Should I harden the steel after or before welding?

steelmade · Feb 25, 2018

I'm working on a project and I just realized that I will need to weld 2 steel plates together. I thought it was possible to get away with bolts and nuts, but thats not the case for me.

The steel absolutely needs to be hardened. The problem is that after welding the two hardened pieces of steel, there will be a heat affected zone with lower hardness.
I was thinking about first welding them together, normalizing 3 times and then hardening+tempering. But wouldn't it stress the weld and make it weak somehow?

I'm very inexperienced with welding, in fact I started 2 weeks ago.
The steel alloy used is 5160, 1/4" thick. The electrodes are 7018 2,5 mm thick, because I found it much easier to start the arc with the thinner ones.

steelmade · Feb 25, 2018

C'mon guys. No one? :\

DDoug · Feb 25, 2018

steelmade said:
C'mon guys. No one? :\

You doo realize it's Sunday Morning in the greater US of A ?
But some of us Heathens aren't in church....So you'll
have to make do for a wee bit.

I hate to suggest this, but with your lack of welding experience, I
would seek out a professional welder.

A quick google search show weldability as "poor" and doesn't indicate
if welded, what can be expected of the part.

Please indicate the usage of this part, loads, stress's, and if
it fails, does someone die ?

Limy Sami · Feb 25, 2018

Accurate and reliable heat treat has to be post weld.

johnoder · Feb 25, 2018

Read up on welding high carbon (the 60 in 5160) before you ruin your project

steve-l · Feb 25, 2018

5160 is a spring steel commonly used for making springs, large knives and swords. It is a high carbon steel alloy with lots of chrome and some manganese for hardenability. With HT RC hardness between 60 and 63 is achievable, but like all hard steels, it does not take kindly to welding, especially with 7018. The weld heat will destroy the 5160 attributes. Even with preheat/postheat and re-heat treatment, the weld metal will not harden. When stressed, failure can be predicted just beyond the weld point. I don't know your project, but you should do something else. Either find a more suitable steel or use another method of fastening and construction.

steelmade · Feb 25, 2018

johnoder said:
Read up on welding high carbon (the 60 in 5160) before you ruin your project

Any suggestions on where to start?
Sorry if it sounds like spoonfeeding. I just don't know what I should look for.

steve-l said:
5160 is a spring steel commonly used for making springs, large knives and swords. It is a high carbon steel alloy with lots of chrome and some manganese for hardenability. With HT RC hardness between 60 and 63 is achievable, but like all hard steels, it does not take kindly to welding, especially with 7018. The weld heat will destroy the 5160 attributes. Even with preheat/postheat and re-heat treatment, the weld metal will not harden. When stressed, failure can be predicted just beyond the weld point. I don't know your project, but you should do something else. Either find a more suitable steel or use another method of fastening and construction.

Oh, why wouldn't the 7018 work?
I'm aware that the weld filler probably won't harden up after quenching, but its OK, as long as the welding doesn't crack or become weaker if normalizing and quench+temper is done after the welding process.
By "just beyond the welding point", you mean that the surrounding area of the weld will be affected? Why exactly? Will the steel lose its chemical integrity because it was exposed to the gases from the welding or will it simply lose the hardness it had previously?

steelmade · Feb 25, 2018

digger doug said:
You doo realize it's Sunday Morning in the greater US of A ?
But some of us Heathens aren't in church....So you'll
have to make do for a wee bit.

I hate to suggest this, but with your lack of welding experience, I
would seek out a professional welder.

A quick google search show weldability as "poor" and doesn't indicate
if welded, what can be expected of the part.

Please indicate the usage of this part, loads, stress's, and if
it fails, does someone die ?

Sorry for that.

I don't know any professional, and yes I searched the internet for the weldability on the 5160 alloy. I was thinking about preheating it with the blow torch before welding.

Welding spring steel - Miller Welding Discussion Forums
A guy named BiLLC said:
A carbon "spring" steel probably contains .70 - .90 percent carbon like AISI 1070 - 1090 steel. That much carbon makes it sensitive to hydrogen embrittlement as well as formation of brittle microstructures such as untempered martensite in the HAZ. Just joining 1070 steel for a static application would require high preheat, a low hydrogen process with a matching strength filler metal, and post weld stress relief.

Based on this, using low hydrogen electrodes are advisable I suppose.
"High preheat" is pretty ambiguous. 400 ºF, 600 Fº? By matching strength filler I think he means that the metal core of the electrode is supposed to have the same mechanical properties as the welded steel, but I don't see how such thing could be arranged. Do they make electrodes that match different steel alloys?
Anyway... I'm making steel targets for pistols. The loads are pistol rounds (.40 SW mainly) impacting it. If it fails, half of the target falls off of the stand, nobody dies. Pistol/rifle targets are disproportionally expensive where I live. But even if no one dies I would prefer that the target doesn't
There is a stand, a square steel plate (3 by 3 inches roughly) that is held by a bolt, and then there should be the main steel target that I'm planning to weld in an angle in order to deflect the rounds. Simply bending isn't an option, I don't have a plate that is big enough neither I know where to get one, they are sold as 6 inches wide and 1/4" thick plates and then you cut it to the desired length.

I also found this:
Low Hydrogen Filler Metals
The term "low hydrogen" has been around for about 60 years. It was first introduced to differentiate this classification of shielded metal arc welding (SMAW) electrode (e.g., E7018) from other non-low hydrogen SMAW electrodes (e.g., E6010). They were created to avoid hydrogen cracking on high strength steels, such as armor plate.
I'm not making an armor plate to wear, I'm an amateur, not stupid. But if they weld armor in tanks and other military vehicles, then there should be a way of working around the HAZ issue.
Using 7018 electrodes is a good choice I presume.

MattiJ · Feb 25, 2018

steelmade said:
Any suggestions on where to start?
Sorry if it sounds like spoonfeeding. I just don't know what I should look for.

Oh, why wouldn't the 7018 work?
I'm aware that the weld filler probably won't harden up after quenching, but its OK, as long as the welding doesn't crack or become weaker if normalizing and quench+temper is done after the welding process.
By "just beyond the welding point", you mean that the surrounding area of the weld will be affected? Why exactly? Will the steel lose its chemical integrity because it was exposed to the gases from the welding or will it simply lose the hardness it had previously?

So soft weld is ok.
How about the base material. How hard you need and how large heat affected zone is tolerable?

hobbyman · Feb 25, 2018

You are on the right track selecting a low hydrogen rod. Since you are welding a high strength alloy keep in mind that E 8018 and E 9018 are available. I am not sure if the minimum order would be too much rod for you to stock.
Preheat! preheat! preheat! the assembly. Since you intend to heat treat afterward don't be shy. I would suggest 400 to 500 F at least. If your pieces are very thick make sure that the heat is through your material. If everything is 1/4 inch this is no problem. The idea of preheat is so that the weldment cools slowly. The longer the weld is at high temp the more hydrogen will move out of the joint. Preheat and lo-hi rods should eliminate underbead cracking. If you can.... muffle the weldment with welding blanket or other insulation to reduce the cooling rate.
Another approach is to use GTAW. Tig welding is naturally lo-hydrogen. Some people would choose a 309 or 312 filler rod to create a weld mix with your alloy which would be high nickel making it tough but soft for machining.

steelmade · Feb 25, 2018

MattiJ said:
So soft weld is ok.
How about the base material. How hard you need and how large heat affected zone is tolerable?

Its ok as long as its tough and doesn't bend easily like copper.
There is another reply waiting for approval, so its not visible. The hardness should be of about 55 HRC. The HAZ should not exist. That is the point of first welding the steel and only then normalizing, quenching and tempering it.
I want the hardenable steel to harden and the weld to stay tough (no cracks or weaknesses).

steelmade · Feb 25, 2018

hobbyman said:
You are on the right track selecting a low hydrogen rod. Since you are welding a high strength alloy keep in mind that E 8018 and E 9018 are available. I am not sure if the minimum order would be too much rod for you to stock.
Preheat! preheat! preheat! the assembly. Since you intend to heat treat afterward don't be shy. I would suggest 400 to 500 F at least. If your pieces are very thick make sure that the heat is through your material. If everything is 1/4 inch this is no problem. The idea of preheat is so that the weldment cools slowly. The longer the weld is at high temp the more hydrogen will move out of the joint. Preheat and lo-hi rods should eliminate underbead cracking. If you can.... muffle the weldment with welding blanket or other insulation to reduce the cooling rate.
Another approach is to use GTAW. Tig welding is naturally lo-hydrogen. Some people would choose a 309 or 312 filler rod to create a weld mix with your alloy which would be high nickel making it tough but soft for machining.

Thanks for the reply hobbyman.

I don't think that my inverter welder will do the job of melting E9018, it goes up only to 160A. Is it any different to start E9018 electrodes? What about maintaining a good weld bead? I also don't own a oven to store electrodes, so I have to buy them, dry it in the kitchen oven and use it in the same day.

