Saya sedang membandingkan beberapa perbedaan komposisi material antara STM dengan mill-certificate vendor manufacture, adakah diantara bapak ibu bisa menjelaskan kepada saya perbedaan lebih tinggi atau rendahnya nilai komposisi tersebut terhadap aplikasi standard dan pengaruhnya terhadap kekuatan material,: (misalnya untuk ASTM A403-WP304) => C’ = 0.08, Mn = 2.00, P’=0.045, S’ = 0.030, Si=1.00, Ni-8.00-11.0 Cr=18.0-20.0. Bagaimana kalau kita mendapatkan salah satu atau lebih nilai-nilai tersebut lebih tinggi atau rendah?

Tanya – ismu.darwanto@ikpt

Saya sedang membandingkan beberapa perbedaan komposisi material antara STM dengan mill-certificate vendor manufacture, adakah diantara apak2/ibu2 bisa menjelaskan kepada saya perbedaan lebih tinggi atau endah nya nilai komposisi tsb terhadap aplikasi standard dan pengaruhnya erhadap kekuatan material, : (misalnya untuk ASTM A403-WP304) => C’ = 0.08 , Mn = 2.00, P’=0.045 , S’ = 0.030, Si= 1.00 , Ni= 8.00-11.0 Cr = 18.0-20.0.
Bagaimana kalau kita mendapatkan salah satu atau lebih nilai2 tsb lebih inggi atau rendah ???
Mohon pencerahan………!!!

Tanggapan 1 – winarto

Untuk Bapak Ismu Darwanto,

Sedit saya ingin sharing mengenai permasalahan material di tempat Bapak.

Grade untuk material yang Bapak miliki yaitu : ASTM A403/A403M-02 merupakan Standard Specification for Wrought Austenitic Stainless Steel iping Fittings, dimana standard grade-nya mengacu pada AISI 304 seperti tertera WP304) yakni : Austenitic stainless steel AISI 304.

Untuk mengetahui kandungan unsur-unsur (komposisi kimia) material steel ipe fitting tersebut, Bapak harus menguji komposisi kimianya dengan eralatan SPECTRO-METER. Umumnya hasil uji komposisi-dengan pektro-meter akan keluar sekitar 14 unsur yaitu: Karbon (C), Mangan Mn), Pospor (P), Sulfur (S), Silikon (Si), Nikel (Ni) dan Kromium (Cr), an unsur-unsur pengikut lainnya. Untuk informasi mengenai pengujian omposisi bisa dilakukan di Departement kami di UI (maaf kalau kalimat erakhir ini merupakan iklan).

Jika dari pengujian komposisi (dengan spectrometer) diperoleh nilai yang ebih kecil atau lebih besar atau tidak dalam rentang (range) yang iijinkan, maka material tersebut tidak masuk dalam spesifikasinya.

Mengenai pengaruh unsur-usur pada stainless steel, saya quote dari eferensi stainless steel handbook yaitu :

The effects of the alloying elements:

The alloying elements each have a specific effect on the properties of he steel. It is the combined effect of all the alloying elements and, o some extent, the impurities that determine the property profile of a ertain steel grade. In order to understand why different grades have ifferent compositions a brief overview of the alloying elements and heir effects on the structure and properties may be helpful.

Chromium (Cr):

This is the most important alloying element in stainless steels. It is his element that gives the stainless steels their basic corrosion esistance. The corrosion resistance increases with increasing chromium ontent. It also increases the resistance to oxidation at high emperatures. Chromium promotes a ferritic structure.

Nickel (Ni)

The main reason for the nickel addition is to promote an austenitic tructure. Nickel generally increases ductility and toughness. It also educes the corrosion rate and is thus advantageous in acid nvironments. In precipitation hardening steels nickel is also used to orm the intermetallic compounds that are used to increase the strength.

Molybdenum (Mo)

Molybdenum substantially increases the resistance to both general and ocalised corrosion. It increases the mechanical strength somewhat and trongly promotes a ferritic structure. Molybdenum also promotes the ormation secondary phases in ferritic, ferritic-austenitic and ustenitic steels. In martensitic steels it will increase the hardness t higher tempering temperatures due to its effect on the carbide recipitation.

Copper (Cu)

Copper enhances the corrosion resistance in certain acids and promotes n austenitic structure. In precipitation hardening steels copper is sed to form the intermetallic compounds that are used to increase the trength.

