KR101723459B1 - Steel material for welded structure - Google Patents

Abstract

At least 0.02% and less than 0.14% of Si, at least 0.05% and at most 2.0% of Mn, at least 0.2% and at most 2.0% of P, at least 0.005% : 0.001% to 0.1%, Cu: 0.1% to 1.0%, and Ni: 0.1% to 1.0% A steel structure which is used outdoors such as a bridge or the like, and a steel structure which is used outdoors such as a bridge can be obtained by setting the composition to contain one or two kinds, furthermore, the content of Cu, Ni and Sn satisfies a predetermined relation and the balance of Fe and inevitable impurities, The present invention provides a welded structural steel excellent in weatherability suitable for use in a member requiring weather resistance under a high salinity environment such as near a coast.

Description

{STEEL MATERIAL FOR WELDED STRUCTURE}

TECHNICAL FIELD The present invention relates to a steel structure used for outdoor use mainly in bridges and particularly to a steel for welded structure excellent in weatherability suitable for use in members requiring atmospheric corrosion resistance under a high salinity environment such as near a coast.

Background Art [0002] Conventionally, in a steel structure used for outdoor use such as a bridge, a weather-resistant steel is used. The weathering steel is a steel material whose corrosion rate is remarkably reduced by covering the rust layer with a highly protective rust layer in which alloying elements such as Cu, P, Cr, and Ni are concentrated in an atmospheric exposure environment.

At present, bridges and the like require long-term durability over 100 years. The weather-resistant steel, due to its excellent weatherability, can withstand the use of the organs without being painted depending on the environment in which it is used. However, the weathering steel has a high amount of airborne salt , It is known that it is difficult to produce a green layer having high protection as described above, and practical weather resistance is hardly obtained.

According to the non-patent reference 1, the conventional weathering steel (JIS G 3114: weather-resistant hot-rolled steel for welded structure) has a salt content of 0.05 mg · NaCl / dm 2 / day ) In mdd), it is said that it can be used as a martial arts area. Therefore, it is the present situation that anti-corrosion treatment such as painting is applied to an ordinary steel material (JIS G 3106: rolled steel for welding structure) in an environment where salinity is high such as near the shore.

However, the paint film deteriorates with the lapse of time, and regular maintenance is required. In addition, the problem of rising labor costs and difficulty in repainting is added. For this reason, development of a steel material that can be used as a martial art has been required even in an environment with a large amount of salinity such as near a coast.

In response to such a demand, steel materials having various alloying elements, particularly Ni containing a large amount of Ni, have been developed as steels that can be used as unpainted areas in a high salinity environment such as near a coast.

For example, Patent Document 1 discloses a high-weatherability steel containing 1% or more of Ni and Cu as an element for improving weatherability.

Further, in Patent Document 2, a steel material containing 1% or more of Ni and Mo and having excellent weather resistance is disclosed.

Further, in Patent Document 3, a steel material excellent in weather resistance is disclosed in which Cu and Ti are added in addition to Ni.

Further, Patent Document 4 discloses a steel material excellent in weatherability with Sn added thereto at a content of 0.5% or less and Sn and / or Sb added thereto.

Patent Document 5 discloses a steel material excellent in weather resistance with W added thereto while suppressing the addition amount of Ni to less than 0.65%.

Japanese Patent Publication No. 3785271 Japanese Patent Publication No. 3846218 Japanese Patent Publication No. 3568760 Japanese Laid-Open Patent Publication No. 2009-179882 Japanese Laid-Open Patent Publication No. 2012-067377

 Highway bridge specification (one common piece, river teaching piece), the same commentary (Japan Road Association, 2002)

However, in Patent Documents 1 and 2, although the weather resistance is improved by increasing the content of Ni, since a large amount of expensive Ni is required, there is a problem that the production cost is increased.

Patent Document 3 discloses a method for improving the weather resistance by suppressing the content of Ni to a low level and further adding Ti. However, there is a problem that toughness of the steel is lowered.

