CN116987959A - Corrosion-resistant high-strength-toughness medium-manganese steel medium plate and preparation method thereof - Google Patents

Abstract

The invention discloses a corrosion-resistant high-strength and high-toughness medium-manganese steel medium plate and a preparation method thereof, wherein Cr, ni, mo, ti, cu element mixing proportion is adopted to compensate potential drop caused by adding a large amount of Mn element; and fine grains of the rust layer to prevent dissolved oxygen from penetrating into a matrix in the rust layer, thereby reducing the corrosion rate of the medium manganese steel; meanwhile, in order to prevent the addition of excessive alloy elements from generating larger carbide precipitated phases in a tissue and strongly deteriorating the impact performance of the material, a low-temperature rolling method is adopted to introduce more dislocation and distortion energy, so that the content of the carbide precipitated phases is reduced and the impact performance is improved; the invention has the beneficial effects that: the corrosion performance of the medium manganese steel is improved, meanwhile, the impact energy at minus 40 ℃ is more than or equal to 110J, and the low-temperature impact energy is not obviously reduced; in addition, the method has simple operation process and is easy to realize industrial production.

Description

A corrosion-resistant, high-strength and tough medium-manganese steel medium-thick plate and its preparation method

Technical field

The invention belongs to the field of metallurgical technology and relates to a medium manganese steel, and more specifically to a corrosion-resistant, high-strength and tough medium-manganese steel and a preparation method thereof.

Background technique

With the rapid development of science and technology, mankind is ushering in a new era of developing and utilizing the ocean. All countries attach great importance to the exploration, protection and development of the ocean. Our country has a long coastline and vast territorial waters, and the utilization of marine resources is very important to our country's development. The exploration and development of marine resources and the protection of marine rights and interests all rely on advanced marine engineering equipment. As offshore engineering equipment gradually develops towards heavy loads, large-scale and automation, the safety requirements of the equipment have also increased, and there are also higher performance requirements for offshore engineering steel. Therefore, high strength, toughness, easy welding, and corrosion resistance are the development trends of steel for marine engineering. The research and development of high-quality marine engineering steel with independent intellectual property rights is of great significance to ensuring national energy security, realizing the development and utilization of marine resources, and improving overall national strength.

At present, in the manufacturing of marine engineering equipment, 355-460MPa steel plates are the most widely used. The 690MPa grade marine engineering steel used in key parts of large marine structures has the characteristics of high strength, low cost and simple process. Compared with traditional medium-thick plates, medium-manganese steel medium-thick plates have many unique advantages. First, the composition design of medium manganese steel significantly improves the hardenability of the material, which is conducive to the preparation of medium-thick steel plates with excellent and uniform structural properties; secondly, the Mn element can be solidly dissolved in the matrix material in large quantities, significantly improving the strength of the steel. Therefore, the addition of Mn element can appropriately reduce the content of C element in steel and improve welding performance; finally, Mn element, as a powerful austenite stabilizing element, can significantly expand the austenite phase area, making medium manganese steel at lower After temperature tempering, a high-strength martensite matrix and a certain amount of retained austenite structure are obtained, which has mechanical properties of high strength and high and low temperature toughness.

However, the addition of a large amount of Mn element to steel will cause the self-corrosion potential of the steel to decrease, and the corrosion resistance of medium-manganese steel is relatively poor. Moreover, the final structure of medium manganese steel is a composite structure of tempered martensite and retained austenite, which easily forms micro-batteries during the corrosion process and accelerates the corrosion rate. At the same time, the tempered martensite matrix contains a large number of high-angle grain boundaries, the grain boundary energy in the structure is high, and the corrosion resistance is poor. Steel used in marine engineering has been in the seawater environment for a long time and is corroded by multiple field coupling conditions such as temperature, humidity, and chloride ion concentration. It is very prone to corrosion degradation and shortens the service life of marine engineering equipment. At present, the commonly used anti-corrosion methods for marine engineering steel include coating protection and paint protection, etc. However, these methods not only increase costs but are also more difficult to maintain. Therefore, how to improve the corrosion resistance of medium manganese steel through composition design and process formulation is an urgent problem to be solved.

