Hot-rolled wire rod and red rust control production process

Abstract

The invention relates to a hot-rolled wire rod and red rust control production process, which is characterized in that the contents of Ni and As are controlled in the aspect of components, so that primary oxide skin is easy to remove, P and rare earth elements are added to the wire rod with the Si content exceeding 0.2%, the melting point of fayalite phase is reduced, and the primary oxide skin is cleaned by controlling the water pressure, the water quantity and the steel billet temperature of high-pressure water dephosphorization. In the rolling process, large rolling reduction in the early stage and small rolling reduction in the later stage are adopted, the cooling water amount is reduced by adopting low water temperature and high spinning temperature, the cooling water amount of each water tank is reasonably distributed, the temperature gradient of the wire rod is controlled, and the adhesiveness of the oxide scale is guaranteed. And the cooling water pressure and the reverse air cleaning pressure are reasonably controlled, the finish rolling speed is properly reduced, and the reaction of high-temperature rolled pieces, water and air is reduced. And meanwhile, the water quality of roller cooling water and water tank cooling water is controlled, and finally oxidation of FeO is reduced on the basis that the normal structure is guaranteed on a Stelmor cooling line, so that the surface quality of a final product is good, and no red rust is generated.

Description

Technical Field

[0001] The invention relates to a hot-rolled wire rod and a red rust control production process, belonging to the technical field of iron and steel metallurgy and steel rolling. Background Art

[0002] As competition in the steel market becomes increasingly fierce, users have increasingly stringent requirements for the surface quality of wire products. During high-temperature rolling and subsequent cooling, the wire surface will react chemically with air to generate iron oxide scale, which is composed of FeO, Fe2O3, and Fe3O4 in a certain proportion and is usually gray or blue-gray. However, under certain conditions, when the proportion of Fe2O3 is high, the iron oxide scale on the wire surface is red, which is usually called red rust on the wire surface.

[0003] Red rust on the wire surface will have an adverse effect on the quality of the finished wire: first, it will cause the product appearance quality to deteriorate and affect the product image; second, the red rust on the surface will have an adverse effect on the mechanical descaling or pickling descaling in the subsequent processing process, making descaling difficult or increasing the acid consumption of pickling, resulting in wire breakage during drawing, increased wire drawing die consumption, and even having varying degrees of impact on the fatigue performance of the steel wire.

[0004] In order to control red rust to ensure the good quality of the finished product surface, the application with publication number CN109355453A discloses a production method for red rust on the surface of hot-rolled strip steel. By controlling the Si content in the molten steel to 0.159-0.185%, controlling the key parameters such as the conductivity, pH value, and reverse air purge pressure of the cooling water, the problem of red rust being easily generated in the production of wire rods is solved. However, for high-strength steel wire rods, it is necessary to add more than 0.2% of Si elements to play a role in solid solution strengthening, improving the hardenability of austenite, and improving the purity of ferrite. In terms of composition, the existing technology controls the Si content in the steel to less than 0.2%, but for Si elements above 0.2%, no method for controlling red rust is given. The application with publication number CN115922155A discloses a production method for removing red rust on the surface of welding wire steel wire rods, using low-temperature heating, controlling the rolling temperature, and using a fast roller process on the air-cooled line to increase the ring density and quickly cool, thereby improving the problem of red rust on the surface of low-carbon steel finished wire rods. However, for some steel grades, low-temperature heating is used. If the heating temperature is too low, it is easy to cause the steel billet to not burn through, the temperature of the steel billet is uneven, and finally the performance of the wire rod is unqualified; on the one hand, low-temperature rolling is easy to cause cracks and ruptures in the oxide scale, resulting in rapid diffusion of oxygen, and FeO is continuously oxidized into Fe2O3 and Fe3O4, causing serious red rust on the surface of the wire rod; on the other hand, low-temperature rolling is limited by production line equipment, and some production line equipment cannot achieve low-temperature rolling. The application with publication number CN107962070A discloses a rolling process for eliminating red rust on the surface of high-speed wire rods. By controlling the oil content of turbid ring water, adjusting the finishing inlet temperature and the wire laying temperature, and increasing the reverse purge pressure, the red rust on the surface of the high-speed wire rod is controlled at a low level, and the oil and gas injection amount is reduced, the oil and gas consumption is reduced, and the cost is reduced, so as to achieve good surface quality of high-speed wire rods under oil and gas lubrication conditions. However, in addition to the oil content in turbid ring water affecting red rust, the chloride ion content, pH value, conductivity, etc. will also affect red rust.

[0005] The mechanism of red rust generation is relatively complex, involving high-temperature oxidation corrosion, high-temperature electrochemical corrosion, etc. Therefore, many factors should be considered in the rolling process, including reasonable design of the composition, optimization of rolling process parameters, control of cooling water quality, etc., so that the final wire rod surface quality is good and no red rust is generated. Summary of the invention

[0006] The invention provides a hot-rolled wire rod and a red rust control production process, which controls the composition and the entire rolling process, so that the surface quality of the final product is good and no red rust is generated.

