JP4593510B2 - High strength bearing joint parts excellent in delayed fracture resistance, manufacturing method thereof, and steel for high strength bearing joint parts - Google Patents

Description

  The present invention relates to a joining part such as a bolt and a pin used for joining parts of civil engineering, architecture, automobiles, various industrial machines and the like, a manufacturing method thereof, and a steel material as a material of the joining part.

  Conventional joint parts, for example, joints by bolts, are mainly friction joints and tensile joints in which tensile stress is applied to the bolts. In this case, if a high-strength bolt with a tensile strength exceeding 1200 MPa is used for strengthening the joint with bolts or making the joint compact, the possibility of delayed fracture increases.

  On the other hand, when the number of bolts is determined in consideration of the strength against a large earthquake in the design of a steel structure, strengthening of the strength of the joint against tensile stress and shear stress is required. In response to this problem, some of the present inventors use a high-strength joint component having a tensile strength of 1700 to 2600 MPa in a joint portion that is a support joint or a combination of a support joint and a friction joint. A method for reducing the size and reducing the size of the joint has been proposed (see, for example, Patent Documents 1 and 2).

  According to these methods, it is possible to ensure sufficient strength of the joint without constantly introducing high tension to the high-strength joint parts, and prevent delayed fracture of the high-strength joint parts due to tensile stress. can do. Further, when the joining form is a support bearing, delayed fracture with respect to the tensile stress caused by the introduced tension can be eliminated. Furthermore, in order to increase the durability of the joint, it is desirable to consider delayed fracture due to shear stress when high shear stress is applied to the bolt.

  So far, as techniques for improving delayed fracture characteristics under the condition where tension is introduced in the tensile direction, for example, Patent Documents 3 to 6 include alloy elements, carbides precipitated during heat treatment, and aspects of prior austenite grains. A technique for improving delayed fracture resistance focusing on the ratio is disclosed. However, a technique for improving delayed fracture resistance under shear stress loading conditions has not been clarified.

Japanese Patent Application No. 2005-184699 Japanese Patent Application No. 2005-271859 Japanese Patent Laid-Open No. 7-70695 Japanese Patent Laid-Open No. 11-236617 JP 2001-32044 A JP 2002-97551 A

  The present invention provides a bearing member having excellent delayed fracture resistance under shear stress loading conditions, a method for manufacturing the bearing member, and a steel material as a material for the bearing member.

  In order to improve the delayed fracture resistance under shear stress loading conditions, the present inventors are effective to refine Fe carbide by adding an appropriate amount of Si and Al, and (ii) It has been found that to secure toughness, it is effective to refine the prior austenite grains, that is, to increase the grain number of the prior austenite.

  This invention is made | formed based on such knowledge, The place made into the summary is as follows.

(1) By mass%, C: 0.5 to 0.8%, Mn: 0.1 to 2%, Cr: 0.1 to 1.5%, Si: 0.05 to 3%, Al: 0.01 to 1% of both are contained so as to satisfy (Si + 1.3 × Al): 0.08 to 3.5%, the balance is made of Fe and inevitable impurities, and the metal structure has an area ratio. 90% or more of tempered martensite and 7% or less of retained austenite , the tempered martensite has Fe carbide having a particle size of 50 nm or less, and the crystal grain size of the prior austenite is JIS G 0551 grain size number 6 or more Ah is, the tensile strength of high-strength bearing capacity bonding component which is excellent in delayed fracture resistance, characterized in der Rukoto least 1800 MPa.

( 2 ) The high strength bearing pressure excellent in delayed fracture resistance according to (1) above, wherein the high strength bearing joint part has a shear delay fracture limit diffusible hydrogen content of 0.4 ppm or more. Joined parts.

( 3 ) In the high-strength bearing member, the energy absorbed by a Charpy impact test using a U-notch 5 mm sub-size test piece having a notch depth of 2 mm according to JIS Z 2242 is 10 J or more (1 ) Or high strength bearing joint parts excellent in delayed fracture resistance as described in (2) .

