Describe the diffusion of carbon in the iron crystal structu

Describe the diffusion of carbon in the iron crystal structure. Explain two heat treating procedures that utilize the diffusion of carbon. Include the mechanical properties that each technique affects.

Solution

When carbon in small quantities is added to iron, ‘Steel’ is obtained. Since the influence of carbon on mechanical properties of iron is much larger than other alloying elements. The atomic diameter of carbon is less than the interstices between iron atoms and the carbon goes into solid solution of iron. As carbon dissolves in the interstices, it distorts the original crystal lattice of iron.

Diffusion of carbon in and-irons is non-uniform: at 550 to 950°C, carbon enriches preferentially the grain boundaries; the diffusivity of carbon along grain boundaries of ferrite is three to four higher than inside the grain. An enrichment with carbon of the-solid solution is also observed in regions adjoining the grain boundaries.

Heat Treatment processes that utilize the diffusion of carbon are

1.Case Hardening: -Diffuse carbon atoms into the host iron atoms at the surface.Case Hardening is a process of hardening ferrous alloys so that the surface layer or case is made substantially harder than the interior or core. The chemical composition of the surface layer is altered during the treatment by the addition of carbon, nitrogen, or both.

Effects: 1. Results in improve of both the wear resistance and the fatigue strength of steel components under dynamic and thermal stresses.

2. Makes the surface layer known as the case significantly harder than the residual material known as the core.

2. CARBURIZING
Carburizing is a process used to harden low carbon steels that normally would not respond to quenching and tempering. This is done for economical reasons (utilizing less expensive steel) or design considerations to provide a tough part with good wear characteristics.

Effects: 1.Increased surface hardness

2. Increased wear resistance

3. Increased fatigue/tensile strengths