A high-temperature pressure-bearing cast steel, its preparation method and application

Abstract

This invention relates to a high-temperature resistant pressure-bearing cast steel, its preparation method, and its application. The composition of the high-temperature resistant pressure-bearing cast steel is as follows: C: 0.15-0.20%, Si≤0.60%, Mn: 0.50-0.90%, P≤0.010%, S≤0.010%, Cr: 1.20-1.50%, Mo: 0.80-1.20%, V: 0.20-0.40%, W: 0.40-0.80%, Co: 0.35-0.65%, with the remainder being Fe and unavoidable impurities. Furthermore, the composition of the high-temperature resistant pressure-bearing cast steel satisfies the following relationship: F1=1.85[W]+3.13[Co], 1.95≤F1≤3.04; where [W] and [Co] represent the weight percentages of W and Co, respectively. The cast steel is preferably subjected to a quenching and tempering heat treatment process and is suitable for use in high-temperature pressure-bearing components such as heat exchangers and reaction vessels.

Description

Technical Field

[0001] This invention relates to a high-temperature pressure-bearing cast steel, its preparation method, and its application, belonging to the technical field of cast steel. The cast steel provided by this invention has excellent high-temperature mechanical properties and a wide range of applications. At the same time, this invention provides a method for preparing the cast steel. Background Technology

[0002] High-temperature pressure vessels, such as reactors and heat exchangers, have high requirements for the high-temperature mechanical properties of steel. In the past, cast steel was used to manufacture high-temperature pressure vessels. However, as the working conditions of high-temperature pressure vessels become increasingly harsh, the high-temperature mechanical properties of cast steel often fail to meet the requirements of high-temperature and pressure-bearing conditions. Therefore, industry technicians now tend to use heat-resistant stainless steels such as martensitic, austenitic, and ferritic stainless steels as the material for high-temperature pressure vessels.

[0003] While using heat-resistant stainless steel as the material for high-temperature pressure vessels can certainly meet performance requirements, this type of stainless steel typically contains high levels of precious elements such as Cr and Ni, often totaling up to 20%, and in some materials even reaching 40%. Cr and Ni are expensive and have limited reserves. The extensive use of Cr and Ni in this type of material is not conducive to cost control, nor to resource conservation. Furthermore, this type of steel usually requires rolling and welding processes to finally obtain high-temperature pressure-bearing components, making its manufacturing process complex and costly.

[0004] If cast steel can be used as the material for high-temperature pressure vessels, its advantages in raw material cost, resource cost, and process cost are obvious. Cast steel has a very low Cr content, and many cast steels do not even contain Ni, resulting in low raw material costs and avoiding the large-scale use of precious metals. In particular, cast steel can be directly cast in one piece, without the rolling, cutting, and welding steps of traditional stainless steel, which also reduces process costs.

[0005] Therefore, in order to fully utilize the aforementioned advantages of cast steel and realize the application of high-temperature cast steel to replace high-temperature stainless steel in pressure-bearing components, improving the high-temperature mechanical properties of high-temperature cast steel has become an urgent problem to be solved. Summary of the Invention

[0006] This invention provides a high-temperature resistant pressure-bearing cast steel, its preparation method, and its applications. The cast steel designed by this invention exhibits excellent high-temperature mechanical properties, making it suitable for use as a material for high-temperature pressure vessels. It can be widely applied to high-temperature pressure-bearing components such as heat exchangers and reactors. Compared to traditional high-temperature resistant stainless steel, it offers significant advantages in raw material cost, resource advantage, and process cost. This allows for a large-scale replacement of high-temperature resistant stainless steel with high-temperature resistant cast steel, substantially reducing material costs while meeting high-temperature mechanical performance requirements. Furthermore, this invention also provides a method for preparing the aforementioned high-temperature resistant pressure-bearing cast steel.

[0007] The technical objective of this invention is achieved through the following means.

[0008] The purpose of this invention is to provide a high-temperature resistant pressure-bearing cast steel with the following composition: C: 0.15-0.20%, Si≤0.60%, Mn: 0.50-0.90%, P≤0.010%, S≤0.010%, Cr: 1.20-1.50%, Mo: 0.80-1.20%, V: 0.20-0.40%, W: 0.40-0.80%, Co: 0.35-0.65%, with the remainder being Fe and unavoidable impurities. Furthermore, the composition of the high-temperature resistant pressure-bearing cast steel satisfies the following relationship: F1=1.85[W]+3.13[Co], 1.95≤F1≤3.04; where [W] and [Co] represent the weight percentages of W and Co, respectively.

[0009] As mentioned earlier, traditional high-temperature pressure-bearing cast steels lack sufficient high-temperature mechanical properties, limiting their widespread use in demanding operating conditions. Through extensive experimental research, the inventors of this invention discovered that adding a certain amount of W and Co, and rationally controlling their content within a specific range, can significantly improve the high-temperature mechanical properties of cast steel. This broadens its application scope, enabling the replacement of high-temperature stainless steel with high-temperature cast steel in high-temperature pressure-bearing components. It also reduces raw material costs, avoids the large-scale use of expensive resources, simplifies the manufacturing process, and lowers process costs.

[0010] The role of each element in the high-temperature pressure-bearing cast steel of this invention is described below.

[0011] Carbon: Carbon improves the hardenability of steel and is one of the important strengthening elements in steel. It enhances the strength of steel through solid solution strengthening and precipitation strengthening. By controlling the carbon content at a level of 0.15-0.20%, it is possible to ensure that cast steel has the optimal balance between hardenability and toughness.

[0012] Silicon: Silicon is a deoxidizing element in steel. Silicon also has the function of solid solution strengthening. However, if the silicon content is too high, it will lead to a decrease in the toughness of cast steel. This invention controls the silicon content to be below 0.6%.

[0013] Manganese: Manganese plays a role in solid solution strengthening in steel. It can improve both strength and toughness of cast steel. However, excessive manganese content can lead to component segregation, affecting the casting quality of cast steel and deteriorating its performance. The manganese content in this invention is controlled at 0.50-0.90%.

[0014] Phosphorus and sulfur: Phosphorus and sulfur are unavoidable impurity elements in steel. Excessive content will drastically deteriorate the performance of cast steel. In this invention, the phosphorus and sulfur content is controlled below 0.01%. The lower the phosphorus and sulfur content, the better, provided that the cost is acceptable.

[0015] Chromium: Chromium is an important strengthening element in steel. Controlling its content within a reasonable range is crucial for ensuring excellent high-temperature strength. Too low a chromium content results in insufficient strengthening, while too high a chromium content not only increases costs but also reduces toughness. This invention controls the chromium content to be between 1.20% and 1.50%.

[0016] Molybdenum: Molybdenum can refine grains and is an important element for improving the hardenability of steel and the room temperature and high temperature strength of cast steel. Too low a molybdenum content results in insufficient strengthening effect and significant temper brittleness in the steel, while too high a molybdenum content leads to saturation of the strength-enhancing effect and a decrease in plasticity. This invention controls the molybdenum content to be between 0.80% and 1.20%.

[0017] Vanadium: Vanadium can refine the grain structure, improve strength and toughness, and also plays a role in ensuring high-temperature strength. Vanadium is a strong carbide-forming element, and it readily combines with carbon to form vanadium carbide. Its fine and dispersed distribution in the cast steel structure can effectively ensure its mechanical properties at both room temperature and high temperature. In this invention, the vanadium content is controlled at 0.20-0.40%.

[0018] Tungsten and Cobalt: The inventors discovered that adding appropriate amounts of tungsten and cobalt to the cast steel system of this invention can significantly improve the high-temperature strength of the cast steel. The inventors determined the optimal amounts of tungsten and cobalt through experiments, which are 0.40-0.80% tungsten and 0.35-0.65% cobalt. If the content of tungsten or cobalt is too low, the improvement effect on the high-temperature strength of the cast steel is not significant. However, if the content of tungsten or cobalt is too high, not only will the effect of improving the high-temperature strength reach its peak, but it will also begin to have a negative impact on the high-temperature strength and lead to an increase in the cost of cast steel.

[0019] Even more unexpectedly, the inventors discovered during the experiments that simply meeting the aforementioned tungsten and cobalt addition amounts did not always guarantee satisfactory high-temperature strength. It was also necessary to synergistically control the tungsten and cobalt content. Through repeated experimentation, the inventors found that, within the aforementioned range, controlling the tungsten and cobalt content relationship to meet certain conditions could yield cast steel with excellent high-temperature strength. Therefore, the inventors experimentally summarized and planned the crucial tungsten and cobalt content relationship for this invention: F1 = 1.85[W] + 3.13[Co], 1.95 ≤ F1 ≤ 3.04; where [W] and [Co] represent the weight percentages of W and Co, respectively.

[0020] Furthermore, the inventors' research and experiments revealed that when the composition of the high-temperature pressure-bearing cast steel also satisfies the following relationship, it is particularly advantageous for obtaining superior high-temperature pressure-bearing cast steel: F2=0.34[Cr]+0.57[Mo]+1.26[V]+2.24[W]+4.03[Co], 3.9≤F2≤5.1; where [Cr], [Mo], [V], [W], and [Co] represent the weight percentages of Cr, Mo, V, W, and Co, respectively.

[0021] Furthermore, the high-temperature mechanical properties of the aforementioned high-temperature pressure-bearing cast steel satisfy: R p0.2,600℃ ≥300MPa, R p0.2,650℃ With a strength of ≥240MPa, it can meet the requirements for long-term stable operation at 650℃.

[0022] As a non-limiting description, the room temperature mechanical properties of the high-temperature pressure-bearing cast steel are: R p0.2 ≥450 MPa, R m ≥600MPa, elongation ≥15%, room temperature KV2 ≥30J.

[0023] As a non-limiting description, the high-temperature pressure-bearing cast steel is preferably heat-treated cast steel. As an example, the heat treatment is quenching and tempering; wherein the quenching temperature is 930-970℃ and the tempering temperature is 700-760℃.

[0024] This invention also provides a method for preparing high-temperature pressure-bearing cast steel, comprising the following steps: melting and casting to obtain cast steel that meets the aforementioned composition and content requirements, and then subjecting the cast steel to quenching and tempering heat treatment. Preferably, the quenching temperature is 930-970℃, the tempering temperature is 700-760℃, and the quenching medium is air, water, or oil, and the tempered steel is air-cooled to room temperature.

[0025] The present invention also provides the use of the aforementioned high-temperature pressure-bearing cast steel or the high-temperature pressure-bearing cast steel prepared by the aforementioned method in high-temperature pressure vessels; as a non-limiting description, the high-temperature pressure vessel can be a heat exchanger, a reaction vessel, or other high-temperature pressure-bearing components.

[0026] The present invention has the following technical effects.

[0027] This invention optimizes and adjusts the composition of cast steel by controlling the content of various elements, particularly by adding appropriate amounts of tungsten and cobalt, and synergistically controlling the content relationship between tungsten and cobalt. This results in a pressure-bearing cast steel with excellent high-temperature mechanical properties, capable of long-term stable operation at 650℃. Compared to commonly used heat-resistant stainless steel, the high-temperature pressure-bearing cast steel obtained by this invention has similar performance, a simpler composition, and a lower content of expensive metals, which helps to reduce costs and conserve precious metal resources. Furthermore, the cast steel can be directly formed without the need for complex subsequent forming processes such as continuous casting, rolling, and welding, saving process costs. This enables the use of high-temperature cast steel to replace high-temperature stainless steel in pressure equipment, greatly expanding the application scope of inexpensive cast steel in high-temperature pressure-bearing fields. Detailed Implementation

[0028] To enable those skilled in the art to fully understand the technical solution and beneficial effects of the present invention, the following detailed explanation is provided in conjunction with specific experimental examples.

[0029] According to the composition and element content relationship of the present invention, molten steel is smelted and cast to obtain cast steel. The P and S contents are both controlled at 0.008±0.001%. The composition test results are shown in Table 1. In Table 1, F1=1.85[W]+3.13[Co], F2=0.34[Cr]+0.57[Mo]+1.26[V]+2.24[W]+4.03[Co], and the ingot size is 1200mm×600mm×450mm.

[0030] Table 1: Composition of each cast steel, %, balance is Fe.

[0031]

[0032] All cast steels underwent a tempering treatment of water quenching after holding at 940℃ for 2 hours, followed by air cooling after holding at 720℃ for 4 hours. Subsequently, the room temperature strength, elongation, toughness, and high-temperature strength of each cast steel were tested. Room temperature strength and elongation were tested according to GB / T228.1-2021, room temperature toughness according to GB / T229-2020, and high-temperature strength according to GB / T228.2-2015. The test results are recorded in Table 2.

[0033] Table 2: Various mechanical properties of cast steel.

[0034]

[0035] The above embodiments and comparative examples will be further analyzed and explained below with reference to Tables 1 and 2.

[0036] The composition and element content relationships F1 of test numbers 1-6 in Table 2 all meet the requirements of this invention, and their final room temperature mechanical properties meet the standards, and their high temperature mechanical properties can meet R. p0.2,600℃ ≥300MPa, R p0.2,650℃ The invention requires a strength of ≥240 MPa; therefore, the above-mentioned test numbers are embodiments of the present invention. Specifically, the elemental content relationship F2 of test numbers 2, 4, and 6 satisfies the preferred range of 3.9 to 5.1 of the present invention. The tests confirm that the above-mentioned test numbers, while meeting the room temperature mechanical properties requirements, exhibit superior high-temperature mechanical properties and can meet the R... p0.2,600℃ ≥360MPa, R p0.2,650℃ The high-temperature strength performance level is ≥300MPa; therefore, Examples 2, 4, and 6 are preferred embodiments of the present invention. At least one of W, Co, and F1 in test numbers 7-21 fails to meet the requirements of the invention. Test results confirm that although its room temperature mechanical properties meet the standard, its high-temperature mechanical properties are poor and cannot meet the requirements of the present invention. p0.2,600℃ ≥300MPa, R p0.2,650℃ The requirement of ≥240MPa, test number 7-21 is a comparative example of the present invention.

[0037] Below, we will analyze the above comparison in detail.

[0038] Comparative Example 7 is a comparative example of Example 3. With other components the same as in Example 3, the tungsten content was increased. The adjusted tungsten content is still within the scope of the present invention. However, the tungsten and cobalt content relationship F1 is higher than the requirements of the invention. The results show that, since F1 does not meet the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0039] Comparative Example 8 is a comparative example of Example 4. With other components the same as in Example 4, the tungsten content was reduced. The adjusted tungsten content is still within the range of the present invention. However, the tungsten and cobalt content relationship F1 is lower than the requirements of the invention. The results show that, because F1 does not meet the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0040] Comparative Example 9 is a comparative example of Example 5. With other components the same as in Example 5, the cobalt content was reduced. The adjusted cobalt content is still within the scope of the present invention. However, the content relationship F1 of tungsten and cobalt is lower than the requirements of the invention. The results show that, since F1 does not meet the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0041] Comparative Example 10 is a comparative example of Example 6. With other components the same as in Example 6, the cobalt content was increased. The adjusted cobalt content is still within the scope of the present invention. However, the content relationship F1 of tungsten and cobalt is higher than the requirements of the invention. The results show that, since F1 does not meet the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0042] Comparative Example 11 is a comparative example of Example 4. With other components the same as in Example 4, the tungsten content was increased. The adjusted tungsten and cobalt content relationship F1 is still within the scope of the present invention, but the tungsten content is higher than the requirements of the invention. The results show that, due to the tungsten content not meeting the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0043] Comparative Example 12 is a comparative example of Example 4. With other components the same as in Example 4, the cobalt content was reduced. The adjusted tungsten and cobalt content relationship F1 is still within the scope of the present invention, but the cobalt content is lower than the requirements of the invention. The results show that, due to the cobalt content not meeting the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0044] Comparative Example 13 is a comparative example of Example 5. With other components the same as in Example 5, the tungsten content was reduced. The adjusted tungsten and cobalt content relationship F1 is still within the scope of the present invention, but the tungsten content is lower than the requirements of the invention. The results show that, due to the tungsten content not meeting the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0045] Comparative Example 14 is a comparative example of Example 5. With other components the same as in Example 5, the cobalt content was increased. The adjusted tungsten and cobalt content relationship F1 is still within the scope of the present invention, but the cobalt content is higher than the requirements of the invention. The results show that, due to the cobalt content not meeting the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0046] Comparative Example 15 is a comparative example of Example 1. With other components the same as in Example 1, the tungsten content was reduced, and the adjusted tungsten and cobalt content relationship F1 was not within the scope of the present invention, and the tungsten content was lower than the requirements of the invention. The results showed that, due to the tungsten content and F1 not meeting the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C was low and could not meet the requirements of the invention.

[0047] Comparative Example 16 is a comparative example of Example 1. With other components the same as in Example 1, the cobalt content was reduced, and the adjusted tungsten and cobalt content relationship F1 was not within the scope of the present invention, and the cobalt content was lower than the requirements of the invention. The results showed that, due to the cobalt content and F1 not meeting the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C was low and could not meet the requirements of the invention.

[0048] Comparative Example 17 is a comparative example of Example 2. With other components the same as in Example 2, the tungsten content was increased. The adjusted tungsten and cobalt content relationship F1 is also outside the scope of this invention, and the tungsten content is higher than the requirements of the invention. The results show that, due to the tungsten content and F1 not meeting the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0049] Comparative Example 18 is a comparative example of Example 2. With other components the same as in Example 2, the cobalt content was increased. The adjusted tungsten and cobalt content relationship F1 is also outside the scope of this invention, and the cobalt content is higher than the requirements of the invention. The results show that, due to the cobalt content and F1 not meeting the requirements of the invention, the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0050] Comparative Example 19 is a comparative example of Example 3. With other components the same as in Example 3, tungsten was used instead of cobalt. The adjusted tungsten and cobalt content relationship F1 is still within the scope of the present invention, but the tungsten content is higher than the requirements of the invention and does not contain cobalt. The results show that, due to the tungsten content not meeting the requirements of the invention and the absence of cobalt, the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0051] Comparative Example 20 is a comparative example of Example 3. With other components the same as in Example 3, cobalt was used instead of tungsten. The adjusted content relationship of tungsten and cobalt, F1, is also not within the scope of this invention. Since the cobalt content is higher than the requirements of the invention and does not contain tungsten, and F1 does not meet the requirements of the invention, the results show that the yield strength of the cast steel at 600°C and 650°C is low and cannot meet the requirements of the invention.

[0052] Comparative Example 21 is a comparative example of Example 6. While other components are the same as in Example 6, tungsten and cobalt are omitted. Therefore, the content relationship F1 of tungsten and cobalt is necessarily outside the scope of this invention. The results show that, due to the absence of tungsten and cobalt, the yield strength of the cast steel at 600°C and 650°C is particularly low, which cannot meet the requirements of the invention and cannot meet the needs of high-temperature working conditions.

[0053] In summary, it is clear that by adding tungsten and cobalt in combination and synergistically controlling their content relationship, this invention can ensure the production of cast steel with excellent high-temperature strength properties. The cast steel is suitable for use as high-temperature pressure-bearing components, such as heat exchangers, reaction vessels, and other high-temperature pressure vessels. It has the characteristics of excellent high-temperature performance, low raw material cost, and simple preparation process, and can replace expensive and costly heat-resistant stainless steel.

[0054] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0055] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-temperature-resistant pressure-containing cast steel, characterized by, The high-temperature-resistant pressure-bearing cast steel has the following components: C: 0.15-0.20%, Si≤0.60%, Mn: 0.50-0.90%, P≤0.010%, S≤0.010%, Cr: 1.20-1.50%, Mo: 0.80-1.20%, V: 0.20-0.40%, W: 0.40-0.80%, Co: 0.35-0.65%, the rest being Fe and inevitable impurities, and the components of the high-temperature-resistant pressure-bearing cast steel satisfy the following relationships: F1=1.85[W]+3.13[Co], 1.95≤F1≤3.04; F2=0.34[Cr]+0.57[Mo]+1.26[V]+2.24[W]+4.03[Co], 3.9≤F2≤5.1; wherein [Cr], [Mo], [V], [W] and [Co] represent the weight percentage content of Cr, Mo, V, W and Co respectively.

2. The high-temperature and pressure-resistant cast steel according to claim 1, characterized in that, The high-temperature mechanical property of the high-temperature-resistant pressure-bearing cast steel satisfies: R p0.2,600℃ ≥ 300 MPa, R p0.2,650℃ ≥ 240 MPa.

3. The high-temperature and pressure-resistant cast steel according to claim 1, characterized in that, The high-temperature-resistant pressure-bearing cast steel is a cast steel in a heat-treated state.

4. The high-temperature and pressure-resistant cast steel according to claim 3, characterized in that, The heat treatment is quenching + tempering.

5. The high-temperature and pressure-resistant cast steel according to claim 4, characterized in that, The quenching temperature is 930-970°C, and the tempering temperature is 700-760°C.

6. The method of claim 1-5, wherein the method is characterized by, The cast steel satisfying the component and content relationship requirements is obtained by smelting and casting, and then the cast steel is subjected to heat treatment of quenching + tempering.

7. The method for preparing high-temperature pressure-bearing cast steel according to claim 6, characterized in that, The quenching temperature is 930-970°C, and the tempering temperature is 700-760°C.

8. The method for preparing a high-temperature pressure-bearing cast steel according to claim 6, characterized in that, The quenching medium is air or water or oil, and the cast steel is air-cooled to room temperature after tempering.

9. Use of the high-temperature-resistant pressure-bearing cast steel according to any one of claims 1-5 or prepared by the preparation method of the high-temperature-resistant pressure-bearing cast steel according to any one of claims 6-8 in a high-temperature pressure vessel, wherein the high-temperature pressure vessel is a heat exchanger or a reaction kettle.

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