TECH 31065 Lecture Notes - Lecture 6: Decarburization, Steelmaking, Astm International
11 May 2018
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Secondary Steelmaking Processes
• Degassing (Deoxidation)
• Decarburization
• Desulphurization
• Re-heating
• Slag Fluidizing
Ingots
• Less than 10% of all steel made is poured into ingots (Specialty Steels)
• “Rimmed” Steel has some porosity, very slight piping and higher purity on the outer
edges
• “Killed” or “Blocked” Steel (containing aluminum and/or silicon as a de-oxidizer) has
greater piping but very little porosity (preferred)
Dendrites
• Christmas tree shaped structures that form on the chilled surface of metal
o like ice crystals forming on glass
• Require nucleation to form
• Dendrites eventually become crystals or “grains”
Steel Products
• Fine grained steels usually have higher strength than coarse grained steels of the same
chemistry
• Slabs are bigger than Blooms
• Blooms are bigger than Billets
• They can all be rolled into shapes like Sheets, Structural Steel and Pipe
Hot Rolled Steel
• Steel is red hot from a Soaking Pit
• Steel will re-crystallize and not get harder (grains do not get smaller)
• Steel will have a dark mill scale on the surface
• Steel is relatively weak and soft
• Steel is cheap to make
Cold Rolled Steel
• Steel is cold
• Steel will work harden
o grains get smaller
• Steel may require annealing between rolls to prevent fracturing
• Steel will have a smooth and clean surface finish
o must be pickled in an acid bath before rolling
• Steel is strong and hard
o twice the UTS of HRS
• Steel is more expensive to make
Steel Specifications
find more resources at oneclass.com
find more resources at oneclass.com
