A high-temperature corrosion-resistant and wear-resistant cast steel, its production method and application

Abstract

The present invention relates to the technical field of metal materials, and specifically discloses a high-temperature corrosion-resistant and wear-resistant cast steel, its production method and application. The weight percentage of its components is: C 0.8% - 1.4%, Si 1.0% - 3.0%, Cr 28.0% - 33.0%, Mo 1.0% - 3.0%, Mn ≤ 1.0%, P ≤ 0.040%, S ≤ 0.040%, and the balance is Fe and unavoidable impurities. By controlling the contents of C, Si, Cr and Mo elements, the present invention realizes the matching of the high-temperature performance, wear resistance and corrosion resistance of the cast steel, and realizes the purpose of the cast steel having a ferrite + carbide structure through composition control, so that high-temperature wear-resistant and corrosion-resistant castings can be prepared without the quenching process of the traditional process. The process is simple, the production efficiency can be effectively improved, the production cost can be reduced, thereby significantly improving the market competitiveness of the enterprise, and having broad application prospects in the field of automotive engines.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and particularly relates to a high-temperature corrosion-resistant and wear-resistant cast steel, a production method thereof, and an application thereof. Background Art

[0002] At present, as an important part of the intake and exhaust system of an automobile engine, turbochargers are divided into two types: wastegate valve type and variable geometry turbocharger according to the control method of the boost pressure. Both types need to use a linkage mechanism to drive a rocker shaft assembled in the turbocharger housing through a shaft hole from the outside of the turbocharger to adjust the opening degree of the wastegate valve and the nozzle opening degree to achieve the purpose of controlling the boost. The rocker of the wastegate valve type turbocharger is generally installed on the turbine housing; the rocker of the variable geometry turbocharger is generally installed on the bearing housing. Both structures require a bushing embedded in the shaft hole to form a more reasonable friction pair with the rocker shaft, rather than directly contacting and mating the rocker shaft with the housing material. Since the turbocharger operates at a very high temperature and the rocker shaft and the bushing are directly exposed to the engine exhaust gas and cannot be lubricated by engine oil, lubricating oil, etc., and can only operate in a dry grinding manner, there are very high requirements for the wear resistance of the friction pair. Secondly, the bushing is installed on the housing by an interference fit. The temperature change of the exhaust gas caused by the start-stop of the engine and different working conditions will cause the temperature of the corresponding turbocharger housing to change continuously. Therefore, the bushing material and the housing material need to have similar thermal expansion coefficients to avoid the bushing from loosening during use. In addition, the rocker and the bushing, as part of the turbocharger, are exposed in the automobile engine compartment. In addition to being corroded by the engine exhaust gas, they also have to withstand the rust problems caused by humid air, water splashed from the ground, snow melting agents, etc. In extreme cases, it will cause the turbocharger to become stuck. Therefore, the bushing material needs to have sufficient corrosion resistance to meet the reliability requirements.

[0003] The currently common wear-resistant steel is ZGMn13, which is a high-manganese steel with an austenitic structure. Although its wear resistance is relatively high, the high-manganese steel material represented by ZGMn13 has poor corrosion resistance, a high thermal expansion coefficient, and insufficient high-temperature performance. Therefore, developing a cast steel with wear resistance, corrosion resistance, and excellent high-temperature performance is of great significance for improving the service life of automobile engines. Summary of the Invention

[0004] Aiming at the problem that the existing wear-resistant steel cannot simultaneously meet the requirements of excellent wear resistance, corrosion resistance, and high-temperature performance, the present invention provides a high-temperature corrosion-resistant and wear-resistant cast steel, a production method thereof, and an application thereof.

[0005] To solve the above technical problems, the technical solution provided by the embodiment of the present invention is:

[0006] In a first aspect, the present invention provides a high-temperature corrosion-resistant and wear-resistant cast steel, the component weight percentages of which are as follows: C 0.8% to 1.4%, Si 1.0% to 3.0%, Cr 28.0% to 33.0%, Mo 1.0% to 3.0%, Mn ≤ 1.0%, P ≤ 0.040%, S ≤ 0.040%, and the balance is Fe and inevitable impurities.

