Rare earth Ce modified super duplex stainless steel and preparation method thereof

Abstract

The super duplex stainless steel consists of the following components in percentage by mass: not less than 0.01% and not more than 0.05% of C, not less than 0.01% and not more than 0.20% of Si, not less than 0.50% and not more than 2.0% of Mn, not less than 4.0% and not more than 10.0% of Ni, not less than 20.0% and not more than 35.0% of Cr, not less than 1.50% and not more than 6.50% of Mo, not less than 0.15% and not more than 0.40% of N, not less than 0.008% and not more than 0.05% of Ce and the balance of Fe. 0.2% < = (C + N) < = 0.45%, 5.0% < = Ni + Mn < = 11.0%, and 25% < = Cr + Mo < = 40%. By means of the preparation method, it can be guaranteed that the proportion of the ferrite phase and the austenite phase is within a reasonable range, and the super duplex stainless steel has high strength, high plasticity and good corrosion resistance.

Description

Technical Field

[0001] The invention relates to the technical field of alloys, and in particular to a rare earth Ce modified super duplex stainless steel and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of nuclear power, chemical industry and marine engineering construction, their equipment has increasingly shown a development trend of "large-scale, high efficiency and long life", and the requirements for "large size, high strength and high corrosion resistance" have been put forward for engineering equipment steel. Super duplex stainless steel represented by SAF2507 has high Cr / Mo / N content, and its pitting resistance equivalent value (PREN) is above 40. It has excellent corrosion resistance and can meet the application requirements of severe corrosive environments.

[0003] Super duplex stainless steel has high technical content and high added value. However, ferrite and austenite have significant differences in crystal structure, chemical composition, mechanical properties, etc., which leads to poor deformation coordination of the two-phase structure during hot working, easy cracking of the edges, and low yield rate. In order to avoid scrapping due to severe cracking, super duplex stainless steel mostly adopts a two-fire rolling process, that is, after the ingot is opened and cooled, it is thoroughly ground, and then reheated and rolled for the second time. The two-fire rolling process not only seriously reduces production efficiency, but also greatly increases production costs. At the same time, super duplex stainless steel has a high content of Cr / Mo / N elements, a high precipitation nose temperature of the brittle phase and a fast precipitation speed. Harmful phases such as σ phase and nitride are easily precipitated during hot rolling, cooling after rolling and heat treatment, affecting the comprehensive performance of the material.

[0004] For example, the Chinese invention patent application with patent application number CN202211537853.X (publication number CN115725902A) discloses "Economic duplex stainless steel containing rare earth metal Ce and its preparation method". This patent adds a trace amount of Ce (0.01-0.07%) to the economical duplex stainless steel, so that the obtained micro-alloyed economical duplex stainless steel has better elongation, impact toughness and corrosion resistance than ordinary economical duplex stainless steel. However, the economical duplex stainless steel involved in the invention has Cr 20.5-21.5%, Ni 1.5-2.5%, Mo≤0.6%, N 0.15-0.20%, and the alloy element content is low, and the corrosion resistance is low; the temperature of the solid solution treatment is 1150℃, and the holding time is 2h. The heat treatment process temperature is high, the time is long, and the energy consumption is large; the tensile strength is 523-542MPa, and the tensile strength is low, which is difficult to meet the high strength requirements of engineering structures for steel.

[0005] Another example is the Chinese invention patent application with patent application number CN202211683591.8 (publication number CN115874017A), which discloses "A method for reducing hot rolling cracks in super duplex stainless steel". By strictly controlling the content of silicon and aluminum, boron and rare earth microalloying, and inclusion refinement technology, the hot rolling cracks of super duplex stainless steel can be significantly reduced by using one-hot rolling to improve its yield rate and reduce production costs. This patent mainly reduces hot rolling cracks by controlling oxides and inclusions during the smelting process, but lacks the necessary control over the pass reduction rate and rolling temperature in the hot rolling process.

