Production method for improving fatigue resistance and toughness of steel wire rod for welding wire

Abstract

The invention relates to a production method for improving fatigue resistance and toughness of a steel wire rod for a welding wire, which comprises the following steps of: mixing molten iron and scrap steel into a converter, smelting to obtain molten steel, sequentially adding silicon iron, silicon manganese and lime into the molten steel in the tapping process, and determining whether sulfur-containing slag is added into the molten steel or not according to the content of S in the molten steel; adding low-titanium and low-aluminum silicon iron and manganese metal to adjust the components of molten steel according to the target components of the steel grade, and then carrying out LF (Ladle Furnace) refining; and then carrying out protective casting, carrying out segmented heating on a steel billet, rolling the steel billet into a wire rod, carrying out water cooling, cooling and spinning, placing the wire rod on a Stelmor slow cooling line for slow cooling, and sending the wire rod into a heat preservation vestibule for slow cooling. The steel wire rod for the welding wire has good quality and stable mechanical properties from inside to outside through component control and process adjustment and optimization aiming at factors such as carbon segregation and inclusions in the production process, so that the fatigue resistance and toughness of the steel wire rod for the welding wire are improved.

Description

Technical Field

[0001] The invention relates to the technical field of steel rolling production, in particular to a production method for improving fatigue resistance and toughness of a steel wire rod for welding wire. Background Art

[0002] Inclusions seriously affect the comprehensive properties of steel. Non-metallic inclusions exist in steel as independent phases, which destroy the continuity of the steel matrix, increase the heterogeneity of the steel structure, and seriously affect the various properties of steel. For example, non-metallic inclusions lead to stress concentration and cause fatigue fracture; inclusions with large numbers and uneven distribution will significantly reduce the plasticity, toughness, weldability and corrosion resistance of steel; sulfides in the form of a network in steel will cause hot brittleness. Therefore, the number and distribution of inclusions are recognized as an important indicator for assessing the quality of steel. The properties, forms, distribution, size and content of non-metallic inclusions are different, and the effects on steel properties are also different. Therefore, improving the quality of metal materials, producing clean steel, or controlling the properties and required forms of non-metallic inclusions is an arduous task in the smelting and ingot casting process. Summary of the invention

[0003] The purpose of the present invention is to provide a production method for improving the fatigue resistance and toughness of steel wire rods for welding wire, thereby improving the fatigue resistance and toughness of steel wire rods for welding wire.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] The present invention provides a production method for improving fatigue resistance and toughness of a steel wire rod for welding wire, comprising the following steps:

[0006] S1: molten steel smelting, molten iron and scrap steel are added into a converter for smelting to obtain molten steel, ferrosilicon-silicon manganese-lime are added to the molten steel in sequence during the steel tapping process, and whether to add sulfur-containing slag to the molten steel is determined according to the S content in the molten steel; wherein the scrap steel ratio is 5-10%, and the smelting end temperature is 1630-1650°C;

[0007] S2: LF refining, according to the target composition of the steel grade, adding low-titanium, low-aluminum ferrosilicon and metallic manganese to adjust the composition of the molten steel in step (1), followed by LF refining, wherein the LF refining station entry temperature is ≥1550°C, and the ladle bottom blowing flow rate is 200-250NL / min;

[0008] S3: Casting, the molten steel obtained in the refining step is subjected to protective casting, the superheat of the molten steel in the tundish of the open-casting furnace is 25-30°C, the superheat of the molten steel in the tundish of the continuous casting furnace is 15-20°C, the pulling speed is 2.39-2.43 m / min when the specification of the ingot is 150*150 mm, and the pulling speed is 1.58-1.62 m / min when the specification of the ingot is 180*180 mm;

[0009] S4: heating, heating the steel billet obtained in the casting process in stages, wherein the preheating stage temperature is 700-800°C, the first stage heating temperature is 760-840°C, the second stage heating temperature is 890-970°C, and the soaking stage temperature is 1060-1090°C;

[0010] S5: temperature-controlled rolling, rolling the steel billet obtained in the heating step into a wire rod, cooling it with water, and spinning it, wherein the starting rolling temperature is 1000-1020°C, the final rolling temperature is 950-970°C, and the spinning temperature is 900-920°C;

[0011] S6: Slow cooling and heat preservation. The wire rod obtained in the temperature-controlled rolling process is placed on a Stelmor slow cooling line for slow cooling, and then sent into a heat preservation corridor for slow cooling. The Stelmor slow cooling rate is ≤1°C / S, the temperature entering the heat preservation corridor is 730-770°C, the heat preservation time in the heat preservation corridor is 90-150min, and the temperature exiting the heat preservation corridor is ≤300°C.

