JP2000054062A - High friction steel material for joint, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit the formation of an internal oxidation layer and to prevent intergranular oxidation by adding slight amounts of Ni, Cu, and Mo to a steel and controlling the concentration Ni/Cu and the thickness of an Ni-, Cu-, and Mo-concentrated layer formed on an internal oxidation layer, respectively. SOLUTION: The steel has a composition which consists of, by weight, 0.15-0.20% C, 0.4-1.6% Mn, <=0.1% Si, 0.1-0.5% Cr, 0.001-0.10% Al, 0.3-1.5% Ni, 0.3-1.5% Cu, 0.1-0.7% Mo, 0.001-0.010% N, and the balance Fe and in which the concentration of Ni/Cu is regulated to >=0.8. A cast billet of the steel is reheated to 1100 to 1300 deg.C and hot rolling is started, and rolling where cumulative draft at <=950 deg.C becomes >=40%, is applied. By this method, the steel material, which has an internal oxidation layer of <=2 μm thick in the steel-material surface and also has an Ni-, Cu-, and Mo-concentrated layer of >=2 μm thick on the internal oxidation layer and in which the sum of the concentrations of these elements is regulated to >=4.0% and the thickness with a Vickers hardness exceeding Hv 420 in the region between the surface and a position at a depth of 3 mm from the surface is regulated to >=0.5 mm, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structural member of a building, and more particularly to a joint such as a split T-section steel and a rolled steel plate for a joint formed from a high-tensile-rolled section steel used as a joining member of a building. The present invention relates to a member and a method for manufacturing the member.

[0002]

2. Description of the Related Art Steel materials used for columns are required to have higher tensile strength, higher toughness, lower yield ratio, and higher reliability of welded joints due to the increasing height of buildings and stricter safety standards. Is required. In order to satisfy such required characteristics, conventionally, heat treatment such as normalizing treatment has been performed after the completion of rolling. However, as a matter of course, the addition of this heat treatment step increased the production cost, and the development of a shaped steel material by a new alloy design and a method for producing the same using a new alloy so that high-performance material properties and weld joint properties can be obtained as-rolled We are in need.

[0003] Rolled H-section steel is often used as the above-mentioned steel section, but when an H-section steel is manufactured by universal rolling, restrictions on rolling conditions (rolling temperature, rolling reduction) from rolling molding and restrictions thereof are imposed. Due to the peculiarity of the shape, differences occur in the rolling finish temperature, rolling reduction, and cooling rate in each part of the web, flange, and fillet. For example, a rolled steel material for a welding structure (JIS
G3106) and the like. Furthermore, since high-temperature rolling is aimed at in order to obtain the dimensional accuracy of the product by rolling molding, the thick flange part becomes high-temperature rolling,
The cooling of the steel material after the end of the rolling is also gradually cooled. As a result, the microstructure becomes coarse and the strength and toughness decrease.

On the other hand, there is TMCP as a method of refining the structure in the rolling process, but it is difficult to apply low-temperature and large-reduction rolling such as TMCP to steel materials because the rolling conditions are limited in section steel rolling. In the field of heavy steel plates, it manufactures hawk-strength and high-toughness steels using the precipitation effect of nitrides such as VN.
For example, JP-B-62-50548, JP-B-62-5
A technique disclosed in Japanese Patent No. 4862 is proposed. However, when these methods are applied to the production of a symmetrical joint member according to the present invention, since high-concentration solute N is contained, high-carbon island-like martensite is formed in the generated bainite structure. In addition, the toughness was remarkably reduced, and it was difficult to clear the standard value.

