阅读说明：本技术 一种适用于氧化物强化钢的选区激光熔化增材制造方法 (selective laser melting additive manufacturing method suitable for oxide reinforced steel ) 是由 翟玉涛 宋亮亮 毛小东 黄群英 吴宜灿 于 2019-10-17 设计创作，主要内容包括：本发明属于3D打印技术领域,具体涉及一种适用于氧化物强化钢的选区激光熔化增材制造方法。所述方法首先通过将含钇纳米氧化物与9-18Cr铁素体/奥氏体钢粉末混合均匀后装入送粉箱中；其次在计算机中建立三维实体模型,并进行分层切片处理,设定每层粉末层的铺粉厚度和沉降补偿；再次采用激光束按照分层切片形状对粉末层进行依次成型,最后进行热处理后得到。所述方法可一次实现高性能ODS钢的成型,具有成型质量好、无微裂纹、致密度高、和综合力学性能好的优点；成型后残余应力小且分布均匀,工件变形小,成型精度高。(The invention belongs to the technical field of 3D printing, and particularly relates to a selective laser melting additive manufacturing method suitable for oxide reinforced steel. Firstly, uniformly mixing yttrium-containing nano oxide and 9-18Cr ferrite/austenitic steel powder, and then loading the mixture into a powder feeding box; secondly, establishing a three-dimensional solid model in a computer, carrying out layered slicing treatment, and setting the powder laying thickness and settlement compensation of each powder layer; and sequentially forming the powder layer by adopting the laser beam according to the shape of the layered slice, and finally performing heat treatment to obtain the powder. The method can realize the molding of the high-performance ODS steel at one time, and has the advantages of good molding quality, no microcrack, high density and good comprehensive mechanical property; the residual stress after molding is small and evenly distributed, the deformation of the workpiece is small, and the molding precision is high.)

1. a selective laser melting additive manufacturing method suitable for oxide reinforced steel is characterized in that: the method comprises the following steps:

(1) Taking yttrium-containing nano oxide and 9-18Cr ferrite/austenitic steel powder as raw materials, wherein the mass fraction of the yttrium-containing nano oxide is 0.2-5% by taking the total mass of the raw materials as 100%: the mass fraction of 9-18Cr ferrite/austenitic steel powder is 95-99.8%, the grain diameter of 9-18Cr ferrite/austenitic steel powder is less than or equal to 5 mu m, and the grain diameter of the raw materials is less than or equal to 75 mu m, and the raw materials are uniformly mixed and then are put into a powder feeding box of SLM equipment;

(2) Establishing a three-dimensional solid model for a part to be molded by using mapping software in a computer, inputting the three-dimensional solid model into molding control software for layering and slicing processing to obtain a layering and slicing shape, and setting the powder laying thickness and sedimentation compensation of each powder layer; wherein the powder spreading thickness is 20-70 μm, and the settlement compensation is as follows: according to the melting and solidification characteristics of the molding material, the powder spreading thickness is increased by 10-50 mu m when 10-20 layers are deposited;

(3) selective laser melting and rapid forming: the laser beam is adopted to sequentially form the powder layer according to the layered slice shape, each layer adopts a multiple laser scanning forming strategy, and the laser forming process comprises the following steps: laser power is 50-500W, laser beam diameter is 50-150 μm, scanning speed is 200-1000mm/s, scanning mode: jump and turn in the layer and cross between layers, the scanning distance is 20-80 μm, the lapping rate is 20-50%, the powder is preheated to 150-400 ℃; wherein, a forming chamber of the SLM equipment is protected by protective gas, the pressure is always maintained at 10-40mbar, and the temperature is maintained at 300 +/-50 ℃; the same forming process is adopted for each layer of internal deposition, and an orthogonal scanning strategy is adopted between each two layers;

(4) and carrying out heat treatment after the forming is finished to obtain the nano oxide reinforced steel.

2. The selective laser melting additive manufacturing method suitable for oxide reinforced steel according to claim 1, wherein: the yttrium-containing nano oxide in the step (1) is Y-Ti-O, Y-Si-O, Y-Al-O, Y-Zr-O or Y-Hf-O.

3. The selective laser melting additive manufacturing method suitable for oxide reinforced steel according to claim 1, wherein: in the step (1), the mass fraction of fine powder, the mass fraction of medium powder and the mass fraction of coarse powder in the 9-18Cr ferrite/austenite steel powder are respectively 15-25%, 50-70% and 15-25%; wherein the grain size of the fine powder with the grain size of 5 mu m or less is less than 20 mu m, the grain size of the medium powder with the grain size of 20 mu m or less is less than 60 mu m, and the grain size of the coarse powder with the grain size of 60 mu m or more is less than 75 mu m.

