How to ensure the corrosion resistance of the raw materials of roller chains?

How to ensure the corrosion resistance of the raw materials of roller chains?

1. Material selection
1.1 Select steel with strong corrosion resistance
Steel is the main raw material of roller chains, and its corrosion resistance directly affects the service life and performance of roller chains. Selecting steel with strong corrosion resistance is the first step to ensure the corrosion resistance of roller chains.
Application of stainless steel materials: Stainless steel is one of the commonly used corrosion-resistant steels. It contains a certain proportion of chromium elements, which can form a dense chromium oxide film on the surface to prevent the corrosive medium from contacting the inside of the steel. For example, the chromium content of 304 stainless steel is about 18%, which has good corrosion resistance and is suitable for general corrosive environments. In some special environments, such as seawater environments with high chloride ion content, 316 stainless steel has stronger pitting resistance due to the addition of molybdenum elements, and its corrosion resistance is about 30% higher than that of 304 stainless steel.
Corrosion resistance of alloy steel: Alloy steel can significantly improve the corrosion resistance of steel by adding a variety of alloy elements, such as nickel, copper, titanium, etc. For example, the addition of nickel can improve the stability of the passivation film of steel, and copper can improve the corrosion resistance of steel in the atmospheric environment. After proper heat treatment, some high-strength alloy steels can form a uniform oxide film on the surface, further enhancing their corrosion resistance. Taking an alloy steel containing nickel and copper as an example, its corrosion rate in an industrial atmospheric environment is only 1/5 of that of ordinary carbon steel.
The effect of steel surface treatment on corrosion resistance: In addition to selecting suitable steel, surface treatment is also an important means to improve the corrosion resistance of steel. For example, a layer of zinc, nickel and other metals is plated on the surface of steel through plating technology to form a physical barrier to prevent corrosive media from contacting the steel. The galvanized layer has good corrosion resistance in the atmospheric environment, and its corrosion resistance life can reach decades. The nickel-plated layer has higher hardness and better wear resistance, and can also effectively improve the corrosion resistance of steel. In addition, chemical conversion film treatment, such as phosphating, can form a chemical conversion film on the surface of steel to improve the corrosion resistance and coating adhesion of steel.

2. Surface treatment
2.1 Galvanizing
Galvanizing is one of the important methods for roller chain steel surface treatment. By coating the steel surface with a layer of zinc, its corrosion resistance can be effectively improved.
Protection principle of the galvanized layer: Zinc forms a dense zinc oxide film in the atmospheric environment, which can prevent the corrosive medium from contacting the steel. When the galvanized layer is damaged, zinc will also act as a sacrificial anode to protect the steel from corrosion. Studies have shown that the corrosion resistance of the galvanized layer can reach decades, and its corrosion rate in a general atmospheric environment is only about 1/10 of that of ordinary steel.
The effect of galvanizing process on corrosion resistance: Common galvanizing processes include hot-dip galvanizing, electrogalvanizing, etc. The zinc layer formed by hot-dip galvanizing is thicker and has better corrosion resistance, but some unevenness may occur on the surface. Electrogalvanizing can control the thickness of the zinc layer to make the surface more uniform and smooth. For example, by using the electrogalvanizing process, the thickness of the zinc layer can be controlled between 5-15μm, and its corrosion resistance is comparable to that of hot-dip galvanizing, and the surface quality is better, which is suitable for roller chain products with high surface requirements.
Maintenance and precautions of the galvanized layer: The galvanized layer needs to be maintained during use to avoid mechanical damage. If the galvanized layer is damaged, it should be repaired in time to prevent the steel from being exposed to the corrosive medium. In addition, in some special environments, such as strong acidic or alkaline environments, the corrosion resistance of the galvanized layer will be affected to a certain extent, and it is necessary to select a suitable galvanizing process and subsequent protective measures according to the specific environment.
2.2 Nickel plating treatment
Nickel plating is another effective method to improve the corrosion resistance of roller chain steel. The nickel plating layer has good corrosion resistance and wear resistance.
Corrosion resistance of nickel plating: Nickel has stable electrochemical properties and can form a stable passivation film in many corrosive media, thereby effectively preventing the corrosive medium from contacting the steel. The corrosion resistance of the nickel plating layer is better than that of the zinc plating layer, especially in an environment containing chloride ions, and its pitting resistance is stronger. For example, in a seawater environment containing chloride ions, the corrosion resistance life of the nickel plating layer is 3-5 times that of the zinc plating layer.
Nickel plating process and its impact on performance: Common nickel plating processes include electroplating and chemical nickel plating. The electroplated nickel layer has a high hardness and good wear resistance, but it has high requirements for the flatness of the substrate surface. Chemical nickel plating can form a uniform coating on the surface of a non-conductive substrate, and the thickness and composition of the coating can be adjusted through process parameters. For example, by using the chemical nickel plating process, a nickel plating layer with a thickness of 10-20μm can be formed on the surface of the roller chain steel, and its hardness can reach more than HV700, which not only has good corrosion resistance, but also has good wear resistance.
Application and limitations of nickel plating: Nickel plating is widely used in roller chain products with high requirements for corrosion resistance and wear resistance, such as in the chemical industry, food processing and other industries. However, the nickel plating process is relatively complex and costly, and in some strong acid and strong alkali environments, the corrosion resistance of the nickel plating layer will also be limited to a certain extent. In addition, the wastewater generated during the nickel plating process needs to be strictly treated to avoid environmental pollution.

