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Hypoallergenic Surgical Cast Stainless Steel
Sander Klemp – Muskegon, MI
Technical Alloy Sales Representative
Davis Alloys – Sharpsville, PA
Special Thanks to
My father & mentor, Ted Klemp III
Halloween 2018
Human Development Timeline
◼ Stone age – 20,000 – 8,000 BC
◼ Bronze age – 8,000 – 1,200 BC
◼ Iron age – 1,200 BC – 1700 AD
◼ Industrial Age – 1700 – 1850 AD
◼ Corrosion Resistent Alloy Age – 1850 AD - Today
History of Stainless Steel
◼ Early 1800s James Stoddart, Michael Faraday and Robert Mallet
noted resistance of iron-chromium alloys to oxidizing agents.
◼ 1840s Sheffield and Krupp produced chromium steel. Krupp
employed its use in cannons in the 1850s.
◼ 1861 chromium steel patient issued to Robert Forester Mushet
History of Stainless Steel
◼ 1890’s German chemist Has Goldschmidt developed
aluminathermic process for producing carbon-free chromium
◼ 1904-1911, several researches prepared alloys that would be
considered stainless today.
◼ 1908 Germain ship builders Friedrich Krupp Germaniawerft built
366 ton sailing yacht “Germania” featuring a chrome-nickel hull.
History of Stainless Steel
Germania
◼ 1914 by Harry Brearley of Sheffield, UK. developed a stainless
steel had 12.8% chromium content
◼ Produced while trying to solve erosion issues gun barrels for
the British army
◼ Firth Vickers marketed “Staybrite” stainless steel had 12.8%
chromium content.
◼ Chromium is required for all stainless steels
History of Stainless Steel
◼ Stainless steel advancements occurred very quickly
◼ Settling on a name did not!
◼ In US stainless steel was referred to by names like “Allegheny
Metal” and “Nirosta Steel”
◼ Trade journal in 1921 referred to it as “unstainable steel” which
eventually turned into “stainless steel”
History of Stainless Steel
Types of Stainless Steels – Common Names
◼ Ferritic
◼ Martensitic
◼ Precipitation Hardening
◼ Duplex
◼ Austenitic
Super Stainless Steel Grades
◼ Super Ferritic - 28% chromium +, 446 Stainless Steel
◼ Super Austenitic – high nickel, molybdenum, nitrogen etc.
CK3MCuN/254-SMO
◼ Super duplex – 2207
Surgical Stainless Steel?
◼ “Surgical Stainless Steel” has no formal definition
◼ Typically refers to a stainless steel used in biomedical
applications
◼ Commonly accepted types of “Surgical Stainless Steel” include
1. Austenitic - 316L
2. Martensitic – 420 & 440
◼ Mainly a marketing term
Consumer Products That Use “Surgical Stainless Steel”
Hypoallergenic Stainless Steel?
◼ Austenitic surgical stainless steel relies primarily on nickel to
produce austenitic structure
◼ Nickel is a known allergen
◼ Causes allergic reaction in the form of dermatosis
◼ Purpose of hypoallergenic stainless steel is to develop an
austenitic stainless steel that can be utilized in contact with the
human body without concern of nickel reactions
Nickel
Nickel
◼ Nickel Pellet Nickel Cathode
Nickel Facts
◼ Chemical symbol Ni, atomic number 28
◼ 23rd most abundant metal in earths crust, found only in
combined form (ore)
◼ Named after German ore “Kupfernickel”
◼ Nickel is ferromagnetic – iron, cobalt and gadolinium (Curie
temp of 68 F.)
◼ Earths inner core is made up of primarily iron and nickel
◼ Along with iron, nickel is responsible for the earths magnetic
field without which we would not be here!
Nickel Facts
◼ 2,700,000 tons produced annually
◼ Indonesia is currently largest nickel ore producer – 800,000 tons
◼ Russia, China and Canada also significant nickel producers
◼ Over 50% of nickel is used for low alloy and stainless steel
production.
◼ Super alloy and non-ferrous alloy production, batteries and
chemical industry.
Nickel Related Health Issues
◼ Most common is allergic reactions
◼ More common in women than in men – Jewelry?
