Abstract: The microstructure and solidification behaviour of stainless steel layer in composite pipe were investigated by means of TEM and SEM. The results show that the crystal of stainless steel layer grows in columnar grains. The columnar grains consists of austenite. A thin layer of ferrite exists between the columnar grains. The intermetallic compound AINi precipitates in ferrite zone. The σ phase precipitates at the phase boundaries between austenite and ferrite.