JPH08197102A - Manufacture of extremely thick wide-flange steel excellent in toughness and weldabitlity - Google Patents

Abstract

PURPOSE: To obtain an extremely thick wide-flange steel excellent in impact toughness and weldability by executing air cooling after applying reduction to flange parts in a specified temp. range to the steel whose chemical composition and C-equivalent are specified. CONSTITUTION: A steel base stock which consists of, by weight, 0.05-0.15% C, <=0.20% Si, 1.00-1.80% Mn, 0.0020-0.0070% N, <=0.050% Al, 0.010-0.15% V, 0.003-0.20% Nb, one or more kinds of 0.05-0.60% Cu, 0.05-0.6% Ni, 0.05-0.5% Cr, 0.02-0.30% Mo and the balance Fe and whose C-equivalent which is expressed by the equation is <=0.40% is used. After heating this base stock to 1200-1350 deg.C, the reduction of <=40% in cumulative draft is applied to the flange parts at the temp. range of 1200-1000 deg.C. Next, the base stock is air-cooled to the room temp. As necessary, 0.002-0.005% B is incorporated in the composition of the base stock. In this way, the high-strength, extremely thick wide- flange steel having small variations in strength in the thickness direction is easily manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing so-called extra-thick H-section steel (sheet thickness of 40 mm or more) excellent in impact toughness and weldability, which is used in construction, civil engineering structures and the like.

[0002]

2. Description of the Related Art In the fields of architecture and civil engineering, JIS G
General structural rolled steel and JIS specified in 3101
The H-section steel obtained by hot-rolling the rolled steel material for welded structure specified by G 3106 is widely used. On the other hand, with the recent demand for larger structures, H-section steels used for large structures tend to be thicker and stronger.

However, when an extremely thick H-section steel having a plate thickness of more than 40 mm is manufactured by a conventional hot rolling method using a high-strength steel having a tensile strength (TS) of 490 MPa or more as a raw material, the product is produced. In order to secure the target strength of, the C equivalent of the material had to be higher than usual. As a result, when the product H-section steel is welded, problems such as easy occurrence of weld cracks and low toughness of the weld heat affected zone (so-called HAZ portion) have occurred. In addition, in general, in the rolling process of H-section steel, due to the constraint of dimensional accuracy in shaping,
It is desirable that the temperature is high and the pressure is light so as to facilitate the deformation. In particular, when manufacturing the above-mentioned thick H-section steel with a large plate thickness, the material is 1250 ° C because the deformation resistance during rolling is large.
130 which is heated to the above high temperature and is relatively easy to deform
Rolling is preferably performed in a high temperature range of 0 to 1000 ° C. However, if an extremely thick H-section steel is manufactured under such conditions,
There is another problem that the crystal grains in the material once coarsened by heating at a high temperature are not refined by rolling and a product having good toughness cannot be obtained.

Therefore, research has been conducted for a long time to secure the toughness and weldability of the ultra-thick H-section steel.
(Thermo Mechanical Contro
It has been said that it is effective to reduce the C equivalent by utilizing the led process). For example, Japanese Patent Publication Sho 56
-35734 gazette is C 0.01-0.30%, M
After hot working a steel material containing n 0.30 to 1.50% into an H-shaped steel in the austenite region, the flange is rapidly cooled from the outer surface to a temperature range of Ar _{1 to} Ms points, and then air-cooled to finely Reinforcement H for forming various low-temperature transformation products
A method for manufacturing a shaped steel has been disclosed. In addition, JP-A-58-104
No. 42, C 0.005 to 0.2%, Mn 0.
Steel material containing 3 to 2.5%, Si 1.0% or less, 0.005 to 0.2% of one or two of Nb and V, and the balance of iron or inevitable impurities at 1000 to 1300 ° C. It is heated and processed in a temperature range of at least 980 ° C to Ar ₃ to reduce the surface area by 30% or more, and then ferrite is precipitated, followed by rapid cooling to form a two-phase layered structure of ferrite and martensite. A method of manufacturing high toughness and high strength steel is disclosed.

However, since the techniques described in these publications are rapidly cooled from the flange outer surface side after hot rolling, differences in strength and toughness occur in the flange thickness section, and rapid cooling causes residual stress and strain. When applied to the production of extra-thick H-section steel, many problems have occurred.

[0006]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention has a variation in the strength and toughness of the flange even when hot rolling is performed under the same conditions as when rolling an H-section steel having a normal plate thickness.
Alternatively, it is an object of the present invention to provide a method for producing an extremely thick H-section steel which is excellent in toughness and weldability without generating residual stress, strain, and the like.

