High nitrogen austenitic valve steel wire and method for manufacturing the same

Abstract

The application belongs to the field of metallurgy, and discloses a high-nitrogen austenitic gas valve steel wire rod and a manufacturing method thereof. The manufacturing method comprises the following steps: heating a 21-4N initial-rolled square billet after being ground; sequentially performing rough rolling, medium rolling, fine rolling and high-speed water-penetrating rolling on the heated 21-4N initial-rolled square billet to obtain a wire rod; and performing yarn laying and air cooling on the wire rod to obtain a disc round product. The application adopts a high-temperature soaking mode to heat the rolled steel billet, and reduces the temperature difference between the inside and outside of the rolled steel billet during rolling, thereby improving the hot working plasticity of the 21-4N, avoiding the generation of disc round surface cracks, and improving the disc round surface quality. The high-speed wire rod adopts water-penetrating temperature control rolling, and the yarn laying is followed by air cooling for rapid cooling, so as to ensure that the internal grain size and lamellar precipitates of the wire rod are qualified.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy, and particularly relates to a high-nitrogen austenitic valve steel wire and its manufacturing method. Background Technology

[0002] The steel used in this invention is 53Cr21Mn9Ni4N (abbreviated as 21-4N), containing 0.48-0.58% C, 20.0-22.0% Cr, 8.0-10.0% Mn, 3.25-4.5% Ni, and 0.35-0.50% N. This steel is mainly hardened by carbide and nitride precipitation, and has high strength, toughness, and wear resistance at a service temperature of 700℃. It also has structural stability and oxidation resistance under thermal cycling. Due to its excellent performance, it is a very important material for engine exhaust valves. However, because this steel is a high-carbon, high-chromium, high-manganese, and nitrogen-containing steel, and requires C+N≥0.90%, it has poor thermoplasticity and a narrow hot deformation temperature range. Surface cracks are prone to occur during wire rolling, leading to scrap. Furthermore, if the cooling rate is low between 1050 and 750℃, layered precipitates are likely to occur, resulting in scrap.

[0003] In the existing technology, 21-4N wire rod is produced in small coils using small rolling mills. The coil weight is small, the production efficiency is low, and the phenomena of mixed crystals and excessive layered precipitates occur from time to time, making the quality uncontrollable. Large coils of 21-4N wire rod are produced using bar and wire rod mills. The coil weight is large and the production efficiency is high, but the finished coil surface is prone to surface cracks, large grain size differences (mixed crystals), and excessive layered precipitates still exist.

[0004] Currently, there is very little research in China on the manufacturing method of high-nitrogen austenitic valve steel 21-4N wire. Therefore, it is necessary to provide a high-nitrogen austenitic valve steel wire and its manufacturing method to solve the problems of surface cracks, large grain size differences, and excessive layered precipitates on the finished coil of 21-4N wire. Summary of the Invention

[0005] In order to overcome the defects of the existing technology, the present invention aims to provide a high-nitrogen austenitic valve steel wire and its manufacturing method, and solve the problems of surface cracks, large grain size differences, and excessive layered precipitates on the finished coil of 21-4N wire.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for manufacturing high-nitrogen austenitic valve steel wire includes the following steps:

[0008] The 21-4N primary rolled square billet after grinding was heated;

[0009] The heated 21-4N primary rolled square billet is subjected to rough rolling, intermediate rolling, finish rolling and high-speed wire rod water-cooled rolling in sequence to obtain wire rod;

[0010] The wire is coiled and air-cooled to obtain a finished coiled product.

[0011] Further, the 21-4N primary rolled square billet after grinding is heated, including:

[0012] The 21-4N primary rolled square billet after grinding is heated to 1190-1210℃ using a step heating method and held at that temperature for more than 1.0 hour.

[0013] Furthermore, the refurbished 21-4N primary rolled square billet is heated to 1190-1210℃ using a step-by-step heating method, including:

[0014] The total heating time for step heating is controlled to be more than 3 hours.

[0015] Further, the heated 21-4N primary rolled square billet is subjected to rough rolling, intermediate rolling, finish rolling, and high-speed wire rod water-cooled rolling to obtain wire rod, including:

[0016] Before rough rolling the heated 21-4N primary rolled square billet, turn off the high-pressure water descaling of the rough rolling mill and turn on the iron oxide scale removal device of the rough rolling mill.

[0017] When performing intermediate rolling, finishing rolling, and high-speed wire rod water rolling on the rough-rolled round billet, reduce the cooling water of the rolling mill and reheat the rough-rolled round billet.

