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Why is martensite so hard?

Untempered martensite is a strong, hard, brittle material. The stronger and harder it is, the more brittle it is. The strength and hardness is a due to elastic strain within the martensite, which is a result of too many carbon atoms being in the spaces between the iron atoms in the martensite.

Is martensite FCC or BCC?

As a result of the quenching, the face-centered cubic austenite transforms to a highly strained body-centered tetragonal form called martensite that is supersaturated with carbon. The shear deformations that result produce a large number of dislocations, which is a primary strengthening mechanism of steels.

Is Cementite FCC or BCC?

The alpha phase is called ferrite. Ferrite is a common constituent in steels and has a Body Centred Cubic (BCC) structure [which is less densely packed than FCC]. Fe3C is called cementite and lastly (for us), the “eutectic like” mixture of alpha+cementite is called pearlite.

What is the shape of soft martensite phase is?

Body-centered cubic (bcc) packings of atoms tend to be most stable near the melting point because the atoms have room to vibrate (important at high temperatures): face-centered cubic (fcc) crystals are common among metals at low temperatures because the atoms pack well.১২ এপ্রিল, ১৯৯৬

Is Cast Iron FCC or BCC?

Table 1: Crystal Structure for some Metals (at room temperature)

Aluminum FCC FCC
Cadmium HCP BCC
Iron BCC HCP
Lead FCC HCP
Magnesium HCP

Is BCC or FCC stronger?

Yes the APF is important, the atomic packing factor, that is the reason FCC has more slip systems, because of the way the atoms are arranged in the crystal. Thus FCC metals deform easier than BCC metals and thus they are more ductile. BCC metals are infact stronger than FCC metals. HCP metals are the most brittle.৪ মার্চ, ২০০৯

How do you know if its BCC or FCC?

If the unit cell also contains an identical component in the center of the cube, then it is body-centered cubic (bcc) (part (b) in Figure 12.5). If there are components in the center of each face in addition to those at the corners of the cube, then the unit cell is face-centered cubic (fcc) (part (c) in Figure 12.5).১২ আগস্ট, ২০২০

What is the hardest phase of Fe C system?

Martensite

Why is Cementite brittle?

The ferrite is soft and ductile, whereas the cementite is hard and brittle. The steel has an increased mechanical strength because of both the presence of the two phases and because of their pearlite microstructure, however this comes at the cost of reduced ductility.

What is FE-C diagram?

Phases in Fe–C Phase Diagram • Fe3C (iron carbide or cementite) It is an intermetallic compound between iron and carbon. It contains 6.67 % carbon and is hard and brittle. This intermetallic compound is a metastablephase and it remains as a compound indefinitely at room temperature.

What happens when manganese is added to steel *?

Manganese removes oxygen and sulfur when iron ore (an iron and oxygen compound) is converted into iron. It also is an essential alloy that helps convert iron into steel. As an alloy it decreases the brittleness of steel and imparts strength.

Why is SI added to steel?

Silicon, 14Si28.0855 Silicon increases strength and hardness but to a lesser extent than manganese. It is one of the principal deoxidizers used in the making of steels to improve soundness, i.e. to be free from defects, decays or damages. Silicon is present in all steels to a certain extent.

Why nitrogen is added in stainless steel?

High-strength austenitic stainless steels can be produced by replacing carbon with nitrogen. Nitrogen has greater solid-solubility than carbon, is a strong austenite stabilizer, potent interstitial solid-solution strengthener, and improves pitting corrosion resistance.৩০ মার্চ, ১৯৯৬

Why Sulphur is added to steel?

Sulphur improves machinability but lowers transverse ductility and notched impact toughness and has little effects on the longitudinal mechanical properties. Free cutting steels have sulphur added to improve machinability, usually up to a maximum of 0.35%.১৩ অক্টোবর, ২০১৫

Which type of steel is referred to as red hard steel?

(also called heat resistance), the ability of steel, upon heating to red heat, to retain the great hardness and durability obtained through heat treatment. For example, high-speed steel retains Rockwell C hardness of up to 60 at 620°-650°C. Hard alloys have the highest level of red-hardness (up to 900°C).

Why chromium is added to steel?

Chromium (Cr): Chromium is added to steel to increase resistance to oxidation. This resistance increases as more chromium is added. Nickel (Ni): Nickel is added in large amounts, over about 8%, to high Chromium stainless steels to form the most important class of corrosion and heat resisting steels.

How do you reduce Sulphur in steel?

Desulfurization of steel by injection of active agents Injection of desulfurizing agents to a molten steel is the most effective method of sulfur removal. Injection methods usually combine supply of a disperse desulfurizing agent (powder) with stirring by argon blowing.৩১ মে, ২০১২

How is phosphorus removed from steel?

The method entails melting a prepared slag in a separate furnace and tapping into the ladle before steel tapping. The induction furnace steel is then tapped onto this slag. The rapid mixing of the slag with the steel during tapping completes the removal of phosphorus even while tapping is going on.২ ফেব, ২০১৭

What is acid slag?

Slag is a multi-component system and in steelmaking it consists of acidic oxides such as SiO2 and P2O5, and basic oxides such as FeO, CaO, MgO etc. In some slags Al2O3 is also present. In the last lecture we noted that acidic oxides are network formers, whereas basic oxides are network breakers.

What is desulphurization process?

Desulfurization or desulphurisation is a chemical process for the removal of sulfur from a material. This involves either the removal of sulfur from a molecule (e.g. A=S → A:) or the removal of sulfur compounds from a mixture such as oil refinery streams.

Why is desulphurization needed?

Removal of sulphur from hot metal is called desulphurization of hot metal. Sulphur is a desirable element in steel when good machinability is required from the steel product. It forms undesirable sulphides which promotes granular weakness and cracks in steel during solidification. …১৬ অক্টোবর, ২০১৩

Why is Sulphur removed from crude oil?

The purpose of removing the sulfur is to reduce the SO2 emissions. The HDS process involves catalytic treatment with hydrogen to convert the various sulfur compounds present to hydrogen sulfide.২৫ মে, ২০১৬

What is FGD system?

Flue gas desulfurization (FGD) is a set of technologies used to remove sulfur dioxide (SO2) from exhaust flue gases of fossil-fuel power plants, as well as from the emissions of other sulfur oxide emitting processes.

How is FGD conducted?

Question Types There should be three types of questions in a focus group discussion: Probe questions: these introduce participants to the discussion topic and make them feel more comfortable sharing their opinion with the group. Follow-up questions: delve further into the discussion topic and the participants’ opinions.১১ সেপ্টেম্বর, ২০১৭

How is SO2 removed from flue?

Wet scrubbing using a slurry of alkaline sorbent, usually limestone or lime, or seawater to scrub gases; Spray-dry scrubbing using similar sorbent slurries; Dry sorbent injection systems that introduce powdered hydrated lime (or other sorbent material) into exhaust ducts to eliminate SO2 and SO3 from process emissions.

How is Sulphur dioxide removed from the air?

It involves mixing of crushed limestone/lime with water to form a slurry and spraying it into the sulphur containing flue gases. The sorbent reacts with SO2 and forms an aqueous slurry of calcium sulphite. About 90% SO2 removal can be achieved.১০ জুন, ২০১৫