High-strength cast iron surface corrosion inhibition method and vermicular cast iron workpiece

Abstract

The present application relates to the technical field of metal corrosion and protection, and particularly relates to a high-strength cast iron surface corrosion inhibition method and vermicular cast iron workpiece. The present application adopts potassium silicate and sodium metaborate to obtain a boron heteropolysilicate composite inorganic main agent through pre-hydrolysis copolymerization, boron atoms are embedded into Si-O silicon oxygen main chain through copolymerization reaction to form boron-silicon heteropolyoligomer anion, which is different from simple mixing of two kinds of silicates at the molecular level, and is combined with long-chain alkyl imidazoline, trimethylolpropane, EDTA disodium, KH-550 silane coupling multiple types of auxiliary agents to synergistically act, so that a series of technical problems such as easy precipitation of traditional silicate corrosion inhibitor tank solution, easy cracking of film layer, and incomplete plugging of graphite channel are solved.

Description

Technical Field

[0001] This invention belongs to the field of metal corrosion and protection technology, specifically relating to a method for inhibiting corrosion on the surface of high-strength cast iron and vermicular graphite cast iron workpieces. Background Technology

[0002] Vermicular graphite cast iron matrix is ​​composed of ferrite and pearlite, and is a high-strength cast iron. The vermicular graphite inside overlaps and penetrates the matrix, forming a three-dimensional continuous conductive penetration channel. The graphite potential is significantly higher than that of the iron matrix, which will form a full-area penetrating micro-galvanic corrosion system. Water and chloride ions can easily penetrate deep into the interior along the graphite gaps, eventually causing deep corrosion of the casting layer by peeling.

[0003] Currently, silicate-based corrosion inhibitors are used in the industry, but they are difficult to adapt to the special corrosion structure of vermicular graphite cast iron. Sodium silicate-based corrosion inhibitors form films quickly, but the resulting ferrosilicon gel is brittle and has poor water resistance. During drying, white silica spots easily precipitate on the workpiece surface, and a complete protective film cannot form deep within the workpiece. Free sodium ions within the system continuously absorb moisture, opening corrosion pathways, resulting in a short salt spray protection lifespan under humid and hot environments. Potassium silicate-based corrosion inhibitors offer better water resistance and film flexibility, but they struggle to penetrate the micron-sized worm-like crevices within vermicular graphite cast iron. After film formation, numerous pinholes remain within the film layer, resulting in poor deep corrosion inhibition. Conventional silicate-long-chain imidazoline composite systems lack gel stabilizing components and three-dimensional cross-linking structures. Silicate components are prone to flocculation and precipitation within the corrosion bath. Organic corrosion inhibitors can only form films through monolayer physical adsorption, failing to construct a continuous hydrophobic barrier network. The interfacial bonding strength between the inorganic gel layer and the organic film is low, leading to film detachment after high and low temperature cycling, making it difficult to meet the long-term service requirements of power castings. Addressing the shortcomings of existing technologies, this invention uses borosilicate polysilicate obtained through pre-hydrolysis copolymerization as the inorganic film-forming agent. Boron atoms are embedded in the silicon-oxygen framework to regulate the crystallization behavior and permeability of the iron silicate gel at the molecular level. Combined with specialized cross-linking, stabilizing, and silane coupling agents, a multi-layered synergistic composite protection system is constructed, overcoming the deficiencies of existing corrosion inhibitor formulations. Summary of the Invention

[0004] This invention relates to a method for inhibiting corrosion on the surface of high-strength cast iron and vermicular graphite cast iron workpieces. It employs a borosilicate composite inorganic main agent obtained by pre-hydrolyzing and copolymerizing potassium silicate and sodium metaborate. Boron atoms are embedded into the Si-O silicon-oxygen backbone through a copolymerization reaction to form borosilicate oligomeric anions, which differ from a simple mixture of two silicates at the molecular level. Combined with long-chain alkyl imidazoline, trimethylolpropane, disodium EDTA, and KH-550 silane coupling agents, this method synergistically solves a series of technical problems associated with traditional silicate corrosion inhibitors, such as easy sedimentation of the bath solution, easy cracking of the film layer, and incomplete sealing of graphite channels.

[0005] A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT300 and RuT420 vermicular graphite cast iron sequentially in an alkaline degreasing solution during the pretreatment stage. The degreasing solution is prepared by mixing 4%-8% sodium hydroxide with 2%-4% sodium carbonate. The treatment temperature is controlled at 50-60℃, and the immersion time is 10-15 minutes. After degreasing, the workpiece is rinsed with pure water for 1-3 minutes. Then, it is activated with a 4%-6% citric acid aqueous solution at room temperature for 3-5 minutes. After activation, it is rinsed twice with pure water, with each rinse lasting 1-2 minutes. After rinsing, it is dried with hot air at 65-75℃ for 15-25 minutes to thoroughly remove oil and dust impurities from the inside of the vermicular graphite channels and fully expose the active interface between the metal and graphite to facilitate subsequent film formation reactions.

