WO2012115281A1

WO2012115281A1 - Steel exhibiting superior weather resistance

Info

Publication number: WO2012115281A1
Application number: PCT/JP2012/055299
Authority: WO
Inventors: 進一三浦; 勇鹿毛; 務小森; 星野　俊幸
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2011-02-25
Filing date: 2012-02-24
Publication date: 2012-08-30
Also published as: JP5120510B2; CN103403211A; KR20150068500A; CN103403211B; JP2012188754A; KR20130123432A; US20140056752A1; MY153707A

Abstract

Provided is a steel exhibiting superior weather resistance. Specifically, a weather-resistant steel material characterised by containing, in mass%: more than 0.06 - less than 0.14% of C; 0.05 - 2.00% inclusive of Si; 0.20 - 2.00% inclusive of Mn; 0.005 - 0.030% inclusive of P; 0.0001 - 0.0200% inclusive of S; 0.001 - 0.100% inclusive of Al; 0.10- 1 .00% inclusive of Cu; 0.10 - 0.65% inclusive of Ni; 0.0001-1.000% inclusive of Mo, and preferably 0.005 - 1.000% inclusive of Mo; 0.005 - 0.200% inclusive of Nb; and iron and unavoidable impurities as the remainder.

Description

Steel material with excellent weather resistance

The present invention mainly relates to steel structures (Steel Structures) used outdoors such as bridges, and particularly requires high weather resistance in a high salinity environment such as coastal environments. The present invention relates to a steel material suitable as a member.

Conventionally, in steel structures used outdoors such as bridges, weathering steel has been used. Weatherproof steel is corrosion-induced by covering the surface with a highly protective rust layer enriched with alloy elements such as Cu, P, Cr, Ni, etc. in an atmosphere exposure environment (atmospheric environment). rate) is a steel material with a significant reduction. Due to its excellent weather resistance, it is known that bridges using weather resistant steel often withstand service for decades while still being paintless.

However, it is known that the highly protective rust layer is difficult to generate in an environment where the amount of airborne salt (amount of air-borne salt) is large, such as the vicinity of the coast, and it is difficult to obtain practical weather resistance (hereinafter referred to as " The amount of incoming salt is a value measured by the method of JIS Z2382.

According to Non-Patent Document 1, conventional weathering steel (JIS G3114: weathering hot rolled steel for welded structure) has an incoming salt content of 0.05 mg · NaCl / dm ² / day (hereinafter, unit (mg · (In some cases, NaCl / dm ² / day) may be expressed in mdd). Therefore, in an environment with a large amount of salinity such as the vicinity of the coast, ordinary steel (JIS G3106: rolled steel for welded structure) is used after being subjected to anticorrosion measures such as painting. Note that dm means a decimator.

In coating, the coating film deteriorates with the passage of time, and periodic maintenance and repair are required. In addition, the labor cost increases and the difficulty of repainting is added. For these reasons, steel materials that can be used without painting are now required, and there is a high demand for steel materials that can be used without painting.

In response to this situation, in recent years, steel materials containing a large amount of various alloy elements, particularly Ni, have been developed as steel materials that can be used without coating in a high-flying salinity environment such as the vicinity of the coast.
For example, Patent Document 1 discloses a high weather resistance steel material to which Cu and 1 wt% or more of Ni are added as a weather resistance improving element. Patent Document 2 discloses a steel material excellent in weather resistance to which 1 mass% or more of Ni and Mo are added.

Further, Patent Document 3 discloses a weather-resistant steel material in which Ti is added in addition to Cu and Ni. Furthermore, Patent Document 4 discloses a steel material for welded structure containing a large amount of Ni and additionally containing Cu, Mo, Sn, Sb, P, and the like.

Japanese Patent No. 3785271 Japanese Patent No. 3846218 Japanese Patent No. 3466076 Japanese Patent Laid-Open No. 10-251797

However, as in Patent Documents 1, 2, and 3, when the Ni content is increased, there is a problem that the price of the steel material increases due to an increase in alloy cost.

In addition, as in Patent Document 4, in steel materials that increase the content of Ni and P and contain Cu, Mo, Sn, Sb, etc., the price of the steel materials increases due to an increase in alloy costs, and further, the inclusion of P Due to the high amount, weldability decreases.

In view of such circumstances, an object of the present invention is to provide a steel material that is low in cost and excellent in weather resistance.

