Metal cored welding wire and method of additive manufacturing of martensitic stainless steel structural components

Abstract

This invention discloses a metal-type flux-cored welding wire, comprising a flux core and a welding sheath. The flux core is composed of the following components by mass percentage: 6%-7% chromium powder, 2%-3% silicon powder, 5%-8% copper powder, 0.2%-0.5% titanium powder, 2%-3% niobium powder, 0.3%-0.5% lanthanum oxide, and the remainder being iron powder, with the sum of the mass percentages of the above components being 100%. This metal-type flux-cored welding wire can be used to fabricate martensitic stainless steel structural components, and the resulting structural components exhibit excellent mechanical properties. An additive manufacturing method for martensitic stainless steel structural components is also disclosed.

Description

Technical Field

[0001] This invention belongs to the field of wire arc additive manufacturing technology, specifically relating to a metal-type flux-cored welding wire, and also to an additive manufacturing method for martensitic stainless steel structural parts. Background Technology

[0002] Stainless steel is one of my country's three pillar materials, and with the rapid development of my country's modern industry, higher requirements have been placed on the comprehensive mechanical properties of stainless steel. Martensitic stainless steel, as an advanced high-strength steel, possesses high strength and high toughness, while also exhibiting good resistance to water erosion and weak acid corrosion. Therefore, it is widely used in the manufacture of components such as steam turbine rotor blades, oil well pipes, shafts and bushings, fastening bolts, and hydraulic press valve plates, making it an important engineering structural material. Currently, martensitic stainless steel structural components in my country are manufactured using traditional processes (casting and forging). These processes are difficult and costly when manufacturing large structural components, and are prone to defects, resulting in poor tensile properties of the components.

[0003] Wire arc additive manufacturing (WAAM) is a manufacturing method that uses an electric arc as a heat source to melt metal wire and deposit it layer by layer on a substrate according to a predetermined path. Compared to traditional subtractive manufacturing, it generally does not require molds and has a shorter production cycle, lower cost, higher material utilization, and higher degree of automation, making it particularly advantageous for manufacturing large-sized components with complex shapes. Currently, welding wires on the market are mainly for welding materials, and there are no dedicated wires for arc additive manufacturing and remanufacturing. Furthermore, the thermal processes in welding additive manufacturing differ significantly, and existing welding wires often fail to meet the requirements of additive manufacturing. Summary of the Invention

[0004] The first objective of this invention is to provide a metal-cored welding wire that can be used to prepare martensitic stainless steel structural components, and the prepared structural components have excellent mechanical properties.

[0005] The second objective of this invention is to provide an additive manufacturing method for martensitic stainless steel structural components, wherein the structural components prepared using the aforementioned metal-cored welding wire as raw material have excellent mechanical properties.

[0006] The first technical solution adopted in this invention is a metal-type flux-cored welding wire, comprising a flux core and a welding sheath, wherein the flux core is composed of the following components by mass percentage: 6%-7% chromium powder, 2%-3% silicon powder, 5%-8% copper powder, 0.2%-0.5% titanium powder, 2%-3% niobium powder, 0.3%-0.5% lanthanum oxide, and the remainder being iron powder, the sum of the mass percentages of the above components being 100%.

[0007] The invention is further characterized in that,

[0008] The weld bead is made of austenitic stainless steel strip, and the filling rate of the flux core powder is controlled at 25wt%-30wt%.

[0009] The second technical solution adopted in this invention is an additive manufacturing method for martensitic stainless steel structural components, which is carried out according to the following steps:

[0010] Step 1: Weigh the following powders according to their mass percentages: chromium powder 6%-7%, silicon powder 2%-3%, copper powder 5%-8%, titanium powder 0.2%-0.5%, niobium powder 2%-3%, lanthanum oxide 0.3%-0.5%, and the remainder is iron powder. The sum of the mass percentages of the above components is 100%.