In Patent Document 4, the weather resistance is improved by suppressing the Ni content to a low level and further adding Sn and / or Sb. However, when the steel strip is heated during rolling, There was a problem of falling behind.

In Patent Document 5, although the weatherability is improved by suppressing the content of Ni to a low level and further adding W, W is an expensive and high-scarcity element although it is a trace amount, and therefore, .

An object of the present invention is to provide a welded structural steel excellent in weatherability which can be used without being coated in a high salt environment such as near a coast.

However, in order to solve the above problems, the inventors of the present invention have extensively studied the composition of a steel material from the viewpoint of weatherability in a high salt environment. In addition, the "high salt environment" means an environment in which the salinity of the fish is 0.01 mg · NaCl / dm 2 / day or more.

As a result, Cu, Ni, and Sn and / or Nb are contained in a mixed manner, and in particular, the content of Cu, Ni, and Sn is satisfactorily determined to satisfy a large amount of rare and expensive elements such as Ni and W It was recognized that the weatherability of the steel material in the high salt environment can be improved while ensuring the production of the steel composition without containing the steel.

The present invention is based on the above recognition.

That is, the structure of the present invention is as follows.

1.% by mass,

C: not less than 0.02% and not more than 0.14%

Si: not less than 0.05% and not more than 2.0%

Mn: not less than 0.2% and not more than 2.0%

P: not less than 0.005% and not more than 0.03%

S: not less than 0.0001% and not more than 0.02%

Al: 0.001% or more and 0.1% or less,

Cu: not less than 0.1% and not more than 1.0%

Ni: not less than 0.1% and not more than 1.0%

Nb: not less than 0.004% and not more than 0.2%

And Sn: 0.001% or more and 0.2% or less, and further, the content of Cu, Ni and Sn satisfies the relationship of the following formula (1), and the balance of Fe and inevitable impurities The welded structural steel.

group

([% Cu] + 10 [% Sn]) / 2 [% Ni] (One)

However, [% M] is the content (mass%) of the M element in the steel.

2. The steel according to claim 1,

Cr: not less than 0.2% and not more than 2.0%

Ti: 0.005% or more and 0.200% or less,

V: not less than 0.005% and not more than 0.200%

Zr: 0.005% or more and 0.200% or less,

B: 0.0001% or more and 0.0050% or less,

Mg: 0.0001% or more and 0.0100% or less,

Co: 0.01% or more and 1.00% or less,

Mo: 0.005% or more and 1.000% or less,

Sb: 0.005% or more and 0.200% or less and

REM: 0.0001% or more and 0.1000% or less.

According to the present invention, it is possible to obtain a steel for welding structure excellent in weatherability, which can be used as a non-coated steel in a high salt environment.

Further, since the steel for welding structure of the present invention does not require periodic repair coating even when it is applied to steel structures such as bridges used in a high salt content environment where the salinity is higher than 0.05 mdd and moreover 0.20 mdd or higher, The cost can be greatly reduced.

Fig. 1 is a plot of corrosion amounts of the steel species A and the reference steel, AK, as the inventive examples, with respect to the amount of salinity.

(Mode for carrying out the invention)

Hereinafter, the present invention will be described in detail.

First, among the elements contained in the steel material of the present invention, Cu, Ni, Nb and Sn which are particularly important for improving the weather resistance will be described.

Cu and Ni densify the green layer formed on the surface of the steel sheet and prevent the chloride ions, which are corrosion promoting factors, from penetrating through the green layer to reach the steel substrate.

Further, Nb is concentrated in the vicinity of the interface between the green layer and the base metal in the anode portion, thereby suppressing the anode reaction and the cathode reaction. Similarly to Nb, Sn is concentrated in the vicinity of the interface between the green layer and the base metal in the anode portion, thereby suppressing the anode reaction and the cathode reaction.

