Quenched and tempered steel
Quenched and tempered steel is a special type of high-quality engineering steel that undergoes a two-stage heat treatment process – quenching followed by tempering. The purpose of this process is to achieve high core strength, good toughness, a uniform microstructure, and to prevent internal stresses.
These steels are among the most commonly used materials in engineering, as they combine durability, elasticity, strength, and good machinability in the delivery condition.
⚙️ Properties
High strength and toughness after heat treatment
Excellent hardenability (also suitable for more massive parts)
Good machinability in the soft-annealed condition
Resistance to material fatigue
Achievable strength up to 1000–1400 MPa
Dimensional stability after proper processing
Suitable for dynamically loaded parts
🧩 Applications
Shafts, pins, axles, bolts and studs
Piston rods, hydraulic components
Gears, pinions, clutch parts
Flywheels, rotors, spindles
Dynamically loaded machine components
Parts for mining, agricultural and transport machinery
🔥 Heat Treatment (Approximate Values)
| Process | Temperature | Cooling | Structure | Purpose |
|---|---|---|---|---|
| Soft annealing | 680–750 °C | slow cooling in air / furnace | ferrite + pearlite | softening of the material, improved machinability |
| Recrystallization annealing | 550–650 °C | air | recrystallized ferrite | removal of work hardening after cold forming |
| Normalizing | 840–950 °C | air | fine-grained pearlite + ferrite | structure homogenization, grain refinement |
| Homogenization annealing | 1100–1200 °C | furnace | uniform structure | removal of segregation in forgings |
| Quenching | 800–900 °C (depending on steel grade) | oil / water / polymer / air | martensite | increase in hardness and strength |
| Low tempering | 150–250 °C | air | tempered martensite | stabilization after quenching, high hardness |
| Medium tempering | 300–450 °C | air | tempered martensite | balanced ratio of hardness and toughness |
| High tempering | 500–650 °C | air | tempered martensite | strength + toughness (quenching and tempering) |
| Quenching and tempering (quenching + high tempering) | 800–900 °C + 500–650 °C | oil → air | tempered martensite | strength 900–1400 MPa, tough core |
| Nitriding | 480–580 °C | gas / plasma nitriding | Fe + Al/Cr/Mo nitrides | extremely hard surface 900–1200 HV |
| Carbonitriding (case hardening) | 880–940 °C | oil / water | martensitic surface | hard surface + tough core |
| Post-weld tempering | 530–650 °C | air | ferrite + pearlite (stable) | removal of internal stresses |
🧠 Interesting fact
During the heat treatment of steel, a structure called martensite is formed during quenching – it is so hard that it could often be used to cut other steels.
At the same time, it is so brittle that without tempering, it could crack even under a strong hammer impact.
