JPH10176240A - Wide flange shape for tunnel timbering and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a wide flange shape for tunnel timbering good in weld cracking resistance, extremely small in hydrogen defects, furthermore good in toughness and having tensile strength of a 590N/mm<2> class and to provide a method for producing the same. SOLUTION: This steel has a compsn. contg., by weight, 0.04 to 0.13% C, 0.05 to 0.40% Si, 0.3 to 1.5% Mn and 0.005 to 0.10% Al, furthermore contg., as impurities, <=0.010% S, <=0.020% P and <=2.5ppm H, and the balance Fe with inevitable impurities. The steel is rolled under the rolling conditions of >=1200 deg.C heating temp. and >=900 deg.C rolling finishing temp. and is thereafter cooled to <=650 deg.C at a cooling rate of 2 to 30 deg.C/s, by which the wide flange shape for tunnel timbering in which both of the flange thickness and web thickness are regulated to 6 to 25mm, having 590 to 780N/mm<2> tensile strength and having a structure in which the fraction of (ferrite + pearlite) is regulated to >=60% can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength H-section steel used for supporting tunnel construction and a method for producing the same.

[0002]

2. Description of the Related Art Various types of tunnel support patterns have been put into practical use in accordance with geological conditions, and details thereof are described in Tunnel Standard Specifications (mountain edition).
Although the method of driving the rock bolt into the ground is common, the main methods for supporting the inner wall of the tunnel are the method of spraying concrete and the method of bending a steel support into an arch shape. Conventionally, a 400 N / mm ² class high-tensile shaped steel with good bending workability has been used as a steel support. However, due to the recent increase in the cross-section of the tunnel, the cross-sectional shape of the tunnel has become flatter from the conventional circular shape, and the load form has been changed from the case where only the axial force was the main external force to the one where the axial force and the bending force were combined. It has changed. Therefore, when a conventional 400 N / mm ² class steel support is used, a large cross-sectional area and a large cross-sectional modulus are required, and the construction period is prolonged and the construction cost is greatly increased. .

However, there has been no example in which a support exceeding 400 N / mm ² class has been used for supporting a tunnel. This is because tunnel support requires not only strength but also many requirements such as good weld cracking resistance, no hydrogen defects, and good toughness. Was difficult to satisfy.

[0004]

[SUMMARY OF THE INVENTION] The present invention, resistance to weld cracking resistance is extremely small satisfactory hydrogen defects, and further toughness good tensile strength 590N / mm ² or higher grade tunnel支保Engineering for H-shaped steel It is an object of the present invention to provide a manufacturing method thereof.

[0005]

SUMMARY OF THE INVENTION The present invention can advantageously eliminate the above-mentioned drawbacks of the conventional H-shaped steel for tunnel support, has good weld cracking resistance, and has very few hydrogen defects.
Further, the present invention relates to an H-section steel for tunnel shoring having a tensile strength of 590 N / mm ² or more, which has good toughness, and a method for producing the same. The points of the summary are as follows. (1) By weight%, C: 0.04% to 0.13%, Si: 0.05% to 0.40%, Mn: 0.3% to 1.5%, Al: 0.005% to 0.10%, as impurities S: 0.010% or less, P: 0.020% or less, H: limited to 2.5 ppm or less, and the balance of the flange and the web made of Fe and unavoidable impurities is 6 mm or more. 2
A tensile strength of 590 N / mm ² or more and 780 N or less, wherein the total of ferrite and pearlite structure is 60% or more and 90% or less over the entire surface.
/ Mm ² or less tunnel支保Engineering for H-shaped steel.

Further, the present invention provides the H-section steel for tunnel support according to the above (1), wherein the steel component is as follows:
The components described in each item of (7) to (7) can be further contained for each item described or in combination of each item. (2) Ti: 0.002% to 0.10% by weight,
Nb: One or two or more of 0.005% to 0.10% are contained. (3) V: 0.005% to 0.1% by weight. (4) By weight%, Cu: 0.05% to 0.5%, Ni: 0.05% to 0.5%, Cr: 0.05% to 0.5%, Mo: 0.05% to 0.5%, Co: 0.05% to 0.5%, W: 0.05% to 0.5%. (5) B: 0.0002% to 0.0025% by weight
Containing. (6) Rem: 0.002% to 0.10% by weight,
Ca: one or two of 0.0003% to 0.0030%
Contain more than one species. (7) Mg: 0.0003% to 0.01% by weight.

