Introduction to common heat treatment processes for roller chains

Introduction to common heat treatment processes for roller chains
In the manufacturing process of roller chains, heat treatment process is a key link to improve their performance. Through heat treatment, the strength, hardness, wear resistance and toughness of roller chains can be significantly improved, thereby extending their service life and meeting the use requirements under various complex working conditions. The following is a detailed introduction to several common heat treatment processes for roller chains:

I. Quenching and tempering process
(I) Quenching
Quenching is a process of heating the roller chain to a certain temperature (usually above Ac3 or Ac1), keeping it warm for a certain period of time, and then cooling it rapidly. Its purpose is to make the roller chain obtain a high hardness and high strength martensitic structure. Commonly used quenching media include water, oil and salt water. Water has a fast cooling speed and is suitable for roller chains with simple shapes and small sizes; oil has a relatively slow cooling speed and is suitable for roller chains with complex shapes and large sizes.
(II) Tempering
Tempering is a process of reheating the quenched roller chain to a certain temperature (usually below Ac1), keeping it warm, and then cooling it. Its purpose is to eliminate the internal stress generated during the quenching process, adjust the hardness, and improve toughness. According to the tempering temperature, it can be divided into low-temperature tempering (150℃-250℃), medium-temperature tempering (350℃-500℃) and high-temperature tempering (500℃-650℃). Low-temperature tempering can obtain tempered martensite structure with high hardness and good toughness; medium-temperature tempering can obtain tempered troostite structure with high yield strength and good plasticity and toughness; high-temperature tempering can obtain tempered troostite structure with good comprehensive mechanical properties.

2. Carburizing process
Carburizing is to make carbon atoms penetrate into the surface of the roller chain to form a high-carbon carburized layer, thereby improving the surface hardness and wear resistance, while the core still maintains the toughness of low-carbon steel. Carburizing processes include solid carburizing, gas carburizing and liquid carburizing. Among them, gas carburizing is the most widely used. By placing the roller chain in a carburizing atmosphere, carbon atoms are infiltrated into the surface at a certain temperature and time. After carburizing, quenching and low-temperature tempering are usually required to further improve the surface hardness and wear resistance.

3. Nitriding process
Nitriding is to infiltrate nitrogen atoms into the surface of the roller chain to form nitrides, thereby improving the surface hardness, wear resistance and fatigue strength. The nitriding process includes gas nitriding, ion nitriding and liquid nitriding. Gas nitriding is to place the roller chain in a nitrogen-containing atmosphere, and at a certain temperature and time, allow nitrogen atoms to infiltrate the surface. The roller chain after nitriding has high surface hardness, good wear resistance, and small deformation, which is suitable for roller chains with complex shapes.

4. Carbonitriding process
Carbonitriding is to infiltrate carbon and nitrogen into the surface of the roller chain at the same time to form carbonitrides, thereby improving the surface hardness, wear resistance and fatigue strength. The carbonitriding process includes gas carbonitriding and liquid carbonitriding. Gas carbonitriding is to place the roller chain in an atmosphere containing carbon and nitrogen, and at a certain temperature and time, allow carbon and nitrogen to infiltrate the surface at the same time. The roller chain after carbonitriding has high surface hardness, good wear resistance, and good anti-bite performance.

5. Annealing process
Annealing is a process in which the roller chain is heated to a certain temperature (usually 30-50℃ above Ac3), kept warm for a certain period of time, slowly cooled to below 500℃ with the furnace, and then cooled in the air. Its purpose is to reduce hardness, improve plasticity and toughness, and facilitate processing and subsequent heat treatment. The roller chain after annealing has uniform structure and moderate hardness, which can improve cutting performance.

6. Normalizing process
Normalizing is a process in which the roller chain is heated to a certain temperature (usually above Ac3 or Acm), kept warm, taken out of the furnace and cooled in the air. Its purpose is to refine the grains, make the structure uniform, improve hardness and strength, and improve cutting performance. The roller chain after normalizing has uniform structure and moderate hardness, which can be used as the final heat treatment or as a preliminary heat treatment.

