Introduction:
Nowadays, allover the world, the production of surgical needles is usually made of stainless steels. A stainless steel means a steel containing Chromium (Cr). The main function of this Chromium addition is to increase the corrosion resistance of the steel. Surgical needles have complicated shape and should present the best compromise between higher final strength, no breakage during use, good attaching for the suture thread and good constant penetration in the tissues. The surgical needles may be coated by silicon to improve the penetration power, in the same time this coating has an impact on the needles shining. In order to manufacture surgical needles, we can find 3 main stainless steels families:

• Martensitic
• Maraging
• Austenitic

The qualitative parameters for the surgical needles:

1. Bending strength:
   Is the maximum force (N.cm) required to bend the needle backward until 90 degrees.
2. Ductility:
   Is the number of needle bendings backward and forward 90 degrees before the needle breakage
3. Corrosion resistance:
   Is the corrosion resistance of the needle while immersed in Copper Sulfate and Sodium Chloride Solutions.
4. Hardness:
   Is the Vickers (HV) hardness of the steel, after having cut the needle. Measured by micro-hardness tester.

General types of needles metals:

1. Martensitic steel (AISI 420 and 420F series):
   Chemical Composition: Carbon(0.1-0.4%) and Chromium(11.5-14.5%) . It is the oldest stainless steel used in manufacturing of surgical needles and still the basic one of the market for its good price. However its main draw back is the very limited bending resistance, ductility and corrosion resistance.
2. Maraging steel:
   Chemical composition: Low content of Carbon, Nickel(4-12%) and Chromium(10-17%). This steel was originated from 400 family with some modification (additional elements) for hardening precipitation. The additional elements like Titanium, Copper, Molybdenum, Nobium, and Aluminum give this type of steel more bending resistance (40% above classical 420F martensitic needles, high ductility, easy attaching and high corrosion resistance.
3. Austenitic Stainless steel (AISI 300):
   Chemical composition: Carbon (<0.15%), Nickel(6-13%), Chromium(17-20%), with additional element like Molybdenum, Copper, and Manganese. This Austenitic steel (300 family) is the latest and highest quality in the surgical needles manufacturing. It has excellent mechanical performances for needle application. These performances are today the best in the market worldwide.