A rare earth-containing high-temperature resistant austenitic stainless steel, its manufacturing method and application

Abstract

This invention belongs to the field of special steel material manufacturing technology, specifically relating to a rare-earth-containing high-temperature resistant austenitic stainless steel, its manufacturing method, and its applications. The rare-earth-containing high-temperature resistant austenitic stainless steel provided by this invention comprises, by weight percentage: C: 0.08–0.10%, Si: 1.70–2.00%, Mn: 0.80–1.20%, Cr: 20.50–20.80%, Ni: 10.50–11.00%, N: 0.16–0.20%, Re: 0.05–0.08%. The cold-rolled stainless steel sheet produced according to the method of this invention exhibits good high-temperature strength and heat resistance, and can be used continuously at 1050℃, meeting the application requirements in the preparation of hot-end components for automotive exhaust systems.

Description

Technical Field

[0001] This invention belongs to the field of special steel material manufacturing technology, specifically relating to a rare earth-containing high-temperature resistant austenitic stainless steel, its manufacturing method, and its application. Background Technology

[0002] The 310S austenitic heat-resistant stainless steel that meets the usage requirements has a Cr mass fraction of 25% and a Ni mass fraction of 19%. Its manufacturing cost is four times that of ferritic heat-resistant stainless steel, while the lower grade 309S has significantly worse oxidation resistance when the service temperature exceeds 900℃.

[0003] Therefore, we need to develop an austenitic heat-resistant stainless steel with higher oxidation resistance, thermal fatigue resistance, excellent formability, and lower cost to meet the increasing service temperature requirements of automotive exhaust hot-end materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a rare-earth-containing high-temperature resistant austenitic stainless steel, its manufacturing method, and its applications.

[0005] Specifically, the rare-earth-containing high-temperature resistant austenitic stainless steel provided by the present invention comprises, by weight percentage: C: 0.08-0.10%, Si: 1.70-2.00%, Mn: 0.80-1.20%, Cr: 20.50-20.80%, Ni: 10.50-11.00%, N: 0.16-0.20%, and Re: 0.05-0.08%.

[0006] The above-mentioned rare earth-containing high-temperature resistant austenitic stainless steel, by weight percentage, includes: C: 0.08-0.09%, Si: 1.8-1.9%, Mn: 0.80-0.90%, Cr: 20.50-20.60%, Ni: 10.50-10.70%, N: 0.18-0.20%, Re: 0.05-0.06%, with the balance being Fe and unavoidable impurities.

[0007] On the other hand, the present invention also provides a method for manufacturing rare earth-containing high-temperature resistant austenitic stainless steel, comprising the following steps:

[0008] (1) Steel with qualified composition is obtained by smelting in an AOD furnace and refining in an LF furnace;

[0009] The composition of the molten steel is the same as that of the rare earth-containing high-temperature resistant austenitic stainless steel mentioned above.

[0010] (2) The molten steel is continuously cast to obtain a billet;

[0011] (3) The billet is subjected to hot rolling, cold rolling and solution treatment in sequence to obtain a cold-rolled plate of rare earth-containing high-temperature resistant austenitic stainless steel.

[0012] The above-mentioned method for manufacturing rare earth-containing high-temperature resistant austenitic stainless steel involves a furnace life of ≥5 cycles during the AOD furnace smelting process, using 0.6 kg / t aluminum powder and 0.5 kg / t silicon-calcium powder for slag adjustment, and a reduction time of ≥10 min.

[0013] In the above-mentioned method for manufacturing rare earth-containing high-temperature resistant austenitic stainless steel, the steel temperature is 1585±5℃ during the LF furnace refining process, and the rare earth cored wire is fed in at a rate of 16.0~16.5m / t.

[0014] In the above-mentioned method for manufacturing rare earth-containing high-temperature resistant austenitic stainless steel, during continuous casting, a tundish covering agent is used for protective casting, and the inner walls of the long nozzle, stopper rod, top nozzle and submerged nozzle are made of silicon, magnesium or zirconium, and the surface grinding rate of the billet is ≥5%.

