o Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to modify or improve its mechanical properties.o The definition of alloy steel does not include those effects which are negative or cure of ills that the steel might possess were the alloying element(s) not added.o The term "alloy steel" is the standard term referring to steels with other alloying elements in addition to the carbon. Common alloyants include Mn, Ni, Cr, Mo, V, Si and B . Less common alloyants include Al, Co, Cu, Ti, W, Sn, Zn, Pb and Zr.
Alloy steel has some of its properties better than carbon steel. They are as follows:-o Tensile strengtho Hardnesso Toughnesso Wear Resistanceo Creepo High Temperature Resistanceo To achieve some of these improved properties the metal may require heat treating.
o low-alloy steels : increase strength and hardenabilityo high-alloy steels : improves corrosion resistance and stability at high or low temperature.o Most commonly, the phrase "alloy steel" refers to low- alloy steels.o One more classification method is based upon the compositiono Simple alloy steel is alloy steel containing one alloying element, for example, simple nickel steel.o Quaternary alloy steel is alloy steel that contains two alloying elements, as, Chromium Vanadium steel.o Complex steel is alloy steel containing more than two alloying elements such as high speed tool steel.
It’s a complex and highly specialized process which can be summarized as :- Electric Arc furnace/Mini Blast Furnace Ladle Furnace Vacuum Degassing Continous Casting Hot Rolling Downstream Processing(recovery and purification)Alloy Steel may be supplied in:- As rolled condition Heat treated Cold finished Smooth turned Centre less Ground
Alloy steels are manufactured in the form of: Bars Wires Wire Rod Bright BarsSizes Alloy steel products are manufactured in size ranging from 5mm to 400mm width or diameter.Shapes: Alloy Steel products are manufactured in the following shapes: Square Round Rectangle Hexagon Flat Customized Shapes
Alloying elements are added to achieve certain properties in the material. added in lower percentages (less than 5%) to increase strength or hardenability added in larger percentages (over 5%) to achieve special properties, such as corrosion resistance or extreme temperature stability. Mn, Si, or Al are added during the steelmaking process to remove dissolved oxygen, sulphur and phosphorus from the melt. Mn, Si, Ni, and Cu are added to increase strength by forming solid solutions in ferrite.
Carbon:- Fe is alloyed with carbon to make steel and has the effect of increasing the hardness and strength by heat treatment but the addition of carbon enables a wide range of hardness and strength. Manganese- added to steel to improve hot working properties and increase strength, toughness and hardenability.- It is an austenite forming element and has been used as a substitute for nickel in the A.I.S.I 200 Series of Austenitic stainless steels (e.g. A.I.S.I 202 as a substitute for A.I.S.I 304)- Used as deoxidizer.
Nickel- added in large amounts, over about 8%, to high chromium stainless steel to form the most important class of corrosion and heat resistant steels.- the tendency of nickel to form austenite is responsible for a great toughness and high strength at both high and low temperatures.- Nickel also improves resistance to oxidation and corrosion. Chromium- to increase resistance to oxidation. This resistance increases as more chromium is added.- When added to low alloy steels, chromium can increase the response to heat treatment, thus improving hardenability and strength.- Increase strength by forming second-phase carbide.
Molybdenum- when added to chromium-nickel austenitic steels, improves resistance to pitting corrosion- When added to low alloy steels, molybdenum improves high temperature strengths and hardness. Titanium- The main use of titanium as an alloying element in steel is for carbide stabilisation as it forms TiC in solid phase.- Thus tends to minimize the occurrence of inter- granular corrosion, as with A.I.S.I 321, when adding approximately 0.25%/0.60% titanium Copper- Improves corrosion resistance
Phosphorus- Phosphorus is usually added with sulphur to improve machinability in low alloy steels,- Phosphorus, in small amounts, aids strength and corrosion resistance.- Phosphorus additions are known to increase the tendency to cracking during welding. Sulphur and Selenium- improves machinability. Silicon- used as a deoxidizing (killing) agent.- contributes to hardening of the ferritic phase in steels and for this reason silicon killed steels are somewhat harder and stiffer than aluminium killed steels. Cobalt- improves strength at high temperatures and magnetic permeability.- But Co containing steel cannot be used in Nuclear plants as it is radioactive.
Alloy Steels are specifically produced for sophisticated engineering applications. Alloy Steels finds its applications in various areas: Automotive Transmission Parts, Engine Components, Steering Components, High Tensile Fasteners, Fuel Injection Pumps, Bearing Axles, Gears, Crankshaft, Transmission Chains, Springs, Combustion chamber, Axles, Wheel Hubs Engineering Cutting Tools, Structural Steel Industry Mining Machinery, Energy exploration machinery, food-processing units(non-corrosive environment) Construction Reinforcing Bars Agriculture Tractor Parts Home Utensils, Decorative purposes Railways Wagon Axles, Crankshafts, Cushioning Device Components, Steel Liners, Traction Gears Military Ordnance, gun barrels, projectiles, missile components
The application of alloy steel is increasing everyday. Wide use in Automotive industries The other major consuming sectors like auto ancillary, seamless pipes and tubes, engineering and railways etc. have also consumed rising quantity of alloy steel. Forging industry is the largest consumer of alloy steel, which in turn caters to the need of automotive and auto ancillary sector. The industry has registered a growth of over 15% p.a. for the last two years. CARE(Credit Analysis & Research Limited) Research expects the domestic alloy steel demand to grow at a CAGR of 13.6% during the period FY11 to FY16.
Pakistan authorities have allowed import of only alloy steel items through Wagah border, banning entry of non alloy steel items through this route. South Africa’s imports of alloy steel is increasing at a high rate. Mr Wang Yong chairman of Xiwang Special Steel Co. a subsidiary of Shandong Province based China steelmaker Xiwang Group has stated that construction work on the company high strength alloy steel pipe project will start early in the second half year of this year with commissioning expected in the third quarter. The planned annual output capacity is 2 million tonnes. Iran produced 307,300 tonnes of alloy steel last calendar year which ended on March 19th 2012 showing 11.3% increase on the previous year. It expects to increase its production capacity by 80% in next few years. Iran exported 180,000 tonnes of alloy steel previous year
According to provisional data released by Joint Plant Committee, given below are the production, import, export and consumption figures for alloy steel for April 2012. (all data is in ‘000 tonnes)
Alloy steel (including stainless steel) constitutes only approx. 10% of the overall annual steel production in India. But its share is approx. 20% in terms of value since the products are substantially value added for specific end users. Alloy steels are specifically produced for use in sophisticated engineering products for various critical applications such as :-- machined components- engine parts- steering components and bearings- automobile industry.