D AY 17 S TEELS AND S TAINLESS S TEEL

P RECIPITATION H ARDENING – S TEELS Key to all of this: Very Low Carbon Content. Various amounts of alloying metals. 1. Starts off similar to quenching and tempering. We get austenite by heating. 2. We quench, getting a supersaturated solution. 3. We age, getting precipitates of intermetallic compounds to form in a very fine dispersion. This is NOT the same as TM.

A36 S TEEL 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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HSLA S TEELS 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.

HSLA

M EDIUM C ARBON S TEELS 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.

M EDIUM C ARBON S TEEL A PPLICATION

T OOL S TEELS 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 1%C, some Cr, Cu, Mn and V < 1.0%. It’s really a plain carbon steel. Used for drills and cutting blades.

T OOL S TEEL A PPLICATION

S TAINLESS S TEEL 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.

F AMILIES OF S TAINLESS S TEEL 1. Ferritic 2. Austenitic 3. Martensitic 4. Precipitation Hardenable

F ERRITIC S TAINLESS S TEELS Typical: AISI % 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.

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. %20rev%20May% pdf

SSINA Stainless Steel Design Guidelines

A USTENITIC S TAINLESS S TEEL 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.)

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 pdf

A USTENITIC S TAINLESS Cookware Cryogenic Tanks

T YPICAL A USTENITIC S TAINLESS S TEEL 304 Stainless Steel. Low carbon (<0.08%C) % 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!)

SSINA Stainless Steel Design Guidelines

M ARTENSITIC S TAINLESS S TEELS 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

T YPICAL M ARTENSITIC S TAINLESS S TEEL 410 Stainless Steel. Low carbon (<0.15%C). 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. ucts/medical-pins

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. eets/Atlas%20Grade%20datasheet%20440C%20rev%20May% pdf

SSINA Stainless Steel Design Guidelines

P RECIPITATION H ARDENED S TAINLESS 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.

T YPICAL P-H S TAINLESS S TEEL 17-7 Stainless Steel. Low carbon (<0.09%C). 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.

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 pdf

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