CN108517473B

CN108517473B - High-strength stainless steel powder based on SLM (Selective laser melting) process and preparation method thereof

Info

Publication number: CN108517473B
Application number: CN201810717090.4A
Authority: CN
Inventors: 梁剑雄; 王长军; 刘振宝; 杨志勇; 孙永庆; 李文辉; 曹呈祥; 雍兮; 胡家齐; 张梦醒
Original assignee: Central Iron and Steel Research Institute
Current assignee: Central Iron and Steel Research Institute
Priority date: 2018-06-29
Filing date: 2018-06-29
Publication date: 2019-12-24
Anticipated expiration: 2038-06-29
Also published as: CN108517473A

Abstract

A high-strength stainless steel powder based on an SLM (selective laser melting) process and a preparation method thereof belong to the field of metal materials for additive manufacturing. The powder comprises the following chemical components in percentage by weight: c: < 0.03%, Cr: 12.0 to 13.0%, Ni: 8.0-10.0%, Mo: 2.0-2.5%, Al: 0.8-1.2%, Y: 0.02 to 0.10%, Si: < 0.1%, Mn: < 0.01%, P: < 0.005%, S: < 0.002%, O: less than 0.020%, and the balance of Fe and inevitable impurities. The manufacturing process comprises the following steps: preparing mother alloy, preparing powder by a vacuum induction melting gas atomization method, and mechanically vibrating under the protection of inert gas and classifying and screening the powder by airflow and collecting. Compared with the prior art, the powder has the advantages that the yield of fine powder with the granularity range of 15-53 mu m required by the SLM process is obviously improved, the powder has good sphericity and low oxygen content and impurity content, can be used as a powder consumable of a high-strength complex precise component for SLM printing in the field of space navigation engineering, and can also be popularized to the related fields of medical treatment, ocean engineering and the like.

Description

High-strength stainless steel powder based on SLM (Selective laser melting) process and preparation method thereof

Technical Field

The invention belongs to the field of metal materials for additive manufacturing, and particularly provides high-strength stainless steel powder for an SLM (selective laser melting) process and a preparation method thereof.

Background

The additive manufacturing (3D printing) has the technical advantages of no restriction of the complexity of parts, high material utilization rate, significantly shortened development period, etc., and has become one of the most potential manufacturing techniques in the future. The current metal additive manufacturing technology mainly comprises a selective laser melting technology (SLM), a laser net shape forming technology (LENS) and an electron beam melting technology (EBM). The SLM printing technology has the advantages of being complex in structure, high in size precision and the like, so that the SLM printing technology is widely applied to precise and complex parts in the fields of aerospace and medical instruments and is the most main development trend in the field of metal additive manufacturing in the future. Because the SLM technology requires a small particle size range (15-53 μm), most of the prior art at home and abroad mainly uses gas atomization for powder preparation. Vacuum induction melting gas atomization (VIGA) is the only method capable of efficiently preparing metal powder by SLM technology in large batch and at low cost, and the principle of the method is that liquid metal flow is broken into small liquid drops by high-speed airflow and solidified into powder. The atomized powder has the advantages of high sphericity, controllable powder granularity, low oxygen content, low production cost, suitability for the production of various metal powders and the like, and becomes the main development direction of the preparation technology of high-performance and special alloy powder.

Disclosure of Invention

The invention aims to provide high-strength stainless steel powder based on an SLM (selective laser melting) process and a preparation method thereof, and the high-strength stainless steel metal powder based on the SLM process is manufactured through alloy components, a smelting mode and a matched powder making process design, so that the problem of material selection bottleneck of high-strength-level metal powder consumable materials in the field of domestic SLM additive manufacturing is solved.

The high-strength stainless steel powder comprises the following chemical components in percentage by weight: c: < 0.03%, Cr: 12.0 to 13.0%, Ni: 8.0-10.0%, Mo: 2.0-2.5%, Al: 0.8-1.2%, Y: 0.02 to 0.10%, Si: < 0.1%, Mn: < 0.01%, P: < 0.005%, S: < 0.002%, O: less than 0.020%, and the balance of Fe and inevitable impurities.

