Steelworking

[Optimist]

Steel is one of the basic materials of modern civilization. Since I have done gunsmithing for quite a few years, it is a material I have a more than passing familiarity with. Steel is a form of iron with a limited amount of carbon in it, between a tenth of a percent, and two percent. Iron with no carbon at all is a very soft, ductile material. Iron with more than two percent is a tougher material, and, beyond about 4 percent, it is a very hard and brittle one.

Alloying elements like chromium, nickel, vanadium, tungsten and even lead are used in making up modern steels, and these different materials, alone or in combination, produce some strong effects on the basic iron-carbon mix. If there is interest in this matter, I will continue posting.

[Sniper-T]

As a steel worker for the last 25+ years; I have somewhat of a vested interest in it. Always looking to learn more.

Carry on!

[The Stig]

Yes, please do. We like subject matter experts.

[realist]

Optimist, Realist here. Do those two attract or repel, oh well. Working with metal is high on my list. I am taking up welding and would appreciate additional posts. Thanks

[Optimist]

Okay, I'll put together a basic presentation on how the carbon content of steel works, and how the level of carbon in the steel acts to change temperatures at which heat treatment needs to be done, and I'll post that, and the diagram, next weekend. If any of you have ever heated and cooled steel, there are points you may be familiar with, and others you may not have noticed. Generally, when you have a piece of red-hot steel in your tongs, you are moving pretty fast to try to accomplish something before the metal cools down, so it is easy to miss some of the finer points in the rush.

First things first, steel at room temperature is a mass of crystals, and the kind of crystals they are depends on the amount of carbon that is mixed in with the iron. For pure iron, with no carbon at all, the crystal structure will be ferrite, a very soft and ductile material, of pretty low strength. It is very strongly magnetic. If you heat this pure iron to about 1450 degrees Fahrenheit, it will no longer attract a magnet. The ferrite crystals are changing into a crystal structure called austenite. At the point where the ferrite stops attracting a magnet, you keep on pumping in more heat, but the iron doesn't get any hotter by the temperature you're measuring. This continues until all the ferrite is converted, and then the temp begins rising again. This plateau is called the calesence point. That heat was bound up in changing the crystal state of the material. Remember it, because this heat will come back around again when we cool the metal down.

[Optimist]

Now we have a piece of red-hot metal. It's somewhere above 1400 degrees, where the ferrite has turned itself into another kind of crystal called austenite. Austenite is not attracted to a magnet. (For future reference, that is why some kinds of stainless steel don't attract a magnet either; they're stuck in a stage where they are made up of austenite crystals, even after they have cooled down.) If we let this metal cool down, it cools to a point a little below the place where it stopped heating when we were making it hotter, and then the temp begins going up again. That is the austenite changing back to ferrite, and, when it does, it gives off heat.

[sidewinder]

Melt shops are dirty. Welding is harmful to your health. It was my favorite thing. I miss welding.

Welded stainless, brass, copper, cast iron, common iron through galvanized, oil, grease, lead based paint, rust, water & dirt.

It's a cold profession in the winter and hot in the summer. Same with melt shops. Which are loud and dangerous.

Welded on & in hot metal ladles, water cooled ductwork, induction furnaces, continuous casters, arc furnaces, cupolas, BOF furnaces, AODs, hot metal cranes, strip mills, rolling mills, bloomers, coilers, shot blasters, acid tubs, conveyers, locomotives, trucks, fabrication and anything else you can find in a steel mill. Seen and fixed cut throughs, doubleups, structural failures, new construction, rebuilds, explosion & fire damage. Worked with pipe fitters, millwrights, hydraulics, bricklayers, electricians, machinists, riggers, carpenters, mechanics, repairman.

Had many fellow workers killed by huge vehicles, overhead cranes, burned, electrocuted, falling & crushed. When I first started it was common to see men with lost arms and fingers. Safety conditions have greatly improved.

Years ago for every steelworker laid off 14 people in related industries lost jobs. Over 100,000 steel workers jobs have been lost. That equals over 1 million related jobs lost.

Stainless steel is non magnetic depending on how much the nickel content is. Nickel is not magnetic. The most expensive and best stainless steel has a high nickel content. The same nickel that is in a nickel nickel.

[nepreneaux]

So I am thinking D2 or 01 for making a knife. Which one?

[Optimist]

Stainless steel is non magnetic depending on how much the nickel content is. Nickel is not magnetic. The most expensive and best stainless steel has a high nickel content. The same nickel that is in a nickel nickel.

Reason the high-nickel stainless steels ain't magnetic is that the nickel locks the crystal structure into an austenite structure, one that don't allow magnets to attract to the steel because the poles of the iron atoms aren't oriented the way they are in all the other structures. Now a steel nickel is 19 parts nickel (the old pre-1984 ones, anyhow) and one part copper. If you are melting up steel in a crucible, you could, feasibly, use nickels to add that metal to your melt. I'm getting the piece about alloys ready for you guys, and it should be ready next weekend.

