JPH07310141A - Seawater resistant steel for high temperature and high humidity environment and method for producing the same - Google Patents

Abstract

(57) [Summary] [Purpose] To provide seawater resistant steel with a small amount of corrosion and a small amount of pitting corrosion in a hot and humid environment such as a ballast tank of a tanker. [Structure] Cr: 0.5 to 3.5% as a main component, N
i: 1.5% or less, Mo: 0.8% or less, and / or 0.005 to 0.05% Nb,
Steel containing at least one of 0.005 to 0.05% Ti, and 3 to 20 after hot rolling of steel of such composition.
Accelerated cooling at a cooling rate in the range of ℃ / sec, 400 ~ 6
It is manufactured by stopping cooling in the range of 00 ° C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel material for ships, and particularly when it is applied to a high temperature and high humidity environment of a ship, that is, a severe environment where ballast tanks, seawater pipes, etc. are exposed, maintenance for preventing corrosion of the ship. The present invention relates to a steel material and a method for manufacturing the same for achieving freeness and safety.

[0002]

[Prior Art] 19 by the regulations of the International Maritime Organization (IMO)
Tankers built after July 1993 are obliged to have a double hull structure. The double hull section is used as a ballast tank and has a structure that protects the freight oil tank, and is intended to prevent marine pollution due to leaked oil in the event of an accident.

The double hull structure significantly increases the surface area of the ballast tank exposed to seawater (2 to 3).
Therefore, problems in painting and anticorrosion will be highlighted. As for painting, tar epoxy resin paint is applied once or twice, but it is a work in a narrow space, and 3K
Has become a representative workplace of. Repairing is more costly than new building, high risk, and shortage of workers is also a problem. In terms of anticorrosion, tar epoxy resin paint and cathodic protection are used together, but seawater enters and leaves the ballast tank, creating a severe corrosive environment. When seawater is present in the ballast tank, it is hardly corroded due to the effect of cathodic protection, but the top of the ballast tank and the back of the upper deck, which are not submerged in seawater, are hot and have a harsh corrosive environment called splash zones. If there is no seawater in the ballast tank, the environment will be high temperature and high humidity, and the effect of cathodic protection cannot be expected, and only tar epoxy resin paint will be used. The life of such a ballast tank is said to be about 10 years, which is half the life of a ship (20 years). For the remaining 10 years, repair painting must be used to maintain safety.

The ballast tank has a major problem of coating work under such severe corrosive environment and adverse conditions, and improvement of the steel material, that is, development of a steel material for ships excellent in seawater resistance under high temperature and high humidity environment is desired. It is rare. Meanwhile, the development of seawater resistant steel for use in the marine environment began in the mid-1960s. The corrosion resistance of seawater resistant steel depends on the properties of the rust layer, and it is believed that alloying elements are involved in the properties of the rust layer. Although the effects of alloying elements on corrosion resistance are different in the ocean atmosphere, splash zone, and sea, Cr, Ni, Mo, and Cu are generally said to be effective elements for corrosion resistance in this environment. Based on these results, seawater resistant steels for welded structures have been developed according to the usage environment such as splash zone, undersea, or both. These are used for sluice gates, steel sheet piles, buoys, piers, etc.

One example of seawater resistant steel is disclosed in Japanese Patent Laid-Open No. 51-25420, but these steel materials are used in the above-mentioned marine structures and port facilities, and the environment thereof is about atmospheric temperature. The environment in which the steel of the present invention is used, that is, the seawater flows in and out, and the corrosive environment is different from the hot and humid ballast tank environment. Therefore, Cu is an essential element in the seawater-resistant steel materials represented by JP-A-51-25420, but Cu is not added in the steel of the present invention. This is because the inside of the ballast tank is a corrosive environment in which high temperature and high humidity allow seawater to flow in and out, and Cu is considered to have no effect on the corrosion resistance or adversely affect the corrosion resistance in this environment.

Japanese Patent Application Laid-Open No. 5-302148 discloses a material having seawater resistance and no Cu added, which is used in order to obtain a ferromagnetic ferrite. Si: 0.5-2%, Al :
It also contains 0.5 to 3%. In addition, Japanese Patent Laid-Open No. 64-79346 is disclosed. Since it contains 7% to 20% of Al, there is no problem in applications where welding is scarcely performed, such as in reinforcing bars, but there is a problem in applications where welding is frequently used, such as the ballast tank to which the present invention is applied.

