Rapid pickling method for medium-high carbon hot-rolled steel plate

Abstract

The invention discloses a rapid pickling method for a medium-high carbon hot-rolled steel plate. The problems that an existing medium-high carbon hot-rolled steel plate is low in pickling efficiency, poor in pickling quality and high in pickling cost are mainly solved. According to the technical scheme, the rapid acid pickling method for the medium-high carbon hot-rolled steel plate comprises the steps that (1) the medium-high carbon hot-rolled steel plate is subjected to acid pickling, specifically, a hot rolled steel coil is uncoiled through an uncoiler, then the hot-rolled steel plate with the thickness being 2.0-10.0 mm is subjected to acid pickling through acid pickling liquid in a three-section type series acid pickling tank, and the acid pickling liquid is hydrochloric acid; the acidity of the acid liquor in the first-section pickling tank is controlled to be 80-130 g / L, the temperature of the pickling liquor is controlled to be 80-90 DEG C, and the temperature of the hot-rolled steel plate is controlled to be 90-110 DEG C when the hot-rolled steel plate enters the pickling liquor in the first-section pickling tank; and 2) rinsing, drying, oiling and coiling the pickled hot-rolled steel plate. According to the method, the pickling speed can be increased by 20%-50%, the pickling quality is high, and the pickling cost is low.

Description

TECHNICAL FIELD

[0001] The present application relates to a pickling method of hot-rolled steel plate, in particular to a rapid pickling method of medium-high carbon hot-rolled steel plate, specifically to a pickling method of hot-rolled steel plate with a thickness of 2.0-10.0 mm, w[C] of 0.1%-1.0% in steel, w[Mn] of 0.3%-1.2%, and the sum of the rest of the alloy content ≤1.5%, belonging to the technical field of pickling of hot-rolled steel plate. BACKGROUND

[0002] In the production process of hot-rolled steel plate, a relatively thick iron oxide scale, also known as "primary iron oxide scale", is generated in the heating furnace. Most of it can be removed by high-pressure water phosphorus removal before rough rolling. During high-temperature rolling, iron oxide scale, i.e. "secondary iron oxide scale", continues to be generated. However, most of it can be removed by high-pressure water phosphorus removal after the end of finish rolling. Finally, after coiling into a steel coil, the surface of the steel coil continues to generate iron oxide scale, also known as "tertiary iron oxide scale".

[0003] The "tertiary iron oxide scale" is affected by the composition of the steel grade and the cooling process, and there are great differences in the structure of the iron oxide scale.

[0004] For low-carbon steel plates with carbon content less than 0.1% and micro-alloy content less than 0.1%, the cooling speed after hot rolling and coiling is relatively fast, and the iron oxide scale is mainly loose and porous FeO. The acid solution can quickly reach the base layer through the cracks and holes on the surface of the iron scale, so the pickling is relatively easy and the pickling speed is relatively fast.

[0005] For medium-high carbon steel plates with C content greater than 0.1% and alloy content greater than 0.1%, the cooling speed has a more significant impact on the structure and performance of the strip than low-carbon low-alloy steel due to the high C, Mn and alloy content. Slow cooling is usually required, and the eutectoid reaction between Fe3O4 and Fe that inevitably occurs during this process greatly increases the density of the iron oxide scale structure and greatly increases the difficulty of pickling.

[0006] The pickling process of medium-high carbon hot-rolled steel plate is currently mainly based on hydrochloric acid pickling. The steel plate is immersed in acid solution at 60-85°C for a certain period of time or subjected to turbulent pickling, and the removal of the iron oxide scale is completed through the hydrogen evolution reaction and the dissolution of the iron oxide scale. The more dense the structure of the iron oxide scale, the more difficult the pickling and the longer the pickling time.

[0007] For difficult-to-pickling steel grades, the existing process can only extend the pickling time and reduce the pickling speed. However, for medium-high carbon steel, too long pickling time may also cause intergranular corrosion, surface roughness, and even blackening, etc.