Nepreneaux, it depends on what you want to do with the knife, and how good your heat treat plant is. Most knives and other hand tools I make up from 1095, or W1, which is pretty close. They have to be kept oiled, or they rust. O1 is a tougher steel, and if I was to make a blade for batonning, it would be one I would consider. D2 is one of the steels I'd consider putting back in annealed form for making things that absolutely had to be unbustable, like firing pins and such. It's too expensive a material for me to use for a knife....

[Sniper-T]

Opt...

You a metalugist? What's your background?

Great info, thanks for taking the time to post!

[Optimist]

Gunsmith, with a lively curiosity as to what is going on when I heat, quench and temper a piece of steel.

[Optimist]

Steel is iron with more than a trace and up to two percent of carbon. Plain carbon steels have been around for a long time, particularly in the field of edged weapons, but a thorough understanding of the way plain carbon steel works did not come into being and get recorded until the latter part of the 1700s. The way carbon steel reacts to heat and quenching is a matter of crystal formation in the structure of the metal, and to have a good grasp of this, there were five basic crystalline structures discovered and described by the late 1800s, and these structures and their implications for making objects of steel were fairly common knowledge to steelworkers by about 1920. Then, in the middle 1930s, a pair of different structures were isolated. Each of these structures handles carbon in a different fashion, and has a different structure as a crystal. When they are present in the metal, they have certain effects on the property of that metal, to include its strength, and its magnetic properties.

Let's take these one at a time, because it is simpler that way. In practice, these mingle, join and conjoin, conjugate, segregate, and, in general do things that no self-respecting mink breeder would consider permitting to remain on the premises....

The basic five structures are:

Austenite


Face-centered cubic crystal, present above the critical temperature of the iron-carbon solution, which does not attract a magnet. This feature of the structure was known well before its comprehension in terms of structure. In heat-treating steel, austenite is the point from which the structure is altered. Carbon is freely soluble in austenite, though other structures have less of an affinity for it.
Ferrite

Tetragonal crystal, present when temperature falls below the critical temperature range. In iron with no carbon, this is the sole structure present. Ferrite does not allow iron to remain inside the crystal structure.

Pearlite

A pearlite colony, or structure, consists of two interwoven crystals, one of ferrite, and the other of cementite. Due to the regularity of the structure when polished and etched, then examined under the microscope, this was long thought to be a homogeneous structure, different from both ferrite and cementite. With the advent of X-ray microscopy, the crystalline nature of the structure became apparent. The ferrite and cementite orient to one another in fairly regular fashion, which is apparent on polishing and etching to examine the crystalline structure. Eutectic steel, 1080, is of the right proportion to allow its room-temperture form to be completely made up of pearlite, given a slow cooling.

Cementite

Cementite is a chemical compound of iron and carbon, with the chemical formula Fe3C, or three iron atoms bonded to one atom of carbon. As such, it may be considered a carbonate of iron. It is a hard formation, though not as hard as martensite.

Martensite

Consists of carbon dispersed at the boundary of a tetragonal ferrite crystal. Since the carbon is insoluble in ferrite, and is locked at the perimeter of the ferrite crystal, there is a considerable stress between the crystals. This stress makes martensite quite brittle. Martensite is formed by a very rapid cooling of austenite that forces the carbon to the crystal boundaries. The stress at these points makes the carbon very hard, on the close order of diamond in hardness. Heating relaxes the crystalline boundaries, and softens the martensite. The process is called tempering.

The two later structures are dependent on the presence of alloying materials. Plain carbon steel does not furnish a good matrix for their development. Bainite structures come into existance when alloy steel is cooled from austenite to a point above the quench temperature for martensite formation, and held there long enough for the structures to develop. This sort of interrupted quench gives a material almost as hard as martensite, but considerably more ductile, and tougher. One of the early methods for interrupted quenching was called Austempering, and the process was patented. Further investigations led to other variations called martempering and isothermal tempering. Exact methods varied. so as to avoid the Austempering patents.

Upper bainite

Lower bainite

Here is a diagram for heating characteristics of the iron-carbon solution. Keep in mind that this is a diagram for carbon steel. Alloy steels vary considerably from these values.


Temperatures of steel range from the melting point, and that attendant heat above the melting point that is required to enable the steel to be poured as a liquid, down to the critical point. As a liquid, the steel has no crystalline structure, being an amorphous fluid. At approximately 1400 degrees centigrade, for pure iron, it begins to freeze. As the level of carbon increases, the freezing point drops, and there is a stage in iron content between zero and 4.3 percent iron where it is slushy, and a mixture of austenite and liquid. Above 4.3 percent, it is a mixture of cementite and liquid. The iron solidifies at 1130 degrees centigrade into austenite, or a mixture of austenite and cementite.

