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Welding Heat treated 4130

Welding Heat treated 4130

Welding Heat treated 4130

Russ0448 (Mechanical) May 9, 2003
I'm looking to weld 4130 (4" round bar) to a lower carbon steel (pipe) that is unknown. The required strength of the 4130 will call for it to be heat-treated. The required strength = 100 Ksi Yield. The question is that would it be better to heat treat the 4130 before welding?
The process that I have seen before is of heat-treating the 4130 component then weld and then stress relieve. With this in mind, would the stress reliving (by heating the welded component) have a large impact on the previous heat treatment?
Also What type of preheating of the material would be recommended?

RE: Welding Heat treated 4130

If your 4130 is a 4" dia. solid bar, you will be lucky to reach 100 ksi YS, even quenching in water.  If it's solid, you may have to quench it in ice-cold brine to get your strength.

Different story if it's a 4" tube!

Whatever, when you weld it the strength in the HAZ will drop way down, so you won't have to be concerned about what stress-relieving will do.

RE: Welding Heat treated 4130

Let me clarify, the 4" Dia. round bar will be milled to a 2.36 dia. for 4" of it total length of 4 9/16" the 9/16" will be 4" dia.
The weld will be located at the 4" section, with the high stress seen just pass the 4" to 2.36" step on the 2.36” dia side. The high stress is due to bending.
Being that the stress, due to bending, drops down after the increase in the dia.(Area of weld), and the area of concern is at a distance 9/16" plus the vertical distance due to the step. Then it may be that the heat will not reach the area of concern. This was just a thought that I will probably not pursue. In any case, would heat-treating the entire piece be the better option?
Would localized heat-treating after be a better option?


RE: Welding Heat treated 4130

As far as welding goes, 4130 can be welded with either type of PWHT.  The Q&T PWHT is most beneficial in cyclical loading to produce the most homogeneous properties and least residual stresses.  A stress relief PWHT is probably used more often though.  The PWHT temperature is usually limited to 25-50F below the previous tempering temperature of the base metal.  This way the PWHT has minimal impact on the material properties.  The HAZ for a weld in 4130 material (at least for thick sections) is usually harder than the base material.  The rapid quench that the base matal provides is faster than a water quench, so the part of the HAZ that was re-austenitized is very hard , and the main reson that the PWHT is required.  The portion of the HAZ that only got tempered may be slightly softer than the base material, but the time at temperature is short enough that it is not usually detremental.  Because the slightly softer zone is so thin though, deformation is restrained by the harder surrounding base & weld material, so a cross weld tensile test will not normally fail in the HAZ.  You also want to choose filler metal based on your PWHT.  If you WQ&T, you want a matching filler (several companies make 4130 filler metals), and for a SR PHWT, you will probably want to use a 110 or 120 ksi tensile filler metal designed for a SR PWHT.

Preheat, for a material of given composition and strength, all depends on the thickness of the component, (which you say is 9/16"), and the heat input of the weld.  Those two things control the cooling rate.  A conservative preheat for your situation would probably be 250-300F.  Depending on the size of your weld, you could probably establish a lower preheat by testing. You also want to establish a maximum interpass temperature also for Q&T steels.  4-500F is a reasonable limit, in order to prohibit too much grain coarsening, or overtempering in the HAZ.

Also, I don't think that it would be impossible to get 100ksi YS in a 4" dia. 4130 bar.  We achieve 110 ksi YS no problem in the center of a 7" thick x 14" wide x 20" long block from 8630 after water quench and tempering at 1150F, and I wouldn't think that it is much more hardenable than 4130.

RE: Welding Heat treated 4130

You may want to consider AISI 8620. Strength will be lower, it is a carburizing grade, but very weldable.  It would simplify some of your welding of heat treated material concerns -- which I agree should be of great concern.

Also T1 Steel is another alternative that would eliminate heat treat.

RE: Welding Heat treated 4130


If you do persue this, simply buy 4130 heat treated to your requirements.  You can still easily machine it, and the welding heat won't affect the critical area.

Then do a PWHT as per GRoberts said.


You probably have heats of 8630 that are near the max. in the hardenability elements. Depending on the heats, 8630 can be somewhat deeper hardening than 4130.

I have some old Bethlehem steel data which shows a YS of 86 ksi on a 4" round, temp. at 900 deg. F.  That drops to 72 ksi when temp. at 1100 deg.  Both were water quenched-maybe they used hot water? <g>

RE: Welding Heat treated 4130


I would imagine that the YS would depend a lot upon where the particular heat is whithin the chemistry range.  Unless Russ0448 is buying a whole heat, it can be hard to controll.  We do have good control over out quench tank temperature though.

RE: Welding Heat treated 4130

Unfortunately the 4130 has already been ordered and at the machine shop. I'm going to let them machine the component, and heat-treat the component to the 100 Ksi.

I'll plan on asking for a preheat of 300 F and a 450 F interpass temperature. (Per GRoberts)

I'll plan to match the filler to the low carbon material strength by using a Low Hydrogen 7018 rod.

And then request stress relieving at a temperature of 100 F below 4130 tempering temperature.

How dose this sound?



RE: Welding Heat treated 4130

Sounds good to me-I don't see any problems here.

RE: Welding Heat treated 4130

Looks like a plan to me.  The only other possibility that I know of, is some people like to use 8018-C1 or C3 instead of 7018 when welding 4130/8630 to carbon steel, but I don't know how much more effective it is.  They like the higher toughness, but if you get 7018-1, there should be adequate tougness anyway.

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