[0006] The components of the corrosion inhibitor are formulated according to the following mass percentages: borohydric polysilicate composite inorganic main agent accounts for 12-25%, C12-C18 long-chain alkyl imidazoline accounts for 15-30%, trimethylolpropane crosslinking aid accounts for 2-4%, disodium EDTA stabilizing aid accounts for 0.8-1.5%, KH-550 silane coupling aid accounts for 0.5-1.2%, and the balance is deionized water.

[0007] The boropolysilicate composite inorganic main agent needs to be prepared in advance. Potassium silicate and sodium metaborate are added to warm water at 55-65℃ in a mass ratio of 6.5-7.5:2.5-3.5, and stirred at a constant temperature for 1.5-2.5 hours to complete the pre-hydrolysis copolymerization. During the reaction, BO-Si bonding occurs, and boron atoms are embedded in the silicon-oxygen chain to form a boron-doped oligomeric silicon-oxygen heteropoly anionic aqueous solution.

[0008] The corrosion inhibitor is prepared at an environment controlled at 20-30℃ and a stirring speed of 100-150 r / min. The order of addition is as follows: first, add the pre-synthesized borohydric silicate and disodium EDTA, and stir for 10-20 min to achieve complete dissociation. Then, add the long-chain alkyl imidazoline and KH-550 silane coupling agent and stir for 8-12 min. Finally, add the trimethylolpropane crosslinking aid and continue stirring for 25-35 min to obtain a stable corrosion inhibitor without flocculation or white silica scale precipitation.

[0009] In the corrosion-inhibiting immersion film-forming process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 20-28℃ for 25-35 minutes, turning the workpiece every 6-10 minutes to ensure that small-molecule borosilicate heteropoly anions diffuse inward along the micron-level channels of the worm-like graphite, forming a flexible iron silicate gel in situ. After immersion, the workpiece enters the high-temperature cross-linking and curing process. The workpiece is drained of residual liquid and dried with hot air at 80-100℃ for 8-12 minutes. During the drying process, the borosilicate silicate gel undergoes dense shrinkage and three-dimensional cross-linking of long-chain imidazoline molecules, while the chemical bonding between the inorganic gel and the organic film is achieved by relying on silane coupling agents.

[0010] The preferred ratio range is: 16-20 wt% boropolysilicate composite inorganic main agent, 20-24 wt% C12-C18 long-chain alkyl imidazoline, 2.5-3.5 wt% trimethylolpropane, 1.0-1.4 wt% disodium EDTA, 0.7-0.9 wt% KH-550, with the balance being deionized water; The preferred process range is immersion at room temperature for 28-32 minutes and drying at 85-95℃ for 8-12 minutes, within which the overall anti-corrosion performance is optimal.

[0011] The inorganic film-forming component of this invention, a borosilicate composite inorganic main agent, is prepared by pre-hydrolyzing and copolymerizing potassium silicate and sodium metaborate. It relies on BO-Si copolymerization to form a borosilicate heteropoly oligomeric anionic framework. The borosilicate system can use boron atoms to complex free potassium ions within the system, preventing the precipitation of white silica spots on the workpiece surface after drying. Simultaneously, boron can regulate the crystallization rate, preventing the rapid formation of a hard shell on the workpiece surface, thus achieving simultaneous film formation on the surface and deep layers of graphite, eliminating internal cavitation pores. The boron-doped structure can reduce gel crystallinity and decrease the internal stress caused by thermal shrinkage of the film. The low-molecular-size borosilicate heteropoly anions can penetrate deep into the continuous channels of worm-like graphite, reacting with the dissolved ferrous iron in situ to form a low-crystallinity flexible iron silicate gel, completely filling the three-dimensional conductive pathways and fundamentally cutting off global micro-galvanic corrosion. C12-C18 long-chain alkyl imidazoline organic main agents have long hydrophobic carbon chains, which can be uniformly adsorbed on the entire surface of the workpiece to form a hydrophobic substrate. When combined with crosslinking aids, they construct a three-dimensional continuous hydrophobic network, blocking corrosive media such as water, oxygen, and chloride ions from contacting the metal substrate. Trimethylolpropane crosslinking aids have polyhydroxy functional groups, inducing long-chain alkyl imidazolines to undergo three-dimensional crosslinking polymerization, forming a continuous hydrophobic film without breaks or cracks. This solves the defects of single imidazoline monolayer films, such as easy breakage and poor barrier ability, and is suitable for the continuous and interconnected microstructure of worm graphite. Disodium EDTA precisely controls the uniformity of ferric silicate gel deposition, avoiding the formation of filling blind spots in graphite gaps. KH-550 silane coupling agent chemically bonds one end of its silanol group to the borosilicate inorganic gel, while the other end's amino group combines with the crosslinked organic film, eliminating the interfacial gaps between the inorganic gel layer and the organic film, preventing the entire film layer from falling off under thermal cycling, and simultaneously improving the overall hydrophobicity of the film layer, reducing the penetration rate of corrosive media.

