KR850000980B1 - Ferrite stainless steel - Google Patents

Abstract

up to 0.08% C, up to 0.06 % N, 28.5- 30.5% Cr, 3.60-5.60% Mo, up to 2.00% Mn, 2.00-5.00% Ni, up to 2.00% Si, up to 0.5% Al for deoxidising, up to 2.00% of Ti, Zr and Nb, balance mainly Fe. The Ti, Zr and Nb contents are as follows: %Ti/ 6+%Zr/7+%Nb/8 at least %C+%N more than 0.0275%. The steel is useful as a welded article. It has superior crevice corrosion, especially in the as-welded state. The increased Ni content gives the steel improved toughness, both before and after welding.

Description

Ferritic stainless steel

The present invention relates to ferritic stainless steel.

Patent application No. 80-1438, filed simultaneously with this specification, describes ferritic stainless steel with good crevice and particle corrosion resistance.

The above-mentioned patent application No. 80-1438 contains up to 2% of an element composed of titanium, zirconium and corumium and has a carbon + nitrogen content of more than 275 ppm according to the following formula: US Patent Nos. 3,932,174 and 3,929,473 Is distinguished from the call.

% Ti / 6 +% Zr / 7 +% Cb / 8≥% C +% N

That is, the 80-1438 application, while having better material properties, allows the content of carbon + nitrogen to contain more than the conventional patents, resulting in significant economic benefits in the production of stainless steel over the conventional patents. The higher carbon and nitrogen content allows melting and fabrication in less expensive processes in the steels of patents 3,932,174 and 3,929,473.

The present invention is to provide a steel with higher toughness in the specification patent application No. 80-1438. In addition to a stabilizer consisting of titanium zirconium and corumium and more than 275 ppm of carbon + nitrogen, the steel of the present invention contains 2.00-5.00%, in particular 3.00-4.50% of Nickel, while the steel of specification patent application 1438 Up to 8.00% usually contains up to 1.00% Nickel.

Increasing the nickel content increases the toughness in the patent application No. 80-1438 alloy. For the reasons mentioned above, the alloys of the present invention can be clearly distinguished from the alloys of US Pat. Nos. 3,932,174 and 3,929,473 and 4,119,765. The alloy of patent 4,119,765 is characterized by a lower maximum molybdenum content than the content of the present invention.

Another relevant reference is the document entitled "Ferritic Stainless Steel Corrosion Resistance and Economics," published on July 24, 1976, by Remus A. Lula, in Metal Progress. It does not describe the ferritic stainless steel of the present invention.

It is therefore an object of the present invention to provide ferritic stainless steel. The ferritic stainless steel of the present invention is characterized by good before and after welding, excellent gap and particle corrosion resistance and good weldability. The alloys contain up to 0.08% carbon, up to 0.06% nitrogen, 25.00-35.00% chromium, 3.60-5.60% molybdenum, up to 2.00% manganese, 2.00-5.00% nickel, up to 2.00% silicon, It consists of elements consisting of up to 0.5% aluminum, up to 2.00% titanium, zirconium and corumium and the rest of iron. The sum of carbon and nitrogen is 0.0275%

% Ti / 6 +% Zr / 7 +% Cb / 8≥% C +% N

Typically, carbon and nitrogen are present in amounts of at least 0.005% and 0.010%, respectively, and their sum exceeds 0.0300%, chromium and molybdenum are present at 28.50-30.50% and 3.75-4.75%, respectively. Each is present in an amount of 1.00% or less, aluminum is used only as a reducing agent, the content is less than 0.1% is effective.

Titanium, corumium and zirconia are added to improve the cracking and intergranular corrosion resistance of the alloy. In some respects this is a modification of the high carbon nitrogen of US Pat. No. 3,929,473. Stabilizers are added to the high carbon and nitrogen variants of US Pat. No. 3,929,473 without destroying the toughness and weldability of the alloy. It is also within the scope of the present invention to add the desired amount of stabilizer, such as titanium or corium, although it would be appropriate to add at least 0.15% of titanium as long as the presence of corium does not adversely affect the weldability of the alloy. Corumium has an advantageous effect on the toughness of the alloy compared to titanium.

In a particular embodiment of the present invention, at least 0.15% Corumbium and at least 0.15% Titanium are required and it is suitable that Titanium, Corumbium and Zirconium are present in amounts up to 1.00% according to the following equation.

% Ti / 6 +% Zr / 7 +% Cb / 8 = 1.0 ~ 4.0 (% C +% N)

Nickel is added to the alloy of the present invention to increase the toughness of the alloy, usually in the amount of 2.00-5.00%, especially 3.00-4.50%.

The ferritic stainless steel of the present invention is particularly suitable for use in welded products. The following examples are intended to illustrate the invention in various respects. The ingot from Example 24 (Example AX) was heated to 2050 ° F., hot rolled to 0.125 inch steel sheet, then annealed at a temperature of 1950 ° F. or 2050 ° F., cold rolled to about 0.062 inch steel sheet, and then annealed at 1950 ° F. or 2050 ° F. Let's do it.