[0018] Furthermore, the heated 21-4N primary rolled square billet is sequentially subjected to rough rolling, intermediate rolling, finish rolling, and high-speed wire rod water-cooled rolling to obtain wire rod, which also includes:

[0019] The 180mm*180mm initial rolled square billet is rolled into a Φ100mm round billet through rough rolling;

[0020] A Φ100mm round billet is rolled into a Φ40mm round billet by intermediate rolling.

[0021] A Φ40mm round billet is rolled into a Φ16-20mm round billet through precision rolling;

[0022] Φ16-20mm round billets are rolled into Φ5.5-15mm wire rods by high-speed wire rod water rolling.

[0023] Furthermore, the Φ16-20mm round billet is rolled into Φ5.5-15mm wire rod through high-speed wire rod water-cooled rolling, including:

[0024] The billet temperature before entering the TMB rack is controlled at 1030-1050℃.

[0025] Further, the wire is coiled and air-cooled to obtain a finished coiled product, including:

[0026] The spinning temperature should be controlled between 800℃ and 850℃.

[0027] Furthermore, the process of spinning the wire into coils and air-cooling it to obtain a finished coiled product also includes:

[0028] After the blank is spun into a coil, it is cooled to below 100°C and then coiled and collected into rolls.

[0029] Furthermore, the mass percentages of each element in the 21-4N primary rolled square billet are: 0.48-0.58% C, 20.0-22.0% Cr, 8.0-10.0% Mn, 3.25-4.5% Ni, and 0.35-0.50% N.

[0030] On the other hand, the present invention also discloses a high-nitrogen austenitic valve steel wire, which is prepared by the above-described method.

[0031] The technical effects and advantages of this invention are as follows:

[0032] This invention uses a high-temperature homogenization heating method to heat the rolled steel billet, while reducing the temperature difference between the inside and outside of the rolled steel billet during the rolling process, improving the hot working plasticity of 21-4N, avoiding surface cracks in the coil, and improving the surface quality of the coil; the high wire rod of this invention adopts water-cooled temperature control rolling, and is rapidly cooled by air cooling after wire drawing, thereby ensuring that the internal grain size and layered precipitates of the wire rod are qualified.

[0033] The 21-4N finished wire obtained by the method of the present invention has a grain size of 7-10 according to the GB / T6394 rating requirements, a grain size difference of no more than 3 levels in the same field of view, ≤10% of layered precipitates, uniform structure without twins, and no surface defects such as cracks or laps.

[0034] The 21-4N finished wire rod produced by this invention has a hot-rolled black skin state delivery hardness ≤380HBS. The decarburization layer is measured according to GB224-87, and the decarburization layer is not greater than 0.1mm. The qualified grade of the acid-etched low-magnification structure meets the following requirements: general porosity ≤2 grade, central porosity ≤2 grade, segregation ≤2 grade.

[0035] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0036] Figure 1This is a flowchart illustrating a method for manufacturing a high-nitrogen austenitic valve steel wire according to the present invention.

[0037] Figure 2 This is a schematic diagram of the high-nitrogen austenitic valve steel wire product from Example 1;

[0038] Figure 3 This is a schematic diagram of the high-nitrogen austenitic valve steel wire product of Example 2. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Figure 1 This is a flowchart of a method for manufacturing a high-nitrogen austenitic valve steel wire according to the present invention, as shown below. Figure 1 As shown, the present invention provides a method for manufacturing high-nitrogen austenitic valve steel wire, comprising the following steps:

[0041] The 21-4N primary rolled square billet after grinding was heated;

[0042] The heated 21-4N primary rolled square billet is subjected to rough rolling, intermediate rolling, finish rolling and high-speed wire rod water-cooled rolling in sequence to obtain wire rod;

[0043] The wire is coiled and air-cooled to obtain a finished coiled product.

[0044] Furthermore, when heating the 21-4N primary rolled square billet after grinding, a step heating method is used to heat the 21-4N primary rolled square billet to 1190-1210℃ and hold it at that temperature for more than 1.0 hour.

[0045] Furthermore, when the 21-4N primary rolled square billet is heated to 1190-1210℃ using step heating, the total heating time of step heating is controlled to be more than 3 hours to ensure that the 21-4N primary rolled square billet is thoroughly and evenly heated.

[0046] Furthermore, before rough rolling the heated 21-4N pre-rolled square billet, the high-pressure water descaling of the roughing mill is turned off, and water can be intermittently supplied to cool the rolls. The iron oxide scale removal device of the roughing mill is turned on, with only air supply and no water supply. When the round billet after rough rolling is subjected to intermediate rolling, finishing rolling and sizing reduction rolling, the cooling water of the mill is reduced, and the round billet after rough rolling is reheated. This reduces the surface cooling of the billet, reduces the temperature difference between the inside and outside of the billet, and ensures the heat workability of the rolled product and the surface quality of the wire rod.

[0047] Furthermore, when the heated 21-4N primary rolled square billet is subjected to rough rolling, intermediate rolling, finish rolling and high-speed wire rod water-cooled rolling in sequence, the 180mm*180mm primary rolled square billet is rolled into a Φ100mm round billet through rough rolling; the Φ100mm round billet is rolled into a Φ40mm round billet through intermediate rolling; the Φ40mm round billet is rolled into a Φ16-20mm round billet through finish rolling; and the Φ16-20mm round billet is rolled into a pressed Φ5.5-15mm wire rod through high-speed wire rod water-cooled rolling.

[0048] Furthermore, when rolling Φ16-20mm round billets into Φ5.5-15mm wire rods by high-speed wire rod water rolling, the billet temperature before entering the TMB stand is controlled at 1030~1050℃.

[0049] Furthermore, when the wire is coiled and air-cooled to obtain the finished coil, the coiling temperature is controlled at 800℃~850℃, and the coiled blank is air-cooled to below 100℃ before being coiled and collected into rolls.

[0050] Furthermore, the mass percentages of each element in the 21-4N primary rolled square billet are: 0.48-0.58% C, 20.0-22.0% Cr, 8.0-10.0% Mn, 3.25-4.5% Ni, and 0.35-0.50% N.

[0051] On the other hand, the present invention also discloses a high-nitrogen austenitic valve steel wire, which is prepared by the above-described method.

[0052] Example 1

[0053] The method described in this invention is used to produce 21-4N Φ6.0mm wire rod with heat number 121F-3567. The billet used for rolling is a 180 square initial rolled billet that has been ground. The actual process of rolling the wire rod is as follows:

[0054] S1. The 21-4N primary rolled square billet after grinding was heated by a walking beam furnace. The heating parameters of the walking beam furnace are shown in Table 1.

[0055] Table 1

[0056]

[0057] S2. The heated 180 square millimeter initial rolled billet is subjected to rough rolling, intermediate rolling, finish rolling and sizing rolling in sequence. Before rolling, the high-pressure water descaling is turned off and the iron oxide scale removal device of the rough rolling mill is turned on (only air is turned on); the head of the billet is rolled in water-closed rolling on the roughing mill, and the cooling water of the intermediate, finish and sizing mills is turned off; the roller table heating device (with heat insulation cover) is turned on after the roughing mill and before the intermediate mill. The 180 square millimeter initial rolled billet needs to be rolled by 35 stands of the bar and wire rod mill. It is rolled into a Φ100mm round billet by the initial rolling mill, into a Φ40mm round billet by the intermediate rolling mill, and into a Φ16mm round billet by the finish rolling mill.

[0058] S3. The Φ16mm round billet rolled by the finishing mill is subjected to high-speed wire rod water quenching to obtain Φ6.0mm wire rod. The water quenching parameters of water tanks 1#, 3#, and 4# and the temperature control of thermometers GW11 and GW14 are shown in Table 2.

[0059] Table 2

[0060]

[0061] S4. The wire is coiled and air-cooled. All 11 fans are turned on and the wire is cooled to 25-65℃ before being collected into coils.

[0062] The metallographic and low-magnification test results of the high-nitrogen austenitic valve steel wire prepared in Example 1 are shown in Table 3, the longitudinal mechanical properties are shown in Table 4, and the measured values ​​of the shape deviation are shown in Table 5.

[0063] Table 3

[0064]

[0065] Table 4

[0066]

[0067] Table 5

[0068] Furnace number Nominal diameter (mm) Diameter tolerance (mm) Out-of-roundness (mm) 121F-3567 φ6.0 0.13 0.06 Standard requirements φ5.5~8 0～+0.15 Not exceeding 1 / 2 of the dimensional tolerance

[0069] The metallographic and low-magnification test results, longitudinal mechanical properties, and measured shape deviations of the high-nitrogen austenitic valve steel wire prepared in this embodiment all meet the standard requirements. Figure 2 This is a schematic diagram of the high-nitrogen austenitic valve steel wire product from Example 1, as shown below. Figure 2 As shown, the wire rod surface is well-finished, with no cracks, folds, scars, or inclusions.

[0070] Example 2

[0071] The method described in this invention is used to produce 21-4N Φ7.0mm wire rod with heat number 121F-3567. The billet used for rolling is a 180 square initial rolled billet that has been ground. The actual process of rolling the wire rod is as follows:

[0072] S1. The 21-4N primary rolled square billet after grinding was heated by a walking beam furnace. The heating parameters of the walking beam furnace are shown in Table 6.

