High-performance nodular cast iron for reciprocating piston type compressor unit and smelting process thereof

Abstract

The invention relates to the technical field of compressors, in particular to high-performance nodular cast iron for a reciprocating piston type compressor unit and a smelting technology of the high-performance nodular cast iron. The high-performance nodular cast iron for the reciprocating piston type compressor unit comprises the following chemical elements in percentage by weight: 3.2-3.6 wt% of C; 2.4 to 2.9 wt% of Si; 0.3 to 0.4 wt% of Mn; p is less than or equal to 0.05 wt%; s is less than or equal to 0.03 wt%; 0.03 to 0.06 wt% of Mg; 0.01 to 0.05 wt% of a rare earth metal; ti is less than or equal to 0.04 wt%; less than or equal to 0.03 wt% of Sb; 0.3 to 0.6 wt% of Cu and Ni; and the balance of iron and inevitable impurities. On the basis of traditional QT450-10 nodular cast iron, nickel and copper elements are introduced, the mechanical performance of the nodular cast iron is improved, and a manufactured compression cylinder product meets the requirements of application scenes with higher requirements for the compression cylinder.

Description

Technical Field

[0001] This invention relates to the field of compressor technology, specifically to high-performance ductile iron for reciprocating piston compressor units and its smelting process. Background Technology

[0002] Since its invention in the 1940s, ductile iron has been widely used in various fields due to its excellent mechanical properties, such as high strength, corrosion resistance, oxidation resistance, and shock absorption, as well as its relatively low production cost. Reciprocating piston natural gas compressors play a crucial role in peak shaving and supply assurance of oil and gas resources. As one of the core components of reciprocating piston natural gas compressors, ductile iron compressor cylinders have stringent requirements for mechanical properties due to their harsh operating environments, complex stresses, and long service cycles.

[0003] Currently, the main material used in manufacturing compression cylinders is ductile iron of grade QT450-10. This ductile iron has a tensile strength requirement of 450 MPa and an elongation requirement of 10%. Its main matrix is ​​ferrite, and its chemical composition is: C 3.4-3.8 wt%; Si 2.1-2.7 wt%; Mn 0.30-0.40 wt%; P ≤0.05 wt%; Mg 0.04-0.65 wt%; rare earth metals 0.01-0.05 wt%; the balance being iron and unavoidable impurities. However, with the increasing application of reciprocating piston natural gas compressors and the increasing demands on their power and pressure, it is necessary to improve the performance of ductile iron of grade QT450-10 to enhance its mechanical properties.

[0004] In the prior art, CN104264033A discloses a high-strength, high-rigidity ductile iron material for compressors. This ductile iron material is used to manufacture the upper and lower bearings of compressors, which can significantly improve their strength and rigidity. However, its toughness is poor, making it difficult to use as a compressor cylinder.

[0005] CN106048400A discloses a ductile iron for compressor cylinder blocks and its preparation method. This ductile iron comprises various non-metallic, metallic, and transition metal elements. The addition and synergistic effect of these elements improves the oxidation resistance, corrosion resistance, wear resistance, and compressive and shock resistance of the air conditioning compressor cylinder block, thereby extending its service life under harsh operating conditions. However, although the tensile strength of this ductile iron reaches over 650 MPa, its elongation is only up to 12.0%, which is not a significant improvement compared to the elongation requirement of QT450-10; furthermore, the main matrix structure of this ductile iron is pearlite.

[0006] Therefore, developing ductile iron with excellent comprehensive mechanical properties to meet the stringent requirements of compression cylinders remains a challenge. Summary of the Invention

[0007] This invention provides high-performance ductile iron for piston compressor units and its smelting process. By changing the proportions of carbon (C), silicon (Si), manganese (Mn), and sulfur (S) in conventional ductile iron and controlling the residual amount of magnesium (Mg), nickel (Ni) and copper (Cu) are introduced, and the sum of the contents of nickel and copper after introduction is clearly defined, the mechanical properties of ductile iron are improved. The compressor cylinder products manufactured from this ductile iron meet the needs of application scenarios with higher requirements for compressor cylinders.

