Heat treatment method for niobium-containing austenitic stainless steel hot-rolled medium plate used at high temperature

Abstract

The invention relates to a heat treatment method of a niobium-containing austenitic stainless steel hot-rolled medium plate for high temperature use, which is characterized in that a steel plate is rapidly heated to 1221-1235 DEG C within 10 minutes, so that NbC or Nb (CN) nanoscale precipitated phases in the full thickness range of the steel plate are almost dissolved at the same time, and uniform growth of crystal grains in the full thickness range of the steel plate is realized; and the control target that the grain size is controlled to be 3-6 levels is achieved in combination with short heat preservation time, and the strict requirements for short-time high-temperature mechanical performance and high-temperature long-time performance of niobium-containing austenitic stainless steel in part of high-temperature application fields are met.

Description

Technical Field

[0001] The invention relates to the technical field of steel materials, and in particular to a heat treatment method for hot-rolled medium and thick plates of niobium-containing austenitic stainless steel for high-temperature use. Background Art

[0002] On the basis of austenitic stainless steel, a certain amount of Nb element is added, such as 347, 316Nb, 309Nb, 310Nb and other austenitic stainless steels, which can fix the C element in austenitic stainless steel in NbC or Nb(CN), significantly improving the intergranular corrosion resistance of austenitic stainless steel. At the same time, the nano-sized NbC or Nb(CN) precipitated in the austenite matrix hinders the movement of dislocations, improving the precipitation strengthening effect and creep resistance. According to the equal strength temperature theory, the coarser the grains, the fewer the grain boundaries, and the better the high temperature and long-term performance. When the grains are fine, good short-term high temperature yield strength can be obtained. When the grain size is controlled to level 3-6, good short-term high temperature mechanical properties and high temperature and long-term performance can be obtained. However, due to the pinning effect of NbC or Nb(CN) nano-scale precipitates, the grain size of hot-rolled medium and thick plates of niobium-containing austenitic stainless steel obtained by conventional heat treatment process is generally fine-grained, mixed-grained or uniformly large-grained (0-2 levels). It is difficult to control the grain size to 3-6 levels, which limits the application of niobium-containing austenitic stainless steel in high temperature resistant fields.

[0003] In order to obtain niobium-containing austenitic stainless steel with relatively coarse grains, patent CN114643282A discloses a rolling method for controlling the grain size of heat-resistant 347H stainless steel medium plate. The rolled grain of 347H stainless steel medium plate is controlled to level 5-7 by optimizing the hot rolling process. However, this method has strict requirements on the equipment conditions for medium and thick plates, and the grain size of 5-7 cannot meet the stringent requirements of some high-temperature application fields for the high-temperature and long-term performance of niobium-containing austenitic stainless steel.

[0004] The present invention proposes to raise the temperature of the steel plate to a temperature far higher than the dissolution temperature of the NbC or Nb(CN) precipitated phase in a very short time, so that the NbC or Nb(CN) nano-scale precipitated phase in the full thickness of the steel plate is dissolved almost simultaneously, thereby achieving uniform grain growth in the full thickness of the steel plate. Combined with a shorter holding time, the grain size is controlled within the control target of 3-6 levels, meeting the stringent requirements of some high-temperature application fields on the short-term high-temperature mechanical properties and high-temperature long-term performance of niobium-containing austenitic stainless steel. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems and provide a method for heat treatment of hot-rolled medium and thick plates of niobium-containing austenitic stainless steel for high temperature use.

[0006] The object of the present invention is achieved as follows: A method for heat treatment of niobium-containing austenitic stainless steel hot-rolled medium and thick plates for high-temperature use comprises the following steps: Step 1: Preparation of hot-rolled steel plates: preparing stainless steel hot-rolled medium and thick plates, and the stainless steel hot-rolled medium and thick plates need to be uniformly organized over the entire thickness range; Step 2: placing the stainless steel hot-rolled medium and thick plates in a preheating section of a continuous heat treatment furnace, and controlling the temperature at 860-880°C. After the plate temperature reaches 860-880°C, the steel plates are transported to a heat preservation section through a roller; Step 3: controlling the temperature of the heat preservation section of the continuous heat treatment furnace at 1221-1235°C, and the plate temperature of the stainless steel hot-rolled medium and thick plates reaches 1221-1235°C within 10 minutes; Step 4: after the temperature of the stainless steel hot-rolled medium and thick plates reaches 1221-1235°C, they are kept warm for 3-9 minutes, and then immediately taken out of the furnace and water-cooled.