Most steel with which we, as artisans are concerned run less than one percent of iron, and 1095, or cutlery steel runs only .95 percent. For most of our needs, capability of heating to
900 degrees centigrade will bring us into the range to convert our steels into austenite, and, as soon as the metal won't attract a magnet, then it's ready for whatever heat treat we're after doing with it. A cavet here. We are talking about carbon steels here. Alloy steels need heat treatment too, and they hit critical temps at a different set of values.

Upper critical temperature is the temperature above which all of the steel is austenite.

Lower critical temperature is the temperature at which steel, being heated from lower temperatures, begins to change to an austenite structure. The calescence point, with its interesting effects on heat input, occurs within this range. During the process of heating steel, at the calesence point, the steel continues to accept external heat energy, but the temperature stops rising. This energy is being absorbed to change the state of the structure, in the same manner that water changing to ice exhibits that phenomenon. It gives the energy back out upon cooling, which means that the temperature will exhibit a rise as the structure begins to change back. Since we cannot move steel from one place to another intantaneously, this is a very handy thing for the heat treater, or the man who is working to forge the material.... A point to remember is that the calescence point varies with the content of the alloy, and time duration is one of the things that is widely variable.

Eutectic points are a chemical term that define places in a solution where a stable balance of components is reached. The iron-carbon solution has two eutectic points. One occurs when the iron has eight tenths of a percent of carbon dissolved. A carbon steel so composed is referred to as 1080, and is called eutectoid steel by the old coots. The second eutectoid point occurs at about four percent carbon, and is of concern to ironworkers more than it is to steel men. That is a matter for further discussion at a different time.


















When a steel part is hardened, it is heated to a high temperature in order to convert the entire structure to the austenite phase. As discussed earlier, austenite is a single-phase structure of iron and carbon stable at high temperatures. If the steel were cooled slowly, the austenite would transform to pearlite, the equilibrium phase at room temperature. A pearlitic structure is an annealed structure and is relatively soft with low physical properties. If the steel is cooled very rapidly, a very hard and strong structure called martensite forms that is a metastable phase of carbon dissolved in iron. It may be tempered to produce lower hardness structures that are less brittle. Intermediate cooling rates will produce other structures referred to as bainites, although this type of structure is only produced in quantity in an alloy steel. Eutectoid carbon steels produce predominantly martensite or pearlite, depending on the cooling rate.


Well, the pictures didn't make the copy and paste. Guess I'll have to do something else about this one....

[Optimist]

Alloys

Alloying elements modify steel in different ways, depending on what they do to the iron and
carbon; due to the way they affect the crystalline structure, and to the way they change
the way that the iron handles carbon and carbide formation. Some of the alloy elements have strong effects on both fronts.

Let's look at the effects on crystal structure first. These effects are displayed at the molecular level, by expanding or contracting the g-field. An expanded g-field, due to heat, is what changes ferrite and cementite into austenite, with application of heat for heat treatment, so the austenite stabilizers, or g-field expanders are doing by structure what heat does by increased energy levels. The following alloying elements are g-field ezpanders:

Nickel
Cobalt
Manganese
Copper
Carbon
Nitrogen

Other alloy elements work by decreasing the g-field , which occurs during cooling, and encourages formation of ferrite and cementite. Again, these ferrite stabilizers are doing by structure what occurs naturally in cooling from the austenite stage. The following alloying elements are g-field reducers:

Silicon
Chromium
Tungsten
Molybdenum
Phosphorus
Aluminum
Tin
Antimony
Arsenic
Zirconium
Niobium
Boron
Sulfur
Cerium

That's a quick overview of alloy elements and structure changes. Let's move on to what these elements do to the carbon structure of steel. Again, there are two classes. One class forms carbides, as iron does with carbon to form cementite (Fe3C). The carbide formers may go into solid solution in cementite, making structures that are hard and tough at low concentrations, or they may form into carbide crystal structures of their own outside the crystals of cementite and martensite, though manganese only dissolves in cementitie.

Carbide formers include:

Manganese
Chromium
Molybdenum
Tungsten
Vanadium
Niobium
Titanium
Zirconium

Alloy elements which do not form carbides usually are found at the crystal boundary.
These include:

Nickel
Cobalt
Copper
Silicon
Phosphorus
Aluminum


CARBON

The amount of carbon (C) required in the finished steel limits the type of steel that can be made.
As the C content of rimmed steels increases, surface quality deteriorates. Killed steels in the
approximate range of 0.15–0.30% C may have poorer surface quality and require special
processing to attain surface quality comparable to steels with higher or lower C contents.
Carbon has a moderate tendency for macrosegregation during solidification, and it is
often more significant than that of any other alloying elements. Carbon has a strong tendency to segregate at the defects in steels (such as grain boundaries and dislocations). Carbideforming elements may interact with carbon and form alloy carbides. Carbon is the main hardening element in all steels except the austenitic precipitation hardening (PH) stainless steels, managing steels, and interstitial-free (IF) steels. The strengthening effect of C in steels consists of solid solution strengthening and carbide dispersion strengthening. As the C content in steel increases, strength increases, but ductility and weldability decrease [4,5].

