A pickling and passivation integrated liquid and its process and application

Abstract

The present invention provides a pickling and passivation integrated solution, a process, and applications thereof. The pickling and passivation integrated solution comprises a mixed solution of sulfuric acid and nitric acid, wherein the sulfate ion concentration in the mixed solution is ag / L and the nitrate ion concentration is bg / L, satisfying the following conditions: a = (8-15) × b, and 60 g / L ≤ a + b ≤ 500 g / L. The pickling and passivation integrated process specifically comprises placing the black stainless steel to be treated into the pickling and passivation integrated solution, subjecting it to a pickling and passivation process at a pickling and passivation temperature of 50-90°C for a certain time t, ultimately yielding bright white stainless steel and waste liquid. After pickling and passivation, the plate surface exhibits a bright white color with a metallic luster, and its surface roughness is low, far superior to existing technologies. The passivation film thickness is qualified, and the plate surface quality is good.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel pickling, and in particular to a pickling and passivation integrated liquid and a process thereof. Background Art

[0002] As a metal material, stainless steel has good corrosion resistance, mechanical and processing properties, and is widely used in aerospace, petrochemical, marine, and pharmaceutical fields due to its low price and recyclability. Surface quality is one of the important factors in measuring stainless steel sheets and strips, which directly affects the performance and market competitiveness of the product. The surface quality of stainless steel sheets and strips mainly depends on the rationality of the pickling process after heat treatment (such as hot rolling and annealing). The complexity of the oxide layer structure on the surface of stainless steel not only affects the pickling speed, but also affects the electrochemical process of stainless steel during the pickling process, thereby affecting the surface quality of stainless steel after pickling. At present, the nitric acid and hydrofluoric acid mixed acid pickling process is mostly used for hot-rolled annealed stainless steel strips at home and abroad, which not only has serious NO x There are pollution problems, and there are also phenomena such as large surface roughness. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a highly efficient, environmentally friendly, economical and high-quality pickling and passivation integrated liquid and process thereof.

[0004] In one aspect, the present invention provides a pickling and passivation integrated solution comprising a mixed solution of sulfuric acid and nitric acid. The sulfate ion concentration in the mixed solution is a g / L, and the nitrate ion concentration is b g / L, satisfying the following conditions: a = (8-15) × b, and 60 g / L ≤ a + b ≤ 500 g / L. The nitrate ion concentration should not be too low, and as the nitrate ion concentration increases, the time required to complete the pickling and passivation process is significantly reduced. Furthermore, the sulfate and nitrate ion concentrations should not be too high, as such concentrations can inhibit the pickling and passivation process and prolong the reaction time.

[0005] On the other hand, the present invention provides an integrated pickling and passivation process, which adopts the above-mentioned pickling and passivation integrated liquid. The integrated process is specifically as follows: the stainless steel to be treated is placed in the above-mentioned pickling and passivation integrated liquid, and after a pickling and passivation process for a certain time t, bright white stainless steel and waste liquid are finally obtained; the pickling and passivation temperature T of the process is 50~90°C, and the pickling and passivation time satisfies t=k×(a / b)×T+C, where k is a coefficient with a value range of 0.05s / °C~0.2s / °C, and C is a constant with a value range of 25s~270s.

[0006] On the other hand, the present invention also provides another integrated pickling and passivation process, which specifically comprises: placing the stainless steel to be treated into a treatment tank, wherein the treatment tank contains a metal salt mixture containing nitrate ions, sulfate ions, and Fe3+ ions, then adding an appropriate amount of the above-mentioned pickling and passivation integrated liquid to the treatment tank to obtain a reaction liquid, starting the pickling and passivation process, and finally obtaining bright white stainless steel and waste liquid after a certain time t' of the pickling and passivation process;

[0007] The total concentration of metal ions in the reaction solution is d≤140 g / L, and the concentration of iron ions in the reaction solution is 30-120 g / L.

[0008] Furthermore, in the pickling and passivation integrated process of the present invention, the sulfate ion concentration a1 g / L in the reaction solution is 140-550 g / L, the nitrate ion concentration b1 g / L is 3-60 g / L, and the H + The concentration is N H , N H >0.1mol / L.

[0009] Furthermore, in the pickling and passivation integrated process of the present invention, the pickling and passivation temperature T of the integrated process is 50~90°C, and the pickling and passivation time satisfies t' = C' - k'×N H ×T, where k' is a coefficient ranging from 0.1 L·s / mol·℃ to 2.5 L·s / mol·℃, and C' is a constant ranging from 400s to 900s.

[0010] The coefficient k' is primarily influenced by the characteristics of the stainless steel's oxide layer, while the constant C' is primarily influenced by the characteristics of the passivation layer. As the concentration of metal ions (such as iron, manganese, and chromium) increases, the time it takes to complete the pickling and passivation of hot-rolled annealed stainless steel black belt increases. While ensuring pickling quality, the pickling solution must have a high total acidity to ensure smooth pickling at high metal ion concentrations.

[0011] Furthermore, in the pickling and passivation integrated process of the present invention, under the condition that the oxide scale per unit surface area is completely removed per unit time, the total concentration change rate ρ of the three metal ions of iron, chromium and manganese in the waste liquid first increases and then decreases, and meets the requirement of 2.34 mg / L / s / cm 2 ≤ρ≤4.33mg / L / s / cm 2 .

[0012] The analysis of the metal ion concentrations before and after the reaction by ICP showed that, under the condition that other conditions remained unchanged, as the concentrations of the metal ions in the initial solution increased, the concentrations of the metal ions in the solution first increased and then decreased. The maximum rate of change of the concentration of the metal ions in the solution was 4.33 mg / L / s / cm 2 .

[0013] On the other hand, the present invention also provides an application of any of the above-mentioned pickling and passivation integrated liquids and any of the above-mentioned pickling and passivation integrated processes, wherein the pickling and passivation integrated liquid or the pickling and passivation integrated process is used in the pickling and passivation process of stainless steel.

[0014] Compared with the prior art, the present invention has the following beneficial technical effects:

[0015] The pickling and passivation integrated liquid and its process and application described in the present invention, wherein the pickling and passivation integrated liquid and its process are suitable for pickling special-shaped parts, especially annealed stainless steel, with simple process and equipment and high production efficiency. In the specific process, on the one hand, the pickling and passivation integrated liquid undergoes an oxidation-reduction reaction with the oxide scale on the surface of the stainless steel to generate soluble or insoluble salts, and the hydrogen generated in the reaction can also accelerate the shedding and peeling of the oxide scale, thereby accelerating the removal of the oxide scale; on the other hand, when the chromium-poor layer is completely dissolved, nitric acid contacts the metal matrix to generate a dense passivation film, which can prevent the metal matrix from being further corroded, and realize the two processes of pickling and passivation in one step. Through the pickling process provided by the present invention, the oxide scale on the surface of the annealed stainless steel can be completely removed, and the plate surface after pickling and passivation presents a bright white color with a metallic luster, and the plate surface quality is good. In addition, the pickling and passivation integrated liquid and its process described in the present invention are not only applicable to the pickling and passivation process carried out under the conditions of no metal ions or a small amount of metal ion concentration, but are also applicable to the pickling and passivation process with a high metal ion concentration. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below with reference to specific embodiments. Example 1:

[0017] The present invention discloses an integrated pickling and passivation liquid, which consists of a mixed solution of sulfuric acid and nitric acid. The concentration of sulfate ions in the mixed solution is ag / L, the concentration of nitrate ions is bg / L, and the following conditions are satisfied: a=(8-15)×b, and 60 g / L≤a+b≤500 g / L. Example 2:

[0018] The invention discloses an application of an integrated pickling and passivation liquid. The integrated pickling and passivation liquid described in Example 1 is used in an integrated pickling and passivation process for stainless steel. The stainless steel after the integrated pickling and passivation process exhibits a bright white color with a metallic luster, a low surface roughness value, a qualified passivation film thickness, and a good plate surface quality. Example 3:

[0019] The invention discloses an integrated pickling and passivation process, which specifically comprises the following steps: after continuous casting, hot rolling and annealing of stainless steel, stainless steel strips of the same coil number are cut from the site and processed into stainless steel strips to be treated with a size of 2×5 cm and a thickness of 3 mm.

[0020] The stainless steel to be treated is placed in the above-mentioned pickling and passivation integrated liquid, wherein the concentration of sulfate ions in the pickling and passivation integrated liquid is 300 g / L, the concentration of nitrate ions is 20 g / L, and the pickling and passivation temperature T is 50°C; wherein, in the formula t=k×(a / b)×T+C, k=0.1s / °C and C=85s; after 160s of pickling and passivation, bright white stainless steel and waste liquid are finally obtained.

[0021] Through the statistical analysis of the surface roughness meter, it can be found that the surface roughness value of the stainless steel white skin that has completed the pickling and passivation process is low and the plate surface quality is good. Example 4:

[0022] The only difference between Example 4 and Example 3 is that the pickling and passivation temperature T is 60°C. In the formula t = k × (a / b) × T + C, k = 0.1 s / °C, and C = 20 s. After 110 s of pickling and passivation, bright white stainless steel and waste liquid are finally obtained. At this point, the surface roughness of the stainless steel white skin is low, and the plate surface quality is good. Example 5:

[0023] The only difference between Example 5 and Example 3 is that the pickling and passivation temperature T is 70°C. In the formula t = k × (a / b) × T + C, k = 0.05 s / °C, and C = 37.5 s. After 90 seconds of pickling and passivation, bright white stainless steel and waste liquid are finally obtained. At this point, the surface roughness of the stainless steel white skin is low, and the plate surface quality is good.

[0024] The results of the experiment showed that when the pickling passivation temperature T≥60℃, the time for complete removal of the oxide scale on the surface of the annealed stainless steel strip will be stable at around 100s. Example 6:

[0025] A pickling and passivation integrated process, the process specifically comprises: placing the black stainless steel to be treated into a treatment tank, the treatment tank containing a mixed liquid, and then adding an appropriate amount of the pickling and passivation integrated liquid in Example 1 to the treatment tank to obtain 200 ml of a reaction solution, wherein the concentration of sulfate ions in the reaction solution is 140 g / L, the concentration of nitrate ions is 20 g / L, the concentration of iron ions is 34.4 g / L, and the concentration of N H =2.26mol / L. The reaction solution also contains metal ions such as chromium and manganese. (The molar mass of iron is 56 g / mol, the molar mass of nitrate is 62 g / mol, and the molar mass of sulfate is 96 g / mol.)

[0026] The pickling and passivation process begins. The pickling and passivation temperature T is 60°C. According to the formula t' = C' - k'×N H In ×T, k'=2.5 L·s / mol·℃, C'=639s, and it takes about 300s of pickling and passivation to finally obtain bright white stainless steel and waste liquid. The change in the concentration of metal ions in the solution before and after the reaction first increases and then decreases, reaching a maximum of 4.33mg / L / s / cm 2 .

[0027] Comparative Example 1:

[0028] Comparative Example 1: The only difference between Comparative Example 1 and Example 4 is that the concentration of sulfate ions in the pickling and passivation integrated solution is 100 g / L and the concentration of nitrate ions is 70 g / L. After 120 seconds of pickling and passivation, the surface of the annealed stainless steel strip is rough, the quality is very poor, and there is residual oxide scale.

[0029] Comparative Example 2:

[0030] The only difference between Comparative Example 2 and Example 6 is that the pickling passivation time is 100s. Since there is a high concentration of metal ions in the reaction solution, the pickling passivation process has a certain inhibitory effect. The surface of the annealed stainless steel strip is rough and of poor quality, and there is residual oxide scale.

Claims

1. A pickling and passivation integrated liquid, characterized in that: The pickling and passivation integrated solution is composed of a mixed solution of sulfuric acid and nitric acid, the concentration of sulfate ions in the mixed solution is ag / L, the concentration of nitrate ions is bg / L, and the following conditions are satisfied: a=(8~15)×b, and 60≤a+b≤500.

2. A pickling and passivation integrated process, characterized in that: The integrated process specifically comprises: placing the stainless steel to be treated into the pickling and passivation integrated solution as claimed in claim 1, and undergoing a pickling and passivation process for a certain time t, thereby finally obtaining bright white stainless steel and waste liquid; The pickling passivation temperature T of the process is 50~90℃, and the pickling passivation time satisfies t=k×(a / b)×T+C, where k is a coefficient with a value range of 0.05s / ℃~0.2s / ℃, and C is a constant with a value range of 25s~270s.

3. A pickling and passivation integrated process, characterized in that: The integrated process is specifically as follows: the stainless steel to be treated is placed in a treatment tank, and the treatment tank contains nitrate ions, sulfate ions, Fe 3+ ions, and then adding an appropriate amount of the pickling and passivation integrated liquid as claimed in claim 1 to the tank to be treated to obtain a reaction liquid, starting the pickling and passivation process, and finally obtaining bright white stainless steel and waste liquid after a certain time t' of the pickling and passivation process; Wherein, the total concentration of metal ions in the reaction solution is d≤140 g / L, and the concentration of iron ions in the reaction solution is 30~120 g / L; The sulfate ion concentration a1 g / L in the reaction solution is 140-550 g / L, the nitrate ion concentration b1 g / L is 3-60 g / L, and the H + The concentration is N H , N H >0.1mol / L.

4. The pickling and passivation integrated process according to claim 3, characterized in that: The pickling and passivation temperature T of the integrated process is 50~90℃, and the pickling and passivation time satisfies t' = C' - k'×N H ×T, where k' is a coefficient ranging from 0.1 L·s / mol·℃ to 2.5 L·s / mol·℃, and C' is a constant ranging from 400s to 900s.

5. An application of the pickling and passivation integrated liquid according to claim 1 or the pickling and passivation integrated process according to any one of claims 2 to 4, characterized in that: The integrated pickling and passivation liquid or the integrated pickling and passivation process is used in the pickling and passivation process of stainless steel.