JPH08284912A - Steel material for friction-grip-joining high strength bolt - Google Patents

Abstract

PURPOSE: To provide a steel material for friction-grip-joining a high strength bolt which provides high slide coefficient stably by providing a recessed section and a projection an a friction-grip-joint surface and a hard surface. CONSTITUTION: The composition of a steel material contains 0.10 to 0.25% of C, 0.05 to 0.60% of Si, 1.0 to 2.5% of Mn, 0.060% or less of Al, 0.005 to 0.030% of Ti, 0.0005 to 0.0030% of B, and 0.0060% or less of N at weight%. Furthermore, it contains in arbitrary combination of the first class or second class or more in a scope of 0.5% or less of Cu, 0.5% or less of Ni, 0.5% or less of Cr, 0.5% or less of Mo, 0.05% or less of Nb, and 0.05% or less of V. Moreover, it has a recessed section and a projection having irregularities in the height of 0.2 to 1.0mm on a friction-grip-joint surface of the steel material which satisfies Ti-3.4N>0, and the section of 0.5mm or more from its surface has Vickers hardness of 250 or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high strength bolt friction joining steel material, which can be used for a friction joining portion of a steel structure in a building or a bridge.

[0002]

2. Description of the Related Art In high-strength bolt friction welding, the friction surface which is important in terms of welding strength in the design and construction guidelines of the Japan Institute of Architecture is a good red rust surface with black skin removed and a slip coefficient of 0.
It is said that it is necessary to perform a treatment exceeding 45 and to confirm the slip coefficient by a slip proof test. Normal,
It is known that in a good red rust state, the slip coefficient exceeds 0.45, and the slip proof test is often omitted.

Although a slip coefficient of about 0.6 may be obtained in the red rust state, the rust formation state varies depending on environmental factors, steel material composition, etc., so that there are large variations, and the slip coefficient is designed to be 0.45. It seems that It is clear that the slip coefficient of the friction-bonded surface is preferably as high as possible in terms of bonding strength, and in JP-A-51-52628, the joint surface is made uneven before construction, or in JP-A-1-206104. High corrosion resistance is generated by spraying corrosion resistant metal. However, the slip coefficient of the friction-bonded surface tends to increase as the surface roughness of the steel material increases, but there is a problem in that even if the surface roughness is increased, it does not exceed a certain value.

[0004]

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a steel material for high-strength bolt friction welding, which has a rough surface on the friction-bonding surface and has a hard surface to stably exhibit a high slip coefficient. It is intended.

[0005]

That is, the gist of the present invention is as follows. Steel composition is wt%
C: 0.10-0.25%, Si: 0.05-0.
60%, Mn: 1.0 to 2.5%, Al: 0.060%
Hereinafter, Ti: 0.005 to 0.030%, B: 0.00
05: 0.0030%, N: 0.0060% or less, Cu: 0.5% or less, Ni: 0.5% or less,
Cr: 0.5% or less, Mo: 0.5% or less, Nb: 0.
05% or less, V: 0.05% or less in the range of 1 or 2
Included in any combination of one or more kinds, and Ti-3.4N>
The difference in height on the friction-bonded surface of the steel material that satisfies 0: 0.2 to
A steel material for high-strength bolt friction welding, which has irregularities of 1.0 mm and has a Vickers hardness of 250 or more from 0.5 mm or more from the surface.

[0006]

In order to increase the slip coefficient of steel, a method of increasing the surface roughness of the friction-bonded surface by shot blasting or grid blasting is used. However, in blasting, the surface roughness, that is, the difference in height of the surface irregularities, is at most 150 μm, depending on the steel type and shot grains
However, there is a limit to the increase in the slip coefficient. Further, according to the research conducted by the present inventors, in order to increase the slip coefficient with the same surface roughness, it is necessary to increase the hardness (surface hardness) of the friction-bonded surface. That is,
The present invention was made based on the new finding that the slip coefficient can be remarkably improved by providing the friction-bonded surface with appropriate irregularities and increasing the surface hardness.