[0007] The technical solution adopted by the present invention to solve its technical problem is: A hot-rolled wire rod, the chemical composition of which is determined by Si content, expressed in mass percentage. When 0.06%≤Si<0.2%, C is 0.06-0.82%, Mn is 0.3-0.6%, P≤0.02%, S≤0.015%, Ni≤0.014%, As≤0.015%, Ni+As≤0.02%, and the rest is Fe and unavoidable impurities; When 0.2%≤Si≤0.3%, C is 0.25-0.82%, Mn is 0.3-0.6%, P is 0.05%-0.06%, S≤0.015%, Ni≤0.014%, As≤0.015%, Ni+As≤0.02%, REM is 0.02-0.03%, and the rest is Fe and unavoidable impurities, wherein REM is one, two or three of the rare earth elements Ce, Sc and Y; The red rust control production process for the hot-rolled wire rod specifically comprises the following steps: Step S1, heating the steel billet, feeding the steel billet into a heating furnace, adopting segmented heating, and setting the temperature of different stages according to different silicon contents, until the steel billet is heated to a preset temperature that meets the rolling requirements; Step S2, high-pressure water dephosphorization, four sides of the spray beam, three nozzles are installed on each side, the water pressure of the nozzle located in the middle is set to 18-20MPa, the water pressure of the other two nozzles is set to 15-17MPa, the inclination angle between the center axis of the nozzle and the normal line of the steel billet is in the range of 15-18°, and the straight-line distance between the nozzle and the surface of the steel billet is 150-160mm; the nozzle is used to spray high-pressure water onto the surface of the steel billet to peel off and wash away the oxide scale; Step S3, rough rolling, using the rollers of the rough rolling unit to roll the steel billet for multiple passes, rolling the steel billet with a large deformation amount, wherein the elongation coefficient of each pass is set to 1.4-1.5; Step S4, intermediate rolling, rolling the steel billet in multiple passes on the intermediate rolling mill to reduce the cross-sectional dimensions of the steel after rough rolling, wherein the elongation coefficient of each pass is set to 1.4-1.5; Step S5, continue rolling the steel billet. After pre-finish rolling, set two water tanks to spray water on the wire rod for cooling. Set the water pressure of the water tank to 3-5 MPa, the water volume of each water tank to 200-300 L / min, the water pressure of the roller cooling water to 5.5-7 bar, and the water volume to 500-700 L / min. Step S6, finishing rolling, continuously rolling the wire rod on the finishing rolling mill, setting the elongation coefficient of each pass of the finishing rolling to 1.2-1.25; Step S7, water cooling after finishing rolling, set six water tanks, and open three of them, set the water volume of each water tank to 600-800L / min, the roller cooling water pressure to 3.5-6bar, and the reverse air cleaning pressure to 4-7bar; Step S8, spinning silk; Step S9, Stelmore air cooling, setting the cooling speed according to different carbon contents and different temperature ranges of the wire rod; Step S10, coiling, collecting the wire rods after air cooling into coils; Step S11, packaging, using packaging materials to bundle and fix the wire rod coil; Further, in step S1, when 0.06%≤Si<0.2%, the preheating section temperature of the heating furnace is set to 800-900°C, the heating section temperature is set to 880-980°C, and the soaking section temperature is set to 1040-1140°C; When 0.2%≤Si≤0.3%, set the preheating section temperature of the heating furnace to 910-960℃, the heating section temperature to 1060-1100℃, and the soaking section temperature to 1130-1170℃; The heating time of the steel billet in the heating furnace lasts for 90-100 minutes. The preheating section and soaking section of the heating furnace are kept in a reducing atmosphere, and the heating section is kept in an oxidizing atmosphere. The temperature difference of the steel billet is controlled to be ≤30℃. Furthermore, in step S3, the water pressure of the rough rolling roll cooling water is set to 6-8 bar, and the water volume is set to 1200-1500 L / min; In step S4, the water pressure of the cooling water for the intermediate rolling mill is set to 6-8 bar, and the water volume is set to 1200-1500 L / min; In step S6, the roller cooling water pressure of the finishing rolling is set to 5.5-7 bar, the water volume is set to 500-700 L / min, and the final rolling speed is set to ≥105 m / s; Further, the various indicators of the water quality of the cooling water in step S3-step S7 are specifically set as follows: chloride ion ≤100mg / L, calcium and magnesium ions ≤250mg / L, dissolved oxygen ≤0.2mg / L, conductivity ≤1000us / cm, pH value range of 7.0-8.0, suspended solids ≤10mg / L, turbidity ≤10NTU, oil ≤0.3mg / L, total iron ≤1.0mg / L, total phosphorus ≤0.5mg / L, and water temperature of 15-25°C; Furthermore, the water quality in the water tank and the water quality of the roller cooling water are optimized respectively. Among them, the various indicators of the water quality in the water tank are set as follows: chloride ion ≤70mg / L, calcium and magnesium ions ≤250mg / L, dissolved oxygen ≤0.1mg / L, conductivity ≤900us / cm, pH value range of 7.0-8.0, suspended solids ≤10mg / L, turbidity ≤10NTU, grease ≤0.3mg / L, total iron ≤0.8mg / L, total phosphorus ≤0.5mg / L, water temperature is 15-20℃; The various indicators of roller cooling water quality are set as follows: chloride ion ≤80mg / L, calcium and magnesium ions ≤200mg / L, conductivity ≤800us / cm, pH value range 7.0-7.5, suspended solids ≤4mg / L, turbidity ≤4NTU, grease ≤0.1mg / L, total phosphorus ≤0.3mg / L, water temperature 20-25℃; Further, in step S7, the six water tanks are numbered in sequence, namely, water tank No. 1, water tank No. 2, ..., water tank No. 6, and the three water tanks that are turned on are water tank No. 1, water tank No. 3, and water tank No. 5; Further, in step S8, the spinning temperature range is set to 880-940°C; Further, in step S9, when the wire rod temperature ranges from 450°C to 600°C, the air cooling rate is set to 3.5°C / s to 5.5°C / s; When the wire rod temperature is >600℃, the cooling rate of steel with a carbon content of 0.06%-0.25% is set to 1.5-2.5℃ / s, the cooling rate of steel with a carbon content of 0.25%-0.6% is set to 4-9℃ / s, and the cooling rate of steel with a carbon content of 0.6%-0.82% is set to 11-15℃ / s.

[0008] Through the above technical solution, compared with the prior art, the present invention has the following beneficial effects: 1. The hot-rolled wire rod provided by the present invention strictly controls the content of Ni and As in terms of composition, reduces the enrichment of the two at the interface between the oxide layer and the matrix, and makes it easy to remove the primary oxide scale; 2. The hot-rolled wire rod provided by the present invention takes into account the working conditions when the Si content is greater than 0.2%, adds P element in the composition to reduce the melting temperature of fayalite and the adhesion of iron oxide scale, and removes the primary oxide scale by controlling the water pressure, water volume and billet temperature of high-pressure water dephosphorization. At the same time, rare earth elements are added to inhibit the segregation of P element at the grain boundary and avoid cold brittleness of steel; 3. The red rust control production process provided by the present invention adopts a large reduction in the early stage and a small reduction in the later stage during the rolling process to avoid the cracking and oxidation of the oxide scale. The cooling water volume is reduced by adopting a low water temperature and a high spinning temperature, and the cooling water volume of each water tank is reasonably distributed to control the temperature gradient of the wire rod to ensure the adhesion of the oxide scale. 4. The red rust control production process provided by the present invention reasonably controls the cooling water pressure and the reverse air cleaning pressure, appropriately reduces the final rolling speed, and reduces the reaction between high-temperature rolled pieces, water and air; at the same time, the water quality of the roller cooling water and the water tank cooling water is strictly controlled to avoid accelerated corrosion and the formation of red rust. Finally, by reducing the oxidation of FeO on the basis of ensuring normal organization on the Stelmor cooling line, the surface quality of the final product is good and no red rust is generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0010] Figure 1 The wire rod is produced according to the embodiment provided by the present invention; Figure 2 It is the wire rod produced according to the comparative example provided by the present invention. DETAILED DESCRIPTION

[0011] The present invention will now be described in further detail with reference to the accompanying drawings.

