Duplex stainless steel powder for laser additive manufacturing and preparation method and application thereof

Abstract

A duplex stainless steel powder for laser additive manufacturing and a preparation method and application thereof, belonging to the technical field of nitrogen-containing stainless steel powder preparation, wherein the components of the duplex stainless steel powder are calculated by mass percentage: C: 0.09-0.20%, Mn: 5.00-15.00%, Mo: 1.00-5.00%, Ni: 5.00-15.00%, Cr: 10.00-30.00%, N: 0.10-0.40%, S: ≤0.02%, P: ≤0.02%, Fe: balance. The present invention utilizes vacuum induction melting and high-pressure inert gas atomization methods to control the conditions such as the addition time of a mixture of metal manganese particles and nitrogen-containing alloy particles, thereby achieving the purpose of controlling the nitrogen content in the alloy powder.

Description

Technical Field

[0001] The present invention belongs to the technical field of nitrogen-containing stainless steel powder preparation, and in particular relates to a duplex stainless steel powder for laser additive manufacturing, and a preparation method and application thereof. Background Art

[0002] Duplex stainless steel is composed of ferrite and austenite, and the content of the two phases is basically the same. This structural feature of duplex stainless steel makes it have the advantages of both ferritic stainless steel and austenitic stainless steel. Compared with austenitic stainless steel, duplex stainless steel has high strength and better resistance to stress corrosion and corrosion fatigue; compared with ferritic stainless steel, duplex stainless steel performs better in plasticity and toughness, and its brittle transition temperature is low, and its resistance to cold brittleness is better. Duplex stainless steel is widely used in petrochemical, marine engineering, construction engineering and other fields due to its good mechanical properties and corrosion resistance.

[0003] With the rapid development of powder metallurgy, laser additive manufacturing (LAM) technology has shown significant advantages. Duplex stainless steel powder products produced by laser additive manufacturing technology have many advantages: (1) They are not limited by the complex structure of the product and can produce parts with various complex shapes and structures; (2) They can be formed in one step and without a mold, avoiding the tedious processing of traditional metal component casting, forging, welding and other processes, and can achieve rapid manufacturing of complex shapes and multi-layer structures, greatly shortening the product development cycle, with low production costs, and can achieve single-piece product trial production; (3) The utilization rate of raw materials is close to 100%, which greatly saves the manufacturing cost of the product; (4) The product has excellent mechanical properties; in the laser additive manufacturing process, due to the high cooling rate of the molten pool, good controllability of the organizational structure and the use of special powder materials, it can achieve the effects of improving static strength, fatigue strength and surface hardness, thereby improving the performance of the product.

[0004] In addition, the laser additive manufacturing (LAM) technology of powder metallurgy can not only repair damaged parts, but also enhance the surface performance of materials. Therefore, the LAM technology of powder metallurgy also provides a new means for repairing metal structures and extending their service life.

[0005] The laser additive manufacturing industry has certain requirements for duplex stainless steel powder, such as the proportion of non-metallic inclusions in the powder, whether the powder can be mass-produced, the uniformity of the powder composition (stability of the nitrogen content in the batch product) and sphericity. There are many methods for preparing duplex stainless steel powder, such as solid powder nitridation, centrifugal atomization, gas atomization, etc. Among them, the solid powder nitridation method has a long preparation cycle, poor powder sphericity, poor fluidity, and especially cannot avoid the oxidation and contamination of the powder during the nitridation process. This will directly affect the subsequent forming and application of the powder and is not suitable for laser additive manufacturing. In the centrifugal atomization method, its preparation cost is too high and the production efficiency is low, which is not suitable for large-scale production and is not conducive to mass production in the laser additive manufacturing industry. In summary, compared with the solid powder nitridation method and the centrifugal atomization method, the nitrogen-containing steel powder prepared by the gas atomization method has the advantages of uniform powder particle size, high sphericity, low oxygen content, rapid condensation structure and large-scale production capacity, which meets the requirements of laser additive manufacturing.

[0006] Nitrogen contributes to the formation, stability and expansion of the austenite phase in steel, and a reasonable nitrogen content can effectively improve the stability of austenite in steel. The conventional vacuum gas atomization method simply uses the secondary addition of nitrogen-containing alloys to supplement the nitrogen content in the alloy. The control method of nitrogen content in the whole process is single, resulting in unstable nitrogen yield, which is sometimes high and sometimes low. Ultimately, the nitrogen content in the powder is unstable, which does not meet the expected nitrogen content requirements, causing the phase structure of the alloy to change, and the expected organizational structure cannot be achieved, affecting the final performance of duplex stainless steel, and seriously restricting the application of duplex stainless steel in high-end industries. Therefore, how to accurately control the nitrogen content in duplex stainless steel powder is still a technical problem that needs to be solved urgently, which largely restricts the application of duplex stainless steel powder in the field of high-end manufacturing. Summary of the invention

[0007] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a duplex stainless steel powder for laser additive manufacturing and a preparation method and application thereof, which utilizes vacuum induction melting and high-pressure inert gas atomization methods to control the conditions such as the addition time of the mixture of metallic manganese particles and nitrogen-containing alloy particles, thereby achieving the purpose of controlling the nitrogen content in the alloy powder.

[0008] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0009] A duplex stainless steel powder for laser additive manufacturing, wherein the components of the duplex stainless steel powder are, by mass percentage, C: 0.09-0.20%, Mn: 5.00-15.00%, Mo: 1.00-5.00%, Ni: 5.00-15.00%, Cr: 10.00-30.00%, N: 0.10-0.40%, S: ≤0.02%, P: ≤0.02%, and Fe: balance.