The present invention will be described below. From the viewpoint of the slip coefficient, the higher the roughness of the friction-bonded surface and the higher the hardness, the better. First of all, how to make unevenness on the friction-bonded surface is transfer by a roll with unevenness, mechanical processing, laser processing,
There are electric discharge machining, a chemical method and the like, and any method may be used. The height difference of the unevenness at this time is required to be equal to or more than the height difference that can be easily applied by blasting or the like in order to positively increase the slip coefficient,
It is limited to 0.2 mm or more. However, this height difference is 1.
If it exceeds 0 mm, the slip coefficient is not significantly improved, so the upper limit was made 1.0 mm. The shape of the unevenness is a pyramid (FIG. 1A) or a mountain (FIG. 1A) as shown in FIG.
It is preferable that the tip is sharp as in (b)).

The slip coefficient cannot be remarkably improved only by increasing the surface roughness by making the friction-bonded surface uneven as described above, and in addition to this, it is necessary to increase the surface hardness. Quenching is generally the easiest method to increase the surface hardness, but when irregularities on the surface are to be applied by laser machining, electrical discharge machining, etc., local heat input during processing and subsequent cooling In some cases, only the surface is quenched and the quenching process becomes unnecessary. The surface irregularities may be applied in any state before and after the quenching treatment, but it is obvious that the machining is easy before the quenching treatment.

When the surface is roughened by roll transfer, it is most efficient to work hot in the final rolling pass on the steel rolling line, and the surface is hardened by cooling (quenching) immediately after rolling. It is possible to make it inexpensive, and most preferable for mass production. In order to remarkably improve the slip coefficient, the higher the surface hardness, the better, and the Vickers hardness was limited to 250 or more. Although the upper limit is not particularly specified, it is naturally limited by the range of the composition to be described later. Further, this hardness does not have to cover the entire cross section of the steel material, and may have a depth of at least 0.5 mm from the surface of the friction joint surface.

In order to obtain the above hardness by quenching treatment, it is necessary to limit the steel material composition and enhance the quenchability. C is the most effective element for enhancing the hardenability.
To easily obtain Vickers hardness of 250 or more, 0.1
It is necessary to add 0% or more. However, even if the C content is increased and the hardness is increased more than necessary, the effect of improving the slip coefficient is slowed down. Therefore, the upper limit was limited to 0.25%.

Si is an element necessary for deoxidizing steel and is 0.05%.
It is necessary to add above. However, if a large amount is added, the toughness of the steel is deteriorated, and the unevenness of the surface may become a potential crack to cause cracking. Therefore, the upper limit was limited to 0.60%. Mn is an element essential for increasing the hardenability and ensuring the toughness of the base material, and the lower limit thereof is 1.0%.
However, even if too much is added, the effect of increasing the hardness with respect to the amount added is slowed down, so the upper limit was made 2.5%.

Al is an element necessary for deoxidizing steel, but it is not always necessary because it contains other deoxidizing elements.
The lower limit is not limited. On the other hand, excessive addition deteriorates the toughness of the steel, and unevenness on the surface may cause latent cracks to cause cracking, so the upper limit was made 0.060%. Ti is added in order to fix N and effectively act B to significantly enhance the hardenability. When Ti and N in the following formulas are the amounts of Ti and N contained in steel, Ti-3. It is necessary to satisfy 4N> 0. The meaning of this formula is that stoichiometrically, Ti is added in an amount more than (excessive) enough to completely fix N. However, if too much is added to satisfy the above formula, not only is it expensive, but TiC precipitates and also fixes C, so the upper limit was limited to 0.030%. On the other hand, the lower limit value is set to 0.005% because N on steelmaking is always included as described later.

Similar to C, B is an element that remarkably increases the hardenability, and addition of 0.0005% or more remarkably contributes to the increase in hardness. However, if it exceeds 0.0030%, the effect becomes small with respect to the added amount, so the upper limit is 0.003.
It was set to 0%. N is an impurity element in the present invention,
The smaller the amount, the better. However, it is contained in the steel for melting.
However, if too much, it is necessary to increase the Ti content to completely fix it, which leads to an increase in cost.
Only the upper limit was limited to 0.0060%.