3. Heat treatment process
3.1 Quenching and tempering treatment
Quenching and tempering treatment is a key process for heat treatment of roller chain raw materials. Through the combination of quenching and high-temperature tempering, the comprehensive performance of steel can be significantly improved, thereby enhancing its corrosion resistance.
The role of quenching and parameter selection: Quenching can quickly cool steel, form high-strength structures such as martensite, and improve the hardness and strength of steel. For roller chain raw materials, commonly used quenching media include oil and water. For example, for some medium-carbon alloy steels, oil quenching can avoid the generation of quenching cracks and obtain higher hardness. The selection of quenching temperature is crucial, generally between 800℃-900℃, and the hardness after quenching can reach HRC45-55. Although the hardness of the quenched steel is high, the internal residual stress is large and the toughness is poor, so high-temperature tempering is required to improve these properties.
Optimization of high temperature tempering: High temperature tempering is usually carried out between 500℃-650℃, and the tempering time is generally 2-4 hours. During the tempering process, the residual stress in the steel is released, the hardness decreases slightly, but the toughness is significantly improved, and a stable tempered troostite structure can be formed, which has good comprehensive mechanical properties and corrosion resistance. Studies have shown that the corrosion resistance of steel after quenching and tempering can be improved by 30%-50%. For example, in an industrial atmospheric environment, the corrosion rate of the raw materials of roller chains that have been quenched and tempered is only about 1/3 of that of untreated steel. In addition, quenching and tempering can also improve the fatigue performance of steel, which is of great significance for the long-term use of roller chains under dynamic loads.
The mechanism of the influence of quenching and tempering on corrosion resistance: Quenching and tempering improves the microstructure of steel, improves its surface hardness and toughness, and thus enhances its ability to resist erosion by corrosive media. On the one hand, higher hardness can reduce the mechanical wear of the corrosive medium on the surface of the steel and reduce the corrosion rate; on the other hand, a stable organizational structure can slow down the diffusion rate of the corrosive medium and delay the occurrence of corrosion reactions. At the same time, quenching and tempering can also improve the steel’s resistance to hydrogen embrittlement. In some corrosive environments containing hydrogen ions, it can effectively prevent the steel from failing prematurely due to hydrogen embrittlement.

