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Table
9.6
Typical mechanical properties and applications of low-alloy steels
Alloy
AISI-SAE
number
Chemical
composition
(wt %)
Condition
Tensile
strength
Yield
strength
gation (%)
Typical
applications
MPa
MPa
Elon:
liiilllii
Manganese
steels
1340
0.40
C,
1.75 Mn
Annealed
704
435
20
High-strength bolts
Tempered*
1587
1421
12
Chromium
steels
5140
0.40 C, 0.80
Cr,
Annealed
573
297
29
Automobile
0.80 Mn
Tempered*
1580
1449
10
transmission gears
5160
0.60
C,
0.80 Cr,
Annealed
725
276
17
Automobile coil and
0.90 Mn
Tempered*
2000
1773
9
leaf springs
S
!hromium-
molybi
ienum
steels
4140
0.40 C,
1.0
Cr,
Annealed
655
421
26
Gears for aircraft gas
0.9 Mn,
Tempered*
1550
1433
9
turbine engines,
0.20 Mo
transmissions
Nickel-molybdenum steels
4620
0.20
C,
1.83 NI,
Annealed
517
373
31
Transmission gears,
0.55 Mn,
Normalized
573
366
29
chain pins, shafts,
0.25 Mo
roller bearings
4820
0.20 C, 3.50 NI,
Annealed
683
462
22
Gears for steel mill
0.60 Mn,
Normalized
690
483
60
equipment, paper
0.25 Mo
machinery, mining
machinery, earth-
moving equipment
Nickel (1.83 % )-chromium-molybdenum steels
4340 (E)
0.40
C,
1.83 Ni,
Annealed
745
469
22
Heavy sections,
0.90 Mn,
Tempered*
1725
1587
10
landing gears,
0.80 Cr,
truck parts
0.20 Mo
Nickel
(0.55 % )-chromram-moIybdemim
steels
8620
0.20 C, 0.55 Ni,
0.50 Cr,
0.80 Mn,
0.20 Mo
Annealed
Normalized
531
635
407
359
31
26
Transmission gears
8650
0.50 C, 0.55 Ni,
Annealed
710
386
22
Small machine
0.50 Cr, 0.80
Mn,
Tempered*
1725
1552
10
axles, shafts
0.20 Mo
*Tempered at 315°C.
80
alyuminiy elektroliz vannalarida olinadi. Alyuminiy xom ashyosini elektrolitik
rafinirlash yo‘li bilan yuqori tozalikdagi alyuminiy markasi olinadi.
Alyuminiy — kumushsimon oq rangdagi, elektr va issiqlik o‘tkazuvchanligi
katta bo‘lgan yengil metalldir; uning zichligi 2700 kg/m3, tozaligiga qarab
suyuqlanish temperaturasi 660—667°S chegarada o‘zgaradi. Yumshatilgan
alyuminiyning mustahkamligi kichik (σv = 80—100 MPa), qatiqligi past (NV 20—
40), lekin plastikligi yuqori (σ=35-40%). Alyuminiy bosim ostida yaxshi ishlanadi,
payvandlanadi, lekin kesib ishlanishi yomon. Atmosfera va chuchuk suvda
korroziyaga chidamliligi yuqori. Havoda alyuminiy tez oksidlanib, yupka pishiq
oksid pardasi bilan qoplanadi. Bu parda esa metall qatlamiga kislorod utkazmaydi
va uni korroziyalalishdan saqlaydi.
Alyuminiyning boshqa metall va nometallar (mis, marganets, magniy,
kremniy, temir, nikel, titanberilliy va boshqalar) bilan qotishmalari konstruksion
materiallar sifatida keng qullaniladi. Alyuminiy qotishmalarida toza alyuminiyning
yaxshi xossalari bilan birga legirlovchi qo‘shilmalarning yuqori mustahkamlik
xossalari mujassamlangan. Masalan, temir, nikel, titan alyuminiy qotishmalarining
otashga chidamliligini oshiradi. Mis, marganets, magniy, alyuminiy qotishmalariga
mustaxkamlovchi termik ishlov berishni ta’minlaydi. Legirlash va termik ishlov
berish natijasida alyuminiyning mustahkamligi σv 100 dan 500 MPa gacha,
qattiqligi NV 20 dan 150 gacha oshadi. Barcha alyuminiy qotishmalari
deformatsiyalanadigan va quymabop xillarga bo‘linadi.
Deformatsiyalanadigan alyuminiy qotishmalari. Deformatsiyalanadigan alyuminiy
qotishmalari shtamplash, presslash, bolgalash orqali listlar, tasmalar, shakldor
profillar, simlar va turli detallar olishda ishlatiladi. Deformatsiyalanadigan
alyuminiy qotishmalari ximiyaviy tarkibiga ko‘ra 7 ta gruppaga bo‘linadi; ularning
tarkibida 2—3 ta va undan ham ko‘proq legirlovchi element bo‘lib, har biridan
0,2—4% gacha bo‘ladi. Masalan, alyuminiyning, magniy va marganets bilan
81
qotishmasi yoki alyuminiyning mis, magniy, marganets bilan qotishmasi shular
jumlasidandir.
Deformatsiyalanadigan qotishmalar termik ishlash yuli bilan puxtalanadigan
va puxtalab bo‘lmaydigan xillarga buushnadi. Mexanik va termik ishlov beriladigan
deformatsiyalanadigan qotishmalar ishlov berish xarakterini kursatuvchi harflar
bilan belgilanadi (9-jadvaldagi eslatmaga qarang).
Termik
ishlash
yuli
bilan
puxtalab
bo‘lmaydigan
qotishmalarga
alyuminiyning marganets bilan (AMs) hamda magniy va marganets bilan (AMg)
qotishmalari kiradi. Ularning mustaxjamligi juda past, korroziyaga chidamliligi
yuqori, payvandlanuvchanligi, plastikligi yaxshi (9-jadval).
Termik ishlash yuli bilan puxtalanadigan qotishmalar (9-jadvalga qarang) termik
ishlov berish natijasida yuqori mexanik xossalarga erishadi, korroziyaga darshiligi
yaxshilanadi. Alyuminiyning mis, magniy, marganets bilan qotishmalari
(dyuralyuminiylar) va alyuminiyning mis, magniy, marganets hamda rux bilan
qotishmalari (yuqori mustaxkamlikdagi qotishmalar) keng tarqalgan.
Dyuralyuminiylar D harfi bilan markalanadi, undan keyin turuvchi raqam
qotishmaning shartli nomerini bildiradi. Dyuralyuminiyga termik ishlov berish
toblashdan, tabiiy yoki sun’iy eskirtirishdan iborat. Toblash uchuy
qotishmalar500°S gacha qizdiriladi va suvda sovitiladi. Dyuralyuminiy xona
temperaturasida 5-7 sutka davomida tabiiy eskirtiriladi.
82
Figure 9.42
Decomposition products created by the aging of a supersaturated solid solution of a precipitation-hardenable alloy. The highest energy level is for the
supersaturated solid solution, and the lowest energy level is for the equilibrium precipitate. The alloy can go spontaneously from a higher energy level to a lower one
if there is sufficient activation energy for the transformation and if the kinetic conditions are favorable.
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