KR19980051159A - Method for manufacturing tempered high tensile steel sheet for medium and high temperature pressure vessels with excellent room temperature and high temperature strength - Google Patents

Abstract

The present invention is a medium and high temperature pressure excellent in room temperature and high temperature strength to ensure the safety of the structure even when the strength at room temperature as well as the drop in strength when used for a long time at high temperature due to the characteristics of the material used in the equipment for recovering waste heat, such as power plants It relates to a method for producing a tempered high tensile strength steel sheet for containers.

The manufacturing method of this invention is C: 0.10-0.16%, Si: 0.50-0.70%, Mn: 0.40-0.65%, P: 0.020% or less, Sol-Al: 0.030% or less, Cr: 1.10- in weight%. A steel slab composed of 1.40%, Mo: 0.50-0.60%, remaining Fe and other unavoidable impurities was rolled in a conventional manner, and after being annealed normally, ferrite + perlite, which is the basic structure of the base metal structure of the steel sheet, was bainite + martensite. In order to soften some low-temperature metamorphic structure of the site and to increase the yield strength with respect to tensile strength, it is a technical gist of 1.9t-1.9t + 20 minutes at 650-730 degreeC.

Description

Method for manufacturing tempered high tensile steel sheet for medium and high temperature pressure vessel with excellent room temperature and high temperature strength

뵨 Invention is a medium and high temperature pressure that has excellent room temperature and high temperature strength so that the structure can be secured even at low temperature when it is used for a long time at high temperature as well as strength at room temperature. The present invention relates to a method for manufacturing a tempered high tensile strength steel sheet for containers, and more specifically, to a ferrite + perlite, which is a basic structure of the base metal structure of steel sheet, mixed with some low-temperature transformation tissues (bainite + martensite), thereby causing an upper and lower yield point. Tensile strength is higher than the regulated value due to the occurrence of loss, that is, continuous yielding, but yield strength is 40 ~ 50% of the tensile strength. Due to the softening process, the softening of the tissue causes a slight drop in the tensile strength and an increase in the yield strength, that is, the yield ratio. In Fig secure 50kg class that does not deteriorate at a high temperature to obtain a sufficient yield strength of 60-70% of the tensile strength for prolonged use, it is for a method of manufacturing a high-temperature steel.

Tempered high tensile strength steel sheets used as materials for facilities that recover waste heat, such as power plants, require excellent physical properties so that the structure can be secured not only in strength at room temperature but also in strength reduction when used at high temperatures for a long time. It is required to have excellent room temperature and high temperature strength as a steel material that requires base metal weldability due to the characteristics of the structure connected by welding.

Steel plate used as the material of the equipment to recover the waste heat of the power plant is a trend to use a high alloy steel gradually because of the difficult use and the development of the use technology, in the case of the conventional production technology by adding Mo alone alone, general rolling Only Mo, which has good heat resistance, was added to the five elements, because Mo alone alone was enough to withstand the steel.

However, in order to double the heat resistance performance, the effect of the complex addition is superior to increase the amount of Cr-Mo added.

Therefore, the present invention has the heat resistance (prevention of strength drop) to prevent softening by inhibiting grain growth at high temperature of the alloying element Cr-Mo added to the present invention and producing carbonitrides (Mo ₂₃ C ₆ , Cr ₂₃ C ₆ ). It is an object of the present invention to provide a method for manufacturing a tempered high tensile strength steel sheet for a medium and high temperature pressure vessel excellent in room temperature and high temperature strength using excellent performance. In other words, after annealing, the ferrite + perlite, which is the basic structure of the base material of the steel plate, is mixed with some low-temperature transformation structure (bainite + martensite), resulting in the loss of the upper and lower yield points, that is, the continuous yield phenomenon. However, yield strength is the lower limit of 40-50% of tensile strength, and it is treated at the proper temperature that promotes softening of the base metal tissue through low temperature transformation tissue change formed at the time of retreat. Its purpose is to provide a safe method of manufacturing 50kg grade medium and high temperature steel sheet that does not deteriorate even if used for a long time at high temperature by securing sufficient yield strength of 60 ~ 70% of tensile strength by increasing yield strength, that is, yield ratio. .

1 is a block diagram illustrating a manufacturing process of the present invention;

2 (a), (b) is a tissue photograph obtained after the heat treatment of the invention material obtained by the present invention,

3 is a structure photograph obtained after the heat treatment of the comparative material.

