General Hot Rolled Steel Information
What is an alloy?
An alloy is simply a mixture of metals melted together to form a new metal with characteristics distinct from those of the metals from which it is made.
What is a steel alloy?
A steel alloy is an alloy that is primarily iron, with small quantities of  other elements mixed in during the melting process which vary the properties of the iron to maximize a particular characteristic of the final alloy.
Some make the iron not rust (chromium and nickel), some make the iron possible to harden with heat treatment (carbon), Some make the iron easy to machine (lead), and so on. By varying the type and amount of the alloying element, even in minute quantities, a huge range of steels is produced, used for a myriad of industrial purposes.
Why does Hot Rolled Steel have a rough, blue-grey finish, while Cold Finished Steel has a smooth grey finish?
Hot Rolled Steels are just that - They are heated up red-hot and pushed through rollers that squeeze the metal, literally squishing it into a particular profile, depending on the shape of the rollers. The process takes a long time, and because the steel is so hot for so long in the open air of the steel mill, the surface of the metal has has a long time to oxidize, producing a thick, tough oxide scale with the characteristic blue grey finish of the final product.
Cold Finished Steels are just that - the final rolling is done when the steel is cold (room temperature), the whole operation bathed in oil, so the finished product is unoxidized, the grey of the actual steel, and as smooth as the rollers that do the processing. 
Why are there so many shapes available in Hot Rolled Steel and so few in Cold Finished Steel?
Steel is a very tough material when it is cold. However, if it is heated past a particular temperature (usually a red-heat) it immediately  turns plastic and can be bent, formed, hammered, and squeezed very easily. For example, few of us would be able to bend a bar of 1” thick steel at room temperature no matter how hard we tried, but if the middle of the bar were heated until it glowed a healthy cherry red color (about 1650 degress Fahrenheit), most of us would have very little trouble bending the bar back upon itself until both ends touched. And when it cooled it would regain it’s toughness and strength in that bent condition. 
This means that the intricate profiles apparent in, say, a Beam or Channel are formed fairly easily in the hot condition, but would be impossible to produce in the cold condition, and only flat, hex or round shapes that are relatively simple profiles are available in Cold Finished Steels.  
Can Hot Rolled Steels be chemically colored or patinated?
No. The chemical coloring of metals relies on the action of the chemicals with the metal itself. The only surface exposed on a Hot Rolled Steel product is the blue oxide scale, which is virtually inert. In order to color the metal, either the grey of the base metal must be exposed by grinding and then can be colored, or pigmented lacquers or paints must be used on the surface. Because the surface is rough, it takes paints and lacquers very well. 
Is it necessary to specify the alloy as well as the shape and size?
There are lots of steel alloys, and they are very important to the eventual success of the project, but are more an issue for the engineers and fabricators than the architect. They will be far more aware of which physical characteristics of each of the alloys will dictate the appropriate alloy for the job, and their choice of alloy will not affect the final aesthetic or finish since the Hot Rolled Steel alloys all have similar finish characteristics. What it all means is, that for aesthetic purposes all the alloys are interchangeable.
If this area is of interest, look up the ASTM specifications of all the alloys at http:
Some Things to be aware of:
1) Hot Rolled Steel products are NOT a consistent blueish color. This is particularly true with hot rolled sheet, over the surface of which the color varies dramatically, more blue at the edges, more grey in the center of the sheet.

2) The shapes available in hot rolled steels are availble in 12ft, 20ft, and sometimes 40ft lengths, so check with your supplier.

3) The blue scale finish on hot rolled products is incidental to the process of producing the product, and so, is not controlled in any way. This gives rise to fairly strong inconsistencies in the finish, particularly in sheet and plate.

4) Again, the blue scale on the metal prevents any chemical coloring on the surface ot the metal unless the scale is removed, exposing the bare metal beneath.

