[23]
(1. 6) 1. 4509 < 10 (1. 8) < 10 (1. 7) - (16. 5)*) 345 mV 1. 4162.
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[24]
(16. 1)*) 21% Cr ferritic.
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[33]
(3. 8) As could be expected, the duplex 1. 4162 performs the best under both test potentials. The 645 mV CPT values range from the MAG welded 19 to LBW and RSW 23 °C and the 345 mV values from LBW 17 to RSW 33 °C. The excellent performance of LBW and RSW specimens is very surprising, because the rapid cooling associated with both these processes favours ferritic solidification and hence higher ferrite content (e. g. ferrite number or percentage) that should affect the corrosion resistance negatively rather than positively. It should, however, be noticed that the scatter with the 1. 4162 RSW samples is relatively large. Still, the CPT is at least equal to that of the base material. Somewhat similar tendency to 1. 4162 can be seen in the CPT results of RSW 1. 4509, but in this case, and also lesser with LBW samples, the scatter is so extraordinary large that justified conclusions are difficult to make. For the novel 21% Cr ferritic the scatter is considerably smaller and the CPT results appear very promising: both the base material and RSW CPT is at least equal or even higher than that of the duplex 1. 4162. This sets great expectations for service properties even in process environments. However, the discrepancy between LBW and RSW results need further analysis work. As mentioned earlier, relatively rapid cooling rates are typical of both of these methods, yet the CPT behaviour is very different. Unlike with the duplex 1. 4162, the primary solidification mechanism remains the same regardless of cooling conditions, so alternative explanations will have to be found for this phenomenon. Finally, quite a few of the studied cases, especially with the medium Cr ferritic 1. 4509 (indicated by an asterisk in Table 4 still require further experimental and analysis work (i. e. more repetitions), because of inconsistencies in results, typically appearing as excessive scatter and/or totally unpredictable and irregular behavior of test results within the repetitions. This inconsistency may also depend on the specimen pre-treatment issues, such as pickling: the same pickling procedure may not necessarily be the optimal one for all the materials, and the pickling conditions – substance, time and temperature – should probably be controlled very carefully in order to ensure of the repeatability. Once the above issues have been carefully studied, the usability of CPT testing for this kind of ranking and comparison purposes should be seriously evaluated. Summary and conclusions This study covers the very preliminary welding experiments and characterisation results of a novel low nickel duplex and two low carbon, double stabilised ferritic stainless steel grades. The materials and their laser and resistance spot welded joints were subjected to mechanical testing and critical pitting temperature (CPT) corrosion tests. Based on the results, the following can be concluded: · The base material strength values were reached in most weld tensile test cases, indicated by base material failure. Only the laser welded duplex grade 1. 4162 remains somewhat below the base material level and also shows fracture locating in the weld metal · Comprehensive CPT data were achieved for all the base materials and their welds using two different polarisation potentials · Regarding both parent material and weld tests the lean duplex 1. 4162 showed the best overall performance · The new high-Cr ferritic grade is promising in both as-received and welded conditions · The medium-Cr 1. 4509 shows great inconsistencies; further experiments are needed to analyse e. g. the pickling effect on the results.
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