the section chosen, some expansion of the weld has occurred during 

 the forming operation. 



Although not evident in the photographs of the macro-sections, 

 a significantly greater number of discontinuities were observed in 

 sections of the GMA short circuit weld deposit than in either the 

 GMA spray weld or GTA weld deposits. This was true both before and 

 after forming for the GMA welds. The GTA weld had been removed 

 when the disc was machined, so that this area of the weld was not 

 involved in tlie forming operation. Despite the numerous fissures 

 observed in the GMA short circuit weld after forming, they did not 

 cause catastrophic failure of the head during the forming operation. 

 It is believed that the high quality of the GMA spray weld deposit 

 may have acted to contain these discontinuities during forming. 



Microscopic examination of weld and base metal areas in the 

 flange and curved sections of the head showed that no fissures had 

 occurred either in the weld or in the base metal in the region ex- 

 tending up to 10 inches from the edge of the head. Typical fissures 

 found in the weld between 10 inches from the edge and the apex are 

 shown in the photomicrograph in Figure 14. These fissures appeared 

 to have formed by growth and joining of pores and other discontin- 

 uities in the weld. The majority of the fissures were found in 

 the short circuit weld deposit where the greatest incidence of dis- 

 continuities had been observed before forming. Despite indications 

 of porosity in the weld near the skirt of the head, these pores did 

 not grow into fissures. This result may be attributed to the state 

 of stress in the skirt area; longitudinal tension/lateral compression 

 as compared with biaxial tension in areas of the weld nearer the 

 apex of the head where minor discontinuities grew into fissures. 



ELEVATED TEMPERATURE TESTS 



Although weld properties overmatched those of the base plate at 

 room temperature, the performance of the weld during the hot pressing 

 operation suggested that the strength of the weld, at the forming 

 temperature of 1750°F, was lower than that of the base plate at that 

 temperature, causing the weld to undergo considerably greater plastic 

 strain than the base metal. In order to confirm this hypothesis, 

 elevated temperature tests were conducted on samples of weld and base 

 metal obtained from the run-off tabs of the as-welded plate. The 

 results of these tests are shown in Table 5 along with data on room 

 temperature properties for purposes of comparison. 



The data indicate that although weld strength exceeded that of 

 the base plate at yO^F, the reverse was true at 1750°F, the forming 



109 



