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304 and 304L Stainless Steel

Both 304 stainless steel and 304L stainless steel provide a general purpose stainless steel with goodresistance to atmospheric corrosion, to many organic and inorganic chemicals and to food and beverages.

Our in-house processing capabilities allow us to process stainless steel to your eact re!uirements.The Difference Between 304 and 304L"he difference between 304 and 304L stainless steel is that 304L has a .03 ma carbon and is good forwelding whereas 304 has a mid range level of carbon.

304 and 304L are austenitic alloys, which means that a nonmagnetic solid solution of ferric carbide orcarbon in iron is used in giving this stainless steel its corrosion-resistant properties.

Properties and Uses"hese alloys contain chromium and nic#el, as well as carbon, to provide good forming and weldingproperties, corrosion and oidation resistance, toughness in low temperatures, ease of fabrication, andattractive appearance.

"hese 304 and 304L stainless steel products are used for tan#s, tools, food industry machinery andappliances, architectural trim, filtration screens, and fasteners in corrosive marine environments.

316 and 316L Stainless Steel

Both 3$% and 3$%L stainless steel provide an etra level of resistance to atmospheric corrosion, to manyorganic and inorganic chemicals and to food and beverages.

&e can process this steel to fit your applications using our in house processing capabilities and service on

your timeline."he 'ifference Between 3$% and 3$%L (tainless (teel

"he difference between 3$% and 3$%L stainless steel is that 3$%L has a .03 ma carbon and is good forwelding whereas 3$% has a mid range level of carbon.

3$% and 3$%L are austenitic alloys, meaning that these stainless steel products gain corrosion resistancefrom use of a nonmagnetic solid solution of ferric carbide or carbon in iron in the manufacturing process.

)n addition to chromium and nic#el, these alloys contain molybdenum, which also ma#es them morecorrosion resistant. *ven greater corrosion resistance is delivered by 3$+L, in which molybdenum contentincreases to 3 to 4 from the to 3 found in 3$% and 3$%L.

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roperties and /ses of 3$% and 3$%L (tainless (teel

"hese alloys are #nown for their ecellent welding properties, oined by both fusion and resistanceprocesses. "he 3$%L low carbon version is preferred in corrosive environments. )t is important to ma#e surthat copper and 1inc do not become contaminants at the site of welds, as this can create crac#ing.

)t is common to fabricate 3$% and 3$%L into many different shapes. "hey may be formed on e!uipmentsimilar to carbon steel, and are readily blan#ed and pierced. *cellent malleability means they performwell in deep drawing, spinning, stretching and bending.

(ubect2 (* B3$.3-004, "able 33$.$.$, 5e!uirements for 6eat "reatment of 7arbon (teel ipe'ate )ssued2 (eptember 0, 00%8ile2 0%-3+9uestion2 )n accordance with (* B3$.3-004, is &6" re!uired for circumferential ointsin ) :L ;%: pipe when the thic#ness is greater than $< mm =3>4 in.?@5eply2 Aes, unless the provisions of para. 33$.. are met.

(ubect2 (* B3$.3-004, aras. 304.$., 'esign of (traight ipe /nder )nternal ressure and304..$, ipe Bends'ate )ssued2 (eptember 0, 00%

8ile2 0%-$0<$9uestion =$?2 (* B3$.3-004, para. 304.$. provides two e!uations to calculate pressuredesign thic#ness for straight pipe, e!. =3a? and e!. =3b?, the former using the outside diameterand the latter using the inside diameter. 'o these two e!uations yield the same results@5eply =$?2 Aes, when the corrosion allowance in para. 304.$.$ is applied to the inside diameterof the pipe.9uestion =?2 )n accordance with (* B3$.3-004, para. 304..$, may the minimum re!uiredthic#ness of the etrados of a bend, after bending, in its finished form, as calculated by e!. =3e?,be less than as re!uired for straight pipe by e!. =3a?@5eply =?2 Aes, provided the re!uirements of para. 304..$ are met.

'ear *;perts ) have a !uery regarding &6" re!uirement. &6" re!uirment of pipe =Based on thic#ness?