These effects are insufficient to contain each element alone, but the corrosion inhibiting effect is greatly improved by the synergistic effect obtained by containing Cu, Ni and Nb and / or Sn in combination, As a result, it can be considered that the weather resistance that can withstand use in a high salt environment is manifested.

Next, the reason why the composition of the steel material in the present invention is limited to the above range will be described. The unit of the content of the elements in the composition of the steel sheet is "% by mass ", and is expressed simply as "% "

C: not less than 0.02% and not more than 0.14%

C is an element for improving the strength of the steel, and it is necessary to contain C in an amount of 0.02% or more in order to secure a predetermined strength. On the other hand, when the C content is 0.14% or more, the weldability and toughness are deteriorated. Therefore, the C content should be 0.02% or more and less than 0.14%.

Si: not less than 0.05% and not more than 2.0%

Si is required to be contained in an amount of not less than 0.05% as a deoxidizing agent for steelmaking and to secure the predetermined strength by improving the strength of the steel material. On the other hand, if Si is contained in an excess amount exceeding 2.0%, the toughness and weldability are remarkably deteriorated. Therefore, the Si content is set to 0.05% or more and 2.0% or less.

Mn: not less than 0.2% and not more than 2.0%

Mn is an element for improving the strength of the steel, and it is necessary to contain Mn in an amount of 0.2% or more in order to secure a predetermined strength. On the other hand, if Mn is contained in an excess amount exceeding 2.0%, toughness and weldability deteriorate. Therefore, the Mn content should be 0.2% or more and 2.0% or less.

P: not less than 0.005% and not more than 0.03%

P is an element that improves the weatherability of the steel material. In order to obtain such an effect, P must be contained in an amount of 0.005% or more. On the other hand, if P exceeds 0.03%, the weldability deteriorates. Therefore, the P content should be 0.005% or more and 0.03% or less.

S: not less than 0.0001% and not more than 0.02%

When S is contained in an amount exceeding 0.02%, weldability and toughness are deteriorated. On the other hand, if the S content is lowered to less than 0.0001%, the production cost increases. Therefore, the S content should be 0.0001% or more and 0.02% or less.

Al: 0.001% or more and 0.1% or less

Al is an element necessary for deoxidation at the time of steel making. In order to obtain such an effect, Al must be contained in an amount of 0.001% or more. On the other hand, if the Al content exceeds 0.1%, the weldability is adversely affected. Therefore, the Al content is set to 0.001% or more and 0.1% or less.

Cu: 0.1% or more and 1.0% or less

Cu has an effect of improving the weatherability of the steel material by forming a dense green layer by making the green particles fine. This effect is obtained when the Cu content is 0.1% or more. On the other hand, if the Cu content exceeds 1.0%, the consumption of Cu increases, resulting in an increase in cost. Therefore, the Cu content should be 0.1% or more and 1.0% or less. And preferably 0.2% or more and 1.0% or less.

Ni: 0.1% or more and 1.0% or less

Ni has an effect of improving the weatherability of the steel material by forming a dense green layer by making the green particles fine. In order to sufficiently obtain this effect, it is necessary to contain 0.1% or more of Ni. On the other hand, if the Ni content exceeds 1.0%, the consumption of Ni increases, resulting in an increase in cost. Therefore, the Ni content is set to 0.1% or more and 1.0% or less. And preferably 0.2% or more and 1.0% or less.

Nb: 0.004% or more and 0.2% or less, and Sn: 0.001% or more and 0.2% or less

Nb is concentrated in the vicinity of the interface between the green layer and the base iron in the anode portion, thereby suppressing the anode reaction and the cathode reaction. In order to sufficiently obtain these effects, it is necessary to contain Nb in an amount of 0.004% or more. On the other hand, when the Nb content exceeds 0.2%, the toughness is lowered. Therefore, the content of Nb is 0.004% or more and 0.2% or less. It is preferably not less than 0.004% and not more than 0.1%.

Further, Nb coexists with Sn, which has the effect of remarkably improving the weatherability of the steel in a high-salt environment.

