Mild Steel TIG problems

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Hello, im having a lot of trouble getting good clean welds (TIG) with mild Steel (or maybe its high carbon steel... im really not too sure).  Not always... but most times i get porosity and cracks through the weld.  My Argon flow is at around 7 liters/minute, using a 10mm (ID) cup. Im thinking maybe it could be too much Argon flow... which would be thermal-shocking the weld??.   I prepare the surface by first grinding back to bare metal and then giving it a wipe with Acetone.
Reply:not enough gas flow for that cup size. You probably need closer to 12-17 lpm.   from CK worldwide. Miller Multimatic 255
Reply:Where the heck did u get 12-17 lpm from??  According to the chart, im right on the money!.
Reply:I was looking at a size 10 cup, plus porosity is almost always a sign of either not enough gas coverage or contaminationMiller Multimatic 255
Reply:Originally Posted by Louie1961I was looking at a size 10 cup, plus porosity is almost always a sign of either not enough gas coverage or contamination
Reply:... well thats the thing... my gas flow seems to be right... and you would think that grinding the metal and then hitting it with Acetone would ensure a contaminant-free surface!  So whats going on?
Reply:you could have really crappy steel.   It could really be a multitude of things, because there are just so many variables with TIG.  10mm is small, so you're likely using a #6 cup.  10mm = #6 cup, so you need around 5-6 LPM, and if you are using a standard cup, then you need to keep the stick-out to one-half the cup diameter or less.  Otherwise you risk contamination.This is my "TIG Checklist":Machine:Amperage:Tungsten blend/size:Filler rod/diameter:Argon Flow CFH:AC balance (if applicable):Pulse Parameters if applicable):EP/EN currents/ratios (if applicable):material thickness:joint configuration:pre-weld prep routine:torch size/style + air or water cooled:Std or gas lens collet body:nozzle size:pre-flow:post-flow:pictures/videos of torch angle, travel direction, speed descriptions:Argon does not have a high heat-capacity, so thermal shock is likely out of the question.  Also, the steel could just be really crappy steel.  Have you tried on other pieces of steel? 1st on WeldingWeb to have a scrolling sig! HTP Invertig 400HTP Invertig 221HTP ProPulse 300HTP ProPulse 200 x2HTP ProPulse 220MTSHTP Inverarc 200TLP HTP Microcut 875SC
Reply:What exactly do you mean by "crappy steel"??Cracks were formed when just doing bare passes on 3mm steel plate. I think it was around 100amps, DCEN.  Its a "CT-518" machine (they're all over ebay).  The Torch has no cooling.   This cup is the biggest of 3 that came with the welder.  Im using a 2% Thoriated Tungsten... i alternate between 1/16 and 3/32.  P.S. congratulations on the scrolling signature.  Quite the achievement.
Reply:Originally Posted by Marek0086What exactly do you mean by "crappy steel"??Cracks were formed when just doing bare passes on 3mm steel plate. I think it was around 100amps, DCEN.  Its a "CT-518" machine (they're all over ebay).  The Torch has no cooling.   This cup is the biggest of 3 that came with the welder.  Im using a 2% Thoriated Tungsten... i alternate between 1/16 and 3/32.  P.S. congratulations on the scrolling signature.  Quite the achievement.
Reply:Pics?
Reply:Does your tungsten remain fairly clean in spite of crapped up metal?
Reply:The weldability of the base metal might be wrong for your application. Are you running 100% Argon? Or are you running a mixture? Lets see some pictures of the welds. That will show us your base metal as well your working with.