[0012] The mechanism of red rust is relatively complex. It is essentially a diffusion process of the oxide layer on the surface of the wire rod. Fe diffuses from the matrix to the outside, and O diffuses from the outside to the inside. When Fe reacts with O attached to the surface of the matrix to generate FeO, FeO is oxidized to generate Fe3O4, and Fe3O4 is further oxidized to generate Fe2O3. Iron and steel materials will undergo oxidation reactions with both O2 and H2O. When iron and steel materials coexist with air and water under high temperature conditions, they will react to generate Fe2O3. Therefore, to avoid the generation of red rust, it is actually necessary to reduce the amount of Fe2O3 generated.

[0013] In order to solve the above problems, the present application considers various factors, rationally designs the composition, optimizes the rolling process parameters, controls the cooling water quality, etc., so that the surface quality of the final wire rod is good and no red rust is generated.

[0014] As described in the background technology, the prior art does not provide a method for controlling red rust when the Si content is above 0.2%. Therefore, the chemical composition of the hot-rolled wire rod provided in this application is designed differently according to the different Si contents. In terms of mass percentage, When 0.06%≤Si<0.2%, C is 0.06-0.82%, Mn is 0.3-0.6%, P≤0.02%, S≤0.015%, Ni≤0.014%, As≤0.015%, Ni+As≤0.02%, and the rest are Fe and unavoidable impurities. When 0.2%≤Si≤0.3%, C is 0.25-0.82%, Mn is 0.3-0.6%, P is 0.05%-0.06%, S≤0.015%, Ni≤0.014%, As≤0.015%, Ni+As≤0.02%, REM is 0.02-0.03%, and the rest are Fe and unavoidable impurities, wherein REM is one, two or three of the rare earth elements Ce, Sc and Y.

[0015] The innovative design of the above ingredients is first to control the content of Ni and As. As residual elements in the wire rod, Ni and As are mainly enriched between the oxide layer and the matrix due to selective oxidation during the cooling process or secondary heating process, making the oxide layer difficult to remove. During the rolling process, the oxide scale enters the workpiece, causing surface defects or roll wear, and eventually easily leading to the generation of red rust. Another reason is that the market demand for green low-carbon electric furnace steel products is increasing, so the content of residual elements such as Ni and As in steel increases with the increase of scrap steel ratio. Ni and As are mainly enriched between the oxide layer and the matrix, which also makes the FeO layer difficult to remove. Therefore, in the composition design, the content of these two elements is controlled to Ni≤0.014%, As≤0.015%, Ni+As≤0.02%.

[0016] Secondly, for wire rods with Si content above 0.2%, Si element, as an important solid solution strengthening element in steel, can improve the strength of ferrite. It is also an important deoxidizer, which helps to reduce the oxygen content in steel and reduce inclusions. At the same time, Si element has the effect of inhibiting the formation of network cementite. When the Si content in steel is ≥0.2%, when heated at high temperature, Si element is easy to diffuse to the interface between FeO and the steel surface, and form a molten liquefied film composed of FeO and Fe2SiO4. When the temperature of the billet is reduced to below 1173℃, the liquefied film will undergo eutectic reaction to generate iron olivine (Fe2SiO4), which will form an anchor-like morphology after solidification, pinning the FeO layer and increasing the viscosity of the oxide scale. The pinned FeO is difficult to be completely removed during dephosphorization, and the residual FeO causes the formation of Fe2O3, resulting in an increase in the proportion of Fe2O3 after oxidation, resulting in red rust. Therefore, the present application adds P element in the composition design. Under normal circumstances, P is a harmful element in steel and will increase the cold brittleness of steel. However, P will form Fe3(PO4)2 or P2O5 on the metal surface. The existence of Fe3(PO4)2 phase can reduce the melting temperature of Fe2SiO4 phase. When the descaling temperature is higher than the melting temperature of Fe2SiO4 phase, Fe2SiO4 phase is in liquid state. Liquid Fe2SiO4 separates and destroys the adhesion of iron oxide scale, making it very easy to remove. Moreover, both Fe3(PO4)2 and P2O5 will decompose or gasify above 950℃. Therefore, when the Si content in steel is 0.06%-0.2%, the P content is controlled at P≤0.02%. When 0.2%≤Si≤0.3%, the P element is controlled at 0.05-0.06%.

[0017] Compared with the P content added in the traditional process, the content added in this application is still slightly higher. Considering the possible segregation problem, rare earth elements (REM) are added to the composition design with Si content ≥ 0.2%. Rare earth elements can inhibit the segregation of P elements at the grain boundary, strengthen the grain boundary, and improve the strength and toughness of the wire rod. It can be used as a pearlite phase deformation nucleus particle, increase the number of nucleations, and refine the pearlite lamella spacing. At the same time, rare earth elements can deform the oxides and sulfides in the molten steel to generate small, nearly spherical rare earth compounds, improve the drawing performance and corrosion resistance. However, if the rare earth element content is too high, the number of inclusions will increase and the generated composite compounds will aggregate into larger particles. After rolling, string inclusions will form, which will deteriorate the performance of the wire rod. This application controls the rare earth content to 0.02-0.03%.

