NiCrNbN austenite heat-resistant cast steel material and preparation method thereof

Abstract

The invention relates to a NiCrNbN austenite heat-resistant cast steel material and a preparation method thereof, and belongs to the technical field of casting materials. The technical problem to be solved by the invention is to provide the NiCrNbN austenite heat-resistant cast steel material with a high strength grade in a high-temperature environment. The material is composed of the following components in percentage by weight: 0.07-0.09% of C; 0.60% to 0.80% of Si; 0.40% to 0.60% of Mn; cr: 19.00% to 22.00%; ni: 24.00% to 26.00%; 0.20% or less of Mo; 1.00% to 1.20% of Nb; 0.060% to 0.080% of N; less than or equal to 0.020% of P; less than or equal to 0.020% of S; and the balance of Fe and inevitable impurities. According to the NiCrNbN casting material, the specific chemical component proportion is adopted, the higher specific mechanical property can be guaranteed, the NiCrNbN casting material can be used under the high-temperature condition, and a new way is provided for design and material selection of steel castings of coiling drums of large steckel mills. The preparation method adopts a specific heat treatment process, the method is simple and easy to operate, and the obtained product is stable in mechanical property, reliable in quality and suitable for production of large steel castings for coiling drums of large steckel mills.

Description

TECHNICAL FIELD

[0001] The application relates to an NiCrNbN austenitic heat-resistant cast steel material and a preparation method thereof, and belongs to the technical field of cast steel materials. BACKGROUND

[0002] The mandrel mill is key equipment for producing medium plate and high-strength steel strip, and the winding drum is a core component on the production line. The winding furnace mainly functions to wind and heat the rolled piece in the reversible rolling process of the medium plate and the steel strip, and ensure the finish rolling temperature of the head and tail of the steel strip, which is crucial for ensuring the product quality. The hub is a core transmission component of the winding drum, and its working environment is extremely harsh: it is in a high-temperature environment of 750-1000 DEG C for a long time, bears a huge combined alternating load of bending and torsion, and needs to frequently bear the impact caused by forward and reverse driving. Such working conditions put extremely harsh requirements on the high-temperature strength, high-temperature persistent creep property, fatigue resistance and organizational stability of the hub material.

[0003] At present, the winding drum hub of the mandrel mill production line in many domestic plants generally adopts austenitic heat-resistant steel such as HK series in ASTM A297 standard or 310S. The manufacturing process mainly includes integral casting or forming by rolling and welding of steel plates. However, due to the limitation of the comprehensive performance of the material itself, the service life of such hub components is generally short, usually only 5 to 7 months. Frequent replacement not only greatly increases the equipment maintenance cost and shutdown loss, but also seriously affects the continuity and stability of the production line.

[0004] The main reason is that the austenitic stainless steel has a relatively high chromium-nickel equivalent, and there are a large number of delta ferrite in the original structure, and a large number of alpha phase (mainly M 23 C6 type and M6C type) and sigma phase (mainly (FeNi)2(CrMo)3) harmful phases are precipitated during high-temperature use, which reduces the strength of the material and increases the brittleness, and under the long-term harsh working conditions, the workpiece deforms, cracks or even breaks.

[0005] The main reason for the early failure of the above-mentioned material is the instability of the microstructure. The traditional austenitic stainless steel such as HK and 310S has a relatively high chromium-nickel equivalent in the chemical composition, and there are a large number of delta ferrite in the original structure. During the long-term high-temperature service of the hub, these metastable structures will further evolve, which will promote a large number of alpha phase (mainly M 23 C6 type and M6C type) and sigma phase (mainly (FeNi)2(CrMo)3) harmful phases to precipitate, which reduces the strength of the material and increases the brittleness, and under the long-term harsh working conditions, the workpiece deforms, cracks or even breaks.