[0008] High-performance ductile iron is used in reciprocating piston compressor units. The chemical element composition and content of the high-performance ductile iron are as follows: C 3.2~3.6wt%; Si 2.4~2.9wt%; Mn 0.3~0.4wt%; P ≤0.05wt%; S ≤0.03wt%; Mg 0.03~0.06wt%; rare earth metals 0.01~0.05wt%; Ti ≤0.04wt%; Sb ≤0.03wt%; Cu+Ni 0.3~0.6wt%; balance is iron and unavoidable impurities.

[0009] In the chemical composition of the high-performance ductile iron for reciprocating piston compressor units of the present invention, both carbon (C) and silicon (Si) elements promote the spheroidization of ductile iron and improve the mechanical strength of the ductile iron matrix. However, excessive silicon content will directly affect the low-temperature impact performance of ductile iron products. Under the premise that the content of other elements remains unchanged, when the silicon content exceeds 3.0 wt%, its low-temperature impact performance is reduced to less than 50% of that when the silicon content is 2.4 wt%. Therefore, it is necessary to strictly control the silicon content in ductile iron. The main function of manganese (Mn) is to lower the eutectoid transformation temperature, thereby stabilizing and refining the pearlite structure, which improves the strength and hardness of ductile iron. However, it will reduce the plasticity and toughness of ductile iron products. At the same time, the increase in manganese content will also increase the pearlite content in the matrix structure and reduce the ferrite content, thus affecting the corrosion resistance of ductile iron products. Therefore, the manganese content needs to be controlled at 0.4 wt% or below. Although magnesium (Mg) is an element that promotes spheroidization, if the residual magnesium content exceeds 0.06 wt%, it will form internal oxides, affecting the morphology and properties of graphite. Therefore, the residual magnesium content must be controlled to 0.06 wt% or less. Nickel (Ni) and copper (Cu) stabilize and refine the microstructure of ductile iron and improve its performance. However, when their combined content exceeds 0.6 wt%, a large amount of pearlite is formed, significantly increasing the tensile and yield strength of ductile iron, but drastically reducing its toughness. Furthermore, while increasing nickel and copper content improves the fluidity of molten iron, it also significantly increases the shrinkage tendency during solidification, easily leading to keyholes and shrinkage porosity within the ductile iron. Through extensive experimental data, the inventors determined that the optimal combined content of these two components in ductile iron is 0.3–0.6 wt%.

[0010] The smelting process for high-performance ductile iron in this reciprocating piston compressor unit includes the following steps: 1) Material preparation: Prepare pig iron, carbon raiser, scrap steel, recycled materials and alloy materials; 2) Smelting: Based on high current rapid melting, pig iron is melted in the furnace, and then carbon raiser, scrap steel, recycled material and alloy material are added in sequence, and the temperature is raised to obtain cast iron liquid; 3) Casting: The molten cast iron is taken out of the furnace, spheroidized and then cast to obtain high-performance ductile iron for reciprocating piston compressor units.

[0011] In one specific embodiment of the present invention, in step 2), the temperature at which pig iron is melted in the furnace is 1220-1350°C.

[0012] In one specific embodiment of the present invention, step 2) melting, the heating melting is to heat to the melting temperature of 1480-1530°C and hold at that temperature for 3-10 minutes.

[0013] In one specific embodiment of the present invention, in step 2) smelting, sampling and analysis are performed during the heating and smelting process, and the chemical composition content of the molten steel is detected; if the chemical composition content of the molten steel is not qualified, carbon raiser, scrap steel, recycled material or alloy material is added to the molten steel to adjust the chemical composition content of the molten steel until the sampling and analysis are qualified.

[0014] In one specific embodiment of the present invention, the sampling analysis includes: taking samples to detect the C and Si content in the molten steel when the steel temperature is 1400-1430°C.

[0015] In one specific embodiment of the present invention, the sampling analysis further includes: sampling and spectral analysis in front of the furnace when the temperature of molten steel is 1420-1450°C.

[0016] In one specific embodiment of the present invention, in step 3), the temperature of the cast iron molten iron when it exits the furnace is 1440–1480°C.

[0017] In one specific embodiment of the present invention, in step 3), the spheroidization temperature is 1400°C.

[0018] In one specific embodiment of the present invention, step 3) casting involves removing the slag from the surface of the molten cast iron before casting.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. The content of carbon, silicon, manganese, phosphorus and sulfur elements in the ductile iron of the present invention is adjusted, and nickel and copper with a total content of 0.3 to 0.6 wt are introduced to improve the mechanical properties of ductile iron products. 2. The tensile strength, yield strength, and elongation of the ductile iron of this invention are 565 MPa, 410 MPa, and 17.5%, which meet the requirements of the standard. Furthermore, the tensile strength, yield strength, and elongation of the ductile iron have been improved to varying degrees, enriching the database of basic materials for ductile iron. 3. This invention improves the tensile strength of ductile iron and also increases its elongation. The resulting compression cylinder products meet the needs of applications requiring higher performance from reciprocating piston compressors. Attached Figure Description

[0020] Figure 1 The figure shows the results of the molten iron flow test of high-performance ductile iron and QT450-10 ductile iron for reciprocating piston compressor unit of the present invention; wherein, (a) is the molten iron flow test result of high-performance ductile iron for reciprocating piston compressor unit, and (b) is the molten iron flow test result of QT450-10 ductile iron. Figure 2 This is a test report on the pressure resistance of the compression cylinder product cast from high-performance ductile iron for the reciprocating piston compressor unit of the present invention. Figure 3 This is a hydrogen corrosion resistance test report for the compression cylinder product cast from high-performance ductile iron for reciprocating piston compressor units according to the present invention. Detailed Implementation

[0021] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] The compression cylinder is one of the core components of a reciprocating piston natural gas compressor. Its main function is to form a compression volume with the piston, withstand gas pressure, accommodate the piston's reciprocating motion, and bear the compressor's pressure and load. Considering the compression cylinder's service environment and manufacturing process requirements, ductile iron is an advantageous material for manufacturing the compression cylinder. However, ductile iron must possess at least the following characteristics: 1. It has good filling capacity, ensuring that the complex cavity components of the compression cylinder can be filled with molten iron; 2. High yield strength to prevent deformation during use; 3. Excellent comprehensive mechanical properties to meet the requirements of service conditions.

[0023] Refer to JB / T9104-2013 "Technical Conditions for Ductile Iron for Positive Displacement Compressor Units" for ductile iron grade QT450-10. The main matrix structure of this grade of ductile iron is ferrite. The required compressive strength is 450 MPa, the required yield strength is 310 MPa, and the required elongation (elongation at break) is 10%. Therefore, ductile iron grade QT450-10 is currently used to manufacture the compression cylinder of reciprocating piston natural gas compressors.

[0024] The material formulation of the compressor directly determines the performance of the compressor cylinder. In order to meet the requirements of greater power and greater pressure, the material formulation of QT450-10 ductile iron needs to be improved to enhance the comprehensive mechanical properties of QT450-10 ductile iron.

[0025] The chemical element composition and content of traditional QT450-10 ductile iron are as follows: C 3.4~3.8wt%; Si 2.1~2.7wt%; Mn 0.3~0.4 wt%; P ≤0.05 wt%; Mg 0.04~0.65wt%; rare earth metals 0.01~0.05 wt%; the balance is iron and unavoidable impurities.

[0026] In traditional QT450-10 ductile iron, carbon (C) primarily promotes graphitization and is a key characteristic of cast iron. During production, higher carbon content increases the fluidity of molten iron, giving it better filling ability. However, excessively high carbon content can lead to graphite floating, reducing the mechanical properties of the product.

[0027] The main function of silicon (Si) is similar to that of carbon (C), both being elements that promote graphitization. The increase in silicon content shifts the eutectic point of the iron-carbon phase diagram to the left, similar to 1 / 3 of that of carbon, thus narrowing the solidification range and increasing the fluidity of molten iron. However, excessive silicon content can lead to increased brittleness of the material and reduced mechanical properties of the product.

[0028] The main function of manganese (Mn) is to lower the eutectoid transformation temperature, thereby stabilizing and refining the pearlite structure, thus improving the strength and hardness of the bulk material, but reducing its plasticity and toughness. Simultaneously, increasing the manganese content increases the pearlite content and decreases the ferrite content in the microstructure, thus affecting the product's corrosion resistance.