( 4 ) In the high-strength bearing member, the initial hydrogen content is less than 0.4 ppm, and the high resistance to delayed fracture resistance according to any one of (1) to ( 3 ) above Strength bearing parts.

( 5 ) In the high-strength bearing member, the mass content is further limited to P: 0.015% or less and S: 0.01% or less, in the above (1) to ( 4 ) High-strength bearing parts with excellent delayed fracture resistance as described in any of the above.

( 6 ) In the high-strength bearing member, in addition, by mass%, Mo: 0.05-2%, W: 0.05-1%, B: 0.0001-0.005% or The high strength bearing joint having excellent delayed fracture resistance according to any one of the above (1) to ( 5 ), comprising two or more kinds.

( 7 ) In the high-strength bearing member, the mass% is V: 0.05 to 1%, Ti: 0.001 to 0.05%, Nb: 0.001 to 0.05%. The high strength bearing joint having excellent delayed fracture resistance according to any one of the above (1) to ( 6 ), comprising one or more kinds.

( 8 ) A material for manufacturing a high-strength bearing member having excellent delayed fracture resistance according to any one of (1) to ( 4 ) above by molding and heat treatment , %, C: 0.5-0.8%, Mn: 0.1-2%, Cr: 0.1-1.5%, Si: 0.05-3%, Al: 0. High strength bearing with excellent delayed fracture resistance including both 01 to 1% so as to satisfy (Si + 1.3 × Al): 0.08 to 3.5%, the balance being Fe and inevitable impurities Steel material for joining parts.

( 9 ) A material for producing a high-strength bearing member having excellent delayed fracture resistance as described in ( 5 ) above by molding and heat-treating , and further in mass%, P: The steel material for high-strength bearing members with excellent delayed fracture resistance according to ( 8 ) above, which is limited to 0.015% or less and S: 0.01% or less.

( 10 ) A material for producing a high-strength bearing member having excellent delayed fracture resistance as described in ( 6 ) above by molding and heat-treating , and further, in mass%, Mo: ( 8 ) or ( 9 ) above, characterized by containing one or more of 0.05-2%, W: 0.05-1%, B: 0.0001-0.005% Steel material for high strength bearing parts with excellent delayed fracture resistance as described.

( 11 ) A material for producing a high-strength bearing member having excellent delayed fracture resistance as described in ( 7 ) above by molding and heat-treating , and further in mass%, V: The above ( 8 ) to ( 10 ) characterized by containing one or more of 0.05 to 1%, Ti: 0.001 to 0.05%, Nb: 0.001 to 0.05%. The steel material for high-strength bearing parts with excellent delayed fracture resistance as described in any of the above.

( 12 ) A method for producing a high-strength bearing member having excellent delayed fracture resistance according to any one of (1) to ( 7 ), which is described in any one of ( 8 ) to ( 11 ) above After the steel was molded and heated to 850 to 1000 ° C. and subjected to quenching treatment, the heating rate was set to 10 ° C./s or more, the tempering temperature T [° C.] was set to the range of 200 to 450 ° C., and tempered. A method for producing a high-strength bearing member, characterized in that the tempering treatment is performed with the time t [s] in the range of 1 to 7200 s and the tempering parameter P defined by the following formula (1) as 6000 to 12000.
P = (T + 273) {log (t / 3600) + 21.3-5.8C
-(Si + 1.3Al)} (1)
Here, C, Si, and Al are component contents [% by mass].

  ADVANTAGE OF THE INVENTION According to this invention, the high strength bearing joint component excellent in the delayed fracture resistance with respect to a shear stress, its manufacturing method, and the steel for high strength bearing joint components can be provided, and industrial contribution is remarkable. .

  The present invention relates to a support joint, a manufacturing method thereof, and a joining component used when constructing a steel structure by bearing joint, and if necessary, a combination of one or both of friction joining and tensile joining. This is a steel material.

