Effect of chromium on low-temperature deformation of high-purity iron
A series of very low interstitial Fe-Cr alloys containing 0, 1, 3, 5, and 10 wt% Cr were prepared by vacuum melting and fabricated under argon to 1.83 mm diam wires exposed in an alumina system to wet hydrogen for 200 h at 1423 K followed by 1000 h in ZrH2-purified hydrogen at 1573 K. The wires were then transverse-rolled into thin sheet and cut into tensile specimens subjected to electropolishing and strained to fracture in a series of cryogenic baths ranging from 4.2 K to room temperature. It is shown that small Cr additions lower the twinning stress so that yielding occurs by twinning rather than by slip. Cr in amounts up to 10 wt% has little effect on the yield strength of high-purity Fe between 147 and 300 K, and ductility is not greatly affected at any test temperature. Higher solute contents provide appreciable strengthening only at temperatures of 112 K and below.