Wire rod for fastener with complex-phase structure, fastener and manufacturing method of wire rod

Abstract

The invention discloses a steel wire rod with a complex phase structure for a fastener, which contains Fe and inevitable impurities, and further contains the following chemical elements in percentage by mass: 0.40 to 0.70 percent of C, 0.30 to 0.70 percent of Mn, 0.10 to 0.70 percent of Si, 0.50 to 2.00 percent of Cr, 0.50 to 2.00 percent of Mo, 0.03 to 0.30 percent of Nb, 0.10 to 0.80 percent of V, 0.02 to 0.08 percent of Ti and the balance of Fe. And the microstructure is bainite and retained austenite. The invention further discloses a high-strength fastener which is made of the steel wire rod. The invention further discloses a manufacturing method of the wire rod for the fastener. The manufacturing method comprises the following steps: smelting and casting; rolling into a wire rod; and controlling cooling.

Description

Technical Field

[0001] The present invention relates to a steel material and a preparation method thereof, and in particular to a fastener wire rod and a preparation method thereof. Background Art

[0002] As one of the important materials for high-strength fasteners, high-strength cold heading steel has been widely used in key fields such as automobiles, machinery manufacturing, energy, transportation, bridges, construction, aerospace, and military equipment due to its excellent mechanical properties and strength.

[0003] With the growing demand for high-performance equipment, the performance requirements for high-strength cold-heading steel are constantly increasing. In particular, when facing complex and harsh engineering application environments, the toughness, durability and delayed fracture resistance of high-strength cold-heading steel are posed with higher challenges. At present, due to the good delayed fracture resistance of Cr and CrMo steels, they are used in high-strength fasteners. For example, 40Cr, 35CrMo and 40CrMo are still widely used in the manufacture of 10.9 and 12.9 grade fasteners. With the higher stress design requirements and lightweight development of structural parts, there is an urgent need for ultra-high strength bolts above grade 12.9.

[0004] For example: The Chinese patent document with publication number CN110791715A, publication date February 14, 2020, and titled "A 14.9-grade high-strength bolt steel containing niobium and titanium and resistant to atmospheric corrosion and its production method" discloses a production method for 14.9-grade high-strength bolt steel containing niobium and titanium and resistant to atmospheric corrosion. It improves atmospheric corrosion resistance by adding elements such as Ni and Cu to obtain higher notch toughness, and refines the grains by adding elements such as Nb, V, and Ti to achieve a tensile strength of 1400 MPa.

[0005] A Chinese patent application, CN106795598A, published on May 3, 2017, and titled "High-Strength Bolt Steel and High-Strength Bolt," discloses a high-strength bolt steel and high-strength bolt. The steel achieves a strength of 1500 MPa through heat treatment at temperatures above 920°C (1420°F) and tempering above 570°C (1420°F). However, the steel's high carbon content (0.50-0.65%) negatively impacts its cold working properties.

[0006] Chinese patent publication number CN1900343A, published on January 24, 2007, and entitled "Method for producing steel with excellent delayed fracture resistance and a tensile strength of 1600 MPa or higher, and formed products thereof," discloses a method for producing steel with excellent delayed fracture resistance and a tensile strength of 1600 MPa or higher, and formed products thereof. The method employs the addition of 3.0 to 10.0% Mo to precipitate carbides and produce significant secondary hardening, thereby increasing the steel's strength. While the resulting steel achieves a tensile strength of 1600 MPa, the alloy composition is not designed appropriately, with a high Mo content, resulting in excessively high costs. Summary of the Invention

[0007] One of the purposes of the present invention is to provide a wire rod for fasteners having a complex phase structure. The wire rod for fasteners having a complex phase structure has excellent mechanical properties, especially after heat treatment, through reasonable composition design, and can be effectively used in ultra-high strength fastener products in the fields of automobiles, building structures, wind power, etc.

[0008] To achieve the above object, the present invention provides a wire rod for fasteners having a complex phase structure, which contains Fe and unavoidable impurities, and further contains the following chemical elements in the following mass percentages:

[0009] C: 0.40~0.70wt.%, Mn: 0.30~0.70wt.%, Si: 0.10~0.70wt.%, Cr: 0.50~2.00wt.% , Mo: 0.50~2.00wt.%, Nb: 0.03~0.30wt%, V: 0.10~0.80wt%, Ti: 0.02~0.08wt.%;

[0010] Its microstructure is bainite + retained austenite.