  As shown in FIG. 3A, friction bonding is a bonding method in which a joint member, for example, a joint member is tightened with a bolt, and stress is transmitted by friction force generated between the members. As shown in FIG. 3 (b), this is a joining method in which stress is transmitted by shearing the shaft portion and supporting pressure of the member.

  Friction welding and bearing welding are similar in appearance in that the stress transmitted at the joint is in the direction perpendicular to the bolt axis, but the stress transmission forms are completely different. Another joining type. In addition, tensile joining is a joining method that transmits stress in the axial direction of a joined part, for example, a bolt, such as a joined part of a flanged steel pipe shown in FIG. 4, and between members obtained by tightening the bolt. The stress is transmitted using the compression force.

  The inventors of the present invention have proposed that the critical diffusible hydrogen amount at which delayed fracture does not occur under the shear stress applied to the joint component of the bearing joint, that is, the steel structure and precipitates that affect the shear delayed fracture critical diffusible hydrogen amount. The impact of.

  First, hydrogen sampled from steel materials having various strengths produced by quenching and tempering were occluded by electrolytic hydrogen charging and cadmium plating was performed to prevent hydrogen release during the test. After the cadmium plating, a shear delayed fracture test is performed using the test apparatus shown in FIG. 1, and a shear stress of 90% of the shear tensile strength is applied. As shown in FIG. The amount of diffusible hydrogen was determined.

  The jigs 1 and 2 shown in FIG. 1 are set so that the test piece insertion holes 4 and 5 coincide with each other, and the test piece 3 is passed through the test piece insertion holes 4 and 5. Thereafter, a constant tensile stress was applied to the jigs 1 and 2 with a tensile tester, and a constant shear stress was applied to the test piece 3 to measure the rupture time. The shear tensile strength is the maximum value of the shear stress obtained using the jig shown in FIG.

  In addition, after the test, after removing the plating from the test piece, the amount of diffusible hydrogen in each test piece was determined by temperature rising analysis using a gas chromatograph. In addition, the test piece was cooled with dry ice until the measurement of the amount of diffusible hydrogen after removing the plating to prevent the hydrogen from being diffused. In the present invention, the amount of diffusible hydrogen is the amount of hydrogen released between room temperature and 300 ° C. when the temperature is raised at 100 ° C./hr.

  FIG. 2 shows an example in which the relationship between the amount of diffusible hydrogen [ppm] and the fracture time [min] until delayed fracture is analyzed. A right-pointing arrow in the figure means that it is not broken. The smaller the amount of diffusible hydrogen contained in the sample, the longer the time until delayed fracture occurs.

The upper limit of the amount of hydrogen that does not cause delayed fracture at 6000 minutes was defined as the shear delayed fracture limit diffusible hydrogen amount _HCS, and the delayed fracture characteristics were evaluated based on this value. As a result, it was found that by setting (Si + 1.3 × Al) to 0.08 to 3.5%, Fe carbides are finely dispersed during tempering, and delayed fracture resistance under shear stress is improved. .

  In the present invention, Fe carbide is a general term for cementite and epsilon carbide.

  In addition, cracks due to bending stress also occur under shear stress. Therefore, it has been found that the bearing member is required to have a delayed fracture characteristic and hardly cause cracking under bending stress, that is, toughness, and that refinement of prior austenite grains is effective.

  First, the reasons for limiting the component composition of steel as the object of the present invention will be described.

  C is an essential element for securing the strength of the steel material, but if it is less than 0.5%, the required strength cannot be obtained within a predetermined tempering temperature range, while if it exceeds 0.8%, toughness is obtained. And the retained austenite increases, so the content was limited to 0.5 to 0.8%.

  Mn is an effective component for improving hardenability, and is also effective for deoxidation and desulfurization. If it is less than 0.1%, the above effect cannot be obtained. On the other hand, if it exceeds 2%, segregation is promoted, so the content is limited to a range of 0.1 to 2%.

  Cr is an element that enhances hardenability and temper softening resistance, but if it is less than 0.1%, the effect cannot be obtained, while if it contains more than 1.5%, undissolved carbide tends to increase. Therefore, it was limited to the range of 0.1 to 1.5%.

