Application of muffle furnace tempering in metal materials

The application of muffle furnace tempering in the field of metal materials is extensive and critical, mainly covering materials such as steel, high-speed steel, cold work die steel, gear steel, spring steel, etc. By precisely controlling the tempering temperature and process, the mechanical properties and service life of materials can be significantly optimized. The following are specific application scenarios and effects:

1. Steel materials: Refine grain size and enhance overall performance
Normalization treatment
Heat the steel above the critical temperature (Ac3 or Accm), keep it warm, and then air cool it. This process can refine grain size, eliminate network carbides, and improve machinability. For example, after normalizing, the hardness of medium carbon steel decreases to HB180-220, making it easier for subsequent mechanical processing.
Tempering adjustment
After quenching, steel needs to be tempered to eliminate internal stress and adjust its structure. For example, after quenching, the hardness of 45 steel reaches HRC50-55, but it is brittle; After low-temperature tempering at 200 ℃, the hardness decreased to HRC45-50 and the toughness significantly improved, making it suitable for shaft parts.

2. High speed steel: balanced hardness and red hardness
Typical process
High speed steel (such as W18Cr4V) needs to be quenched at 1260 ℃ and tempered three times at 560 ℃. During the tempering process, martensite decomposes into tempered martensite and carbides, with a hardness of HRC67. At the same time, the red hardness (at 600 ℃) remains HRC52, ensuring that the cutting performance of the tool can still be maintained at high temperatures.
Effect Comparison
Untrained high-speed steel has a high hardness (HRC68 or higher), but it is extremely brittle and prone to blade breakage; After tempering, the toughness is increased by 30% and the service life is extended to more than twice the original.

3. Cold work die steel: optimizing surface and core properties
Low temperature tempering
Cold work die steel (such as Cr12MoV) undergoes quenching at 1020 ℃ and low-temperature tempering at 200 ℃, resulting in a surface hardness of HRC60-62 and a core toughness of HRC35-40. This process greatly increases the stamping frequency of the mold and extends its lifespan by multiple times.
Cryogenic treatment assistance
Some processes add -196 ℃ liquid nitrogen cryogenic treatment for 2 hours before tempering, which promotes the transformation of residual austenite into martensite, further increases the hardness by HRC1-2, and further enhances the wear resistance.

4. Gear steel: Improving contact fatigue life
Carburizing quenching+tempering
Gear steel (such as 20CrMnTi) undergoes carburizing at 860 ℃, pre cooling at 200 ℃, oil quenching, and tempering at 180 ℃, resulting in a surface hardness of HRC58-62 and a core hardness of HRC35-42. The tempering process eliminates quenching stress and homogenizes the microstructure of the carburized layer, resulting in longer bending fatigue life and meeting high load transmission requirements.
Comparison effect
Although the surface hardness of gears that have not been tempered is high, their contact fatigue life is short and they are prone to pitting corrosion; After tempering, the lifespan is increased by multiple times, significantly improving transmission reliability.

5. Spring steel: strengthening elasticity and tensile properties
Medium temperature tempering
Spring steel (such as 60Si2Mn) undergoes quenching at 870 ℃ and tempering at 450 ℃, resulting in higher tensile strength and greater elastic limit. The tempering process forms a tempered martensite structure, balancing high strength and good elasticity, suitable for automotive suspension springs.
performance advantage
Compared to untempered spring steel, tempered springs are less prone to fracture and have an extended service life when subjected to dynamic loads.

6. Process optimization direction
Gradient tempering
For complex shaped parts, segmented tempering is adopted, such as first low-temperature tempering at 200 ℃ to eliminate surface stress, and then medium temperature tempering at 400 ℃ to adjust the core structure and avoid cracking.
atmosphere control
Temper under vacuum or inert gas (such as N ₂) protection to prevent metal oxidation and decarburization.
Intelligent control
Adopting an intelligent muffle furnace, the temperature fluctuation is controlled within ± 1 ℃ through PID algorithm to ensure the repeatability of tempering process and improve the yield of finished products.