[0012] Furthermore, the chemical elements of the applicable steel wire rod for welding wire are, in mass percentage, C: 0.06-0.07%, Si: 0.81-0.85%, Mn: 1.41-1.47%, P≤0.013%, S: 0.009-0.012%, A1≤0.0070%, Ca≤0.0010%, Ti≤0.10%, Cr≤0.10%, Re≤0.05%, Mo≤0.10%, and the remainder is Fe and unavoidable impurities.

[0013] Furthermore, in step S1, before the molten iron is smelted, it is necessary to perform KR desulfurization on the molten iron. The molten iron is taken every 4 minutes to analyze the S content. When the S content is between 0.002% and 0.006%, the desulfurization is stopped and slag removal is performed. The slag removal rate is ≥95%. After KR desulfurization, the molten iron has C: 3.8-4.2%, S: 0.002-0.006%, Si: 0.3-0.5%; and Mn: 0.15-0.3%.

[0014] Furthermore, in step S1, before the molten steel is tapped, a composite deoxidizer is added to the bottom of the ladle at a rate of 1 to 1.2 kg / t of steel for deoxidation, and the composite deoxidizer is a FeCaAlReSi composite deoxidizer.

[0015] Furthermore, in step S1, when 1 / 4 of the molten steel is tapped, 3-4 kg / t of aluminum particles and 15-17 kg / t of high manganese alloy are added to the molten steel in sequence; when 3 / 5 of the steel is tapped, 10-12 kg / t of calcium silicate synthetic slag is added to the molten steel; and before the tapping is completed, all of the alloy and the calcium silicate synthetic slag are added.

[0016] Furthermore, in step S1, during the steel tapping process, the ladle bottom blowing and stirring are turned on throughout the whole process, the ladle bottom blowing flow rate is 550-600L / min, and the bottom blowing flow rate at the end of steel tapping is 120-180NL / min.

[0017] Furthermore, in step S1, the element contents of the molten steel at the smelting end point are: C: 0.03-0.06%, O≤0.015%, P≤0.010%, S≤0.012%.

[0018] Furthermore, in step S2, after the molten steel is adjusted to the target composition, before LF refining, the slag composition is adjusted by adding lime, silicon carbide and a modifier to obtain the slag basicity CaO / SiO 2 =1.5~1.9, T.Fe+MnO content ≤3.5%; during this period, the ladle bottom blowing flow rate is 150~200NL / min.

[0019] Furthermore, the components of the modifier include: Al≥30%, Al2O3: 10-30%, H2O<1%, SiO2<10%, CaO>20%, and the particle size of the modifier is: 5mm-50mm.

[0020] Furthermore, after adjusting the slag composition, the temperature is raised by power, the heating rate is 1.5-2.5°C / min, and the ladle bottom blowing flow rate is 150-200NL / min;

[0021] Subsequently, the ladle bottom blowing is adjusted to a soft stirring mode, during which the ladle bottom blowing flow rate is 30 to 80 NL / min and the soft stirring time is ≥20 min.

[0022] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0023] The present invention adjusts and refines various process parameters of the production process from molten steel smelting to heat preservation and slow cooling, thereby firstly ensuring that the produced steel wire rod for welding wire has no abnormal structure and good mechanical properties.

[0024] Furthermore, the addition of composite deoxidizer has an unexpectedly good deoxidation effect. At the same time, the increase in the Mn / Si ratio promotes the fluidity of the molten steel, so the inclusions are promoted to float and the removal effect is very obvious. On the basis of the above, the Si content is controlled to greatly reduce the SiO 2And containing SiO 2 Inclusions with high silicate content have a significant effect on improving the fatigue resistance and toughness of steel wire rods for welding wire. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The present invention provides a production method for improving fatigue resistance and toughness of steel wire rod for welding wire, comprising a molten steel smelting process, a LF refining process, a casting process, a heating process, a temperature-controlled rolling process and a slow cooling and heat preservation process in sequence. The chemical elements of the steel wire rod for welding wire suitable for the above-mentioned improvement method are as follows by mass percentage: C: 0.06-0.07%, Si: 0.81-0.85%, Mn: 1.41-1.47%, P≤0.013%, S: 0.009-0.012%, A1≤0.0070%, Ca≤0.0010%, Ti≤0.10%, Cr≤0.10%, Re≤0.05%, Mo≤0.10%, and the balance is Fe and unavoidable impurities.