[0010] A method for preparing the duplex stainless steel powder for laser additive manufacturing comprises the following steps:

[0011] Step S01, the raw materials are pure iron, metal manganese particles, carburizer, electrolytic nickel, metal molybdenum, metal chromium, and nitrogen-containing alloy particles. All raw materials except the metal manganese particles and the nitrogen-containing alloy particles are added into a smelting crucible, and the metal manganese particles and the nitrogen-containing alloy particles are mixed evenly and then placed into an alloy secondary feeding bin;

[0012] Step S02, the smelting chamber is closed, and the vacuum pump is turned on to evacuate the system. When the vacuum degree of the smelting chamber and the atomizing chamber reaches less than 1Pa, the evacuation is stopped, and then inert gas is filled into the smelting chamber and the atomizing chamber to make the pressure of the smelting chamber and the atomizing chamber reach a slightly positive pressure, and then the vacuum pump is turned on to evacuate and clean the furnace, and the vacuum degree of the smelting chamber and the atomizing chamber is controlled to be ≤200Pa;

[0013] Step S03, the heating system of the smelting crucible and the tundish is powered on to increase the temperature. After all the raw materials in the smelting crucible are melted, the temperature of the alloy melt in the smelting crucible reaches 1450-1650°C, and then the temperature is kept for 5-10 minutes; then vacuum carbon deoxidation refining is performed, the vacuum degree of the control system is controlled at 10-200Pa, and the refining is performed for 4-8 minutes, and then the vacuum pump is controlled to increase the vacuum degree of the system to within 1Pa and the refining is performed for 2-5 minutes, and then the inert gas is filled into the smelting chamber and the atomizing chamber to make the pressure of the smelting chamber reach 0.11-0.13Mpa;

[0014] Step S04, after step S03 is completed, the frequency of the induction power supply of the melting crucible is adjusted to make the temperature of the molten alloy melt at 1450-1750°C, a mixture of manganese particles and nitrogen-containing alloy particles is added, alloying for 3-10 minutes, stirring, and the temperature of the tundish is controlled to reach 1300-1450°C during the entire refining and secondary charging alloying process, and the temperature is kept for 15-25 minutes;

[0015] Step S05, pouring the molten alloy melt into a tundish, introducing the molten alloy melt into a gas atomization system through a guide pipe at the bottom of the tundish, and atomizing the molten alloy melt with high-pressure inert gas to obtain alloy powder;

[0016] Step S06: After the alloy powder obtained in step S05 is fully cooled, it is taken out and subjected to airflow classification or ultrasonic vibration screening under the protection of an inert gas atmosphere to obtain a duplex stainless steel powder.

[0017] Furthermore, in step S01, the nitrogen-containing alloy particles include chromium nitride, manganese nitride, and chromium iron nitride.

[0018] Furthermore, in step S01, the raw material pure iron has Fe>99.95%, the metal manganese particles have Mn>99.5%, the metal manganese particles have a size of 1-5 mm, the carburizer has C>99.95%, the electrolytic nickel has Ni>99.9%, the metal molybdenum has Mo>99.9%, the metal chromium has Cr>99.8%, the chromium nitride has N: 10-15%, Si: 0.2-0.5%, Fe: 0.1-0.3%, and the balance is chromium; the manganese nitride has N: 6-10%, Fe: 1.0-3.0%, Si: 0.2-0.6%, and the balance is manganese; the chromium nitride has N: 5-12%, Cr: 30-60%, Si: 0.05-0.15%, C: 0.1-0.2%, and the balance is iron; the nitrogen alloy particles have a size of 2-5 mm.

[0019] Furthermore, in the step S01, the smelting crucible is made of fused magnesia with a mass percentage of MgO not less than 95% or alumina with a mass percentage of Al2O3 not less than 95%.

[0020] Furthermore, in step S02, the inert gas is high-purity argon gas, and the gas purity is not less than 99.99%.

[0021] Furthermore, in step S03, the inert gas is a mixed gas of high-purity argon and high-purity nitrogen, wherein the high-purity argon accounts for 80-90%, the high-purity nitrogen accounts for 10-20%, and the gas purity is not less than 99.99%.

[0022] Furthermore, in step S05, the atomization system includes an annular gap atomization spray disc and a nozzle with a circular hole, the diameter of the nozzle circular hole is 3.5 to 6 mm, and the pressure of the high-pressure inert gas is 3 to 6 MPa; the inert gas is a mixture of high-purity argon and high-purity nitrogen, the high-purity argon accounts for 85 to 95%, the high-purity nitrogen accounts for 5 to 15%, and the gas purity is not less than 99.99%.

[0023] The duplex stainless steel powder for laser additive manufacturing is used for selective laser melting 3D printing of duplex stainless steel components.

[0024] The present invention determines the temperature of the molten steel when the nitrogen-containing alloy is added by considering the melting points of different nitrogen-containing alloys. Since different nitrogen-containing alloys have different melting points, if the molten steel temperature is too high, the nitrided alloy will be melted quickly and decomposed in large quantities, and the nitrogen will be oversaturated locally, causing nitrogen to overflow from the molten steel and causing serious loss of nitrogen; if the molten steel temperature is too low, the nitrogen-fixing capacity of the molten steel is low, and the nitrogen-containing alloy melts slowly, causing loss of nitrogen.

[0025] The nitrogen-containing alloy of the present invention is added simultaneously with the metal manganese particles. Manganese can improve the solubility of nitrogen in the molten steel. As the manganese particles melt, a manganese-rich zone is formed, and the nitrogen fixing capacity of the molten steel is improved.

[0026] The inert protective gas of the smelting chamber of the present invention is a mixed gas of high-purity nitrogen and argon, which increases the nitrogen partial pressure of the gas in the smelting chamber. At the same time, the smelting chamber maintains a positive pressure, reducing the overflow of nitrogen in the molten steel.

[0027] The inert gas used in atomization of the present invention is a mixed gas of a small amount of nitrogen and a large amount of argon, which makes up for the loss of nitrogen content in the process of molten steel solidifying into powder.

[0028] The beneficial effects of the present invention are as follows: the method for preparing duplex stainless steel powder for laser additive manufacturing of the present invention utilizes vacuum induction melting plus high-pressure inert gas atomization method to prepare duplex stainless steel powder suitable for laser additive manufacturing, and controls the nitrogen component by controlling the addition time, addition temperature, alloying time, furnace pressure, inert gas type and other preparation conditions of the mixture of metal manganese particles and nitrogen-containing alloy particles, thereby achieving the purpose of controlling the nitrogen content in the alloy powder, so that the powder nitrogen content deviation (mass percentage) is within the target value of ±0.01%, thereby meeting the strict composition requirements of the laser additive manufacturing industry for duplex stainless steel powder, and solving the problem that its application in high-end industries such as aerospace is restricted. DETAILED DESCRIPTION

[0029] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below in conjunction with embodiments and through specific implementation methods.