[0007]

The steel materials currently applied to ships are manufactured by the component design and process design in consideration of strength, toughness and weldability, but most of the measures concerning corrosion resistance and corrosion resistance are At present, it is not taken into consideration. Therefore, the present invention provides a steel material having excellent corrosion resistance particularly for ballast tanks having a severe corrosive environment, seawater piping, etc. by adding alloy elements and accelerated cooling after rolling.

The corrosive environment of the ballast tank is the inflow and outflow of seawater and the hot and humid environment as described above. The corrosive environment assuming a tanker is as follows. When transporting crude oil from the Middle East to Japan, from Japan to the Middle East,
The oil tank is empty, keeping the ship in balance and filling the ballast tank with almost full seawater for safe navigation. At this time, the corrosive environment is close to the splash zone in seawater and above the ballast tank. If the cargo oil tank is full of crude oil and you are heading to Japan from the Middle East, drain the seawater from the ballast tank and empty it. At this time, the inside of the ballast tank becomes hot and humid due to the seawater remaining on the bottom of the ship and the heat from the deck. One cycle exposed to these corrosive environments is about 40 days.

An object of the present invention is to solve the above problems and to provide a steel material having excellent seawater resistance in a hot and humid environment and a method for producing the steel material.

[0010]

In order to simulate these corrosive environments, the inventors investigated the influence of alloying elements using a corrosion test apparatus as shown in FIG. As a result, they have found that a steel material having the following chemical composition has excellent corrosion resistance. Then, they found that the corrosion resistance can be further improved by a proper manufacturing method.

That is, the present invention is as follows. First
Of the present invention, C: 0.1% or less by weight, Si: 0.50% or less,
Mn: 1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50 to 3.
It is a seawater resistant steel for high temperature and high humidity environments, characterized in that it contains 50% and the balance is Fe and inevitable impurities. The second invention is C: 0.1% or less by weight% and Si: 0.50% or less by weight. , Mn:
1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50 to 3.50%
A seawater resistant steel for high-temperature and high-humidity environment, characterized in that it contains 1.5% or less of the total of one or more kinds of 1.5% or less of Ni and 0.8% or less of Mo, and the balance is Fe and inevitable impurities. According to the third aspect of the invention, C: 0.1% or less by weight, Si: 0.
50% or less, Mn: 1.50% or less, Al: 0.005 to 0.050%, C
r: 0.50 to 3.50% and 0.005 to 0.05% Nb, 0.0
A fifth aspect of the present invention is a seawater resistant steel for high temperature and high humidity environment, characterized by containing 0.005 to 0.05% of a total of one or more kinds of Ti of 05 to 0.05%, and the balance being Fe and inevitable impurities. % By weight, C: 0.1% or less, Si: 0.50% or less, Mn: 1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50 to 3.50%,
And, the total of one or more of 1.5% or less of Ni and 0.8% or less of Mo is 1.5% or less, 0.005 to 0.05% of Nb, 0.005 to 0.
The present invention is a seawater resistant steel for high temperature and high humidity environment, characterized by containing 0.005 to 0.05% of one or more of 05% Ti, and the balance being Fe and unavoidable impurities. C: 0.1% or less, Si: 0.50% or less, Mn: 1.50% or less, A
l: 0.005 to 0.050%, Cr: 0.50 to 3.50%, the balance consisting of Fe and unavoidable impurities, after hot rolling,
A method for producing seawater resistant steel for high temperature and high humidity environment, which comprises performing accelerated cooling at a cooling rate in the range of 3 to 20 ° C / sec, stopping the accelerated cooling at a temperature of 400 to 600 ° C, and then performing air cooling. According to the sixth aspect of the invention, C: 0.1% or less by weight, Si: 0.50
% Or less, Mn: 1.50% or less, Al: 0.005 to 0.050%, Cr:
Steels containing 0.50 to 3.50%, 1.5% or less of Ni and 0.8% or less of Mo in total of 1.5% or less, and the balance of Fe and unavoidable impurities, after hot rolling, 3 ~ 20 ° C
Accelerated cooling at a cooling rate in the range of / sec, and the accelerated cooling is 400
A seventh aspect of the present invention is a method for producing seawater resistant steel for high temperature and high humidity environment, which is characterized by stopping at a temperature of ~ 600 ° C and then performing air cooling. The seventh invention is C: 0.1% or less by weight% and Si: 0.50%. Below, M
n: 1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50 to 3.5
0% and 0.005 to 0.05% Nb, 0.005 to 0.05%
The total content of one or more of Ti is 0.005 to 0.05% and the balance is Fe.
After hot rolling, a steel material consisting of
Accelerated cooling at a cooling rate in the range of 20 ° C / sec.
A eighth aspect of the present invention is a method for producing seawater resistant steel for high temperature and high humidity environment, which is characterized by stopping at a temperature of 400 to 600 ° C. and then performing air cooling. The eighth invention is C: 0.1% or less by weight% and Si: 0.50. % Or less, Mn: 1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50
~ 3.50% and 1.5% or less of Ni, 0.8% or less of Mo
The total of one or more types is 1.5% or less, and 0.005 to 0.05%
Nb, 0.005 to 0.05% Ti total of one or more of 0.005 to
A steel material containing 0.05% and the balance of Fe and inevitable impurities is hot-rolled, and then accelerated cooling is performed at a cooling rate in the range of 3 to 20 ° C / sec, and the accelerated cooling is stopped at a temperature of 400 to 600 ° C. Then, the method is a method for producing seawater resistant steel for high temperature and high humidity environments, which is characterized by performing air cooling thereafter.