[0027] Specifically, in the molten steel smelting process, the purpose is to add molten iron and scrap steel into a converter for smelting to obtain molten steel, and in the process of tapping, ferrosilicon alloy and silicon-manganese alloy are added to the molten steel in sequence, and at the same time, it is determined whether to add sulfur-containing slag to the molten steel according to the S content in the molten steel; wherein, the scrap steel adopts high-quality steel, the scrap steel ratio is 5-10%, and the smelting end temperature is 1630-1650°C; and the element content of the molten steel at the smelting end point is C: 0.03-0.06%, O≤0.015%, P≤0.010%, S≤0.012%.

[0028] The purpose of controlling the C content is to reduce the C content within a reasonable range, thereby reducing the impact of segregation. The purpose of controlling the O content is to control the amount of oxide inclusions generated to prevent excessive oxides from forming in the steel billet, which may affect the stability of grain boundaries. P and S are harmful elements. S and Fe form FeS with a low melting point, which is hot brittle. P is prone to segregation and forms FeP with Fe. 3 , which significantly reduces the plasticity and toughness, increases the brittleness, and especially increases the brittle transition temperature of steel, causing the cold brittleness of steel. At the same time, it can deteriorate the welding performance of steel, reduce plasticity, and deteriorate the cold bending performance. Therefore, the P content is controlled to be ≤0.010% and the S content is ≤0.012% in the present invention.

[0029] Before the above molten steel is tapped, the bottom of the ladle is deoxidized by adding a FeCaAlReSi composite deoxidizer at a rate of 1-1.2 kg / t of steel. The addition of Re element helps to form liquid deoxidation products, facilitates the floating and removal of deoxidized products, improves the purity and performance of steel, has high efficiency and high speed, and can improve durability in subsequent product applications. At the same time, it can form Mo-Re and Cr-Re with Mo and Cr elements, which have good plasticity.

[0030] When the converter is 1 / 4 of the steel tapped, 3-4 kg / t of aluminum particles and 15-17 kg / t of high manganese are added to the molten steel in the form of alloy. When the converter is 3 / 5 of the steel tapped, 10-12 kg / t of calcium silicate synthetic slag is added to the molten steel. Before the end of the steel tapping, the alloy and the calcium silicate synthetic slag are all added. In addition, the ladle bottom blowing and stirring are turned on throughout the steel tapping process, with a ladle bottom blowing flow rate of 550-600 L / min and a bottom blowing flow rate of 120-180 NL / min after the steel tapping is completed.

[0031] In the process of molten steel smelting, due to SiO 2 The high melting point and high viscosity are not conducive to slag removal. Therefore, the present invention controls 1.7≤Mn / Si≤1.8. Within this range, SiO can be fully consumed. 2 Reacts with MnO to form MnO·SiO 2 The liquid deoxidation product can improve the fluidity of molten steel, and has a significant effect on the removal of inclusions by floating up. In addition, it is beneficial to the subsequent continuous casting production and improves the plasticity of the wire rod.

[0032] For the aforementioned LF refining process, since the amount of carbon added during the steel-making process is large, one of the purposes of LF refining is to adjust the C content. Take samples to measure the chemical composition of molten steel and slag, open the ladle bottom blowing and stirring, and the ladle bottom blowing flow rate is 100-150NL / min. After the molten steel and slag components are tested, low-titanium, low-aluminum ferrosilicon and metallic manganese are added according to the target composition of the steel grade to adjust the molten steel composition, during which the ladle bottom blowing flow rate is 200-250NL / min.

[0033] Specifically, Si is the alloy element with the strongest graphitization effect. Whether in liquid or solid steel, Si combines with Fe more strongly than C. The presence of Si in molten steel will reduce the solubility of C. Therefore, the higher the Si content, the lower the C content, and more C will be squeezed out. With the reduction of C content, C segregation in the ingot will be significantly improved. However, the Si content cannot be too high. Excessive Si will form SiO 2 and high content of 2FeO-SiO 2 Silicate compounds, these spherical non-deformed inclusions will exist in the steel billet and affect the fatigue resistance. Therefore, in the present invention, the Si content in the steel billet is controlled to be 0.81-0.85%.

