Preheating-free 690MPa-grade high-strength and high-toughness steel and submerged-arc welding method thereof

Abstract

The invention relates to preheating-free 690MPa-grade high-strength and high-toughness steel and a submerged-arc welding method thereof, and belongs to the technical field of welding. The submerged-arc welding method comprises the following steps: preheating a welding flux, wherein the welding flux needs to be baked before being used; the welding wire and the baked welding flux are filled into automatic submerged arc welding equipment for welding; welding parameter setting is adjusted; in the welding process, an alternate welding method that the welding directions of the previous welding process and the next welding process are opposite is adopted; and finally, welding seam forming and inspection are conducted. The welding flux and the welding wire are used in cooperation, stable submerged-arc welding of 690 MPa-grade high-strength steel is achieved under the condition that preheating is not needed, the comprehensive performance of weld metal is excellent, the low-temperature impact toughness is remarkably improved, and the strict requirement of a high-strength steel structure for the performance of a welded joint is met. The yield strength of deposited metal is 700 MPa or above, the tensile strength is 750 MPa or above, the ductility is 24% or above, and the impact absorbing energy at the temperature of-50 DEG C is 91 J or above.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of welding technology, in particular to a preheating-free 690MPa grade high-strength and high-toughness steel and a submerged arc welding method thereof. BACKGROUND

[0002] 690MPa grade high-strength and high-toughness steel is a kind of structural material with high yield strength and excellent low-temperature toughness, which is widely used in fields such as marine engineering equipment, cross-sea bridges, pressure vessels, ship structures and high-stress pipeline steels. With the development of equipment manufacturing industry towards high strength, lightweight and high reliability, the comprehensive performance of welded joints has become one of the key factors limiting the engineering application of high-strength steel.

[0003] In the welding process of high-strength steel, the problems of cold crack tendency and heat-affected zone (HAZ) organization coarsening are particularly prominent. The carbon equivalent (Ceq) of 690MPa grade high-strength steel is usually above 0.6%, and the welding thermal cycle is easy to form high-hardness martensite or bainite structure in the weld zone, and the aggregation of diffusible hydrogen is easy to induce delayed cracking. In addition, when the welding residual stress and constraint degree are high, the risk of hydrogen-induced cold cracking (HIC) increases significantly, so the existing method mainly uses preheating to eliminate defects.

[0004] However, the preheating operation has significant limitations in large-scale structure manufacturing: (1) high energy consumption and low construction efficiency, which is not conducive to batch and automated welding production; (2) frequent thermal cycles leading to organization coarsening, which easily reduces the low-temperature toughness of weld and heat-affected zone; (3) difficulty in controlling residual stress and deformation, which affects the dimensional accuracy of the structure; (4) not conducive to on-site construction and low-temperature environment operation, especially in offshore or polar engineering conditions.

[0005] Therefore, there is an urgent need for a preheating-free welding method to ensure that 690MPa grade steel has high strength and excellent low-temperature toughness. SUMMARY

[0006] In view of the above analysis, the present application aims to provide a preheating-free 690MPa grade high-strength and high-toughness steel and a submerged arc welding method thereof, which ensures that the 690MPa grade steel has high strength and excellent low-temperature toughness.

[0007] In one aspect, the present application provides a preheating-free 690MPa grade high-strength and high-toughness steel submerged arc welding method, comprising the following steps:

[0008] Step one: preheating treatment of flux, the flux needs to be baked before use;

[0009] Step two: preparation of welding materials, fill the welding wire and the baked flux into the automatic submerged arc welding equipment for welding;

[0010] Step three: welding parameter setting;

[0011] Step four: welding process control, in the welding process, the alternating welding method of the previous and the next welding direction is adopted;

[0012] Step five: weld forming and inspection.

[0013] Further, in step one, the flux is a basic sintering type smelting flux, and the chemical composition is as follows in terms of mass percentage: CaO+MgO: 30.2-33.2%; Al2O3+MnO2: 22.3-25.3%; SiO2+TiO2: 13.3-19.3%; CaF2: 20.4-26.4%; S<0.01%, P<0.02%, water content<0.01%.

[0014] Further, the basicity of the flux is 1.5-3.5.

[0015] Further, the flux is baked at 300-350 DEG C for more than 2 hours before use.