[0006] In addition, the starting rolling temperature in this patent is preferably 1200-1280°C, and the final rolling temperature is preferably not less than 950°C. High rolling temperature can easily cause excessive grain growth and affect the mechanical properties of the material. Summary of the invention

[0007] The first technical problem to be solved by the present invention is to provide a rare earth Ce modified super duplex stainless steel having high strength, high plasticity and good corrosion resistance in view of the above-mentioned prior art.

[0008] The second technical problem to be solved by the present invention is to provide a preparation method of the rare earth Ce modified super duplex stainless steel according to the above prior art.

[0009] The technical solution adopted by the present invention to solve the above-mentioned first technical problem is: a rare earth Ce modified super duplex stainless steel, characterized in that: it is composed of the following components in terms of mass percentage: 0.01≤C≤0.05%, 0.01%≤Si≤0.20%, 0.50%≤Mn≤2.0%, 4.0%≤Ni≤10.0%, 20.0%≤Cr≤35.0%, 1.50%≤Mo≤6.50%, 0.15%≤N≤0.40%, 0.008%≤Ce≤0.05%, and the balance is Fe;

[0010] Furthermore, 0.2%≤(C+N)≤0.45%, 5.0%≤Ni+Mn≤11.0%, and 25%≤Cr+Mo≤40%.

[0011] The technical solution adopted by the present invention to solve the above second technical problem is: a preparation method of the above rare earth Ce modified super duplex stainless steel, characterized in that it comprises the following steps:

[0012] 1) Ingredients: electrolytic chromium, electrolytic manganese, pure iron, molybdenum, nickel, silicon, chromium nitride iron alloy and rare earth Ce alloy are selected according to the above mass percentages;

[0013] 2) Smelting: firstly, electrolytic chromium, pure iron, molybdenum, nickel and silicon are placed in a smelting furnace for smelting, and then electrolytic manganese and chromium nitride iron alloy are added for smelting after melting, and then rare earth Ce alloy is added after melting to obtain molten steel;

[0014] 3) Casting: pouring molten steel into a casting mold to obtain an ingot, and controlling the casting temperature to be 1470-1530°C;

[0015] 4) Forging: After cutting off the riser part of the ingot, forging is performed to obtain a forging blank;

[0016] 5) Hot rolling: hot rolling the forged billet, followed by water cooling to obtain a hot-rolled plate;

[0017] 6) Heat treatment: The hot-rolled plate is subjected to solution treatment and then rapidly cooled.

[0018] Preferably, in step 2), when adding electrolytic manganese and chromium nitride ferroalloy for smelting, nitrogen is introduced for protection to improve the yield of nitrogen element.

[0019] Preferably, in step 4), the initial forging temperature is controlled to be 1150-1200°C, and the final forging temperature is 950-1000°C. Controlling the initial forging temperature at 1150-1200°C can ensure sufficient solid solution of elements such as Cr, Mo, Ni, and N, and prevent excessive growth of the structure due to excessive temperature; controlling the final forging temperature at 950-1000°C can avoid the precipitation of brittle phases such as σ phase; on the other hand, forging in this temperature range can ensure that the ratio of ferrite and austenite phases is within a reasonable range, that is, the ferrite ratio is 60-75%, and the austenite ratio is 40-25%.

[0020] Preferably, in step 4), the total forging deformation is 30% to 50%. Controlling the deformation in this way can ensure a fine microstructure and disperse the rare earth inclusions, while avoiding cracking caused by excessive deformation.

[0021] Preferably, in step 5), the hot rolling start temperature is controlled to be 1150-1200°C, which can not only ensure the sufficient solid solution of elements such as Cr, Mo, Ni, and N, but also prevent excessive growth of the structure due to excessively high temperature; the final rolling temperature is controlled to be 950-1020°C to inhibit the precipitation of brittle phases and prevent cracking caused by too low rolling temperature.

[0022] Preferably, in step 5), the proportion of ferrite in the initial hot-rolled structure is 60-80%, the proportion of austenite is 40-20%, the dynamic recovery / recrystallization degree of ferrite phase is 60%-90%, and the dynamic recovery / recrystallization degree of austenite is 40%-60%, which increases the coordinated deformation consistency of the two-phase structure during rolling, reduces edge cracking, and improves the yield rate.