[0015] The above-mentioned method for manufacturing rare earth-containing high-temperature resistant austenitic stainless steel involves heating in a billet heating furnace during hot rolling, with a soaking zone temperature of 1300–1320°C, a total furnace dwell time of ≥200 min, and a finishing mill exit temperature of 1100–1120°C.

[0016] In the above-mentioned manufacturing method of rare earth-containing high-temperature resistant austenitic stainless steel, the hot-rolled plate is annealed and pickled during the cold rolling process, and the deformation rate of the first cold rolling pass after pickling is 15-30%, while the deformation rate of the finished product pass is ≤15%.

[0017] In the above-mentioned method for manufacturing rare earth-containing high-temperature resistant austenitic stainless steel, the solution treatment temperature is 1150-1160℃.

[0018] In another aspect, the present invention also provides the application of the above-mentioned rare earth-containing high-temperature resistant austenitic stainless steel or the rare earth-containing high-temperature resistant austenitic stainless steel obtained by the above-mentioned manufacturing method in the preparation of the hot end of an automotive exhaust system.

[0019] The technical solution of the present invention has the following beneficial effects:

[0020] (1) This invention develops a new type of austenitic stainless steel product with Cr, Ni and rare earth elements as the main oxidation-resistant elements. By adding a certain amount of rare earth elements, the oxidation resistance of the material is greatly improved. By reasonably controlling the C content, the product has high high-temperature strength.

[0021] (2) This invention starts from the oxidation characteristics and reaction mechanism of rare earth elements in the smelting and continuous casting process, and overcomes the long-standing problem in the production of rare earth stainless steel slabs, achieving high-efficiency production.

[0022] (3) This invention obtains high-temperature resistant austenitic stainless steel cold-rolled plates of different thicknesses through a reasonable rolling, solution and pickling process. It is a unique product in China and is used in the field of exhaust systems of international high-end brand automobiles. Detailed Implementation

[0023] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0024] When a range of values ​​is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0025] In the first aspect, the present invention provides a rare earth-containing high-temperature resistant austenitic stainless steel, which uses rare earth elements to replace Ni elements as the main oxidation-resistant elements, while increasing the Si content. The resulting stainless steel has oxidation resistance comparable to 310S stainless steel with higher Cr and Ni content. This saves Ni resources while giving the steel excellent performance, with a maximum service temperature of up to 1050℃.

[0026] Specifically, the rare earth-containing high-temperature resistant austenitic stainless steel provided by the present invention comprises, by weight percentage: C: 0.08-0.10%, Si: 1.70-2.00%, Mn: 0.80-1.20%, Cr: 20.50-20.80%, Ni: 10.50-11.00%, N: 0.16-0.20%, Re: 0.05-0.08%, with the balance being Fe and unavoidable impurities.

[0027] In some preferred embodiments, the rare earth-containing high-temperature resistant austenitic stainless steel of the present invention comprises, by weight percentage: C: 0.08-0.09%, Si: 1.8-1.9%, Mn: 0.80-0.90%, Cr: 20.50-20.60%, Ni: 10.50-10.70%, N: 0.18-0.20%, Re: 0.05-0.06%, with the balance being Fe and unavoidable impurities.

[0028] Practice has shown that the solid solution of rare earth elements in heat-resistant steel can significantly improve the high-temperature oxidation resistance, high-temperature strength, and thermoplasticity of the steel. This invention utilizes the advantages of rare earth elements to improve the heat resistance of low-grade austenitic heat-resistant steel, while reducing the content of Cr and Ni elements, thus greatly reducing the cost of raw materials.

[0029] Secondly, the present invention provides a method for manufacturing rare earth-containing high-temperature resistant austenitic stainless steel, comprising the following steps:

[0030] AOD furnace smelting

[0031] Rare earth elements enhance the oxidation resistance of materials, but they are also extremely reactive in reducing properties. Therefore, a certain amount of Al must be maintained in the molten steel during the smelting process to inhibit the excessive formation of rare earth oxides. Preferably, slag is prepared using 0.6 kg / t aluminum powder and 0.5 kg / t calcium silicate powder, with a reduction time ≥ 10 min.