[0007]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventor earnestly conducted various experiments and researches and obtained the following new findings. 1. By adding alloy elements such as Nb, V, Cu, and Ni to the material, even if hot-rolled into an extremely thick H-section steel, a predetermined strength can be ensured with air cooling thereafter. In other words, even when manufactured by air cooling, variations in strength and toughness, residual stress, and strain do not occur in the flange plate thickness section. 2. Good weldability can be ensured by adjusting the alloy components so that the C equivalent of the material is 0.40% or less. 3. By adding REM, Ti, and N to the material,
Suppresses coarsening of γ crystal grains when the material is heated,
Further, by precipitating BN in the material during rolling and precipitating ferrite by using this as a nucleus, an extremely thick H-section steel with good toughness can be obtained. 4. The weld heat affected zone can also have improved toughness due to the grain refining action of REM, TiN, and BN.

The present invention has been made based on these findings, and specifically, C: 0.05 to 0.15% by weight,
Si: 0.20 wt% or less, Mn: 1.00 to 1.80
% By weight, N: 0.0020 to 0.0070% by weight, A
1: 0.050% by weight or less, V: 0.010 to 0.15
% By weight, Nb: 0.003 to 0.020% by weight, and Cu: 0.05 to 0.6% by weight, Ni: 0.0
5 to 0.6% by weight, Cr: 0.05 to 0.5% by weight, M
o: 0.02 to 0.3% by weight of one kind or two or more kinds, and the balance Fe and inevitable impurities, and C defined by the following formula.
The material whose equivalent weight is 0.40% or less is 1200-135
After heating to 0 ° C., the flange portion is subjected to cumulative reduction of 40% or more in the temperature range of 1200 to 1000 ° C.,
It is a method for producing an extremely thick H-section steel having excellent toughness and weldability, which is characterized by cooling to room temperature. Further, in the present invention, B: 0.0002 to 0.005 wt% is added to the above material, and Ti: 0.005 to 0.02 wt%, R
EM: 0.001 to 0.02% by weight, Ca: 0.001
It is also a method for producing an extra-thick H-section steel excellent in toughness and weldability, characterized in that one kind or two kinds or more of 0.01 wt% is added.

In this case, a more preferable effect can be obtained when the Si content in the material is 0.1% by weight or less. C equivalent (%) = C (%) + Si (%) / 24 + Mn
(%) / 6 + Ni (%) / 40 + Cr (%) / 5 + Mo
(%) / 4 + V (%) / 14 ... (1) formula

[0010]

In the present invention, C: 0.05 to 0.15% by weight,
Si: 0.20 wt% or less, Mn: 1.00 to 1.80
% By weight, N: 0.01% by weight or less, Al: 0.05% by weight or less, V: 0.010 to 0.15% by weight, Nb: 0.
003 to 0.020 wt% and contains Cu: 0.0
5 to 0.6% by weight, Ni: 0.05 to 0.6% by weight, C
r: 0.05 to 0.5% by weight, Mo: 0.02 to 0.3
After containing 0% by weight of one or more of the materials, the balance Fe and unavoidable impurities, and the C equivalent ((1) formula) is 0.40% or less, after heating to 1200 ~ 1350 ℃, 1
Since the flange portion is subjected to a cumulative reduction of 40% or more in the temperature range of 200 to 1000 ° C. and then air-cooled to room temperature, variations in the strength and toughness of the flange, residual stress, strain, etc. occur. It has become possible to manufacture extremely thick H-section steel with excellent toughness and weldability. Further, in the present invention, B: 0.0002 to 0.
Addition of 0050% by weight or Ti: 0.00
5 to 0.020% by weight, REM: 0.001 to 0.02
The above effect is further clarified because one kind or two kinds or more of wt% and Ca: 0.001 to 0.01 wt% is added.

The reasons for limiting the chemical composition of the material and the rolling conditions in the present invention will be explained below. First, regarding the chemical composition, C must be at least 0.05 wt% or more in order to secure the strength required for the base metal portion and the welded portion, but if it exceeds 0.15 wt%, the base metal toughness and Since the weldability deteriorates,
It was limited to 0.05 to 0.15% by weight. If the amount of Si increases, the toughness of the base material and the HAZ part deteriorates, and the oxidation becomes remarkable in the rolling heating at 1200 ° C. or higher, and the surface quality of the H-section steel after rolling deteriorates.
The upper limit was 0% by weight. Si is 0.10% by weight
Better results are obtained with the following.

