WO2015029553A1 - ステアリングラックバー用圧延丸鋼材およびステアリングラックバー - Google Patents
ステアリングラックバー用圧延丸鋼材およびステアリングラックバー Download PDFInfo
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- WO2015029553A1 WO2015029553A1 PCT/JP2014/066200 JP2014066200W WO2015029553A1 WO 2015029553 A1 WO2015029553 A1 WO 2015029553A1 JP 2014066200 W JP2014066200 W JP 2014066200W WO 2015029553 A1 WO2015029553 A1 WO 2015029553A1
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- round steel
- rack bar
- steel material
- steering rack
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- 239000000463 material Substances 0.000 title claims abstract description 120
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- 229910001567 cementite Inorganic materials 0.000 claims abstract description 50
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 claims abstract description 50
- 229910001562 pearlite Inorganic materials 0.000 claims abstract description 48
- 239000000126 substance Substances 0.000 claims abstract description 18
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- 239000012535 impurity Substances 0.000 claims abstract description 14
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 9
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 8
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 7
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 7
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Images
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- C—CHEMISTRY; METALLURGY
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- C22C—ALLOYS
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- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/16—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling wire rods, bars, merchant bars, rounds wire or material of like small cross-section
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- B21B3/02—Rolling special iron alloys, e.g. stainless steel
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D3/00—Steering gears
- B62D3/02—Steering gears mechanical
- B62D3/12—Steering gears mechanical of rack-and-pinion type
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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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
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- Y02P10/25—Process efficiency
Definitions
- the present invention relates to a rolled round steel material for a steering rack bar and a steering rack bar.
- a steering rack bar (hereinafter also simply referred to as “rack bar”) used in a steering device is an important part that shows a skeletal role that steers the traveling direction of an automobile and connects the left and right wheels. Yes, if this is damaged, the steering wheel operation becomes impossible. For this reason, high reliability is requested
- rack bars have been subjected to tempering treatment for quenching and tempering of rolled round steel materials of medium carbon steel, and then, after being drawn, if necessary, drilling and gear cutting by cutting are performed.
- the mold part has been manufactured by induction hardening and tempering. Note that the rolled round steel material means that the shape of the cross section is processed into a circle by rolling, and the gear cutting means that a tooth mold part is formed.
- the rack bar subjected to induction hardening is required to prevent cracks generated in the induction hardening layer from propagating through the base material and causing breakage even when an excessive load is applied.
- the rack bar is deep hole processed in the length direction of the central portion in the radial direction.
- the round steel material used as the material for the rack bar is required to have good machinability and excellent base material impact characteristics (base material toughness) that resist the progress of cracks.
- the present inventors have proposed, for example, the following steel materials as steel materials used for such a steering rack bar.
- the chemical composition has a fn1 value of 1.20 or less, and the microstructure is composed of ferrite, lamellar pearlite, and spherical cementite.
- the crystal grain size is 10 ⁇ m or less, and the lamellar spacing of lamellar perlite is 200 n
- Area percentage of the microstructure of the following lamellar pearlite is the number of 20-50% and spheroidal cementite 4 ⁇ 10 5 cells / mm 2 or more, the steel material is disclosed for induction hardening.
- this rolled steel material for induction hardening may further contain one or more selected from Cu, Ni, Mo, Ti, Nb and V.
- the Ceq value represented by (1) or less satisfies the total content of Si, Mn and Cr of 1.2 to 3.5%.
- the microstructure is composed of ferrite, lamellar pearlite and spherical cementite, and the average crystal grain size of the ferrite is
- a rolling steel material for induction hardening is disclosed that is 10 ⁇ m or less, the area ratio of the lamellar pearlite in the microstructure is 20% or less (including 0%), and the number of spherical cementite is 6 ⁇ 10 5 pieces / mm 2 or more. .
- this rolled steel material for induction hardening may further contain one or more selected from Cu, Ni, Mo, Ti, Nb and V.
- An object of the present invention is to provide a rolled round steel material that can be suitably used as a raw material for a rack bar to be induction-hardened, and a rack bar using the same.
- An object of the present invention is to provide a rolled round steel material excellent in base material toughness and machinability and a rack bar using the same without particularly adding an expensive element or tempering treatment. To do. It is another object of the present invention to provide a rolled round steel material that can easily process a deep hole in the length direction of the central portion in the radial direction, and a rack bar that can retain a generated crack.
- the high base metal toughness targeted by the present invention is a V notch having a notch angle of 45 °, a notch depth of 2 mm and a notch bottom radius of 0.25 mm as defined in JIS Z 2242 (2005) in the state of rolled steel.
- the present inventors have obtained a high base metal toughness without performing a tempering treatment in medium carbon steel, and means for ensuring good machinability at the center.
- Various laboratory studies were conducted.
- the ferrite is fine and stretched in a direction parallel to the rolling direction, and the cementite in the lamellar pearlite is made spherical cementite so that the lamellar pearlite is less than a specific ratio, and the spherical cementite is more than a specific amount. If included, resistance to cracks that progress in a cross section perpendicular to the rolling direction is increased, so that the base material toughness can be increased.
- (C) S combines with Mn to form MnS, and extends in the longitudinal direction of the steel material (direction parallel to the rolling direction) to improve toughness. Moreover, if a specific amount of S is contained, the chip resistance is improved and the cutting resistance is lowered, so that the machinability is improved.
- a portion requiring base metal toughness for preventing breakage is a region from the surface of the round steel material to a position of a half radius. Therefore, in the case of a rolled round steel material whose microstructure is composed of ferrite, lamellar pearlite, and cementite, the microstructure in the above-mentioned region is fine and finely stretched in a direction parallel to the rolling direction, lamellar pearlite limited to a specific ratio or less. And if it consists of more than a specific amount of spherical cementite, the base material toughness for preventing breakage can be obtained.
- the inventors of the present invention based on the knowledge (A) to (E) above, specifically, in order to further improve the toughness, specifically, Charpy impact using a V-notch Charpy impact test piece in the state of rolled steel.
- Charpy impact using a V-notch Charpy impact test piece in the state of rolled steel In order to set the impact value at a test temperature of 25 ° C. in the test to 160 J / cm 2 or more, the influence of component elements was investigated. As a result, the following knowledge was obtained.
- (F) B has the effect of suppressing the release of strain at high temperatures by strengthening the grain boundaries and suppressing the segregation of P and S at the austenite grain boundaries during induction hardening. As a result, the toughness is further increased.
- the present invention has been completed based on the above findings, and the gist thereof is the rolled round steel material for steering rack bars and the steering rack bar described below.
