JPH02138440A - Seawater corrosion resisting steel excellent in rust resistance - Google Patents

Abstract

PURPOSE:To manufacture a seawater corrosion resisting steel excellent in rust resistance in a severe salt-corrosion environment by incorporating specific percentages of C, Si, Mn, Al, P, S, Cr, and rare earth elements to iron and also regulating Al content so that it is equal to or higher than Cr content. CONSTITUTION:A steel having a composition which consists of <=1.0% C, <=0.25% Si, <=2.0% Mn, 7.0-20.0% Al, <=0.015% P, <=0.005% S, >5.5-15.5% Cr, 0.001-0.5%, independently or in combination, of rare earth elements, such as Ce, La, and Y, and the balance iron with inevitable impurities and in which Al>=Cr is satisfied is prepared. By this method, steel materials to be exposed to salt damage, steel materials effective in maintaining the durability of a concrete structure in which steel materials are embedded, and steel materials for concrete use can be obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is applicable to steel structures and concrete structures, especially those installed in marine environments, beach areas, and environments where road antifreeze is sprayed. , and further relates to steel used in harsh saline environments in transportation equipment such as automobiles and vehicles that run in these environments.

That is, the purpose of the present invention is to provide a steel suitable for the above-mentioned uses, and since the steel itself has good seawater resistance, it can be used to prevent deterioration of structures installed in oceans and coastal areas. This relates to seawater-resistant steel that is useful for preventing the deterioration of transportation equipment such as automobiles that run on expressways where road antifreeze agents such as NaCl and CaCl are sprayed.

(Prior Art) Recently, various prevention methods have been proposed and put into practice to prevent deterioration of steel structures and concrete structures installed in oceans and coastal areas.

The biggest cause of deterioration of steel structures is corrosion caused by seawater itself,
This is due to corrosion caused by sea salt particles, etc., but the biggest cause of concrete deterioration is that salt penetrating through concrete walls corrodes the reinforcing bars embedded in the concrete.
Since its volume is approximately 2.2 times that of steel, it cannot withstand the expansion force and cracks occur in the concrete along the buried reinforcing bars.

If the crack becomes 0.2 or higher, external corrosion factors such as oxygen, salt, and carbon dioxide in the air will more easily penetrate into the vicinity of the buried reinforcing steel inside through the crack, further promoting the corrosion of scrap iron. This will promote the carbonation of concrete and hasten the deterioration of concrete.

In addition, in winter, on expressways where road antifreeze has been sprayed, the concentrated salt causes rapid deterioration of not only the roads, but also the cars traveling on these roads due to corrosion, and various prevention methods are used to prevent this deterioration. However, this has not completely stopped the deterioration.

Now, among these, salt damage deterioration of concrete has recently received a lot of attention, so conventional techniques for preventing this deterioration will be described below.

In order to prevent such deterioration of concrete, the present inventors conducted research to improve the salt resistance of the reinforcing bars themselves by controlling the chemical composition of the reinforcing bars themselves, and as a result of their research, they developed reinforcing bars for concrete with significantly improved salt resistance. (Unexamined Japanese Patent Publication No. 57-4805
4, Japanese Patent Application Laid-Open No. 59-44457).
These contents have already been published in various other areas. (
For example °“0FFSIIOREGOTEBORG '8
1” Paper Na42 Goteborg 5W
EDEN1981, “Cement Concrete” No.
, 434 (1983) P, 23/31. “Corrosion of Reinforcement in Concrete Construction”
einforcement in ConcreteC
” P, 4191983
1985, Nα229 January issue P, 155/164゜Shokokusha).

In addition, the salt resistance mechanism of the steel components of reinforcing bars at an early stage, which contributes to improving the salt resistance of reinforcing bars themselves, is also described in detail in these published papers.

(Problem to be Solved by the Invention) The present invention is based on the conventional development of the present inventors, and is based on the steel structures used in the marine environment, seashore areas, and highways where road antifreeze is sprayed, which has recently become a particular problem. The goal is to completely stop the corrosion and deterioration of transportation equipment such as cars and vehicles, as well as the deterioration of concrete structures with buried steel materials. Among these, I would like to focus on prevention of salt damage deterioration of concrete, which has recently become a problem.

The present invention focuses on the development of conventional salt-resistant concrete reinforcing bars, and has recently become a particular problem in reinforcing steels made of salt that exists in a free Ct- state, such as sea salt particles and seawater splashes that penetrate concrete walls. The purpose is to prevent corrosion of concrete and the accompanying cracking and deterioration of concrete.

