Steelage Overseas Pvt. Ltd. - FAQ
(1) What is Stainless Steel?
Stainless steel is also known as inox steel or inox which contain 10.5 or 11% of chromium. Stainless steel is used in different industrial applications and home décor products because of its durability, corrosion resistance power, low maintenance and low cost. Stainless steel is 100% recyclable and can be melt and used for other applications.
The other alloy used to make stainless steel is nickel, nitrogen, molybdenum, titanium, niobium and other elements that used in various properties in machining, welding and forming.
(2) Stainless Steel History
Stainless steel was first researched by Leon Guillet of France in the year 1904. In the year 1908 Monnartz and Borchers of Germany found evidence of the presence of chromium (10.5%) level on corrosion resistance as well as the importance of low carbon content and role of molybdenum in chlorides for increasing corrosion resistance. English metallurgist Harry Brearley invents stainless steel in 1912 during his search for an alloy to protect cannon bores from erosion. In 1915 stainless steel was used in World War I in manufacture air craft valve.
(3) Why stainless steel is stainless?
It was accidently discover by English metallurgist Harry Brearly that adding chromium to low carbon steel gives it stain resistance. Adding other alloy like nickel, molybdenum, niobium and chromium enhance the corrosion resistance of stainless steel. In stainless steel the chromium combines with the oxygen that create a thin invisible layer of chrome that contain oxide which improve corrosion resistance power of stainless steel. If stainless steel is cut or scratched then other oxide will quickly form the layer on the surface and prevent corrosion.
(4) What are the advantages of using Stainless steel over wood and plastic?
The main advantage of using stainless steel instead of wood and plastic is its durability, corrosion resistance and low maintenance. Even after scratched or broken stainless steel it works for long time and create a thin layer of oxide quickly form over the surface and protect from corrosion. Other advantage of stainless steel is its long life, it said that stainless steel life expectancy is over 75 years and its recyclable.
These are the main advantages of using Stainless steel instead of wood and plastic.
(5) Difference between stainless steel and Galvanized steel.
Galvanized steel has a coating of zinc which seals the cut or broken area of steel. If stainless steel cut or broken the oxide layer form and recover the exposed surface that protect it from oxidative corrosion. Stainless steel contain atleast 10.5% to 12% chromium while Galvanized steel is a steel with a layer of zinc deposited on the surface this means the Galvanized steel have rust resistance power and have short life compare to stainless steel.
(6) Types of Stainless Steel.
Usually stainless steel divided into 5 different types – Ferritic, Austenitic, Martensitic, Duplex and Precipitation Hardening. But the main types of stainless steel are Ferritic, Austenitic and Martensitic.
These steels as its name describe have Ferritic (body centered cubic crystal). Ferritic steel are based on Chromium with less than 0.1% Carbon alloy. Because of its less ductile strength it can be used in limited applications where welding is not require. These steel have lack of toughness compare to austenitic steel. Also it is not hardenable by heat treatment.
These alloy contain Nickel, Manganese and Nitrogen and this is very common type of steel. The most popular austenitic steel type is 304, sometimes which is called T304 or simply 304. They cannot be hardened. Its corrosion resistance can be improved by adding Chromium, Molybdenum and Nitrogen. These steels are generally non magnetic but depends upon the compositions and the work hardening of the steel some magnetic effects exhibits in this steel.
These steels are very much similar to the ferritic steel but because of the high volume of Carbon up to 1% it can be hardened and tempered much lick carbon and other low alloy steels. Martensitic steels give great hardness to the steel but it also reduces the toughness of steel and makes it brittle.
(7) What are the elements of Stainless Steel?
Stainless steel is an iron alloy which contains atleast 10.5% to 12% of Chromium and other elements such as Nickel, Molybdenum, Titanium, Manganese, Sulphur, Niobium, Nitrogen and Silicon.
(8) What are the designation systems of Stainless Steel?
Stainless steel designation derived from different sources like “18/8” or “l8/10” for instance is a non-technical description often seen describing grade 304 or its equivalents.
(9) What is No. 4 Stainless Steel Finish?
- Widely used system is AISI three digit designations such as 304 or 316. These designations are sometimes being adopted with slight variations by Standards bodies. Many countries like Japan, Britain and Australia are also understood stainless steel grades in ASTM specifications which tend to be used, or atlest understood in almost every country. Extra letters designate alloy variants, such as 304L, 316LN or 310S.
- The UNS numbers abbreviation of unified numbering system is systematic scheme in which each metal is designated by a based of five digits to identify material composition. For example the AISI number Grade 304 is UNS S30400, 304L is S30403 and 304H is S30409 where S indicates Stainless Steel alloy.
- European designations originated as German Werkstoff Numbers for example 1.4301 for Grade 304 or DIN grade designations lex X5CrNi 189 for 304. Other European countries also use similar descriptive. These designations are now incorporated in “Euronorm” specification which replaced national specification throughout the European Union.
- Steel original manufacturer have been often give proprietary designations to their products. Standard designations are later added and being used because alloys are widely accepted and used but the still proprietary designations persist. For example “253 MA” which is an Avesta Sheffi trademark whose UNS equivalent is S30815. “SAF2304” is Sandvik trademark whose UNS equivalent is S32304.
This is one of the most common ground unidirectional finish which is obtained using 150 grit abrasive. This is general purpose finish and used widely in restaurant equipment and sink because it cant show scratch easily.
(10) What is No. 6 finish?
These finish produces using rotating cloth mops which are loaded with abrasive paste. This number 6 finish creates the “Satin Blend” steel look, even create non-directional texture effects.
(11) What is No. 7 finish?
This is a buffed finish which create mirror look of the steel. To achieve no. 7 finish of reflection from the stainless steel it is require to use finer quality abrasives and finishing it with Buffing compounds.
(12) What is Stainless Steel No. 8finish?
This finish create similar effects as of number 7 but the buffing process is being done using finer buffing compounds to create a true mirror type reflection with high clarity.
(13) Can stainless steel rust? Why? (I thought stainless did not rust!)
Stainless does not "rust" as you think of regular steel rusting with a red oxide on the surface that flakes off. If you see red rust it is probably due to some iron particles that have contaminated the surface of the stainless steel and it is these iron particles that are rusting. Look at the source of the rusting and see if you can remove it from the surface. If the iron is embedded in the surface, you can try a solution of 10% nitric and 2% hydrofluoric acid at room temperature or slightly heated. Wash area well with lots and lots of water after use. Commercially available "pickling paste" can also be used.
(14) What is the difference between 304 and 316 stainless steel?
304 contain 18% chromium and 8% nickel. 316 contain 16% chromium, 10% nickel and 2% molybdenum. The "moly" is added to help resist corrosion to chlorides (like sea water and de-icing salts)
(15) Is stainless steel magnetic?
There are several "types" of stainless steel. The 300 series (which contains nickel) is NOT magnetic. The 400 series (which just contains chromium and no nickel) ARE magnetic.
(16) What is "passivation"?
When the amount of chromium (in an iron matrix) exceeds 10 ½%, a complex chrome oxide forms instantaneously that prevents the further diffusion of oxygen into the surface and results in the "passive" nature of stainless steel and its resistance to oxidation (or corrosion). A chemical "dip" into 10% nitric acid plus 2% hydrofluoric acid bath will enhance the development of this "passive" oxide.
(17) What are the Conditions which Favour Use of Stainless Steel?
(18) Can stainless steel be "welded"?
- Corrosive Environments
- Very low (cryogenic) temperatures — prevents brittleness
- High temperatures — prevents scale maintains strength
- High strength vs mass
- Hygienic conditions required — easy cleanability
- Aesthetic appearance — no rust, thus no paint necessary
- No contamination — prevents catalytic reactions
- Discharge slideability from hoppers
- Wet abrasion resistance
- Non-magnetic properties of austenitic grades
Key Considerations in Working Stainless Steels
- Know the material: this improves decision making, avoids problems and saves costs.
- Know the grade of material: Connect material selection is vital risk taking is costly.
- Know the design: Good design ensures savings for fabricator and user.
- Know surface finishes: Good finishes perform wall look good and promote sales.
- Know your supplier
- Apply good housekeeping: Good housekeeping saves rectification costs.
- Apply accurate identification: Lost identity can prove costly.
- Apply production planning: Planning saves costs and promotes quality.
YES. Stainless steel is easily welded, but the welding procedure is different than that used with carbon steel. The "filler" rod or electrode must be stainless steel
(19) Can Stainless steel be "hardened"?
YES. The 300 series stainless steel can be "hardened" BUT only by "work hardening." That is by cold working the material, either by cold rolling down to lighter and lighter gauges, or by "drawing" through a die or other size altering operation. "Annealing" stainless steel will REMOVE the work hardening effect. YES and NO. The 400 series have two different stainless steel structures. One is called "ferritic" (409, 430, 434. 439) which cannot be hardened by heat treatment. The other is called "martensitic" (403, 410, 416, 420, & 440 A,B,C) which CAN be hardened by heat treatment.
(20) What does the "L" designation mean?
