metalurgi baja tahan karat
DESCRIPTION
baja Tahan karatTRANSCRIPT
-
Stainless Steels
Idenifikasi
Manufaktur
Ketahanan korosi
-
Stainless steel is ideal for critical applications.
Unfortunately, even stainless steel is not 100%
safe from corrosion
Stainless steel is only 'stainless if...
The stainless steel family is quite large and
specialized. There are hundreds of grades and
sub grades, and each is designed for a special
application.
-
Chapter 17 Stainless Steels
With >12% Cr addition, the austenite phase field becomes
an island, forming a gamma loop on the phase diagram.
Cr in steel is the magic
element.
Minimum 12% Cr untuk menghasilkan passive
layer:
Makin banyak Cr makin baik, dengan batasan:
12>%Cr>30
Kandungan Cr yang sering digunakan: 16>%Cr>22
kandungan Cr yang terlalu tinggi akan menghasilkan
fasa brittle
-
Diagram fasa Fe-Cr: pembentukan sigma phase (>30 % Cr)
-
Chapter 17 Stainless Steels
Sigma phase
embrittlement occurs
during prolonged
heating in the range
540C to 760C
(1000F to 1400F).
-
Chapter 17 Stainless Steels
The base composition contains 18% Cr because greater or
lesser amounts of chromium require more nickel to ensure a
completely austenitic structure at room temperature.
-
Chapter 17 Stainless Steels Untuk memprediksi struktur metalurgi berdasarkan komposisi,
dapat dilihat grafik CrE vs NiE pada diagram Schaeffler.
-
Chapter 17 Stainless Steels Ferritizers, austenitizers, and carbide formers are added
to stainless steels for their effects on properties.
-
Ada 5 tipe baja tahan karat yang masuk dalam kategori
wrought stainless steels, yaitu :
martensitic, ferritic, austenitic, precipitation-hardening, and duplex stainless steels.
Cast stainless steels memiliki variasi struktur metalurgi dan
diklasifikasikan sebagi tipe keenam.
-
Several organizations produce designations for
stainless steels.
UNS : Unified Numbering System
ACI : American Concrete Institute
-
Austenitic stainless steel
the most popular of the stainless steels because of their ductility, ease of working and good corrosion resistance.
All were derived from the 18Cr-8Ni stainless steels
-
The most common grade is Type 304 or 304L, which
makes up over 60% of all the stainless steel made in the
United States today
The other grades are developed from the 188 base by
adding alloying elements to provide special corrosion
resistant properties or better weldability
The major weakness of the austenitic stainless steels is
their susceptibility to chloride stress corrosion cracking
-
Ferritic Stainless Steel
Ferritic stainless steels are resistant to chloride stress corrosion cracking, and have high strength
-
SEA-CURE stainless, one of the most popular
superferritic alloys, is widely used in marine
applications
Grades like SEA-CURE stainless have the highest
modulus of elasticity of the common engineering
alloys, which makes them highly resistant to
vibration
The most widely used ferritic stainless steel is Type
409, a 10.5% Ce alloy with no nickel, used for
automotive exhaust systems
-
Duplex Stainless Steel
The steels are characterized by having both austenite and ferrite in their microstructure, hence the name Duplex
Stainless Steel.
A ferrite matrix with islands of austenite characterizes the lower nickel grades, and an austenite matrix with islands of
ferrite characterizes the higher nickel range.
When the matrix is ferrite, the alloys are resistant to chloride stress corrosion cracking.
When the matrix is austenitic, the alloys are sensitive to chloride stress corrosion cracking.
Having high strength, good corrosion resistance and good ductility
-
The room temperature
microstructure of the duplex
stainless steels contains
approximately equal amounts
of ferrite and austenite.
Most duplex stainless steels
contain approximately 70% Fe,
20% Cr to 25% Cr, 4% Ni to
7% Ni, and 2% Mo to 4% Mo.
-
Carpenter 7-Mo PLUS has the best corrosion resistance against nitric acid of any of the stainless steels because of its
very high chromium content and duplex structure
-
Martensitic Stainless Steels
Basically, they are stainless tool steels because they use the
same hardening and tempering mechanisms
Martensitic stainless steels are used in bearing races for corrosion proof bearings and other areas where erosion
corrosion is a problem.
These stainless steels are not especially corrosion resistant, barely as good as Type 304
Their ability to maintain a keen edge comes from their high hardness and corrosion resistance.
-
Precipitation Hardening Stainless Steel
These steels are the latest in the development of special
stainless steels and represent the area where future
development will most likely take place
They are somewhat soft and ductile in the solution-annealed
state, but when subjected to a relatively low precipitation
hardening temperature, 1000F (540C), their strength more
than doubles and they become very hard.
-
The strengthening mechanism comes from the formation
of submicroscopic precipitates, which are compounds of
aluminum, copper, titanium, or molybdenum.
These precipitates provide resistance to strain exerted on
the structure.
The precipitates are so small they can be observed only
at extremely high magnifications with special electron
microscopes
-
Properties of Stainless Steel Alloys, ASTM Minimums,
Unless Otherwise Stat