[0007] Compared with the prior art, for the high-temperature corrosion-resistant and wear-resistant cast steel provided by the present invention, by controlling the contents of C, Si, and Cr, the microstructure of the prepared cast steel is a structure of ferrite and carbide. Among them, the carbide plays a strengthening role, improving the strength, impact resistance, and wear resistance of the cast steel; the ferrite structure has a lower thermal expansion coefficient than the austenite structure and lower thermal stress at high temperatures, significantly improving the high-temperature performance of the cast steel. In addition, since the structure of the cast steel is ferrite, subsequent quenching treatment can be omitted, which is beneficial to simplifying the process, saving energy and reducing consumption, and reducing the risk of thermal deformation caused by quenching; in addition, adding 1.0% to 3.0% of Mo plays a role in strengthening the grain boundary and improving the friction performance, further improving the corrosion resistance and wear resistance of the cast steel.

[0008] The present invention realizes the matching of the high-temperature performance, wear resistance, and corrosion resistance of the cast steel by controlling the contents of C, Si, Cr, and Mo elements, and achieves the purpose of the cast steel having a ferrite + carbide structure through composition control, so that high-temperature wear-resistant and corrosion-resistant castings can be prepared without the quenching process of the traditional process. The process is simple, the energy consumption is low, the production efficiency can be effectively improved, and the production cost can be reduced, thereby significantly improving the market competitiveness of the enterprise. It has a broad application prospect in the field of automotive engines and has a high popularization and application value.

[0009] The functions and proportioning of each element are as follows:

[0010] C is the most important component element in steel and is also the main element determining the metallographic structure and properties of carbon steel after solidification. Controlling the C content within 0.8% to 1.4% can not only increase the content of ferrite in the metallographic structure, thereby improving the wear resistance and high-temperature resistance of the steel, but also C can form carbides with Cr and Mo, thereby improving the high-temperature strength of the steel; in addition, C within the above content range can also increase the fluidity of the molten steel and reduce pouring defects.

[0011] Si is an element that can dissolve in ferrite to play a role in solid solution strengthening. Si promotes the formation of ferrite and can increase the proportion of ferrite in steel. It is generally believed that a high Si content will reduce the impact toughness. Especially when it exceeds 1%, the impact energy decreases significantly. Therefore, the Si content in general wear-resistant steels is lower than 1%. The inventors of the present invention unexpectedly found that when the Si content is appropriately increased to more than 2% and higher, under the working conditions of the engine exhaust system, not only does it not lead to a decrease in wear resistance, but instead a smaller total wear amount is achieved. The inventors believe that this is related to the fact that Si can form SiO2 on the surface of the casting, thereby improving the gas corrosion resistance of the material, especially possibly related to the improvement of the corrosion resistance in a reducing atmosphere formed under incomplete combustion of the fuel. The inventors also unexpectedly found that the increase in the Si content also improves the casting process performance of the material, which is beneficial to reducing casting defects and thus reducing the reject rate.

[0012] At high temperatures, Cr forms a dense Cr2O3 oxide layer on the surface of the material, which can effectively prevent gas hot corrosion. Controlling Cr within the range of 28.0% - 33.0% can not only increase the content of ferrite in the steel, but also ensure that after Cr combines with C to form carbides, there is still enough Cr remaining in the ferrite to play a role in solid solution strengthening, and it also forms carbides mainly composed of M23C6 with carbon elements, which is beneficial to improving the high-temperature strength of the material.

[0013] Mo can promote the formation of ferrite, strengthen the grain boundaries, and improve the high-temperature strength. Compared with Cr, Mo preferentially forms carbides with carbon, preventing chromium depletion at the grain boundaries and significantly improving the corrosion resistance of the material. Mo forms compounds with associated elements such as sulfur that are inevitable in steel, and it can play a good lubricating role when in contact and friction with other materials, which is very beneficial to improving the wear resistance of the material. However, the price of Mo raw materials is relatively high, and when the content reaches more than 2%, the performance improvement is not obvious. Therefore, the Mo content is controlled at 1% - 3%. Si and Mo can synergistically increase the transformation temperature from ferrite to austenite, so that the material still has a ferrite structure at high temperatures and does not undergo austenite phase transformation.