[0012]

The present invention will be described in detail below. An object of the present invention is to provide a seawater resistant steel for high-temperature and high-humidity environment, which can reduce the amount of corrosion under repeated environment in seawater and 100% humidity atmosphere and can maintain a smooth corroded surface without causing local corrosion. It is to be.

Regarding the reduction of the amount of corrosion, the inside of the ballast tank is protected by painting and cathodic protection, but the small amount of corrosion means that rust is not generated on the coated surface, and the smooth corrosion surface is exhibited. This is to avoid a situation where corrosion causes strain concentration or metal fatigue. In order to satisfy these two points, in the present invention, it is effective to add appropriate amounts of Cr, Ni, Mo, Nb, and Ti. Further, by suppressing the formation of carbides after hot rolling, Cr, Mo
It has been found that the effect of.

The reasons for limiting the composition of seawater resistant steel for high-temperature and high-humidity environments and the reasons for limiting the manufacturing method thereof will be described below. C: 0.1% or less C is more advantageous in corrosion resistance and weldability as the added amount is smaller, but since it is an element that influences strength, the upper limit was made 0.1%.

Si: 0.50% or less Si does not adversely affect toughness as the amount of Si added decreases, so the upper limit was made 0.50%. Mn: 1.50% or less Mn is an element that plays an important role in strength, toughness, and weldability, but if it exceeds 1.50%, it adversely affects toughness and weldability, so the upper limit was made 1.50%.

Al: 0.005 to 0.050% Al is added as a deoxidizing agent, but is set to 0.005 to 0.050% within a range that does not adversely affect weldability. Cr: 0.50 to 3.50% Cr is the most effective element for corrosion resistance in the present invention. Since the corrosive environment is harsh, addition of less than 0.50% has no effect on reduction of the amount of corrosion and on smooth corroded surfaces. 0.50
%, The effect on these will start to appear, so the lower limit was made 0.50%. When the Cr addition amount is gradually increased, a clear effect appears in reducing the corrosion amount. But 3.
If it exceeds 50%, the surface condition will rapidly become pitting. further
When the amount of Cr added is increased and the amount of Cr added is 9%, the corrosion morphology with only pitting corrosion is almost equal to that of stainless steel. The upper limit of Cr addition was set to 3.50% because the area where the amount of corrosion is reduced and a smooth corrosion surface is exhibited is up to 3.5%. Preferably 1.2-3.
The addition amount of 0% Cr is good.

If Cr takes the form of a carbide or a nitride, the amount of effective Cr decreases, so it is desirable to keep Cr in a solid solution state. Ni: 1.5% or less Addition of Cr improves the corrosion resistance, but more preferably, addition of Ni is effective in improving the corrosion resistance and making the corroded surface uniform. But,
If the amount of Ni added exceeds this range, the strength and hardness of the steel material tend to increase, and problems with the material, weldability, etc. are expected. Therefore, the amount of Ni added was 1.5% or less.