[0012] Pretreatment thoroughly removes oil and oxidized dust from the inside of the worm-like graphite channels, eliminating physical obstacles to gel deposition. The corrosion inhibitor uses a pre-synthesized borohydric silicate as the main agent, avoiding problems such as easy surface crusting and insufficient deep sealing. Stepwise low-speed feeding and stirring prevents excessively high local silicon-oxygen concentrations from causing premature gel failure. Long-term room-temperature immersion provides sufficient diffusion reaction time for borohydric silicate anions, ensuring synchronous film formation in the graphite area. The medium- and high-temperature drying process simultaneously completes gel densification and organic molecule cross-linking and shaping, ultimately forming an integrated protective structure of borohydric silicate gel sealing graphite channels, three-dimensional cross-linked organic film, and silane-bonded double-layer composite film. Detailed Implementation

[0013] Example 1 In the pretreatment stage, RuT420 vermicular graphite cast iron was sequentially immersed in an alkaline degreasing solution. The sample size was 50mm×30mm×5mm. The degreasing solution was prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature was 55℃ and the immersion time was 12min. After degreasing, the sample was rinsed with pure water for 2min. Then, it was activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the sample was rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the sample was dried with hot air at 70℃ for 20min.

[0014] The corrosion inhibitor is formulated according to the following mass percentages: 12% borohydric polysilicate composite inorganic main agent, 20% C15 long-chain alkyl imidazoline, 2% trimethylolpropane crosslinking aid, 0.8% EDTA disodium stabilizing agent, 0.7% KH-550 silane coupling aid, and the balance being deionized water.

[0015] The preparation process of borohydric polysilicate composite inorganic main agent is as follows: potassium silicate and sodium metaborate are added to 60℃ warm water at a mass ratio of 7:3 and stirred at a constant temperature for 2 hours to complete the pre-hydrolysis copolymerization.

[0016] The corrosion inhibitor was prepared under controlled environmental conditions of 25℃ and low stirring speed of 120r / min. The order of addition of materials was as follows: first, pre-synthesized borohydric silicate and disodium EDTA were added and stirred for 15min to achieve complete dissociation; then, long-chain alkyl imidazoline and KH-550 silane coupling agent were added and stirred for 10min; finally, trimethylolpropane crosslinking aid was added and stirred for 30min to obtain a stable corrosion inhibitor without flocculation or white silica scale precipitation.

[0017] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 25 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 80°C for 10 minutes.

[0018] Atmospheric corrosion rate testing was conducted according to GB / T 19292.1-2018 standard, involving 30 days of alternating wet and dry outdoor exposure. The annual corrosion rate was calculated, with lower values ​​indicating superior long-term corrosion resistance. The 48-hour neutral salt spray test was conducted according to GB / T 10125-2021 standard, using 5% NaCl and continuous spraying at 35℃. Rating was based on rust area, with level 9 being the best. The workpiece's atmospheric corrosion rate was 0.009 mm / a, and its 48-hour salt spray rating was level 8.

[0019] Example 2 In the pretreatment stage, RuT420 vermicular graphite cast iron was immersed in an alkaline degreasing solution. The workpiece size was 50mm×30mm×5mm. The degreasing solution was prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature was 55℃ and the immersion time was 12min. After degreasing, the workpiece was rinsed with pure water for 2min. Then, it was activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, it was rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, it was dried with hot air at 70℃ for 20min.

[0020] The corrosion inhibitor is formulated according to the following mass percentages: 18% borohydric polysilicate composite inorganic main agent, 22% C15 long-chain alkyl imidazoline, 3% trimethylolpropane crosslinking aid, 1.2% EDTA disodium stabilizing agent, 0.8% KH-550 silane coupling aid, and the balance being deionized water.

[0021] The preparation process of the borohydric polysilicate composite inorganic main agent is as follows: potassium silicate and sodium metaborate are added to 60°C warm water at a mass ratio of 7:3 and stirred at a constant temperature for 2 hours to complete the pre-hydrolysis copolymerization.

[0022] The corrosion inhibitor was prepared under controlled environmental conditions of 25℃ and low stirring speed of 120r / min. The order of addition of materials was as follows: first, pre-synthesized borohydric silicate and disodium EDTA were added and stirred for 15min to achieve complete dissociation; then, long-chain alkyl imidazoline and KH-550 silane coupling agent were added and stirred for 10min; finally, trimethylolpropane crosslinking aid was added and stirred for 30min to obtain a stable corrosion inhibitor without flocculation or white silica scale precipitation.

[0023] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 30 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 90°C for 10 minutes.

[0024] The atmospheric corrosion rate was 0.006 mm / a and the salt spray level was 9 after 48 hours, according to the method of Example 1.