  Si increases temper softening resistance and prevents coarsening of cementite, but if less than 0.05%, the effect cannot be obtained, while if added over 3%, the toughness deteriorates. Limited to a range of 05-3%. Furthermore, from the viewpoint of obtaining excellent delayed fracture characteristics, the preferred lower limit is 0.1%.

Al has the effect of preventing austenite grains from coarsening by forming AlN during deoxidation and heat treatment. Further, fine AlN is effective for fine dispersion of cementite because it becomes a nucleus of intra-particle precipitation of fine cementite. If the Al content is less than 0.01%, these effects are insufficient. On the other hand, if containing more than 1% Al, deterioration of toughness due to Al ₂ O ₃ inclusions occurs, so it was limited to the range of 0.01 to 1%. In particular, when it is desired to reduce Al ₂ O ₃ inclusions, the upper limit is preferably 0.5% or less.

  In the present invention, it is further necessary to satisfy the specific relationship between the Si content and the Al content, and (Si + 1.3 × Al) is limited to a range of 0.08 to 3.5%. Yes. The lower limit is set to 0.08% in order to achieve fine dispersion of Fe carbides during tempering, and the upper limit is set to 3.5% to ensure toughness. Furthermore, from the viewpoint of obtaining finer Fe carbide, the preferred range is 0.1 to 3%.

  P and S are impurities, and the content is preferably limited.

  P segregates at the prior austenite grain boundaries, embrittles the grain boundaries, and lowers the delayed fracture resistance. Therefore, by suppressing the content to 0.015% or less, better delayed fracture resistance can be obtained. Can do.

  Since S has the same effect as P, by suppressing it to 0.01% or less, more excellent delayed fracture resistance can be obtained.

  Furthermore, you may contain 1 type, or 2 or more types of Mo, W, and B.

  Mo is an element effective for improving the hardenability and is added as 0.05% or more in order to give strength to the steel by being precipitated as fine carbides during tempering. On the other hand, even if added in excess of 2%, the effect is saturated.

  W is an element effective for improving hardenability, and is added as 0.05% or more in order to give strength to the steel by precipitating as fine carbides during tempering. On the other hand, even if added in excess of 1%, the effect is saturated, so it is preferable that the content be in the range of 0.05% to 1%.

  B is effective for improving the hardenability when added in a small amount, and 0.0001% or more is preferable for obtaining the effect. On the other hand, even if added over 0.005%, the effect is saturated, so it is preferable that the content be in the range of 0.0001 to 0.005%.

  Furthermore, you may contain 1 type, or 2 or more types of V, Ti, and Nb.

  V imparts strength to the steel by making the prior austenite grains fine and precipitating as fine carbides during tempering, so 0.05% or more is preferably added. On the other hand, even if added in excess of 1%, the effect is saturated.

  Since Ti is also an element effective for refinement of prior austenite grains, 0.001% or more is preferably added. On the other hand, even if added over 0.05%, the effect is saturated, so it is preferable to set the content within the range of 0.001 to 0.05%.

  Nb has the same effect as Ti, so 0.001% or more is preferably added. On the other hand, even if added over 0.05%, the effect is saturated, so it is preferable to set the content within the range of 0.001 to 0.05%.

  In the present invention, the contents of N and O which are impurities are not particularly limited, but if N and O each contain more than 0.01%, inclusions such as nitrides and oxides are likely to be generated. , Each is preferably 0.01% or less.

  Next, the structure of the joined part which is the subject of the present invention will be described.

  In order to have sufficient strength and toughness and delayed fracture resistance as the structure of the joined part in the present invention, it is necessary that 90% or more of the area ratio is tempered martensite. The balance of the tempered martensite is composed of one or more or all of retained austenite, bainite, ferrite and pearlite.