[0018] As for other component designs, carbon is the most basic strengthening element in steel. With the increase of C content, the strength and hardness of steel increase, and the toughness decreases. Therefore, the C content is designed to be 0.06-0.82%. Manganese plays a role in solid solution strengthening and fine grain strengthening in steel, which can stabilize austenite, enhance hardenability, improve the strength and low-temperature toughness of steel, and help reduce the brittle-ductile transition temperature of steel. Therefore, the Mn content is designed to be 0.3-0.6%. Sulfur is a harmful impurity element, and the lower the content, the better, so the S in the wire rod is controlled to be ≤0.015%.

[0019] In addition to designing the chemical composition of the wire rod, the entire rolling process also needs to be designed accordingly. In the wire production process, there are several stages where iron oxide scale is easily generated. In the heating furnace, the surface of the steel billet contacts the high-temperature furnace gas, an oxidation reaction occurs, and a primary iron oxide scale is formed. During the rolling process, especially in the rough rolling stage, the oxide scale on the surface of the steel billet may be broken or peeled off by the roller, and new oxide scale will continue to form. The oxide scale generated in this process becomes a secondary oxide scale. During the finishing rolling process, due to the high rolling temperature and large deformation, the oxide scale is formed relatively quickly, and the oxide scale in this process is a tertiary oxide scale. After spinning, a fourth iron oxide scale will be formed. Therefore, the entire rolling process must be controlled to avoid the generation of red rust.

[0020] The red rust control production process provided for the hot-rolled wire rod specifically comprises the following steps: Step S1, heating the billet, sending the billet into the heating furnace, the heating time of the billet in the heating furnace lasts for 90-100 minutes, the whole heating process adopts segmented heating, the preheating stage is a reducing atmosphere, the temperature is slowly increased, the thermal stress of the surface and the core is reduced, and the further formation of oxide scale is inhibited. The heating stage heats up quickly to reduce the oxidation of the billet surface, the steel temperature in the soaking stage is relatively high, and a reducing atmosphere is used to avoid further oxidation, and at the same time, the temperature difference of the billet is controlled to be within 30°C. If the heating temperature is uneven and the temperature difference of the wire rod is large, the oxide scale at high temperature is thick and dense, and the oxide scale at low temperature is thin and easy to fall off, which does not protect the substrate. When the temperature difference of the wire rod exceeds 60°C, red rust can be clearly seen on the surface of the wire rod.

[0021] During segmented heating, the temperature of different stages is set according to the different silicon contents. This is because when 0.06%≤Si<0.2%, the billet heating process uses low-temperature heating, so that the heating temperature is below the melting point of the fayalite phase, to avoid the melting of fayalite, solidification and pinning of the FeO layer, and it is difficult to remove the primary oxide scale in the dephosphorization process. When 0.2%≤Si≤0.3%, the billet heating process uses high-temperature heating, so that the heating temperature is above the melting point of the fayalite phase. In the subsequent high-pressure water dephosphorization process, the billet temperature is controlled above the melting point of fayalite, and high-pressure water is used to remove phosphorus and remove it completely.

[0022] The specific design is that when 0.06%≤Si<0.2%, the preheating section temperature of the heating furnace is set to 800-900℃, the heating section temperature is set to 880-980℃, and the soaking section temperature is set to 1040-1140℃; when 0.2%≤Si≤0.3%, the preheating section temperature of the heating furnace is set to 910-960℃, the heating section temperature is set to 1060-1100℃, and the soaking section temperature is set to 1130-1170℃.

[0023] Step S2, high-pressure water dephosphorization, using a nozzle to spray high-pressure water onto the surface of the billet to peel off and wash away the oxide scale. Considering that when 0.06%≤Si<0.2%, the surface temperature of the billet is 1030-1130, and the corner temperature is 1020-1120℃; when 0.2%≤Si≤0.3%, the surface temperature of the billet is ≥1120℃, and the corner temperature is ≥1110℃. Especially when the Si content is greater than 0.2%, by adding the P element, the melting temperature of fayalite is reduced. When the descaling temperature is higher than the melting temperature of the Fe2SiO4 phase, the Fe2SiO4 phase is in a liquid state and is removed by high-pressure water. Due to the large temperature drop at the corner of the billet, the nozzle pressure, angle, distance and other parameters are controlled during high-pressure water dephosphorization to make the surface temperature and corner temperature of the billet above the melting temperature of the Fe2SiO4 phase, and ensure that the oxide scale is cleanly removed to avoid FeO residue and the generation of red rust.

[0024] Regarding parameters such as nozzle pressure, angle, distance, etc., specifically, there are four sides of the spray beam, with three nozzles installed on each side. The water pressure of the nozzle in the middle is set to 18-20MPa, and the water pressure of the other two nozzles is set to 15-17MPa. The inclination angle range between the center axis of the nozzle and the normal line of the billet is 15-18°, and the straight-line distance between the nozzle and the billet surface is 150-160mm.

[0025] Step S3, rough rolling, using the rollers of the rough rolling unit to roll the steel billet for multiple passes, rolling the steel billet with a large deformation, wherein the elongation coefficient of each pass is set to 1.4-1.5; Step S4, intermediate rolling, rolling the steel billet for multiple passes on the intermediate rolling unit to reduce the cross-sectional size of the steel after rough rolling, wherein the elongation coefficient of each pass is set to 1.4-1.5. In both the rough rolling and intermediate rolling stages, the roller cooling water pressure is set to 6-8 bar, and the water volume is set to 1200-1500 L / min.

[0026] Step S5, continue rolling the steel billet. After pre-finish rolling, set two water tanks to spray water on the wire rod for cooling. Set the water pressure of the water tank to 3-5 MPa, the water volume of each water tank to 200-300 L / min, the water pressure of the roller cooling water to 5.5-7 bar, and the water volume to 500-700 L / min. Step S6, finishing rolling, continuously rolling the wire rod on the finishing rolling unit, setting the elongation coefficient of each pass of finishing rolling to 1.2-1.25, the final rolling speed ≥105m / s, the roller cooling water pressure to 5.5-7bar, and the water volume to 500-700L / min.

