FIELD OF INVENTION

The invention in general relates to the field of metallurgy. More particularly, it relates to the manufacturing process of a special steel alloy that can get cooled to room temperature without need for any quenching action. More specifically, the invention relates to the manufacture of an air hardening alloy steel which finds its application in the manufacture of armour.

BACKGROUND OF THE INVENTION

Alloy steels employed in the manufacture of armory need to be rapidly quenched in oil /water during hardening process to achieve properties such as high hardness.

For rapid quenching, there arises the need of providing fixtures / equipments which are costly to hold the hot components of the armory and quench them in oil / water.

Further the quenching action must be carried out in quick time. Otherwise delay in quenching action (known as quench delay) will affect the achieving of properties of hardness of the alloy steel.

Furthermore the plates of the alloy steel of the armory get warped during quenching which is difficult to be levelled and achieve the desired degree of flatness as the alloy steel has been imparted with property of high hardness.

SUMMARY OF THE INVENTION

In one aspect the invention provides 0.3C-3.0Ni-2Si- lCr-0.5Mo-B low alloy steel which is air hardenable in nature. It also possesses a very high degree of toughness and high hardness (520 -560 BHN) when compared to other oil hardened grades of alloy steels.

Another aspect of the invention is to ensure that the alloy steel is homogenous throughout the components of the arnory materials made of it by addition of alloying materials in appropriate proportion and remelting in Electro Slag Remeiting furnace.

A further aspect of the invention is to provide the necessary properties of high hardness and strength to the plates of armory made out of the alloy steel by giving them low temperature tempering,

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

Carrying out of the process of primary melting is done in electric arc furnace. Here the alloying elements are added in certain proportion as per the designed range. Sulphur and phosphorus are kept as low as possible. The molten metal is cast in a cylindrical mould.

This casting is thoroughly conditioned and subsequently remelted in Electro Slag Remelting Furnace. This ensures the material is homogenous, sound (without porosity / pipes / gas holes etc) and clean (free from inclusions).

The materia] is then hot worked to plates. The plates are air hardened from austenitising temperature. These plates are then given low temperature tempering / stress relieving to obtain high hardness / strength and tough plates.

The steel can also be bent to desired shape at high temperature (hardening temperature) and allowed to cool to room temperature. Thus resulting in complete transformation to martensite resulting in high hardness. The resultant structure is then tempered at low temperature to relieve the transformation stresses but at the same time retain the high hardness. The tempering treatment and balanced composition results in excellent impact toughness even at ultra high strength levels. The combination of high hardness and adequate toughness results in maintaining excellent ballistic resistance.

TERMINOLOGY/ CHEMICAL FORMULAE INVOLVED-

C -> Carbon
Ni -> Nickel
Si -> Silicon
Cr -> Chromium
Mo -> Molybdenum
B -> Boron

CLAIMS:-

1. An alloy steel which is air hardenable, the alloy steel comprising of

Carbon (C)
Nickel (Ni)
Silicon (Si)
Chromium (Cr)
Molybdenum (Mo)
and Boron (B)
Wherein the alloy has hardness in the range of 520 - 560 BHN

2. A method for manufacturing of air hardening alloy steel as claimed in claim L the method comprises the steps of primary melting of the alloy carried out in electric arc furnace wherein the alloying elements are added in appropriate proportions as per the designed range keeping sulphur and phosphorus content low.

3. A method for manufacturing of air hardening alloy steel as claimed in claim 2, wherein the molten metal is cast in cylindrical mould and is thoroughly conditioned and remelied in Electro Slag Remelting furnace to ensure homogeneity of constituent materials of the alloy to produce an ingot

4. A method for manufacture of air hardening alloy steel as claimed in claim 3, wherein the cast molten metal, ESR ingot is hot worked to obtain plates which are air hardened and further given low temperature tempering to achieve plates with high hardness / strength and toughness.