[0030] The invention provides a duplex stainless steel powder for laser additive manufacturing, a preparation method and an application thereof, wherein the duplex stainless steel powder for laser additive manufacturing comprises the following components by mass percentage: C: 0.09-0.20%, Mn: 5.00-15.00%, Mo: 1.00-5.00%, Ni: 5.00-15.00%, Cr: 10.00-30.00%, N: 0.10-0.40%, S: ≤0.02%, P: ≤0.02%, and Fe: balance.

[0031] The present invention also provides a method for preparing the duplex stainless steel powder for laser additive manufacturing, comprising the following steps:

[0032] Step S01, the raw materials are pure iron, metal manganese particles, carburizer, electrolytic nickel, metal molybdenum, metal chromium, and nitrogen-containing alloy particles. All raw materials except metal manganese particles and nitrogen-containing alloy particles are added into a smelting crucible. In principle, small particles of raw materials are placed at the bottom of the crucible, and high-temperature alloys are placed in the middle high-temperature zone, so that the bottom is tight and the top is loose. After the metal manganese particles and the nitrogen-containing alloy particles are evenly mixed, they are placed in the alloy secondary feeding bin. The nitrogen-containing alloy particles include chromium nitride, manganese nitride, and chromium iron nitride.

[0033] The raw material pure iron contains Fe>99.95%, the metal manganese particles contain Mn>99.5%, the metal manganese particles have a size of 1~5mm, the carburizer contains C>99.95%, the electrolytic nickel contains Ni>99.9%, the metal molybdenum contains Mo>99.9%, the metal chromium contains Cr>99.8%, the chromium nitride contains N: 10~15%, Si: 0.2~0.5%, Fe: 0.1~0.3%, and the balance is chromium; the manganese nitride contains N: 6~10%, Fe: 1.0~3.0%, Si: 0.2~0.6%, and the balance is manganese; the ferrochromium nitride contains N: 5~12%, Cr: 30~60%, Si: 0.05~0.15%, C: 0.1~0.2%, and the balance is iron; the nitrogen alloy particles have a size of 2~5mm.

[0034] The mixture of metallic manganese particles and nitrogen-containing alloy particles is added through the alloy silo to ensure that the nitrogen element is fully dissolved in the molten steel.

[0035] The smelting crucible is mainly made of fused magnesia (MgO mass percentage is not less than 95%) or alumina (Al2O3 mass percentage is not less than 95%).

[0036] Step S02, the smelting chamber is closed, and the vacuum pump is turned on to evacuate the system. When the vacuum degree of the smelting chamber and the atomizing chamber reaches less than 1Pa, the evacuation is stopped, and then the smelting chamber and the atomizing chamber are filled with inert gas to make the pressure of the smelting chamber and the atomizing chamber reach a slight positive pressure (0.10-0.12MPa), and then the vacuum pump is turned on to evacuate and clean the furnace, and the vacuum degree of the smelting chamber and the atomizing chamber is controlled to be ≤200Pa. The inert gas is high-purity argon gas, and the gas purity is not less than 99.99%.

[0037] Step S03, the heating system of the smelting crucible and the tundish is powered on to heat up. After all the raw materials in the smelting crucible are melted, the temperature of the alloy melt in the smelting crucible reaches 1450-1650°C, and then it is kept warm for 5-10 minutes; then vacuum carbon deoxidation refining is carried out, the vacuum degree of the control system is controlled at 10-200Pa, and the refining is carried out for 4-8 minutes, and then the vacuum pump is controlled to increase the vacuum degree of the system to within 1Pa and the refining is carried out for 2-5 minutes, and then the inert gas is filled into the smelting chamber and the atomizing chamber to make the pressure of the smelting chamber reach 0.11-0.13Mpa. The inert gas is a mixed gas of high-purity argon and high-purity nitrogen, with high-purity argon accounting for 80-90%, high-purity nitrogen accounting for 10-20%, and the gas purity is not less than 99.99%.

[0038] Step S04: After step S03 is completed, the frequency of the induction power supply of the melting crucible is adjusted to make the temperature of the molten alloy melt at 1450-1750° C., a mixture of manganese particles and nitrogen-containing alloy particles is added, and alloying is performed for 3-10 minutes with stirring. During the entire refining and secondary feeding alloying process, the temperature of the tundish is controlled to reach 1300-1450° C. and kept warm for 15-25 minutes.

[0039] Step S05, pour the molten alloy melt into the tundish, and introduce the molten alloy melt into the gas atomization system through the guide pipe at the bottom of the tundish, and obtain alloy powder by high-pressure inert gas atomization treatment. The gas atomization system includes an annular seam gas atomization spray disc and a nozzle with round holes. The guide pipe is made of ZrO2 or Al2O3, and the purity (mass percentage) is not less than 99%. The material of the nozzle with round holes is ZrO2, and the purity (mass percentage) is not less than 99%. The inert gas is a mixed gas of high-purity argon and high-purity nitrogen, with high-purity argon accounting for 85-95%, high-purity nitrogen accounting for 5-15%, and the gas purity is not less than 99.99%.

[0040] The atomization treatment is to use the high-pressure inert gas sprayed from the annular gap of the atomization spray disc to break the molten alloy melt flowing out of the nozzle into fine droplets. The droplets are cooled and solidified to form powder during the flight. The diameter of the nozzle hole is 3.5-6mm, and the pressure of the high-pressure inert gas is 3-6MPa.

[0041] The present invention also includes step S06, placing the solidified duplex stainless steel powder obtained in step S05 into a powder collecting tank, taking it out after being fully cooled, and using air flow classification or ultrasonic vibration screening under the protection of an inert gas atmosphere to obtain duplex stainless steel powder with a suitable particle size, and finally vacuum packaging the finished product.

