Method for preparing high-chromium-molybdenum ferritic stainless steel cold-rolled welded plate

Abstract

The invention relates to the technical field of high-chromium-molybdenum ferritic stainless steel, in particular to a method for preparing a high-chromium-molybdenum ferritic stainless steel cold-rolled welding plate. In order to solve the problem that brittle phase precipitation and grain coarsening are easy to occur during welding in the existing method for preparing the high-chromium-molybdenum ferrite stainless steel cold-rolled welded plate, the invention provides a novel method for preparing the high-chromium-molybdenum ferrite stainless steel cold-rolled welded plate. The method sequentially comprises the following steps of solution treatment, cold rolling, welding, recrystallization annealing and stress relief annealing. According to the method for preparing the high-chromium-molybdenum ferritic stainless steel cold-rolled welded plate, by means of the mode that cold rolling is conducted firstly, then welding is conducted, and finally recrystallization annealing is conducted, grains in a welding heat affected zone are remarkably refined, and meanwhile the problems that due to welding conducted after recrystallization annealing, secondary heating is conducted on the heat affected zone, the grains are coarsened, and the plasticity and toughness of materials are deteriorated are solved.

Description

Technical Field

[0001] The invention relates to the technical field of high-chromium-molybdenum ferrite stainless steel, in particular to a method for preparing a high-chromium-molybdenum ferrite stainless steel cold-rolled welded plate. Background Art

[0002] High chromium (25-30wt.%) and molybdenum (0.5-4wt.%) ferritic stainless steel has good thermal conductivity, excellent pitting and stress corrosion resistance, and low thermal expansion coefficient. It has been widely used in chemical, heat exchanger, petroleum refining equipment and other industries. Although high content of chromium and molybdenum elements significantly improves the corrosion resistance of ferritic stainless steel, at the same time, high content of chromium and molybdenum elements will also promote α ， Brittle phases such as α phase, σ phase and χ phase precipitate, which deteriorates the mechanical properties and corrosion resistance of ferritic stainless steel.

[0003] Welding is one of the main means of manufacturing high chromium-molybdenum ferritic stainless steel connecting plates, pipes, and complex-shaped components. The existing method for preparing high chromium-molybdenum ferritic stainless steel cold-rolled welded plates mainly includes the following steps: smelting, forging or continuous casting, hot rolling, solution (annealing) treatment, pickling, cold rolling, recrystallization annealing, and welding. However, in the actual production process, this method is prone to brittle phase precipitation and grain coarsening in the heat-affected zone (HAZ) and grain coarsening in the molten pool (the grains in the molten pool include the columnar crystal zone (CCZ) and the equiaxed crystal zone (ECR)) due to the high heat input generated during welding. Figure 1 As shown, the weld joint of high chromium-molybdenum ferritic stainless steel cold-rolled welded plate becomes brittle and the mechanical properties decrease, which seriously affects the product quality. Summary of the invention

[0004] In order to solve the problem that brittle phase precipitation and grain coarsening are easy to occur during welding in the existing method for preparing high chromium-molybdenum ferritic stainless steel cold-rolled welded plate, the present invention provides a new method for preparing high chromium-molybdenum ferritic stainless steel cold-rolled welded plate.

[0005] The present invention is achieved by adopting the following technical solutions: A method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate comprises the following steps in sequence: 1) Solution treatment: The hot-rolled high chromium-molybdenum ferrite stainless steel plate is subjected to solution treatment at a heating temperature of 1020-1180°C, a holding time of 3-120 min, a heating rate of ≥10°C / min, and then immediately cooled; 2) Cold rolling; 3) Welding: During the welding process, the heat-affected zone completes recrystallization, and cold rolling deformation is used to promote the precipitation of nano-scale Laves phase in the heat-affected zone, hindering the growth of grains in the heat-affected zone; 4) Recrystallization annealing: heating temperature 1010℃-1150℃, holding time 0.5-50 min, heating rate ≥50℃ / min, quench immediately after annealing, cool to room temperature, cooling rate ≥50℃ / s; (welding first, then recrystallization annealing can make part of the welding heat input kinetic energy directly act on grain nucleation and growth, thereby weakening the overall welding heat input kinetic energy, effectively reducing the width of the heat affected zone (HAZ), and achieving the purpose of refining grains and improving the mechanical properties of materials. If brittle phases precipitate during welding, recrystallization annealing can also melt the brittle phases precipitated during welding, achieving the purpose of weakening precipitation embrittlement) 5) Stress relief annealing: The heating temperature is 200-600°C, the holding time is 0.5-50h, and then cooled to room temperature to obtain a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate.

