What's this alloy?
what's its number in ASTM or DIN

Stellite #6...

Stellite is the brand name of a hardfacing alloy which is widely used for valve seats, especially for valves subjected to abrasive service.
It is made by a company whose name is Stellite Coatings in the USA and Deloro Stellite in the rest of the world. They know their product better than anybody else. Get in touch with them and ask them. They'll be pleased to solve your doubt.
Phone number of Stellite Coatings, located in Goshen, IN is: 574-534-2585. www.stellite.com
Giovanni S. Crisi
Sao Paulo - Brazil

I have welded Stellite #6 to 410ss valves and valve seats where I work for the past 16 years.These valves are in steam turbine cases.Our spec that was developed by our company uses a 600 - 700 deg preheat.We sometimes put the larger valves in a furnace for stress relief at 1000 deg for 1 hr and then cool down at 200 deg per hr to 400 deg where the part is then cooled in still air.(No fans)The inlays we do usually are no more than 1/2" thick.
We also preheat the smaller valves the same and immediately after welding we heat them to 1000 deg with a torch and temp stick and wrap them in insulation and allow it to cool to room temp.
Stellite is very suscepticle to cracking if allowed to cool quickly.If we preheat and weld properly and still get cracks then we will butter the weld area with Inconel 82 and overlay the Stellite onto this and have had very good results.Your weld configuration may not allow this but it may help you if possible.
Sorry for the long reply but hope it helps.If you need more info please mail me and I will try and help in any way I can.