A low heat crack sensitivity submerged arc welding solid wire and a preparation method thereof

Abstract

The application discloses a low heat crack sensitivity submerged arc welding solid wire suitable for high-strength and light-weight austenitic alloy steel and a preparation method thereof, and belongs to the field of special alloy welding materials. The chemical components of the submerged arc welding solid wire are as follows in percentage by mass: Mn: 25-28%, C: 0.35-0.44%, Si: 1.25-1.5%, Cr: 6.5-8.0%, Ni: 2.0-3.5%, Mo: 1.2-2.0%, Ti: 0.08-0.15%, P: less than or equal to 0.005%, S: less than or equal to 0.003%, and the rest is iron and inevitable impurities. The preparation method of the submerged arc welding solid wire comprises the following steps: smelting and casting, forging, hot rolling, drawing and copper plating on the outer surface. The submerged arc welding solid wire has excellent process performance, the weld appearance is beautiful, and the strength is matched with the 450MPa-grade austenitic light-weight steel.

Description

Technical Field

[0001] This invention belongs to the field of special alloy welding materials, and is particularly suitable for welding engineering construction of high-strength, lightweight, austenitic alloy steel. It provides a solid welding wire for submerged arc welding with low thermal cracking sensitivity and its preparation method. Background Technology

[0002] With the continuous development of society and the economy, a series of problems such as excessive energy consumption and environmental pollution in transportation equipment have become increasingly serious. Solutions include, on the one hand, adopting clean energy alternatives, and on the other hand, reducing the weight and energy consumption of transportation equipment. Therefore, lightweight transportation equipment has always been a focus of energy conservation and environmental protection. To this end, Fe-Mn-Al-C alloy steel reduces material density by adding the lightweight element Al (generally more than 5%). Simultaneously, appropriate amounts of austenite-stabilizing elements such as Mn and C are added to form a high-strength, lightweight austenitic alloy steel, a structural and functional integrated material with broad application prospects. With the progress in the research and development of high-strength, lightweight, austenitic alloy steel, its use in transportation equipment has great development potential. Welding is the main method for joining and forming these materials. Among them, submerged arc welding is a commonly used, efficient, and high-quality welding method. This method involves burning an electric arc under a layer of flux to perform welding. Its inherent advantages, such as stable welding quality, high welding productivity, and the absence of arc light and fume pollution, make it the primary welding method for the fabrication of important steel structural components such as pressure vessels, pipeline connections, and box girder columns. In recent years, although many new, efficient, and high-quality welding methods have emerged, the application of submerged arc welding has remained unaffected. From the perspective of the share of deposited metal weight among various fusion welding methods, submerged arc welding accounts for approximately 10%, and this has remained relatively stable for many years. However, submerged arc welding wire suitable for high-strength, lightweight austenitic new alloy steels is currently neither practical nor widely available on the market.

[0003] A comparison with existing patent literature reveals that the "fully automatic submerged arc solid welding wire for preparing high-manganese steel LNG storage tanks" disclosed in Chinese invention patent CN107052618A comprises, by weight percentage: 0.25~0.45% C, 23~26% Mn, 6.0~8.0% Ni, 3.0~5.0% W, 0.02~0.004% N, ≤0.001% S, ≤0.002% P, with the remainder being iron and unavoidable impurities. This patent discloses a special solid welding wire for submerged arc welding of high-strength manganese steel. The solidification mode of the deposited metal in the weld is all austenitic solidification, exhibiting strong hot cracking sensitivity. The patented welding wire contains a certain amount of nitrogen, which readily combines with aluminum in high-strength lightweight steel to form AlN inclusions. Most importantly, it fails to address the problem of aluminum in the weld body easily transferring to the weld and forming Al2O3 inclusions, leading to a significant reduction in the weld's mechanical properties.

[0004] The Chinese invention patent CN112171109A discloses a "fully automatic submerged arc welding solid wire for nickel-saving high-manganese low-temperature steel," whose composition, by weight percentage, includes: 0.25~0.45% C, 26~31% Mn, 0.03~0.10% Si, ≤1.2% Ni, 2.0~6.0% Cr, ≤1% Mo, 0.02~0.008% N, ≤0.001% S, ≤0.002% P, with the remainder being iron and unavoidable impurities. In the welding process of this patent, the solidification mode of the deposited metal is entirely austenitic, which also exhibits strong hot cracking sensitivity. Furthermore, due to the poor fluidity of the deposited metal, it is unable to promptly remove Al2O3 inclusions, significantly reducing the mechanical properties of the weld.

