Selected Metals: History and Engineering Data

Selected Metals: History and Engineering Data

Carbon Steels

Perhaps the moniker "carbon steel" should be replaced with something less misleading because all steel contains carbon . Iron, the basic ingredient of steel, has so much carbon in its pig iron form that carbon actually has to be removed to produce what we call "carbon steel". So what makes carbon steel different from other steels? One definition for carbon steel is: it must have been refined (high carbon content removed from pig iron) and it contains no purposefully added alloying elements other than carbon (for clarity, steel can be produced by reducing the carbon in the pig iron to a level that produces steel OR all of the cabon can be removed and then contolled amounts of cabon put back in).

Residual elements may still be found in carbon steel such as those added for deoxidation or to counter the effects of oxygen and sulphur. In the American Iron and Steel Institute (AISI) standard and the Society of Automotive Engineers (SAE) standard there are % limits placed on the residual elements that may occur in the mix. For example all steel contains manganese . For some iron ores (like the ore used by the Spartans in ancient Greece) manganese is already in the ore in fairly large quantities. Manganese helps in the refining process to remove unwanted oxygen and sulphur. If the ore is lacking in manganese then manganese is usually added in the steel making process. However for AISI/SAE designation of carbon steel there is a limit as to the amount of manganese that can be present.. Just remember that carbon steel has carbon as the primary additional element and has no intentionally mixed alloys included to change the mechanical properties of the steel.

There are hundreds of types of carbon steel each with their own unique characteristics. Presented below are four common carbon steels that are familiar to most machinists (note how the percentage of carbon effects the uses and properties of the steel).

G10100 (AISI/SAE 1010)

• Carbon less than 0.10%
• Machinability good
• Hardenability case harden only
• Weldability good by all techniques.
• Applications screws, bolts, and other cold headed products
• Comments a general purpose steel that is low in strength unless quenched and tempered

G10180 (AISI/SAE1018)

• Carbon 0.15 to 0.20%
• Machinability medium plus
• Hadenability case harden to RC 42 if less than 4" thick
• Weldability good by most techniques
• Applications wide variety
• Comments easy to machine, nice finish, great mechanical properties - a good all-around steel that is available in many cold rolled sizes. A nice steel for fixturing with welded risers and gussets. This carbon steel is probably the most common in the machine shop.

G10300 (AISI/SAE 1030)

• Carbon 0.25 to 0.30%
• Machinability good
• Hardenability good with water quenching
• Weldability good by all methods but requires preheating for large sections.
• Applications machinery parts that require strength and hardness
• Comments a good, strong, machinable, steel that is available from all suppliers and in most shapes

G10400 (AISI/SAE 1040)

• Carbon 0.35 to 0.45%
• Machinability medium plus
• Hadenability very good with water quenching
• Weldability good by all methods but requires pre/post heating for large sections
• Applications crankshafts, heavy duty couplings, and cold headed parts
• Comments a good, strong, machinable, steel that is available from all suppliers and in most shapes. It work hardens rather vigorously so sharp cutters and lots of coolant is a must

NOTES
Why should a machinist care about weldability of the metal*? The answer to this question may not be too obvious. The reason is that there are many times when a tooling fixture like the one on the left must be designed and built in the shop. Welding risers and gussets into an assembly is usually faster than trying to machine, screw, dowel, and assemble each of them. Therefore the machinist/engineer must select a steel that is strong, weldable, can be stress relieved, and is easy to machine after welding. Knowing the weldability of steel is sometimes just as important as knowing its hardness, and machinability. R.S.
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The following are general vocabulary terms used in the machine shop to define particular groups of steel. They are important terms and should be completely understood.
Use these glossary links to examine and understand their meanings. R.S.
Hot rolled steel
Cold rolled steel
Mild steel
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Another vocabulary note: The percentage of carbon in steel is often referred to in terms of "points". For example a steel with 0.70% carbon is said to contain 70 points of carbon.R.S.