Contents of the invention

In view of the above-mentioned problem of poor corrosion resistance of medium manganese steel, the present invention proposes a medium-thick plate of corrosion-resistant, high-strength and tough medium-manganese steel, using a mixed ratio of Cr, Ni, Mo, Ti, and Cu elements to improve the natural corrosion resistance of medium-manganese steel. Corrosion potential, thereby compensating for the potential drop caused by adding a large amount of Mn elements; and using Cr, Ni, Mo, Ti, and Cu elements to enrich the rust layer during the corrosion process, refine the rust layer grains, and hinder dissolution Oxygen penetrates into the matrix inside the rust layer, thereby reducing the corrosion rate of medium manganese steel; at the same time, in order to prevent the addition of too many alloying elements from forming a larger carbide precipitation phase in the structure and strongly deteriorating the impact properties of the material, low-temperature rolling is used The tempering method introduces more dislocations and distortion energy, speeds up the diffusion efficiency of Mn elements into austenite during the tempering process, increases the content of retained austenite, and enriches more C elements in the retained austenite. Reduce the content of carbide precipitation phase and improve impact performance;

The chemical composition of the medium manganese steel in weight percentage is: C: 0.02~0.08%, Mn: 4.00~8.00%, Si: 0.10~0.5%, S: <0.01%, P: <0.01%, Al: 0.01~ 0.05%, Cu: 0.02~0.5%, Ni: 0.02~0.60%, Mo: 0.02~0.40%, Cr: 0.02~3.0%, Ti: 0.02~0.4%, the balance is Fe and other unavoidable impurities; so The structure of the medium manganese steel is a composite structure of tempered martensite and retained austenite.

The corrosion-resistant, high-strength and tough medium-manganese steel medium-thick plate has a thickness of 20-50mm, a yield strength of 690-750MPa, a tensile strength of 780-850MPa, an elongation of 26-35%, and an impact energy of -40°C ≥110J. .

The preparation process steps of the corrosion-resistant, high-strength and tough medium-manganese steel medium-thick plate are:

(1) Hot rolling treatment

The alloy billet is heated in the furnace to 1000-1200°C according to the weight ratio and kept for 2 hours; a billet with a thickness of 100mm is prepared, and then two-stage controlled rolling is carried out. The austenitized billet is rough rolled in 4 passes, and then 5 passes are carried out. Pass finishing rolling; the rough rolling temperature is 1000℃-1050℃, and the finishing rolling temperature is controlled at 780℃-880℃; after the finishing rolling is completed, water cooling is performed to room temperature at a cooling rate of 15~35℃/s to obtain the medium-thickness after quenching plate;

(2) Tempering treatment

After the heating furnace is heated to 630-690°C, the quenched medium-thick plate is placed into the furnace, kept at temperature for 50-100 minutes, and then air-cooled to room temperature to obtain a corrosion-resistant, high-strength, medium-manganese medium-thick plate.

The beneficial effects of the present invention: while improving the corrosion performance of medium manganese steel, the -40°C impact power is ≥110J, and the low-temperature impact power does not significantly decrease; in addition, the method of the present invention has a simple operation process and is easy to realize industrial production.

Description of the drawings

Figure 1 is a process schematic diagram of the preparation method of the present invention;

Figure 2 is the metallographic structure of the corrosion-resistant, high-strength, medium-manganese medium-thick plate in Example 1;

Figure 3 is the SEM morphology and structure of the corrosion-resistant, high-strength and tough medium-manganese medium-thick plate in Example 1.

Figure 4 is the relationship curve between the corrosion weight loss and the corrosion time of the corrosion-resistant high-strength medium-manganese medium-thick plate and Q345B in Examples 1-3.

Figure 5 is the electrochemical polarization curve of the corrosion-resistant high-strength and tough medium-manganese medium-thick plate corrosion sample in different periods in Example 1.

Figure 6 is the SEM morphology of the rust layer of the corrosion-resistant, high-strength, medium-manganese medium-thick plate in Example 1.

