Duplex stainless steel resistant to corrosion of molten copper liquid

Abstract

The invention discloses a duplex stainless steel resistant to molten copper corrosion, which comprises the following components in percentage by mass: 20-28% of Cr, 4-6.5% of Ni, 0.6-1.2% of Mn, 0.4-0.8% of Si, less than or equal to 0.03% of P, less than or equal to 0.05% of C, less than or equal to 0.008% of S, 0.1-0.3% of N, 2-5% of Mo and the balance of Fe, the duplex stainless steel has a ferrite and austenite duplex structure, and the volume fractions of the ferrite and the austenite are 35-65%. And heat treatment is conducted on the duplex stainless steel resistant to molten copper liquid corrosion, heat preservation solution treatment is conducted for 1-2 h at the temperature of 1050-1200 DEG C, cooling is conducted after solution treatment, and the cooling mode is rapid water cooling or air cooling. When the duplex stainless steel resistant to corrosion of the molten copper liquid is in direct contact with the molten copper liquid, the duplex stainless steel has high corrosion resistance, and obvious intergranular corrosion does not occur.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature corrosion-resistant materials, and more specifically, to the composition and structure of a stainless steel material with a relatively high ability to resist corrosion by high-temperature molten copper liquid. Background Art

[0002] In the copper and copper alloy melting and casting production process, some important components need to be in direct contact with the molten copper liquid, such as the stopper rod for controlling the flow rate in the ladle and the steel belt for transporting the copper liquid. Currently, most domestic and foreign manufacturers choose ferritic stainless steel materials as the stopper rod or steel belt materials; although stainless steel has good oxidation resistance, ferritic stainless steel will experience high-temperature grain growth and the precipitation of chromium-rich compounds at grain boundaries, resulting in high-temperature brittleness problems, which cause excessive corrosion and insufficient service life in the use of ferritic stainless steel materials. Duplex stainless steel structure especially refers to ferritic-austenitic duplex stainless steel, in which the volume fraction of the ferritic phase or the austenitic phase is ≥ 15%. This type of steel has less tendency to intergranular corrosion and stress corrosion, and has good strength and toughness. The corrosion resistance of duplex stainless steel with different tissue ratios to molten copper liquid has not been reported. Theoretically, duplex stainless steel with specific components and ratios has stronger corrosion resistance than ferritic stainless steel. Summary of the Invention

[0003] In order to solve the above-mentioned deficiencies and drawbacks of the prior art, the primary object of the present invention is to provide a duplex stainless steel resistant to molten copper liquid corrosion, which has excellent high-temperature oxidation resistance and the ability to resist corrosion by molten copper liquid.

[0004] The object of the present invention is achieved by the following technical solutions: A duplex stainless steel resistant to molten copper liquid corrosion, characterized in that, by mass percentage (%): it contains Cr 20 - 28%, Ni 4 - 6.5%, Mn 0.6 - 1.2%, Si 0.4 - 0.8%, P ≤ 0.03%, C ≤ 0.05%, S ≤ 0.008%, N 0.1 - 0.3%, Mo 2 - 5%, and the rest is Fe. The duplex stainless steel has a ferritic and austenitic duplex structure, and the volume fractions of the ferritic phase and the austenitic phase are both 35 - 65%.

[0005] Further, the Cr is 22 - 28%, Ni is 5 - 6.2%, C ≤ 0.03%, Mo is 3 - 5%, S ≤ 0.001%, P ≤ 0.03%, and the volume fractions of the ferritic phase and the austenitic phase are both 48 - 52%.

[0006] Further, the duplex stainless steel can be produced into plates, pipes, sheets, strips, coils, bars, rods, wires, profiles.

[0007] The present invention also discloses a heat treatment method for a duplex stainless steel resistant to molten copper liquid corrosion, comprising the following steps: S1. Heat treat the above-mentioned duplex stainless steel resistant to molten copper liquid corrosion: perform solution treatment at 1050 - 1200°C for 1 - 2 h with heat preservation, S2. After solution treatment, perform cooling, and the cooling method is rapid water cooling or air cooling.