Alloy Steel

Alloy steels are those carbon steels that have certain other elements purposefully mixed in during processing to achieve various results in the performance of the steel. As mentioned in the previous page there are sometimes unintentional alloys in steel.. These impurities can be present in the iron ore or can be added for refining purposes but they are not included to manipulate the physical characteristics of the steel. For example the problem with the iron ore in the British Isles is that it contains too much phosphorus which makes the steel brittle. The solution - circa 1800 - was to add chalk to the molten metal* which caused the phosphorous to mix with the slag and the slag could be easily removed in the steel making process. This steel, should it contain some residual chalk residue, is not an alloy steel because no alloys were intentionally added to the steel to change the properties. Only to make the refining easier.

The first alloy steel was invented by Robert Hadfield in Sheffield England. By mixing large quantities of manganese with the iron and carbon he made an alloy steel that was extremely hard wearing and most suitable for train rails. For many decades this steel was known as "manganese steel". Note that manganese was already used in the steel making process and was limited as an impurity to no more than 0.7% content. Hadfields manganese steel had about 1.6 % manganese.

Many other alloying elements have followed which produce steels with greater strength, fatigueresistance, corrosion resistance, and other physical attributes. Alloy elements are commonlychromium, molybdenum, manganese, and nickel.  Following are three molybdenum alloy steels that are familiar to most machinists (note how carbon content and alloy effect their properties).

N41300 (AISI/SAE 4130)

• Carbon 0.25 to 0.35%
• Alloy molybdenum and chromium
• Machinability medium plus when normalized
• Hadenability very good. Should not be case hardened
• Weldability good by all methods
• Application aircraft engine mountings and welded tubing.
• Comments a good, strong, machinable, steel that is available from all suppliers and in most shapes.

N41400 (AISI/SAE 4140)

• Carbon 0.38 to 0.43%
• Alloy molybdenum, manganese, chromium,
• Machinability very good
• Hadenability good oil hardened steel
• Weldability good
• Applications nearly everything
• Comments a common low alloy steel noted for toughness, good torsional strength and good fatigue strength. This alloy steel is the most common and is available in nearly all sizes and shapes.

N43300 (AISI/SAE 4330)

• Carbon 0.28 to 0.32%
• Alloy molybdenum, nickel, chromium,
• Machinability good only if annealed
• Hadenability good oil hardened steel
• Weldability good by all methods but requires pre/post heating for large sections
• Applications gears, aircraft landing gear, axles or shafts for power transmission
• Comments a common low alloy steel noted for toughness, good torsional strength and good fatigue strength. This alloy steel is quite common and is available in nearly all sizes and shapes

"Free machining" is a common term used in the machine shop to categorize the steels that are the easiest to machine.
Free Machining steels are relatively low carbon steels that have been resulfurized to make steel that produces better chips (chip fracturing) and requires less horsepower to machine. R.S.
A peculiar aside --- AISI/SAE steel designations determine that any steel that begins with the designation numeral "1" is classified as a carbon steel, not an alloy steel. Alloy steels begin with some other digit, such as "2" for nickel steel and "4" for molybdenum steel. Therefore any number other than "1" designates a steel with some primary alloying element. Yet manganese steel does not have its own numeral at the beginning of the designator. Instead, manganese steel, is a subset of carbon steel with a designator of 13xx where the "13" designates this carbon steel as a manganese steel...go figure. R. S.

300 Series Stainless Steels

Stainless steel was invented by Englishman Harry Brearley in 1913. While attempting to find a more wear resistant steel he alloyed it with a larger than normal quantity of chromium and found the result to be highly resistant to the acid etching pen that he used to mark his specimens (chromium had been used as an alloy in steels for a few years but in only very small quantities). As is often the case with invention, serendipity brings forth something new and unexpected. In this instance a stainlesssteel was invented while attempting to find a more wear resistant steel..
Over the years many alloys have been mixed into stainless steel however the most common alloying elements are chromium and nickel. Therefore carbon and chromium/nickel percentages give the best profile of this steel.
S300xx (AISI/SAE 300) series are austenitic steels that provide the best corrosion resistance of all the stainless steels. However they will not heat treat like carbon steels and this limits them in strength. 300 series is easy to segregate from other steels because it is non-magnetic.
Following are a few 300 series stainless steels familiar to most machinists (note how carbon, chromium, and nickel effect the properties of the steel).
S30300 (AISI/SAE 303)

• Carbon 0.15%
• Chromium 17 to 19%
• Nickel 8 to 10%
• Other alloys manganese, sulphur, phosphorus, silicon, zirconium,molybdenum
• Machinability excellent
• Hadenability none
• Weldability not recommended
• Applications nearly everything
• Comments one of the most popular easier machining stainless steels.  Available in all sizes and forms.

