A high-Cr and low-Ni flux-cored wire for a magnesium reduction tank, its preparation method and application

Abstract

The present invention discloses a high-Cr and low-Ni flux-cored wire for a magnesium reduction tank, its preparation method and application. The flux-cored wire comprises a powder core and a welding skin. The powder core comprises the following components by mass percentage: 1.0-1.5% of Si powder, 8.0-10.0% of Mn powder, 40.0-50.0% of Cr powder, 12.0-15.0% of Ni powder, 3.0-4.0% of Nb powder, 1.0-1.5% of Ti powder, 0.8-1.0% of Al powder, 0.1-0.3% of graphene, and the balance is Fe powder, and the sum of the mass percentages of the above components is 100%. The preparation method is as follows: the above alloy powders are mixed and then dried, and then wrapped with 0Cr19Ni10 strip and drawn to obtain the flux-cored wire. The flux-cored wire of the present invention is used for welding a magnesium reduction tank, and the obtained head has high strength and good toughness, and no defects are generated in the weld seam.

Description

Technical Field

[0001] The present invention belongs to the field of metal materials, and particularly relates to a high-Cr low-Ni flux-cored wire for a magnesium reduction tank, a preparation method and an application thereof. Background Art

[0002] In order to obtain magnesium resources in ores, it is necessary to carry out magnesium smelting treatment to obtain metallic magnesium. In the magnesium smelting technology, the magnesium reduction tank is the most important equipment unit, and its material is usually austenitic heat-resistant stainless steel. During the magnesium smelting process, the working temperature of the reduction tank is 500-1200°C, and a vacuum of about 20 Pa is drawn inside the tank. During its service process, it will be subjected to loads generated by its own weight and atmospheric pressure. Under high temperature and long-term load-bearing work, the reduction tank is prone to deformation and damage. The cylinder body and the head of the reduction tank are connected by welding. Due to the non-equilibrium characteristics of the welding process, the structure of the head is uneven and there are large welding residual stresses, resulting in premature failure of the weld between the cylinder body and the head of the reduction tank, which has a huge impact on production. Therefore, solving the welding problem between the head and the tank body of the reduction tank is the key to the development of the magnesium smelting industry. Summary of the Invention

[0003] The purpose of the present invention is to provide a high-Cr low-Ni wire for a magnesium reduction tank to achieve the optimal matching between the base metal and the head during the welding of the cylinder body of the magnesium reduction tank.

[0004] Another purpose of the present invention is to provide a preparation method of a high-Cr low-Ni wire for a magnesium reduction tank.

[0005] Still another purpose of the present invention is to provide a welding method specifically for welding a magnesium reduction tank and a head.

[0006] The present invention is implemented through the following technical solutions:

[0007] A high-Cr low-Ni flux-cored wire for a magnesium reduction tank, comprising flux powder and a welding skin. The flux powder comprises the following components by mass percentage: 1.0-1.5% of Si powder, 8.0-10.0% of Mn powder, 40.0-50.0% of Cr powder, 12.0-15.0% of Ni powder, 3.0-4.0% of Nb powder, 1.0-1.5% of Ti powder, 0.8-1.0% of Al powder, 0.1-0.3% of graphene, and the balance is Fe powder.

[0008] Further, the particle size of the graphene is 10-20 μm.

[0009] Further, the material of the welding skin is 06Cr19Ni10.

[0010] Further, the thickness of the welding skin is 0.4 mm and the width is 7 mm.

[0011] Furthermore, the powder filling rate of the flux-cored wire is controlled at 30-35%.

[0012] A preparation method of a high-Cr low-Ni flux-cored wire for a magnesium reduction tank is as follows:

[0013] Step 1: Weigh the powder Si powder, Mn powder, Cr powder, Ni powder, Nb powder, Ti powder, Al powder, graphene according to the mass percentages described in Claim 1, and the rest is Fe powder. The sum of the mass percentages of the above components is 100%.

[0014] Step 2: Place the powder weighed in Step 1 in a vacuum heating furnace for heating. The heating temperature is 280-300°C, and the heat preservation time is 1-3 h to remove the crystal water in the powder; the powder after removing the crystal water is placed in a powder mixer for sufficient mixing, and the mixing time is 1-3 h.

