Andy, good information, but may I respectfully add just a little?
Actually, the preheat temperature of the martinsitic stainless steels should be determined by the carbon content of the steel. 410 has a maximum carbon content of 0.15%. For martinsitic steels with a carbon content of 0.05-0.15%, the preheat should be a minimum of 400F (204C). The ASME Boiler and Pressure Vessel Code recommends a minimum preheat of 400F for those materials listed as P-6 in Section IX. The martinsitic transformation temperature ranges and air hardening characteristics of these steels are sufficiently high that preheating at 600F and below has minimal effect on the hardness of the HAZ or weld metal. A recommended technique is to use a high preheat (400F min.) and interpass temperature (also 400F) and very slowly, as Andy said, cool through the martinsite transformation temperature range to about 200-250F and then directly go to the tempering.
Andy, I respectfully wanted to clarify the minimum preheat temperature recommendations for a 410. You are right, though, that distortion will have to be carefully monitored, but that is the nature of the beast if using a martinsitic stainless steel. The recommended preheat, interpass temperature, and PWHT requirements are what they are for achieving maximum properties. Thank you.