JPS63255341A - Highly corrosion resistant steel plate for welding construction excellent in salt damage resistance - Google Patents

Abstract

PURPOSE:To obtain a highly corrosion resistant steel plate for welding construction excellent in salt damage resistance and having superior strength even if used in a uncoated state, by specifying a composition consisting of C, Si, Mn, P, Cu, R, Al, and Fe. CONSTITUTION:The highly corrosion resistant steel plate for welding construction excellent in salt damage resistance has a composition consisting of, by weight, <=0.10% C, <=0.75% Si, 0.3-1.5% Mn, 0.04-0.15% P, 0.1-0.6% Cu, 3-10% Cr, 0.02-1.0% Al, and the balance Fe with inevitable impurities and further containing, if necessary, one or more kinds among >=0.1% Ni, >=0.01% Mo, 0.01-0.15% V, 0.01-0.15 Nb, 0.002-0.05% Ti, 0.002-0.05 Zr, and 0.0003-0.002% B and/or either or both of 0.001-0.1% Ce and >=0.001% Ca. This plate can be used for uncoated bridges in the shoreline.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is a method for improving salt damage resistance and strength, which can be used unpainted in environments such as coastal areas where the presence of sea salt particles accelerates metal corrosion. This article relates to highly resistant and corrosion-resistant steel plates for excellent welded structures.

[Prior art] P-Cu-Cr steel exhibits excellent weather resistance in normal atmospheric corrosion environments and is used unpainted in the above environment, but corrosion is accelerated by the presence of sea salt particles. The corrosion weight loss when used in such environments is almost the same as ordinary steel, which has poor corrosion resistance.

On the other hand, for steels used in environments where they are directly exposed to seawater, seawater-resistant steels containing Cr or AI have been developed for the purpose of improving corrosion resistance. However, this steel does not have high enough corrosion resistance that it can be used without painting, and it is customary to apply heavy painting.

[Problems to be solved by the invention] However, when the steel structure is large-scale, such as a bridge, the cost of painting to prevent corrosion is enormous, so corrosion caused by sea salt particles may occur. There was a need to develop a steel plate that could withstand unpainted use in environmental conditions.

The present invention has been made in response to such demands, and is directed toward adding metals, particularly Cr and P, to steel.

The object of the present invention is to provide a highly corrosion-resistant steel plate for welded structures that has excellent salt damage resistance and good strength even when used without coating by adjusting the amount of Cu added.

Means for solving the C problem] The present invention provides C≦0.10%, St≦0.75%, 0.3%
≦Mn≦1.5, 0.04≦P≦0.15%, 0.1
%≦Cu≦0.6%, 3%<Cr510%, 0.02
%≦AI≦1.0%, with the balance consisting of iron and inevitable impurities.

In addition, the following (2) to (4) are also important means for solving the problems of the present invention.

(2) In addition to the structural requirements of (1) above, Ni≧0.1
%, Mo≧0.01%, 0.01%≦V≦0.15%
, 0.01%≦Nb≦0.15%, 0.002%≦
Ti≦0.05% 0.002%≦Zr≦0.05%,
Containing one or more selected from the group consisting of 0.0093%≦B≦0.002%.

(3) In addition to the constituent requirements of (1) above, an additional 0.00
Containing one or two selected from the group consisting of 1%≦Ce≦0.1% and Ca≧0.001%.

(4) Furthermore, in addition to the structural requirements of (2) above, o, oot≦
Containing one or two selected from the group consisting of Ce≦0.1% and Ca≧0.001%.

[Function] The present inventors focused on the effect of improving weather resistance and seawater resistance of Cr, and (a) 0.05%Cw4 (b) 0.05%C-0.1%P steel (c ) 0.05%C-0.3%Cu steel (d) 0.0
Test steels were prepared by varying the Cr content in the range of 0 to 10% for 5%C-0, 1%P-0, 3%Cu steel, and an atmospheric exposure test was conducted in a coastal area for 3 years. The results are shown in FIG.

In Figure 1, a, b, c, and d are the base steel components (a), (b), (c), and (d), respectively.
As is clear from Figure 1, the corrosion loss decreases as the Cr content increases in all component systems, but in cases a, b, and c, layered peeling rust occurs. On the other hand, in d, by containing more than 3% of Cr, the annual corrosion loss was 0.02 mm.
It was found that within this range, no rust delamination occurred at all.

P-Cu-Cr steel shows good corrosion resistance because of P and Cu.
As a result of Cr being concentrated on the steel surface and forming an amorphous layer, the rust that forms on that surface becomes a dense stable rust layer that makes a major contribution to preventing the acceleration of corrosion of steel. It seems that this is for the purpose.

The present invention was completed as a result of further research and consideration based on the results of this experiment, and the reason for limiting the composition of the highly corrosion resistant steel plate according to the present invention will be explained below.

C≦0.10% If the C content exceeds 0.10%, the hot cracking resistance and cold cracking resistance of the weld zone will deteriorate, and the base metal and weld heat affected zone (hereinafter referred to as H
(sometimes abbreviated as AZ) tends to cause deterioration in low-temperature toughness.

