welding effects/defects

Question 1

why residual stresses made?

Answer 1

high thermal gradients and solidification shrinkage of weldpool. relieved by local plastic deformation or cracking

Question 2

welding defects list?

Answer 2

undercutting, surface defects. penetration, lack of fusion, inclusions, porosity, hot cracking

Question 3

undercutting?

Answer 3

burning of side walls of joint, or reduction in thickness at connection. weaken jiont by reducing CSA. stress concentration points.

Question 4

penetration (welding defect)?

Answer 4

lack of penetration -> lack of strength

Question 5

lack of fusion in welding?

Answer 5

failure to fuse adjacent layers. caused by failure to raise metal to MP, lack of heat energy, or insulating layer of oxide

Question 6

inclusions, weld defect?

Answer 6

slag or other stuff entrapped in weld metal (slag, bad preparation, mill scale, atmospheric contamination)

Question 7

porosity weld defect?

Answer 7

groups of small cavities caused by gaps entrapped in weld. could be large cavities, called blown holes.

Question 8

heat treatments of steel examples?

Answer 8

annealing, normalising, quenching/tempering

Question 9

zones of weld (microstructure)?

Answer 9

fusion zone (quenching, loss of alloying elements)
overheated zone (1100-1150deg, grain coarsening)
annealed zone (900deg, refined structure)
transformation zone (720-910deg, recrystallization in alpha gamma region)