MANGANESE

Manganese (Mn) is present in virtually all steels in amounts of 0.30% or more [13]. Manganese is essentially a deoxidizer and a desulfurizer [14]. It has a lesser tendency for macrosegregation than any of the common elements. Steels above 0.60% Mn cannot be readily rimmed. Manganese is beneficial to surface quality in all carbon ranges (with the exception of extremely low-carbon rimmed steels) and reduction in the risk of red-shortness. Manganese favorably affects forgeability and weldability. Manganese is a weak carbide former, only dissolving in cementite, and forms alloying cementite in steels [5]. Manganese is an austenite former as a result of the open g-phase field.
Large quantities (>2% Mn) result in an increased tendency toward cracking and distortion
during quenching [4,5,15]. The presence of alloying element Mn in steels enhances the
impurities such as P, Sn, Sb, and As segregating to grain boundaries and induces temper
embrittlement [5].

SILICON

Silicon (Si) is one of the principal deoxidizers used in steelmaking; therefore, silicon content
also determines the type of steel produced. Killed carbon steels may contain Si up to a
maximum of 0.60%. Semikilled steels may contain moderate amounts of Si. For example,
in rimmed steel, the Si content is generally less than 0.10%.
Silicon dissolves completely in ferrite, when silicon content is below 0.30%, increasing its
strength without greatly decreasing ductility. Beyond 0.40% Si, a marked decrease in ductility is noticed in plain carbon steels [4].
If combined with Mn or Mo, silicon may produce greater hardenability of steels [5]. Due
to the addition of Si, stress corrosion can be eliminated in Cr–Ni austenitic steels. In heat treated steels, Si is an important alloy element, and increases hardenability, wear resistance, elastic limit and yield strength, and scale resistance in heat-resistant steels [5,15]. Si is a noncarbide former, and free from cementite or carbides; it dissolves in martensite and retards the decomposition of alloying martensite up to 3008C.

PHOSPHORUS

Phosphorus (P) segregates during solidification, but to a lesser extent than C and S. Phosphorus dissolves in ferrite and increases the strength of steels. As the amount of P increases, the ductility and impact toughness of steels decrease, and raises the cold-shortness [4,5]. Phosphorus has a very strong tendency to segregate at the grain boundaries, and causes the temper embrittlement of alloying steels, especially in Mn, Cr, Mn–Si, Cr–Ni, and Cr–Mn steels. Phosphorus also increases the hardenability and retards the decomposition of martensite-like Si in steels [5]. High P content is often specified in low-carbon free-machining steels to improve machinability. In low-alloy structural steels containing ~0.1% C, P increases strength and atmospheric corrosion resistance. In austenitic Cr–Ni steels, the addition of P can cause precipitation effects and an increase in yield points [15]. In strong oxidizing agent, P causes grain boundary corrosion in austenitic stainless steels after solid solution treatment as a result of the segregation of P at grain boundaries [5].

SULFUR

Increased amounts of sulfur (S) can cause red- or hot-shortness due to the low-melting sulfide eutectics surrounding the grain in reticular fashion [15,16]. Sulfur has a detrimental effect on transverse ductility, notch impact toughness, weldability, and surface quality (particularly in the lower carbon and lower manganese steels), but has a slight effect on longitudinal mechanical properties.
Sulfur has a very strong tendency to segregate at grain boundaries and causes reduction of
hot ductility in alloy steels. However, sulfur in the range of 0.08–0.33% is intentionally added to free-machining steels for increased machinability [5,17] .
Sulfur improves the fatigue life of bearing steels [18], because (1) the thermal
coefficient on MnS inclusion is higher than that of matrix, but the thermal coefficient of
oxide inclusions is lower than that of matrix, (2) MnS inclusions coat or cover oxides (such as alumina, silicate, and spinel), thereby reducing the tensile stresses in the surrounding matrix
[5,10,19].

ALUMINUM

Aluminum (Al) is widely used as a deoxidizer and a grain refiner [9]. As Al forms very hard
nitrides with nitrogen, it is usually an alloying element in nitriding steels. It increases scaling resistance and is therefore often added to heat-resistant steels and alloys. In precipitation hardening stainless steels, Al can be used as an alloying element, causing precipitation hardening reaction. Aluminum is also used in maraging steels. Aluminum increases the corrosion resistance in low-carbon corrosion-resisting steels. Of all the alloying elements, Aluminum is one of the most effective elements in controlling grain growth prior to quenching. Aluminum has the drawback of a tendency to promote graphitization.

