Hi Al-Anizi,
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Originally Posted by S.Al-Anizi
Sorry for not contributing (for good or bad  ) to this thread anymore, I really like the level of professional conversation and the sharing of facts and experiences around, by all those great people who have contributed to this thread. I have not lost interest in this topic, its just that I seemed to have lost it somewhere from the 5th page, I do not understand 75% of the metallurgical words tossed about  Still, interesting and very informative though.  |
I was really worried that this might happen - I apologize - We turned this thread into an insider's discussion. I don't know hat we can do to remedy the situation - Perhaps, the underlisted glossary may render the technical terms used a little more understandable.
Austenite: A crystal structure of iron and its alloys that is known for its softness and malleability. It only can be found once the steel is heated to red heat. If it is rapidly cooled (quenched) it transforms into Marteniste. If, on the other hand, it is cooled slowly, it will transform into Ferrite and Cementite.
Austenite - Retained: Austenite that fails to transform into Martensite upon quenching and is retained as such at room temperature. Retained Austenite is much more likely to form with steels with a carbon content greater than 0.8%, that is , hypereutectoid. It is generally considered highly undesirable as it is a source of weakness. Usually, the quenched steel is a mixture of Martensite and Austenite in varying proportions - Depending where it is located, a small amount of Retained Austenite can usually be tolerated.
Carburization: Iron is heated in the presence of carbon so that it may absorb this element. This is obtained by heating above red heat, when the crystal structure changes to Austenite, which readily absorbs carbon.
Cementite: An intermetallic compound of iron and carbon. It is both extremely hard and brittle. It is usually, though not always, found as tiny globules, in which case it is called sperodized Cementaite or as very thin plates (lamellae) in the structure known as Pearlite.
De-Carburization: The removal of carbon from steel by heating to above red heat so that the crystal structure changes to Austenite and in an oxygen rich atmosphere. The carbon leaves the steel to combine with the oxygen.
Eutectoid Steel: A steel of 0.8% carbon content - Optimal composition for hardness and toughness.
Hypo-eutectoid Steel: A steel with a carbon content of less than 0.8% carbon, but usually more than 0.4% carbon
Hyper-eutectoid Steel: A steel with a carbon content in excess of 0.8% but less than 2%. These steels are considered very difficult to harden by transforming Austentie to Martensite (by quenching from red heat) because of the tendency of the high carbon Austenite to remain as such down to room temperature.
Ferrite: The crystal structure of unhardened near pure iron that prevails at room temperature. It is fairly soft and malleable, though not to the same extent as Austenite. As the carbon content of steel approaches 0.8%, Ferrite is increasingly complemented by the presence of Pearlite.
Hardening: A process by which steel is rendered both hard and tough. This is usually attained by the transformation of Austenite to Martensite by fisrt heating to red heat and then rapidly cooling, usually by quenching into water or oil. Afterwards the had and brittle Martensitic steel is toughened through tempering, by reheating to a lower temperature (than red heat). And alternative to hardening by heating and quenching is to cold work (work hardening) the steel - This is the same effect as when we bend coat-hanger wire backwards and forwards; Whilst this can increase both the hardness and toughness of steel, it is not as effective as heating and quenching.
Martensite: The crystal structure of steel hardened by quenching from red heat. Since in the as quenched state it is very brittle, it is normally softened and made less so by tempering. The maximum carbon content of Austenite that can be converted to Martensite is around 1% - Any more than this value will result in the retention of Austentite down to room temperature.
Pearlite: The microstructure of unhardened eutectoid steel, that is, with a carbon content of 0.8%. When viewed under the microscope it consists of very thin layers of Cementite alternating with Ferrite and has the appearance of mother-of-pearl, hence its name. Under 0.8%C Pearlite is accompanied by Ferrite and above that composition by Cementite.
Sorbite: A name given to Martensite which has been tempered.
Sponge/Bloom/Bloomery Iron: Is and extremely low carbon steel that is obtained by heating the iron ore (Iron Oxide) with carbon to red heat, without any melting taking place. The oxygen in the ore combines with the carbon, in a process known as `reduction', to leave behind the very low carbon steel in a sponge like state. The pores of the iron sponge, the Bloom, are full of slag (coarse glass) from the ore. This slag has to be removed by extensive hammering in the red hot state, by squeezing it out of the many pores. To render it into hardenable steel it has to be Carburized. This method was used extensively in antiquity to prodce iron and steel.
Steel: An alloy of iron and carbon. The stuff from which swords and dagger are made (after the bronze age). Ideally, it is both hard and tough.
Tempering: The re-heating of as quenched steel to render it less brittle, at the expense of some loss of hardness. Tempering is carried out at temperatures at which shiny steel changes its colour to that of straw or even blue.
Wootz/Puald/Bulat/Crucible Steel: Steel made in ancient India by heating iron ore with carbon in a crucible. Wootz differs from `sponge/Bloom' iron in as much that it it melts in the crucible and thus the slag and other impurities float to the surface.
Cheers
Chris