In addition to the above components, Cu and N are further contained.
All of i, Cr, Mo, Nb, and V are added to increase the quench hardening ability. The harder the alloy is, the more it is added, and the harder it is. Even if the cooling rate during quenching is relatively slow, it is possible to easily obtain a surface hardness of Vickers hardness of 250 or more. The upper limit of the addition amount is not limited by the weldability like general steel materials because the steel material of the present invention is not welded by its nature, and not only the effect on the hardenability but also the alloy cost regulation. Cu, Ni, Cr, Mo 0.5%, N
b and V were set to 0.05%. These selective elements have an additive property with respect to the hardenability as well as being added alone, and thus can be used in any combination of two or more kinds.

Other impurities (P, S, etc.) inevitably present in the steel are not particularly limited.

[0016]

EXAMPLES Table 1, Table 2 (continuation-1 of Table 1), Table 3 (continuation-2 of Table 1), Table 4 (continuation-3 of Table 1) are for illustrating the usefulness of the present invention. Steels A to AE are components of the present invention, and steels R1 to R4 are comparative components. These steels were hot-rolled to a plate thickness of 12 mm, and the slip coefficient was measured using a test piece as shown in FIG. 2 for a steel material having surface irregularities and surface hardness specified in the present invention. In the measurement, the base material 1 to be joined, the jig plate 4 is SM490A steel, the bolt 3 is F15T, and the splice plate 2 is the steel material of the present invention.

Tables 5 and 6 (continuation of Table 5) show height differences and shapes of irregularities on the friction-bonding surface of the splice plate, and 2
The depth from the surface of 50 Hv or more, the slip coefficient, the uneven processing method, and the surface hardening method are shown.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

[Table 5]

[0023]

[Table 6]

In Tables 5 and 6, Examples 1 to 31 all have the components specified in the present invention, the unevenness of the friction-bonded surface, the surface hardness, etc., and therefore exhibit a high slip coefficient of 0.9 or more. are doing. The surface layer was hardened by offline quenching after unevenness processing as a seed, or by direct quenching after unevenness transfer by a roll in the final pass in the hot rolling step, but the surface unevenness was partially processed by laser. This shows an example in which the required curing depth (0.5 mm or more) can be obtained from the surface by properly adjusting the laser output.

On the other hand, in Comparative Examples 32 to 37,
The slip coefficient is generally low because any one or more of the steel composition, surface hardness, hardening depth, and unevenness of the friction joint surface depart from the scope of the present invention. In Comparative Examples 33 and 34 using steels R2 and R3, Si and Al were excessively added, respectively, which did not cause a big problem at the time of steel material production and uneven processing. The toughness after quenching is low, and irregularities on the friction-bonded surface may occur as latent cracks, which may impair the reliability of the friction-bonded portion.

[0026]

According to the present invention, a stable and high slip coefficient (0.9 or more) can be easily obtained. As a result, it can be provided as a structural member that enhances the reliability of the high-strength bolt friction joint in the fields of construction and bridges, and its industrial value is great.

[Brief description of drawings]

FIG. 1 is a schematic view showing an uneven shape of the most preferable friction-bonding surface of the present invention.

FIG. 2 is a view showing a test body for measuring a slip coefficient.

[Explanation of symbols]

 1 Base material to be joined 2 Splice plate (steel of the present invention) 3 Bolt 4 Jig plate

Claims (1)

[Claims] 1. The steel composition is wt%, C: 0.10 to 0.25%, Si: 0.05 to 0.60%, Mn: 1.0 to 2.5%, Al: 0.060. % Or less, Ti: 0.005 to 0.030%, B: 0.0005 to 0.0030%, N: 0.0060% or less, and further Cu: 0.5% or less, Ni: 0.5 % Or less, Cr: 0.5% or less, Mo: 0.5% or less, Nb: 0.05% or less, V: 0.05% or less, and may be contained in one kind or in any combination of two or more kinds. And, the friction-bonded surface of the steel material satisfying Ti-3.4N> 0 has unevenness of height difference: 0.2 to 1.0 mm, and 0.5 mm or more from the surface has Vickers hardness of 250 or more. A steel material for high-strength bolt friction welding characterized by the following.