[0006] In order to seek higher performance materials, the industry began to focus on some high-heat-resistant stainless steel produced by rolling process, such as the technology in the documents of patents CN105051233A, CN104169450A, CN1274865C, CN1233865C, etc. Such rolling materials usually have finer, more uniform grain structure and more excellent high-temperature mechanical properties through plastic deformation and heat treatment. However, the rolling material itself has inherent limitations: its shape complexity is low, usually only simple shapes such as plates, rods, profiles, etc. For large complex components such as the hub, if rolling materials are used for mechanical processing and manufacturing, the material utilization rate is extremely low, the processing allowance is huge, and the production cost is high. In addition, the anisotropy of the mechanical properties of the rolling material may also become a potential design hidden danger under complex stress state. Therefore, the rolling high-heat-resistant steel is not the best choice for manufacturing large complex structural parts.

[0007] In the prior art, the patent with application number 201210389339.6 discloses a high-heat-resistant cast austenitic stainless steel, which aims to improve performance through composition design (containing W, Nb, Mo and other strengthening elements). However, the carbon content of this material is relatively high (0.1-0.20%), which still tends to promote the precipitation of a large amount of carbides in high-temperature long-term service, which is not conducive to the stability of the structure and long-term durability. And its published 900℃ high-temperature yield strength (greater than 60MPa) index still needs to be further improved to meet the needs of higher load and longer design life for the aforementioned extreme working conditions.

[0008] In summary, it is necessary to develop a new type of high-heat-resistant cast austenitic stainless steel, which has the advantages of near-net-shape forming of the casting process (suitable for complex components, high material utilization rate) and more excellent high-temperature comprehensive performance (higher high-temperature strength, endurance life and excellent structure stability), thereby significantly prolonging the service life of key components such as the hub, which has become a technical problem to be solved in the field. SUMMARY

[0009] In view of the above defects, the technical problem solved by the present application is to provide a NiCrNbN austenitic heat-resistant cast steel material with high strength grade in high-temperature environment.

[0010] The NiCrNbN austenitic heat-resistant cast steel material of the present application is composed of the following components by weight percentage: C: 0.07-0.09%; Si: 0.60-0.80%; Mn: 0.40-0.60%; Cr: 19.00-22.00%; Ni: 24.00-26.00%; Mo: ≤0.20%; Nb: 1.00-1.20%; N: 0.060-0.080%; P≤0.020%; S≤0.020%; and the balance is Fe and unavoidable impurities.

[0011] In one embodiment of the present application, the mechanical properties of the NiCrNbN austenitic heat-resistant cast steel material are: R p0.2 ≥ 200 MPa, R m ≥ 400 MPa, A ≥ 10%; R p0.2 ≥ 110 MPa, R m ≥ 220 MPa, A ≥ 20%; R p0.2 ≥ 100 MPa, R m ≥ 160 MPa, A ≥ 20%; R p0.2 ≥ 60 MPa, R m ≥ 90 MPa, A ≥ 20%; R p0.2 ≥ 50 MPa, R m ≥ 65 MPa, A ≥ 20%.

[0012] In one embodiment of the present application, the microstructure of the material is a matrix austenite and a small amount of intergranular carbide. The small amount in the present application refers to less than 5% in area percentage.

[0013] The present application also provides a preparation method of the NiCrNbN austenitic heat-resistant cast steel material.

[0014] The preparation method of the NiCrNbN austenitic heat-resistant cast steel material comprises smelting, casting and heat treatment, wherein the heat treatment method is:

[0015] a. heating: heating the castings obtained after casting to 1070-1090℃;

[0016] b. holding: after heating to the temperature, the holding time is determined according to the diameter of the hottest section of the thickest part of the castings, and the holding time is 4-6h per 100mm of diameter;

[0017] c. cooling: cooling the castings after holding by immersing them in a cooling liquid until the temperature of the workpiece is ≤120℃ and then taking out for air cooling.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] The NiCrNbN cast steel material of the present application adopts a specific chemical composition ratio, which can ensure higher specific mechanical properties, R p0.2 ≥ 200 MPa, R m ≥ 400 MPa, A ≥ 10%; the NiCrNbN cast steel material can be used under high temperature conditions, R p0.2 ≥ 110 MPa, R m≥220MPa, A≥20%; when tensile test at 800℃, R p0.2 ≥100MPa, R m ≥160MPa, A≥20%; when tensile test at 900℃, R p0.2 ≥60MPa, R m ≥90MPa, A≥20%; when tensile test at 1000℃, R p0.2 ≥50MPa, R m ≥65MPa, A≥20%; it provides a new way for designing and selecting material of large-scale furnace roll mill coiling cylinder cast steel.