[0005] In summary, the submerged arc welding wires described in existing patents and literature not only exhibit a fully austenitic solidification mode in the weld metal, resulting in strong hot cracking sensitivity, but also have low Si content, leading to poor deoxidation effects with Mn. Furthermore, the high viscosity of the weld metal hinders its ability to improve fluidity. These two factors significantly increase the likelihood of Al elements from the weld matrix transitioning into the weld and being oxidized to Al2O3 during the welding of high-strength lightweight steel. This excess Al cannot be promptly removed, forming inclusions and reducing the weld's mechanical properties. Therefore, it is necessary to explore a dedicated submerged arc welding wire for austenitic lightweight steel, capable of producing welded joints with excellent comprehensive mechanical properties when welding high-strength, lightweight austenitic alloy steels. Summary of the Invention

[0006] This invention provides a low-hot-cracking-sensitivity submerged arc welding wire suitable for high-strength austenitic lightweight steel and its preparation method. Based on extensive experimental data, this invention proposes the chemical composition and preparation method of the submerged arc welding wire, overcoming the deficiencies of existing technologies and solving existing problems in high-quality welding operations of high-strength, lightweight austenitic alloy steel.

[0007] A solid submerged arc welding wire with low hot cracking sensitivity for high-strength austenitic lightweight steel, wherein the chemical composition of the solid submerged arc welding wire, by weight percentage, comprises: Mn: 25~28%, C: 0.35~0.44%, Si: 1.28~1.45%, Cr: 6.5~8.0%, Ni: 2.1~3.4%, Mo: 1.2~2.0%, Ti: 0.08~0.15%, P≤0.005%, S≤0.003%, with the balance being Fe and unavoidable impurities.

[0008] The preparation method for the above-mentioned submerged arc welding wire includes the following five steps:

[0009] 1) Smelting and casting: Smelting is carried out in a vacuum induction furnace. The furnace is loaded with materials according to the target composition. The molten steel is cast into round ingots. The casting temperature of the molten steel is 1500-1600℃. The ingots are demolded 30 minutes after casting and air-cooled to room temperature.

[0010] 2) Forging: The ingot obtained in step 1) is forged by heating it to 1180±20℃ and holding it for more than 2 hours to ensure the homogeneity of the ingot's composition and microstructure. The initial forging temperature is 1100±30℃, and the final forging temperature is ≥950℃. The forged ingot is formed into a square billet with dimensions of 50×50×1500mm.

[0011] 3) Hot rolling: The billet is hot rolled into φ7.5mm wire rod. The heating temperature is 1200±20℃, and the holding temperature is 1h. The exit temperature of the high-speed wire rod is 1050±30℃, and the wire drawing temperature is ≥970℃. The rolled wire rod is then cooled in water at a temperature not less than 950℃.

[0012] 4) Drawing: The obtained φ7.5mm wire rod is drawn, undergoing rough drawing, solution treatment, surface cleaning, and fine drawing to finally obtain φ4mm welding wire. Solution treatment eliminates work hardening during the drawing process. The solution temperature is 1050-1100℃, held for 1 hour, and then water-cooled to room temperature.

[0013] 5) Copper plating: The obtained φ4mm welding wire is surface treated, including surface cleaning in alkaline scrubbing tank and acid rinsing tank, forming a thin film of 0.2-0.3 micrometers through copper plating tank, and then washed in water washing tank and hot water tank to finally obtain the finished submerged arc welding wire.

[0014] The high-strength austenitic lightweight alloy steel low-heat cracking sensitive submerged arc welding solid welding wire of the present invention is preferably used with flux SJ105. The controlled interpass temperature of the welded workpiece is ≤80℃, the welding current is 390-420A, the welding voltage is 30-32V, the welding speed is 35-40cm / min, and the heat input is 15-20kJ / cm.

