What are the different types of tempering?

Tempering is an essential secondary heat treatment process after steel quenching, designed to eliminate quenching residual stress, reduce material brittleness, adjust hardness and toughness balance and stabilize workpiece size. According to different heating temperature ranges, mechanical property adjustment goals and industrial usage scenarios, industrial tempering is strictly divided into three standard types: low-temperature tempering, medium-temperature tempering and high-temperature tempering. Each type corresponds to exclusive temperature parameters, material performance changes and applicable workpieces, and cannot be replaced mutually in industrial production.

Low-temperature tempering (150°C – 250°C) is mainly used for high-hardness, high-wear-resistant precision parts. After quenching, tool steel, mold steel, bearing steel and precision gear parts retain ultra-high hardness but carry huge internal stress and brittleness. Low-temperature tempering removes partial quenching stress while basically maintaining the high hardness of quenched steel. Workpieces after treatment feature high surface hardness, strong wear resistance and stable dimensional accuracy, effectively preventing tiny deformation and cracking during long-term service. This tempering type is widely used for cutting tools, measuring tools, precision molds and bearing components that require strict size stability and wear resistance.

Medium-temperature tempering (350°C – 500°C) focuses on balancing hardness and elasticity. After medium-temperature tempering, steel obtains excellent elastic performance and appropriate hardness, effectively avoiding brittle fracture under alternating load. The internal residual stress is fully released, and the material microstructure is optimized to form stable tempered troostite structure. This tempering process is the standard treatment for elastic components in machinery and automotive industries, including various industrial springs, spring steel parts, clutch components and vibration-resistant mechanical parts. Parts treated by medium tempering have strong fatigue resistance and long service life under repeated compression and stretching conditions.

High-temperature tempering (500°C – 650°C) is matched with quenching process to form the classic "quenching and tempering treatment". High-temperature tempering completely eliminates quenching residual stress, greatly improves steel toughness and plasticity, and reduces hardness moderately. The material forms uniform tempered sorbite microstructure, achieving the best comprehensive mechanical properties with high strength, good toughness and strong impact resistance. It is the most widely used tempering type in structural steel processing, suitable for automotive shaft parts, engine components, mechanical structural parts, high-strength bolts and construction machinery accessories that bear complex impact and load forces.

In addition to the three mainstream classification standards based on temperature, tempering can also be divided into conventional air tempering, oil tempering and vacuum tempering according to heating environment. Vacuum tempering effectively avoids surface oxidation and decarbonization, ensuring smooth surface and precise size of high-precision parts. Continuous furnace tempering and batch furnace tempering are classified by production mode, adapting to mass production and small-batch customized processing respectively.

Choosing the correct tempering type is critical to final product quality. Improper tempering temperature will lead to insufficient stress relief, unqualified hardness, poor toughness or serious part deformation. Professional tempering furnaces with precise temperature zoning and programmable heating curves ensure accurate implementation of various tempering processes, helping manufacturers obtain consistent and reliable mechanical properties of steel workpieces.