Strengthening low carbon steel sheet - by nitriding after rolling to form fine nitride dispersion

摘要

Deep drawing quality steel contg. (by wt.) 0.002-0.015% C, =0.012% N, =0.08% Al, and in solution =1 of 0.02-0.2% Ti, 0.225-0.3% Nb, or 0.025-0.o% Zr is reduced to its final thickness and possibly annealed and formed to shape, and is then heated at 1100-1350 degrees F in a hydrogen-ammonia atmosphere 1100-1350 degrees F in a hydrogen-ammonia atmosphere to increase the yield strength to =50 k.s.i. by formation of a fine nitride dispersion, the ammonia concentration being in the range 2-10% by vol. and insufficient under the prevailing conditions to permit formation of iron nitride or iron-nitrogen austenite.