[0015] Step 3: Use alcohol to remove the grease on the surface of the welding belt, and wrap the powder prepared in Step 2 in the welding belt through a flux-cored wire drawing device to form a rough wire.

[0016] Step 4: Draw the rough wire prepared in Step 3 multiple times until it is finally drawn to the preset diameter range.

[0017] Step 5: After the flux-cored wire is drawn, it is wound on a wire spool by a wire winding machine and finally sealed in a vacuum packaging bag of the flux-cored wire for standby.

[0018] Furthermore, in Step 4, the aperture of the first drawing die is 2.6 mm. After the first drawing process is completed, the apertures of the second to the Nth dies are sequentially reduced, N≥2, and finally a flux-cored wire with a diameter of 1.2 mm is obtained.

[0019] A welding method uses the high-Cr low-Ni flux-cored wire for a magnesium reduction tank prepared by the above method to weld the cylinder body and the head of the magnesium reduction tank. During welding, the butt joint of the cylinder body and the head of the magnesium reduction tank is designed as follows: the thickness a of the cylinder body and the head of the magnesium reduction tank at the butt joint is made 10-20 mm, and slopes b and root faces c are respectively made on the opposite sides of the cylinder body and the head of the magnesium reduction tank. The two side slopes form a V-shaped groove. Among them, the groove angle is 90±5°, the size of the root face c is 2-3 mm, and the gap d between the cylinder body and the head of the magnesium reduction tank at the butt joint is 1.0-1.5 mm.

[0020] Furthermore, the welding power source is a CMT welding machine. The root pass welding current is 180-220 A, and the filling and capping welding currents are 150-180 A. Multi-layer and multi-pass welding is used, that is, the specific welding sequence is root pass weld bead - filling weld bead - capping weld bead.

[0021] According to the tissue and performance characteristics of the retort material, the present invention designs the matching welding consumables to achieve the optimal matching between the head and the base metal. The welding consumables of the present invention will improve the service life of the retort and enhance the market competitiveness of the magnesium smelting industry, having important engineering practical value. The specific beneficial effects are as follows:

[0022] (1) The present invention is applicable to the welding of the cylinder body and the head of the magnesium smelting retort, which can effectively solve problems such as cracking and insufficient service life during the welding process. The obtained head has high strength and good toughness, and no defects are generated in the weld.

[0023] (2) The present invention uses 06Cr19Ni10 strip to wrap alloy powder for wire drawing. Since the steel strip is austenitic stainless steel with relatively high Cr and Ni contents, the target alloy composition of the wire can be easily obtained through the adjustment of the powder.

[0024] (3) In order to ensure the serviceability of the weld at high temperatures, the present invention adds Cr element to the wire, and forms a dense Cr 2 O 3 oxide film to protect the weld metal; adds Ni and Mn elements to promote the formation of austenite phase in the weld; adds Ti and Al elements to strengthen the austenite phase by forming precipitation phases; adds Nb element to inhibit the occurrence of intergranular Cr depletion by preferentially combining with C.

[0025] (4) Graphene with a particle size of 10 - 20 mm is added to the wire of the present invention. This kind of graphene particle size is easy to mix evenly with other metal powders during powder mixing and is not prone to agglomeration.

[0026] (5) By adding various alloy elements, the present invention realizes solid solution strengthening, precipitation strengthening and carbide strengthening, so as to ensure the high temperature resistance and corrosion resistance of the weld.

[0027] (6) The composition of the wire can be flexibly adjusted through powder proportioning; compared with solid wires, the cladding efficiency of flux-cored wires is higher.

[0028] (7) The preparation process of this wire is simple. The wire with a wire diameter of 1.2 mm can be used for MIG / MAG welding and also for TIG welding, with a wide application range. Description of the Drawings

[0029] Figure 1 It is the groove form during the welding of the cylinder body and the head of the magnesium smelting retort.

[0030] Figure 2 It is the welding sequence during the welding of the cylinder body and the head of the magnesium smelting retort.

[0031] Figure 3 It is the metallographic structure morphology diagram of the weld when the flux-cored wire prepared in Example 2 is used to weld the cylinder body and the head of the magnesium smelting retort.

[0032] Figure 4 The metallographic structure morphology diagram of the interface between the weld and the base metal when the flux-cored wire prepared for Example 2 is used to weld the cylinder body and the head of the magnesium reduction tank. Detailed implementation manners

[0033] The present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0034] A high-Cr low-Ni wire for magnesium reduction tank of the present invention includes a flux and a welding skin. The flux includes the following components by mass percentage: 1.0 - 1.5% of Si powder, 8.0 - 10.0% of Mn powder, 40.0 - 50.0% of Cr powder, 12.0 - 15.0% of Ni powder, 3.0 - 4.0% of Nb powder, 1.0 - 1.5% of Ti powder, 0.8 - 1.0% of Al powder, 0.1 - 0.3% of graphene, and the rest is Fe powder. The sum of the mass percentages of the above components is 100%.

[0035] The particle size of each component in the flux is 100 - 200 mesh; the particle size of the graphene is 10 - 20 μm.

[0036] The welding skin is 06Cr19Ni10, with a thickness of 0.4 mm and a width of 7 mm.

[0037] The filling rate of the flux-cored wire is controlled at 30 - 35%.

[0038] The functions and roles of the main alloy components in the flux-cored wire are as follows:

[0039] (1) Cr element (added from the flux and the steel strip): Cr can react to form a dense Cr 2 O 3 oxide film, which covers the surface of the clad metal and plays a role in improving the high-temperature oxidation resistance of the clad metal. Cr can also improve the corrosion resistance to reducing media, and improve the resistance to local corrosion and corrosion cracking performance. According to the Cr content of the base metal, considering the element loss during the welding process, the Cr element designed in the wire is slightly higher than that of the base metal.

[0040] (2) Ni element (added from the flux and the steel strip): Ni is an austenite-forming element. Adding Ni to steel can improve its toughness. However, Ni is a strategic resource and is expensive. Therefore, the Ni content in the wire of the present invention is equivalent to that of the base metal. Compared with the commonly used austenitic welding materials on the market now, the reduction of the Ni content can significantly reduce the cost.

[0041] (3) Si and Mn elements (from powder and steel strip addition): Si and Mn have a combined deoxidizing effect. Similar to Cr, Si can form an oxide film at high temperatures, playing a role in protecting the clad metal against oxidation. After adding Mn, the crack resistance of the weld can be improved; in addition, Mn is also an austenite-forming element, which can increase the content of austenite phase in the weld; compared with Ni, Mn is much cheaper, so by adding a certain amount of Mn and reducing Ni to increase the content of austenite, it has the effect of reducing costs.

[0042] (4) Ti and Al elements (from powder addition): Al can form an Al 2 O 3 oxide film at high temperatures. The composition of this oxide film is stable and, together with Cr 2 O 3 can greatly improve the oxidation resistance of heat-resistant steel. Ti and Al can also react with Ni to form intermetallic compounds, which precipitate during high-temperature service, thereby playing a role in improving the strength and toughness of the weld metal.

[0043] (5) Nb element (from powder addition): Since Cr is a carbide-forming element, it is prone to react with C to form chromium carbides after long-term service at high temperatures, resulting in chromium-depleted zones in the grains. Especially when chromium depletion occurs at the grain boundaries, the corrosion resistance of the grain boundaries will be significantly reduced. To solve the above problems, the strong carbide-forming element Nb is added to the powder. Nb preferentially reacts with C to form carbides, thus avoiding the reaction between Cr and C. In addition, the dispersed distribution of Nb carbides in the matrix can play a role in increasing the strength of the weld.

[0044] (6) Graphene (from powder addition): Graphene is a two-dimensional material with a large specific surface area and high reactivity. The carbon content of the base material is about 0.3%, and the carbon content of the steel strip is relatively low, so C element needs to be added to the powder. When the C element is added in the form of graphene, it can better promote the relevant reactions.

[0045] The preparation method of the above high-Cr low-Ni welding wire for magnesium reduction tank is as follows:

[0046] Step 1: Weigh the powder Si powder 1.0 - 1.5%, Mn powder 8.0 - 10.0%, Cr powder 40.0 - 50.0%, Ni powder 12.0 - 15.0%, Nb powder 3.0 - 4.0%, Ti powder 1.0 - 1.5%, Al powder 0.8 - 1.0%, graphene 0.1 - 0.3% respectively by mass percentage, and the rest is Fe powder. The sum of the mass percentages of the above components is 100%.

[0047] Step 2: Place the weighed medicinal powder obtained in Step 1 into a vacuum heating furnace for heating. The heating temperature is 280 - 300 °C, and the heat preservation time is 1 - 3 h to remove the crystal water in the medicinal powder. The dried medicinal powder is placed in a powder mixer for sufficient mixing, and the mixing time is 1 - 3 h.

[0048] Step 3: Use alcohol to remove the grease on the surface of the 06Cr19Ni10 strip. Wrap the medicinal powder prepared in Step 2 inside the 06Cr19Ni10 strip through a flux-cored wire drawing device. The aperture of the first drawing die is 2.6 mm.

[0049] Step 4: After the first process of drawing is completed, gradually reduce the aperture of the die, and finally obtain a flux-cored wire with a diameter of 1.2 mm.

[0050] Step 5: After the drawing of the flux-cored wire is completed, wind it on a wire spool by a wire winding machine, and finally seal it in a vacuum packaging bag of the flux-cored wire for standby.

[0051] The particle size of each component in the medicinal powder described in Step 1 is 100 - 200 mesh, and the particle size of graphene is 10 - 20 μm.

[0052] The filling amount of the flux-cored wire in Step 3 is controlled at 30% - 35%.

[0053] The welding skin in Step 3 is a 06Cr19Ni10 strip, with a thickness of 0.4 mm and a width of 7 mm for the 06Cr19Ni10 strip.

[0054] When using the above high-Cr low-Ni wire for magnesium reduction tank welding, the butt joint of the magnesium reduction tank cylinder body and the head is designed as follows: The thickness a of the magnesium reduction tank cylinder body and the head at the butt joint is both made 10 mm. On the opposite sides of the magnesium reduction tank cylinder body and the head, slopes b and root faces c are respectively made. The two side slopes form a V-shaped groove. Among them, the groove angle is 90 ± 5°, the size of the root face c is 2 - 3 mm, and the gap d between the magnesium reduction tank cylinder body and the head at the butt joint is 1.0 - 1.5 mm, as Figure 1 shown. When welding with the wire of the present invention, the welding sequence is: backing weld pass - filling weld pass - capping weld pass, as Figure 2 shown. The welding power source is a CMT welding machine. The backing welding current is 180 - 220 A, and the filling and capping welding currents are 150 - 180 A. Multi-layer and multi-pass welding is used to reduce the welding heat input and avoid the generation of welding cracks.

[0055] Example 1

[0056] Step 1: Weigh the powder of Si powder 1.0%, Mn powder 8.0%, Cr powder 40.0%, Ni powder 12.0%, Nb powder 3.0%, Ti powder 1.0%, Al powder 0.8%, graphene 0.1% respectively by mass percentage, and the rest is Fe powder. The sum of the mass percentages of the above components is 100%.

[0057] Step 2: Place the powder weighed in Step 1 in a vacuum heating furnace for heating. The heating temperature is 280°C and the heat preservation time is 1 h to remove the crystal water in the powder. The dried powder is placed in a powder mixer for sufficient mixing, and the mixing time is 1 h.

[0058] Step 3: Use alcohol to remove the grease on the surface of 06Cr19Ni10 strip. Wrap the powder prepared in Step 2 in the 06Cr19Ni10 strip through a flux-cored wire drawing device. The aperture of the first drawing die is 2.6 mm.

[0059] Step 4: After the first process of drawing is completed, gradually reduce the aperture of the die, and finally obtain a flux-cored wire with a diameter of 1.2 mm.