Si≦0.75% St is an effective element for deoxidizing molten steel and improving its strength, but when added in an amount exceeding 0.75%, it tends to cause deterioration of low temperature toughness.

0.3%≦Mn≦1.5% Mn is an element effective in deoxidizing molten steel and improving its strength.

If the amount added is less than 0.3%, the above addition effect cannot be obtained,
On the other hand, adding more than 1.5% tends to cause deterioration in corrosion resistance and strength.

0.04%≦P≦0.15% P is a component that effectively participates in the formation of stable rust by coexisting with Cu, but if the amount added is less than 0.04%, the formation of stable rust is insufficient. There is no effect of addition, and on the other hand, if it exceeds 0.15%, it tends to cause embrittlement of the base metal and deterioration of weldability.

0.1%≦Cu≦0.6% Cu, together with P, is an effective component for forming stable rust, but 0.1%≦Cu≦0.6%
．． If the amount is less than 1%, there is no effect of addition, while the amount added is 0.6%.
If it exceeds the above, hot workability tends to be inhibited.

3%<Cr≦10% Cr is effective in improving the corrosion resistance of steel, but if the amount added is less than 3%, there is no effect, and in order to obtain a reliable addition effect, it is necessary to add 3.5% or more. desirable. On the other hand, if it exceeds 10%, weldability and base metal toughness tend to deteriorate significantly.

002%≦A 1≦1.0% A1 is a component that improves the corrosion resistance of steel, but 0.02%
If it is less than %, there is no effect of addition. On the other hand, if it exceeds 1.0%, fluidity deteriorates and the smoothness of the steel manufacturing process tends to be hindered.

In addition to the above-mentioned elements, the steel plate according to the present invention further contains Ni and Mo for the purpose of improving the strength of the steel plate base material.

One or more elements selected from the group consisting of V, Nb, Ti, Zr, and B can be added.

Ni≧0.1% If it is less than 0.1%, the necessary strength cannot be obtained. On the other hand 1.0
If the amount exceeds 1.0%, the effect of addition will hardly change even if the amount added is increased, so from the point of view of economic efficiency, the amount added is preferably 1.0% or less.

0.01%≦MO≦1.0% MO has the effect of significantly increasing the strength of the base material even when added in a small amount, and is an element that is particularly useful for ensuring the strength of thick materials.
．． If the amount is less than 0.01%, the addition effect cannot be obtained. On the other hand, 1.0%
If it exceeds this, the HAZ in particular tends to harden and weldability deteriorates.

0.01%≦V≦0.15% 0.01%≦Nb≦0.15% ■ and Nb are both effective elements for increasing the strength of the base material when added in trace amounts, but when the amount added is 0.01%≦V≦0.15%, If the content is less than 0.1%, no effect can be obtained from the addition of any element, while if it exceeds 0.15%, the weldability decreases more significantly than the increase in base metal strength.

0.002%≦Ti≦0.05% 0.002%≦Zr≦0.05% Both Ti and Zr are elements that are effective in improving HAZ toughness and increase the strength of the base material. 002%
The addition effect cannot be obtained unless the amount added is 0.
．． If it exceeds 0.05%, non-metallic inclusions of Ti or Zr will increase and large nitrides will precipitate, which will conversely reduce HA.
The Z toughness tends to deteriorate and the strength of the base material also tends to decrease.

0.0003%≦B≦0.002% B is an effective element for preventing grain boundary segregation of P in the quenching and tempering treatment of steel, and for maintaining the toughness and strength of the base metal. In order to obtain the effect of its addition, it is necessary to add it in an amount of 0.0003% or more, but on the other hand, if it exceeds 0.002%, the B compound will be generated and the strength of the base material will deteriorate significantly.

Furthermore, in the present invention, the above-mentioned AI, Ni, and Mo.

Apart from V, Nb, Ti, Zr and B, or together with these, 1f! from among Ca and Ce! Alternatively, 2 ffl of the element can be added. Both Ca and Ce are oxysulfide-forming elements, so adding them improves the properties and shape of inclusions in steel, reduces the hot cracking susceptibility of welds, and reduces the susceptibility of the base metal in two directions. The properties and HAZ toughness of the base material can be improved.

Ca≧0.001% Ca is usually, for example, Ca-5t, Ca(CN)2゜CaC
, etc. is added to molten steel in the form of an alloy compound, but if it is less than 0.001%, no effect can be obtained.

0.001%≦Ce≦0.1% If Ce is less than 0.001%, the above-mentioned inclusion control effect is poor and the addition effect cannot be obtained. On the other hand, if it exceeds 0.1%, large inclusions such as CeS will accumulate at the bottom of the steel ingot, causing defects in ultrasonic testing of the steel plate.

[Example] Next, tests were conducted on a steel plate as an example of the present invention and a comparative steel plate different from a conventional steel plate and a conventional copper plate.

Table 1 shows the chemical composition of the test materials.

In addition, Q, DQ, and T in the notes column of Table 1 mean the following, respectively.