Sn also forms an oxide film containing Sn at the steel / green layer interface to suppress the anode reaction and the cathode reaction of the steel, thereby improving the weatherability of the steel material. In order to sufficiently obtain these effects, it is necessary to contain 0.001% or more of Sn. On the other hand, when the Sn content exceeds 0.2%, the ductility and toughness of the steel are deteriorated. Therefore, the Sn content is 0.001% or more and 0.2% or less. It is preferably not less than 0.001% and not more than 0.1%. More preferably, it is 0.001% or more and 0.05% or less.

As described above, this Sn coexists with Nb, which has the effect of remarkably improving the weatherability of the steel in a high salt content environment.

Here, the effect of the present invention can be exhibited by containing at least any one of Nb and Sn. However, if both Nb and Sn are contained, the effect of improving weather resistance is more remarkable. Further, in securing the mechanical properties and weldability of the steel, there is an advantage that the content of Nb and Sn can be reduced without deteriorating weatherability. For this reason, it is preferable to include both Nb and Sn.

Further, in the present invention, it is not sufficient that each component satisfies the above-mentioned range. When Sn is contained, it is necessary to satisfy the following expression (1) with respect to the contents of Ni, Cu and Sn.

([% Cu] + 10 [% Sn]) / 2 [% Ni] (One)

However, [% M] is the content (mass%) of the M element in the steel.

The effect of inhibiting the corrosion of the element contributing to the improvement of the above-mentioned weather resistance can be attained while maintaining the composition ([% Cu] +10 [% Sn]) / 2 [% Ni] It is to be exercised as much as possible.

Although the basic components have been described above, in the present invention, other components described below can be appropriately contained as required.

Cr: not less than 0.2% and not more than 2.0%

Cr is an element that forms a dense green layer by finely dividing rust grains and improves weather resistance. In order to obtain this effect sufficiently, Cr must be contained in an amount of 0.2% or more. On the other hand, if it exceeds 2.0%, the weldability is lowered. Therefore, the Cr content is 0.2% or more and 2.0% or less.

Ti: not less than 0.005% and not more than 0.200%

Ti is an element for increasing the strength of the steel material. In order to sufficiently obtain this effect, Ti should be contained in an amount of 0.005% or more. On the other hand, if it exceeds 0.200%, the toughness deteriorates. Therefore, the Ti content is set to 0.005% or more and 0.200% or less.

V: not less than 0.005% and not more than 0.200%

V is an element that increases the strength of the steel. In order to obtain this effect sufficiently, V should be contained in an amount of 0.005% or more. On the other hand, if it exceeds 0.200%, the effect becomes saturated. Therefore, the V content should be 0.005% or more and 0.200% or less.

Zr: 0.005% or more and 0.200% or less

Zr is an element for increasing the strength of a steel material. In order to sufficiently obtain this effect, Zr should be contained in an amount of 0.005% or more. On the other hand, if it exceeds 0.200%, the effect becomes saturated. Therefore, the Zr content should be 0.005% or more and 0.200% or less.

B: 0.0001% or more and 0.0050% or less

B is an element that increases the strength of the steel. In order to sufficiently obtain this effect, B should be contained in an amount of 0.0001% or more. On the other hand, if it exceeds 0.0050%, the toughness deteriorates. Therefore, the B content is 0.0001% or more and 0.0050% or less.

Mg: 0.0001% or more and 0.0100% or less

Mg is an element effective for fixing the S in the steel to improve the toughness of the weld heat affected zone. In order to obtain this effect sufficiently, Mg should be contained in an amount of 0.0001% or more. On the other hand, if it exceeds 0.0100%, the amount of inclusions in the steel increases, resulting in deterioration of toughness. Therefore, the Mg content is 0.0001% or more and 0.0100% or less.