[0015] When the workpiece is made of 450MPa grade austenitic light alloy steel, the metallographic structure of the weld is austenite plus ferrite with a content of ≤5%.

[0016] The mechanical properties of the weld formed when the workpiece is made of 450MPa grade austenitic light alloy steel are as follows: yield strength of 450-500MPa, tensile strength of 710-790MPa, elongation of 35-50%, and impact energy of 80-120J at -40℃.

[0017] The low-thermal-cracking-sensitive submerged arc welding solid welding wire and its preparation process provided by this invention, with the aid of specially selected flux and welding process, can produce welds in high-strength, lightweight austenitic alloy steel workpieces that also possess the excellent properties of the base alloy steel.

[0018] (1) The metallographic structure of the weld seam described in the submerged arc welding of the present invention is austenite + a small amount of ferrite (content ≤5%).

[0019] (2) The tensile strength of the weld is 710-790MPa, the elongation is 35-50%, and the impact energy at -40℃ is 80-120J.

[0020] When welding high-strength austenitic lightweight steel, a structure of austenite plus a small amount of ferrite is desired. When the weld solidifies in the FA mode, ferrite forms along the smooth, straight austenite grain boundaries, creating an uneven ferrite-austenite grain boundary structure that makes crack propagation difficult. Simultaneously, ferrite has a low coefficient of thermal expansion, which can accommodate the shrinkage stress during weld solidification and cooling, significantly improving the weld's resistance to solidification cracking. Excellent toughness can be achieved when the ferrite content at adjacent transition interfaces of the weld is ≤5%.

[0021] (3) The chemical structure of the welding wire of the present invention contains an appropriate amount of Si element, which ensures that the deposited metal has good fluidity and plays a joint deoxidation role with Mn, preventing the Al element diffused into the weld from being oxidized, preventing the formation of excessive Al2O3 inclusions, and ensuring the mechanical properties of the weld.

[0022] (4) This invention directly uses the existing commercial SJ105 flux for high-strength lightweight alloy steel of 450-500MPa grade, which is a national standard product. There is no need to develop a special flux. Only the relevant welding operation specifications are standardized. Welding can achieve high-quality engineering with slag shell removal, no porosity, no slag inclusion and no cracks.

[0023] (5) The welding process of the present invention does not require preheating before welding and postheating after welding. The process is simple and easy to implement. The weld formed is aesthetically pleasing and has good strength, plasticity and toughness, that is, excellent comprehensive performance. Detailed Implementation

[0024] The invention further illustrates, with reference to the embodiments, how the invention effect of the low hot cracking sensitivity submerged arc welding solid welding wire for 450MPa grade austenitic lightweight steel is achieved. Table 1 lists the chemical composition of the welding wires of Examples 1 to 3 and the comparative examples provided by the present invention.

[0025] Table 1 Chemical composition of submerged arc welding solid welding wire: Examples and comparative examples (mass percentage)

[0026] Element C Mn Si Ni Cr Mo Ti Fe Example 1 0.4 26.6 1.28 2.8 7.2 1.5 0.08 margin Example 2 0.44 27.0 1.45 3.4 7.8 1.2 0.15 margin Example 3 0.36 27.8 1.36 2.1 6.5 1.8 0.12 margin Comparative Example 0.25 25.0 0.50 3.0 3.5 0.8 0.10 margin

[0027] Example 1:

[0028] A solid submerged arc welding wire with low hot cracking sensitivity for 450MPa grade austenitic lightweight alloy steel, wherein the chemical composition of the welding wire, by weight percentage, comprises: 0.40% C, 26.6% Mn, 1.28% Si, 2.8% Ni, 7.2% Cr, 1.5% Mo, 0.08% Ti, P≤0.005%, S≤0.003%, with the balance being Fe and unavoidable impurities.

[0029] The submerged arc welding wire has a diameter of 4.0 mm. A fully automatic submerged arc welding method is used to weld 20 mm thick austenitic lightweight steel. The chemical composition of the austenitic lightweight steel, by weight percentage, includes: C 0.6-1.0%, Mn 22-25%, Al 5-8%, and the mechanical properties are: Rp0.2: 440-500 MPa, Rm: 700-850 MPa, A≥40%, KV2≥120 J at -40℃.

[0030] The austenitic lightweight steel test plate described in this embodiment has a Y-shaped bevel with a single-sided bevel angle of 30° and a blunt edge of 4mm. The flux used is SJ105, and the interpass temperature is controlled to be ≤80℃. The specific welding process parameters are: welding current of 390-420A, welding voltage of 30-32V, welding speed of 35-40cm / min, and heat input of 15-20kJ / cm.

[0031] The microstructure and mechanical properties of the weld metal after welding in this embodiment were tested: the weld structure is austenite + a small amount of ferrite, no hot cracks were generated, the yield strength of the weld metal is 475MPa, the tensile strength is 728MPa, the elongation is 40%, and the impact energy at -40℃ is 108J.

[0032] Example 2:

[0033] The chemical composition of the welding wire used in this embodiment, by weight percentage, includes: 0.44% C, 27% Mn, 1.45% Si, 3.4% Ni, 7.8% Cr, 1.2% Mo, 0.15% Ti, P≤0.005%, S≤0.003%, with the balance being Fe and unavoidable impurities.

[0034] Example 3:

[0035] The chemical composition of the welding wire used in this embodiment, by weight percentage, includes: C 0.36%, Mn 27.8%, Si 1.36%, Ni 2.1%, Cr 6.5%, Mo 1.8%, Ti 0.12%, P ≤ 0.005%, S ≤ 0.003%, with the balance being Fe and unavoidable impurities.

[0036] After selecting the chemical composition mass percentages for Examples 1-3 above, a 4.0mm diameter submerged arc welding wire was prepared according to the aforementioned matching preparation process steps. A fully automated submerged arc welding standard was used to weld 20mm thick high-strength austenitic lightweight steel. The chemical composition of the high-strength austenitic lightweight steel, by weight percentage, includes: C 0.6-1.0%, Mn 22-25%, Al 5-8%; its mechanical properties are: Rp0.2: 440-500MPa, Rm: 700-850MPa, A≥40%, KV2≥120J at -40℃. The bevel type of the high-strength austenitic lightweight steel test welding specimens in Examples 1-3 is Y-type, with a single-sided bevel angle of 30°, a blunt edge of 4mm, and SJ105 flux. The interpass temperature is controlled to be ≤80℃. The specific welding process parameters are as follows: welding current is 390-420A, welding voltage is 30-32V, welding speed is 35-40cm / min, and heat input is 15-20kJ / cm.

[0037] The microstructure and mechanical properties of the weld metal after welding in Examples 1-3 were tested: the weld microstructure was austenite + a small amount of ferrite, and no hot cracks were generated. The yield strength, tensile strength, elongation and low temperature impact resistance of the weld metal are shown in Table 2, which is a comparison table of the mechanical properties of welds in Examples 1-3 and the comparative examples.

[0038] Comparative example:

[0039] The chemical composition of the comparative welding wire, by weight percentage, includes: 0.25% C, 25.0% Mn, 0.50% Si, 3.0% Ni, 3.5% Cr, 0.8% Mo, 0.10% Ti, P≤0.005%, S≤0.001%, with the balance being Fe and unavoidable impurities.

[0040] The comparative submerged arc welding wire has a diameter of 4.0 mm. A fully automated submerged arc welding method is used to weld 20 mm thick austenitic lightweight steel. The chemical composition of the austenitic lightweight steel, by weight percentage, includes: C 0.6–1.0%, Mn 22–25%, Al 5–8%. Its mechanical properties are: Rp0.2: 440–500 MPa, Rm: 700–850 MPa, A ≥ 40%, KV2 ≥ 120 J at -40℃. The test plate has a Y-type bevel with a single-sided bevel angle of 30° and a blunt edge of 4 mm. SJ105 flux is used, and the interpass temperature is ≤ 80℃. Specific welding process parameters are: welding current 390-420 A, welding voltage 30-32 V, welding speed 35-40 cm / min, and heat input 15-20 kJ / cm.

[0041] The microstructure and mechanical properties of the weld metal after the welding was completed were tested: the weld microstructure was austenitic, hot cracks were generated, the yield strength of the weld metal was 390 MPa, the tensile strength was 687 MPa, the elongation was 28%, and the impact energy at -40℃ was 46 J.

