Chapter 20 Questions - Chapter 20 Questions 20.1 Why are metals heat treated A Metals are heat-treated to effect metallurgical changes that beneficially

Chapter 20 Questions - Chapter 20 Questions 20.1 Why are...

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Chapter 20 Questions 20.1 Why are metals heat treated? A: Metals are heat-treated to effect metallurgical changes that beneficially alter properties. 20.2 Identify the important reasons why metals are annealed. A: (1) to control properties, (2) to reduce brittleness and improve toughness, (3) to recrystallize cold-worked metals, and (4) to relieve stresses from prior metalworking. 20.3 What is the most important heat treatment for hardening steels? A: Martensite formation by heating steel into the austenite region and quenching. 20.4 What is the mechanism by which carbon strengthens steel during heat treatment? A: When steel containing carbon is heat-treated, martensite is formed which is a hard and brittle non-equilibrium phase of steel. The extreme hardness of martensite results from the lattice strain created by carbon atoms trapped in the body-centered tetragonal structure, thus providing a barrier to slip. 20.5 What information is conveyed by the TTT curve?

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