Elec 371 - Surgical Instruments 1 Surgical Instruments Iron-Based Metal Compounds Iron (Fe) • Crystalline Structure – Atoms arranged in a lattice • Alpha Iron – < 910° C • Gamma Iron – 910°-1400° C • Melting point – 1540° C Ferrite (Steel) • Iron Alloy – Fe + Other atoms – At least 50% Fe • Stainless steel – 11% to 30% Cr – Up to 2% C
9
Embed
Surgical Instruments - UBCleos/pdf/e371/notes/SurgInst.pdf · Elec 371 -Surgical Instruments 4 Hardening Quench Hardening – Heat to Gamma • face centered • higher C solubility
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Elec 371 - Surgical Instruments
1
Surgical Instruments
Iron-Based Metal Compounds
Iron (Fe)
• Crystalline Structure– Atoms arranged in a lattice
• Alpha Iron– < 910° C
• Gamma Iron– 910°-1400° C
• Melting point– 1540° C
Ferrite (Steel)
• Iron Alloy– Fe + Other atoms
– At least 50% Fe
• Stainless steel– 11% to 30% Cr
– Up to 2% C
Elec 371 - Surgical Instruments
2
Atomic Structure of Iron Crystal
Body CenteredFerrite (α iron)
Face CenteredAustenite (γ iron)
910° C(threshold temp)
Heat
Cool
Non-magneticLarger interstitial gaps
Magnetic
Alloys - Substitutional Atoms
• Similar size as Fe
• Replace Fe atoms• Chromium (Cr)
• Molybdenum (Mo)
• Nickel (Ni)
Elec 371 - Surgical Instruments
3
Alloys - Interstitial Atoms
• Smaller than Fe
• Occupy gaps
• Greater solubility in Gamma
• Precipitate out during cooling• Carbon (C)
• Nitrogen (N)
Iron Alloy Atoms
Substitutional Atoms
• Chromium (Cr)– Corrosion Resistance
• Molybdenum (Mo)– Extra corrosion resistance
• Nickel (Ni)– Austenite
– Stabilizes Gamma at room temp
– Bright finish
Interstitial Atoms
• Carbon (C)– Smaller atomic radius than
substitutional atoms
• Nitrogen (N)– Smaller atomic radius than C
– Greater solubility
Elec 371 - Surgical Instruments
4
Hardening
Quench Hardening– Heat to Gamma
• face centered
• higher C solubility
– Carburize• Add C and/or N
– Quench• Cool rapidly in oil bath
• Rapid transition traps C/N atoms
– Martensite• Disorganized crystal structure
Work Hardening– Mechanical manipulation
– Non-uniform
– Result• Low strain
• Brittle
Softening
Annealing• Heat
– Target temperature / long time– Gamma throughout
• Cool slowly– Carbon precipitates out
• 0.00005% to 2% (by weight)
• Result– Ductile throughout
Tempering• Heat
– High temperature / short time– Gamma surface / Alpha core
• Cool slowly– C precipitates from surface
• Result– Ductile surface– Hard interior
Elec 371 - Surgical Instruments
5
Classes of Stainless Steel
• Ferrite– Fe + Cr
– Magnetic
– Ductile
– Low Cost
• Martensite– Fe + Cr + (C / N)
– Magnetic
– Hard
• Austenite– Fe + Cr + Ni (+ C / N)
– Non-magnetic
– May be quench hardened• Not as hard as Martensite