Strong-plasticity martensitic steel for blade and additive manufacturing method of strong-plasticity martensitic steel

Abstract

According to the high-plasticity martensitic steel for the blade and the additive manufacturing method of the high-plasticity martensitic steel, the content of Cr, C, Ni, Nb and N elements is changed on the basis of GTD-450 alloy components, burdening, vacuum melting and electrode bar preparation are conducted according to the atomic percent required to be designed, then martensitic steel alloy powder is prepared through a plasma rotating electrode method, and the high-plasticity martensitic steel for the blade is obtained. A martensitic steel alloy part is manufactured through a selective laser melting technology in an additive mode, and then hot isostatic pressing densification treatment and heat treatment structure regulation and control are conducted. According to the martensitic steel with high plasticity and excellent fatigue performance, martensitic steel alloy powder with the particle size range of 15-53 microns is prepared through a plasma rotating electrode method, and then a martensitic steel alloy part with excellent comprehensive mechanical performance is obtained through an additive manufacturing and post-processing method.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal additive manufacturing, and in particular relates to a high-plasticity martensitic steel for blades and an additive manufacturing method thereof. Background Art

[0002] GTD-450 alloy is a new type of martensitic aged stainless steel, which is often used to manufacture compressor blades of gas turbines. It has high strength, toughness and corrosion resistance. In actual working process, blades are susceptible to fatigue failure due to asymmetric cyclic loads. Therefore, in order to extend the service life of GTD-450 steel blades, it is an important research direction to improve the plasticity and fatigue properties of typical GTD-450 steel through material composition design. With the continuous increase in the installed capacity of domestic gas turbines, the demand for domestic substitution and rapid maintenance of compressor blades is also increasing. The powder bed-based laser selective melting (SLM) additive manufacturing method is very suitable for the manufacture of GTD-450 alloy gas turbine compressor blades and has broad application prospects.

[0003] Laser selective melting additive manufacturing based on powder bed requires sintering preparation with metal powder as raw material, and the characteristics of powder directly affect the quality of formed parts. Due to the particularity of the material grades used in power station components, it is necessary to develop corresponding special powders for additive manufacturing. The metal powder of GTD-450 steel for gas turbine blades was developed using the plasma rotating electrode (PREP) process. The advantages of using the rotating electrode method to prepare metal powder are that the powder particle size distribution is narrow, the particle size is more controllable, the sphericity and sphericity rate are high, the powder gas content is low, the bonding powder is less, the inclusions are less, the surface is bright and clean, there is basically no hollow powder or satellite powder, and the quality is good.

[0004] Since the structure of the additively manufactured GTD-450 alloy is different from that of the traditional forged state, its rapid solidification structure and its heat treatment process are special, and it is necessary to explore a method to improve the structure and performance of the additively manufactured GTD-450 alloy. Previous studies have found that the additively manufactured GTD-450 alloy has pore defects caused by incomplete melting of metal powder, which makes it difficult for its mechanical properties to meet the requirements (tensile strength R m ≤1090MPa, yield strength R p0.2 ≤647MPa, elongation after fracture A≤4.5%, section shrinkage Z≤11%) steel mechanical properties (R m ≥965MPa, R p0.2 ≥827MPa, A≥16%, Z≥50%). If GTD-450 alloy deposited parts are directly manufactured by additive manufacturing, there will be a possibility of local rapid failure. Therefore, it is necessary to regulate the organization and performance of GTD-450 alloy deposited parts through post-processing. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a method for preparing high-plasticity martensitic steel for blades and its additive manufacturing, prepare martensitic steel alloy powder by PREP process, adopt SLM technology to manufacture martensitic steel alloy samples, and regulate the deposition state structure of additively manufactured martensitic steel alloy by hot isostatic pressing + heat treatment method, so as to achieve the purpose of eliminating hole defects, improving structure and enhancing comprehensive mechanical properties.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing high-plasticity martensitic steel for blades and its additive manufacturing method comprises the following steps:

[0008] 1) Optimization design of GTD-450 alloy composition: Based on the typical GTD-450 alloy composition, the contents of Cr, C, Ni, Nb and N are changed to obtain the chemical composition of the strong and plastic martensitic steel alloy;

[0009] 2) Preparation of powder by plasma rotating electrode method: the ingredients are prepared according to the desired atomic percentage, vacuum smelting is performed, and the obtained alloy ingot is then prepared into an electrode rod to obtain a strong and plastic martensitic steel alloy rod. The strong and plastic martensitic steel alloy powder is prepared by plasma rotating electrode method;

[0010] 3) Selective laser melting additive forming: Selective laser melting technology is used to perform additive manufacturing of martensitic steel alloy powder to obtain additively manufactured strong and plastic martensitic steel alloy deposited samples;

[0011] 4) Hot isostatic pressing densification treatment: The additively manufactured sample is placed in a hot isostatic pressing equipment mold, the equipment temperature is 1100-1300°C, and the pressure is 280-320MPa, and the deposited state sample of the additively manufactured strong plastic martensitic steel alloy is densified;

[0012] 5) Heat treatment organization control: The high-plasticity martensitic steel alloy after densification treatment is further heat treated at a temperature of 1000-1200°C for 20-40 minutes to fully austenitize the sample, oil quench to room temperature, and then keep at 550°C-600°C for 2-4 hours, and air cool to room temperature to prepare a high-plasticity martensitic steel alloy product with high mechanical strength.

[0013] Furthermore, the process parameters of the plasma rotating electrode method in step 2) are: working pressure of 0.08-0.15 MPa, plasma arc current of 800-1200 A, voltage of 40-60 V, electrode rod speed of 15000-20000 r / min, and high-purity argon gas as the atomizing medium.

[0014] Furthermore, the average particle size of the martensitic steel alloy powder prepared by the plasma rotating electrode method in step 2) is ≤53 μm, and the sphericity is ≥90%.

[0015] Furthermore, the process parameters of additive manufacturing in step 3) are: laser power 45-135 W, scanning speed 300-2000 mm / s, scanning spacing 0.04-0.1 mm, and powder layer thickness 0.02-0.04 mm.

[0016] The present invention also provides a high-plasticity martensitic steel alloy for blades, wherein the raw materials for preparing the alloy are composed of the following components by weight: C 0.25-0.50%; Si 0.2-0.10%; Mn 0.50-0.10%; P 0.005-0.025%; S0.001-0.005%; Cr 14.0-16.0%; Ni 6.0-7.0%; Mo 0.5-1.0%; Nb 0.30-0.50%; Cu1.25-1.75%; V 0.020-0.10%; N 0.010-0.030%; and the balance is Fe.

[0017] Furthermore, the raw materials for preparing the high-plasticity martensitic steel alloy for blades are composed of the following components by weight: 0.035% C, 0.20% Si, 0.50% Mn, 0.005P, 0.001% S, 16% Cr, 7% Ni, 0.8% Mo, 0.4% Nb, 1.5Cu, 0.02% V, and the balance is Fe.

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

[0019] Compared with the typical GTD-450 alloy, the contents of Cr, Ni, Nb, N, and C elements are changed in the high-plasticity martensitic steel alloy of the present invention to improve the comprehensive mechanical properties of GTD-450 steel. The advantages of using the rotating electrode method to prepare metal powders are that the powder particle size distribution is narrow, the particle size is more controllable, the sphericity and sphericity rate are high, and the powder gas content is low. The present invention proposes a method for controlling the organization of additively manufactured martensitic steel alloys, and adopts specific hot isostatic pressing + heat treatment process parameters to significantly reduce the porosity of additively manufactured martensitic steel alloys, which can improve the comprehensive mechanical properties of additively manufactured martensitic steel alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The invention discloses the preparation and manufacturing process of the martensitic steel alloy powder.

[0021] Figure 2 This is the morphology of martensitic steel alloy powder prepared by plasma rotating electrode method. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with specific embodiments:

[0023] Embodiment 1:

[0024] The present invention provides a method for preparing martensitic steel alloy powder for blades and its additive manufacturing method (see Figure 1 ), martensitic steel alloy powder was prepared by PREP process, martensitic steel alloy samples were manufactured by SLM technology, and the deposition state structure of additively manufactured martensitic steel alloy was regulated by hot isostatic pressing + heat treatment method.