[0005] Further, in the joining of columns and beams in a section steel having a flange, for example, an H section steel, a member connecting the H sections is a T-shaped cast steel member or a large number of thick steel sheets having ordinary strength and toughness. A so-called diaphragm joint (FIG. 1) for contacting the joint portion and joining with high-strength bolts has to be preliminarily applied or employed during steel frame assembly processing. In the Great Hanshin Earthquake and the North Rigi Earthquake, there has been a fact that the failure of the steel structure originated from this weld defect. Also, due to the lack of reliability of the welding connection, a method of mechanically connecting the column and the beam to each other by bolt connection via a T-shaped steel joint without welding has been adopted. However, in order to realize the above-mentioned joint method, it is necessary to develop a T-section steel having a higher friction coefficient that is hardened with a higher strength.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has been made in consideration of the following problems.
An object of the present invention is to provide a joint member such as a split T-section steel, a rolled steel plate for a joint formed from a high-tensile rolled section steel used as a joint member of a building, and a method of manufacturing the same.

[0007]

The present invention is used as a joint member such as a split T-section steel or a rolled steel plate for a joint formed from a high-tensile-rolled section steel used as a joint member of the above-mentioned building. To suppress the formation of an internal oxide layer acting from corrosion as a starting point and to prevent grain boundary oxidation, a small amount of Ni, Cu, Mo
By controlling the concentration ratio of u, and further controlling the thickness of the internal oxide layer on the steel material surface, the thickness of the Ni, Cu, and Mo concentrated layers formed on the internal oxide layer, and the total amount of these element concentrations. It has succeeded in developing a rolled steel excellent in weather resistance and fatigue resistance, and the gist is as follows.

1) In weight%, C: 0.15 to 0.20
%, Cr: 0.1 to 0.5%, and further, a trace amount of Ni,
An architectural steel material to which Cu and Mo are added as essential elements, wherein a concentration ratio of Ni / Cu is 0.8 or more, an internal oxide layer on the steel material surface is 2 μm or less, and a thickness of 2 μm is formed on the internal oxide layer.
m having a concentration layer of Ni, Cu, Mo of not less than m, and a total amount of these element concentrations of not less than 4.0% by weight, and a Vickers hardness Hv of more than 420 within a depth of 3 mm from the surface. Is 0.5 mm or more.

2) In weight%, C: 0.15 to 0.20
%, Mn: ≦ 0.4%, Si: ≦ 0.1%, Cr: ≦
0.1%, Al: 0.001 to 0.10%, Ni: 0.
8 to 3.0%, Cu: 0.8 to 1.5%, Mo: 0.4
0.7 to 0.7%, N: 0.001 to 0.010%, and the concentration ratio of Ni / Cu is 0.8 or more, with the balance being Fe and impossible, and Cu and Mo added as essential elements. Construction steel material, wherein the internal oxide layer on the surface of the steel material is 2
μm or less, Ni having a thickness of 2 μm or more on the internal oxide layer,
It has a concentrated layer of Cu and Mo and the total amount of these element concentrations is 4.0% by weight or more, and the thickness exceeding Vickers hardness Hv: 420 within a depth of 3 mm from the surface is 0.5 m.
A high-friction joint steel material having at least m.

3) By weight%, Nb: 0.005 to
0.10%, V: 0.01 to 0.20%, Ti: 0.0
05 to 0.025%, B: 0.0003 to 0.0030
% Of the steel material for high friction joints according to the above 2), wherein the steel material contains any one or more of the above-mentioned steel materials. 4) In weight%, Ca: 0.0005 to 0.005
0%, Mg: 0.0005 to 0.010%, REM:
A rolled steel material excellent in weather resistance and fatigue resistance according to the above 2) or 3), which contains any one or more of 0.0005 to 0.010%.

5) In weight%, C: 0.15 to 0.20
%, Mn: ≦ 0.4%, Si: ≦ 0.1%, Cr: ≦
0.1%, Al: 0.001 to 0.10%, Ni: 0.
8 to 3.0%, Cu: 0.8 to 1.5%, Mo: 0.4
~ 0.7%, N: 0.001 to 0.010%, and the Ni / Cu concentration ratio is 0.8 or more, and the balance is 1100 to 1100%.
After reheating to a temperature range of 1300 ° C., hot rolling was started and 9
Rolling is performed so that the cumulative draft of 50 ° C. or less is 40% or more, hot rolling is completed at 900 ° C. or more, and the thickness of the internal oxide layer on the steel material surface is 2 μm or less as it is hot rolled. It has a concentrated layer of Ni, Cu, Mo of 2 μm or more, the total amount of these elements is 4.0% by weight or more, and the thickness exceeding Vickers hardness Hv: 420 within a depth of 3 mm from the surface. A method for producing a steel material for a high friction joint, which has a diameter of 0.5 mm or more.