- the average grain size of ferrite in the region from the surface to the half position of the radius is 10 ⁇ m or less, and the area ratio of lamellar pearlite is less than 20%.
- the number of spherical cementites in the cementite is 4 ⁇ 10 5 pieces / mm 2 or more, the area ratio of lamellar pearlite in the center is 20% or more, and the number of spherical cementites in the cementite is 4 ⁇ 10 5.
- the steering rack bar according to the above (1) which contains at least one selected from Ca: 0.0005 to 0.005% and Pb: 0.05 to 0.30% by mass% Rolled round steel material.
- Impurity refers to what is mixed from ore as a raw material, scrap, or the manufacturing environment when industrially producing steel materials.
- Spherical cementite refers to cementite having a ratio of major axis L to minor axis W (L / W) of 2.0 or less.
- the central part refers to a part at a distance from the center to a quarter of the radius.
- “Use as untempered” means to use without performing so-called “tempering” of quenching and tempering.
- the rolled round steel material for the steering rack bar of the present invention does not necessarily contain expensive V, and Charpy impact using a V-notch Charpy impact test piece in the rolled round steel material state without any tempering treatment. Since it has a high base metal toughness with an impact value at a test temperature of 25 ° C. of 160 J / cm 2 or more in the test and a good machinability for machining a deep hole in the center, It is suitable for use as a material.
- the steering rack bar of the present invention can be obtained by using the rolled round steel material for the steering rack bar as it is not tempered.
- FIG. 1 is a front view (overall view)
- FIG. 2B is a side view
- C 0.38 to 0.55%
- C has the effect of improving the strength of steel, induction hardenability, and the strength of a hardened layer formed by induction hardening.
- the content is less than 0.38%, the desired effect due to the above action cannot be obtained.
- the content of C exceeds 0.55%, the base material toughness decreases. Therefore, the C content is set to 0.38 to 0.55%.
- content of C shall be 0.40% or more. Further, the C content is preferably 0.51% or less.
- Si 1.0% or less
- Si is a deoxidizing element and is an element that improves the strength of ferrite by solid solution strengthening. However, if the Si content exceeds 1.0%, the machinability is lowered and it is difficult to machine deep holes. Therefore, the Si content is set to 1.0% or less. The Si content is preferably 0.8% or less.
- the Si content is preferably 0.03% or more, and more preferably 0.10% or more. preferable.
- Mn 0.20 to 2.0% Mn combines with S to form MnS, and has an effect of lowering cutting resistance by improving machinability, especially chip disposal when machining deep holes. It has the effect of suppressing progress and increasing toughness. Mn is an element effective for improving the induction hardenability and also an element for improving the strength of the ferrite by solid solution strengthening. However, when the content of Mn is less than 0.20%, the desired effect due to the above action cannot be obtained. On the other hand, if Mn is contained exceeding 2.0%, the machinability is lowered, and it becomes difficult to process a deep hole. Therefore, the Mn content is set to 0.20 to 2.0%. In order to stably obtain the above effects while keeping the alloy cost low, the Mn content is preferably 0.40% or more, and preferably 1.50% or less. .
- S 0.005 to 0.10%
- S is an important element in the present invention.
- S combines with Mn to form MnS, and has the effect of lowering the cutting resistance by improving the machinability, especially chip disposal when processing deep holes. It has the effect of suppressing progress and increasing toughness.
- the S content is set to 0.005 to 0.10%.
- the S content is preferably 0.010% or more, and more preferably 0.015% or more.
- the S content is preferably 0.08% or less.
- Cr 0.01 to 2.0% Cr is an element effective for improving the induction hardenability and is an element for improving the strength of the ferrite by solid solution strengthening, so it is necessary to contain 0.01% or more. However, if the Cr content exceeds 2.0%, the machinability is lowered and it is difficult to machine deep holes. Therefore, the Cr content is set to 0.01 to 2.0%. Note that the Cr content is preferably 0.05% or more, and more preferably 0.10% or more. Further, the Cr content is preferably 1.8% or less.
- Al 0.003 to 0.10%
- Al has a deoxidizing action.
- the Al content is set to 0.003 to 0.10%.
- the Al content is preferably 0.08% or less.
- the Al content is preferably 0.005% or more, and more preferably 0.010% or more.
- B 0.0005 to 0.0030% B strengthens the grain boundary, thereby suppressing the release of strain at high temperature and improving the induction hardenability, and further suppressing the segregation of P and S at the austenite grain boundary during induction hardening. As a result, the toughness is further increased.
- the above effect is remarkable when the B content is 0.0005% or more. However, even if it contains B exceeding 0.0030%, the above-mentioned effect is saturated and the cost is increased. Therefore, the content of B is set to 0.0005 to 0.0030%.
- the B content is preferably 0.0010% or more, and more preferably 0.0020% or less.
- Ti 0.047% or less Ti is preferentially bonded to impurity element N in the steel and fixes N, thereby suppressing the formation of BN and causing B to exist as a solid solution B. Therefore, Ti is effective in securing the effect of strengthening the grain boundary, the effect of improving the induction hardenability, and the effect of suppressing the segregation of P and S at the austenite grain boundary at the time of induction hardening. It is an element. However, if the Ti content exceeds 0.047%, the toughness of the base metal is significantly reduced. Therefore, the Ti content is set to 0.047% or less.
- Cu 0 to 1.0% Since Cu has the effect of improving induction hardenability and increasing the base material toughness, Cu may be added to improve the base material toughness. However, if the Cu content exceeds 1.0%, the machinability is lowered, and it becomes difficult to machine deep holes. Therefore, the amount of Cu in the case of inclusion is set to 1.0% or less. Note that the amount of Cu is preferably 0.80% or less.
- the amount of Cu is preferably 0.05% or more, and more preferably 0.10% or more.
- Ni 0 to 3.0% Since Ni has the effect of improving induction hardenability and increasing the base material toughness, Ni may be included to improve the base material toughness. However, if the Ni content exceeds 3.0%, the machinability is lowered and it is difficult to machine deep holes. Therefore, the amount of Ni in the case of inclusion is set to 3.0% or less. Note that the amount of Ni is preferably 2.0% or less.
- the amount of Ni is preferably 0.05% or more, and more preferably 0.10% or more.
- Mo 0 to 0.50% Mo improves the induction hardenability and has the effect of increasing the base material toughness, so Mo may be included to improve the base material toughness. However, when the Mo content exceeds 0.50%, the machinability is lowered and it is difficult to machine deep holes. Therefore, the amount of Mo in the case of inclusion is set to 0.50% or less. The amount of Mo is preferably 0.40% or less.
- the amount of Mo is preferably 0.05% or more, and more preferably 0.10% or more.