[0025] The method for preparing the high-toughness martensitic steel alloy in Example 1 of the present invention specifically comprises the following steps:

[0026] 1) Optimization design of GTD-450 alloy composition: Based on the typical GTD-450 alloy composition, the contents of Cr, C, Ni, Nb and N are changed to obtain the chemical composition of the strong and plastic martensitic steel alloy.

[0027] The raw material for preparing the high-ductility martensitic steel alloy in Example 1 of the present invention is composed of the following components by weight: 0.35% C; 0.20% Si; 0.50% Mn; 0.005% P; 0.001% S; 16.0% Cr; 7.0% Ni; 0.8% Mo; 0.40% Nb; 1.50% Cu; 0.020% V; 0.011% N; and the balance is Fe.

[0028] 2) Preparation of powder by plasma rotating electrode method: The raw materials for preparing the strong and plastic martensitic steel alloy in step 1) are prepared according to the atomic percentage, vacuum smelting, and the alloy ingot is prepared into an electrode rod to prepare a strong and plastic martensitic steel alloy rod with a diameter of 75 mm and a length of 500 mm. The strong and plastic martensitic steel alloy rod is prepared into powder by plasma rotating electrode method powder making process, and the powder making process parameters are: working pressure is 0.1 MPa, plasma arc current is 1000A, voltage is 50V, electrode rod speed is 18000r / min, and high-purity argon is used as atomizing medium.

[0029] The spherical martensitic steel alloy powder prepared by the plasma rotating electrode method is the SLM forming raw material. The particle size range of the martensitic steel alloy powder is basically 20-50μm, and the average particle size is 35μm. Figure 2 As shown, the powder composition prepared by the rotating electrode method meets the requirements, the powder has good sphericity and fluidity, the particle size is ≤53μm, and the sphericity is ≥0.9.

[0030] 3) Selective laser melting additive manufacturing: Selective laser melting technology was used for additive manufacturing of martensitic steel alloy powder. The sample was manufactured using BLT-S200 under argon protection. The process parameters for additive manufacturing of martensitic steel alloy by selective laser melting were: laser power 135 W, scanning speed 800 mm / s, scanning spacing 0.06 mm, and powder layer thickness 0.02 mm.

[0031] According to the above process, an additively manufactured strong-plastic martensitic steel alloy deposited sample was prepared and marked as a strong-toughness martensitic steel additively manufactured sample.

[0032] 4) Hot isostatic pressing densification treatment: the additive manufacturing sample obtained in step 3) is placed in a hot isostatic pressing equipment mold, the equipment temperature is 1200° C., the pressure is 300 MPa, and the temperature is kept for 4 hours to perform densification treatment on the deposited sample of the additively manufactured strong and plastic martensitic steel alloy;

[0033] 5) Heat treatment organization control: The strong and plastic martensitic steel alloy after densification treatment is further heat treated. The martensitic steel is heated to 1100°C (fully austenitized) in a furnace, kept at this temperature for 30 minutes, and then oil quenched to room temperature. Then, the temperature is heated to 580°C in a furnace, kept at this temperature for 3 hours, and then air-cooled to room temperature. Thus, a strong and plastic martensitic steel alloy product with high mechanical strength is prepared, which is marked as a sample of the strong and tough martensitic steel heat-treated state.

[0034] Embodiment 2:

[0035] The alloy sample was prepared using the chemical composition of a typical GTD-450 alloy, and the preparation method and steps thereof were repeated in Example 1, with the only difference being that "in step 1), the chemical composition of the raw material for preparing the strong and ductile martensitic steel alloy was replaced with the chemical composition of the raw material for preparing the typical GTD-450 alloy", and the other conditions remained unchanged. Therefore, in Example 2, in step 3), the selective laser melting additive forming was performed to finally obtain a sample in a typical GTD-450 additive manufacturing state, and in step 5), the heat treatment microstructure was controlled to finally obtain a sample in a typical GTD-450 heat-treated state.

[0036] The chemical composition of the raw material for preparing the typical GTD-450 alloy in Example 2, calculated by weight fraction, consists of the following components: 0.042% C; 0.30% Si; 0.46% Mn; 0.015P; 0.002% S; 14.8% Cr; 6.47% Ni; 0.68% Mo; 0.33% Nb; 1.63Cu; 0.031% V; and the balance is Fe.

