Metallurgy Surrounding the Manufacture of Eisenhower Dollars
The production of Eisenhower dollars in 1971 by the US mint was a challenge in every way. The circulating business strike planchets were made of the same copper-nickel composition that the dime, quarter and half dollar were made from since 1965. While the process of striking that alloy had by now become common, the mint was entering somewhat of an unknown with a copper-nickel clad coin the size of the Eisenhower dollar. Some were to be struck in a silver-clad composition, but coins that same size having similar malleability were last struck in production during 1935 with the end of the Peace dollar. Coins of such large diameter coupled with the advent of copper-nickel planchets made the Eisenhower dollar new territory for the mint and its production operations.
Basic Striking Process and Metallurgical Terminology
The striking of coins is a cold-working method, which in essence is a forging operation. A slug of metal is placed between two die halves which are then pressed together, squeezing the metal slug into die cavities that have been cut as recesses in relation to the die faces (a negative in the surface of the die face). When the halves separate, the metal slug is removed and then has a positive (relief) image mirroring that of the die cavities.
Forging a slug of metal to become a coin is simply called “coining”. A typical forging operation often times refers to a basic shape of metal, such as a cube, sometimes being pressed multiple times through multiple die stages to achieve the final desired shape, which incidentally may not be anything remotely similar to the original cube. Coining is usually not a dramatic change in geometry from the initial metal disc shape (known as a planchet) to the final completed coin.
Metal used for coinage undergoes physical changes during manufacturing, especially the raw planchet on its journey to finished coin. The tool steel used to make dies and hubs, however, also under goes marked physical changes in order to meet various striking operation service requirements. To be knowledgeable about these physical changes, it is helpful become familiar with a few simple but key terms associated to metals and metallurgy. They are:
Hardness: the resistance of a metal to scratching or indentation
Strength: The amount of energy a metal can absorb before plastically deforming;
Toughness: a metal’s ability to absorb energy and plastically deform prior to any failure
Ductility: the ability of metal to permanently deform before it fractures, ruptures, tears, etc.
Do not allow these definitions to become sticking points. As simple as they may sound, they can sometimes be hard to visualize without seeing the concept in action first hand, let alone apply scientifically. Often times one term will ebb into the boundaries of another depending on application and circumstances, yet these definitions can be correctly construed in numerous ways for numerous alloys and are at the heart of minting metallurgy.
To fully understand the actual, physical formation of Eisenhower dollars from raw metal stock, one must have a brief and very basic understanding of the manufacturing process. Round discs, known as planchets, were punched from large metal sheets of either the copper-nickel or sliver clad material. At this stage, the flat disc of metal is known as a type one planchet. Following this, the planchets had a rounded rim formed on them and were then known as type two planchets. As we know from historical documents and former mint employees, Eisenhower dollars were struck with large automatically feeding and ejecting presses, using roughly 180 tons of force to strike a metal planchet between a hammer and anvil die at the rate of roughly 100 coins per minute. The anvil die (bottom die) carries the artwork of the coin’s reverse, while the hammer die (upper die) carries the coin’s obverse artwork.
Metal compositions for Eisenhower dollar planchets were the following:
Copper-Nickel Clad: inner core of copper sandwiched between two outer layers of copper-nickel alloy comprised of 25% nickel and 75% copper. Used for all circulating business strikes and clad proofs.
Silver Clad: inner core of 20% silver and 80% copper alloy sandwiched between two outer layers of 80% silver and 20% copper alloy (± a small tolerance on all percentages given). Popularly known as 40% silver clad. Used for silver uncirculated and silver proof coins.
As you can see, business strike copper-nickel coins are mostly copper in reality. Copper is typically rather soft (ductile) compared to most other metals. The nickel contained in the copper-nickel clad composition adds a degree of hardenability and wear resistance. The silver clad coins themselves contain approximately 60% copper as well. Silver too is ductile by nature, and therefore the silver clad coins were softer than the copper-nickel clad counterparts. This allowed the silver uncirculated and proof coins to be stuck in a higher relief and still maintain crisp details, as the metal “flowed” much more readily into the die cavities.