NITROGEN

Nitrogen (N) is one of the important elements in expanded g-field group. It can expand and
stabilize the austenitic structure, and partly substitute Ni in austenitic steels. If the nitride forming elements V, Nb, and Ti are added to high-strength low-alloy (HSLA) steels, fine
nitrides and carbonitrides will form during controlled rolling and controlled cooling. Nitrogen
can be used as an alloying element in microalloying steels or austenitic stainless steels,
causing precipitation or solid solution strengthening [5]. Nitrogen induces strain aging,
quench aging, and blue brittleness in low-carbon steels.

CHROMIUM

Chromium (Cr) is a medium carbide former. In the low Cr/C ratio range, only alloyed cementite (Fe,Cr)3C forms. If the Cr/C ratio rises, chromium carbides (Cr,Fe)7C3 or (Cr,Fe)23C6 or both, would appear. Chromium increases hardenability, corrosion and oxidation resistance of steels, improves high-temperature strength and high-pressure hydrogenation properties, and enhances abrasion resistance in high-carbon grades. Chromium carbides are hard and wear-resistant and increase the edge-holding quality. Complex chromium–iron carbides slowly go into solution in austenite; therefore, a longer time at temperature is necessary to allow solution to take place before quenching is accomplished [5,6,14]. Chromium is the most important alloying element in steels. The addition of Cr in steels enhances the impurities, such as P, Sn, Sb, and As, segregating to grain boundaries and induces temper embrittlement.

NICKEL

Nickel (Ni) is a noncarbide-forming element in steels. As a result of the open g-phase field, Ni is an austenite-forming element [5,11,15]. Nickel raises hardenability. In combination with Ni,Cr and Mo, it produce greater hardenability, impact toughness, and fatigue resistance in steels [5,10,11,18]. Nickel dissolving in ferrite improves toughness, decreases FATT 50% (8C), even at the subzero temperatures [20]. Nickel raises the corrosion resistance of Cr–Ni austenitic stainless steels in nonoxidizing acid medium.

MOLYBDENUM

Molybdenum (Mo) is a pronounced carbide former. It dissolves slightly in cementite, while
molybdenum carbides will form when the Mo content in steel is high enough. Molybdenum
can induce secondary hardening during the tempering of quenched steels and improves the
creep strength of low-alloy steels at elevated temperatures. The addition of Mo produces fine- grained steels, increases hardenability, and improves fatigue strength. Alloy steels containing 0.20–0.40% Mo or V display a delayed temper embrittlement, but cannot eliminate it. Molybdenum increases corrosion resistance and is used to a great extent in high-alloy Cr ferritic stainless steels and with Cr–Ni austenitic stainless steels. High Mo contents reduce the stainless steel’s susceptibility to pitting [5,15]. Molybdenum has a very strong solid solution strengthening in austenitic alloys at elevated temperatures. Molybdenum is a very important alloying element for alloy steels.

TUNGSTEN

Tungsten (W) is a strong carbide former. The behavior of W is very similar to Mo in steels.
Tungsten slightly dissolves in cementite. As the content ofWincreases in alloy steels,Wforms
very hard, abrasion-resistant carbides, and can induce secondary hardening during the
tempering of quenched steels. It promotes hot strength and red-hardness and thus cutting
ability. It prevents grain growth at high temperature. W and Mo are the main alloying
elements in high-speed steels [5,13]. However, W and Mo impair scaling resistance.

VANADIUM

Vanadium (V) is a very strong carbide former. Very small amounts of V dissolve in cementite. It dissolves in austenite, strongly increasing hardenability, but the undissolved vanadium carbides decrease hardenability [5]. Vanadium is a grain refiner, and imparts strength and toughness. Fine vanadium carbides and nitrides give a strong dispersion hardening effect in microalloyed steels after controlled rolling and controlled cooling. Vanadium provides a very strong secondary hardening effect on tempering, therefore it raises hot-hardness and thus cutting ability in high-speed steels. Vanadium increases fatigue strength and improves notch sensitivity.
Vanadium increases wear resistance, edge-holding quality, and high-temperature strength.
It is therefore used mainly as an additional alloying element in high-speed, hot-forging, and
creep-resistant steels. It promotes the weldability of heat-treatable steels. The presence of V retards the rate of tempering embrittlement in Mo-bearing steels.

NIOBIUM AND TANTALUM

Niobium (Nb) and tantalum (Ta) are very strong carbide and nitride formers. Small amounts
of Nb can form fine nitrides or carbonitrides and refine the grains, therefore increasing the
yield strength of steels. Niobium is widely used in microalloying steels to obtain high strength and good toughness through controlled rolling and controlled cooling practices. A 0.03% Nb in austenite can increase the yield strength of medium-carbon steel by 150 MPa. Niobiumcontaining nonquenched and tempered steels, including microalloyed medium-carbon steels and low-carbon bainite (martensite) steels, offer a greatly improved combination of strength and toughness. Niobium is a stabilizer in Cr–Ni austenitic steels to eliminate intergranular corrosion.

