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

摘要

In our previous paper, the eutectic liquid that appears between the cementite (θ) foil and austenite was proposed to be most suitable for rapid transient-liquid-phase (TLP) bonding of steels. A partial substitution with Cr was required for metastable 6 to be thermodynamically stable up to the solidus temperature. On the other hand, the liquid region disappeared quickly by C diffusion, leaving severe Cr segregation along the bonded interface. The present study aims to decrease the ratio of Cr substitution in 9 so as to eliminate the homogenization step and allow the use of steel parts as-bonded. Compared to θ with a higher Cr substitution, the synthesized θ with 1 mass% Cr (1Cr-θ) showed an enhanced tendency to decompose on cooling from 1 373 K. However, the 1Cr-θ foil was confirmed to give the eutectic liquid that dissolved V during TLP bonding of V-microalloyed steels. After holding for 180 s at 1 453 K, a gradient ferrite-pearlite microstructure was obtained in the bond without any boundaries or hard layers due to Cr segregation. The bonded steel showed a tensile strength and elongation corresponding to those of the original V-steel.