[0008] The Chinese patent application of Chinese patent CN113584498A discloses a hot-rolled stainless steel annealing and pickling process and pickling equipment. By controlling the temperature of the stainless steel annealing furnace cooling section outlet strip steel at 60-200℃, and then through the heat preservation cavity for heat preservation, the strip steel temperature is higher than 100℃ when entering the pre-pickling tank with a concentration of 20-60g / L of hydrochloric acid. When the high-temperature stainless steel strip is in contact with the low-temperature pickling liquid, the surface of the strip will undergo a strong physical and chemical reaction to quickly peel off the thick oxide scale on the surface. Finally, the removal of the surface oxide scale is completed through multi-stage low-temperature hydrochloric acid pickling of 20-150g / L. When the high-temperature strip enters the acid liquid, a violent physical and chemical reaction occurs at the interface. In terms of physical reaction, the acid liquid in contact with the high-temperature steel plate can peel off part of the surface layer of the oxide scale due to the high-temperature gasification, but for stainless steel with Cr content >10% and very dense oxide scale structure, this physical process basically does not affect the subsurface and bottom layer of the oxide scale, therefore, the pickling acceleration effect is limited. In terms of chemical reaction, the concentration of H+ ions in the hydrochloric acid solution and the pickling liquid temperature directly determine the pickling rate. Although the high-temperature strip can instantaneously increase the interface temperature, the acidity in the preheating tank in contact with the disclosed technical solution is too low, far lower than the concentration required for conventional hydrochloric acid pickling, therefore, the high-temperature strip cannot quickly undergo a chemical reaction. In addition, to achieve a preheating temperature of 100℃, the process section speed and temperature of the continuous annealing furnace also have a high requirement on the temperature adjustment capacity of the heat preservation cavity, and there are technical problems of complex process, high pickling cost, and low pickling efficiency.

[0009] The Chinese patent application of Chinese patent CN104694942A discloses a method for producing hot-rolled pickled plates and a hot-rolled pickled plate pickling system. The method starts pickling when the temperature of the hot-rolled steel coil decreases to 50℃-120℃, the temperature of the first pickling tank is 53-88℃, and the free acidity is 20-50g / L. The pickling is carried out in a spray type manner. There are technical problems of low acidity, low temperature, and low pickling efficiency.

[0010] The existing technology lacks an effective rapid pickling method for medium and high carbon hot-rolled steel plates. The medium and high carbon hot-rolled steel plates have problems of poor pickling quality, low pickling efficiency, and high pickling cost. SUMMARY

[0011] The purpose of the present application is to provide a rapid pickling method for medium and high carbon hot-rolled steel plates, mainly solving the problems of low pickling efficiency, poor pickling quality, and high pickling cost of existing medium and high carbon hot-rolled steel plates. The method realizes low-cost and high-efficiency pickling of hot-rolled steel plates with a thickness of 2.0-10.0mm, w[C] of 0.1%-1.0% in steel, w[Mn] of 0.3%-1.2%, and the sum of the remaining alloy content ≤1.5%. The medium and high carbon hot-rolled steel plates pickled by the method have no residual oxide scale on the surface and high surface quality.

[0012] The technical idea of the present application is that by controlling the temperature of the hot-rolled strip entering the acid solution to start pickling, the surface layer of the oxide scale is quickly stripped by the gasification effect while a large number of micropores are formed on the surface layer of the oxide scale, and the high-concentration H+ quickly penetrates into the base layer to generate hydrogen evolution reaction, thereby greatly shortening or even skipping the pickling incubation period in the initial stage of pickling reaction, and greatly improving the pickling speed of the steel.

[0013] The technical solution adopted by the present application is a rapid pickling method for a medium-high carbon hot-rolled steel plate, which comprises the following steps:

[0014] 1) Pickling the medium-high carbon hot-rolled steel plate, first unwinding the hot-rolled steel coil by an uncoiler, and then pickling the hot-rolled steel plate with a thickness of 2.0-10.0 mm by the acid solution in the three-stage series-connected pickling tank, wherein the acid solution is hydrochloric acid, the acidity of the acid solution in the first-stage pickling tank is controlled to be 80-130 g / L, the temperature of the acid solution is 80-90℃, and the temperature of the hot-rolled steel plate entering the acid solution in the first-stage pickling tank is controlled to be 90-110℃; the w[C] in the hot-rolled steel plate is 0.1%-1.0%, the w[Mn] is 0.3%-1.2%, and the sum of the remaining alloy contents is ≤1.5%;

[0015] 2) Rinsing, drying, oiling and coiling the hot-rolled steel plate after pickling.

[0016] Further, the mass percentage of Fe3O4 in the oxide scale on the surface of the hot-rolled steel plate before pickling is 65%-85%, the mass percentage of eutectoid iron Fe is 10%-30%, and the sum of the mass percentages of FeO and Fe2O3 is ≤5%.

