Carbon Equivalent (Pcm) Limits for Thick Carbon and Low Alloy Steels

摘要

Experimentally determined preheating/interpass temperatures necessary to prevent hydrogen-assisted cracking of restrained butt welds were established and compared to the best algorithms available to predict such cracking. Weldability tests on large-size plates of ABS & MIL-S-22698 Grades B D and DH-36 as well as ASTM A612 steels were conducted at Electric Boat Corporation using three different plate thicknesses three welding procedures and two levels of diffusible hydrogen. The plate thicknesses were 25mm (1 in) 44mm (1.75in) and 64mm (2.5in). The welding procedures included: FCAW with E71T- 1MH8 FCAW with low-hydrogen E71T-12MJH4 and pulsed GMAW with MIL-70S-3 electrodes. Navy-modified WIG tests of sub-size specimens were also performed to determine preheat/interpass temperatures and to compare them with preheat temperatures obtained from the weldability tests conducted on large-size plates. Factors affecting hydrogen-assisted cracking were also evaluated; such as (a) the effect of composition of plates produced in integrated mills vs 100% scrap mills and (b) the effect of fillet joints vs butt joints. The best preheat prediction algorithm to match the experimental results was found. Recommendations to establish Pcm limits to reduce hardenability and possibly reduce the minimum required preheat temperature to 16 degrees C (60 degrees F) for Grades B D and DH-36 shipbuilding steels are presented.