Detailed ways

The hot rolling mill used in the embodiment of the present invention is a Φ450 hot rolling mill designed and manufactured by the State Key Laboratory of Rolling Technology and Continuous Rolling Automation of Northeastern University;

The heating furnace used in the hot rolling process of the present invention is a high-temperature box-type resistance furnace, model RX4-85-13B;

The heating furnace used for tempering treatment in the present invention is a box-type resistance furnace, model RX-36-10;

The corrosion test equipment of the present invention adopts a periodic infiltration corrosion test box, the model is ZQFS-1200OZ.

Example 1

To prepare a corrosion-resistant, high-strength, ultra-low carbon medium-manganese medium-thick plate with a thickness of 20mm, the process steps are as follows:

(1) Hot rolling treatment

The alloy billet is heated to 1200°C in the furnace and kept for 3 hours. The chemical composition of the alloy billet in weight percentage is: C: 0.06%, Mn: 4.0%, Si: 0.27%, S: 0.002%, P: 0.003%, Al: 0.02%, Cu: 0.34%, Ni: 0.60%, Mo: 0.2%, Cr: 1.22%, Ti: 0.4%, the balance is Fe and other inevitable impurities. A billet with a thickness of 130 mm was prepared, and then two-stage controlled rolling was performed. The austenitized billet was rough rolled in 4 passes, with a reduction rate of 50.0%; after being warmed, 5 passes of finish rolling were performed, with a reduction rate of 50.0%. 50.0%, rolled into a 20mm thick hot-rolled plate, the rough rolling temperature is 1000℃-1026℃, and the finishing rolling temperature is 780℃-807℃. After hot rolling, water cool to room temperature at a cooling rate of 35°C/s to obtain a quenched medium-thick plate.

(2) Tempering treatment

After the heating furnace is heated to 630°C, the quenched medium-thick plate is put into the furnace, kept for 50 minutes after reaching the temperature, and then air-cooled to room temperature to obtain a 20mm thick, corrosion-resistant, high-strength, ultra-low carbon medium-manganese medium-thick plate. The final medium and thick plate structure is a composite structure of tempered martensite and retained austenite. The metallographic structure of the corrosion-resistant, high-strength and tough medium-manganese medium-thick plate in Example 1 is shown in Figure 2. The SEM morphology of the corrosion-resistant, high-strength and tough medium-manganese medium-thick plate in Example 1 is shown in Figure 3.

(3)Corrosion test

Corrosion performance test of the corrosion-resistant, high-strength, medium-manganese medium-thick plate prepared in this example: Q345B was used as the reference sample, and a periodic infiltration corrosion test chamber was used to conduct an accelerated corrosion test. The solution was accelerated using a 3.5% NaCl solution (simulating a marine environment). Corrosion test. The temperature of the aqueous solution was controlled at 45°C, the baking temperature in the test box was controlled at 70°C, and the humidity in the box was 70%. Each infiltration cycle is 1 hour, of which the soaking time is 0.2 hours, and the test is conducted for a total of 360 hours. Samples were taken at 24h, 72h, 144h, 240h, and 360h after the experiment started for morphology observation, weight loss measurement and corrosion product morphology observation. Draw the relationship curve of corrosion weight loss and corrosion time, see Figure 4. Conduct electrochemical tests on rusty samples and draw polarization curves, as shown in Figure 5. The SEM morphology of the rust layer of the corrosion sample is shown in Figure 6.

The corrosion-resistant, high-strength and ultra-low carbon medium-manganese medium-thick plate with a thickness of 20mm has a composite structure of tempered martensite and retained austenite. The yield strength is 750MPa, the tensile strength is 850MPa, and the elongation after fracture is 35%. The impact energy at -40℃ is 164J.