S30400 (AISI/SAE 304)

• Carbon 0.18% max
• Chromium 18 to 20%
• Nickel 8 to 12%
• Other alloys manganese, sulphur, phosphorus, silicon
• Machinability slow speeds heavy feeds, use chip breaker, will work harden
• Hadenability none
• Weldability fusion welding and resistance welding
• Applications nearly everything
• Comments This is the oldest and most widely used austenitic stainless steel. It possesses an excellent combination of strength, corrosion resistance and machinability. All sizes and forms are available.

S31600 (AISI/SAE 316)

• Carbon 0.08%
• Chromium 16 to 18%
• Nickel 10 to 14%
• Other alloys manganese, sulphur, phosphorus, silicon, molybdenum
• Machinability slow speeds heavy feeds, use chip breaker, will work harden
• Hadenability none
• Weldability fusion and resistance - no
• Applications marine hardware
• Comments best corrosion resistance of the three, widely available.

400 Series Stainless Steels

S400xx (AISI/SAE 400) series are martensitic and steels that are not quite as corrosion resistant as the 300 series. However the non-ferritic varieties will heat treat quite well with ordinary methods. This provides a great deal of utility because the engineer can design machinery that will stand up to caustic cleaning solutions - like that present in food processing plants - yet still have strong hardened machine components. Most 400 series stainless steel is magnetic like carbon steel.

Following are three 400 series stainless steels which the machinist will be familiar: Note how carbon, chromium, and nickel change their properties.
S41600 (AISI/SAE 416 )

• Carbon 0.08%
• Chromium 16 to 18%
• Nickel 10 to 14%
• Other alloys manganese, sulphur, phosphorus, silicon, molybdenum
• Machinability easy to machine
• Hadenability good oil hardening
• Weldability not recommended
• Applications shafting, axles, screw machine parts
• Comments the first free machining stainless.  Widely available

S43100 (AISI/SAE 431)

• Carbon 0.2%
• Chromium 15 to 17%
• Nickel 1.25 to 2.5%
• Other alloys manganese, sulphur, phosphorus, silicon
• Machinability galling chips and inferior finishing
• Hadenability oil or air quenching
• Weldability arc welding only
• Applications aircraft fasteners and bolts
• Comments excellent strength, high hardness levels, best corrosion resistance of any 400 series stainless steel.

S44000 (AISI/SAE 440)

• Carbon 0.60 to 1.2%
• Chromium 15 to 17%
• Nickel none
• Other alloys manganese, sulphur, phosphorus, silicon, molybdenum
• Machinability tough stringy chips, use carbide chip breaker, will grind nicely
• Hadenability good hardening with air or oil quench
• Weldability do not weld
• Applications molds, dies, valve components
• Comments this steel has three sub-parts, 440A, 440B, and 440C, all of which can harden progressively from Rockwell 56 to Rc 60. Poor corrosion resistance.