[0023] The ferrite ratio in the finish-rolling structure is 50-70%, and the brittle phase and inclusion ratio is 0.05%-1.5%, preventing the excessive brittle phase and inclusions from degrading the material properties.

[0024] Preferably, in step 5), the rolling deformation per pass is controlled to be 15%-30%. The deformation per pass ≥15% can ensure more sufficient deformation of the billet and avoid coarse grain structure or low degree of dynamic recovery / recrystallization in the core of the billet due to insufficient deformation; the deformation per pass ≤30% can prevent cracking caused by excessive deformation per pass.

[0025] In addition, in step 5), the hot-rolled edge crack of the rare-earth Ce-modified super duplex stainless steel is controlled below 3 mm, improving the self-healing ability of the crack during subsequent rolling and preventing the crack from spreading widely.

[0026] Preferably, in step 6), the solution treatment temperature is 1030-1080 °C, the holding time is 10-20 min, and water cooling is used, which can not only ensure the full solution of alloying elements but also reduce the precipitation of brittle phases.

[0027] Preferably, in step 6), the ferrite ratio after solution treatment is 40-60%, and the inclusion ratio does not exceed 0.5%, ensuring that the ferrite and austenite ratios are similar and avoiding excessive inclusions from degrading the material properties.

[0028] Compared with the prior art, the advantages of the present invention are as follows: 1. In the alloy composition design of the rare-earth Ce-modified super duplex stainless steel of the present invention, 0.2% ≤ (C + N) ≤ 0.45%, 5.0% ≤ Ni + Mn ≤ 11.0%, 25% ≤ Cr + Mo ≤ 40%. This can not only ensure the balance of the ferrite and austenite ratios but also obtain good corrosion resistance, with the pitting equivalent PREN value above 30. Controlling 0.2% ≤ (C + N) ≤ 0.45% can not only ensure the austenite stability and improve the material strength but also avoid the deterioration of processing performance caused by excessive C and N contents. Controlling 25% ≤ Cr + Mo ≤ 40% can not only ensure the strength and corrosion resistance of the steel but also prevent the accelerated precipitation of brittle phases such as σ due to excessive Cr and Mo contents.

[0029] 2. The smelting process of the present invention is simple, and by adding a trace amount of Ce (0.008-0.05%) to super duplex stainless steel, it can play a beneficial role in purification, modification and microalloying, and can effectively modify the inclusions in the alloy, change the size, shape, distribution, as-cast structure and anisotropy of the inclusions in the steel, refine the grains, and improve the thermoplasticity, corrosion resistance and mechanical properties of the material. During the hot rolling process, the phase boundaries and inclusions will become the preferred nucleation sites of brittle phases such as σ. The addition of rare earth elements changes the properties of the inclusions and refines the grains, so that the precipitation behavior of the brittle phase changes, and the precipitation of the brittle phase can be inhibited, thereby improving the hot processing performance and mechanical / corrosion resistance of the material.

[0030] 3. In the present invention, the initial forging temperature, the final forging temperature and the forging deformation are controlled to ensure a fine microstructure and an appropriate ferrite / austenite two-phase ratio, so that rare earth inclusions are dispersed, and the precipitation of brittle phases such as σ phase is avoided, providing a suitable initial structure for subsequent hot rolling processing. Controlling the hot rolling start temperature can ensure that the initial hot rolling structure has an appropriate two-phase ratio, avoiding the two-phase ratio range with poor thermoplasticity, and controlling the final rolling temperature at the same time to avoid the precipitation of brittle phases.

[0031] By comprehensively controlling the rolling temperature, the amount of deformation per pass, and the interval between passes, the deformation penetration during hot rolling can be promoted, the structure of the core of the steel billet can be refined, and the "δ ferrite → austenite" phase transformation can be used to refine the grains during hot working to obtain a fine hot-rolled structure. Furthermore, through solid solution treatment, the phase ratio, grain size, inclusions and precipitation phases in the microstructure of the rare earth Ce modified super duplex stainless steel are adjusted to improve its strength, plasticity and corrosion resistance. Finally, through rare earth microalloying and forging and rolling process control, hot rolling crack defects are reduced or suppressed, the hot rolling yield of super duplex stainless steel is improved, and at the same time, the rare earth Ce modified super duplex stainless steel has better strength, elongation, corrosion resistance and hot working performance than conventional super duplex stainless steel.

