KR19990052502A - Method for manufacturing thick steel plate with excellent corrosion resistance fatigue corrosion resistance - Google Patents

Abstract

The present invention relates to the provision of a method for producing a thick steel sheet excellent in strength and toughness, in particular excellent in corrosion resistance to emulsion corrosion.

The method of the present invention is C: 0.03-0.20% by weight, Si: 0.05-0.5%, Mn: 0.5-2.0%, P: 0.03% or less, S: 0.01% or less, Al: 0.001-0.1%, Ti: It contains 0.005-0.020% as the base component system, and in addition to the base component, a steel is prepared so as to contain at least one of Cr, W, and Cu in the range of 0.1-0.35%, and the steel is between 1110-1250 ° C. After reheating to a temperature of 800 ℃ to complete the rolling to the target thickness at a temperature of 800 ℃ or more, and immediately after rolling to cool the temperature section of 800-500 ℃ at a cooling rate of 5-15 ℃ / sec to produce a thick steel sheet It features.

Description

Method for manufacturing thick steel plate with excellent corrosion resistance fatigue corrosion resistance

The present invention relates to a method for producing a thick steel sheet excellent in strength and toughness and particularly excellent in corrosion resistance to emulsion corrosion.

Crude oil generally contains about 10ppm of H2S gas, but recently low-grade crude oil containing more than 100ppm is also produced. In the case of containing a large amount of H2S gas in the crude oil can reduce the life of the steel due to the action of corrosion, hydrogen embrittlement, etc. In particular, it is well known by many studies that accelerate the fatigue crack propagation rate 10 times or more have.

However, ships used for transporting crude oil have to allow the presence of cracks of a certain size due to the cracking during the ship manufacturing process or use, as in most other ships. Taking into account the presence of such cracks, the ship's life is managed and the repair time is determined. When a large amount of H2S gas is contained in the transported crude oil, the fatigue crack propagation speed is accelerated by 10 times or more, There is a fatal problem where destruction can occur. Accordingly, many studies have been carried out on the acceleration of fatigue crack propagation velocity that occurs when shipbuilding steel plate is used in crude oil containing a large amount of H2S gas, and the cause and mechanism of acceleration are somewhat identified. However, proposals and studies for suppressing the acceleration of fatigue crack propagation by H2S gas are still insufficient. However, in order to reduce the fatigue crack propagation rate in an air environment, the crystal grains of steel materials are increased or directional. It is proposed to arrange them in such a way that they are not applicable to the acceleration of fatigue crack propagation velocity due to the action of hydrogen atoms on the crack tip.

The present invention has been researched and solved to solve the problems described above, crude oil containing a large amount of H2S gas by applying a manufacturing process to control the cooling after rolling and rolling by adding an appropriate amount of alloy to the existing thick steel plate component system for shipbuilding It is an object of the present invention to provide a method for producing a thick steel sheet in which the fatigue crack propagation rate is not accelerated.

Hereinafter, the present invention will be described in more detail with reference to Examples.

In the present invention, C: 0.03-0.20%, Si: 0.05-0.5%, Mn: 0.5-2.0%, P: 0.03% or less, S: 0.01% or less, Al: 0.001-0.1%, Ti: 0.005- 0.020% or the like as a basic component system, and in addition to these basic components, a steel material prepared to contain at least one of Cr, W, and Cu in the range of 0.1-0.35% is prepared, and the steel is 1110-1250 ° C. After reheating to a temperature of between, to complete the rolling to the target thickness at a temperature of 800 ℃ or more, and immediately after rolling to cool the temperature section of 800-500 ℃ at a cooling rate of 5-15 ℃ / sec to produce a thick steel sheet It is characterized by.

Hereinafter, the reason for limitation of the above conditions will be described.

The C is an essential basic component for securing the strength of the steel, but when contained in a large amount, the toughness and weldability are lowered, so that in the case of the steel, the range is 0.03-0.20%.

In addition, the Si is an important deoxidizer in steel production, and at the same time acts as a solid solution strengthening element, but excessively contained deteriorates the toughness of the weld, so the range of 0.05-0.5% is preferable.

Mn is basically an element added to secure strength, but if it is contained in an excessive amount, the toughness of the weld deteriorates and the weld phase itself deteriorates, so 0.5-2.0 is an appropriate addition range.

P and S are inevitably contained in the iron ore manufacturing process, but P is easy to segregate and easily form low temperature metamorphic structure in the segregated part, so the upper limit is 0.03%, and S increases nonmetallic inclusions to deteriorate toughness. Therefore, the upper limit was limited to 0.01% or less.

