Casting method of isothermal quenching ductile iron wind power planetary support

Abstract

The invention relates to a casting method of an isothermal quenching ductile iron wind power planetary support, the isothermal quenching ductile iron is selected to manufacture the wind power planetary support, the isothermal quenching ductile iron is based on nodular cast iron, and the nodular cast iron comprises the following components in percentage by weight: 3.50-3.70% of C, 2.50-2.70% of Si and 1t of Mn; 0.30%, P: lt; 0.03%, S: lt; the alloy comprises the following components in percentage by weight: 0.02% of Mn, 0.035-0.055% of Mg, 0.01-0.02% of Re, 0.60-0.80% of Cu, 0.30-0.40% of Mo and less than 0.5% of Mn + Mo, so that the service life of the alloy is greatly prolonged. And meanwhile, the purposes of saving energy, reducing weight and saving materials (generally, the weight can be reduced by 1 / 4-1 / 3) can be achieved.

Description

Technical Field

[0001] This invention relates to the field of casting technology, and in particular to a casting method for isothermally quenched ductile iron wind turbine planetary support. Background Technology

[0002] As is well known, traditional wind turbine planetary support structures are made of ordinary pearlitic ductile iron (mostly QT700-2 or QT800-2) and cast using resin sand casting. The working environment of wind turbines (strong winds, cold, humidity, etc.) is harsh, and with unpredictable and drastic changes in wind speed, the planetary support structure is subjected to reciprocating cycles of random amplitude loads for extended periods. In actual operation, this affects its service life, often preventing it from reaching its design life. Furthermore, due to limitations in material properties, wind turbine planetary support structures are often designed to be very thick and large, which correspondingly increases the unit's power consumption.

[0003] Against this backdrop, the use of new ultra-high performance metallic materials can improve performance and reliability, thereby achieving the goals of energy saving (electricity saving), material saving (weight reduction), and extending service life.

[0004] The advantages of isothermal quenched ductile iron as an engineering material are its good comprehensive mechanical properties (see Table 1), good wear resistance, and high yield strength ratio.

[0005] Table 1 It is particularly noteworthy that isothermally quenched ductile iron possesses excellent wear resistance. Numerous tests have shown that isothermally quenched ductile iron exhibits better wear resistance than any ordinary ductile iron of the same hardness. This is due to its matrix structure, which consists of hard acicular ferrite and work-hardening carbon-rich austenite. Summary of the Invention

[0006] The present invention aims to improve the performance and reliability of existing wind turbine planetary support materials, thereby achieving the goals of energy saving (electricity saving), material saving (weight reduction), and extending their service life. Therefore, it provides a casting method for isothermal quenched ductile iron wind turbine planetary support.

[0007] This invention first provides an isothermally hardened ductile iron engineering material, which is based on ductile iron and comprises the following components by weight fraction: C: 3.50-3.70%, Si: 2.50-2.70%, Mn: <0.30%, P: <0.03%, S: <0.02%, Mg: 0.035-0.055%, Re: 0.01-0.02%, Cu: 0.60-0.80%, Mo: 0.30-0.40%, and the total amount of Mn+Mo is less than 0.5%.

[0008] This invention also provides a casting method for isothermally quenched ductile iron wind turbine planetary support, comprising: Step 1: Melt molten ductile iron in an induction furnace, with a tapping temperature of 1480-1500℃; Step Two: The molten ductile iron after being tapped from the furnace undergoes spheroidizing treatment and inoculation treatment. The chemical composition requirements for the molten iron after treatment are as follows: C: 3.50-3.70%, Si: 2.50-2.70%, Mn: <0.30%, P: <0.03%, S: <0.02%, Mg: 0.035-0.055%, Re: 0.01-0.02%, Cu: 0.60-0.80%, Mo: 0.30-0.40%, total Mn+Mo less than 0.5%; Step 3: The molten iron processed in Step 2 is used to obtain the blank of the wind turbine planetary support through the iron mold sand covering molding process; Step 4: Machin the casting blank of the part obtained in Step 3, leaving a deformation allowance; Step 5: Perform isothermal quenching on the wind turbine planetary support structure after machining in Step 4. Austenitizing heating: 890–910℃, time: 5–6 hours; Isothermal quenching temperature: 350~370℃, time: 1-2h; The microstructure of the above-mentioned parts after isothermal quenching is acicular ferrite + carbon-rich austenite + spheroidal graphite; its mechanical properties are: tensile strength (σb) 810-990MPa, elongation (δ) 6.0-10.0%, Brinell hardness (HB) 260-310. Step Six: Perform metallographic examination on the above parts after isothermal quenching. If they pass the examination, the finished product is obtained.

[0009] The isothermal quenching heat treatment of the above-mentioned parts in step five of the present invention is carried out in a salt bath. The salt used as the quenching medium is potassium nitrate and sodium nitrate, and the addition ratio is 50% each.

[0010] The as-cast microstructure of the ductile iron described in this invention is pearlitic ductile iron. The pearlite content is greater than 80%, the spheroidization rate is grade 2-3, and the graphite spheroid size is grade 5-7.

