Question

Define alloy steel. discuss the effect of nickel, chromium and manganese on steel.

Answer 1

Alloy Steel:- Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. 

Influence of Ni (Nickel) on steels

Ni (Nickel) strengthens low C steels. It increases steel strength, impact strength and toughness. It also improves toughness at low temperatures when added in small amounts.  Ni increases elastic limit of steel.

Ni when added to steel, increases its density and hardness. It improves steel’s resistance to oxidation and corrosion. It also improves abrasive resistance of steel.

Ni is heat resistant, and when combined with steel, it increases the heat resistance of that steel. Ni is rust resistant, making it ideal for the production of stainless steel.

Addition of Ni in steel decreases the value of distortion (distortion energy) at the time of quenching.

When steel is coated with Ni, or plated with Ni, then the Ni provides a scratch resistant surface to steels.

Influence of chromium on steel

Cr increases the hardenability of steel while there is a minimal effect on the ductility. Cr by forming carbides increases the edge holding quality of steel. The tensile strength of steel increases by 8 to 100 N/sq mm for every 1 % of Cr added. The yield strength also increases but the notch impact value reduces.

Cr is normally added to steel for increasing oxidation resistance, and for improving high temperature strength. Corrosion resistance of Cr steels increases sharply at a Cr level of greater than 12 %. Cr forms a very coherent oxide layer on the steel surface that prevents further oxidation and thus provides resistance to corrosion in the steels.

Effect of Manganese (Mn) on steel

Manganese increases hardenability and tensile strength of steel, but to a lesser extent than carbon. It is also able to decrease the critical cooling rate during hardening, thus increasing the steels hardenability much more efficient than any other alloying elements. Manganese also tends to increase the rate of carbon penetration during carburizing and acts as a mild deoxidizing agent. However when too high carbon and too high manganese accompany each other, embrittlement sets in. Manganese is capable to form Manganese Sulphide (MnS) with sulphur, which is beneficial to machining. At the same time, it counters the brittleness from sulphur and is beneficial to the surface finish of carbon steel.

Answer 2

Alloy steel can be defined as a type of steel in which several elements like manganese, molybdenum, chromium, nickel, vanadium, boron and silicon are alloyed together.

Explanation:

• In alloy steel, several elements are alloyed together in order to hardness, strength, toughness and wear resistance.
• The amount of elements vary between $1$ and $\[50\% \]$.
• It is a classified into two types:

1. High alloy steel
2. Low alloy steel

• Chromium improves the mechanical properties of the alloy. It also increases the hardness, strength and ability for heat treatment.
• Nickel also improves the mechanical properties and increases the impact strength and toughness, even at lower temperatures.
• Manganese helps with the heat-treating process of the alloy. It reduces the risk of defects during the quenching and heating process. It also helps in increasing hardness and strength.

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