[0027] The design means for controlling the rolling process to avoid the generation of red rust in step S3-step S6 are mainly described from the following parts: due to the different plastic deformation capabilities of the oxide scale and the matrix, the rough rolling and the intermediate rolling can adopt a large reduction to make the oxide scale deform evenly and become thinner, so that the adhesion with the matrix is ​​enhanced, and it is not easy to crack or fall off, so as not to fall off and press into the matrix to cause defects. The finishing rolling adopts a small reduction to reduce the deformation of the oxide scale and avoid the cracking of the oxide scale. Because the finishing rolling temperature is lower than the rough rolling temperature, the FeO component in the oxide scale has reduced plasticity at low temperatures. If the finishing rolling adopts a large reduction, it is easy to cause the oxide scale to break and increase the contact area with the air, thereby greatly accelerating the reaction of FeO→Fe3O4→Fe3O4, increasing the amount of Fe2O3 generated, and causing red rust on the surface of the final wire rod. In the finishing process, low water temperature and high wire-spinning temperature can be used to reduce the water volume in the water tank after finishing rolling, and evenly distribute the water volume in the water tank to avoid excessive temperature gradient of the wire rod during water cooling, ensure the adhesion of the iron oxide scale on the substrate surface, and make the surface temperature of the wire rod uniform in the recovery section. If the cooling speed of the previous water tank is too fast, the surface temperature of the oxide scale will be greatly reduced and easy to fall off. In the recovery section or the oxygen-rich environment of the next water tank, the oxidation reaction will be accelerated, and red rust will be easily produced.

[0028] Step S7, water cooling after finishing rolling, set up six water tanks, and open three of them, and number the six water tanks in sequence, namely No. 1 water tank, No. 2 water tank... No. 6 water tank, and the three opened water tanks are No. 1 water tank, No. 3 water tank and No. 5 water tank, to ensure that the water can be evenly distributed. Set the water volume of each water tank to 600-800L / min, the water pressure of the roller cooling water to 3.5-6bar, and the reverse air cleaning pressure to 4-7bar. Appropriately increase the final rolling speed. The lower the final rolling speed, the longer the coexistence time of the high-temperature rolled piece, water and air, which means that the time for Fe, O2 and H2O to react to generate Fe2O3 is prolonged, and the red floating rust on the surface of the wire is more obvious.

[0029] Cooling water is involved in the rolling process of step S3 to step S7. Here, the preferred control of various indicators in the cooling water quality is first given, that is, setting chloride ion ≤100mg / L, calcium and magnesium ions ≤250mg / L, dissolved oxygen ≤0.2mg / L, conductivity ≤1000us / cm, pH value range of 7.0-8.0, suspended matter ≤10mg / L, turbidity ≤10NTU, oil ≤0.3mg / L, total iron ≤1.0mg / L, total phosphorus ≤0.5mg / L, and water temperature of 15-25℃.

[0030] Next, we will explain the design of each of the above components in detail. The higher the chloride ion content in the cooling water, the more serious the degree of steel corrosion. This is because chloride ions can attack the surface of steel and promote corrosion reactions. They also have strong penetrability and can easily penetrate the protective film on the metal surface, causing corrosion. The high temperature causes the water on the surface of the steel billet to evaporate instantly, and the chlorine-containing electrolyte in the cooling water crystallizes and adheres to the surface of the sample. After the wire rod is cooled, the humid air moistens the surface of the wire rod, and the chloride-containing electrolyte dissolves, forming an electrolyte with a high chloride ion content on the surface of the steel billet, and rust gradually appears on the surface of the steel plate. Therefore, this application needs to control the chloride ion to ≤100mg / L. When the concentration of calcium and magnesium ions is too high, they will react with CO3 in the water. 2- 、SO4 2-Silicate and other ions form scale and deposit on the metal surface, destroying the integrity and density of the passivation film, and providing a pitting corrosion source for other inorganic ions. Therefore, this application needs to control calcium and magnesium ions to ≤250mg / L. Dissolved oxygen content Since oxygen is a depolarizer, in general, the more oxygen there is in the water, the more serious the corrosion of the steel. Therefore, this application needs to control the dissolved oxygen to ≤0.2mg / L. The conductivity of cooling water directly affects the corrosion rate of steel. Cooling water with high conductivity means that the water contains more ions. These ions play a conductive role in the electrochemical corrosion process and accelerate the corrosion of steel. Specifically, cooling water with high conductivity contains more chloride ions, which makes the steel more susceptible to corrosion. Therefore, this application needs to control the conductivity to ≤1000us / cm. The smaller the pH value of the cooling water, the greater the acidity, which accelerates the corrosion of the metal. In a weakly alkaline solution, under the same chloride ion concentration conditions, OH - The intervention of OH - With Cl - Competitive adsorption occurs on the material surface, inhibiting the Cl - Corrosion on the surface of the material. Therefore, keeping the pH value of the cooling water weakly alkaline can effectively alleviate the corrosion of the steel plate surface, and the pH value needs to be controlled at 7.0-8.0. The high content of suspended matter, impurities and oil in the cooling water will reduce the thermal conductivity of the cooling water, hinder the transfer of heat, reduce the cooling capacity, promote the formation of a steam film on the surface of the wire rod, and accelerate the reaction degree between the metal and steam on the surface of the wire rod, thereby promoting the formation of red rust on the surface of the wire rod. Therefore, this application needs to control the water quality of the cooling water to suspended matter ≤10mg / L, turbidity ≤10NTU, and grease ≤0.3mg / L. The total iron content in the cooling water of the steel plant has a significant effect on the corrosion of the wire rod. Iron ions are a kind of fouling substance in water. High concentrations of total iron will promote the growth of iron bacteria and form microbial corrosion. At the same time, it will also produce potential corrosion and accelerate the corrosion rate. High concentrations of total iron will promote the corrosion process, cause damage to pipelines and equipment, and reduce equipment life. When the total phosphorus content is too high, it will not only cause eutrophication of the water body, but also easily lead to the accumulation of scale, thereby reducing the cooling efficiency. Therefore, this application requires that the water quality of cooling water be controlled within the range of total iron ≤ 1.0 mg / L and total phosphorus ≤ 0.5 mg / L.

