Crystal lattices
The lattice is not decorative theory. It determines the number of slip systems, dislocation mobility, diffusion of interstitial atoms, transformation stresses and therefore the behaviour of weld metal and the HAZ.
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The lattice is not decorative theory. It determines the number of slip systems, dislocation mobility, diffusion of interstitial atoms, transformation stresses and therefore the behaviour of weld metal and the HAZ.
Plastic slip is not initiated by nominal tensile stress alone, but by the resolved shear component on a specific slip plane and in a specific slip direction. Texture, grain orientation and the dendritic structure of weld metal therefore change local plasticity.
A smaller grain size generally increases yield strength because grain boundaries impede dislocations. A coarse-grained HAZ has the opposite problem: lower toughness and greater susceptibility to brittle fracture.
Hydrogen is a highly mobile interstitial element. It is particularly dangerous in the combined presence of martensite, tensile stress and traps at grain boundaries or inclusions.
What the module covers
- Crystal lattices, slip systems and atomic defects
- Why a welding engineer needs this
- Schmid’s law
- Hall–Petch
- Hydrogen in the lattice
- Dislocations and strengthening
- 1 Slip plane + slip direction
- 2 Twinning
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