7. Aging treatment process
Aging treatment is a process in which the roller chain is heated to a certain temperature, kept warm for a certain period of time, and then cooled. Its purpose is to eliminate residual stress, stabilize the size, and improve strength and hardness. Aging treatment is divided into natural aging and artificial aging. Natural aging is to place the roller chain at room temperature or natural conditions for a long time to gradually eliminate its residual stress; artificial aging is to heat the roller chain to a higher temperature and perform aging treatment in a shorter time.

8. Surface quenching process
Surface quenching is a process of heating the surface of the roller chain to a certain temperature and cooling it rapidly. Its purpose is to improve the surface hardness and wear resistance, while the core still maintains good toughness. Surface quenching processes include induction heating surface quenching, flame heating surface quenching, and electric contact heating surface quenching. Induction heating surface quenching uses the heat generated by the induced current to heat the surface of the roller chain, which has the advantages of fast heating speed, good quenching quality, and small deformation.

9. Surface strengthening process
The surface strengthening process is to form a strengthening layer with special properties on the surface of the roller chain through physical or chemical methods, thereby improving the surface hardness, wear resistance and fatigue strength. Common surface strengthening processes include shot peening, rolling strengthening, metal infiltration strengthening, etc. Shot peening is to use high-speed shot to impact the surface of the roller chain, so that residual compressive stress is generated on the surface, thereby improving fatigue strength; rolling strengthening is to use rolling tools to roll the surface of the roller chain, so that the surface produces plastic deformation, thereby improving surface hardness and wear resistance.

10. Boriding process
Boriding is to infiltrate boron atoms into the surface of the roller chain to form borides, thereby improving surface hardness and wear resistance. Boriding processes include gas boriding and liquid boriding. Gas boriding is to place the roller chain in a boron-containing atmosphere, and at a certain temperature and time, allow boron atoms to infiltrate the surface. The roller chain after boriding has high surface hardness, good wear resistance, and good anti-bite performance.

11. Composite secondary quenching heat treatment process
Compound secondary quenching heat treatment is an advanced heat treatment process, which significantly improves the performance of roller chains through two quenching and tempering processes. This process usually includes the following steps:
(I) First quenching
The roller chain is heated to a higher temperature (usually higher than the conventional quenching temperature) to completely austenitize its internal structure, and then rapidly cooled to form a martensitic structure. The purpose of this step is to improve the hardness and strength of the roller chain.
(II) First tempering
The roller chain after the first quenching is heated to a medium temperature (usually between 300℃-500℃), kept warm for a certain period of time and then cooled. The purpose of this step is to eliminate the internal stress generated during the quenching process, while adjusting the hardness and improving the toughness.
(III) Second quenching
The roller chain after the first tempering is heated again to a higher temperature, but slightly lower than the first quenching temperature, and then rapidly cooled. The purpose of this step is to further refine the martensitic structure and improve the hardness and wear resistance of the roller chain.
(IV) Second tempering
The roller chain after the second quenching is heated to a lower temperature (usually between 150℃-250℃), kept warm for a certain period of time and then cooled. The purpose of this step is to further eliminate internal stress, stabilize the size, and maintain high hardness and wear resistance.

12. Liquid carburizing process
Liquid carburizing is a special carburizing process that allows carbon atoms to penetrate the surface by immersing the roller chain in a liquid carburizing medium. This process has the advantages of fast carburizing speed, uniform carburizing layer, and good controllability. It is suitable for roller chains with complex shapes and high dimensional accuracy requirements. After liquid carburizing, quenching and low-temperature tempering are usually required to further improve the surface hardness and wear resistance.