[0032] 4. The rare earth Ce modified super duplex stainless steel prepared by the present invention has a tensile strength of 900-1200 MPa, a yield strength of 600-800 MPa, an elongation after fracture of 25-40%, and a PREN value of 35-50 at room temperature. Thus, the rare earth Ce modified super duplex stainless steel has excellent hot working performance and high tensile strength, yield strength, elongation after fracture and good corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a macroscopic photo of hot rolling of Example 1;

[0034] Figure 2 The XRD phase analysis results of the hot-rolled plate in Example 1;

[0035] Figure 3 Tensile curve after solution treatment of the hot-rolled sheet in Example 1. Detailed implementation manners

[0036] The present invention will be further described in detail below in conjunction with specific embodiments.

[0037] Example 1:

[0038] The rare earth Ce-modified super duplex stainless steel in this example is composed of the following components by mass percentage: C: 0.02%, Si: 0.10%, Mn: 1.50%, Ni: 7.2%, Cr: 25.1%, Mo: 3.5%, N: 0.30%, Ce: 0.01%, and the balance is Fe.

[0039] Among them, (C + N) = 0.32%, (Ni + Mn) = 8.7%, (Cr + Mo) = 28.6%.

[0040] The preparation method of the above rare earth Ce-modified super duplex stainless steel successively includes the following steps:

[0041] 1) Batching: Select electrolytic chromium, electrolytic manganese, pure iron, molybdenum, nickel, silicon, ferrochromium nitride alloy and rare earth Ce alloy according to the above mass percentage;

[0042] 2) Melting: First, place electrolytic chromium, pure iron, molybdenum, nickel and silicon in a melting furnace for melting. After melting, add electrolytic manganese and ferrochromium nitride alloy for melting. After melting, add rare earth Ce to obtain molten steel; before melting, the raw materials are rust-removed, degreased, dust-removed and dried to ensure that the surface of the raw materials is clean and rust-free; when adding electrolytic manganese and ferrochromium nitride alloy for melting, nitrogen is introduced for protection;

[0043] 3) Casting: Pour the molten steel into a mold, and control the casting temperature at 1500 °C; before casting, the mold shell for casting can be heated to 600 °C for standby;

[0044] 4) Forging: After cutting off the riser part of the ingot, perform forging to obtain a forged blank. The initial forging temperature is controlled at 1160 °C, the final forging temperature is 980 °C, and the total forging deformation is 40%.

[0045] 5) Hot rolling: The forged billet is subjected to hot rolling. The starting hot rolling temperature is controlled at 1180 °C. In the initial structure of hot rolling, the ferrite proportion is 70% and the austenite proportion is 30%. The finishing rolling temperature is controlled at 980 °C. The single-pass deformation of the first five passes is controlled at 25%, and the single-pass deformation of the last four passes is 15%. The time interval between passes is 5 seconds. After hot rolling, water cooling is carried out to obtain hot-rolled sheets. After testing, the dynamic recovery / recrystallization degree of the ferrite phase is 70%, and that of the austenite is 40%. In the finishing rolling structure, the ferrite proportion is 65%, and the proportion of brittle phases and inclusions is 1%.

[0046] 6) Heat treatment: The hot-rolled sheets are subjected to solution treatment and then water cooling. The solution treatment temperature is 1050 °C, and the holding time is 15 min, followed by water cooling. After solution treatment, the ferrite proportion is 60%, and the proportion of brittle phases and inclusions is 0.3%.

[0047] The hot-rolled edge cracks of the above-mentioned rare earth Ce-modified super duplex stainless steel are less than 1 mm. At room temperature, the tensile strength is 940 MPa, the yield strength is 700 MPa, the elongation after fracture is 28%, and the PREN value is 41.45. Thus, the rare earth Ce-modified super duplex stainless steel has excellent hot working performance, high tensile strength, yield strength, elongation after fracture, and good corrosion resistance.

