Welding 4130 Chromoly - How to Test Welds For Penetration

There is a lot of discussion about welding 4130 chromoly steel on the internet forums and discussion boards. But putting aside from all the questions about preheat, filler metal, and electrode type and size, What about Weld testing?

How do you know you are getting adequate penetration in your welds. The short answer is- you can't. You can never be absolutely sure you achieved the right amount of penetration on some welds without destroying the weld by slicing and dicing and metallographic testing. But the good news is that you can be pretty darn sure.

By running test welds utilizing the exact same material thickness and joint design and then by following the procedures to the letter, you can be pretty darn sure that your welds are good.

Here is the basic procedure for testing the welds in 4130 chromoly steel:

Determine the different weld joint configurations that you need to test

Prepare the weld joints in the same exact manner as you will for production welds.

Weld the test joints and write down all the settings like preheat if used, amperage, electrode type and size, filler metal type and size etc.

Once the test welds are complete and cool, determine several locations to examine cross sections

Section the test welds using a slitting wheel.

Polish the test weld cross section starting at 180 grit silicon carbide abrasive, then 240,320, and finally 400 grit paper.

Swap with a Q-tip and Muriatic Acid as used in swimming pools (follow all recommendations for safety listed on the MSDS of the acid)

Rinse quickly with a baking soda and water solution to neutralize

Examine the weld using 10x power

If penetration is acceptable, you now have a welding procedure for welding 4130 chromoly that is proven. If this procedure is followed and the welds are also visually inspected, you can be pretty darn sure you have adequate penetration and a high quality weld.

Its also a good idea to weld another test weld same as above and subject it to the BFH test. (that's Big Freakin Hammer). That's always a down and dirty test that tells you something about weld quality. Plus its fun to break stuff.

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