6) By weight%, Nb: 0.005 to
0.10%, V: 0.01 to 0.20%, Ti: 0.0
05 to 0.025%, B: 0.0003 to 0.0030
%, The method for producing a steel material for a high-friction joint according to the above item 5), wherein the steel material contains at least one of the following. 7) By weight%, Ca: 0.0005 to 0.005
0%, Mg: 0.0005 to 0.010%, REM:
The method for producing a steel material for a high-friction joint according to the above item 5) or 6), comprising one or more of 0.0005 to 0.010%.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION
As a result of intensive studies on the fracture mechanism of welds in Pa-class H-section steels, the split T-section steels with high strength and high frictional properties have been developed to obtain a surface hardness that satisfies a high coefficient of friction. Hardened, surface hardness Hv ≧ 420
, But even if quenching is performed, it is 0.1 mm from the surface.
Up to 5 mm, the surface hardness cannot be obtained because the martensitic transformation does not occur completely. The reason for this is that when the slab is heated at a high temperature, the Mn diluted band and (MnS
i) It was found that this was caused by the rise of the γ / α transformation point due to the presence of -O and the formation of the grain boundary oxide layer caused by the formation of firelite by the addition of Si. Further, the present inventors have conducted intensive studies on the mechanism of grain boundary oxidation of a 60 Kgf-class high-strength H-section steel. As a result, the formation of an internal oxide layer was caused by seam flaws generated on the inner surface of the flange of the high-strength H-section steel. This seam flaw acts as a starting point of corrosion and pitting corrosion and significantly impairs weather resistance. Then, it was also clarified that the seam flaw was formed by wrinkles formed in the strain concentration portion on the inner surface of the flange due to slab edging, and that the seam flaws were caused by the breakage. The present inventors have taken measures to prevent the occurrence of seam flaws. We studied the formation and influence of the grain boundary oxide layer on the slab surface by the addition of trace elements that contribute to the suppression of wrinkle formation, and the study on the suppression of the formation of the grain boundary oxide layer.

As a result, in order to solve the above-mentioned problems, it is considered that the thickness of the internal oxide layer is reduced and an alloy-concentrated layer is formed on the internal oxide layer. First, the formation of the grain boundary oxide layer increases the thickness of the internal oxide layer and decreases the surface quench hardening property. To suppress this, it is effective to lower the Si (prevent the generation of grain boundary firelite) and to add Cr, which is an element that is more easily oxidized than Mn. In addition, C is less oxidizable than iron
u, Ni, and Mo are concentrated on the internal oxide layer by high-temperature oxidation, thereby improving the surface quench hardening property.

It has been found that the formation of the internal oxide layer described above and trace elements such as Cr, Ni, Cu, and Mo added as reinforcing elements have a large effect. That is, the internal oxide layer formed on the surface layer of the ground iron is composed of a single or composite oxide of Si, Mn, and Fe, that is, Fe and MnO, SiO
_It can be seen that they are formed in a dealloyed layer in which particles such as ₂ are mixed, and these elements combine with oxygen in the air to form as firelite (2SiO ₂ FeO), which becomes the starting point of welding cracks. It was found that grain boundary oxidation occurred.

[0016] By adding Cr, the formation of the grain boundary oxide layer can be suppressed, and corrosion and pitting depth can be suppressed.
By reducing the amount of Si, the formation of grain boundary oxidized firelite can be suppressed, so that the corrosion and the pit depth can be suppressed from expanding. Further, the prevention of MnS formation also made it possible to suppress corrosion and increase the pit depth. This means that the amount of S can also be reduced by reducing the amount of solute S, and the amount of solute S is reduced by sulfide generation by Ca, Mg, and REM.