- said Cu, Ni, and Mo can be contained only in any 1 type in them, or 2 or more types of composites.
- the total amount of these elements may be 4.50%, but is preferably 3.20% or less.
- Nb 0 to 0.10%
- Nb has the effect
- Nb also has the effect of improving the strength of steel. However, if the Nb content exceeds 0.10%, the effect is saturated and the cost increases, and the toughness is reduced. For this reason, the amount of Nb in the case of inclusion is set to 0.10% or less. Note that the amount of Nb is preferably 0.08% or less.
- the amount of Nb is preferably 0.010% or more, and more preferably 0.015% or more.
- V 0 to 0.30%
- V combines with C or N in steel to form carbides or carbonitrides and has the effect of refining crystal grains. V also has the effect of improving the strength of the steel. However, if the V content exceeds 0.30%, the effect is saturated and the cost increases, and the toughness is reduced. For this reason, the V amount in the case of inclusion is set to 0.30% or less. Note that the amount of V is preferably 0.25% or less.
- the amount of V is preferably 0.01% or more, and more preferably 0.02% or more.
- said Nb and V can be contained only in any 1 type in them, or 2 types of composite.
- the total amount of these elements may be 0.40%, but is preferably 0.33% or less.
- Ca 0 to 0.005% Ca has the effect
- the amount of Ca is preferably 0.0035% or less.
- the amount of Ca is preferably set to 0.0005% or more.
- Pb 0 to 0.30% Pb, like Ca, has the effect of improving the machinability of steel. For this reason, you may contain Pb as needed. However, if the Pb content exceeds 0.30%, the machinability improving effect is saturated, the hot workability is excessively lowered, and the manufacture becomes difficult. Therefore, the amount of Pb in the case of inclusion is set to 0.30% or less.
- the amount of Pb is desirably 0.05% or more.
- said Ca and Pb can be contained only in any 1 type in them, or 2 types of composite.
- the total amount of these elements is preferably 0.30% or less.
- the chemical composition of the rolled round steel material for a steering rack bar of the present invention is such that the balance is Fe and impurities, P and N in the impurities are P: 0.030% or less and N: 0.008% or less, , 3.4N ⁇ Ti ⁇ 3.4N + 0.02 (1) It satisfies.
- P 0.030% or less
- P is contained as an impurity in steel and causes grain boundary segregation and center segregation, leading to a decrease in base material toughness.
- the content of P is set to 0.030% or less.
- the P content is preferably 0.020% or less.
- N 0.008% or less N is also contained in the steel as an impurity.
- N has a large affinity with B, and when it binds to B in steel to form BN, the effect of strengthening grain boundaries, the effect of improving induction hardenability by including B, and The effect of suppressing the segregation of P and S at the austenite grain boundary during induction hardening cannot be expected.
- the N content is set to 0.008% or less.
- the microstructure of the rolled round steel material of the present invention is composed of ferrite, lamellar pearlite, and cementite, and in the cross section perpendicular to the rolling direction, the average grain size of ferrite in the region from the surface to a half position of the radius is 10 ⁇ m or less.
- the area ratio of pearlite is less than 20%, and the number of spherical cementites of cementite is 4 ⁇ 10 5 pieces / mm 2 or more. Further, the area ratio of lamellar pearlite in the center is 20% or more, and spherical pieces of cementite.
- the number of cementite is less than 4 ⁇ 10 5 pieces / mm 2 , and the average ferrite content in the region from the surface to the half radius position in the cross section passing through the center line of the round steel material and parallel to the rolling direction
- the aspect ratio must be 3 or higher.
- the average particle diameter of the ferrite in the region from the surface to a half position of the radius exceeds 10 ⁇ m in the cross section perpendicular to the rolling direction, the target base material toughness is obtained. It is difficult to obtain. Therefore, the average particle diameter of the ferrite is set to 10 ⁇ m or less.
- the average particle size of the ferrite is preferably 8 ⁇ m or less.
- the average grain size of the ferrite is preferably as small as possible for strengthening by refining crystal grains.
- special processing conditions or equipment are required, which is industrially realized. Difficult to do. Therefore, the lower limit of the average grain size of the ferrite as a size that can be industrially realized is about 1 ⁇ m.
- the average particle diameter of ferrite in the region from the surface to the half position of the radius is, for example, a position 1 mm from the surface of the rolled round steel material and a quarter of the radius from the surface.
- Position hereinafter referred to as “R / 4 position”, where “R” refers to the radius of the rolled round steel, and the same shall apply hereinafter
- R / 2 1/2 position of the radius from the surface
- the area ratio of the lamellar pearlite in the region from the surface to the half position of the radius is 20% or more in the cross section perpendicular to the rolling direction, the toughness of the base material is reduced. . Therefore, the area ratio of the lamellar pearlite is defined as less than 20%.
- the area ratio of the lamellar pearlite is preferably 15% or less, and may be 0%.
- the area ratio of lamellar pearlite in the region from the surface to the half position of the radius is, for example, 1 mm from the surface of the rolled round steel material, R / 4 position, and R / What is necessary is just to obtain
- the number of spherical cementite in the region from the surface to the half position of the radius is less than 4 ⁇ 10 5 / mm 2 .
- the base material toughness is reduced. Therefore, the number of spherical cementite was set to 4 ⁇ 10 5 pieces / mm 2 or more.
- the number of spherical cementite is preferably 5.0 ⁇ 10 5 pieces / mm 2 or more, and preferably 1.0 ⁇ 10 12 pieces / mm 2 or less.
- the number of spherical cementite in the region from the surface to the half position of the radius is, for example, 1 mm from the surface of the rolled round steel, R / 4 position, and R / 2. What is necessary is just to obtain
- the area ratio of the lamellar pearlite at the center is defined as 20% or more.
- the area ratio of the lamellar pearlite is preferably 25% or more, and preferably 80% or less.
- the “center portion” refers to a portion at a distance from the center to 1 ⁇ 4 of the radius.
- the area ratio of the lamellar pearlite at the center is, for example, 3/4 position (hereinafter referred to as “3R / 4 position”) and center from the surface of the rolled round steel material.
- 3R / 4 position 3/4 position
- the area ratios of the two lamellar pearlites may be obtained by arithmetic averaging.
- the number of spherical cementite at the center is 4 ⁇ 10 5 pieces / mm 2 or more, the toughness is increased and the chip disposal is reduced. Cutting resistance increases and machinability decreases. Therefore, the number of spherical cementite was defined as less than 4 ⁇ 10 5 pieces / mm 2 .
- the number of spherical cementite may be 0 piece / mm 2 , but is preferably 1 ⁇ 10 2 pieces / mm 2 or more, and is preferably 3 ⁇ 10 5 pieces / mm 2 or less.