TITANIUM

Titanium (Ti) is a very strong carbide and nitride former. The effects of Ti are similar to those of Nb and V, but titanium carbides and nitrides are more stable than those of Nb and V. It is widely used in austenitic stainless steels as a carbide former for stabilization to eliminate intergranular corrosion. By the addition of Ti, intermetallic compounds are formed in maraging steels, causing age hardening. Titanium increases creep rupture strength through formation of special nitrides and tends significantly to segregation and banding [15].
Ti, Nb, and V are effective grain inhibitors because their nitrides and carbides are quite
stable and difficult to dissolve in austenite. If Ti, Nb, and V dissolve in austenite, the
hardenability of alloy steels may increase strongly due to the presence of Mn and Cr in steels.
Mn and Cr decrease the stability of Ti-, Nb-, and V-carbides in steels [5].

RARE EARTH METALS

Rare earth metals (REMs) constitute the IIIB group of 17 elements in the periodic table. They are scandium(Sc) of the fourth period, yttrium(Y) of the fifth period, and the lanthanides of the sixth period, which include the elements, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm; Tu), ytterbium (Yb), and lutecium (or lutecium, Lu). Their chemical and physical properties are similar. They generally coexist and are difficult to separate in ore beneficiation and metal extraction so they are usually supplied as a mixture and used in various mixture states in metallurgical industries. REMs are strong deoxidizers and desulfurizers, and they also react with the low-melting elements, such as antimony (Sb), tin (Sn), arsenic (As), and phosphorus (P), forming high-melting compounds and preventing them from causing the red-shortness and temper embrittlement [21,22]. The effects of REM on shape control and modification of inclusions would improve transversal plasticity and toughness, hot ductility, fatigue strength, and machinability. REMs tend strongly to segregate at the grain boundaries and increase the hardenability of steels [21,23].

COBALT

Cobalt (Co) is a noncarbide former in steels. It decreases hardenability of carbon steels, but
by addition of Cr, it increases hardenability of Cr–Mo alloy steels. Cobalt raises the martensitic transformation temperature ofMs (8C) and decreases the amount of retained austenite in alloy steels. Cobalt promotes the precipitation hardening [5]. It inhibits grain growth at high temperature and significantly improves the retention of temper and high-temperature strength, resulting in an increase in tool life. The use of Co is generally restricted to high-speed steels, hot-forming tool steels, maraging steels, and creep-resistant and high-temperature materials [13,15].

COPPER

Copper (Cu) addition has a moderate tendency to segregate. Above 0.30% Cu can cause
precipitation hardening. It increases hardenability. If Cu is present in appreciable amounts,
it is detrimental to hot-working operations. It is detrimental to surface quality and exaggerates the surface defects inherent in resulfurized steels. However, Cu improves the atmospheric corrosion resistance (when in excess of 0.20%) and the tensile properties in alloy and low-alloy steels, and reportedly helps the adhesion of paint [6,14]. In austenitic stainless steels, a Cu content above 1% results in improved resistance to H2SO4 and HCl and stress corrosion [5,15].

BORON

Boron (B), in very small amounts (0.0005–0.0035%), has a starting effect on the hardenability of steels due to the strong tendency to segregate at grain boundaries. The segregation of B in steels is a nonequilibrium segregation. It also improves the hardenability of other alloying elements. It is used as a very economical substitute for some of the more expensive elements. The beneficial effects of B are only apparent with lower- and medium-carbon steels, with no real increase in hardenability above 0.6% C [14]. The weldability of boron-alloyed steels is another reason for their use. However, large amounts of B result in brittle, unworkable steels.

Z IRCONIUM

Zircon ium (Zr) is add ed to killed HSLA steel s to obtain impr ovement in inclus ion characteristics, particularly sulfide inclusions, where modifications of inclusion shape improve ductility in transverse bending. It increases the life of heat-conducting materials. It is also a strong carbide former and produces a contracted austenite phase field [5,15].

L EAD

Lea d (Pb) is sometime s added (in the range of 0.2–0.5 %) to carbon and alloy steels through mechanical dispersion during teeming to improve machinability.

T IN

Tin (Sn ) in relatively small amounts is harmful to steels. It has a very strong tendency to segregate at grain boundaries and induces temper embrittlement in alloy steels. It has a detrimental effect on the surface quality of continuous cast billets containing small amounts of Cu [24]. Small amounts of Sn and Cu also decrease the hot ductility of steels in the austenite þ ferrite region [25].