Manganese (Mn)

Manganese is generally used in stainless steels in order to improve hot uctility. Its effect on the ferrite/austenite balance varies with emperature: at low temperature manganese is a austenite stabiliser but t high temperatures it will stabilise ferrite. Manganese increases the olubility of nitrogen and is used to obtain high nitrogen contents in ustenitic steels.

Silicon (Si)

Silicon increases the resistance to oxidation, both at high temperatures nd in strongly oxidising solutions at lower temperatures. It promotes a erritic structure.

Carbon (C)

Carbon is a strong austenite former and strongly promotes an austenitic tructure. It also substantially increases the mechanical strength. arbon reduces the resistance to intergranular corrosion. In ferritic tainless steels carbon will strongly reduce both toughness and orrosion resistance. In the martensitic and martensitic-austenitic teels carbon increases hardness and strength. In the martensitic steels n increase in hardness and strength is generally accompanied by a decrease in toughness and in this way carbon reduces the toughness of hese steels.

Nitrogen (N)

Nitrogen is a very strong austenite former and strongly promotes an ustenitic structure. It also substantially increases the mechanical trength. Nitrogen increases the resistance to localised corrosion, specially in combination with molybdenum. In ferritic stainless steels itrogen will strongly reduce toughness and corrosion resistance. In the artensitic and martensitic-austenitic steels nitrogen increases both ardness and strength but reduces the toughness.

Titanium (Ti)

Titanium is a strong ferrite former and a strong carbide former, thus owering the effective carbon content and promoting a ferritic structure n two ways. In austenitic steels it is added to increase the resistance o intergranular corrosion but it also increases the mechanical roperties at high temperatures. In ferritic stainless steels titanium s added to improve toughness and corrosion resistance by lowering the mount of interstitials in solid solution. In martensitic steels itanium lowers the martensite hardness and increases the tempering esistance. In precipitation hardening steels titanium is used to form the intermetallic compounds that are used to increase the strength.

Niobium (Nb)

Niobium is both a strong ferrite and carbide former. As titanium it romotes a ferritic structure. In austenitic steels it is added to
improve the resistance to intergranular corrosion but it also enhances echanical properties at high temperatures. In .S. it is also referred to as Columbium (Cb).

Aluminium (Al)

Aluminium improves oxidation resistance, if added in substantial mounts. It is used in certain heat resistant alloys for this purpose. n precipitation hardening steels aluminium is used to form the ntermetallic compounds that increase the strength in the aged ondition.

Cobalt (Co)

Cobalt only used as an alloying element in martensitic steels where it ncreases the hardness and tempering resistance, especially at higher emperatures.

Vanadium (V)

Vanadium increases the hardness of martensitic steels due to its effect n the type of carbide present. It also increases tempering resistance. anadium stabilises ferrite and will, at high contents, promote ferrite n the structure. It is only used in hardenable stainless steels.

Sulphur (S)

Sulphur is added to certain stainless steels, the free-machining grades, n order to increase the machinability. At the levels present in these rades sulphur will substantially reduce corrosion resistance, ductility nd fabrication properties, such as weldability and formability.

Cerium (Ce)

Cerium is one of the rare earth metals (REM) and is added in small mounts to certain heat resistant temperature steels and alloys in order o increase the resistance to oxidation and high temperature corrosion.

Corosion Properties.

The reason for the good corrosion resistance of stainless steels is that hey form a very thin, invisible surface film in oxidising environments. his film is an oxide that protects the steel from attack in an ggressive environment. As chromium is added to a steel, a rapid eduction in corrosion rate is observed to around 10% because of the ormation of this protective layer or passive film. In order to obtain a ompact and continuous passive film, a chromium content of at least 11% s required. Passivity increases fairly rapidly with increasing chromium ontent up to about 17% chromium. This is the reason why many stainless teels contain 17-18% chromium.

Mechanical Properties (for austenitic Stainless steel i.e: ASTM A403 ith grade AISI 304.

Austenitic steels generally have a relatively low yield stress and are haracterised by strong work hardening. The strength of the austenitic teels increases with increasing levels of carbon, nitrogen and, to a ertain extent, also molybdenum. The detrimental effect of carbon on orrosion resistance means that this element cannot be used for ncreasing strength. Austenitic steels exhibit very high ductility: they ave a high elongation and are very tough. Some austenitic stainless teels with low total content of alloying elements, e.g. Type 301 and 04, can be metastable and may form martensite either due to cooling
below ambient temperature or through cold deformation or both.

Demikian semoga informasi ini berguna,

Tanggapan dari rekan-rekan Mailing List Migas Indonesia mengenai pembahasan diatas dapat dilihat dalam file berikut: