The key difference between pearlite and bainite is that the pearlite contains alternating layers of ferrite and cementite whereas the bainite has a plate-like microstructure.
The names pearlite and bainite refer to two different microstructures of steel. These structures form when we make changes to austenite by changing the temperature accordingly. Let us discuss the further differences between pearlite and bainite.
CONTENTS
1. Overview and Key Difference
2. What is Pearlite
3. What is Bainite
4. Side by Side Comparison – Pearlite vs Bainite in Tabular Form
5. Summary
What is Pearlite?
Pearlite is a type of microstructure in steel having a two-layered phase of alternating layers of ferrite and cementite. Ferrite and cementite are two different allotropes of iron. This microstructure occurs in steel and cast iron. When we cool the steel slowly, this microstructure forms via a eutectoid reaction (a three-phase reaction by which, on cooling, a solid transform into two other solid phases at the same time). This is because, during the slow cooling, austenite cools below its eutectoid temperature (727 °C).
Figure 01: Pearlite Structure
Steels with the pearlite microstructure have a eutectoid composition of iron and carbon. Therefore, the steels having either pearlite or near-pearlite microstructures can be easily drawn into thin wires. Most of the times, these wires are bundled together so that the sellers can sell them as piano wires and ropes for suspension bridges.
What is Bainite?
Bainite is a type of microstructure in steel that has a plate-like structure. This structure forms when the steel is at around 125–550 °C. Furthermore, it also forms when austenite cools until it passes a temperature at which austenite structure is no longer stable (thermodynamically unstable) when compared with ferrite or cementite.
Figure 02: Bainite Structure
The bainite structure mainly consists of cementite and ferrite, and this ferrite is rich with dislocations. Therefore, this large density of dislocations in ferrite makes it hard.
What is the Difference Between Pearlite and Bainite?
Pearlite is a type of microstructure in steel that has a two-layered phase of alternating layers of ferrite and cementite. It forms when austenite cools below its eutectoid temperature (727 °C). Moreover, this structure occurs in steel and cast iron. On the other hand, Bainite is a type of microstructure in steel that has a plate-like structure. The structure is the main difference between pearlite and bainite. Furthermore, bainite forms when austenite cools: until it passes a temperature at which austenite structure is no longer stable (thermodynamically unstable). In addition, this structure also occurs in steel.
Summary – Pearlite vs Bainite
Pearlite and Bainite are two main microstructures in steel. The difference between pearlite and bainite is that the pearlite contains alternating layers of ferrite and cementite whereas the bainite has a plate-like microstructure.
Reference:
1. “Pearlite.” Wikipedia, Wikimedia Foundation, 5 July 2018. Available here
2. “Bainite.” Wikipedia, Wikimedia Foundation, 3 July 2018. Available here
Image Courtesy:
1.’Pearlite’By Michelshock – McGill University, (Public Domain) via Commons Wikimedia
2.’Dqsk-steel-bainitic-weld-tem-image’By J. Horton. (Public Domain) via Commons Wikimedia