The corrosion resistance of spot-welded and induction-heated austenitic stainless steels EN 1.4301 and EN 1.4318 was investigated in 3.5% sodium chloride solution at ambient temperature. In potentiostatic measurements pitting corrosion of spot-welded and induction-heated samples occurs at lower potentials than in the base materials. The corrosion pits initiate on the heat-tinted areas. In immersion tests the surface of the spot welds was not attacked but crevice corrosion was found between the sheets around the spot welds. The compositions and structures of the heat-tinted oxides were investigated by surface spectroscopy. The results indicate the yellow, red and blue oxides to have a double-layered structure with an iron-rich and chromium-depleted outer layer and a less iron and more chromium containing inner layer. A chromium-depleted layer was found in the base material under the yellow heattinted oxide on an induction-heated sample. Significant amounts of copper contamination were found on the spot-weld surface near the weld edge.

Mechanical and corrosion properties of spot-welded highstrength austenitic stainless steels EN 1.4318 2H/C1150 and EN 1.4318 2H/C850 were studied. Microhardness measurements, lap shear and cross-tension tests, corrosion fatigue tests and corrosion tests were carried out. The corrosion environment was 3.5% sodium chloride solution at þ50 8C in the corrosion fatigue tests and 3.5% sodium chloride solution at ambient temperature in the electrochemical pitting corrosion tests. Stainless steel EN 1.4318 2H/ C850, t ¼ 1.92 mm, exhibited better fatigue endurance than EN 1.4318 2H/C1150, t ¼ 1.2 mm, and EN 1.4318 2H/C850, t ¼ 1.0 mm, stainless steels did. There were no significant differences between the stainless steels of different strength levels (2H/C850 vs. 2H/C1150) in the line load range analysis of the fatigue data. High hardness gradient was found in the heat-affected zone (HAZ) of EN 1.4318 2H/C1150 stainless steels. EN 1.4318 2H/C1150, t ¼ 1.2 mm, stainless steels seemed to have slightly higher lap shear strength with the same nugget diameter as EN 1.4318 2H/850, t ¼ 1.9 mm, stainless steel. In the case of EN 1.4318 2H/C1150 stainless steel increase in the nugget diameter bigger than required 5Ht did not increase the cross-tension force significantly. The pitting corrosion susceptibility of the spot-welded samples and the base materials of the steels EN 1.4318 2H/C850 and EN 1.4318 2H/C1150, t ¼ 1.2 mm, was investigated by measuring the corrosion current for 1 h at þ100 mV versus saturated calomel electrode (SCE) in 3.5% sodium chloride solution at ambient temperature. Pitting corrosion occurred in all spot-welded samples but not in the base materials. There was a difference between the investigated steels in the location of the pits. In stainless steels EN 1.4318 2H/C850 the pits appeared around the spot weld, but in the steel EN 1.4318 2H/C1150, t ¼ 1.2 mm, the pits are located mainly at the spot-weld area.

Corrosion fatigue and fatigue properties of spot-welded austenitic stainless steels EN 1.4301 and EN 1.4318 in 2B or 2F and 2H conditions were investigated in 3.5% sodium chloride (NaCl) solution and in air. The shear-loaded specimens were single spot overlap joints.The effect of steel grade, load, frequency, temperature and type of chloride on fatigue strength of the 1.0 mm thick steel specimens was evaluated by using the Taguchi Method Ò . Increase of the load, rise of temperature and lowering of the frequency accelerate corrosion fatigue of the spot-welded steel samples. Type of chloride had only a minor effect on fatigue strength. The 2B grade spot-welded steel samples exhibited better fatigue strength than the 2H grade samples of the same steels.On the basis of the results obtained by the Taguchi Method Ò the S-N curves were defined for the spot-welded 1.9 mm thick steels in 3.5% sodium chloride solution at 50 8C. For reference the fatigue experiments were performed in air at the ambient temperature. Comparison of the results shows that corrosive environment decreases remarkably the fatigue strength of the spot-welded steels. The EN 1.4301 2H and EN 1.4318 2H steels have no distinctive difference in their corrosion fatigue strength even though they show a different fatigue behaviour in air.The microscopic investigations indicate that the fatigue cracks in the spot welds initiate from either side of the recrystallised area in the HAZ outside the spot-weld nugget both in air and in the corrosive environments. Pre-exposure in the corrosive environment seems to have no major influence on the crack initiation, because the cracks do not initiate at the heat-tinted area of the crevice where the crevice corrosion occurs.

Corrosion fatigue and fatigue properties of weld-bonded and spot-welded austenitic stainless steels EN 1.4301 and EN 1.4318 in 2B or 2F and 2H conditions were investigated. The corrosive environment was 3.5% NaCl solution at þ 50 C. In air the fatigue strengths of the weld-bonded single spot lap-jointed specimens were significantly higher than those of the spot-welded specimens used as reference. In the corrosive environment the difference was markedly reduced. The failure mode of the weld-bonded specimens was adhesive in the corrosive environment and cohesive in air. The difference in the failure mode of the weld-bonded joints did not affect the fatigue crack initiation in stainless steels, which always occurred at the outer edge of the corona bond area.

Corrosion performance of NiCr and NiCrBSi coatings produced by APS, HVOF, and HVAF was studied by electrochemical measurements and immersion tests in 0.5 and 3.5 wt.% NaCl solutions. In the electrochemical measurements, the NiCr coatings performed better than the NiCrBSi coatings. The effect of the coating process on the corrosion resistance of the material was significantly lower than that of the selected materials, NiCr or NiCrBSi. All the coatings showed a tendency to passivate but suffered from localized corrosion. During immersion exposure for ten weeks, localized corrosion appeared at heterogeneous areas of the coatings, including voids, defects, or powder particles that had not melted during the spraying process.