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  • Welding of Alloy Steels
  • Welding of Low Alloy High Strength Steels

Welding of Alloy Steels

Welding of Alloy Steel - Alloy steel contains elements such as chromium, nickel, vanadium, molybdenum, tungsten, cobalt, boron and copper; and manganese, silicon, phosphorus and sulphur in amounts greater than normally are present.
The purpose of adding alloying elements into steel is to achieve Strengthening of the ferrite
Corrosion resistance
Better hardenability
Grain size control
Greater strength
Improved machinability
Improved high or low temperature stability
Improved ductility, etc.

Given below is the composition of a typical alloy steel
1. Carbon in steel affects hardness, tensile strength, machinability and melting point.
2. Manganese contributes markedly to strength and hardness. It lowers both ductility and weldability, if present in high percentage with high carbon content in steel.
3. Silicon improves oxidation resistance and strengthens low alloy steels.
4. Nickel increases toughness and resistance to .impact. It renders high chromium iron alloy austenitic. It strengthens steels and lessens distortion in quenching.
5. Chromium adds to depth hardenability with improved resistance to abrasion. It helps preventing corrosion and oxidation.
6. Molybdenum promotes harden ability of steel, makes it fine grained, counteracts tendency towards temper brittleness, raises tensile and creep strength at high temperatures, etc.

7. Vanadium promotes fine grains in steel, increases strength while retaining ductility, etc.
8. Tungsten improves hardness and strength at high temperatures, resists heat and promotes fine grain.
9. Cobalt contributes to red-hardness by hardening ferrite.
10. Copper (0.20.5%) when added to steel increases resistance to atmospheric corrosion and acts as a strengthening agent.
11. Aluminium produces fine austenitic grain size and acts as a deoxidizer.
12. Sulphur imparts free machining properties.
13. Boron (0.0010.003%) is a powerful hardenability agent.
14. Titanium reduces martensitic hardness in chromium steels.

Alloy steels can be classified as
(a) Low alloy steels (total alloy content up to 5%)
(b) Medium alloy steels (total alloy content from 5 to 8%).
(c) High alloy steels (total alloy content above 8%).

Some of the popular alloy steels are
(i) Low alloy, high strength steels. (A typical composition is C 0.12%, Mn 0.60%, Si 0.30%, Cu 1.1%, Ni 0.55%, Fe balance).
(ii) Chromium steels.
(iii) Nickel steels.
(iv) High nickel chromium steels.
(v) Low carbon molybdenum steels
(vi) Tools steels.
(vii) Stainless steels.
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