  The area ratio of tempered martensite is determined from a photograph of the structure taken by observing the structure before quenching and before tempering with an optical microscope. This is because it is difficult to distinguish between tempered martensite and tempered bainite in the structure after tempering. Moreover, since the martensite produced | generated after hardening becomes tempered martensite as it is by tempering, the quantity of tempered martensite is equivalent to the quantity of martensite before tempering.

  The area ratio of tempered martensite was obtained by taking a sample for observing the structure from as-quenched bonded parts, mirror polishing, etching with nital, and observing any 10 fields of view with an optical microscope at 500 times and taking a photograph. Then, the inside of the visual field is subjected to image analysis, and the area ratio of the portion excluding residual austenite, bainite, ferrite and pearlite is obtained as the amount of tempered martensite.

  The amount of retained austenite can be determined from an optical micrograph, but since it is a small amount, it is preferably measured by an X-ray diffraction method.

  Residual austenite causes generation of work-induced martensite that degrades delayed fracture resistance, and is therefore preferably 7% or less.

  Furthermore, refinement of prior austenite grains is necessary from the viewpoint of improving toughness against bending stress. Therefore, in the present invention, the crystal grain size of prior austenite is limited to grain size number 6 or more of JIS G 0551.

Moreover, in a high-strength joint component, in order to ensure the delayed fracture resistance with respect to sufficient shear stress, it is preferable that the particle size of Fe carbide is 50 nm or less. The particle size of the Fe carbides, scanning electron microscope and photographed and observed by 10000 times any 20 fields by (S canning E lectron M icroscope, called. SEM), the maximum particle size within its field of view .

  In the SEM observation, the sample is etched by a constant potential electrolytic corrosion method using a non-aqueous solvent electrolyte. The average particle size of Fe carbide is preferably as small as possible, but when it becomes finer than 25 nm, discrimination by SEM is difficult.

  Next, the characteristics of the high strength bearing joint part of the present invention will be described.

  If the amount of shear delay fracture limit diffusible hydrogen is less than 0.4 ppm, there is a high possibility that delayed fracture will occur due to hydrogen entering the steel material due to corrosion or the like, so the lower limit is preferably set to 0.4 ppm. If the composition and structure of the steel are within the above ranges, the shear lag fracture limit diffusible hydrogen content is 0.4 ppm or more.

  The tensile strength is preferably 1800 MPa or more. This is based on the results of calculations by the present inventors that the number of bolts necessary for bearing support can be significantly reduced when a joining part having a tensile strength of 1800 MPa or more is used. In the current technology, it is difficult to make the tensile strength exceed 2600 MPa.

  If the absorbed energy by the Charpy impact test using a JIS Z 2242 notch depth 2 mm U-notch 5 mm sub-size test piece is less than 10 J, there is a high possibility that a crack due to bending stress will occur if the amount of hydrogen that has penetrated increases. Therefore, the lower limit is preferably 10J. If the steel material satisfies the components and structures of the present invention, the absorbed energy is 10 J or more.

  If the initial hydrogen content of the high-strength bearing member before use exceeds the shear lag fracture limit diffusible hydrogen content, delayed fracture due to shear stress is likely to occur during use. For this reason, the initial hydrogen content of the high-strength bearing member is preferably less than 0.4 ppm. In the present invention, the initial hydrogen content is the amount of hydrogen released between room temperature and 300 ° C. in a temperature rising analysis at 100 ° C./hr after taking a sample from a high strength bearing member before use after production. .

  The steel material which is the material of the high strength bearing joint part of the present invention is in mass%, C: 0.5 to 0.8%, Mn: 0.1 to 2%, Cr: 0.1 to 1.5% Si: 0.05 to 3%, Al: 0.01 to 1% are included so as to satisfy (Si + 1.3 × Al): 0.08 to 3.5%, and the balance is Steel made of Fe and inevitable impurities.

  The component composition of steel is preferably limited to P: 0.015% or less and S: 0.01% or less. Moreover, you may contain 1 type (s) or 2 or more types, Mo: 0.05-2%, W: 0.05-1%, B: 0.0001-0.005%, V: 0.05- You may contain 1 type, Ti: 0.001-0.05%, Nb: 0.001-0.05% 1 type (s) or 2 or more types. The reason for limiting the component composition of the steel material is the same as the reason for limiting the components of the high-strength bearing member.