[0011] Step 2: Heat-treat the powder weighed in Step 1 in an inert gas atmosphere, and then keep it at that temperature;

[0012] Step 3: After heat preservation, the flux-cored powder obtained in Step 2 is cooled to room temperature in the furnace. The flux-cored powder is then filled into the U-shaped groove of the austenitic stainless steel strip and formed into a 2.50mm welding wire after passing through the closed forming roller. Finally, a 1.20mm metal mold flux-cored welding wire is made by gradually reducing the diameter.

[0013] Step 4: Using the metal-cored welding wire obtained in Step 3, adder manufacturing is carried out using MIG welding as the heat source to prepare martensitic stainless steel structural parts.

[0014] The invention is further characterized in that,

[0015] In step 2, the inert atmosphere is argon; in step 2, the heating temperature for heat treatment is 200℃~300℃, and the holding time is 2~3h.

[0016] In step 3, the filling rate of the core powder is controlled at 25wt%-30wt%.

[0017] The specific process of step 4 is as follows: the metal-cored welding wire prepared in step 3 is loaded into the fully automatic welding robot, the welding path is planned, the layer height is determined, and the program is written and input into the fully automatic welding robot. The welding machine command is run, and the martensitic stainless steel structural part of the present invention is obtained by using MIG welding as the heat source for additive manufacturing.

[0018] In step 4, the process parameters for MIG welding are: welding speed of 0.18 m / min to 0.22 m / min; torch lifting height of 3.5 mm to 5 mm per layer; and argon as the shielding gas.

[0019] The beneficial effects of this invention are:

[0020] (1) The present invention provides a metal flux-cored welding wire with a short preparation cycle, high production efficiency, and continuous production capability. It can be used for additive manufacturing of complex parts in the fields of national defense, energy, petroleum, chemical industry, aerospace and bioengineering. The flux-cored welding wire transfers alloy elements into the weld through the flux core inside the steel sheet during the welding process, thereby making it easy to adjust the content of alloy composition.

[0021] (2) In the technical solution of the present invention, the flux-cored welding wire used is different from the solid welding wire. The flux-cored welding wire transfers the alloy elements into the weld through the flux core inside the steel sheet during the welding process. Therefore, it is very convenient to adjust the content of the alloy composition. The solid welding wire needs to be re-smelted every time the alloy composition is adjusted. In addition, during the drawing process of the solid welding wire, some steel ingots have very poor drawability and are not easy to draw into the required welding wire.

[0022] (3) This invention provides a method for preparing martensitic stainless steel structural parts using MIG welding as a heat source, metal-cored welding wire as raw material, and additive manufacturing technology. The method involves placing uniformly mixed flux-cored powder in a tube furnace, continuously introducing argon gas, and holding at 200℃~300℃ for 2h~3h. This method effectively avoids the oxidation of alloying elements and reduces the oxygen content of the martensitic stainless steel structural parts. The method uses a fully automated welding robot for additive manufacturing of martensitic stainless steel, resulting in high additive manufacturing efficiency. Wire arc additive manufacturing can be implemented through welding robot programming. The present invention provides the following advantages in additive manufacturing: less spatter, more stable arc, aesthetically pleasing weld formation with minimal collapse, smooth weld surface free of porosity and slag inclusions. After additive manufacturing, the welding area is hammered to reduce residual welding stress and improve the fatigue resistance of the structural components. Based on MIG welding, the present invention uses metal-cored welding wire as raw material to prepare martensitic stainless steel, which has the following advantages: high weld metal deposition rate, high production efficiency, good structural component formability, less slag inclusions in the weld, and lower cost, making it suitable for automated production; less spatter and stable droplet transfer during welding.

