Table 3. Heat treatments for the PH alloys used in the study. Alloy
PH13-8+Mo PH17-4
PH17-4+Co
steel, weld thermal simulations were performed to correlate mechani- cal properties to microstructure changes in the heat affected zone. For comparison, as-cast and cast and heat treated Eglin steel un- derwent mechanical testing, as well. Dilatometry and heat affected zone simulations were performed on a Gleeble thermo-mechanical simulator. Autogenous gas tungsten arc welding passes were performed
2
Procedure In addition to de-
veloping a continuous cooling transforma- tion diagram for Eglin
Solution Treatment
1,700F/1 hour in nitrogen; fan cool to ambient temperature, then water cool to below 60F
1,925F/1 hour; air cool to below 90F 1,920F/1 hour; quench in room temperature oil
Aging Treatment
1,000F/4 hours then fan cool 1,075F/1.5 hours and air cool
900F/1.5 hours and air cool
Table 4. Various heat treatments the weldments of PH13-8+Mo, PH17-4 and PH17-4+Co underwent before performing hardness traces.
Sample
A B C D
Condition Welded in the aged condition
Welded in the aged condition; aged after welding Solution treated then welded
Solution treated then welded; aged after welding E Welded in the aged condition; after welding, solution treated and then aged
on each of the PH alloys in differ- ent heat treat conditions and with a variety of post-weld heat treatments (Tables 3-4).
Te Eglin dilatometry experi- ments showed four distinct regions form within Eglin steel depending on the cooling rate (Fig. 1). At cool- ing rates above 1C/second, a mar- tensitic microstructure was formed with a hardness of about 520HV. Intermediate cooling rates (1C/ second to 0.2C/second) produced a material with a mixed martensitic/ bainitic microstructure with a hard- ness that ranges from 520 to 420HV. Slower cooling rates (0.1C/second to 0.03C/second) led to the forma- tion of bainitic microstructures with a hardness of about 420HV. Te slowest cooling rates of 0.01C/sec- ond formed a bainitic microstructure with pearlite at the prior austenite grain boundaries.
a general continuous cooling trans- formation diagram was developed for use with forging, casting, rolling, fusion welding and heat treating (Fig. 2). Together with plots of hardness as a function of cooling rate and the microstructural investigation, the fol-
3 44 | METAL CASTING DESIGN & PURCHASING | Jan/Feb 2014
lowing conclusions were made: • Cooling rates greater than 0.3C/
Results and Conclusions
Through various
studies on phase trans- formation of Eglin steel,
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