[0032] Preferably, the AOD furnace used has a furnace life of ≥5 cycles.

[0033] LF furnace refining

[0034] During the refining process in the LF furnace, the molten steel temperature is 1585±5℃, and the rare earth cored wire is fed in at a rate of 16.0~16.5m / t.

[0035] The molten steel smelted in the refining furnace comprises, by weight percentage: C: 0.08–0.10%, Si: 1.70–2.00%, Mn: 0.80–1.20%, Cr: 20.50–20.80%, Ni: 10.50–11.00%, N: 0.16–0.20%, Re: 0.05–0.08%, with the balance being Fe and unavoidable impurities; preferably, it comprises: C: 0.08–0.09%, Si: 1.80–1.90%, Mn: 0.80–0.90%, Cr: 20.50–20.60%, Ni: 10.50–10.70%, N: 0.18–0.20%, Re: 0.05–0.06%, with the balance being Fe and unavoidable impurities.

[0036] Continuous casting

[0037] Rare earth elements readily form high-melting-point inclusions after alloying, which react with the refractory material and accumulate at the nozzle. Therefore, the biggest challenge in the production of rare earth stainless steel is nozzle nodule formation during continuous casting. Analysis reveals that these nodules are high-melting-point rare earth compounds formed by the reaction of rare earth oxides with aluminum refractory materials, adhering to the inner wall of the refractory material.

[0038] Al2O3+Ce2O3=Ce2O3·Al2O3ΔG=-79500-20.92T

[0039] Preferably, the present invention uses a tundish covering agent for protective casting, and the inner walls of the long gate, stopper rod, top gate, and submersible gate are all made of silica, magnesium, or zirconium. After several rounds of testing, the inner wall of the silica gate was completely free of nodules, ultimately achieving low-cost and high-efficiency production of the material.

[0040] The surface grinding rate of the cast billet is ≥5%.

[0041] Hot rolling

[0042] Due to the high alloy content of the material, the resistance to rolling deformation is large. The billet is heated at high temperature for a long time to reduce the resistance to rolling deformation. The heating is carried out according to the upper limit of the heat treatment zone of the hot continuous rolling furnace. The holding time is also longer than that of ordinary stainless steel to ensure that the billet is heated and thoroughly heated in the high temperature zone before rolling. In order to avoid excessive temperature drop during the rolling process, the number of descaling passes is reduced to ensure the rolling temperature.

[0043] Preferably, in the hot rolling process of the present invention, a billet heating furnace is used for heating, the temperature of the soaking zone is 1300~1320℃, the total furnace dwell time is ≥200min, and the finishing mill exit temperature is 1100~1120℃.

[0044] Cold rolling

[0045] Due to the material properties, in order to ensure uniform plate shape, this invention adopts slow rolling with a small deformation rate.

[0046] Preferably, the deformation rate of the first cold rolling pass after pickling is 15-30%, and the deformation rate of the finished product pass is ≤15%.

[0047] Solution treatment

[0048] Heat-resistant steel is solution-treated at a higher temperature than ordinary stainless steel to ensure a coarser grain size (grade 7), thus providing excellent resistance to high-temperature fatigue and creep.

[0049] Preferably, the solution treatment temperature is 1150–1160°C.

[0050] This invention increases the C and Si content in steel and adds a certain amount of rare earth elements. The material's high-temperature oxidation resistance is comparable to that of 310S stainless steel, and is significantly better than that of 309S and 444 ferritic stainless steel. Its high-temperature strength is higher than that of 310S stainless steel, and its high-temperature fatigue strength and thermal fatigue life are better than those of similar imported products. The finished steel is 10,000 yuan cheaper per ton than that of 310S.