[0023] (4) Currently, most raw materials for arc additive manufacturing of martensitic stainless steel in my country use solid welding wire. However, solid welding wire requires re-smelting every time the alloy composition is adjusted, resulting in a long and complex preparation cycle. This invention patent uses metal-cored welding wire as the raw material for arc additive manufacturing of martensitic stainless steel. The alloying elements are transferred into the weld through the flux core inside the steel sheet during the welding process, and the transfer of reinforcing phases such as La2O3 and NbC into the weld is relatively convenient. As a high-melting-point compound, La2O3 can act as a non-uniform nucleation point in the molten pool, increasing the external nucleation source, or segregating at grain boundaries, hindering grain growth and improving the strength of the martensitic stainless steel structural component. This structural component has excellent mechanical properties.

[0024] (5) This invention uses MIG welding to provide the heat source for preparing martensitic stainless steel structural parts. Compared with CO2 gas shielded welding, MIG welding has a stable arc, stable droplet transfer, less welding spatter, and better weld formation. Compared with TIG welding, MIG welding uses welding wire as the electrode, with high welding wire and current density, high welding wire melting efficiency, small welding deformation, and high productivity, making it suitable for automated production. In TIG welding, a small amount of tungsten melts and evaporates during the welding process, and tungsten particles entering the molten pool can cause tungsten inclusions, affecting the welding quality. In addition, TIG welding has a limited current carrying capacity, the arc is easy to spread and not easy to concentrate, and the weld penetration is relatively small. Attached Figure Description

[0025] Figure 1 The image shows the metallographic structure of the martensitic stainless steel structural component prepared in Example 1 of this invention.

[0026] Figure 2 The image shows the metallographic structure of the martensitic stainless steel structural component prepared in Example 2 of this invention.

[0027] Figure 3 The image shows the metallographic structure of the martensitic stainless steel structural component prepared in Example 3 of this invention.

[0028] Figure 4 The stress-strain test curve of the martensitic stainless steel structural component prepared in Example 3 of the present invention is shown. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0030] This invention provides a metal-type flux-cored welding wire, comprising a flux core and a welding sheath, wherein the flux core is composed of the following components by mass percentage: 6%-7% chromium powder, 2%-3% silicon powder, 5%-8% copper powder, 0.2%-0.5% titanium powder, 2%-3% niobium powder, 0.3%-0.5% lanthanum oxide, and the remainder being iron powder, the sum of the mass percentages of the above components being 100%.

[0031] The weld bead is made of austenitic stainless steel strip, and the filling rate of the flux core powder is controlled at 25wt%-30wt%.

[0032] The functions and roles of each component in this welding wire are as follows:

[0033] Silicon (Si) has a good solid solution strengthening effect in ferrite and austenite. Secondly, Si is generally used for deoxidation to reduce the embrittlement of the weld overlay metal caused by oxygenation.

[0034] Chromium (Cr) is the main alloying element in martensitic stainless steel. In martensitic stainless steel, Cr increases the solubility of carbon, enhancing the resistance of austenitic stainless steel to intergranular corrosion. This effectiveness of Cr is greatly enhanced when Mo is also present in the steel. Cr also plays an important role in improving the wear resistance of weld overlay alloys. Cr in the microstructure readily incorporates into carbides such as Fe7C3 and Fe in atomic form. 23 In C6, some Fe atoms are substituted to form a complex phase (Fe,Cr)7C3, (Fe,Cr) 23 C6, etc. The Cr element in the weld overlay alloy can dissolve in γ-Fe and α-Fe to improve the high-temperature strength and toughness of the alloy, improve the low-temperature toughness and corrosion resistance, improve hardenability, and produce a solid solution strengthening effect.

[0035] Copper (Cu) is an important alloying element in martensitic stainless steel. Its main role is to improve the cold working and forming properties of martensitic stainless steel. When combined with Mo, it further improves the corrosion resistance of martensitic stainless steel in reducing media.

