an invention that reduces the amount of retained austenite after induction hardening.
• the non-heat treated steel for induction hardening described in Patent Document 3 there is no description regarding fatigue strength and durability ratio, and these characteristics are not considered at all.
• an appropriate amount of S, Pb, Bi, Te, Se, and Ca may be added to improve machinability.
• the tensile strength is 1100 MPa or more, the machinability is improved. The effect is known to be small.
• Patent Document 4 describes an invention in which the improvement in strength after hot forging is suppressed to ensure machinability, and the fatigue strength of the entire component is improved by increasing the depth of the surface hardened layer by induction hardening. Has been.
• Patent Document 5 proposes that it is effective to reduce the high-carbon island-like martensite and retained austenite in the bainite-based metal structure.
• the durability ratio is at most 0.56 or less, and there is a limit to increasing the strength without reducing the machinability, and these fatigue strengths are both low.
• Patent Document 6 describes a crankshaft that can achieve high wear resistance and fatigue strength, and that achieves both high machinability and a method for manufacturing the crankshaft.
• the microstructure of the hot forged product before soft nitriding is made to be a bainite-based (70% or more) microstructure, and this hot forged product is soft nitrided under a temperature condition of 550 to 650 ° C.
• the mechanical properties such as fatigue strength of the crankshaft are improved.
• the steel material components are obtained using the parameters Hg representing the amounts of C, Si, Mn, Cr, Mo and V of the steel material with specific relational expressions. Is stipulated.
• nitrocarburizing treatment usually requires exposure to an atmosphere containing nitrogen and heating in a temperature range below the austenitizing temperature. Compared with surface hardening treatment by induction hardening, the equipment and cost are reduced. It takes. In addition, because the steel material intended for soft nitriding over a certain time has a large amount of Si, in the induction hardening by instantaneous induction heating only on the surface, residual austenite remains in the internal structure, and high fatigue strength is I can't get it.
• the present invention advantageously solves the above-described problems and controls the microstructure in the part by non-heat treated steel for hot forging that enables induction hardening and cooling after hot forging.
• An object of the present invention is to provide a hot forged non-heat treated product that suppresses a decrease in machinability associated with strength and improves fatigue strength, and a manufacturing method thereof.
• the present invention uses a steel in which a large amount of Mo is added to high carbon steel that can be induction hardened to obtain a high surface hardness, and in the cooling process after hot forging, a large amount of Mo carbonitride is precipitated, It has been found that it has a high durability ratio by reducing the defect density such as dislocation, and suppresses the deterioration of machinability associated with high strength, and obtains a hot forged non-heat treated product with improved fatigue strength, The present invention has been completed.
• “carbonitride” used in the present specification means carbonitride and carbide.
• the gist of the present invention is as follows.
• the steel component according to the above (1) or (2) is included, the steel structure is an area ratio of 95% or more is a bainite structure, and the average size of Mo carbonitride dispersed in the steel is 4 nm.
• a hot-forged non-tempered product capable of induction hardening characterized by being 11 nm or less.
• the steel material comprising the component composition described in (1) or (2) above is heated to 1000 ° C. or more and 1250 ° C. or less for hot forging, and after the hot forging, the average cooling rate up to 200 ° C. Is heated at 0.05 ° C./second or more and 0.80 ° C./second or less, and induction hardening is performed on a portion where strength is required.
• the steel of the present invention is optimal as a raw material for hot forged non-heat treated steel parts capable of induction hardening with high fatigue strength while suppressing an increase in cutting cost.
• the manufacturing method of this invention can manufacture the hot forging non-tempered goods which can be induction-hardened which has a high durability ratio and high fatigue strength.
• the hot forged non-heat treated product of the present invention can be induction hardened when used as a part for automobiles or industrial machines, so that the parts can be further strengthened, and the weight of the vehicle can be reduced. Contributes to reducing fuel consumption and cost.
• the present invention has been made for the first time after further studies based on these findings.
• C 0.45 to 0.60% C is an important element that determines the strength of steel. Compared to other alloy elements, the alloy cost is low. If a large amount of C can be added, the alloy cost of the steel material can be reduced. Further, the surface hardness after induction hardening is determined by the amount of C in the steel, and in order to obtain the required strength, the lower limit is made 0.45%. However, when a large amount of C is added, residual austenite or island martensite in which C is concentrated at the boundary of the lath during bainite transformation is formed and the durability ratio is lowered, so the upper limit is made 0.60%.
• the steel which can be induction-hardened of the present invention is steel that can have a surface hardness after the induction-hardening treatment that is higher than the required strength. Therefore, in the present invention, it is steel having a C content of 0.45% or more. In order to obtain higher strength, an amount of C exceeding 0.5% is preferable.
• Si 0.02 to 0.15% Si is an element that increases the amount of retained austenite in steel by bainite transformation in the cooling process after hot forging.
