Day 17 Steels and Stainless Steel

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Day 17 Steels and Stainless Steel
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Precipitation Hardening Steels

• Key to all of this Very Low Carbon Content.
  Various amounts of alloying metals.
• Starts off similar to quenching and tempering.
  We get austenite by heating.
• We quench, getting a supersaturated solution.
• We age, getting precipitates of intermetallic
  compounds to form in a very fine dispersion.
  This is NOT the same as TM.

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A36 Steel

• This is the basic structural steel. Widely used
  in load bearing structures.
• NOT quenched and tempered.
• Yield strength 250 Mpa, or 36 Ksi
• UTS 550 Mpa, 80 Ksi.
• Ductility 20 in 200 mm.
• About 0.26 C by weight, 0.75 Mn, small amounts
  of Cu, S, and P.

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A36 Application
http//www.tms.org/pubs/journals/JOM/0112/Eagar/Ea
gar-0112.html
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HSLA Steels

• This is a family of steels. Very low carbon
  content. ( say about 0.05 C) 1.5 Mn. Some
  other metals Called microalloyed.
• Yield strength 345 Mpa, or 50 Ksi
• UTS 483 Mpa, 70 Ksi.
• Ductility 18 in 200 mm.
• Cr, Cu, V and Mn are added.
• About 4 times the corrosion resistance of A36.
• This is automobile body stuff. It is
  precipitation hardened. Aging during the paint
  bake.

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HSLA
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Medium Carbon Steels

• Typical carbon content 0.40. Can be quenched
  and tempered for many applications ie. Bolts
  and shafts of relatively small diameter.
• Yield strength 469 Mpa, or 68 Ksi
• UTS 664 Mpa, 96 Ksi.
• Ductility 26 in 50 mm.
• Not a lot of alloying mats plain carbon.
• Other applications railway tracks, wheels,
  gears, bushings, etc.

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Medium Carbon Steel Application
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Tool Steels

• Carbon Content is high. These will be quenched
  and tempered. Typical member of the family AISI
  Type W2. Water quenched and tempered.
• Yield strength 1090 Mpa, or 158 Ksi
• UTS 1185 Mpa, 172 Ksi.
• Ductility 11 in 200 mm.
• Composition 1C, some Cr, Cu, Mn and V lt 1.0.
  Its really a plain carbon steel.
• Used for drills and cutting blades.

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Tool Steel Application
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Stainless Steel

• Problem with steel corrosion protection with a
  surface layer. Iron oxide is not tenacious
  meaning that it easily flakes off, leaving more
  bare metal open to attack.
• Solution Add more than 10.5 Cr, Chrominum.
  This Cr forms a very tenacious oxide. If
  chipped off, it repairs itself. It is a
  passivated layer.
• Having over 10.5 Cr is a common factor in all
  stainless steel.
• But, inside the stainless steels there are many
  different kinds. Most have very low carbon
  content.

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Families of Stainless Steel

1. Ferritic
2. Austenitic
3. Martensitic
4. Precipitation Hardenable

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http//www.estainlesssteel.com/stainlesssteelandni
ckelcharts.shtml
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Ferritic Stainless Steels

• Typical AISI 409.
• 11 Cr. 0.08 C.
• Yields at 205 Mpa, 30 Ksi.
• Ductility is 20 EL in 2 in.
• This is the cheapest of all stainless steels.
  Uses agricultural spray tanks and automotive
  exhaust components.

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Grade 409 is a titanium-stabilised ferritic
stainless steel. Although regarded as a
general-purpose chromium stainless steel the
almost exclusive application for Grade 409
is automotive exhaust systems. Its applications
are those where appearance is a secondary
consideration to mechanical properties and
corrosion resistance, particularly at
high temperatures, and where some weldability is
required.
http//www.atlasmetals.com.au/files/ASM20Grade20
Datasheets/Atlas20Grade20datasheet2040920rev2
0May202008.pdf
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SSINA Stainless Steel Design Guidelines
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Austenitic Stainless Steel

• Key here we add a lot of nickel say around 10
  in addition to the Cr. This stabilizes the
  austenite so that it will not become ferrite at
  low temperatures.
• Result we have an FCC steel that is corrosion
  resistant. Also non-magnetic.
• Not strong, but very very tough and ductile. (No
  DBTT).
• Of course, this is more expensive stuff. World
  demand for Ni is very high. Why? (Ni is now at
  about 12/lb.)

