Slip and dislocations


Slip Steel is malleable, meaning it can be drawn or pressed into many different shapes without breaking. It is also ductile, which means that it can be drawn into bars or even thin wires without breaking. The concept of slip partially accounts for this behavior.


Picture 1
When steel bends, what actually happens is that layers of ions in the steel are slipping over other layers and then forming attractions with the ions now around them. This is why the steel bends without breaking. See Picture 1.

Dislocations The lattice structure naturally contains many defects, that is, missing ions in layers. When a force is placed on the steel, dislocations move through the lattice structure. Unlike slip, only a relatively few number of ions need to move, not an entire layer. See Picture 2.

Together, dislocation and slip account for malleability and ductility of steel.


Picture 2
Grains and dislocations Grain boundaries hinder the movement of dislocations. The more grain boundaries that exist, the more difficult it is for dislocations to move, and as a result, the steel is harder, stronger, and stiffer.

Coarse grained steel contains fewer grains and grain boundaries than fine grained steel with many more grains and boundaries. Because of this, fine-grained steel has the potential to be stronger and more ductile than coarse grained steel.

Often times, elements like vanadium are added to the mixture of steel to provide nuclei around which grains can grow. The objective of this process is to produce finer grained steel, and vanadium is well known for its ability to assist in the control of grain size.