[0042] The duplex stainless steel powder for laser additive manufacturing prepared by the present invention is used for selective laser melting 3D printing of duplex stainless steel components.

[0043] Example 1

[0044] The ingredients are prepared according to the duplex stainless steel composition in Table 1.

[0045] Table 1 is a table of composition of duplex stainless steel of Example 1

[0046]

[0047] The raw materials are pure iron (Fe>99.95%), metal manganese particles (Mn>99.5%, particle size is 1~5mm), carburizer (C>99.95%), electrolytic nickel (Ni>99.9%), metal molybdenum (Mo>99.9%), metal chromium (Cr>99.8%), and nitrogen-containing alloy particles are manganese nitride (N: 6.8%, Fe: 2.2%, Si: 0.41%, the balance is manganese), and the melting point of manganese nitride is 1300℃. First, all raw materials except manganese particles and manganese nitride alloy particles are added into the melting crucible, and after the manganese particles and manganese nitride alloy particles are evenly mixed, they are placed into the alloy secondary feeding bin.

[0048] Close the melting chamber and turn on the vacuum pump to evacuate the system. When the vacuum degree of the melting chamber and the atomizing chamber reaches less than 1Pa, stop the vacuum operation. Then fill the furnace chamber and the atomizing chamber with inert gas to make the pressure of the melting chamber and the atomizing chamber reach a slightly positive pressure (0.105MPa). Then turn on the vacuum pump again to evacuate the system and wash the furnace. Control the vacuum degree of the melting chamber and the atomizing chamber to 170Pa. The heating system of the melting crucible and the tundish starts to supply power to increase the temperature. After all the raw materials in the melting crucible are melted, the temperature of the alloy melt in the melting crucible reaches 1450℃ and is kept warm for 5 minutes; then the vacuum carbon deoxidation refining operation is started. First, the vacuum degree of the system is controlled at 150Pa, and the refining is performed for 5 minutes. Then the vacuum pump is controlled to increase the vacuum degree of the system to less than 1Pa and the refining is performed for 2.5 minutes. Then, inert gas is filled into the melting chamber and the atomization chamber. The high-purity argon gas accounts for 90% of the inert gas, and the high-purity nitrogen accounts for 10%, so that the pressure in the melting chamber reaches 0.11MPa; the frequency of the induction power supply of the melting crucible is adjusted to ensure that the temperature of the molten alloy is at 1450℃ (150℃ higher than the melting point of manganese nitride). The mixture of metallic manganese particles and manganese nitride particles is added through the alloy silo. After the addition is completed, alloying is carried out for 4 minutes. During the entire refining and secondary charging alloying process, the temperature of the tundish is controlled to reach 1350°C and is kept warm for 15 minutes. The molten alloy melt is poured into the tundish, and the molten alloy melt is introduced into the gas atomization system through the guide pipe at the bottom of the tundish. It is atomized by high-pressure inert gas (high-purity argon accounts for 95% and high-purity nitrogen accounts for 5%) to obtain alloy powder. The diameter of the nozzle circular hole is 4.0mm, and the pressure of the high-pressure inert gas is 3.5MPa.

[0049] The solidified powder enters the powder collecting tank, is taken out after being fully cooled, and is sieved by ultrasonic vibration under the protection of inert gas atmosphere to obtain duplex stainless steel powder with suitable particle size. Finally, the finished product is vacuum packaged.

[0050] After analysis, the composition of the duplex stainless steel powder prepared in Example 1 is shown in Table 8, and the composition meets the requirements, especially the nitrogen content (mass percentage) of the powder is controlled to be 0.145%, which deviates negatively from the target limit by 0.005%.

[0051] Example 2

[0052] The ingredients are prepared according to the duplex stainless steel composition in Table 2.

[0053] Table 2 is the composition table of duplex stainless steel of Example 2

[0054]

[0055] The raw materials are pure iron (Fe>99.95%), metal manganese particles (Mn>99.5%, particle size is 1~5mm), recarburizer (C>99.95%), electrolytic nickel (Ni>99.9%), metal molybdenum (Mo>99.9%), metal chromium (Cr>99.8%), and nitrogen-containing alloy particles are ferrochrome nitride (N: 8%, Cr: 45%, Si: 0.15%, C: 0.18%, and the balance is iron). The melting point of ferrochrome nitride is 1450°C. First, all raw materials except manganese particles and ferrochrome nitride alloy particles are added into the melting crucible, and after the manganese particles and ferrochrome nitride alloy particles are evenly mixed, they are put into the alloy secondary feeding bin.

[0056] Close the melting chamber, turn on the vacuum pump to evacuate the system, and stop the vacuum operation when the vacuum degree of the melting chamber and the atomizing chamber reaches less than 1Pa. Then fill the furnace chamber and the atomizing chamber with inert gas to make the pressure of the melting chamber and the atomizing chamber reach a slightly positive pressure (0.11MPa). Then turn on the vacuum pump again to evacuate the system and wash the furnace. Control the vacuum degree of the melting chamber and the atomizing chamber to 110Pa. The heating system of the melting crucible and the tundish starts to supply power to increase the temperature. After all the raw materials in the melting crucible are melted, the temperature of the alloy melt in the melting crucible reaches 1570℃ and is kept warm for 7 minutes; then the vacuum carbon deoxidation refining operation is started. First, the vacuum degree of the system is controlled at 130Pa, and the refining is carried out for 6 minutes. Then the vacuum pump is controlled to increase the vacuum degree of the system to less than 1Pa and the refining is carried out for 3 minutes. Then, inert gas is filled into the melting chamber and the atomization chamber. The high-purity argon gas accounts for 85% of the inert gas, and the high-purity nitrogen accounts for 15%, so that the pressure in the melting chamber reaches 0.12MPa; the frequency of the induction power supply of the melting crucible is adjusted to ensure that the temperature of the molten alloy is at 1600℃ (150℃ higher than the melting point of ferrochromium nitride). The mixture of metallic manganese particles and ferrochromium nitride particles is added through the alloy silo. After the addition is completed, alloying is carried out for 7 minutes. During the entire refining and secondary alloying process, the temperature of the tundish is controlled to reach 1420°C and is kept warm for 20 minutes. The molten alloy melt is poured into the tundish, and the molten alloy melt is introduced into the gas atomization system through the guide pipe at the bottom of the tundish. It is atomized by high-pressure inert gas (high-purity argon accounts for 90% and high-purity nitrogen accounts for 10%) to obtain alloy powder. The diameter of the nozzle circular hole is 4.5mm, and the pressure of the high-pressure inert gas is 4.5MPa.

