Microstructure and Bond Strength of Steels Using Low-Cr-Substituted Cementite Foil

Abstract

In the preceding paper, the eutectic liquid that appears between cementite (θ) foil and austenite has been proposed the most suitable for rapid transient-liquid-phase (TLP) bonding of steels. A partial substitution with Cr was required for metastable θ to be thermodynamically stable up to solidus temperature. On the other hand, the liquid region disappeared quickly by C diffusion and results in a severe Cr segregation at bonded interface. This work aims to decrease the ratio of Cr substitution in θ so as to eliminate a time for homogenization and to allow the use of as-bonded steel parts. The synthesized θ with 1 mass% of Cr (1Cr-θ) showed an enhanced tendency of decomposition on cooling from 1373K. However, the 1Cr-θ filler has been confirmed to give the eutectic liquid that dissolved V during TLP bonding of V-microalloyed steels. After holding for 180 s at 1453K, a gradient ferrite–pearlite microstructure has been attained in the bond without any boundaries or intermediate phases. The bonded steel showed a tensile strength and elongation corresponding to the original V-steel.