Corrosion Resistance of Stainless Steels Intended to Come into Direct or Prolonged Contact with the Skin

Abstract

The biocompatibility of materials in contact with a living tissue becomes a puzzle in the overall picture of assessing the toxic effects of chemicals that come into contact with us. Allergic reactions to substances are a significant and growing health problem affecting large parts of the population in Europe. Wristwatches are objects worn in prolonged contact with the skin, being subject to localized corrosion, especially pitting and crevice types, in sulfide-chloride medium, and high wear in the bracelets joints. Watches of medium quality are usually made of stainless steels. The X2 CrNiMo 17-12-2 316L grade as well as X1 CrNiMo 20-25-5 Cu 1 or 904L are commonly used, having good resistance to generalized corrosion. The passive layer is nevertheless insufficient to ensure complete immunity in all cases of localized corrosion encountered during wear. For this reason, a high-corrosion-resistant steel: X1 CrNiMo 18-15-4 N 0.15 or 317LMN, from three different suppliers was evaluated. Metallographic characterization was carried out. The corrosion behavior evaluation was performed for the generalized corrosion, pitting and crevice corrosion and galvanic corrosion. Galvanic couples steel 317LMN-gold 18K alloy 3N and gold 18K 5M were used. The results of the generalized and pitting corrosion test indicated three basic groups. All of the 317LMNs were similar. The 316L variants tested noticeably worse. The 904Ls were difficult to discern, but certainly easier than the 316Ls and, possibly, at least comparable to the 317LMNs.

Keywords: 316L; 317LMN; 904L; Kendal tests; austenitic stainless steels; galvanic couplings; generalized corrosion; localized corrosion; mixed potential.

Figure 1

(a) Steel–brazing–gold 18K. (b) Link gold 18K-steel with pins.

Figure 2

(a) Potential-current relationships for the case of a galvanic couple between two corroding metals. A: more noble metal; B: less noble metal [35].(b) Effects of polarization on metal potential (Evans diagrams).

Figure 3

Measurement by microelectrode technique on the steel part of the bracelet.

Figure 4

Metallographic structures, performed by optical microscopy, for # 1, # 5, # 7, and # 8 steels. (a) #1 317LMN: Supplier 2; (b) #8 316L: Supplier 1; (c) #5 317LMN: Supplier 1; (d) #7 317LMN: Supplier 1.

Figure 4

Metallographic structures, performed by optical microscopy, for # 1, # 5, # 7, and # 8 steels. (a) #1 317LMN: Supplier 2; (b) #8 316L: Supplier 1; (c) #5 317LMN: Supplier 1; (d) #7 317LMN: Supplier 1.

Figure 5

Semi-logarithmic potentiodynamic curves for all grades.

Figure 6

Semi-logarithmic potentiodynamic curves for the 316L (#8 and #9) grades and 904L (#10, #11, and #12) grades, which are currently used for items in contact with the skin.

Figure 7

Potentiodynamic curves in linear axes for 317LMN, 904L, and 316L steels.

Figure 8

Linear potentiodynamic curves of 316L (#8 and #9) and 904L (#9, #10, and #11) steels, usually used in watchmaking.

Figure 9

Potentiostatic scan curves for #2 and #11steels evaluated for crevice-pitting corrosion.(a) #2- 317LM* 20-19-4; (b) #11-904L*** 20-25-5 Cu.

Figure 10

Sample #8 after the crevice-pitting corrosion test.

Figure 11

Galvanic currents measured in coupling #1/(3N, 5N)18K gold and #10/(3N, 5N)18K gold.

Figure 12

Galvanic currents measured in couplings #8/(3N, 5N)18K gold.

Figure 13

Determination of I_coupling and E_coupling for the coupling gold 18K/steels. (a) Coupling #1/3N; (b) Coupling #10/5N.

Figure 14

Evans diagrams drawn for studied steel/gold couplings. (a) Coupling #1/3N; (b) Coupling #1/5N.