A NTIMONY

Antimony (Sb) has a strong tendency to segregate during the freezing pro cess, and has a
detrimental effect on the surface qua lity of continuous cast billets. It also has a very strong
tendency to segregate at grain boundaries and cause temper embrittlement in alloy steels.

C ALCIUM

Calcium (Ca) is a strong deoxidizer; silicocalcium is used usually in steelmaking. The combination of Ca, Al, and Si forms low-melting oxides in steelmaking, and improves machinability.

[Optimist]

Okay, folks, here's where the road forks. The next set of logical information will involve heat treating temps, techniques and the hardware and software required to do it. Alternatively, we can discuss the specific alloys in some depth. Which way do you want to go?

[bacpacker]

My vote would be for heat treating info. I'll take whichever info though. Some good stuff to learn here.

[Sniper-T]

x2 on the heat treat.

[izzyscout21]

OR........STart a separate thread on both........hummmmm.....hmmmm............

I have cast my vote

[Optimist]

Okay, heat treat this weekend, alloys next. If I'm in town tomorrow, I'll drop the next installment on ya. Otherwise, it will be Sunday. I gotta get some practice with the new digital camera so I can post pictures. It needs visual aids to do this right, durn it....

[Optimist]

Got wound up in some data entry chores for my kid brother. He's a CPA, and it's coming on tax season, so he has some things that come up that take an extra pair of hands. Myself, I believe we need an IRS/legislator season, opening date on April 16 each year, but that is a matter for another thread....

Anyhow, I need to get some pics of the salt pots, the forge, and some of the other impedimentia of the heat treating game ready for this next part of the thread. Gunfixr, how do you guys handle this at your shop?

[Optimist]

HEAT TREAT

With due attention to the matters we discussed in the earlier parts of this thread, we can now look at heat treating a piece of steel. There are several items here that are going to affect our methods, depending on the alloy we choose to work with, and the tools we have available.

The old technology uses coal or charcoal, and a blower to get the metal up to heat. This is a simple forge system, and you can make a pretty good one for rough work with a car wheel, a trash can, and a squirrel cage fan to furnish air blast. The car wheel will burn out if you don't line it with some kind of refractory (river bed clay was used in the old days, and it will work, but it is messy), but old car wheels are cheap, and five or six ought to furnish a goodly supply until you can build a better furnace. Since you are working out in the open air with your steel in a rig like this, you can't control the carbon content on the surface as well as you can with a closed oven. If the fire has more oxygen than is being consumed with your coal or charcoal, you are running too much air, and you are going to burn carbon out of the surface of your metal, which will make it softer when you quench it.

If your fire does not have enough oxygen to get a complete burn, you are going to put more carbon into the metal, which is not as bad a thing as pulling carbon out. A little farrther along, we will look at how to do this intentionally. It's called case or pack hardening, and it really makes for a hard surface with a tougher, softer inside alloy. The ideal fire for the forge is a neutral burn that uses all your fuel effectively, without pumping enough air to scale your steel.
Now I am going to say this. Any forge setup will be different. You can use the same size Subaru wheel as I did, pack it with red clay mud from the same part of the creek, use the same brand of squirrel cage blower I do, and 'try to hold your mouth just right', and you'll still get steel harder or softer than I will when we go to quenching it. Every forge is a law unto itself. I suspect that the primitive peoples of the world used this in part as a justification for a fire god....

At this point, I will leave managing the forge fire and move on to other things. The object of heat treating steel is to get it above the upper critical point for long enough to get the heat all the way through it (and there are big differences in heating time for a piece that is a a quarter of an inch thick and a piece that is an inch). Some folks try to judge this matter by color. For myself, I keep a magnet handy, and when the steel stops attracting the magnet, I am above critical, and it is time to do whatever I was planning to do to it before it cools down.

As a suggestion, it is better to plan your work so that you are working metal, or getting it ready to quench and temper. Trying to manage both in one heating is usually counterproductive, and a flawed heat treat usually leads to a tool that fails in use.

I'm going to give an example using a plain carbon steel, 1080, since that is one of the more readily adapted cutlery steels. Plow disks are made from this stuff, and they make up into pretty good tools of various sourts. Also, since 1080 falls at the eutectic point of the iron diagram that was shown in the first part of the thread (oh,but we didn't get the pictures into that thread, did we? Well, if you want the full version with pictures, you can e-mail me. PM me for details.) where the upper and lower critical tempeatures are the same. Presuming that you have already done your shaping, and are ready to quench, there are three steps to the business.

First, get the metal up to temperature. As soon as it stops attracting the magnet, you are ready to quench.

Second, get the metal into the quench with all due haste, and make sure you swish it around in there to keep from developing spots where the quench makes a bubble and doesn't cool. That spot will be soft if you do. Once you have it cooled, check it over for cracks. Steel changes size when the crystal structure changes, and the stresses can crack your workpiece in short order.