[0051] Thirdly, the present invention also provides the application of rare earth-containing high-temperature resistant austenitic stainless steel in the preparation of the hot end of an automotive exhaust system.

[0052] The cold-rolled sheet produced according to the method of the present invention has good high-temperature strength and heat resistance, and can be used for a long time at 1050°C, meeting the application requirements in the preparation of hot ends of automotive exhaust systems.

[0053] Example

[0054] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments, unless otherwise specified, are performed according to conventional methods and conditions.

[0055] Example 1

[0056] (1) Initial steel was smelted in an AOD furnace with a steel volume of 40 tons. During the reduction period, 24 kg of aluminum powder and 20 kg of silicon-calcium powder were added. The reduction time was 20 min. The steel exiting the AOD furnace had the following composition: C: 0.085%, Si: 1.81%, Mn: 0.83%, Cr: 20.55%, Ni: 10.59%, and N: 0.18%.

[0057] (2) The furnace temperature of the LF furnace is 1585℃. After the temperature is suitable, 650m of rare earth cored wire is fed in. After feeding the wire, the rare earth content in the steel is 0.05%.

[0058] (3) XL-20 slag is used as the tundish covering agent during continuous casting. The inner walls of the long nozzle, stopper rod, top nozzle and submerged nozzle are all made of silica. The billet grinding rate is 6.5%.

[0059] (4) The billet is fed into the hot rolling furnace. The temperature of the soaking section is 1310℃. After holding for 100 minutes, it is hot rolled into a coil with a thickness of 5.0mm. The exit temperature of the rough rolling is 1100℃.

[0060] (5) Cold-rolled into 1.5mm thick coils, with a first deformation rate of 20% and a last deformation rate of 5%, a solution temperature of 1150℃, and pickled after solution treatment.

[0061] The high-temperature resistant austenitic stainless steel cold-rolled coil products produced by this invention have oxidation resistance rates as shown in Table 1, which are comparable to those of 310S stainless steel.

[0062] Table 1 High-Temperature Oxidation Resistance Rates of Various Stainless Steels

[0063]

[0064] Example 2

[0065] (1) Initial steel was smelted in an AOD furnace with a steel volume of 180 tons. During the reduction period, 108 kg of aluminum powder and 90 kg of silicon-calcium powder were added. The reduction time was 22 min. The steel exiting the AOD furnace had the following composition: C: 0.083%, Si: 1.88%, Mn: 0.84%, Cr: 20.54%, Ni: 10.61%, and N: 0.19%.

[0066] (2) The furnace temperature of the LF furnace is 1580℃. After the temperature is suitable, 2900m of rare earth cored wire is fed in. After feeding the wire, the rare earth content of the steel is 0.06%.

[0067] (4) XL-20 slag is used as the tundish covering agent during continuous casting. The inner walls of the long nozzle, stopper rod, top nozzle and submerged nozzle are all made of silica. The billet grinding rate is 5%.

[0068] (4) The billet is fed into the hot rolling furnace. The temperature of the soaking section is 1310℃. After holding for 100 minutes, it is hot rolled into a coil with a thickness of 4.0mm. The exit temperature of the rough rolling mill is 1110℃.

[0069] (5) Cold rolled into 1.2mm thick coils, with a first deformation rate of 18% and a last deformation rate of 8%, a solution temperature of 1150℃, and pickling after solution treatment.

[0070] The high-temperature resistant austenitic stainless steel cold-rolled coil products produced by this invention have high-temperature strength as shown in Table 2, which is higher than that of 310S stainless steel.