Currently, free salt near the buried reinforcing bars of concrete structures that are more than 10 years old, which is a problem in various fields, can reach as much as 1.0% in terms of NaC1 in the harsh marine environment, causing severe corrosion of the reinforcing bars and resulting damage to the concrete. This causes cracking and growth. Therefore, even with such a high concentration of salt, the corrosion of the buried reinforcing steel bars was completely stopped, and the conc IJ
- It is desirable to stop cracking from occurring.

(Means for Solving the Problems) The above objects of the present invention are achieved by providing a steel having the following structure.

(1) C: 1.0% or less, Si: 0.25% or less, Mn
: 2.0% or less, Δ1, 7.0-20.0%, P,
0.015% or less, S i O, 005% or less, Cr
; more than 5.5 to 15.5% and Ce, La, Y
Rare earth elements such as 0.001-0.
A seawater-resistant steel with excellent rust resistance, characterized in that the content is 5%, the balance is iron and unavoidable impurities, and Al≧Cr.

(2) C: 1.0% or less, Si: 0.25% or less, Mn
; 2.0% or less, 81; 7. 0-20.0%, P
, 0.015% or less, S , 0.005% or less,
Cr; more than 5.5 to l 5.5% and Ce, La
, rare earth elements such as Y alone or in combination 0.001
~0.5%, and further contains T1. V, Nb.

One or two of W, Co, Mo, and B in a total of 0.01 to 0.5% for elements other than B, and B is 0.0001%.
A seawater-resistant steel with excellent rust resistance, containing ~0.005%, the balance consisting of iron and unavoidable impurities, and characterized by being Cr over At.

(3) C: 1.0% or less, St: 0.25% or less, M+
12.0% or less, ^l; 7. 0-20.0%, P
, 0.015% or less, S , 0.005% or less,
Cr; more than 5.5 to 15.5% and Ce, La,
Rare earth elements such as Y alone or in combination from 0.001
0.5%, further contains 0.1 to 5.5% of one or both of Cu and Ni, the balance being iron and inevitable impurities, and Cr on At. Seawater resistant steel with excellent rust resistance.

(41Ci 1.0% or less, St; 0.25% or less, Mn
; 2.0% or less, /'J; 7. 0-20.0%,
P i O, 0.015% or less, S, 0.005% or less, Cr; more than 5.5 to 15.5%, and Ce, La
, rare earth elements such as Y alone or in combination 0.001
~0.5%, and further contains T1. V, Nb.

One or two of W, Co, Mo, and B, with a total of 0.01 to 0.5% of elements other than B, and B is o, oooi~
Contains 0.005% and further contains one or both of Cu and Ni.
A seawater-resistant steel with excellent rust resistance, characterized by containing 0.1 to 5.5% of seeds, the balance consisting of iron and inevitable impurities, and being Cr over At.

The greatest feature of the present invention is that M is contained in the steel in an amount of 7.0 to 20.0%.
In addition, by containing a large amount of Cr (more than 5.5% to 15.5%) while maintaining the relationship of AI content ≧ Cr content, a strong passive film can be created in environments exposed to high concentrations of salt. The purpose is to generate , almost eliminate rusting, and completely stop corrosion of steel. Furthermore, even if the concrete in which these steels are buried is exposed to high concentrations of salt, the buried reinforcing steel in the concrete forms a strong passive film, which almost eliminates rusting and completely prevents concrete deterioration. It's about letting people know. That is, the idea is not to suppress the growth of rust as in conventional inventions, but to eliminate or suppress the generation of rust even in the presence of high concentrations of salt as described above. The cause of this is currently under investigation and has not been clearly determined, but it is believed that the Al C13 produced by the reaction of C1- with C1-, which is melted from the alloy according to the present invention.
reacts with O1+- in water to immediately form extremely stable Al (
It is presumed that the purpose of this change is to grow and block corrosion factors.

The reasons for limiting each component in the present invention will be explained below.

The reason why the amount of C is limited to 1.0% or less is that if the amount of C exceeds 1.0%, embrittlement will occur. Further, the reason why Mn1l is limited to 2.0% or less is that exceeding 2.0% causes embrittlement, and the preferable range is 0.8% or less. The reason why the amount of Si was set to 0.25% or less is that 5ifl is 0.
．． This is because if it exceeds 25%, the graphitization of cementite in the steel is significantly promoted and workability deteriorates. In general, the lower the amount of Si, the lower the occurrence of defects, so it is desirable that the amount of Si be lower. The most desirable range is 5il
i is less than 0.05%.