The action and the proportion of each element of the invention are as follows:

carbon: carbon as interstitial solid solution atoms can improve the matrix strength of steel, but the toughness and weldability of steel are impaired as the strength increases. In addition, the presence of carbon in the steel results in a matrixCr precipitation during aging₂₃C₆And the carbides are subjected to the treatment, so that the seawater corrosion resistance of the steel is obviously reduced. Comprehensively, the carbon of the steel is controlled within 0.03 percent.

Chromium: chromium is the most important alloy element with corrosion resistance, the environmental corrosion resistance and the oxidation resistance of the steel are obviously improved along with the increase of the chromium content, and the lower limit of the chromium content causing the corrosion resistance mutation is about 12 percent according to the research. In addition, the existence of chromium element in the steel can also improve the tempering resistance so as to maintain the dislocation strengthening and solid solution strengthening effects. Therefore, the chromium content of the steel is within the range of 12.0-13.0%.

Nickel: nickel plays two main roles in the present invention: firstly, nickel is used as an austenite forming element, so that an austenite phase region can be enlarged, and the content of delta ferrite in steel can be reduced. Secondly, nickel can form gamma' -Ni with aluminum in the matrix during aging treatment₃The intermetallic strengthening phase of Al, beta-NiAl and the like obviously improves the strength of the steel. However, too high a nickel content would result in M of the steel_sThe point temperature is significantly reduced, resulting in an increase in the content of retained austenite in the matrix structure and a decrease in the strength of the steel. Comprehensively considered, the nickel content of the steel is 8.0-10.0%.

Molybdenum: molybdenum as a ferrite-forming element can significantly improve the hardenability of steel, and in martensitic chromium-nickel stainless steel, molybdenum can form Mo having a hexagonal crystal structure during aging, in addition to improving the corrosion resistance of steel₂C carbide, thereby improving the tempering stability and the secondary hardening effect of the steel. However, too high a molybdenum content promotes the formation of delta ferrite, which adversely affects the steel strip. Comprehensively considered, the content of molybdenum in the steel is 2.0-2.5%.

Aluminum: aluminum is the strengthening phase element in the invention, and on the one hand, dispersed and fine Ni is formed in the aging process₃The precipitation phase of Al, NiAl and the like plays a remarkable precipitation strengthening effect. On the other hand, however, too much Ni₃The Al and NiAl particles can cause the impact toughness and the corrosion resistance of the steel to be obviously reduced. Comprehensively considered, the aluminum content of the steel is controlled to be 0.8-1.2%.

Yttrium: the yttrium is used as the most important alloy element of the invention, and has the functions of purifying matrix structure, desulfurizing, deoxidizing and modifying brittle inclusions, and the yttrium is added into the steel to reduce the surface tension of the whole molten liquid, so that the fine powder yield is obviously improved in the later atomization powder preparation process, particularly the fine powder yield within the range of 15-53 mu m. However, too high a content of yttrium may combine with oxygen to form yttrium oxide inclusions, which may adversely affect the mechanical properties of the steel. Comprehensively considered, the yttrium content of the steel is 0.02-0.10%.

Silicon and manganese: the silicon and manganese have the main deoxidation effect in the steel, and because the steel of the invention adopts pure metal materials and adopts a vacuum induction and vacuum consumable duplex ultrapure smelting process, excessive silicon and manganese are not required to be added for deoxidation. In addition, the lower silicon and manganese contents are very beneficial to the corrosion resistance of the steel, especially the pitting corrosion resistance and the crevice corrosion resistance. In conclusion, the silicon and manganese of the steel of the invention are controlled within 0.1% and 0.01%, respectively.

Phosphorus and sulfur: the steel of the invention adopts a vacuum induction and vacuum self-consumption duplex ultrapure smelting process and simultaneously adopts pure metal materials for smelting, and the contents of phosphorus and sulfur can be respectively controlled within 0.005 percent and 0.002 percent.

Oxygen: harmful gas elements in the metal powder cause more hollow powder to be formed and simultaneously obviously reduce the plasticity and toughness of a later-stage printing part. Because the powder base metal is smelted by adopting a vacuum induction and vacuum consumable double ultrapure smelting process and the vacuum induction smelting gas atomization method powder preparation technology, the oxygen content can be controlled within 0.020%.