• Si content exceeds 0.15%, the fatigue strength and the durability ratio are significantly reduced. Therefore, the amount is limited to 0.15% or less. However, if the content is suppressed to less than 0.02%, the manufacturing cost becomes great, so the lower limit is made 0.02%.
• Mn 1.50 to 3.00%
• Mn is an element that promotes bainite transformation, and is an important element for making the structure bainite in the cooling process after hot forging. Furthermore, it combines with S to form sulfides and has the effect of improving machinability. In order to exert these effects, the lower limit is made 1.50%. On the other hand, if an amount of Mn exceeding 3.00 is added, the hardness of the substrate increases and becomes brittle, so that the machinability is significantly lowered.
• the upper limit is 3.00. In particular, an amount of Mn exceeding 2.0% is preferable because a bainite structure with an area ratio of 95% is obtained even at a low cooling rate.
• P 0.0002 to 0.150% Since P usually contains 0.0002% or more as an inevitable impurity in steel, the lower limit is made 0.0002% or more. When P is added in a large amount, P segregates at the grain boundaries of prior austenite and promotes cracking after induction hardening, so the upper limit is made 0.150%. Preferably it is 0.100% or less, More preferably, it is 0.050% or less.
• S 0.001 to 0.200%
• S forms sulfides with Mn and has an effect of improving machinability, and in order to exert the effect, the lower limit is made 0.001%.
• S forms sulfides with Mn and has an effect of improving machinability, and also has an effect of suppressing the growth of austenite grains and maintaining high toughness. In order to exert these effects, the lower limit is made 0.001%.
• the upper limit is made 0.200%.
• Cr 0.02 to 1.00% Cr, like Mn, is an element effective for promoting the bainite transformation, and in order to exert its effect, the lower limit is made 0.02%. However, if a large amount of Cr is added, the Fe-based carbide is stabilized and the surface hardness when induction hardening is reduced, so the upper limit is made 1.00%.
• Al 0.001 to 0.300%
• Al precipitates and disperses in the steel as a nitride, thereby preventing the austenite structure from coarsening during forging reheating and preventing the subsequent bainite structure from becoming coarse.
• Al combines with oxygen during machining, adheres to the tool surface, and is effective in preventing tool wear.
• the lower limit is made 0.001%.
• it is 0.050% or more, more preferably 0.100%.
• the upper limit is set to 0.300%.
• V 0.01 to 0.30%
• V is an element effective for promoting the bainite transformation, and is an element effective for forming a carbonitride, strengthening the precipitation of the bainite structure, and increasing the strength and durability ratio.
• a content of 0.01% or more is necessary.
• the upper limit is made 0.30%.
• Mo 0.03-1.00%
• Mo is not only an element effective for promoting bainite transformation, but also has the highest solid solubility in austenite compared to alloy elements such as V, Ti, Nb, etc., which can provide precipitation strengthening due to alloy carbide, and in the cooling process A large amount of Mo carbonitride is obtained.
• precipitation of carbonitride such as Mo used for precipitation strengthening is not preferable because not only fatigue strength but also tensile strength is increased and machinability is remarkably lowered.
• the size of Mo carbonitride is controlled to 4 nm or more and 11 nm or less, only the fatigue strength can be increased without increasing the tensile strength affecting the machinability, that is, the fatigue strength and the durability ratio are increased. I understood it. In order to exhibit this effect, a content of 0.03% or more is necessary. On the other hand, if it exceeds 1.00%, the effect is saturated, so the upper limit is made 1.00%.
• N 0.0020 to 0.0070% N is generally used to form a nitride with V to prevent coarsening of the austenite structure during hot forging, but V nitride serves as the nucleus of pro-eutectoid ferrite. The transformation is promoted to reduce the strength and durability ratio.
• the upper limit of the N amount is set to 0.0070%.
• the lower limit is made 0.0020%.
• Ca, Te, Zr containing one or more of Ca: 0.0002 to 0.0100%, Te: 0.0002 to 0.1000%, Zr: 0.0002 to 0.2000% are: All of them have an effect of forming oxides, becoming crystallization nuclei of Mn sulfide, and uniformly and finely dispersing Mn sulfide. In addition, any element dissolves in Mn sulfide, reduces its deformability, suppresses elongation of Mn sulfide shape after rolling or hot forging, and reduces the anisotropy of mechanical properties There is. In order to exert these effects, the lower limits of Ca, Te, and Zr are each 0.0002%.
• the structure is defined as a bainite structure with an area ratio of 95% or more. If the main structure is a bainite structure, it has a high durability ratio, but the remaining structure is ferrite, residual austenite, or island martensite. This is because the durability ratio is significantly reduced when the content is 5% or more. The fewer these remaining structures are, the higher the durability ratio is, and the area ratio is preferably 97% or more.