[0048] Example 2:

[0049] The rare earth Ce-modified super duplex stainless steel of this example is composed of the following components by mass percentage: C: 0.03%, Si: 0.15%, Mn: 0.8%, Ni: 9.3%, Cr: 30.5%, Mo: 4.5%, N: 0.20%, Ce: 0.03%, and the balance is Fe. Among them, (C + N) = 0.23%, (Ni + Mn) = 10.1%, and (Cr + Mo) = 35%.

[0050] The preparation method of the above-mentioned rare earth Ce-modified super duplex stainless steel successively includes the following steps:

[0051] 1) Batching: Select electrolytic chromium, electrolytic manganese, pure iron, molybdenum, nickel, silicon, chromium nitride ferroalloy, and rare earth Ce alloy according to the above mass percentages;

[0052] 2) Melting: First, place electrolytic chromium, pure iron, molybdenum, nickel, and silicon in a melting furnace for melting. After melting, add electrolytic manganese and chromium nitride ferroalloy for melting. After melting, add rare earth Ce alloy to obtain molten steel. Before melting, the raw materials are rust-removed, degreased, dust-removed, and dried to ensure that the surface of the raw materials is clean and rust-free. When adding electrolytic manganese and chromium nitride ferroalloy for melting, nitrogen is introduced for protection;

[0053] 3) Casting: Pour molten steel into a mold to obtain an ingot, and control the casting temperature at 1520 °C; before casting, the mold shell for casting can be heated to 600 °C for standby;

[0054] 4) Forging: After cutting off the riser part of the ingot, perform forging to obtain a forged blank. The initial forging temperature is controlled at 1180 °C, the final forging temperature is 1000 °C, and the total forging deformation is 50%.

[0055] 5) Hot rolling: Perform hot rolling on the forged blank. Control the starting hot rolling temperature at 1200 °C. The proportion of ferrite in the initial hot rolling microstructure is 80%, and the proportion of austenite is 20%. Control the final rolling temperature at 1020 °C. Control the single-pass deformation of the first three passes at 30%, and the single-pass deformation of the last six passes at 15%. The interval time between passes is 5 seconds. After hot rolling, perform water cooling to obtain hot-rolled sheets; after testing, the degree of dynamic recovery / recrystallization of the ferrite phase is 80%, the degree of dynamic recovery / recrystallization of the austenite is 50%, and the proportion of ferrite in the final rolling microstructure is 70%, and the proportion of brittle phases and inclusions is 0.5%.

[0056] 6) Heat treatment: Perform solution treatment on the hot-rolled sheets and then perform water cooling. The solution treatment temperature is 1060 °C, the holding time is 15 min, and water cooling is performed. After solution treatment, the proportion of ferrite is 55%, and the proportion of brittle phases and inclusions is 0.2%.

[0057] The hot-rolled edge cracks of the above rare earth Ce-modified super duplex stainless steel are less than 2.5 mm. At room temperature, the tensile strength is 1000 MPa, the yield strength is 730 MPa, the elongation after fracture is 30%, and the PREN value is 48.55. Thus, the rare earth Ce-modified super duplex stainless steel has excellent hot working performance and high tensile strength, yield strength, elongation after fracture, and good corrosion resistance.

[0058] Example 3:

[0059] The rare earth Ce-modified super duplex stainless steel of this example is composed of the following components by mass percentage: C: 0.05%, Si: 0.20%, Mn: 1.8%, Ni: 4.5%, Cr: 22.3%, Mo: 6.5%, N: 0.36%, Ce: 0.05%, and the balance is Fe. Among them, (C + N) = 0.41%, (Ni + Mn) = 6.3%, (Cr + Mo) = 28.8%.

