Welding Of AISI 4140

Weld something with less carbon like 1018 CRS.

http://engstandards.lanl.gov/esm/welding/welding_specs/1000-4140.pdf

See if answers your question, http://www.azom.com/article.aspx?ArticleID=6116 "When welding AISI 4140 steel (in any condition) only low hydrogen electrodes should be used."

If it is indeed cluster porosity that you are experiencing then "arc blow" is the most likely cause.

Here is a good article on the subject.

We had a welder who always used to coil his Earth because he said this would always stop ^^, don't know if it does but he was convinced :-)

Hi there, Which pass are you getting porosity on? if its your first run and its a butt weld I would try using filler wire or some kind of backing! Also check your gas type/pressure

I am using ER90S-B3 as filler wire.1st pass is without filler. I have also varied gas flow rate from 20 cfh to 25 cfh but still problem is there. What shoul i do now?

I would try welding some standard carbon steel or stainless using the same procedure then at least you'll know its not your welding set that is faulty, Has the parent material been cleaned/ground up? To TIG weld everything has to be really clean!! Also you can have too much gas, maybe try going down to 10/12 cfh, sorry if you know all this already

Getting porosity from the first pass.