In the present invention, in order to solve the above-described problems, the component composition of steel materials has been intensively studied from the viewpoint of weather resistance in a high salt environment. As a result, it has been found that the weather resistance of a steel material in a high salinity environment is improved by compositely containing Mo and Nb in a base steel containing Cu and Ni.

The present invention has been made on the basis of the following knowledge, and the gist thereof is as follows.

1st invention is mass%, C: more than 0.06% and less than 0.14%, Si: 0.05% or more and 2.00% or less, Mn: 0.20% or more and 2.00% or less, P : 0.005% to 0.030%, S: 0.0001% to 0.0200%, Al: 0.001% to 0.100%, Cu: 0.10% to 1.00% Ni: 0.10% or more and 0.65% or less, Mo: 0.001% or more and 1.000% or less, preferably Mo: 0.005% or more and 1.000% or less, Nb: 0.005% or more It is a steel material excellent in weather resistance characterized by containing 0.200% or less and the balance being iron and inevitable impurities.

In the second invention, further, by mass, Cr: 0.2% to 1.0%, Co: 0.01% to 1.00%, REM: 0.0001% to 10000% Sn: One or two or more selected from 0.005% or more and 0.200% or less. Steel material having excellent weather resistance according to the first invention.

The third invention further includes, in mass%, Ti: 0.005% to 0.200%, V: 0.005% to 0.200%, Zr: 0.005% to 0.200%. B: 0.0001% or more and 0.0050% or less; Mg: one or more selected from 0.0001% or more and 0.0100% or less; This steel material is excellent in weather resistance as described in the invention.

According to the present invention, a structural steel material having a low cost and excellent weather resistance can be obtained.
The structural steel material of the present invention has a practical weldability at a low cost without containing a large amount of an expensive element such as Ni by containing a combination of elements effective for improving weather resistance, It can have excellent weather resistance in a high salinity environment such as the vicinity. In particular, it has a remarkable effect in a high flying salt environment where the flying salt amount exceeds 0.05 mdd.

It is a schematic diagram which shows the conditions and cycle of a corrosion test.

The reasons for limiting the respective constituent requirements of the present invention will be described below.
1. About component composition First, the reason which prescribed | regulated the component composition of the steel of this invention is demonstrated. In addition, all component% means the mass%.

C: More than 0.06% and less than 0.14% C is an element that improves the strength of the structural steel material, and needs to be contained more than 0.06% in order to ensure a predetermined strength. On the other hand, if it is 0.14% or more, weldability and toughness deteriorate. Therefore, the C content is in the range of more than 0.06% and less than 0.14%. Preferably, it is 0.08% or more from the viewpoint of securing strength, more preferably less than 0.10% from the viewpoint of weldability and toughness.

Si: 0.05% or more and 2.00% or less Si should be contained in an amount of 0.05% or more as a deoxidizer during steelmaking and as an element for improving the strength of the structural steel material and ensuring a predetermined strength. is there. On the other hand, if it exceeds 2.00% and it contains excessively, toughness and weldability will deteriorate remarkably. Therefore, the Si amount is set in the range of 0.05% or more and 2.00% or less. Preferably, it is 0.10% or more and 0.80% or less.

Mn: 0.20% or more and 2.00% or less Mn is an element that improves the strength of the structural steel material, and it is necessary to contain 0.20% or more in order to ensure a predetermined strength. On the other hand, when it contains excessively exceeding 2.00%, toughness and weldability will deteriorate. Therefore, the Mn content is in the range of 0.20% or more and 2.00% or less.
Preferably, it is 0.20% or more and 1.50% or less.

P: 0.005% or more and 0.030% or less P is an element that improves the weather resistance of the structural steel. In order to acquire such an effect, it is necessary to contain 0.005% or more. On the other hand, if it exceeds 0.030%, weldability deteriorates. Therefore, the P content is in the range of 0.005% to 0.030%. Preferably, it is 0.005% or more and 0.025% or less.

S: 0.0001% or more and 0.0200% or less If S exceeds 0.0200%, weldability and toughness deteriorate. On the other hand, when the content is reduced to less than 0.0001%, the production cost increases. Therefore, the S content is in the range of 0.0001% to 0.0200%. Preferably, it is 0.0003% or more and 0.0050% or less.

