How can I make carbon steel harder?

Question

I hear that heating and sudden cooling works, but I'm not a metal worker. Any help? What would a simple forge be consisted of? I'm talking about one that uses only what someone from the 1800s would have usedf (non-electric). I've researched this on the 'Net, but can't find a good answer for a very green novice wannabe forger. Know of any very descriptive links (please post link)?

Answer 1

The forge or smithy is the workplace of a smith or a blacksmith. Forging is the term for shaping metal by plastic deformation. Cold forging is done at low temperatures, while conventional forging is done at high temperatures, which makes metal easier to shape and less likely to fracture.

A basic smithy contains a forge, sometimes called a hearth for heating the metals, commonly iron or steel to a temperature where the metal becomes malleable (typically red hot), or to a temperature where work hardening ceases to accumulate, an anvil to lay the metal pieces on while hammering, and a slack tub to rapidly cool, and thus harden, forged metal pieces in. Tools include tongs to hold the hot metal, and hammers to strike the hot metal.

Once the final shape has been forged, iron and steel in particular often get some type of heat treatment. This can result in various degrees of hardening or softening depending on the details of the treatment.

Both carbon and alloy steels are suitable for case-hardening; typically mild steels are used, with low carbon content, usually less than 0.3% (see plain-carbon steel for more information). These mild steels are not normally hardenable due to the low quantity of carbon, so the surface of the steel is chemically altered to increase the hardenability. Case hardened steel is usually formed by diffusing carbon (carburization), nitrogen (nitridization) and/or boron (boriding) into the outer layer of the steel at high temperature, and then heat treating the surface layer to the desired hardness.

The term case hardening is derived from the practicalities of the carburization process itself, which is essentially the same as the ancient process. The steel work piece is placed inside a case packed tight with a carbon-based case hardening compound. This is collectively known as a carburizing pack. The pack is put inside a hot furnace for a variable length of time. Time and temperature determines how deep into the surface the hardening extends. However, the depth of hardening is ultimately limited by the inability of carbon to diffuse deeply into solid steel, and a typical depth of surface hardening with this method is up to 1.5 mm. Other techniques are also used in modern carburizing, such as heating in a carbon rich atmosphere. Small items may be case hardened by repeated heating with a torch and quenching in a carbon rich medium, such as the commercial product Casenite.

Surface hardening a process which includes a wide variety of techniques is used to improve the wear resistance of parts without affecting the softer, tough interior of the part. This combination of hard surface and resistance and breakage upon impact is useful in parts such as a cam or ring gear that must have a very hard surface to resist wear, along with a tough interior to resist the impact that occurs during operation. Further, the surface hardening of steels has an advantage over through hardening because less expensive low-carbon and medium-carbon steels can be surface hardened without the problems of distortion and cracking associated with the through hardening of thick sections.
The purpose of heat treating plain-carbon steel is to change the mechanical properties of steel, usually ductility, hardness, yield strength, and impact resistance. Note that the electrical and thermal conductivity are slightly altered. As with most strengthening techniques for steel, the modulus of elasticity (Young's modulus) is never affected. Steel has a higher solid solubility for carbon in the austenite phase, therefore all heat treatments, except spheroidizing and process annealing, start by heating to an austenitic phase. The rate at which the steel is cooled through the eutectoid reaction affects the rate at which carbon diffuses out of austenite. Generally speaking, cooling quickly will give a finer pearlite (until the martensite critical temperature is reached) and cooling slowly will give a coarser pearlite. Cooling a hypoeutectoid (less than 0.8 wt% C) steel results in a pearlitic structure with α-ferrite at the grain boundaries. If it is hypereutectoid (more than 0.8 wt% C) steel then the structure is full pearlite with small grains of cementite scattered throughout. The relative amounts of constituents are found using the lever rule.
For more:
http://en.wikipedia.org/wiki/Mild_steel

Answer 2

Try going to AnvilFire.com

They have some blacksmithing tutorials that are very helpful. A simple Coal Forge is not that difficult to make...and often just as easy to find at local farm auctions, or especially at antique engine/blacksmith swap meets. There are several great books out there, too...that will really give you the info you need.