[0025] Example 3 A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT420 vermicular graphite cast iron in an alkaline degreasing solution during the pretreatment stage. The workpiece size is 50mm×30mm×5mm. The degreasing solution is prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature is 55℃, and the immersion time is 12min. After degreasing, the workpiece is rinsed with pure water for 2min. Then, it is activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the workpiece is rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the workpiece is dried with hot air at 70℃ for 20min.

[0026] The corrosion inhibitor is formulated according to the following mass percentages: 25% borohydric polysilicate composite inorganic main agent, 30% C15 long-chain alkyl imidazoline, 4% trimethylolpropane crosslinking aid, 1.5% EDTA disodium stabilizing agent, 1.2% KH-550 silane coupling aid, and the balance being deionized water.

[0027] The preparation process of borohydric polysilicate composite inorganic main agent is as follows: potassium silicate and sodium metaborate are added to 60℃ warm water at a mass ratio of 7:3 and stirred at a constant temperature for 2 hours to complete the pre-hydrolysis copolymerization.

[0028] The corrosion inhibitor was prepared under controlled environmental conditions of 25℃ and low stirring speed of 120r / min. The order of addition of materials was as follows: first, pre-synthesized borohydric silicate and disodium EDTA were added and stirred for 15min to achieve complete dissociation; then, long-chain alkyl imidazoline and KH-550 silane coupling agent were added and stirred for 10min; finally, trimethylolpropane crosslinking aid was added and stirred for 30min to obtain a stable corrosion inhibitor without flocculation or white silica scale precipitation.

[0029] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 35 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 100°C for 10 minutes.

[0030] The atmospheric corrosion rate was 0.007 mm / a and the salt spray level was 9 after 48 hours, according to the method of Example 1.

[0031] Example 4 A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT420 vermicular graphite cast iron in an alkaline degreasing solution during the pretreatment stage. The workpiece size is 50mm×30mm×5mm. The degreasing solution is prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature is 55℃, and the immersion time is 12min. After degreasing, the workpiece is rinsed with pure water for 2min. Then, it is activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the workpiece is rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the workpiece is dried with hot air at 70℃ for 20min.

[0032] The corrosion inhibitor is formulated according to the following mass percentages: 18% borohydric polysilicate composite inorganic main agent, 22% C15 long-chain alkyl imidazoline, 3% trimethylolpropane crosslinking aid, 1.2% EDTA disodium stabilizing agent, 0.8% KH-550 silane coupling aid, and the balance being deionized water.

[0033] The preparation process of borohydric polysilicate composite inorganic main agent is as follows: potassium silicate and sodium metaborate are added to 55℃ warm water at a mass ratio of 6.5:3.5 and stirred at a constant temperature for 1.5h to complete the pre-hydrolysis copolymerization.

[0034] The corrosion inhibitor was prepared under controlled environmental conditions of 25℃ and low stirring speed of 120r / min. The order of addition of materials was as follows: first, pre-synthesized borohydric silicate and disodium EDTA were added and stirred for 15min to achieve complete dissociation; then, long-chain alkyl imidazoline and KH-550 silane coupling agent were added and stirred for 10min; finally, trimethylolpropane crosslinking aid was added and stirred for 30min to obtain a stable corrosion inhibitor without flocculation or white silica scale precipitation.

[0035] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 30 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 90°C for 10 minutes.

[0036] The atmospheric corrosion rate was 0.007 mm / a and the salt spray level was 9 after 48 hours, according to the method of Example 1.

[0037] Example 5 A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT420 vermicular graphite cast iron in an alkaline degreasing solution during the pretreatment stage. The workpiece size is 50mm×30mm×5mm. The degreasing solution is prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature is 55℃, and the immersion time is 12min. After degreasing, the workpiece is rinsed with pure water for 2min. Then, it is activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the workpiece is rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the workpiece is dried with hot air at 70℃ for 20min.

[0038] The corrosion inhibitor is formulated according to the following mass percentages: 18% borohydric polysilicate composite inorganic main agent, 22% C15 long-chain alkyl imidazoline, 3% trimethylolpropane crosslinking aid, 1.2% EDTA disodium stabilizing agent, 0.8% KH-550 silane coupling aid, and the balance being deionized water.

[0039] The preparation process of borohydric polysilicate composite inorganic main agent is as follows: potassium silicate and sodium metaborate are added to 65℃ warm water at a mass ratio of 7.5:2.5 and stirred at a constant temperature for 2.5h to complete the pre-hydrolysis copolymerization.

[0040] The corrosion inhibitor was prepared under controlled environmental conditions of 25℃ and low stirring speed of 120r / min. The order of addition of materials was as follows: first, pre-synthesized borohydric silicate and disodium EDTA were added and stirred for 15min to achieve complete dissociation; then, long-chain alkyl imidazoline and KH-550 silane coupling agent were added and stirred for 10min; finally, trimethylolpropane crosslinking aid was added and stirred for 30min to obtain a stable corrosion inhibitor without flocculation or white silica scale precipitation.

