JP2001234285A - High strength and high toughness steel bar for earthquake proof damper excellent in low cycle fatigue characteristic nd producing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel bar for an earthquake proof damper in which the increase of strength for increasing energy absorption and the improvement of the low cycle fatigue life are made consistent and moreover excellent in low temperature toughness and to provide a producing method therefor. SOLUTION: This high strength and high toughness steel bar for an earthquake proof damper excellent in low cycle fatigue characteristics has a composition containing, by mass, 0.02 to 0.15% C, 0.01 to 1.5% Si, 0.2 to 3.0% Mn, 0.001 to 0.3% Al and 0.001 to 0.02% N and, if required, containing other elements, and in which carbon equivalent is 0.3 to 0.8%. Moreover, this steel can be product by performing heat treatment to 850 to 1,100 deg.C and hot-forming or performing normalizing treatment so as to be heated at 850 to 1,100 deg.C after hot forming.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, high-toughness seismic isolation device having excellent low cycle fatigue characteristics, which is used in a seismic isolation damper device for absorbing vibration energy acting on a building structure or the like due to an earthquake or the like. The present invention relates to a steel bar for a damper and a method for manufacturing the same.

[0002]

2. Description of the Related Art Various methods, such as oil dampers and viscous dampers, have been proposed as seismic isolation dampers for absorbing vibration energy acting on building structures and the like due to an earthquake or the like. Further, as a seismic isolation damper device using a steel material, for example, JP-A-60-258343, JP-A-1-268933, JP-A-5-263549.
Some methods have been proposed as disclosed in Japanese Unexamined Patent Application Publication No. Hei 7-76552.

On the other hand, the characteristics required for a steel rod for a seismic isolation damper include a high energy absorption capacity for absorbing vibration energy by plastic deformation and a low cycle fatigue characteristic in a region where plastic strain is 10% or more. Furthermore, when the seismic isolation damper is used in cold regions, low temperature toughness is also required. The energy absorption capacity of a steel rod increases as the strength of the steel rod increases. However, low cycle fatigue life generally decreases with increasing strength. That is, the energy absorption capacity of the steel rod and the low cycle fatigue life are in a contradictory relationship. Also,
The low-temperature toughness also decreases as the strength increases.

As a steel material for a damper, Japanese Unexamined Patent Publication No.
No. 651, the yield strength is 20 to 35 kgf / mm ² , the tensile strength is 35 to 50 kgf / mm ² , the elongation is 20% or more, and the number of low cycle fatigue at a total axial strain of 5% is 30.
Steel rods that are more than times have been proposed. In addition, Japanese Unexamined Patent Publication
Japanese Patent No. 31467 proposes a method of manufacturing a steel material for a vibration energy absorbing member. However, the tensile strength of steel is 50 kgf / mm ² or less in any of the technologies, and there is a limit in enhancing the energy absorbing ability.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and relates to a steel rod for a seismic isolation damper, which has a high strength and a low cycle fatigue life for enhancing energy absorption capacity. It is an object of the present invention to provide a steel rod for a seismic isolation damper having excellent low-temperature toughness and a method of manufacturing the same.

[0006]

Means for Solving the Problems As means for achieving high strength of steel materials, refinement of ferrite is strengthened. Precipitation strengthening. Solid solution strengthening. Increase in cementite fraction. There are high strength bainite and martensite. Although it is possible to increase the strength of the steel material by any of the above means, it is necessary to consider the low cycle fatigue characteristics aimed at by the present invention.

[0007] Since the effect of the above strengthening means on the low cycle fatigue characteristics is not clear, the present inventors first analyzed in detail the above factors which affect the low cycle fatigue life and energy absorption capacity. As a result, in order to increase the strength of the steel rod, that is, to realize a steel rod having high energy absorption capacity and excellent low cycle fatigue life, ferrite refinement, Ti (CN) , V
It has been found that precipitation strengthening using carbonitrides such as (CN) and Nb (CN), and then solid solution strengthening using Si, Mn, Ni and the like are good. It was also clarified that these strengthening methods do not impair the low temperature toughness. In addition, we have established a manufacturing technology for steel bars for seismic isolation dampers in order to sufficiently exert ferrite refinement and precipitation strengthening.