[0057] The solidified powder enters the powder collecting tank, is taken out after being fully cooled, and is sieved by airflow classification under the protection of an inert gas atmosphere to obtain duplex stainless steel powder with a suitable particle size. Finally, the finished product is vacuum packaged.

[0058] After analysis, the composition of the duplex stainless steel powder prepared in Example 2 is shown in Table 8, and the composition meets the requirements, especially the nitrogen content (mass percentage) of the powder can be controlled at 0.254%, which is 0.004% away from the target limit.

[0059] Example 3

[0060] The ingredients are prepared according to the duplex stainless steel composition in Table 3.

[0061] Table 3 is the composition table of duplex stainless steel of Example 3

[0062]

[0063] The raw materials are pure iron (Fe>99.95%), metal manganese particles (Mn>99.5%, particle size is 1~5mm), recarburizer (C>99.95%), electrolytic nickel (Ni>99.9%), metal molybdenum (Mo>99.9%), metal chromium (Cr>99.8%), and nitrogen-containing alloy particles are chromium nitride (N: 13.1%, Si: 0.29%, Fe: 0.19%, and the balance is chromium). The melting point of chromium nitride is 1590°C. First, all raw materials except manganese particles and chromium nitride alloy particles are added into the melting crucible. After the manganese particles and chromium nitride alloy particles are evenly mixed, they are put into the alloy secondary feeding bin.

[0064] Close the melting chamber and turn on the vacuum pump to evacuate the system. When the vacuum degree of the melting chamber and the atomizing chamber reaches less than 1Pa, stop the vacuum operation. Then fill the furnace chamber and the atomizing chamber with inert gas to make the pressure of the melting chamber and the atomizing chamber reach a slightly positive pressure (0.115MPa). Then turn on the vacuum pump again to evacuate the system and wash the furnace. Control the vacuum degree of the melting chamber and the atomizing chamber to 90Pa. The heating system of the melting crucible and the tundish starts to supply power to increase the temperature. After all the raw materials in the melting crucible are melted, the temperature of the alloy melt in the melting crucible reaches 1650℃ and is kept warm for 8 minutes; then the vacuum carbon deoxidation refining operation is started. First, the vacuum degree of the system is controlled at 100Pa, and the refining is performed for 7 minutes. Then the vacuum pump is controlled to increase the vacuum degree of the system to less than 1Pa and the refining is performed for 4 minutes. Then, inert gas is filled into the melting chamber and the atomization chamber. The high-purity argon gas accounts for 80% of the inert gas, and the high-purity nitrogen accounts for 20%, so that the pressure in the melting chamber reaches 0.13MPa; the frequency of the melting crucible induction power supply is adjusted to ensure that the temperature of the molten alloy melt is 1740℃ (150℃ higher than the melting point of chromium nitride). The mixture of metallic manganese particles and chromium nitride particles is added through the alloy silo. After the addition is completed, alloying is carried out for 9 minutes. During the entire refining and secondary charging alloying process, the temperature of the tundish is controlled to reach 1450°C and is kept warm for 23 minutes. The molten alloy melt is poured into the tundish, and the alloy melt is introduced into the gas atomization system through the guide pipe at the bottom of the tundish. It is atomized by high-pressure inert gas (high-purity argon accounts for 85% and high-purity nitrogen accounts for 15%) to obtain alloy powder. The diameter of the nozzle circular hole is 6.0 mm, and the pressure of the high-pressure inert gas is 5.0 MPa.

[0065] The solidified powder enters the powder collecting tank, is taken out after being fully cooled, and is sieved by ultrasonic vibration under the protection of inert gas atmosphere to obtain duplex stainless steel powder with suitable particle size. Finally, the finished product is vacuum packaged.

[0066] After analysis, the composition of the duplex stainless steel powder prepared in Example 3 is shown in Table 8, and the composition meets the requirements, especially the nitrogen content (mass percentage) of the powder can be controlled at 0.356%, which is 0.006% away from the target limit.

[0067] Comparative Example 1

[0068] The ingredients are prepared according to the duplex stainless steel composition in Table 4.

[0069] Table 4 is the composition table of duplex stainless steel of comparative example 1

[0070]

[0071] According to the steps of Example 1, the temperature of the alloy melt is changed when the mixture of metal manganese particles and manganese nitride particles is added. The raw materials are pure iron (Fe>99.95%), metal manganese particles (Mn>99.5%, particle size is 1-5mm), carburizer (C>99.95%), electrolytic nickel (Ni>99.9%), metal molybdenum (Mo>99.9%), metal chromium (Cr>99.8%), nitrogen-containing alloy particles are manganese nitride (N: 8%, Fe: 2.2%, Si: 0.41%, the balance is manganese), and the melting point of manganese nitride is 1300°C. First, all raw materials except manganese particles and manganese nitride alloy particles are added into a smelting crucible, and after the manganese particles and manganese nitride alloy particles are evenly mixed, they are placed into the alloy secondary feeding bin.

