Carbon Equivalence and Weldability of Microalloyed Steels
TENNESSEE UNIV KNOXVILLE WELDING RESEARCH AND ENGINEERING GROUP
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This effort sought to determine the validity of carbon equivalent formulae to predict weldability of low carbon microalloyed steels. The HAZ of a range of steels was characterized HSLA 80-130, HY 130, DQ and AC types and Yuriokas formula was found to be the most accurate in predicting HAZ hardness. The CE1 carbon equivalent formula was also found to most accurately predict hardenability except that the effect of copper is not linear above 0.5. The hydrogen sensitivity was evaluated by the Implant, Battelle and UT-Mod Hydrogen Sensitivity tests at two hydrogen levels. The lower critical stress in the implant test was used to define the critical preheat temperatures for steels evaluated. The HLSA 80 type materials may require a preheat of 150 F under highly restrained conditions with hydrogen present. HLSA 130 was found to be superior to HY 130 in regard to hydrogen cracking sensitivity. The high strength steels can be ranked in the order of increasing preheat cracking as HSLA 100-- HSLA 130--DQ 125--HY 130 DQ 80 and AC 50 steels responded well to testing at high hydrogen levels 20ppm and ambient temperature preheat. A soft zone was found in the HAZ of the HSLA, DQ and AC steels which was a function of weld heat input. The soft zone in the copper bearing HLSA steel could be eliminated by PWHT. A probe study showed that the HSLA steel is similar to A 1710 grades with regard to PWHTReheat cracking and that the HAZ toughness decrease is also similar to the A 710 grades.
- Metallurgy and Metallography
- Marine Engineering