The invention relates to high-strength stainless steel powder and a preparation method thereof, wherein the preparation method comprises the following steps:

(1) preparing a master alloy: preparing a master alloy by adopting vacuum induction smelting (VIM) and vacuum consumable remelting (VAR), wherein the master alloy comprises the following components: < 0.03%, Cr: 12.0-13%, Ni: 8.0-10.0%, Mo: 2.0-2.5%, Al: 0.8 to 1.2%, Si: < 0.1%, Mn: < 0.01%, P: < 0.005%, S: < 0.002%, O: less than 0.0025 percent, and the balance of Fe and inevitable impurities.

(2) Preparing powder by VIGA: putting the master alloy into a smelting crucible, vacuumizing the smelting chamber, filling high-purity argon gas with the purity of more than 99.999 percent until the pressure of the smelting chamber is recovered to the standard atmospheric pressure when the pressure is reduced to be below 0.1Pa (the process can be repeated for a plurality of times in a circulating way for metal powder with low requirement on gas content), carrying out induction heating on the master alloy until the heating temperature is 1580-1700 ℃, adding metal yttrium after the master alloy is completely molten, preserving the heat for 3-5 minutes, pouring molten metal into a middle tundish, and carrying out ultrasonic gas atomization powder preparation: the atomization medium is high-purity argon with the purity of more than 99.999 percent, the atomization pressure is 5-7 MPa, and the atomized metal powder is cooled in a cooling chamber and collected in a powder collection tank.

(3) Powder screening and collecting: and under the protection of inert gas, carrying out mechanical vibration and airflow classification screening on the metal powder in the powder collection tank, and carrying out vacuum-pumping sealing packaging on the metal powder in a screened 15-53 mu m particle size range for a Selective Laser Melting (SLM) technology.

Compared with the prior art, the invention has the advantages that: the yield of the fine powder of the metal powder in the granularity range (15-53 mu m) required by the SLM technology is obviously improved, and the cost of powder consumables is obviously reduced. In addition, the metal powder has good sphericity, good fluidity and low oxygen content and impurity content, can be used as a powder consumable of high-strength complex precise components for SLM printing in the field of space navigation engineering, and can also be popularized to the related fields of medical treatment, ocean engineering and the like.

Drawings

FIG. 1 example 1 metal powder macrostructure diagram.

FIG. 2A micro-topography of the metal powder of example 1 showing the surface features of the powder.

FIG. 3 metallographic images of the powder of example 2 showing the internal solidification structure characteristics of the powder.

FIG. 4 macrostructural graph of metal powder in example 3.

FIG. 5 micro-topography of the metal powder of example 3.

Detailed Description

The examples of the present invention are three high strength stainless steel powders with different yttrium contents, and the chemical compositions are shown in table 1. The preparation method comprises the following steps: (1) preparing a master alloy: in the embodiment, a vacuum induction furnace and a vacuum consumable electrode furnace are adopted to prepare the master alloy by a duplex smelting process, and the chemical components of the master alloy are as follows: 0.028%, Si: 0.066%, Mn: 0.006%, P: 0.0045%, S: 0.0008%, Cr: 12.52%, Ni: 8.54%, Mo: 2.30%, Al: 1.14%, O: 0.0022%, and the balance of Fe and inevitable impurities. (2) Preparing powder by VIGA: putting the master alloy into a VIGA smelting crucible, vacuumizing, filling more than 99.999% of high-purity argon until the pressure is recovered (repeating for three times) when the pressure is reduced to be below 0.1Pa, carrying out induction heating on the master alloy until the temperature is 1600-1680 ℃, adding different contents of metal yttrium after the master alloy is completely melted, and carrying out ultrasonic atomization for preparing powder after heat preservation for 3 minutes: the atomization medium is high-purity argon with the purity of more than 99.999 percent, the atomization pressure is 5.5-6.5 MPa, and the atomized metal powder is collected in a powder collection tank after being cooled. (3) Powder screening and collecting: and respectively carrying out mechanical vibration and airflow classification screening on the metal powder with different yttrium contents in the three furnaces, and carrying out vacuum sealing packaging on the screened metal powder with the granularity of 15-53 mu m.

