Heat treatment of ferrous metals

Question 1

Define annealing

Answer 1

Heating to proper temperature then slowly cooling it down.
- Reduces internal stress,
- Produces a coarse grain structure = Soft and ductile
- Improves toughness

Question 2

Define Quenching

Answer 2

Quenching is the rapid cooling of a workpiece in water, gas, oil, polymer, air, or other fluids to obtain certain material properties. It produces very fine grains and martensite, increasing hardness but reducing toughness.

Question 3

Define normalising

Answer 3

A high temperature austenitizing heating cycle followed by cooling in still or agitated air. It also produces uniform and refined grains by air cooling.

Question 4

Define Hardening

Answer 4

Heating a metal then putting it in water, this allows the metal object from the high temperature at which it has been shaped.

Question 5

Define Tempering

Answer 5

Heating the metal to some temperature below the critical point for a certain period of time, then allowing it to cool in still air.

Question 6

What changes in the properties of steel after heat treatments?

Answer 6

The heat treatment develops hardness, softness, and improves the mechanical properties such as tensile strength, yield strength, ductility, corrosion resistance and creep rupture.

Question 7

What are the changes in properties of ferrous metals?

Answer 7

The changes include mechanical strength and electrical conductivity to alternations in magnetic behaviour and corrosion resistance.

Question 8

Low carbon’s microstructure after annealing

Answer 8

In this paper, a simple modified process is introduced to improve the mechanical properties of plain low carbon steel. The plain low carbon steel sheet with mainly ferrite and minor amount of pearlite starting microstructure was simply cold-rolled to a reduction of 50% and subsequently intercritical annealed at various temperatures. (a) as-received, (b) 50% cold-rolled (c) intercritical annealed at 750°C, (d) intercritical annealed at 800°C and (e) intercritical annealed at 850°C for 5 min. Observed from transverse direction.

Question 9

Mild Carbon steel’s microstructure after annealing.

Answer 9

Atoms migrate in the crystal lattice and the number of dislocations decreases, leading to a change in ductility and hardness.

Question 10

High Carbon steel’s microstructure after annealing.

Answer 10

Annealing refines the grain structure of high carbon steel, resulting in more uniform and consistent properties

Question 11

Different microstructures for Low/Mild & High Carbon steel.

Answer 11

Shows some microstructures for various steels.

Question 12

Normalised Mild carbon steel microstructure

Answer 12

The steel is first heated until it completely transforms to austenite. Followed by air-cooling at about 100 °F (38 °C) per minute

Question 13

Normalising grain structure

Answer 13

Normalising involves heating a steel up into the austenite region well above the UCT.

Question 14

Induction hardening process

Answer 14

This process uses a high-frequency alternating current to rapidly heat the outer surface of the wheel. The wheel is then quenched, forming martensite at the surface.

Question 15

What is the effect of grain structure on the hardening process?

Answer 15

The surface has a fine martensite grains which improves hardness and wear-resistant.

Question 18

Tempering microstructure of low carbon steel

Answer 18

Martensitic blocks became coarser and dislocation annihilation continuously took place during tempering process.

Question 19

Tempering microstructure of mild carbon steel

Question 20

Tempering microstructure of high carbon steel