(8) The present invention further provides a steel slab or a slab containing the component described in any one of the above (1) to (7), which is heated to 1200 ° C. or more, and then heated to 900 ° C. or more. Flange thickness 6mm or more and 25mm or less, web thickness 6mm
Finish rolling to H-beam in the range of 25mm or less,
After rolling, 650 at a cooling rate of 2 ° C / s or more and 30 ° C / s or less.
C. or less, and the total of ferrite and pearlite structure is adjusted to 60% to 90%. A method for producing an H-section steel for tunnel support having a tensile strength of 590 N / mm ² or more and 780 N / mm ² or less. is there.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The technical idea underlying the present invention is as follows.
If a conventional steel support of 400 N / mm ² class is used for a tunnel having a large cross section, a large cross-sectional area and a large section modulus are required, so that the construction period becomes longer and the construction cost is greatly increased. In order to have a section modulus that can withstand a large-sized tunnel with a conventional size, the strength of the H-section steel is 590.
N / mm ² or more is required.

Generally, as a method for increasing the strength of steel, mechanisms such as solid solution strengthening, precipitation effect, transformation strengthening, and work hardening are used. The thickness differs depending on the part like H-section steel,
Therefore, if the cooling rate at the time of transformation after hot rolling is also different, the solution strengthening mechanism is relatively independent of the cooling rate,
It is preferred to use work hardening. However, excessive solid solution strengthening impairs weldability and significantly increases manufacturing costs. In addition, it is almost impossible to produce an H-section steel by cold working because a large amount of power is required for a working apparatus, and therefore, it is impossible to expect high strength by work hardening. The precipitation effect and transformation strengthening have a very large dependence on the cooling rate during transformation, and thus have not been suitable as a mechanism for increasing the strength of H-section steels.

[0010] However, the present inventors, by using a steel of a predetermined component system, rolled into an H-beam of a predetermined size, and further cooled at a predetermined cooling rate after the rolling, 60% of the entire metal structure More than 90% or less is a mixed structure of ferrite and pearlite, and the rest is a higher-strength bainite, martensite, or a mixed structure thereof.
Any strength of 90 N / mm ² or more 780N / mm ² or less in the range it was found that stably obtained.

[0011] In addition, tunnel support has many demands such as good weld cracking resistance, no hydrogen deficiency, good toughness and good ductility, as well as strength.
It was difficult to satisfy these requirements with conventional high-strength steels.However, if a uniform mixed structure of ferrite and pearlite is used with a relatively small alloy addition amount as in the present invention, weld crack resistance, toughness, ductility It was also found that good characteristics were obtained in both cases. Prevention of hydrogen defects can be achieved by limiting the amount of hydrogen in steel.

Hereinafter, the reasons for limiting the manufacturing method will be described in detail. First, the reasons for limiting the components of the starting material in the present invention will be described. C is an effective element for strengthening steel,
If it is less than 0.04%, sufficient strength cannot be obtained. On the other hand, if the content exceeds 0.13%, the composition is excessively hardened and easily cracked.

[0013] Although Si is effective as a deoxidizing element and as a strengthening element for steel, it is not effective at a content of less than 0.05%. On the other hand, if it exceeds 0.4%, the toughness of the welded part is impaired. Mn is an element effective for strengthening steel, and 0.3
%, A sufficient effect cannot be obtained. On the other hand, if the content exceeds 1.5%, the workability of steel deteriorates.

Al is added as a deoxidizing element. 0.0
If the content is less than 05%, the effect is not obtained, and if it exceeds 0.1%, the surface properties of steel are impaired. S produces MnS,
The content is set to 0.
Limit to 01% or less.

Since P deteriorates the toughness, the content of P is set to 0.0
Limit to 2% or less. H causes a hydrogen defect. That is, since hydrogen collects in the porosity in the steel slab or slab before rolling and prevents the porosity from being pressed by rolling, the content is limited to 2.5 ppm or less.

