Stainless Steel Hardware

General Stainless Steel information

Stainless Steel CableStainless Steel Stainless Steel turnbuckle

1. What is "Stainless Steel"? 
Originally, stainless steel was developed for cutlery; its use was later expanded to cover a wide range of steel types and grades for the industrial applications which were looking for the corrosion or oxidation resistance for a specific application or environment.
Inox or Stainless steel, is essentially a low carbon steel which contains chromium at 10% or more by weight. It is this addition of chromium that gives the steel its unique stainless, corrosion-resisting properties, the most important stainless steel feature. The corrosion resistance and other useful properties of the steel such as you to formability and strength, to name just two, are enhanced by increased content and the addition of other elements, like molybdenum, nickel and/or nitrogen.

2. The advantages of stainless steel
Stainless steel is a corrosion-resistant alloy and therefore has a long useful life. For decades, over 90% of stainless steel products have been produced from recycled scrap metal, so saying that the stainless steel industry depends on recycling
is not wrong. Although stainless steel may cost a lot initially, comparing it to the length of its useful life and its other properties, it is more cost-effective than the other alternatives. For example, it is more corrosion-resistant than carbon steel or it is stronger than polymer products, like GRP. Stainless steel also offers other useful properties, depending on its type.

Stainless steel can also be used in various industries; even for food and beverage related industries or surgical instruments. There are no proven health risks from using the normal stainless steel. Even the possible risks from alloy elements like nickel and chromium have been reviewed.

3. Stainless Steel Types
Stainless steel is an outstanding material with its high resistance to oxidation (rust) and corrosion in many different environments. It is, however, important to select the correct type and grade for the particular application because there are many different types and each is made for different applications.

Just adding or reducing some elements can dramatically change the characteristics of the stainless steel. For instance, adding nickel can stabilize the austenitic structure of iron. Adding where as adding carbon will make it harder and stronger. If the nickel is replaced by manganese the austenitic structure will be same but it will be cheaper.

Nickel Molybdenum Chromium
NICKEL MOLYBDENUM CHROMIUM


Stainless steels are commonly divided into five groups:

There are more than 60 grades of stainless steel, however they can be dividedinto 5 groups. Each is identified by the alloying elements which affect their
microstructure.

1. Austenitic (non-magnetic)
Most of the stainless steel products that require the greater resistance to chloride pitting and crevice corrosion, for example flatware, are in this group. The three significant components are carbon, chromium and nickel (or manganese). However, the high molybdenum and nitrogen content, together with the higher nickel content will result in a "superaustenitic" stainless steel for higher effective corrosion resistance, but the higher alloy content of superaustenitic means a higher
cost as well. So, in this case, the duplex steels could be replaced because of the similar performance.

2. Ferritic stainless steel (magnetic)
Chromium is the main alloying component for this stainless steel type. There is low carbon content and very little nickel.
It is the lowest cost stainless steel.

3. Martensitic stainless steel
The compositions are chromium, molybdenum and carbon. There is no nickel.Martensitic stainless steel is not corrosion resistant but it is extremely strong and hard; the drawback being that the carbon which makes it harder also makes it more brittle.

4. Precipitation-hardening martensitic stainless steel
The most common formula (14/4PH) contains chromium and nickel. It is corrosion resistant and also very strong, resisting impacts better than the ordinary martensitic grade.

5. Duplex (ferritic-austenitic)
This is the combination of austenitic and ferritic, making it strong and corrosion resistant. It can be used in a thinner section to save weight and cost.

4. How can stainless steel be corrosion resistant?

"Stainless steel" originated from ‘steel that does not stain, rust or corrode.’ "Corrosion often occurs with carbon steel but not stainless steel in a passive state." If the surface of carbon steel begins to stain it will corrode but this will not occur with 
stainless steel in a passive state. The key to this phenomenon is "Chromium" which must be present at least 10.5% (by weight).
The chromium content of the steel allows the formation of a rough, invisible, adhesive, corrosion-resisting chromium oxide film on the steel surface. If damaged mechanically or chemically, this film is self-healing if there is enough oxygen.

5. Magnetic permeability in stainless steel

Magnetic permeability is the ability of a material to carry magnetism, indicated by the degree of attraction to a magnet. All types of stainless steel, except those in the austenitic group, are attracted to a magnet.

The magnetic property of stainless steel is dependent on the elements added to the alloy. Nickel, which is used to strengthen the oxide layer for corrosive resistance, is also the main factor which modifies the physical structure of stainless steel to be non-magnetic; the more nickel added to the alloy the more the stainless steel becomes non-magnetic.
In the annealed condition, all austenitic grades of stainless steel have a very low magnetic permeability, or almost none. However, in the strong cold working, Grade 304 stainless steel is more magnetic whilst grades 310 and 316 are non-magnetic. 
However, austenitic (300 series) stainless steel, which could be made to be magnetic in the cold work state, could be returned to a non-magnetic again by stress relieving achieved by heating to approximately 700-800 íC.

However, if it is the stainless steel which sensitizes to carbide precipitation, 1,000 - 1,150 íC of full solution treatment can also remove the magnetic response without the danger of lowering the corrosive resistance due to carbides. Consequently, if the magnetic permeability is important in the desired application this should be noted before purchase.