In order to achieve the above object, in the present invention, in weight%, C: 0.10-0.16%, Si: 0.50-0.70%, Mn: 0.40-0.65%, P: 0.020% or less, S: 0.008% or less, Sol-Al Steel slab consisting of: 0.030%, Cr: 1.10-1.40%, Mo: 0.50-0.60%, remaining Fe and other unavoidable impurities is rolled in the usual way, and after being annealed normally, the basic structure of the base metal structure of the steel sheet In order to soften some low-temperature transformation tissues of bainite + martensite to ferrite + perlite and to increase the yield strength against tensile strength, it is subjected to a soaking treatment at 1.9 to 1.9 t + 20 minutes at 650 to 730 ° C. Provides a method of manufacturing 50Kg grade tempered high tensile steel sheet for medium and high temperature pressure vessels having excellent room temperature and high temperature strength.

Hereinafter, the present invention will be described in detail with reference to preferred embodiments.

First, in the present invention, in weight%, C: 0.10-0.16%; Si: 0.50-0.70%, Mn: 0.40-0.65%, P: 0.020% or less, S: 0.008% or less. A steel slab is made of Sol-Al: less than 0.030%, Cr: 1.10-1.40%, Mo: 0.50-0.60%, remaining Fe, and other unavoidable impurities. Same as

While carbon (C) increases the hardness and strength by increasing the hardenability during heat treatment of steel, the amount of carbon is harmful to toughness and solubility when the amount is excessive. It is limited to 0.10 to 0.16%.

Silicon (Si) forms carbides and is dissolved in Fe to increase the elastic limit tensile strength, but when added more than 0.5%, the ferrite structure is lowered and non-metallic inclusions (silicates) are formed to damage the toughness, so the amount of silicon is regulated to 0.50 to 0.70%.

Manganese (Mn) is an quenchability improving element, which can improve the hardness during heat treatment. However, when excessively added, the amount of Mn is limited to 0.40 to 0.65% because the hardness is unstable due to a decrease in quenchability.

Phosphorus (P) is the largest impurity that impairs the low temperature impact toughness of the steel sheet and thus degrades the internal quality, so the content is limited to 0.020% or less.

Sulfur (S) is the same harmful element as the phosphorus (P) component, which causes deterioration of low-temperature impact toughness and impairs weldability in thick plates. Therefore, the amount is limited to 0.008% or less.

Sol-Al is an element complexed with Si, which is deoxidized to the right, and has a very high contribution to the refinement of the grain size, but the grain boundary area is increased due to the grain refinement when excessively added. In addition, the surface cracks and impact toughness of the playing slab is inhibited, so the amount is limited to within 0.030%.

Cr is also an effective element for hardenability and is widely used for increasing hardness and strength. It is harmful to weldability when a large amount is added, and it is disadvantageous to secure hardness when a small amount is limited to 1.10 to 1.40%.

In addition, Mo contributes to the improvement of creep rupture strength in the austenite phase under stress, and improves the hardenability and improves the strength, but may cause brittleness when a large amount is added, and the amount is 0.50 to 0.60 because it is harmful to the deterioration of the weld toughness. Limit to%

In the manufacturing method of the present invention based on steel having the composition range as described above, after the steel slab is rolled under the conditions of a passbook by a process by continuous casting, after the steel sheet is sintered at a temperature range of 890 to 910 ° C., 650 The bar is made at a temperature of -730 ° C, and thus, when used as a steel plate for a medium and high temperature 50kg pressure vessel, it has excellent physical properties even when used for a long time at room temperature and high temperature.

Preferably, sufficient dephosphorization should be performed by a ladle finishing (LF) process to minimize P, which is an impurity element, in the chemical composition of the invention steel for long time use at high temperature (350-500 ° C). As it is used as a material, the room temperature and high temperature strength satisfying the regulation value suitable for the intended use after the usual annealing treatment in order to minimize the impurity element that provides the cause of soft embrittlement in the usual way and to secure the homogeneity and toughness of the steel In order to secure a certain amount of anti-corrosion treatment, the preferred condition is that the base metal structure of the steel sheet is mixed with some low-temperature transformation structure (bainite + martensite) in the ferrite + pearlite, and thus the loss of upper and lower yield points to. That is, it prevents the occurrence of continuous yielding and the tensile strength is higher than the regulated value, but the yield strength indicates the lower limit of the physical property having the yield ratio of 40-50% of the tensile strength. As a result, the suitable titration condition to promote softening of the base material through the transformation of low temperature transformation tissue as the submerging treatment is in the range of 650 to 730 ° C, and the holding time is 1.9t to 1.9t + 20 minutes. The driving energy that causes the tissue to change has a substructure, so that softening does not occur. On the contrary, when it is above the limited range, the increase in the tensile strength and the yield strength decrease due to the increase of the hard low temperature transformation tissue. .