[0037] Typical chemical composition of GTD-450 steel, unit (%)

[0038]

[0039] Application Example 1:

[0040] The samples of the additively manufactured state and heat-treated state of the strong and tough martensitic steel obtained in Example 1, and the samples of the additively manufactured state and heat-treated state of the typical GTD-450 obtained in Example 2 were tested for performance. The mechanical properties of the alloy are shown in Table 1. The tensile test adopts GB / T228.1-2010 "Metallic Material Tensile Test Part 1: Room Temperature Test Method". Test machine name and model: microcomputer-controlled electronic universal testing machine CMT5105. Control mode and test rate: crossbeam displacement control, rate: 0.375mm / min. The inner size of the specimen gauge is 2mm*4mm.

[0041] Table 1

[0042]

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-plasticity martensitic steel for blades and its additive manufacturing method, characterized in that: The following steps are involved: 1) Optimization design of GTD-450 alloy composition: Based on the GTD-450 alloy composition, the contents of Cr, C, Ni, Nb and N are changed to obtain the chemical composition of the strong and plastic martensitic steel alloy; 2) Preparation of powder by plasma rotating electrode method: the ingredients are prepared according to the desired atomic percentage, vacuum smelting is performed, and the obtained alloy ingot is then prepared into an electrode rod to obtain a strong and plastic martensitic steel alloy rod. The strong and plastic martensitic steel alloy powder is prepared by the plasma rotating electrode method; 3) Selective laser melting additive forming: Selective laser melting technology is used to perform additive manufacturing of martensitic steel alloy powder to obtain additively manufactured strong and plastic martensitic steel alloy deposited samples; 4) Hot isostatic pressing densification treatment: The additively manufactured sample is placed in the hot isostatic pressing equipment mold, the equipment temperature is 1100-1300℃, and the pressure is 280-320MPa, and the deposited sample of the additively manufactured strong plastic martensitic steel alloy is densified; 5) Heat treatment organization control: The high-plasticity martensitic steel alloy after densification treatment is further heat treated at 1000-1200 °C for 20-40 min to fully austenitize the sample, oil quench to room temperature, and then keep at 550 °C-600 °C for 2-4 hours, and air cool to room temperature to prepare a high-plasticity martensitic steel alloy product with high mechanical strength.

2. The method for preparing a strong and plastic martensitic steel for blades and its additive manufacturing method as claimed in claim 1, characterized in that: Step 2) The process parameters of the plasma rotating electrode method are: working pressure of 0.08-0.15 MPa, plasma arc current of 800-1200 A, voltage of 40-60 V, electrode rod speed of 15000-20000 r / min, and high-purity argon gas as the atomizing medium.

3. The method for preparing a strong and plastic martensitic steel for blades and its additive manufacturing method as claimed in claim 1, characterized in that: Step 2) The average particle size of the martensitic steel alloy powder prepared by the plasma rotating electrode method is ≤53 μm, and the sphericity is ≥90%.

4. The method for preparing a strong and plastic martensitic steel for blades and its additive manufacturing method as claimed in claim 1, characterized in that: Step 3) The process parameters of additive manufacturing are: laser power 45-135 W, scanning speed 300-2000 mm / s, scanning spacing 0.04-0.1 mm, and powder layer thickness 0.02-0.04 mm.

5. A high-ductility martensitic steel alloy for blades, characterized in that The raw materials for preparing the said alloy are composed of the following components by weight: C 0.25-0.50%, Si 0.2-0.10%, Mn 0.50-0.10%, P 0.005-0.025%, S 0.001-0.005%, Cr 14.0-16.0%, Ni 6.0-7.0%, Mo 0.5-1.0%, Nb 0.30-0.50%, Cu 1.25-1.75%, V0.020-0.10%, N 0.010-0.030%, and the balance is Fe.

6. A high-ductility martensitic steel alloy for blades as claimed in claim 5, characterized in that The raw materials for its preparation are composed of the following components by weight: 0.035% C, 0.20% Si, 0.50% Mn, 0.005P, 0.001% S, 16% Cr, 7% Ni, 0.8% Mo, 0.4% Nb, 1.5Cu, 0.02% V, and the balance is Fe.

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