what's the story with welding grade 8 bolts to mild steel?

I just tig welded these johny joints to some grade 8 bolts and now after thinking I'm all smart my buddy tells me they will probably break off since the grade 8's are hardened!
Did I screw up? they don't seem to ready to come apart, and I see no cracks on the surface. I took my time and tacked them a few times and then welded short sections at a time. Any input appreciated.

Looks exactly like I'd do it.

according to one of my reference books I pretend to use for work (but really use fourwheeling ideas) Grade 8 bolts are quenched (heated really hot, and then cooled really quickly) to harden them, then they are tempered (heated kinda hot) to relieve any residuals stress from the quenching. Resulting in a hard, but relatively ductile material with no residual stress. The threads are then rolled on. Welding on the bolt probably undid all the Grade 8 "goodness", and resulted an expensive bolt with cheap bolt properties.

You may or may not have problems though. It isn't like the bolt now has the structural integrity of a saltine, but a majority of the strength maybe gone. All bolts over Grade 1 are quenched and tempered to some extent so you may have a bolt with 33,000 psi proof strength instead of the 120,000 psi it started out as...

chad

Hey Uncle Freddie...Where did you get that bolt? Did you turn off the hex, or did you find it like that?

I like that idea a lot! Keep us posted as to how well they hold up okay?

Originally posted by RockRover
Hey Uncle Freddie...Where did you get that bolt? Did you turn off the hex, or did you find it like that?

I like that idea a lot! Keep us posted as to how well they hold up okay?
could be allan head....

yeah I turned off the hex part, just to get a better look so that nobody know's it was just a dumb ol bolt
i guess my real question is not if i lost the strength of the grade 8 but rather what are the proper procedures for welding a grade 8 bolt?

i would think that there is not enough weld on that to hold. the arms will take some severe pounding and the welds look small for what they have to hold. i don't think the bolt strenght will be a problem, just that your weld may pull out of the jonny joint. you did a nice job welding them. but i think it would be a lot stronger if you put more of a bevel and built the weld up. some thing in the 3/8ths range with a 45deg. bevel would be much better off. i don't think there is a proper procedure to weld a grade 8 bolt or any other that i have run across. i would just weld it up, quench it then anneal it to a dull red. to take the brittleness out. mike

could someone please explain quenching (obviously dunking it in something ? but what ?), annealing, etc to my computer programming dumba$$ ?

- jack

Originally posted by chadl
Welding on the bolt probably undid all the Grade 8 "goodness" ..........(but) It isn't like the bolt now has the structural integrity of a saltine,

chad

BAWAHAHAHAHAHA:laughing: :laughing: :laughing: :goofball: Damn that was funny:beer:

Here's a few websites I found on the subject.

http://info.lu.farmingdale.edu/depts/met/met205/tempering.html

http://www.umist.ac.uk/MatSci/research/intmic/schools/schools/steel/Default.htm

Basically you need a really hot oven (you might be able to do it with a torch) get it up past it's upper critical point (around 1400 F) , then cool it fast (down to about 400 F in less than 10 seconds) usually with water. A pro at metalurgy could probably tell you when you are at the right heat by the color (i am no pro).

Anyway, afterwards you put it in an oven at around 400 F for about an hour to allow trapped carbon to diffuse and many small carbide precipitates are developed (blatant coping from the above page). I don't remember are the details, but the result is a very tough, but relatively ductile material.

If you don't think you can handle it try talking to your local welding shop, either they could, or could probably recomend someone.

here is some thing that learned from a old black smith 25 years ago. now this was for making knives but it gives you a general idea. magnets and biskets he told me, to heat the metal up to the point that it is no longer magnetic, which is pretty much white hot then quench it. then put in a oven at 375degs for 45 minutes. not rocket science but it makes a pretty good knife.

i've quenched stuff in used motoroil before after welding. i am NOT saying its a good idea, but i have done it. never experienced flames either... anyway, the water will cool your part faster than the oil. you'd probably be safe with a water quench. matt

when you have a high carbon steel the carbon is free to move about at high temp. so whne you quech it it stays in the formation it was at high temp. This causes latice strains in the material (micorscopinc) and results in a very hard brittle material (needle like crystal strucure) and if not careful may even crack during queching (dunking and swirling in water IMEDIATLY) after being removed from the furnace.

temper is heating it up again so some of the carbon can relieve the stress and let the carbon get all nice and round (no sress raisers) this makes it borht ductile and strong.