15 & 17 Stainless

S1xxxx (AISI/ASE 15 and 17) series are martensitic steels that provide good corrosion resistance. They are similar to 400 series in most ways. However they do not use same method of heat treating that is usually used with carbon steels or 400 series stainless steels. They are heat treated using thePrecipitation Hardening (PH) method. Also, this steel - like 400 series - is magnetic

Precipitation Hardening was first used on Aluminum in 1909 by Alfred Wilm. However the application of these principles were not used on stainless steels with any significance until after WWII when the aerospaceindustry began to demand steel with the characteristics PH ultimately provided. These unique heat treating process can be used with both austenitic and martensitic steels which means high corrosion resistance as well as hardenability are available with a single stainless steel

Following are two of these PH stainless steels familiar to most machinists:

S15500 (AISI/SAE 15-5 or 15-5PH)

• Carbon no data
• Chromium no data
• Nickel no data
• Other alloys no data
• Machinability machinable in most conditions
• Hadenability precipitation method
• Weldability resistance methods or shielded fusion
• Applications aircraft parts, valves, fasteners
• Comments martensitic, precipitation hardening, chromium-nickel-copper stainless steel, corrosion resistance comparable to 304 stainless.

S17400 (AISI/SAE 17-4 or 17-4PH)

• Carbon no data
• Chromium no data
• Nickel no data
• Other alloys no data
• Machinability gummy chips, stringy chips, use chip breaker
• Hadenability precipitation method
• Weldability resistance methods or shielded fusion
• Applications jet turbines, chemical plants
• Comments the most widely used precipitation hardening stainless, good corrosion resistance, high harness, toughness and strength.

Aluminum

In 1825 Hans Christian Oersted, a Danish chemist, had extracted 

tiny amounts of aluminum powder from alum (aluminum potassium

 sulfate mined from the earth). He was the first person to do so. However aluminum making was not an economical process until

 1889 when American, Charles Martin Hall, patented an inexpensive method (below) for the production of aluminum, which brought the metal* into wide commercial use.

Aluminum, is not useful in its pure state so it must be alloyed with magnesium and one or more of the following elements: copper, silicon, manganese, chromium.

Annealed aluminum is much too soft and gummy for machining so the machinist usually gets the material after it has been heat treated. This is quite the opposite of most machine shop steels which are usually machined before heat treating. The type of treatment (called temper) is appended to the alloy number as one of the following designator letters:

1. F designates as fabricated
2. O designates annealed
3. W designates solution heat treated
4. H designates strain hardened
5. T designates thermally heat treated

The T temper has ten subdivisions numbered 1-10 that denote the specific process of the thermal heat treatment used. The T temper is the most common designator found in machine shop aluminum.

The following three alloyed aluminums are familiar to machinists: (the machinability characteristics are comparisons of aluminum to aluminum, not comparisons of aluminum to steel.). The American Standard for Metals (ASM) designation is in parenthesis.

A92024 (ASM 2024)

• Primary alloy copper
• Machinability fair, use oil based coolants
• Temper T4 or T6 (i.e. 2024-T4 or 2024-T6)
• Weldability not recommended
• Applications truck wheels, aircraft structures
• Comments a very common aluminum alloy which has a high strength to weight ratio

A96061 (ASM 6061)

• Primary alloy silicon and magnesium
• Machinability very good. The standard that all other aluminums are compared to.
• Temper T4 or T6 (i.e. 2024-T4 or 2024-T6)
• Weldability very good by all techniques
• Applications commonly used in applications that require excellent corrosion resistance such as railroad cars, marine equipment, and other outside structures.
• Comments The most common aluminum alloy available.

A97049 (ASM 7049)

• Primary alloy zinc
• Machinability good, use oil based coolants
• Temper varies
• Weldability not recommended
• Applications aircraft structures
• Comments the machinist nearly always gets this material in a forged condition. Very common for aircraft landing gear, engine mounts, and wing spars.

Copper Alloys -Bronze

Copper has been used for more than 13,000 years and was the only metal* known to man for the majority of that time (the lizard skeleton imbedded in copper shown to the right may be 11,000 years old). It wasn't until somewhere around 5000 BC that copper was mixed with tin to produce a much harder metal*s called bronze. The discovery of bronze was such an important time to historians and archeologists that it has come to be known as the Bronze Age.

Bronze remains a material in common use today. Alloys other than Tin have since been added to copper to produce substantially different properties. The most common alloys are: phosphorus, aluminum, manganese, silicon, nickel, lead, and iron. The first four alloys play the main role in bronze metal*lurgy therefore bronze has been divided into four groups: Phosphor Bronze, Aluminum Bronze, Manganese Bronze, and Silicon Bronze. Following are four bronze alloys, one from each group. Note that the machinability indications are comparing bronze to bronze.