Mo: 0.8% or less Addition of Mo has the same effect as Ni, but it is expected that problems with the material and weldability will occur more than Ni.
The addition range was 0.8% or less. Ni + Mo: 1.5% or less Ni and Mo can be expected to have almost the same effects. As described above, since there are problems in terms of material and weldability for both Ni and Mo, the upper limit was set to 1.5% for Ni + Mo.

Ti: 0.005 to 0.05% Elements effective for corrosion resistance are Cr, Ni and Mo. In the manufacturing process, Cr and Mo are likely to form carbides, and solid solution Cr and solid solution Mo which effectively exhibit corrosion resistance. Spoil. Ti is a carbide-forming element, and since it has a stronger affinity with C than Cr and Mo, Ti carbide is preferentially formed, which reduces the formation of Cr and Mo carbides and prevents a decrease in the amount of solid solution. This effect is not observed at less than 0.005%. If it exceeds 0.05%, the toughness of the base material will be impaired, so it is limited to 0.005 to 0.05%.

Nb: 0.005 to 0.05% Nb is also a carbide-forming element like Ti. By adding Nb
The formation of carbides of Cr and Mo is reduced, and corrosion resistance due to solid solution Cr and solid solution Mo is effectively exhibited. This effect is not observed at less than 0.005%. If it exceeds 0.05%, the toughness is deteriorated, so the upper limit of the amount of Nb added is set to 0.05%.

Nb + Ti: 0.005 to 0.05% Cr, Mo The effect of suppressing the formation of carbides and increasing the amounts of solid solution Cr and Mo to effectively exert the corrosion resistance is Nb and Ti.
Are almost the same. However, the amount of Nb + Ti added is 0.005%
The effect cannot be recognized unless it is above. The upper limit was set to 0.05% from the viewpoint of toughness.

Next, the reasons for limiting the manufacturing conditions for further improving the corrosion resistance of the seawater resistant steel for hot and humid environments will be described. When the cooling rate after hot rolling is less than 3 ° C./sec, Cr carbide and Mo carbide are precipitated during cooling, so the effect of seawater corrosion resistance due to solid solution Cr and Mo is weakened. Therefore, the lower limit of the cooling rate is set to 3 ° C / sec. If the cooling rate exceeds 20 ° C / sec, transformation products increase and the toughness deteriorates, so the upper limit of the cooling rate was set to 20 ° C / sec. If the cooling stop temperature after accelerated cooling exceeds 600 ° C, Cr carbides and Mo after accelerated cooling
Since carbides are precipitated, the effect of solid solution Cr and Mo on the corrosion resistance to seawater is weakened. Therefore, the upper limit of the cooling stop temperature was set to 600 ° C. If the cooling stop temperature after accelerated cooling is less than 400 ° C, transformation products increase and the toughness deteriorates, so the lower limit of the cooling stop temperature was set to 400 ° C.

[0023]

【Example】

Example 1 (Example for Claim 1) A test simulating a ballast tank of a ship was conducted using the test apparatus shown in FIG. Here, the test method will be described. As shown in FIG. 1, test tank 1 was filled with half of test tank 1 with artificial seawater 2 according to ASTM D1141. The test material 4 is immersed in this artificial seawater for 1 week, and then the test material 4 is damp.
The cycle of pulling up in 100% air 3 for 1 week and then again immersing in artificial seawater 2 for 1 week was repeated. The rotation speed of the test material mounting drum 5 is artificial seawater,
Humidity is 0.5 m / sec both in 100% atmospheric air, and air is bubbled from the lower part of the test tank 1 to stir the seawater and supplement the seawater with oxygen. Since the lid of the test tank is close to a closed state, the difference between the artificial seawater and the atmospheric temperature is less than 1 ° C, and the humidity in the atmosphere is almost 100%. In this Example 1, using this device, artificial seawater immersion at 40 ° C. for 1 week and humidity 100
%, A corrosion test was conducted for 5 cycles in the atmosphere of 40 ° C. for 1 week. The test material was heated at 1150 ° C for 1 hour, then hot-rolled, and then air-cooled (cooling rate: 0.5 ° C / se
c).

The components of the test material are shown in Table 1, the corrosion amount measurement results,
Table 2 shows the results of surface condition evaluation and corrosion depth of the corroded surface.
Shown in. The depth of corrosion was measured at 10 points using a depth gauge, and the maximum and average corrosion depths were shown. After the test was completed, the rust was removed, and the surface condition of the corroded surface was judged based on the smoothness of the remaining surface. The more uniform the corrosion is and the smaller the unevenness is, the more the direction is ◎.
It was judged that the corroded surface was non-uniform and the unevenness became large in the order of Δ and ×. Further, FIG. 2 shows the relationship between the Cr amount and the corrosion amount, and FIG. 3 shows the relationship between the Cr amount and the corrosion depth. As a comparative material, NK36 (Nippon Kaiji Kyokai) KA36 was tested at the same time with the steel type conventionally used in ships. The results of the test are as follows.

[0025]

[Table 1]

[0026]

[Table 2]

(1) Corrosion amount The corrosion amount decreases as the Cr addition amount increases, but the corrosion amount slightly increases at 5 to 6% Cr. Further, if the amount of Cr added is increased, the amount of corrosion is reduced. The amount of corrosion was determined from the difference between the weight of the initial test piece and the weight of the test piece that had been rusted after the above corrosion test, and was converted per unit surface area of the test piece. The average amount of reduction in plate thickness is a calculated value from the amount of corrosion. (2) Corrosion depth and corrosion form Corrosion depth is smaller than comparative material KA36 up to 3-4% Cr addition, but if the Cr addition amount is further increased, both maximum corrosion depth and average corrosion depth gradually increase. Become. Below 3.5% Cr, a general corrosion morphology is exhibited, and above that, it is a local corrosion morphology. In Comparative Examples 2 to 4, almost the entire surface was not subjected to uniform corrosion, but was local corrosion. In the localized corrosion state, there are problems in use such as stress concentration. The corrosion amount of steel is small and the corroded surface is smooth. The Cr addition range is 3.5.
% Cr or less, and it can be seen that the effect is small with the addition of less than 0.5%.

Examples 2, 3 and 4 (Examples for Claims 2, 3 and 4) The components of the test material for Claim 2 are shown in Table 3, the corrosion amount measurement results, the surface condition evaluation of the corroded surface and the corrosion depth. The measurement results of are shown in Table 4. The components of the test material for claim 3 are shown in Table 5,
Table 6 shows the corrosion amount measurement results, the surface condition evaluation of the corroded surface, and the corrosion depth measurement results.

The components of the test material for claim 4 are shown in Table 7,
Table 8 shows the corrosion amount measurement results, the surface condition evaluation of the corroded surface, and the corrosion depth measurement results.

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

[Table 5]

[0033]

[Table 6]

[0034]

[Table 7]

[0035]

[Table 8]

The production method of the corrosion test piece, the test method and the evaluation method of the corrosion test, and the test conditions are exactly the same as in Example 1. The Cr addition range in which the corrosion amount of the steel material was small and the corroded surface was smooth was 0.5 to 3.5% Cr as in Example 1. Table 4 compares the invention steel with the Cr content at the same level and the comparative steel. Invention Steels 1 to 3 and Comparative Steel 1 are 1% Cr, Invention Steel 4
~ 6 and Comparative Steel 2 are 2% Cr, Invention Steel 7 and Comparative Steel 3 are 3% Cr
Is. As the amount of Ni + Mo increases, the amount of corrosion and the corrosion depth decrease, and the unevenness of the corrosion surface also decreases, resulting in a uniform corrosion pattern. In particular, the addition of Ni and Mo is effective in reducing the amount of corrosion.

However, invention steels 4, 5, 6 and comparative steel 4,
As can be seen by comparing Nos. 5 and 6, when Ni and Mo are out of the proper range, the toughness deteriorates. Table 6 compares the invention steel and the comparative steel with the same Cr content. Inventive Steel 1 and Comparative Steel 1 are 0.
7% Cr, invention steels 2, 3 and comparative steel 2 are 1% Cr, invention steel 4,
5 and Comparative Steels 3 and 4 are 2% Cr, Invention Steel 6 and Comparative Steel 5 are 3.4%
% Cr. As the amount of Nb + Ti increases, the amount of corrosion,
Corrosion depth becomes smaller. Further, as can be seen by comparing the invention steels 4 and 5 with the comparative steels 6, 7 and 8, the toughness of the base material decreases when the addition amounts of Nb and Ti are large.