Al: 0.001% or more and 0.100% or less Al is an element necessary for deoxidation during steelmaking. In order to acquire such an effect, it is necessary to contain 0.001% or more as Al content. On the other hand, if it exceeds 0.100%, the weldability is adversely affected. Therefore, the Al content is in the range of 0.001% to 0.100%. Preferably, it is 0.010% or more and 0.050% or less. In addition, Al content measured acid-soluble Al.

Cu: 0.10% or more and 1.00% or less Cu has an effect of forming a dense rust layer by refining rust grains and improving the weather resistance of the structural steel material. Such an effect is obtained when the content is 0.10% or more. On the other hand, when it exceeds 1.00%, the cost rises with an increase in Cu consumption. Therefore, the amount of Cu is made 0.10% or more and 1.00% or less. Preferably, it is 0.20% or more and 0.50% or less.

Ni: 0.10% or more and 0.65% or less Ni has the effect of forming a dense rust layer by refining rust grains and improving the weather resistance of the structural steel material. In order to obtain this effect sufficiently, it is necessary to contain 0.10% or more. On the other hand, if it exceeds 0.65%, the cost will increase due to an increase in the consumption of Ni. Therefore, the Ni content is in the range of 0.10% to 0.65%. Preferably, it is 0.15% or more and 0.50 or less.

Mo: 0.001% or more and 1.000% or less Mo is an important requirement in the present invention, and coexisting with Nb has an effect of remarkably improving the weather resistance of the steel material in a high salinity environment. Moreover, the formation of molybdate ions in the rust layer prevents chloride ions, which are corrosion-promoting factors, from passing through the rust layer and reaching the base iron. Further, MoO ₄ ²⁻ is eluted with the anode reaction of the steel material, and the compound containing Mo is precipitated on the steel material surface, thereby suppressing the anode reaction of the steel material. In order to obtain these effects sufficiently, it is necessary to contain 0.001% or more. On the other hand, if it exceeds 1.000%, the cost will increase with the increase in Mo consumption. Therefore, the Mo amount is set to a range of 0.001% to 1.000%. Preferably, they are 0.005% or more and 1.000% or less, More preferably, they are 0.10% or more and 0.70% or less.

Nb: 0.005% or more and 0.200% or less Nb is an important requirement in the present invention. By coexisting with Mo, Nb has an effect of remarkably improving the weather resistance of a steel material in a high salinity environment. Nb has the effect of concentrating in the rust layer near the steel surface and suppressing the anode reaction of the steel. In order to obtain these effects sufficiently, it is necessary to contain 0.005% or more. On the other hand, if it exceeds 0.200%, the toughness of the steel is deteriorated. Therefore, the Nb content is in the range of 0.005% to 0.200%. Preferably, it is 0.010% or more and 0.030% or less.

Although the basic component composition of the present invention is as described above, in order to further improve desired characteristics, one or more of Cr, Co, REM, and Sn can be included as a selective element.

Cr: 0.2% or more and 1.0% or less Cr is effective for forming a dense rust layer by refining rust grains and improving weather resistance. When the effect is exhibited and the content exceeds 1.0%, the weldability is deteriorated. Therefore, when it contains Cr, it is preferable to make the quantity into the range of 0.2% or more and 1.0% or less. More preferably, it is 0.2% or more and 0.7% or less.

Co: 0.01% or more and 1.00% or less Co is distributed over the entire rust layer, and is effective in improving the weather resistance of structural steel by forming a fine rust layer by refining rust grains. If it is contained in an amount of 0.01% or more, the effect is exhibited, and if it is contained in excess of 1.00%, the cost is increased due to an increase in Co consumption. Therefore, when it contains Co, it is preferable to make the quantity into the range of 0.01% or more and 1.00% or less. More preferably, it is 0.10% or more and 0.50% or less.

REM: 0.0001% or more and 0.1000% or less REM is distributed over the entire rust layer and is effective in improving the weather resistance of structural steel by forming a dense rust layer by refining rust grains. Yes, when the content is 0.0001% or more, the effect is exhibited, and when the content exceeds 0.1000%, the effect is saturated. Therefore, when it contains REM, it is preferable to make the quantity into the range of 0.0001% or more and 0.1000% or less. More preferably, it is 0.0010% or more and 0.0100% or less.