[0031] Furthermore, the rollers and water tanks are all involved in cooling water, wherein the roller cooling water is achieved by spraying cooling water onto the roller ring during the rolling process of the steel billet to achieve the purpose of cooling. The parameters such as the water pressure, water volume, water temperature, and water quality of the roller cooling water are reasonably controlled. If the water pressure and water volume are too large, it is easy for water to splash out from the roller surface, and the actual amount of cooling water is insufficient, which causes waste. If the water pressure is too low, the roller surface cooling effect is not good, which is easy to cause cracks on the roller surface and crack the roller ring. Due to the presence of roller lubricating oil, it is necessary to strictly control the grease, suspended matter, turbidity, etc. in the cooling water to avoid insufficient cooling capacity of the cooling water. At the same time, strictly control the indicators such as chloride ions, calcium and magnesium ions, conductivity, and total phosphorus content to prevent the cooling from impacting the roller for a long time, causing corrosion to the roller, and scaling on the heat transfer surface, which affects the heat exchange effect, and increases the surface roughness of the billet, promoting the subsequent generation of red rust. Therefore, the various indicators of the roller cooling water quality are set as follows: chloride ion ≤80mg / L, calcium and magnesium ions ≤200mg / L, conductivity ≤800us / cm, pH value range is 7.0-7.5, suspended solids ≤4mg / L, turbidity ≤4NTU, grease ≤0.1mg / L, total phosphorus ≤0.3mg / L, and water temperature is 20-25℃.

[0032] The cooling water in the water tank is used to cool the wire rod to reach the set spinning temperature. The water quality of the cooling water in the water tank is also optimized to improve the cooling capacity and reduce the corrosion reaction rate. By controlling the cooling water of the roller and the water tank separately, the generation of red rust is effectively reduced. Therefore, the various indicators of the water quality in the water tank are set as follows: chloride ion ≤70mg / L, calcium and magnesium ions ≤250mg / L, dissolved oxygen ≤0.1mg / L, conductivity ≤900us / cm, pH range of 7.0-8.0, suspended solids ≤10mg / L, turbidity ≤10NTU, grease ≤0.3mg / L, total iron ≤0.8mg / L, total phosphorus ≤0.5mg / L, and water temperature of 15-20℃.

[0033] Step S8, spinning, setting the spinning temperature range to 880-940°C.

[0034] Step S9, Stelmore air cooling, set the cooling rate according to the different carbon content and different temperature ranges of the wire rod; when the wire rod temperature range is 450-600℃, set the air cooling rate to 3.5-5.5℃ / s; when the wire rod temperature is >600℃, the cooling rate of steel with a carbon content of 0.06%-0.25% is set to 1.5-2.5℃ / s, the cooling rate of steel with a carbon content of 0.25%-0.6% is set to 4-9℃ / s, and the cooling rate of steel with a carbon content of 0.6%-0.82% is set to 11-15℃ / s.

[0035] Adopt appropriate cooling rate above 600℃ to ensure normal structure of wire rod and avoid abnormal structure. Accelerate cooling rate at 450-600℃ to avoid decomposition of FeO and formation of red rust.

[0036] Step S10, coiling, collecting the wire rods after air cooling into coils.

[0037] Step S11, packaging, using packaging materials to bundle and fix the wire rod coil.

[0038] The final wire rod specification is 5.5-7mm.

[0039] Examples and Comparative Examples In order to verify the feasibility and superiority of the hot-rolled wire rod and red rust control production process provided in the present application, the present application provides examples and comparative examples, and the examples are based on the case where the silicon content in the wire rod exceeds 0.2%.

[0040] Example

[0041] The wire rod specification disclosed in this embodiment is 6.5 mm, and the chemical composition of the wire rod includes, by mass percentage: C: 0.45%, Si: 0.22%, Mn: 0.58%, P: 0.058%, S: 0.012%, Cr: 0.035%, As: 0.004%, Ni+As: 0.016%, Ce: 0.025%, and the rest is Fe and unavoidable impurities; The production process flow of wire rod red rust control includes: billet heating - high-pressure water dephosphorization - rough rolling - intermediate rolling - pre-finishing rolling - water cooling - finishing rolling - water cooling - wire laying - Stelmor air cooling - coiling - packaging.

[0042] (1) The billet is heated in sections, with the preheating section temperature at 920°C, the heating section temperature at 1070°C, the soaking section temperature at 1130°C, and the furnace time at 95 min. The preheating section and soaking section are kept in a reducing atmosphere, the heating section is kept in an oxidizing atmosphere, and the temperature difference of the billet is 20°C.

[0043] (2) High-pressure water dephosphorization: There are three identical high-pressure water descaling nozzles on each of the four sides of the spray beam. The water pressure of the middle nozzle is controlled at 19 MPa, and the water pressure of the two nozzles on both sides is controlled at 16 MPa. The inclination angle between the center axis of the nozzle and the normal direction of the billet is 16°, and the straight-line distance from the nozzle to the billet surface is 155 mm. The surface temperature of the billet is 1120°C and the corner temperature is 1110°C.

[0044] (3) Rough rolling and intermediate rolling: the elongation coefficient of each pass is 1.4-1.45, the roller cooling water pressure is 7 bar, and the water volume is 1350 L / min.

[0045] (4) Pre-finishing rolling: After pre-finishing rolling, two water tanks are opened. The water pressure of the water tanks is 4Mpa, and the water volume of each water tank is 240L / min.

[0046] (5) Finishing rolling: The elongation coefficient of each pass of finishing rolling is 1.2~1.22, and the final rolling speed is 112m / s.

[0047] (6) Water cooling: There are 6 water tanks after finishing rolling. Open water tank No. 1, water tank No. 3 and water tank No. 5. The water volume is evenly distributed. The water volume of each water tank is 650L / min. The cooling water pressure is 4bar, and the reverse air cleaning pressure is 5.5bar.

[0048] (7) The cooling water pressure of the pre-finishing and finishing rolling rolls is 6 bar, and the water volume is 600 L / min.

[0049] (8) Roller cooling water chloride ion: 75 mg / L, calcium and magnesium ions: 180 mg / L, conductivity: 750 us / cm, pH value: 7, suspended matter: 4 mg / L, turbidity: 4 NTU, grease: 0.08 mg / L, total phosphorus: 0.28 mg / L, water temperature: 20°C.

[0050] (9) Cooling water in the water tank: chloride ion: 65 mg / L, calcium and magnesium ions: 210 mg / L, dissolved oxygen: 0.05 mg / L, conductivity: 800 us / cm, pH value: 7, suspended solids: 8 mg / L, turbidity: 8 NTU, oil: 0.1 mg / L, total iron: 0.5 mg / L, total phosphorus: 0.3 mg / L, water temperature: 17 °C.