4. Quality Inspection
4.1 Corrosion Resistance Test Method
The corrosion resistance test of the raw materials of the roller chain is a key link in ensuring its quality. Through scientific and reasonable test methods, the corrosion resistance of the material in different environments can be accurately evaluated, thereby providing a guarantee for the reliability of the product.
1. Salt Spray Test
The salt spray test is an accelerated corrosion test method that simulates an ocean or humid environment and is widely used to evaluate the corrosion resistance of metal materials.
Test Principle: The roller chain sample is placed in a salt spray test chamber so that the sample surface is continuously exposed to a certain concentration of salt spray environment. The chloride ions in the salt spray will accelerate the corrosion reaction of the metal surface. The corrosion resistance of the sample is evaluated by observing the degree of corrosion of the sample within a certain period of time. For example, in accordance with the international standard ISO 9227, a neutral salt spray test is conducted with a salt spray concentration of 5% NaCl solution, a temperature controlled at about 35°C, and a test time of usually 96 hours.
Result evaluation: Corrosion resistance is evaluated based on indicators such as corrosion products, pitting depth, and corrosion rate on the sample surface. For stainless steel roller chains, after a 96-hour salt spray test, the surface pitting depth should be less than 0.1mm and the corrosion rate should be less than 0.1mm/year to meet the use requirements of general industrial environments. For alloy steel roller chains, after galvanizing or nickel plating, the salt spray test results should meet higher standards. For example, after a 96-hour salt spray test, the nickel-plated roller chain has no obvious corrosion on the surface and the pitting depth is less than 0.05mm.
2. Electrochemical test
Electrochemical testing can provide a deeper understanding of the corrosion resistance of materials by measuring the electrochemical behavior of metals in corrosive media.
Polarization curve test: The roller chain sample is used as a working electrode and immersed in a corrosive medium (such as 3.5% NaCl solution or 0.1mol/L H₂SO₄ solution), and its polarization curve is recorded by an electrochemical workstation. The polarization curve can reflect parameters such as the corrosion current density and corrosion potential of the material. For example, for 316 stainless steel roller chain, the corrosion current density in 3.5% NaCl solution should be less than 1μA/cm², and the corrosion potential should be close to -0.5V (relative to saturated calomel electrode), which indicates that it has good corrosion resistance.
Electrochemical impedance spectroscopy (EIS) test: The EIS test can measure the charge transfer impedance and diffusion impedance of the material in the corrosive medium to evaluate the integrity and stability of its surface film. The corrosion resistance of the material can be judged by analyzing parameters such as the capacitive arc and time constant in the impedance spectrum. For example, the charge transfer impedance of the roller chain steel that has been quenched and tempered should be greater than 10⁴Ω·cm² in the EIS test, which indicates that its surface film has a good protective effect.
3. Immersion test
The immersion test is a corrosion test method that simulates the actual use environment. The roller chain sample is immersed in a specific corrosive medium for a long time to observe its corrosion behavior and performance changes.
Test conditions: Select appropriate corrosive media according to the actual use environment of the roller chain, such as acidic solution (sulfuric acid, hydrochloric acid, etc.), alkaline solution (sodium hydroxide, etc.) or neutral solution (such as seawater). The test temperature is generally controlled at room temperature or the actual use temperature range, and the test time is usually several weeks to several months. For example, for roller chains used in chemical environments, they are immersed in 3% H₂SO₄ solution at 40°C for 30 days.
Result analysis: The corrosion resistance is evaluated by measuring indicators such as mass loss, dimensional change, and mechanical property change of the sample. The mass loss rate is an important indicator to measure the degree of corrosion. For stainless steel roller chains, the mass loss rate after 30 days of immersion test should be less than 0.5%. For alloy steel roller chains, the mass loss rate should be less than 0.2% after surface treatment. In addition, the changes in mechanical properties such as tensile strength and hardness of the sample should also be tested to ensure that it can still meet the use requirements in a corrosive environment.
4. On-site hanging test
The on-site hanging test is to directly expose the roller chain sample to the actual use environment and evaluate the corrosion resistance by observing its corrosion for a long time.
Test arrangement: Select a representative actual use environment, such as a chemical workshop, offshore platform, food processing plant, etc., and hang or fix the roller chain sample on the equipment at a certain interval. The test time is usually several months to several years to ensure that the corrosion behavior of the sample in the actual environment can be fully observed.
Result recording and analysis: Observe and test the samples regularly, and record information such as surface corrosion and corrosion product morphology. For example, in a chemical workshop environment, after 1 year of hanging test, there is no obvious corrosion mark on the surface of the nickel-plated roller chain, while a small amount of pitting may appear on the surface of the galvanized roller chain. By comparing the corrosion of samples of different materials and treatment processes in the actual environment, its corrosion resistance can be more accurately evaluated, providing an important basis for the material selection and design of the product.

5. Summary
Ensuring the corrosion resistance of the raw materials of the roller chain is a systematic project, involving multiple links such as material selection, surface treatment, heat treatment process and strict quality inspection. By selecting suitable steel materials with strong corrosion resistance, such as stainless steel and alloy steel, and combining surface treatment processes such as galvanizing and nickel plating, the corrosion resistance of roller chains can be significantly improved. The quenching and tempering treatment in the heat treatment process further enhances the comprehensive performance of steel by optimizing quenching and tempering parameters, so that it has better corrosion resistance and mechanical properties in complex environments.
In terms of quality inspection, the application of various test methods such as salt spray test, electrochemical test, immersion test and on-site hanging test provides a scientific basis for comprehensively evaluating the corrosion resistance of roller chain raw materials. These test methods can simulate different actual use environments and accurately detect the corrosion behavior and performance changes of materials under various conditions, thereby ensuring the reliability and durability of the product in actual applications.
In general, through the coordinated optimization of the above links, the corrosion resistance of roller chain raw materials can be effectively improved, its service life can be extended, and the use requirements in different industrial environments can be met.