JP5008453B2 - High strength bolt friction joint using high strength steel - Google Patents

Description

  The present invention relates to high-strength bolt friction joints of steel materials in architectural steel structures or other steel structures, particularly high-strength bolt friction joints when applying high-strength steel that is expected to expand in the future. It is about.

  Conventionally, in the friction bonded structure using high-strength bolts of steel structures, the naturally occurring red rust is standard on the friction surface of the steel material (see Japan Society for Architectural Engineers “JASS6”). In terms of design, the slip coefficient value is set to a low value (μ = 0.45).

  As an improvement measure, in order to obtain a higher slip coefficient, the following structure and joining method have been proposed.

  (1) As shown in Patent Document 1, a special coating is applied to the surface of a steel material and joined with a high-strength bolt.

  (2) As shown in Patent Document 2, a ceramic plasma spraying treatment is applied to the joining surface of steel materials and joined with a high-strength bolt.

  (3) As shown in Patent Document 3 or Patent Document 4, a combination of steel materials having a large difference in surface roughness and surface hardness.

  (4) As shown in Patent Document 5, only the hardness near the surface is increased.

  (5) As shown in Patent Document 6 and Patent Document 7, the surface is provided with unevenness with a height difference of 0.2 to 1.0 mm, and the surface is further hardened.

Japanese Patent Laid-Open No. 51-052336 JP-A-01-266309 Japanese Patent Laid-Open No. 06-146427 Japanese Patent Application Laid-Open No. 07-238595 Japanese Patent Laid-Open No. 06-226404 Japanese Patent Laid-Open No. 08-081736 JP 08-284912 A Yasuyoshi Uno, Ichiro Inoue, Yumi Shimura, Hirozo Wakiyama: “Fundamental study on friction coefficient between steels with different hardness”, Architectural Institute of Japan, 494, pp.123-128, 1997.4.

  In the case of generating the conventional red rust, since the variation in construction is large and the management of construction quality is very difficult, a slip coefficient value larger than 0.45 cannot be used for joint design. There is.

  In the case of the joining method of (1), it is complicated because it is necessary to apply a special coating to the steel material, and in the case of the joining method of (2), a new dedicated equipment is required in the steel frame processing process. There is a drawback.

  In the joining method (3), it is difficult to control different surface roughness on site, and there may be a problem in procurement of steel materials having different hardness, which is not practical.

  In addition, in the joining method of (4), a steel material in which only the hardness of the surface layer portion is increased is complicated to manufacture and manage the hardness. Further, the surface processing in the joining method (5) is extremely complicated.

  As described above, all of the conventionally proposed joining methods (1) to (5) still have problems and have not yet been widely implemented.

  Moreover, the knowledge of the slip coefficient regarding high-strength steel has not been clarified so far. The investigations so far have focused on general-purpose strength materials, and there is no suggestion on how to work on high-strength steels with completely different metal structures.

  The present invention aims to solve the above-mentioned problems in the prior art, particularly when high-strength steel materials are friction-bonded to high-strength steel, and to ensure the stability of the construction quality of the friction-bonded surface and a high slip coefficient. Is.

  In order to solve the above-described problem advantageously, the present inventors have conducted a number of sliding tests using a group of steel materials including high-strength steel.

  In the slip test, the test piece shown in Fig. 1 was used, and after tightening with a high strength bolt of F14T class, tensile loading was performed, the slip load was obtained, and the slip coefficient was derived. Slip coefficient derivation was performed based on Appendix 7 “Slip coefficient evaluation test method” of “Guidelines for design of steel structure joints” (2nd edition, 1st edition, Architectural Institute of Japan, published on March 1, 2006). .

  Since it is well known that the friction characteristics have a strong correlation with the surface roughness, tests were performed with various changes in the blasting method in order to improve the roughness of the high-strength steel. The grit blasting method is a method that can ensure high roughness even with high-strength steel, but as a result of the slip test, the slip coefficient remained at a relatively low value.

  Accordingly, the present inventors have focused on the shot blast method, which is a method that is widely applied practically and is excellent from the viewpoint of versatility, and intensively studied the correlation with the slip coefficient. In addition, about the accessory plate, considering the same as the base material and versatility, examination was performed using the steel of normal strength. The same blasting conditions were applied to the base material and the accessory plate in order to achieve industrially realistic conditions.

