Reducing Strength of A325 Quenched&Temperred 1

[redrushin]

Does anyone know of an accepted formula or standard for reducing the strength of A325 quenched and tempered bolts once they have been welded to carbon steel? I know AISC says that quenched and tempered bolts should not be heated or welded, but I was looking into some old files and saw that a contractor welded some A325 threaded studs to carbon steel beams. It is unknown as to weather these studs were plain carbon steel or if they were quenched and tempered. They have since been removed and the item was seal welded to the supporting beams. At this point it has become a hypothetical question around the office as to weather or not there is a way to calculate a reduced strength for any material that has been quenched and tempered with out manual testing of a material sample. Thanks for the help.

 

[metengr]

At this point it has become a hypothetical question around the office as to weather or not there is a way to calculate a reduced strength for any material that has been quenched and tempered with out manual testing of a material sample.

Reply; No, because of the number of variables associated the heat input from welding. The simplest, manual test method that could provide some qualitative measure of weld heat input affects on ultimate tensile strength is to run hardness tests on the welded A325 bolts.

 

[gtaw]

I see contractors trying to weld A325 bolts to beams and base plates quite often. As an inspector, I reject them.

I don't see the problem as being a reduction in strength, but rather one of diminished of ductility.

My concern is that welding a martensitic material, i.e., the A325 bolt, has the potential of producing untempered martensite in the heat affected zone of the weld. If the weld is a small tack weld, the heat affected zone will be confined to the outer edge of the bolt head. The temperature rise toward the underside of the bolt head and shank will be minimal. However, if the ever popular flux cored weldiing process is used, a weld all around the head of the bolt can easily raise the temperature above 1350 degrees F. That being the case, the underside of the bolt head where the shank starts, can be heated to the point of being austenized and then cooled very quickly due to the heat sink affect of the beam or base plate to which the bolt is welded. The rapid cooling may be sufficent to form untempered martensite which can have very little ductility. The thought of brittle bolts is frightening to an ex-ironworker.

That's my opinion and I'm sticking to it.

Am I way off track metengr? I'ld be interested in hearing your thoughts on the subject.

Best regards - Al

Best regards - Al

 

[CoryPad]

Al,

I would say you are firmly on the tracks.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[metengr]

Al,
Yes, I echo CoryPad's post above. Welding of high strength fasteners is not a good practice.

 

[redrushin]

Thanks so much for all the input. It is much appreciated.

 

[gtaw]

Thanks fellas for the reality check.

Best regards - Al

Best regards - Al