[0007] The chemical composition and weight percentage of stainless steel hot-rolled medium and thick plates are: C: 0.04%~0.10%, Si≤1.0%, Mn≤2.0%, Cr: 16.0%~26%, Ni: 9.0%~45.0%, P≤0.040%, S≤0.030%, N≤0.40%, Mo≤3.0%, 1.10≥Nb≥8C.

[0008] The beneficial effects of the present invention are as follows: the present invention proposes to raise the temperature of the steel plate to a temperature far higher than the dissolution temperature of the NbC or Nb(CN) precipitated phase in a very short time, so that the NbC or Nb(CN) nano-scale precipitated phase in the full thickness of the steel plate is dissolved almost simultaneously, thereby achieving uniform grain growth in the full thickness of the steel plate, and combining with a shorter holding time to achieve the goal of controlling the grain size at level 3-6, thereby meeting the stringent requirements of some high-temperature application fields on the short-term high-temperature mechanical properties and high-temperature long-term performance of niobium-containing austenitic stainless steel.

[0009] Compared with the existing traditional heat treatment technology of 1050-1200℃ and 1-10min / mm thickness, it solves the problems of grain size of steel plate, fine grain, mixed grain or uniform large grain (0-2 level), and the heat treatment efficiency has been greatly improved. Compared with the method of patent CN114643282A, it has lower requirements on rolling mill equipment, and the obtained grains are coarser and can reach level 3-6, which meets the stringent requirements of some high-temperature application fields for short-term high-temperature mechanical properties and long-term high-temperature performance of niobium-containing austenitic stainless steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention will be further described below in conjunction with the accompanying drawings.

[0011] Figure 1 This is a hot-rolled grain structure diagram of a steel plate according to an embodiment of the present invention.

[0012] Figure 2 This is a diagram showing the effect of the first embodiment of the present invention.

[0013] Figure 3 This is a hot-rolled grain structure diagram of the steel plate of Example 2 of the present invention.

[0014] Figure 4 This is a diagram showing the effect of the second embodiment of the present invention. DETAILED DESCRIPTION

[0015] On the basis of austenitic stainless steel, a certain amount of Nb element is added, such as 347, 316Nb, 309Nb, 310Nb and other austenitic stainless steels, which can fix the C element in austenitic stainless steel in NbC or Nb(CN). The nano-sized NbC or Nb(CN) seriously hinders the movement of dislocations and grain boundaries. When the heat treatment temperature is low, due to the pinning effect of the precipitated phase, the grains cannot grow, and generally the steel plate has fine grains of 8-10 levels. When the heat treatment temperature is high and exceeds the dissolution temperature of NbC or Nb(CN), due to the difference in the dissolution of niobium compounds at different thicknesses, mixed crystals are easily caused. After a long period of heat preservation, the steel plate has uniform coarse grains (0-2 levels).

[0016] The present invention raises the temperature of the steel plate to a temperature far higher than the dissolution temperature (1160°C) of the NbC or Nb(CN) precipitation phase in a very short time, so that the NbC or Nb(CN) nano-scale precipitation phases in the full thickness of the steel plate are dissolved almost simultaneously, so that the grains in the full thickness of the steel plate can grow evenly. The grains grow faster under high temperature conditions, combined with a shorter holding time, to achieve the control target of controlling the grain size at level 3-6. It meets the stringent requirements of some high-temperature application fields for the short-term high-temperature mechanical properties and high-temperature long-term performance of niobium-containing austenitic stainless steel.

[0017] The present invention discloses a method for heat treatment of hot-rolled medium and thick plates of niobium-containing austenitic stainless steel for high-temperature use. The method rapidly heats the steel plate to 1221-1235°C within 10 minutes, so that the NbC or Nb (CN) nano-scale precipitates in the entire thickness of the steel plate are dissolved almost simultaneously, thereby achieving uniform grain growth in the entire thickness of the steel plate. Combined with a shorter insulation time, the grain size is controlled within the range of 3-6, thereby meeting the stringent requirements of some high-temperature application fields for the short-term high-temperature mechanical properties and long-term high-temperature performance of niobium-containing austenitic stainless steel. The specific technical scheme is as follows: (1) Preparation of hot-rolled steel plate: prepare hot-rolled stainless steel plate, and the structure of the steel plate must be uniform throughout the thickness. (2) Place the hot-rolled steel plate in the preheating section of the continuous heat treatment furnace, and control the temperature at 860-880°C. After the plate temperature reaches 860-880°C, transport the steel plate to the insulation section via a roller conveyor; (3) Control the temperature of the insulation section of the continuous heat treatment furnace at 1221-1235°C, and increase the heating power so that the plate temperature reaches 1221-1235°C within 10 minutes. (4) After the steel plate temperature reaches 1221-1235°C, keep it warm for 3-9 minutes. (5) Cool it with water after it is taken out of the furnace.