The use of the letter L after the grade number, i.e., 304L, means that the carbon content is restricted to a MAXIMUM of 0.03% (normal levels are 0.08% max. and in some grades can be as high as 0.15% max.). This lower level of carbon is usually used where "welding" will be performed. The lower level of carbon helps to prevent the chromium from being depleted (by forming chrome carbides at the weld site) and therefore allow it to remain over 10 ½% so it can form the "passive" oxide layer that gives stainless its corrosion resistance.
(21) What is the recycle content of stainless steel?
Stainless steel can be recycled 100%. That is all stainless steel can be re-melted to made a new stainless steel. The typical amount of recycled stainless steel "scrap" that is used to make new stainless steel is between 65 & 80%.
(22) The stainless steel on my refrigerator door, dishwasher, and/or countertop is scratched. How can I remove the scratches?
Scratches are difficult to remove. Most kitchen appliances, sinks, and counters have a polished finish with short directional polishing lines. Restoring a polished finish to its original appearance requires a professional such as a company that specializes in fabricating or polishing stainless steel. If the refrigerator or dishwasher door panel is replaceable, purchasing a new panel is normally more cost effective than professional refinishing. The homeowner may want to consider obtaining replacement panels with angel hair, distressed, swirl, or embossed finish. These finishes help to hide light scratching and can be obtained from companies that specialize in stainless steel finishes. Counters and appliance doors that are not easily removable must be refinished in place. When the counter is refinished, it may have long rather than short polishing lines. If a slightly different finish is acceptable and cost is a consideration, a homeowner can refinish the counter or appliance using a non-metallic abrasive pad such as a Scotch Brite® pad. This can be done by rubbing the surface with the pad using long uniform strokes in the same direction as the current polishing lines. This will not eliminate deep scratches. A professional may offer this finish as a less expensive option. The resulting finish is normally referred to as a hairline or long grain finish. Some appliance companies are starting to offer this finish.
(23) What is the "annealed" condition?
Stainless steel is usually sold in the "annealed" condition. It just means that the material is in the "soft" or annealed condition. The 300 series of stainless steels can not be hardened by heat treatment (like carbon steels) but can be hardened by cold working. This cold work can be eliminated by a heating treatment (annealing) that will restore the original soft condition.
(24) What does the term "CRES" mean?
Answer: CRES is something used to designate stainless steel. It stands for Corrosion Resistant steel. It does not necessarily mean that the steel is in fact stainless steel as there are other materials that are corrosion resistant but not stainless steel.
(25) Can stainless steel be used at very low and very high temperatures?
Answer: Yes. Stainless steel has excellent properties at both extremes of the temperature scale. Stainless steel can be used down to liquid nitrogen temperatures and up to about 1800° F.
(26) What are AISI Specifications for stainless steel?
The AISI (American Iron and Steel Institute) was the originator of the 300 and 400 series numbering system (i.e., Type 304 stainless steel). They also published a Stainless Steel products manual that listed these designations and the chemical analysis as well as most mechanical and physical properties of each individual grade. They are NOT specifications as such, just definitions of the individual grades. Most specifications that are used with stainless steel are from the ASTM (American Society for Testing Material). The Iron & Steel Society took over from the AISI in publishing the Stainless Steel Products Manual a number of years ago.
(27) Can stainless steel be machined?
Yes. However the standard grades of stainless steel are usually "gummy" and will not produce a clean chip when machined or turned. To solve this problem, many companies produce "free-machining" grades of stainless where they add a "chip-breaker" to the matrix. Grade 303 is the free-machining equivalent to grade 304.
(28) I have a stainless steel refrigerator and since some stainless steels are non-magnetic I cannot attach items to the surface magnetically. What is the best way to attach something to stainless steel?
We suggest “Remount Spray Adhesive” for temporary, light weight and repositional bonding. For stronger or more permanent bonding Super 77 (from 3M) is a good suggestion. Removal using 3M Citrus Base Adhesive Remover should easily take care of any residual adhesive.
(29) What is the difference between the “annealed” condition and the “dead soft” condition for stainless steel?
The usual “condition” that stainless steel products (sheets, plates, bars, wire etc.) are supplied to is the “annealed” condition. That means that the last operation is to heat the material up a temperature where the residual stresses of manufacturing can be relieved, and the material will be in the “soft” condition. Most flat rolled products however are made in coils and when a “sheet” is cut from the coil it is usually “flattened” which does add some small amount of stress to the material. Bar products are usually straightened and that adds some small amount of stress as well. The term “dead soft” usually refers to a product where the even this small amount of stress is removed, but as a practical matter, this condition is not readily available.
(30) Do you need to “preheat” stainless steel before welding?
NO. Austenitic stainless steel (the 300 series) do not need to be preheated before welding.
(31) What is the inch dimension for the various “gauges” that are sometime used?
The U.S. Standard Gauges for stainless steel have the following nominal thickness in inches: