CN105483761A - Process for improving intergranular corrosion resistance of 316 stainless steel - Google Patents

Abstract

The invention discloses a process for improving the intergranular corrosion resistance of 316 stainless steel. Firstly, a layer of nickel coating with a proper thickness is plated on the surface of 316 stainless steel by electroplating, and then annealed in sections under the protection of reducing atmosphere. The invention can reduce the carbides (Cr ₂₃ C ₆ , Fe ₂₃ C ₆ ) at the grain boundary in 316 stainless steel, obtain complete austenite, enhance the bonding force between the nickel coating and 316 stainless steel, and improve the intergranular corrosion resistance of 316 stainless steel ability, the invention has simple process, obvious effect, strong operability, and can be used in industrial production on a large scale.

Description

Process for Improving the Intergranular Corrosion Resistance of 316 Stainless Steel

technical field

The invention relates to a surface treatment method of a stainless steel material, in particular to a method for preparing and strengthening a stainless steel surface coating, which is applied in the technical field of material surface corrosion protection.

Background technique

Stainless steel has high corrosion resistance, mainly because of the addition of Cr and Ni. The added Cr and Ni react with oxygen in the air to form a dense oxide film on the surface. This oxide film has high stability in many corrosive media, thus preventing the steel itself from being corroded by corrosive media. 316 austenitic stainless steel is the most widely used Cr-Ni stainless steel, which has good corrosion resistance, heat resistance and mechanical properties.

But stainless steel is also subject to corrosion under certain conditions. Intergranular corrosion is a common form of corrosion in stainless steel, which is a selective corrosion phenomenon that occurs near the grain boundaries. Although the surface of the equipment or parts affected by this kind of corrosion still has a metallic luster, because the contact between the grains has been lost, there is no metallic sound when knocked, and the steel becomes brittle. Microscopically, intergranular corrosion shows the phenomenon of chromium depletion and impurity accumulation due to the appearance of precipitated phases at the grain boundaries, which makes the grain boundaries easily corroded, so that the bonding force between the grains is lost, the metal strength is completely lost, and the equipment breaks down. hair damage.

The necessary condition for austenitic stainless steel to have corrosion resistance is that the mass fraction of chromium must be greater than 12%. When the temperature is between 450°C and 850°C, the diffusion rate of carbon in the stainless steel grain is greater than that of Cr. Because the solubility of carbon in austenite at room temperature is very small, about 0.02% to 0.03%, and the carbon content in general austenitic stainless steel exceeds this value, so the excess carbon is continuously transferred to the austenite crystal. The grain boundary diffuses and combines with Cr to form Cr compounds in the intergranular, such as Cr ₂₃ C ₆ and so on. Studies have shown that the diffusion rate of Cr in the grain is smaller than that of Cr along the grain boundary, and the internal Cr has no time to diffuse to the grain boundary, so the Cr required for the Cr carbide formed in the intergranular is not mainly from the inside of the austenite grain. Instead, it comes from the vicinity of the grain boundary, and as a result, the Cr content near the grain boundary is greatly reduced. When the mass fraction of Cr in the grain boundary is lower than 12%, a so-called "Cr-poor region" is formed. If the passivation film is destroyed, the Cr-poor area will lose its corrosion resistance and cause intergranular corrosion.

The main function of Ni in stainless steel is to form and stabilize austenite, so that the steel can obtain a complete austenite structure, improve the toughness of the material, and at the same time play a very good corrosion resistance. Many studies have shown that the nickel plating layer has passivation in corrosive media, which can improve the intergranular corrosion resistance of stainless steel, but the cost of nickel is relatively high. Increasing the nickel content in stainless steel will inevitably increase the cost of stainless steel, which is not conducive to stainless steel. The development of application industry.

Contents of the invention

In order to solve the problems of the prior art, the object of the present invention is to overcome the deficiencies in the prior art, provide a process for improving the intergranular corrosion resistance of 316 stainless steel, and coat a layer of nickel coating with an appropriate thickness on the surface of 316 stainless steel, and pass The stepwise annealing treatment under the protection of reducing atmosphere, the invention improves the anti-intergranular corrosion ability of 316 stainless steel through electroplating and stepwise annealing under the protection of atmosphere, and the treatment cost is low, so it can be used in industrial production on a large scale.

In order to achieve the above-mentioned purpose of invention and creation, the following technical solutions are adopted:

A process for improving the intergranular corrosion resistance of 316 stainless steel, the steps are as follows:

a. The surface of 316 stainless steel is plated with a layer of nickel coating with a set thickness by electroplating; when electroplating nickel, the preferred electroplating solution formula is: the concentration of nickel sulfate is 150-300g/L, the concentration of nickel chloride The concentration of boric acid is 25-45g/L, the concentration of boric acid is 20-50g/L, the concentration of additive BMP is 0.5-5.0g/L, the pH of the electroplating solution is 3.0-5.0, the electroplating nickel process temperature is 30~60℃, and the electroplating Nickel process current intensity is 1.0~10.0A/dm ² ;

b. Under the protection of a reducing atmosphere, the 316 stainless steel with nickel coating prepared in the step a is subjected to segmental annealing treatment, and the annealing process at each stage is preferably carried out under a hydrogen atmosphere, specifically using a three-stage annealing process, segmental annealing The control conditions of the treatment process are as follows:

The first stage annealing process: the annealing furnace is raised to the annealing temperature at a heating rate of 5~10°C/min, the annealing temperature is 900~1200°C, and the holding time is 12~24h;

The second stage annealing process: After cooling the annealing furnace to a temperature of 300~450°C at a cooling rate of 5~30°C/min, keep it warm for 1~5h;

The third stage annealing process: cooling to room temperature with the furnace.

Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

1. The present invention significantly improves the ability of 316 stainless steel to resist intergranular corrosion, and expands the scope of use of 316 stainless steel;

2. The annealing treatment of the nickel-plated layer in the present invention plays the role of alloying, making Ni form and stabilize austenite, so that 316 stainless steel obtains a complete austenite structure, improves the toughness of the material, and can play a very good role at the same time. corrosion resistance;

3. The annealing treatment of the nickel-plated layer in the present invention plays the role of solid solution treatment, and the carbides such as Cr ₂₃ C ₆ and Fe ₂₃ C ₆ deposited on the grain boundaries of 316 stainless steel are re-dissolved in the austenite grains, The intergranular corrosion resistance of 316 stainless steel after solution treatment is enhanced;

4. the present invention to the annealing treatment of nickel-plated layer, has strengthened the binding force of nickel-plated layer and substrate, has improved the shortcoming of nickel-plated layer and stainless steel binding force difference after electroplating, and such nickel-plated layer has passivation in corrosive medium, Significantly improve the intergranular corrosion resistance of 316 stainless steel;

5. The process of the present invention is simple, the treatment effect is obvious, the operability is strong, and it can be used in industrial production on a large scale.

detailed description

Preferred embodiments of the present invention are described in detail as follows:

Embodiment one:

In this embodiment, a process for improving the intergranular corrosion resistance of 316 stainless steel, the steps are as follows:

a. A 316 stainless steel sample with a size of 80×10×4mm is selected, and a layer of nickel coating with a set thickness is plated on the surface of the 316 stainless steel sample by electroplating. When performing the nickel electroplating process, the formula of the electroplating solution used is: The concentration of nickel sulfate is 150g/L, the concentration of nickel chloride is 25g/L, the concentration of boric acid is 20g/L, the concentration of additive BMP is 0.5g/L, the pH of the electroplating solution is 3.0, and the process temperature of nickel plating is 30 ℃, the current intensity of nickel plating process is 1.0A/dm ² ;

b. Under the protection of a hydrogen reducing atmosphere, the 316 stainless steel sample with a nickel coating prepared in the step a is subjected to segmental annealing treatment, specifically adopting a three-stage annealing process, and the control conditions of the segmental annealing process are as follows:

The first stage annealing process: the annealing furnace is raised to the annealing temperature at a heating rate of 5°C/min, the annealing temperature is 900°C, and the holding time is 12h;

The second-stage annealing process: After cooling the annealing furnace to a temperature of 300°C at a cooling rate of 5°C/min, keep it warm for 1 hour;

The third stage annealing process: the 316 stainless steel sample with nickel coating is cooled to room temperature with the furnace, and finally the corrosion-resistant 316 stainless steel parts are obtained.

The polarization curve in 3.5wt.%NaCl solution was used to evaluate the material corrosion resistance of the corrosion-resistant 316 stainless steel parts prepared in this example, and the parameters are shown in Table 1.

Embodiment two:

This embodiment is basically the same as Embodiment 1, especially in that:

In this embodiment, a process for improving the intergranular corrosion resistance of 316 stainless steel, the steps are as follows:

a. A 316 stainless steel sample with a size of 80×10×4mm is selected, and a layer of nickel coating with a set thickness is plated on the surface of the 316 stainless steel sample by electroplating. When performing the nickel electroplating process, the formula of the electroplating solution used is: The concentration of nickel sulfate is 300g/L, the concentration of nickel chloride is 45g/L, the concentration of boric acid is 50g/L, the concentration of additive BMP is 5.0g/L, the pH of the electroplating solution is 3.0, and the process temperature of nickel plating is 60 ℃, the current intensity of electroplating nickel process is 2.0A/dm ² ;

b. Under the protection of a hydrogen reducing atmosphere, the 316 stainless steel sample with a nickel coating prepared in the step a is subjected to segmental annealing treatment, specifically adopting a three-stage annealing process, and the control conditions of the segmental annealing process are as follows:

The first stage annealing process: the annealing furnace is raised to the annealing temperature at a heating rate of 10°C/min, the annealing temperature is 900°C, and the holding time is 12h;

The second stage annealing process: After cooling the annealing furnace to a temperature of 450°C at a cooling rate of 20°C/min, keep it warm for 5 hours;

The third stage annealing process: the 316 stainless steel sample with nickel coating is cooled to room temperature with the furnace, and finally the corrosion-resistant 316 stainless steel parts are obtained.

The polarization curve in 3.5wt.%NaCl solution was used to evaluate the material corrosion resistance of the corrosion-resistant 316 stainless steel parts prepared in this example, and the parameters are shown in Table 1.

Embodiment three:

This embodiment is basically the same as the previous embodiment, and the special features are:

In this embodiment, a process for improving the intergranular corrosion resistance of 316 stainless steel, the steps are as follows:

a. A 316 stainless steel sample with a size of 80×10×4mm is selected, and a layer of nickel coating with a set thickness is plated on the surface of the 316 stainless steel sample by electroplating. When performing the nickel electroplating process, the formula of the electroplating solution used is: The concentration of nickel sulfate is 200g/L, the concentration of nickel chloride is 30g/L, the concentration of boric acid is 35g/L, the concentration of additive BMP is 2.5g/L, the pH of the electroplating solution is 4.5, and the process temperature of nickel plating is 60 ℃, the current intensity of electroplating nickel process is 10.0A/dm ² ;

b. Under the protection of a hydrogen reducing atmosphere, the 316 stainless steel sample with a nickel coating prepared in the step a is subjected to segmental annealing treatment, specifically adopting a three-stage annealing process, and the control conditions of the segmental annealing process are as follows:

The first stage annealing process: the annealing furnace is raised to the annealing temperature at a heating rate of 5°C/min, the annealing temperature is 1000°C, and the holding time is 24h;

The second stage annealing process: After cooling the annealing furnace to a temperature of 350°C at a cooling rate of 30°C/min, keep it warm for 3 hours;

The third stage annealing process: the 316 stainless steel sample with nickel coating is cooled to room temperature with the furnace, and finally the corrosion-resistant 316 stainless steel parts are obtained.

The polarization curve in 3.5wt.%NaCl solution was used to evaluate the material corrosion resistance of the corrosion-resistant 316 stainless steel parts prepared in this example, and the parameters are shown in Table 1.

Embodiment four:

This embodiment is basically the same as the previous embodiment, and the special features are:

In this embodiment, a process for improving the intergranular corrosion resistance of 316 stainless steel, the steps are as follows:

a. A 316 stainless steel sample with a size of 80×10×4mm is selected, and a layer of nickel coating with a set thickness is plated on the surface of the 316 stainless steel sample by electroplating. When performing the nickel electroplating process, the formula of the electroplating solution used is: The concentration of nickel sulfate is 250g/L, the concentration of nickel chloride is 45g/L, the concentration of boric acid is 25g/L, the concentration of additive BMP is 0.5g/L, the pH of the electroplating solution is 3.0, and the process temperature of nickel plating is 50 ℃, the current intensity of electroplating nickel process is 2.0A/dm ² ;

b. Under the protection of a hydrogen reducing atmosphere, the 316 stainless steel sample with a nickel coating prepared in the step a is subjected to segmental annealing treatment, specifically adopting a three-stage annealing process, and the control conditions of the segmental annealing process are as follows:

The first stage annealing process: the annealing furnace is raised to the annealing temperature at a heating rate of 10°C/min, the annealing temperature is 1100°C, and the holding time is 24h;

The second stage annealing process: After cooling the annealing furnace to a temperature of 350°C at a cooling rate of 30°C/min, keep it warm for 1h;

The third stage annealing process: the 316 stainless steel sample with nickel coating is cooled to room temperature with the furnace, and finally the corrosion-resistant 316 stainless steel parts are obtained.

The polarization curve in 3.5wt.%NaCl solution was used to evaluate the material corrosion resistance of the corrosion-resistant 316 stainless steel parts prepared in this example, and the parameters are shown in Table 1.

Embodiment five:

This embodiment is basically the same as the previous embodiment, and the special features are:

In this embodiment, a process for improving the intergranular corrosion resistance of 316 stainless steel, the steps are as follows:

a. A 316 stainless steel sample with a size of 80×10×4mm is selected, and a layer of nickel coating with a set thickness is plated on the surface of the 316 stainless steel sample by electroplating. When performing the nickel electroplating process, the formula of the electroplating solution used is: The concentration of nickel sulfate is 150g/L, the concentration of nickel chloride is 45g/L, the concentration of boric acid is 20g/L, the concentration of additive BMP is 5.0g/L, the pH of the electroplating solution is 5.0, and the process temperature of nickel plating is 40 ℃, the current intensity of nickel electroplating process is 5.0A/dm ² ;

b. Under the protection of a hydrogen reducing atmosphere, the 316 stainless steel sample with a nickel coating prepared in the step a is subjected to segmental annealing treatment, specifically adopting a three-stage annealing process, and the control conditions of the segmental annealing process are as follows:

The first stage annealing process: the annealing furnace is raised to the annealing temperature at a heating rate of 5°C/min, the annealing temperature is 1200°C, and the holding time is 18h;

The second stage annealing process: After cooling the annealing furnace to a temperature of 300°C at a cooling rate of 25°C/min, keep it warm for 5 hours;

The third stage annealing process: the 316 stainless steel sample with nickel coating is cooled to room temperature with the furnace, and finally the corrosion-resistant 316 stainless steel parts are obtained.

The polarization curve in 3.5wt.%NaCl solution was used to evaluate the material corrosion resistance of the corrosion-resistant 316 stainless steel parts prepared in this example, and the parameters are shown in Table 1.

Experimental test analysis:

The polarization curve in 3.5wt.%NaCl solution was used to evaluate the material corrosion resistance of the corrosion-resistant 316 stainless steel parts prepared in the above examples. The parameters are shown in Table 1.

Table 1. Polarization curve test parameters of the corrosion-resistant 316 stainless steel sample prepared in the above examples in 3.5wt.%NaCl solution

The data in the above table 1 shows that the 316 stainless steel treated by the above embodiments of the present invention has strong corrosion resistance, improved intergranular corrosion resistance, and simple process, which is suitable for industrial production. After the treatment of the above-mentioned embodiments of the present invention, the carbides at the grain boundaries in 316 stainless steel can be reduced, complete austenite can be obtained, the bonding force between the nickel coating and 316 stainless steel can be enhanced, and the ability of 316 stainless steel to resist intergranular corrosion has been improved. important industrial value.

The embodiments of the present invention have been described above, but the present invention is not limited to the above-mentioned embodiments, and various changes can also be made according to the purpose of the invention of the present invention. All changes made under the spirit and principles of the technical solutions of the present invention, Modification, replacement, combination or simplification should all be equivalent replacement methods, as long as they meet the purpose of the invention, as long as they do not deviate from the technical principle and inventive concept of the process of improving the intergranular corrosion resistance of 316 stainless steel, they all belong to this invention. protection scope of the invention.

Claims (3)

1. improve a technique for 316 stainless steel anti intercrystalline corrosion abilities, it is characterized in that, step is as follows:

A. electric plating method is adopted to plate the nickel coating of one deck setting thickness at 316 stainless steel surface;

B. under protection of reducing atmosphere, carry out stepped annelaing process to 316 stainless steels with nickel coating prepared in described step a, concrete employing three sections of annealing treating process, the control condition of stepped annelaing treatment process is as follows:

First stage annealing technique: annealing furnace rises to annealing temperature with the heat-up rate of 5 ~ 10 DEG C/min, annealing temperature is 900 ~ 1200 DEG C, and soaking time is 12 ~ 24h;

Secondary stage annealing technique: after annealing furnace is cooled to temperature 300 ~ 450 DEG C with the cooling rate of 5 ~ 30 DEG C/min, insulation 1 ~ 5h;

Phase III annealing process: cool to room temperature with the furnace.

2. improve the technique of 316 stainless steel anti intercrystalline corrosion abilities according to claim 1, it is characterized in that: in described step a, when carrying out the technique of electronickelling, the plating solution formula adopted is: the concentration of single nickel salt is 150-300g/L, and the concentration of nickelous chloride is 25-45g/L, and the concentration of boric acid is 20-50g/L, the concentration of additive B MP is 0.5-5.0g/L, the pH of electroplate liquid is 3.0-5.0, and electro-nickel process temperature is 30 ~ 60 DEG C, and electro-nickel process strength of current is 1.0 ~ 10.0A/dm ².

3. according to claim 1 or 2, improve the technique of 316 stainless steel anti intercrystalline corrosion abilities, it is characterized in that: in described step a, each step annealing technique is carried out all in a hydrogen atmosphere.