Tham khảo tài liệu 'asm metals handbook - desk edition (asm_ 1998) episode 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Weld Cracking. Austenitic stainless steel welds are extremely tough and ductile and thus cold weld cracking is almost never a problem. However austenitic stainless steels are susceptible to hot cracking or microfissuring as they cool from the solidus to approximately 980 C 1800 F . Microfissuring can be prevented or kept to a minimum by eliminating or reducing tensile stress imposed on the weld during cooling through this range. To some degree microfissuring can be controlled by controlling concentrations of residual elements such as phosphorus. However the most common control measure is to ensure the presence of at least 3 to 4 ferrite in the as-deposited weld. Small amounts of this phase seem to prevent the cracking that often occurs in fully austenitic weld metal. Ferrite content is usually estimated on the basis of composition by use of the DeLong diagram which is a modification of the long-used Schaeffler diagram or more recently developed weld constitution diagrams developed by the Welding Research Council for more highly alloyed weld metals. DeLong s modification takes into account the potent austenitic stabilization effect of nitrogen. Because ferrite contents calculated in this manner are not completely precise it is recommended that for critical applications actual ferrite content be determined by magnetic analysis of as-deposited weld metal. For production welds measurement is especially preferred to calculation in the common instance where a high-ferrite welding electrode is used to weld lower-ferrite base metal. Weld composition then varies with the degree of dilution. Control of ferrite content is not always an acceptable solution to microfissuring. Ferrite is a magnetic phase reduces corrosion resistance in some media and can lead to embrittlement in long-time elevated-temperature service exposure due to precipitation of sigma phase. Ferrite content in the weld can be reduced significantly typically by 2 to 4 by annealing after welding but where .