[0008] The present invention has been made based on the above findings, and the gist thereof is as follows. (1) In mass%, C: 0.02 to 0.15%, Si: 0.01 to 1.5%, Mn: 0.2 to 3.0% Al: 0.001 to 0.3%, N: 0.001 to 0.02%, with the balance being Fe and unavoidable impurities,
The carbon equivalent (Ceq) represented by the formula (1) is 0.3 to 0.8%
High strength and high toughness steel bars for seismic isolation dampers with excellent low cycle fatigue characteristics. Ceq = C% + Si% / 24 + Mn% / 6 + (Cr% + Mo% + V%) / 5+ (Ni% + Cu%) / 15 (1) (2) Steel composition is further increased Cr: 0.05 to 2.0%, Mo: 0.05 to 1.0%, Ni: 0.05 to 5.0%, Cu: 0.05 to 1.5%, B : 0.0003 to 0.005% of one or more of the above.
(1) A steel bar for a high-strength and high-toughness seismic isolation damper having excellent low cycle fatigue characteristics described in (1). (3) One or two types of steel components, in terms of mass%, V: 0.01 to 0.5%, Nb: 0.001 to 0.5%, Ti: 0.003 to 0.1% The above is characterized by including the above
A steel rod for a high-strength and high-toughness seismic isolation damper having excellent low cycle fatigue characteristics as described in (1) or (2). (4) One or two types of steel components, in terms of mass%, Ca: 0.0003 to 0.01%, Mg: 0.0003 to 0.01%, REM: 0.005 to 0.1% The above is characterized by including the above
A steel rod for a high-strength and high-toughness seismic isolation damper having excellent low-cycle fatigue properties according to any one of (1) to (3). (5) A steel rod containing the component according to any one of the above (1) to (4) is heated to 850 to 1100 ° C. and hot-formed to obtain a steel rod having excellent low cycle fatigue properties. Manufacturing method of steel rod for high strength and high toughness seismic isolation damper. (6) After normalizing the steel rod containing the component according to any one of the above (1) to (4) to 850 to 1100 ° C. and performing hot forming, then normalizing to 850 to 1100 ° C. A method for producing a steel bar for a high-strength and high-toughness seismic isolation damper having excellent low-cycle fatigue characteristics, which is subjected to a treatment.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION First, a steel bar for a high-strength and high-toughness seismic isolation damper having excellent low cycle fatigue characteristics according to the present invention has a tensile strength of 550 MPa or more and a 50% fracture surface transition temperature of -30 ° C. or less. Meaning that the fatigue life in a region where the plastic strain applied to the steel rod is 10 to 15% is 12 times or more.

Hereinafter, the reasons for limiting the components of the steel to which the present invention is applied will be described. C: C is an element effective for increasing the strength of the steel rod, but if it is less than 0.02%, 550M which is the object of the present invention.
It is difficult to obtain a tensile strength of Pa or more. on the other hand,
Excessive addition exceeding 0.15% increases the strength, but significantly reduces the low cycle fatigue life and decreases the toughness. Therefore, the addition range of C is set to 0.02 to 0.15%.
Limited to.

Si: Si is an element effective for solid solution strengthening of ferrite and deoxidation of steel, and has an effect of increasing the strength of a steel rod and improving the energy absorbing ability. If the content is less than 0.01%, the above effect cannot be expected. On the other hand, if the content exceeds 1.5%, the effect is saturated. Therefore, the content is limited to the range of 0.01 to 1.5%.

Mn: Mn is not only necessary for deoxidation and desulfurization, but is also an extremely effective element for refining ferrite and strengthening solid solution. It enhances the strength and energy absorption of steel rods. Has the effect of causing. Further, there is an effect of improving the low cycle fatigue life. If the content is less than 0.2%, the above effect cannot be sufficiently exerted. On the other hand, if the content exceeds 3.0%, the effect is saturated, so that the content is limited to the range of 0.2 to 3.0%.

Al: Al is an element effective for deoxidation and grain refinement of ferrite grain size. The grain refinement of ferrite grains increases the strength of a steel rod, increases the energy absorption capacity, and further reduces the cycle fatigue life. And improvement in toughness. If the content is less than 0.001%, the above effects cannot be exhibited,
Even if added over 0.3%, an effect commensurate with the added amount cannot be expected, so the range was limited to the range of 0.001 to 0.3%.