[0016] Further, the chemical composition of the welding wire includes C: 0.07-0.10%; Si: 0.25-0.50%; Mn: 1.20-1.50%; Cr: 0.20-0.50%; Ni: 2.10-3.30%; Mo: 0.45-0.65%; Ti: 0.03-0.05%; S≤0.005%; P≤0.005%; the balance is Fe and inevitable impurities.

[0017] Further, in step three, the welding current is 525-575 A, the welding voltage is 28-30 V, the welding speed is 39-41 cm / min, and the average heat input is 20-26 kJ / cm.

[0018] Further, in step four, the interpass temperature is controlled at 105-120 DEG C.

[0019] Further, the yield strength of the welded joint is ≥700 MPa, the tensile strength is ≥750 MPa, and the impact energy at -50 DEG C is ≥90 J.

[0020] Further, the deposited metal prepared from the welding wire has a microstructure composed of acicular ferrite, lath ferrite and lath bainite.

[0021] In another aspect, the present application provides a preheating-free 690 MPa grade high-strength and high-toughness steel prepared by the submerged arc welding method.

[0022] Compared with the prior art, the present application can at least achieve one of the following beneficial effects:

[0023] 1、The present application can realize stable submerged arc welding of 690MPa high-strength steel without preheating by using flux in cooperation with welding wire, the comprehensive performance of the weld metal is excellent, the low-temperature impact toughness is significantly improved, and the strict requirements of high-strength steel structure on the performance of welded joints are met. The yield strength of the deposited metal is above 700MPa, the tensile strength is above 750MPa, the elongation is above 24%, and the-50℃ impact absorption energy is above 91J.

[0024] 2、By optimizing the C content, Ni ratio and introducing Ti micro-alloying means, the cold crack sensitivity of the weld is effectively reduced. Combined with low S, P control and hydrogen control process, the preheating operation is avoided, the energy consumption is saved and the process is simplified; the yield strength of the deposited metal is above 700MPa, the tensile strength is above 750MPa, the elongation is above 24%, and the-50℃ impact absorption energy is above 91J.

[0025] 3、Under the condition that the Ni content is only 2.20% to 2.60%, the high impact toughness of 91J at-50℃ is realized by multi-element synergistic strengthening of Cr, Mo, Mn and Ti, and the performance is better than that of traditional high-Ni welding wire, and the material cost is reduced by about 30%.

[0026] 4、The present application is designed for 20-26kJ / cm large heat input submerged arc welding process, and uniform acicular ferrite+lamellar ferrite can still be obtained under the conditions of no preheating and multi-layer multi-pass welding, without obvious coarse grain or brittle zone, to ensure the stability of joint performance.

[0027] 5、The flux of the present application is baked at high temperature and designed with CaF2 strong dehydrogenation system, so that the diffusible hydrogen content of the weld is less than 4ml / 100g, the hydrogen-induced crack tendency is significantly reduced, and the long-term service safety is ensured.

[0028] The above technical solutions in the present application can be combined with each other to realize more preferred combination schemes. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification or be understood by implementing the present application. The purpose and other advantages of the present application can be realized and obtained from the contents specifically pointed out in the specification and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0029] The accompanying drawings are included to provide a further understanding of the embodiments, and are not considered limitations on the present application, and the same reference symbols indicate the same parts throughout the drawings.

[0030] Figure 1 The cross-section macroscopic morphology of the deposited metal of Example 1;

[0031] Figure 2 Weld metal microstructure morphology for Example 1;

[0032] Figure 3 Weld metal microstructure morphology for Comparative Example 1. DETAILED DESCRIPTION

[0033] The preferred embodiments of the present application will be specifically described below with reference to the drawings, wherein the drawings constitute a part of the present application and are used together with the embodiments of the present application to explain the principles of the present application, but are not used to limit the scope of the present application.

[0034] 690MPa grade high-strength and high-toughness steel is a kind of structural material with high yield strength and excellent low-temperature toughness, which is widely used in fields such as marine engineering equipment, cross-sea bridge, pressure vessel, ship structure and high-stress pipeline steel. With the development of equipment manufacturing industry towards high strength, light weight and high reliability, the comprehensive performance of welded joints has become one of the key factors restricting the engineering application of high-strength steel.