[0020] The preparation method of the NiCrNbN cast steel material adopts specific heat treatment process, and has the advantages of simple method, easy operation, stable mechanical properties of the obtained product, reliable quality and suitability for the production of large-scale cast steel for large-scale furnace roll mill coiling cylinder. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The metallographic micrograph of the NiCrNbN austenitic heat-resistant cast steel material prepared in Example 1 of the present application.

[0022] Figure 2 The metallographic micrograph of the NiCrNbN austenitic heat-resistant cast steel material prepared in Example 2 of the present application. DETAILED DESCRIPTION

[0023] The NiCrNbN austenitic heat-resistant cast steel material of the present application is composed of the following components by weight percentage: C: 0.07-0.09%; Si: 0.60-0.80%; Mn: 0.40-0.60%; Cr: 19.00-22.00%; Ni: 24.00-26.00%; Mo: ≤0.20%; Nb: 1.00-1.20%; N: 0.060-0.080%; P≤0.020%; S≤0.020%; and the rest is Fe and inevitable impurities.

[0024] The NiCrNbN austenitic heat-resistant cast steel material of the present application reduces the carbon content and quantitatively matches the Nb element, one of the strong carbide forming elements, to inhibit the M 23C6 precipitates in the intergranular, through appropriate element ratio, improves the precipitation behavior of harmful phase α during the high temperature use of the workpiece, and enhances the high temperature strength and the endurance and creep strength of the material. The material uses low silicon, no tungsten, boron, aluminum and titanium, has less alloying elements, reduces the smelting difficulty of the molten steel and the forming difficulty of the casting (reduces the cracking risk), and is also beneficial to the repair and repair welding of casting defects; the hot working process is good, the low chromium content (reduces the risk of σ brittleness), also reduces the forming difficulty of the casting (reduces the cracking risk), and is also beneficial to the repair and repair welding of casting defects. The less alloying elements also reduce the cost to some extent.

[0025] The NiCrNbN austenitic heat-resistant cast steel material has the following characteristics:

[0026] 1) The material has high temperature strength, high temperature endurance performance and process performance as ordinary austenitic stainless steel;

[0027] 2) The material has low chromium-nickel equivalent, and the risk of δ ferrite in the original structure of the material is small;

[0028] 3) The carbon content in the material chemical composition is low, and one of the strong carbide forming elements Nb elements is quantitatively matched to inhibit M 23 C6 precipitates in the intergranular, improves the precipitation behavior of α phase during the high temperature use of the workpiece.

[0029] 4) The high Nb element in the material chemical composition enhances the high temperature strength and endurance and creep strength of the material.

[0030] 5) The high nitrogen content in the material chemical composition can not only replace the role of nickel element, but also can be solid solution strengthening to improve the strength and endurance performance of the material.

[0031] In an embodiment of the present application, the mechanical properties of the NiCrNbN austenitic heat-resistant cast steel material are as follows: when the room temperature tensile test is performed, R p0.2 ≥ 200 MPa, R m ≥ 400 MPa, A ≥ 10%; when the 700℃ tensile test is performed, R p0.2 ≥ 110 MPa, R m ≥ 220 MPa, A ≥ 20%; when the 800℃ tensile test is performed, R p0.2 ≥ 100 MPa, R m ≥ 160 MPa, A ≥ 20%; when the 900℃ tensile test is performed, R p0.2 ≥ 60 MPa, R m ≥ 90 MPa, A ≥ 20%; when the 1000℃ tensile test is performed, R p0.2 ≥ 50 MPa, R m ≥ 65 MPa, A ≥ 20%.

