Welding Flashcards
What is welding?
Welding topology refers to the goemetric configuration of parts joined together using a welding process. it is essentially described the way different pieces are arranged and how the welds connect them.
An heating source generate enough power to melt the edges of the two joining parts and the filler metal
What is brazing?
Brazing is a metal-joining technique that uses a filler metal with a lower metling point than the metals being joined to create a strong bond. Brazing is considered an heterogenous welding since the joint is constituted only by the filler metal.
Heterogenous welding:
It is when the filler metal used has a different composition compared to the base metals being joined.
Which zones can describe the structure of a weld?
- Melted zone: This region was completely molten, it can be a mixture of base and filler metal or made only of base metal
- Heat affected zone: is a par tof the weld shich is not molten during the weld, but its microstructure undergoes a deep change
- Base metal: the part of the weld which is exposed only to a weak heatening, not changeing so much.
What is low temperature brazing?
- Temperature is < 450 dC
- The filler metal has a lower emtling point with respect to the base metal. In this case, pieces can be welded many times. The two adjoining parts cannot be in close contact otherwise the filler metal can not enter and form the joint.
What is high temperature brazing?
- When the temperature is > 600 dC
- The alloys used as filler metla have a melting point lower with respect to the base metal buth higher with respect to the previous case.
- Typically the filler metal is a brass alloy with different melting temperature, depending on the base metal to join
What is welding with gas metling?
a combustion reaction to generate heat and melting point
What is Acelylentic torch?
An acetylene torch is a gas welding and cutting that utilizes the high temperature flame.
The heat is generated form the combustion of a mixture of oxygen and ethylene. The maximum temperature if 3200 dC.
The exothermic reaction delevopes heat but also CO and H2.
What is electric arc welding?
It is a metal joining process that utilizes the intense heat generated by an electric arc to melt the metals at the joint.
An electric arc is used as heat source
The high temperature of the arc melts the metal at the point of contact, creating a molten pool.
Arc temperature is 3200 and therefore both the electrode and the base metal are molten.
What is protected arc welding?
The melt pool is protected by an active gas. Can be TIG, MIG or MAG
What is spot welding?
Used to join to thin sheets together.
How do you do quality control of the welded steels?
- Surface NDT: workpiece are observed only on their outermost layer or immediatly below. Naked eye observation
- Volumetric NDT: X-ray inspection
Which are the most common welded steels?
- Plain carbon steel
- Stainelss steels
What is the heat affected zone (HAZ)?
tHe zone that affects of the heating during welding.
It can be divided into the normalized zone and the overhetaed zone
Normalized zone: har been heated to somewhat over A3.
Overheated zone: Considerably above A3 up to the melting point of the material. The structure of this zone exhibits larger grainsizes.
For what carbon content is steel fully weldable?
Less than 0.41 % C
Plain carbon steel has a maximum preheating at 200 dC
Describe stainless steel welding
Altough the heatnig and cooling caused by welding does not produce any significant structural changes in austenitic material, secondary ohases can occur like ferrite.