[0008] The present invention also discloses an application of a duplex stainless steel resistant to molten copper liquid corrosion. The duplex stainless steel is made into bars or strips of various specifications for use in molten copper liquid.

[0009] Furthermore, the preparation method of the molten copper liquid is as follows: Place pure copper fragments with a purity of 99.9% in a clay crucible, place the clay crucible in a box-type resistance furnace, heat up to 1200°C, and keep it at this temperature for 30 min to melt the copper.

[0010] The effective effect of the present invention: When the duplex stainless steel resistant to molten copper liquid corrosion of the present invention is in direct contact with molten copper liquid, it has high corrosion resistance and does not undergo obvious intergranular corrosion. Description of the Drawings

[0011] Figure 1 It is the metallographic structure diagram of the duplex stainless steel in Example 1; Figure 2 It is the cross-sectional metallographic structure diagram of the stainless steel after being corroded in molten copper liquid for 6 h in Example 1; Figure 3 It is the metallographic structure diagram of the stainless steel in the comparative example; Figure 4 It is the comparison diagram of the change of the bar diameter with the corrosion time in the comparative example and Example 1; Figure 5 It is the macroscopic morphology diagram of the cross-section of the bar after being corroded for 6 h in the comparative example and Example 1; Figure 6 It is the intergranular corrosion characteristic metallographic structure diagram of the stainless steel in the comparative example after being corroded in molten copper liquid for 6 h. Detailed Embodiments

[0012] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. The embodiments described herein are only used to illustrate and explain the present invention, and should not be construed as a limitation to the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention. Example 1

[0013] Taking a duplex stainless steel material as the research object, its composition (mass percentage %) is Cr 21.85, Ni 5.36, Mn 1.05, Si 0.75, P 0.022, C 0.05, S 0.008, N 0.155, Mo 3.18, and the rest is Fe; the heat treatment method is: holding at 1050 °C for 2 hours, and air cooling after taking out of the furnace; its structure is austenite grains with different morphologies distributed on a ferrite matrix, such as Figure 1 shown, and the ratio of the two phases is close to 1:1.

[0014] A number of bars with a diameter of 10 mm and a length of 10 cm were processed from this material; pure copper fragments with a purity of 99.9% were placed in a clay crucible, and the clay crucible was placed in a box-type resistance furnace. The temperature was raised to 1200 °C, and after holding for 30 min, the copper was melted; then one end of the above-mentioned bar with a length close to half was inserted into the molten copper liquid, and the other end was exposed to the high-temperature atmosphere at 1200 °C; then after holding at 1200 °C for 1 h, 2 h, 4 h and 6 h respectively, the bars were taken out. The diameter change of the bars after different corrosion times was measured, as Figure 2 shown. After 6 h of corrosion, the original diameter of 10 mm hardly decreased; the macroscopic morphology of the cross-section after 6 h of corrosion is as Figure 5 shown. It can be seen that the diameter of the duplex stainless steel is about 9.9 mm after 6 h of corrosion, which is only reduced by 1% compared with the original diameter, and the change is very small. The metallographic observation of the cross-section after 6 h of corrosion is as Figure 2 shown. A dense protective layer is formed on the surface of the duplex stainless steel in the molten copper liquid, which hinders the expansion of corrosion. Example 2

[0015] Taking a duplex stainless steel material as the research object, its composition (mass percentage %) is Cr 25.01, Ni 6.02, Mn 0.69, Si 0.4, P 0.023, C 0.021, S 0.001, N 0.251, Mo 3.45, and the rest is Fe; the heat treatment method is: holding at 1100 °C for 2 hours, and rapid air cooling; its structure is austenite grains with different morphologies distributed on a ferrite matrix, and the ratio of the two phases is close to 1:1.