Further, in the present invention, the following components are added as required. Both Nb and Ti function effectively in terms of crystal grain refinement and precipitation hardening when added in a trace amount, but excessively added causes precipitation embrittlement. Therefore, the upper limit of the addition amount is set to 0.10%. If the addition amount is too small, there is no effect. Therefore, the lower limit of the addition amount of Ti is set to 0.002%, and the lower limit of the addition amount of Nb is set to 0.005%.

V brings about precipitation strengthening with a small amount of addition.
Excessive addition causes precipitation embrittlement. Therefore, the upper limit of the addition amount is set to 0.10%. If the addition amount is too small, there is no effect, so the lower limit of the addition amount is made 0.005%.

[0018] Cu, Ni, Cr, Mo, Co and W are all elements that improve the hardenability of steel. In the case of the present invention, the strength of the steel can be increased by its addition, but an excessive amount of addition hardens the steel and makes it easy to crack, so that Cu ≦ 0.5%, Ni ≦ 0.5%, Cr ≦ 0 .5
%, Mo ≦ 0.5%, Co ≦ 0.5%, W ≦ 0.5%. Further, if the addition amount is too small, there is no effect, so the lower limit of the addition amount is set to 0.05% for any element.

B is an element that improves the hardenability of steel. In the case of the present invention, the addition can increase the strength of the steel, but excessive addition increases the amount of B precipitates and impairs the toughness of the steel.
25%. Further, if the addition amount is too small, there is no effect, so the lower limit of the addition amount is set to 0.0002%.

Rem and Ca are effective for detoxifying S. However, if the added amount is small, S remains harmful, and excessive addition impairs toughness, so that Rem: 0.002% to 0.10.
%, Ca: 0.0003% to 0.0030%.

Mg becomes a fine oxide and refines the structure of steel to improve toughness. If the content is less than 0.0003%, the effect is not obtained. If the content exceeds 0.01%, cracks starting from oxides are likely to occur, so that the content is 0.0003% to 0.3%.
01% range.

Next, conditions for the size of the H-section steel in the present invention will be described. 6mm for both flange thickness and web thickness
By limiting to a range of not more than 25 mm and cooling at a predetermined cooling rate after rolling, the fraction of ferrite and pearlite structure can be increased to 60% or more in the component range of the steel of the present invention. If the ferrite + pearlite structure fraction is less than 60%, sufficient toughness cannot be obtained. The shape of ferrite may be granular or acicular. In addition, the tensile strength is 590
If it is N / mm ² , a sufficient section modulus and supporting force can be obtained within this thickness range.

Next, the manufacturing conditions of the H-section steel in the present invention will be described. In order to obtain sufficient strength with the steel of the present invention, it is necessary to sufficiently grow γ grains in the heating step before rolling and to improve the hardenability thereafter, so the lower limit of the heating temperature is set to 1200 ° C. Further, when the rolling end temperature is too low, the transformation is performed in a state where the rolling distortion remains, so that the hardenability decreases. In the steel of the present invention, since austenite needs to be sufficiently recrystallized during hot rolling to remove rolling distortion almost completely, the rolling finish temperature is set to 900 ° C. or higher. If the cooling rate after heating and rolling under such conditions is low, a large ferrite grain size is transformed from the austenite grain boundary having a relatively large grain size, and the toughness is deteriorated. Therefore, after heating / rolling, cooling is performed at a cooling rate of 2 ° C./s or more and 30 ° C./s or less and 650 ° C. or less. Thereby, a relatively fine structure in which the fraction of the mixed structure of ferrite and pearlite is 60% or more and 90% or less and the remainder is bainite or martensite is obtained. The H-shaped steel having such a structure has a predetermined strength and also has good toughness. If the cooling rate is less than 2 ° C./s, the α grain size is coarse and the toughness is deteriorated.
At 0 ° C./s or more, the fraction of the martensite structure becomes too high, and the strength becomes excessive. The cooling stop temperature is 650 ° C
Above, the ferrite grain size becomes coarse, and sufficient toughness cannot be obtained.