- the number of spherical cementite in the central portion is determined by, for example, obtaining the 3R / 4 position of the rolled round steel material and the number of spherical cementite at two central positions, respectively, What is necessary is just to obtain
- the aspect ratio of the ferrite is set to 3 or more.
- the average aspect ratio of the ferrite is preferably 4 or more, and is preferably 45 or less.
- the average aspect ratio of ferrite is, for example, 3 mm at a position of 1 mm, R / 4 position, and R / 2 position from the surface of the rolled round steel material. What is necessary is just to obtain
- microstructure of the rolled round steel material of the present invention described above can be obtained by, for example, hot rolling and cooling a material to be rolled having the chemical composition already described as follows.
- an all continuous hot rolling method including two or more rolling steps is suitable for producing the rolled round steel material for a steering rack bar of the present invention. For this reason, the following description is based on the rolling by the above-mentioned all continuous hot rolling method (hereinafter, simply referred to as “all continuous hot rolling”).
- the heating temperature is higher than 880 ° C.
- the strain is easily released, and in the cross section perpendicular to the rolling direction, the ferrite average particle diameter, lamellar pearlite area ratio, and the number of spherical cementites in the region from the surface to the half position of the radius
- One or more of the above may be out of the conditions described in the section “2. Microstructure”.
- the heating temperature is lower than 670 ° C., one or more of the lamellar pearlite area ratio and the number of spherical cementites in the center in the cross section described above may deviate from the above-described microstructure condition.
- the heating in the temperature range of 670 to 880 ° C. performed before hot rolling not only the temperature of the material to be rolled (raw material) is raised to a predetermined area but also the temperature in the cross section of the raw material is made uniform. In order to achieve this, heat treatment for a long time may be performed, and in this case, ferrite decarburization may occur on the surface of the material. Therefore, in order to suppress the ferrite decarburization, the heating time in the temperature range is preferably 3 hours or less.
- the surface temperature of the material to be rolled is 500 to 820 ° C.
- the cumulative area reduction in the temperature range of 650 to 820 ° C. is 30% or more
- the area ratio is 35% or more.
- the “surface temperature of the material to be rolled” does not include the surface temperature of the material to be rolled during the intermediate cooling step described later.
- v (m / s) is the rolling material speed (hereinafter referred to as “finishing speed”), “Rd ( %) ”Is the total area reduction rate of all continuous hot rolling, and“ T (° C.) ”is the heating temperature of the material to be rolled, and fn (1) expressed below satisfies 0 or more.
- the “total area reduction ratio” means that when the cross-sectional area before rolling of the material to be rolled in all-continuous hot rolling is A 0 and the cross-sectional area after leaving the final rolling mill is A f , It indicates a value (%) obtained by the equation ⁇ (A 0 ⁇ A f ) / A 0 ⁇ ⁇ 100.
- the surface temperature of the material to be rolled exceeds 820 ° C. during rolling, the strain is easily released, and in the cross section perpendicular to the rolling direction, the ferrite average in the region from the surface to a half position of the radius
- One or more of the particle size, the lamellar pearlite area ratio, and the number of spherical cementites may deviate from the conditions described in the section “2. Microstructure”.
- the surface temperature of the material to be rolled during rolling is preferably 500 to 820 ° C.
- the cumulative reduction in area in the temperature range of 650 to 820 ° C. is less than 30%, the ferrite average particle diameter and lamellar pearlite area ratio in the region from the surface to the half position of the radius in the cross section perpendicular to the rolling direction. And one or more of the numbers of spherical cementite may deviate from the microstructure conditions described above.
- the upper limit of the cumulative area reduction at 650 to 820 ° C. is about 99.5% in order to prevent a significant increase in the production line.
- the region from the surface in the cross section parallel to the rolling direction through the center line of the material to be rolled to the half position of the radius In some cases, one or more of the average aspect ratio of the ferrite and the number of spherical cementites in the region from the surface to the half position of the radius in the cross section perpendicular to the rolling direction deviate from the above-described microstructure condition.
- the upper limit of the cumulative area reduction at 500 ° C. or more and less than 650 ° C. is about 80% in order to prevent a significant increase in the production line.
- [2] is an expression obtained empirically in order to make the microstructure of the central portion in the cross section perpendicular to the rolling direction as described in the section “2. Microstructure”.
- fn (1) is less than 0, in the cross section perpendicular to the rolling direction, one or more of the area ratio of the lamellar pearlite at the center and the number of spherical cementites may deviate from the microstructure conditions described above.
- intermediate cooling such as water cooling may be performed in an intermediate step.
- the surface temperature of the material to be rolled may temporarily fall below 500 ° C. during the intermediate cooling step.
- the next rolling step is started after reheating to a temperature of 500 ° C or higher by sensible heat inside the material to be rolled, There may be no influence that the surface temperature of the rolled material temporarily falls below 500 ° C.
- the untransformed austenite of the material to be rolled is transformed into a hard phase such as martensite or bainite, the microstructure defined in the present invention may not be obtained.
- the intermediate cooling step is such that the time ⁇ t until the reheat to a temperature of 500 ° C. or higher after the surface temperature of the material to be rolled temporarily falls below 500 ° C. is 10 seconds or less. It is desirable. Furthermore, when aiming at more stable production by all-continuous hot rolling, an intermediate cooling step in which ⁇ t is 8 seconds or less is preferable.
- the temperature range up to 500 ° C. is finally cooled under the condition that the surface cooling rate is 0.5 to 200 ° C./s. Is good.
- the surface cooling rate in the above temperature range is less than 0.5 ° C./s after completion of all-continuous hot rolling, in the cross section perpendicular to the rolling direction, the area ratio of lamellar pearlite in the center and the number of spherical cementite One or more may deviate from the conditions described in the section “2. Microstructure”.
- the cooling rate of the surface exceeds 200 ° C./s, untransformed austenite is hard like martensite or bainite. It may transform into a phase.
- Example 1 Square billets (160 mm square and 10 m long) made of steels AZ having the chemical composition shown in Table 1 were prepared.
- the square billet was rolled into a steel bar having a diameter of 34 mm by a fully continuous hot rolling line equipped with a cooling facility under the conditions shown as test numbers 1 to 34 in Table 2. Specifically, after processing to a diameter of 60 mm by a rough rolling mill row and processing to a diameter of 50 mm by an intermediate rolling mill row, processing to a steel bar having a diameter of 34 mm by a finishing rolling mill row, the “total area reduction ratio: Rd” is 96.4% hot rolling was performed.