[0011] The present invention also provides the application of the isothermally quenched ductile iron in wind turbine planetary supports.

[0012] The beneficial effects of this invention are: This invention first provides a casting method for isothermally quenched ductile iron wind turbine planetary support. This isothermally quenched ductile iron material is based on ductile iron and comprises the following components by weight: C: 3.50-3.70%, Si: 2.50-2.70%, Mn: <0.30%, P: <0.03%, S: <0.02%, Mg: 0.035-0.055%, Re: 0.01-0.02%, Cu: 0.60-0.80%, Mo: 0.30-0.40%, with the total Mn+Mo content less than 0.5%. Mn and Mo are elements that cause severe grain boundary segregation. Therefore, limiting the total Mn and Mo content to less than 0.5% reduces their impact on material toughness. The addition of Cu can, to some extent, weaken the tendency of Mn and Mo to deflect at grain boundaries, thereby reducing the negative effects of Mn and Mo on ductility and toughness.

[0013] This invention also provides a casting method for isothermally quenched ductile iron wind turbine planetary support. This method uses a sand-coated iron mold casting process to cast the treated molten iron into a blank. The sand-coated iron mold increases the cooling rate and refines the microstructure, specifically the microstructure of the ductile iron before isothermal quenching, such as the size and number of graphite spheres, and especially the pearlite / ferrite ratio in the matrix. These factors significantly influence the time required for austenite to reach carbon saturation during isothermal quenching and the transformation of the matrix structure during isothermal quenching. This, in turn, affects the stability of the mechanical properties of the isothermally quenched ductile iron. Therefore, the ductile iron blanks for the aforementioned parts need to be obtained through a sand-coated iron mold casting process to ensure the consistency of the pearlite / ferrite ratio in the matrix. Experimental results show that the isothermally quenched ductile iron of this invention has a tensile strength (σb) of 810-990 MPa, an elongation (δ) of 6.0-10.0%, and a Brinell hardness (HB) of 260-310. Attached Figure Description

[0014] Figure 1 Micrograph of isothermally quenched ductile iron in Example 1 of this invention - Metallographic structure of wind turbine planetary support: acicular ferrite + carbon-rich austenite. Detailed Implementation

[0015] Example 1 A casting method for isothermally quenched ductile iron wind turbine planetary support, comprising: Step 1: Melt molten ductile iron in an induction furnace, with a tapping temperature of 1490℃; Step Two: The molten ductile iron after being tapped from the furnace undergoes spheroidizing treatment and inoculation treatment. The chemical composition after treatment is as follows: Step 3: The molten iron processed in Step 2 is poured into the casting blank of the above-mentioned parts using the iron mold sand covering molding process; Step 4: After leaving a margin for the processed casting blank obtained in Step 3, perform machining. Step 5: Perform isothermal quenching on the parts that have been machined in Step 4. Austenitizing heating at 900℃ for 6 hours; Isothermal quenching temperature 370℃, time 2h; The metallographic structure of the above parts after isothermal quenching is acicular ferrite + carbon-rich austenite + spheroidal graphite. Step Six: Perform metallographic examination on the parts after isothermal quenching. If the examination is qualified, the finished product is obtained.

[0016] Figure 1 This is a micrograph of the isothermally quenched ductile iron from Embodiment 1 of the present invention. Figure 1 It can be seen that the metallographic structure of the above-mentioned parts after heat treatment is acicular ferrite + carbon-rich austenite + spheroidal graphite. Experimental results show that the tensile strength (σb) of the product obtained in Example 1 is 830 MPa; the elongation (δ) is 10%; and the Brinell hardness (HB) is 262.

[0017] Example 2 Step 1: Melt ductile iron in an induction furnace at a tapping temperature of 1480℃; Step Two: The molten ductile iron after being tapped from the furnace undergoes spheroidizing treatment and inoculation treatment. The chemical composition after treatment is as follows: The molten iron processed in step two is poured into the casting blanks of the above-mentioned parts through the iron mold sand covering molding process. Step 4: After leaving a margin for the processed casting blank obtained in Step 3, perform machining. Step 5: Perform isothermal quenching on the parts that have been machined in Step 4. Austenitizing heating at 910℃ for 6 hours; Isothermal quenching temperature 350℃, time 2h; The metallographic structure of the above parts after isothermal quenching is acicular ferrite + carbon-rich austenite + spheroidal graphite. Step Six: Perform metallographic examination on the above parts after isothermal quenching. If they pass the examination, the finished product is obtained.

[0018] Experimental results show that the tensile strength (σb) of the product obtained in Example 2 is 970 MPa; the elongation (δ) is 6.0%; and the Brinell hardness (HB) is 300.

[0019] Example 3 Step 1: Melt molten ductile iron in an induction furnace at a tapping temperature of 1500℃; Step Two: The molten ductile iron after being tapped from the furnace undergoes spheroidizing treatment and inoculation treatment. The chemical composition after treatment is as follows: The molten iron processed in step two is poured into the casting blanks of the above-mentioned parts through the iron mold sand covering molding process. Step 4: After leaving a margin for the processed casting blank obtained in Step 3, perform machining. Step 5: Perform isothermal quenching on the parts that have been machined in Step 4. Austenitizing heating at 890℃ for 6 hours; Isothermal quenching temperature 360℃, time 2h; The metallographic structure of the above parts after isothermal quenching is acicular ferrite + carbon-rich austenite + spheroidal graphite. Step Six: Perform metallographic examination on the above parts after isothermal quenching. If they pass the examination, the finished product is obtained.

[0020] Experimental results show that the tensile strength (σb) of the product obtained in Example 3 is 920 MPa; the elongation (δ) is 8.2%; and the Brinell hardness (HB) is 290.

[0021] The wind turbine planetary support structures obtained in Examples 1-3 were tested for the amount and carbon content of retained austenite, as shown in Table 2. Table 2 As can be seen, within the given composition range and heat treatment conditions, the carbon-rich austenite content of the wind turbine planetary carriers obtained in Examples 1-3 ranges from 6.0% to 10.44%. This is because under the relatively high isothermal transformation conditions (350-370°C), the carbon diffusion rate of the wind turbine planetary carrier is faster, thereby increasing the amount of carbon enriched in the austenite. Generally, isothermal transformations above 350°C can increase the amount and carbon content of the already formed stable austenite. This is necessary to ensure the toughness of the material and meet the service conditions of the workpiece.

[0022] Initial machined parts are obtained from the isothermal-quenched wind turbine planetary carrier blanks. A preliminary surface quality inspection is performed on key areas to ensure the parts are free of obvious defects, providing a reliable foundation for subsequent finishing. Finishing operations are then performed on the initial machined parts, transforming them into finished parts. Strict machining accuracy is maintained to ensure that the dimensions and geometric tolerances of key areas meet design requirements, laying the foundation for subsequent testing. Key areas from the finished parts are selected for ultrasonic testing to obtain internal defect distribution data, ensuring the absence of cracks or porosity and verifying the structural integrity of the parts. Metallographic examination is then conducted on the key areas of the ultrasonically tested finished parts to obtain microstructure and chemical composition data, determining whether they meet the preset mechanical property standards and ensuring that the final machined parts meet the requirements of grade QTD800-10.

[0023] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A casting method for isothermally quenched ductile iron wind turbine planetary support, characterized in that, A type of isothermally hardened ductile iron was selected to manufacture the planetary support structure for wind turbines. This isothermally hardened ductile iron is based on ductile iron, which comprises the following components by weight percentage (%): C: 3.50-3.70%, Si: 2.50-2.70%, Mn: <0.30%, P: <0.03%, S: <0.02%, Mg: 0.035-0.055%, Re: 0.01-0.02%, Cu: 0.60-0.80%, Mo: 0.30-0.40%, and the total amount of Mn+Mo is less than 0.5%.

2. The casting method of isothermally quenched ductile iron wind turbine planetary support according to claim 1, characterized in that, include: Step 1: Melt molten ductile iron in an induction furnace, with a tapping temperature of 1480-1500℃; Step Two: The molten ductile iron after being tapped from the furnace undergoes spheroidizing treatment and inoculation treatment. The chemical composition requirements for the molten iron after treatment are as follows: C: 3.50-3.70%, Si: 2.50-2.70%, Mn: <0.30%, P: <0.03%, S: <0.02%, Mg: 0.035-0.055%, Re: 0.01-0.02%, Cu: 0.60-0.80%, Mo: 0.30-0.40%, total Mn+Mo less than 0.5%; Step 3: The molten iron processed in Step 2 is used to obtain the blank of the wind turbine planetary support through the iron mold sand covering molding process; Step 4: Machin the casting blank of the part obtained in Step 3, leaving a deformation allowance; Step 5: Perform isothermal quenching on the wind turbine planetary support structure after machining in Step 4. Austenitizing heating: 890–910℃, time: 5–6 hours; Isothermal quenching temperature: 350~370℃, time: 1-2h; The microstructure of the above-mentioned parts after isothermal quenching is acicular ferrite + carbon-rich austenite + spheroidal graphite; its mechanical properties are: tensile strength (σb) 810-990 N / mm3, elongation (δ) 6.0-10.0%, Brinell hardness (HB) 260-310. Step Six: Perform metallographic examination on the above parts after isothermal quenching. If they pass the examination, the finished product is obtained.

3. The casting method for an isothermally quenched ductile iron wind turbine planetary support according to claim 2, characterized in that, The isothermal quenching heat treatment of the above-mentioned parts in step five is carried out in a salt bath. The salt used as the quenching medium is potassium nitrate and sodium nitrate, with each added in a 50% ratio.

4. The casting method of an isothermally quenched ductile iron wind turbine planetary support according to claim 2, characterized in that, The as-cast microstructure of the ductile iron is pearlitic ductile iron, with a pearlite content of more than 80%, a spheroidization rate of 2-3, and a graphite spheroid size of 5-7.

5. The application of the isothermal hardened ductile iron as described in claim 1 in wind turbine planetary carriers.

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