4. The selective laser melting additive manufacturing method suitable for oxide reinforced steel according to claim 1, wherein: in the step (3), a multi-scanning forming strategy is adopted for in-layer deposition forming of each layer: firstly, scanning with a low-power laser: laser power is 50-200W, laser beam diameter is 80-150 μm, scanning speed is 400-1000mm/s, scanning mode: skipping and turning, wherein the scanning distance is 20-80 mu m, and the powder is preheated to 150-400 ℃; secondly, high-power laser scanning is adopted: laser power 300-500W, laser beam diameter 50-150 μm, scanning speed 400-1000mm/s, scanning mode: skipping and changing directions, wherein the scanning distance is 20-80 mu m; finally, medium power laser scanning is used: the laser power of 200-300W is 200W when the small power and the medium power are different, the high power and the medium power are 300W when the medium power are different, the diameter of the laser beam is 80-150 μm, the scanning speed is 400-1000mm/s, and the scanning mode is as follows: scanning with high-power scanning passes in a staggered mode, wherein the staggered distance is 10-60 mu m, and the scanning distance is 20-80 mu m; wherein, the lap joint rate between scanning tracks is 20-50%.

5. The selective laser melting additive manufacturing method suitable for oxide reinforced steel according to claim 1, wherein: and (4) the protective gas in the step (3) is inert gas or nitrogen.

6. the selective laser melting additive manufacturing method suitable for oxide reinforced steel according to claim 1, wherein: the heat treatment in the step (4) comprises the following steps: heating to 900-1200 deg.C with a heating rate of 5-30 deg.C/min, maintaining for 60-180min, and cooling with a cooling rate of 5-50 deg.C/min.

Technical Field

The invention belongs to the technical field of 3D printing, and particularly relates to a selective laser melting additive manufacturing method suitable for oxide reinforced steel.

Background

Oxide Dispersion Strengthened Steel (ODS Steel) is widely considered to be an important candidate structural material (mainly 9-18Cr ferrite/austenite Steel) of advanced nuclear energy system key components such as a future fourth-generation nuclear reactor fuel cladding material, a high-temperature structural member material, a future fusion reactor cladding first wall and the like due to excellent radiation swelling resistance, helium brittleness resistance and good high-temperature strength and creep property, and has a severe service environment, needs to bear high-energy neutron irradiation, high surface heat flow, high nuclear thermal deposition, liquid metal corrosion, high pressure, complex mechanical load and the like, and has extremely high requirements on structural materials, molding quality and product molding precision. The conventional preparation process of ODS steel mainly comprises the following steps: the preparation scale of the ODS steel is small due to the limitation of mechanical alloying efficiency and the capability of hot-curing molding equipment, and industrial large-scale production is difficult to realize.

In addition, because the specific gravity of the nano oxide in the ODS steel is smaller than that of the matrix alloy, the oxide particles float upwards to the surface of a welding seam along with the melting of welding seam metal in the traditional fusion welding process, so that the oxide dispersion strengthening particles in the structure are separated and aggregated, the dispersion distribution state of the nano oxide in the steel is damaged, the high-temperature creep property and the radiation resistance of a welding joint are reduced, and finally the material performance is deteriorated. Therefore, the part molding of ODS steel also becomes a bottleneck limiting its part fabrication and large-scale application in the nuclear power field.

in recent years, a rapidly developed additive manufacturing (3D printing) technology provides a new approach for forming ODS steel, a Selective Laser Melting (SLM) technology is one of additive manufacturing rapid forming technologies, and the SLM process has the characteristics of extremely high micro-zone rapid Melting and solidification, high front edge cooling rate, and high thermal gradient convection stirring. According to the precipitation dynamics characteristic of the yttrium (Y) -containing nano oxide, the SLM process is adopted to minimize the aggregation of the nano oxide and maintain the dispersion distribution, the agglomeration of the nano oxide can be avoided, the direct and rapid molding of ODS steel from powder to parts can be realized, and the ODS steel has the advantages of good molding surface quality, small roughness, integral molding of complex structures and the like; the forming process is the key of the technology because the physical properties of different materials are greatly different. At present, in the existing SLM preparation method of ODS steel, the main problems of more microcracks, low density (higher density reaching about 90% of a forging), poor mechanical property and the like of the formed ODS steel are not effectively solved.

Disclosure of Invention

In view of the above, the present invention aims to provide a selective laser melting additive manufacturing method suitable for oxide-reinforced steel, which greatly improves the material forming performance, reduces the generation rate of microcracks, reduces the spheroidization phenomenon, and improves the overall forming quality.