[0035] In the welding process of high-strength steel, the cold crack tendency and the problem of heat-affected zone (HAZ) microstructure coarsening are particularly prominent. The carbon equivalent (Ceq) of 690MPa grade high-strength steel is usually above 0.6%, and the welding thermal cycle is easy to form high-hardness martensite or bainite structure in the weld zone, and the aggregation of diffusible hydrogen is easy to induce delayed cracking. In addition, when the welding residual stress and constraint degree are high, the risk of hydrogen-induced cold cracking (HIC) increases significantly, so the existing method mainly uses preheating to eliminate defects.

[0036] However, the preheating operation has significant limitations in large structure manufacturing: (1) high energy consumption and low construction efficiency, which is not conducive to batch and automated welding production; (2) frequent thermal cycles lead to microstructure coarsening, which easily reduces the low-temperature toughness of the weld and heat-affected zone; (3) residual stress and deformation control is difficult, which affects the dimensional accuracy of the structure; (4) not conducive to on-site construction and low-temperature environment operation, especially in offshore or polar engineering conditions.

[0037] Therefore, the present application provides a preheating-free 690MPa grade high-strength and high-toughness steel submerged arc welding method, which comprises the following steps:

[0038] Step one: preheating treatment of flux, the flux needs to be baked before use;

[0039] Step two: preparation of welding materials, fill the welding wire and the baked flux into the automatic submerged arc welding equipment for welding;

[0040] Step three: setting of welding parameters;

[0041] Step four: welding process control, in the welding process, the alternating welding method of the opposite direction of the previous and the next welding direction is adopted;

[0042] Step five: weld forming and inspection.

[0043] Compared with the prior art, the welding flux is used in cooperation with the welding wire, so that stable submerged arc welding of the 690MPa high-strength steel can be realized without preheating, the comprehensive performance of the weld metal is excellent, the low-temperature impact toughness is significantly improved, and the strict requirements of the high-strength steel structure on the performance of the welded joint are met. The yield strength of the deposited metal is above 700MPa, the tensile strength is above 750MPa, the elongation is above 24%, and the-50℃ impact absorption energy is above 91J.

[0044] Specifically, the welding flux is an alkaline sintering type smelting flux, and the chemical composition of the welding flux is as follows in terms of mass percentage: CaO+MgO: 30.2-33.2%; Al2O3+MnO2: 22.3-25.3%; SiO2+TiO2: 13.3-19.3%; CaF2: 20.4-26.4%; S < 0.01%, P < 0.02%, and the water content < 0.01%.

[0045] It should be noted that the welding flux has good slag forming property and deoxidizing capacity, can effectively adsorb inclusions and harmful elements in the weld metal, improve the purity of the weld metal, and reduce the cold crack sensitivity. At the same time, the ratio of CaF2 to Al2O3 in the welding flux helps to form a moderate alkaline slag system, and enhances the impact toughness and crack resistance of the weld metal. In the welding process, the welding flux has good arc stability and forming property, and can obtain a dense and well-formed weld metal structure. The welding flux is baked at high temperature and is designed with a CaF2-strengthened dehydrogenation system, so that the diffusion hydrogen content of the weld is lower than 4ml / 100g, the hydrogen-induced crack tendency is significantly reduced, and the long-term service safety is ensured.

[0046] Specifically, the basicity of the welding flux is 1.5-3.5.

[0047] Specifically, the welding flux is baked at 300-350℃ for more than 2 hours before use.

[0048] It should be noted that the welding flux needs to be baked before use to remove the water content therein and prevent the cold crack caused by the increase of hydrogen content in the welding process. The welding flux is baked at 300-350℃ for 2 hours, and then is taken out and placed in a heat preservation container for use.

[0049] Specifically, the chemical composition of the welding wire comprises, in percentage by mass, C: 0.07% to 0.10%; Si: 0.25% to 0.50%; Mn: 1.20% to 1.50%; Cr: 0.20% to 0.50%; Ni: 2.10% to 3.30%; Mo: 0.45% to 0.65%; Ti: 0.03% to 0.05%; S: ≤0.005%; P: ≤0.005%; and the balance of Fe and inevitable impurities.