[0034] After the molten steel composition reaches the target composition, lime, silicon carbide and modifier are added to adjust the slag composition to obtain the slag basicity CaO / SiO 2 =1.5~1.9, T.Fe+MnO content ≤3.5%, during which the ladle bottom blowing flow rate is 150~200NL / min. Then, the power is turned on to increase the temperature so that the molten steel temperature reaches the target value. The medium-intensity power supply mode is adopted, the heating rate is 1.5~2.5℃ / min, and the ladle bottom blowing flow rate is 150-200NL / min. Finally, the ladle bottom blowing is adjusted to the soft stirring mode, the soft stirring time is ≥20min, and the ladle bottom blowing flow rate is 30~80NL / min during the soft stirring stage to obtain the slag basicity CaO / SiO 2 =1.5~1.9.

[0035] Regarding the above-mentioned modifier, the components of the modifier used in the embodiment of the present invention include: Al≥30%, Al 2 O 3 :10~30%,H 2 O<1%, SiO 2 <10%, CaO>20%, and the particle size of the modifier is: 5mm~50mm. This type of modifier can form white slag faster, the refining slag has better activity, and the ability to absorb inclusions is stronger. Specifically, it can effectively reduce the oxygen content of the ladle top slag, reduce steelmaking production costs, and reduce the blockage of the nozzle during continuous casting.

[0036] After using the top slag modifier, the top slag turns white faster. The low-carbon, low-silicon steel is directly continuously cast after being treated by the argon blowing station. The molten steel has good fluidity and there is no nozzle blockage. The smoke and dust are not large, which can meet the requirements of steelmaking and environmental protection. In addition, the desulfurization effect on the molten steel is also good, and the desulfurization rate reaches 40%.

[0037] The control of the final slag basicity is to ensure the fluidity of the refined slag and fully absorb the inclusions in the steel. The entire LF refining process adopts a small and medium bottom blowing control mode. In the waiting stage, small and medium bottom blowing is used for stirring to prevent the slag from being brought into CaO. When adding alloys to adjust the composition, the bottom blowing is appropriately increased, but not too strong. It is necessary to ensure that the alloy is melted into the molten steel with uniform composition, but the slag cannot be rolled up to a large extent; when adding lime and silicon carbide to adjust the slag composition, the bottom blowing of appropriate intensity is used to promote the reaction and melting of the slag, but it cannot be rolled into the molten steel to a large extent. The small bottom blowing in the soft stirring stage is to remove the inclusions in the molten steel, and the slag cannot be rolled into the molten steel.

[0038] For the above-mentioned casting process, the molten steel produced in the above-mentioned LF refining process is protected cast, the superheat of the molten steel in the tundish of the open pouring furnace is 25-30°C, the superheat of the molten steel in the tundish of the continuous pouring furnace is 15-20°C, the pulling speed is 2.39-2.43m / min when the specification of the ingot is 150*150mm, and the pulling speed is 1.58-1.62m / min when the specification is 180*180mm.

[0039] During casting, full-process protective casting is adopted, and the argon gas flow rate at the long water nozzle is controlled at 200-300L / min. Controlling it within this range can effectively prevent the molten steel from inhaling air and causing secondary oxidation, thereby improving product quality.

[0040] In addition, the present invention adopts an arc-type continuous casting machine for casting, and the arc radius is 9 to 12 m. The casting speed of the continuous casting machine is controlled within a narrow range. In addition to ensuring the stability of the casting speed, the probability of the protective slag being involved is also extremely low, which can promote the formation of excellent surface quality and internal quality of the steel billet. In addition, the superheat of the molten steel in the tundish of the open-casting furnace is 25 to 30°C or the superheat of the molten steel in the tundish of the continuous casting furnace is 15 to 20°C. Production under this superheat can ensure smooth casting, and inclusions in the steel can also achieve a good floating effect for easy removal.

[0041] In the present invention, the water flow rate of the crystallizer in the continuous casting process is controlled at 120-130L / min, the crystallizer liquid level fluctuation range is ±3mm, the crystallizer electromagnetic stirring current is 300-320A, and the frequency is 2.5Hz. The molten steel is stirred by electromagnetic stirring, and the current and frequency of the electromagnetic stirring are controlled to promote the upward movement of inclusions and bubbles before the molten steel solidifies, reduce impurities inside the steel billet, and effectively interrupt the columnar crystals at the solidification front of the molten steel, so that they are mixed with the molten steel again and can serve as the core of the equiaxed crystals; at the same time, the fluidity of the molten steel is increased, the heat transfer between the solidification phases is improved, the directional growth of the columnar crystals is inhibited, the formation of equiaxed crystals is promoted, and the segregation of dendrites is reduced.