[0014] P and S are chemical elements that are likely to cause cold brittleness and hot brittleness in steel, which will reduce the plasticity of the steel. Therefore, the content of P is controlled below 0.040%, the content of S is controlled below 0.040%, and the lower the better.

[0015] The above components are combined with each other in a specific ratio, which can better meet the requirements of matching wear resistance, corrosion resistance, and high-temperature performance in the production of wear-resistant cast steel.

[0016] Furthermore, the weight percentage of the components of the high-temperature corrosion-resistant and wear-resistant cast steel is as follows: C 1.0% - 1.2%, Si 2.0% - 3.0%, Cr 31.0% - 33.0%, Mo 1.5% - 2.5%, Mn ≤ 1.0%, P ≤ 0.040%, S ≤ 0.040%, and the balance is Fe and inevitable impurities.

[0017] The above preferred content ranges of C, Si, Cr, and Mo can further improve the high-temperature wear resistance and corrosion resistance of the material.

[0018] Furthermore, its microstructure is ferrite and carbide.

[0019] To ensure the wear resistance and corrosion resistance of the steel under engine operating conditions, it is necessary for the material to have a stable ferrite structure at room temperature. The friction coefficient between ferrite and ferrite, and between ferrite and austenite is significantly lower than that between austenite and austenite. Ferrite has a lower thermal expansion coefficient than austenite, lower thermal stress at high temperatures, and has more advantages than austenite in an environment where the working temperature is lower than 800°C. Moreover, the ferrite matrix material does not require quenching and tempering heat treatment. As a bushing material, it can be directly machined to the final part size without heat treatment or only with simple annealing treatment after casting. And it is easier to machine parts compared to the structures after quenching and tempering such as austenite or sorbite, which can reduce production costs, energy consumption, and improve production efficiency.

[0020] Furthermore, the yield strength of the high-temperature corrosion-resistant and wear-resistant cast steel at room temperature ≥ 425 MPa, the tensile strength ≥ 650 MPa, the elongation ≥ 8%, and the hardness ≥ 26 HRC.

[0021] Furthermore, the yield strength of the high-temperature corrosion-resistant and wear-resistant cast steel at 600°C ≥ 146 MPa, the tensile strength ≥ 252 MPa, and the elongation ≥ 11%.

[0022] Furthermore, the thermal expansion coefficient of the high-temperature corrosion-resistant and wear-resistant cast steel at 100°C is 10.3×10 -6 / °C, the thermal expansion coefficient at 200°C is 10.6×10 -6 / °C, the thermal expansion coefficient at 300°C is 11.0×10 -6 / °C, the thermal expansion coefficient at 400°C is 11.3×10 -6 / °C, the thermal expansion coefficient at 500°C is 11.7×10 -6 / °C, the thermal expansion coefficient at 600°C is 12.3×10 -6 / °C, the thermal expansion coefficient at 700°C is 13.1×10 -6 / °C.

[0023] The present invention also provides a production method of the above high-temperature corrosion-resistant and wear-resistant cast steel, comprising the following steps:

[0024] S1, melting the steel-making raw materials, heating up to 1520°C - 1550°C, adding calcium oxide for slag-making, and removing the slag;

[0025] S2, tapping the steel, adding a deoxidizer to the molten steel during tapping for deoxidation, and pouring the deoxidized molten steel to obtain the high-temperature corrosion-resistant and wear-resistant cast steel.

[0026] As a specific embodiment, in S2, the deoxidizer is calcium-silicon alloy, the addition amount of the deoxidizer is 0.15% - 0.30% of the mass of the molten steel, and the deoxidation time is 3 min - 5 min.

[0027] As a specific embodiment, in S2, the pouring temperature is 1470°C - 1570°C.

[0028] Exemplarily, the steel-making raw materials include: 15% - 35% of steel, 20% - 60% of return materials, 5% - 40% of micro-carbon ferrochrome, 0.5% - 2.5% of ferromolybdenum alloy, and 0.5% - 2.5% of ferrosilicon alloy.

