1994 Volume 12 Issue 4 Pages 521-527
In order to determine optimum parameters of PWHT (Post Weld Heat Treatment) for improving the toughness of HAZ of 780 and 980 MPa class HSLA steels welded with high heat inputs, the effect of PWHT on the toughness of simulated weld HAZ of the steels has been systematically investigated in relation to the decomposition of the M-A (Martensite-Austenite) constituent.
The optimum PWHT time and temperature proposed by considering the practical workability are 8 hr's and 623 K for the weld CGHAZ (Coarse Grain HAZ) and ICCGHAZ (Intercritically Reheated CGHAZ) of the employed steels of 780 and 980 MPa classes.
The optimum PWHT parameters have been tested on specimens actually welded with a heat input twice as high as the conventional. The toughness of the actually welded specimen, estimated from CTOD value, is also improved significantly by PWHT under the proposed conditions, and satisfies demands for practical application. The tensile strength of the actually specimen welded with a heat input twice as high as the conventional, estimated from wide tensile test pieces, has been presumed to satisfy the specification of weld joint using 780 MPa class HSLA steel.
The tensile strength of the actually welded joint, although it includes the HAZ softening zone, is calculated to be a value satisfying the specification of 780 MPa class steels, provided that the width of the test specimen is more than 5 times as large as the thickness.