- ⁇ Rough rolling mill row Consists of 8 rolling mills
- Intermediate rolling mill row Consists of four rolling mills
- -Finish rolling mill row Consists of four rolling mills
- Cooling zone Between the eighth rolling mill in the rough rolling mill row and the first rolling mill in the intermediate rolling mill row, and one in the fourth rolling mill and the finishing rolling mill row in the intermediate rolling mill row Installed between eye rolling mills.
- the surface temperature of the material to be rolled during rolling and the surface temperature of the material to be rolled in the cooling process after completion of all-continuous hot rolling are measured using a radiation thermometer, and after the intermediate cooling step, The time ⁇ t ′ until the start of the subsequent rolling process was measured.
- the cooling rate is set by cooling in the air or changing the cooling medium such as air cooling. And finally cooled to 500 ° C. The subsequent cooling was allowed to cool in the atmosphere.
- the rough rolling mill row, the intermediate rolling mill row, and the finishing rolling mill row are denoted as “rough row”, “intermediate row”, and “finishing row”, respectively.
- “input temperature” and “out temperature” in the rough column, intermediate column, and finish column shown in Table 2 are respectively applied to the rough column, intermediate column, and finish column measured using a radiation thermometer. Is the surface temperature of the material to be rolled at the time immediately before entering the material to be rolled and the surface temperature of the material to be rolled as measured above using a radiation thermometer. It calculated
- the time ⁇ t ′ from the intermediate cooling step to the start of the subsequent rolling step was 8 seconds or less in all cases.
- microstructure, tensile properties, impact properties and machinability of each steel bar obtained as described above were investigated by the following methods.
- test piece having a length of 20 mm is cut out from each steel bar having a diameter of 34 mm, and the cross section perpendicular to the rolling direction of these test pieces and the cross section parallel to the rolling direction through the center line are each a test surface. Embedded and mirror polished.
- the microstructure was developed by corroding with 3% nitric alcohol (nitral liquid) and observed with a scanning electron microscope (hereinafter referred to as “SEM”). At the same time, the average particle diameter of ferrite and the area ratio of lamellar pearlite were investigated.
- a total of 12 structures were observed at a magnification of 2000 times in a 90 ° increment in the circumferential direction with a SEM in a total of 12 visual fields for a total of 12 visual fields, and the phases constituting the microstructure were identified.
- the average particle diameter of ferrite and the area ratio of lamellar pearlite were determined using image analysis software using the photographed image.
- the magnification is 5000 times
- the 3R / 4 position is 4 fields in 90 ° increments in the circumferential direction for the 3R / 4 position.
- a total of 5 visual fields were observed, and the number of spherical cementites per 1 mm 2 area was calculated by using image analysis software.
- the cross section passing through the center line and parallel to the rolling direction was further subjected to electrolytic polishing after mirror polishing and observed by an electron beam backscattering pattern method (hereinafter referred to as “EBSD”).
- EBSD electron beam backscattering pattern method
- the average aspect ratio of the ferrite was determined by measuring the orientation of the ferrite and analyzing the image with an orientation difference of 15 ° or more as the grain boundary.
- tensile properties For the tensile properties, a 14A test piece (however, the diameter of the parallel part: 4 mm) specified in JIS Z 2241 (2011) was taken so that the R / 4 position of each steel bar having a diameter of 34 mm was the central axis of the test piece. Then, a tensile test was performed at room temperature with a gauge distance of 20 mm, and tensile strength (MPa) was obtained.
- the impact characteristics of the V-notch Charpy impact test specimen described above are such that the direction of the notch is the surface and the R / 4 position of each steel bar having a diameter of 34 mm is exactly the notch bottom position.
- the sample was collected and subjected to a Charpy impact test at 25 ° C. to determine an impact value (J / cm 2 ).
- the machinability was determined by cutting each steel bar with a diameter of 34 mm to a length of 170 mm and then using a gun drill with a diameter of 8.0 mm to deepen in the rolling direction on the basis of the center of the cross section perpendicular to the rolling direction under the following conditions. Cutting resistance was evaluated by measuring the torque when deep hole machining was performed up to 150 mm. ⁇ Rotation speed: 2300 rpm Feed: 0.05 mm / rev, and Feed hydraulic pressure: 5 MPa.
- the target of the base material toughness is an impact value of 160 J / cm 2 or more.
- the target of machinability was that the torque, which is an index of cutting resistance, was 300 N ⁇ cm or less.
- Table 3 shows the results of each of the above surveys.
- cross section perpendicular to the rolling direction and “cross section passing through the center line of the round steel material and parallel to the rolling direction” are denoted as “cross section” and “longitudinal section”, respectively.
- ⁇ indicates that both the impact characteristics and machinability targets are satisfied, while “ ⁇ ” indicates that at least one of the above targets has been achieved. It means not.
- the Si content of the steel R used is as high as 1.25%, which exceeds the value specified in the present invention.
- the torque when deep drilling is performed with a gun drill is as high as 345 N ⁇ cm.
- the Mn content of the steel S used is as high as 2.31%, which exceeds the value specified in the present invention. For this reason, the torque when drilling deep holes with a gun drill is as high as 325 N ⁇ cm.
- the C content of the steel T used is as high as 0.62%, which exceeds the value specified in the present invention.
- the V-notch Charpy impact value is as low as 105 J / cm 2 .
- the Cr content of the steel U used is as high as 2.41%, which exceeds the value specified in the present invention. For this reason, the torque when deep drilling is performed with a gun drill is as high as 340 N ⁇ cm.
- the steel V used does not contain B, deviates from the chemical composition defined in the present invention, and the average grain of ferrite in the region from the surface to the half position of the radius in the cross section perpendicular to the rolling direction.
- the diameter, the area ratio of lamellar pearlite, and the number of spherical cementite were also 11.8 ⁇ m, 22.1%, and 2.1 ⁇ 10 5 pieces / mm 2 , respectively, which were out of the ranges defined in the present invention.
- the V-notch Charpy impact value is as low as 110 J / cm 2 .
- the N content of the steel W used is as high as 0.012%, which exceeds the value specified in the present invention, and is a region from the surface in a cross section perpendicular to the rolling direction to a position at half the radius.
- the average particle diameter of ferrite and the number of spherical cementites are also 11.2 ⁇ m and 3.8 ⁇ 10 5 pieces / mm 2 , respectively, which are out of the ranges defined in the present invention. For this reason, the V-notch Charpy impact value is as low as 115 J / cm 2 .
- the Ti content of the used steel X is as high as 0.057%, which exceeds the value specified in the present invention. For this reason, the V-notch Charpy impact value is as low as 145 J / cm 2 .