[0029] Exemplarily, after adding calcium oxide for slag-making, it is left standing for 3 min - 5 min and then the slag is removed.

[0030] It should be noted that the pouring can be carried out by investment casting or sand casting, and after the pouring is completed, it can be directly machined to the final part size.

[0031] The production method of the high-temperature corrosion-resistant and wear-resistant cast steel provided by the present invention can directly obtain a ferritic-based casting through pouring, without the quenching process in the traditional process, thus effectively reducing energy consumption and production costs, improving production efficiency, and avoiding the risk of thermal deformation easily caused by the traditional quenching process, improving the machinability. More importantly, on the premise of omitting the traditional quenching treatment process, it also significantly improves the high-temperature wear resistance and corrosion resistance of the cast steel, and has broad application prospects in the field of automotive engines.

[0032] In a third aspect, the present invention also provides an application of the above high-temperature corrosion-resistant and wear-resistant cast steel in the preparation of wear-resistant and corrosion-resistant parts.

[0033] Furthermore, the wear-resistant and corrosion-resistant parts are the bushings of automotive engine turbochargers.

[0034] The high-temperature corrosion-resistant and wear-resistant cast steel provided by the present invention has a ferrite + carbide structure and still has a ferrite structure at high temperatures, without undergoing austenite phase transformation. It has excellent high-temperature wear and corrosion resistance. Moreover, after casting and forming, it does not require quenching treatment and can be directly machined to the final part size, reducing production costs and energy consumption, significantly improving production efficiency, having high practical value, and having broad application prospects in the field of automotive engines. Detailed implementation manners

[0035] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further details the present invention in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] To better illustrate the present invention, the following further gives examples for illustration.

[0037] Embodiment 1

[0038] The embodiment of the present invention provides a high-temperature wear-resistant and corrosion-resistant cast steel, and its chemical composition is as follows:

[0039] C 1.16%, Si 2.43%, Cr 32.3%, Mo 1.95%, Mn 0.41%, P 0.032%, S 0.040%, and the balance is Fe and unavoidable impurities.

[0040] The production method of the above high-temperature wear-resistant and corrosion-resistant cast steel is as follows:

[0041] Step 1: Weigh scrap steel, return scrap, micro-carbon ferrochromium, ferromolybdenum alloy and ferrosilicon alloy according to the above composition design ratio and add them into an induction furnace. Melt the steelmaking raw materials, heat up to 1530 °C, add calcium oxide for slag making, and let the molten steel stand for 4 minutes to remove slag;

[0042] Step 2: Tap the molten steel from the induction furnace into a pouring ladle. During the tapping process, add 0.2% calcium-silicon alloy by the mass of the molten steel for deoxidation. After adding the deoxidizer for 5 minutes, control the temperature of the molten steel at 1500 °C for pouring to obtain the high-temperature corrosion-resistant and wear-resistant cast steel.

[0043] Embodiment 2

[0044] The embodiment of the present invention provides a high-temperature wear-resistant and corrosion-resistant cast steel, and its chemical composition is as follows:

[0045] C 1.11%, Si 2.53%, Cr 30.0%, Mo 2.11%, Mn 0.29%, P 0.027%, S 0.035%, and the balance is Fe and unavoidable impurities.

[0046] The production method of the above high-temperature wear-resistant and corrosion-resistant cast steel is as follows:

[0047] Step 1: Weigh scrap steel, return materials, micro-carbon ferrochromium, ferromolybdenum alloy and ferrosilicon alloy according to the above composition design ratio, add them into an induction furnace, melt the steelmaking raw materials, heat up to 1520 °C, add calcium oxide to make slag, and let the molten steel stand for 3 minutes to remove the slag;

[0048] Step 2: Tap the molten steel from the induction furnace into the pouring ladle. During tapping, add 0.15% of calcium-silicon alloy by the mass of the molten steel to deoxidize the molten steel. After adding the deoxidizer for 4 minutes, control the temperature of the molten steel at 1470 °C for pouring to obtain high-temperature corrosion-resistant and wear-resistant cast steel.