If it was glowing red you lost your temper :(

there isn't a good way to get it back without doing the process over again of heating and queching and your oven doesn't go high enough.

it's probably not that big of a deal

hey since we seem to have all the metalurgists in this thread, does anyone know what type of heat treatment your average axle shafts get from the factory (nothing exoctic, just the old junk you find laying around), I haven't been able to find this anywhere.

chad

Originally posted by gunracer1
i would think that there is not enough weld on that to hold.

I say that the weld will hold. It looks like a 3/4" NF bolt so the cross sectional area (guestimating for threads) is about .4 sqin. If the head is about 1" dia, then the bead would need to be about .3" to make the same cross sectional area as the bolt it's self. Looking at the picture you should be pretty close to that. However, given the size of the bolt and the threads, I'd guess that you'll pull the threads off the bolt before you break the bold or the weld. :p

Question, if you have access to a lathe, why didn't you just turn down and thread a piece of bar stock (say 1018 or if your worried about strength, 4140)? At least that way you would know you have a decent quality material and heat tread would not be as critical.....

OK you've heard our guesses, so hurry up and break it so we can find out who was right... :D :D :D

Originally posted by chadl
type of heat treatment your average axle shafts get from the factory (nothing exoctic, just the old junk you find laying around

I'm not a metallurgist, but I play one on BBS's :D :D

Domestic or foreign? :)

Axles are a little different, most of them are not hardened all the way thru. The majority of axles are induction hardened, a process which uses a magnet coil to heat the metal from the outside in. With this process they can control how deep the heat penetrates before the metal is cooled. Most axle manufactures are kinda protective of their exact details. You'll also find that most foreign axles are hardened further and deeper than most American made ones. I've always guessed that the foreign axles use lower quality base material and they try to make up for it with heat treat.

Oil is a better quench than water.
Reason? Water boils on contact leaving the steel to cool in air (bubbles) and in a speckled fashion. This quench is neither fast nor even.
Oil does not boil nearly as much and better stays in contact with the steel, causing a faster, harder, even quench.
The steel should be suspended in the quench until cooled sufficnetly.
I like to use peanut oil because heating it smells like popcorn instead of a fried mill ...:)
You should not 'swirl' when quenching unless done in a scientifically controlled enviroment.
Casual swirling exposes the steel to alternating warm and cool layers which causes an uneven crystalline structure.

Originally posted by okcrawler


I'm not a metallurgist, but I play one on BBS's :D :D

Domestic or foreign? :)

Axles are a little different, most of them are not hardened all the way thru. The majority of axles are induction hardened, a process which uses a magnet coil to heat the metal from the outside in. With this process they can control how deep the heat penetrates before the metal is cooled. Most axle manufactures are kinda protective of their exact details. You'll also find that most foreign axles are hardened further and deeper than most American made ones. I've always guessed that the foreign axles use lower quality base material and they try to make up for it with heat treat.

thanks for the info... I'm specifically looking at a 79 ford D44. the reason I ask is (I posted this earlier this week) I'm considering welding several beads over the yoke of the u-joint to thicken it up, since the existing metal is about paper thing (I don't know if it's worn or just came that way). anway the idea was to kind of strengthen the ears until I can save up enough for aftermarket shafts (yes I'm very cheap) I know that the welding would probably ruin whatever heat treatment was done to the yokes, so I have held off on my experiment. Now I'm wondering if I do it, could I have a pro "re-harden" it. But from what it sounds, the process is pretty involved, and would be tough for the "backyard blacksmith" to replicate. After reading your post, I do remember many moons ago about the fact that "power shafts" (in general) are often harden on the outside to reduce "crack propigation", but leave a ductile center to allow for some "springiness" I wonder if I could weld, then quench and temper the ears (like we've discussed above) without affecting the shaft, that would probably be difficult.