13. Hardening process
Hardening refers to improving the hardness and wear resistance by improving the internal structure of the roller chain. The specific steps are as follows:
(I) Heating
The roller chain is heated to the hardening temperature to dissolve and diffuse elements such as carbon and nitrogen in the chain.
(ii) Insulation
After reaching the hardening temperature, keep a certain insulation time to make the elements diffuse evenly and form a solid solution.
(iii) Cooling
Quickly cool the chain, the solid solution will form a fine grain structure, improve the hardness and wear resistance.

14. Metal Infiltration Process
The metal infiltration process is to infiltrate metal elements into the surface of the roller chain to form metal compounds, thereby improving the surface hardness and wear resistance. Common metal infiltration processes include chromization and vanadium infiltration. The chromization process is to place the roller chain in a chromium-containing atmosphere, and at a certain temperature and time, chromium atoms infiltrate the surface to form chromium compounds, thereby improving the surface hardness and wear resistance.

15. Aluminization Process
The aluminization process is to infiltrate aluminum atoms into the surface of the roller chain to form aluminum compounds, thereby improving the surface’s oxidation resistance and corrosion resistance. Aluminization processes include gas aluminization and liquid aluminization. Gas aluminization is to place the roller chain in an aluminum-containing atmosphere, and at a certain temperature and time, aluminum atoms infiltrate the surface. The surface of the roller chain after aluminum infiltration has good oxidation resistance and corrosion resistance, and is suitable for use in high temperature and corrosive environments.

16. Copper infiltration process
The copper infiltration process is to infiltrate copper atoms into the surface of the roller chain to form copper compounds, thereby improving the surface wear resistance and anti-bite performance. The copper infiltration process includes gas copper infiltration and liquid copper infiltration. Gas copper infiltration is to place the roller chain in a copper-containing atmosphere, and at a certain temperature and time, copper atoms are infiltrated into the surface. The surface of the roller chain after copper infiltration has good wear resistance and anti-bite performance, and is suitable for use under high-speed and heavy-load conditions.

17. Titanium infiltration process
The titanium infiltration process is to infiltrate titanium atoms into the surface of the roller chain to form titanium compounds, thereby improving the surface hardness and wear resistance. The titanium infiltration process includes gas titanium infiltration and liquid titanium infiltration. Gas titanium infiltration is to place the roller chain in a titanium-containing atmosphere, and at a certain temperature and time, titanium atoms are infiltrated into the surface. The surface of the roller chain after titanium infiltration has good hardness and wear resistance, and is suitable for working conditions with high hardness and high wear resistance requirements.

18. Cobalting process
The cobalting process is to infiltrate cobalt atoms into the surface of the roller chain to form cobalt compounds, thereby improving the hardness and wear resistance of the surface. The cobalting process includes gas cobalting and liquid cobalting. Gas cobalting is to place the roller chain in a cobalt-containing atmosphere, and at a certain temperature and time, cobalt atoms are infiltrated into the surface. The roller chain surface after cobalting has good hardness and wear resistance, and is suitable for working conditions with high hardness and high wear resistance requirements.

19. Zirconization process
The zirconization process is to infiltrate zirconium atoms into the surface of the roller chain to form zirconium compounds, thereby improving the hardness and wear resistance of the surface. The zirconization process includes gas zirconization and liquid zirconization. Gas zirconization is to place the roller chain in a zirconium-containing atmosphere, and at a certain temperature and time, zirconium atoms are infiltrated into the surface. The roller chain surface after zirconization has good hardness and wear resistance, and is suitable for working conditions with high hardness and high wear resistance requirements.

20. Molybdenum infiltration process
The molybdenum infiltration process is to infiltrate molybdenum atoms into the surface of the roller chain to form molybdenum compounds, thereby improving the hardness and wear resistance of the surface. The molybdenum infiltration process includes gas molybdenum infiltration and liquid molybdenum infiltration. Gas molybdenum infiltration is to place the roller chain in a molybdenum-containing atmosphere, and at a certain temperature and time, allow molybdenum atoms to infiltrate the surface. The surface of the roller chain after molybdenum infiltration has good hardness and wear resistance, and is suitable for working conditions requiring high hardness and high wear resistance.