KR19980052517A - High strength austenitic stainless steel with excellent corrosion resistance and weather resistance and steel sheet manufacturing method using the same - Google Patents

Abstract

An object of the present invention is to provide a high-strength austenitic stainless steel excellent in corrosion resistance and weather resistance and a method for producing an austenitic stainless steel sheet using the same.

The present invention for achieving the above object by weight% C: 0.07% or less, Si: 1.0% or less, Mn: 2.0% or less, Cr: 18-20%, Ni: 7-10%, Al: 0.005% or less, P: 0.05% or less, S: 0.01% or less, Ti: 0.03% or less, B: 0.003% or less, N: 0.1-0.25%, high-strength austenitic stainless steel with excellent corrosion resistance and weather resistance composed of residual Fe and other unavoidable impurities The present invention relates to a steel slab, and the present invention provides a hot-rolled steel sheet by heating the steel slab at a temperature range of 1230-1300 ° C. for 200-240 minutes and then hot rolling the steel slab; Hot-rolling the hot rolled steel strip at an ambient temperature of 1130-1170 ° C .; In the manufacturing method of high strength austenitic stainless steel sheet having excellent corrosion resistance and weather resistance comprising the step of cold rolling to prepare a cold rolled steel strip, cold-rolled annealing at an ambient temperature of 1130-1170 ℃, and then pickling and temper rolling. Let that point be about that.

Description

High strength austenitic stainless steel with excellent corrosion resistance and weather resistance and steel sheet manufacturing method using the same

The present invention relates to austenitic stainless steel and steel sheet manufacturing method using the same, which is commonly used for high-strength structural materials and stone-resistant parts, and more particularly, high-strength austenitic stainless steel excellent in corrosion resistance and weather resistance, and a steel sheet manufacturing method using the same It is about.

In general, austenitic stainless steels represented by 18Cr-8Ni (STS304) steel have excellent moldability, corrosion resistance, and welding characteristics, compared to ferritic, and thus are used in various linear products, construction materials, and steel pipes.

However, when the austenitic stainless steel is required for better corrosion resistance and high strength properties, in the conventional case, a method of compensating the strength by applying an added steel grade of expensive Cr and Mo components or by applying a material thickness upward There was a drawback that the manufacturing cost rises. In addition, the austenitic stainless steel has excellent corrosion resistance due to the passivation film formed on the surface, but may cause local corrosion depending on the corrosion environment and material conditions. In particular, the generation and growth of pitting in the corrosion atmosphere of tap water or buried soil is pointed out as an important factor of water pipe leakage accident.

This stainless steel formula occurs at the site where the passivation film is locally destroyed by material and environmental factors. Among these factors, sulfate inclusions exposed on the alloy surface act as important formula generators. In the case of sulphate inclusions, since the inclusions dissolve more easily than the base metals, the metal part without the protective film is exposed to the corrosive environment at the interface between the inclusions and the soybeans, and intensive dissolution occurs at this site to act as a starting point of the formula. Therefore, in order to suppress the occurrence of such a formula, it is necessary to reduce the inclusions acting as a starting point of the formula or to increase the dissolution resistance of the inclusions and to improve the repassivation ability of the soja in order to suppress the growth of the pits. need.

The present invention has been proposed to solve the above problems, and the present invention avoids expensive Cr, Mo application that is increased in order to meet the demand of better corrosion resistance and high strength properties in austenitic stainless steel, and adds N It is therefore an object of the present invention to provide austenitic stainless steels whose strength is higher by improving the corrosion resistance and strength at a lower cost and by reducing the inclusions that are the starting point of corrosion.

In addition, the present invention is to provide a method for producing austenitic stainless steel sheet having excellent corrosion resistance and weather resistance, high strength by limiting the heat treatment temperature in manufacturing the austenitic stainless steel as a steel sheet. .