[0032] wherein R p0.2 , R m , A, Z are terms in GB / T 228, R p0.2 is the yield strength at a specified plastic elongation of 0.2%; R m is the tensile strength; A is the elongation at break of an original gauge length of 50 mm; Z is the reduction of area. The room temperature test refers to the standard GB / T 228.1-2021 "Metallic Materials-Tensile Testing-Part 1: Method of Room Temperature Test"; the 700℃, 800℃, 900℃, 1000℃ tensile test refers to the standard GB / T 228.2-2015 "Metallic Materials-Tensile Testing-Part 2: Method of High Temperature Test".

[0033] In an embodiment of the present application, the microstructure of the material is a matrix austenite and a small amount of intergranular carbide. The small amount in the present application refers to less than 5% in area percentage, which is obtained by observing the two-dimensional section of the material through a microscope and quantitatively calculated through image analysis.

[0034] The present application also provides a preparation method of the NiCrNbN austenitic heat-resistant cast steel material.

[0035] The preparation method of the NiCrNbN austenitic heat-resistant cast steel material comprises smelting, casting and heat treatment, wherein the heat treatment method is:

[0036] a. heating: heating the castings obtained after casting to 1070℃-1090℃;

[0037] b. holding: after heating to the temperature, the holding time is determined according to the diameter of the hottest section at the thickest part of the castings, and the holding time is 4-6h per 100mm of diameter;

[0038] c. cooling: cooling the castings after holding by immersing them in a cooling liquid until the workpiece temperature is ≤120℃ and then taking them out for air cooling.

[0039] The preparation method of the NiCrNbN austenitic heat-resistant cast steel material, by specific alloy element collocation, at the same time, the holding time is calculated by a specific method, so that the holding temperature of heat treatment is appropriately reduced, thereby reducing the damage and consumption of the heat treatment heating furnace, and saving energy. The determination method of heating and holding time ensures the heat penetration of the thick part of the large castings, and fully ensures the overall heat treatment quality of the castings; the heat treatment cooling method can better ensure the uniform cooling of the large castings, and at the same time, avoid cracks in the heat treatment cooling process.

[0040] The specific embodiments of the present application are further described below in conjunction with examples, and the present application is not limited in the scope of the described examples.

[0041] Example 1

[0042] The steel is smelted according to the following components, and the specific components are shown in Table 1, and then cast, and the sand castings 1 after casting are heat treated, the heat treatment process is that the castings are heated to a temperature range of 1070-1090℃, the holding time is calculated according to the maximum hot section circle diameter (mm) / 100x4, and the holding time is 10 hours, and the castings are immersed into the quenching liquid within 5 minutes after being discharged to cool to a workpiece temperature ≤120℃, and then taken out for air cooling, to obtain the NiCrNbN austenitic heat-resistant cast steel material. The metallographic structure of the material is shown in Figure 1 .

[0043] It can be seen from Figure 1 that the heat-resistant cast steel material obtained in the embodiment has an organization composed of austenite and 4% intergranular carbides.

[0044] The mechanical properties are detected, and the results are shown in Table 3.

[0045] Table 1 Chemical composition of the material (wt. %)

[0046]

[0047] Example 2

[0048] The steel is smelted according to the following components, and the specific components are shown in Table 2, and then cast, and the sand castings 2 after casting are heat treated, the heat treatment process is that the castings are heated to a temperature range of 1070-1090℃, the holding time is calculated according to the maximum hot section circle diameter (mm) / 100x6, and the holding time is 14 hours, and the castings are immersed into the quenching liquid within 5 minutes after being discharged to cool to a workpiece temperature ≤120℃, and then taken out for air cooling, to obtain the NiCrNbN austenitic heat-resistant cast steel material. The microstructure of the material is shown in Figure 2 .