In addition, when Al is an element that is essentially added for deoxidation but contains 0.1% or more, an element effective for improving low-temperature toughness of the welded part, but the effect is saturated at 0.02% or more, so the upper limit is 0.02%.

The Cr, W, Cu is an element which is added to improve the corrosion resistance fatigue resistance, which is an object of the present invention is particularly effective in reinforcing steel. However, if it contains a large amount, the weld toughness is deteriorated, and difficulty occurs in the steelmaking process, so 0.1-0.35% is set as the addition range, respectively.

In order to finally produce the steel of such a component system, it must be rolled, and the reheating temperature for rolling is limited to 1100-1250 ° C. In order to sufficiently solidify the added alloying element and to secure the workability suitable for rolling, it must be heated to 1100 ℃ or higher. On the other hand, if it is heated too high, the abnormal coarsening phenomenon of austenite grains occurs, so the upper limit is 1250 ℃. .

The finish rolling is preferably finished in the austenite temperature range in order to prevent the stretching of the final structure and suppress the occurrence of mixing, for this purpose, the finish rolling temperature was 800 ℃ or more.

Accelerated cooling is carried out immediately after rolling to refine the grains of steel produced and to improve strength and toughness. The end temperature of water cooling is 500 ℃ ± 20 ℃. The reason why the accelerated cooling stop temperature is limited is that rapid cooling below this temperature increases strength but deteriorates toughness, and when cooling is terminated above the temperature, strength is not sufficiently secured. Cooling rate is limited to 5-15 ℃ / sec, this is also to maintain the balance between strength and toughness.

The thick steel sheet manufactured by applying the present invention configured as described above is excellent in that the fatigue crack propagation speed is significantly reduced as compared to the general ship steel plate even when used in the case of containing a large amount of H2S gas in crude oil. It provides corrosion resistance fatigue corrosion resistance.

Hereinafter, the effect of this invention is given and demonstrated to an Example.

Example

In order to compare the steel of the present invention with excellent corrosion resistance fatigue corrosion resistance in crude oil containing H2S gas compared with the existing steel materials prepared steels having the composition of Table 1 and after the experimental rolling and compared the corrosion resistance fatigue corrosion resistance It was. The slab reheating was performed at 1150 ° C. for 2 hours to ensure sufficient heating. The final rolling temperature was 830 ° C. and the plate thickness was 20 mm. After rolling was completed, water cooling was performed between 800-500 ° C. at a cooling rate of 7 ° C./sec.

TABLE 1

C Si Mn P S Al Ti Cr W Cu Existing Steel 0.148 0.375 1.41 0.021 0.005 0.037 - - - - Inventive Steel A 0.143 0.25 1.05 0.010 0.005 0.003 0.015 0.28 - - B 0.139 0.27 0.97 0.008 0.004 0.028 0.013 - 0.26 - C 0.142 0.25 1.02 0.008 0.005 0.03 0.016 0.16 - 0.28

As can be seen in Table 2, the thick steel sheet produced by the method of the present invention was excellent in corrosion resistance fatigue corrosion resistance. In other words, the fatigue crack propagation speed acceleration is suppressed to within 2 times that of the air under given experimental conditions, and the corrosion propagation crack propagation rate in the crude oil containing H2S gas in contrast to that of ordinary steel is accelerated by 10-20 times. There was an effect that the phenomenon persisted significantly.

TABLE 2

Erosion Corrosion Fatigue Crack Propagation Rate

Da / dn at 20mm / cycle in air Crude oil da / dn at 20mm / cycle Acceleration ratio (times) (in crude oil / air) Existing Steel 3.90 * ^10-5 5.83 * ^10-4 14.9 Inventive Steel A 4.2 * ^10-5 7.8 * 10- ^-5 1.86 Inventive Steel B 3.6 * ^10-5 8.2 * ^10-5 2.3 Invention Steel C 5.5 * ^10-5 8.7 * ^10-5 1.6

Claims (1)

By weight%, C: 0.03-0.20%, Si: 0.05-0.5%, Mn: 0.5-2.0%, P: 0.03% or less, S: 0.01% or less, Al: 0.001-0.1%, Ti: 0.005-0.020% A steel material is contained in the base component system, and in addition to the base component, the steel is formed so as to contain at least one of Cr, W, and Cu in the range of 0.1-0.35%, and the material is reheated to a temperature between 1110-1250 ° C. After the completion of the rolling to a target thickness at a temperature of 800 ℃ or more, and immediately after rolling the temperature range of 800-500 ℃ at a cooling rate of 5-15 ℃ / sec to produce a thick steel sheet Thick steel sheet manufacturing method with excellent corrosion corrosion fatigue properties.