[0060] Step 5: After the drawing of the flux-cored wire is completed, wind it on a wire reel by a wire winding machine, and finally seal it in a vacuum packaging bag of the flux-cored wire for standby.

[0061] When welding the magnesium reduction tank with the high-Cr low-Ni welding wire prepared in Example 1, the butt joint of the magnesium reduction tank cylinder body and the head is designed as follows: the thickness a of the magnesium reduction tank cylinder body and the head at the butt joint is both made 20 mm. The opposite sides of the magnesium reduction tank cylinder body and the head are respectively made with slopes b and root faces c. The two side slopes form a V-shaped groove. Among them, the groove angle is 90±5°, the size of the root face c is 2 - 3 mm, and the gap d between the magnesium reduction tank cylinder body and the head at the butt joint is 1.0 - 1.5 mm, as Figure 1 shown. When welding with the welding wire of the present invention, the welding sequence: root pass - filler pass - cover pass, as Figure 2 shown. The welding power source is a CMT welding machine. The root welding current is 180 - 220 A, and the filler and cover welding currents are 150 - 180 A. Multi-layer and multi-pass welding is adopted to reduce the welding heat input and avoid the generation of welding cracks.

[0062] After testing, the tensile strength of the welded head of the magnesium reduction tank is 570 MPa, the cross-sectional shrinkage rate is 15%, and the micro-Vickers hardness in the weld center area is 310 HV0.2.

[0063] Example 2

[0064] Step 1: Weigh the following powders by mass percentage respectively: 1.5% of Si powder, 10.0% of Mn powder, 50.0% of Cr powder, 15.0% of Ni powder, 4.0% of Nb powder, 1.5% of Ti powder, 1.0% of Al powder, 0.3% of graphene, and the rest is Fe powder. The sum of the mass percentages of the above components is 100%.

[0065] Step 2: Place the powders weighed in Step 1 in a vacuum heating furnace for heating. The heating temperature is 300 °C and the holding time is 3 h to remove the crystal water in the powders. After drying, place the powders in a powder mixer for sufficient mixing for 3 h.

[0066] Step 3: Remove the grease on the surface of the 06Cr19Ni10 strip with alcohol, and wrap the powders prepared in Step 2 in the 06Cr19Ni10 strip through a flux-cored wire drawing device. The aperture of the first drawing die is 2.6 mm.

[0067] Step 4: After the first-pass drawing is completed, gradually reduce the aperture of the die, and finally obtain a flux-cored wire with a diameter of 1.2 mm.

[0068] Step 5: After the flux-cored wire drawing is completed, wind it on a wire reel by a wire winding machine, and finally seal it in a vacuum packaging bag of the flux-cored wire for standby.

[0069] When welding the magnesium smelting reduction tank with the high-Cr low-Ni welding wire prepared in Example 2, the butt joint of the cylinder body and the head of the magnesium smelting reduction tank is designed as follows: The thickness a of both the cylinder body and the head of the magnesium smelting reduction tank at the butt joint is made 20 mm. On the opposite sides of the cylinder body and the head of the magnesium smelting reduction tank, a slope b and a root face c are respectively made. The two side slopes form a V-shaped groove. Among them, the groove angle is 90 ± 5°, the size of the root face c is 2 - 3 mm, and the gap d between the cylinder body and the head of the magnesium smelting reduction tank at the butt joint is 1.0 - 1.5 mm, as Figure 1 shown. When welding with the welding wire of the present invention, the welding sequence is: backing weld - filling weld - capping weld, as Figure 2 shown. The welding power source is a CMT welding machine. The backing welding current is 180 - 220 A, and the filling and capping welding currents are 150 - 180 A. Multilayer multi-pass welding is adopted to reduce the welding heat input and avoid the generation of welding cracks..

[0070] After testing, the tensile strength of the welded head of the magnesium smelting reduction tank is 580 MPa, the cross-sectional shrinkage rate is 14%, and the micro-Vickers hardness in the weld center area is 315 HV0.2.