[0029] Phosphorus (P) is a harmful element for ductile iron. Phosphorus dissolved in molten iron will form binary or ternary phosphorus eutectics between grains, which will destroy the intergranular bonding force, reduce the strength, plasticity and toughness of the product, and increase the tendency of shrinkage porosity and shrinkage cavities.

[0030] Sulfur (S) is a harmful element for ductile iron, strongly inhibiting graphite spheroidization. High sulfur content in molten iron increases its viscosity, reduces its filling capacity, and also hinders gas escape from the molten iron, easily creating porosity inside the product and directly affecting its performance.

[0031] Based on the traditional QT450-10 ductile iron formula, this invention adds nickel (Ni) and copper (Cu) elements to the high-performance ductile iron for reciprocating piston compressor units to improve the mechanical properties of ductile iron. The specific chemical element composition and content are as follows: C 3.2~3.6wt%; Si 2.4~2.9wt%; Mn 0.3~0.4wt%; P ≤0.05wt%; S ≤0.03wt%; Mg 0.03~0.06wt%; rare earth metals 0.01~0.05wt%; Ti ≤0.04wt%; Sb ≤0.03wt%; Cu+Ni 0.3~0.6wt%; balance is iron and unavoidable impurities.

[0032] Nickel (Ni) and copper (Cu) can improve the mechanical properties of QT450-10 ductile iron, but when their total content exceeds 0.6wt%, a large amount of pearlite structure will be formed. Although this can significantly improve the tensile strength and yield strength of the product, the toughness will decrease sharply, affecting the overall mechanical properties. In addition, as the total content of nickel and copper increases, the fluidity of molten iron can be improved, but it will also significantly increase the shrinkage tendency of molten iron during solidification. This makes it very easy to form shrinkage cavities inside the product, which is detrimental to the mechanical properties of ductile iron.

[0033] Titanium (Ti) and antimony (Sb) are both harmful elements. The increase of titanium (Ti) content will cause the generated TiC particles to hinder the diffusion of C atoms, resulting in the distortion of graphite spheres, a decrease in spheroidization rate, and a reduction in ferrite content. Antimony (Sb) is conducive to the formation of pearlite matrix structure in ductile iron, improving tensile strength and hardness, but it affects the toughness of ductile iron, especially its elongation.

[0034] The formulation of high-performance ductile iron for the reciprocating piston compressor unit of the present invention improves the fluidity of molten iron and gives it better filling ability.

[0035] The high-performance ductile iron for reciprocating piston compressor units of the present invention has excellent mechanical properties. To prepare this high-performance ductile iron for reciprocating piston compressor units by smelting, a smelting process is provided, including the following steps: 1) Material preparation: Prepare pig iron, carbon raiser, scrap steel, recycled materials and alloy materials; 2) Smelting: Based on high current rapid melting, pig iron is melted in the furnace, and then carbon raiser, scrap steel, recycled material and alloy material are added in sequence, and the temperature is raised to obtain cast iron liquid; 3) Casting: The molten cast iron is taken out of the furnace, spheroidized and then cast to obtain high-performance ductile iron for reciprocating piston compressor units.

[0036] It should be noted that in step 3), casting is performed after spheroidization to obtain a high-performance ductile iron compression cylinder, which is one of the core components of a reciprocating piston compressor.

[0037] In some instances, step 2) smelting involves melting pig iron in a furnace at a temperature of 1220–1350°C.

[0038] In some instances, step 2) melting involves heating to a melting temperature of 1480–1530°C and holding at that temperature for 3–10 minutes.

[0039] In some instances, sampling and analysis are performed during the heating and smelting process to detect the chemical composition content of the molten steel; if the chemical composition content of the molten steel is not up to standard, carbon raisers, scrap steel, recycled materials or alloy materials are added to the molten steel to adjust the chemical composition content of the molten steel until the sampling and analysis are up to standard.

[0040] In some instances, the sampling analysis includes taking samples at a steel temperature of 1400–1430°C to detect the C and Si content in the molten steel.

[0041] In some instances, the sampling analysis also includes: sampling and spectral analysis in front of the furnace when the molten steel temperature is 1420–1450°C.

[0042] In some instances, in step 3), the casting temperature of the molten iron is 1440–1480°C.

[0043] In some instances, step 3) involves casting, where the spheroidization temperature is 1400°C.

[0044] In some instances, step 3) involves casting, where slag on the surface of the molten cast iron is removed before casting.

[0045] The high-performance ductile iron for reciprocating piston compressor units prepared by the smelting process of this invention has good filling capacity, ensuring that the complex cavity parts of the compressor cylinder can be filled with molten iron; and it has high tensile strength, yield strength, elongation (elongation at break) and hardness, with excellent comprehensive mechanical properties, which can prevent the compressor cylinder from deforming during use and meet the requirements of service conditions.

[0046] To further demonstrate the role of high-performance ductile iron in improving the mechanical properties of the compression cylinder in the reciprocating piston compressor unit of the present invention, the following embodiments and comparative examples are provided: The specific amounts and chemical composition of pig iron, scrap steel, recycled materials, and alloy materials in the following examples and comparative examples can be selected and adjusted as needed.

[0047] Example 1 This embodiment provides a method for producing a high-performance ductile iron compression cylinder, including: 1. Prepare pig iron, carbon raiser, scrap steel, recycled materials and alloy materials; 2. Smelting: Based on high current rapid melting, pig iron is melted in the furnace, and then carbon raiser, scrap steel, recycled material and alloy material are added in sequence. The temperature is raised and smelted to obtain cast iron liquid. 3. Casting: After the molten cast iron is taken out of the furnace and spheroidized, it is poured into a mold to obtain a high-performance ductile iron compressor cylinder for reciprocating piston compressor units.

[0048] The chemical elemental composition and content of this compression cylinder are as follows: C 3.40wt%; Si 2.65wt%; Mn 0.35wt%; Mg 0.045wt%; rare earth metals 0.03wt%; Cu 0.22wt%; Ni 0.22wt%; balance is iron and <0.04wt% Ti, <0.03wt% Sb, <0.05wt% P, <0.03wt% S.

[0049] The compression cylinder prepared in this embodiment was subjected to pressure resistance test and hydrogen corrosion resistance test. During the casting of the compression cylinder, the auxiliary parts were cast and mechanical property test was performed. The fluidity test was performed on the molten iron before casting.

[0050] Example 2 This embodiment refers to the production method of Embodiment 1 to produce a compression cylinder. The chemical elemental composition and content of the compression cylinder are as follows: C 3.31wt%; Si 2.47wt%; Mn 0.34wt%; Mg 0.045wt%; rare earth metals 0.02wt%; Cu 0.26wt%; Ni 0.25wt%; balance is iron and <0.04wt% Ti, <0.03wt% Sb, 0.025wt% P, and 0.021wt% S.

[0051] In this embodiment, the auxiliary parts are cast during the casting of the compression cylinder, and mechanical property tests are performed.

[0052] Example 3 This embodiment refers to the production method of Embodiment 1 to produce a compression cylinder. The chemical elemental composition and content of the compression cylinder are as follows: C 3.39wt%; Si 2.32wt%; Mn 0.38wt%; Mg 0.045wt%; rare earth metals 0.022wt%; Cu 0.22wt%; Ni 0.3wt%; balance is iron and <0.04wt% Ti, <0.03wt% Sb, 0.023wt% P, and 0.012wt% S.

[0053] In this embodiment, the auxiliary parts are cast during the casting of the compression cylinder and mechanical property tests are performed.

[0054] Comparative Example 1 This comparative example produces a compression cylinder according to the production method of Example 1. The chemical elemental composition and content of this compression cylinder are as follows: C 3.32wt%; Si 2.37wt%; Mn 0.35wt%; Mg 0.045wt%; rare earth metals 0.022wt%; Cu 0.18wt%; Ni 0.5wt%; balance is iron and <0.04wt% Ti, <0.03wt% Sb, 0.024wt% P, and 0.012wt% S.

[0055] This comparative example involves casting the auxiliary parts during the casting of the compression cylinder and conducting mechanical property tests.

[0056] Comparative Example 2 This comparative example produces a compression cylinder according to the production method of Example 1. The chemical elemental composition and content of this compression cylinder are as follows: C 3.42wt%; Si 2.28wt%; Mn 0.32wt%; Mg 0.044wt%; rare earth metals 0.025wt%; Cu 0.25wt%; balance iron and <0.04wt% Ti, <0.03wt% Sb, 0.025wt% P, 0.012wt% S.

[0057] This comparative example involves casting the auxiliary parts during the casting of the compression cylinder and conducting mechanical property tests.

[0058] Performance testing 1. Mechanical property testing Mechanical properties were tested on the compression cylinders obtained from ductile iron casting in Examples 1-3 and Comparative Examples 1-2. The tensile strength R... m Yield strength R p0.2 The results of elongation (elongation at break) A and hardness value (HB) are shown in Table 1.

[0059] Table 1 Note: In Table 1, "Standard Requirement A" refers to the mechanical property requirements for ductile iron of grade QT450-10 in standard JB / T 9104-2013; "Standard Requirement B" refers to the mechanical property requirements for ductile iron in standard ASTM A536-1984(R2019).

[0060] As shown in Table 1, the high-performance ductile iron compression cylinder of the reciprocating piston compressor unit of the present invention, compared with the QT450-10 ductile iron compression cylinder in JB / T9104-2013, has a higher tensile strength R. m Increased by 115 MPa, yield strength R p0.2 The tensile strength R increased by 100 MPa, and the elongation at break (A) increased by 75%; compared with the compression cylinder product cast according to ASTM A536-1984 (R2019), its tensile strength R... m Increased by 117 MPa, yield strength R p0.2 The strength was increased by 100 MPa, and the elongation at break (A) was increased by 45.8%; the yield ratio was increased from 0.68 in JB / T9104-2013 and 0.69 in ASTM A536-1984(R2019) to 0.72. This shows that the high-performance ductile iron used in the reciprocating piston compressor unit of the present invention improves the deformation resistance of the compressor cylinder product.

[0061] As can be seen from the results of Comparative Example 1, when the sum of the contents of Cu and Ni is 0.68 wt%, the tensile strength R of ductile iron is... m and yield strength R p0.2 Although superior to Examples 2 and 3, its elongation was significantly reduced; this indicates that when the combined content of Cu and Ni exceeds 0.6 wt%, the toughness of ductile iron will decrease sharply.

[0062] The results of Examples 1-3 and Comparative Examples 1-2 also show that introducing Cu into conventional QT450-10 ductile iron can increase the elongation (elongation at break) of the ductile iron. When Ni is further introduced into ductile iron with Cu already present, the effect of the introduced Ni on the mechanical properties of the ductile iron can be divided into three main stages as the Ni content increases: In the first stage, as the Ni content increases from 0 to 0.22 wt%, Ni can enhance the tensile strength R of the ductile iron. m and yield strength R p0.2 In the second stage, the Ni content increased from 0.22 wt% to 0.3 wt%. Ni can increase the elongation (elongation at break) of ductile iron, but the tensile strength R... m and yield strength R p0.2 The elongation (elongation at break) of ductile iron initially decreases sharply, then increases; in the third stage, as the Ni content increases from 0.3 wt% to 0.5 wt%, the elongation at break of ductile iron decreases sharply, and the tensile strength R... m and yield strength R p0.2 Building upon the second stage, further increases are made; based on the premise that the sum of Cu and Ni content in ductile iron is 0.3-0.6 wt%, the Cu content is preferably 0.20-0.26 wt%, and Ni is appropriately added to meet the requirements of the sum of Cu and Ni content, thus ductile iron with excellent mechanical properties can be prepared.

[0063] 2. Liquidity Test The fluidity of molten iron from high-performance ductile iron used in the reciprocating piston compressor unit of Example 1 and molten iron from traditional QT450-10 ductile iron was tested using a triple-helix alloy fluidity tester. All parameters, including casting speed and temperature, were kept consistent during the casting of the triple-helix disc. The results are shown in the attached figure. Figure 1 The graph shows the results of the molten iron fluidity test.

[0064] Depend on Figure 1 As can be seen, the three-spiral disk cast from high-performance ductile iron in the reciprocating piston compressor unit of Example 1 is significantly longer than the three-spiral disk cast from traditional QT450-10 ductile iron. This indicates that the molten iron produced by the newly developed formula, which optimizes the content of known elements in traditional QT450-10 ductile iron and adds nickel (Ni) and copper (Cu), has better fluidity and filling ability.

[0065] 3. Pressure resistance test The pressure resistance test was conducted on the high-performance ductile iron compression cylinder of the reciprocating piston compressor unit in Example 1. The test report is attached. Figure 2 As shown.

[0066] From the appendix Figure 2It is evident that the high-performance ductile iron for reciprocating piston compressor units prepared by this invention produces compressor cylinders that function normally during both the pressure boosting and holding stages, without any abnormalities such as pressure leakage. Furthermore, within the specified test pressure range, the pressure and duration it withstands meet the design requirements. This demonstrates that the ductile iron compressor cylinders produced using the formula of this invention, which uses high-performance ductile iron for reciprocating piston compressor units, have pressure-bearing capacity that meets design requirements.

[0067] 4. Hydrogen corrosion resistance testing and evaluation Hydrogen corrosion resistance testing was performed on the compressor cylinder of the reciprocating piston compressor unit in Example 1, which was cast from high-performance ductile iron. The results are attached. Figure 3 As shown.

[0068] From the appendix Figure 3 As can be seen, when the hydrogen corrosion resistance test was performed on the samples of the cast compression cylinder products in accordance with GB / T 8650-2015 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", no hydrogen blistering was observed in the samples.

Claims

1. A high-performance ductile iron for reciprocating piston compressor units, characterized in that, The chemical element composition and content of the high-performance ductile iron are as follows: C 3.2~3.6wt%; Si 2.4~2.9wt%; Mn 0.3~0.4wt%; P ≤0.05wt%; S ≤0.03wt%; Mg 0.03~0.06wt%; rare earth metals 0.01~0.05wt%; Ti ≤0.04wt%; Sb ≤0.03wt%; Cu+Ni 0.3~0.6wt%; balance is iron and unavoidable impurities.

2. The smelting process of high-performance ductile iron for reciprocating piston compressor units as described in claim 1, characterized in that, Includes the following steps: 1) Material preparation: Prepare pig iron, carbon raiser, scrap steel, recycled materials and alloy materials; 2) Smelting: Based on high current rapid melting, pig iron is melted in the furnace, and then carbon raiser, scrap steel, recycled material and alloy material are added in sequence, and the temperature is raised to obtain cast iron liquid; 3) Casting: The molten cast iron is taken out of the furnace, spheroidized and then cast to obtain high-performance ductile iron for reciprocating piston compressor units.

3. The smelting process according to claim 2, characterized in that: Step 2) Smelting: The temperature at which pig iron is melted in the furnace is 1220-1350℃.

4. The smelting process according to claim 2, characterized in that: Step 2) Melting: The heating process involves raising the temperature to 1480-1530℃ and holding it at that temperature for 3-10 minutes.

5. The smelting process according to claim 2, characterized in that: Step 2) Smelting: During the heating and smelting process, samples are taken for analysis and the chemical composition content of the molten steel is tested. If the chemical composition content of the molten steel is not up to standard, carbon raiser, scrap steel, recycled material or alloy material is added to the molten steel to adjust the chemical composition content of the molten steel until the sample analysis is up to standard.

6. The smelting process according to claim 5, characterized in that: The sampling analysis includes taking samples to detect the C and Si content in the molten steel when the steel temperature is 1400-1430℃.

7. The smelting process according to claim 6, characterized in that: The sampling analysis also includes: sampling and spectral analysis of the front furnace when the molten steel temperature is 1420-1450℃.

8. The smelting process according to claim 2, characterized in that: Step 3) Casting, the temperature of the molten iron when it comes out of the furnace is 1440-1480℃.

9. The smelting process according to claim 2, characterized in that: Step 3) Casting, the spheroidization temperature is 1400℃.

10. The smelting process according to claim 2, characterized in that: Step 3) Casting: Before casting, remove the slag from the surface of the molten iron.

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