456A Metallurgy & Heat Treatment

Question 1

What is the carbon equivalent (CE) formula used in Canada (IIW formula) for assessing the weldability of carbon-manganese steels?

Accepted Answer

CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

Answer

CE = C + Mn/4 + Si/4

Answer

CE = C + (Mn+Si)/6 + (Cr+Ni)/10

Answer

CE = C × (1 + Mn/6) × (1 + Cr/5)

Question 2

What microstructural phase forms in carbon steel when austenite is cooled extremely rapidly (quenched)?

Accepted Answer

Martensite

Answer

Pearlite

Answer

Bainite

Answer

Ferrite

Question 3

What is the purpose of 'tempering' a hardened steel weld or HAZ?

Accepted Answer

Reheating the hardened zone to a temperature below the lower critical temperature to reduce brittleness while maintaining hardness

Answer

Rapidly cooling the steel to lock in a hard martensitic structure

Answer

Heating steel above the upper critical temperature to dissolve carbides

Answer

Normalizing the steel by air cooling from above the critical temperature

Question 4

What is the 'heat-affected zone' (HAZ) in a weld and why is it often the weakest area of a welded joint?

Accepted Answer

The area adjacent to the fusion line that experienced elevated temperatures during welding; it can contain coarse grains, martensite, or soft zones depending on the steel and cooling rate

Answer

The weld metal itself, which has lower strength than the base metal

Answer

The zone where the weld reinforcement meets the base metal surface

Answer

The area preheated before welding to prevent cold cracking

Question 5

What is 'hot cracking' (solidification cracking) in welds and which elements in steel promote it?

Accepted Answer

Cracking during weld metal solidification; promoted by high sulfur, phosphorus, and low melting point impurities that form liquid films at grain boundaries

Answer

Cracking after complete solidification due to residual stresses; promoted by high carbon

Answer

Cracking during preheat application; promoted by high manganese

Answer

Cracking during PWHT; promoted by high chromium

Question 6

What is 'lamellar tearing' and in what type of steel joint configuration does it occur?

Accepted Answer

Subsurface cracking parallel to the plate surface caused by through-thickness tensile stresses acting on non-metallic inclusions; occurs in T-joints and corner joints with through-thickness loading

Answer

Surface cracking along the weld toe caused by fatigue loading

Answer

Intergranular cracking in the HAZ of hardenable steels

Answer

Root cracking in groove welds caused by hydrogen