Biomedical alloys like Titanium, CrCoMo and ASTM F138 stainless steel do not show satisfactory cost/benefit ratios. The high quality alloys (Ti and CoCrMo) are very expensive, whereas the steel does not show great corrosion resistance and also contains Ni. Recently several published papers showed that nickel is an allergenic element. Based on this information laws have been introduced in the European Community and in the USA in order to restrict the use of nickel containing materials for application on human body.

Based on the fact that nitrogen causes significant improvements to austenitic stainless steels properties, two new high nitrogen nickel free stainless steels were designed in order to reach better cost/benefit ratios. Mn and N (0.4 wt%) substituted Ni and Mo was added to one of alloys to improve corrosion resistance. The steels were melted in a vacuum induction furnace. The ingots were forged and solubilized for three hours at 1423K and water-cooled to guarantee a fully austenitic structure and no nitride precipitation.

All tests were performed with the two new alloys and the ASTM F138 (target to be replaced), in order to allow comparative tests. After ordinary metallographic tests using regular procedures, biocompatibility tests were performed in grown up male mice, in which the alloys were subcutaneously implanted for 11 and 47 days. Tension tests were also carried out. The resulting mechanical properties were always higher than those specified in the ISO 7206 - 3 standard for ASTM F138 stainless steels.

Pitting corrosion resistance of the alloys was analyzed through potentiokinetic reactivation, whereas the intergranular corrosion was analyzed through practice A 262 ASTM standard (types of corrosion to which implants are vulnerable). One of the high nitrogen alloys showed higher corrosion properties when compared with the ASTM F138 steel.

These results are discussed considering nitrogen enhancement of mechanical and corrosion properties when in solution in stainless steels.