Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 10: Problem 31

Cite two reasons why martensite is so hard and brittle.

Short Answer

Expert verified
Answer: The two main reasons for martensite's hardness and brittleness are: 1. Rapid cooling of austenite: Martensite forms due to rapid cooling or quenching of steel from its high-temperature phase (austenite). This process traps carbon atoms within the lattice structure, causing a highly strained and asymmetric crystalline structure. 2. Lattice structure of martensite: Martensite has a body-centered tetragonal (BCT) crystal structure, which is distorted due to the presence of trapped carbon atoms. This causes increased internal stress within the martensite crystals, making them hard and brittle.

Step by step solution

01

Reason 1: Rapid Cooling of Austenite

Martensite is a very hard and brittle crystalline structure formed during the rapid cooling or quenching of steel from its high-temperature phase called austenite. This rapid cooling does not allow the carbon atoms present in the austenite to diffuse out, thereby causing them to get trapped within the lattice structure in a supersaturated solid solution. As a result, the lattice structure is distorted, producing a highly strained and asymmetric crystalline structure which makes martensite extremely hard and brittle.
02

Reason 2: Lattice Structure of Martensite

Martensite has a body-centered tetragonal (BCT) crystal structure, unlike the face-centered cubic (FCC) structure found in austenite. This BCT structure is formed due to the presence of carbon atoms trapped in the lattice during rapid cooling. The carbon atoms cause distortion in the lattice, leading to an increased internal stress within the martensite crystals. This high stress within the lattice structure is responsible for making martensite hard and brittle. In summary, martensite's hardness and brittleness can be attributed to the rapid cooling process that traps carbon atoms within the lattice structure and the distorted body-centered tetragonal lattice structure caused by these trapped carbon atoms.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Rank the following iron-carbon alloys and associated microstructures from the hardest to the softest: (a) 0.25 wt\% C with coarse pearlite, (b) 0.80 wt\% \(C\) with spheroidite, (c) \(0.25 \mathrm{wt} \% \mathrm{C}\) with spheroidite, and (d) 0.80 wt\% C with fine pearlite. Justify this ranking.

Compute the rate of some reaction that obeys Avrami kinetics, assuming that the constants \(n\) and \(k\) have values of 2.0 and \(5 \times 10^{-4}\), respectively, for time expressed in seconds

For a eutectoid steel, describe isothermal heat treatments that would be required to yield specimens having the following Brinell hardnesses: (a) \(180 \mathrm{HB}\) (b) \(220 \mathrm{HB}\), and (c) 500 HB.

What is the driving force for the formation of spheroidite?

Cite two important differences between continuous cooling transformation diagrams for plain carbon and alloy steels.
See all solutions

Recommended explanations on Physics Textbooks

Radiation

Read Explanation

Geometrical and Physical Optics

Read Explanation

Atoms and Radioactivity

Read Explanation

Kinematics Physics

Read Explanation

Wave Optics

Read Explanation

Medical Physics

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free