◼ Nickel allergies increasing rapidly among young people
Nickel Allergies in Men & Women Under 30
Stainless Steel in Medical and Dental Fields
◼ Most common stainless steel biomedical implant is CF3M/316L
◼ 10-12% nickel
◼ Used in orthopedic implants, dental implants, orthodontics,
medical and dental tools
Stainless Steel Biomedical Implant issues
◼ Not as biocompatible due to nickel concentrations
◼ Over time can be rejected by the body
Potential Nickel Health Related Issues
High concentrations of nickel and nickel ions can cause:
◼ rash, skin irritation
◼ Cardiovascular disease
◼ Carcinogenicity
◼ Only an issue when material starts to degrade/corrode
Nickel/Stainless Steel Issues in Dental Field
◼ Stainless steel commonly used in orthodontics
◼ Most common complaint associated with stainless steel in
dental/orthodontic industry is dermatosis
◼ Nickel is most common metal to cause dermatosis in
orthodontics
◼ More complaints associated with nickel related dermatosis then
all other metallic elements combined
Previous Nickel Free Austenitic Stainless Steels
1% Nitrogen, 23% Chromium, 3% Molybdenum
◼ Effective at promoting austenitic matrix
◼ Strong
◼ Can not be easily cast, especially in air
◼ Very difficult to machine
35% Manganese
◼ Effective at promoting austenitic matrix
◼ Poor microcleanliness
◼ Average wear resistance
◼ Susceptible to localized corrosion
Alternative Austenitic Cast Stainless Steel -Considerations
◼ Contain less than 0.30% nickel
◼ Austenitic
◼ Strength
◼ Wear Resistant
◼ Corrosion Resistant
◼ Had to have good “castability”
Austenite Forming Elements
◼ Carbon
◼ Nitrogen
◼ Nickel
◼ Cobalt
◼ Manganese
◼ Copper
Austenite
◼ Formed by alloying iron with austenite stabilizing elements
◼ Also referred to as gamma phase, gamma iron and γ
◼ Face centered Cubic (FCC) crystal structure
◼ Non-magnetic allotrope of iron
◼ Typically ductile compared to ferrite
◼ Dissolves carbon readily
Ferrite Forming Elements
◼ Chromium
◼ Vanadium
◼ Titanium
◼ Aluminum
◼ Tungsten
◼ Molybdenum
◼ Silicon
Austenite – Face Centered Cubic
Ferrite
◼ Primary structure/phase of low alloy steel and cast irons at room
temperature
◼ Also referred to as alpha/delta phase, alpha/delta iron.
◼ Body Centered Cubic (BCC)
◼ Magnetic at room temperature
◼ Two types alpha α and delta δ
◼ Very low carbon solubility limit 0.001% C at 32 F.
Ferrite – Body Centered Cubic
Alloying Element Effects
◼ Carbon – Strong austenite former, levels above 0.03% increase
susceptibility to sensitization, significantly increases mechanical
strength.
◼ Silicon – Ferrite former, improves fluidity, used as a
degassing/deoxidation agent, improves resistance to oxidation,
increases strength
◼ Manganese – Austenite former, used as a deoxidation and degassing
agent. Can be used to improve high temperature ductility. Increases
solubility of nitrogen in stainless steel.
◼ Chromium – Ferrite former, most important element for promoting
corrosion resistance, improves wear and abrasion resistance.
Increases hardness. Increases solubility of nitrogen in stainless steel
Alloying Element Effects
◼ Cobalt – Austenite former, improves strength, especially at
elevated temperatures. Improves resistance and wear
resistance.
◼ Molybdenum – Strong ferrite former. Increases resistance to
uniform and localized corrosion. Slightly improves mechanical
properties. Enhances effects of other alloying elements.
◼ Nitrogen – Strong austenite former. Significantly increases
mechanical strength. Improves resistance to localized
corrosion, especially when used synergistically with
molybdenum.
Alloy Development – Predictive Diagrams
◼ Schaeffler Diagram
◼ Nickel and chrome equivalents calculated
◼ Used to predict microstructure of stainless steel welds
◼ Still widely used by casting industry
◼ Does not take cobalt into account
Alloy Development – Schaeffler Diagram
Alloy Development – Predictive Diagrams
◼ Delong Diagram
◼ Used to predict ferrite/delta ferrite concentrations
◼ Designed for stainless steel welds
◼ Uses WRC number to predict %ferrite.