[0050] Compared with the prior art, the welding wire provided by the application effectively reduces the cold crack sensitivity of the weld by optimizing the C content, Ni ratio and introducing Ti micro-alloying means. Combined with low S, P control and hydrogen control process, the preheating-free welding of the 690MPa grade low-temperature high-strength steel under normal temperature or low-temperature conditions is realized, the traditional preheating operation is avoided, the energy consumption is saved and the process is simplified; the deposited metal has a yield strength of more than 700MPa, a tensile strength of more than 750MPa and an elongation of more than 24%, and a-50℃ impact absorption of more than 91J.

[0051] Under the condition that the Ni content is only 2.20% to 2.60%, high impact toughness of 91J at-50℃ is realized through the synergistic strengthening of Cr, Mo, Mn and Ti, and the performance is better than that of the traditional high-Ni welding wire, and the material cost is reduced by about 30%.

[0052] The functions of the elements are as follows:

[0053] C (0.07% to 0.10%): C is controlled at 0.07% to 0.10% in the application to compensate for the insufficient hardening under the high heat input of submerged arc welding, so as to ensure that the deposited metal and the heat-affected zone can still obtain sufficient strength under the condition of slow cooling speed. In order to avoid the increase of cold crack sensitivity caused by too high C, the application strictly matches with low S and P content, uses Ti to capture N, and adjusts the Mn / Mo content to control the total hardening tendency, so as to balance the strength and cold crack resistance.

[0054] Si (0.25% to 0.50%): Si is mainly used for deoxidization and improving the fluidity of the molten pool, and is also helpful to promote the formation of acicular / needle-like ferrite and fine bainite. The deoxidization effect is ensured while the negative impact on impact toughness is reduced as much as possible. Good deoxidization reduces the source of hydrogen content, which is conducive to reducing the diffusible hydrogen and reducing the risk of cold cracking.

[0055] Mn (1.20% to 1.50%): provides necessary deoxidization, desulfurization and solid solution strengthening, while avoiding too high Mn to increase the overall hardening tendency. Mn helps to inhibit the formation of brittle martensite under the slow cooling condition of submerged arc welding, thereby supporting the preheating-free process.

[0056] Cr (0.20%~0.50%): Cr can improve the strength of the base and the high temperature softening ability, and can promote the stability of bainite / tempered structure. Ensure the strength while avoiding excessive loss of plasticity and toughness. Cr and Mo cooperate: Cr and Mo cooperate to promote high-strength and toughness bainite / tempered structure to adapt to the heat cycle of submerged arc welding.

[0057] Ni (2.10%~3.30%): Ni is an important element for reducing the brittle transition temperature (DBTT) and improving low temperature impact toughness. The present application enhances the low temperature toughness redundancy under the premise of controllable cost.

[0058] Mo (0.45%~0.65%): Mo in the present application is beneficial to improve the strength after quenching and tempering, improve high temperature tempering stability, and has limited effect on toughness within the control range. And Mo and Cr together promote the formation of fine bainite or fine tempered structure, improve the strength retention ability under high heat input, and cooperate with Ni to reduce DBTT.

[0059] Ti (0.03%~0.05%): The amount of Ti is precisely controlled, which preferentially combines with N to form stable TiN particles as fine non-metallic inclusions, promotes the formation of acicular ferrite or dispersed crystal nucleus, thereby refining the weld metal structure. Stable TiN can reduce harmful MnS type inclusions with low melting point and easy to form into a strip, reduce the formation of local brittle zone, and is beneficial to the cold crack resistance of preheating-free welding.

[0060] S, P (≤0.005%): In the present application, S and P are strictly controlled to significantly reduce the influence of segregation and inclusions on brittleness and hot crack sensitivity. The strict reduction of S and P directly reduces the combination position of crack source and diffusible hydrogen, which supports the reliability of the preheating-free process from the metallurgical root.

[0061] Submerged arc welding belongs to a welding method with large heat input and slow cooling. The slow cooling rate itself can reduce the tendency of martensite formation, but it can also lead to structure coarsening and strength reduction. In the case of not using preheating, the present application obtains 690MPa level mechanical properties by moderately increasing C, and cooperating with high content of Mo and appropriate amount of Cr to make up for the strength loss caused by heat input; at the same time, by reducing Mn, strictly controlling S and P, and adding Ti to capture inclusions / nitrogen, diffusible hydrogen and harmful sulfide network are inhibited, thereby controlling the cold crack sensitivity, and achieving the safety window of preheating-free.