The present inventors have found that Ni, C with remarkable grain boundary oxidation
Experiments were performed on u-added steel using various steel types. 6
A small amount of Mo, Cr was added to a 0 Kgf-class high-strength section steel, and the vacuum-melted ingot shown in Table 1 was cut in half and heated in a reheating furnace at a temperature within 1300 ° C. for about 4.5 hours. The effects of these added elements on the grain boundary oxidation behavior were investigated by observation, CMA, and SEM analysis.

FIG. 2 shows the relationship between the addition amount of each alloy and the total length of the grain boundary oxidation in the case where the addition amounts of Mo, Cr, and Mo + Cr are changed. (Total length of grain boundary oxidized portions existing in a cross-sectional length of 60 mm on the sample surface.) FIG. 3A is a photograph of a cross-sectional structure of a Cr-free (Cr-free) steel, and FIG. The cross-sectional structure photographs of the 0.20% added steel are shown. As can be seen from these cross-sectional structure photographs, it is clear that grain boundary oxidation is significantly suppressed by the addition of 0.1 to 0.1% of Cr. On the other hand, Mo tends to promote grain boundary oxidation, as can be seen from FIG.

Further, the present inventors have found that Mo: 0.20%,
CMA analysis was performed on steel to which Cr: 0.2%, Mo: 0.1% + Cr: 0.1% were added.
It was found that Mo was dispersed as oxide in the scale, whereas Cr was dispersed as Cr oxide in the internal oxide layer. This tendency was extremely remarkable when Mo and Cr were added in combination. It was also found that Mo was present only in the scale and on the surface of the internal oxide layer, and that Cr was present only in the internal oxide layer. Further, Cr and [O] at the same site where the Cr: 0.20% added steel was subjected to CMA analysis
As a result of investigating the composite concentration distribution of Cr, when the threshold level of [O] was lowered, the distribution region of Cr oxide was expanded from the vicinity of the scale / internal oxide layer interface to the inside. It was also found that the / Cr ratio tended to decrease. Further, when the SEM analysis was performed on the central part in the depth direction of the internal oxide layer of the same sample as the above steel, Mo:
At the tip of the grain boundary oxide layer of 0.20% steel, Si and O estimated to be firelite (2FeO.SiO ₂ ) are detected, and from the oxide particles in the internal oxide layer, in addition to Si and O, Mn was detected. On the other hand, in the steel with 0.20% Cr added, Cr was detected in the oxide particles in the internal oxide layer in addition to Si and O.

Then, various factors for improving the resistance to welding cracking are examined, and it is considered that the mechanism for suppressing the formation of the grain boundary oxide layer due to the addition of Cr is caused by the following factors. Oxygen, although inward diffusion of γ grain boundaries in the path from the surface, Cr is to produce immediately Cr oxide for easily oxidized than Fe, does not form a grain boundary oxidized layer, Cr ₂
O ₃ and FeO easily produce FeO · Cr ₂ O ₃ spinel, which is thought to require a large amount of cation vacancies. Cr and Fe diffuse through the cation vacancies. Ions and oxygen that diffuses inward through the γ grain boundaries combine to form FeO.Cr ₂ O ₃ spinel, which inhibits grain boundary diffusion of oxygen to form oxides. The generation of low melting point firelite is suppressed, and no grain boundary oxide layer is formed.

As described above, in the present invention, Si, which causes the above-mentioned firelite formation, is reduced as much as possible, the internal oxide layer is made extremely thin, and the Mn content is reduced.
By reducing the generation of MnS, which is a starting point of pitting corrosion and significantly impairs weather resistance, a high-tensile H-section steel excellent in pitting corrosion resistance and weather resistance can be obtained. In the present invention, the content S
By adding Ca, Mg, and REM in addition to reducing the amount, the amount of dissolved S can be reduced together with the formation of sulfide.