After the planchets were punched from large sheets of raw metal stock (type 1 planchet), they were run through an Upset Mill where a rounded fullness was formed on the rim of the blank coin, thus creating a type two planchet. The process of manufacturing a type two planchet by pushing up the edges to form a coin’s rim causes internal stress on the planchet. Note: any time metal is deformed plastically at ambient temperature (“cold-worked”), much of the energy applied to the metal is transformed into heat. However, some energy remains stored within the metal work piece. This energy takes the form of a distortion within the lattice structure of the metal or “grains”. These strained areas are typically known as dislocations. For example, if one would dramatically bend a piece of copper and then attempt to bend it back into original shape, an “orange peel” effect would be seen on the surface at the bend due to slippage between the grains and the ensuing dislocations.
These dislocations can be visually compared to bumps or folds in a rug. When one steps down on a raised fold, it doesn’t go away but instead moves (like a wave in water) to either side or possibly both sides of the initial push point. If there are numerous folds close together, it is difficult for them to move if pushed. Within metal, when two or more dislocations meet they too will most likely become stuck and immobile. That area of metal then becomes tough or hard to move, and the metal can’t continue to plastically deform as it did before being cold worked. It has lost its ductility. The metal is now considered to be work-hardened. If one were to try moving or deforming it further (bending, twisting, forging, etc.), the metal would break or tear instead of remaining intact.
To relieve the work-hardened grain structure of any non-ferrous metals (those metals other than iron), the metal is given heat treatment with what is known as an annealing cycle. Annealing is the softening of a metallic structure by heating it to a specific temperature and allowing it to cool in a particular medium at a specific slow rate. Many metals can simply be allowed to cool in air until reaching room temperature. Without going into elaborate detail, the annealing process whereby a non-ferrous metal is heated sufficiently to restore some of the original ductility and relieve most of the strain energy in the dislocations between grains is known as recovery.
To completely soften and restore the original properties of the non-ferrous metal, it must be heated above what’s known as the recrystallization temperature, in a process called annealing. It is at the recrystallization temperature that new grains form and grow until an entirely strain-free matrix is formed. There are many specific annealing processes that may be applied due to the wide range of possible heating temperatures and the final results (softness/hardness) required of the work piece. While there are eventual limitations, once the non-ferrous metal is annealed it may again be cold worked and put through the annealing process and repeated as necessary until the metal is fully formed into the final desired shape.
The actual method of annealing the type 2 copper-nickel business strike planchets saw them loaded into rotary furnaces called annealing drums. The simplistic explanation of a rotary drum is a cylinder with auger-type blades/fins on the inside walls. One end of the cylinder is heated to the required processing temperature and the planchets are inserted into this end. The entire drum revolves, and the interior auger configuration moves the planchets towards the opposite and cooler end where they are discharged. The angle of the auger protrusions inside and the speed of drum revolution determined the dwell time of the annealing process which typically is an hour or two.
It should be noted that this operation was a major source for numerous small marks or “chicken scratches” on the surface of many copper-nickel business strike coins. Planchets continually rolled and hit against one another the entire time they were in the annealing drum furnaces sp the planchets emerged literally covered with cuts and hits. This planchet damage was mostly struck out during coining but “Annealing Marks” persist to some degree on most Ike dollars and can be difficult to distinguish from post-minting hits and dings.
Also contained in the annealing drum was quite a bit of very small dust-like metal shavings produced from the many planchets rubbing on one another throughout the annealing cycle, which would fuse to the surface of any planchet inadvertently wedged “stuck” in the drum for several cycles. This created the phenomena of the “sintered planchets” sometimes found on copper-nickel clad coins: subsequently struck coins will look bronze toned but the toning is refractory to acetone and “dips”.
Also note that proof planchets did not go through annealing drums, but were instead annealed on belts that ran horizontally through furnace chambers. This method was employed for these particular coins to eliminate planchet on planchet contact, thereby enhancing the clean and smooth finishes we see on these coins.
