Bolt Grade vs welding

[PaulW_NJ]

Does a Grade 8 bolt get it's strength from being quench hardened, or by it's alloy? The reason I ask is that I have a 3 point hitch heavy bracket with stripped threads, and plan to weld a bolt into the hole. I'd like to use Grade 8 for it's strength. But will the welding soften the strength of the bolt as it would any quench hardened material?

 

[NBAllen]

Yes. Both actually.

A Grade 8 fastener is made from a "medium-carbon alloy" and is quenched and tempered.

I can't accurately answer the softening question. The yield strength of a Grade 8 fastener is a minimum of 130,000 psi. Yield strength on a Grade 5 is 92,000 psi.

Nathaniel

 

[Anonymous-0]

If you weld the head of the bolt it should still have stronger threads on the other end unless it's a fairly small bolt and gets too hot. Overall the bolt might be a little weaker but in most cases that won't matter too much.

 

[Anonymous-0]

BOLTS BUILT FOR CAT ARE TOUGH BUT NOT HARD. GRADE 8 CAN BE CUT WITH A HACK SAW BUT STIL 130000 PSI.CHEAPER GRADE 8 ARE CASE HARDENED AND PLATED TO GET THAT STRONG. RENE'

 

[Puddles]

Are you planning on welding the bolt in the bracket from the back side? If so you might try picking up a small tub of heat clay at your local welding supply. Pack the threads with the clay.

 

[petetx]

grade 8s get brittle when welded they are still strong but won't take a lot of constant shock used to back weld the nuts on b-8 studs and if you hammered to heavy with a big impact they would break

 

[T_Bone]

Hi Paul,

Depends on the grade 8 bolt. Now days there made all over the world so sometimes you just don't know what quality your getting even tho it has a stamped head.

As the other guys stated, it's hardness comes from both sources. If your just going to weld the on the head and the bolt shoulder has plently of support, then a rag soaked with water wrapped around the threads and exposed shank may very well be enough to keep the threads strong and pliable.

This should be enough to keep the bolt in the hole without breaking the weld and still function some what close to a grade 8 bolt strength.

As to post heat treatment, if you don't have experience in heat treatment then I would think you would have more of a chance of failure trying post heat treatment vs no heat treatment.

If the bolt has no shoulder support, then I think your wasting your time and a new design is needed.

T_Bone

 

[Kentb of SWMO]

Once you weld on a piece of steel that has been heat treated you SCREW-UP the heat treat and ALL bets are off.

Kent

 

[comtcwby]

Any time that you are welding, you will change the molecular structure of the materials that have been welded. The material, as in the case of a grade 8 bolt does get its strength from the tempering. If you ever do lots of welding, you will find that the material that has cracks, will be close to the welded areas in what is called the heat affected zone. Due to the density of tempered materials, the heat affected zone will become brittle in comparison. Post weld heat treatment can be and should be done if you want the most strength, but you are talking about equipment and time that most of us dont have access to. If you decide to weld the head on to the area, try quenching the material all around the welded area with oil immediatly after welding it for your closest thing to post treating. At least the material will get some of its strength back but will still be somewhat brittle in comparison to the none heated areas. thats my .02 $.
Glen