  After melting, the steel composed of these components is cast or forged by casting or forging, reheated and hot-rolled. When the bearing member is a bolt, a pin or the like, the steel material is also preferably a wire, but depending on the shape of the bearing member, it may be a hot-rolled sheet. The heating temperature may be 100 to 1250 ° C., and the area reduction rate of the wire rod rolling and the rolling reduction of the plate rolling may be 50% or more, preferably 80% or more, and more preferably 90%.

  The manufacturing method of the bearing support joining component of this invention is demonstrated.

  Steel is annealed as necessary, and hot forging, cold forging, drawing, rolling, and cutting are combined as appropriate to achieve a specific shape, that is, a bearing-type high-strength bolt and high-strength rivet that do not introduce axial force. After forming into a high resistance pin, a shearing resistance body such as a self-drilling screw or a driving rod that does not open a hole, a quenching process, a carburizing quenching process, or an induction quenching process is performed, and a tempering process is performed. In the present invention, quenching and tempering are important.

  The heating temperature of the steel in the quenching process needs to be 850 ° C. or higher in order to make the structure before the quenching process austenite. On the other hand, if the heating temperature exceeds 1000 ° C., the austenite grains become coarse, and the crystal grain size of the prior austenite becomes less than 6. When the steel heated to this temperature range is quenched, a martensite structure with an area ratio of 90% or more can be obtained. The quenching process may be water quenching or oil quenching.

  Subsequent tempering is the most important in the present invention, and by setting this condition in an appropriate range, fine Fe carbides can be precipitated, and the steel material can be imparted with characteristics excellent in toughness and delayed fracture resistance. it can.

  The tempering treatment of the present invention uses a rapid heater represented by high-frequency induction heating in order to achieve a high temperature and a short time. In this case, if the heating rate of the tempering treatment is less than 10 ° C./s, the tempering cannot be accurately controlled, so that it is 10 ° C./s or more. Although the upper limit of the heating rate is not specified, it is difficult to make it higher than 300 ° C./s with the current technology.

  If the tempering temperature is less than 200 ° C. and the tempering time is less than 1 s, the toughness becomes insufficient. Further, when the tempering temperature exceeds 450 ° C. and the tempering time exceeds 7200 s, the strength decreases and the Fe carbide becomes coarse. Therefore, it is necessary that the tempering temperature is in the range of 200 to 450 ° C. and the tempering time is in the range of 1 to 7200 s.

  Furthermore, the tempering parameter P defined by the following formula (1) is set to 6000 by the tempering temperature T [° C.], the tempering time t [s], C, Si, and Al (content of each component [% by mass]). ˜12000 is required.

  When the tempering parameter P exceeds 12000, the required strength cannot be obtained. When the tempering parameter P is less than 6000, tempering is insufficient, and Fe carbide is not sufficiently precipitated. To do. If the tempering parameter P is smaller than 6000, the initial hydrogen content of the bearing joint may be 0.4 ppm or more.

P = (T + 273) {log (t / 3600) + 21.3-5.8C
-(Si + 1.3Al)} (1)

  Steel having chemical components shown in Table 1 was melted, cast, reheated to 1000 to 1250 ° C., and hot-rolled into a wire rod shape having a diameter of 16 mm with a reduction in area of 99%. In Table 1, a blank means that the content of each component was less than the detection limit, and an underline is attached to what is outside the scope of the present invention. After processing into bolt shape, quenching from the heating temperature shown in Table 2, taking samples for structure observation from some bolts, and tempering other bolts under the conditions (temperature, time) shown in Table 2 It was.

  A No. 2 round bar tensile test piece of JIS Z 2201 having a diameter of 6 mm was taken from the shaft portion of the bolt, and a tensile test was performed in accordance with JIS Z 2241. The Charpy impact test was performed at room temperature using a U-notch 5 mm sub-size test piece having a notch depth of 2 mm according to JIS Z 2242.