[0062] Inert particles such as TiN, together with Si and Mn, promote the nucleation of fine acicular ferrite or dispersed bainite, and inhibit the formation of coarse lath / network structure, so that the microstructure of the material is mainly composed of fine acicular ferrite and fine granular bainite (or fine tempered structure after tempering), which has good energy absorption capacity at low temperature. The addition of Ni further reduces the ductile-brittle transition temperature of the material, and the cooperation of Mo and Cr can improve the strength without sacrificing the plasticity.

[0063] The capture of S, P and Ti to N, combined with high cleanliness smelting (such as vacuum degassing, secondary refining) and control of the moisture content / hygroscopicity of the welding wire coating during production, can reduce the diffusible hydrogen content to a low level, significantly reducing the risk of cold cracking, thereby providing the necessary metallurgical guarantee for the preheating-free process.

[0064] The high heat input of submerged arc welding prolongs the cooling time, and the present application makes a trade-off in three aspects: slightly high C and Mo / Cr to ensure strength, Ni and microstructure refinement measures to ensure toughness, and low S, P and Ti capture to ensure low hydrogen / low crack sensitivity, so as to realize the feasibility of preheating-free.

[0065] Preferably, the chemical composition of the welding wire comprises, by mass percentage, C: 0.075%-0.082%; Si: 0.34%-0.42%; Mn: 1.25%-1.44%; Cr: 0.25%-0.44%; Ni: 2.50%-3.14%; Mo: 0.54%-0.65%; Ti: 0.032%-0.046%; S≤0.005%; P≤0.005%; and the balance being Fe and unavoidable impurities.

[0066] Specifically, the deposited metal prepared from the welding wire has a yield strength of 700 MPa or higher, a tensile strength of 750 MPa or higher, an elongation of 24% or higher, and an impact absorption energy at -50°C of 91 J or higher.

[0067] Specifically, the deposited metal prepared from the welding wire has a microstructure composed of acicular ferrite, lath ferrite and lath bainite.

[0068] It should be noted that acicular ferrite is a typical high-toughness microstructure in low-carbon, low-alloy high-strength steel, which has a fast growth rate, small grain size and complex grain boundaries, effectively improves the fracture resistance and significantly enhances the low-temperature impact toughness; lath ferrite can maintain a fine morphology after multi-layer and multi-pass thermal cycling, which helps to maintain the strength and plasticity synergy of the deposited metal; and the appropriate amount of lath bainite further improves the tensile strength and hardenability, while not forming a continuous hard and brittle network structure, and not affecting the overall toughness. The microstructure is uniformly distributed, and there is no obvious coarse grain, segregation or brittle structure region.

[0069] The present application can obtain stable and refined multi-phase structure even under the condition of no preheating, low ambient temperature and high heat input by precise alloy composition control and reasonable cooling and heating control strategy, so that the deposited metal still has excellent impact toughness under the environment below-50 DEG C, which is significantly better than the traditional same grade high strength welding wire, and meets the service requirements of structure welding in extremely cold area.

[0070] The present application provides a preparation method of a preheating-free 690MPa grade high-strength and high-toughness submerged-arc welding wire.

[0071] Specifically, the preparation method of the welding wire comprises the following steps:

[0072] S1: smelting, vacuum induction furnace or electric arc furnace + refining process is used for smelting, and S and P are ensured to be ≤0.005%. The composition of molten steel is controlled to be uniform, the hydrogen content is controlled to be <2ppm, the pouring temperature is 1550-1580 DEG C, and a steel ingot with uniform composition and low inclusions is obtained.

[0073] S2: forging, the cast ingot is heated and kept at 1150-1180 DEG C, and then is forged, and the final forging temperature is controlled to be 850-900 DEG C, so that the as-cast structure is broken and the grains are refined, and a uniform and dense forged blank is obtained.

[0074] S3: rolling, the forged blank is heated and hot-rolled in multiple passes, the rolling temperature is 1050-1100 DEG C, and the final rolling temperature is controlled to be higher than 850 DEG C, so that a coil with a diameter of Φ6.5mm is obtained, and the structure is ensured to be fine and the surface quality is good.

