Heat Treatment in Metallurgical and Materials Engineering

What is the purpose of martempering in hardened steel?

In the process of martempering, when does the cooling stop?

What type of microstructure is expected from the austempering process?

What is the expected hardness range after tempering tool steel from Rc65 to Rc45-55?

Which temperature is used for heating in both martempering and austempering processes?

Which process aims to achieve a microstructure with lower stresses?

What type of transformation occurs during austempering?

At what temperature does cooling stop before quenching in martempering?

Which microstructure is associated with good strength and ductility in this context?

In austempering, what is the purpose of more than critical cooling before isothermal transformation?

Heat Treatment Processes

Bulk Annealing: Heating temperature above A3 (Hypoeutectoid) or A1 (Hypereutectoid), cooling in furnace; resulting in coarse microstructure, lower strength, and higher ductility.
Normalizing: Heating temperature above A3 (Hypoeutectoid) or Acm (Hypereutectoid), cooling in air; resulting in fine microstructure, more strength, and lower ductility.
Spheroidization Annealing: Heating temperature below A1, cooling not specific; resulting in globular cementite in ferrite matrix, increasing both strength and ductility.
Stress Relief Annealing: Heating temperature below recrystallization temperature (~550°C), cooling not specific; relieving stresses developed during cold working, machining, or welding.

Hardening and Tempering

Hardening: Heating temperature above A3 (Hypoeutectoid) or A1 (Hypereutectoid), cooling rapidly; resulting in martensite, high hardness, and poor ductility.
Tempering: Heating temperature 400-500°C, cooling not specific; resulting in martensite with carbon precipitates, improving ductility at the cost of strength.

Other Heat Treatment Processes

Martempering: Heating temperature above A3 (Hypoeutectoid) or A1 (Hypereutectoid), cooling rapidly, then quenching; reducing thermal stresses in hardened steel, resulting in martensite with lower stresses.
Austempering: Heating temperature above A3 (Hypoeutectoid) or A1 (Hypereutectoid), cooling rapidly, then isothermal transformation in bainite region; resulting in bainite, good strength and ductility.

Critical Temperatures

A1: Isotherm at eutectoid alloying.
A3: Phase boundary between austenite and two-phase (austenite + ferrite).
Acm: Phase boundary between austenite and two-phase (austenite + cementite).

Test your knowledge on heat treatment processes such as bulk annealing, normalizing, surface hardening, tempering, mar tempering, and more. Explore different types of annealing techniques and thermomechanical processes. Understand holding temperatures and critical temperatures for various heat treatment methods.