[0071] Figure 3 It is the metallographic structure morphology diagram of the weld when the flux-cored wire prepared in Example 2 is used to weld the cylinder body and the head of the magnesium smelting reduction tank. It can be seen from the figure that the weld is an austenite structure, showing a columnar dendritic morphology.

[0072] Figure 4 When the flux-cored wire prepared for Case 2 is used to weld the cylinder body and the head of the magnesium reduction tank, the metallographic structure morphology diagram of the interface between the weld and the base metal is shown. It can be seen from the figure that the base metal α is austenite structure, and the weld β is also austenite structure (showing dendritic morphology). The weld and the base metal show the characteristics of epitaxial growth. The fusion line γ at the weld / base metal interface is clear, and no defects such as cracks and pores are found.

[0073] Example 3

[0074] Step 1: Weigh the following powders by mass percentage: 1.2% Si powder, 9.0% Mn powder, 45.0% Cr powder, 13.0% Ni powder, 3.5% Nb powder, 1.2% Ti powder, 0.9% Al powder, 0.2% graphene, and the rest is Fe powder. The sum of the mass percentages of the above components is 100%.

[0075] Step 2: Place the powders weighed in Step 1 in a vacuum heating furnace for heating. The heating temperature is 290 °C and the holding time is 2 h to remove the crystal water in the powders. After drying, the powders are placed in a powder mixer for sufficient mixing, and the mixing time is 2 h.

[0076] Step 3: Use alcohol to remove the grease on the surface of the 06Cr19Ni10 strip. Wrap the powders prepared in Step 2 inside the 06Cr19Ni10 strip through a flux-cored wire drawing device. The aperture of the first drawing die is 2.6 mm.

[0077] Step 4: After the first drawing process is completed, gradually reduce the aperture of the die, and finally obtain a flux-cored wire with a diameter of 1.2 mm.

[0078] Step 5: After the flux-cored wire drawing is completed, wind it on a wire reel through a wire winding machine, and finally seal it in a vacuum packaging bag of the flux-cored wire for standby.

[0079] When welding the magnesium reduction tank with the high-Cr low-Ni wire prepared in Example 3, the butt joint of the cylinder body and the head of the magnesium reduction tank is designed as follows: The thickness a of both the cylinder body and the head of the magnesium reduction tank at the butt joint is made 15 mm. On the opposite sides of the cylinder body and the head of the magnesium reduction tank, slopes b and root faces c are respectively made. The two side slopes form a V-shaped groove. Among them, the groove angle is 90 ± 5°, the size of the root face c is 2 - 3 mm, and the gap d between the cylinder body and the head of the magnesium reduction tank at the butt joint is 1.0 - 1.5 mm, as Figure 1 shown. When welding with the wire of the present invention, the welding sequence is: root pass - filler pass - cover pass, as Figure 2 shown. The welding power source is a CMT welding machine. The root welding current is 180 - 220 A, and the filler and cover welding currents are 150 - 180 A. Multi-layer multi-pass welding is adopted to reduce the welding heat input and avoid the generation of welding cracks.

[0080] After testing, the tensile strength of the welded head of the magnesium reduction tank is 590 MPa, the percentage reduction of area is 13%, and the micro-Vickers hardness in the center area of the weld is 325 HV0.2.

[0081] Example 4

[0082] Step 1: Weigh the powder respectively according to the mass percentage: 1.4% of Si powder, 8.5% of Mn powder, 46.0% of Cr powder, 12.0% of Ni powder, 3.6% of Nb powder, 1.3% of Ti powder, 0.85% of Al powder, 0.13% of graphene, and the rest is Fe powder. The sum of the mass percentages of the above components is 100%.

[0083] Step 2: Place the powder weighed in Step 1 in a vacuum heating furnace for heating. The heating temperature is 285 °C and the holding time is 1.3 h to remove the crystal water in the powder; the dried powder is placed in a powder mixer for sufficient mixing, and the mixing time is 1.3 h.

[0084] Step 3: Use alcohol to remove the grease on the surface of the 06Cr19Ni10 strip, and wrap the powder prepared in Step 2 in the 06Cr19Ni10 strip through a flux-cored wire drawing device. The aperture of the first drawing die is 2.6 mm.

[0085] Step 4: After the first process of drawing is completed, gradually reduce the aperture of the die, and finally obtain a flux-cored wire with a diameter of 1.2 mm.

[0086] Step 5: After the flux-cored wire drawing is completed, wind it on a wire spool by a wire winding machine, and finally seal it in a vacuum packaging bag of the flux-cored wire for standby.

[0087] When welding the magnesium reduction tank with the high-Cr low-Ni wire prepared in Example 4, the butt joint of the cylinder body and the head of the magnesium reduction tank is designed as follows: the thickness a of the cylinder body and the head of the magnesium reduction tank at the butt joint are both made 16 mm. On the opposite sides of the cylinder body and the head of the magnesium reduction tank, slopes b and root faces c are respectively made. The two side slopes form a V-shaped groove. Among them, the groove angle is 90 ± 5°, the size of the root face c is 2 - 3 mm, and the gap d between the cylinder body and the head of the magnesium reduction tank at the butt joint is 1.0 - 1.5 mm, as Figure 1 shown. When welding with the wire of the present invention, the welding sequence is: backing weld pass - filler weld pass - capping weld pass, as Figure 2 shown. The welding power source is a CMT welding machine. The backing welding current is 180 - 220 A, and the filler and capping welding currents are 150 - 180 A. Multi-layer and multi-pass welding is adopted to reduce the welding heat input and avoid the generation of welding cracks.

[0088] After testing, the tensile strength of the welded head of the magnesium reduction tank is 560 MPa, the percentage reduction of area is 17%, and the micro-Vickers hardness in the center area of the weld is 305 HV0.2.

[0089] Example 5

[0090] Step 1: Weigh the powder respectively according to the mass percentage: 1.1% of Si powder, 8.1% of Mn powder, 49.0% of Cr powder, 14.0% of Ni powder, 3.1% of Nb powder, 1.4% of Ti powder, 0.95% of Al powder, 0.25% of graphene, and the rest is Fe powder. The sum of the mass percentages of the above components is 100%.

[0091] Step 2: Place the powder weighed in Step 1 in a vacuum heating furnace for heating. The heating temperature is 295 °C and the heat preservation time is 2.3 h to remove the crystal water in the powder. The dried powder is placed in a powder mixer for sufficient mixing, and the mixing time is 2.3 h.

[0092] Step 3: Use alcohol to remove the grease on the surface of the 06Cr19Ni10 strip. Wrap the powder prepared in Step 2 in the 06Cr19Ni10 strip through a flux-cored wire drawing device. The aperture of the first drawing die is 2.6 mm.

[0093] Step 4: After the first drawing process is completed, gradually reduce the aperture of the die, and finally obtain a flux-cored wire with a diameter of 1.2 mm.

[0094] Step 5: After the flux-cored wire drawing is completed, wind it on a wire reel by a wire winding machine, and finally seal it in a vacuum packaging bag of the flux-cored wire for standby.

[0095] When welding the magnesium smelting reduction tank with the high Cr low Ni wire prepared in Example 5, the butt joint of the cylinder body and the head of the magnesium smelting reduction tank is designed as follows: The thickness a of the cylinder body and the head of the magnesium smelting reduction tank at the butt joint is both made 12 mm. Slopes b and root faces c are respectively made on the opposite sides of the cylinder body and the head of the magnesium smelting reduction tank. The two side slopes form a V-shaped groove. Among them, the groove angle is 90 ± 5°, the size of the root face c is 2 - 3 mm, and the gap d between the cylinder body and the head of the magnesium smelting reduction tank at the butt joint is 1.0 - 1.5 mm, as Figure 1 shown. When welding with the wire of the present invention, the welding sequence is: backing weld pass - filler weld pass - capping weld pass, as Figure 2 shown. The welding power source is a CMT welding machine. The backing welding current is 180 - 220 A, and the filler and capping welding currents are 150 - 180 A. Multi-layer and multi-pass welding is adopted to reduce the welding heat input and avoid the generation of welding cracks.