[0072] Close the melting chamber and turn on the vacuum pump to evacuate the system. When the vacuum degree of the melting chamber and the atomizing chamber reaches less than 1Pa, stop the vacuum operation. Then fill the furnace chamber and the atomizing chamber with inert gas to make the pressure of the melting chamber and the atomizing chamber reach a slightly positive pressure (0.105MPa). Then turn on the vacuum pump again to evacuate the system and wash the furnace. Control the vacuum degree of the melting chamber and the atomizing chamber to 170Pa. The heating system of the melting crucible and the tundish starts to supply power to increase the temperature. After all the raw materials in the melting crucible are melted, the temperature of the alloy melt in the melting crucible reaches 1450℃ and is kept warm for 5 minutes; then the vacuum carbon deoxidation refining operation is started. First, the vacuum degree of the system is controlled at 150Pa, and the refining is performed for 5 minutes. Then the vacuum pump is controlled to increase the vacuum degree of the system to less than 1Pa and the refining is performed for 2.5 minutes. Then, inert gas is filled into the melting chamber and the atomization chamber. The high-purity argon gas accounts for 90% of the inert gas, and the high-purity nitrogen accounts for 10%, so that the pressure in the melting chamber reaches 0.11MPa; the frequency of the induction power supply of the melting crucible is adjusted to ensure that the temperature of the alloy liquid is 1580℃ (higher than the melting point of manganese nitride 280℃). The mixture of metallic manganese particles and manganese nitride particles is added through the alloy silo. After the addition is completed, alloying is carried out for 4 minutes. During the entire refining and secondary alloying process, the temperature of the tundish is controlled to reach 1350°C and is kept warm for 15 minutes. The molten alloy melt is poured into the tundish, and the alloy melt is introduced into the gas atomization system through the guide pipe at the bottom of the tundish. It is atomized by high-pressure inert gas (high-purity argon accounts for 95% and high-purity nitrogen accounts for 5%) to obtain alloy powder. The diameter of the nozzle circular hole is 4.0mm, and the pressure of the high-pressure inert gas is 3.5MPa.

[0073] The solidified powder enters the powder collecting tank, is taken out after being fully cooled, and is sieved by ultrasonic vibration under the protection of inert gas atmosphere to obtain duplex stainless steel powder with suitable particle size. Finally, the finished product is vacuum packaged.

[0074] After analysis, the composition of the duplex stainless steel powder prepared in Comparative Example 1 is shown in Table 8. The nitrogen composition does not meet the requirements, and the powder nitrogen content loss is large, which is 0.109% (mass percentage), and the negative deviation from the target limit is 0.041%.

[0075] Comparative Example 2

[0076] The ingredients are prepared according to the duplex stainless steel composition in Table 5.

[0077] Table 5 is the composition table of duplex stainless steel of comparative example 2

[0078]

[0079] According to the steps of Example 2, the method of adding metal manganese particles is changed, and metal manganese particles are added before adding ferrochrome nitride. The raw materials are pure iron (Fe>99.95%), metal manganese particles (Mn>99.5%, particle size is 1-5mm), carburizer (C>99.95%), electrolytic nickel (Ni>99.9%), metal molybdenum (Mo>99.9%), metal chromium (Cr>99.8%), nitrogen-containing alloy particles are ferrochrome nitride (N: 8%, Cr: 45%, Si: 0.15%, C: 0.18%, the balance is iron), and the melting point of ferrochrome nitride is 1450°C. First, all raw materials except manganese particles and ferrochrome nitride alloy particles are added into a smelting crucible, and manganese particles and ferrochrome nitride alloy particles are placed separately and put into the alloy secondary feeding bin.

[0080] Close the melting chamber, turn on the vacuum pump to evacuate the system, and stop the vacuum operation when the vacuum degree of the melting chamber and the atomizing chamber reaches less than 1Pa. Then fill the furnace chamber and the atomizing chamber with inert gas to make the pressure of the melting chamber and the atomizing chamber reach a slightly positive pressure (0.11MPa). Then turn on the vacuum pump again to evacuate the system and wash the furnace. Control the vacuum degree of the melting chamber and the atomizing chamber to 110Pa. The heating system of the melting crucible and the tundish starts to supply power to increase the temperature. After all the raw materials in the melting crucible are melted, the temperature of the alloy melt in the melting crucible reaches 1570℃ and then is kept warm for 7 minutes; then the vacuum carbon deoxidation refining operation is started. First, the vacuum degree of the system is controlled at 130Pa, and the refining is carried out for 6 minutes. Then the vacuum pump is controlled to increase the vacuum degree of the system to less than 1Pa and the refining is carried out for 3 minutes. Then, inert gas is filled into the melting chamber and the atomization chamber. The high-purity argon gas accounts for 85% of the inert gas, and the high-purity nitrogen accounts for 15%. The pressure in the melting chamber reaches 0.12MPa, and metallic manganese particles are added; the frequency of the induction power supply of the melting crucible is adjusted to ensure that the temperature of the molten alloy is at 1600℃ (higher than the melting point of ferrochromium nitride by 150℃), and then a mixture of ferrochromium nitride particles is added, and the alloy is supplemented through the alloy silo. After the addition is completed, alloying is carried out for 7 minutes. During the entire refining and secondary alloying process, the temperature of the tundish is controlled to reach 1420°C and is kept warm for 20 minutes. The molten alloy melt is poured into the tundish, and the molten alloy melt is introduced into the gas atomization system through the guide pipe at the bottom of the tundish. It is atomized by high-pressure inert gas (high-purity argon accounts for 90% and high-purity nitrogen accounts for 10%) to obtain alloy powder. The diameter of the nozzle circular hole is 4.5mm, and the pressure of the high-pressure inert gas is 4.5MPa.

[0081] The solidified powder enters the powder collecting tank, is taken out after being fully cooled, and is sieved by airflow classification under the protection of an inert gas atmosphere to obtain duplex stainless steel powder with a suitable particle size. Finally, the finished product is vacuum packaged.

[0082] After analysis, the composition of the duplex stainless steel powder prepared in Comparative Example 2 is shown in Table 8. The nitrogen composition does not meet the requirements, and the nitrogen content of the powder is reduced to 0.215% (mass percentage), which deviates negatively from the target limit by 0.035%.

[0083] Comparative Example 3

[0084] The ingredients are prepared according to the duplex stainless steel composition in Table 6.