1 is a graph showing the cross-sectional reduction rate according to the specimen temperature during hot rolling of the invention steel according to the present invention

2 is a graph showing the oxidative increase according to the specimen heating time for hot rolling

3 is a graph showing the recombination behavior according to the annealing temperature of the invention steel according to the present invention

4 is a graph showing the martensite fraction according to the cold reduction rate

In the present invention, C: 0.07% or less, Si: 1.0% or less, Mn: 2.0% or less, Cr: 18-20%, Ni: 7-10%, Al: 0.005% or less, P: 0.05% or less, S: 0.01% or less, Ti: 0.03% or less, B: 0.003% or less, N: 0.1-0.25%, and a high-strength austenitic stainless steel having excellent corrosion resistance and weather resistance composed of residual Fe and other unavoidable impurities.

In addition, the present invention is a method for producing austenitic stainless steel sheet, by weight% C: 0.07% or less, Si: 1.0% or less, Mn: 2.0% or less, Cr: 18-20%, Ni: 7-10 %, Al: 0.005% or less, P: 0.05% or less, S: 0.01% or less, Ti: 0.03% or less, B: 0.003% or less, N: 0.1-0.25%, steel slabs composed of residual Fe and other unavoidable impurities Manufacturing a hot rolled steel strip by heating and then hot rolling in a temperature range of 1230-1300 ° C. for 200-240 minutes; Hot-rolling the hot rolled steel strip at an ambient temperature of 1130-1170 ° C; Cold rolling to produce a cold rolled steel strip, cold-rolled annealing at an ambient temperature of 1130-1170 ℃, followed by pickling and temper rolling to produce a high-strength austenitic stainless steel sheet having excellent corrosion resistance and weather resistance It is about.

Hereinafter, the reason for limiting the steel component of the present invention and the reason for addition thereof will be described.

The C is a strong austenite phase stabilizing element, which has the effect of reducing the content of delta-ferrite phase during slab casting to improve hot workability and reducing the amount of Ni added, and if the content is too large, carbide precipitation during annealing and welding construction It is feared that the corrosion resistance by Therefore, the present invention is to limit the content of C to 0.07% or less.

The Si is advantageous for high temperature oxidation resistance, but when the addition amount is too large, the delta-ferat content is increased, the hot workability is decreased, and the formation of interpositional defects due to the increase of Si inclusions is feared. Therefore, in the present invention, the content of Si is limited to 1.0% or less.

When Mn and S are added in a large amount of Mn, high-temperature oxidation resistance is lowered, and a high affinity with S in steel acts as a starting point of corrosion in the presence of MnS-type inclusions, and S is hot-workable. It lowers and, in particular, segregates at the grain boundaries of the austenite phase during solidification, causing the occurrence of linear bonds during hot rolling. Therefore, in the present invention, Mn is limited to 2.0% or less, and S is limited to 0.010% or less.

If the amount of Cr is too small, the corrosion resistance and high temperature oxidation resistance are lowered. If the amount is too large, the delta-ferrite content is increased and the hot workability is lowered, so the present invention is limited to 18-20%.

Ni is added in consideration of the stability, processability, corrosion resistance and manufacturing cost of the austenite phase, in the present invention is limited to 7-10%.

The Al is a component that improves the high temperature oxidation resistance, and as the addition amount thereof increases, inclusions due to Al oxide increase during steelmaking, causing surface defects. Therefore, in the present invention, the amount of Al added is limited to 0.005% or less.

When the content of P is large, workability and stone resistance are lowered, so the content is limited to 0.05% or less.

The Ti is advantageous in terms of tensile strength by preventing the surface defects during hot rolling by preventing high temperature oxidation when the slab is heated at high temperature for hot rolling. If the amount is too large, surface defects are caused by Ti oxide. Therefore, the amount of the addition is limited to 0.03% or less.

The B is effective for preventing surface defects generated during hot rolling because it has an effect of improving high temperature hot workability, but when the amount is too large, B process compound is formed to significantly lower the melting point to lower the hot workability. Therefore, in the present invention, B limits the addition amount to 0.003% or less.