As a result, regarding the slip coefficient,
(1) The higher the strength of the base material, the lower the slip coefficient.
(2) For the accessory plate, a material equivalent to the base material strength is superior, and decreases when a general-purpose strength material is used.
(3) There is an optimum point in the grain size of the abrasive.
(4) Higher hardness of the abrasive is advantageous.
(5) The smaller the maximum height (Rz) of the roughness curve of the base metal joint surface, the better the slip coefficient.
(6) The slip coefficient improves as the roughness curve peak-to-valley spacing (RSm) of the base material joint surface increases.
I was able to obtain the knowledge.

  The possible reasons for these trends are described below.

(1) The slip coefficient decreases as the strength of the base material increases. The strength of the base material shows a negative correlation with the slip coefficient. At first glance, since the shear fracture limit characteristic during friction increases as the strength increases, it is natural to think that the slip coefficient also increases, and a negative correlation as in the present invention has not been known so far. Actually, for example, Patent Document 5 describes the knowledge of expecting a high coefficient of friction by applying a steel material produced using a double-phase slab and increasing the hardness of only the surface.

  However, it can be said that the idea that the critical shear stress increases as the strength increases is based on the assumption that the fracture resistance of the metal structure is constant. In practice, general high-strength materials for general use, especially materials that consider welding, use a metal structure with extremely high dislocation density, and the critical properties at the time of shear failure are lower than those for general-purpose strength steel. It has been known. The decrease in the slip coefficient due to the application of high-strength steel is considered to occur because the decrease in fracture resistance due to the metal structure is dominant compared to the contribution due to the increase in strength.

(2) As for the accessory plate, the same material as the base material strength is superior, and it decreases when a general-purpose strength material is used. For example, in Patent Document 5 and Non-Patent Document 1 described above, It is described that it is advantageous to use a steel material different from the base material. However, according to the experiments by the present inventors, the dissimilar material joint (when using different steel materials) has a smaller slip coefficient than the joint material joint (when using the same kind of steel material).

  According to the surface observation after the experiment, all the undulations of the soft steel plate were scraped and a slip phenomenon occurred. This is considered to be due to the fact that the surface on the soft material side is subjected to the same blasting as that on the hard material side, and the effective shear stress of the soft material is low.

  Although it may be possible to improve the slip characteristics by controlling and optimizing the undulations on the soft material side, it may require different surface treatments depending on the member during practical construction Therefore, realization is difficult from the viewpoint of cost.

(3) There is an optimum point in the particle size of the abrasive. Since the shot ball is basically spherical, the vertex angle discussed in the friction theory does not change much even if the particle size is changed. However, in practice, the apex angle tends to decrease by decreasing the particle size.

  For this reason, if the particle size is reduced, the slip coefficient is lowered due to the small apex angle. In addition, when the particle size is too large, it is considered that the sum of the contact areas projected on the surface perpendicular to the loading direction is reduced and the sum of the frictional forces at the contact portions is reduced. That is, it is considered that there is an optimum point for improving the slip coefficient in the particle diameter. In this series of experiments, 0.8mm was the best result.

(4) About the higher hardness of the abrasive material It is obvious that it is important to secure roughness to improve the slip coefficient, but when high strength material is used for the member When the shot ball dynamically collides with the surface of the steel material, the plastic deformation on the shot ball side increases, and the desired roughness cannot be imparted to the steel material.

  That is, in order to give the steel material a desired undulation, it is necessary to suppress plastic deformation on the shot ball side, and increasing the hardness of the shot ball is effective.

(5) The slip coefficient is improved when the maximum roughness curve (Rz) of the base metal joint surface is small.In grit blasting, Rz can be increased relatively easily compared to shot blasting. The contact area is reduced. In addition, in the industrial category of collision energy, when the Rz of the joint surface is increased, the vertical angle of the undulations becomes sharp and is easily scraped off by friction, and the intended slip coefficient cannot be obtained.

  In particular, this tendency becomes significant because high strength steel has high yield stress and requires more collision energy to generate undulations. That is, at the same collision energy, Rz is moderately suppressed, and a relatively large RSm described below makes it possible to obtain a high slip coefficient efficiently and industrially.

