It has been thought for some time that there may well be a yield point in steel due to hydrogen. This letter is to describe experiments that demonstrate the presence of such a yield point.
The base material used was commercial hotrolled SAE 1020. The specimens were plungeground from l/2 in. rod to an 0.20-in. specimen diameter. They were subsequently polished, using 1, 0, 3/O emery paper, degreased, annealed in dry hydrogen for 1 hour at 600ยฐC and cooled in the same atmosphere in a water-cooled extension of the furnace. In an attempt to remove any dissolved hydrogen, this treatment was followed by vacuum annealing at 600ยฐC for 7 hours, and cooling under vacuum.
In order both to eliminate the carbon and nitrogen yield points and to allow for the subsequent absorption of large quantities of hydrogen, the specimens were prestrained 15% at -78ยฐC in a bath of dry ice and alcohol, unloaded, and placed immediately in liquid nitrogen to eliminate possible aging.
Group I of the specimens was tested at -150ยฐC in a bath of liquid Freon 12 immediately after up-quenching from -196ยฐC.
Group II was charged with hydrogen electrolytically for 4 hours in a solution of 4'% H&S04 with addition of Asz03 as a catalytic poison. Current density was in the neighborhood of 0.2 amp/in2, and the bath temperature never rose above 30ยฐC. The specimens were washed and placed in liquid nitrogen immediately, then tested at -150ยฐC as for Group I.