[0006] In the specific preparation method, the hot-rolled high chromium-molybdenum ferrite stainless steel plate is subjected to step 1) solid solution treatment, the heating temperature is 1020-1180°C, the holding time is 3-120min, and the heating rate is ≥10°C / min, the purpose is to make the hot-rolled deformed structure complete the recrystallization behavior, avoid the σ phase, χ phase, α phase ，The precipitation of equal brittle phases and the precipitation of nano-scale Laves phase are promoted at the same time, which plays the purpose of pinning grain boundaries and refining grains, increasing the deformation resistance in step 2) cold rolling, improving deformation energy storage, increasing the driving force of recrystallization, increasing the nucleation rate, refining grains, strengthening the performance of high chromium-molybdenum ferrite stainless steel plates, and preventing cold rolling cracking; then step 2) cold rolling is carried out to obtain a sufficient deformation structure. After cold rolling, the internal deformation energy storage of the plate is improved, and a large number of microstructural defects such as shear bands and subgrain boundaries are formed, which can provide nucleation power and nucleation points for the recrystallization and precipitation of nano-scale Laves phase in the heat affected zone during step 3) welding, and also provide nucleation points for the recrystallization process of the parent material (BM) in step 4; in step 3) welding, the heat affected zone completes recrystallization during the welding process, and cold rolling deformation is used to promote the precipitation of nano-scale Laves phase in the heat affected zone, hindering the growth of grains in the heat affected zone; in step 4), the recrystallization annealing is carried out by annealing temperature of 1010-1150℃, holding time of 0.5-50min, heating rate ≥50 ℃ / min, and the process of rapid cooling immediately after annealing, with the cooling medium temperature ≤20℃, allows the base material (BM) still in the state of cold-rolled deformation to recrystallize, forming fine equiaxed grains to strengthen the overall material properties. At the same time, the Laves phase is used to pin the grain boundaries in advance during the welding process to ensure that the grains in the heat-affected zone and the molten pool area are not coarsened, and to eliminate some of the stresses formed during the welding process. If brittle phases are precipitated during the welding process, recrystallization annealing can also melt the brittle phases precipitated during the welding process to achieve the purpose of weakening precipitation embrittlement. Among them, recrystallization annealing If the temperature is too high, it will easily lead to grain coarsening. If the temperature is too low, it will not only cause the precipitation of brittle phases, but also lead to insufficient recrystallization of the deformed structure of the parent material. Rapid cooling is performed to avoid the precipitation of brittle phases. Step 5) stress relief annealing, the heating temperature is 200-600℃, the holding time is 0.5h-50h, to eliminate the residual thermal stress inside the high chromium-molybdenum ferrite stainless steel cold-rolled welded sheet, and at the same time avoid the appearance of brittle phases such as σ phase, χ phase and α phase, and improve the plastic toughness of the material. Among them, if the heating temperature is too high, it will easily lead to the precipitation of brittle phases, and if the heating temperature is too low, the stress relief effect will be weakened.

[0007] Furthermore, in step 3), laser welding is used for welding.

[0008] Furthermore, the power during laser welding is 1000-5000W, the speed is 1000-5000mm / min, the defocus is -3-3mm, the spot radius is 0.1-1mm, and the fixed laser focal length is 100-200mm.

[0009] Furthermore, in step 2), the total reduction ratio during cold rolling is ≥40%.

[0010] Furthermore, before welding, the high chromium-molybdenum ferrite stainless steel plates after the cold rolling treatment in step 2) are clamped, fixed and butted to facilitate welding and ensure welding quality.

[0011] Furthermore, in step 3), the butt joint gap of the high chromium-molybdenum ferrite stainless steel plates after the cold rolling treatment in step 2) is ≤0.5mm before welding to prevent welding defects such as weld penetration and pits caused by a larger butt joint gap, thereby affecting the welding quality.

[0012] Furthermore, before the high chromium-molybdenum ferrite stainless steel plate after the cold rolling treatment in step 2) is clamped and fixed and butted, it is first surface treated to prevent impurities such as rust, oil, cutting fluid, etc. from entering the molten pool to cause welding defects such as undercut, slag inclusion, and cracks, thereby ensuring welding quality.

[0013] Furthermore, in step 2), the high chromium-molybdenum ferrite stainless steel plate after the solution treatment in step 1) is pickled and then cold rolled to remove the oxide scale on the surface of the material, improve the surface quality after cold rolling, and further improve the welding quality.