Die Steel Metallurgy and Die Hardening
While the key factor in the formability of a copper-nickel or a silver clad Eisenhower planchet is its ductility, the keys to usability and survivability for a die or hub are toughness, strength, and hardness. Dies and hubs are made from tool steel. Steels are much different from non-ferrous metals due to the atomic structure of iron, the majority base metal of any steel. To achieve these characteristics (among some lesser others), the dies or hubs are hardened (the opposite of annealing) by heat treatment after impressions or reliefs are fully detailed. It is very common for dies and hubs to undergo several different heat treatments that range from annealing to hardening, depending on their next intended process (striking coins or being used to form other dies/hubs).
A die or hub must be at its hardest optimal strength for service, meaning the highest hardness to perform the service requirement without being so hard that the die or hub becomes brittle and fractures upon impact or very early in its service life. As tool steels are taken to a higher degree of hardness, the trade-off is lower toughness and impact strength. When hardening steel, it is usually desirable to transform the microstructure of the steel to a phase called martensite. In a very general sense, it is the hardest and toughest microstructure of steels.
To very briefly summarize the process of how a working die had been made during the Eisenhower dollar era (as well as long before and for some years thereafter), one must start with the master artwork sculpted in relief (positive features rising off the surface) on what is commonly known as a galvano. Each side of the coin starts with its own Galvano. Just as had been practiced for many years, the artwork of the galvano was transferred by a reducing lathe to make a master hub (a positive relief identical to that side of the eventual coin). The master hub was then used to make a master die (a negative impression of the master hub and of the eventual coin). The purpose of a master die is to make numerous working hubs that are in turn used to make the many working dies. These dies will be used in the coining presses to strike coins from raw type two planchets.
Whether it be forming a master die, working hub, or working die, each of these start as blanks of tool steel (cylinders about two inches long) in a fully annealed (softened) condition that are then hydraulically squeezed against hardened opposite forms. The force of this single squeeze will cause extensive stress in the tool steel blank and therefore leave areas of non-uniform hardness “work hardening” throughout the face of work piece. After this first squeeze, the work piece is fully annealed again and squeezed a second time. The process of annealing and squeezing is repeated several more times until the full impression or relief details are completely imparted on the work piece, generally five or six times (possibly ten times in the case of sinking the Master Die). The work piece hub or die must be annealed to its softest condition to receive each squeeze, or they will readily crack and fracture. Fully annealing tool steels can often times require several days with many hours of furnace time to be performed properly and can be very tricky work.
Also note that the blank of tool steel receiving the impact, whether hub or die, was elevated in temperature. This was done to allow the work piece to be in its softest possible state. It is not uncommon for some manufacturing processes to do this near 2000°. The temperature range and method used by the mint during the Eisenhower dollar era is not specifically known at this time, but it it’s reasonable to assume that standard industry practices of the day were employed.
After the hub or die is completely formed, it is hardened for service requirements. When steel is hardened, the metal’s micro-structure is altered and the grains of the metal are reformed due to atomic changes in the metal make-up. To achieve a required hardness level in tool steel, the metal must typically be heated to a specific temperature and then (depending on alloy) be quenched at a specific temperature, and in a specific medium (air, water, oil, molten salt, etc.).
One must note that when hardening steel, it is hardened to a range. For example, some tool steels might be hardened to 58 – 63 on the Rockwell C scale (HRc), others might be at 44 – 47 HRc, depending on the service requirements. What this means is that each individual die half getting heat treated may or may not be at the exact same hardness as other die halves of the same alloy. One might be at 53.58, another at 55.62. They will all be close in the grand scheme of their service requirements with most likely no appreciable difference in performance, but rest assured no two hubs or dies will be the exactly the same hardness. There are variables present when engaged in any heat treat process.
