hamid,
There is ample information on the internet for PWHT temps. However, it is common to use 4130 in the as welded condition. A common practice for the as welded condition is to use less alloyed filler metal such an A1 suffix (as opposed to a D series filler) and allow dilution to strengthen the weld. If you are going to heat treat a D series may be preferred since you will lose strength. However, in general, the cold rolled and stressed relieved condition presents problems since its MSTS is usually around 105ksi. This is tough to get after a cook.
High preheat is the key. I run 4130 at 500deg.
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