  Here, only the surface properties of the base material are subject to evaluation because the strength of the accessory plate is equal to or less than that of the base material and the same blasting conditions are applied. This is because the degree is small.

(6) The roughness curve of the base metal joint surface increases as the spacing between peaks and valleys (RSm) increases, and the slip coefficient improves. In shot blasting, the apex angle of undulations becomes duller and the apex angle interval widens than grit blasting. As a result, the contact area at the time of joining increases. This means that Rz is small and RSm is large.

  In addition, this makes the undulations have a relatively large resistance to friction and improves the slip coefficient. Of course, it is possible to obtain such surface properties even with grit blasting, but the slip coefficient is relatively low.

The inventors of the present invention applied shot blasting or grit blasting under the same conditions to a base material made of high strength steel of 700 MPa class or higher and a base plate made of steel having the same or lower strength as the high strength steel. A high-strength bolt friction joint jointed with high-strength bolts by superimposing these surfaces was subjected to a sliding test, and based on the knowledge obtained, quantitative evaluation of each parameter was performed. The index shown in (2) was obtained.

  The strength of the base material and the accessory plate is the tensile strength obtained by a tensile test using a tensile test piece taken from the original thickness of the steel material or from 1/4 of the thickness in parallel to the outer surface.

Expression (1) is a shot blast condition for obtaining a slip coefficient of 0.45 or more , and Expression (2) is a shot blast condition for obtaining a surface mode for obtaining a slip coefficient of 0.45 or more.

(1) Shot blasting conditions for obtaining a slip coefficient of 0.45 or more The strength of the base material and the accessory plate, and the shot blasting conditions satisfy the following relationship.
0.11 × TSB + 1.2 × (TSB-TSS) -2.9 × (HVS-TSB / 3.11) + 303 × | GSS-0.8 | ≦ 0… (1)
here,
TSB: Base material strength [MPa]
TSS: Plywood strength [MPa]
HVS: Average Vickers hardness of abrasive
GSS: Average particle size of abrasives [mm]

(2) Shot blasting conditions for obtaining a surface mode for obtaining a slip coefficient of 0.45 or more The strength of the base material and the shot blasting conditions satisfy the following relationship.
2.36 × (HVS-TSB / 3.11) -105 × | GSS-0.8 | ≧ 700… (2)
here,
TSB: Base material strength [MPa]
HVS: Average Vickers hardness of abrasive
GSS: Average particle size of abrasives [mm]

In both formulas (1) and (2), it is advantageous that the strength of the base material is low. This is because the degree of control of the correlation between the strength of the base material and the accessory plate, and the hardness of the abrasive is large, and it is considered that it is effective in a wide range as long as this relationship is maintained. From the correlation with the upper limit of the hardness of the abrasive, the upper limit of the base metal strength is set to 1200 [MPa].

  According to the present invention, conventionally, in high-strength bolt friction welding of high-strength steel for which the relationship with the slip coefficient has not been sufficiently grasped, it is possible to ensure the stability of the construction quality of the friction joint surface and the high slip coefficient. it can.

  In other words, variations in construction, which are problems in high-strength bolt friction welding, are prevented, management of construction quality is easy, and no special painting or processing is required. Economically and efficiently, high strength with excellent quality A high-strength bolt friction joint using steel is obtained.

  Hereinafter, the reason why the bonding structure of the present invention is defined as described above will be described in detail.

  Grit blasting or shot blasting is used for the surface treatment of the steel material. This is a widely used method at present, and is a very effective method in consideration of the reality. The surface property of the joint surface is controlled so as to satisfy the following conditions based on the reason detailed in the section for solving the problem. Other conditions may be in accordance with ordinary methods.

(1) Shot blasting condition A
0.11 × TSB + 1.2 × (TSB-TSS) -2.9 × (HVS-TSB / 3.11) + 303 × | GSS-0.8 | ≦ 0… (1)
here,
TSB: Base material strength [MPa]
TSS: Plywood strength [MPa]
HVS: Average Vickers hardness of shot blasting abrasive
GSS: Average particle size of shot blasting abrasive [mm]

Incidentally, the base material strength and添板strength remains the original thickness of the steel, or you 1/4 the thickness and tensile strength obtained by a tensile test using a tensile test piece parallel to collect on the outer surface.