[0014] Furthermore, in step 2), the solution used for pickling is a sulfuric acid solution.

[0015] Furthermore, in step 1), the cooling rate of the rapid cooling is ≥50°C / s.

[0016] The beneficial effects of the present invention are as follows: In the method for preparing a high chromium-molybdenum ferritic stainless steel cold-rolled welded plate of the present invention, by first cold-rolling, then welding and finally recrystallization annealing, the nano-scale Laves phase is induced to precipitate in the heat affected zone during the welding process based on the cold rolling deformation, which hinders the recrystallization and grain growth of the cold-rolled deformation structure in the heat affected zone, significantly refines the grains in the welding heat affected zone, and avoids the problem of grain coarsening and deterioration of the plastic toughness of the material caused by secondary heating of the heat affected zone caused by welding after recrystallization annealing; in addition, during the recrystallization annealing process after welding, the deformed structure of the base material (BM) is recrystallized to form fine equiaxed crystals, and the heat affected zone has precipitated nano-scale Laves phase in advance, which can pin the grain boundary, hinder the grain coarsening of the heat affected zone during the recrystallization annealing process, and obtain a fine structure, thereby solving the problem of brittle phase precipitation and grain coarsening in the cold-rolled welded plate prepared by the existing preparation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0019] Figure 1 It is a schematic diagram of the microstructure of the weld of the high chromium-molybdenum ferrite stainless steel cold-rolled plate after recrystallization annealing described in the background technology; Figure 2 Schematic diagram of the heat-affected zone of the high-chromium-molybdenum ferrite stainless steel cold-rolled plate after welding according to the present invention (the white dots in the figure are nano-scale Laves phases that have not been formed); Figure 3 This is a schematic diagram of the weld microstructure of the high chromium-molybdenum ferrite stainless steel cold-rolled plate after welding according to the present invention; Figure 4 This is a schematic diagram of the weld microstructure of the high chromium-molybdenum ferrite stainless steel cold-rolled thin plate after recrystallization annealing after welding according to the present invention. DETAILED DESCRIPTION

[0020] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0021] In the description, it should be noted that the terms "first" and "second" are only used for descriptive purposes and should not be understood as indicating or implying relative importance. It should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two elements. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0023] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0024] Embodiment 1: A method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate, comprising the following steps in sequence: 1) Solution treatment: The hot-rolled high chromium-molybdenum ferrite stainless steel plate is solution treated at a heating temperature of 1020°C, a holding time of 5 min, a heating rate of 10°C / min, and then immediately rapidly cooled at a cooling rate of 50°C / s; 2) Cold rolling: The high chromium-molybdenum ferrite stainless steel plate after the solution treatment in step 1) is pickled and then cold rolled. The solution used in the pickling is sulfuric acid solution, and the total reduction rate during cold rolling is 40%; 3) Welding: Before welding, the high chromium-molybdenum ferrite stainless steel plate after cold rolling in step 2) is surface treated, and then clamped and fixed, and butted. The butt gap is 0.5mm. Laser welding is used during welding. The power of laser welding is 1000W, the speed is 5000mm / min, the defocus is -3mm, the spot radius is 0.1mm, and the fixed laser focal length is 100mm; 4) Recrystallization annealing: heating temperature 1010℃, holding time 3min, heating rate 50℃ / min, quenching immediately after annealing, cooling to room temperature, cooling rate 50℃ / s; 5) Stress relief annealing: the heating temperature is 350°C, the holding time is 1 hour, and then cooled to room temperature to obtain a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate.

[0025] The high chromium-molybdenum ferrite stainless steel cold-rolled welded plate prepared by the above process was sampled and subjected to microhardness test and tensile property test. The test results are shown in Table 1.

[0026] Table 1

[0027] Among them, the elongation ratio is the ratio of the uniform elongation of the high chromium-molybdenum ferritic stainless steel cold-rolled welded plate obtained in this embodiment 1 to the uniform elongation of the high chromium-molybdenum ferritic stainless steel plate after cold rolling treatment in step 2) (the uniform elongation of the high chromium-molybdenum ferritic stainless steel plate after cold rolling treatment in step 2) is 20.04%).