Mn is an indeterminate element for ensuring the strength of the steel material, and its lower limit is 1.00% by weight. However, if the Mn content exceeds 1.8% by weight, the weldability and the toughness of the HAZ part deteriorate significantly, so the upper limit is 1.8% by weight.
And Al needs to be 0.005% by weight or more for deoxidation, but the deoxidation effect cannot be improved even if more than 0.05% by weight is added, so the upper limit is 0.05% by weight.
And

Nb is an element effective in securing strength,
It suppresses recrystallization and grain refinement in hot rolling, and forms coarse bainite after rolling air cooling to reduce toughness. Therefore, Nb needs to be 0.003 wt% or more to secure the strength,
If added in excess of 0.02% by weight, recrystallization grain refinement cannot be achieved in light reduction rolling of extra-thick H-section steel and toughness decreases, and weldability gradually deteriorates. did.

Cu, Ni, Cr and Mo are all effective elements for improving the hardenability and enhance the strength in air cooling after hot rolling. In order to improve strength, 0.05% by weight, 0.05% by weight, 0.05% by weight, 0.02% by weight or more are required, respectively. Further, Cu and Ni hardly deteriorate the weldability, but Cu has a drawback that the hot workability is deteriorated. In order to suppress the hot workability of Cu, it is necessary to add almost the same amount of Ni, but Ni is 0.6% by weight.
If added in excess, the manufacturing cost becomes too high, so the upper limits of Cu and Ni were made 0.6 wt%. Cr, M
If o exceeds 0.5% by weight and 0.3% by weight, respectively, the weldability and the low temperature toughness are impaired.

V is a precipitation strengthening element and improves the strength of the air-cooled material. In particular, the strengthening is large when V is added to steel containing 0.003% or more of Nb. And, when the addition amount is 0.010% by weight or less, there is no effect, and
If it exceeds the weight%, the toughness of the HAZ part deteriorates, so
It was limited to 0.005 to 0.15% by weight. Ca controls the morphology of MnS generated in the material, and particularly improves the ductility and toughness in the plate thickness direction. However, if it is less than 0.001% by weight, there is no practical effect, and if it exceeds 0.01% by weight, C
A large amount of aO or CaS is generated, which rather deteriorates the cleanliness and toughness of steel, so the range of addition of Ca is 0.00
It was set to 1 to 0.01% by weight.

Ti is formed by forming TiN in the material,
When heated to 00 to 1350 ° C., it has an effect of suppressing the coarsening of the γ crystal grains and, in common with B, has an effect of making the ferrite grains after rolling fine. Therefore, Ti is 0.005
It is necessary to add more than wt%, but if added over 0.02 wt%, the toughness of the base metal and the welded HAZ part is rather deteriorated.

REM is stable even at high temperatures and, like TiN, suppresses the coarsening of γ crystal grains at high temperatures, and
It has an effect of making ferrite grains fine after the rolling and quenching. To fully exert this effect, addition of 0.001% by weight or more is necessary, but if it exceeds 0.02% by weight, the cleanliness and toughness of steel deteriorate. B precipitates as BN during rolling and makes ferrite grains fine after rolling and air cooling, and the effect is obtained at 0.0002% by weight or more. But,
If it exceeds 0.005% by weight, the effect of refining becomes small and the toughness of the steel decreases, so 0.0002 to 0.00
The amount added was limited to the range of 5% by weight.

N is necessary to form TiN and BN in the material, and 0.002% by weight or more is necessary to obtain the effect of refining the ferrite grains, but 0.0
If it exceeds 07% by weight, the toughness of the base material and the welded HAZ part deteriorates, so the range was limited to 0.002 to 0.007% by weight. In addition, in order to form BN in the presence of Ti, an excess amount of N with respect to Ti (TiN) is required.
The i / N ratio is N rather than the stoichiometric combination of Ti.
Is preferably in a slightly excessive combination, that is, a combination of 2 to 3 is desirable.

When the C equivalent (formula (1)) of the material exceeds 0.40%, the structure mainly of bainite becomes air-cooled after hot rolling, and it becomes impossible to reduce the grain size due to ferrite precipitation.
As a result, the toughness of the base material is reduced, island martensite is likely to be generated in the welded HAZ portion, and the toughness is deteriorated. Therefore, the C equivalent is limited to 0.40% or less. next,
The reasons for limiting the conditions for rolling the above material will be described. It is sufficient that the heating temperature for hot rolling is 1200 to 1350 ° C., which is applied to the rolling of ordinary H-section steel that is not extremely thick. Then, during hot rolling, the cumulative rolling reduction is set to 40% or more in the temperature range of 1200 to 1000 ° C. The reason is that coarse crystal grains are recrystallized into fine grains by rolling to ensure high toughness. is there. In rolling, if a rolling reduction / pass of 7% or more is repeated for 4 passes or more, a better result can be obtained for recrystallization grain refinement. In the following examples, the excellent mechanical properties of the extra-thick H-section steel obtained by the manufacturing method according to the present invention will be confirmed.