Sn: 0.005% or more and 0.200% or less Sn concentrates in the rust lower layer and is effective in suppressing the anode reaction of the steel material, and when 0.005% or more is contained, the effect is exhibited, 0.200% Exceeding this causes deterioration of toughness. Therefore, when it contains Sn, it is preferable to make the quantity into 0.005% or more and 0.200% or less of range. More preferably, it is 0.010% or more and 0.100% or less.

Furthermore, in the present invention, one or more of Ti, V, Zr, B, and Mg can be included as a selective element.

Ti: 0.005% or more and 0.200% or less Ti is an effective element for increasing the strength of the steel material, and when 0.005% or more is contained, the effect is exhibited. It causes deterioration. Therefore, when Ti is contained, the amount is preferably in the range of 0.005% or more and 0.200% or less. More preferably, it is 0.010% or more and 0.100% or less.

V: 0.005% or more and 0.200% or less V is an effective element for increasing the strength, and when 0.005% or more is contained, the effect is exhibited, and when it exceeds 0.200%, the effect is saturated. . Therefore, when V is contained, the amount is preferably in the range of 0.005% to 0.200%. More preferably, it is 0.010% or more and 0.100% or less.

Zr: 0.005% or more and 0.200% or less Zr is an effective element for increasing the strength, and when 0.005% or more is contained, the effect is exhibited, and when it exceeds 0.200%, the effect is saturated. . Therefore, when Zr is contained, the amount is preferably in the range of 0.005% to 0.200%. More preferably, it is 0.010% or more and 0.100% or less.

B: 0.0001% or more and 0.0050% or less B is an element necessary for increasing the strength, but if the amount is less than 0.0001%, the effect cannot be sufficiently obtained. On the other hand, if it exceeds 0.0050%, the toughness is deteriorated. Therefore, when it contains B, it is preferable to make the quantity into 0.0001 to 0.0050% of range. More preferably, it is 0.0005% or more and 0.0040% or less.

Mg: 0.0001% or more and 0.0100% or less Mg is an element effective for fixing the S in the steel and improving the toughness of the weld heat affected zone, and exhibits the effect of containing 0.0001 or more. If it exceeds 0.0100%, the amount of inclusions in the steel increases, but the toughness deteriorates. Therefore, when it contains Mg, it is preferable to make the quantity into 0.0001% or more and 0.0100% or less of range. More preferably, it is 0.0005% or more and 0.0030% or less.

The balance other than the above components is composed of Fe and inevitable impurities. Here, N: 0.010% or less and 0: 0.010% or less are acceptable as inevitable impurities. Also,
Since Ca contained as an unavoidable impurity is present in a large amount in steel, the toughness of the weld heat affected zone is deteriorated, so 0.0010% or less is preferable.

2. Production Conditions The steel material having excellent weather resistance according to the present invention is a hot rolling of a slab obtained by ordinary continuous casting or a lump method with a steel having the above composition. Accordingly, steel plates such as a steel plate, a shaped steel, a steel sheet, and a bar steel are manufactured. The heating and rolling conditions may be appropriately determined according to the required material, and a combination of heat treatment such as controlled rolling, accelerated cooling, or reheating is also possible. .

Steels having the chemical compositions shown in Table 1-1 and Table 1-2 are melted and heated to 1150 ° C., followed by hot rolling and air cooling to room temperature. A 6 mm thick steel plate was prototyped. Next, a test piece of 35 mm × 35 mm × 4 mm was taken from the obtained steel plate. The test piece is ground (surface grinding) so that the surface roughness Ra is 1.6 μm or less, and (edge face) and the back side (back side) is sealed with tape (seal). And the surface was also tape-sealed so that the area of the exposed area was 25 mm × 25 mm.
About the test piece obtained by the above, the weather resistance evaluation test was done and the weather resistance was evaluated.

As the weather resistance evaluation test, a corrosion test was performed that simulates the environment inside a girder without rain, which is considered to be the most severe environment in structures such as actual bridges. The corrosion test was performed by repeating the temperature and humidity cycle in a state where salt was attached to the surface of the test piece.

As shown in FIG. 1, the temperature and humidity cycle has a drying process at a temperature of 40 ° C. and a relative humidity of 40% RH for 11 hours, and then a transition time of 1 hour, followed by a temperature of 25 ° C. and a relative humidity of 95% RH. The wetting process was taken as 11 hours, then a transition time of 1 hour was taken, and a total of 24 hours was taken as one cycle, simulating the actual temperature and humidity cycle.

