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

作者：Tanaka Kouji^*; Takamiya Hiroyuki; Iwata Noritoshi; Nakanishi Koukichi

来源：ISIJ International, 2011, 51(3): 423-428.

• transient-liquid-phase bonding
• eutectic liquid
• cementite
• diffusion simulation
• dissolution
• segregation

In our previous paper, the eutectic liquid that appears between the cementite (theta) 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 theta 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 theta so as to eliminate the homogenization step and allow the use of steel parts as-bonded. Compared to theta with a higher Cr substitution, the synthesized theta with 1 mass% Cr (1Cr-theta) showed an enhanced tendency to decompose on cooling from 1 373 K. However, the 1Cr-theta 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.