[0016] A number of bars with a diameter of 40 mm and a length of 100 cm were processed from this material. The pure copper was melted at 1200 °C in a clay crucible. Then one end of the above-mentioned bar with a length close to half was inserted into the molten copper liquid, and the other end was exposed to the high-temperature air. Then after holding at 1200 °C for 6 h respectively, the bars were taken out. It was found that the diameter was about 9.92 mm after 6 h of corrosion, which was only reduced by 0.8% compared with the original diameter. It shows that this duplex stainless steel bar has good corrosion resistance to molten copper liquid.

[0017] Comparative Example 1 Taking ferritic stainless steel material as the research object, its composition (mass percentage %) is Cr 25.19, Ni 0.42, Mn 1.3, Si 0.32, P 0.032, C 0.095, S 0.0025, N 0.13, and the rest is Fe; the heat treatment method is: holding at 1050 °C for 2 hours and air cooling after furnace discharging; its structure is single-phase ferritic grains of different sizes, such as Figure 3 shown. The large grain size is about 200 microns, and the small grain size is about 40 microns.

[0018] A number of bars with a diameter of 10 mm and a length of 10 cm are processed from this material. Pieces of pure copper with a purity of 99.9% are placed in a clay crucible, and the clay crucible is placed in a box-type resistance furnace. The temperature is raised to 1200 °C, and after holding for 30 min, the copper is melted; then one end of the above bar with a length close to half is inserted into the molten copper liquid, and the other end is exposed to the high-temperature atmosphere at 1200 °C; then after holding at 1200 °C for 1 h, 2 h, 4 h, and 6 h respectively, the bars are taken out. The diameter changes of the bars after different corrosion times are measured, as Figure 4 shown; after 6 h of corrosion, the original diameter of 10 mm is reduced to 7.5 mm; the macroscopic morphology of the cross-section after 6 h of corrosion is as Figure 5 shown. It can be seen that the diameter of this ferritic stainless steel decreases significantly after 6 h of corrosion. The metallographic structure of the cross-section after 6 h of corrosion is observed metallographically, as Figure 6 shown. The ferritic stainless steel corrodes along the grain boundaries typically during the corrosion process in the molten copper liquid.

[0019] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A duplex stainless steel resistant to molten copper liquid corrosion, characterized in that: By mass percentage, it contains 20 - 28% Cr, 4 - 6.5% Ni, 0.6 - 1.2% Mn, 0.4 - 0.8% Si, P ≤ 0.03%, C ≤ 0.05%, S ≤ 0.008%, N 0.1 - 0.3%, Mo 2 - 5%, and the balance is Fe. The duplex stainless steel has a ferritic and austenitic duplex structure, and the volume fractions of the ferrite and the austenite are both 35 - 65%.

2. The duplex stainless steel resistant to molten copper corrosion according to claim 1, wherein The Cr is 22 - 28%, Ni is 5 - 6.2%, C ≤ 0.03%, Mo is 3 - 5%, S ≤ 0.001%, P ≤ 0.03%, and the volume fractions of the ferrite and the austenite are both 48 - 52%.

3. The duplex stainless steel resistant to molten copper corrosion according to any one of claims 1-2, characterized in that, The duplex stainless steel can be produced into plates, tubes, sheets, strips, coils, bars, rods, wires, profiles.

4. A heat treatment method for a duplex stainless steel resistant to molten copper corrosion, characterized in that, The heat treatment method of the duplex stainless steel resistant to molten copper liquid corrosion according to any one of claims 1 - 2 is solution treatment by holding at 1050 - 1200 °C for 1 - 2 h, and the cooling method after the solution treatment is rapid water cooling or air cooling.

5. Application of a duplex stainless steel resistant to molten copper corrosion, characterized in that, The duplex stainless steel is made into bars or strips of various specifications for molten copper liquid. The preparation method of the molten copper liquid is as follows: Put pure copper chunks with a purity of 99.9% into a clay crucible, place the clay crucible in a box - type resistance furnace, heat it up to 1200 °C, and keep it warm for 30 min to melt the copper.

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