[0096] After testing, the tensile strength of the welded head of the magnesium smelting reduction tank is 572 MPa, the cross-sectional shrinkage rate is 16.5%, and the micro Vickers hardness in the center area of the weld is 335 HV0.2.

Claims

1. A high-Cr and low-Ni flux-cored wire for magnesium reduction pots, comprising flux powder and a welding skin, Characterized in that: The flux powder includes the following components by mass percentage: 1.0 - 1.5% of Si powder, 8.0 - 10.0% of Mn powder, 40.0 - 50.0% of Cr powder, 12.0 - 15.0% of Ni powder, 3.0 - 4.0% of Nb powder, 1.0 - 1.5% of Ti powder, 0.8 - 1.0% of Al powder, 0.1 - 0.3% of graphene, and the rest is Fe powder; the particle size of the graphene is 10 - 20 μm.

2. A high-Cr and low-Ni flux-cored wire for magnesium reduction pots according to claim 1, Characterized in that: The material of the welding skin is 06Cr19Ni10.

3. A high-Cr and low-Ni flux-cored wire for magnesium reduction pots according to claim 1, Characterized in that: The thickness of the welding skin is 0.4 mm and the width is 7 mm.

4. A high-Cr and low-Ni flux-cored wire for magnesium reduction pots according to claim 1, Characterized in that: The powder filling rate of the flux-cored wire is controlled at 30 - 35%.

5. A preparation method of a high-Cr and low-Ni flux-cored wire for magnesium reduction pots according to any one of claims 1 - 4, Characterized in that, The specific steps are as follows: Step 1: Weigh the flux powder Si powder, Mn powder, Cr powder, Ni powder, Nb powder, Ti powder, Al powder, and graphene respectively according to the mass percentage in claim 1, and the rest is Fe powder, and the sum of the mass percentages of the above components is 100%; Step 2: Place the flux powder weighed in Step 1 in a vacuum heating furnace for heating, the heating temperature is 280 - 300 °C, and the heat preservation time is 1 - 3 h to remove the crystal water in the flux powder; the flux powder after removing the crystal water is placed in a powder mixer for sufficient mixing, and the mixing time is 1 - 3 h; Step 3: Use alcohol to remove the grease on the surface of the welding skin belt, and wrap the flux powder prepared in Step 2 in the welding skin belt through a flux-cored wire drawing device to form a rough wire; Step 4: The rough wire prepared in Step 3 is finally drawn to a preset diameter range through multiple draws; Step 5: After the flux-cored wire drawing is completed, it is wound on a wire spool by a wire winding machine and finally sealed in a vacuum packaging bag of the flux-cored wire for standby.

6. A preparation method of a high-Cr and low-Ni flux-cored wire for magnesium reduction pots according to claim 5, Characterized in that: In Step 4, the aperture of the first drawing die is 2.6 mm. After the first drawing process is completed, the apertures of the second to the Nth dies are sequentially reduced, N≥2, and finally a flux-cored wire with a diameter of 1.2 mm is obtained.

7. A welding method using the high-Cr and low-Ni flux-cored wire for magnesium reduction pots prepared in claim 5 or 6, Characterized in that: It is used for welding the cylinder body and the head of the magnesium reduction pot.

8. A welding method according to claim 7, Characterized in that: During welding, the butt joint between the cylinder body and the head of the magnesium reduction tank is designed as follows: the thickness a of both the cylinder body and the head of the magnesium reduction tank at the butt joint is made to be 10 - 20 mm. On the opposite sides of the cylinder body and the head of the magnesium reduction tank, slopes b and root faces c are respectively made. The two side slopes form a V-shaped groove. Among them, the groove angle is 90 ± 5°, the size of the root face c is 2 - 3 mm, and the gap d between the butt joint of the cylinder body and the head of the magnesium reduction tank is 1.0 - 1.5 mm.

9. The welding method according to claim 8, characterized in that: the welding power source is a CMT welding machine, the root pass welding current is 180 - 220 A, the filling and capping welding current is 150 - 180 A, and multi-layer and multi-pass welding is adopted, that is, the specific welding sequence is root pass - filling pass - capping pass.

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