C64200 

• Primary alloy aluminum
• Machinability good
• Weldability fair for all methods except oxy
• Applications valve and pump components, marine equipment
• Comments a free machining and anti galling copper alloy

C67500

• Primary alloy manganese
• Machinability fair, galls easily
• Weldability best to solder or braze
• Applications valve and pump parts, bearings, heavy duty mechanical components
• Comments hot forgeable alloy combining high strength and good corrosion resistance

C67500

• Primary alloy phosphor
• Machinability very good
• Weldability best to solder or braze
• Applications bearing and cam followers
• Comments very good wear resistance

C65500

• Primary alloy silicon
• Machinability poor, galls easily
• Weldability best to braze while other methods are good
• Applications valve guides, valve stems, fasteners, pole line hardware, and marine fittings.
• Comments moderate strength, good corrosion resistance, similar to C64200 in properties and applications.

Copper Alloys, Brass

Brass, like bronze, is a copper alloy but has a primary alloying element of zinc instead of tin. Zinc alloying of copper to produce brass had been around since the discovery of bronze. However it was not as easy to produce brass and therefore was not as commonly used.

Over the last few centuries the alloying of copper-tin and copper-zinc with other elements has become so nearly alike, and the results so similar, that today there are very few functional differences between bronze and brass. Generally, whatever you can be accomplished with a particular bronze alloy can be accomplished with some other kind of brass alloy and visa versa. However, there is one significant difference worth mentioning. Brass, when polished, looks like gold but bronze does not polish as nicely. So brass has more decorative uses than bronze and - throughout out history - has been used this way.

The two primary brasses of interest are those called by their color because the hue of the metal*s distinguishes it from its siblings. Red brass contains has less zinc (more copper) and yellow brass contains more zinc (less copper). It is not uncommon for the seasoned machinist to request this copper alloy simply by stating its color: "Red Brass" or "Yellow Brass"

C36000

• Primary alloy Lead
• Machinability the best of the brass family
• Weldability soldering and brazing
• Applications screw machine products
• Comments the most free machining of all metal*s. The standard by which all brass machinability is judged.

C35300

• Primary alloy lead
• Machinability almost as good as C3600
• Weldability soldering and brazing
• Applications screw machine products, hose fittings, lock parts.
• Comments less free machining than C3600 but more formable for forgings, cold heading, etc.

C35300

• Primary alloy iron
• Machinability poor for brass
• Weldability soldering and brazing
• Applications electrical hardware, fasteners, fittings
• Comments a cold form brass that is machined after heading.

Tool Steels

The term "tool steel" can be applied logically to any steel that is used as a tool. However tool steel is generally considered to be those steels that can be machined in an annealed condition, heat treated to a very high hardness, and then ground to size and finish. In the common machine shop vernacular different types of tool steel are often differentiated by AISI single letter that identifies the kind of quenching used in heat treat, the application of the tool steel, or its main alloy. The most common quenching techniques being air-hardening (A), oil-hardening (O), and water-hardening (W). Other steels are chromium tool steel (H), die steel (D), high speed steel (M), cobalt tool steel (T), and shock-resistant tool steel (S). Listed below are the properties of one each of these groups.

The following examples would be familiar to most machinist. Especially those machinist involved in tool and die work.

T3102 (AISI A2)

• Hardness 56 - 62 RC Air quenching
• Machinability 85% of W steels (baseline)
• Applications die shapes, slitters and similar where wear resistance is important.
• Comments This alloy is one of the Cold Work, Medium Air Hardening type tool steels. It contains chromium and molybdenum with a relatively high (1%) carbon content and is capable of deep hardening from air quench so as to minimize distortion.

T31501 (AISI O1)

• Hardness 57 - 62 RC oil quenching
• Machinability 90% of W steels (baseline)
• Applications short run tooling for blanking dies, cold forming dies and cutting tools
• Comments This alloy is one of the Cold Work, oil hardening type tool steels. It is relatively inexpensive containing small amounts of manganese, tungsten and chromium. Hardening by oil quench minimizes distortion and cracking.