- the Ti content of the steel Y used is lower than [3.4N], which is the lower limit of the formula (1), deviating from the conditions defined in the present invention, and from the surface in the cross section perpendicular to the rolling direction.
- the average particle diameter of ferrite in the region up to half the radius, the area ratio of lamellar pearlite, and the number of spherical cementites were 12.1 ⁇ m, 20.2%, and 2.9 ⁇ 10 5 pieces / mm 2 , respectively. It is outside the range defined by the present invention. For this reason, the V-notch Charpy impact value is as low as 110 J / cm 2 .
- the Ti content of the steel Z used is higher than [3.4N + 0.02], which is the upper limit of the formula (1), and deviates from the conditions specified in the present invention. For this reason, the V-notch Charpy impact value is as low as 130 J / cm 2 .
- test numbers 27 to 31 Although the chemical composition of the steel B used satisfies the conditions specified in the present invention, the microstructure is outside the range specified in the present invention. For this reason, one of the impact characteristics and the machinability has not reached the target.
- the average particle diameter of ferrite, the area ratio of lamellar pearlite, and the number of spherical cementite in the region from the surface to the half position of the radius in the cross section perpendicular to the rolling direction are 14 respectively.
- 0.1 ⁇ m, 32.8%, and 4.0 ⁇ 10 4 pieces / mm 2 which are outside the range defined in the present invention.
- the V-notch Charpy impact value is as low as 105 J / cm 2 .
- the average aspect ratio of ferrite in the region from the surface to the half position of the radius in the cross section passing through the center line and parallel to the rolling direction is 1.9, which is out of the range specified in the present invention. Yes.
- the V-notch Charpy impact value is as low as 115 J / cm 2 .
- the number of spherical cementite in the region from the surface to the half position of the radius in the cross section perpendicular to the rolling direction is 3.3 ⁇ 10 5 pieces / mm 2, and the rolling direction passes through the center line.
- the average aspect ratio of the ferrite in the region from the surface to the half position of the radius in the cross section parallel to is 1.6, which is outside the range defined in the present invention. For this reason, the V-notch Charpy impact value is as low as 110 J / cm 2 .
- test number 31 in the cross section perpendicular to the rolling direction, the area ratio of lamellar pearlite at the center and the number of spherical cementites were 17.2% and 6.1 ⁇ 10 5 pieces / mm 2 , respectively. It is out of the specified range. For this reason, the torque when deep drilling is performed with a gun drill is as high as 335 N ⁇ cm.
- the average aspect ratio of the ferrite in the region from the surface to the half position of the radius in the cross section passing through the center line and parallel to the rolling direction is defined by the present invention. You are out of range. For this reason, the V-notch Charpy impact value is as low as 105 J / cm 2 .
- the average aspect ratio of the ferrite in the region from the surface to the half position of the radius in the cross section passing through the center line and parallel to the rolling direction is 2.6, which is out of the range specified in the present invention. Yes. For this reason, the V-notch Charpy impact value is as low as 115 J / cm 2 .
- rolling is performed at 650 to 820 ° C. in the rough and finish rows.
- the cumulative reduction in area is [(area reduction in the coarse) + (100% -Area reduction ratio just before entering the finishing row) x Area reduction rate of the finishing row].
- Example 2 The rack bar was simulated using the steel bars of 34 mm in diameter of test number 2, test number 11, test number 13, test number 16, test number 20, test number 28, test number 32, and test number 34 obtained in Example 1. A test piece was prepared.
- a steel bar having a diameter of 34 mm was shot peened, the surface scale was removed, and then a drawing process was performed to a diameter of 31 mm with a lubricating oil applied to the surface.
- induction hardening was carried out by variously adjusting the conditions of induction hardening so that the hardened layer depth (depth from the surface where the Vickers hardness is 450) at the tooth bottom corresponding portion of the rack bar was 1 mm. Thereafter, for the purpose of preventing cracking after induction hardening, a tempering treatment was performed at 180 ° C. for 2 hours.
- the fractured surface was photographed in appearance, and by image analysis processing, the area ratio of cracks that developed during the bending test was obtained for the entire section, Progress resistance was evaluated.
- the damage prevention characteristic aimed at the area ratio of the crack which progressed at the time of the said bending test being 30% or less.
- Table 4 shows the results of each of the above surveys.
- “ ⁇ ” marks in the “Evaluation” column indicate that the area ratio of cracks developed during the bending test is 30% or less, which satisfies the target, while “ ⁇ ” marks indicate the above target. Indicates that you are not satisfied.
- the rolled round steel material for the steering rack bar of the present invention does not necessarily contain expensive V, and Charpy impact using a V-notch Charpy impact test piece in the rolled round steel material state without any tempering treatment. Since it has a high base metal toughness with an impact value at a test temperature of 25 ° C. of 160 J / cm 2 or more in the test and a good machinability for machining a deep hole in the center, It is suitable for use as a material.
- the steering rack bar of the present invention can be obtained by using the rolled round steel material for steering rack bar as it is not tempered.