Hot-rolled and cold-treated specimens are continuously evaluated for toughness, while other specimens are evaluated for toughness after TIG welding.

The chemical compositions of the examples are shown in Table 1 below.

TABLE 1

Examples A-F do not have a Nickel content of 2.00-5.00% as examples other than the present invention. The present invention is in accordance with the Nickel content in excess of 2.00%.

Additional data including the chemical composition of the examples are shown in Table 2.

TABLE 2

Toughness: hot rolled and annealed material (0.125 × 0.394 inch specimens) cold rolled and annealed material (0.062 × 0.394 inch specimens), welded water wells (0.062 × 0.394 inch specimens) and welded and annealed material (0.062 × 0.394 inch specimens) Evaluated by measuring transition temperature using V-notch specimens with transverse shielding for. The transition temperature is based on 50% intrinsic-50% shredded appearance. The transition temperatures for the hot rolled and cold rolled specimens are shown in Table 3, where Example A-L was annealed at 1950 ° F and other examples were annealed at 2050 ° F.

TABLE 3

The transition temperatures for the welded specimens and the welded and annealed specimens are shown in Table 4 below. Examples A-F are annealed at 1950 ° F. prior to welding, other embodiments are annealed at 2050 ° F. and all examples are quenched in water. Examples A-F are post weld annealed at 1950 ° F. and other embodiments at 2050 ° F. and all examples are quenched after welding annealing.

TABLE 4

Examples G-X are within the scope of the present invention while Examples A-F do not, and Examples G-X contain at least 2.00% Nickel. Therefore, Nickel's advantages are clearly shown in Tables 3 and 4. Example G-X has a lower transition temperature and therefore has substantially higher toughness than Examples A-F.

Lower transition temperatures for Example G-X are given in Table 5 below, which is the composition of Tables 3 and 4.

In all examples the maximum transition temperature for Examples G-X is lower than the minimum transition temperature for Examples A-F. The data shows that Examples G-X have higher toughness than Examples A-F.

TABLE 5

Additional specimens of Example G-X are evaluated for crevice and particle corrosion resistance. These specimens are fabricated like the specimens above. Crevice corrosion resistance is assessed by immersing a specimen with a 1 × 2 inch surface in a 10% ferric chloride solution for 72 hours. The test is made by using polytetra pulluloethylene on the front and back of the crevice at 122 ° F and fixing it in position with a pair of rubber bands stretched in both longitudinal and transverse directions at 90 ° F. And G48-76 of the American Testing and Materials Association for Materials.

The evaluation results are shown in Table 6 below, and the specimens were evaluated under cold rolling and annealing conditions, welding conditions and welding and annealing conditions.

TABLE 6

* Annealing at 2050 ° F-subcooling

Table 6 shows that the crevice corrosion resistance of Example G-X is very good. Therefore, it can be seen that the alloy of the present invention is characterized by having excellent crevice corrosion resistance.

Particle corrosion resistance is assessed by immersing the specimens of 1 × 2 inch surface in copper sulfate 50% sulfuric acid solution for 120 hours. The test results yielded a corrosion rate of 24.0 mils per year (0.0020 inches per month) and satisfactory microscopic testing, which is recommended for use in testing stabilized high chromium ferrite stainless steel.

The results of the evaluation are shown in Table 7, and the specimens were welded and weld annealed.

TABLE 7

* Annealing at 2050 ° F-subcooling

** NA: Particle erosion or particle dropping member. Examples G-L and S-X from Table 7 showed excellent particle corrosion resistance and each specimen passed the test.

The results of these tests show that the toughness which is the object of the present invention in the range of 2% or more and 5% or less of the nickel described in the present invention is superior to the patent application No. 80-1438 of the present applicant, and satisfies the requirements as ferritic stainless steel. To demonstrate that an excellent steel is achieved by the present invention. It will be apparent to those skilled in the art that the novel principles of the present invention described above in connection with particular embodiments may be embodied in various other imitations and the same applications. Accordingly, it is not intended to be limited by the described embodiments within the limits of the appended claims.

Claims (1)

Up to 0.08% carbon by weight, up to 0.06% nitrogen, 28.5-30.5% chromium, 3.60-5.60% molybdenum, up to 2.00% manganese, 2.00-5.00% nickel, up to 2.00% silicon, up to 0.5% One or two or more of the aluminum, titanium, titanium, zirconium and corium elements of the element group and the balance of up to 20 ..% are composed of iron and the titanium, zirconium and corium The composition ratio of is based on the following equation, the ferrite stainless steel having excellent corrosion resistance and toughness, characterized in that the sum of the carbon + nitrogen of more than 0.0275% and good corrosion resistance against welding gap corrosion at 50 ℃ (122 ℉) . % Ti / 6 +% Zr / 7 +% Cb / 8≥% C +% N