N: N has an effect of reducing austenite grains and ferrite grains by forming carbonitrides by combining with Al and Ti. Further, Ti, V, N
When b is added, precipitation hardening occurs due to precipitation of those carbonitrides. As a result, the strength of the steel rod is increased, the energy absorbing ability is improved, and the low cycle fatigue life and toughness can be improved. If the amount of N added is less than 0.001%, the above effect cannot be sufficiently exerted. On the other hand, if it exceeds 0.02%, the amount of solute N increases and the toughness decreases. .02%
Restricted to the range.

The above are the basic components of the steel bar of the present invention.
In the present invention, one or more of Cr, Mo, Ni, Cu, and B are used to increase the hardenability and increase the strength of the steel rod.
In order to reduce the grain size of ferrite and strengthen precipitation, V, T
One or more kinds of i and Nb, and one or more kinds of Ca, Mg and REM can be contained in order to reduce the size of ferrite.

Cr: Cr is an element effective for improving the strength of a steel rod, but it needs to be added in an amount of 0.05% or more in order to produce a clear effect, while adding more than 2.0%. Then, since the toughness tends to deteriorate, 0.05 to 2.0%
Restricted to the range.

Mo: Mo is an element that is extremely effective in improving the strength of steel bars and the fire resistance of seismic isolation dampers when required. If it is less than 0.05%, the above effect cannot be sufficiently exhibited, and even if it exceeds 1.0%, an effect commensurate with the added amount cannot be expected.
Restricted to the range.

Ni: Ni is an extremely effective element for increasing the strength and the absorbed energy of the steel rod and for improving the low cycle fatigue life and low temperature toughness. However, in order to exert the effect sufficiently, 0.05% or more is required. Need to be added. on the other hand,
Even if added in excess of 5.0%, the effect is saturated, so the upper limit was made 5.0%.

Cu: Cu also has the same effect as Ni, but if it is less than 0.05%, a sufficient effect cannot be expected. On the other hand, if it exceeds 1.5%, the hot workability deteriorates. It was limited to the range of 0.05 to 1.5%.

B: B has the effect of increasing the hardenability and increasing the strength when added in a small amount. However, if less than 0.0003%, the above effect cannot be expected, and even if added over 0.005%, the effect will not increase. In order to saturate, it was limited to the range of 0.0003 to 0.005%.

V: V forms a carbonitride by combining with N and carbon, and is an extremely effective element for strengthening the precipitation of ferrite and strengthening the grain refinement of ferrite. As a result, the strength of the steel rod increases, the energy absorbing ability increases, and the low cycle fatigue life and low temperature toughness can be improved. The above effect cannot be sufficiently exerted when the content is less than 0.01%, and the effect is saturated even when added over 0.5%. Therefore, the content is limited to the range of 0.01 to 0.5%.

Nb: Nb also has the same effect as V,
If the amount is less than 0.001%, the effect cannot be sufficiently expected. On the other hand, if the amount exceeds 0.5%, the effect is saturated.
It was limited to the range of 001 to 0.5%.

Ti: Ti also has the same effect as V and Nb, but if less than 0.003%, the effect cannot be exhibited.
%, The effect is saturated.
Limited to the range of ~ 0.1%.

Ca, Mg, REM: Ca, Mg, REM
All form fine oxides or sulfides or mixtures thereof, and are effective elements for refining ferrite. As a result, it is possible to increase the strength of the steel rod, improve the energy absorbing ability, and improve the low cycle fatigue life and the low temperature toughness. The lower limit contents for exhibiting these effects are 0.0003% for Ca and Mg, and 0.005% for REM. On the other hand, if added excessively, sulfides and oxides become coarse and the toughness is reduced. Therefore, the upper limits are respectively limited to 0.01% for Ca and Mg and 0.1% for REM.

Other elements are not particularly limited, but P is preferably 0.02% or less and S: 0.02% or less from the viewpoint of preventing a decrease in toughness.

In addition to the above limitation of the chemical composition, in the present invention, the carbon equivalent (Ceq) represented by the formula (1) is limited to 0.3 to 0.8 for the following reason. Ceq = C% + Si% / 24 + Mn% / 6 + (Cr% + Mo% + V%) / 5+ (Ni% + Cu%) / 15 (1) Carbon equivalent is 0.3% If it is less than this, it is difficult to produce a high-strength steel rod having a tensile strength of 550 MPa or more, which is the object of the present invention. On the other hand, if the carbon equivalent exceeds 0.8%, martensite which deteriorates toughness and low cycle fatigue properties is likely to be generated, so the upper limit was limited to 0.8%.

Next, a method for producing a high-strength and high-toughness steel rod for a damper having excellent low cycle fatigue characteristics will be described.
The steel rod for a damper rolled to a predetermined diameter by hot rolling is cooled after being formed into a predetermined shape by hot, or by refining crystal grains after hot forming, the strength,
It is manufactured in a process that goes through a normalizing process to improve toughness and low cycle fatigue characteristics. An important point in producing a steel rod having excellent grain strength and high strength / high toughness and low cycle fatigue properties is to finally refine the ferrite grains.

Hot forming condition of steel rod for damper: The hot forming temperature for forming the hot-rolled steel rod into a predetermined shape is 1
If the temperature exceeds 100 ° C., the austenite grains become coarse, making it difficult to finally obtain a fine ferrite structure, resulting in a decrease in toughness and low cycle fatigue life. Further 110
When the temperature exceeds 0 ° C., the decarburization of the surface layer of the steel rod becomes remarkable, so that the fatigue characteristics deteriorate. On the other hand, if the temperature is lower than 850 ° C., it is difficult to completely austenite, so that the hot forming temperature range is 850 ° C.
範 囲 1100 ° C.

Normalizing conditions: If the normalizing temperature after hot forming exceeds 1100 ° C., it is difficult to form a fine ferrite structure, and furthermore, the surface layer is significantly decarburized. As a result, strength, toughness, and low cycle fatigue properties are likely to be reduced. On the other hand, if the temperature is lower than 850 ° C., complete austenitization is difficult, so the normalizing temperature range is limited to the range of 850 to 1100 ° C.

Although the hot rolling conditions are not limited, the following finishing rolling conditions are preferred from the viewpoint of reducing the size of ferrite grains. If the finishing temperature of the hot rolling exceeds 1000 ° C., the austenite grains cannot be refined, so that the steel material has a coarse ferrite structure. Even if a steel material having a coarse ferrite structure is hot worked into a steel bar for a damper having a predetermined shape, it is difficult to finally obtain a fine ferrite structure. If the ferrite grain size of the steel rod for the damper is coarse, the low cycle fatigue properties and the low temperature toughness decrease. For this reason, it is a preferable range that the hot rolling finishing temperature is 1000 ° C. or less. In addition, the rolling reduction of the finish rolling is 2
If it is less than 0%, it is difficult to refine the ferrite, so that
The lower limit of the rolling reduction is preferably 20% or more.

[0031]

EXAMPLES Hereinafter, the effects of the present invention will be described more specifically with reference to examples. A test material having the chemical composition shown in Table 1 was finished to a diameter of 50 to 100 mm by hot rolling. The finish rolling of hot rolling was performed under the conditions of a finishing temperature of 800 to 950 ° C. and a finish reduction of 25 to 40%. Then, it was formed into a steel rod having a predetermined shape by heating. Air cooling was performed after hot forming. In the normalizing process, the film was kept at a predetermined temperature for one hour, and then air-cooled.

[0032] Tensile test pieces and Charpy impact test pieces were sampled from the steel rods after the hot forming or the normalizing treatment, and their properties were evaluated. 50% Charpy impact properties
It was evaluated by the fracture surface transition temperature (vTrs) (JIS No. 4 test piece). Further, using the seismic isolation device shown in FIG. 1, a fatigue test was performed under the condition that the horizontal amplitude was 50 cm. The low cycle fatigue properties of the steel rod were evaluated based on the number of times the steel rod breaks and the accumulated energy absorbed. Table 2 shows the production conditions and the results of the tensile test, the fracture surface transition temperature, and the low cycle fatigue properties of the steel rod.

In Table 2, Test No. 1 to 12 are comparative examples, and 13 to 40 are examples of the present invention. As can be seen from the table, each of the examples of the present invention has a tensile strength of 550 MPa or more, a fracture surface transition temperature of -30 ° C. or less, and the number of breaks and the accumulated absorbed energy in the low cycle fatigue properties are comparative examples. Higher and better. On the other hand, in Comparative Example No. In any one of 1-3, 6-8, the C content is 0.1.
Since it exceeds 15%, the fracture surface transition temperature is high, and the number of fractures in the low cycle fatigue test does not reach the number of 12 intended in the present invention. In addition, No. No. 9 is an example in which martensite was generated in part because the carbon equivalent exceeded 0.8, in which the fracture surface transition temperature was significantly deteriorated and the number of fractures was extremely reduced. In addition, in Comparative Example No.
Nos. 4 and 5 are examples in which although the fracture surface transition temperature and the number of fractures are all good, the carbon equivalent is less than 0.3, and thus the strength of 550 MPa or more intended in the present invention has not been reached. In addition, in Comparative Example No. 10 to 12 are all hot forming temperatures or normalizing temperatures of 1100 ° C.
In this case, the crystal grain coarsened due to exceeding, and as a result, the fracture surface transition temperature was low, and the number of fractures did not reach the purpose.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

As is clear from the above embodiments, the present invention is intended to achieve both high strength and high toughness and excellent low cycle fatigue characteristics of a steel rod for a seismic isolation damper. Is extremely remarkable.

[Brief description of the drawings]

FIG. 1 shows a seismic isolation device used in an experiment, wherein (a) shows a plane and (b) shows a side surface.

[Explanation of symbols]

 1: Steel rod for seismic isolation damper 2: Steel rod mounting member 3: Steel rod fixing hardware

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C22C 38/58 C22C 38/58 F16F 1/02 F16F 1/02 A (72) Inventor Atsushi Watanabe Futtsu, Chiba 20-1 Shintomi, Nippon Steel Corporation Technology Development Division (72) Inventor Mitsuru Sugisawa 20-1 Shintomi, Futtsu-shi, Chiba F-term in Technology Development Division Nippon Steel Corporation Reference 3J059 AB05 AB07 AB11 AD06 BA01 BC02 BD01 GA42 4K032 AA01 AA02 AA11 AA12 AA14 AA15 AA16 AA17 AA19 AA21 AA22 AA23 AA24 AA31 AA32.

Claims (6)

[Claims] C: 0.02 to 0.15%, Si: 0.01 to 1.5%, Mn: 0.2 to 3.0%, Al: 0.001 to 0.3% by mass. %, N: 0.001 to 0.02%, the balance being Fe and unavoidable impurities,
The carbon equivalent (Ceq) represented by the formula (1) is 0.3 to 0.8%
High strength and high toughness steel bars for seismic isolation dampers with excellent low cycle fatigue characteristics. Ceq = C% + Si% / 24 + Mn% / 6 + (Cr% + Mo% + V%) / 5+ (Ni% + Cu%) / 15 ・ ・ ・ (1) 2. The steel composition further includes, by mass%, Cr: 0.05 to 2.0%, Mo: 0.05 to 1.0%, Ni: 0.05 to 5.0%, Cu: 0. And B is 0.0003 to 0.005%.
High strength and high toughness steel bars for seismic isolation dampers with excellent low cycle fatigue characteristics as described. 3. The steel composition further comprises one or more of V: 0.01 to 0.5%, Nb: 0.001 to 0.5%, Ti: 0.003 to 0.1% by mass%. 2. The method according to claim 1, wherein the composition contains at least two types.
Or high strength with excellent low cycle fatigue characteristics described in 2.
Steel rod for high toughness seismic isolation damper. 4. The steel composition further comprises one or more of mass%, Ca: 0.0003 to 0.01%, Mg: 0.0003 to 0.01%, REM: 0.005 to 0.1%. 2. The method according to claim 1, wherein the composition contains at least two types.
4. A steel bar for a high-strength and high-toughness seismic isolation damper having excellent low-cycle fatigue characteristics according to any one of the above items 3 to 3. 5. A high-strength steel with excellent low cycle fatigue characteristics, wherein a steel rod containing the component according to any one of claims 1 to 4 is heated to 850 to 1100 ° C. to perform hot forming. Manufacturing method of steel rod for high toughness seismic isolation damper. 6. A normalizing treatment in which a steel rod containing the component according to any one of claims 1 to 4 is heated to 850 to 1100 ° C., hot-formed, and then heated to 850 to 1100 ° C. A method for producing a high-strength, high-toughness steel rod for a seismic isolation damper having excellent low-cycle fatigue characteristics, which is characterized by being applied.