$<mm plate 2 3 mm &hy there is a different in &6" re!uirement based on thic#ness for pipe and plate

5egards

)nspector $<+ Aour !uestion if it is related to power plant re!uirements in variations in code limits for

&6" - yes different codes allow variations in limits for &6" from thic#ness and also materials grades

from $ to 3. ( B 3$.$ ower iping code gives eemptions based on hardenability criteria for

materials =(ee "able $3 in B 3$.$ 00$ edition? ( B 3$.3 code for rocess iping re!uires &6" for $ t

3 grade materials if thic#ness C 0.+:D. B 3$.3 also specifies the minimum ".( criteria for &6" . (ee

"able 333.$.$- B 3$.3 code. s additional criteria for 3 material this code specifies a limit of : B6E fo&6". ressure vessel code eemptions from &6" are also based =in part? on the hardenability of the

materials. Eos. =established by (* (ection ); for the general purpose of weldability? are used, althoug

in this case they are not necessarily good criteria. review of the strengths of the materials in (ection );

reveals that Eo. $ materials may have minimum specification tensile strengths within the range of 4: to

<: #si. 7arbon e!uivalence is a better and more reliable measure of the hardenability of materials than th

Eos. reheat is also a consideration when determining the resultant hardness of weldments. s the

temperature of the material prior to welding increases, the cooling rate =and therefore the hardness? will

decrease. "he 7ode eemptions for thic#er materials usually re!uire a minimum preheat. Fenerally

variation in limits from iping vs ressure Gessel late &6" is based on lower hardenability, particular

material grade, "ensile (trength, re heat operations before welding and choice of heat input from weldin

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processes =variations from ")FH(&H(ubmerged rc etc?. 6ope this helps 7.G.(rinivasan Eishi *ngineers

vt Ltd )ndia pril +, 0$0 *-mail2 nishiIvsnl.com C'ear *;perts C C) have a !uery regarding &6"

re!uirement. C C&6" re!uirment of pipe =Based on thic#ness? $<mm C plate 2 3 mm C C&hy there is a

different in &6" re!uirement based on Cthic#ness for pipe and plate @ C C5egards

Jupdated2L(" *')"*' OE pr-+-$0 " 023 =7'"?K"he difference in &6" re!uirements for pressure

piping and pressure vessels depends upon the acceptable hardenability. 8or the case of pressure vessels,

resulting hardenability of materials after welding is acceptable up to 3 mm and in pressure piping code

(* B3$.3, it is advisable to post weld heat treat any weld above 0 mm so that the resulting residual

stress and hardness should come within the acceptable range. 5egards, shfa! nwer

http2HHforums.thepetrostreet.com C'ear *;perts C C) have a !uery regarding &6" re!uirement. C C&6"

re!uirment of pipe =Based on thic#ness? $<mm C plate 2 3 mm C C&hy there is a different in &6"

re!uirement based on Cthic#ness for pipe and plate @ C C5egards

Pipes

"he purpose with a pipe is the transport of a fluid li#e water, oil or similar, and the most import propertythe capacity or the inside diameter.

8or a (*HE() B 3%.$0 &elded and (eamless &rought (teel ipe the inside diameter - ID - of a NPS 2

inches pipe with

• schedule 40 is .0%+D

• schedule 0 is $.<3<D

"he inside diameters are close to D and the nominal diameter related to the inside diameter. Outsidediameter are .3+:D for both schedules.

(ince the outside diameter of a single nominal pipe si1e is #ept constant the inside diameter of a pipe willdepend on the DscheduleD or the thic#ness of the pipe. "he schedule and the actual thic#ness of a pipevaries with the si1e of the pipe.

)t is common to identify pipes in inches by using E( or DEominal ipe (i1eD. "he metric e!uivalent is calle'E or Ddiametre nominelD. "he metric designations conform to )nternational (tandards Organi1ation =)(O?usage and apply to all plumbing, natural gas, heating oil, and miscellaneous piping used in buildings. "heuse of E( does not conform to merican (tandard pipe designations where the term E( means DEationalipe "hread (traightD.

Eominal Bore =EB? may be specified under British standards classifications along with schedule =wallthic#ness?.

"he tolerances are looser to pipes compared with tubes and they are often less epensive to produce.

