Hypoallergenic Surgical Cast Stainless Steel · 1861 chromium steel patient issued to Robert Forester Mushet. History of Stainless Steel 1890’s German chemist Has Goldschmidt developed

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


◼ 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.


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


◼ 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”


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


◼ 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


◼ 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 – 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


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


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


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


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


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


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

Documents

Hypoallergenic Surgical Cast Stainless Steel · 1861 chromium steel patient issued to Robert Forester Mushet. History of Stainless Steel 1890’s German chemist Has Goldschmidt developed