[0041] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 30 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 90°C for 10 minutes.

[0042] The atmospheric corrosion rate was 0.007 mm / a and the salt spray level was 9 after 48 hours, according to the method of Example 1.

[0043] Comparative Example 1 A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT420 vermicular graphite cast iron in an alkaline degreasing solution during the pretreatment stage. The workpiece size is 50mm×30mm×5mm. The degreasing solution is prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature is 55℃, and the immersion time is 12min. After degreasing, the workpiece is rinsed with pure water for 2min. Then, it is activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the workpiece is rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the workpiece is dried with hot air at 70℃ for 20min.

[0044] The corrosion inhibitor is formulated according to the following mass percentages: 12% sodium silicate and potassium silicate physical mixture (7:3), 15% C15 long-chain alkyl imidazoline, 2% trimethylolpropane crosslinking aid, 0.8% disodium EDTA stabilizer, 0.5% KH-550 silane coupling aid, and the remainder is deionized water.

[0045] The corrosion inhibitor was prepared under controlled environmental conditions of 25℃ and low stirring speed of 120r / min. The order of adding materials was as follows: first, add the sodium silicate / potassium silicate mixture and disodium EDTA, and stir for 15min to achieve full dissociation; then add the long-chain alkyl imidazoline and KH-550 silane coupling agent and stir for 10min; finally, add the trimethylolpropane crosslinking aid and continue stirring for 30min.

[0046] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 25 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking curing process, the workpiece is drained of residual liquid on the surface, and dried with hot air at 80°C for 10 minutes.

[0047] According to the method tested in Example 1, the atmospheric corrosion rate was 0.018 mm / a, and the salt spray level was 7 after 48 hours. Without boron atoms participating in the silicon-oxygen chain copolymerization modification, free potassium and sodium ions in the system could not complex, resulting in white silica spots that precipitate during drying and form corrosion active sites. The silica gel lacks a flexible control mechanism, is highly brittle, and cannot completely fill the deep gaps in the graphite, significantly reducing its ability to inhibit deep corrosion.

[0048] Comparative Example 2 A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT420 vermicular graphite cast iron in an alkaline degreasing solution during the pretreatment stage. The workpiece size is 50mm×30mm×5mm. The degreasing solution is prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature is 55℃, and the immersion time is 12min. After degreasing, the workpiece is rinsed with pure water for 2min. Then, it is activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the workpiece is rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the workpiece is dried with hot air at 70℃ for 20min.

[0049] The corrosion inhibitor is formulated according to the following mass percentages: 12% borohydric polysilicate composite inorganic main agent, 15% C15 long-chain alkyl imidazoline, 2% trimethylolpropane crosslinking aid, 0.8% disodium EDTA stabilizer, 0.5% KH-550 silane coupling aid, and the balance being deionized water.

[0050] The preparation process of borohydric polysilicate composite inorganic main agent is as follows: potassium silicate and sodium metaborate are added to 60℃ warm water at a mass ratio of 9:1 and stirred at a constant temperature for 2 hours to complete the pre-hydrolysis copolymerization.

[0051] The corrosion inhibitor was prepared under controlled environmental conditions of 25℃ and low stirring speed of 120r / min. The order of addition of materials was as follows: first, pre-synthesized borohydric silicate and disodium EDTA were added and stirred for 15min to achieve complete dissociation; then, long-chain alkyl imidazoline and KH-550 silane coupling agent were added and stirred for 10min; finally, trimethylolpropane crosslinking aid was added and stirred for 30min to obtain a stable corrosion inhibitor without flocculation or white silica scale precipitation.

[0052] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 25 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 80°C for 10 minutes.

[0053] According to the method tested in Example 1, the atmospheric corrosion rate was 0.015 mm / a, and the salt spray level was 7 after 48 hours. The sodium metaborate content was too low, resulting in insufficient silicon-oxygen chain boron doping sites, weakening the effect of complexing free metal ions and regulating gel flexibility, reducing the uniformity of gel filling in graphite gaps, and making the film prone to microcracks.

[0054] Comparative Example 3 A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT420 vermicular graphite cast iron in an alkaline degreasing solution during the pretreatment stage. The workpiece size is 50mm×30mm×5mm. The degreasing solution is prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature is 55℃, and the immersion time is 12min. After degreasing, the workpiece is rinsed with pure water for 2min. Then, it is activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the workpiece is rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the workpiece is dried with hot air at 70℃ for 20min.

[0055] The corrosion inhibitor is formulated according to the following mass percentages: 12% borohydric polysilicate composite inorganic main agent, 15% C15 long-chain alkyl imidazoline, 2% trimethylolpropane crosslinking aid, 0.8% EDTA disodium stabilizing agent, 0.5% KH-550 silane coupling aid, and the balance being deionized water.

