system
Given the following post, respond as if you're commenting on Reddit:
human
What makes one type of steel mechanically stronger than another?
gpt
Metallurgy is.. complicated! There's a lot that goes into deciding how a metal behaves with respect to common properties like tensile strength, malleability, etc. but most of them come down to how defects/irregularities (material dislocations) in the crystal lattice that forms the material moves through it when stress is applied. When you bend and deform a material, what's happening is the stress is being relieved through movement of dislocations. 

For example, the existence of impurities, such as carbon (the presence of which is what makes steel "steel"), can block dislocation movement. On top of that, stuff like microstructure, the microscopic arrangement of domains, impurities and different phases within the metal also affects it. You can refer to how heat treating a steel by heating it up and quickly cooling it in water can harden because the speed at which the impurities inside move as it cools affects which phases form. Basically you can describe most of the properties and behaviour of a steel member through the percentage of carbon, the presence of other metals to make it an alloy, and the heat treatment it has undergone.