[0060] The preparation method of the above rare earth Ce-modified super duplex stainless steel successively includes the following steps:

[0061] 1) Batching: Select electrolytic chromium, electrolytic manganese, pure iron, molybdenum, nickel, silicon, ferroniobium nitride alloy, and rare earth Ce alloy according to the above mass percentage;

[0062] 2) Melting: First, electrolytic chromium, pure iron, molybdenum, nickel, and silicon are placed in a melting furnace for melting. After melting, electrolytic manganese and ferrochromium nitride alloy are added for melting. After melting, rare earth Ce alloy is added to obtain molten steel. Before melting, the raw materials are rust-removed, degreased, dust-removed, and dried to ensure that the surface of the raw materials is clean and rust-free. When adding electrolytic manganese and ferrochromium nitride alloy for melting, nitrogen is introduced for protection.

[0063] 3) Casting: The molten steel is cast into a mold to obtain an ingot, and the casting temperature is controlled at 1480 °C. Before casting, the mold shell for casting can be heated to 600 °C for standby.

[0064] 4) Forging: After cutting off the riser part of the ingot, forging is carried out to obtain a forging blank. The initial forging temperature is controlled at 1150 °C, the final forging temperature is 950 °C, and the total forging deformation is 30%.

[0065] 5) Hot rolling: The forging blank is subjected to hot rolling treatment. The hot rolling starting temperature is controlled at 1150 °C. The proportion of ferrite in the initial hot rolling structure is 62%, and the proportion of austenite is 38%. The final rolling temperature is controlled at 960 °C. The single-pass deformation of the first four passes is controlled at 25%, and the single-pass deformation of the last five passes is 20%. The interval time between passes is 5 seconds. After hot rolling, water cooling is carried out to obtain hot-rolled sheets. After testing, the dynamic recovery / recrystallization degree of the ferrite phase is 70%, the dynamic recovery / recrystallization degree of austenite is 55%, the proportion of ferrite in the final rolling structure is 65%, and the proportion of brittle phases and inclusions is 0.4%.

[0066] 6) Heat treatment: The hot-rolled sheets are solution-treated and then water-cooled. The solution treatment temperature is 1030 °C, the holding time is 20 min, and water cooling is carried out. After solution treatment, the proportion of ferrite is 52%, and the proportion of brittle phases and inclusions is 0.3%.

[0067] The hot-rolled edge cracks of the above rare earth Ce-modified super duplex stainless steel are less than 1.5 mm. At room temperature, the tensile strength is 1180 MPa, the yield strength is 790 MPa, the elongation after fracture is 25%, and the PREN value is 49.51. Thus, the rare earth Ce-modified super duplex stainless steel has excellent hot working performance, high tensile strength, yield strength, elongation after fracture, and good corrosion resistance.

[0068] Example 4:

[0069] The rare earth Ce-modified super duplex stainless steel of this example is composed of the following components by mass percentage: C: 0.01%, Si: 0.05%, Mn: 1.0%, Ni: 8.5%, Cr: 33.5%, Mo: 1.5%, N: 0.20%, Ce: 0.05%, and the balance is Fe. Among them, (C + N) = 0.21%, (Ni + Mn) = 9.5%, (Cr + Mo) = 35%.

[0070] The preparation method of the above-mentioned rare earth Ce-modified super duplex stainless steel successively includes the following steps:

[0071] 1) Batching: Select electrolytic chromium, electrolytic manganese, pure iron, molybdenum, nickel, silicon, chromium nitride ferroalloy and rare earth Ce alloy according to the above mass percentages;

[0072] 2) Melting: First, place electrolytic chromium, pure iron, molybdenum, nickel and silicon in a melting furnace for melting. After melting, add electrolytic manganese and chromium nitride ferroalloy for melting. After melting, add rare earth Ce to obtain molten steel; before melting, the raw materials are rust-removed, degreased, dust-removed and dried to ensure that the surface of the raw materials is clean and rust-free; when adding electrolytic manganese and chromium nitride ferroalloy for melting, nitrogen is introduced for protection;

[0073] 3) Casting: Pour the molten steel into a mold to obtain an ingot, and control the casting temperature at 1500 °C; before casting, the casting mold shell can be heated to 600 °C for standby;

[0074] 4) Forging: After cutting off the riser part of the ingot, perform forging to obtain a forging blank. The initial forging temperature is controlled at 1180 °C, the final forging temperature is 980 °C, and the total forging deformation is 40%.