[0028] Embodiment 2: A method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate, comprising the following steps in sequence: 1) Solution treatment: The hot-rolled high chromium-molybdenum ferrite stainless steel plate is solution treated at a heating temperature of 1100°C, a holding time of 60 min, a heating rate of 50°C / min, and then immediately rapidly cooled at a cooling rate of 60°C / s; 2) Cold rolling: The high chromium-molybdenum ferrite stainless steel plate after the solution treatment in step 1) is pickled and then cold rolled. The solution used in the pickling is sulfuric acid solution, and the total reduction rate during cold rolling is 60%; 3) Welding: Before welding, the high chromium-molybdenum ferrite stainless steel plate after the cold rolling treatment in step 2) is surface treated, and then clamped and fixed, and butted. The butt gap is 0.5mm. Laser welding is used during welding. The power of laser welding is 2000W, the speed is 3000mm / min, the defocus is 0mm, the spot radius is 0.5mm, and the fixed laser focal length is 150mm; 4) Recrystallization annealing: heating temperature 1030℃, holding time 2min, heating rate 50℃ / min, quenching immediately after annealing, cooling to room temperature, cooling rate 50℃ / s; 5) Stress relief annealing: The heating temperature is 450°C, the holding time is 25 hours, and then cooled to room temperature to obtain a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate.

[0029] The high chromium-molybdenum ferrite stainless steel cold-rolled welded plate prepared by the above process was sampled and subjected to microhardness test and tensile property test. The test results are shown in Table 2.

[0030] Table 2

[0031] Among them, the elongation ratio is the ratio of the uniform elongation of the high chromium-molybdenum ferritic stainless steel cold-rolled welded plate obtained in this embodiment 2 to the uniform elongation of the high chromium-molybdenum ferritic stainless steel plate after cold rolling treatment in step 2) (the uniform elongation of the high chromium-molybdenum ferritic stainless steel plate after cold rolling treatment in step 2) is 20.04%).

[0032] Embodiment 3: A method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate, comprising the following steps in sequence: 1) Solution treatment: The hot-rolled high chromium-molybdenum ferrite stainless steel plate is solution treated at a heating temperature of 1100°C, a holding time of 60 min, a heating rate of 50°C / min, and then immediately rapidly cooled at a cooling rate of 60°C / s; 2) Cold rolling: The high chromium-molybdenum ferrite stainless steel plate after the solution treatment in step 1) is pickled and then cold rolled. The solution used in the pickling is sulfuric acid solution, and the total reduction rate during cold rolling is 60%; 3) Welding: Before welding, the high chromium-molybdenum ferrite stainless steel plate after the cold rolling treatment in step 2) is surface treated, and then clamped and fixed, and butted. The butt gap is 0.5mm. Laser welding is used during welding. The power of laser welding is 2000W, the speed is 3000mm / min, the defocus is 0mm, the spot radius is 0.5mm, and the fixed laser focal length is 150mm; 4) Recrystallization annealing: heating temperature 1030℃, holding time 2min, heating rate 50℃ / min, quenching immediately after annealing, cooling to room temperature, cooling rate 50℃ / s; 5) Stress relief annealing: The heating temperature is 450°C, the holding time is 25 hours, and then cooled to room temperature to obtain a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate.

[0033] The high chromium-molybdenum ferrite stainless steel cold-rolled welded plate prepared by the above process was sampled and subjected to microhardness test and tensile property test. The test results are shown in Table 3.

[0034] Table 3

[0035] Among them, the elongation ratio is the ratio of the uniform elongation of the high chromium-molybdenum ferritic stainless steel cold-rolled welded plate obtained in this embodiment 3 to the uniform elongation of the high chromium-molybdenum ferritic stainless steel plate after cold rolling treatment in step 2) (the uniform elongation of the high chromium-molybdenum ferritic stainless steel plate after cold rolling treatment in step 2) is 20.04%).

[0036] In the above three embodiments, by first cold rolling and then welding and finally recrystallization annealing, the nano-scale Laves phase is precipitated in advance in the heat affected zone of the welding process based on the cold rolling deformation (see Figure 2 ), hindering the recrystallization and grain growth of the cold-rolled deformation structure in the heat-affected zone, and significantly refining the grains in the heat-affected zone of welding (see Figure 3 and the data in Table 1, Table 2, and Table 3), while avoiding the problem of grain coarsening and deterioration of material plasticity and toughness caused by secondary heating of the heat affected zone caused by welding after recrystallization annealing; in addition, during the recrystallization annealing process after welding, the deformed structure of the base material (BM) recrystallizes to form fine equiaxed crystals, while the heat affected zone has pre-precipitated nano-scale Laves phase, which can pin the grain boundaries and hinder the grain coarsening of the heat affected zone during the recrystallization annealing process, thereby obtaining a fine structure (see Figure 4 Since the materials prepared in the three embodiments are very similar, only one set of drawings of embodiment 1 is shown in the present invention), thereby solving the problem that the cold-rolled welded plate prepared by the existing preparation method is prone to brittle phase precipitation and grain coarsening.