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Tubes

"he nominal dimensions of tubes are based on the outside diameter. )f we loo# at 7opper "ubes - ("B the outside diameter of a D pipe is .$:D, relatively close to D.

"he inside diameter of a tube will depend on the thic#ness of the tube. "he thic#ness is often specified asa gauge. )f we loo# at 7opper "ubes - (" Bthe wall thic#ness of 0.03Dof a D pipe is gauge $4.

"he tolerances are higher with tubes compared to pipes and tubes are often more epensive to producethan pipes.

Tube S Pipe 

)n the steel manufacturing industry one often hear terms such as steel pipes or steel tubing. "o thosewor#ing in this industry it is often not clear what the difference is between a steel pipe and a tube. fterall theyre both ust hollow cylinders, so many people thin# that the word has the eact same meaning."hats however wrong. "here are a couple of #ey differences between steel tubes and pipes2

$. pipe is a vessel - a tube is structural

. pipe is measured )' - a tube is measured O'

hollow cylinder has 3 important dimensions which are2

"he outside diameter =od?

"he inside diameter =id?

"he wall thic#ness =wt?

"hese three are related by a very simple e!uation2

od M id N wt

 

One can completely specify a piece of pipeHtube by supplying any two of these numbers.

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"ubing is more used in structures so the od is the important number. "he strength of a steel tube dependson the wall thic#ness. (o tubing is specified by the outside diameter and the wall thic#ness. (teel tubes aralso not only supplied in round sections but can be formed into s!uare and rectangular tubes. *ach s!uareor rectangular steel tube has a different mother tube, meaning that they are formed from the originalround tube. "he round tube will pass through a forming and a si1ing section on the tube mill. 'uring thesame process it will continue through a couple of sets of tur#s which will form the round tube to a s!uareor a rectangular steel section.

ipes are normally used to transport gases or fluids so it is important to #now the capacity of the pipe.

6ere the internal cross-sectional area =defined by the id? is important. )ts therefore not surprising thatpipes are specified by the inside diameter =id?. )t is common to identify pipes in inches by using E( orDEominal ipe (i1eD. "he metric e!uivalent is called 'E or Ddiameter nominalD. "he metric designationsconform to )nternational (tandards Organi1ation =)(O? usage and apply to all plumbing, natural gas, heatinoil, and miscellaneous piping used in buildings. plumber always #nows that the id on the pipe label is ona nominal id. s an eample, a =nominal? $H wrought steel pipe will typically have a measured id of0.%< =schedule 40? or 0.$: =schedule 0?. =ore below about those schedule numbers.?

"he #ey in the difference is the application where both tube and pipe are used for. 8or instance, a=nominal? $H schedule 40 pipe will have a wall thic#ness of

0.0% =idM0.%<? while a $H schedule 0 pipe will have a wall thic#ness of 0.0<: =idM0.$:?.

nd these schedule numbers do not reflect a constant wall thic#ness. 8or

instance, a =nominal? $H4 schedule 40 pipe has a wt M 0.0 while the same

pipe in schedule 0 has wt M 0.$$<

Fenerally spea#ing, a tube will have a consistent O' and its )' will change.

(teel tubes used in structural applications would most li#ely be seam welded while pipes are normally a

seamless steel product. (ome steel tubes are also used in the transport of fluids, even though they areseam welded. "hese include steel tubes for water pipes and welded tubes are commonly used in theagricultural industry for manufacturing spindles. (uch tubes will undergo a process called pressure testingwere the tube is sealed at both ends and water is pumped through the tube up to a certain level ofpressure. "his will !uic#ly indicate if there is a lead or a bad spot in the weld of the circular hollow sectiotested.