Q: Off-line quenching (quenching temperature = 930°C) DQ: Direct quenching after rolling (quenching temperature: 950°C) T: Tempering Tempering temperature: 640°C) These Nos., 1.2, 5, 7 , 8.11 to 15 were exposed to the coastline for 3 years, and a salt resistance test was conducted by investigating the amount of reduction in plate thickness during that period and the occurrence of delaminated rust during that period. The results are shown in Table 2.

Table 2 According to the results of this investigation, conventional steel and comparison t! 4 (hereinafter referred to as steel etc. for cars) (NO, 12 to 15), the plate thickness reduction amount is 0.10 to 0.18 mm or more,
All of the steels of the present invention (No. 1.2, 5, 7, 8°11) were 0.03 mm or less. Further, although layered peeling rust occurred in conventional steels, etc., it did not occur at all in the steel of the present invention.

Next, mechanical properties, weldability, and welded joint performance tests were conducted for each of steel Nos. 1 to 15 in Table 1. Regarding mechanical properties, tensile strength and base material notch toughness are
For weldability, we measured the preheating temperature to prevent cold cracking, and for weld joint performance, we measured the notch toughness of a submerged arc weld joint bond at a heat input of 35 J/cm. The results are shown in Table 3.

Table 3 As is clear from the results in Table 3, the present invention wI (No.

The mechanical properties, weldability, and welded joint performance of Nos. 1 to 11) were comparable to those of conventional steels (Nos. 12 to 15).

In terms of tensile strength, conventional steel etc. have a tensile strength of 44 to 55 kgf/
mm2, whereas the steel of the present invention is 44 to 65 kgf/m
m2, which is not inferior to conventional steels, etc. In particular, inventive steels No. 7, No. 11, excellent strength levels of 60 kg were obtained by quenching and tempering treatment.

Next, the base material vEo was 11 to 23 kgf-m for the comparison steel, whereas it was 12 to 24 kgf-m for the steel of the present invention, and the two were almost equivalent.

It was found that the cold crack prevention temperature of the steel of the present invention is good at room temperature or 50°C, and is particularly superior to 125°C of the conventional steel of NO.14.

The bond part vEo of the comparative steel was 7 to 13 kgf-+n, whereas the inventive steel had a value of 11 to 20 kgf-m, and overall the bond part vEo of the inventive steel was better. .

[Effects of the Invention] Since the present invention is constructed as described above, it can be used for steel structures such as unpainted bridges on coastlines, which was previously considered impossible, and exhibits excellent corrosion resistance. be.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the influence of Cr content on corrosion resistance tests in coastal areas for each component steel.

Claims (1)

[Claims] (1) C≦0.10% (meaning of weight %, the same applies hereinafter) Si
≦0.75%, 0.3%≦Mn≦1.5%, 0.04%
≦P≦0.15%, 0.1%≦Cu≦0.6%, 3%<
Contains Cr≦10%, 0.02%≦Al≦1.0%,
A highly corrosion-resistant steel plate for welded structures with excellent salt damage resistance, characterized by the remainder being iron and unavoidable impurities. (2) C≦0.10%, Si≦0.75%, 0.3%≦
Mn≦1.5%, 0.04%≦P≦0.15%, 0.1
%≦Cu≦0.6%, 3%<Cr≦10%, 0.02%
Contains ≦Al≦1.0%, Ni≧0.1%, Mo≧0.01%, 0.01%≦V≦
0.15%, 0.01%≦Nb≦0.15%, 0.00
2%≦Ti≦0.05%, 0.002%≦Zr≦0.0
5%, 0.0003%≦B≦0.002%, containing one or more selected from the group consisting of
A highly corrosion-resistant steel plate for welded structures with excellent salt damage resistance, characterized by the remainder being iron and unavoidable impurities. (3) C≦0.10%, Si≦0.75%, 0.3%≦
1.5%, 0.04%≦P≦1.5%, 0.1%≦Cu
≦0.6%, 3%<Cr≦10%, 0.02%≦Al≦
Contains 1.0%, further contains one or two selected from the group consisting of 0.001%≦Ce≦0.1%, Ca≧0.001%, and the balance consists of iron and inevitable impurities. A highly corrosion-resistant steel plate for welded structures with excellent salt damage resistance. (4) C≦0.1%, Si≦0.75%, 0.3%≦M
n≦1.5%, 0.04%≦P≦0.15%, 0.1%
≦Cu≦0.6%, 3%<Cr≦10%, 0.02%≦
Contains Al≦1.0%, Ni≧0.1%, Mo≧0.01%, 0.01%≦V≦
0.15%, 0.01%≦Nb≦0.15%, 0.02
%≦Ti≦0.05%, 0.02%≦Zr≦0.05%
, 0.0003%≦B≦0.002%, and furthermore, 0.001%≦Ce≦0.1%, Ca≧0.001%. A highly corrosion-resistant steel plate for welded structures with excellent salt damage resistance, characterized by containing one or two selected from the group consisting of iron and unavoidable impurities.