[0018] The chemical element composition of the Nb-containing austenitic stainless steel is: the chemical composition of the steel plate is as follows by weight percentage: C 0.04%~0.10%, Si≤1.0%, Mn ≤2.0%, Cr 16.0%~26%, Ni 9.0%~45.0%, P≤0.040%, S≤0.030%, N ≤0.40%, Mo≤3.0%, 1.10≥Nb≥8C.

[0019] The specific implementation of the method is described in detail below in conjunction with examples, but the specific implementation of the present invention is not limited to the following examples. Embodiment 1

[0020] According to the process of the present invention, 30 mm thick * 2500 mm wide steel plate is produced: the steel plate composition is as follows: C: 0.06%, Si: 0.48%, Mn: 1.3%, P: 0.019%, S: 0.002%, Cr: 17.3%, Ni: 9.1%, Mo: 0.02%, N: 0.03%, Nb: 0.65%.

[0021] The implementation steps are as follows: (1) Prepare hot-rolled steel plate samples, the hot-rolled grain size of the steel plate is 7.5, and the structure is as follows: Figure 1 As shown. (2) Place the hot-rolled steel plate in the preheating section of the continuous heat treatment furnace, and control the temperature at 875°C. After the plate temperature reaches 875°C, transport the steel plate to the insulation section via a roller conveyor; (3) The temperature of the insulation section of the continuous heat treatment furnace is controlled at 1230°C. Increase the heating power and the plate temperature reaches 1230°C after 8 minutes. (4) After the steel plate temperature reaches 1230°C, keep it warm for 8 minutes. (5) Cool it with water after it is taken out of the furnace.

[0022] After the above steps are implemented, the structure of the steel plate is as follows Figure 2 , the grain size is level 4-5. Embodiment 2

[0023] According to the process of the present invention, 12 mm thick * 2500 mm wide steel plate is produced: the steel plate composition is as follows: C: 0.06%, Si: 0.37%, Mn: 0.9%, P: 0.020%, S: 0.001%, Cr: 23.2%, Ni: 35.8%, Mo: 0.07%, N: 0.19%, Nb: 0.55%.

[0024] The implementation steps are as follows: (1) Prepare hot-rolled steel plate samples, the hot-rolled grain size of the steel plate is 8.5, and the structure is as follows: Figure 3As shown. (2) Place the hot-rolled steel plate in the preheating section of the continuous heat treatment furnace, and control the temperature at 875°C. After the plate temperature reaches 875°C, transport the steel plate to the insulation section via a roller conveyor; (3) The temperature of the insulation section of the continuous heat treatment furnace is controlled at 1225°C. Increase the heating power and the plate temperature reaches 1225°C after 5 minutes. (4) After the steel plate temperature reaches 1225°C, keep it warm for 3 minutes. (5) Cool it with water after it is taken out of the furnace.

[0025] After the above steps are implemented, the structure of the steel plate is as follows Figure 4 , the grain size is level 4-5.

[0026] The above description is only a specific embodiment of the present invention, but the structural features of the protection scope of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are all covered by the patent scope of the present invention.

Claims

1. A method for heat treatment of hot-rolled medium and thick plates of niobium-containing austenitic stainless steel for high temperature use, characterized in that: The following steps are involved: Step 1: Preparation of hot-rolled steel plate: Prepare hot-rolled stainless steel medium and thick plates. The hot-rolled stainless steel medium and thick plates should be uniformly organized over the entire thickness range. Step 2: Place the hot-rolled stainless steel plate in the preheating section of the continuous heat treatment furnace, and control the temperature at 860-880°C. After the plate temperature reaches 860-880°C, transport the steel plate to the insulation section via a roller conveyor; Step 3: The temperature of the insulation section of the continuous heat treatment furnace is controlled at 1221-1235°C, and the plate temperature of the hot-rolled medium and thick stainless steel plate reaches 1221-1235°C within 10 minutes; Step 4: When the temperature of hot-rolled stainless steel plates reaches 1221-1235°C, keep it warm for 3-9 minutes, then immediately take it out of the furnace and cool it in water.

2. The method for heat treatment of hot-rolled medium and thick plates of niobium-containing austenitic stainless steel for high temperature use according to claim 1, characterized in that: The chemical composition and weight percentage of stainless steel hot-rolled medium and thick plates are: C: 0.04%~0.10%, Si≤1.0%, Mn≤2.0%, Cr: 16.0%~26%, Ni: 9.0%~45.0%, P≤0.040%, S≤0.030%, N≤0.40%, Mo≤3.0%, 1.10≥Nb≥8C.

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