!hat is the difference between Pipe and Tube"

)n short2 Tube is measured by outside diameter, pipe is measured by inside diameter ."here is often confusion as to which si1e die the customer actually needs - ipe (i1e or "ubing (i1e.Peep in mind that pipe si1e refers to a nominal - not actual - inside pipe diameter. (chedule refers to the

pipes wall thic#ness. "he actual physical O' is larger than its nominal O'."he dimensions provided for tubing on the other hand refer to the actual outside diameter. )n other wordsthe actual physical O' of a tube is ust the same as its nominal O'. "he si1e of a tube will #eep the sameO' no mater what the wall thic#ness is.8or eample2 "he actual outside diameter of $QR pipe is $.%:R - while $QR tube has a true $.:R outsidediameter.7onse!uently, both the si1e of tube and pipe is measured by its O' and the thic#ness.!h# the difference between Pipe and Tube"

ipes are used to transport something, and tubes to construct somethingS hence, tubes are defined by theoutside diameter and wall thic#ness =for construction stability?, and pipes are measured by inside diameteto allow a calculation for transportation vi1., speed, volumes etc. =O' M )' N T &"?

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$e#

)'2 )nside 'iameter

O'2 Outside 'iameter

&"2&all "hin#ness

"o an outsider, pipes and tubes may seem li#e they should be synonymous. "o a marine engineer, the

measurements, standards and language used to distinguish the two couldnUt be more different. )n fact,differences in nomenclature and measurements could cause !uite the headache if tubes and pipes were

mista#enly assumed to be interchangeable.

The % &ain Differences Between Pipes and Tubes

V "ubes can come in different shapes li#e s!uare, rectangular and cylindrical. ipe is always cylindrical or

round.

V &hile rigid tubes are fre!uently used in structural applications, copper and brass tubes can be rather

fleible. ipes are typically always rigid and resistant to bending.

V &hen it comes to classification, pipes use schedule and nominal diameter. 8or eample, a pipe could

have a :0mm nominal diameter and a schedule of 0. "ubes are classified by their outside diameter

measurement and thic#ness. copper tube, for instance, could be $0 mm with a mm thic#ness.

V ipes accommodate larger applications with si1es that range from a half-inch to several feet. "ubes are

generally used in applications that re!uire smaller diameters. &hile $0-inch pipes are common, itUs rare

that you will come across a $0-inch tube.

V "ubes are often put to use in applications that re!uire precise outside diameters, li#e with cooler tubes

heat echanger tubes and boiler tubes.

V ipes have a pressure rating and are schedule, which is why they are often used to carry fluids that mus

be contained.V "he thic#ness of tubes increases in standard increments such as $ mm or mm. ipe thic#ness depends

on the schedule, so there is no fied increment.

V Woining pipes is more labor intensive as it re!uires welding, threading or flanges. "ubes can be oined

!uic#ly and easily with flaring, bra1ing or couplings, but for this reason, they donUt offer the same stabilitLO& "* 75BOE ("**L =L"7(? (*L*(( )* (* (333 F5.%

&hat is the difference between L"7( and 7arbon steel@

&hats the difference in composition@

&hen L"7( is used generally@

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&hats the temperature range, that these materials can be used@

)s there any relation between Pilled carbon steel, L"7(, stainless steel, carbon steel=normal?@ 6ow to

categoriseHclassify these@

 

(teel is considered to be carbon steel when no minimum content is specified or re!uired for chromium, cobalt,

columbium JniobiumK, molybdenum, nic#el, titanium, tungsten, vanadium or 1irconium, or any other element to be

added to obtain a desired alloying effectS when the specified minimum for copper does not eceed 0.40 per centS or

when the maimum content specified for any of the following elements does not eceed the percentages noted2

manganese $.%:, silicon 0.%0, copper 0.%0.

Low-temperature carbon steels have been developed chiefly for use in low-temperature e!uipment and especially f

welded pressure vessels.

"hey are low- to medium-carbon =0.0 to 0.30?, high-manganese =0.+0 to $.%0?, silicon =0.$: to 0.%0? steels, whi

have a fine-grain structure with uniform carbide dispersion. "hey feature moderate strength with toughness down to

X :0Y8 =X4%Y7?.

8or grain refinement and to improve formability and weldability, carbon steels may contain 0.0$ to 0.04 columbium7alled columbium steels, they are used for shafts, forgings, gears, machine parts, and dies and gages. /p to 0.$:

sulfur, or 0.04: phosphorus, ma#es them free-machining, but reduces strength.

L"7( is a Eic#el based alloy steel plates especi ally used for low temperature applications below - $:0 deg 8. ainly

used in cryogenic construction of space ships, low temperature application in chemical plant below -:: deg 7.