• the average size of Mo carbonitride dispersed in steel is 4 nm or more and 11 nm or less
• the reason why the average size of Mo carbonitrides in the bainite structure is specified to be 4 nm or more is that when the average size is less than 4 nm, the fatigue strength is high but the tensile strength is also high and the durability ratio is small. This is because it is impossible to achieve both fatigue strength and machinability. More preferably, the average size is 8 nm or more.
• the upper limit value of the average size of Mo carbonitride is defined as 11 nm because when the average size exceeds 11 nm, not only the tensile strength but also the fatigue strength is remarkably lowered, so that high fatigue strength cannot be achieved.
• the shape of Mo carbonitride is acicular and the size of Mo carbonitride used in this specification is the length in the longitudinal direction.
• Step is heated to 1000 ° C or lower and 1250 ° C or higher
• the reason why the steel material having the above-described component composition is heated to 1000 ° C. or lower and 1250 ° C. or higher is to sufficiently precipitate carbonitrides of Mo and V in the cooling process, before hot forging. This is because Mo and V are sufficiently dissolved in the steel by heating. If the heating temperature is less than 1000 ° C., Mo and V cannot be sufficiently dissolved in the steel, the precipitation strengthening amount in the subsequent cooling process is small, and the fatigue strength and durability ratio are small. On the other hand, raising the heating temperature more than necessary promotes the growth of austenite grains, and the structure transformed in the subsequent cooling process becomes coarse, and the durability ratio decreases. Therefore, the upper limit of the heating temperature is 1250 ° C.
• the average cooling rate is 0.05 ° C / second or more and 0.80 ° C / second or less to 200 ° C or less
• the average cooling rate up to 200 ° C or less is specified to be 0.05 ° C / second or more and 0.80 ° C / second or less because the time staying in the temperature range where Mo carbonitride precipitates is lengthened. This is because the precipitation amount is increased in the cooling process and the carbonitride size is controlled.
• the average cooling rate is 0.80 ° C./second or more, the precipitation amount of Mo carbonized vagina is not sufficiently obtained, and the effect of improving the strength and the durability ratio is small.
• an average cooling rate of 0.50 ° C./second or less is desirable. More preferably, it is 0.30 ° C./second or less.
• the average cooling rate is less than 0.05 ° C./second, proeutectoid ferrite having an area ratio of 5% or more is generated at the bainite lath boundary, and the fatigue strength and the durability ratio are significantly reduced.
• the present invention provides a hot forged non-tempered product capable of induction hardening with high fatigue strength, it is desirable that the tensile strength be 1300 MPa or less in order to ensure sufficient machinability. .
• a JIS Z 2201 No. 14 tensile test piece and a JIS Z 2274 No. 1 bending bending fatigue test piece were sampled from the center of these forgings, and the tensile strength and fatigue strength were determined.
• the fatigue strength was defined as the stress amplitude that did not break in 10 7 rotations in the rotating bending fatigue test.
• the ratio of the obtained fatigue strength and tensile strength was obtained as the durability ratio (fatigue strength / tensile strength).
• tissue observation was extract
• the area ratio of bainite is determined by polishing the specimen until it becomes a mirror surface, then performing repeller etching, and confirming the microstructure of proeutectoid ferrite, residual austenite, island martensite, and the like other than bainite.
• the microphotographs were taken by 10 fields of view and then calculated by image analysis.
• the average size of the Mo carbonitride was observed in 10 views of 15,000-fold transmission electron micrographs taken with a transmission electron microscope after finishing the test piece into a thin film by electrolytic polishing.
• the length in the longitudinal direction of the Mo carbonitride was determined by image analysis, and the average value was determined.
• Each of the present invention steels 1 to 18 has a bainite structure of 95% or more in area ratio, the average size of Mo carbonitride is 4.6 nm or more and 10.8 nm or less, and the durability ratio is 0.58 or more. Has a high durability ratio.
• the tensile strength is 1300 MPa or less, but as is apparent when compared with the comparable tensile strength, the conventional example No. Higher fatigue strength is achieved than tempered steel of 28 carbon steel.
• Comparative Example No. Nos. 23, 24 and 27 have a high content of either C, Si or N. 21 is within the specified steel composition range, but the average cooling rate is not specified, the amount of the remainder such as ferrite and residual austenite is large at the bainite lath boundary, and the average size of Mo carbonitride is not specified, Low strength and durability ratio.
• No. Nos. 19 and 22 have steel compositions or heat treatment conditions that are not specified, and sufficient precipitation strengthening cannot be obtained, resulting in a low durability ratio. No. Since the heating temperature of No. 20 was increased more than necessary, the bainite structure was coarsened, and the durability ratio was rather low.
• No. No. 25 has Mn added more than necessary, has high tensile strength, and is very difficult to cut. On the other hand, no. In No. 26, Al is added more than necessary, and the fatigue strength and durability ratio are lowered.

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• 2012
  • 2012-08-03 WO PCT/JP2012/069861 patent/WO2013018893A1/ja active Application Filing
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