[0017] The reasons for adopting the production process of the present application are as follows:

[0018] 1. Setting of the temperature of the hot-rolled steel plate entering the acid solution in the first-stage pickling tank

[0019] The pickling of the steel plate is usually divided into three stages, the initial stage of pickling, also called the pickling incubation period, the acid solution infiltrates the surface of the steel plate, H+ diffuses to the matrix along the microcracks of the oxide scale, and a small amount of hydrogen is evolved, and the reaction is slow; in the middle stage of pickling, the oxide scale is dissolved and peeled off due to the reaction of H+ and Fe matrix to generate hydrogen, the reaction speed is fast, and the oxide scale is largely removed; in the final stage of reaction, most of the oxide scale has been removed, but the acid pickling speed is significantly reduced due to the enrichment of residual alloy elements and the formation of passivation film. In the above three stages, the pickling incubation period accounts for about one-third of the entire pickling time.

[0020] Applicant found through research that for medium and high carbon steel plates with C content greater than 0.1% and alloy content greater than 0.1%, due to high C, Mn and alloy content, the cooling speed has a more significant effect on the structure and performance of the strip than low carbon low alloy steel, in order to ensure the uniformity of the structure and performance, slow cooling with a cooling speed less than 20℃ / h is usually adopted after hot rolling and coiling, when the temperature drops to about 500℃, the originally FeO-based oxide scale inevitably undergoes eutectoid reaction to generate eutectoid products of Fe3O4 and Fe, greatly increasing the density of the oxide scale structure. Meanwhile, with the slow cooling, alloy elements in the steel also diffuse into the oxide scale, further improving the density of the oxide scale of this type of steel, greatly increasing the pickling difficulty.

[0021] For medium and high carbon alloy steel, after slow cooling after hot rolling and coiling, the final oxide scale structure is 10%-30% eutectoid Fe, 65%-85% Fe3O4 and ≤5% FeO and Fe2O3. Compared with the loose FeO-based oxide scale in low carbon low alloy steel, the structure of this type of oxide scale is more dense. However, the alloy content of less than 1.5% will not form a corrosion-resistant alloy layer in the oxide scale like high-silicon silicon steel and high-Cr and Nb stainless steel.

[0022] After the high-temperature strip enters the acid solution, the surface oxide scale is quickly stripped due to physical gasification, and H+ quickly penetrates into the substrate layer due to the microcracks in the oxide scale and the large number of micro-pores formed on the oxide scale by gasification tearing, and immediately undergoes hydrogen evolution reaction at high temperature to strip the surface oxide scale, thereby greatly shortening the incubation period and increasing the pickling speed.

[0023] In consideration of the above, the present application sets the temperature of the hot-rolled steel plate when entering the first-stage pickling tank to be 90-110℃, when the temperature of the hot-rolled steel plate when entering the first-stage pickling tank is less than 90℃, the gasification stripping effect cannot be achieved, and when the temperature of the hot-rolled steel plate when entering the first-stage pickling tank is greater than 110℃, the gasification effect is too strong and will also cause loss of hydrochloric acid.

[0024] 2. The acidity and pickling temperature of the acid solution in the first-stage pickling tank are set

[0025] In the above initial pickling stage, the large number of micro-pores formed on the oxide scale by the gasification tearing of the high-temperature strip create conditions for the rapid entry of the acid solution into the base layer of the oxide scale, but the stripping of the final oxide scale mainly relies on the H + The reduction reaction releases hydrogen gas, which causes the stripping of the oxide scale when the hydrogen gas overflows, therefore, the H +The concentration and the temperature of the acid liquor must meet certain requirements to reflect the rapid stripping effect caused by a large amount of hydrogen evolution in the initial reaction. At present, the length of most pickling production lines is more than 60 m. Since the acid liquor is fed from the outlet of the pickling tank and discharged from the inlet, the acidity of the acid liquor in the first-stage pickling tank is usually less than 50-60 g / L. Therefore, it is difficult to play the role of accelerating the stripping of the gasified high-temperature strip after pickling. If the temperature is also low, the effect of hydrogen evolution in pickling cannot be played.

[0026] The present application finds the influence of the acidity and the temperature in the first-stage pickling tank in the initial pickling period. After comprehensive consideration, the acidity of the acid liquor in the first-stage pickling tank is set to 80-130 g / L, and the temperature of the pickling liquor is set to 80-90℃. If the acidity and the temperature of the acid liquor in the first-stage pickling tank are too low, the stripping effect of a large amount of hydrogen evolution in the initial pickling cannot be played. If the acidity and the temperature of the acid liquor in the first-stage pickling tank are too high, it is difficult to control economically and practically.

