There are two ways to increase steel's strength at the expense of its ductility: cold working (work hardening) and hardening (heat hardening). Any steel can be cold worked, but heat hardening only works for steels with a carbon content above 0,2-0.3% (an exception to this rule are maraging steels, which do not contain carbon).

Work hardening

hi aparna,

alpha-ferrite is pure iron itself abliet with low carbon content(max:0.025%). It's soft structure in Iron-Iron Carbide Diagram. In order to increase its strength and decrease its ductility the following methods can be adopted:

1. by Cold working: increases strength and decreases ductility, and increases dislocation density.High cold working may lead to increase in strength of steel steeply there by making the steel brittle. You need to Anneal the material in order to reduce the strength and ductility viz. recovery,re crystallization,grain growth.

Cold Working and Annealing Combination Cycle helps us right proportions of Strength and Ductility.

2. by Hardening: This involves heating steel above Austenite Stage and cooling at the Critical Cooling Rate by which Martenstite Transformation Occurs(check TTT diagram for Hypo-Eutectiod,Eutectiod Steels). Martensite has Body Centred Tetragonal Structure while alpha-iron has BCC. The additional carbon ineffect expands the c-axis ,transforming the structure to BCT rather than BCC.This produces totally hard brittle structure.You can do tempering appropriately to reduce brittleness(Strength) and increase ductility.

Option 1 is easier than 2,cost effective and better dimensional control.

thanks & regards,

g.sudhakar

phd(materials engineering)

hcu.

Thank you all for your valuable comments.