Often times these variables need attention to some small degree. There must be furnace considerations for carburizing/decarburizing atmospheres, soak time, space around the actual work piece to allow even heating, quench time , types of furnace used, quench media, etc. Also note that the alloy’s chemical make-up from batch to batch of raw steel will vary. Like hardness requirements, steel is manufactured to ranges or maximums. They contain several other required elements like silicon, manganese, carbon (usually the most critical), sulphur, nickel, etc. Throw in these variables with the heat treating variables, and it becomes a lot easier to see that no two die halves will ever be perfectly identical in hardness, and indeed may even be on opposite ends of the hardness range allowed for a particular specification. It is not uncommon for a heat treater to perform two slightly different heat treat cycles to achieve the same hardness range on two different batches of the same alloy.
Initial Die Steel for Eisenhower Dollars
During all of 1971, it is well known that the mint was using a die steel called W-1 to produce all coinage. This information has been documented in several publications going as far back as 1972. It was originally confirmed by Howard F. Johnson at the U.S. Mint for Russel Rulau of Coin World in a July 24, 1972 letter (FIGURE 1). Note: as rudimentary as it may sound, tool steel alloys are designated (usually) by a simple number, preceded by a letter. Most often the letter stands for characteristics like water quench hardenable (W), oil quench hardenable (O), shock resistant (S), hot work (H), and so on through a number of different designations and classes. Many of the readily noticeable differences in relief and other characteristics on Eisenhower dollars from 1971 through the end of 1972 can be directly attributed to the particular die steel alloys being used.
FIGURE 1: Treasury Department letter addressed to Russel Ralau of Coin World. The information contained on this document has been used for several publications since the original letter. Take note the last statement of the letter about testing new die steel
The important aspect when hardening W class tool steels is to quench them rapidly from the austenitizing (softest microstructure phase) temperature, which is around 1500° for W-1. However, as hardenable steel, it is very important to know that W-1 does not through-harden. What does that mean? The outer surfaces in contact with the quenching medium will achieve the most martensitic structure and hence the highest hardness, toughness, etc. For example, if one were to cut through a W-1 die, the hardness readings of the steel decreases as one moves towards the center of the die’s cross sectional thickness. This is due to the fact that the inner cross section of metal does not come in direct contact with the quenching media and therefore can‘t quench fast enough to completely transform the soft austenite to martensite. The inner areas end up retaining an austenite phase in the metal matrix. This condition allows for a small degree of plasticity of the die when striking the planchet, and could easily lead to what was known as die-sink.
Die-sink occurs when the dies deform to a very small degree as opposed to remaining completely rigid when contacting the planchet under full pressure. Relatively speaking, the softer inner areas of the die were allowing a fair amount of plasticity of the central die face as compared to remaining rigid as a more through-hardenable tool steel would perform. Die sink from the operating strength of the W-1 tool steel was not allowing the mint to get coins that were fully struck up on the 1971 through July 1972 Ikes, thus necessitating a low relief design for the business strikes. The die sink phenomena lead the mint to search for a better tool steel to strike the large Eisenhower dollars.
The New Die Steel: Building a Case
We know that the mint experimented with new die steel in production runs of the Eisenhower dollar in 1972, first in February/March and again in July/August to prove out the elimination of die sink. This was the limited minting of the now famous 1972(P) Type 2 with its high relief reverse, the same high-relief reverse used at the San Francisco Mint for 1972 uncirculated silver and 1971/1972 proof reverses. By all available accounts, this 1972 Type-2 “variant” Ike was first discovered by Herbert Hicks in Boston, MA in March 1972. Later that year the director of the mint, Mary Brooks, in a letter printed in the August 30 1972 Coin World, wrote the following:
“‘The use of an improved through-hardened tool steel, she said, has eliminated the sinking tendencies which were encountered earlier when we tried to strike the circulating cupronickel clad dollars with the higher relief dies, Mrs. Brooks stated.”
From a mint document found and shared with the Ike Group by Roger Burdette dated May 9, 1974 (FIGURE 2), we see that the penny was still being struck with dies made from W-1 tool steel. However, we also see reference to die steel labeled as “5210” being used for all other denominations.