The shear delay fracture limit diffusible hydrogen amount H _CS was measured by using a test piece of 5φ × 6 mm subjected to hydrogen charging and cadmium plating by the test machine shown in FIG. Moreover, initial hydrogen content was measured without performing hydrogen charge to some test pieces.

  The amount of tempered martensite was obtained from a microstructure photograph of a sample taken from a bolt before quenching, sampled from a bolt before tempering, mirror-polished and etched, observed with an optical microscope at an arbitrary 10 field of view at 500 times. . Moreover, based on JIS G 0551, the particle size number of the prior austenite was measured.

  The particle size of Fe carbide was determined by etching the sample by a constant-potential electrolytic corrosion method using a non-aqueous solvent electrolyte, taking 10,000 times a photo of any 20 fields of view using the SEM, and measuring the maximum size within the field of view. Adopted. The amount of retained austenite was determined by quantitative analysis by X-ray diffraction.

No. 1-14 are examples of the present invention, as shown in Table 2, the critical diffusible hydrogen amount H _CS shear stress is at least 0.4 ppm, the tensile strength is high strength and more 1800 MPa, to shear stress Excellent delayed fracture resistance.

  On the other hand, no. No. 15, the amount of C is less than the lower limit of the present invention, and the tensile strength is below 1800 MPa. No. No. 21 is Mn. In No. 23, Cr is less than the lower limit of the present invention, respectively, and quenching is insufficient or resistance to temper softening is insufficient, so that the tensile strength does not reach 1800 MPa.

  No. No. 21 is an additive amount of Al less than the lower limit of the present invention, the grain size of the prior austenite is small, and the Fe carbides are coarsened, so that the delayed fracture resistance to shear stress despite low tensile strength. Is inferior.

No. Nos. 16 to 20 are examples in which H _CS 0.4 ppm or more could not be achieved and delayed fracture resistance against shear stress was insufficient. Comparative Example No. No. 16 has a C amount of No. 16. No. 19 has an Al content of No. 19. 20, Si, respectively, exceeds the upper limit of the present invention, since the absorption energy is low, H _CS occurs because of crack due to bending stress is reduced.

No. 17, Si content and Si + 1.3Al is to lower than the lower limit of the present invention, the particle size of Fe carbides exceeds the 50 nm, H _CS is reduced.

No. No. 22 is Mn. 24, Cr, respectively, exceeds the upper limit of the present invention, the absorption energy decreases by the presence of segregation and undissolved carbides, due to the occurrence of crack due to bending stress is considered that H _CS is lowered.

No. 18, Si + 1.3Al is higher than the range of the present invention, further, P value becomes lower than 6000, H _CS is significantly reduced, the initial hydrogen content be 0.4ppm or more.

No. No. 26 is an example in which the P value is lower than 6000, the _HCS is remarkably lowered, and the initial hydrogen content is 0.4 ppm or more. On the other hand, the P value is higher than 12000. No. 25 has a reduced tensile strength.

It is a figure which shows typically a shear delay fracture test apparatus. It is a figure which shows an example of the relationship between the amount of diffusible hydrogen [ppm] and the fracture | rupture time [min] until it leads to a delayed fracture. (A) which shows a joining aspect shows the aspect of friction joining, (b) is a figure which shows the aspect of bearing support joining. It is a figure which shows the aspect of tension joining.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Jig 2 Jig 3 Test piece 4 Jig 1 Test piece insertion hole 5 Jig 2 Test piece insertion hole

Claims (12)

% By mass
C: 0.5-0.8%
Mn: 0.1 to 2%,
Cr: 0.1 to 1.5%
Containing
Si: 0.05-3%,
Al: 0.01 to 1%
Both
(Si + 1.3 × Al): 0.08 to 3.5%
The balance is composed of Fe and inevitable impurities, the metal structure is composed of tempered martensite with an area ratio of 90% or more and residual austenite of 7% or less , and the tempered martensite has a particle size of 50 nm or less. has a Fe carbide, high-strength Bearing grain size of prior austenite is Ri der size number 6 or more JIS G 0551, tensile strength excellent in delayed fracture resistance, characterized in der Rukoto than 1800MPa Joined parts. 2. The high strength bearing joint having excellent delayed fracture resistance according to claim 1, wherein the high strength bearing joint has a shear delay fracture limit diffusible hydrogen content of 0.4 ppm or more. 3. The absorbed energy by Charpy impact test using a U-notch 5 mm sub-size test piece having a notch depth of 2 mm according to JIS Z 2242 is 10 J or more in the high-strength bearing member. High strength bearing joints with excellent delayed fracture resistance as described. In the high-strength bearing capacity bonding component, high strength Bearing joint which is excellent in delayed fracture resistance as set forth in any one of claim 1 to 3, wherein the initial hydrogen content of less than 0.4ppm parts. In the high-strength bearing member, further in mass%,
P: 0.015% or less,
The high strength bearing joint having excellent delayed fracture resistance according to any one of claims 1 to 4 , wherein S is limited to 0.01% or less. In the high-strength bearing member, further in mass%,
Mo: 0.05-2%,
W: 0.05 to 1%
B: 0.0001 to 0.005%
The high strength bearing joint part excellent in delayed fracture resistance according to any one of claims 1 to 5 , characterized by containing one or more of the following. In the high-strength bearing member, further in mass%,
V: 0.05 to 1%
Ti: 0.001 to 0.05%,
Nb: 0.001 to 0.05%
1 or 2 types or more of these are included, The high strength bearing joint components excellent in the delayed fracture resistance of any one of Claims 1-6 characterized by the above-mentioned. A high-strength bearing member having excellent delayed fracture resistance according to any one of claims 1 to 4 , which is a material for manufacturing by molding and heat treatment , and in mass%,
C: 0.5-0.8%
Mn: 0.1 to 2%,
Cr: 0.1 to 1.5%
Containing
Si: 0.05-3%,
Al: 0.01 to 1%
Both
(Si + 1.3 × Al): 0.08 to 3.5%
A steel material for a high-strength bearing member having a balance of Fe and inevitable impurities. A material for producing a high-strength bearing member excellent in delayed fracture resistance according to claim 5 by molding and heat-treating , further, in mass%,
P: 0.015% or less,
S: Restricted to 0.01% or less, The steel material for high-strength bearing members with excellent delayed fracture resistance according to claim 8 . A high-strength bearing member having excellent delayed fracture resistance according to claim 6 , a material for manufacturing by molding and heat treatment ,
Mo: 0.05-2%,
W: 0.05 to 1%
B: 0.0001 to 0.005%
The steel material for high-strength bearing members with excellent delayed fracture resistance according to claim 8 or 9 , characterized by containing one or more of the following. A high-strength bearing member having excellent delayed fracture resistance according to claim 7 , a material for manufacturing by molding and heat-treating , and further, in mass%,
V: 0.05 to 1%
Ti: 0.001 to 0.05%,
Nb: 0.001 to 0.05%
1 or 2 types or more of these are contained, The steel material for high strength bearing joint parts excellent in the delayed fracture resistance of any one of Claims 8-10 characterized by the above-mentioned. A claim 1-7 High Strength Bearing joining component manufacturing method having excellent delayed fracture resistance as set forth in any one of molding a steel according to any one of claims 8 to 11 After heating to 850 to 1000 ° C. and quenching treatment, the heating rate is set to 10 ° C./s or more, the tempering temperature T [° C.] is set to 200 to 450 ° C., and the tempering time t [s]. Is a range of 1 to 7200 s, a tempering parameter P defined by the following formula (1) is set to 6000 to 12000, and a tempering process is performed.
P = (T + 273) {log (t / 3600) + 21.3-5.8C
-(Si + 1.3Al)} (1)
Here, C, Si, and Al are component contents [% by mass].

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