In Table 8, as in the above, the invention steel and the comparative steel having the same Cr content are compared. As mentioned above, Ni,
The addition of Mo, Nb and Ti reduces the amount of corrosion and the depth of corrosion. Example 5 (Example against Claim 5) Inventive steels 2, 3 and 4 of Table 1 used in the example of Claim 1 as test materials and conventional steel KA36 as comparative material were used at 1150 ° C. After heating for 1 hour, hot rolling was performed, and a test piece obtained from the test material manufactured under the manufacturing conditions shown in Table 9 was used as Example 1.
A corrosion test was conducted using the same test equipment used in. The test method, evaluation method, and test conditions of the corrosion test are exactly the same as in Example 1. Table 10 shows the results of measuring the amount of corrosion, the evaluation of the surface condition of the corroded surface, the results of measuring the corrosion depth, and the results of the base material Charpy impact test.

[0039]

[Table 9]

[0040]

[Table 10]

The results are summarized below.
It (1) Corrosion amount In Example 1 in which the test material was manufactured under the condition of air cooling after rolling,
The addition of Cr reduces the amount of corrosion compared to the conventional steel KA36, but rolling
The subsequent accelerated cooling and cooling stop conditions are manufactured within the range of the conditions of the present invention.
By manufacturing, the amount of corrosion is further significantly reduced. Rotten
Regarding the food depth, it is necessary to manufacture under the conditions within the scope of the present invention.
Therefore, the corrosion depth tends to be smaller. (2) Toughness Even if the manufacturing is carried out under the conditions within the scope of the present invention, the toughness is not deteriorated.
Not seen but above cooling rate upper limit or cooling stop
Below the lower temperature limit, the absorbed energy ( _VE₀)
Rises and the toughness deteriorates.

Examples 6, 7, and 8 (Examples for Claims 6, 7, and 8) After heating at 1150 ° C. for 1 hour, hot rolling was performed, and the test materials manufactured under the manufacturing conditions shown in Table 9 were obtained. The test piece was subjected to a corrosion test using the same test equipment used in Example 1. Corrosion amount measurement results, surface condition evaluation of corroded surfaces, corrosion depth measurement results, and base material Charpy impact test results are shown for claim 6.
Table 11 for claim 7 and table 13 for claim 8
Shown in. Invention steel 7 in Table 11 is invention steel 7 used in the embodiment of claim 2, invention steel 6 in Table 12 is invention steel 6 used in the embodiment of claim 3,
The invention steel 6 in 13 is the invention steel 6 used in the embodiment of claim 4. The test method, evaluation method, and test conditions of the corrosion test are exactly the same as in Example 1.

After hot rolling, the amount of corrosion is reduced by manufacturing under accelerated cooling and cooling stop conditions within the scope of the present invention.
Regarding the corrosion depth, the corrosion depth tends to be reduced by manufacturing under the conditions within the scope of the present invention. Even if the production is carried out under the conditions within the scope of the present invention, the toughness is not deteriorated, but if the upper limit of the cooling rate is exceeded or the lower limit of the cooling stop temperature is exceeded, the Charpy absorbed energy at 0 ° C. (
_V E ₀ ) rises and the toughness deteriorates.

[0044]

[Table 11]

[0045]

[Table 12]

[0046]

[Table 13]

[0047]

INDUSTRIAL APPLICABILITY As described above, the seawater resistant steel for high temperature and high humidity environments according to the present invention has excellent corrosion resistance when applied to ballast tanks, seawater pipes, etc. of ships that are in a severely corrosive environment. It contributes to the maintenance-free maintenance of the ship and also adds and maintains the safety of the ship.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of a ballast tank simulation test device.

FIG. 2 is a characteristic diagram showing the effect of Cr addition amount on the corrosion amount of test materials (invention steel and comparative steel).

FIG. 3 is a characteristic diagram showing the influence of the Cr addition amount on the maximum corrosion depth and the average corrosion depth of the test materials (invention steel and comparative steel).