Example 2

To prepare a corrosion-resistant, high-strength, ultra-low-carbon medium-manganese medium-thick plate with a thickness of 30mm, the process steps are as follows:

(1) Hot rolling treatment

The alloy billet is heated to 1000°C in the furnace and kept for 3 hours. The chemical composition of the alloy billet in weight percentage is: C: 0.08%, Mn: 5.00%, Si: 0.10%, S: 0.002%, P: 0.003%, Al: 0.05%, Cu: 0.02%, Ni: 0.4%, Mo: 0.4%, Cr: 3.0%, Ti: 0.02%, the balance is Fe and other inevitable impurities. A billet with a thickness of 130 mm was prepared, and then two-stage controlled rolling was performed. The austenitized billet was rough rolled in 4 passes, with a reduction rate of 55.0%; after being warmed, 5 passes of finish rolling were performed, with a reduction rate of 55.0%. 45.0%, rolled into a 30mm thick hot-rolled plate, the rough rolling temperature is 1020℃-1041℃, and the finishing rolling temperature is 790℃-830℃. After hot rolling, water cool to room temperature at a cooling rate of 22°C/s to obtain a quenched medium-thick plate.

(2) Tempering treatment

After the heating furnace is heated to 670°C, the hot-rolled and quenched steel plate is put into the furnace, kept for 70 minutes after reaching the temperature, and then air-cooled to room temperature to obtain a 30mm thick, corrosion-resistant, high-strength, ultra-low carbon medium manganese plate.

Corrosion performance test of the corrosion-resistant, high-strength, medium-manganese medium-thick plate prepared in this example: Q345B was used as the reference sample, and a periodic infiltration corrosion test chamber was used to conduct an accelerated corrosion test. The solution was accelerated using a 3.5% NaCl solution (simulating a marine environment). Corrosion test. The temperature of the aqueous solution was controlled at 45°C, the baking temperature in the test box was controlled at 70°C, and the humidity in the box was 70%. Each infiltration cycle is 1 hour, of which the soaking time is 0.2 hours, and the test is conducted for a total of 360 hours. Samples were taken for weight loss measurement at 24h, 72h, 144h, 240h, and 360h after the experiment started.

The corrosion-resistant, high-strength and ultra-low carbon medium-manganese medium-thick plate with a thickness of 30mm has a composite structure of tempered martensite and retained austenite. The yield strength is 720MPa, the tensile strength is 830MPa, and the elongation after fracture is 31%. The impact energy at -40℃ is 134J.

Example 3

To prepare a corrosion-resistant, high-strength, ultra-low-carbon medium-manganese medium-thick plate with a thickness of 50mm, the process steps are as follows:

(1) Hot rolling treatment

The alloy billet is heated to 1100°C in the furnace and kept for 5 hours. The chemical composition of the alloy billet in weight percentage is: C: 0.02%, Mn: 8.00%, Si: 0.50%, S: 0.002%, P: 0.003%, Al: 0.01%, Cu: 0.5%, Ni: 0.02%, Mo: 0.02%, Cr: 0.02%, Ti: 0.2%, the balance is Fe and other inevitable impurities. A billet with a thickness of 150 mm was prepared, and then two-stage controlled rolling was performed. The austenitized billet was rough rolled in 4 passes, with a reduction rate of 62.5%; after being warmed, 5 passes of finish rolling were performed, with a reduction rate of 62.5%. 37.5%, rolled into a 50mm thick hot-rolled plate, the rough rolling temperature is 1030℃-1050℃, and the finishing rolling temperature is 830℃-880℃. After hot rolling, water cool to room temperature at a cooling rate of 15°C/s to obtain a quenched medium-thick plate.

(2) Tempering treatment

After the heating furnace is heated to 690°C, the hot-rolled and quenched steel plates are put into the furnace, kept warm for 100 minutes, and then air-cooled to room temperature. A corrosion-resistant, high-strength, medium-manganese medium-thick plate with a thickness of 50 mm was obtained.

Corrosion performance test of the corrosion-resistant, high-strength, medium-manganese medium-thick plate prepared in this example: Q345B was used as the reference sample, and a periodic infiltration corrosion test chamber was used to conduct an accelerated corrosion test. The solution was accelerated using a 3.5% NaCl solution (simulating a marine environment). Corrosion test. The temperature of the aqueous solution was controlled at 45°C, the baking temperature in the test box was controlled at 70°C, and the humidity in the box was 70%. Each infiltration cycle is 1 hour, of which the soaking time is 0.2 hours, and the test is conducted for a total of 360 hours. Samples were taken for weight loss measurement at 24h, 72h, 144h, 240h, and 360h after the experiment started.