[0020]

EXAMPLE As shown in Table 1 and Table 2, the steel pieces made of the materials A to F of the present invention and the materials G to I for comparative examples were heated to 1250 to 1350 ° C., Table 3
Further, under various rolling conditions and cooling conditions shown in Table 4, an extremely thick H-section steel having a flange plate thickness of 65 to 100 mm was manufactured. Then, at the position of 1/4 of the flange width of each extra-thick H-section steel, the No. 4 tensile test piece and No. 4 specified by the Japanese Industrial Standard are defined from the portion 8 mm below the surface and the portion 1/2 thickness. Impact test pieces were sampled and their mechanical properties (yield strength (YS), tensile strength (TS), yield ratio (YR) and impact value (vE ₀ )) were investigated. The survey results are shown in Table 3 above.
And 4 simultaneously.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

[Table 4]

As shown in Table 3, in the extreme-pressure H-section steel obtained by the manufacturing method according to the present invention, even if the flange plate thickness is 75 mm or more, the difference in strength and toughness between the surface layer and the center is small, and TS is 530.
High strength of MPa or more and high toughness of 90 J or more can be obtained with vEo. However, as is clear from Tables 2 and 4, the G steel of the comparative example has a high C content and a C equivalent, and therefore has a low impact toughness of 62 J or less in vEo. Further, since the H steel of the comparative example does not contain Nb and V, the strength is 460 in TS.
It is as low as 480 MPa, and high strength of 490 MPa or more cannot be obtained with TS. Furthermore, since the steel I of Comparative Example has a high Nb content, fine grains cannot be obtained and good base material toughness cannot be secured.

The comparative steels and the A-3 steels in Table 4 have the same chemical composition as the raw material of the A steel according to the present invention, but since the cumulative rolling reduction during rolling is small, fine grains cannot be obtained and the toughness is high. Low. Also,
Since the cooling after rolling was water cooling, the difference in strength between the surface layer and the center was significant. Next, in order to evaluate the weld crack susceptibility, the “oblique y-type weld crack test” defined in JIS Z 3158 was performed. Among the steels of the present invention, for C, D, E steels and comparative steel G having relatively high C equivalents, test pieces of 50 mm in thickness, 200 mm in length and 150 mm in width were cut out from a flange, and a coated arc welding rod for high strength steel was obtained. Was tested at 170 amps and 24 volts at 150 mm / min.
At that time, the preheating temperature of welding was set to 50 ° C. Cracks occurred in the comparative steel G under the same welding conditions, but no cracks occurred in the test pieces made of the C, D, and E steels obtained by the manufacturing method according to the present invention.

[0027]

As described above, according to the present invention, a steel material for construction and civil engineering structures is excellent in impact toughness and weldability,
It has become possible to easily manufacture a high-strength ultra-thick H-section steel with a small strength variation in the plate thickness direction.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C22C 38/00 B 38/48 38/54 38/58 (72) Inventor Akihiro Matsuzaki Chuo-ku, Chiba City 1st Kawasaki-cho Inside the Technical Research Institute of Kawasaki Steel Co., Ltd. (72) Inventor Shinichi Amano 1st Kawasaki-cho Chuo-ku, Chiba City Inside the Technical Research Institute of Kawasaki Steel Co., Ltd. None) Inside Kawashima Steel Works Mizushima Steel Works

Claims (3)

[Claims] 1. C: 0.05 to 0.15% by weight, Si:
0.20% by weight or less, Mn: 1.00 to 1.80% by weight, N: 0.0020 to 0.0070% by weight, Al:
It contains 0.050% by weight or less, V: 0.010 to 0.15% by weight, Nb: 0.003 to 0.02% by weight, and Cu: 0.05 to 0.60% by weight, Ni: 0. .05
0.6% by weight, Cr: 0.05 to 0.5% by weight, Mo:
Containing 0.02 to 0.3% by weight of one or more of
The balance of Fe and unavoidable impurities, the material having a C equivalent of 0.40% or less defined by the following formula is 1200 to 1350 ° C.
After heating to 100 ° C., the flange portion is subjected to a cumulative reduction of 40% or more in the temperature range of 1200 to 1000 ° C., and then air-cooled to room temperature, which is an extremely thick H-section steel excellent in toughness and weldability. Manufacturing method. C equivalent (%) = C (%) + Si (%) / 24 + Mn
(%) / 6 + Ni (%) / 40 + Cr (%) / 5 + Mo
(%) / 4 + V (%) / 14 ... (1) Formula 2. The above material, B: 0.002-0.00
The method for producing an extremely thick H-section steel according to claim 1, characterized in that 5% by weight is added. 3. The material further comprises Ti: 0.005
.About.0.02% by weight, REM: 0.001 to 0.02% by weight, Ca: 0.001 to 0.01% by weight, or one or more kinds thereof are added. A method for producing an extremely thick H-section steel excellent in the described toughness and weldability.