Physical Properties of Materials
Heat conduction, expansion, melting point, electrical and magnetic properties
AI generated Every material brings its own physical quirks: heat conduction, expansion, melting point, electrical and magnetic properties. They determine how a metal distorts during , how much heat it conducts away, and whether it can be magnetized. Knowing these helps you avoid distortion, arc blow, and weld defects.
Besides strength and microstructure, every material brings physical properties that often cause more trouble in than strength does. You should know the four most important ones.
Thermal conductivity. It tells you how fast a metal conducts away the heat you put in. Aluminum and copper conduct heat excellently — that's why you need much more power there just to keep a weld pool, and the heat dissipates into the part in a flash. Steel and especially stainless steel conduct noticeably worse; there the heat builds up, and distortion happens faster.
Thermal expansion. Metals expand when heated and contract when cooled. The for (stainless steel) is almost twice that of . That's why stainless steel distorts much more during than structural steel — and why you need to tack more, preheat, and plan the welding sequence with stainless.
Melting point & . Pure metals melt at one temperature, alloys over a range. The determines how mushy the weld pool gets and how prone it is to (more on that in the article Solidification of the Melt).
Electrical & magnetic properties. Electrical conductivity affects the and current flow; magnetic properties influence arc blow — the deflection of the by magnetic fields. Ferritic steels are magnetic, austenitic stainless steels are not. When DC welding thick ferritic parts, can push the sideways.
These four properties are interrelated and explain typical workshop problems:
• Distortion in stainless steel: high expansion + poor heat conduction → heat builds up locally → strong shrinkage.
• Cold aluminum welds: high heat conduction → the part draws heat away before the weld pool properly melts.
• Arc blow: magnetic fields on thick, magnetizable parts deflect the .
The remedies are always the same: apply heat where it's needed, control distortion with tack welds and weld sequence, and for arc blow switch polarity or welding direction.