FIGURE 2: Mint document discovered by Roger Burdette during his research on Peace Dollars. Memorandum is addressed to Mary Brooks, then director of the U.S. Mint. Die steel alloy is listed in the third column from left. Note the correction and addition of information.
This brings us to what may be a revelation, but in fact has no “concrete” evidence: the 5210 alloy as listed on the May 9, 1974 document from the mint. Could what is listed as 5210 in actuality be an alloy commonly known as 52100? Is it possible that the number is a typographical error from many translations, or the early technology of the mint’s data control system could only store 4 digits, or it was their internal type steel code? 52100 is a very though-hardenable tool steel, which lines up extremely well with the August 30, 1970 statement from Mary Brooks.
At that point in history, the late 1960’s and early 1970’s, 52100 was gaining acceptance in the stamping industry for just that purpose – stamping dies. Previously the alloy had been used primarily for bearing cups, races, rollers, and balls. The ramp-up of 52100’s wide-spread use in those applications dates back to World War II. This alloy of tool steel is indeed a through hardenable variety, meaning that when quenching the steel from high temperature, the microstructure of the steel more readily and much more completely transformed to the harder and tougher martensite phase throughout the entire cross section of the die. By the late 1960’s, 52100 was being further developed for more of a widespread use in stamping dies.
The fact that 52100 can be hardened evenly throughout the entire work piece cross section (due to its chemical make-up) is very important to the minting operation. This means the alloy would have much more strength against the die sink that the mint was suffering due to the W-1 alloy dies. 52100 can also be cryogenically heat treated, meaning it can be frozen many degrees below 0°F and achieve a very complete martensitic transformation of the microstructure (actual U.S. Mint processing is unknown). This alloy would have been well suited for use by the mint, especially in achieving full strikes on copper nickel-clad planchets that are somewhat harder than the silver clad counterparts.
A 2003 Maine Statehood quarter die was obtained and run through some very basic metallurgical testing by the author. This included determining the chemical composition of the die steel and recording hardness measurements. Upon completion of spectro-analysis (a method to determine percentages of each element within an alloy), the metal composition was found to be an exact match for 52100. Hardness readings ranged from HRc 57 – 63. Note the die face had been purposely destroyed at the mint and hardness readings on that surface may have some variability.
The presumed use of 52100 as a die steel replacement for W-1 at the mint for Eisenhower dollars now becomes almost too obvious and logical to not be true based on the document found by Roger Burdette, the statement from Mary Brooks, and the recent chemical analysis of the 2003 Maine quarter die. It would certainly stand to reason that the Mint would look to employ the new 52100 dies on the Eisenhower dollars first. A coin of that size experiencing difficulties such as die sink and coins not being fully struck-up would enjoy the most benefit. Perhaps, according to the May 9, 1974 mint document, this is why the penny was still using the W-1 tool steel at least up through that year; the very high copper composition was naturally softer and had dramatically less surface area to strike. W-1 may have been sufficient and conversion to 52100 may not have been a priority.
At this time, there are no other known documents relating specifically to the particular die steel the mint tested and presumably put into production for all of 1973. Unfortunately, no known 1973 – 1978 Eisenhower dollar dies are known to exist for performing chemical analysis. It should be noted that respected author Alan Herbert, who did extensive research at the mint during that era, recalls the new die steel referred to as 52100 but does not have any written documentation detailing such information.
Finally, in the Ike era, it’s sad but true that the Mint had an in-bred culture of secrecy so record keeping was minimal and most Mint records that were created were systematically destroyed within a few years.
Die Clash and Die Wear Metallurgy
In general, if two random pieces of metal with a sizeable difference in hardness are struck together, then the metal that is softer will “take the abuse” and have contact marks in left its surface, leaving the harder one unscathed. The same will hold true for two die halves. As we know, die clashes occur when the anvil and hammer dies come together in the press without a planchet in between them. By nature, the die half with the lower hardness should be on the receiving end of the abuse; in other words, it will have an impression left in it from the other ever-so-slightly harder die half. However, since they are the same alloy and should at least be in the same hardness range, both dies will probably incur damage to a lesser degree. If the press is not stopped, the ensuing planchets entering the die chamber will incur the clash marks that were just imparted on each die half during the clash episode.