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Grade 304 is the standard "18/8" austenitic
stainless it is the most versatile and most
widely used stainless steel. It has excellent
forming and welding characteristics. Grade 304
can be severely deep drawn without intermediate
annealing, which has made this grade dominant in
the manufacture of drawn stainless parts such as
sinks, hollow-ware and saucepans. Grade 304L,
the low carbon version of 304, does not require
post-weld annealing and so is extensively used in
heavy gauge components (over about 6mm). Grade
304H with its higher carbon content finds
application at elevated temperatures. The
austenitic structure also gives these grades
excellent toughness, even down to cryogenic
temperatures.
http//www.atlasmetals.com.au/files/ASM20Grade20
Datasheets/Atlas20Grade20datasheet2030420rev2
0May202008.pdf
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Austenitic Stainless
Cryogenic Tanks
Cookware
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Typical Austenitic Stainless Steel

• 304 Stainless Steel.
• Low carbon (lt0.08C). 18-20 Cr. Nickel 8-10.
• Microstructure is austenite base.
• Yield 215 Mpa. 31 Ksi.
• UTS 505 Mpa, 73 Ksi.
• Ductility EL 70.
• Uses beer kegs, cooking equipment, cryogenic
  vessels, surgical equipment (not scalpels!)

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SSINA Stainless Steel Design Guidelines
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Martensitic Stainless Steels

• These steels have (close to, less Cr than
  austenitic) the corrosion resistance of other
  stainless, but they have very high strength.
• How? They are quenched and tempered. The basic
  structure is TM. For this we have 0.1 to 1.0
  C. (Not as much Ni we want some for
  hardenability, but not enough to prevent the
  martensite transformation.
• Result High strength

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Typical Martensitic Stainless Steel

• 410 Stainless Steel.
• Low carbon (lt0.15C). 12.5 Cr. Little Ni.
• Quenched and Tempered
• Yield 721 Mpa. 105 Ksi.
• UTS 834 Mpa, 121 Ksi.
• Ductility EL 21.5.
• Uses Scalpels, cutlery. Nozzles, shears, valves
  and pump components.

http//www.matthewsgauge.com/mgi/products/medical-
pins
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Grade 440C is capable of attaining, after heat
treatment, the highest strength, hardness
(Rockwell C 60) and wear resistance of all the
stainless alloys. Its very high carbon content of
1.0 is responsible for these characteristics,
which make 440C particularly suited to such
applications as ball bearings and valve parts.
http//www.atlasmetals.com.au/files/ASM20Grade20
Datasheets/Atlas20Grade20datasheet20440C20rev
20May202008.pdf
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SSINA Stainless Steel Design Guidelines
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Precipitation Hardened Stainless

• Very low carbon content. Has about 7 Ni and
  about 17 Cr.
• Steel experiences a martensite transformation.
  Can be through cold work or rapid cooling. This
  produces the supersaturated solid solution.
• Aging produces the fine dispersion of
  precipitates that give this steel extremely high
  strength.

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Typical P-H Stainless Steel

• 17-7 Stainless Steel.
• Low carbon (lt0.09C). 17 Cr. 7 Ni.
• Quenched and Aged. Sometimes Cold-worked aged.
• Yield 1590 Mpa. 231 Ksi.
• UTS 1650 Mpa, 239 Ksi.
• Ductility EL 1.
• Uses High strength high temperature
  applications. Chemical processing equipment,
  heat exchangers, boiler tubes.

http//www.superior-ny.com/mk41.htm
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Grade 630 martensitic precipitation hardening
stainless steel has a combination of high
hardness and strength after suitable heat
treatment. It also has similar corrosion and heat
resistance to Grade 304. The terms "Type 630" and
"17-4PH" refer to the same grade. The great
benefit of this grade (and of other precipitation
hardening grades of stainless steel) is that they
are generally supplied in the solution treated
condition, in which they are just machinable, and
then can be age hardened to achieve quite high
strengths. This aging treatment is so low in
temperature that there is no significant
distortion. These grades are therefore well
suited to production of long shafts, which
require no re-straightening after heat treatment.
http//www.atlasmetals.com.au/files/ASM20Grade20
Datasheets/Atlas20Grade20datasheet2063020rev2
0May202008.pdf
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