Annealing is a heat treating process that modifies the material properties of metals that have different crystal structures at low and high temperatures. Annealing softens the metal, increases fatigue strength and relieves internal stresses in the metal introduced earlier in the laser machining stage. Temperature and time determine the particular thermal cycle. The cycle begins by controlling the heating rate until the metal reaches the annealing temperature, holding that temperature for a certain period, and adjusting the cooling rate according to the desired properties.

annealing

Before/after annealing

Material purity and grain size affect the physical properties of the material. The quality of the original ingot determines material purity, whereas grain size can be influenced by the annealing process, aiming at achieving homogeneous, fine grains.

Homogenous composition and distribution of the grains together with fine grain size improve the material’s break elongation, tensile strength, fatigue strength, corrosion resistance and surface smoothness. These physical properties enable smaller struts, thinner walls, and improved surface quality.

STI uses annealing to improve the mechanical properties of metals, such as: Stainless steel (316LVM), titanium and cobalt-chrome alloys (L605/MP35N). STI performs annealing at various controlled heating and cooling temperatures (≤ 1,250°C). The specific parameters for performing a particular annealing cycle depend on the material being treated and the intended application.

STI uses three furnace systems and has developed specific heat treatment profiles for each of the metal alloys commonly applied for implants manufacturing. To achieve optimal results, STI fine tunes the annealing profile for each product by measuring tensile strength and break elongation in-house and determining grain size through the services of the Technion’s Metallurgic Department.