[0075] S4: pickling and annealing, the hot-rolled coil is pickled to remove the oxide skin, and then is annealed at 650-700 DEG C, so that the structure is restored and the plasticity is improved, and the subsequent cold working is facilitated.

[0076] S5: bright drawing, the coil after annealing is cold-drawn in multiple passes under clean and lubricated conditions, the pass compression rate is controlled to be ≤15%, and the welding wire with a diameter of Φ4.0mm is drawn. Surface defects need to be strictly controlled during the drawing process, the diameter of the welding wire is kept uniform, and the surface roughness is ≤Ra0.8.

[0077] S6: surface layer winding, a copper plating layer or other anti-oxidation layer is uniformly applied on the surface of the welding wire, the thickness of the copper plating layer is controlled to be 0.20-0.35μm, so that the corrosion resistance and arc stability of the welding wire during storage and welding are ensured. Finally, the welding wire with a diameter of Φ4.0mm is obtained.

[0078] It should be noted that, in the whole welding wire preparation process, the chemical composition and purity of smelting, the temperature range and deformation of forging and rolling, the temperature and atmosphere of annealing, and the pass compression ratio and lubrication conditions of drawing are strictly controlled, which are the key to ensure that the welding wire has stable composition, excellent strength and toughness, and good welding process performance.

[0079] Specifically, the average value of the diffusible hydrogen content of the welding wire is below 3.28 ml / 100g.

[0080] It should be noted that, if the hydrogen content is too high, hydrogen atoms are easy to gather at grain boundaries, dislocations and inclusions, inducing hydrogen-induced cold cracking and brittle fracture, thereby weakening the load-carrying capacity of the weld and significantly reducing the low-temperature impact absorption energy, which increases the risk of cold cracking, especially in high-strength steel. Once the cold cracking occurs, the effective load-carrying area of the weld will decrease, resulting in unstable strength performance or even premature failure. Therefore, the low level of 3.28 ml / 100g controlled by the present application effectively ensures the strength stability and excellent low-temperature impact performance of the weld metal.

[0081] Specifically, in step three, the welding current is 525-575 A, the welding voltage is 28-30 V, the welding speed is 39-41 cm / min, and the average heat input is 20-26 kJ / cm.

[0082] Specifically, in step four, the interpass temperature is controlled at 105-120 DEG C.

[0083] It should be noted that the welding current is set at 525-575 A, the welding voltage is controlled at 28-30 V, and the welding speed is controlled at 39-41 cm / min. When the above parameters are used in combination, the average heat input of welding is 24 kJ / cm, which can ensure that the deposited metal obtains refined acicular ferrite and bainite structure, and realizes excellent strength and low-temperature toughness.

[0084] During the welding process, the interpass temperature should be strictly controlled between 105-120 DEG C to avoid coarse structure caused by too high temperature or cold cracking caused by too low temperature. After welding, check whether the weld surface forming is smooth, and whether there are defects such as pores, incomplete fusion, and slag inclusion.

[0085] In order to more clearly describe the present application, the following examples and comparative examples are further illustrated.

[0086] Example 1

[0087] Preparation of welding wire:

[0088] S1: smelting, smelting is carried out by using vacuum induction furnace or electric arc furnace + refining process, and it is ensured that S, P ≤ 0.005%. The molten steel composition is controlled to be uniform, the hydrogen content is less than 2 ppm, the pouring temperature is 1550-1580 ℃, and the ingot with uniform composition and low inclusions is obtained.

[0089] S2: forging, the ingot is heated and kept at 1150-1180 ℃, and then forging is carried out, and the final forging temperature is controlled at 850-900 ℃, so as to break the as-cast structure and refine the grains, and the uniform and dense forged blank is obtained.

[0090] S3: rolling, the forged blank is hot rolled by multiple passes after heating, the rolling temperature is 1050-1100 ℃, and the final rolling temperature is controlled at above 850 ℃, and the Φ6.5 mm wire rod is obtained, and it is ensured that the structure is fine and the surface quality is good.

[0091] S4: pickling and annealing, the hot rolled wire rod is pickled to remove the oxide skin, and then annealing treatment is carried out at 650-700 ℃, so as to restore the structure and improve the plasticity, and facilitate the subsequent cold working.

