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Module 5 - Dental Materials > Base Metal Casting Alloys Stainless Steel > Flashcards

Base Metal Casting Alloys Stainless Steel Flashcards

1
Q

What is 18/8 stainless steel? How is it manipulated and what is it used for?

A
  • 18% Cr, 8% Ni.
  • Cannot be heat treated hence rely on COLD WORKING
  • non-cutting instruments, wires, denture bases.
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2
Q

What does steel consist of?

A
  • Alloy of IRON and less than 2% carbon.
  • If more than 2% would make it BRITTLE and unsuitable for cold working.
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3
Q

What can be done to avoid miscasting in CoCr and NiCr alloys?

A
  • Additional casting thrust.
  • Porous investment material.
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4
Q

What determines whether there will be a hypo or hyper eutectoid alloy?

A

The % of carbon.

(more carbon = hyper)

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5
Q

What are the 5 constituents of Nickel Chrome?

A
  • Nickel (main constituent).
  • Chromium (NO LESS THAN 20%).
  • Molybdenum (NO LESS THAN 4%).
  • Beryllium (NO LESS THAN 2%  concern as CARCINOGEN).
  • Cobalt + Nickel + Chromium (NO LESS THAN 85%).
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6
Q

What happens if steel is above Tc?

A

AUSTENITE - Interstitial solid solution of carbon in a face centered cubic iron matrix.

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7
Q

What is the passivating effect?

A

Chromium oxide PROTECTS AGAINST EROSION.

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8
Q

Give an example of a hyper eutectoid alloy and what it is used for in dentistry.

A

Cementite - hard and brittle.

Cutting instruments like burs.

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9
Q

What happens if steel is below Tc?

A

2 forms:

  • Ferrite (dilute solid solution of carbon 0.02% in Fe).
  • Cementite (specific compound with satisfied valence requirements Fe3C).
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10
Q

What 2 methods can be used to join 18/8 stainless steel?

A
  • SOLDERING (Ag solder)
  • WELDING
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11
Q

What is the function of Chromium in CoCr?

A

HARDNESS AND CORROSION RESISTANCE via PASSIVATING EFFECT

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12
Q

What is the temperature change of welding proportional to?

A

I^2Rt

I = current
R = electrical resistance
t = time current passes

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13
Q

What is the function of trace elements in CoCr?

A

IMPROVE CASTING AND HANDLING.

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14
Q

What are two examples of wrought alloys? What are these used for in dentistry?

A

Steel and Stainless Steel.

Used for instruments, burs, wires and denture bases.

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15
Q

Give an example of a hypo eutectoid alloy and what it is used for in dentistry.

A

Ferrite - soft and ductile.

  • used for NON CUTTING INSTRUMENTS, ex. forceps.
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16
Q

What is martensitic stainless steel composed of? How is it manipulated and what is it used for?

A

No Nickel, 12% Chromium

  • Heat treatment possible, used for probes and cutting instruments.
17
Q

How are Co/Cr or Ni/Cr fused?

A

By ELECTRICAL INDUCTION or OXYACETYLENE TORCH.

18
Q

What is the function of each of the components of stainless steel?

A
  • Chromium: CORROSION RESISTANCE by PASSIVATING EFFECT
  • Nickel: CORROSION RESISTANCE + STRENGTH
19
Q

What affects wire stiffness?

A

Thickness.

20
Q

What is springback ability?

A

Ability to undergo large deflections without permanent deformations.

21
Q

What are Steel and Stainless Steels?

A

WROUGHT ALLOYS

22
Q

What can be used to speed up NiCr finishing?

A

Sandblasting.

23
Q

How are wrought alloys manipulated? What may occur due to this manipulaiton?

A

Hammered, bent, drawn into shape at temperatures way below their RECRYSTALLIZATION TEMPERATURE.

Work Hardening.

24
Q

What are 3 common traits of CoCr and NiCr

A
  • Fusion temperature 1200-1500.
  • Difficult to finish.
  • Density lower than gold alloys.
25
Q

What is the function of Nickel in CoCr?

A

Adds hardness and strength.

26
Q

What is a concern with beryllium?

A

CARCINOGEN.

27
Q

What is the effect of the addition of chromium and nickel to stainless steel?

A

Reduce the critical temperature.

28
Q

What are the 3 grades of 18/8 Stainless steel?

A

Where less than 0.15% C:

  • 3 Grades: Soft, Half Hard, Hard.
29
Q

When does the steel eutectoid alloy form?

A

At critical temperature when carbon concentration is 0.8%

30
Q

What is the mixture of cementite and ferrite called?

A

Pearlite.

31
Q

What is stainless steel composed of?

A

Steel and Chromium

May also add nickel.

32
Q

What is the formula for springback potential?

A

Springback potential = yield stress/ modulus of elasticity.

33
Q

What can be used to speed up CoCr finishing?

A

Sandplasting and electrolytic polishing.

34
Q

What are the 5 constituents of Cobalt Chrome?

A
  • Cobalt.
  • Chrome (no less than 25%)
  • Molybdenum (no less than 4%).
  • Cobalt + Nickel + Chromium (no less than 85%).
  • All plus TRACE ELEMENTS Silicone, Carbon, Beryllium.
35
Q

What is the function of Cobalt in CoCr?

A

Adds hardness and strength.

36
Q

What elements do base metal casting alloys not contain?

A

Ag, Au, Pt, Pd.

37
Q

What is the critical temperature of steel?

A

723 celsius

38
Q

What is the carbon content of ferrite?

A

up to 0.02%

39
Q

Chemical formula of cementite

A

specific compound with satisfied valence requirements Fe3C

Module 5 - Dental Materials (1 decks)

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