5) Most hot rolled products are very soft and bendable. This is really only noticable in the smaller bar sizes, but it can affect the final product if you are relying on the product to take a lot of strain.
If you are looking for a stiffer product, use Cold Finished Steel.

6) Hot rolled plate is a very rough product, and should be treated as such. 

7) All hot rolled products weld, bend, drill, and form very easily, and as well are the least expensive of the steels, giving rise to the least expensive finished product of any of the steels.

8) Nearly all metalwork involves welding or soldering the metal. How those welds are addressed is often the difference between a hack job and good craftsmanship. If hot rolled steel is welded, either the un-dressed welds are left as a part of the aesthetic, or they will have to be ground down by hand. Grinding and dressing the welds, of course, removes the blue scale at the weld zone while leaving the blue scale on the rest of the material. This aesthetic difference must be addressed at every weld. It is possible to return the color, but not the texture, of the blue scale at the ground weld joint where the metal has been exposed by heating up the joint red hot and allowing to cool.

9) A reminder - Pipe is specified by the inside diameter, Tubing is specified by the outside diameter. 

10) Hot rolled steel stock products mostly have a rounded appearance at the corners and edges and relatively inexact dimensions, whereas cold finished steels are much smoother and more precise.
General Stainless Steel Information
What is a Stainless Steel Alloy?
A Stainless Steel alloy is an alloy primarily of iron, with a relatively substantial content of chromium and nickel added during the alloying process. Metallurgists have produced a whole range of different stainless steel alloys, the most notable for architects being the variation of the chemistry of stainless steel alloy #316 to produce a higher corrosion-resistant alloy which is used in many marine environments.
Chromium and nickel impart the “stainless” aspect to an otherwise rustable steel (and are also responsible for the price of stainless steels being 10 times that of hot rolled and cold finished steels).
What Stainless Steel alloys are commonly available?
There are 24 or so commonly available stainless steel alloys you can get, though most of them are available only in plate form, and not really very relevant to architectural metalwork. 
The three that are regularly encountered are:
1) Alloy 303 - a free machining grade that cuts, drills and machines very well, but doesn't weld as nicely as 304. It is available in most shapes except sheet.
2) Alloy 304 - a nicely welding alloy that does not machine quite as nicely as 303, available more commonly in sheet and plate but is available in some bar forms as well.
3) Alloy 316 - a high corrosion resistant alloy that is used in environments of extreme weathering such as chemical environments or marine environments. This alloy also has been found by architects to polish to a brighter high polish than the other alloys. This alloy is not as common as the other two, but it is available in most of the same shapes as the other two but in fewer sizes.
Do the different alloys have a different color or aspect?
No. Aside from the quality of alloy 316 appearing to polish up brighter than the other alloys,  they are aesthetically interchangeable.  
Is it necessary to specify the alloy?
Only if there is some physical characteristic of the alloy that will have some bearing on the success of the project (such as corrosion resistance) is it necessary to specify the actual alloy. Generally, the fabricator will purchase the material on the basis of shape or form, and it will arrive with the most commonly available and least expensive alloy present locally. These alloys will for the most part be restricted to alloy 303 or alloy 304, and will be interchangeable, weld, machine, and finish interchangeably, and can be treated aesthetically as though they are the same alloy. It must be mentioned that alloy 316, which is a high-corrosion resistant alloy, is sometimes specified in architectural metal projects that are in more extreme environments, such as seaside houses, or chemical plants. This alloy is regularly produced in a somewhat restricted subset of shapes and sizes, so if you are designing in this alloy, contact a local supplier of stainless steels to get an idea of what would be available to your local fabricator before you steam ahead with specifying alot of material.
If there is any question of the integrity of the material in any way, the designs must be approved by an engineer, but you will be able to accept substitutions of alloys with confidence that the resulting product will be aesthetically acceptable.
Is this really the full set of shapes available in stainless steel? 
Well...There are thousands of proprietary stainless steel products made on a regular basis, from thousands of individual companies around the country - but this group of basic stock stainless steel products is where they all went to get the fundamental materials they made their own products from.     
Stainless Steel is regularly produced in only a restricted set of shapes and dimensions due to the nature of the material and the shapes and sizes in which people need it and will buy it (it's tough to work with, and expensive). 
What we are publishing on this website are the alloys, shapes, and size ranges that are the regularly produced stock metal products in each of the metal groups.  There are some stainless steel suppliers that stock different specialty stainless products for a particular company or sector of the industry, and you may run across them occasionally (for example, stainless steel "zee"s, or a different size of I beam, etc). While you should keep track of these suppliers, these products are not included here because they are not generally available coast to coast. 
"Stock metal products" are the bottom rung of the US metals industry - the angles, beams, channels, sheets, plates, tubing, coil, round, square, hex, and flat bars regularly produced in the USA from which most architectural and ornamental metalwork is made.
The shapes and sizes of the metals represented in this website represent the products at the bottom rung of the stock metal products carried on a regular basis in warehouses around the country, produced and sold for general use, without any specific request from any particular sector of the fabrication market.
Once you familiarize yourself with these materials and the nomenclature by which they are known, it will be far easier to wander into the vast array of specialty materials and proprietary products that are produced in metals
Stainless steel, hot rolled steel, cold finished steel, and aluminum are all fairly common, and most shapes are carried by most suppliers. Where you'll see a difference in suppliers stocks is in the numbers of different sizes of each shape that is stocked.
Some things to be aware of:
1) It Is Poor Quality Material
In general, stainless steel products are of fairly poor finish, inaccurate dimensions, soft, and difficult to work. Overall, it is a fairly low quality product. Some exceptions to this are the cold finished stainless steel shapes, such as round, square, and hex bar, and of course, stainless steel sheet is a consistently good quality product. Stainless steel sheet is even available in a pre-finished satin polished condition, with protective vinyl on the surface. 

2) High Polish
Stainless steel sheet and plate are both occasionally available in stock in the high polished condition, but not regularly, and so samples of these are not present in the Guide. You should, however, be aware that these do exist, and it could create a substantial savings if you were to locate already prefinished material.

3) Magnetic?
Stainless steel is not magnetic, nor does it rust. Even in the worst natural environments it will simply get dingy and grey, easily brightened by abrading the surface. However, in marine environments it is recommended that alloy 316 is specified as it has superior corrosion resistance, and is available in most shapes, albeit in a somewhat restricted set of dimensions.

4) Corrosion, and your fabricator's dirty abrasives
Occasionally a fabricated stainless steel piece will begin to have specks or streaks of rust that appear on the surface after a short time of weathering. Unless there are extraordinarily corrosive conditions present near the piece, this type of discoloration is most likely due to contamination of the surface of the stainless steel with particles of another metal such as steel, or any of the copper alloys.
This often happens if the fabricator sands or polishes the stainless steel piece using an abrasive belt, paper, or cloth that was previously used on another metal, and the particle residue in the used abrasive cloth or sandpaper gets embedded in the stainless steel as it is sanded.
It is imperative that only abrasives that are fresh, or have previously been used on stainless steel be used on new stainless steel work.

5) Temper 
This is the quality of metal that describes its ability to spring back after it is flexed - in effect, the stiffness. It doesn't have anything to do with how hard the metal is. Soft temper means that when it is bent, it stays bent, and it doesn't take much force to bend it. Hard temper means that when it is bent, it springs back flat, and it takes a lot of force to put a kink into it. There are several degrees of temper; Soft, 1/4 Hard, 1/2 Hard, 3/4 Hard, and Hard. All metals are subject to temper, and it is a quality of the product that is imparted at the mill. It has no impact on hardness, color, machinability or weldability. However, bending (kinking) and heating to a high temperature can remove the temper and soften the metal at that point. This is called annealing. 
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