1984 Volume 2 Issue 3 Pages 483-490
The transformation behavior of the ferritic weld metal in 9%Ni steel was investigated using a dilatation technique. (1) Along dendrite interfaces of the ferritic weld metal, segregations of silicon, manganese and nickel are formed. (2) The Ac transformation temperatures of the ferritic weld metal are lowered mainly by the increased nickel addition (11%Ni) to the weld metal. (3) On account of the nickel segregation along the dendrite interfaces, the Ac transformation temperatures of the interfaces are further lowered. (4) In the reheating process of the ferritic weld metal, it commences the true Ac1 (austenite) transformation from the dendrite interfaces. (5) The optimum tempering temperature of the ferritic weld metal is in the range from the true Ac1 temperature to about 600 degree C. The micro-struc-ture of the tempered ferritic weld metal comprises ferrite, retained austenite and cementite precipitating along the dendrite interfaces. (6) At reheating temperatures higher than about 600 degree C, the martensite transformation begins to occur from the dendrite interfaces during cooling. At a temperature of about 700 degree C (Ac3), the whole structure becomes martensite. (7) At reheating temperatures higher than about 1100 degree C, the bainite transformation followed by the martensite transformation is performed during cooling. (8) It is attributable to the manganese segregation which lowers the carbon activity that the cementite precipitation during tempering is concentrated at the dendrite interfaces. (9) Although the toughness of the ferritic weld metal is deteriorated, the sites of the cementite precipitation can be dispersed by increasing silicon content in the weld metal.