Welding parameters

The enhanced strength and corrosion properties of duplex stainless steels depend on maintaining equal amounts of the austenite and ferrite phases. The welding thermal cycle can dismpt this balance therefore, proper weld-parameter and filler metal selection is essential. Precipitation-hardened stainless steels derive their additional strength from alloy precipitates in an austenitic or martensitic stainless steel matrix. To obtain weld properties neat those of the base metal, these steels are heat treated after welding. 

A hot tap shall not be considered a routine procedure, but shall be used only when there is no practical alternative. A hot-tap thermal analysis program shall be used to review, analyze, and provide the product flow and weld parameters during the hot tap. Examples of conditions where hot tapping is not permitted are as follows ... 

To perform automatic TIG orbital welding, the use of a machine with a printout of the welding parameters is preferable. Develop a set of acceptable... 

The surface smoothness of the machines in the machine building industry is of the order of a tenth part of a millimeter. Welded parts on such a machine must be processed as the welding may be 2 mm or more thick. To reduce this thickness to the lowest possible measure and to save electrodes and avoid additional machine processing of the welding, an experiment has been designed to model the influence of welding parameters on welding thickness. Factors and varia-... 

Risk evaluation programmes exist, for pressure vessels, which take into account European Directives [12] the risk factor - related to material brittleness and embrittlement, corrosion effects and localised stresses - is elevated and requires the adoption of rigorous safety measures. The manufacture and control procedures - including welding parameters and structural solutions - should be, in this case, more accurate and devoted to avoid the described defects. 

There is clearly a microstructural dependence, and studies on HAZs show corrosion to be appreciably more severe when the material composition and welding parameters are such that hardened structures are formed. It has been known for many years that hardened steel may corrode more rapidly in acid conditions than fully tempered material, apparently because local microcathodes on the hardened surface stimulate the cathodic hydrogen evolution reaction. (Bond)5... 

Weldability of the CP-Ti was not as good as that of the Ti 15-3-3-3. Sound welds were produced, but flash was excessive and the volume of material expelled from the weld zone resulted in substantial sheet thinning the sheet thinning was particularly significant because of the gage of the base metal sheet (2 mm). Figure lb shows a top surface view of the weld in which the heavy flash is visible. The production of flash appears to be related to sticking of weld material to the FSW tool. Weld parameter optimization should result in improved weld quality. 

The ultrasonic welding of ETFE can be achievedl" with a weld factor of 0.8. The success of this technique is dependent on joint design and welding parameters such as the contact time and pressure. Typical welding conditions include a contact pressure of 170 kPa and a cycle time of 2 secs. 

Cederqvist studied 17 different tool materials to friction stir weld 50 mm thick copper (Ref 33), and the first material evaluations were for use as the tool pin. Tungsten carbide-cobalt pins provided the initial welding parameter development, but tool life issues (due to large spindle eccentricities) made this tool material impractical for production. Likewise, eccentricity issues caused PCBN, alumino-silicate, and yttria-stabilized zirconium oxide pins to fail within the plunge or dwell sequence of the friction stir welds. A majority of e pins manufactured from refractory metals (four molybdenum-base and three tungsten-base) did not have dimensional... 

The sharp temperature gradient at or near the tool/workpiece interface constrains the thermally softened, plasticized zone within the region bounded by the tool shoulder, anvil, and parent material. Weld parameters, coupled with the pin tool design and materials, control the volume of metal heated, of which a portion is then swept by the mechanical working portion... 

Alloy composition weld parameters not transferable from one aluminum alloy to another... 

Figure 5.28(b) illustrates the ability to fully recover hardness when welding in the T4 temper followed by an artificial age, whereas when welding in the T6 temper (Fig. 5.28a), small hardness minima still are evident in the HAZ. Note the similarity in hardness drop for the T6 temper between Fig. 5.27 and 5.28(a), except for the hardness isotherm in Fig. 5.27 attributable to the tool shoulder. This one difference may be due to location of the hardness trace, sheet thickness, and/or weld parameters. However, with potentially different welding practices, that is, different heat inputs between these two research studies, it is interesting that the hardness curves are nearly identical. 

A-36. Almost 200 m (over 200 yd) of A-36 have been welded using PCBN tools. A wide range of weld parameters has been found to give fully consolidated welds. Surface quality is excellent. No mechanical property data are available. 

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