Further, in the present invention, the above-mentioned factors for improving the weather resistance are searched from the viewpoint of the manufacturing process, and Ni, C
In the case of a high-strength H-section steel to which u and Mo are added, a concentrated layer of Ni, Cu, and Mo is formed on the internal oxide layer, and the amount of the concentrated layer formed is extremely dependent on the slab heating temperature. That the slab heating is 1100 ° C. to 130 ° C.
When performed at a high temperature of 0 ° C., preferably at 1300 ° C. for 4.5 hours, as shown in FIG.
It was also found that a Cu, Mo concentrated layer was formed with a thickness of 2 μm or less. On the other hand, in the case of the conventional low-temperature slab heating of 1100 ° C. or less, as shown in FIG. Corrosion and pit depth are also suppressed, and weather resistance can be improved by the effect of increasing the generation rate of stable rust.

On the other hand, from the viewpoint of fatigue strength,
As described above, Si and M are more easily oxidized than iron (FeO).
By reducing the amount of each of n, the generation of an internal oxide layer acting as a starting point for corrosion is significantly suppressed, thereby preventing a reduction in fatigue strength due to a softened layer and a grain boundary oxide layer accompanying the generation of an internal oxide layer. Can be. The grain boundary oxide layer causes stress concentration due to the notch effect, and similarly causes a reduction in fatigue strength. In addition, by reducing the amount of Si, the fatigue strength can be increased due to the effect of suppressing generation of the grain boundary oxidized firelite layer. Further, by heating the slab at a high temperature of 1100 ° C. to 1300 ° C., preferably 1300 ° C. for 4.5 hours as described above, Ni, Cu, M
Since the o-enriched layer is formed with a thickness of 2 μm or less, the fatigue strength increases due to the effect of suppressing the softening of the oxide layer inside the surface layer. Further, since the fatigue strength has a substantially linear relationship with the yield strength and the tensile strength, the fatigue strength increases with the increase in the yield strength and the tensile strength.

Next, the range of alloy components of the steel material for a high friction joint according to the present invention and the method for producing the same will be described in detail.
Carbon (C) is 0.15 to 50% in order to secure the yield strength and tensile strength of the base material of the high-tensile H-section steel of 60 kgf class.
Add in the range of 0.20%. Silicon (Si) is necessary for securing the strength of the base material, preliminary deoxidation of molten steel, and the like.
% Or more is preferable because it forms MnSi.O and increases the tendency to form 2SiO ₂ FeO which promotes the increase of the internal oxide layer and the grain boundary oxidation.

Manganese (Mn) is an element necessary for securing the strength of the base material, but forms an allowable concentration for the toughness and cracking of the base material and the welded portion, and MnS, and serves as a starting point of pitting corrosion and weather resistance. Because it significantly inhibits, the upper limit is set to 1.
It needs to be 6%. Chromium (Cr) is an important element in the present invention. Since the generation of FeO.Cr ₂ O ₃ spinel suppresses the production of low melting point firelite and does not form a grain boundary oxide layer, From the standpoint of increasing the base material strength, at least 0.1% or more is necessary, but an excessive addition exceeding 0.5% becomes Cr.O, forms an internal oxide layer, and becomes a starting point of corrosion. Therefore, the upper limit is set to 0.5%.

Aluminum (Al) is a powerful deoxidizing element, and is added with an upper limit of 0.1% in order to deoxidize and clean steel, precipitate AlN, fix dissolved N, and improve toughness. Is done. However, when Ca, Mg, REM, etc. are added and these fine oxides are used positively,
When a large amount of Al is added, the formation of fine oxides such as Ca, Mg, and REM is hindered.

Next, in the present invention, addition of Ni, Cu and Mo is essential. Both of these elements are important elements for enhancing the toughness of the base material and forming a layer of Ni, Cu, and Mo having a thickness of 2 μm or more on the internal oxide layer, as elements for increasing the strength. The addition amount of Ni is 0.3 to 3.0%,
u is added in the range of 0.3 to 1.5%. Mo is an element effective for securing the base metal strength and high-temperature strength. However, an excessive addition precipitates Mo carbides and saturates the hardenability improving effect as solid solution Mo. Need to be added.

Further, in the present invention, it is effective to include an appropriate amount of one or more of Nb, V, Ti, and B as further additional elements. Niobium (Nb) and vanadium (V) are Nb: 0.005 to 0.10%, V: 0.01 for the purpose of increasing hardenability and increasing strength.
~ 0.20% is added in each case. However, when the content exceeds 0.005% in the case of Nb and 0.20% in the case of V, the precipitation amount of Nb carbonitride or V carbonitride increases, and the effect as solid solution Nb or solid solution V is increased. Is saturated and Nb:
The upper limits are 0.10% and V: 0.20%, and the lower limits are Nb: 0.00 in terms of hardenability and strength of the base material.
5%, V: 0.01%.

Titanium (Ti) precipitates TiN and suppresses the formation of island martensite by reducing solid solution N, and the finely precipitated TiN contributes to the refinement of the γ phase.
By the action of these Tis, the structure is refined and the strength and toughness are improved. However, an excessive addition of 0.1% or more causes T
Since iC is precipitated and the toughness of the base metal and the heat affected zone is deteriorated by the precipitation effect, the upper limit is set to 0.1%.

Boron (B) is an important element for the hardenability of steel, and is added in an amount of 0.0003 to 0.0030%. Nitrogen (N) forms nitrides and contributes to crystallization of γ grains. However, since excess solute N degrades toughness, the content of N is 0.001 to 0.010%. Magnesium, Ca, and REM are added to form sulfides of Mg, Ca, and REM with higher temperature stability and to fix sulfur for the purpose of preventing the generation of MnS that becomes a starting point of pitting corrosion and lowers the weather resistance. Things.

Further, magnesium (Mg) reduces the Mg content by alloying, suppresses the deoxidation reaction at the time of addition to molten steel, secures safety at the time of addition and improves the yield of Mg, and further improves the yield of MgO. 0.0005 to 0.010% is added for the purpose of generating fine oxides and finely dispersing them to contribute to improvement in strength and toughness of steel. Ca and REM are 0.0005 to 0.005% and 0.0005%, respectively, for the purpose of preventing slab cracking.
It is added in the range of ~ 0.010%.

The reason for setting the concentration ratio of Ni / Cu to 0.8 or more is to prevent surface cracking of the Cu-added steel due to high-temperature heating. In this crack, Cu is concentrated on the internal oxide layer by heating at a high temperature of 1100 ° C. or more, and the molten Cu enters the γ grain boundary to cause Cu melting crack. To prevent this, 1100
Heat at low temperature below ℃ or Ni / Cu ≧ 0.8Ni
This is because it can be prevented by adding and increasing the melting point.

The reason that the thickness of the internal oxide layer on the surface of the steel material is set to 2 μm or less is that the presence of the internal oxide layer having a thickness of 20 μm actually forms the surface softened layer to a depth of 200 μm, which is about 20 times. When the thickness of the internal oxide layer is 2 μm, the depth of the surface softened layer is 20
μm, which is a limit thickness for preventing fatigue and corrosion. Ni, C
The reason why the thickness of the concentrated layer of u and Mo is set to 2 μm or more is as follows.
From the results of measurement with PMA, it was confirmed by a salt spray test that the weather resistance effect was small when the thickness of the Ni, Cu, and Mo concentrated layers was 2 μm or less, so the thickness was set to 2 μm or more. Furthermore,
The total amount of the above elemental concentrations of Ni, Cu, and Mo is 4.0% by weight.
The reason for the above is that according to a heating experiment at 1250 ° C., the concentration of Cu and Ni on the internal oxide layer is about 5 to 10%.
And Mo was 2 to 5 times. Moreover, if the total of these concentrations is 4.0% by weight or less, the desired weather resistance and fatigue characteristics cannot be achieved.

In addition, the reason why the thickness exceeding the surface hardness Hv420 is required to be 0.5 mm or more is to improve the joint performance by forming a projection on the surface and cutting the projection into the beam steel material. Therefore, the hardened layer is harder and the effect increases as the thickness becomes thicker. However, as a result of measuring the required high friction coefficient, these values were obtained, so that the thickness exceeding the surface hardness Hv420 was limited to 0.5 mm or more. Was.