[0011] Furthermore, in the wire rod for fasteners of the present invention, the mass percentage of each chemical element is:

[0012] C: 0.40~0.70wt.%, Mn: 0.30~0.70wt.%, Si: 0.10~0.70wt.%, Cr: 0.50~2.00wt.%, Mo: 0.50~2.00wt.%, Nb: 0.03~0.30wt%, V: 0.10~0.80wt%, Ti: 0.02~0.08wt.%; the balance is Fe and unavoidable impurities.

[0013] In the high-strength fastener wire rod with a complex phase structure described in the present invention, the design principles of the various chemical elements are as follows:

[0014] C: In the high-strength fastener wire rod with a complex structure described herein, C is an element that contributes significantly to strength. Adding an appropriate amount of C to the steel contributes to its strength. However, it is important to note that the C content in the steel should not be too high, as excessive C content can adversely affect the low-temperature impact properties of the steel. Therefore, in the present invention, the C content is controlled within a range of 0.40 to 0.70 wt.%.

[0015] Mn: In the high-strength fastener wire rod with a complex structure described herein, Mn is a key element for stabilizing the austenite phase. It also stabilizes sulfur in the steel by forming MnS, thereby preventing hot brittleness. However, excessive Mn content can cause segregation at grain boundaries, reducing grain boundary strength. Therefore, in the present invention, the Mn content is controlled between 0.30 and 0.70 wt.%.

[0016] Si: In the high-strength fastener wire rod with a duplex structure described herein, Si inhibits cementite precipitation in bainitic steel and dissolves in ferrite, thereby providing solid solution strengthening and improving the steel's strength and hardness. However, excessive Si content significantly reduces the steel's plasticity and toughness. Therefore, in the present invention, the Si content is controlled within a range of 0.10 to 0.70 wt.%.

[0017] Cr: In the high-strength fastener wire rod with a complex phase structure described in the present invention, the Cr element has the effect of improving the hardenability of steel and promoting the precipitation of microalloy carbides, precipitating Cr and Mo composite carbides M 23 The C6 phase, Cr, and Mn composite carbide M7C3 phase, can improve steel strength and refine grain size. However, it's important to note that the Cr content in steel should not be too high. Excessive Cr content can reduce the steel's cold working properties and increase production costs. Therefore, in the present invention, the Cr content is controlled within a range of 0.50 to 2.00 wt.%.

[0018] Mo: In the high-strength fastener wire rod with a duplex structure described herein, Mo plays a similar role to Cr, producing significant strengthening effects by precipitating Mo-containing carbides. However, it is important to note that excessive Mo addition to the steel is undesirable, as this increases material costs. Therefore, considering cost factors, the Mo content in the present invention is controlled within a range of 0.50 to 2.00 wt.%.

[0019] Nb, V, and Ti: In the high-strength fastener wire rod with a complex structure described herein, Nb, V, and Ti form precipitates with carbon in the steel, refining the austenite grains during the heating phase, thereby improving the strength and toughness of the steel plate. However, excessive Nb, V, and Ti content can form coarse inclusions, adversely affecting the steel's performance. Therefore, in the present invention, the mass percentage of Nb is controlled between 0.03 and 0.30 wt%, the mass percentage of V is controlled between 0.10 and 0.80 wt%, and the mass percentage of Ti is controlled between 0.02 and 0.08 wt%.

[0020] Furthermore, the wire rod for fasteners of the present invention further contains 0<Al≤2.00wt.%, 0<Co≤2.00wt.%, and the mass percentage of the two satisfies Al / Co=0.8~1.4.

[0021] Al, Co: In the high-strength fastener wire rod with a complex phase structure described in the present invention, the Al and Co elements can increase the phase transformation free energy difference, promote the bainite phase transformation, and shift the phase transformation kinetic curve to the left, thereby promoting bainite transformation. Therefore, in the present invention, the mass percentage of the Al element can be controlled within the range of 0 < Al ≤ 2.00 wt.%, and the mass percentage of the Co element can be controlled within the range of 0 < Co ≤ 2.00 wt.%. In addition, the addition of Al and Co within a certain range has a better effect on promoting bainite transformation. Based on this, in the present invention, the mass percentage of Al and Co can be controlled to satisfy Al / Co = 0.8 to 1.4.