[0042] The electromagnetic stirrer of the crystallizer in the present invention is 800 mm high, and its center is located 500 mm below the meniscus of molten steel in the crystallizer. By setting the electromagnetic stirring position in the crystallizer, a suitable magnetic induction intensity is generated at the meniscus position, which promotes the melting and uniform spreading of protective slag, achieves a good lubrication effect, and promotes the floating of inclusions into the protective slag for removal. The vibration parameters of the continuous casting machine crystallizer are a vibration range of ±3.25 mm and a vibration frequency of 93 to 97 cpm. The molten steel is stirred by electromagnetic stirring, and the current and frequency of the electromagnetic stirring are controlled to promote the upward movement of inclusions and bubbles before the molten steel solidifies, reduce impurities inside the steel billet, and effectively interrupt the columnar crystals at the solidification front of the molten steel, so that they are mixed with the molten steel again and can serve as the core of the equiaxed crystals; at the same time, the fluidity of the molten steel is increased, the heat transfer between the solidification phases is improved, the directional growth of the columnar crystals is inhibited, the generation of the equiaxed crystals is promoted, and the dendrite segregation is reduced.

[0043] In addition, the surface of the molten steel in the tundish is covered with protective slag and passes through the crystallizer. The chemical composition of the protective slag is SiO 2 :33~37%, CaO: 30~32%, MgO: 1.0~2.0%, Al 2 O 3:1.0~3.0%,Na 2 O: 5-7%, F: 2-3%, C: 14-17%, and the rest are inevitable impurities. The melting point of the protective slag is 1180-1200°C, the binary basicity is 0.8-0.9, the viscosity at 1300°C is 0.60-0.70 Pa·s, the consumption of the mold protective slag is 0.3-0.4 kg per ton of steel, and the reasonable setting of the protective slag covering the surface of the molten steel in the tundish effectively prevents the secondary oxidation of the molten steel.

[0044] The water volume of the secondary cooling zone of the continuous casting machine is 0.49-0.90L / kg, which is divided into 4 or 5 zones. When the water volume is 0.9L / kg, the water distribution ratio of each zone is 40:39:10:7:4:; when the water volume is 0.49L / kg, the water distribution ratio of each zone is 26:26:23:25. By reasonably controlling the distribution ratio and cooling intensity of each zone of the secondary cooling water, the cooling efficiency is maximized, the secondary dendrite spacing is effectively shortened, and the central segregation of elements is suppressed, which has a good effect.

[0045] Through the reasonable setting of various process parameters in casting, there are no horizontal and vertical cracks on the surface of the continuous casting billet, no defects such as shrinkage cavities, and the elements are evenly distributed. The size of inclusions within the range of 0 to 2 mm under the skin of the continuous casting billet is ≥35μm and the density is 0.01 to 0.03 pieces / mm 2 .

[0046] In the above heating process, a regenerative blast furnace gas heating furnace is used for segmented heating, with the preheating temperature of 700-800°C, the first heating temperature of 760-840°C, the second heating temperature of 890-970°C, and the soaking temperature of 1060-1090°C. By controlling the heating temperature and time, the continuous casting billet is austenitized more fully, the carbon in the steel is diffused more fully, and the surface decarburization caused by the billet staying in the high temperature section of the furnace for a long time is avoided, and the distribution is uniform.

[0047] In the temperature-controlled rolling process, the starting rolling temperature is set at 1000-1020°C, and the steel billet is successively subjected to rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling to form a wire rod. Specifically, the final rolling temperature is 950-970°C, and the wire is spun at 900-920°C. By controlling the starting rolling temperature of the welding wire steel, rolling at a lower temperature can avoid the abnormal organization caused by coarse austenite grains, reasonably controlling the dissolution of carbides in the steel at the lower limit of the final rolling temperature, and controlling the upper limit of the final rolling temperature to avoid the coarse austenite grains causing a decrease in cross-sectional shrinkage and plasticity. The control of the wire-spinning temperature is studied based on the Si and Mn content in the steel combined with the changes in the CCT image transformation curve. Wire-spinning within this temperature range can obtain iron oxide scale with good appearance and easy removal, avoid secondary oxidation caused by the shedding of iron oxide scale, and obtain the required uniform ferrite + pearlite wire rod structure.

[0048] In the slow cooling and insulation process, the wire rod produced in the aforementioned temperature-controlled rolling process is placed on the Stelmor slow cooling line for slow cooling, and then hot-coiled and sent into the insulation corridor for slow cooling, wherein the Stelmor slow cooling rate is ≤1°C / S, the temperature entering the insulation corridor is 730-770°C, the insulation time in the insulation corridor is 90-150min, and the temperature out of the insulation corridor is ≤300°C.