[0056] The preparation process of borohydric polysilicate composite inorganic main agent is as follows: potassium silicate and sodium metaborate are added to 60℃ warm water at a mass ratio of 1:1 and stirred at a constant temperature for 2 hours to complete the pre-hydrolysis copolymerization.

[0057] The corrosion inhibitor was prepared under controlled environmental conditions of 25℃ and low stirring speed of 120r / min. The order of addition of materials was as follows: first, pre-synthesized borohydric silicate and disodium EDTA were added and stirred for 15min to achieve complete dissociation; then, long-chain alkyl imidazoline and KH-550 silane coupling agent were added and stirred for 10min; finally, trimethylolpropane crosslinking aid was added and stirred for 30min to obtain a stable corrosion inhibitor without flocculation or white silica scale precipitation.

[0058] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 25 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 80°C for 10 minutes.

[0059] Tested according to the method in Example 1, the atmospheric corrosion rate was 0.014 mm / a, and the salt spray level was 7 after 48 hours. Excess sodium metaborate and excessive boron disrupted the polymerization equilibrium of the silicon-oxygen chains, increased the size of heteropoly anions, reduced their ability to penetrate the fine channels of worms, and left corrosion cavities inside the graphite.

[0060] Comparative Example 4 A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT420 vermicular graphite cast iron in an alkaline degreasing solution during the pretreatment stage. The workpiece size is 50mm×30mm×5mm. The degreasing solution is prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature is 55℃, and the immersion time is 12min. After degreasing, the workpiece is rinsed with pure water for 2min. Then, it is activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the workpiece is rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the workpiece is dried with hot air at 70℃ for 20min.

[0061] The corrosion inhibitor is formulated according to the following mass percentages: 12% borohydric polysilicate composite inorganic main agent, 15% C15 long-chain alkyl imidazoline, 2% trimethylolpropane crosslinking aid, 0.8% EDTA disodium stabilizing agent, 0.5% KH-550 silane coupling aid, and the balance being deionized water.

[0062] The borohydric polysilicate composite inorganic main agent is prepared by stirring in warm water at 25°C for 2 hours, with a mass ratio of potassium silicate to sodium metaborate of 7:3.

[0063] The corrosion inhibitor was prepared under controlled environmental conditions of 25℃ and low stirring speed of 120r / min. The order of addition of materials was as follows: first, pre-synthesized borohydric silicate and disodium EDTA were added and stirred for 15min to achieve complete dissociation; then, long-chain alkyl imidazoline and KH-550 silane coupling agent were added and stirred for 10min; finally, trimethylolpropane crosslinking aid was added and stirred for 30min to obtain a stable corrosion inhibitor without flocculation or white silica scale precipitation.

[0064] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 25 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 80°C for 10 minutes.

[0065] As tested according to Example 1, the atmospheric corrosion rate was 0.013 mm / a, and the salt spray level was 7 after 48 hours. Without constant temperature heating, the BO-Si copolymerization reaction was incomplete, resulting in insufficient formation of borosilicate heteropoly anions. This reduced the combined effects of complexation, penetration, and gel regulation, thus weakening the deep protective effect of graphite.

[0066] Comparative Example 5 A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT420 vermicular graphite cast iron in an alkaline degreasing solution during the pretreatment stage. The workpiece size is 50mm×30mm×5mm. The degreasing solution is prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature is 55℃, and the immersion time is 12min. After degreasing, the workpiece is rinsed with pure water for 2min. Then, it is activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the workpiece is rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the workpiece is dried with hot air at 70℃ for 20min.

[0067] The corrosion inhibitor is formulated according to the following mass percentages: 12% borohydric polysilicate composite inorganic main agent, 15% C15 long-chain alkyl imidazoline, 0.8% EDTA disodium stabilizer, 0.5% KH-550 silane coupling agent, and the balance is deionized water. No trimethylolpropane crosslinking agent is added.

[0068] The preparation process of borohydric polysilicate composite inorganic main agent is as follows: potassium silicate and sodium metaborate are added to 60℃ warm water at a mass ratio of 7:3 and stirred at a constant temperature for 2 hours to complete the pre-hydrolysis copolymerization.

[0069] The corrosion inhibitor was prepared under controlled environmental conditions of 25℃ and low stirring speed of 120r / min. The order of addition of materials was as follows: first, pre-synthesized borohydric silicate and disodium EDTA were added and stirred for 15min to achieve complete dissociation; then, long-chain alkyl imidazoline and KH-550 silane coupling agent were added and stirred for 10min. There was no crosslinking aid addition step. After stirring for 30min, the corrosion inhibitor was obtained.

[0070] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 25 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 80°C for 10 minutes.

[0071] As tested according to Example 1, the atmospheric corrosion rate was 0.016 mm / a, and the salt spray level was 7 after 48 hours. Due to the lack of trimethylolpropane, the long-chain alkyl imidazoline could not undergo three-dimensional cross-linking, forming only a single-layer hydrophobic film. The film contained numerous gaps, allowing water vapor and chloride ions to easily penetrate and contact the substrate.