[0036] In martensitic stainless steel, titanium (Ti) has a much stronger affinity for carbon than Cr, and is often used as a stabilizing element. It preferentially combines with carbon to form TiC, thereby improving the resistance of martensitic stainless steel to intergranular corrosion. At the same time, it can also serve as a heterogeneous nucleation site in the molten pool, promoting the refinement of the grains of the weld overlay alloy.

[0037] Lanthanum oxide (La₂O₃), as a high-melting-point compound, can act as a non-uniform nucleation site in the molten pool, increasing the number of external nucleation sources, or segregating at grain boundaries, hindering grain growth and improving the strength of martensitic stainless steel structural components. Furthermore, La can interact with oxides and sulfides in the molten steel, causing them to become nearly spherical, further enhancing the strength of martensitic stainless steel structural components and reducing the anisotropy of martensitic components prepared by arc additive manufacturing technology.

[0038] Niobium (Nb) can combine with carbon to form NbC. NbC has a face-centered cubic structure and is generally distributed uniformly in the martensite grains in granular form. It can pin dislocations, hinder dislocation movement, form dislocation loops to produce a strengthening effect, and NbC has a significant inhibitory effect on grain growth and coarsening, thereby improving the strength of martensitic stainless steel structural components.

[0039] This invention also provides an additive manufacturing method for martensitic stainless steel structural components, specifically comprising the following steps:

[0040] Step 1: Weigh the following powders according to their mass percentages: chromium powder 6%-7%, silicon powder 2%-3%, copper powder 5%-8%, titanium powder 0.2%-0.5%, niobium powder 2%-3%, lanthanum oxide 0.3%-0.5%, and the remainder is iron powder. The sum of the mass percentages of the above components is 100%.

[0041] Step 2: Heat-treat the powder weighed in Step 1 in an inert gas atmosphere, and then keep it at that temperature;

[0042] In step 2, the inert atmosphere is argon.

[0043] In step 2, the heating temperature for heat treatment is 200℃~300℃, and the holding time is 2h~3h.

[0044] Step 3: After heat preservation, the flux-cored powder obtained in Step 2 is cooled to room temperature in the furnace. The flux-cored powder is then filled into the U-shaped groove of the austenitic stainless steel strip and formed into a 2.50mm welding wire after passing through the closed forming roller. Finally, a 1.20mm metal mold flux-cored welding wire is made by gradually reducing the diameter. The filling rate of the flux-cored powder is controlled at 25wt%-30wt%.

[0045] Step 4: Using the metal-cored welding wire obtained in Step 3, adder manufacturing is carried out using MIG welding as the heat source to prepare martensitic stainless steel structural parts.

[0046] The specific process of step 4 is as follows: the metal-cored welding wire prepared in step 3 is loaded into the fully automatic welding robot, the welding path is planned, the layer height is determined, and the program is written and input into the fully automatic welding robot. The welding machine command is run, and the martensitic stainless steel structural part of the present invention is obtained by using MIG welding as the heat source for additive manufacturing.

[0047] In step 4, the process parameters for MIG welding are: welding speed of 0.18 m / min to 0.22 m / min; torch lifting height of 3.5 mm to 5 mm per layer; and argon as the shielding gas.

[0048] Example 1

[0049] Step 1: Weigh the following powders according to their mass percentages: chromium powder 6%, silicon powder 2%, copper powder 5%, titanium powder 0.5%, niobium powder 3%, lanthanum oxide 0.5%, and the remainder is iron powder. The sum of the mass percentages of the above components is 100%.

[0050] Step 2: Mix all the raw materials weighed in Step 1 evenly and place them in a tube furnace. Keep the furnace at 200°C for 2 hours under the condition of continuous argon gas introduction.