[0049] In addition, the inlet roller speed of the Stelmor slow cooling line in the present invention is 0.152-0.168 m / s, and the outlet roller speed is 0.237-0.262 m / s, during which the heat preservation cover is completely closed. Moreover, after the wire rod is slowly cooled on the Stelmor line in the first step, it is hot-coiled and then slowly cooled in the heat preservation corridor. During the period of exiting the heat preservation corridor-hot-coiled-entering the heat preservation corridor, it is in a relatively closed environment, and the ambient temperature fully meets the cooling speed of the wire rod and will not produce abnormal structures such as bainite and martensite.

[0050] By controlling the slow cooling speed, it is ensured that the wire rod has no abnormal structure. The slow cooling speed of the inner and outer rings of the slow cooling wire rod in the heat preservation corridor is consistent. More importantly, there is no problem of different cooling speeds at the overlap point and the non-overlap point. At the same time, the fine-grained austenite of the wire rod can be transformed and decomposed to obtain uniform ferrite and pearlite structures, and the metallographic structure transformation is more sufficient, reducing the concentrated stress of the wire rod.

[0051] The present invention will be further described in detail below in conjunction with specific Examples 1 to 4 and Comparative Examples 1 to 4.

[0052] S1--Steel smelting

[0053] The smelting raw materials consisting of desulfurized molten iron and scrap steel were smelted in a 180t converter. The total loading amount of the smelting raw materials, the weight percentage of molten iron in the smelting raw materials, the smelting time, the addition of deoxidizer, the mass percentage of C and O during steel tapping, and the steel tapping temperature of the above four embodiments and four comparative examples are shown in Table 1:

[0054] Table 1

[0055]

[0056] S2--LF refining

[0057] The molten steel obtained in the molten steel smelting process was refined in the LF furnace, wherein the refining time, soft stirring time, modifier addition, final slag basicity, T.Fe+MnO content, and tapping temperature of the four embodiments and four comparative examples are shown in Table 2:

[0058] Table 2

[0059]

[0060] S3--Casting

[0061] The molten steel obtained from the refining process is cast with full protection, including long nozzle argon sealing + immersion nozzle protection casting. During casting, the casting billet is kept at a constant pulling speed, and the crystallizer electromagnetic stirring current is controlled to be 300-320A and the frequency is 2.5Hz. Among them, the crystallizer water flow rate, long nozzle argon flow rate, open-casting furnace / continuous casting furnace tundish molten steel superheat, secondary cooling water volume and distribution ratio and pulling speed of different specifications of steel billets in 4 embodiments and 4 comparative examples are shown in Table 3:

[0062] Table 3

[0063]

[0064] S4--Heating

[0065] The obtained steel billet is heated under temperature control in a regenerative gas heating furnace. The first heating temperature, the second heating temperature, the soaking temperature, and the holding time of the four embodiments and the four comparative examples are shown in Table 4:

[0066] Table 4

[0067]

[0068] S5--temperature controlled rolling

[0069] The steel billet obtained in the heating process is descaled by high-pressure water and then rolled into a wire rod. The starting rolling temperature, the outlet temperature of the finishing mill, and the wire laying temperature of the four embodiments and the four comparative examples are shown in Table 5.

[0070] Table 5

[0071]

[0072] S6--Slow cooling and heat preservation

[0073] The wire rod obtained in the temperature-controlled rolling process is kept warm and slowly cooled on the Stelmor slow cooling line, the insulation cover and the fan tuyere are all closed, and the cooling rate of the wire rod in the phase change temperature range is ≤1°C / s. In addition, the inlet roller speed and the outlet roller speed of the Stelmor slow cooling line of the four embodiments and the four comparative examples are controlled as shown in Table 6. Among them, the cooling rate of the wire rod in the phase change temperature range can be calculated by testing the temperature between the insulation covers of the wire rod with an infrared thermometer.