◼ Does not take cobalt into account
Alloy Development – Delong Diagram
Alloy Development – Predictive Diagrams
◼ Modified Schaeffler diagram developed by Iron and Steel
Institute of Japan
◼ Adds cobalt into nickel equivalent equation
◼ Used to develop hypoallergenic stainless steel
Alloy Development – Modified Schaeffler Diagram
Alloying Element Selction –Cobalt as Nickel Replacement
Cobalt
Pros
◼ Austenite former
◼ Similar properties to nickel
◼ Ferromagnetic
◼ Excellent corrosion resistance
◼ Superior wear resistance
◼ Highly biocompatible
Alloying Element Selction –Cobalt as Nickel Replacement
Cobalt
Cons
◼ Cost ~ 2.5X cost of nickel in todays market
◼ Relatively weak austenite stabilizer compared to nickel
◼ Could not directly replace nickel as primary austenite stabilizing
element
◼ Another austenite stabilizing element needed
Iron-Chromium-Cobalt Ternary Diagram – 800 C.
Iron-Nickel-Chromium Ternary Diagram
Iron-Cobalt Binary Diagram
Iron-Nickel Binary Diagram
Cobalt
Cobalt - Facts
◼ Cobalt’s chemical symbol is Co, Atomic number is 27, Cobalt is
ferromagnetic
◼ Cobalt Name derived from German “Kobold” meaning goblin or
goblin ore, due to the toxic fumes it released when smelted for
copper.
◼ Critical to human health, makes up the backbone of Vitamin B12
◼ Cobalt was used in 2010 when German researchers first imaged
an atoms spin changing
◼ Cobalt-60 is radioactive and is used for treatment of cancer
Cobalt – Fun Facts
◼ Cobalt is commonly associated with the color blue and since
ancient times minerals containing cobalt were used to create
blue pigments. Cobalt is still used to create paint pigments
today.
◼ 2014 Astrophysicists identified a new cobalt isotope, Cobalt-56,
observed being ejected from a supernova 11 million light years
from earth. The supernova ejected 60% of the suns mass in
cobalt-56! But the isotope has a half life of 77 days and decays
into iron-56
◼ Democratic Republic of the Congo is the largest cobalt producer
to date. 2017 Congo produced 64,000 tons, second largest
producer Russia produced 5,600 tons, while the US produced a
whooping 650 tons!
Cobalt
Cobalt – Production and Mining
◼ USGS estimates total global reserves of cobalt at 7,100,000 tons.
DRC has largest reserve at 3,500,000 tons. Australia produced
5,000 in 2017 but has an estimated reserve of 1,200,000 tons.
◼ Typically mined as a by-product of copper and/or nickel. Due to
this the price and production quantities depend on heavily on
the demand and price of copper and to a lesser degree nickel.
◼ Despite DRC being of primary concern of the UN conflict
minerals. Cobalt by itself not listed as a conflict metal. Tantalum,
tungsten, tin and gold are to date the only metals directly listed
in the UN polices.
Cobalt – Historical Annual Production
Graph displaying global production of cobalt over the past 120
years
Cobalt – Industrial uses
◼ Recent demand increases due to use in lithium-ion batteries
◼ Potential for conflict over scares cobalt deposits
◼ Majority of cobalt is used in manufacture of Li-Ion batteries, also
used to produce rare earth magnets, paints, ceramics and super
alloys.
◼ Cobalt aluminate used in investment cast shell production for
grain refinement
Cobalts Effect on Steel and Stainless Steel
◼ Hardness - Additions of cobalt can produce a hardness increase
of 5 HV (Vickers) per 1% per weight in austenite
◼ Delta ferrite – Alloying elements in stainless steels have
different influences on the position of the ferrite/austenite phase
boundary, cobalt has a slightly lower effect on delta ferrite
compared to nickel, so in traditional stainless steel is not used
for this purpose.
◼ Transformation Temperatures: - Cobalt is unique as an alloying
element in stainless steel in that it favors the austenitic
structure at the ferrite/austenite phase boundary and raising the
martensitic transformation temperature. Beneficial for its effects
on martensitic transformation in maraging steels.
Alloying Element Selection – Nickel Replacement
Nitrogen
◼ Strong austenite former.