To achieve the above object, the technical solution of the present invention is as follows.

A selective laser melting additive manufacturing method suitable for oxide reinforced steel comprises the following steps:

(1) taking yttrium (Y) -containing nano oxide and 9-18Cr ferrite/austenitic steel powder as raw materials, wherein the mass fraction of the yttrium-containing nano oxide is 0.2-5% by taking the total mass of the raw materials as 100%: the mass fraction of 9-18Cr ferrite/austenitic steel powder is 95-99.8%, the grain diameter of 9-18Cr ferrite/austenitic steel powder is less than or equal to 5 mu m, and the grain diameter of the raw materials is less than or equal to 75 mu m, and the raw materials are uniformly mixed and then are put into a powder feeding box of SLM equipment;

preferably, the 9-18Cr ferrite/austenite steel powder comprises 15-25% of fine powder, 50-70% of medium powder and 15-25% of coarse powder by mass; wherein the particle size of the fine powder with the particle size of 5 mu m or more is less than 20 mu m, the particle size of the medium powder with the particle size of 20 mu m or more is less than 60 mu m, and the particle size of the coarse powder with the particle size of 60 mu m or more is less than 75 mu m, so that the powder laying process has higher apparent density and better compactness after forming;

preferably, the yttrium (Y) -containing nano oxide is Y-Ti-O, Y-Si-O, Y-Al-O, Y-Zr-O or Y-Hf-O, and the type of the oxide can be selected according to the service environment requirements of the matrix material, such as high temperature resistance, corrosion resistance, irradiation resistance and the like.

(2) Establishing a three-dimensional solid model for a part to be molded by using mapping software in a computer, inputting the three-dimensional solid model into molding control software for carrying out layered slicing processing to obtain a layered slice shape, selecting a molding direction and adding supports according to the structure and the size of a molded part, and setting the powder laying thickness and settlement compensation of each powder layer according to the physical properties of materials; wherein the powder spreading thickness is 20-70 μm, and the settlement compensation is as follows: according to the melting and solidification characteristics of the molding material, the powder spreading thickness is increased by 10-50 mu m when 10-20 layers are deposited;

(3) Selective laser melting and rapid forming: the laser beam is adopted to sequentially form the powder layer according to the layered slice shape, each layer adopts a multiple laser scanning forming strategy, and the laser forming process comprises the following steps: laser power is 50-500W, laser beam diameter is 50-150 μm, scanning speed is 200-1000mm/s, scanning mode: jump and turn in the layer and cross between layers, the scanning distance is 20-80 μm, the lapping rate is 20-50%, the powder is preheated to 150-400 ℃; wherein, a forming chamber of the SLM equipment is protected by protective gas and the pressure is always maintained at 10-40 mbar; the temperature in the forming chamber is maintained at 300 +/-50 ℃; the same forming process is adopted for the inner deposition of each layer, and an orthogonal scanning strategy is adopted between each two layers, namely, the laser scanning direction of the layer to be formed is rotated by 90 degrees relative to the laser scanning direction of the deposited forming layer of the previous layer, so that the residual stress after forming is reduced;

Preferably, a multi-scanning forming strategy (generally three-scanning forming is adopted) is adopted for in-layer deposition forming of each layer, so that the crack probability in the forming process is reduced, spheroidization is reduced, and the forming quality is improved; firstly, scanning by low-power laser according to the cross section profile of a layered slice shape, wherein the scanning lap joint rate between 2 deposition passes in the same layer and between two layers is 20-50%, scanning the paved powder layer by the low-power laser, heating and preheating the powder without melting the powder so as to reduce the temperature gradient in the forming process and reduce the crack generation probability, and the laser scanning and preheating process comprises the following steps: laser power is 50-200W, laser beam diameter is 80-150 μm, scanning speed is 400-1000mm/s, scanning mode: skipping and turning, wherein the scanning distance is 20-80 mu m, and the powder is preheated to 150-400 ℃; secondly, the powder is melted by high-power laser scanning, and the forming process comprises the following steps: laser power 300-500W, laser beam diameter 50-150 μm, scanning speed 400-1000mm/s, scanning mode: skipping and changing directions, wherein the scanning distance is 20-80 mu m; finally, the medium power laser is scanned in a staggered way to carry out laser repair so as to reduce the defects of spheroidization and microcrack, and the forming process comprises the following steps: the laser power of 200-300W is 200W when the small power and the medium power are different, the high power and the medium power are 300W when the medium power are different, the diameter of the laser beam is 80-150 μm, the scanning speed is 400-1000mm/s, and the scanning mode is as follows: the scanning is staggered with the high-power melting scanning pass, the staggered distance is 10-60 mu m, the scanning distance is 20-80 mu m, and the lap ratio between the scanning passes is 20-50%. The forming of each layer adopts a multiple scanning forming strategy, compared with the existing one-time scanning forming, the powder preheating before melting deposition forming and the reduction spheroidization laser scanning after deposition forming are added, the crack generation probability in the forming process can be reduced, the spheroidization is reduced, and the quality of deposition forming is improved.

