Matsushita supplement Zaida

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Specifications	Matsushita supplement Zaida
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ABSTRACT. Development of high- strength steels in recent years has re- quired the weld metal to also improve in terms of mech

Specifications	Matsushita supplement Zaida
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Content	ABSTRACT. Development of high- strength steels in recent years has re- quired the weld metal to also improve in terms of mechanical properties. How- ever, strengthening the weld metal tends to increase susceptibility to hydrogen-as- sisted cracking (HAC); therefore, dif- fusible hydrogen content in the weld metal, attributed to be a major cause of HAC, must be drastically reduced. Flux ingredients containing fluoride ions (F-1) such as fluorspar (CaF2) have been re- ported to reduce diffusible hydrogen content in steel welds. It is believed fluo- ride reacts with hydrogen in the arc at- mosphere to form HF, which is removed from the molten iron because of its low solubility. Preliminary thermodynamic calcula- tions considering the reaction between hydrogen in the arc atmosphere and the fluoride in the slag were performed and predict that KF, MnF3and K3AlF6are more effective in reducing hydrogen than CaF2, which is a common flux ingredient. To verify their predicted effectiveness, ex- perimental FCAW consumables with ad- ditions of these fluorides were designed and fabricated at the Colorado School of Mines (CSM). Welds were produced using these electrodes and the amounts of diffusible hydrogen were measured. The experiments proved the effectiveness of fluoride additions as predicted by the thermodynamic calculations. For exam- ple, reductions of 39–67%, 21–34% and 22–31% in diffusible hydrogen were achieved with the additions of 7.4 wt-% of KF, 4.8 wt-% of MnF3and 5.5 weight percent of K3AlF6, respectively, in com- parison with the experimental results with those of the base electrode (with only CaF2). Introduction Development of High-Strength, Low-Alloyed (HSLA) Steels For the welding of high-strength struc- tural steels, the achievement of high weldability (lower susceptibility for hy- drogen-assisted cracking [HAC]), to- gether with performance requirement has been the most important issue. The strength of quench and temper (QT) steel is based on high hardenability, i.e., high carbon and alloying contents. Therefore, low-temperature products such as bai- nite and martensite tend to appear in the heat-affected zone (HAZ) after welding. These products exhibit high dislocation density, which elevates the internal stress in the HAZ. Since HAC tends to occur in the stress-concentrated areas in the pres- ence of hydrogen, it is highly likely HAC occurs in the HAZ of welded joints of QT steels. To avoid HAC, preheating or postheating is performed, as seen in ship- building practices. However, for cost sav- ings, it would be preferred these processes be eliminated or simplified. To satisfy these requirements, research and development programs of structural steels have been directed toward their weldability and mechanical properties. The high-strength, low-alloyed (HSLA) steels were developed by mini- mizing the impurities and alloying ele- ment contents. The HSLA-80 and HSLA- 100 steels developed by the U.S. Navy during the 1980s contain very low car- bon (0.04%) and sulfur (0.005%) con- tents, and a certain amount of copper ad- dition (1.20 – 1.60%) (Ref. 1). Since carbon is the most influential element on the HAC susceptibility, the low carbon contents of the HSLA steels make them very weldable, although their carbon equivalent values (CEV) may be as high as those of the QT steels. On the other hand, the mechanical properties of the HSLA steel welds are as excellent as the QT steels. This enhancement is mainly obtained by copper precipitation strengthening because of higher addi- tions of copper in these HSLA steels. These steels are also processed by ther- momechanical-controlled processing (TMCP), which includes controlled (low finishing temperature) rolling, acceler- ated cooling from the rolling temperature and direct quenching after rolling. These technologies have also provided excel- lent performance to high-strength steels. Development of Welding Materials for High-Strength Steels Regarding the welding materials for high-strength steels, the mechanical properties of weld metals must match those of the base materials and meet sets of preestablished specifications. Thus, the reduction of weld metal diffusible hy- drogen content becomes the major issue. The reported improvement of weld metal strengths was achieved by optimizing the CEV; therefore, as the strength in weld metals increases, a higher HAC suscepti- bility may result. The upper limit of ac- ceptable weld metal diffusible hydrogen content for high-strength steel welding WELDING RESEARCH SUPPLEMENT \| 295-s RESEARCH/DEVELOPMENT/RESEARCH/DEVELOPMENT/RESEARCH/DEVELOPMENT/RESEARCH/DEVELOPMENT Hydrogen Control in Steel Weld Metal by Means of Fluoride Additions in Welding Flux BY M. MATSUSHITA AND S. LIU Experiments proved the effectiveness of fluoride additions in reducing hydrogen in weld metal KEY WORDS Hydrogen-Assisted Cracking High-Strength Low-Alloy Steels Gas Metal Arc Welding Flux Cored Welding Wires Diffusible Hydrogen M. MATSUSHITA and S. LIU are with the Cen- ter for Welding, Joining and Coatings Re- search, Colorado School of Mines, Golden, Colo.
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Following Datasheets	10-2000-MOON-s (8 pages) 10-2000-NELSON-s (11 pages) 10-2002-HUANG-s (12 pages) 10-2002-VIANCO-s (10 pages) 10-2002-XIE-s (8 pages) 10-2003-COLLINS-s (8 pages) 10-2003-GOULD-s (5 pages) 10-2003-MENDEZ-s (11 pages) 10-2003-SOLOMON-s-1 (10 pages) 10-2003-VIANCO-s (10 pages)
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