As for hardening, you did not mention if your steel is "low-carbon (mild)" steel, or already a "medium-carbon" or "high-carbon" steel. If your steel has a very low carbon content (.15-.3%)...then no amount of heating it and quenching it will make it any harder. Carbon is the alloying agent that affects that. Case hardening, as listed below, is a way of infusing carbon into the outside layer of otherwise "low-carbon" steel, allowing you to harden the outside layer...but it will not match the strength of steel who's carbon content is high throughout.

Also, if you start out with steel that already has a high carbon content, there are rules for forging it properly. It cannot be heated too hot, or hammered while too cold.

There is a point when high carbon steel reaches the optimum point for quenching. I think it's officially called the "critical range" or something like that. Heat it higher, and you risk messing up the crystaline structure of the steel. Oddly enough, when in the critical range, the steel will lose it's magnetism, and a "magnet test" is one method of finding out if it's ready to quench.

After quenching, it's brittle...and must be tempered to whatever degree is needed for its intended purpose. Do not hammer fully hardened steel...it will shatter, and possibly send shrapnel into you.

I recommend some books, if only for the fun of learning about the centuries-old technique of shaping metal. Alex Bealer's "the art of blacksmithing" is a good one. So is "the back yard blacksmith" by Lorelei Sims...who can be found at blacksmithchic.com

Answer 3

It's not really that hard. You can use your charcoal grill to do it.
First build a large fire in it and then bury the steel in the coals. It'll only take about ten minuites or so for the steel to heat through. Then pick it out of the coals with tongs and drop it into a bucket of water. Repeat as desired. Eventually it'll get as brittle as glass. To fix this, you must anneal the metal.
Again heat the metal in the coals, only this time let it stay there until the coals go all the way out all by themselves. Next day when all the way cool, Take it out and clean it off. Viola!, you have hardened steel.

Answer 4

Hardening carbon steel is the easy bit. The trouble is that you end up with something that is harder than glass and just as brittle. The skill is in the subsequent tempering of the item to give it the right combination of hardness and strength.

Try a search for "hardening and tempering"

Have you tried a search on "Armourer's forge"?

This site may be of interest:

http://www.armourarchive.org/essays/build_a_forge/

Answer 5

Plain-carbon steel is a metal alloy, a combination of two elements, iron and carbon, where other elements are present in quantities too small to affect the properties. The only other alloying elements allowed in plain-carbon steel are: manganese (1.65% max), silicon (0.60% max), and copper (0.60% max).

Steel with a low carbon content has the same properties as iron, soft but easily formed. As carbon content rises the metal becomes harder and stronger but less ductile and more difficult to weld.

High carbon steel: approximiately 0.55% to 0.95% carbon content with 0.30 to 0.90% manganese content..[1] Very strong, used for springs and high-strength wires.[4]

Very high carbon steel: approximately 0.96% to 2.1% carbon content, specially processed to produce specific atomic and molecular microstructures.[1]

Steel can be heat-treated which allows parts to be fabricated in an easily-formable soft state. If enough carbon is present, the alloy can be hardened to increase strength, wear, and impact resistance. Steels are often wrought by cold-working methods, which is the shaping of metal through deformation at a low equilibrium or metastable temperature.

Answer 6

heating it past 2000 degrees or Chery red hot and quenching it in used motor oil. used oil has more carbon in it. this makes the steel hard but brittle. now you want to put it in a hot oven say 500 degrees for several hours maybe even a day then allow it to cool in a closed oven till room temperature. this will take away the brittleness.

Answer 7

forging metal to the right temper is very hard... the metal has to be the right color before you dip it in the water. some people use molten salt, oil and other things. it takes many years to know how to do it and how to do it right.p.s. by color i mean the color of the metal when its heated before dipping. sorry i don't have a link sweety. good luck.

Answer 8

i know that folding metal makes it harder. but yeah, heating it and then suddenly cooling it forms stronger bonds between the molecules.