What if I heat the whole piece of steel up to 1300 F and then weld it?
I thought about this, but I'm afraid that the temperature of the liquefied steel would get so high that it would vaporize or something.

I could fire up the gas forge and bring the temperature to about 1300 F and stick the welded steel in there to cool slowly.

Dave G. · Feb 25, 2018

Why not redesign your joint and braze the parts together? With the proper design and braze alloy you can achieve very good joint efficiency (look at all the old steel tubed racing bikes with lugged and brazed frames). The brazing temp should be 50F lower than the final tempering temp for your 5160.

steelmade · Feb 25, 2018

Dave G. said:
Why not redesign your joint and braze the parts together? With the proper design and braze alloy you can achieve very good joint efficiency (look at all the old steel tubed racing bikes with lugged and brazed frames). The brazing temp should be 50F lower than the final tempering temp for your 5160.

I don't own a torch capable of that.
Unfortunately I'm young, which means that I don't have a lot of money to spend on good quality tools.

The only machine that is capable of welding is my inverter, which goes up to 160 A.

gbent · Feb 25, 2018

If you absolutely need a good weld, preheat first, then weld with Inconel 625, then heat treat.

You don't have enough experience welding. If you have one chance to get it right get an experienced welder to do the job.

Typically, carbon steels have a tradeoff between hardness and toughness. You want a tough weld, but you want the parent metal to be hard? While that situation is not unheard of, one normally wants the weld properties to match that of the parent material.

If you share the desired end result and application you may get some help and other ideas beyond just welding.

steve-l · Feb 25, 2018

steelmade said:
I don't own a torch capable of that.
Unfortunately I'm young, which means that I don't have a lot of money to spend on good quality tools.

The only machine that is capable of welding is my inverter, which goes up to 160 A.

Well then, there it is. You can't get there from where you are with the tools you possess. Simple, don't do it.

steelmade · Feb 25, 2018

gbent said:
If you absolutely need a good weld, preheat first, then weld with Inconel 625, then heat treat.

You don't have enough experience welding. If you have one chance to get it right get an experienced welder to do the job.

Typically, carbon steels have a tradeoff between hardness and toughness. You want a tough weld, but you want the parent metal to be hard? While that situation is not unheard of, one normally wants the weld properties to match that of the parent material.

If you share the desired end result and application you may get some help and other ideas beyond just welding.

Isn't Inconel 625 a steel alloy? I haven't heard of an electrode by this nomenclature.
I have welded before, but I'll practice before actually joining the pieces together.

Well, I the weld and the metals joined can all have the same properties, then great. It would be desirable actually. But I figured that to achieve such properties in the weld I would need fancy electrodes that require lots of current, which my inverter is not much capable of.

After I make a decision and proceed to weld the steel the results will be posted here, but please don't laugh on my poor welding skills if it turns out ugly or wrong somehow. :P

steelmade · Feb 25, 2018

steve-l said:
don't do it.

Not an option.

steve-l · Feb 25, 2018

steelmade said:
Not an option.

Out of curiosity then, why would you ask for advice if you were going to ignore it anyway?

hobbyman · Feb 25, 2018

steelmade said:
Thanks for the reply hobbyman.
I don't think that my inverter welder will do the job of melting E9018, it goes up only to 160A. Is it any different to start E9018 electrodes? What about maintaining a good weld bead? I also don't own a oven to store electrodes, so I have to buy them, dry it in the kitchen oven and use it in the same day.

What if I heat the whole piece of steel up to 1300 F and then weld it?
I thought about this, but I'm afraid that the temperature of the liquefied steel would get so high that it would vaporize or something.

I could fire up the gas forge and bring the temperature to about 1300 F and stick the welded steel in there to cool slowly.

No need to get that hot.. Even the most critical stuff is rarely preheated above 1100 F. The high strength low hydrogen rods weld just like E 7018. The amperage will be the same setting. You will not notice any difference as you are welding... In fact there is E 11018
People don't talk about it much but most modern low hydrogen electrodes are sealed to keep moisture out and baking the rods is a belt and suspenders thing. Technically code welding demands drying out rods before use and only taking out a 2 hour supply. Preheating allows any hydrogen to migrate out when cooling slowly. The hydrogen atom is extremely small and it will migrate out if given a chance. There are some areas in the world where they rarely use low hydrogen electrodes but they do use preheat to compensate.
Many old hands would laugh at the idea of preheating 1/4 thick material at all.

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