[0092] S5: bright drawing, the annealed wire rod is cold drawn by multiple passes under clean and lubricated conditions, the pass compression rate is controlled to be ≤ 15%, and the welding wire with a diameter of Φ4.0 mm is drawn. Surface defects need to be strictly controlled during the drawing process, the wire diameter is kept uniform, and the surface roughness is ≤ Ra0.8.

[0093] S6: surface layer winding, a copper plating layer or other anti-oxidation layer is uniformly applied on the surface of the welding wire, so as to ensure the corrosion resistance and arc stability of the welding wire during storage and welding. Finally, the welding wire with a diameter of Φ4.0 mm is obtained.

[0094] The welding wires with different compositions are prepared by using the above method, and the composition of the welding wire is shown in Table 1 (the ratio of alloy raw materials can be adjusted during the smelting stage to obtain welding wires with different compositions).

[0095] Table 1 Composition of examples and comparative examples of the application (mass fraction, %)

[0096] Group C Si Mn S P Cr Ni Mo Ti Example 1 0.075 0.34 1.36 0.004 0.005 0.25 2.49 0.56 0.032 Example 2 0.082 0.42 1.44 0.004 0.005 0.37 2.63 0.54 0.041 Example 3 0.097 0.37 1.25 0.004 0.005 0.44 3.14 0.55 0.046 Comparative Example 1 0.087 0.52 1.45 0.005 0.009 0.62 4.75 0.82 0.003 Comparative Example 2 0.115 0.65 1.76 0.008 0.013 1.43 3.97 0.65 0.005 Comparative Example 3 0.127 0.57 1.34 0.005 0.005 1.59 4.69 0.73 0.004

[0097] Welding process:

[0098] The diameter of the submerged arc welding wire of the application is φ4.0 mm, the welding is carried out by using the above welding wire, the test plate is 20 mm thick S690 high-strength steel, the welding adopts straight weld, the flux JF690 is used, and the following steps are included.

[0099] Step one: flux preheating treatment, baking at 300-350 ℃ for 2 hours;

[0100] The main chemical composition of the JF690 flux is:

[0101] CaO + MgO: 32.2%; Al2O3 + MnO2: 23.3%; SiO2 + TiO2: 19.3%; CaF2: 25.2.%;

[0102] wherein the sulfur (S) content is less than 0.01%, the phosphorus (P) content is less than 0.02%, the water content is less than 0.01%, and the alkalinity is controlled between 1.5 and 3.5;

[0103] Step two: welding material preparation, according to the welding process requirements, the welding wire and the baked flux are filled into the automatic submerged arc welding equipment, and the flux layer thickness is adjusted to ensure stable arc combustion;

[0104] Step three: welding parameter setting; the welding current is 540 A, the welding voltage is 29 V, the welding speed is 40 cm / min, the average heat input is 22-24 kJ / cm, the ambient temperature is 3°C, and the relative humidity is 48%;

[0105] Step four: welding process control, during the welding process, the interpass temperature should be strictly controlled between 105-120°C;

[0106] Step five: weld forming and inspection.

[0107] Examples 4-6 and Comparative Examples 4-6

[0108] Examples 4-6 and Comparative Examples 4-6 are prepared in substantially the same manner as the examples, except as shown in Table 2.

[0109] Table 2 Examples 4-6 and Comparative Examples 4-6

[0110]

[0111] The preheating temperature in Table 2 refers to the preheating temperature of the base material (test plate).

[0112] The mechanical properties of the deposited metal are shown in Table 3, the diffusible hydrogen content of the deposited metal is shown in Table 4, and the rigid butt weld crack test results are shown in Table 5.

[0113] Table 3 Mechanical properties of the deposited metal of the examples and comparative examples of the present application

[0114]

[0115]

[0116] Table 4 Measurement of diffusible hydrogen content of the deposited metal of the examples and comparative examples of the present application

[0117]

[0118]

[0119] The rigid butt welding crack test was conducted at an ambient temperature of 18-20°C and a relative humidity of 23-25%, and the test results are shown in Table 5.