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Abstract
Description
ミクロ組織がフェライト、ラメラーパーライトおよびセメンタイトからなり、圧延方向と垂直な断面において、表面から半径の1/2位置までの領域のフェライトの平均粒径が10μm以下、ラメラーパーライトの面積率が20%未満およびセメンタイトのうちの球状セメンタイトの個数が4×105個/mm2以上であり、さらに、中心部のラメラーパーライトの面積率が20%以上およびセメンタイトのうちの球状セメンタイトの個数が4×105個/mm2未満であり、しかも、その丸鋼材の中心線を通って圧延方向と平行な断面において、表面から半径の1/2位置までの領域のフェライトの平均アスペクト比が3以上である、ステアリングラックバー用圧延丸鋼材。
3.4N≦Ti≦3.4N+0.02・・・(1)
上記の(1)式中の元素記号は、その元素の質量%での含有量を意味する。
C:0.38~0.55%
Cは、鋼の強度、高周波焼入れ性および高周波焼入れで形成された硬化層の強度を向上させる作用を有する。しかしながら、その含有量が0.38%未満では、前記作用による所望の効果が得られない。一方、Cの含有量が0.55%を超えると、母材靱性が低下する。したがって、Cの含有量を0.38~0.55%とした。なお、前記の効果を安定して得るために、Cの含有量は、0.40%以上とすることが好ましい。また、Cの含有量は、0.51%以下とすることが好ましい。
Siは、脱酸元素であり、さらに、固溶強化によってフェライトの強度を向上させる元素である。しかしながら、Siの含有量が1.0%を超える場合には、被削性が低下して、深穴を加工することが困難になる。したがって、Siの含有量を1.0%以下とした。Siの含有量は、0.8%以下とすることが好ましい。
Mnは、Sと結合してMnSを形成し、被削性、なかでも深穴を加工する際の切屑処理性を高めることで切削抵抗を低くする作用を有し、さらに延伸したMnSが亀裂の進展を抑制して靱性を高める効果を有する。また、Mnは、高周波焼入れ性を向上させるのに有効な元素であるとともに、固溶強化によってフェライトの強度を向上させる元素でもある。しかしながら、Mnの含有量が0.20%未満の場合、前記作用による所望の効果が得られない。一方、2.0%を超えてMnを含有させると、被削性が低下して、深穴を加工することが困難になる。したがって、Mnの含有量を0.20~2.0%とした。なお、合金コストを低く抑えたうえで前記の効果を安定して得るために、Mnの含有量は、0.40%以上とすることが好ましく、また、1.50%以下とすることが好ましい。
Sは、本発明において重要な元素である。Sは、Mnと結合してMnSを形成し、被削性、なかでも深穴を加工する際の切屑処理性を高めることで切削抵抗を低くする作用を有し、さらに延伸したMnSが亀裂の進展を抑制して靱性を高める効果を有する。しかしながら、Sの含有量が0.005%未満では、こうした効果が得られない。一方、Sの含有量が多くなって、MnSを多く形成しすぎると、逆に靱性を低下させる。したがって、Sの含有量を0.005~0.10%とした。なお、Sの含有量は、0.010%以上とすることが好ましく、0.015%以上とすればより好ましい。また、Sの含有量は、0.08%以下とすることが好ましい。
Crは、高周波焼入れ性を向上させるのに有効な元素であるとともに、固溶強化によってフェライトの強度を向上させる元素であるため、0.01%以上含有させる必要がある。しかしながら、Crの含有量が2.0%を超えると、被削性が低下して、深穴を加工することが困難になる。したがって、Crの含有量を0.01~2.0%とした。なお、Crの含有量は、0.05%以上とすることが好ましく、0.10%以上とすればより好ましい。また、Crの含有量は、1.8%以下とすることが好ましい。
Alは、脱酸作用を有する。しかしながら、Alの含有量が0.003%未満の場合、前記作用による所望の効果が得られない。一方、Alの含有量が0.10%を超える場合には、高周波焼入れ性の低下が著しくなり、さらに、母材靱性の劣化も招く。したがって、Alの含有量を0.003~0.10%とした。なお、Alの含有量は、0.08%以下とすることが好ましい。一方、Alの脱酸効果を安定して得るためには、Alの含有量は、0.005%以上とすることが好ましく、0.010%以上とすれば一層好ましい。
Bは、粒界を強化することにより、高温時のひずみの解放を抑え、かつ、高周波焼入れ性を向上させる作用、さらには高周波焼入れ時のオーステナイト粒界におけるPおよびSの偏析を抑制する作用を有し、その結果として、靱性が一層高まる。上記の効果はBの含有量が0.0005%以上で顕著である。しかしながら、0.0030%を超えてBを含有させても前記の効果は飽和し、コストが嵩むばかりである。したがって、Bの含有量を0.0005~0.0030%とした。Bの含有量は0.0010%以上とすることが好ましく、また、0.0020%以下とすることが好ましい。
Tiは、鋼中の不純物元素のNと優先的に結合し、Nを固定することで、BNの形成を抑制し、Bを固溶Bとして存在させる。そのため、Tiは、上記したBの、粒界を強化する効果、高周波焼入れ性を向上させる効果、ならびに高周波焼入れ時のオーステナイト粒界におけるPおよびSの偏析を抑制する効果を確保するのに有効な元素である。しかしながら、Tiの含有量が0.047%を超えると、母材靱性の著しい低下をきたす。このため、Tiの含有量を0.047%以下とした。
Cuは、高周波焼入れ性を向上させ、母材靱性を高める作用を有するので、母材靱性向上のためにCuを含有させてもよい。しかしながら、Cuの含有量が1.0%を超えると、被削性が低下して、深穴を加工することが困難になる。したがって、含有させる場合のCuの量を1.0%以下とした。なお、Cuの量は、0.80%以下とすることが好ましい。
Niは、高周波焼入れ性を向上させ、母材靱性を高める作用を有するので、母材靱性向上のためにNiを含有させてもよい。しかしながら、Niの含有量が3.0%を超えると、被削性が低下して、深穴を加工することが困難になる。したがって、含有させる場合のNiの量を3.0%以下とした。なお、Niの量は、2.0%以下とすることが好ましい。
Moは、高周波焼入れ性を向上させ、母材靱性を高める作用を有するので、母材靱性向上のためにMoを含有させもよい。しかしながら、Moの含有量が0.50%を超えた場合、被削性が低下して、深穴を加工することが困難になる。したがって、含有させる場合のMoの量を0.50%以下とした。なお、Moの量は、0.40%以下とすることが好ましい。
Nbは、鋼中のCあるいはNと結合して炭化物あるいは炭窒化物を形成し、結晶粒を微細化する作用を有する。また、Nbには、鋼の強度を向上させる作用もある。しかしながら、Nbの含有量が0.10%を超えると、その効果が飽和してコストが嵩むのみならず、靱性の低下を招く。このため、含有させる場合のNbの量を0.10%以下とした。なお、Nbの量は、0.08%以下とすることが好ましい。
Vは、鋼中のCあるいはNと結合して炭化物あるいは炭窒化物を形成し、結晶粒を微細化する作用を有する。また、Vには、鋼の強度を向上させる作用もある。しかしながら、Vの含有量が0.30%を超えると、その効果が飽和してコストが嵩むのみならず、靱性の低下を招く。このため、含有させる場合のVの量を0.30%以下とした。なお、Vの量は、0.25%以下とすることが好ましい。
Caは、鋼の被削性を向上させる作用を有する。このため、必要に応じてCaを含有させてもよい。しかしながら、Caの含有量が0.005%を超えると、熱間加工性の低下をきたし、製造性が低下してしまう。したがって、含有させる場合のCaの量を0.005%以下とした。Caの量は、0.0035%以下とすることが好ましい。
