one for the metalurgists ...

[Phil Russell]

There is often a recommendation to have a metal (steel) part welded to effect some sort of repair. I have often wondered how 'hard' the resultant weld metal is. So: if you weld mild steel is the welded area 'harder' than the surrounding mild steel? I have often thought it would be but never had it confirmed.
Any professional verdict?
Cheers, Phil

[DedIdick]

Depends on the heat treatment applied.

[rancidtom]

It depends on the filler metal used and also the rate of cooling after welding if not a mild steel filler, the process used may also affect the carbon content of the filler metal and hence the hardness/brittleness post welding. Welding rods and filler wire are available in many alloys to match the parent metal and the final properties required of a weld. Welding can be done to produce hard facing for cutting tools, impact resistance or other specialised requirements and these properties may be refined by subsequent heat treatment. Joining steels of different types can be done with suitable filler rods and processes.

[angrybear]

There is often a recommendation to have a metal (steel) part welded to effect some sort of repair. I have often wondered how 'hard' the resultant weld metal is. So: if you weld mild steel is the welded area 'harder' than the surrounding mild steel? I have often thought it would be but never had it confirmed.
Any professional verdict?
Cheers, Phil

For a simple "hit it with the mig" type weld, the longer it takes to cool the "softer" that area will be, because the time allows the atoms within the metal to relax, if you quench or force cool the job it will be harder but hard can often also be brittle.

[Phil Russell]

Somehow I knew the answer was not going to be simple .. at least to me. In my case I have a small welder that plugs into the mains ... arc welder ?.... and use the rods supplied with it. I have no idea what composition they are but come with flux on the outside. I have welded mild steel plate, not elegantly I admit, and also repaired things like garden forks where a prong has broken off. I have made various targets and repaired a few pistons from old rifles and cocking links as well, finishing off with vigorous filing. But I have often wondered about the nature of the hardness of the welded joint. Maybe the answer is ... it all depends.
Maybe ignorance is bliss.
Funny thing is, I always used to look for an evening class on welding but never found one in the area.
Thanks for the information though.
Cheers, Phil