[Explanation of symbols]

 1 Test Tank 2 Artificial Sea Water 3 Humidity 100% Atmosphere 4 Test Material 5 Test Material Mounting Drum 6 Rotating Axis 7 Heater 8 Air Bubbling Piping 9 Test Material Position (Seawater) 10 Test Material Position (Atmosphere) 11 Artificial Sea Water Surface

 ─────────────────────────────────────────────────── ─── Continuation of front page (31) Priority claim number Japanese Patent Application No. 6-53916 (32) Priority date Hei 6 (1994) March 24 (33) Country of priority claim Japan (JP) (72) Inventor Mitsuo Kimura 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Corporation Steel Research & Development Division Steel Research Laboratory (72) Inventor Yoshiyuki Saito 1 Kawasaki-cho, Chuo-ku, Chiba City Kawasaki Steel Corporation Steel Development・ In the Steel Research Laboratory, Production Division

Claims (8)

[Claims] 1. By weight%, C: 0.1% or less, Si: 0.50% or less, Mn: 1.50% or less, Al: 0.005-0.050%, Cr: 0.50.
A seawater resistant steel for high temperature and high humidity environments, characterized by containing ~ 3.50% and the balance being Fe and inevitable impurities. 2. By weight%, C: 0.1% or less, Si: 0.50% or less, Mn: 1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50.
~ 3.50% and 1.5% or less Ni, 0.8% or less Mo
1. A seawater resistant steel for high temperature and high humidity environments, characterized by containing at least 1.5% of one or more of the above, and the balance consisting of Fe and inevitable impurities. 3. C: 0.1% or less, Si: 0.50% or less, Mn: 1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50 by weight%.
~ 3.50% and 0.005 to 0.05% Nb, 0.005 to 0.
A seawater resistant steel for high temperature and high humidity environments, characterized by containing 0.005 to 0.05% of a total of one or more kinds of 05% Ti, and the balance being Fe and unavoidable impurities. 4. By weight%, C: 0.1% or less, Si: 0.50% or less, Mn: 1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50.
~ 3.50% and 1.5% or less Ni, 0.8% or less Mo
The total of one or more types is 1.5% or less, and 0.005 to 0.05%
Nb, 0.005 to 0.05% Ti total of one or more of 0.005 to
A seawater resistant steel for high temperature and high humidity environments, characterized by containing 0.05% and the balance being Fe and inevitable impurities. 5. In weight%, C: 0.1% or less, Si: 0.50% or less, Mn: 1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50.
~ 3.50%, the balance is Fe and inevitable impurities, after hot rolling, accelerated cooling at a cooling rate in the range of 3 ~ 20 ℃ / sec, the accelerated cooling temperature of 400 ~ 600 ℃. A method for producing seawater resistant steel for high temperature and high humidity environments, which comprises stopping at 1, and then performing air cooling. 6. By weight%, C: 0.1% or less, Si: 0.50% or less, Mn: 1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50.
~ 3.50% and 1.5% or less Ni, 0.8% or less Mo
Steel containing 1.5% or less of the total of one or more of the above, with the balance being Fe and inevitable impurities, after hot rolling at 3 to 20 ° C / sec.
Accelerated cooling at a cooling rate in the range of 400 to 6
A method for producing seawater resistant steel for hot and humid environments, which comprises stopping at a temperature of 00 ° C and then performing air cooling. 7. By weight%, C: 0.1% or less, Si: 0.50% or less, Mn: 1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50.
~ 3.50% and 0.005 to 0.05% Nb, 0.005 to 0.
After hot rolling a steel material containing 0.005 to 0.05% of the total of one or more kinds of 05% Ti and the balance Fe and unavoidable impurities,
A method for producing seawater resistant steel for high temperature and high humidity environment, which comprises performing accelerated cooling at a cooling rate in the range of 3 to 20 ° C / sec, stopping the accelerated cooling at a temperature of 400 to 600 ° C, and then performing air cooling. 8. In weight%, C: 0.1% or less, Si: 0.50% or less, Mn: 1.50% or less, Al: 0.005 to 0.050%, Cr: 0.50.
~ 3.50% and 1.5% or less Ni, 0.8% or less Mo
The total of one or more types is 1.5% or less, and 0.005 to 0.05%
Nb, 0.005 to 0.05% Ti total of one or more of 0.005 to
A steel material containing 0.05% and the balance of Fe and unavoidable impurities is hot-rolled, and then accelerated cooling is performed at a cooling rate in the range of 3 to 20 ° C / sec, and the accelerated cooling is stopped at a temperature of 400 to 600 ° C. Then, the method for producing seawater resistant steel for high temperature and high humidity environment is characterized by performing air cooling thereafter.