The type of steel obtained by adding alloying materials such as chromium, nickel and molybdenum in order to increase its strength, corrosion and thermal resistance is called alloy steel. Alloy steels, which can be used in cutting, drilling and shaping processes with environments where corrosion is suitable, are produced to be used under heavy operating conditions. The steels, which are divided into two groups as stainless steels and tool steels, have a wide usage area.
- a) Stainless Steels:
Stainless Steel: It is an iron-based alloy with more than 10.5% chromium, and it is possible to add alloy materials such as nickel, molybdenum, titanium, copper, aluminum, nitrogen, sulphur, silicon, selenium, niobium to this steel group in order to strengthen its properties. Stainless steel, which is preferred in applications where corrosion is important, is also divided into 5 groups.
1-Martensitic stainless steel: This distorted volume-centered steel group has a hardened and crystalline structure. Steels in this group are heat-treated and can be hardened for chromium and carbon alloy materials. Martensitic stainless steels show corrosion resistance in mild environments.
2-Ferritic stainless steel: This steel group containing 10.5-30% chromium has a crystal structure. Although ferritic stainless steels, which also show ferromagnetic properties, have high formable properties, their temperature resistance is low.
3-Austenitic stainless steel: This steel group, which has a surface-centered crystal structure, is obtained by using nickel, manganese, nitrogen elements and can be hardened by exposing the material to cold process.
4-Duplex stainless steel: Steels in this group, which contain equal amounts of ferrite and austenite phases and 17-30% Cr and 3-13% Ni alloy elements, show resistance to stress corrosion cracking.
5-Precipitation hardened stainless steel: It is a group of steel with a chromium-nickel alloy containing elements such as titanium, aluminum and copper that provide precipitation hardening. This steel group, which can be converted into martensite structure, is exposed to heat treatment.
- b) Tool Steels
This steel group used in processes such as cutting, drilling and shaping is high alloyed. In tool steels that can be used in the processing of workpieces either in cold or hot state; there are high proportions of mobile, vanadium, chromium, manganese and tungsten elements. Tool steels, which are produced for the use of heavy loads; are resistant to cracking, abrasion and deformation for a long time and maintain these properties at high temperatures.