[0042] The above comparative examples were found to have defects such as cracks, inclusions, and porosity after ultrasonic testing 24 hours after welding. Samples were taken from the weld and their tensile properties and impact properties at -40℃ were tested. The results are shown in Table 2.

[0043] Table 2 Comparison of mechanical properties of welds in Examples 1-3 and comparative examples.

[0044] serial number Yield strength / MPa Tensile strength / MPa Elongation / % -40℃KV2 / J Example 1 475 728 40 108 Example 2 490 754 38 98 Example 3 458 746 48 118 Comparative Example 390 687 28 46

[0045] The metallographic structures of Examples 1-3 are all austenite + ferrite, while the metallographic structure of Comparative Example 1 is austenite. This is mainly because the content of ferrite-forming elements in the comparative example is too low, resulting in a single austenite structure, which greatly increases the hot cracking sensitivity of the weld and causes cracks to occur during actual welding. The carbon and alloying element content in the comparative example is relatively low compared to the examples, resulting in lower weld strength. In particular, the silicon content is lower than the range of this invention, resulting in insufficient fluidity and deoxidation, which leads to the generation of excessive Al2O3 in the weld and a serious reduction in impact strength.

Claims

1. A low heat crack sensitivity submerged arc welding solid wire, characterized by: The chemical components of the solid welding wire are as follows in percentage by mass: Mn: 25-28%, C: 0.35-0.44%, Si: 1.28-1.45%, Cr: 6.5-8.0%, Ni: 2.1-3.4%, Mo: 1.2-2.0%, Ti: 0.08-0.15%, P≤0.005%, S≤0.003%, and the balance of Fe and inevitable impurities; The preparation method of the hot crack sensitive submerged arc welding solid welding wire comprises the following steps: 1) smelting and casting: smelting in a vacuum induction furnace, charging the furnace according to the target component, pouring the molten steel into a round ingot, the molten steel pouring temperature is 1500-1600 DEG C, demolding after 30 min, and the ingot is air-cooled to room temperature; 2) forging: the ingot obtained in step 1) is forged, heated to 1180±20 DEG C, and kept for more than 2h, the blooming forging temperature is 1100±30 DEG C, the final forging temperature is greater than or equal to 950 DEG C, and the square billet with a size of 50*50*1500mm is formed; 3) hot rolling: the square billet is hot rolled into a φ7.5mm wire rod, the heating temperature is 1200±20 DEG C, the holding time is 1h, the rolling high line outlet temperature is 1050±30 DEG C, the wire rod is cooled by water, and the water inlet temperature is not less than 950 DEG C; 4) drawing: the obtained φ7.5mm wire rod is drawn, respectively through rough drawing, solid solution, surface cleaning and fine drawing, finally obtaining a φ4mm welding wire: the solid solution treatment eliminates the work hardening phenomenon in the drawing process, the solid solution temperature is 1050-1100 DEG C, the holding time is 1h, and the water cooling is to room temperature; 5) copper plating: the obtained φ4mm welding wire is surface treated, including alkali scrubbing tank and acid rinsing tank surface dirt removal, brushing through the copper plating tank to form a 0.2-0.3 micron film layer, and then washing through the water tank and hot water tank, finally obtaining the finished submerged arc welding wire; When the welding workpiece is a 450MPa grade austenitic lightweight alloy steel, the mechanical indexes of the weld formed are as follows: the yield strength is 450-500MPa, the tensile strength is 710-790MPa, the elongation is 35-50%, and the impact energy at-40 DEG C is 80-120J.

2. The hot crack sensitive submerged arc welding solid wire of claim 1, wherein, The welding process parameters are as follows: the welding flux is SJ105, the interlayer temperature of the workpiece before welding is controlled to be less than or equal to 80 DEG C, the welding current is 390-420A, the welding voltage is 30-32V, the welding speed is 35-40cm / min, and the heat input is 15-20kJ / cm.

3. The hot crack sensitive submerged arc welding solid wire of claim 2 wherein: When the welding workpiece is a 450MPa grade austenitic lightweight alloy steel, the metallographic structure of the weld formed is austenite + content less than or equal to 5% ferrite.