(2) Shot blasting condition B
2.36 × (HVS-TSB / 3.11) -105 × | GSS-0.8 | ≧ 700… ( 2 )
here,
TSB: Base material strength [MPa]
HVS: Average Vickers hardness of shot blasting abrasive
GSS: Average particle size of shot blasting abrasive [mm]

  Note that the base metal strength and the strength of the accessory plate are the tensile strengths obtained by performing a tensile test using a tensile test piece taken from the original thickness of the steel material or from 1/4 of the thickness parallel to the outer surface.

In both formulas (1) and (2), it is advantageous that the strength of the base material is low. This is because the degree of control of the correlation between the strength of the base material and the accessory plate, and the hardness of the abrasive is large, and it is considered that it is effective in a wide range as long as this relationship is maintained. From the correlation with the upper limit of the hardness of the abrasive, the upper limit of the base metal strength is set to 1200 [MPa].

  The steel material used for the joint structure is high-strength steel. As for the manufacturing method of high-strength steel, it is desirable to have the chemical composition range shown below in consideration of performing welding. This rule is not necessarily indispensable if only considering the realization of a joint structure with excellent friction characteristics, but it is desirable to control within this range considering the wide range of characteristics required for steel for building structures. is there. However, this does not mean that the technical scope of the present invention is narrowly interpreted.

  C is added for the purpose of securing the strength of the base material. If the content is less than 0.04% by mass, not only the required strength cannot be secured, but also the lath formation in the FL (melting line) becomes insufficient and the toughness of the HAZ (welding heat affected zone) near the FL also decreases. To do. On the other hand, if the content exceeds 0.15% by mass, the toughness deterioration of HAZ, particularly HAZ near FL, becomes remarkable. Furthermore, the hardness of the steel sheet surface tends to increase, which causes the slip coefficient to decrease.

  Therefore, the desirable range of the C content is 0.04 to 0.15% by mass. In addition, from the viewpoint of improving the toughness of the welded portion, the C content is preferably as small as possible, and a preferable range is 0.05 to 0.12% by mass.

  Si is basically added for the purpose of deoxidation and ensuring strength, but the effect is not sufficient at 0.05% by mass or more, and excess Si exceeding 0.6% by mass is used for the HAZ part and the base material. In the part, island martensite is increased and toughness is decreased. In addition, the base material toughness is reduced through the increase in the amount of inclusions. Therefore, the desirable range of the Si content is 0.05 to 0.6% by mass.

  In addition, from the viewpoint of improving the toughness of the welded portion, the Si content is preferably as small as possible, and a preferable range is 0.05 to 0.4 mass%.

  Mn is added to ensure the strength and toughness of the deoxidizer, the base material, and the hardenability of the HAZ. If the content is 0.4% by mass or less, not only these effects can be obtained, but also ferrite side plates are generated in the HAZ, so that lath formation is insufficient and the toughness of the welded portion is lowered.

  On the other hand, excessive Mn exceeding 2% by mass brings about non-uniformity of base material characteristics in the thickness direction due to center segregation. Therefore, the desirable range of the Mn content is 0.4 to 2.0% by mass.

  P is unavoidably present in the steel as an impurity. If it exceeds 0.05% by mass, it is accompanied by remarkable deterioration of toughness and weld crack resistance, so it is necessary to make it 0.05% by mass or less. The lower limit is not particularly specified because P is preferably as small as possible.

  If S is too much, center segregation is promoted, or a large amount of stretched MnS is produced and accompanied by remarkable ductile crack generation characteristics, so the upper limit is made 0.003 mass%. The lower limit is not particularly specified because S is preferably as small as possible.

  Al must generally be added as a deoxidizer. In order to obtain the effect, addition of 0.002% by mass or more is necessary. However, excessive Al whose content exceeds 0.05% by mass reduces the toughness of the base metal part and the welded part through an increase in precipitates such as AlN. Therefore, the desirable range of the Al content is 0.002 to 0.05% by mass.

  N in the steel causes toughness deterioration through the formation of precipitates. Unless N is 0.01 mass% or less, it cannot be avoided that the toughness of HAZ deteriorates. Moreover, since it is effective also in refinement | miniaturization of a HAZ structure | tissue through formation of AlN or TiN, addition of 0.0015 mass% or more is required. Therefore, the desirable range of the N content is 0.0015 to 0.01% by mass.

