Alloying elements

Question 1

What are some reasons for alloying?

Answer 1

• Higher strength
• Improved corrosion resistance
• Greater hardening depth (martensitic hardening)
• Improved resistance to tempering,
• Greater resistance to wear
• Improved certain physical properties (yield strength, tensile strength, hardness but NOT STIFFNESS - A HIGHER AMOUNT IS NEEDED TO CHANGE YOUNG’S MODULUS)

Question 2

How do alloying elements influence the hardness of a material?

Answer 2

Alloying elements lead to slower transformation behavior - they shift the perlite and bainite regions (see figures).
By adding alloying elements a larger hardening depth can be achieved (see figures).

Question 3

What are some methods for alloying?

Answer 3

Solution hardening - enhancing material properties by forming a solid solution that strengthens the matrix
Carbides (already in the material) - hinder grain growth in the austenite region.

Question 4

What is intercrystalline corrosion?

Answer 4

Through welding, chromium depletes to grain boundaries, if the concentration of Cr is below 12% this can result in corrosion between grains.

Question 5

How can intercrystalline corrosion be solved? Propose solutions and explain them.

Answer 5

Heating the material to 1050 degrees and quenching it - chromium will dissolve completely and not form again
Carbon concentration lower than 0.03% - because chromium is already a part of carbon adding less carbon can prevent this type of corrosion
Adding more stable carbides like Ti and Nb.