[0085] Table 6 is the composition table of duplex stainless steel of comparative example 3

[0086]

[0087] The steps of Example 3 are followed, and the inert gas used in the smelting chamber and atomization is changed to high-purity argon gas, and no nitrogen is mixed. The raw materials are pure iron (Fe>99.95%), metal manganese particles (Mn>99.5%, particle size is 1-5mm), carburizer (C>99.95%), electrolytic nickel (Ni>99.9%), metal molybdenum (Mo>99.9%), metal chromium (Cr>99.8%), and the nitrogen-containing alloy particles are chromium nitride (N: 13.1%, Si: 0.29%, Fe: 0.19%, and the balance is chromium), and the melting point of chromium nitride is 1590°C. First, all the raw materials except manganese particles and chromium nitride alloy particles are added into the smelting crucible, and after the manganese particles and chromium nitride alloy particles are evenly mixed, they are placed into the alloy secondary feeding bin.

[0088] Close the melting chamber and turn on the vacuum pump to evacuate the system. When the vacuum degree of the melting chamber and the atomizing chamber reaches less than 1Pa, stop the vacuum operation. Then fill the furnace chamber and the atomizing chamber with inert gas to make the pressure of the melting chamber and the atomizing chamber reach a slightly positive pressure (0.115MPa). Then turn on the vacuum pump again to evacuate the system and wash the furnace. Control the vacuum degree of the melting chamber and the atomizing chamber to 90Pa. The heating system of the melting crucible and the tundish starts to supply power to increase the temperature. After all the raw materials in the melting crucible are melted, the temperature of the alloy melt in the melting crucible reaches 1650℃ and is kept warm for 8 minutes; then the vacuum carbon deoxidation refining operation is started. First, the vacuum degree of the system is controlled at 100Pa, and the refining is performed for 7 minutes. Then the vacuum pump is controlled to increase the vacuum degree of the system to less than 1Pa and the refining is performed for 4 minutes. After that, inert gas is filled into the melting chamber and the atomization chamber. The inert gas is high-purity argon gas, and the pressure in the melting chamber reaches 0.13MPa. The frequency of the induction power supply of the melting crucible is adjusted to ensure that the temperature of the molten alloy is at 1740℃ (150℃ higher than the melting point of chromium nitride). The mixture of metallic manganese particles and chromium nitride particles is added through the alloy silo. After the addition is completed, alloying is carried out for 9 minutes. During the entire refining and secondary alloying process, the temperature of the tundish is controlled to reach 1450°C and is kept warm for 23 minutes. The molten alloy melt is poured into the tundish, and the alloy melt is introduced into the gas atomization system through the guide pipe at the bottom of the tundish. It is atomized by high-pressure inert gas (high-purity argon) to obtain alloy powder. The diameter of the nozzle circular hole is 6.0 mm, and the pressure of the high-pressure inert gas is 5.0 MPa.

[0089] The solidified alloy powder enters the powder collecting tank, is taken out after being fully cooled, and is sieved by ultrasonic vibration under the protection of inert gas atmosphere to obtain duplex stainless steel powder with suitable particle size. Finally, the finished product is vacuum packaged.

[0090] After analysis, the composition of the duplex stainless steel powder prepared in Comparative Example 3 is shown in Table 8. The composition does not meet the requirements, and the nitrogen content of the powder is reduced to 0.322% (mass percentage), which deviates negatively from the target limit by 0.028%.

[0091] Comparative Example 4

[0092] The ingredients are prepared according to the duplex stainless steel composition in Table 7.

[0093] Table 7 is the composition table of duplex stainless steel of Comparative Example 4

[0094]

[0095] According to some steps of Example 3, the temperature of the alloy melt when chromium nitride is added is reduced, the method of adding metal manganese particles is changed (separate from chromium nitride particles), and the inert gas used in the smelting chamber and atomization is changed to high-purity argon gas without mixing nitrogen. The raw materials are pure iron (Fe>99.95%), metal manganese particles (Mn>99.5%, particle size is 1-5mm), carburizer (C>99.95%), electrolytic nickel (Ni>99.9%), metal molybdenum (Mo>99.9%), metal chromium (Cr>99.8%), nitrogen-containing alloy particles are chromium nitride (N: 13.1%, Si: 0.29%, Fe: 0.19%, the balance is chromium), and the melting point of chromium nitride is 1590°C. First, all raw materials except manganese particles and chromium nitride alloy particles are added into the smelting crucible, and the manganese particles and chromium nitride iron alloy particles are placed separately and put into the alloy secondary feeding bin.

[0096] Close the melting chamber and turn on the vacuum pump to evacuate the system. When the vacuum degree of the melting chamber and the atomizing chamber reaches less than 1Pa, stop the vacuum operation. Then fill the furnace chamber and the atomizing chamber with inert gas to make the pressure of the melting chamber and the atomizing chamber reach a slightly positive pressure (0.115MPa). Then turn on the vacuum pump again to evacuate the system and wash the furnace. Control the vacuum degree of the melting chamber and the atomizing chamber to 90Pa. The heating system of the melting crucible and the tundish starts to supply power to increase the temperature. After all the raw materials in the melting crucible are melted, the temperature of the alloy melt in the melting crucible reaches 1650℃ and is kept warm for 8 minutes; then the vacuum carbon deoxidation refining operation is started. First, the vacuum degree of the system is controlled at 100Pa, and the refining is performed for 7 minutes. Then the vacuum pump is controlled to increase the vacuum degree of the system to less than 1Pa and the refining is performed for 4 minutes. After that, inert gas is filled into the melting chamber and the atomization chamber. The inert gas is high-purity argon gas. The pressure in the melting chamber reaches 0.13MPa, and metal manganese particles are added; the frequency of the induction power supply of the melting crucible is adjusted to ensure that the temperature of the molten alloy is 1670℃ (80℃ higher than the melting point of chromium nitride); the mixture of chromium nitride particles is supplemented with alloy through the alloy silo. After the addition is completed, alloying is carried out for 9 minutes. During the entire refining and secondary alloying process, the temperature of the tundish is controlled to reach 1450°C and is kept warm for 23 minutes. The molten alloy melt is poured into the tundish, and the alloy melt is introduced into the gas atomization system through the guide pipe at the bottom of the tundish. It is atomized by high-pressure inert gas (high-purity argon) to obtain alloy powder. The diameter of the nozzle circular hole is 6.0 mm, and the pressure of the high-pressure inert gas is 5.0 MPa.