[0120] Table 5 Results of rigid butt welding crack test of the examples and the comparative examples of the present application

[0121]

[0122] It can be seen from the examples 1-6 and the comparative examples 1-6 and in reference to Tables 1-5 that, by using the welding method of the examples of the present application, in cooperation with the flux and the welding wire, and in cooperation with the control of the corresponding welding parameters, the base material (the product to be welded) does not need to be preheated during the welding process, and the 690MPa grade low-temperature high-strength steel after welding has high strength and low-temperature toughness, the yield strength of the deposited metal is above 700MPa, the tensile strength is above 750MPa, the elongation is above 24%, and the impact absorption energy at -50°C is above 91J. At the same time, the average value of the diffusible hydrogen content of the welding wire is below 3.28ml / 100g, which reflects the significant advantage of the clean metallurgy and the hydrogen and impurity control process used in the welding wire of the present application in reducing the diffusible hydrogen level, and reduces the risk of hydrogen-induced cold cracking.

[0123] Under the conditions of normal temperature, a relative humidity of 23-25%, and a high welding heat input, the weld metal has a surface crack rate, a cross-section crack rate, and a root crack rate of 0%, and no cold cracks of any form are found.

[0124] The above only describes the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions easily thought of by those skilled in the art within the technical scope disclosed by the present application should be covered within the protection scope of the present application.

Claims

1. A preheat-free submerged arc welding method for a 690 MPa grade high-strength high-ductility steel, characterized by, The method comprises the following steps: Step 1: flux preheating treatment, the flux needs to be baked before use; Step 2: welding material preparation, the welding wire and the baked flux are filled into the automatic submerged arc welding equipment for welding; Step 3: welding parameter setting; Step 4: welding process control, the alternating welding method of opposite welding direction between the previous pass and the next pass is adopted during the welding process; Step 5: weld forming and inspection.

2. The preheat-free submerged-arc welding method of a 690 MPa grade high-strength and high-ductility steel according to claim 1, characterized by, In step 1, the flux is an alkaline sintering type smelting flux, and the chemical composition of the flux is as follows in terms of mass percentage: CaO+MgO: 30.2-33.2%; Al2O3+MnO2: 22.3-25.3%; SiO2+TiO2: 13.3-19.3%; CaF2: 20.4-26.4%; S<0.01%, P<0.02%, and water content<0.01%.

3. The preheat-free submerged-arc welding method of a 690 MPa grade high-strength and high-ductility steel according to claim 2, characterized by, The alkalinity of the flux is 1.5-3.

5.

4. The preheat-free submerged-arc welding method of a 690 MPa grade high-strength and high-ductility steel according to claim 1, characterized by, The flux is baked at 300-350℃ for more than 2 hours before use.

5. The preheat-free submerged-arc welding method of a 690 MPa grade high-strength and high-ductility steel according to claim 1, characterized by, The chemical composition of the welding wire includes C: 0.07-0.10%; Si: 0.25-0.50%; Mn: 1.20-1.50%; Cr: 0.20-0.50%; Ni: 2.10-3.30%; Mo: 0.45-0.65%; Ti: 0.03-0.05% in terms of mass percentage; S≤0.005%; P≤0.005%; the balance is Fe and inevitable impurities.

6. The preheat-free submerged-arc welding method of a 690 MPa grade high-strength and high-ductility steel according to claim 1, characterized by, In step 3, the welding current is 525-575A, the welding voltage is 28-30V, the welding speed is 39-41cm / min, and the average heat input is 20-26kJ / cm.

7. The preheat-free submerged-arc welding method of a 690 MPa grade high-strength and high-ductility steel according to claim 1, characterized by, In step 4, the interpass temperature is controlled at 105-120℃.

8. The preheat-free submerged-arc welding method of a 690 MPa grade high-strength and high-ductility steel according to claim 1, characterized by, The yield strength of the welded joint is ≥700MPa, the tensile strength is ≥750MPa, and the impact absorbed energy at-50℃ is ≥90J.

9. The preheat-free submerged-arc welding method of a 690 MPa grade high-strength and high-ductility steel according to claim 1, characterized by, The deposited metal is prepared from the welding wire, and the microstructure of the deposited metal is composed of acicular ferrite, lath ferrite and lath bainite.

10. A pre-heat free 690 MPa grade high strength high toughness steel, characterized in that, The welded joint is prepared by the submerged arc welding method according to any one of claims 1-9.

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