Transcript 35MM Slides for 4/2/98 Chap 5 Meeting

Modern Methods of Ferritic
Nitrocarburizing (FNC)
H-13
section
28” dia
48” depth
open
basket
Open bed at
temperature
Loaded basket,
ready for carousel
Removal from
fluidized quench
Ferritic Nitrocarburizing (FNC)
How we got here
 1900’s
– Dr. Adolph Fry
 Discovered that Nitrogen and Iron had affinity to
one another.
 Developed nitrogen iron equilibrium table
 Nitralloy steels
 Studied effect of adding other alloys Vanadium,
Tungsten, Manganese, Molybdenum, Titanium
Ferritic Nitrocarburizing (FNC)
Continued 2
 1900’s
Adolph Machlet – New Jersey
 American Gas Company - Elizabeth
 Applied for patents which were received
June 24, 1913
 US saw no commercial benefit at the time
Ferritic Nitrocarburizing (FNC)
Continued 3
 1927 Pierre Aubert – Chicago
 At SME convention presented research for
practical applications in Europe
 Included railway steel, machine tools,
auto, aviation.
 Benefits – hard surface, core not changed,
high wear, unaffected by temper, corrosion
resistance.
Ferritic Nitrocarburizing (FNC)
Continued 4
 1928 – McQuaid and Ketchum
 Timken – Detroit Axle Co.
 Metallurgists – practical applications
 Used work of Fry and Machlet as pivot point
 1929 – Robert Sergeson
 Central Alloy Steel – Canton, OH
 Varying Al content in nitro alloy steel with effect
of nickel
Ferritic Nitrocarburizing (FNC)
Others
 V. O. Homberg & J.P. Walsted - MIT
 Effect of varying temperature – white layer
 Equipment preheat and decarburization effect
 Dr. Carl F. Floe – Assoc MIT
 Continued study of white (epsilon) layer
 The Flow Process – methods to change
compound layer
 Eventually this research lead to “Ion Nitriding” – in
effort to shorten cycle times, reduce distortion, and
improve metallurgical properties.
Types of Nitriding
 Fluidized
Bed Nitriding and FNC
 Nitempering
 Controlled Nitrocarburizing
 Soft Nitriding
 Triniding
 Nitroc Process
 Vacuum Nitrocarburizing
 Nitrotec Process
 Austenite Nitrocarburizing
FNC – Thermochemical Diffusion
 Process
where N2,C, and sometimes a
very small degree of O2 atoms are
diffused into the surface of a ferrous
substrate forming a compound layer
and subsurface diffusion layer.
 Done in relatively short period of time
at sub critical steel temperatures
 Wear properties, Corrosion (solder),
and improved fatigue resistance.
Prominent Developments FNC
 Salt Bath Nitrocarburizing
 Started about 55 years ago
commercially.
 1959 – Germany patented Tuffride
 1970’s – EPA regs prohibiting
cyanide base materials
 Tufftride replaced with Melonite
and French process called Sur-sulf
 These two processes still in use
today.
Prominent Developments FNC
Continued
 Gas – Originally patented in 1961
by Joseph Lucas Industries Ltd.
 1965 – B. Presnosil Published
results of study doing Gas.
 During following quarter of a
century – developed Triniding (NH3
and exothermic gas), Nitemper,
Lindure and a two stage process
(Deganit) from Germany
Fluidized (FNC) Bed Phenomenon
 An
1879 patent discusses baking minerals
under fluidized bed conditions
 Bed of finely-divided heated particles, usually
Aluminum oxide made to behave like a liquid
by moving exothermic and reactive gases
through the medium
 Smooth or bubbly properties – determines
fluidization quality.
 Size and hetrogeneity (other offspring) of bubbles
– influences rate of the solid mixing
 Bed geometry, gas flow rate, type of gas
distributor
 Vessel features – baffles, screens, heat
exchangers
Analogy of Fluidized Bed and Liquids
 Plunging
your hand into a fluidized bed
(unheated of course) gives the sensation of
placing your hand in a bucket of water. Light
objects introduced in the bed will float if light
enough.
 Behaving as a liquid causes the entire
introduced object (metal) to be in complete
contact with the aluminum oxide separated
by the reactive gas/gases that surround the
media and cause diffusion and white layer
creation.
 The heat from the bed starts the diffusion
Fluidized (FNC) Heat
Transfer Factors
 Cleanliness of tool steel
 Mild to aggressive alkaline bath at elevated
temperature – bed & part contamination
 Particle
diameter – influences heat
transfer
 In practice 100 micro mm (.3940 micro inches)
 Bed material density
 Optimum value 1280-1600 kg/cu m or 80-100lb/cu. ft.
Fluidized
velocity of gas/gases
Optimizing heat transfer to bed
 Optimizing gas/gases flow rate
 Between 2 to 3 times the minimum fluidization
velocity
 Curve peaking
 To high – particle entrapment – high gas
consumption
 To low - poor heat transfer – lack of
uniformity
 Bed screws do not provide consistency
Relationship of gas fluidization
velocity to heat transfer rate
Heat transfer rate falls
off rapidly
Relationship of Bed Temperature
to necessary Flow Rate
Higher bed
temperatures require
less gas flow
Objective to get maximum heat
transfer to part and optimize velocity
of the gas/gases
Higher bed temperatures
require less gas flow
Heat transfer rate falls off rapidly
without optimized gas flow rate
Now a better way to attain
repeatability - flow and heat
 Computer
control and automation
 Adjustable ceramic screens
 Eclipse valves with flow meters
 Sensor feedback to computer
controls and automation system
First Fully Automated System in the
United States and Canada
H-13 after only 2 hours in bed
(N2,NH3,CH4)
Vickers
hardness
from surface
Compound layer 5-20 microns = .0002-.0008 inches
Diffusion layer 102-203 microns = .004-.008 inches
Future Uses of Fluidized Beds
of Hard PVD (below 700o F)
thermochemical surface treatments in
Australia – grant by IR & D board
 Coatings such as vanadium carbonitride,
and chromium carbonitride at low
temperature by diffusion-based
treatments
 Patents already applied for and equipment
available to perform new range of low
temperature surface treatments – Qab.
 Development
Range of coatings - QAB
Nitrogen Based
Nitriding
Ferritic
Austenitic
Alloy Based
Chromium
Vanadium
Titanium
Niobium
Carbon Based
Carburizing
CD Carburizing
Carbonitriding
Courtesy of QHT
Ray Reynoldson
Nitrogen and Alloy based below 700o C
Carbon based above 700o C
Process to form CrCN - QAB
Courtesy of QHT
Ray Reynoldson
Aluminum Oxide media to obtain CrCN is coated
Hardness Profile - QAB
Thickness
controlled
by time of
processing
CrCN = 1550v
NitroC = 950v
Courtesy of QHT
Ray Reynoldson
Qab Profile for CrCN and Nitrocarburized structure
Distribution of Elements in White Layer
Thickness
controlled
by time of
processing
CrCN = 1550v
NitroC = 950v
Courtesy of QHT
Ray Reynoldson
% of Cr highest near surface
Field test results CrCN
Courtesy of QHT
Ray Reynoldson
TOOLING CIRCLE OF LIFE
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