[0049] It can be seen from Figure 2 that the heat-resistant cast steel material obtained in the embodiment has an organization composed of austenite and 2.5% intergranular carbides.

[0050] The mechanical properties are detected, and the results are shown in Table 3.

[0051] Table 2 Chemical composition of the material (wt. %)

[0052]

[0053] Comparative Example 1 (low solid solution temperature)

[0054] The same as example 1, only the solution temperature of the heat treatment process is different, and the heat treatment process is as follows: the cast piece 3 is heated to a temperature range of 1040-1060 DEG C, the holding time is calculated according to the maximum hot circle diameter (mm) / 100x4, and the holding time is 10 hours, the cast piece is immersed in a quenching liquid within 5 minutes after being taken out of the furnace, and is cooled to a workpiece temperature of less than or equal to 120 DEG C, and then is taken out and air-cooled, so as to obtain a NiCrNbN austenitic heat-resistant cast steel material. The mechanical properties are detected, and the results are shown in Table 3.

[0055] Comparative example 2 (high solution temperature)

[0056] The same as example 1, only the solution temperature of the heat treatment process is different, and the heat treatment process is as follows: the cast piece 4 is heated to a temperature range of 1091-1110 DEG C, the holding time is calculated according to the maximum hot circle diameter (mm) / 100x4, and the holding time is 10 hours, the cast piece is immersed in a quenching liquid within 5 minutes after being taken out of the furnace, and is cooled to a workpiece temperature of less than or equal to 120 DEG C, and then is taken out and air-cooled, so as to obtain a NiCrNbN austenitic heat-resistant cast steel material. The mechanical properties are detected, and the results are shown in Table 3.

[0057] Table 3 Mechanical properties

[0058]

[0059] From the above examples, it can be seen that the NiCrNbN cast piece material obtained by the method has stable mechanical properties and good heat resistance, and can be used for the production of large-scale cast steel pieces for a large-scale furnace and rolling mill coiling drum.

Claims

1. Austenitic heat-resistant cast steel material of the type NiCrNbN, characterised in that: consists of the following components in weight percentage Composition: C: 0.07~0.09%; Si: 0.60~0.80%; Mn: 0.40~0.60%; Cr: 19.00~22.00%; Ni: 24.00~26.00%; Mo: ≤0.20%; Nb: 1.00~1.20%; N: 0.060~0.080%; P ≤0.020%; S ≤0.020%; the rest is Fe and inevitable impurities.

2. The NiCrNbN austenitic heat-resistant cast steel material according to claim 1, characterized in that: The mechanical properties are as follows: at room temperature, R p0.2 ≥ 200 MPa, R m ≥ 400 MPa, A ≥ 10%; at 700°C, R p0.2 ≥ 110 MPa, R m ≥ 220 MPa, A ≥ 20%; at 800°C, R p0.2 ≥ 100 MPa, R m ≥ 160 MPa, A ≥ 20%; at 900°C, R p0.2 ≥ 60 MPa, R m ≥ 90 MPa, A ≥ 20%; at 1000°C, R p0.2 ≥ 50 MPa, R m ≥ 65 MPa, A ≥ 20%.

3. The NiCrNbN austenitic heat-resistant cast steel material according to claim 1, characterized in that: The microstructure of the material is matrix austenite and a small amount of intergranular carbide, the amount being less than 5% in area percentage.

4. A method for producing the NiCrNbN austenitic heat-resistant cast steel material according to any one of claims 1 to 3, comprising smelting, casting and heat treatment, characterized in that: The heat treatment method is: a. heating: heating the casting obtained after casting to 1070~1090℃; b. holding: after heating to the temperature, the holding time is determined according to the diameter of the hottest section at the thickest part of the casting, the holding time being 4~6h per 100mm of diameter; c. cooling: after holding, the casting is immersed in a cooling liquid to cool until the workpiece temperature is ≤120℃ and then taken out for air cooling.

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