Effect of Hydrogen on Toughening of a Low Alloy Steel

摘要

A low alloy steel containing 0.10C, 0.25Si, 0.87Mn, 0.56Cr, 0.47Ni, 0.21Mo, 0.023S and 0.01P (mass percent) was cold rolled to 1.6 mm thick sheets and recrystallised at 700 deg C to get ferrite grains of 8, 21.5 and 32.5 mum with a random distribution of some spheroidal carbide particles and a few inclusions. Tensile specimens prepared from these sheets were cathodically charged in 1 N NaOH and 0.1 N H_2SO_4 solutions for periods varying from 2 to 24 h, with a current density of 50 mA/cm~2. Tensile tests were carried out with a cross-head velocity of 1.2 mm/min, fracture surfaces were examined by SEM and the deformed structure was examined by TEM. The increase in hydrogen content, up to certain limit, has been effective to cause an increase in both ultimate tensile stress and percent elongation resulting a toughening of the steel, while the work hardening is not remarkable. Increase in the ferrite grain size has been observed to enhance this effect. The tensile behaviour has been correlated with observed fracture characteristics and dislocation substructure in the ferrite matrix. The toughening effect has been explained in the light of dislocation solute interactions and the damage caused by hydrogen.