*amples2

(-03 (teel late Frades , B, ', * and 8 Eic#le lloy (teel lates. 8or low temperatures =-$:0 deg 8?

Low "emperature 7arbon (teel "ubes (" 334 Fr.$

(" 333XX(eamless and &elded (teel ipe for Low-"emperature (ervice2

ainly Frade：

Frade $, Frade 3, Frade 4, Frade %, Frade +, Frade , Frade <, Frade $0, Frade $$

(" 40 8or L"7( 8ittings.

3:0-L8 is a standard 8or 8langes.

(teel that are generally #illed include2

Z (teels with carbon contents greater then 0.:

Z ll forging grades of steel.

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Z (tructural steels with carbon content between 0.$: to 0.:.

Z (ome special steel in the lower carbon ranges.

(ee the classification of carbon steel clic#ing source lin#s.

"here is a relation between Pilled carbon steel, L"7(, stainless steel, carbon steel=normal? and it is the iron,carbon

and different alloying elements in varying !uantity which ma#es them fall under different categories.

'arbon steel is steel in which the main interstitial alloying constituent is carbon in the range of 0.$[.0.

"he merican )ron and (teel )nstitute =)()? defines carbon steel as the following2 D(teel is considered to be carbon

steel when no minimum content is specified or re!uired

for chromium, cobalt, molybdenum, nic#el, niobium, titanium, tungsten, vanadium or 1irconium, or any other

element to be added to obtain a desired alloying effectS when the specified minimum for copper does not eceed 0.

percentS or when the maimum content specified for any of the following elements does not eceed the percentages

noted2 manganese $.%:, silicon 0.%0, copper 0.%0.DJ$K

"he term Dcarbon steelD may also be used in reference to steel which is not stainless steelS in this use carbon steel

may include alloy steels.

s the carbon percentage content rises, steel has the ability to become harder and stronger through heat treatingS

however it becomes less ductile. 5egardless of the heat treatment, a higher carbon content reduces weldability. )n

carbon steels, the higher carbon content lowers the melting point.JK

'ontents

  JhideK

• $ "ypes

o $.$ ild and low-carbon steel 

o $. 6igher carbon steels

• 6eat treatment

• 3 7ase hardening

• 4 8orging temperature of steel 

• : (ee also

• % 5eferences

• + Bibliography

T#pes(edit)

See also: SAE steel grades

7arbon steel is bro#en down into four classes based on carbon content2

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&ild and low*carbon steel(edit)

ild steel, also called plain*carbon steel, is the most common form of steel because its price is relatively low while

provides material properties that are acceptable for many applications, more so than iron. Low-carbon steel contain

approimately 0.0:[0.3 carbonJ$K ma#ing it malleable and ductile. ild steel has a relatively low tensile strength, b

it is cheap and malleableS surface hardness can be increased through carburi1ing.J3K

)t is often used when large !uantities of steel are needed, for eample as structural steel. "he density of mild steel

approimately +.: gHcm3 =+:0 #gHm3 or 0.4 lbHin3?J4K and the Aoungs modulus, li#e all steels, is $0 Fa

=30,000,000 psi?.J:K

Low-carbon steels suffer from yield-point runout where the material has two yield points. "he first yield point =or

upper yield point? is higher than the second and the yield drops dramatically after the upper yield point. )f a low-

carbon steel is only stressed to some point between the upper and lower yield point then the surface may

develop L\der bands.J%K Low-carbon steels contain less carbon than other steels and are easier to cold-form, ma#ing

them easier to handle.J+K

+i,her carbon steels(edit)

7arbon steels which can successfully undergo heat-treatment have a carbon content in the range of 0.30[$.+0 by

weight. "race impurities of various other elements can have a significant effect on the !uality of the resulting steel.

"race amounts of sulfur in particular ma#e the steel red-short, that is, brittle and crumbly at wor#ing temperatures.

Low-alloy carbon steel, such as 3% grade, contains about 0.0: sulfur and melts around $,4%[$,:3 Y7 =,:<<[

,00 Y8?.JK anganese is often added to improve the hardenability of low-carbon steels. "hese additions turn the

material into a low-alloy steel by some definitions, but )()s definition of carbon steel allows up to $.%: manganese

by weight.