Preferably, the protective gas is an inert gas or nitrogen.

(4) and carrying out heat treatment after the forming is finished to obtain the nano oxide reinforced steel.

Preferably, the heat treatment process comprises: heating to 900-1200 ℃ along with the furnace at the heating rate of 5-30 ℃/min, preserving heat for 60-180min to ensure that the nano oxide is dispersed and separated out and reaches a stable state, cooling to below 50 ℃ along with the furnace at the cooling rate of 5-50 ℃/min, and discharging to ensure that the nano oxide is completely separated out, reduce the residual stress, and improve the radiation resistance, the high temperature resistance and the overall performance of the material. The ODS steel is subjected to heat treatment mainly for promoting the precipitation of nano oxides, and the heat treatment of the invention is used for ensuring the complete precipitation of the nano oxides. Due to the layer-by-layer stacking forming characteristic of the SLM technology, a next pass has a certain heat treatment effect on an adjacent deposited and formed previous pass between adjacent laser scanning passes in the same layer; meanwhile, between the upper and lower deposition layers, the deposition forming layer has a certain heat treatment effect on the upper deposition forming layer. Therefore, the ODS steel has the precipitation of partial or even all nano oxides in the SLM forming process, the vacuum heat treatment after the forming can further ensure the complete precipitation of the nano oxides, and simultaneously, the residual stress of the formed workpiece is reduced, and the comprehensive mechanical property of the workpiece is improved.

has the advantages that:

(1) The invention can overcome the problems of low efficiency and small scale of the existing mechanical alloying-hot pressing method for preparing ODS steel, and greatly improve the forming efficiency of the ODS steel; the ODS steel component can be directly formed by powder raw materials and can be completed only by a small amount of machining, and the preparation process of the traditional ODS steel component which needs powder-mechanical alloying-hot press forming-machining-welding forming-machining is greatly shortened; the forming of the ODS steel component is one of key technologies restricting the application of the ODS steel component, the traditional fusion welding easily causes the aggregation of nano oxides, thereby destroying the dispersion distribution state of the nano oxides in steel, causing the reduction of the high-temperature creep property and the radiation resistance of a welding joint, and finally causing the deterioration of the material performance; according to the selective laser melting rapid forming technology, the laser spot diameter is small, a tiny micro-melting pool can be formed, the large contact surface of the micro-melting pool and the surrounding matrix has a high cooling rate, and the dispersion distribution of the formed nano oxides and the irradiation-resistant and high-temperature-resistant characteristics of the formed ODS steel component can be guaranteed to be unchanged.

(2) The existing SLM process generally adopts one-time scanning deposition molding, each two layers are mostly copied by a mechanical process, microcracks are formed after molding, and the overlapping part of laser scanning passes in the layers has a serious spheroidization phenomenon, so that the mechanical property after molding is seriously influenced. In addition, the scanning mode is the same between every 2 settled layers, so that the residual stress after forming is large, and the deformation of the workpiece after forming is large. The invention optimizes the powder grain size ratio, adopts an in-layer multi-scanning forming strategy, and simultaneously adopts an orthogonal scanning forming mode between every two deposited layers, thereby greatly improving the forming performance of the material, reducing the probability of microcrack generation, reducing the spheroidization phenomenon, reducing the residual stress after forming, improving the forming quality and improving the mechanical property after forming the material.

drawings

FIG. 1 is a schematic view of a tube component of a miniaturized Chinese lead based stack fuel assembly can as described in example 1;

FIG. 2 is a schematic view of a configuration of a impeller part of a Chinese lead-based stack primary loop liquid metal coolant-driven pump described in embodiment 2;

Fig. 3 is a schematic structural view of a first wall member of a cladding of a Chinese Fusion Engineering Test Reactor (CFETR) according to embodiment 3.

Detailed Description

the invention is described in detail below with reference to the figures and the embodiments. The following examples are only illustrative of the present invention, and the scope of the present invention shall include the full contents of the claims, not limited to the examples.