[0051] Step 3: Place the austenitic stainless steel strip with a width of 7mm and a thickness of 0.3mm on the feeding machine of the welding wire forming machine. Roll the austenitic stainless steel strip into a U-shaped groove through the pressing groove of the forming machine. Put the flux-cored powder obtained in Step 2 into the U-shaped groove. The filling rate of the flux-cored powder is controlled at 25wt%. Then, use the forming machine to press and close the U-shaped groove. Wipe it clean with acetone or anhydrous ethanol and then draw it to a diameter of 1.20mm. Wipe the oil stains on the welding wire with a cotton cloth soaked in acetone or anhydrous ethanol. Finally, the welding wire is straightened, coiled into a disc, and sealed and packaged by the wire drawing machine to obtain the martensitic stainless steel metal mold flux-cored welding wire for additive manufacturing.

[0052] Step 4: Load the prepared additive manufacturing martensitic stainless steel metal mold flux-cored welding wire into the fully automatic welding robot, plan the welding path, determine the layer height, and input the program into the welding machine. Run the welding machine commands and use MIG welding as the heat source for additive manufacturing to obtain the martensitic stainless steel structural part of this invention. The specific welding process parameters are: welding speed of 0.20 m / min; torch lifting of 3.5 mm per layer; shielding gas of argon. The metallographic structure of the structural part prepared in this embodiment is shown in the figure. Figure 1 As shown, the molding is good.

[0053] Example 2

[0054] Step 1: Weigh the following powders according to their mass percentages: 7% chromium powder, 3% silicon powder, 8% copper powder, 0.2% titanium powder, 2% niobium powder, 0.3% lanthanum oxide, and the remainder is iron powder. The sum of the mass percentages of the above components is 100%.

[0055] Step 2: Mix all the raw materials weighed in Step 1 evenly, place them in a tube furnace, and keep them at 230°C for 3 hours under the condition of continuous argon gas introduction.

[0056] Step 3: Place the austenitic stainless steel strip with a width of 7mm and a thickness of 0.3mm on the feeding machine of the welding wire forming machine. Roll the austenitic stainless steel strip into a U-shaped groove through the pressing groove of the forming machine. Put the flux-cored powder obtained in Step 2 into the U-shaped groove. The filling rate of the flux-cored powder is controlled at 26wt%. Then, use the forming machine to press and close the U-shaped groove. Wipe it clean with acetone or anhydrous ethanol and then draw it to a diameter of 1.20mm. Wipe the oil stains on the welding wire with a cotton cloth soaked in acetone or anhydrous ethanol. Finally, the welding wire is straightened, coiled into a disc, and sealed and packaged by the wire drawing machine to obtain the martensitic stainless steel metal mold flux-cored welding wire for additive manufacturing.

[0057] Step 4: The fully automated welding robot for the additive manufacturing martensitic stainless steel flux-cored wire prepared in Step 3 is used. The welding path is planned, the layer height is determined, and the program is written and input into the welding machine. The welding machine commands are run, and MIG welding is used as the heat source for additive manufacturing to obtain the martensitic stainless steel structural part of the present invention. The specific parameters of the welding process are: welding speed of 0.22 m / min; welding torch lifting of 5 mm per layer; shielding gas of argon. The metallographic structure of the structural part prepared in this embodiment is shown in the figure. Figure 2 As shown, the molding is good.

[0058] Example 3

[0059] Step 1: Weigh the following powders by mass percentage: 6.5% chromium powder, 2.5% silicon powder, 7% copper powder, 0.4% titanium powder, 2.5% niobium powder, 0.4% lanthanum oxide, and the remainder is iron powder. The sum of the mass percentages of the above components is 100%.

[0060] Step 2: Mix all the raw materials weighed in Step 1 evenly, place them in a tube furnace, and keep them at 250°C for 2.5 hours under continuous argon gas supply.