Low carbon steel

]0.3 carbon content, see above.

&edium carbon steel

pproimately 0.30[0.:< carbon content.J$K Balances ductility and strength and has good wear resistanceS used for

large parts, forging and automotive components. J<KJ$0K

+i,h*carbon steel

pproimately 0.%[0.<< carbon content.J$K Gery strong, used for springs and high-strength wires.J$$K

Ultra*hi,h*carbon steel

pproimately $.0[.0 carbon content.J$K (teels that can be tempered to great hardness. /sed for special purposes

li#e =non-industrial-purpose? #nives, ales or punches. ost steels with more than $. carbon content are made

using powder metallurgy. Eote that steel with a carbon content above .$4 is considered cast iron.

+eat treatment(edit)

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)ron-carbon phase diagram, showing the temperature and carbon ranges for certain types of heat treatments.

ain article: !eat treatment

"he purpose of heat treating carbon steel is to change the mechanical properties of steel, usually ductility, hardness

yield strength, or impact resistance. Eote that the electrical and thermal conductivity are only slightly altered. s

with most strengthening techni!ues for steel, Aoungs modulus =elasticity? is unaffected. ll treatments of steel trad

ductility for increased strength and vice versa. )ron has a higher solubility for carbon in the austenite phaseS therefo

all heat treatments, ecept spheroidi1ing and process annealing, start by heating the steel to a temperature at whicthe austenitic phase can eist. "he steel is then !uenched =heat drawn out? at a high rate causing cementite to

precipitate and finally the remaining pure iron to solidify. "he rate at which the steel is cooled through

the eutectoid temperature affects the rate at which carbon diffuses out of austenite and forms cementite. Fenerally

spea#ing, cooling swiftly will leave iron carbide finely dispersed and produce a fine grained pearlite =until

the martensite critical temperature is reached? and cooling slowly will give a coarser pearlite. 7ooling a

hypoeutectoid steel =less than 0.++ wt 7? results in a lamellar-pearlitic structure of iron carbide layers with ^-

ferrite =pure iron? between. )f it is hypereutectoid steel =more than 0.++ wt 7? then the structure is full pearlite wi

small grains =larger than the pearlite lamella? of cementite scattered throughout. "he relative amounts of

constituents are found using the lever rule. "he following is a list of the types of heat treatments possible2

• Spheroidi-in,2 (pheroidite forms when carbon steel is heated to approimately +00 Y7 for over 30 hours.(pheroidite can form at lower temperatures but the time needed drastically increases, as this is a diffusion-

controlled process. "he result is a structure of rods or spheres of cementite within primary structure =ferrite or

pearlite, depending on which side of the eutectoid you are on?. "he purpose is to soften higher carbon steels an

allow more formability. "his is the softest and most ductile form of steel. "he image to the right shows where

spheroidi1ing usually occurs.J$K

• .ull annealin,2 7arbon steel is heated to approimately 40 Y7 above c3 or c$ for $ hourS this ensures all

the ferrite transforms into austenite =although cementite might still eist if the carbon content is greater than

the eutectoid?. "he steel must then be cooled slowly, in the realm of 0 Y7 =% Y8? per hour. /sually it is ust

furnace cooled, where the furnace is turned off with the steel still inside. "his results in a coarse pearlitic

structure, which means the DbandsD of pearlite are thic#. 8ully annealed steel is soft and ductile, with no interna

stresses, which is often necessary for cost-effective forming. Only spheroidi1ed steel is softer and more ductile.

• Process annealin,2 process used to relieve stress in a cold-wor#ed carbon steel with less than 0.3 wt 7.

"he steel is usually heated up to ::0[%:0 Y7 for $ hour, but sometimes temperatures as high as +00 Y7. "he ima

rightward shows the area where process annealing occurs.

• /sothermal annealin,2 )t is a process in which hypoeutectoid steel is heated above the upper critical

temperature and this temperature is maintained for a time and then the temperature is brought down below

lower critical temperature and is again maintained. "hen finally it is cooled at room temperature. "his method

rids any temperature gradient.