[0037] Comparative Example 1: The hot-rolled high-chromium-molybdenum ferritic stainless steel plate is solution treated, the heating temperature is 1000°C, the holding time is 5 min, the heating rate is 20°C / min, and then immediately cooled quickly, the obtained stainless steel hot-rolled solution plate is pickled, and the pickled stainless steel hot-rolled solution plate is cold rolled with a reduction rate of 70%, thereby obtaining a high-chromium-molybdenum ferritic stainless steel plate with a thickness of 0.7 mm, which is kept at 1050°C for 1 min and then rapidly cooled to room temperature, the surface of the high-chromium-molybdenum ferritic stainless steel cold-rolled plate to be welded after recrystallization annealing is smoothed, the stainless steel sheet is clamped and fixed using a press-down fixture, and then welded with a welding power and welding speed of 2000w-2000mm / min, a defocus of -3.0mm, a spot radius of 0.1mm, and a laser focal length of 100mm.

[0038] The high chromium-molybdenum ferrite stainless steel cold-rolled welded plate prepared by the above process was sampled and subjected to microhardness test and tensile property test. The test results are shown in Table 4.

[0039] Table 4

[0040] Elongation percentage: the ratio of the uniform elongation of this example to the uniform elongation of the cold-rolled annealed sheet (the uniform elongation of the cold-rolled annealed sheet is 20.04%).

[0041] It can be concluded from the above three embodiments and comparative examples that the elongation after fracture and grain coarsening problems of the high chromium-molybdenum ferrite stainless steel cold-rolled welded plate prepared by the preparation method described in the present invention are effectively improved, and its mechanical properties are effectively improved.

[0042] The above is only a specific implementation of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions are given with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of each embodiment, and they should all be covered by the protection scope of the claims. .

Claims

1. A method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate, characterized in that: The steps are as follows: 1) Solution treatment: The hot-rolled high chromium-molybdenum ferrite stainless steel plate is subjected to solution treatment at a heating temperature of 1020-1180°C, a holding time of 3-120 min, a heating rate of ≥10°C / min, and then immediately cooled; 2) Cold rolling; 3) Welding; 4) Recrystallization annealing: heating temperature 1010℃-1150℃, holding time 0.5-50 min, heating rate ≥50℃ / min, quench immediately after annealing, cool to room temperature, cooling rate ≥50℃ / s; 5) Stress relief annealing: The heating temperature is 200-600°C, the holding time is 0.5-50h, and then cooled to room temperature to obtain a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate.

2. The method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate according to claim 1, characterized in that: In step 3), laser welding is used for welding.

3. The method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate according to claim 2, characterized in that: The power during laser welding is 1000-5000W, the speed is 1000-5000mm / min, the defocus is -3-3mm, the spot radius is 0.1-1mm, and the fixed laser focal length is 100-200mm.

4. The method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate according to claim 3, characterized in that: In step 2), the total reduction ratio during cold rolling is ≥ 40%.

5. The method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate according to claim 4, characterized in that: Before welding, the high chromium-molybdenum ferrite stainless steel plates that have been cold-rolled in step 2) are clamped, fixed, and butted.

6. The method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate according to claim 5, characterized in that: In step 3), before welding, the butt joint gap of the high chromium-molybdenum ferrite stainless steel plates after the cold rolling treatment in step 2) is ≤0.5 mm.

7. The method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate according to claim 6, characterized in that: Before clamping and butting the high chromium-molybdenum ferrite stainless steel plate after the cold rolling treatment in step 2), the surface treatment is first performed.

8. The method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate according to claim 7, characterized in that: In step 2), the high chromium-molybdenum ferrite stainless steel plate after the solution treatment in step 1) is pickled and then cold rolled.

9. The method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate according to claim 8, characterized in that: In step 2), the solution used for pickling is a sulfuric acid solution.

10. The method for preparing a high chromium-molybdenum ferrite stainless steel cold-rolled welded plate according to claim 9, characterized in that: In step 1), the cooling rate of the rapid cooling is ≥50°C / s.

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