  Cu is not particularly required in the present invention. Cu is added for the purpose of securing the strength of the base material. On the other hand, if the content exceeds 0.8% by mass, the toughness of the HAZ heated below the AC3 transformation point is deteriorated. Therefore, the desirable range when adding Cu is 0.8 mass% or less.

  Ni is not particularly required in the present invention. Ni is added for the purpose of securing the strength of the base material. However, since it is an expensive element and adding a large amount impairs economic efficiency, a desirable range when adding Ni is 3 mass% or less.

  Cr is not particularly required in the present invention. Cr is useful for enhancing the carbon dioxide gas corrosion resistance and enhancing the hardenability. If the content exceeds 1% by mass, it is difficult to suppress the curing of HAZ even if other component conditions are satisfied, and the carbon dioxide corrosion resistance improving effect is saturated. Therefore, the desirable range when adding Cr is 1.0 mass% or less.

  Mo is not particularly required in the present invention. Mo has the effect of improving the strength and toughness of the base material. If it exceeds 0.8% by mass, the hardness of the HAZ increases, and the toughness and SSC resistance are impaired. Therefore, the desirable range when adding Mo is 0.8 mass% or less.

  V is not particularly required in the present invention. V improves the strength of the base material mainly by carbonitride precipitation during tempering. On the other hand, if it exceeds 0.1% by mass, the performance improvement effect of the base material is saturated, leading to toughness deterioration. Therefore, the desirable range when adding V is 0.8 mass% or less.

  Nb is not particularly required in the present invention. Nb is an element having an effect of improving the low temperature toughness by refining the structure, and is added for the purpose of ensuring the strength of the base material and the low temperature toughness. On the other hand, excessive Nb exceeding 0.1% by mass forms coarse carbides and nitrides and lowers toughness. Therefore, a desirable range in the case of adding Nb is 0.1% by mass or less.

  Ti is not particularly required in the present invention. Ti is mainly used as a deoxidizing element, but forms an oxide phase composed of Al, Ti, and Mn. When the content exceeds 0.1% by mass, the formed oxide becomes Ti oxide or Ti—Al oxide, and the dispersion density decreases, particularly in the heat-affected zone of the small heat input weld zone. The ability to refine the tissue is lost. For this reason, the desirable range when adding Ti is 0.1 mass% or less.

  B is not particularly necessary in the present invention. B is added for the purpose of securing the strength of the base material. If the content is less than 0.0001% by mass, the required strength cannot be obtained. On the other hand, excessive B exceeding 0.002 mass% causes precipitation of coarse boron compounds and deteriorates toughness. Therefore, a desirable range when adding B is 0.0001 to 0.002 mass%.

  Ca is not particularly required in the present invention. Ca reacts with S in the steel to form acid / sulfide (oxysulfide) in the molten steel. Unlike MnS, this acid / sulfide does not extend in the rolling direction during rolling and is spherical after rolling. Therefore, it has the effect of suppressing weld cracks and hydrogen-induced cracks starting from the ends of the elongated inclusions. When the content exceeds 0.004 mass%, the toughness may be deteriorated. Therefore, the addition amount when adding Ca is 0.004 mass% or less.

  Mg is not particularly required in the present invention. Mg produces a fine Mg-containing oxide and is effective in reducing the γ grain size. If it exceeds 0.006% by mass, the amount of oxide becomes excessive and ductility is reduced. Therefore, the upper limit of the addition amount when adding Mg is 0.006% by mass.

  REM is not particularly necessary in the present invention. REM contributes to refinement of the structure of the weld heat affected zone and fixation of S, but it becomes an inclusion and reduces cleanliness. Inclusions formed by the addition of REM have a relatively small influence on the toughness deterioration, so that a decrease in the toughness of the base material can be tolerated even if included by 0.004 mass% or less. Therefore, the upper limit of the amount added when REM is added is 0.004% by mass.

  About the manufacturing method of these steels, the slab obtained by the continuous casting method is hot-rolled, subjected to quenching and tempering, or subjected to tempering treatment after direct quenching, etc. By performing the tempering treatment, reducing the surface hardness has an effect on the slip coefficient. During the tempering process, it is desirable to control the temperature to Ac1 to Ac1-100 ° C., which is highly effective.

