Use the SEARCH function. Search preheat and user G.S.Crisi.
He has a formula (post on here somewhere) that I have lost thru the many changes and migrations of PC's. It uses the Carbon content to determine preheat range of materials.
I prefer review AWS D1.1 Annex normative I. The PCm es very importan in Hydrogen control, because, is possible risk cracking for hydrogen inducen Dayanara
Tp = 697*CET + 160 tanh (d/35) + 62*HD^0.35 +(53*CET-32)*Q-330 [Degree C] where: d is the thickness in mm HD is the hydrogen content in ml/100g per ISO 3690 weld deposit method typical values HD = 5 ml/100g - SMAW, FCAW, SAW and HD = 3 ml/100g for GMAW Q is the actual heat input in KJ/mm Q = eff*Voltage*Amperage/(weld speed) typical eff = 0.8 SMAW, GMAW = 0.7 GTAW = 0.9 FCAW = 1.0 SAW
tanh() is the Hyperbolic tangent
If you want to experiment iterative approach
1. measure the temperature of the steel 2. weld the first pass mesaure the time it takes the weld to go from 800 to 500 degree C adjust the preheat to obtain a t8/5 greater than 8 seconds; allowing the HAZ and weld emough time to transform from martensite.