[0074] Table 6

[0075]

[0076] Then, the wire rod after slow cooling on the Stettelmo line was sent to the insulation corridor for the second stage of insulation and slow cooling. The temperature entering the insulation corridor, the insulation time of the insulation corridor, and the temperature leaving the insulation corridor of the four embodiments and the four comparative examples are shown in Table 7:

[0077] Table 7

[0078]

[0079] In the present invention, according to the production methods corresponding to the above four embodiments and four comparative examples, the finally prepared steel wire rods for welding wire were inspected, wherein the chemical composition and weight percentage of each finished product are shown in Table 8:

[0080] The chemical composition of the steel billets used in the steel wire rods for welding wire corresponding to Examples 1-4 and Comparative Examples 1 to 4 is shown in Table 8:

[0081] Table 8: Composition of steel billets used in various embodiments and comparative examples (wt / %)

[0082]

[0083]

[0084] At the same time, the performance tests were carried out on the wire rods prepared in the above embodiments and comparative examples, and the test results are shown in Table 9.

[0085] Table 9 Performance test results

[0086]

[0087] It can be seen from the above embodiments and comparative examples that the cold heading steel wire rod and the preparation method thereof in the embodiments of the present invention, by taking the control of key elements such as C, Ca, O, S, Si, Mn, Ti as an example, lays a good foundation for the excellent mechanical properties of the steel wire rod, and the spatter rate is very low and the spatter is small when it is subsequently drawn into welding wire.

[0088] The present invention improves each process flow from steel pretreatment to slow cooling and controls key parameters, so that the manufactured welding wire steel wire rod has good surface quality and uniform internal structure, with a small number of inclusions and a small appearance, especially SiO 2 And containing SiO 2 The control of higher silicate inclusions makes their proportion in the inclusions very small, so that the number of fractures after repeated deformation during the drawing process of the welding wire is very small. In addition, the control of material purity makes the produced steel wire rod have excellent fatigue resistance and toughness, which is also closely related to the excellent mechanical properties and surface quality of the steel wire rod.

[0089] However, the steel wire rod in the comparative example has problems such as excessive tensile strength or poor yield strength mechanical properties due to the fact that key elements are not within the appropriate range, and both have a high wire breakage rate. When used for welding after drawing, there are also large spatters and high spatter rates. That is, the steel wire rod in the comparative example has many internal inclusions, resulting in a high wire breakage rate during drawing, and the surface quality also has defects such as roughness and uneven color. In terms of fatigue resistance and toughness, it is far inferior to the steel wire rod in the embodiment.

[0090] In summary, the present invention effectively controls the composition of the welding wire steel rod, reduces the influence of C segregation for the C element, controls the O content to avoid the formation of oxide inclusions, controls the Mn and S elements to avoid the formation of FeS that affects the grain boundaries, and controls the Mn / Si ratio to enhance the fluidity of the molten steel and promote the floating of inclusions.

[0091] In addition, the areas involving the control of inclusions in the process have been optimized and adjusted. In the converter smelting, a composite deoxidizer is used for deoxidation, which not only has a good deoxidation effect and increases plasticity, but also greatly reduces SiO 2 The formation of. In LF refining, the final slag basicity is controlled to ensure the fluidity of the refined slag and fully absorb the inclusions in the steel. Reasonable process parameters are set in continuous casting to avoid secondary oxidation, and the inclusion size within the range of 0 to 2 mm under the skin of the continuous casting billet is controlled to be ≥35μm, and the density is 0.01 to 0.03 pieces / mm 2 , and the removal effect of other types of inclusions is excellent.

[0092] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A production method for improving fatigue resistance and toughness of steel wire rod for welding wire, characterized in that: The steps include: S1: molten steel smelting, molten iron and scrap steel are added into a converter for smelting to obtain molten steel, ferrosilicon-silicon manganese-lime are added to the molten steel in sequence during the steel tapping process, and whether to add sulfur-containing slag to the molten steel is determined according to the S content in the molten steel; wherein the scrap steel ratio is 5-10%, and the smelting end temperature is 1630-1650°C; S2: LF refining, according to the target composition of the steel grade, adding low-titanium, low-aluminum ferrosilicon and metallic manganese to adjust the composition of the molten steel in step (1), followed by LF refining, wherein the LF refining station entry temperature is ≥1550°C, and the ladle bottom blowing flow rate is 200~250NL / min; S3: Casting, the molten steel obtained in the refining step is subjected to protective casting, the superheat of the molten steel in the tundish of the open-casting furnace is 25-30°C, the superheat of the molten steel in the tundish of the continuous casting furnace is 15-20°C, when the specification of the ingot is 150*150mm, the pulling speed is 2.39-2.43m / min, when the specification of the ingot is 180*180mm, the pulling speed is 1.58-1.62m / min; S4: heating, heating the steel billet obtained in the casting process in stages, wherein the preheating stage temperature is 700-800°C, the first stage heating temperature is 760-840°C, the second stage heating temperature is 890-970°C, and the soaking stage temperature is 1060-1090°C; S5: temperature-controlled rolling, rolling the steel billet obtained in the heating step into a wire rod, cooling it with water, and spinning it, wherein the starting rolling temperature is 1000-1020°C, the final rolling temperature is 950-970°C, and the spinning temperature is 900-920°C; S6: Slow cooling and heat preservation. The wire rod obtained in the temperature-controlled rolling process is placed on a Stelmor slow cooling line for slow cooling, and then sent into a heat preservation corridor for slow cooling. The Stelmor slow cooling rate is ≤1°C / S, the temperature entering the heat preservation corridor is 730~770°C, the heat preservation time in the heat preservation corridor is 90~150min, and the temperature exiting the heat preservation corridor is ≤300°C.

