This is very useful presentation to understand basic concept of Stainless steel and its metallurgical aspects

1. Gateway Arch in St Louis – 304 series SS
F-35 Joint Strike Fighter (JSF) Lightning II,
built by Lockheed Martin – airframe 17-7
PH – 600 series SS
Prepared By: Mr. Prashant S. Kshirsagar
(Sr.Manager-QA dept.)

2. Definition of Stainless Steel
History of Stainless steel
Properties of Stainless steel
Different types of Stainless steel
Different grades of Stainless
steel
Application of Stainless steel

3. Stainless steel is an alloy of Iron
with a minimum of 10.5%
Chromium.
Chromium produces a thin layer of
oxide on the surface of the steel
known as the 'passive layer'. This
prevents any further corrosion of
the surface. Increasing the amount
of Chromium gives an increased
resistance to corrosion.
Stainless steel also contains varying amounts of Carbon,
Silicon and Manganese. Other elements such as Nickel and
Molybdenum may be added to impart other useful properties
such as enhanced formability and increased corrosion
resistance.

4. There is a widely held view that
stainless steel was discovered in 1913
by Sheffield metallurgist Harry
Brearley. He was experimenting with
different types of steel for weapons and
noticed that a 13% Chromium steel had
not corroded after several months.

5. Electrical Resistivity
• Electrical resistance is higher
than that for plain-carbon
steels
Thermal Conductivity
• Stainless Steel has lower thermal conductivity than
Carbon steel

6. Coefficient of Thermal Expansion
• Stainless steel is having
greater coefficient of thermal
expansion than plain-carbon
steels
High Strength
• Exhibit high strength at room and elevated temperatures
Melting Temperature
Plain-carbon:1480-1540 °C
Martensitic: 1400-1530 °C
Ferritic: 1400-1530 °C
Austenitic: 1370-1450 °C

7. Austenitic: This SS is having
Austenitic structure (i.e. FCC) at
room temp. They contain 16-25%
chromium, and nitrogen. They are
hardened only by cold working.
Good toughness, formability, easily
weldable, high corrosion resistance.
Nonmagnetic except after excess
cold working or welding due to
martensitic formation. Can be
successfully used from cryogenic
temperatures to the red-hot
temperatures of furnaces and jet
engines. They are susceptible to SCC.
App.: Automotive, Architecture, Food
and beverage equip., Industrial
equip.

8. Martensitic: They have a structure i.e.
BCT. Due to addition of ‘C’ (0.15-1%),
they can be hardened and strengthened
by heat treatment. When steel is heated
it transform from ferrite to austenite &
on slow cooling it transforms back to
ferrite. However, with fast cooling
through quenching in water or in oil
the carbon atoms become trapped in a
somewhat distorted atomic matrix and
structure becomes i.e. BCT. The main
alloying element is ‘Cr’ i.e. 12-15%
approx. App.: Steam turbine blades,
valves body and seats, bolts and screws,
springs, knives, surgical instruments,
and chemical engg. equipments.

9. Ferritic: This SS is having Ferritic
structure (i.e. BCC) at room temp.
It containing 11.5-19% ‘Cr’ & C:
0.20max. They are having good
corrosion resistance, magnetic
and hardenable only by cold
working. They are less expensive
than Austenitic SS.
Limitations: i) poor toughness at
sub zero temp ii) Poor weldability
due to embrittlement.
App.: Automotive, building
construction, Cladding, Urban
furniture, commercial food
equipment, industrial application

10. Duplex SS: This SS is having
austenitic (50%) + ferritic (50%)
microstructure. This SS is
containing high Cr: 20.1-25.4%, Ni:
1.4-7%, Mo: 0.3-4% (e.g.2205;
2507). Combining many of the best
features of both austenitic (i.e.
application in cryogenic temp. to
red-hot temp.) and ferritic types. It
is magnetic, non-hardnable by heat
treatment, has high TS than
austenitic type, weldability similar
to the austenitic stainless steel.
App.: Heat exchangers, pressure
vessels, Chemical-petrochemical
ind., Oil-Gas ind., Nuclear Power
plant

11. Precipitation hardening: This SS are not
defined by their microstructure, but
rather by strengthening mechanism
(e.g.17-4pH (martensite) or 17-7pH
(austenitic)). These grades may have
austenitic, semi-austenitic or martensitic
microstructures and can be hardened by
aging at elevated temp. i.e. 480deg.C to
620deg.C. The strengthening effect is due
the formation of intermetallic precipitates
from elements such as copper or
aluminum. Have the highest strength and
to be used for specialized application
where high strength together with good
corrosion resistance is required.
App.: Aerospace, defense, offshore oil &
gas industries, missile components, motor
shafts, valve stems, gears

13. Austenitic grades
302
General
purpose
303 304EN 304ECu 308L 304 310 316 317LN
High Sulphur Higher Ni Cu addition Higher Lower Cr & Ni Mo added More Mo & Cr
+ Calcium for cold for cold Cr & Ni C for increased for increased with reduced
added heading heading for use better for high corrosion C for better
for better application in welding corrosion temperature resistance corrosion
machinability control resistance
303 Cu 304LN 304 HC 309L 304HS+Ca 316HS+Ca
Cu & S for Lower C Higher Cu Higher For bright bar For bright bar
enhanced content and for cold Cr & Ni with better with better
drawability higher Ni headed nuts for welding machinability machinability
and good for better and bolts
machinability drawability
302 HQ 304L 316L
Low C and Low C - better C reduced
high Cu for corrosion for
severely cold resistance. welding
headed parts Wire drawing fabrication
& forging.
321 316Ti
Ti added Ti added
to prevent to prevent
carbide Carbide
precipitation precipitation
Ferritic grades Martensitic grades
430 410
General General
purpose purpose
405 409 Ti 430L 430F 431 403 420 416
Low Cr; Al For improvedLow Carbon, S added Cr increased Special Increased S increased
added to corrosion low Nitrogen for Ni added quality for C to for
prevent resistance for fine wire improved for better turbines & improve improved
hardening and drawing machinability corrosion highly mechanical machinability
when cooled weldability resistance & stressed properties
from elevated good mech. parts
temperature properties
201
N & Mn partially replaces Ni

14. Although stainless steel is much more resistant to corrosion
than ordinary carbon or alloy steels, in some circumstances it
can corrode. It is 'stain-less' not 'stain-impossible'. In normal
atmospheric or water based environments, stainless steel will
not corrode.
In more aggressive conditions, the basic types of stainless
steel may corrode
1) Pitting corrosion
2) Crevice corrosion
3) General/Uniform corrosion
4) Stress corrosion cracking
5) Intergranular corrosion
6) Galvanic corrosion

15. Stainless steels of various kinds are used in thousands of applications. Some of the main
applications are as follows:
Domestic – cutlery, sinks, saucepans, washing machine drums, microwave oven liners,
razor blades
Architectural/Civil Engineering – cladding, handrails, door and window fittings, street
furniture, structural sections, reinforcement bar, lighting columns, lintels, masonry
supports
Transport – exhaust systems, car trim/grilles, road tankers, ship containers, ships
chemical tankers, refuse vehicles
Chemical/Pharmaceutical – pressure vessels, process piping.
Oil and Gas – platform accommodation, cable trays, subsea pipelines.
Medical – Surgical instruments, surgical implants, MRI scanners.
Food and Drink – Catering equipment, brewing, distilling, food processing.
Water – Water and sewage treatment, water tubing, hot water tanks.
General – springs, fasteners (bolts, nuts and washers), wire.