[0071] Table 2 High-Temperature Strength of Heat-Resistant Steel (Rm, MPa)

[0072] Temperature (°C) 310S 309S This invention 600 407 400 426 700 316 240 331 800 203 180 216 900 128 78 135 1000 90 35 95

[0073] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art should understand that these embodiments are merely illustrative of the invention and should not be construed as limiting its scope. It should be noted that any variations and substitutions equivalent to these embodiments should be considered to be covered within the scope of the claims. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A rare-earth-containing high-temperature resistant austenitic stainless steel, characterized in that, By weight percentage, it comprises: C: 0.08~0.10%, Si: 1.70~2.00%, Mn: 0.80~1.20%, Cr: 20.50~20.80%, Ni: 10.50~11.00%, N: 0.16~0.20%, RE: 0.05~0.08%, with the balance being Fe and unavoidable impurities; The manufacturing method of the rare earth-containing high-temperature resistant austenitic stainless steel includes the following steps: (1) Steel with qualified composition is obtained by smelting in an AOD furnace and refining in an LF furnace; (2) The molten steel is continuously cast to obtain a billet; (3) The billet is subjected to hot rolling, cold rolling and solution treatment in sequence to obtain a cold-rolled plate of rare earth high-temperature resistant austenitic stainless steel. In the hot rolling process, a billet heating furnace is used for heating, with a soaking zone temperature of 1300~1320℃, a total furnace dwell time of ≥200min, and a finishing mill exit temperature of 1100~1120℃; in the cold rolling process, the hot-rolled plate is annealed and pickled, and the deformation rate of the first cold rolling pass after pickling is 15~30%, while the deformation rate of the finished product pass is ≤15%; the solution treatment temperature is 1150~1160℃.

2. The rare-earth-containing high-temperature resistant austenitic stainless steel according to claim 1, characterized in that, By weight percentage, it includes: C: 0.08~0.09%, Si: 1.8~1.9%, Mn: 0.80~0.90%, Cr: 20.50~20.60%, Ni: 10.50~10.70%, N: 0.18~0.20%, RE: 0.05~0.06%, with the balance being Fe and unavoidable impurities.

3. A method for manufacturing rare earth-containing high-temperature resistant austenitic stainless steel, characterized in that, Includes the following steps: (1) Steel with qualified composition is obtained by smelting in an AOD furnace and refining in an LF furnace; The composition of the molten steel is the same as that of the rare earth-containing high-temperature resistant austenitic stainless steel according to any one of claims 1 to 2. (2) The molten steel is continuously cast to obtain a billet; (3) The billet is subjected to hot rolling, cold rolling and solution treatment in sequence to obtain a cold-rolled plate of rare earth high-temperature resistant austenitic stainless steel. In the hot rolling process, a billet heating furnace is used for heating, with a soaking zone temperature of 1300~1320℃, a total furnace dwell time of ≥200min, and a finishing mill exit temperature of 1100~1120℃; in the cold rolling process, the hot-rolled plate is annealed and pickled, and the deformation rate of the first cold rolling pass after pickling is 15~30%, while the deformation rate of the finished product pass is ≤15%; the solution treatment temperature is 1150~1160℃.

4. The method for manufacturing rare-earth-containing high-temperature resistant austenitic stainless steel according to claim 3, characterized in that, During the AOD furnace smelting process, the furnace life is ≥5 times, slag is adjusted with 0.6 kg / t aluminum powder and 0.5 kg / t silicon-calcium powder, and the reduction time is ≥10 min.

5. The method for manufacturing rare-earth-containing high-temperature resistant austenitic stainless steel according to claim 3, characterized in that, During the refining process in the LF furnace, the molten steel temperature is 1585±5℃, and the rare earth cored wire is fed in at a rate of 16.0~16.5m / t.

6. The method for manufacturing rare earth-containing high-temperature resistant austenitic stainless steel according to claim 3, characterized in that, During continuous casting, a tundish covering agent is used for protective casting. The inner walls of the long nozzle, stopper rod, top nozzle, and submerged nozzle are made of silica, magnesium, or zirconium. The surface grinding rate of the billet is ≥5%.

7. The application of the rare earth-containing high-temperature resistant austenitic stainless steel according to any one of claims 1 to 2 or the rare earth-containing high-temperature resistant austenitic stainless steel obtained by the manufacturing method according to any one of claims 3 to 6 in the preparation of the hot end of an automotive exhaust system.

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