Next, the manufacturing method of the present invention will be described. An important process in the present invention is to perform high-temperature slab heating at a slab heating temperature of 1100 to 1300 ° C. This is to form a concentrated layer of Ni, Cu, Mo on the internal oxide layer with a thickness of 2 μm or more by the high-temperature heating oxidation in the above-mentioned high-temperature slab heating.

In the high temperature heating oxidation, N is deposited on the internal oxide layer.
The reason why i, Cu, and Mo are concentrated is that the formation energy of these metal oxides is higher than that of iron oxide (FeO).
This is because oxides cannot be generated and are left on the internal oxide layer to be concentrated. As a result of heating at 1250 ° C., Ni, Cu, M
A thick layer of o is formed with a thickness of about 30 μm. This is stretched by rolling, and becomes thinner almost in proportion to the stretching ratio. That is, when the thickness is reduced to 1/10,
Its thickness is approximately 3 μm.

Further, as described above, the slab heated at a high temperature is subjected to hot rolling. In this hot rolling, rolling is performed so that the cumulative draft at 950 ° C. or less is 40% or more. There is a need. Cumulative reduction at 950 ° C or lower is 4
The reason for hot rolling at 0% or more is that in order to achieve microstructure refinement by controlling rolling temperature and rolling reduction, it is necessary to apply a reduction of 40% or more in the austenite recrystallization / non-recrystallization temperature range. Because there is.

[0038]

<Example 1> As a prototype H-section steel, a steel having the chemical composition values shown in Table 1 was melted in a converter, an alloy was added, and a preliminary deoxidation treatment was performed to adjust the oxygen concentration of the molten steel. Thereafter, an Mg alloy, Ca, and REM are added, and 250 to 3
It was cast into a 00 mm thick slab.

[0039]

[Table 1] The cooling of the slab was controlled by selecting the amount of water in the secondary cooling zone below the mold and the speed of drawing the slab. The slab thus obtained was heated at a high temperature of 1280 ° C., and after being subjected to a rough rolling step, was rolled into an H-beam by a universal rolling mill row shown in FIG. The rolling and accelerated cooling conditions at this time are shown in Table 2.

[0040]

[Table 2] Table 3 shows the mechanical properties of the H-section steel obtained by this rolling.

[0041]

[Table 3] FIG. 6 shows the cross-sectional shape of the H-section steel and the sampling position of the mechanical test piece. In FIG. 6, at the center (1 / 2t ₂ ) of the thickness t ₂ of the flange 2, 1/4 (1/1) of the entire flange width (B) is used.
The mechanical properties described above were determined using a test piece taken from 4B). The reason for obtaining the mechanical properties of this portion is that the flange 1 / 4F portion shows the average mechanical properties of the H-section steel and can represent the mechanical properties of the H-section steel.

As described above, when all the conditions of the steel composition and the production method according to the present invention are all satisfied, it is possible to produce a steel material for a high friction joint having sufficient strength and low temperature toughness as shown in Table 3. Become. In addition, the rolled section steel to which the present invention is applied is not limited to the H section steel of the above-described embodiment, but may be a section steel having a flange such as an I section steel, an angle section steel, a groove section steel, an unequal thickness angle section steel, or the like. Of course, it can be applied.

[0043]

As described above, the present invention relates to a structural member of a building, in particular, a split T-shaped steel and a rolled steel plate for a joint formed from a high tension rolled steel used as a joining member of a building. It is possible to provide a joint member such as the above and a method for manufacturing the same.

[Brief description of the drawings]

FIG. 1 is a diagram showing a diaphragm joint.

FIG. 2 is a diagram showing the influence of Mo and Cr on grain boundary oxidation.

3A is a cross-sectional structure diagram of a conventional Cr-free steel, and FIG.
1 is a cross-sectional structure diagram of Cr: 0.20% added steel according to the present invention.

