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Heat treatment and processing properties of SCM415H steel
The standard heat treatment process for SCM415H, a carburizing steel, is as follows:
**Preliminary Heat Treatment—Normalizing or Annealing:** Heat to 880~920℃, hold, then air cool (normalizing) or slow furnace cooling (annealing). The purpose is to homogenize the microstructure, eliminate forging banding segregation, reduce hardness to ≤179 HB for easier machining, and refine the grain size, providing fine primary austenite grains for subsequent carburizing (intrinsically fine-grained steel, grain size ≥5).
**Carburizing:** Gas carburizing is typically performed at 920~940℃, controlling the surface carbon potential at 0.75%~0.90%. The carburizing time is calculated based on the target hardened layer depth (typically 0.6~1.2 mm effective hardened layer). For deformation-sensitive parts, carbonitriding (830~880℃) can be used to shorten the time and reduce deformation.
SCM415H steel quenching:
Direct quenching: After carburizing, pre-cool to 830~860℃ and directly oil quench. Suitable for applications with fine grains and permissible deformation.
Reheat quenching: After carburizing, air cool/slow cool, then reheat to 800~840℃ for oil quenching or high-pressure gas quenching. This method better controls deformation and microstructure and is the mainstream practice for mass-produced precision gears.
Low-temperature tempering: Hold at 150~200℃ for 1.5~2 hours, then air cool. This eliminates quenching stress, reduces brittleness, and maintains a surface hardness above 58 HRC. Avoid prolonged tempering at 250~400℃ to prevent a significant decrease in surface hardness.
Supplementary tempering (after grinding): After precision grinding, stress-relief tempering at 120~160℃ can be performed to prevent grinding burns and cracks.
Important points to note: The carburizing temperature is relatively high (around 930℃). It is essential to confirm that the material's inherent fine grain size meets the requirements (Al deoxidized fine-grained steel). Otherwise, coarse grains will make the carburized layer brittle and significantly reduce the impact value. Additionally, carburized parts should be tempered promptly after quenching and should not be left untempered for extended periods to prevent delayed cracking.
**Preliminary Heat Treatment—Normalizing or Annealing:** Heat to 880~920℃, hold, then air cool (normalizing) or slow furnace cooling (annealing). The purpose is to homogenize the microstructure, eliminate forging banding segregation, reduce hardness to ≤179 HB for easier machining, and refine the grain size, providing fine primary austenite grains for subsequent carburizing (intrinsically fine-grained steel, grain size ≥5).
**Carburizing:** Gas carburizing is typically performed at 920~940℃, controlling the surface carbon potential at 0.75%~0.90%. The carburizing time is calculated based on the target hardened layer depth (typically 0.6~1.2 mm effective hardened layer). For deformation-sensitive parts, carbonitriding (830~880℃) can be used to shorten the time and reduce deformation.
SCM415H steel quenching:
Direct quenching: After carburizing, pre-cool to 830~860℃ and directly oil quench. Suitable for applications with fine grains and permissible deformation.
Reheat quenching: After carburizing, air cool/slow cool, then reheat to 800~840℃ for oil quenching or high-pressure gas quenching. This method better controls deformation and microstructure and is the mainstream practice for mass-produced precision gears.
Low-temperature tempering: Hold at 150~200℃ for 1.5~2 hours, then air cool. This eliminates quenching stress, reduces brittleness, and maintains a surface hardness above 58 HRC. Avoid prolonged tempering at 250~400℃ to prevent a significant decrease in surface hardness.
Supplementary tempering (after grinding): After precision grinding, stress-relief tempering at 120~160℃ can be performed to prevent grinding burns and cracks.
Important points to note: The carburizing temperature is relatively high (around 930℃). It is essential to confirm that the material's inherent fine grain size meets the requirements (Al deoxidized fine-grained steel). Otherwise, coarse grains will make the carburized layer brittle and significantly reduce the impact value. Additionally, carburized parts should be tempered promptly after quenching and should not be left untempered for extended periods to prevent delayed cracking.