[0051] (10) Spinning temperature: 900℃.

[0052] (11) Stelmore air cooling: When the wire rod temperature is greater than 600°C, the cooling rate is 5.5°C / s; when the wire rod temperature is between 450-600°C, the cooling rate is 4°C / s.

[0053] The obtained finished wire rod roll is as follows Figure 1 shown.

[0054] Comparative Example: The wire rod disclosed in this comparative example has a specification of 6.5 mm, and the chemical composition of the wire rod includes, by mass percentage: C: 0.45%, Si: 0.21%, Mn: 0.58%, P: 0.018%, S: 0.012%, Ni: 0.03%, As: 0.02%, Ni+As: 0.05%, and the rest is Fe and unavoidable impurities; The production process flow of wire rod red rust control includes: billet heating - high-pressure water dephosphorization - rough rolling - intermediate rolling - pre-finishing rolling - water cooling - finishing rolling - water cooling - wire laying - Stelmor air cooling - coiling - packaging.

[0055] (1) The billet is heated in sections, with the preheating section temperature at 900°C, the heating section temperature at 980°C, the soaking section temperature at 1050°C, and the furnace time at 80 min. The preheating section and soaking section are kept in a reducing atmosphere, the heating section atmosphere is kept in an oxidizing atmosphere, and the temperature difference of the billet is 40°C.

[0056] (2) High-pressure water dephosphorization: There are three identical high-pressure water descaling nozzles on each of the four sides of the spray beam. The water pressure of the middle nozzle is controlled at 10 MPa, and the water pressure of the two nozzles on both sides is controlled at 10 MPa. The inclination angle between the center axis of the nozzle and the normal direction of the billet is 20°, and the straight-line distance from the nozzle to the billet surface is 170 mm, so that the surface temperature of the billet is 1040°C and the corner temperature is 1020°C.

[0057] (3) Rough rolling and intermediate rolling: the elongation coefficient of each pass is 1.2~1.25, the roller cooling water pressure is 4.5 bar, and the water volume is 1000L / min.

[0058] (4) Pre-finishing rolling: After pre-finishing rolling, a water tank is opened, the water pressure of the water tank is 6Mpa, and the water volume of the water tank is 580L / min.

[0059] (5) Finishing rolling: The elongation coefficient of each pass of finishing rolling is 1.4-1.45, and the final rolling speed is 110m / s.

[0060] (6) Water cooling: There are 6 water tanks after finishing rolling. Open water tank No. 1, water tank No. 3 and water tank No. 5. The water volume of the water tanks is: 1200L / min, 1000L / min, 100L / min respectively. The cooling water pressure is: 3bar, and the reverse air cleaning pressure is: 3bar.

[0061] (7) The cooling water pressure of the pre-finishing and finishing rolling rolls is 4 bar, and the water volume is 400 L / min.

[0062] (8) Roller cooling water chloride ion: 150 mg / L, calcium and magnesium ions: 300 mg / L, conductivity: 1500 us / cm, pH value: 8.5, suspended matter: 15 mg / L, turbidity: 10 NTU, oil: 3 mg / L, total phosphorus: 1.5 mg / L, water temperature: 28 °C.

[0063] (9) Water tank cooling water chloride ion: 120mg / L, calcium and magnesium ions: 270mg / L, dissolved oxygen: 0.5mg / L, conductivity: 1200us / cm, pH value: 6.5, suspended solids: 15mg / L, turbidity: 13NTU, oil: 5mg / L, total iron: 2.5mg / L, total phosphorus: 4mg / L, water temperature: 25℃.

[0064] (10) Silk spinning temperature: 880℃.

[0065] (11) Stelmore air cooling: When the wire rod temperature is greater than 600°C, the cooling rate is 8°C / s; when the wire rod temperature is between 450-600°C, the cooling rate is 2°C / s.

[0066] The obtained finished wire rod roll is as follows Figure 2 shown.

[0067] contrast Figure 1 and Figure 2 It can be seen that the surface quality of the wire rod produced according to the embodiment is good and free of red rust, while the surface of the wire rod produced according to the comparative example has serious red rust.

[0068] In summary, the hot-rolled wire rod and red rust control production process provided by the present application controls the content of Ni and As in the composition, so that the primary oxide scale is easy to remove. For wire rods with Si content greater than 0.2%, P and rare earth elements are added to reduce the melting point of the iron olivine phase. The primary oxide scale is cleaned by controlling the water pressure, water volume and billet temperature of high-pressure water dephosphorization. The rolling process adopts a large reduction in the early stage and a small reduction in the later stage to avoid the cracking and oxidation of the oxide scale. The cooling water volume is reduced by adopting low water temperature and high wire laying temperature, and the cooling water volume of each water tank is reasonably distributed to control the temperature gradient of the wire rod to ensure the adhesion of the oxide scale. Reasonably control the cooling water pressure and reverse air cleaning pressure, appropriately reduce the final rolling speed, and reduce the reaction of high-temperature rolled pieces, water and air. At the same time, the water quality of the roller cooling water and the water tank cooling water is strictly controlled to avoid accelerated corrosion and cause red rust. Finally, by reducing the oxidation of FeO on the basis of ensuring normal organization on the Stelmor cooling line, the surface quality of the final product is good and no red rust is produced.

[0069] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0070] The meaning of "and / or" described in this application means that the situations where each exists alone or both exist at the same time are included.

[0071] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0072] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A hot rolled wire rod, characterized in that: The chemical composition of the wire rod is determined by the Si content, expressed in mass percentage. When 0.06%≤Si<0.2%, C is 0.06-0.82%, Mn is 0.3-0.6%, P≤0.02%, S≤0.015%, Ni≤0.014%, As≤0.015%, Ni+As≤0.02%, and the rest is Fe and unavoidable impurities; When 0.2%≤Si≤0.3%, C is 0.25-0.82%, Mn is 0.3-0.6%, P is 0.05%-0.06%, S≤0.015%, Ni≤0.014%, As≤0.015%, Ni+As≤0.02%, REM is 0.02-0.03%, and the rest are Fe and unavoidable impurities, among which REM is one, two or three of the rare earth elements Ce, Sc and Y.