[0072] Comparative Example 6 A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT420 vermicular graphite cast iron in an alkaline degreasing solution during the pretreatment stage. The workpiece size is 50mm×30mm×5mm. The degreasing solution is prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature is 55℃, and the immersion time is 12min. After degreasing, the workpiece is rinsed with pure water for 2min. Then, it is activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the workpiece is rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the workpiece is dried with hot air at 70℃ for 20min.

[0073] The corrosion inhibitor is formulated according to the following mass percentages: 12% borohydric polysilicate composite inorganic main agent, 15% C15 long-chain alkyl imidazoline, 2% trimethylolpropane crosslinking aid, 0.5% KH-550 silane coupling aid, and the balance is deionized water. No disodium EDTA stabilizer is added.

[0074] The preparation process of borohydric polysilicate composite inorganic main agent is as follows: potassium silicate and sodium metaborate are added to 60℃ warm water at a mass ratio of 7:3 and stirred at a constant temperature for 2 hours to complete the pre-hydrolysis copolymerization.

[0075] The corrosion inhibitor was prepared at an environment controlled at 25°C and a stirring speed of 120 r / min. The order of adding materials was as follows: first, add the pre-synthesized borohydric polysilicate and stir for 15 min; then add the long-chain alkyl imidazoline and KH-550 silane coupling agent and stir for 10 min; finally, add the trimethylolpropane crosslinking aid and continue stirring for 30 min.

[0076] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 25 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 80°C for 10 minutes.

[0077] According to the method tested in Example 1, the atmospheric corrosion rate was 0.017 mm / a, and the salt spray level was 7 after 48 hours. Without EDTA disodium complexation, calcium and iron impurities in the water were present. These impurities induced premature flocculation of borosilicates, leading to silica scale formation in the bath, a significant decrease in film uniformity, and incomplete sealing of local graphite channels.

[0078] Comparative Example 7 A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT420 vermicular graphite cast iron in an alkaline degreasing solution during the pretreatment stage. The workpiece size is 50mm×30mm×5mm. The degreasing solution is prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature is 55℃, and the immersion time is 12min. After degreasing, the workpiece is rinsed with pure water for 2min. Then, it is activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the workpiece is rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the workpiece is dried with hot air at 70℃ for 20min.

[0079] The corrosion inhibitor is formulated according to the following mass percentages: 12% borohydric polysilicate composite inorganic main agent, 15% C15 long-chain alkyl imidazoline, 2% trimethylolpropane crosslinking aid, 0.8% disodium EDTA stabilizer, and the balance is deionized water. No KH-550 silane coupling aid is added.

[0080] The borohydride polysilicate composite inorganic main agent needs to be prepared in advance. Potassium silicate and sodium metaborate are added to 60°C warm water at a mass ratio of 7:3 and stirred at a constant temperature for 2 hours to complete the pre-hydrolysis copolymerization.

[0081] The corrosion inhibitor was prepared at an environment controlled at 25°C and a stirring speed of 120 r / min. The order of adding materials was as follows: first, add the pre-synthesized borohydric silicate and disodium EDTA, and stir for 15 min to achieve full dissociation; then add the long-chain alkyl imidazoline and stir for 10 min; finally, add the trimethylolpropane crosslinking aid and continue stirring for 30 min.

[0082] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 25 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 80°C for 10 minutes.

[0083] As tested according to Example 1, the atmospheric corrosion rate was 0.016 mm / a, and the salt spray level was 7 after 48 hours. Lacking a silane coupling agent, the inorganic silica gel layer and the organic hydrophobic film are only physically bonded, without chemical bonds. Under alternating hot and cold temperatures, the interface between the two layers easily separates and detaches, damaging the protective barrier.

[0084] Comparative Example 8 A method for inhibiting corrosion on the surface of vermicular graphite cast iron involves immersing RuT420 vermicular graphite cast iron in an alkaline degreasing solution during the pretreatment stage. The workpiece size is 50mm×30mm×5mm. The degreasing solution is prepared by mixing 6% sodium hydroxide and 3% sodium carbonate by mass. The treatment temperature is 55℃, and the immersion time is 12min. After degreasing, the workpiece is rinsed with pure water for 2min. Then, it is activated with a 5% citric acid aqueous solution at room temperature for 4min. After activation, the workpiece is rinsed twice with pure water, with each rinse lasting 1.5min. After rinsing, the workpiece is dried with hot air at 70℃ for 20min.

[0085] The corrosion inhibitor is formulated according to the following mass percentage ratios: 12% borohydric polysilicate composite inorganic main agent, 15% C15 long-chain alkyl imidazoline, and the remainder is deionized water. No functional additives such as trimethylolpropane, disodium EDTA, or KH-550 are added.

[0086] The preparation process of borohydric polysilicate composite inorganic main agent is as follows: potassium silicate and sodium metaborate are added to 60℃ warm water at a mass ratio of 7:3 and stirred at a constant temperature for 2 hours to complete the pre-hydrolysis copolymerization.

[0087] The corrosion inhibitor was prepared at an environment controlled at 25°C and a stirring speed of 120 r / min. The order of adding materials was as follows: first, add the pre-synthesized borohydride and stir for 15 min, then add the long-chain alkyl imidazoline and stir for 40 min.

[0088] In the corrosion inhibition immersion film formation process, the pretreated workpiece is completely immersed in the corrosion inhibitor solution at 25°C for 25 minutes, and the workpiece is turned over every 8 minutes. After immersion, the workpiece enters the high-temperature cross-linking and curing process, where the residual liquid on the surface of the workpiece is drained, and it is dried with hot air at 80°C for 10 minutes.

[0089] According to the test method in Example 1, the atmospheric corrosion rate was 0.021 mm / a, and the salt spray level was 6 after 48 hours. At the same time, the absence of three key additives, namely crosslinking, stabilizing, and silane coupling, resulted in poor bath stability, no continuous hydrophobic network in the organic film, and easy delamination of the inorganic-organic film. With multiple defects superimposed, the overall anti-corrosion performance was the worst.

Claims

1. A method for inhibiting corrosion on the surface of high-strength cast iron, characterized in that, Includes the following steps: Step 1: In the pretreatment stage of the workpiece, the vermicular graphite cast iron is immersed in an alkaline degreasing solution for treatment. After degreasing, it is rinsed with pure water for 1-3 minutes. Then, it is activated with a 4%-6% citric acid aqueous solution at room temperature for 3-5 minutes. After activation, it is rinsed with pure water twice and then dried with hot air. Step 2: The order of adding materials to the corrosion inhibitor is as follows: first, add the pre-synthesized boropolysilicate and disodium EDTA; then add the C12-C18 long-chain alkyl imidazoline and KH-550 silane coupling agent and stir; finally, add the trimethylolpropane crosslinking aid and continue stirring. The corrosion inhibitor is formulated according to the following mass percentages: borohydric polysilicate composite inorganic main agent 12-25%, C12-C18 long-chain alkyl imidazoline 15-30%, trimethylolpropane crosslinking aid 2-4%, disodium EDTA stabilizer 0.8-1.5%, KH-550 silane coupling aid 0.5-1.2%, with the remainder being deionized water. The borohydride polysilicate composite inorganic main agent needs to be prepared in advance. Potassium silicate and sodium metaborate are added to warm water at 55-65℃ in a mass ratio of (6.5-7.5):(2.5-3.5) and stirred at a constant temperature for 1.5-2.5h to complete the pre-hydrolysis copolymerization. Step 3: In the corrosion inhibition immersion film formation process, the pre-treated workpiece is completely immersed in the corrosion inhibitor solution. After immersion, it enters the high-temperature cross-linking and curing process. The workpiece is drained of residual liquid on the surface and dried with hot air.

2. The method according to claim 1, characterized in that, The corrosion inhibitor is formulated by mass percentage as follows: 16-20 wt% borohydric silicate composite inorganic main agent, 20-24 wt% C12-C18 long-chain alkyl imidazoline, 2.5-3.5 wt% trimethylolpropane, 1.0-1.4 wt% disodium EDTA, 0.7-0.9 wt% KH-550, with the balance being deionized water.

3. The method according to claim 1, characterized in that, In step three, soak at room temperature for 28-32 minutes and dry at 85-95℃ for 8-12 minutes.

4. The method according to claim 1, characterized in that, In step one, the degreasing solution is prepared by mixing 4%-8% sodium hydroxide with 2%-4% sodium carbonate by mass. The treatment temperature is controlled at 50-60℃ and the soaking time is 10-15 minutes.

5. The method according to claim 1, characterized in that, In step three, soak the workpiece at 20-28℃ for 25-35 minutes, turning it over every 6-10 minutes.

6. The method according to claim 1, characterized in that, In step one, each rinse lasts 1-2 minutes, followed by hot air drying at 65-75℃ for 15-25 minutes.

7. The method according to claim 1, characterized in that, In step three, dry with hot air at 80-100℃ for 8-12 minutes.

8. The method according to claim 1, characterized in that, Step two involves preparing the corrosion inhibitor at an environment controlled at 20-30℃ and a stirring speed of 100-150 r / min. The order of adding materials is as follows: first, add the pre-synthesized borohydric silicate and disodium EDTA, and stir for 10-20 min to achieve complete dissociation; then, add C12-C18 long-chain alkyl imidazoline and KH-550 silane coupling agent and stir for 8-12 min; finally, add trimethylolpropane crosslinking aid and continue stirring for 25-35 min.

9. The method according to claim 1, characterized in that, The vermicular graphite cast iron is of type RuT300 and RuT420.

10. A vermicular graphite cast iron workpiece, characterized in that, Obtained by processing using the method described in any one of claims 1-9.