Die clash marks occur primarily from device edges. These are the edges or corners that are formed where the die’s fields meet the incuse artwork. Regardless of alloy, upon clashing, dies will flex ever so slightly (plastically) and the cavity edge is what will get imprinted due the impact force. Examples of these edges are the outline of Eisenhower’s head and neck on the obverse die or the outline of eagle’s wings on the reverse die.
Because the die halves are in the same hardness range and toughness, damage to each half may very likely be minimal to the naked eye if they only clashed together once and if the dies clashed squarely, that is, the two die faces were perfectly parallel at impact. To understand a given set of clash images on a clashed Ike, therefore, one needs to take into account how “square” the die halves were to each other at the instant of contact. If they were loose in the die holders or set out of square by a mere few thousandths of an inch in one direction, that would be all it takes to determine which part of the dies hit each other first, and consequently where the die clash is made more prevalent.
It should be noted that die halves are not set up to physically come together and actually touch each other during production. There is a closing height which is set between the die faces. In the case of automated coining, it would be a distance between halves that properly squeezes the planchet metal into the die cavities, but no further. During a clash event, however, play in the various press mechanisms allowed the die faces to come together or “slap” each other under certain circumstances with a high velocity impact. Having no planchet between them can also allow the anvil die to rotate with each slap, accounting for rotated multiples of the same clash mark sometimes seen on clashed coins.
A die clash event is probably the most stress the die steel will see in its lifetime of service. Many die cracks can be generated and propagated because of these events, let alone complete loss of a die half or even the entire die set in some instances. To put it differently, having a “soft” copper-nickel or especially silver clad planchet between the die halves when they come together dramatically cushions the impact by absorbing the energy due to their materials being much softer than the dies. The energy is then dispelled by way of heat. For extreme comparison, many steel forgings come out of their dies red-hot from the heat generated, though the cold forging of coins left them only pleasantly warm to in the hand because not much metal is moved about in a coining press.
Fatigue also plays a part in the die metal’s useful service life as well. As the dies perform more strikes, they also become more fatigued due to work-hardening, potentially leading to cracking of the die face or even total die failure. Striking causes localized frictional heat, and heat can cause fatigue in many alloys under specific conditions. As a die wears through its useful striking life, the fields tend to also take on a rougher appearance due to fatigue. The continual repeated hammering of the die onto metal planchets, even though they are much softer, causes very small dislocations of the grains on the die face over time. In turn, these lead to “die flow lines” and the orange-peel effect most usually seen on the fields during late die states.
Die cracks can be common as well. Again, this failure is often times due to a combination of factors or events, such as a harder-than-normal die, metal fatigue from high numbers of strikes, die clashes, or even small defects within the original die steel. They can be very small (visible only under 100x magnification) and propagate slowly over a dies life, or they can be sudden and instantaneous causing complete die fracture and failure.
In addition, the last hardening of a die could leave “check cracks” over the die’s face, microscopic die cracks that were sometimes large enough to be caught by Mint employees with a 10X loupe or microscope. The life of these dies could be extended by polishing out the check cracks prior to shipping the die to its intended Mint.
This has been a rather brief overview of the metallurgy of minting Eisenhower dollars. Metallurgy is a very deep field of endeavor which sometimes doesn’t follow the “rules” we think it should. Many times certain aspects can be explained in more than one way.
The Eisenhower dollar was a great undertaking for the US Mint, and presented many new hurdles to be overcome in manufacturing Ike dies and forging Ike coins. By today’s standards, the minting technology in the 1970’s was quite primitive. In many cases we can only speculate and postulate what really happened, and how. Some information about the actual minting of the Eisenhower Dollar Coin is only now being pieced together but it’s a slow and difficult process as most minting records are likely lost forever due to the US Mint’s culture of secrecy.