YIELDING AND FLOW CHARACTERISTICS OF LOW-CARBON STEEL BETWEEN AMBIENT AND LIQUID NITROGEN TEMPERATURES

The yielding behavior and flow characteristics of a low-carbon rimmed steel and a titanium-stabilized steel were examined between ambient and liquid nitrogen temperatures. The initial grain size and carbide morphology were varied by suitable thermal-mechanical treatments, while temper rolling was used to prestrain representative samples. Yielding at room temperature occurred heterogeneously in the annealed rimmed steel, and homogeneously in the titanium steel. With tensile testing at low temperatures, plastic instability upon yielding was observed in both steels. The plastic instability transition temperature, TPI, was analyzed in terms of the quantities σi and ky in the Hall-Petch relationship, σy2 = σi + ky d-1/2, and the influence of interstitial content and temper reduction on σi and ky are discussed. In the annealed condition TPI for the titanium steel was found to be approximately 100 F lower than for the rimmed steel. However, a strong grain size dependency was observed for both steels, i.e., only moderate to fine grained specimens exhibited a TPI. Temper rolling raised TPI for the titanium steel with all reductions, while for the rimmed steel TPI was lowered initially for temper reductions up to approximately 0.75 percent. Electron microscopic examination did not reveal any correlation between TPI and deformation structure. © 1969 by ASME.