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Metalurgi Baja Tahan Karat

Mar 04, 2016

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Indra Ramdhan

baja Tahan karat
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  • 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