[0061] Step 3: Place the austenitic stainless steel strip with a width of 7mm and a thickness of 0.3mm on the feeding machine of the welding wire forming machine. Roll the austenitic stainless steel strip into a U-shaped groove through the pressing groove of the forming machine. Put the flux-cored powder obtained in Step 2 into the U-shaped groove. The filling rate of the flux-cored powder is controlled at 30wt%. Then, use the forming machine to press and close the U-shaped groove. Wipe it clean with acetone or anhydrous ethanol and then draw it to a diameter of 1.20mm. Wipe the oil stains on the welding wire with a cotton cloth soaked in acetone or anhydrous ethanol. Finally, straighten the welding wire, coil it into a disc, and seal it in packaging to obtain the martensitic stainless steel metal mold flux-cored welding wire for additive manufacturing.

[0062] Step 4: Load the prepared martensitic stainless steel flux-cored welding wire for additive manufacturing from Step 3 into a fully automated welding robot. Plan the welding path, determine the layer height, and input the program into the welding machine. Run the welding machine commands and use MIG welding as the heat source for additive manufacturing to obtain the martensitic stainless steel structural component of this invention. The specific welding parameters are: welding speed of 0.21 m / min; torch height of 4.6 mm per layer; and argon as the shielding gas. The metallographic structure of the structural component prepared in this embodiment is shown in the figure. Figure 3 As shown, the martensitic structural component prepared in this embodiment has good forming and is free of defects. The stress-strain test curve results of the structural component prepared in this embodiment are as follows. Figure 4 As shown, the yield strength is 750 MPa and the tensile strength is 938 MPa, and the resulting martensitic stainless steel additive manufacturing structure has excellent mechanical properties.

Claims

1. A metal-type flux-cored welding wire, characterized in that, It includes a flux core and a solder coating. The flux core is composed of the following components by mass percentage: 6%-7% chromium powder, 2%-3% silicon powder, 5%-8% copper powder, 0.2%-0.5% titanium powder, 2%-3% niobium powder, 0.3%-0.5% lanthanum oxide, and the remainder is iron powder. The sum of the mass percentages of the above components is 100%. The weld bead is made of austenitic stainless steel strip, and the filling rate of the flux core powder is controlled at 26wt%-30wt%.

2. An additive manufacturing method for martensitic stainless steel structural components, characterized in that, Please follow these steps: Step 1: Weigh the following powders according to their mass percentages: chromium powder 6%-7%, silicon powder 2%-3%, copper powder 5%-8%, titanium powder 0.2%-0.5%, niobium powder 2%-3%, lanthanum oxide 0.3%-0.5%, and the remainder is iron powder. The sum of the mass percentages of the above components shall be 100%. Step 2: Heat-treat the powder weighed in Step 1 in an inert gas atmosphere, and then keep it at that temperature; In step 2, the inert atmosphere is argon; in step 2, the heating temperature for heat treatment is 230℃~300℃, and the holding time is 2~3h. Step 3: After heat preservation, the flux-cored powder obtained in Step 2 is cooled to room temperature in the furnace. The flux-cored powder is then filled into the U-shaped groove of the austenitic stainless steel strip and formed into a 2.50mm welding wire after passing through the closed forming roller. Finally, a 1.20mm metal mold flux-cored welding wire is made by gradually reducing the diameter. In step 3, the filling rate of the core powder is controlled between 26wt% and 30wt%. Step 4: Using the metal-cored welding wire obtained in Step 3, adder manufacturing is carried out using MIG welding as the heat source to prepare martensitic stainless steel structural parts.

3. The additive manufacturing method for martensitic stainless steel structural parts according to claim 2, characterized in that, The specific process of step 4 is as follows: the metal-cored welding wire prepared in step 3 is loaded into the fully automatic welding robot, the welding path is planned, the layer height is determined, and the program is written and input into the fully automatic welding robot. The welding machine command is run, and the martensitic stainless steel structural parts are obtained by additive manufacturing using MIG welding as the heat source.

4. The additive manufacturing method for martensitic stainless steel structural parts according to claim 3, characterized in that, In step 4, the process parameters for MIG welding are: welding speed of 0.18 m / min to 0.20 m / min; torch lifting height of 3.5 mm to 5 mm per layer; and argon as the shielding gas.

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