PbもCaと同様に、鋼の被削性を向上させる作用を有する。このため、必要に応じてPbを含有させてもよい。しかしながら、Pbの含有量が0.30%を超えると、前記の被削性向上効果は飽和し、熱間加工性が過度に低下し製造が困難となる。したがって、含有させる場合のPbの量を0.30%以下とした。
3.4N≦Ti≦3.4N+0.02・・・(1)
を満たすものである。
Pは、鋼中に不純物として含有され、粒界偏析および中心偏析を起こし、母材靱性の低下を招き、特に、その含有量が0.030%を超えると、母材靱性の低下が著しくなる。したがって、Pの含有量を、0.030%以下とした。なお、Pの含有量は、0.020%以下にすることが好ましい。
Nも、鋼中に不純物として含有される。Nは、Bとの親和力が大きく、鋼中のBと結合してBNを形成した場合には、Bを含有させたことによる、粒界を強化する効果、高周波焼入れ性を向上させる効果、ならびに高周波焼入れ時のオーステナイト粒界におけるPおよびSの偏析を抑制する効果が期待できない。特に、Nの含有量が多くなって0.008%を超えると、上記のBを含有させたことによる効果が得られない。したがって、Nの含有量を0.008%以下とした。
本発明に係るステアリングラックバー用圧延丸鋼材は、
3.4N≦Ti≦3.4N+0.02・・・(1)
の式を満たす化学組成でなければならない。既に述べたとおり、上記の(1)式中の元素記号は、その元素の質量%での含有量を意味する。
本発明の圧延丸鋼材のミクロ組織は、フェライト、ラメラーパーライトおよびセメンタイトからなり、圧延方向と垂直な断面において、表面から半径の1/2位置までの領域のフェライトの平均粒径が10μm以下、ラメラーパーライトの面積率が20%未満およびセメンタイトのうちの球状セメンタイトの個数が4×105個/mm2以上であり、さらに、中心部のラメラーパーライトの面積率が20%以上およびセメンタイトのうちの球状セメンタイトの個数が4×105個/mm2未満であり、しかも、その丸鋼材の中心線を通って圧延方向と平行な断面において、表面から半径の1/2位置までの領域のフェライトの平均アスペクト比が3以上でなければならない。
fn(1)=v・Rd/100-(1000-T)/100
ただし、「総減面率」とは、全連続式熱間圧延における被圧延材の圧延前の断面積をA0、最終の圧延機を出た後の断面積をAfとした場合に、{(A0-Af)/A0}×100の式で求められる値(%)を指す。
表1に示す化学組成を有する鋼A~Zからなる角ビレット(160mm角で長さが10m)を準備した。
・中間圧延機列:4台の圧延機で構成、
・仕上げ圧延機列:4台の圧延機で構成、
・冷却帯:粗圧延機列の8台目の圧延機と中間圧延機列の1台目の圧延機の間および、中間圧延機列の4台目の圧延機と仕上げ圧延機列の1台目の圧延機の間に設置。
・回転数:2300rpm、
・送り:0.05mm/rev、および
・給油圧:5MPa。
実施例1で得た試験番号2、試験番号11、試験番号13、試験番号16、試験番号20、試験番号28、試験番号32および試験番号34の直径34mmの棒鋼を用いて、ラックバーを模擬した試験片を作製した。
Claims (5)
- 質量%で、
C:0.38~0.55%、
Si:1.0%以下、
Mn:0.20~2.0%、
S:0.005~0.10%、
Cr:0.01~2.0%、
Al:0.003~0.10%、
B:0.0005~0.0030%、
Ti:0.047%以下、
Cu:0~1.0%、
Ni:0~3.0%、
Mo:0~0.50%、
Nb:0~0.10%、
V:0~0.30%、
Ca:0~0.005%、
Pb:0~0.30%、
残部がFeおよび不純物であり、
不純物中のPおよびNが、
P:0.030%以下および
N:0.008%以下であり、
さらに、下記の(1)式を満たす化学組成を有するステアリングラックバー用圧延丸鋼材であって、
ミクロ組織がフェライト、ラメラーパーライトおよびセメンタイトからなり、
圧延方向と垂直な断面において、表面から半径の1/2位置までの領域のフェライトの平均粒径が10μm以下、ラメラーパーライトの面積率が20%未満およびセメンタイトのうちの球状セメンタイトの個数が4×105個/mm2以上であり、さらに、中心部のラメラーパーライトの面積率が20%以上およびセメンタイトのうちの球状セメンタイトの個数が4×105個/mm2未満であり、しかも、
その丸鋼材の中心線を通って圧延方向と平行な断面において、表面から半径の1/2位置までの領域のフェライトの平均アスペクト比が3以上である、ステアリングラックバー用圧延丸鋼材。
3.4N≦Ti≦3.4N+0.02・・・(1)
上記の(1)式中の元素記号は、その元素の質量%での含有量を意味する。 - 質量%で、Cu:0.05~1.0%、Ni:0.05~3.0%およびMo:0.05~0.50%から選択される1種以上を含有する、請求項1に記載のステアリングラックバー用圧延丸鋼材。
- 質量%で、Nb:0.010~0.10%およびV:0.01~0.30%から選択される1種以上を含有する、請求項1に記載のステアリングラックバー用圧延丸鋼材。
- 質量%で、Ca:0.0005~0.005%およびPb:0.05~0.30%から選択される1種以上を含有する、請求項1に記載のステアリングラックバー用圧延丸鋼材。
- 請求項1から4までのいずれかに記載のステアリングラックバー用圧延丸鋼材を非調質のまま用いる、ステアリングラックバー。
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CN106048426A (zh) * | 2015-04-14 | 2016-10-26 | 现代自动车株式会社 | 用于热应变降低的转向齿条的碳钢组合物及其制造方法 |
JP2019502815A (ja) * | 2015-12-17 | 2019-01-31 | ポスコPosco | 強度及び冷間加工性に優れた非調質線材及びその製造方法 |
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CN106048426B (zh) * | 2015-04-14 | 2020-03-27 | 现代自动车株式会社 | 用于热应变降低的转向齿条的碳钢组合物及其制造方法 |
JP2019502815A (ja) * | 2015-12-17 | 2019-01-31 | ポスコPosco | 強度及び冷間加工性に優れた非調質線材及びその製造方法 |
CN114774774A (zh) * | 2022-03-15 | 2022-07-22 | 江阴兴澄特种钢铁有限公司 | 一种大直径低偏析油缸活塞杆用圆钢及其制造方法 |
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CN105492644B (zh) | 2017-04-12 |
EP3040435A4 (en) | 2016-10-05 |
KR20160045831A (ko) | 2016-04-27 |
JP5987992B2 (ja) | 2016-09-07 |
EP3040435B1 (en) | 2017-11-01 |
PL3040435T3 (pl) | 2018-04-30 |
JPWO2015029553A1 (ja) | 2017-03-02 |
US20160186300A1 (en) | 2016-06-30 |
EP3040435B9 (en) | 2018-03-07 |
KR101773729B1 (ko) | 2017-08-31 |
US9976206B2 (en) | 2018-05-22 |
CN105492644A (zh) | 2016-04-13 |
EP3040435A1 (en) | 2016-07-06 |
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