2. The red rust control production process for the hot-rolled wire rod according to claim 1, characterized in that: The specific steps include: Step S1, heating the steel billet, feeding the steel billet into a heating furnace, adopting segmented heating, and setting the temperature of different stages according to different silicon contents, until the steel billet is heated to a preset temperature that meets the rolling requirements; Step S2, high-pressure water dephosphorization, four sides of the spray beam, three nozzles are installed on each side, the water pressure of the nozzle located in the middle is set to 18-20MPa, the water pressure of the other two nozzles is set to 15-17MPa, the inclination angle between the center axis of the nozzle and the normal line of the steel billet is in the range of 15-18°, and the straight-line distance between the nozzle and the surface of the steel billet is 150-160mm; the nozzle is used to spray high-pressure water onto the surface of the steel billet to peel off and wash away the oxide scale; Step S3, rough rolling, using the rollers of the rough rolling unit to roll the steel billet for multiple passes, rolling the steel billet with a large deformation amount, wherein the elongation coefficient of each pass is set to 1.4-1.5; Step S4, intermediate rolling, rolling the steel billet in multiple passes on the intermediate rolling mill to reduce the cross-sectional dimensions of the steel after rough rolling, wherein the elongation coefficient of each pass is set to 1.4-1.5; Step S5, continue rolling the steel billet. After pre-finish rolling, set two water tanks to spray water on the wire rod for cooling. Set the water pressure of the water tank to 3-5 MPa, the water volume of each water tank to 200-300 L / min, the water pressure of the roller cooling water to 5.5-7 bar, and the water volume to 500-700 L / min. Step S6, finishing rolling, continuously rolling the wire rod on the finishing rolling mill, setting the elongation coefficient of each pass of the finishing rolling to 1.2-1.25; Step S7, water cooling after finishing rolling, set six water tanks, and open three of them, set the water volume of each water tank to 600-800L / min, the roller cooling water pressure to 3.5-6bar, and the reverse air cleaning pressure to 4-7bar; Step S8, spinning; Step S9, Stelmore air cooling, setting the cooling speed according to different carbon contents and different temperature ranges of the wire rod; Step S10, coiling, collecting the wire rods after air cooling into coils; Step S11, packaging, using packaging materials to bundle and fix the wire rod coil.

3. The red rust control production process of hot rolled wire rod according to claim 2, characterized in that: In step S1, when 0.06%≤Si<0.2%, the preheating section temperature of the heating furnace is set to 800-900°C, the heating section temperature is set to 880-980°C, and the soaking section temperature is set to 1040-1140°C; When 0.2%≤Si≤0.3%, set the preheating section temperature of the heating furnace to 910-960℃, the heating section temperature to 1060-1100℃, and the soaking section temperature to 1130-1170℃; The heating time of the steel billet in the heating furnace lasts for 90-100 minutes. The preheating section and soaking section of the heating furnace are kept in a reducing atmosphere, and the heating section is kept in an oxidizing atmosphere. The temperature difference of the steel billet is controlled to be ≤30℃.

4. The red rust control production process of hot rolled wire rod according to claim 2, characterized in that: In step S3, the water pressure of the rough rolling roll cooling water is set to 6-8 bar and the water volume is set to 1200-1500 L / min; In step S4, the water pressure of the cooling water for the intermediate rolling mill is set to 6-8 bar, and the water volume is set to 1200-1500 L / min; In step S6, the cooling water pressure of the finishing rolling rolls is set to 5.5-7 bar, the water volume is set to 500-700 L / min, and the final rolling speed is set to ≥105 m / s.

5. The red rust control production process of hot rolled wire rod according to claim 2, characterized in that: The various indicators of the cooling water quality in step S3-step S7 are specifically set as follows: chloride ion ≤100mg / L, calcium and magnesium ions ≤250mg / L, dissolved oxygen ≤0.2mg / L, conductivity ≤1000us / cm, pH value range of 7.0-8.0, suspended matter ≤10mg / L, turbidity ≤10NTU, grease ≤0.3mg / L, total iron ≤1.0mg / L, total phosphorus ≤0.5mg / L, and water temperature of 15-25°C.

6. The red rust control production process of hot rolled wire rod according to claim 5, characterized in that: The water quality in the water tank and the water quality of the roller cooling water are optimized respectively. The various indicators of the water quality in the water tank are set as follows: chloride ion ≤70mg / L, calcium and magnesium ions ≤250mg / L, dissolved oxygen ≤0.1mg / L, conductivity ≤900us / cm, pH value range is 7.0-8.0, suspended solids ≤10mg / L, turbidity ≤10NTU, grease ≤0.3mg / L, total iron ≤0.8mg / L, total phosphorus ≤0.5mg / L, and water temperature is 15-20℃; The various indicators of the roller cooling water quality are set as follows: chloride ion ≤80mg / L, calcium and magnesium ions ≤200mg / L, conductivity ≤800us / cm, pH value range is 7.0-7.5, suspended solids ≤4mg / L, turbidity ≤4NTU, grease ≤0.1mg / L, total phosphorus ≤0.3mg / L, and water temperature is 20-25℃.

7. The red rust control production process of hot rolled wire rod according to claim 2, characterized in that: In step S7, the six water tanks are numbered in sequence, namely, water tank No. 1, water tank No. 2, ..., water tank No. 6, and the three water tanks that are turned on are water tank No. 1, water tank No. 3, and water tank No.

5.

8. The red rust control production process of hot rolled wire rod according to claim 2, characterized in that: In step S8, the spinning temperature range is set to 880-940°C.

9. The red rust control production process of hot rolled wire rod according to claim 2, characterized in that: In step S9, when the wire rod temperature ranges from 450 to 600°C, the air cooling rate is set to 3.5 to 5.5°C / s; When the wire rod temperature is >600℃, the cooling rate of steel with a carbon content of 0.06%-0.25% is set to 1.5-2.5℃ / s, the cooling rate of steel with a carbon content of 0.25%-0.6% is set to 4-9℃ / s, and the cooling rate of steel with a carbon content of 0.6%-0.82% is set to 11-15℃ / s.

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