*3.6. Nickel Release in Relation with the Manufacturing Process*

In our laboratories, a large number of nickel extraction tests in compliance with EN 1811-2011+A1:2015 standard [50] were carried out on the 316 L grades manufactured by five different steelmakers from EU, Japan and USA. There was a significant difference in the quantities of Ni released, compared to the chemical composition of steels, which depends on the steelmaker. The conclusions are presented in Figure 27. It should be pointed out that despite the fact that the grade of steel is in conformity with the classification standards, their behavior was markedly different from one manufacturer to another, due to production parameters, such as the casting volume, alloying additions, and deoxidizing agents.


**Figure 27.** Factors influencing the amounts of nickel released during the manufacturing process.

The heat treatments resulted in a reduction of the nickel release rates. The surface state had little influence. On the other hand, the hardening processes strongly influenced the quantities of nickel released. The increase in hardness greatly decreased the corrosion resistance and increased the amount of nickel released. Another factor which strongly influenced the quantities of nickel released was the inclusion state and the existence of secondary phases in the structure of steels. Being aware of these causes, subcontractors demand from the steelmakers a very strict specification respecting in the manufacturing of steels.
