Question 1

What is the difference between tensile strength and yield strength?

Accepted Answer

Yield strength is the stress at which permanent deformation begins — it is the design limit for most structural applications with a safety factor of 1.5-3×. Tensile strength (UTS) is the maximum stress the material can sustain before necking and fracture. Design to yield; tensile strength provides a safety margin beyond yield.

Question 2

How does heat treatment affect material properties?

Accepted Answer

Heat treatment can dramatically change mechanical properties without altering composition. AISI 4140 steel ranges from 655 MPa tensile (annealed) to 1720 MPa (quenched & tempered at 205°C). Hardening increases strength but reduces ductility and toughness. The optimal treatment depends on the application requirements.