4A is a view showing a state of formation of a concentrated layer of Ni, Cu and Mo in a conventional section steel, and FIG. 4B is a view showing Ni and C according to the present invention.
The figure which shows the formation state of the concentrated layer of u and Mo.

FIG. 5 is a diagram showing a universal rolling mill row used in the present invention.

FIG. 6 is a diagram showing a cross-sectional shape of an H-section steel and a sampling position of a mechanical test piece.

Claims (7)

[Claims] (1) C: 0.15 to 0.20% by weight,
Cr: 0.1 to 0.5%, and trace amounts of Ni and Cu
And Mo as an essential element, wherein the Ni / Cu concentration ratio is 0.8 or more, the internal oxide layer on the steel material surface is 2 μm or less, and Ni, 2 μm or more in thickness on the internal oxide layer. It has a concentrated layer of Cu and Mo, and the total amount of these elements is 4.0% by weight or more, and 3 m from the surface.
A steel material for high-friction joints, wherein a thickness exceeding Vickers hardness Hv: 420 within a depth of m is 0.5 mm or more. 2. C: 0.15 to 0.20% by weight
%, Mn: 0.4 to 1.6%, Si: ≤ 0.1%, Cr: 0.1 to 0.5%, Al: 0.001 to 0.10%, Ni: 0.3 to 1 0.5%, Cu: 0.3-1.5%, Mo: 0.1-0.7%, N: 0.001-0.010%, and the concentration ratio of Ni / Cu is 0. .8 or more, the balance being Fe and unavoidable impurities.
An architectural steel material to which i, Cu and Mo are added as essential elements, wherein an internal oxide layer on the surface of the steel material is 2 μm or less, and a concentrated layer of Ni, Cu and Mo with a thickness of 2 μm or more is provided on the internal oxide layer. A high friction joint characterized in that the total concentration of these elements is 4.0% by weight or more and the thickness exceeding Vickers hardness Hv: 420 is 0.5 mm or more within a depth of 3 mm from the surface. For steel. 3. Nb: 0.005 to 5% by weight
0.10%, V: 0.01 to 0.20%, Ti: 0.0
05 to 0.025%, B: 0.0003 to 0.0030
The steel material for a high friction joint according to claim 2, wherein the steel material contains any one or two or more of the following. 4. The method according to claim 1, further comprising:
0.0050%, Mg: 0.0005 to 0.010%,
The rolled steel material having excellent weather resistance and fatigue resistance according to claim 2 or 3, wherein one or more of REM: 0.0005 to 0.010% is contained. 5. C: 0.15 to 0.20 by weight%
%, Mn: 0.4 to 1.6%, Si: ≤ 0.1%, Cr: 0.1 to 0.5%, Al: 0.001 to 0.10%, Ni: 0.3 to 1 0.5%, Cu: 0.3-1.5%, Mo: 0.1-0.7%, N: 0.001-0.010%, and the concentration ratio of Ni / Cu is 0. 0.8 or more, and the balance is 1 piece of slabs composed of Fe and unavoidable impurities.
After reheating to a temperature range of 100 to 1300 ° C., hot rolling is started, and rolling is performed so that the cumulative draft of 950 ° C. or less becomes 40% or more, and the internal oxide layer on the steel material surface is 2 μm or less, and the internal oxide layer is formed. It has a concentrated layer of Ni, Cu, and Mo having a thickness of 2 μm or more, and has a Vickers hardness H within a depth of 3 mm from the surface when the total amount of these element concentrations is 4.0% by weight or more.
v: A method for producing a steel material for a high friction joint, wherein a thickness exceeding 420 is 0.5 mm or more. 6. Nb: 0.005 to 5% by weight
0.10%, V: 0.01 to 0.20%, Ti: 0.0
05 to 0.025%, B: 0.0003 to 0.0030
The method for producing a steel material for a high-friction joint according to claim 5, wherein the steel material contains one or more of the following. 7. In% by weight, Ca: 0.0005 to
0.0050%, Mg: 0.0005 to 0.010%,
The method for producing a steel material for a high friction joint according to claim 5, wherein the steel material contains one or more of REM: 0.0005 to 0.010%.