Eight! is an important element that holds the key to the present invention, and is particularly effective in suppressing rust formation even at extremely high concentrations of salt. This effect cannot be expected if the M content is less than 7.0%, and if it exceeds 20.0%, it may not only be economically disadvantageous but also cause embrittlement due to difficulty in controlling intermetallic compounds.

The most preferable range is ΔzlB, from 0% to 18%.

The reason why P is set to be 0.015% or less is that if it exceeds 0.015%, it has no effect of suppressing rust formation in an alkaline atmosphere such as concrete, but rather tends to promote it.

The reason why Cr1l is set to exceed 5.5% is that when the M content is 7.0% or more, rust resistance in a seawater environment improves dramatically, but when it exceeds 15.5%, it has the opposite effect. Since some cases of embrittlement were observed, the Crl was set to more than 5.5% to 15.5%. The most preferred range is 6.0-10.0%. The reason for setting the relationship between AtMk and Crl in steel as Al≧Cr is C
This is because when the amount r is within the above range and this relationship is established, long-term rust resistance of the steel plate sprayed in seawater is recognized. The reason for limiting the S amount to 0.005% or less is to reduce MnS fJ, which is the origin of rust. The effect of improving corrosion resistance can also be expected by changing to Ml, Ca)S, etc. Moreover, it is common knowledge to carry out the above-mentioned operation in order to reduce the amount of S in steel.

The main aim of adding rare earth elements such as Ce, La, and Y, singly or in combination, is to significantly reduce S and l through desulfurization in steel, but at the same time, even when the amount of Mn is high, the remaining sulfide is completely reduced to αMnS. It was added in the hope that it would change the chemical properties of rare earth elements into sulfides and oxysulfides, thereby improving salt resistance. The lower limit is the minimum necessary content, and the upper limit is defined to significantly change the properties of these compounds, and is in the range of 0.001 to 0.5%. At this time, in order to promote desulfurization, a Ca compound is added to the molten steel in advance or at the same time, so Ca is often present in an amount of about 0.0002% or less.

Further, in the present invention, T1. V, Nb
.

W, Co, Mo, B, etc. are added as well-known elements to improve the strength and toughness of reinforcing bars, and one or two types are selected and added, and elements other than B do not add up to the total content. Addition amount of 0.01 to 0.5%, B is 0.0001
The amount added is 0.005%, which is already well known for the above purpose. Since these additive elements often exhibit similar addition effects, the purpose can be achieved by adding them singly or usually in combination.

In addition, if necessary, one or both of Cu and Ni may be added in an amount of 0.1 to 0.1 to improve weather resistance before being buried in concrete.
Add 5.5%.

Note that if necessary, for example, when free machinability is required for threaded reinforcing bars, 0.01 to 0.5% of PB can be added.

According to the present invention, the steel composed of the above-mentioned chemical composition can be produced in a converter,
It is melted in an electric furnace, etc., and then undergoes the steps of ingot making and blooming, or after being continuously cast and rolled, it is subjected to heat treatment such as quenching, tempering, or molding as necessary.
It is subjected to heat treatment such as patenting, drawn, and ready for use. The final products include steel pipes, H-shaped steel, steel sheet piles,
It is supplied in the form of reinforced steel bars, wires, steel plates, etc., and can be galvanized or coated with organic coatings as required.

(Example) Example 1 Table 1 shows the chemical composition and corrosion test of steel materials of the present invention obtained by melting in a vacuum melting furnace, ingot making, blooming, and hot rolling, and steel materials made of conventional steel. The results were shown.

A specimen measuring 25 m wide x 60 m long x 2 m thick was taken from the center of the prepared steel plate, and the surface was polished by mechanical grinding.

On the other hand, artificial seawater was prepared as an environment to promote or reproduce the corrosion of steel in seashore areas and seawater in the laboratory.

After that, the surface was ground as described above, and the side and back surfaces were coated with silicone resin. After degreasing, the sample was dried and JISZ
A salt spray test was conducted using No. 2371, and the rusted area was measured after 48 hours. The results are shown in Table 1.

From the results in Table 1, it can be seen that while the conventional steel had 100% rusting, the steels of the present invention had no rusting.

Therefore, it was clearly demonstrated that the steel of the present invention is dramatically superior to conventional steel in terms of rust resistance.

Next, in order to promote or reproduce the salt-induced corrosion of buried reinforcing bars in concrete, CaO, the main component of concrete, was dissolved in a 3.6% NaCl aqueous solution.
A Ca (011) z + Na C1 aqueous solution of 1 and 2 was prepared.

Thereafter, the surface of the sample was ground as described above and the side and back surfaces were coated with silicone resin. After degreasing and drying, the sample was immediately immersed in the above Ca (OH) z + 3.6% NaCl aqueous solution. During the test, wipe the surface of the liquid with liquid paraffin every 3 days. The samples were immersed continuously for 20 days at night, and the state of rust formation was observed. These results are shown in Table 1.

Example 2 After grinding the surface of a hot-rolled steel plate having the components shown in Table 1, it was exposed to a seaside area for one year, and after the exposure, it was pickled, and the corrosion loss was determined and the corrosion rate was calculated.

In addition, hot-rolled reinforcing bars (9InIllφ) made of the ingredients shown in Table 1 were embedded in concrete mortar made of sand containing 1.0% NaCl, Portland cement, water, and gravel.
After curing at room temperature for 8 days, it was exposed to the seashore for 1 year.

The water-cement ratio of the concrete was 0.60, and the fog thickness was 2 cm.

After one year of dew, the concrete was crushed and the rusting status of the reinforcing bars was investigated. The results of these investigations are shown in Table 1.

From the results in Table 1, the steel of the present invention has a high concentration of Na (1.0% in J equivalent) in the concrete, and 3.6% N in water.
It was clearly observed that even at a high concentration of aC1, no rust occurred, and it was found that the deterioration of concrete caused by rust occurrence and rust growth could be completely stopped.

(Effects of the Invention) The present invention is useful as a steel material and concrete steel material that is extremely effective in maintaining the durability of steel materials exposed to salt damage and concrete structures buried in steel materials, and is useful in the marine environment and frozen roads. It can be used in a wide range of applications in environments exposed to severe salt damage, such as in environments where inhibitors are being sprayed.

Claims (4)

[Claims] (1) C: 1.0% or less, Si: 0.25% or less, Mn
; 2.0% or less, Al; 7.0 to 20.0%, P; 0.
Contains 0.015% or less, S: 0.005% or less, Cr: more than 5.5 to 15.5%, and 0.001 to 0.5% of rare earth elements such as Ce, La, and Y, singly or in combination, A seawater-resistant steel with excellent rust resistance, comprising the balance of iron and unavoidable impurities, and having Al≧Cr. (2) C: 1.0% or less, Si: 0.25% or less, Mn
; 2.0% or less, Al; 7.0 to 20.0%, P; 0.
Contains 0.015% or less, S: 0.005% or less, Cr: more than 5.5 to 15.5%, and 0.001 to 0.5% of rare earth elements such as Ce, La, and Y, singly or in combination, Furthermore, one or two of Ti, V, Nb, W, Co, Mo, and B are added in a total of 0.01 to 0.5% for elements other than B, and B is 0.
．． A seawater-resistant steel with excellent rust resistance, characterized by containing 0001 to 0.005%, the remainder consisting of iron and unavoidable impurities, and satisfying Al≧Cr. (3) C: 1.0% or less, Si: 0.25% or less, Mn
; 2.0% or less, Al; 7.0 to 20.0%, P; 0.
Contains 0.015% or less, S: 0.005% or less, Cr: more than 5.5 to 15.5%, and 0.001 to 0.5% of rare earth elements such as Ce, La, and Y, singly or in combination, Furthermore, it contains 0.1 to 5.5% of one or both of Cu and Ni,
The balance consists of iron and inevitable impurities, and Al≧Cr
Seawater-resistant steel with excellent rust resistance. (4) C: 1.0% or less, Si: 0.25% or less, Mn
; 2.0% or less, M; 7.0 to 20.0%, P; 0.0
15% or less, S: 0.005% or less, Cr: more than 5.5
15.5% and 0.001 to 0.5% of rare earth elements such as Ce, La, and Y, singly or in combination, and further contains T.
One or two of i, V, Nb, W, Co, Mo, B,
The total content of elements other than B is 0.01 to 0.5%, and B is 0.
0001 to 0.005%, and further contains 1 of Cu and Ni.
A seawater-resistant steel with excellent rust resistance, characterized in that it contains 0.1 to 5.5% of one or both of the above, the balance being iron and inevitable impurities, and that Al≧Cr.