The General Effects Of Alloying Elements

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The General Effects Of Alloying Elements

مُساهمة من طرف Admin في الجمعة مارس 07, 2008 5:17 am


Alloying Elements



Manganese
Increases strength and hardness; forms a carbide; increases hardenability; lowers the transformation temperature range. When in sufficient quantity produces an austenitic steel; always present in a steel to some extent because it is used as a deoxidiser
Silicon
Strengthens ferrite and raises the transformation temperature temperatures; has a strong graphitising tendency. Always present to some extent, because it is used with manganese as a deoxidiser
Chromium
Increases strength and hardness; forms hard and stable carbides. It raises the transformation temperature significantly when its content exceeds 12%. Increases hardenability; amounts in excess of 12%, render steel stainless. Good creep strength at high temperature.
Nickel
Strengthens steel; lowers its transformation temperature range; increases hardenability, and improves resistance to fatigue. Strong graphite forming tendency; stabilizes austenite when in sufficient quantity. Creates fine grains and gives good toughness.
Nickel And Chromium
Used together for austenitic stainless steels; each element counteracts disadvantages of the other.
Tungsten
Forms hard and stable carbides; raises the transformation temperature range, and tempering temperatures. Hardened tungsten steels resist tempering up to 6000C
Molybdenum
Strong carbide forming element, and also improves high temperature creep resistance; reduces temper-brittleness in Ni-Cr steels. Improves corrosion resistance and temper brittleness.
Vanadium
Strong carbide forming element; has a scavenging action and produces clean, inclusion free steels. Can cause re-heat cracking when added to chrome molly steels.
Titanium
Strong carbide forming element. Not used on its own, but added as a carbide stabiliser to some austenitic stainless steels.
Phosphorus
Increases strength and hardnability, reduces ductility and toughness. Increases machineability and corrosion resistance
Sulphur
Reduces toughness and strength and also weldabilty.
Sulphur inclusions, which are normally present, are taken into solution near the fusion temperature of the weld. On cooling sulphides and remaining sulphur precipitate out and tend to segregate to the grain boundaries as liquid films, thus weakening them considerably. Such steel is referred to as burned. Manganese breaks up these films into globules of maganese sulphide; maganese to sulphur ratio > 20:1, higher carbon and/or high heat input during welding > 30:1, to reduce extent of burning.

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رد: The General Effects Of Alloying Elements

مُساهمة من طرف ENG_3ALIM في الثلاثاء مارس 11, 2008 2:02 am

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