  Table 1 shows the chemical components of the tested steel materials. In Table 1, Ceq is the carbon equivalent (unit%), and Pcm is the weld cracking susceptibility composition (unit%).

  Using these steel materials, the slide test body shown in FIG. 1 was constructed in the manner shown in Table 2, and a tensile test for evaluating the slip coefficient was performed. The high-strength bolts for joining were of the F14T class and had a neck length appropriate for each specimen. Here, the condition that the strength of the accessory plate is the same level as that of the base material and the softness of the base material is combined is added.

This joining type is selected so that the correlation between the blasting condition, the surface mode, and the slip coefficient can be obtained with high accuracy and can be easily applied to various joining types, and the technical scope of the present invention is specified. It is not to be interpreted narrowly only as a joint type. That is, the main high-strength steel as a base material in the present invention, have Na only mnemonic The添板used for indicating the same strength or lower strength of the steel.

Nos. 27 to 30 use 490N class steel as the base material, and both formula (1) and formula (2) satisfy the regulations and have a sufficiently high slip coefficient. However, the present invention because it only when the base material is a high strength steel, here you are listed as comparative examples.

Nos. 35 to 40 are a combination of 1000N class steel base material and general purpose strength steel, and because of the use of low hardness abrasives, RSm is not sufficiently large and the slip coefficient is small. It is less than the target value of 0.45.

  All other examples are within the specified range of the present invention, and exceed the slip coefficient of 0.45, which is a target value. Even when looking at examples within the scope of the present invention, when considering the margin for the target value, as already shown in each figure and each equation, the sign of the coefficient and the meaning of the equation are taken into consideration, and the base material strength Is smaller, the difference in strength between the base material and the base plate is smaller, the larger RSm is advantageous, the lower Rz is advantageous, the higher the hardness of the blast grain, the larger the grain size of the blast grain Has been shown to be more advantageous as it approaches 0.8 mm.

FIGS. 2 and 3 are obtained by arranging the equations (1) to (2) on the horizontal axis from the results of Table 2, and the criticality of each equation is clear in each figure.

  The steel material of the present invention relates to a friction joining structure of steel materials using high-strength bolts in architectural steel structures or other steel structures, especially when applying high-strength steel that is expected to expand in the future. In addition, a high slip coefficient can be realized stably. Thereby, it can contribute to expansion of the freedom degree of design of this structure, and it can be said that a social effect is very large.

It is a figure which shows the example of a form of the sliding test body used regarding this invention. 6 is a graph showing the relationship between Equation (1) and a slip coefficient. 6 is a graph showing the relationship between the formula (2) and the surface mode.

Claims (2)

A high-strength bolt friction joint where a base material made of high-strength steel of 700 MPa class or higher and a base plate made of steel with the same or lower strength as the high-strength steel are overlapped and joined with a high-strength bolt. The overlapping surface of the base material and the accessory plate has a surface aspect in which a slip coefficient of 0.45 or more is ensured under the same shot blast condition or grit blast condition, and the base material and the accessory plate are mutually connected. A high-strength bolt friction joint using high-strength steel, characterized in that shot blasting is performed on the superimposed surfaces under the following conditions .
The strength of the base material and the accessory plate is the tensile strength obtained by a tensile test using a tensile test piece taken from the original thickness of the steel material or from 1/4 of the thickness in parallel to the outer surface.
0.11 × TSB + 1.2 × (TSB-TSS) -2.9 × (HVS-TSB / 3.11) + 303 × | GSS-0.8 | ≦ 0… (1)
here,
TSB: Base material strength [MPa]
TSS: Plywood strength [MPa]
HVS: Average Vickers hardness of shot blasting abrasive
GSS: Average particle size of shot blasting abrasive [mm] 2. The high strength bolt friction joint using high strength steel according to claim 1, wherein shot blasting is performed on the surfaces of the base material and the accessory plate which are overlapped with each other under the following conditions.
2.36 × (HVS-TSB / 3.11) -105 × | GSS-0.8 | ≧ 700… ( 2 )
here,
TSB: Base material strength [MPa]
HVS: Average Vickers hardness of shot blasting abrasive
GSS: Average particle size of shot blasting abrasive [mm]

Images