I need to get parts Salt Bath Nitrided and am looking for companies to do it in the USA. Are there any companies that you would recommend or not recommend using? The parts are made from 4140 / 4142 PHT with an Rc = 30.
Give these people a call and I think they will steer you in the right direction. I have had very good results with their process for liquid nitriding. Checkout the QPQ process.
There is a place just northwest of Houston that I've used quite a bit in the past, they used to be a Kolene shop but last I heard, they had fallen out of favor with them. I don't know why however. They are called Houston Unlimited. here is thier website url:
Is there a reason why you cannot use Kolene? They are a very reputable company in this field, and most companies in the US that perform salt bath nitriding use their process, chemicals, etc. If you absolutely cannot use Kolene or one of their licensed processors, try contacting HEF (