The corrosion-resistant, high-strength and ultra-low carbon medium-manganese medium-thick plate with a thickness of 50mm has a structure of tempered martensite and retained austenite, a yield strength of 690MPa, a tensile strength of 780MPa, and an elongation after fracture of 26%, -40 ℃ impact energy is 110J.

Comparative example 1

To prepare ultra-low carbon medium manganese medium-thick plates with a thickness of 20mm, the process steps are as follows:

(1) Hot rolling treatment

The alloy billet is heated to 1200°C in the furnace and kept for 3 hours. The chemical composition of the alloy billet in weight percentage is: C: 0.06%, Mn: 4.0%, Si: 0.27%, S: 0.002%, P: 0.003%, Al: 0.02%, Cu: 0.34%, Ni: 0.60%, Mo: 0.2%, Cr: 1.22%, Ti: 0.4%, the balance is Fe and other inevitable impurities. A billet with a thickness of 130 mm was prepared, and then two-stage controlled rolling was performed. The austenitized billet was rough rolled in 3 passes, with a reduction rate of 50.0%; after being warmed, 3 passes of finish rolling were performed, with a reduction rate of 50.0%. 50.0%, rolled into a 20mm thick hot-rolled plate, the rough rolling temperature is 1000℃-1026℃, and the finishing rolling temperature is 910℃-980℃. After hot rolling, water cool to room temperature at a cooling rate of 35°C/s to obtain a quenched medium-thick plate.

(2) Tempering treatment

After the heating furnace is heated to 630°C, the quenched medium-thick plate is put into the furnace, kept warm for 50 minutes, and then air-cooled to room temperature to obtain an ultra-low carbon medium-manganese medium-thick plate with a thickness of 20mm. The final medium and thick plate structure is a composite structure of tempered martensite and retained austenite.

The corrosion-resistant, high-strength and ultra-low carbon medium-manganese medium-thick plate with a thickness of 20mm has a composite structure of tempered martensite and retained austenite. The yield strength is 710MPa, the tensile strength is 810MPa, and the elongation after fracture is 19%. The impact energy at -40℃ is 45J.

Comparative example 2

To prepare ultra-low carbon medium manganese medium-thick plates with a thickness of 20mm, the process steps are as follows:

(1) Hot rolling treatment

The alloy billet is heated to 1200°C in the furnace and kept for 3 hours. The chemical composition of the alloy billet in weight percentage is: C: 0.06%, Mn: 4.0%, Si: 0.27%, S: 0.002%, P: 0.003%, Al: 0.02%, Cu: 0.34%, Ni: 0.60%, Mo: 0.2%, Cr: 1.22%, Ti: 0.4%, the balance is Fe and other inevitable impurities. A billet with a thickness of 130 mm was prepared, and then two-stage controlled rolling was performed. The austenitized billet was rough rolled in 4 passes, with a reduction rate of 50.0%; after being warmed, 5 passes of finish rolling were performed, with a reduction rate of 50.0%. 50.0%, rolled into a 20mm thick hot-rolled plate, the rough rolling temperature is 1000℃-1026℃, and the finishing rolling temperature is 910℃-980℃. After the hot rolling is completed, the steel is water-cooled to room temperature at a cooling rate of 35°C/s to obtain a quenched medium-thick plate.

(2) Tempering treatment

After the heating furnace is heated to 630°C, the quenched medium-thick plate is put into the furnace, kept warm for 50 minutes, and then air-cooled to room temperature to obtain an ultra-low carbon medium-manganese medium-thick plate with a thickness of 20mm. The final medium and thick plate structure is a composite structure of tempered martensite and retained austenite.