[0097] The solidified alloy powder enters the powder collecting tank, is taken out after being fully cooled, and is sieved by ultrasonic vibration under the protection of inert gas atmosphere to obtain duplex stainless steel powder with suitable particle size. Finally, the finished product is vacuum packaged.

[0098] After analysis, the composition of the duplex stainless steel powder prepared in Comparative Example 4 is shown in Table 8. The composition does not meet the requirements, and the nitrogen content of the powder is reduced to 0.286% (mass percentage), which deviates negatively from the target limit by 0.064%.

[0099] Table 8 is a table of the composition of the duplex stainless steel powder of Examples 1-3 and Comparative Examples 1-4 (the components in the table are in mass percentage, wt%)

[0100] .

[0101] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Alterations, modifications, substitutions and variations of the above embodiments by a person skilled in the art are all within the scope of the present invention.

Claims

1. A method for preparing duplex stainless steel powder for laser additive manufacturing, characterized in that: The steps include: Step S01, the composition of the duplex stainless steel powder is calculated by mass percentage: C: 0.09-0.20%, Mn: 5.00-15.00%, Mo: 1.00-5.00%, Ni: 5.00-15.00%, Cr: 10.00-30.00%, N: 0.10-0.40%, S: ≤0.02%, P: ≤0.02%, Fe: balance; the raw materials are pure iron, metal manganese particles, carburizer, electrolytic nickel, metal molybdenum, metal chromium, and nitrogen-containing alloy particles. All raw materials except the metal manganese particles and the nitrogen-containing alloy particles are added into a smelting crucible, and the metal manganese particles and the nitrogen-containing alloy particles are evenly mixed and then placed into the alloy secondary feeding bin; In step S01, the nitrogen-containing alloy particles are any one of chromium nitride, manganese nitride, and chromium iron nitride; Step S02, the smelting chamber is closed, and the vacuum pump is turned on to evacuate the system. When the vacuum degree of the smelting chamber and the atomizing chamber reaches less than 1Pa, the evacuation is stopped, and then inert gas is filled into the smelting chamber and the atomizing chamber to make the pressure of the smelting chamber and the atomizing chamber reach a slightly positive pressure, and then the vacuum pump is turned on to evacuate and clean the furnace, and the vacuum degree of the smelting chamber and the atomizing chamber is controlled to be ≤200Pa; Step S03, the heating system of the smelting crucible and the tundish is powered on to increase the temperature. After all the raw materials in the smelting crucible are melted, the temperature of the alloy melt in the smelting crucible reaches 1450-1650°C, and then the temperature is kept for 5-10 minutes; then vacuum carbon deoxidation refining is performed, the vacuum degree of the control system is controlled at 10-200Pa, and the refining is performed for 4-8 minutes, and then the vacuum pump is controlled to increase the vacuum degree of the system to within 1Pa and the refining is performed for 2-5 minutes, and then the inert gas is filled into the smelting chamber and the atomizing chamber to make the pressure of the smelting chamber reach 0.11-0.13MPa; In step S03, the inert gas is a mixed gas of high-purity argon and high-purity nitrogen, wherein the high-purity argon accounts for 80-90%, the high-purity nitrogen accounts for 10-20%, and the gas purity is not less than 99.99%; Step S04, after step S03 is completed, the frequency of the induction power supply of the melting crucible is adjusted to make the temperature of the molten alloy 150°C higher than the melting point of the nitrogen-containing alloy particles, a mixture of metal manganese particles and nitrogen-containing alloy particles is added, alloying for 3 to 10 minutes, stirring, and controlling the temperature of the tundish to reach 1300 to 1450°C during the entire refining and secondary charging alloying process, and keeping the temperature for 15 to 25 minutes; Step S05, pouring the molten alloy melt into a tundish, introducing the molten alloy melt into a gas atomization system through a guide pipe at the bottom of the tundish, and atomizing the molten alloy melt with high-pressure inert gas to obtain alloy powder; Step S06: After the alloy powder obtained in step S05 is fully cooled, it is taken out and subjected to airflow classification or ultrasonic vibration screening under the protection of an inert gas atmosphere to obtain a duplex stainless steel powder.

2. The method for preparing duplex stainless steel powder for laser additive manufacturing according to claim 1, characterized in that: In the step S01, the raw material pure iron contains Fe>99.95%, the metal manganese particles contain Mn>99.5%, the metal manganese particles have a size of 1-5 mm, the carburizer contains C>99.95%, the electrolytic nickel contains Ni>99.9%, the metal molybdenum contains Mo>99.9%, the metal chromium contains Cr>99.8%, the chromium nitride contains N: 10-15%, Si: 0.2-0.5%, Fe: 0.1-0.3%, and the balance is chromium; the manganese nitride contains N: 6-10%, Fe: 1.0-3.0%, Si: 0.2-0.6%, and the balance is manganese; the chromium nitride contains N: 5-12%, Cr: 30-60%, Si: 0.05-0.15%, C: 0.1-0.2%, and the balance is iron.

3. The method for preparing duplex stainless steel powder for laser additive manufacturing according to claim 1, characterized in that: In the step S01, the smelting crucible is made of fused magnesia with a mass percentage of MgO not less than 95% or alumina with a mass percentage of Al2O3 not less than 95%.

4. The method for preparing duplex stainless steel powder for laser additive manufacturing according to claim 1, characterized in that: In step S02, the inert gas is high-purity argon gas, and the gas purity is not less than 99.99%.

5. The method for preparing duplex stainless steel powder for laser additive manufacturing according to claim 1, characterized in that: In step S05, the atomization system includes an annular gap atomization spray disc and a nozzle with a circular hole, the diameter of the nozzle circular hole is 3.5 to 6 mm, and the pressure of the high-pressure inert gas is 3 to 6 MPa; the inert gas is a mixed gas of high-purity argon and high-purity nitrogen, the high-purity argon accounts for 85 to 95%, the high-purity nitrogen accounts for 5 to 15%, and the gas purity is not less than 99.99%.

6. The duplex stainless steel powder for laser additive manufacturing prepared according to the method according to any one of claims 1 to 5 is used for selective laser melting 3D printing of duplex stainless steel components.

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