Jenny’s D-9 Lit Summaries - 3/13/06
Mudali, “Influence of Titanium addition on pitting, crevice and intergranular corrosion resistance of type 316 Austenitic Stainless Steel”
Immersion corrosion tests, pitting and crevice corrosion tests, and intergranular corrosion tests were carried out on two compositions of D-9 stainless steel alloys (aka titanium modified, austenitic ss) and compared to a standard 316 stainless steel alloy. The two D-9 alloys differed mainly in their carbon to titanium ratios, alloy i being 0.024/.21 and alloy ii being 0.035/.34.
For the immersion corrosion tests, the alloy samples were submerged into a boiling solution of 11% H2SO4, 3% HCl, 1% CuCl2, and 1%FeCl3 for 24 hours. The samples were weighed before and after this process to determine the weight loss due to corrosion in milligrams per square decimeter. It was determined that there wasn’t much difference between the two D-9 alloys, but they did lose less than the 316.
Potentiodynamic anodic polarization studies were carried out to test for pitting and crevice corrosion by determining the critical pitting potential and critical crevice potential. Elemental analysis were performed on the pits using an Electron probe microanalyser. The potentials for both D-9 alloys were significantly higher than 326.
Intergranular corrosion tests found that the alloy containing the higher amount of carbon formed a dual oxide structure after sensitizing treatment at 923K for 50 hr. This is most likely because there wasn’t enough Ti to form TiC or TiN, which retards the growth of the dual oxide layer by tying up the C and N. Further testing of the sample that formed a dual structure was performed by immersing in a Cu-CuSO4-H2SO4 solution and then subjecting it to a U-bend test. It did not fail this test and therefore displayed that D-9 has good inter-granular corrosion resistance.
Overall, the addition of titanium kept in solid solution to form D-9 showed
superior corrosion resistance to 316. The pitting and corrosion resistance was higher,
the resistance to chloride attack to the stable passive layer was improved, and the
samples were no longer susceptible to intergranular corrosion.