The document discusses different types of stainless steel, including their compositions and properties. It begins with an overview of crystallography and allotropes, explaining that iron and steel are crystalline and can exist in different forms. It then covers the four main types of stainless steel: ferritic, austenitic, martensitic, and duplex. For each type, the document describes their typical compositions in terms of chromium, nickel, and other elements, as well as their properties such as corrosion resistance, strength, and magnetic permeability.

1. • Crystallography
• Allotropes
• Allotropes of iron
• Applications
STAINLESS STEELS
Pratyush Srivastava
Pawandeep Singh
• FERRITIC
• AUSTENITIC
• MARTENSITIC
• DUPLEX

2. BASICS OF CRYSTALLOGRAPHY
• Iron is a metal, Steel is an alloy made by combining
iron and other elements.
• Iron and steel are crystalline in nature. This means
that there is a repeat pattern at microscopic level.
• Anything that is not crystalline is
amorphous.(glass/wood etc.)

3. ALLOTROPES
• Diamond and coal are both pure carbon. The
chemical composition of both are identical.
• They exist in different physical forms just because
the arrangement of atoms is different.

4. IMPORTANT ATOMIC ARRANGEMENTS
Simple cubic
Body centered
Face centered

5. ALLOTROPES OF IRON
In pure IRON
• Below 910 °C (ie. at room temperature
also) ferrite form is stable.
This form is body centered.
• From 910 to 1390 °C the face centered form of
iron, called austenite (gamma-iron) is stable.
• Above 1,390 °C up to the melting point the
body-centered cubic crystal structure is again
the more stable form called delta iron.

6. TYPES OF STAINLESS STEELS
• Ferritic
• Austenitic
• Martensitic
• Duplex

7. FERRITIC STAINLESS STEEL
• Ferritic stainless steels generally have better engineering
properties than austenitic grades.
• Contains between 10.5% and 27% chromium
• Corrosion resistance is not good. (low chromium and
nickel content).
• They are usually less expensive.
• Ferritic steel is magnetic.
• Common ferritic grades include
• 18Cr-2Mo
• 26Cr-1Mo
• 29Cr-4Mo
• 29Cr-4Mo-2Ni

8. AUSTENITIC STAINLESS STEEL
• Also called series 300 steel
• Make up over 70% of total stainless steel production.
• Contains atleast 16% chromium.
• Nickel is added to stablize austenite at room temperature
• Superaustenitic stainless steels, such as alloy AL-6XN and
254SMO exhibit great resistance to chloride pitting and
crevice corrosion but are very costly.
• Austenitic steel is non-magnetic.
• Type 304 is a surgical steel. Also used for chemical processing
equipment, for food, dairy, and beverage industries, for heat
exchangers, and for the mild chemicals.
• Type 316 is used in construction, for dispensing and in the
most corrosive environments.
• Type 316L used in jewelry and watches.
• Type 347 is used in aircraft industry.

9. MARTENSITIC STAINLESS STEEL
• Also called series 400 steel.
• The martensite is formed by quenching (heating
and rapid cooling ) of austenite.
• These are not very corrosion resistant but are strong
,tough and machinable.
• chromium (12–14%)
• molybdenum (0.2–1%)
• nickel (less than 2%)
• carbon (about 0.1–1%) (extra carbon increases the
hardness but make the steel more brittle)
• It is magnetic.

10. GRADES OF MARTENSITIC STEEL
• Type 410 is used widely where corrosion is not
severe
• Type 410S used against high temperature corrosion.
• Type 414 used in springs and cutlery.
• Type 416 screw machine parts.
• Type 420 surgical instruments.
• Type 431 high strength parts such as valves and
pumps.
• Type 440 fabrication of instruments.

11. DUPLEX
STEEL

12. Duplex steel
• Duplex steel is a better form of stainless steel . It has
Chromium content more than 22% whereas stainless
steel has 18% or less.
• Duplex steel is named so because it has about 50-
50 ratio of austenite and ferrite forms.

13. PROPERTIES:
• Strength: Duplex stainless steels are much stronger than
regular stainless steels.
• Toughness and ductility: Duplex stainless steels have
better toughness and ductility than ferritic grades but
not as good as austenitic stainless steel.
• Corrosion resistance: corrosion resistance is nearly
similar to normal stainless steel (austenitic/ferritic)..
• Stress corrosion resistance:( corrosion at increased rate
under stress) Duplex stainless steels show very good
stress corrosion cracking (SCC) resistance like ferritic
steel
• Cost: Duplex stainless steels have lower nickel and
molybdenum contents than their austenitic
counterparts (of similar corrosion resistance)..this
reduces the alloying costs.
It may often be possible to reduce the section thickness of
duplex stainless steel fabrications due to its increased yield
strength compared to austenitic stainless steel. This results
in significant cost and weight reduction.

14. APPLICATIONS
• Duplex stainless steels are used in the chemical
industry in refineries, gas-processing plants,
pulp and paper plants, and sea water piping
installations.(good resistance to salt water)
• Grade 2205 is most widely used grade of
duplex stainless steel due to its excellent
corrosion resistance and high strength.

15. Stainless Steel - Comparison
of Grade Specifications

16. Stainless Steel - Comparison of Grade Specifications Contd.

17. Stainless Steel - Comparison of Grade Specifications Contd.