[0075] 5) Hot rolling: Perform hot rolling on the forging blank. Control the hot rolling starting temperature at 1200 °C. The proportion of ferrite in the initial hot rolling structure is 75%, and the proportion of austenite is 25%. Control the final rolling temperature at 1000 °C. Control the single-pass deformation of the first four passes at 30%, and the single-pass deformation of the last five passes at 20%. The interval time between passes is 8 seconds. After hot rolling, water cooling is carried out to obtain hot-rolled sheets; after testing, the dynamic recovery / recrystallization degree of the ferrite phase is 70%, the dynamic recovery / recrystallization degree of austenite is 50%, the proportion of ferrite in the final rolling structure is 70%, and the proportion of brittle phases and inclusions is 0.3%.

[0076] 6) Heat treatment: Perform solution treatment on the hot-rolled sheets and then water cooling. The solution treatment temperature is 1080 °C, the holding time is 10 min, and water cooling is carried out. After solution treatment, the proportion of ferrite is 55%, and the proportion of brittle phases and inclusions is 0.1%.

[0077] The hot-rolled edge crack of the above-mentioned rare earth Ce-modified super duplex stainless steel is less than 1 mm. At room temperature, the tensile strength is 1040 MPa, the yield strength is 700 MPa, the elongation after fracture is 38%, and the PREN value is 41.65. Thus, the rare earth Ce-modified super duplex stainless steel has excellent hot working performance, high tensile strength, yield strength, elongation after fracture and good corrosion resistance.

[0078] Example 5:

[0079] The rare earth Ce modified super duplex stainless steel of this embodiment is composed of the following components by mass percentage: C: 0.03%, Si: 0.10%, Mn: 1.2%, Ni: 7.5%, Cr: 28.2%, Mo: 3.6%, N: 0.30%, Ce: 0.03%, and the balance is Fe. Among them, (C+N)=0.33%, (Ni+Mn)=8.7%, (Cr+Mo)=31.8%.

[0080] The preparation method of the rare earth Ce modified super duplex stainless steel comprises the following steps in sequence:

[0081] 1) Ingredients: electrolytic chromium, electrolytic manganese, pure iron, molybdenum, nickel, silicon, chromium nitride iron alloy and rare earth Ce alloy are selected according to the above mass percentages;

[0082] 2) Smelting: firstly, electrolytic chromium, pure iron, molybdenum, nickel and silicon are placed in a smelting furnace for smelting, and then electrolytic manganese and chromium nitride iron alloy are added for smelting after melting, and then rare earth Ce alloy is added after melting to obtain molten steel; before smelting, the raw materials are subjected to rust removal, oil removal, dust removal and drying treatment to ensure that the surface of the raw materials is clean and rust-free; when adding electrolytic manganese and chromium nitride iron alloy for smelting, nitrogen is introduced for protection;

[0083] 3) Casting: Pour the molten steel into the casting mold to obtain an ingot, and control the casting temperature to be 1520°C; before casting, the casting mold shell can be heated to 600°C for standby use;

[0084] 4) Forging: After cutting off the riser portion of the ingot, forging is performed to obtain a forged blank. The initial forging temperature is controlled at 1170° C., the final forging temperature is 960° C., and the total forging deformation is 40%.

[0085] 5) Hot rolling: The forged billet is hot rolled, the hot rolling start temperature is controlled to be 1180°C, the proportion of ferrite in the initial hot rolling structure is 70%, the proportion of austenite is 30%, the final rolling temperature is controlled to be 960°C, the deformation of each pass in the first four passes is controlled to be 30%, the deformation of each pass in the last five passes is controlled to be 20%, the pass interval time is 5 seconds, and the hot-rolled plate is obtained by water cooling; after testing, the dynamic recovery / recrystallization degree of the ferrite phase is 80%, the dynamic recovery / recrystallization degree of the austenite is 60%, the proportion of ferrite in the final rolling structure is 65%, and the proportion of brittle phase and inclusions is 0.3%.