The corrosion-resistant, high-strength and ultra-low carbon medium-manganese medium-thick plate with a thickness of 20mm has a composite structure of tempered martensite and retained austenite. The yield strength is 730MPa, the tensile strength is 840MPa, and the elongation after fracture is 20%. The impact energy at -40℃ is 60J.

The finishing rolling temperatures of Comparative Example 1 and Comparative Example 2 are 910°C-980°C respectively, which is higher than the finishing rolling temperature of 780°C-880°C of the present invention. The number of rough rolling and finishing rolling passes of the blank in Comparative Example 1 is less than that of Example 1. -3. The elongation after break of Comparative Example 1 is 19%, and the impact power at -40°C is 45J. The elongation after break of Comparative Example 2 is 20%, and the impact power at -40°C is 60J, which are all lower than Examples 1-3 of the present invention. The elongation is 26~35%, and the impact energy at -40℃ is ≥110J. It can be seen that the low-temperature rolling method introduces more dislocation and distortion energy, accelerates the diffusion efficiency of Mn elements into austenite during the tempering process, increases the content of retained austenite, and enriches more C elements. In retained austenite, reducing the content of carbide precipitation phases can significantly improve the impact properties of medium manganese steel.

Claims (3)

1. A corrosion-resistant high-strength and high-toughness medium manganese steel medium plate is characterized in that: adopting Cr, ni, mo, ti, cu element mixing proportion to improve the self-corrosion potential of the medium manganese steel, thereby compensating the potential drop caused by adding a large amount of Mn element; the Cr, ni, mo, ti, cu element is enriched in the rust layer in the corrosion process, so that grains of the rust layer are thinned, and the penetration of dissolved oxygen to a matrix in the rust layer is blocked, so that the corrosion rate of medium manganese steel is reduced; meanwhile, in order to prevent the addition of excessive alloy elements from generating larger carbide precipitated phases in a tissue and strongly deteriorating the impact performance of the material, a low-temperature rolling method is adopted to introduce more dislocation and distortion energy, so that the diffusion efficiency of Mn element to austenite in the tempering process is accelerated, the content of residual austenite is increased, more C element is enriched in the residual austenite, the content of carbide precipitated phases is reduced, and the impact performance is improved;

the medium manganese steel comprises the following chemical components in percentage by weight: c: 0.02-0.08%, mn: 4.00-8.00%, si:0.10 to 0.5 percent, S: < 0.01%, P: < 0.01%, al:0.01 to 0.05 percent, cu:0.02 to 0.5 percent, ni:0.02 to 0.60 percent, mo: 0.02-0.40%, cr: 0.02-3.0%, ti: 0.02-0.4%, and the balance of Fe and other unavoidable impurities; the medium manganese steel structure is a composite structure of tempered martensite and retained austenite.

2. The corrosion-resistant high-strength and high-toughness medium manganese steel plate according to claim 1, wherein: the thickness of the corrosion-resistant high-strength and high-toughness medium manganese steel medium plate is 20-50 mm, the yield strength is 690-750 MPa, the tensile strength is 780-850 MPa, the elongation is 26-35%, and the impact energy at minus 40 ℃ is more than or equal to 110J.

3. The corrosion-resistant high-strength and high-toughness medium manganese steel plate according to claim 1, wherein: the preparation process comprises the following steps:

(1) Hot rolling treatment

Heating the alloy blank to 1000-1200 ℃ along with a furnace according to the weight ratio, and preserving heat for 2-5h; preparing a blank with the thickness of 100-150mm, performing two-stage controlled rolling, performing 4-pass rough rolling on the austenitized blank, and performing 5-pass finish rolling; the rough rolling temperature is 1000-1050 ℃, and the finish rolling temperature is controlled at 780-880 ℃; after finishing finish rolling, cooling to room temperature at a cooling rate of 15-35 ℃/s to obtain a quenched medium plate;

(2) Tempering treatment

Heating the furnace to 630-690 ℃, placing the quenched medium plate into the furnace, preserving heat for 50-100 min after reaching the temperature, and then air-cooling to room temperature to obtain the corrosion-resistant high-strength and high-toughness medium plate.