Engineering Stress-Strain Curve The engineering stress-strain curve gives the relationship between stress and strain for a ductile material. It is generally obtained by applying load to a tensile specimen. The curve reveal many properties of a material such as Young's Modulus(E), Yield point, UTS   etc. Stress : The stress in the engineering stress-strain diagram is given by load divided by the original area. Strain : The strain in the engineering stress-strain curve is giver by ratio of change in length / elongation to its initial length. Strain has no unit since it’s a ratio of two quantities. Proportionality limit : In the curve, OA is linear. This is due to the fact that the stress is directly proportional to the strain i.e. it follows Hooke’s law. Hooke’s law states that within the elastic limit the stress is directly proportional to th

                                                                    THE ELLINGHAM DIAGRAM The Ellingham diagram is the simplest method of representing the relationship between the free energy( Δ G) and temperature of various oxides and sulphides. In metallurgy, the Ellingham diagram is used to   find out a suitable reducing agent. In the Ellingham diagram the highly stable oxides are found at the bottom and the less stable oxides are found at the top. An element occupying a lower position in the diagram can reduce the oxides of another element present above it. For example, Mg lies below Si thus Mg can be used as a reducing agent for oxides of Si. Why Ellingham diagram has all straight lines? Reason for upward slope of lines The Ellingham diagram is based on a formula given by: Δ G = Δ H – T Δ S If we draw a graph with Δ G as y-axis and T as x-axis the slope of the curve represents the entropy( Δ S) and the intercept is enthalpy( Δ H). From t

THE IRON-CARBON PHASE DIAGRAM Of all binary alloy systems the one that is possibly the most important for a metallurgist is the iron and carbon system. We know that both steel and cast iron play a important role in structural applications and they both are iron-carbon system. Pure iron upon heating experiences changes in its crystal structure until 1538 °C and melts there. At room temperature it is present at a stable form called ferrite(α), which has a BCC crystal structure. The ferrite transforms to austenite( ט ) at 912°C which has a FCC crystal structure. At 1394°C it again undergoes a phase transformation to                                δ-ferrite which has a BCC crystal structure. Pure iron finally melts at 1538°C. All these changes can be seen in the left vertical axis of the Fe-C phase diagram. In the composition axis at 6.7% formation of a intermediate compound known as Fe 3 C(Cementite) or iron carbide is observed. In real world all steels and cast iron