[0024]

Next, the present invention will be described in detail with reference to examples. First, a steel having the chemical composition shown in Table 1 was formed into an H-shaped steel having the size shown in Table 2 under the manufacturing conditions shown in Table 2. Table 3 shows the metal structure, strength, elongation, toughness, maximum hardness in the maximum hardness test, and the UST defect judgment result of the welded portion at each position of the H-section steel.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

According to Table 3, all of the H-section steels of the present invention have a structure mainly composed of ferrite and pearlite, and have a tensile strength of 5%.
It has 90 N / mm ² or more, and both elongation and impact value are better than conventional steel. Further, it can be seen that the difference in material between the portions of the H-section steel is small and stable. Further, the maximum hardness in the maximum hardness test was about 280, which is much lower than that of the conventional steel, and it is understood that the steel has a sufficient welding crack resistance. Furthermore, there was no rejected material from the UST defect judgment result of the welded portion. Thus, by applying the steel of the present invention and the method of the present invention, a tensile strength of 590 N / having sufficient properties to be used as a support for a large-section tunnel.
It was confirmed that an H-section steel of mm ² or more was obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/54 C22C 38/54 E21D 15/00 E21D 15/00

Claims (8)

[Claims] C .: 0.04% to 0.13%, Si: 0.05% to 0.40%, Mn: 0.3% to 1.5%, Al: 0.005% by weight. % To 0.10%, as impurities S: 0.010% or less, P: 0.020% or less, H: 2.5 ppm or less, and the balance of the thickness of the flange and the web consisting of Fe and inevitable impurities is 6 mm or more and 25 mm or less, and the total of ferrite and pearlite structure is 60% to 90% over the entire surface.
% Or less, wherein the tensile strength is 59% or less.
H-shaped steel for tunnel support of 0 N / mm ² or more and 780 N / mm ² or less. 2. The H-section steel for tunnel support according to claim 1, wherein the steel component further includes: Ti: 0.002% to 0.10%, Nb: 0.005% to 0.10 by weight%. % Or more of 590 N / mm ² or more and 780 N / mm ² or less. 3. The H-section steel for tunnel support according to claim 1, wherein the steel component further comprises:
V: An H-section steel for tunnel support having a tensile strength of 590 N / mm ² or more and 780 N / mm ² or less, characterized by containing 0.005% to 0.1%. 4. The H-section steel for tunnel support according to claim 1, wherein the steel component further comprises: Cu: 0.05% to 0.5%, Ni: 0% by weight. 0.05% to 0.5%, Cr: 0.05% to 0.5%, Mo: 0.05% to 0.5%, Co: 0.05% to 0.5%, W: 0.05 H-shaped steel for tunnel support having a tensile strength of 590 N / mm ² or more and 780 N / mm ² or less, characterized in that it contains one or more kinds of steel. 5. The H-section steel for tunnel support according to claim 1, further comprising B: 0.0002% to 0.0025% by weight as a steel component. Tensile strength characterized by 590 N / mm ² or more 7
H-shaped steel for tunnel support of 80 N / mm ² or less. 6. The H-section steel for tunnel support according to any one of claims 1 to 5, wherein Rem is 0.002% to 0.10%, and Ca is 0% by weight as a steel component. An H-section steel having a tensile strength of 590 N / mm ² or more and 780 N / mm ² or less, characterized by containing one or more kinds of 0.0003% to 0.0030%. 7. The H-section steel for tunnel support according to claim 1, further comprising Mg: 0.0003% to 0.01% by weight as a steel component. A tensile strength of 590 N / mm ² or more, characterized by 78
0N / mm ² or less tunnel支保Engineering for H-shaped steel. 8. A steel slab or a slab having the composition according to claim 1 is heated to 1200 ° C. or more and a flange thickness of 6 mm to 25 mm in a temperature range of 900 ° C. or more.
Hereinafter, the rolling into the H-section steel having a web thickness of 6 mm or more and 25 mm or less is completed, and after rolling, the steel is cooled to 650 ° C. or less at a cooling rate of 2 ° C./s or more and 30 ° C./s or less. Is 60% to 90%, and the tensile strength is 590 N / mm ² or more and 780 N / mm ² or more.
^{2. A} method of manufacturing an H-section steel for tunnel support below ² .