T72301 (AISI W1)

• Hardness 50 - 64 RC water quenching
• Machinability this steel is the most machinable tool steel and serves as a baseline
• Applications hand operated metal* cutting tools, cold heading, embossing taps and reamers as well as cutlery.
• Comments This alloy is one of the common Water Hardening tool steel grades available. W1 is basically a simple high carbon steel and is easily hardened by heating and quenching in water, just as with plain carbon steel alloys.

T20811 (AISI H11)

• Hardness 38 - 54 RC air quenching
• Machinability 75% of W steels (baseline)
• Applications often used for highly stressed structural parts such as aircraft landing gear.
• Comments This alloy is one of the Hot Work, Chromium type tool steels. It is relatively low in carbon content and has good toughness and deep hardens by air quench from heat treatment

T30402 (AISI D2)

• Hardness 54-61 RC air quenching
• Machinability poor- 50% of W steels (baseline)
• Applications Used for long run tooling applications where wear resistance is important, such as blanking or forming dies and thread rolling dies.
• Comments This alloy is one of the Cold Work, high carbon, high chromium type tool steels. D2 is a deep hardening, highly wear resistant alloy. It hardens upon air cooling so as to have minimum distortion after heat treatment.

T11301 (AISI M1)

• Hardness 63 RC oil quenching
• Machinability poor- 50% of W steels (baseline)
• Applications Used for long run tooling applications where wear resistance is important, such as blanking or forming dies and thread rolling dies.
• Comments M1 is a molybdenum, chromium, vanadium alloy tool steel generally known as a Molybdenum High Speed Tool Steel. It is on of the most widely available tool steels in use today. It is similar in properties to the tungsten cobalt tool steels (T series) at a lower cost.

T12004 (AISI T4)

• Hardness 62 - 66 RC oil quenching
• Machinability 55% of W steels (baseline)
• Applications Generally used as cutting tools, broachesand cold extrusion punches. .
• Comments This alloy is a High Speed, tungsten type tool steel. It is a deep hardening alloy capable of Rockwell C 64 hardness.

T41902 (AISI S2)

• Hardness 50-60 RC water quenching
• Machinability 85% of W steels (baseline)
• Applications Used for chisels, hammers and similar repetitive, hard impact, applications.
• Comments This alloy is one of the Shock Resisting tool steel types. It retains reasonableductility even in the hardened condition which enables it to perform in applications where shock impact is imparted to the alloy.

Other Metals

A list of metals and alloys not covered in this topic would be very long. But the four mentioned below are - in this authors opinion - the most common "other metal*s" found in the machine shop.

Cast Iron

The term cast iron, like the term steel, identifies a large family of ferrous alloys. Cast iron has higher carbon and silicon contents than steel. Because of the higher carbon content, the structure of cast iron, as opposed to that of steel, exhibits a rich carbon phase. Two basic types of cast iron can be identified visually: White Iron and Gray Iron. The machinability of cast iron is relatively good. However it must be machined without coolant so particular attention to heat build up is essential. Cast iron machining produces a powder instead of a chip.

Titanium

Titanium has developed a mystique as a nightmare to machine. This is simply not the case. Experienced operators have compared its characteristics to those found in 316 stainless steel. Recommended practice includes high coolant flow (to offset the materials low thermal conductivity), slow speeds and relatively high feed rates. Tooling should be tungsten carbide or cobalt type high speed tools.

Hastelloy (tm)

Conventional machining techniques used for iron based alloys may be used. Machining characteristics are somewhat similar to those for the austenitic (300 Series) stainless steels. This alloy does work-harden during machining and has higher strength and "gumminess" not typical of steels

Inconel (tm)

Conventional machining techniques used for iron based alloys may be used. This alloy does work-harden during machining and has higher strength and "gumminess" not typical of most steels. Heavy duty machining equipment and tooling should be used to minimize chatter or work-hardening of the alloy ahead of the cutting

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