The N has the effect of increasing the yield strength of the material to about twice the C and can obtain high strength properties without deterioration of fracture toughness, since the solid solution of N in austenitic stainless steel is larger than C Cr ₂₃ C ₆ The delay effect of precipitation can improve the intergranular corrosion characteristics. In addition, although there is a characteristic of improving the pitting resistance, in the case where the amount of addition is large, it is possible to give a load of hot rolling due to high hot deformation resistance and low hot workability. Therefore, in the present invention, the amount of N added is limited to 0.1-0.25%.

In the present invention, the addition of N and Mo in the above weight ratio is to improve the pitting resistance through the improvement of the passivation film properties and the repassivating ability of the base metal, and the effect of N and Mo on the pitting resistance of the austenitic stainless steel. The influence is expressed by a Pitting Resistance Number (PREN) such as

PREN =% Cr + 3.3 ×% Mo + 16 ×% N

Among the alloying elements that improve the corrosion resistance, N has the smallest increase in manufacturing cost, and has a high solid solubility in austenitic stainless steel, and can be alloyed by a conventional manufacturing process such as AOD (Argon-Oxygen Decarburization). In addition, N addition can obtain high strength characteristics without deterioration of fracture toughness. Since the solid solubility of N in austenitic stainless steel is larger than C, the intergranular corrosion resistance can be improved by delaying Cr ₂₃ C ₆ precipitation. Can be.

Hereinafter, the steel sheet manufacturing method using the steel having the components as described above in detail for each step.

In the present invention, after the steel of the composition is manufactured as a slab, the steel slab is heated in a temperature range of 1230-1300 ℃ for 200-240 minutes, followed by hot rolling to prepare a hot rolled steel strip.

The hot rolling temperature is 1300 ℃, the rate of cross-sectional reduction is rapidly lowered to facilitate the occurrence of surface defects, and the load of the roll operation is increased below 1230 ℃ in the present invention to 1230-1300 ℃ in order to reduce the hot rolling workability and surface bonding It is limited.

At this time, the heating time can be sufficiently heated in the furnace, it is limited to 220 ± 20 minutes without deterioration of the surface quality by the excessive generation of scale.

In addition, in the present invention, the hot rolled steel strip is subjected to hot rolling annealing at an atmosphere temperature of 1130-1170 ° C.

In the steel according to the present invention, since the recrystallization occurs sufficiently at the steel sheet temperature of about 1135 ° C during hot-annealing, the atmosphere temperature of the annealing furnace is limited to the range of 1130-1170 ° C.

Further, in the present invention, the cold rolled steel sheet is manufactured by cold rolling, cold-rolled and annealed at an ambient temperature of 1130-1170 ° C, and then subjected to pickling and temper rolling.

After cold rolling, cold rolling annealing is carried out at the same temperature range as the above hot rolling annealing, and pickling and temper rolling are performed in a conventional manner.

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

EXAMPLE

After dissolving austenitic stainless steels of the inventive steels (A) and (B) as shown in Table 1 in an electric furnace, removing impurities and adjusting components in an AOD refining furnace, the slab was manufactured in a continuous casting facility, and then 220 at 1250 ° C. After heating for 5 minutes, hot rolling was performed to produce a 5.5 mm hot rolled steel strip. Subsequently, annealing was performed at 1135 ° C (atmosphere temperature 1150 ° C), and then cold rolled steel strips having a thickness of 0.8, 1.0, and 2.5 mm were prepared, and cold-rolled annealing, pickling and temper rolling were performed at 1135 ° C (atmosphere temperature 1150 ° C). After preparing the tensile test, hardness test, corrosion resistance, weather resistance, soil corrosion properties were tested several times, the results are shown in Tables 2 and 3.

In addition, the comparative steel (1) (STS304) and comparative steel (2) (STS316) of the composition range as shown in Table 1 prepared by a conventional method was subjected to the same test several times, the results are shown in Table 2, 3 is shown.

In Table 3, the numbers in [] indicate the number of tests, and the number ranges in () indicate the average value.

TABLE 1

TABLE 2

TABLE 3

As shown in Table 2, the invention steel was superior to the comparative steel (1) (2) yielding strength of about 35kg / mm ² .

In addition, as shown in Table 3, the corrosion resistance, weather resistance, water pipe simulation (Simulation) results of the corrosion of the front surface compared to the comparative steel (1) 304, but compared to the comparative steel (2) (316) heat The intergranular corrosion characteristics were better than the comparable steels (1) and (2) by nitrogen addition.

However, in the case of stainless steel, since the local corrosion is the main corrosion case, it shows excellent corrosion resistance compared to the comparative steel in the results of the ferric chloride test and the official potential test to evaluate the local corrosion characteristics. Good results were obtained in which no corrosion occurred at all during the test. In summary, the corrosion resistance test results showed that the inventive steel had excellent corrosion resistance compared to that of the comparative steel (1), and obtained a good result equal to or higher than that of the comparative steel (2).

Using the inventive steel, the reduction rate of the cross section according to the specimen temperature during hot rolling is measured, and the results are shown in FIG. 1. At this time, the reduction ratio (%) is calculated by the following equation.

Cross-sectional reduction rate (%) = cross-sectional area at break ÷ cross-sectional area of original specimen × 100

As shown in FIG. 1, the cross-sectional reduction rate drastically decreased at 1300 占 폚. Therefore, it can be seen that surface defects are easily generated at a heating temperature of 1300 ° C. or higher.

In addition, the oxidation increase according to the hot rolling heating time was measured using the inventive steel and the comparative steel (STS 304). The results are shown in FIG.

As shown in Figure 2, in the case of the present invention it can be seen that there is no surface quality deterioration due to the over-scale generation in about 220 ± 20 minutes.

In addition, the work hardening index according to the annealing temperature was obtained using the inventive steel, and the measurement results are shown in FIG.

As shown in FIG. 3, the recrystallization was sufficiently performed at the steel sheet temperature of 1135 ° C during annealing.

In addition, using the inventive steel and the comparative steel (STS 304) to calculate the fraction (%) of martensite according to the cold reduction rate (%) is shown in Figure 4 as a result.

As shown in FIG. 4, the metastable austenitic stainless steel exhibited a lower work hardening characteristic than that of the comparative steel (STS 304).

As described above, according to the present invention, austenitic stainless steel having corrosion resistance, weather resistance, and high strength characteristics is provided without increasing the price compared to existing STS 304 steel, so that corrosion resistance demanding material in soil embedding atmosphere, weather resistance required exterior structural material, etc. When applied to the application, the economic effect can be expected to be favorable.

Claims (2)

By weight% C: 0.07% or less, Si: 1.0% or less, Mn: 2.0% or less, Cr: 18-20%, Ni: 7-10%, Al: 0.005% or less, P: 0.05% or less, S: 0.01 A high-strength austenitic stainless steel having excellent corrosion resistance and weather resistance, which is composed of% or less, Ti: 0.03% or less, B: 0.003% or less, N: 0.1-0.25%, residual Fe and other unavoidable impurities. In the method of manufacturing an austenitic stainless steel sheet, By weight% C: 0.07% or less, Si: 1.0% or less, Mn: 2.0% or less, Cr: 18-20%, Ni: 7-10%, Al: 0.005% or less, P: 0.05% or less, S: 0.01 Steel slabs composed of% or less, Ti: 0.03% or less, B: 0.003% or less, N: 0.1-0.25%, residual Fe and other unavoidable impurities are heated in a temperature range of 1230-1300 ° C. for 200-240 minutes, followed by hot rolling. Manufacturing a hot rolled steel strip; Hot rolling annealing the hot rolling at an ambient temperature of 1130-1170 ° C .; Cold rolling to produce a cold rolled steel strip, cold-rolled annealing at an atmosphere temperature of 1130-1170 ℃, and then pickling and temper rolling, high strength austenitic stainless steel sheet excellent in corrosion resistance and weather resistance Manufacturing method.