Any thoughts or opinions on this idea...

Also, Jaffer, was reading the good-old Machinest Handbook, and it looks like your right regarding oil, and it makes sense to me..

chad

Originally posted by morpheus
could someone please explain quenching (obviously dunking it in something ? but what ?), annealing, etc to my computer programming dumba$$ ?

- jack

Here ya go. This is a reasonable explanation and maybe more than you need to know.

http://www.adtdl.army.mil/cgi-bin/atdl.dll/tc/9-237/Ch12.htm#s11

The primary difference between choosing a water quench or oil quench in the rate of quenching. Water is much faster.

After welding on the bolt, the heat affected zone (HAZ) will be in a partially "normalized" state. Whether this is good or bad depends on the application. If you want the maximum tensile strenght and surface hardeness, then re-heat treating would be a good move. If you want the maximum ductility, then the normalized state is desirable. If it is an important application, like on-street steering linkage, then verifying the integrity of the weld (penetration, porosity, cracks, inclusions etc) would be important, but not everyone has easy access to the equipment for non-destructive testing.

The engineering that goes into the weld design and process would also be critical in determining the strenght of the final product.

According to the AISC Steel Manual, using 70ksi electrodes, a 1/8" fillet weld can take 1850 lbs/in of weld in tension, 1/4" fillet can take 3700 lbs/in of weld, 3/8"=5600 lbs/in. (includes safety factors)

So if you've got an 1/8" fillet weld, and 4" of weld, that weld can take 7400 lbs. Of coarse there are a few other factors that come in to play in weld design, like checking the base metal, etc. But basically that is the strength of the weld itself with the applicable safety factors.

Just a little FYI

I had some rod ends in my rear 4-link that rated about 8000 lbs static radial...they lasted 1 day, then they broke, the axle rolled, the pinion went into the bellypan and the rods in my new coilovers turned into pretzels...:barf:

Originally posted by TRD


there isn't a good way to get it back without doing the process over again of heating and queching and your oven doesn't go high enough.



Just to let you guys know, the average self cleaning oven gets to 800º for one hour during the cleaning cycle.

2000F Bright yellow
1900F Dark yellow
1800F Orange yellow
1700F Orange
1600F Orange red
1500F Bright red
1400F Red
1300F Medium red
1200F Dull red
1100F Slight red
1000F Very slight red, mostly grey
0800F Dark grey
0575F Blue
0540F Dark Purple
0520F Purple
0500F Brown/Purple
0480F Brown
0465F Dark Straw
0445F Light Straw
0390F Faint Straw

chemicals are also used in treating metal, such as cyanide gas and such (not recomended for diy operations). did u bevel the head of the bolt? that would create more surface area for the weld. piling more welds on it would not make it any stronger, as long as the edges of the root bead melt into the base metal with no imperfections, it will be fine. btw, welds usually don't break, its almost always what its welded to that breaks (assuming u have a perfect weld).

Originally posted by fcfred
yeah I turned off the hex part, just to get a better look so that nobody know's it was just a dumb ol bolt
i guess my real question is not if i lost the strength of the grade 8 but rather what are the proper procedures for welding a grade 8 bolt?
Nice Job!Looks real Pro.
In My opinion there is no real procedure for welding hardened steel that can be done with the means of an average shop that will keep the hardening properties.
But you can send them off to be rehardened....but $$$. I would make sure that the steels being welded at tha least have the same carbon content and hardening from the beginning though.
-Kerry

looks good could always through a little gusset on each side to give it more surface area to hold to.