AWS D10.18M-D10.18 pdf free download

AWS D10.18M-D10.18 pdf free download.Guide for Welding Ferritic/Austenitic Duplex Stainless Steel Piping and Tubing.
Weld ferrite measurements can be made using either destructive or nondestructive examinations. The most common destructive technique is a ferrite point count which requires removing a section and metallographic preparation and photography. Nondestructive measure- ments can be made using an electronic hand-held mea- suring device described in 11.10. The duplex stainless steels have been known since the 1930s, and these early alloys are often referred to as first- generation DSSs. However, these early grades character- istically had poor weldability and significantly reduced corrosion resistance in the as-welded condition. The addition of nitrogen as an alloying element in the second- generation DSSs is primarily responsible for the improvements in weldability and corrosion resistance. One beneficial role of nitrogen is that of causing austen- ite to form more quickly and at a higher temperature dur- ing the solid state transformation. However, there are incidences such as in rapidly cooled welds where exces- sively high levels of ferrite may be retained. This will be discussed in more detail later.
5.2 Precipitating Phases. As noted above, after the mol- ten metal solidifies as ferrite, some ferrite transforms to austenite down to a temperature of about 1000°C [1832°F]. As the DSS cools below this temperature, other phases such as carbides, nitrides, sigma, and other intermetallic phases can form. Chi phase and other inter- metallic phases are often lumped together with sigma phase, and the term “sigma phase” will be taken here- after to include these other intermetallic phases. Sigma, in significant amounts, can be particularly detrimental in that toughness and corrosion resistance may be reduced. Sigma forms in the temperature range of 700°C to 980°C [1300°F to 1800°F] with the most rapid formation at 870°C [1600°F]. It is formed whenever the alloy is in the 700°C to 980°C [1300°F to 1800°F] temperature range, that is there is an accumulative effect. The total exposure time for sigma formation includes time at the steel mill during in-process heating and exposure time during welding including repair welding unless there is an intervening anneal above 1040°C [1900*F]. The proper level of nitrogen delays sigma formation, but does not prevent it. It has been shown that in the case of alloy 2205 with nitrogen in the upper range of 0.14% to 0.20%，there is about a five minute exposure time at 870°C [1600°F] available before the amount of sigma formed causes a significant loss of toughness and corro- sion resistance.Since time at temperature in processing the wrought products is equally as important as time incurred during welding a very useful document is ASTM A 923. The standard describes three test methods for detecting detri- mental intermetallic phases. The methods include illus- trations of acceptable microstructures, charpy impact test acceptance criteria and a ferric chloride corrosion test. ASTM A 923 can be specified as a procurement require- ment and is particularly useful for the thicker product forms. It is an aid in assuring that a significant portion of the allowable“five minutes at sigma formation tempera- ture”has not been used at the steel mill, allowing less time at temperature during welding.AWS D10.18M-D10.18 pdf download.