2. A production method for improving fatigue resistance and toughness of steel wire rod for welding wire according to claim 1, characterized in that: The chemical elements of the applicable steel wire rod for welding wire are calculated in mass percentage as follows: C: 0.06~0.07%, Si: 0.81~0.85%, Mn: 1.41~1.47%, P≤0.013%, S: 0.009~0.012%, A1≤0.0070%, Ca≤0.0010%, Ti≤0.10%, Cr≤0.10%, Re≤0.05%, Mo≤0.10%, and the balance is Fe and unavoidable impurities.

3. The method for improving fatigue resistance and toughness of steel wire rod for welding wire according to claim 1, characterized in that: In step S1, before the molten iron is smelted, it is also necessary to perform KR desulfurization on the molten iron. The molten iron is taken every 4 minutes to analyze the S content. When the S content is 0.002-0.006%, the desulfurization is stopped and slag removal is performed. The slag removal rate is ≥95%. After KR desulfurization, the molten iron has C: 3.8-4.2%, S: 0.002-0.006%, and Si: 0.3-0.5%; Mn: 0.15~0.3%.

4. The method for improving fatigue resistance and toughness of steel wire rod for welding wire according to claim 1, characterized in that: In step S1, before the molten steel is tapped, a composite deoxidizer is added to the bottom of the ladle at a rate of 1-1.2 kg / t of steel for deoxidation, and the composite deoxidizer is a FeCaAlReSi composite deoxidizer.

5. The method for improving fatigue resistance and toughness of steel wire rod for welding wire according to claim 1, characterized in that: In step S1, when 1 / 4 of the molten steel is tapped, 3-4 kg / t of aluminum particles and 15-17 kg / t of high manganese alloy are added to the molten steel in sequence; when 3 / 5 of the steel is tapped, 10-12 kg / t of calcium silicate synthetic slag is added to the molten steel; before the tapping is completed, all of the alloy and the calcium silicate synthetic slag are added.

6. A production method for improving fatigue resistance and toughness of steel wire rod for welding wire according to claim 1, characterized in that: In step S1, during the steel tapping process, the ladle bottom blowing and stirring are turned on throughout the process, the ladle bottom blowing flow rate is 550-600 L / min, and the bottom blowing flow rate is 120-180 NL / min at the end of steel tapping.

7. A production method for improving fatigue resistance and toughness of steel wire rod for welding wire according to claim 1, characterized in that: In step S1, the element contents of the molten steel at the end of smelting are: C: 0.03-0.06%, O≤0.015%, P≤0.010%, S≤0.012%.

8. The method for improving fatigue resistance and toughness of steel wire rod for welding wire according to claim 1, characterized in that: In step S2, after the molten steel is adjusted to the target composition, before LF refining, the slag composition is adjusted by adding lime, silicon carbide and modifier to obtain slag basicity CaO / SiO2=1.5~1.9 and T.Fe+MnO content ≤3.5%; during this period, the ladle bottom blowing flow rate is 150~200NL / min.

9. A production method for improving fatigue resistance and toughness of steel wire rod for welding wire according to claim 8, characterized in that: The components of the modifier include: Al≥30%, Al2O3: 10-30%, H2O <1%, SiO2 <10%, CaO >20%, and the particle size of the modifier is: 5mm~50mm.

10. A production method for improving fatigue resistance and toughness of steel wire rod for welding wire according to claim 8, characterized in that: After adjusting the slag composition, power is turned on to increase the temperature at a rate of 1.5-2.5°C / min, during which the ladle bottom blowing flow rate is 150-200NL / min; Subsequently, the ladle bottom blowing is adjusted to a soft stirring mode, during which the ladle bottom blowing flow rate is 30-80 NL / min and the soft stirring time is ≥20 min.

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