[0027] Compared with the prior art, the present application has the following positive effects: 1. The method of the present application does not require special heating equipment before pickling of the hot-rolled steel plate. The process is simple, and the pickling cost is low. 2. The temperature of the hot-rolled steel plate entering the first-stage pickling tank and the setting of the acidity and the temperature of the acid liquor in the first-stage pickling tank during the pickling process are based on the principle of the effect of the structure of the iron oxide scale and the acidity in the initial pickling on the gasification and stripping. After pickling, the surface of the medium-high carbon hot-rolled steel plate is free of residual iron oxide scale, the surface quality is high, the pickling efficiency is high, and the pickling speed can be increased by 20%-50%. 3. The method of the present application can be used for continuous pickling production lines and push-pull pickling production lines, and has a wide range of applications.

[0028] The pickling speed of such steel grades can be significantly increased. DETAILED DESCRIPTION

[0029] The present application will be further described below with reference to the examples as shown in Tables 1-4.

[0030] In Examples 1-4, the pickling production line is a push-pull pickling production line.

[0031] A rapid pickling method for a medium-high carbon hot-rolled steel plate, the method comprising:

[0032] 1) pickling the medium-high carbon hot-rolled steel plate, first, using an uncoiler to uncoil the hot-rolled steel coil, then pickling the hot-rolled steel plate with a thickness of 2.0-10.0 mm by using the pickling solution in the three-stage series pickling tank, the pickling solution being hydrochloric acid, the acidity of the pickling solution in the first stage pickling tank being controlled at 80-130 g / L, the temperature of the pickling solution being 80-90℃, and the temperature of the hot-rolled steel plate when entering the first stage pickling tank being controlled at 90-110℃; the w[C] of the hot-rolled steel plate being 0.1%-1.0%, the w[Mn] being 0.3%-1.2%, and the sum of the remaining alloy contents being ≤1.5%;

[0033] 2) rinsing, drying, oiling and coiling the pickled hot-rolled steel plate.

[0034] Table 1 is the chemical composition of the steel of the embodiment of the present application (in terms of weight percentage), the balance being Fe and unavoidable impurities.

[0035] Table 1 is the chemical composition of the hot-rolled steel plate of the embodiment of the present application, the unit being weight percentage.

[0036] Category Steel plate grade C Si Mn Cr V B Example 1 65Mn 0.65 0.2 1.0 0.1 Example 2 51CrV4 0.52 0.2 0.9 1.0 0.15 Example 3 SK95 0.95 0.2 0.4 0.2 Example 4 40MnB 0.41 0.25 1.2 0.002

[0037] Table 2 is the surface scale parameter of the hot-rolled steel plate before pickling of the embodiment of the present application.

[0038]

[0039]

[0040] Table 3 is the pickling process parameter (one) of the embodiment of the present application.

[0041]

[0042] Table 4 is the pickling process parameter (two) of the embodiment of the present application.

[0043]

[0044] Compared with the same grade and same specification hot-rolled steel plate at room temperature, the pickling speed of the steel plate of the embodiment of the present application can be increased by 20-50%.

[0045] In addition to the above embodiments, the present application can also have other implementation manners. Any technical solution formed by equivalent substitution or equivalent transformation falls within the protection scope required by the present application.

Claims

1. A method of rapid pickling of a medium-high carbon hot-rolled steel sheet, characterized in that, The method comprises the following steps: 1) pickling the medium-high carbon hot-rolled steel plate, first unwinding the hot-rolled steel coil by an uncoiler, then pickling the hot-rolled steel plate with a thickness of 2.0-10.0 mm by an acid solution in a three-stage series pickling tank, the acid solution being hydrochloric acid, the acidity of the acid solution in the first-stage pickling tank being controlled at 80-130 g / L, the temperature of the acid solution being 80-90 DEG C, and the temperature of the hot-rolled steel plate when entering the first-stage pickling tank being controlled at 90-110 DEG C; the w[C] of the hot-rolled steel plate being 0.1%-1.0%, the w[Mn] being 0.3%-1.2%, and the sum of the rest alloy contents being ≤1.5%; 2) rinsing, drying, oiling and coiling the hot-rolled steel plate after pickling.

2. The method for rapid pickling of medium-high carbon hot-rolled steel sheets according to claim 1, characterized by, The mass percentage of Fe3O4 in the oxide scale on the surface of the hot-rolled steel plate before pickling is 65%-85%, the mass percentage of eutectoid iron Fe is 10%-30%, and the sum of the mass percentages of FeO and Fe2O3 is ≤5%.

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