[0022] Furthermore, among the inevitable impurities in the wire rod for fasteners of the present invention: P≤0.015wt.%, S≤0.015wt.%.

[0023] It should be noted that in the above-mentioned technical solution of the present invention, the P element and the S element are both impurity elements in the high-strength fastener wire rod with a complex phase structure described in the present invention. When technical conditions permit, in order to obtain steel with better performance and higher quality, the content of impurity elements in the steel should be reduced as much as possible.

[0024] P and S: In the high-strength fastener wire rod with a complex microstructure described herein, the impurity elements P and S tend to segregate at grain boundaries, reducing the steel's toughness and significantly impacting its cold working properties. Therefore, in the present invention, the P content can be controlled to ≤ 0.015 wt.%, and the S content can be controlled to ≤ 0.015 wt.%.

[0025] Furthermore, in the wire rod for fasteners described in the present invention, each chemical element also satisfies: ln([V]+7[Ti]+11[Nb]+0.8[Mo]+1.5[Cr])≥1.35, where [V], [Ti], [Nb], [Mo], and [Cr] are respectively substituted into the numerical values ​​before the mass percentage sign of each chemical element.

[0026] In the high-strength fastener wire rod with a complex microstructure described herein, sufficient precipitation of MC, M3C2, M7C3, and FCC carbides is crucial for ensuring the steel's mechanical properties. To ensure sufficient precipitation of these carbides, the addition of V, Ti, Nb, Mo, and Cr must be controlled to satisfy the formula: ln([V] + 7[Ti] + 11[Nb] + 0.8[Mo] + 1.5[Cr]) ≥ 1.35.

[0027] Furthermore, in the wire rod for fasteners of the present invention, the volume phase ratio of retained austenite is 5 to 20%.

[0028] Furthermore, in the wire rod for fasteners described in the present invention, its performance meets the following requirements: the wire rod tensile strength is 1000-1250 MPa, the yield strength is 820-1140 MPa, and the elongation after fracture is ≥8%.

[0029] Another object of the present invention is to provide a high-strength fastener having excellent mechanical properties and can be effectively applied to bolts and related products in the fields of vehicles and ships, construction engineering, energy, bridges and transportation, and has very good promotion prospects and application value.

[0030] In order to achieve the above-mentioned object, the present invention provides a high-strength fastener made by using the wire rod for fasteners described in the present invention.

[0031] Furthermore, the high-strength fastener of the present invention has a tensile strength of ≥1900 MPa, a yield strength of ≥1400 MPa, and an impact energy of ≥50 J at -20°C.

[0032] Another object of the present invention is to provide a method for manufacturing wire rods for fasteners. The manufacturing method is simple to operate. The high-strength fastener wire rods with complex phase structure obtained by the manufacturing method have excellent mechanical properties. They can be effectively used in bolts and related products in the fields of vehicles and ships, construction engineering, energy, bridges and transportation, and have very good promotion prospects and application value.

[0033] In order to achieve the above object, the present invention provides a method for manufacturing a wire rod for a fastener, which comprises the steps of:

[0034] smelting and casting;

[0035] rolled into wire rod;

[0036] Controlled cooling: Cool to 600-650°C at a rate of 5-20°C / s, then cool at a rate of <0.5°C / s for 500-600s.

[0037] In the present invention, the controlled cooling process is designed to cool to 600-650°C at a rate of 5-20°C / s, and then cool for 500-600s at a rate of <0.5°C / s. This is because: the wire rod for fasteners described in the present invention will undergo bainite transformation in the temperature range of 400-600°C. By changing the transformation time, the volume fraction of retained austenite in the wire rod can be controlled between 5 and 20%.

[0038] Furthermore, in the step of rolling the wire rod into wire rod in the method for manufacturing wire rod for fasteners described in the present invention, the starting rolling temperature is controlled to be 1090-1180°C, the inlet temperature of the finishing mill is 980-1030°C, the inlet temperature of the reducing and sizing mill is 900-950°C, and the spinning temperature is 840-880°C.