Table 2 shows the particle size distribution and the fine powder yield of the powders of the examples. As can be seen, the metal powder of the examples has a narrower particle size distribution interval and an average particle size D as the yttrium content of the metal powder gradually increases₅₀Gradually decreases from 35.86 μm in example 1 to 30.99 μm in example 3. Meanwhile, the yield of the fine powder with the particle size of 15-53 mu m is obviously improved from 28.05% in example 1 to 38.64% in example 3. The results of the tests of the physical properties and flowability of the powders of the examples are shown in Table 3. It can be seen that, as the content of yttrium in the metal powder gradually increases and the apparent density of the powder gradually increases, the angle of repose and the fluidity gradually decrease, which indicates that the addition of metal yttrium can significantly improve the comprehensive physical properties, sphericity and fluidity of the metal powder.

The macro-morphology and the micro-morphology of the metal powder of example 1 are shown in fig. 1 and 2, respectively. As can be seen, the metal powder of example 1 had a high surface finish and good sphericity. FIG. 3 shows the metallographic structure of the solidified structure of the powder of example 2, and it can be seen that the interior of the powder of example is mainly composed of a polygonal fine crystalline structure with a high dislocation density. The macro-morphology and the micro-morphology of the metal powder of example 3 are shown in fig. 3 and 4, respectively. Compared with the metal powder in the embodiment 1 (figure 1 and figure 2), the metal powder in the embodiment 3 has higher yttrium content, the average particle size of the powder is finer, the sphericity is better, and the powder flowability is better, which is consistent with the particle size and physical property detection results of the powder.

The foregoing description of the invention is only a few examples, and the invention is not limited to the specific embodiments described above. The foregoing detailed description is exemplary rather than limiting in nature. All such modifications, whether made by a person skilled in the art or not, are intended to be included within the scope of this invention as defined in the appended claims.

Table 1 chemical composition (wt.%) of the metal powder of the examples, balance Fe

TABLE 2 particle size distribution and Fine powder yield of the powders of the examples

TABLE 3 examples powder physical Properties and flowability measurements

Claims

1. A high-strength stainless steel powder based on an SLM (selective laser melting) process belongs to the field of metal materials for additive manufacturing. The powder comprises the following chemical components in percentage by weight: c: < 0.03%, Cr: 12.0 to 13.0%, Ni: 8.0-10.0%, Mo: 2.0-2.5%, Al: 0.8-1.2%, Y: 0.02 to 0.10%, Si: < 0.1%, Mn: < 0.01%, P: < 0.005%, S: < 0.002%, O: less than 0.020%, and the balance of Fe and inevitable impurities.

2. A method of manufacturing a high strength stainless steel powder for SLM based process according to claim 1, characterized by:

(1) preparing a master alloy: preparing a master alloy by adopting vacuum induction smelting and vacuum consumable remelting, wherein the master alloy comprises the following components: < 0.03%, Cr: 12.0 to 13.0%, Ni: 8.0-10.0%, Mo: 2.0-2.5%, Al: 0.8-1.2%, Y: 0.02 to 0.10%, Si: < 0.1%, Mn: < 0.01%, P: < 0.005%, S: < 0.002%, O: less than 0.0025 percent, and the balance of Fe and inevitable impurities;

(2) preparing powder by VIGA: putting the master alloy into a smelting crucible, vacuumizing the smelting chamber, introducing high-purity argon gas of more than 99.999 percent until the pressure of the smelting chamber is recovered to standard atmospheric pressure when the pressure is reduced to be below 0.1Pa, carrying out induction heating on the master alloy until the heating temperature is 1580-1700 ℃, adding metal yttrium after the master alloy is completely molten, preserving the heat for 3-5 minutes, pouring molten metal into a middle tundish, and carrying out supersonic gas atomization to prepare powder: the atomization medium is high-purity argon with the purity of more than 99.999 percent, the atomization pressure is 5-7 MPa, and atomized metal powder is cooled in a cooling chamber and collected in a powder collection tank;

(3) powder screening and collecting: and under the protection of inert gas, carrying out mechanical vibration and airflow classification screening on the metal powder in the powder collection tank, and carrying out vacuum-pumping sealing packaging on the metal powder which is used for selective laser melting in a screened 15-53 mu m particle size range.