◼ Compensates for cobalt’s mild affinity austenite stabilizing
◼ Improves localized corrosion resistance
◼ Increases strength
Cons
◼ Can reduce ductility due to carbonitride formation
Alloying Element Selection – Nitrogen Solubility in Iron
Hypoallergenic Stainless Steel
◼ Coboferronic 1 chemistry was designed to simulate
austenite/ferrite ratio similar to CF3M
◼ Nitrogen was added due to cobalt’s mild affinity for austenite
stabilization
◼ %cobalt + %nitrogen was estimated to have similar austenizing
power of nickel
◼ Chemical balance was developed to limit delta ferrite formation
to 5-15%
◼ Delta ferrite levels above 15% in CF grades is deleterious to
intergranular corrosion.
Coboferronic
◼ Developed alloy was given trade name of Coboferronic
◼ 3 different chemical compositions developed
◼ Coboferronic 1, 2 & 3
◼ Developed to ascertain austenitic structure without using nickel
or high levels of mangense
Coboferronic Chemical Composition
Coboferronic 1 Coboferronic 2 Coboferronic 3
Carbon 0.020-0.030
Aim = 0.029
0.020-0.030
Aim=0.029
0.20 -0.30
Aim 0.028
Nitrogen 0.14-0.19
Aim = 0.16
0.30-0.35
Aim=0.32
0.30-0.35
Aim = 0.31
Chromium 17.0-21.0
Aim = 17.6
17.0-21.0
Aim = 18.0
17.0-21.0
Aim = 18.50
Cobalt 8.00 – 12.00
Aim = 12.00
8.00 – 12.00
Aim = 12.00
15.00-18.00
Aim = 17.00
Molybdenum 2.0-3.0
Aim =2.20
2.0 – 3.0
Aim = 2.10
2.0 -3.0
Aim = 2.15
Manganese 1.00-1.50
Aim = 1.452.00-2.50
Aim = 2.102.00-2.50
Aim = 2.00
Silicon 0.50 – 1.00
Aim =0.65
0.75 – 1.25
Aim = 1.00
0.75 – 1.50
Aim 1.10
Nickel LAP
AIM = >0.30
LAP
Aim >0.30
LAP
Aim >0.30
Sulphur LAP LAP LAP
Phosphorous LAP LAP LAP
Oxygen LAP LAP LAP
Previous Cobalt Stainless Steels
◼ Quebec firm developed nickel free cobalt stainless steel welding
rod
◼ High manganese 5%+
◼ High Silicon 3%+
◼ Carbon 0.10-0.40
◼ Highly resistant to cavitation erosion
◼ Used as weld filler on land based turbines
◼ Not a casting alloy
Coboferronic 1 Production
◼ Certified ingot produced at Davis Alloys Sharpsville, PA facility
◼ Ingot produced using Davis Alloys proprietary chemical refining
technology, thus limiting deleterious elements and gases.
◼ Experimental heat was produced with elemental aims designed
to promote an austenitic matrix with minor amounts of ferrite
◼ Standard CF3M heat was produced for comparative purposes
Coboferronic 1 Certified Chemistry
◼ Chemistry was obtained by Davis Alloys analytical chemistry laboratory. Results presented
in percent weight as determined by optical emission spectrometry, X-ray fluorescence
spectroscopy for bulk chemistry plus combustion techniques with thermal and infrared
spectroscopy for carbon, sulfur, oxygen and nitrogen
Carbon 0.030 Copper 0.300
Nitrogen 0.159 Tungsten 0.075
Chromium 17.125 Aluminum 0.008
Cobalt 12.250 Boron
CF3M Comparative Heat Chemistry
Carbon 0.023 Copper 0.425
Nitrogen 0.009 Tungsten 0.057
Chromium 18.650 Aluminum
Test Sample Production
◼ Tensile test bars were produced at EPS Industries in Ferrysburg,
MI
◼ Test bars were produced in accordance with ASTM E8 with a
0.250” gauge section
◼ Test bar molds were produced by Shellcast, Inc. in Montague, MI
◼ Test bars utilized a 3 gate system with large center gate
◼ Test bar molds hold only ~ 2 lbs. of alloy
Test Bar Casting Parameters
Shell Temp Max Superheat Temp
Pouring Temp
Additions Test Bar
Molds Cast
CoboFerronic 1 1850 F. 2900 F. 2850 F. 1 lb. FeSi 75%
6
CF3M 1850 F. 2900 F. 2850 F. None 2
Test Bar Production
Test Bar Production
Test Bar Production
Test Bar Production – Pretesting Observations
◼ Coboferronic 1 had excellent surface finish and no visual
external defects of any kind
◼ Foundry workers noted gate grinding took longer and required
more force to remove gates.
◼ Coboferronic was noticeably more magnetic then CF3M
Testing Plan
Coboferronic Testing CF3M Testing
As-Cast As-Cast
Tensile Testing: (4) Test Bars Tensile Testing: (2) Test BarsHardness Profile: (2) Test Bars Microstructure: (1) Test BarMicrostructure: (2) Test Bars
Solution Anneal Solution AnnealTemperature: 1950 F. Temperature: 1950 F.Time at Temp: 1 Hour Time at Temp: 1 hourQuench: Water Quench: Water
Tensile Testing: (4) Test Bars Tensile Testing: (2) Test BarsHardness Profile: (2) Test Bars Microstructure: (1) Test BarMicrostructure: (1) Test Bar
Hardness Data
Coboferronic 1 Hardness Values (As-Cast)
Hardness Data is Presented in Rockwell C (HRC)
CF3M Typical Hardness 24-27 HRC
Coboferronic 1 Sample 1 Coboferronic 1 Sample 2
34.5 27.9
35.1 33.7
34.3 34.0
34.7 35.5
32.9 33.5
35.5 34.5
35.8 33.7
35.5 35.0
Average = 34.79 Average = 33.48
Tensile Test Results Coboferronic 1 vs. CF3M
Bar Number Bar
Condition Material
Tensile
Stress (psi)
Yield
Stress (psi)
Elongation
in 1" (%)
Reduction
of Area (%)
1 As Cast Cobo-1 164,300 84,600 6.2 7.0
2 As Cast Cobo-1 188,000 90,000 10.0 9.3
3 As Cast Cobo-1 166,500 81,100 7.4 7.8
4 As Cast Cobo-1 167,900 92,000 7.0 7.0
5 Solution Cobo-1 215,300 109,300 12.0 21.9
6 Solution Cobo-1 210,800 82,700 15.0 33.3
7 Solution Cobo-1 213,600 63,300 15.0 32.6
8 Solution Cobo-1 212,300 57,200 16.0 34.7
9 Solution CF3M 86,400 42,600 52.0 75.0
10 Solution CF3M 88,000 43,400 48.0 69.1
11 As Cast CF3M 88,100 41,400 46.0 67.8
12 As Cast CF3M 88,500 40,500 43.0 69.1
Coboferronic Microstructure As-Cast
200X – Etch: Electrolytic 10% NaOH
Coboferronic 1 As-Cast Microstructure Analysis
◼ Microstructure of as-cast Coboferronic 1 was found to be delta ferrite
stringers and pools in an austenitic matrix.
Volume% ferrite levels of as-cast Coboferronic 1
Reading Sample Volume %
1 Cobo AC1 22.15
2 Cobo AC2 23.69
3 Cobo AC3 24.26
4 Cobo AC4 18.99
5 Cobo AC5 22.71
Average 22.36
S.D. 2.06
CF3M Microstructure As-Cast
200X – Etch: Electrolytic 10% NaOH
CF3M As-Cast Microstructure Analysis
◼ Microstructure of as-cast CF3M was found to be delta ferrite
stringers in an austenitic matrix.
Volume% ferrite levels of as-cast CF3M
Reading Sample Volume %
1 316 AC1 16.23
2 316 AC2 15.65
3 316 AC3 16.13
4 316 AC4 16.04
5 316 AC5 18.52
Average 16.51
S.D. 1.14
Coboferronic 1 Microstructure Solution Annealed
200X – Etch: Electrolytic 10% NaOH
Coboferronic 1 Solution Annealed Microstructure Analysis
◼ Microstructure of Solution Annealed Coboferronic was modified to
larger delta ferrite pools, with less total ferrite in an austenitic matrix.
Volume% ferrite levels of Solution Annealed Coboferronic 1
Reading Sample Volume %
1 Cobo S1 17.32
2 Cobo S2 17.95
3 Cobo S3 20.22
4 Cobo S4 19.50
5 Cobo S5 23.11
Average 19.62
S.D. 2.27
CF3M Microstructure Solution Annealed
200X – Etch: Electrolytic 10% NaOH
CF3M Solution Annealed Microstructure Analysis
◼ Microstructure of solution annealed CF3M was found to be delta
ferrite stringers in an austenitic matrix.
Volume% ferrite levels of solution annealed CF3M
Reading Sample Volume %
1 316 S1 13.18
2 316 S2 14.08
3 316 S3 14.39
4 316 S4 14.11
5 316 S5 21.14
Average 15.38
S.D. 3.25
Results – Mechanical Properties
◼ Coboferronic 1 had a SIGNIFICANTLY higher UTS and higher
yield strength compared to CF3M.
◼ CF3MN mechanical properties differ only slightly from CF3M
◼ Nitrogen does not account for the variation differences in
mechanical properties from Coboferronic 1 and CF3M.
◼ Coboferronic 1 has lower ductility compared to CF3M, but has
similar ductility to cobalt base surgical implant alloy F75.
Results – Mechanical Properties – Response to Heat Treatment – Coboferronic 1
◼ Coboferronic 1 showed significant response to heat treatment,
especially considering its austenitic structure and low carbon
level
◼ UTS, elongation and reduction of area all increased
SIGNIGICANTLY due to solution anneal heat treatment
◼ Improvements in ductility can be attributed to chrome
carbides/carbonitrides going into solid solution
Coboferronic 1 vs. CF3M Microstructure
◼ Microstructure was primarily austenitic
◼ Coboferronic had only slightly higher concentrations of
ferrite/delta ferrite compared to CF3M
◼ Solution anneal heat treatment lowered ferrite content in both
Coboferronic 1 and CF3M
◼ Delta ferrite appears to have changed from stringer to larger
pool form in Coboferronic
Coboferronic Microstructure –Predictive Diagrams
◼ Based on results it is estimated that cobalt has 25% of the
austenite stabilization affinity compared to nickel.
◼ Results indicate that modified Schaeffler Diagram published by
Iron and Steel Institute of Japan did not factor in cobalt's
reduced affinity for austenite stabilization or was produced with
the assumption nickel would be a primary alloying element
◼ Modified nickel equivalent for cobalt substitution:
%Co X 0.25 + 30 X %C + 0.5 X %Mn
Coboferronic Magnetic Properties
◼ As-Cast sample of Coboferronic 1 had a magnetic permeability
of 5 um.
◼ Solution anneal treatment slightly reduced magnetism.
◼ CF3/CF3M with similar ferrite content has SIGIFICANTLY lower
magnetic permeability
◼ Magnetic properties cannot be explained at this time
Conclusions
◼ Coboferronic 1 is the only grade tested so far
◼ Coboferronic 1 showed significant UTS strength compared to
CF3M.
◼ Coboferronic 1 had significant response to heat treatment
◼ Coboferronic 1 had primarily austenite matrix
Conclusions
◼ Coboferronic 1 magnetic properties were surprising considering
total ferrite content and austenite matrix
◼ Coboferronic 1 high magnetic permeability makes it impractical
for medical implants.
◼ Has potential for other applications beyond scope of intended
fields.
Conclusions – Coboferronic 2 & 3
◼ Coboferronic 2 & 3 should have significantly less ferrite
◼ Should have significantly reduced magnetic properties
◼ Higher potential for orthopedic, dental and orthodontic implants
Conclusions – Future Testing
◼ Will publish complete testing data for Coboferronic 1, 2 & 3 in
Incast 2021 Alloy Issue.
◼ Data will have summary of corrosion testing results, impact
testing, further metallography, scanning electron microscopy
images and spectrums of various phases
Special Thanks for Support and Assistance to….
Kevin Davis, CEO of Davis Alloys. Supported this project from its
inception, without his assistance and belief it wouldn’t have been
possible!
Ryan Elliston, EPS Industries. Without EPS moving production
around to cast my test samples 2 week ago! I wouldn’t have had
ANY results to present!
Bob Johnson, Shellcast Inc. Bob’s dedication to controlled metal
delivery ensures high quality, internally sound tensile bars for
testing!
SanderKlemp
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