[0039] Another object of the present invention is to provide a method for manufacturing high-strength fasteners. The manufacturing method is simple to operate. The high-strength fasteners with a complex phase structure obtained by the manufacturing method have excellent mechanical properties. They can be effectively applied to bolts and related products in the fields of vehicles and ships, construction engineering, energy, bridges and transportation, and have very good promotion prospects and application value.

[0040] In order to achieve the above object, the present invention provides a method for manufacturing a high-strength fastener, which comprises the steps of:

[0041] smelting and casting;

[0042] rolled into wire rod;

[0043] Controlled cooling: Cool to 600-650°C at a rate of 5-20°C / s, then cool at a rate of <0.5°C / s for 500-600s;

[0044] Annealing and drawing;

[0045] Parts shape processing;

[0046] Isothermal heat treatment.

[0047] Furthermore, in the step of rolling into wire rods in the method for manufacturing high-strength fasteners described in the present invention, the starting rolling temperature is controlled to be 1090-1180°C, the inlet temperature of the finishing mill is 980-1030°C, the inlet temperature of the reducing and sizing mill is 900-950°C, and the spinning temperature is 840-880°C.

[0048] The fastener wire rod with a complex phase structure, the fastener, and the manufacturing method thereof of the present invention have the following advantages and beneficial effects compared to the prior art:

[0049] The high-strength fastener wire rod and fastener with a complex phase structure described in the present invention have very significant advantages in chemical composition design, structure, and mechanical property regulation. Their chemical composition is precisely controlled by a design formula to control the content of V, Ti, Nb, Mo, and Cr elements, ensuring the sufficient precipitation of MC phase, M3C2 phase, M7C3 phase, and FCC phase carbides.

[0050] The high-strength fastener wire rod with a complex phase structure and the method for manufacturing the fastener described in the present invention control the transformation of the bainite structure in the wire rod by limiting the cooling rate and time of the wire rod after rolling. In addition, the addition of Al and Co elements can also promote the accelerated transformation of bainite.

[0051] In some embodiments, the high-strength fastener of the present invention has a tensile strength of ≥1900 MPa, a yield strength of ≥1400 MPa, and an impact energy of ≥50 J at -20°C. DETAILED DESCRIPTION

[0052] The wire rod for fasteners with a complex structure, the fasteners, and the manufacturing method thereof according to the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an undue limitation on the technical solution of the present invention.

[0053] Examples 1-8

[0054] The wire rods for fasteners having a complex structure in Examples 1-8 were all prepared by the following steps:

[0055] (1) Smelting and casting:

[0056] In some more specific embodiments, the smelting adopts a VD vacuum treatment process, which can control the vacuum degree to ≤2mbar, the vacuum time to ≥35min, the sedation argon blowing stirring flow rate to ≤200L / min, and the stirring time to ≥35min.

[0057] In addition, in order to further improve the quality of the ingot and ensure the excellent microstructure and properties of the rolled wire rod, the casting can adopt a soft reduction process. As an exemplary design parameter, it can be shown as follows:

[0058] Liquid phase volume fraction / % 30 25 20 15 10 Compression ratio / % 1 0.5 1.5 2.5 2

[0059] (2) Rolling into wire rod: Control the starting rolling temperature to 1090-1180℃, the finishing mill inlet temperature to 980-1030℃, the sizing mill inlet temperature to 900-950℃, and the spinning temperature to 840-880℃.

[0060] (3) Controlled cooling: After spinning, controlled cooling measures must be taken when passing through the Stelmore air cooling line, cooling to 600-650℃ at a rate of 5-20℃ / s, and then cooling at a rate of <0.5℃ / s for 500-600s.

[0061] The fasteners with a complex phase structure of Examples 1-8 were prepared by continuing to use the following steps based on the wire rods obtained in each Example:

[0062] (4) Annealing and drawing;

[0063] (5) Parts shape processing;

[0064] (6) Isothermal heat treatment: Heat to austenitizing temperature 860-940℃, keep warm for 30-90min,

[0065] Then cool to 250-400°C and keep warm for 120-300 minutes.

[0066] Table 1-1 and Table 1-2 list the mass percentages of the chemical elements in the wire rod for fasteners and the fasteners having a complex phase structure according to Examples 1-8 of the present invention.