[0073] Table 6

[0074]

[0075] S2. The heated 180 square millimeter initial rolled billet is subjected to rough rolling, intermediate rolling, finish rolling and sizing rolling in sequence. Before rolling, the high-pressure water descaling is turned off and the iron oxide scale removal device of the rough rolling mill is turned on (only air is turned on); the head of the billet is rolled in water-closed rolling on the roughing mill, and the cooling water of the intermediate, finish and sizing mills is turned off; the roller table heating device (with heat insulation cover) is turned on after the roughing mill and before the intermediate mill. The 180 square millimeter initial rolled billet needs to be rolled by 35 stands of the bar and wire rod mill. It is rolled into a Φ100mm round billet by the initial rolling mill, into a Φ40mm round billet by the intermediate rolling mill, and into a Φ16mm round billet by the finish rolling mill.

[0076] S3. The Φ16mm square billet rolled by the finishing mill is subjected to high-speed wire rod water quenching to obtain Φ7.0mm wire rod. The water quenching parameters of water tanks 1#, 3#, and 4# and the temperature control of thermometers GW11 and GW14 are shown in Table 7.

[0077] Table 7

[0078]

[0079] S4. The wire is coiled and air-cooled. All 11 fans are turned on and the wire is cooled to 25-70℃ before being collected into coils.

[0080] The metallographic and low-magnification test results of the high-nitrogen austenitic valve steel wire prepared in Example 2 are shown in Table 8, the longitudinal mechanical properties are shown in Table 9, and the measured values ​​of the shape deviation are shown in Table 10.

[0081] Table 8

[0082]

[0083] Table 9

[0084]

[0085]

[0086] Table 10

[0087] Furnace number Nominal diameter (mm) Diameter tolerance (mm) Out-of-roundness (mm) 122F-15 φ7.0 0.14 0.06 Standard requirements φ5.5~8 0～+0.15 Not exceeding 1 / 2 of the dimensional tolerance

[0088] The metallographic and low-magnification test results, longitudinal mechanical properties, and measured shape deviations of the high-nitrogen austenitic valve steel wire prepared in this embodiment all meet the standard requirements. Figure 3 This is a schematic diagram of the high-nitrogen austenitic valve steel wire product from Example 2, as shown below. Figure 3 As shown, the wire rod surface is well-finished, with no cracks, folds, scars, or inclusions.

[0089] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of manufacturing a high nitrogen austenitic gas valve steel wire, characterized by, The method includes the following steps: The 21-4N primary rolled square billet after grinding is heated. The mass percentage of each element in the 21-4N primary rolled square billet is: 0.48-0.58% C, 20.0-22.0% Cr, 8.0-10.0% Mn, 3.25-4.5% Ni, and 0.35-0.50% N. The heated 21-4N primary rolled square billet is subjected to rough rolling, intermediate rolling, finish rolling and high-speed wire rod water-cooled rolling in sequence to obtain wire rod; The wire is coiled and air-cooled to obtain a coiled finished product; The heating of the 21-4N primary rolled square billet after grinding includes: The 21-4N primary rolled square billet after grinding is heated to 1190-1210℃ using a step heating method. The total heating time of the step heating method is controlled to be more than 3 hours, and the temperature is kept at that temperature for more than 1.0 hour. The process of sequentially roughing, intermediate rolling, finishing, and high-speed water-cooled rolling of the heated 21-4N primary billet to obtain wire rod includes: Before rough rolling the heated 21-4N primary rolled square billet, turn off the high-pressure water descaling of the rough rolling mill and turn on the iron oxide scale removal device of the rough rolling mill. When performing intermediate rolling, finishing rolling and high-speed wire rod water rolling on the rough rolled round billet, reduce the cooling water of the rolling mill and reheat the rough rolled round billet. The process of sequentially performing rough rolling, intermediate rolling, finish rolling, and high-speed wire rod water-cooled rolling on a heated 21-4N primary billet to obtain wire rod also includes: The 180 mm The 180 mm bloom is rolled into a Φ100 mm round billet; A Φ100mm round billet is rolled into a Φ40mm round billet by intermediate rolling. A Φ40mm round billet is rolled into a Φ16-20mm round billet through precision rolling; Φ16-20mm round billets are rolled into Φ5.5-15mm wire rods by high-speed wire rod water-cooled rolling. The method of rolling Φ16-20mm round billets into Φ5.5-15mm wire rods by high-speed wire rod water-cooled rolling includes: The billet temperature before entering the TMB rack is controlled at 1030-1050℃; The process of spinning the wire into coils and air-cooling to obtain a coiled finished product includes: The spinning temperature should be controlled between 800℃ and 850℃; After the blank is spun into a coil, it is cooled to below 100°C and then coiled and collected into rolls.

2. A high nitrogen austenitic gas valve steel wire, characterized in that The high-nitrogen austenitic valve steel wire is prepared by the method described in claim 1.

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