Co: 0.01% or more and 1.00% or less

Co is distributed throughout the green layer to finely disperse the green particles, thereby forming a dense green layer and improving the weatherability of the steel. In order to sufficiently obtain such an effect, Co should be contained in an amount of 0.01% or more. On the other hand, if it exceeds 1.00%, the consumption of Co increases, which leads to an increase in cost. Therefore, the Co content should be 0.01% or more and 1.00% or less.

Mo: 0.005% or more and 1.000% or less

Mo prevents the chloride ions of the corrosion promoting factor from penetrating through the green layer and reaching the substrate by distributing MoO ₄ ^{2 -} in the green layer due to the elution of MoO ₄ ^{2 -} with the anode reaction of the steel. Further, by precipitating a compound containing Mo on the surface of the steel, the anode reaction of the steel is suppressed. In order to sufficiently obtain these effects, Mo must be contained in an amount of 0.005% or more. On the other hand, if it exceeds 1.000%, the increase in the consumption of Mo leads to an increase in cost. Therefore, the Mo content should be 0.005% or more and 1.000% or less.

Sb: 0.005% or more and 0.200% or less

Sb is an element which improves the weatherability of a steel material by suppressing the anode reaction of the steel material and suppressing the hydrogen generation reaction as the cathode reaction. In order to sufficiently obtain such an effect, Sb must be contained in an amount of 0.005% or more. On the other hand, if it exceeds 0.200%, the toughness deteriorates. Therefore, the content of Sb should be 0.005% or more and 0.200% or less.

REM: 0.0001% or more and 0.1000% or less

The REM is distributed throughout the green layer to refine the green particles, thereby forming a dense green layer and improving the weatherability of the steel. In order to obtain this effect sufficiently, the REM must be contained in an amount of 0.0001% or more. On the other hand, if it exceeds 0.1000%, the effect saturates. Therefore, the REM content is 0.0001% or more and 0.1000% or less.

Ceq: 0.44 mass% or less

When the value of Ceq defined as the following expression is large, the weld heat affected zone is hardened, and there is a high possibility that low-temperature cracks will occur depending on the welding conditions. Therefore, Ceq is preferably 0.44 mass% or less.

Ceq = [% C] + [% Si] / 24 + [% Mn] / 6 + [% Ni] / 40 + [% Cu] / 5 + [% V] / 14

However, [% M] is the content (mass%) of the M element in the steel.

P _CM : not more than 0.25 mass%

In addition, in order to prevent low-temperature cracking in welding and to set the pre-heating temperature at the time of welding to 50 DEG C or less at a level at which there is no problem in practical operation, it is preferable that P _CM defined by the following expression is 0.25 mass% or less.

_{P CM = [% C] +} [% Si] / 30 + [% Mn] / 20 + [% Cu] / 20 + [% Ni] / 60 + [% Cr] / 20 +

[% Mo] / 15 + [% V] / 10 + 5 x [% B]

However, [% M] is the content (mass%) of the M element in the steel.

In the steel material of the present invention, the other components are Fe and inevitable impurities.

Here, as the inevitable impurities, for example, it is acceptable that the content of N is 0.010% or less, the content of O is 0.010% or less, and the content of Ca is 0.0010% or less.

Next, a method of manufacturing a steel according to the present invention will be described.

The molten steel having the composition described above is dissolved in a known furnace such as a converter or an electric furnace, and a slab is formed by a known method such as a continuous casting method or a crushing method. The molten steel may be adjusted in accordance with a known steel smelting method.

Then, the slab obtained as described above is subjected to hot rolling to obtain a steel such as a thick plate, a section steel, a thin steel plate, and a bar steel. Here, the heating conditions and the rolling conditions may be appropriately determined according to the required material, and control rolling, accelerated cooling, reheating heat treatment, or the like may be combined.

Example

Next, an embodiment of the present invention will be described. The present invention is not limited only to these embodiments.