6. Basic rules for stainless steel selection

The first basic rule for choosing the right stainless steel is selecting the grade with the lowest cost but the highest corrosion resistance. The others criteria such as strength or hardness come second.

Furthermore, the selection principle may depend on the three things:

1. Selecting by the alloying component for non-corrosion:
As mentioned above, the most important property of stainless steel is corrosion resistance, therefore the proportion of chromium should be the first thing to consider as the principal ingredient of stainless steel to resist corrosion is "Chromium" (Cr) giving the surface a passive, self-repairing layer. So, increasing the chromium means enhancing the corrosion- and oxidati on-resistance effectiveness. For example, Martensitic 431 at 15% Cr is expected to have a better corrosion resistance than 12% Cr 420 etc.

For corrosion and Oxidation Resistance, 11% minimum chromium is the standard grade for the market. However, adding other alloying elements could enhance the corrosion resistance too, for example, the high molybdenum and nitrogen stainless steel would eliminate pitting and crevice corrosion. Copper is used to build up the corrosion resistance in dangerous environments such as moderate sulphuric acid. The austenitic 904L is the example type for the grade including copper.

2. Selecting by mechanical and physical properties:

The different types of stainless steel have different properties. Not only can adding an alloying component make stainless steel mechanically strong, but the different atomic structures are also a significant factor.

Martensitic stainless steel and precipitation hardening stainless steel can be strengthened by heat treatment but they are used in different situations.

Ferritic stainless steel has always been popular for automotive exhaust systems. It has useful mechanical properties at ambient temperatures, but it has limited ductility. In addition, the ferritic type of stainless steel is not suitable for temperatures which are higher than 600 íC

Austenitic stainless steel has distinct properties. Mechanically, it has more ductility and impact strength at very low temperatures. Physical properties include: it is non-magnetic and has low thermal conductivity.

Duplex stainless steel Due to fact that this stainless steel type is a mix of austenite and ferrite stainless steel, its properties are derived from both those types; however, fundamentally and mechanically it is stronger than either ferrite or austenite.

3. Selecting for forming:

Although stainless steel is formable and machinable, each individual type has different limitations in different conditions. One should therefore select the appropriate type for the appropriate application.

For example, the austenitic type is the best choice for flat product forming such as pressing, drawing, stretch forming and spinning. This stainless steel type is also very ductile. However, the formability of the austenitic is on the same level as nickel. Martensitic is not formable, but is used for cutting blades.

However, for the extreme effectiveness for this selection rule, the control techniques of feed and speed to undercut work hardening layers with the good lubrication and cooling systems should be sufficient as well.

7. The environment types that effect to the selection of stainless steel for external

Membrane Stainless Steel Marine Product
Even though not the most important points, temperature and humidity must be taken into consideration when selecting a stainless steel: after all, it is its corrosion resistance that is important so the conditions of the site must be taken into
account. 
Different places have different environments that affect Stainless Steel differently.pollution, but there are still the exhaust fumes from road traffic and winter road salt spray.

The site-types may be classified briefly into four groups as below:

The Rural site is the unpolluted area, inland and away from an industrial atmospheres or discharges.
The Urban site is the residential, commercial or light industrial area withnon-aggressive airborne 
The Industrial site is typified by air pollution such as sulphur dioxide or gases released from chemical process plants or industry, which can form potentially dangerous acids
The Marine site is an area where wind, sea spray or mist are prevalent. These contain chlorides which can also concentrate on the surface by evaporation.

8. Why Maintenance is Necessary for Stainless Steel?

The attractive and hygienic surface appearance of stainless steel products cannot be regarded as completely maintenance-free. In addition, to achieve maximum corrosion resistance, the surface of the stainless steel must be kept clean. Keeping its good looks and its long life depends on how regularly and how well it is cleaned.

Surface contamination and the formation of deposits are critical factors in reducing its beautiful life. These contaminants may be minute particles of iron or rust from other non-stainless steels used in nearby construction and never removed. Industrial, commercial and even domestic and naturally occurring atmospheric conditions can result in deposits which can be quite corrosive, for example salt deposits from he sea.

Working environments can also create more aggressive conditions, such as the warm, high humidity above indoor swimming pools. These environments can increase the speed of corrosion and therefore require more frequentmaintenance.
Just routine, simple, gentle cleaning will reward the owner with a product which retains its properties and appearance for years to come. The frequency and cost of cleaning materials for stainless steel is lower than for many other materials so this will often out-weigh higher acquisition costs.

9. Stainless Steel Maintenance Program

The common rule for keeping stainless steel in its original, pristine condition is: "clean it when it is dirty". For regular cleaning, just use ordinary soap, or a mild, diluted detergent, or diluted ammonia in warm water; apply with a soft cloth or synthetic sponge. Rinse well, dry with a soft cloth or drip dry. Occasionally the use of a mild household cleaner, a fine synthetic scourer or a brush with nylon bristles may be used. 
Regular cleaning every day for several days will often remove heavy soiling and staining which has occurred will become less noticeable or may even completely disappear.

Suggestions
• Routine, simple and gentle cleaning 
• Use only the above mentioned cleaning products 
• Employ repeated routine cleaning rather than an aggressive
single one

Suggest not to do:
• Use coarse abrasive powders
• Use metallic scourers
• Use "Silver Cleaners"
• Subject stainless steel to "abnormal" use