[0067] Table 1-1. (wt%, the balance is Fe and other inevitable impurities except P and S)

[0068] serial number C Mn Si Cr Mo Nb V Ti Example 1 0.40 0.46 0.34 0.7 2 0.07 0.1 0.05 Example 2 0.51 0.51 0.10 2 1.3 0.09 0.2 0.07 Example 3 0.64 0.30 0.70 1.7 0.5 0.12 0.3 0.08 Example 4 0.70 0.61 0.48 1.4 1.6 0.14 0.4 0.06 Example 5 0.57 0.70 0.61 1.6 0.9 0.3 0.5 0.04 Example 6 0.61 0.49 0.28 0.8 1.1 0.27 0.6 0.02 Example 7 0.49 0.53 0.54 0.5 0.7 0.23 0.7 0.03 Example 8 0.68 0.32 0.39 1.2 1.5 0.03 0.8 0.06

[0069] Table 1-2. (wt%, the balance is Fe and other inevitable impurities except P and S)

[0070]

[0071]

[0072] Table 2 lists the specific process parameters of the fastener wire rods with a complex phase structure and the fasteners in the above process steps according to Examples 1-8 of the present invention.

[0073] Table 2.

[0074]

[0075] The wire rods for fasteners having a complex structure prepared in Examples 1-8 were subjected to microstructural observation according to GB / T 13298-2015 “Methods for the Examination of Metal Microstructures”. The results of the microstructural observation are listed in Table 3 below.

[0076] Table 3 lists the microstructure observation results of the wire rods for fasteners having a complex phase structure according to Examples 1-8 of the present invention.

[0077] Table 3.

[0078]

[0079] In addition, the wire rods for fasteners with a complex structure according to Examples 1-8 of the present invention were sampled again, and the wire rod samples of each example were subjected to relevant mechanical property tests. The obtained mechanical property test results are listed in Table 4. The relevant mechanical property test methods are as follows:

[0080] Mechanical properties test: Room temperature tensile test is carried out according to GB / T 228.1-2010 "Metallic materials tensile test part 1: Room temperature test method", and low temperature impact test is carried out according to GBT229-2007 "Metallic materials Charpy pendulum impact test method".

[0081] Table 4 lists the mechanical property test results of the wire rod for fasteners with a complex phase structure according to Examples 1-8 of the present invention.

[0082] Table 4.

[0083] serial number Tensile strength (MPa) Yield strength (MPa) Elongation after break (%) Example 1 1000 820 10 Example 2 1032 842 12 Example 3 1234 985 14 Example 4 1123 952 11 Example 5 1250 1140 8 Example 6 1084 873 13 Example 7 1154 912 15 Example 8 1213 1124 13

[0084] As can be seen from Table 4, the wire rods for fasteners in the embodiments of the present invention have good mechanical properties, and their mechanical properties meet the requirements of tensile strength between 1000 and 1250 MPa, yield strength between 820 and 1140 MPa, and elongation at break greater than or equal to 8%.

[0085] Furthermore, to verify the mechanical properties of the fasteners having a complex structure according to Examples 1-8 of the present invention, the inventors sampled the fasteners obtained through the above-described process steps and tested the mechanical properties of the fasteners of each example. The obtained mechanical property test results are listed in Table 5. The specific testing methods are as follows:

[0086] Tensile test: The test is carried out in accordance with the national standard GB / T 228.1-2010 "Tensile testing of metallic materials - Part 1: Room temperature test method". The specimens are processed into ASTM American M14 thread tensile specimens. The test environment is room temperature of 10-35℃.

[0087] Table 5 lists the mechanical property test results of the fasteners with complex phase structures according to Examples 1-8 of the present invention.

[0088] Table 5.

[0089]

[0090]

[0091] As can be seen in Table 5, the high-strength fasteners with a complex microstructure according to Examples 1-8 of the present invention exhibit significant advantages in mechanical properties. The high-strength fasteners with a complex microstructure according to Examples 1-8 uniformly exhibited a tensile strength greater than or equal to 1900 MPa, a yield strength greater than or equal to 1400 MPa, and a low-temperature impact energy (V-notch) greater than 50 J at -20°C.

[0092] From the above, it can be seen that compared with the bolt steel in the prior art, the high-strength fastener steel with low-strength and complex phase structure described in the present invention has very significant advantages in chemical composition design and micro-control. It can be effectively applied to bolts and related products in the fields of vehicles and ships, construction engineering, energy, bridges and transportation, and has very good promotion prospects and application value.

[0093] In addition, the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0094] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therefrom that can be directly derived from or easily conceived by those skilled in the art based on the disclosure of the present invention are intended to fall within the scope of protection of the present invention.

Claims

1. A wire rod for fasteners having a complex phase structure, comprising Fe and unavoidable impurities, characterized in that: It also contains the following chemical elements in the following mass percentages: C: 0.40~0.70wt.%, Mn: 0.30~0.70wt.%, Si: 0.10~0.70wt.%, Cr: 0.50~2.00wt.% , Mo: 0.50~2.00wt.%, Nb: 0.03~0.30wt%, V: 0.10~0.80wt%, Ti: 0.02~0.08wt.%; Its microstructure is bainite + retained austenite.

2. The wire rod for fasteners according to claim 1, wherein: The mass percentage of each chemical element is: C: 0.40~0.70wt.%, Mn: 0.30~0.70wt.%, Si: 0.10~0.70wt.%, Cr: 0.50~2.00wt.%, Mo: 0.50~2.00wt.%, Nb: 0.03~0.30wt%, V: 0.10~0.80wt%, Ti: 0.02~0.08wt.%; the balance is Fe and unavoidable impurities.

3. The wire rod for fasteners according to claim 1 or 2, wherein: It also contains 0<Al≤2.00wt.%, 0<Co≤2.00wt.%, and the mass percentage of the two satisfies Al / Co=0.8~1.

4.

4. The wire rod for fasteners according to claim 1 or 2, wherein: Among the inevitable impurities: P ≤ 0.015 wt.%, S ≤ 0.015 wt.%.

5. The wire rod for fasteners according to claim 1 or 2, wherein: The chemical elements also meet the following requirements: ln([V]+7[Ti]+11[Nb]+0.8[Mo]+1.5[Cr])≥1.35, where [V], [Ti], Substitute the values ​​before the mass percentage sign of each chemical element into [Nb], [Mo], and [Cr].

6. The wire rod for fasteners according to claim 1 or 2, wherein: The volume phase ratio of retained austenite is 5-20%.

7. The wire rod for fasteners according to claim 1 or 2, wherein: Its performance meets the following requirements: tensile strength of 1000-1250 MPa, yield strength of 820-1140 MPa, and elongation after fracture ≥8%.

8. A high-strength fastener, characterized in that: The wire rod is made from the wire rod according to any one of claims 1 to 6.

9. The high-strength fastener according to claim 8, wherein: Its tensile strength is ≥1900MPa, yield strength is ≥1400MPa, and impact energy at -20℃ is ≥50J.

10. The method for manufacturing a wire rod for a fastener according to any one of claims 1 to 7, wherein: It includes the steps of: smelting and casting; rolled into wire rod; Controlled cooling: Cool to 600-650°C at a rate of 5-20°C / s, then cool at a rate of <0.5°C / s for 500-600s.

11. The method for manufacturing a wire rod for a fastener according to claim 10, wherein: In the step of rolling into wire rod, the starting rolling temperature is controlled to be 1090-1180°C, the inlet temperature of the finishing mill is controlled to be 980-1030°C, the inlet temperature of the reducing and sizing mill is controlled to be 900-950°C, and the spinning temperature is controlled to be 840-880°C.

12. The method for manufacturing a high-strength fastener according to claim 8 or 9, wherein: Including steps: smelting and casting; rolled into wire rod; Controlled cooling: Cool to 600-650°C at a rate of 5-20°C / s, then cool at a rate of <0.5°C / s for 500-600s; Annealing and drawing; Parts shape processing; Isothermal heat treatment.

13. The manufacturing method according to claim 12, wherein: In the step of rolling into wire rod, the starting rolling temperature is controlled to be 1090-1180°C, the inlet temperature of the finishing mill is controlled to be 980-1030°C, the inlet temperature of the reducing and sizing mill is controlled to be 900-950°C, and the spinning temperature is controlled to be 840-880°C.

Images