[0049] Example 3

[0050] An embodiment of the present invention provides a high-temperature wear-resistant and corrosion-resistant cast steel, and its chemical composition is:

[0051] C 1.12%, Si 2.06%, Cr 32.2%, Mo 2.02%, Mn 0.25%, P 0.039%, S 0.038%, and the balance is Fe and inevitable impurities.

[0052] The production method of the above high-temperature wear-resistant and corrosion-resistant cast steel is as follows:

[0053] Step 1: Weigh scrap steel, return materials, micro-carbon ferrochromium, ferromolybdenum alloy and ferrosilicon alloy according to the above composition design ratio, add them into an induction furnace, melt the steelmaking raw materials, heat up to 1550 °C, add calcium oxide to make slag, and let the molten steel stand for 5 minutes to remove the slag;

[0054] Step 2: Tap the molten steel from the induction furnace into the pouring ladle. During tapping, add 0.3% of calcium-silicon alloy by the mass of the molten steel to deoxidize the molten steel. After adding the deoxidizer for 3 minutes, control the temperature of the molten steel at 1570 °C for pouring to obtain high-temperature corrosion-resistant and wear-resistant cast steel.

[0055] Examples 4 - 13

[0056] The preparation methods of Examples 4 - 13 are the same as those of Example 1, and the specific compositions of each example are shown in Table 1.

[0057] Table 1

[0058]

[0059]

[0060] Comparative Example 1

[0061] This comparative example provides a wear-resistant steel GX60CrMnMoVNbN21-10 (material No. 1.4785, standard: DIN 17480-1998), and the specific composition is as follows:

[0062] Carbon C% Chromium Cr% Manganese Mn% Aluminum Al% Molybdenum Mo% Vanadium V% Niobium Nb% Nitrogen N% 0.62 20.80 10.41 0.43 0.85 0.85 1.06 0.42

[0063] Performance test:

[0064] 1. Mechanical properties at room temperature

[0065] The high-temperature wear-resistant and corrosion-resistant cast steels prepared in Examples 1-13 were subjected to mechanical property tests at room temperature according to GB / T 228.1-2021, and the results are shown in Table 2.

[0066] Table 2 Mechanical properties at room temperature (20 °C)

[0067]

[0068]

[0069] 2. High-temperature mechanical properties

[0070] The high-temperature wear-resistant and corrosion-resistant cast steels prepared in Examples 1-13 were subjected to mechanical property tests at room temperature according to GB / T 228.2-2015, and the results are shown in Table 2.

[0071] Table 2 Mechanical properties at high temperature (600 °C)

[0072] Number Yield strength MPa Tensile strength MPa Elongation % Example 1 178 303 15 Example 2 160 293 13 Example 3 162 287 19 Example 4 177 300 12 Example 5 155 253 14 Example 6 182 333 11 Example 7 146 249 18 Example 8 172 278 12 Example 9 165 288 19 Example 10 147 252 13 Example 11 175 310 13 Example 12 177 299 15 Example 13 156 299 11

[0073] 3. Wear resistance

[0074] The cast steels prepared in Example 1, Example 6, Example 10 and Comparative Example 1 were made into bushings.

[0075] The production process of the bushing prepared in Example 1 is a conventional process in the art: the cast steel is heated and melted in an induction furnace and then cast into a bushing blank by investment casting, the rough profile of the blank is processed, and then it is processed to the final size.

[0076] The production process of the bushing prepared in Comparative Example 1 is a conventional process in the art: the cast steel is heated and melted in an induction furnace and then cast into a bushing blank by investment casting, the rough profile of the blank is processed, and after water toughening heat treatment, it is processed to the final size.

[0077] The rocker arm shaft is prepared from the 1.4845 material by the conventional method in the art. The surface of the rocker arm shaft is subjected to conventional low-temperature gas carbonitriding treatment at a temperature between 550 - 600 °C, and the nitrided layer depth is controlled to be greater than 20 microns. The prepared rocker arm shaft and bushing are installed in the housing component by an interference fit method. The engine durability test is carried out in accordance with GB / T 19055 - 2003 to verify the wear condition of the bushing under actual working conditions, and the results are shown in Table 3.

[0078] Table 3 Maximum wear amount under actual working conditions

[0079]

[0080] 4. Corrosion resistance

[0081] According to GB / T 10125 - 2021, the neutral salt spray test is carried out. After 192 h, no red rust appears on the bushing prepared in Example 1; red rust appears on the bushing prepared in Comparative Example 1 after 96 h. It shows that the corrosion resistance of the cast steel material in the embodiment of the present invention is significantly better than that of the existing 1.4785 material.

[0082] Examples 2 - 13 can all achieve corrosion resistance basically equivalent to that of Example 1, and only the corrosion resistance of Example 10 is slightly lower than that of other examples.

[0083] 5. Coefficient of thermal expansion

[0084] The coefficient of thermal expansion of the cast steel materials in Example 1 and Comparative Example 1 is tested at different temperatures according to GB / T 4339 - 2008. The results are shown in Table 4.

[0085] Table 4 Coefficient of thermal expansion

[0086]

[0087] To sum up, the cast steel material prepared in the embodiment of the present invention still has a ferrite structure at high temperatures and will not undergo austenite phase transformation. When installed in ferritic components (such as gray cast iron, high-silicon molybdenum ductile iron, vermicular graphite cast iron and other housings, boxes) by an interference fit method, due to having a similar coefficient of thermal expansion to the housing, there will be no problems of loosening caused by temperature changes and cracking of the housing caused by thermal stress at high temperatures; and after casting and forming, it can be directly machined to the final part size without heat treatment, significantly improving the production efficiency.

[0088] In the embodiment of the present invention, compared with Comparative Example 1, the tool life can be increased by 10%. The weight of engine bushing parts is only a few tens of grams, and the material itself accounts for a very small proportion in the total cost. The present invention can reduce the machining cost and heat treatment cost, and has an obvious cost advantage compared with Comparative Example 1 and other high manganese steel materials. Moreover, the production efficiency is high, which can effectively improve the market competitiveness of domestic enterprises and has broad application prospects.

[0089] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-temperature corrosion-resistant and wear-resistant cast steel, characterized in that, The weight percentages of its components are as follows: C 0.8% - 1.4%, Si 1.0% - 3.0%, Cr 28.0% - 33.0%, Mo 1.0% - 3.0%, Mn ≤ 1.0%, P ≤ 0.040%, S ≤ 0.040%, and the balance is Fe and unavoidable impurities; Its microstructure is ferrite and carbide; The high-temperature corrosion-resistant and wear-resistant cast steel is prepared by the following method: S1. Melt the steelmaking raw materials, heat up to 1520°C - 1550°C, add calcium oxide to make slag, and remove the slag; S2. Tap the steel, add a deoxidizer to the molten steel during tapping for deoxidation, and pour the deoxidized molten steel to obtain the high-temperature corrosion-resistant and wear-resistant cast steel.

2. The high-temperature corrosion-resistant and wear-resistant cast steel according to claim 1, characterized in that, The weight percentages of its components are as follows: C 1.0% - 1.2%, Si 2.0% - 3.0%, Cr 31.0% - 3. The high-temperature corrosion-resistant and wear-resistant cast steel according to claim 1 or 2, characterized in that, ​ 4. The high-temperature corrosion-resistant and wear-resistant cast steel according to claim 1 or 2, characterized in that, ​ 5. The high-temperature corrosion-resistant and wear-resistant cast steel according to claim 1 or 2, characterized in that, The high-temperature corrosion-resistant and wear-resistant cast steel has a thermal expansion coefficient of 10.3×10 -6 / °C at 100°C, 10.6×10 -6 / °C at 200°C, 11.0×10 -6 / °C at 300°C, 11.3×10 -6 / °C at 400°C, 11.7×10 -6 / °C at 500°C, 12.3×10 -6 / °C at 600°C, 13.1×10 -6 / °C.

6. The production method of the high-temperature corrosion-resistant and wear-resistant cast steel according to any one of claims 1-5, characterized in that, ​ ​ ​ 7. The production method of the high-temperature corrosion-resistant and wear-resistant cast steel according to claim 6, characterized in that, ​ ​ ​ 9. The application according to claim 8, wherein ​

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