• ormali-in,2 7arbon steel is heated to approimately :: Y7 above c3 or cm for $ hourS this ensures thesteel completely transforms to austenite. "he steel is then air-cooled, which is a cooling rate of approimately

3 Y7 =$00 Y8? per minute. "his results in a fine pearlitic structure, and a more-uniform structure. Eormali1ed

steel has a higher strength than annealed steelS it has a relatively high strength and ductility. J$4K

• uenchin,2 7arbon steel with at least 0.4 wt 7 is heated to normali1ing temperatures and then rapidly

cooled =!uenched? in water, brine, or oil to the critical temperature. "he critical temperature is dependent on

the carbon content, but as a general rule is lower as the carbon content increases. "his results in a martensitic

structureS a form of steel that possesses a super-saturated carbon content in a deformed body-centered cubic

=B77? crystalline structure, properly termed body-centered tetragonal =B7"?, with much internal stress. "hus

!uenched steel is etremely hard but brittle, usually too brittle for practical purposes. "hese internal stresses

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cause stress crac#s on the surface. 9uenched steel is approimately three to four =with more carbon? fold harde

than normali1ed steel.J$:K

• &artemperin, 2&aruenchin,2 artempering is not actually a tempering procedure, hence the term

Dmar!uenchingD. )t is a form of isothermal heat treatment applied after an initial !uench of typically in a molten

salt bath at a temperature right above the Dmartensite start temperatureD. t this temperature, residual stresse

within the material are relieved and some bainite may be formed from the retained austenite which did not hav

time to transform into anything else. )n industry, this is a process used to control the ductility and hardness of a

material. &ith longer mar!uenching, the ductility increases with a minimal loss in strengthS the steel is held inthis solution until the inner and outer temperatures e!uali1e. "hen the steel is cooled at a moderate speed to

#eep the temperature gradient minimal. Eot only does this process reduce internal stresses and stress crac#s, bu

it also increases the impact resistance.J$%K

• uench and temperin,2 "his is the most common heat treatment encountered, because the final properties

can be precisely determined by the temperature and time of the tempering. "empering involves reheating

!uenched steel to a temperature below the eutectoid temperature then cooling. "he elevated temperature

allows very small amounts of spheroidite to form, which restores ductility, but reduces hardness. ctual

temperatures and times are carefully chosen for each composition.J$+K

• 5ustemperin,2 "he austempering process is the same as martempering, ecept the steel is held in the molte

salt bath through the bainite transformation temperatures, and then moderately cooled. "he resulting bainite

steel has a greater ductility, higher impact resistance, and less distortion. "he disadvantage of austempering is i

can only be used on a few steels, and it re!uires a special salt bath.J$K

'ase hardenin,(edit)

ain article: "ase hardening

7ase hardening processes harden only the eterior of the steel part, creating a hard, wear resistant s#in =the DcaseD?

but preserving a tough and ductile interior. 7arbon steels are not very hardenableS therefore wide pieces cannot be

through-hardened. lloy steels have a better hardenability, so they can through-harden and do not re!uire casehardening. "his property of carbon steel can be beneficial, because it gives the surface good wear characteristics bu

leaves the core tough.

.or,in, temperature of steel(edit)

J$<K

Steel T#pe &aimum for,in, temperature 27. 8 7' Burnin, temperature 27. 8 7'

$.: carbon $<0 H $04< 00 H $$3

$.$ carbon $<0 H $0 $40 H $$+$

0.< carbon 0:0 H $$$ 30 H $$

0.: carbon 0 H $4< 4%0 H $34<

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0. carbon 4$0 H $3$ %0 H $4+$

3.0 nic#el steel 0 H $4< :00 H $3+$

3.0 nic#el[chromium steel 0 H $4< :00 H $3+$

:.0 nic#el =case-hardening? steel 30 H $+$ %40 H $44<

7hromium[vanadium steel 0 H $4< 4%0 H $34<

6igh-speed steel 3+0 H $<< :0 H$3

(tainless steel 340 H $ :0 H $3

ustenitic chromium[nic#el steel 3+0 H $<< :<0 H $4$

(ilico-manganese spring steel 0 H $4< 4%0 H$34<

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