[0086] 6) Heat treatment: The hot-rolled plate is subjected to solution treatment and then water cooling. The solution treatment temperature is 1050°C, the holding time is 15 minutes, and the water cooling is performed. After the solution treatment, the ferrite ratio is 56%, and the brittle phase and inclusion ratio is 0.05%.

[0087] The above-mentioned rare earth Ce-modified super duplex stainless steel has a hot-rolled edge crack of less than 2 mm, a tensile strength of 1100 MPa at room temperature, a yield strength of 720 MPa, an elongation after fracture of 28%, and a PREN value of 44.88. Thus, the rare earth Ce-modified super duplex stainless steel has excellent hot working performance, high tensile strength, yield strength, elongation after fracture, and good corrosion resistance.

Claims

1. A rare earth Ce modified super duplex stainless steel, characterized in that: The composition is composed of the following components in percentage by mass: 0.01 ≤ C ≤ 0.05%, 0.01% ≤ Si ≤ 0.20%, 0.50% ≤ Mn ≤ 2.0%, 4.0% ≤ Ni ≤ 10.0%, 20.0% ≤ Cr ≤ 35.0%, 1.50% ≤ Mo ≤ 6.50%, 0.15% ≤ N ≤ 0.40%, 0.008% ≤ Ce ≤ 0.05%, and the balance is Fe; Furthermore, 0.2%≤(C+N)≤0.45%, 5.0%≤Ni+Mn≤11.0%, and 25%≤Cr+Mo≤40%.

2. A method for preparing the rare earth Ce modified super duplex stainless steel according to claim 1, characterized in that: The steps include: 1) Ingredients: electrolytic chromium, electrolytic manganese, pure iron, molybdenum, nickel, silicon, chromium nitride iron alloy and rare earth Ce alloy are selected according to the above mass percentages; 2) Smelting: firstly, electrolytic chromium, pure iron, molybdenum, nickel and silicon are placed in a smelting furnace for smelting, and then electrolytic manganese and chromium nitride iron alloy are added for smelting after melting, and then rare earth Ce alloy is added after melting to obtain molten steel; 3) Casting: pouring molten steel into a casting mold to obtain an ingot, and controlling the casting temperature to be 1470-1530°C; 4) Forging: After cutting off the riser part of the ingot, forging is performed to obtain a forging blank; 5) Hot rolling: hot rolling the forged billet, followed by water cooling to obtain a hot-rolled plate; 6) Heat treatment: The hot-rolled plate is solution treated and then water-cooled.

3. The preparation method according to claim 1, characterized in that: In step 2), when electrolytic manganese and chromium nitride ferroalloy are added for smelting, nitrogen is introduced for protection.

4. The preparation method according to claim 2, characterized in that: In step 4), the initial forging temperature is controlled to be 1150-1200°C, and the final forging temperature is 950-1000°C.

5. The preparation method according to claim 2, characterized in that: In step 4), the total forging deformation is 30% to 50%.

6. The preparation method according to claim 2, characterized in that: In step 5), the hot rolling start temperature is controlled to be 1150-1200°C, and the final rolling temperature is controlled to be 950-1020°C.

7. The preparation method according to claim 2, characterized in that: In step 5), the proportion of ferrite in the initial hot-rolled structure is 60-80%, and the proportion of austenite is 20-40%; the dynamic recovery / recrystallization degree of the ferrite phase is 60%-90%, and the dynamic recovery / recrystallization degree of the austenite is 40%-60%; the proportion of ferrite in the final rolled structure is 50-70%, and the proportion of brittle phase and inclusions is 0.05%-1.5%.

8. The preparation method according to claim 2, characterized in that: In step 5), the deformation of each rolling pass is controlled to be 15% to 30%; in step 5), the edge cracks of the rare earth Ce modified super duplex stainless steel during hot rolling are controlled to be less than 3 mm.

9. The preparation method according to claim 2, characterized in that: In step 6), the solution treatment temperature is 1030-1080° C., the holding time is 10-20 min, and the solution is water-cooled.

10. The preparation method according to claim 2, characterized in that: In step 6), after solution treatment, the proportion of ferrite is 40-60%, and the proportion of brittle phase and inclusions does not exceed 0.5%.

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