Hear treatments of steel

1. Obtain specific values of mechanical properties

2. Can be done for Strengthening Purposes (converting structure to martensite)

3. Can be done for Strengthening Purposes (converting structure to martensite)

4. Heat Treating – defined as the controlled heating and cooling of metals for the primary purpose of altering their properties (strength, ductility, hardness, toughness, machinability, etc)

5. Tempering

5.1. Theoretical Background

5.2. LOW TEMPERING

5.2.1. 150÷250 oC (High carbon steel); microstructure: Tempered martensite (60 HRC) • High wear-resistance Ex: wood cutting tool, cold-working die, Piston pin, cam shaft, gear..

5.3. MED TEMPERING

5.3.1. • 300÷450 oC. • Microstructure: Troostit with highest elastic modulus. • For elastic steel 0.5~0.7%C Ex: spring..

5.4. HIGH TEMPERING

5.4.1. • 300÷450 °C • Microstructure: Troostit with highest elastic modulus. • For elastic steel 0.5~0.7%C Ex: spring..

5.5. EMPERING OF STEEL is a process in which previously hardened or normalized steel is usually heated to a temperature below the lower critical temperature and cooled at a suitable rate.

5.6. Increase ductility and toughness , relieve quenching stresses and to ensure dimensional stability.

6. Quenching

6.1. Some Quenching Media

6.1.1. -Water: +Hot water(40-60)°C +Normal water(25-30)°C +Cold water(5-15)°C

6.1.2. -Naoh or water solution

6.1.3. Oils

6.1.4. Gas/air

6.1.5. Molten salt

6.1.6. Emulsion:Oil+water

6.1.7. Liquid Nitrogen

6.2. Temperature

6.2.1. +Hypo-eutectoid and Eutectoid (100% γ): tquenching = Ac3+ (30~50)°C

6.2.2. + Hyper-eutectoid (γ+CeII): tquenching = Ac1+ (30~50)°C

6.3. Increasing hardness, strength, or toughness while minimizing residual stress, distortion, and the possibility of cracking

6.4. QUENCHING refers to the process of rapidly cooling metal parts from the austenite or solution treating temperature.