In addition, if the holding time of the steel sheet is shorter or longer than the limited range time during softening, the softening is not performed equally in the temperature range. Eventually, the non-uniformity of the softening range causes localized material difference of the steel sheet. do.

Therefore, when considering the appropriate conditions of the invention steel, excellent room temperature strength can be obtained, and even if it is used for a long time at a high temperature, it is possible to ensure safety that the strength drop is within a regulated range.

Hereinafter, the present invention will be described in detail through examples.

Example

Cast by cooling method when playing with molten steel made of four kinds of components as shown in Table 1, the steel plate of the thickness of 20mmt and 35mmt by the normal rolling of the thick plate was subjected to heat treatment anneal, and then applied by each temperature The test and the quality of the steel sheet and the outside were examined and the results are shown in Table 2. The internal inspection of the steel sheet was performed by an ultrasonic test, and the surface inspection was performed by a magnetic test (MT). On the other hand, the comparative material is similar to the component but performed a second performance cooling, it is confirmed that there is a material difference in the retention time difference. In other words, if the holding time is long at the same temperature, the softening action is increased, and the hard phase (bainite + martensite) obtained after the annealing is further advanced to the soft phase (bainite + ferrite) to decrease the tensile strength and increase the yield strength at the same time. It seems to have improved because there is time to progress the action.

On the other hand, the comparative materials (1 to 4), when more or less than the limiting temperature and time of the invention, exceeds the tensile strength at room temperature strength (Comparative materials 1 to 3), or the yield strength at high temperature is not suitable for use purposes Will have In the case of Comparative Material 4, it is a steel plate material for guaranteeing high temperature vessel of 217 ° C used in marine structural steel material, and it adds Mo and Nb and V excellent in room temperature strength instead of high Cr-Mo of component steel. Although the strength at was satisfactory, the high temperature strength was deteriorated compared to the Cr-Mo steel.

The properties of the present invention are desirable properties if the tensile strength at room temperature is 52.6-65.0 kg / mm ² , the yield strength is at least 31.7 kg / mm ² , and the tensile strength at high temperature (500 ° C.) is at least 45.6 kg / mm ² . Evaluated as having.

Table 1 Component Comparison of Invention Material and Comparative Material

※ Comparative material D: 0.0: 0.029%, V: 0.054% added

Table 2

The structure | tissue photograph of the invention material manufactured by such a method of this invention was shown to FIG. 2 (a), (b), and the structure | tissue photograph of a comparative material was shown in FIG.

As described above, according to the present invention, by controlling the steel composition and the heat treatment conditions appropriately, a fine high tensile strength steel sheet having excellent physical properties is produced, in which the steel sheet has little change in physical properties even when it is used for a long time at room temperature and high temperature, thereby maintaining durability and safety. , Manufactured steel sheet has an effect that can be widely used as a 50kg pressure vessel material for medium and high temperature guarantee.

Claims (1)

By weight%, C: 0.10-0.16%, Si: 0.50-0.70%, Mn: 0.40-0.65%, P: 0.020% or less, S: 0.008% or less, Sol-Al: within 0.030%, Cr: 1.10-1.40 Steel slab composed of%, Mo: 0.50-0.60%, remaining Fe and other unavoidable impurities, and then rolled in a usual manner, followed by annealing the passbook, and then bainite + martensite on ferrite + perlite, the basic structure of the base metal structure of the steel sheet. In order to soften some low temperature metamorphic tissues, it is necessary to perform 1.9t ~ 1.9t + 20 minutes of reflection treatment at 650∼730 ℃ to increase the yield strength against tensile strength. Manufacturing method of 50Kg tempered high tensile steel sheet for pressure vessel.