. Stainless steel
Stainless steel is a corrosion resistent alloy of iron , chromium , and other element it is known for its ability to resist oxidation and rusting due to the formation of a passive chromium oxide layer on its surface . This makes it highly suitable for application requiring durability , hygiene , and aesthetic appeal.
Manufacturing process of stainless steel .
The production of stainless steel involve several steps.
1. Raw material selection .
Iron ore , chromium , nickel and other alloying element are selected based on desired grade.
2. Melting .
Raw material are melted in an electric arc furnace (EAF) or basic oxygen furnace (BOF).
3. Refining .
The molten metal is refined to remove impurities and adjust chemical composition .
4. Casting .
The refined metal is cast into semi-finished forms like slabs,billets ,or blooms ,
5. Hot rolling .
The semi-finished forms are heated and rolled into plates , sheets or coils.
6.Annealing and pickling .
Annealing restore ductility , and pickling removes scales from the surfaces .
7. Cold rolling.
Enhance surface finish and achieves precise dimension .
8. Finishing .
Polishing ,grinding , or coating to meet specific application needs.
Composition of stainless steel .
The key component of stainless seel are.
Iron (Fe)- The base metal .
Chromium(Cr)-Minimum 10.5% forms a passive layer of chromium oxide for corrosion resistence.
Nickel (Ni) - Improves toughness , corrosion resistence and ductility .
Carbon (C) -Typically less than 1% influences strength and hardness.
Molybdenum(Mo) - Enhance resistance to pitting and crevice corrosion .
Other element .
Manganese- improves hardness and strength .
Silicon (Si) -enhance oxidation resistence .
Nitrogen (N)- Add strength and improves pitting resistence.
Titanium (Ti), and Niobium (Nb)- stabilizes structures too present carbide precipitation .
Types of stainless steel .
Stainless steel is categorised into five main families based on their microstructure .
1.Austenitic stainless steel .
Structure- Face centered cubic (FCC) .
Grade- 304 , 316 .
Property - High corrosion resistence ,
excellent weldability , non- magnetic.
Application -Food processing , chemical tanks , marine components.
2.Ferritic stainless steel .
Structures - body centered cubic(bcc).
. Grade-430, 409 .
Properties- Moderates corrosion resistence , magnetic , good ductility .
Application - automotive exhaust system appliances .
3. Martensitic stainless steel .
Structures- Body centered tetragonal (Bct).
Grade- 410, 420 .
Properties - High strength ,and hardness, moderates corrosion resistence.
Application- Cutlery , surgical instrument .
4.Duplex stainless steel .
Structure- Balanced mixture of austenitic and ferritic phases.
Grade-2205, 2507.
Properties- Superior strength , high corrosion resistence .
Application - Oil and gas , chemical processing .
5.Precipitation Hardening (PH) stainless steel .
Structures- Martensitic or semi- austenitic.
Grade- 17 -A PH, 15-5 Ph.
Property - high strength, excellent corrosion resistence.
Application- Aerospace , nuclear industries .
Properties of stainless steel.
1. Mechanical property.
Tensile strength- varies by grade ,typically range from 400 - 1200 mpa.
Hardness- low to high , depending on carbon content and heat treatment.
Ductility - excellent in austenitic grades, moderates in ferritic and duplex grades.
Toughness- High especially in austenitic stainless steel at low temprature.
2. Corrosion resistence .
Resistence to rusting , pitting , and stress corrosion cracking.
Enhanced by chromium,nickel and molybdenum content .
3. Thermal property .
Low thermal conductivity - slower heat transfer compared to carbon steel .
Thermal expansion - higher in austenitic grades.
Other important property .
Non- magnetic - Austenitic grades are generally non- magnetic , other types may be magnetic.
Recyclable- Eco-friendly and sustainable.
Grade of stainless steel .
Stainless steel is classified into grades based on its composition and properties . Common standard include.
American( AISI/ASTM).
1. 304- general purpose , high corrosion resistence .
2. 316- marine grade, with molybdenum for enhanced corrosion resistence.
3. 410- high strength and hardness , moderates corrosion resistence.
4. 17-4 PH- precipitation , hardened for high strength and corrosion resistence.
European(EN).
1. 1.4301 (304)- for general purpose .
2. 1.4404(316)- Low carbon version for improved weldability.
Japanese(JIS).
1. S U S B 0 4 -Equivalent to A I S I 304.
2. S U S B 1 6- Equivalent to A I S I 316.
Uses of stainless steel.
Food industry - Tanks, utensils , conveyors system.
Medical field- surgical instrument .
Aerospace ans automotive - Exhaust system , high strength components.
Energy- Pipelines, like gas pipeline , water supply pipeline ,
Architecture- like roofing , over bridges, structural components.
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