Artificial seawater was dripped onto the surface of the test piece before the drying step so that the salt content attached to the surface of the test piece was 1.4 mg / dm ² before the start of the temperature and humidity cycle and every 7 cycles.

Under this condition, a test of 182 cycles of temperature and humidity was performed in 26 weeks.

After completion of the corrosion test, 1% of distilled water is added to 3 mL of 37% hydrochloric acid (hydrochloric acid), 3.5 g of hexamethylenetetramine, 3.5 g of Hibiron (inhibitor manufactured by Aiko Chemical Co., Ltd.). The test piece was immersed in a rust removal solution (liter) and derusted, and the weight was measured. The weight was measured in accordance with the method described in the 145th Corrosion and Corrosion Prevention Symposium document “Improvement in the accuracy of corrosion depletion evaluation method”. Furthermore, the difference between the obtained weight and the initial weight was obtained and divided by the area of the test target surface of the test piece to calculate the average thickness reduction amount on one side of the test piece.

In addition, about 0.5 mdd of incoming salt is equivalent to an environment with a lot of incoming salt, such as near the coast. From the knowledge so far, the reduction in steel plate thickness (182 days) in this corrosion test is the amount of incoming salt. It has been found that the steel sheet thickness reduction due to corrosion when exposed to an actual environment of about 0.5 mdd for 182 days is equivalent.

Further, when the amount of corrosion after 100 years is obtained by extrapolation from the average thickness reduction amount obtained by the test, if the average thickness reduction amount obtained in the period of this corrosion test is 22 μm or less, 100 years The subsequent reduction in the average thickness is expected to be 0.5 mm or less with no occurrence of delamination rust.

In general, the standard of applicability of unpainted weathering steel to bridges is known to have a thickness reduction of 0.5 mm or less after 100 years. If the average thickness reduction amount obtained is 22 μm or less, application to a bridge made of unpainted weathering steel becomes possible.
From the above, in Table 1-1 and Table 1-2, it was determined that the weather resistance was excellent with respect to steel materials having an average thickness reduction of 22 μm or less.

The corrosion test results obtained above are shown in Table 1-1 and Table 1-2 together with the component composition.

From Table 1-1 and Table 1-2, the steel type No. which is an invention example. In 1 to 17 and 32 to 37, the reduction in plate thickness was 19.7 to 22.0 μm, both being 22 μm or less, and excellent weather resistance.
On the other hand, steel type No. which is a comparative example. In 18 to 31, the steel type No. Since 18 to 24 do not contain any one or more of the essential components Cu, Ni, Mo, and Nb, steel type No. No. 25 has Cu less than the lower limit. Nos. 26 and 29 have a Mo of less than the lower limit. 27, Nb is less than the lower limit. In No. 28, Ni is less than the lower limit. No. 30 has a Sn of less than the lower limit. Since Nb is less than the lower limit of No. 31, the thickness reduction amount is 24.3 to 30.7 μm, which exceeds 22 μm, indicating that the weather resistance is greatly inferior to that of the inventive examples.

Claims

By mass%, C: more than 0.06% and less than 0.14%, Si: 0.05% or more and 2.00% or less, Mn: 0.20% or more and 2.00% or less, P: 0.005% or more 0.030% or less, S: 0.0001% to 0.0200%, Al: 0.001% to 0.100%, Cu: 0.10% to 1.00%, Ni: 0.10 %, 0.65% or less, Mo: 0.001% or more and 1.000% or less, Nb: 0.005% or more and 0.200% or less, with the balance being iron and inevitable impurities.
Furthermore, the steel material of Claim 1 which contains Mo: 0.005% or more and 1.000% or less by the mass%.
Further, by mass, Cr: 0.2% to 1.0%, Co: 0.01% to 1.00%, REM: 0.0001% to 0.1000%, Sn: 0.005 The steel material of Claim 1 or 2 containing 1 type, or 2 or more types chosen from% or more and 0.200% or less.
Further, by mass, Ti: 0.005% to 0.200%, V: 0.005% to 0.200%, Zr: 0.005% to 0.200%, B: 0.0001 The steel material according to any one of claims 1 to 3, comprising one or more selected from the group consisting of 1% or more and 0.0050% or less and Mg: 0.0001% or more and 0.0100% or less.