Debasis Mitra You are right Centfi-cast Heat Resistant Austenitic grade super alloy castings do not need pre-heat or post weld HT (normally speaking). For a repair weld, a pre-heat would certainly help especially since the component is static cast and nor centri cast. In Centri-cast, a little homogenized distribution of equi-axed grains will be there. You cannot expect the same 100% in Static Cast components. For Pre-heat, a temperature of 250 deg cent would be adeequate. To my mind, a 400 deg cent pre-heat is nto called for crack repair of static cast heat resistant grade super alloy materials used in ethylene cracker service. There is no correlation of pre-heat and grain size. At pre-heat temperature even upto 400 deg cent these heat resistant grade materials do not undergo any change at all except at solution heat treating temperature of above 1150-1200 deg centirgrafe Regards C.V.SRinivasan Nishi Engineers Pvt Ltd Chennai Indai Oct 9 E-mail: nishi@vsnl.com/nishi@hathway.com >Normally austenitic centrifugally cast items does not call >for any preheat before welding . But is there any opinion >regarding requirement of weld preheat ( 400 C) for >statically cast austentic items like WYE Fittings or Elbows? >This is because there exist some confusion. Also is there >any corelations between Preheat Temp. and Grain size? >regards >Debasis >METALLURGIST / ASNT NDT Level III (RT,UT,MT) >Sr. Engineer (Inspection Dept.) >HALDIA PETROCHEMICALS LIMITED / INDIA

The stainless stee l corrosion resistant is not necessary to pre-heat, but the Heat Resistant is necessary because your microstructure is austenitic and complex carbides eutectics in the boundary. This carbides give the heat resisting , but the elongment is down. Usually the Heat Resistant is furnished in as cast condition and your elongment is the 5 a 10%. The pre- heat is necessary to avoid cracks, 250 C is indicated to HP40 microalloyed, HK40, but 28Cr48NiW and HK 50 is necessary to increase this pre-heating until 400 C. Other problems is the litlle thin cracks in the thermicall Zone, to avoid this Interpass temperature must be low and the finish the welding, Cooling slowly. In Materials ageing because the work, has many secundaries carbides and creep damages what difficult the welding, them the pre heating must be upper than the new alloy. Regards Eng. Aguinaldo Gonsalez Metallurgist Foundry Processes