Third, if it isn't cracked, get it into an oven heated to your tempering temperature.if you are after a heat treat that is going to give uniform hardness throughout. Differential quenching is a nice technique for cutting tools, but that is a matter for considerably later in the game. When you can get one piece to the hardness you want, and do it several times running, then it is time to look at differential hardening.

Safe hardening begins with proper layout. You do not want to cut your steel to square corners. This gives stress a place to start a crack, and heat treating is very stressful on the metal. If you are cutting a straight line, drill a round hole where the cut is to end, and go from there. I keep some 1/4" carbide bits for just this sort of task if I am working on pre-hardened steel, or I make sure that I am dealing with annealed stock.

The Ozark method of annealing steel involves a brush fire, and making sure the steel cools down slowly. I like to make sure I have enough wood scrap to get a fire that will last for several hours, and I make sure the steel is in the heart of it. Set the fire, and collect your steel the next day after it has had a time to cool down. It will be soft enough to drill if you do. This even works well with one-inch thick truck springs, so it will work very well with lighter stock. An old gunsmith name of Bill Holmes published this years ago in his series of 'how to build a gun' books.

So let's go by a list.

First, get the steel annealed.

Second, get the steel cleaned off and mark out your outliine in chalk.

Third, center punch your corners. You will be drilling these.

Fourth, get a friend with a plasma cutter to cut between the drilled holes for you, or get a cutoff disk for the little angle head grinder (the shield won't fit, so you'll have to be careful). Make sure you have the work tied down well. I use a big vise, but you can do this with a hole and bolt through the workbench top if you have no other options.

Fifth, shape the workpiece. If you're making a 'hawk out of a plow disk, you'll have to flatten it, and you'll probably want to do this hot. There are several options if you don't have an anvil. One is to scrounge a frog plate from a nearby railroad. There are usually discards along the right-of-way, and one of these hammered into a stump with a brace of railway spikes (same source) makes a handy field anvil. Another option is to talk the local tumbstone maker out of a broken stone. The granite is hard stuff, and flat surfaces on one of these will make a good anvil surface that won't break unless you try to use it with cold steel instead of hot.

Sixth, get your materials together. You'll want a forge, a quench barrel, and an oven for getting the steel up to tempering heat. Since this can run up to 500 or more degrees, you may want to scrounge some potassium nitrate or other salt that will melt at the temperatures you are wanting to temper at, and a pot deep enough to hold the melted salt, and your workpiece. We'll go into how these get used next week.

[bacpacker]

I figure this is coming at some point can you discuss oil quench vs water quench? Great review tonight, thanks

[Optimist]

Based on alloys, Bakpacker. Oil is a slower quench, less shock to the steel, but not nearly as fast a quench as water or brine. Some of your alloy steels just won't put up with a water quench, they'll crack out. Some of the carbon steels don't harden worth diddly-squat with an oil quench, they stay soft. Some of the steels (A2 for a sample) don't need any quench at all. They take a high heat to get 'em past critical, but then they harden down just sitting there in still air. That help any?

[bacpacker]

Sure did. My past job I had to work with some machine shops to build repair parts for us. Some of the stuff was very material specific. I never did get a good handle on quenching the metal. This makes more sense now.

One of the parts we used was made from a 1065 grade steel (this stuff all came from Europe). Have you ever fooled with that grade steel? I never could find a good vendor here for it.

[Optimist]

It's a plain carbon steel with an oddball amount of carbon in it. Standards are 1018, 1040, 1060, 1076/1080 and 1095 cutlery steel. Myself, I like 1040 because it is weldable, which 1060 and up is finicky about. My guess would be that it is German or Scandinavian in origin, and carries an odd designation in their system. It would make good strikers or firing pins, with a proper heat treat, but I generally use 1060 for that.

[bacpacker]

We used some 1060 as well. We ran 2 16 position automated machines that built a ceramic head with a bunch of components installed and welded together. The Calibration blocks made from the 1065 were inserted into the ceramic and then had 2 contacts loaded into them. This held the contacts in place before they were welded on the outside of the ceramic to a tab for electrical connection.
The reason the 1065 was used, I'm pretty sure, was to absorb the wear from the ceramic. They were inserted and removed 30,000 per day. We got 3/4 months out of them before they would wear out. They were really hard as well and we did have some issues with the contact holder breaking.

[Optimist]

Bet it was Scandinavian steel, then, because that stuff has a mix of alloying agents in the ore that have to be mixed in expensively to get the same result elsewhere. And yes, you can get those carbon steels harder than an IRS agent's heart when dealing with a Republican....

[bacpacker]

Thanks for the info, that explains some of the problems we were having.

[Optimist]

Steel is fascinating stuff, and the more I monkey with it, the more interesting it gets. Them little bitty crystals do the durndest things....