The steel having the composition shown in Table 1 was dissolved in a solvent and continuously cast into a slab. Subsequently, the steel sheet was heated to 1150 占 폚, hot-rolled, and air-cooled to room temperature to obtain a steel sheet having a thickness of 6 mm. Table 2 shows the results of investigations as to whether surface cracks occurred during the production.

A specimen of 100 mm x 50 mm x 5 mm was taken from the obtained steel sheet and subjected to a grinding process so that the surface of the specimen had an arithmetic average roughness Ra of 1.6 or less. In addition, the same grinding process was carried out using both the end face and the back face as test target faces.

The thus obtained test pieces were subjected to the following weather resistance test to evaluate the weather resistance.

· Weatherability test

The test specimens were exposed for one year in the outdoors in four domestic coastal areas (0.20mdd in fresh water, 0.30mdd in Oihama, 0.36mdd in Miyakojima, and 0.50mdd in Okinawa) with different salinity. The exposure was carried out by placing test pieces on the exposed base of the cover. This is to simulate the environment inside the non-rainbow piers, where steel is considered to be the most stringent when applied to structures such as actual bridges.

After one year of exposure, the recovered test pieces were rust-removed by immersing them in an aqueous solution containing hexamethylenetetramine added to hydrochloric acid. Thereafter, the weight of the removed test piece was measured, and the difference from the initial weight was obtained. The value was divided by the surface area of the test piece, and the average plate thickness reduction amount (unit: mm) per one side was obtained as the corrosion amount. The corrosion test was carried out twice for one steel piece and the average value of the corrosion amount in the two tests was used.

In addition, the contrast between the reference steel toughness AK and the corrosion resistance was obtained as the corrosion resistance ratio. It was judged that the weathering resistance was good when the corrosion resistance ratio was less than 1 in the environment of the salinity trace of all four.

These results are shown in Table 2.

1 shows plots of corrosion amounts of the steel species A and the reference steel, AK, as the inventive examples, with respect to the amount of salinity.

From Table 2 and Fig. 1, it can be seen that, in all of the inventive examples, the corrosion rate is less than 1 in the environment of all four salinity levels, and good weatherability is obtained. Particularly, in an environment where the amount of salinity is not more than 0.30 mdd, the amount of corrosion for one year is 0.036 mm at maximum, and, for example, when the steel is applied to a bridge, durability equivalent to 100 years can be obtained.

Further, regarding the inventive examples, surface cracks did not occur at the time of production.

On the other hand, in the steel types AL, AM and AN as comparative examples, surface cracks occurred at the time of production, and the steel types AL and AN also had poor weatherability.

Claims (2)

In terms of% by mass,
C: not less than 0.02% and not more than 0.14%
Si: not less than 0.05% and not more than 2.0%
Mn: not less than 0.2% and not more than 2.0%
P: not less than 0.005% and not more than 0.03%
S: not less than 0.0001% and not more than 0.02%
Al: 0.001% or more and 0.1% or less,
Cu: not less than 0.1% and not more than 1.0%
Ni: not less than 0.1% and not more than 1.0%
Nb: not less than 0.004% and not more than 0.2%
And Sn: 0.001% or more and 0.2% or less, and further, the content of Cu, Ni and Sn satisfies the relationship of the following formula (1), and the balance of Fe and inevitable impurities The welded structural steel.
group
([% Cu] + 10 [% Sn]) / 2 [% Ni] (One)
However, [% M] is the content (mass%) of the M element in the steel. The method according to claim 1,
Wherein the steel material further comprises, by mass%
Cr: not less than 0.2% and not more than 2.0%
Ti: 0.005% or more and 0.200% or less,
V: not less than 0.005% and not more than 0.200%
Zr: 0.005% or more and 0.200% or less,
B: 0.0001% or more and 0.0050% or less,
Mg: 0.0001% or more and 0.0100% or less,
Co: 0.01% or more and 1.00% or less,
Mo: 0.005% or more and 1.000% or less,
Sb: 0.005% or more and 0.200% or less and
And REM: 0.0001% or more and 0.1000% or less.

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