What is stainless?
Stainless steel should contain not less than 10,5% chrome. This element is combined with free oxygen in the air and creates an invisible layer, which prevents corrosion. The surface strength of these stainless materials is further improved by including other alloys such as nickel and molybdenum with high amounts of chrome.
What does 18/10 mean in stainless steel?
The first ratio is the ratio of chrome in stainless, e.g. 18%. The second ratio is the ratio of nickel content. E.g. 10% nickel is indicated. The higher the values of ratios, the higher the corrosion strength. 18/10 “300” series indicates the stainless quality, while s18/0 indicates zero nickel content. “400” series demonstrates that it is stainless and the material does not have the same corrosion strength as “300” series, and can hold a magnet.
Can stainless materials be subject to corrosion?
Unlike carbon steel, there is not a red oxide layer that is formed in time on the surface of stainless steel. However, such formations can be observed on the stainless surface, which demonstrates that some iron particles contact with the surface and affect it. Thus, contact with metals which particularly contain aluminum, copper and iron should be avoided.
What are the differences between 304 and 316 stainless steel?
304 contains 18% chrome and 8% nickel, while 316 contain 16% chrome, 10% nickel and around 2% molybdenum. Addition of molybdenum helps to improve its corrosion strength against chlorides.
Can stainless steel hold a magnet?
Stainless steel “can hold” a magnet. Particularly 400 series of steel have magnetic sensitivity (ferritic characteristics) since they do not contain nickel. However, 300 series of steel can be magnetized when they undergo cold working, surface working (sandblasting) and other physical changes and stress.
What is passivation?
When the chrome ratio is more than 10,5%, the material is coated with a chrome-oxide layer which has oxygen impermeability and which is resistant to oxidation and corrosion. This “passive” layer is compensated with 10% nitric acid and 2% hydrofluoric acid solutions to improve its strength. This process is called passivation.
Can stainless steel be “hardened”?
Yes, 300 series of steel can be hardened by “working”; however, this working should always be included in the cold process, which is the process of shaping the material through application of physical strength. This shaping is based on the principle of variation between forms and dimensions. Tempering can sustain hardening after cold processing or it may not sustain it depending on the characteristics of the form. 400 series of steel have two different structures. The first one is “ferritic" (409, 430, 434. 439) which cannot be hardened via tempering. The second group is “martensitic” (403, 410, 416, 420, & 440 A,B,C), which can be hardened via thermal process.
What does “L” mean?
The letter “L” which can be seen next to the stainless quality unit (e.g. 304L) indicates that carbon content is not more than 0,03% (at normal levels it can be 0,08%, and or 0,15 maximum in some quality groups). This characteristic ensures that the high temperature in the welding area does not lead to formation of carbide on the material and thus 10,5% of chrome ratio is retained in the protective layer by showing a flexible physical characteristic.
How can scratched stainless material be fixed?
Stainless materials can be easily scratched, but elimination of scratches is not easy. They can be restored after certain professional applications; however, renewal of a refrigerator, dishwasher panel or a fittings component, which are replaceable, can be more economically effective. Scratches can be fixed by using a mob or Scotch Brite® pad, but these are not helpful in eliminating deep scratches.
What is thermal process “tempering”?
Stainless materials are usually commercialized after undergoing a thermal process. Here, there is a distinction between tempered and non-tempered materials. 300 series of stainless materials are hardened not with a thermal process but with cold working (like carbon steel). The tensions caused by cold working are normalized with the help of thermal processing.
Can stainless steel be used in extremely high or low temperatures?
Yes, stainless materials have excellent characteristics according to various temperature parameters at extreme points chosen according to the “quality.” Stainless materials can be used in the low ranges of temperatures for low liquid nitrogen (such as -196°C) and at high temperatures (such as 1000°C).
What do the AISI characteristics of stainless material mean?
AISI (American Iron and Steel Institute) is particularly used in definitions of 300 and 400 series. E.g. AISI 304. The institute has also prepared a manual for chemical compensations and mechanical values of stainless materials in each quality group. These explanations are not specifications; they are descriptions. Specifications have been published as a book by the ASTM (American Society for Testing and Materials).
Can stainless materials be processed?
Yes, in fact standard quality stainless steel has a very flexible structure. It is difficult to generate sensitive products with a proper form during processing; however many manufacturers have developed the 303 series with the same values which eliminates the flexibility to solve this problem.
What does 2B surface mean in stainless materials?
These are thermally processed, passivated, matt surfaces which are processed by cold drawing. They are the surfaces with the most comprehensive use. It has a gray, matt and slightly reflecting appearance.
Should stainless material be heated before welding?
No, stainless steel materials which are defined as austenitic (e.g. 300 series) do not require heating before welding process.
What does sandblasting mean?
It is the process of cleaning stainless material surface at high speed using materials consisting of very fine particles. Although sand is the most frequently used material, it has been replaced with other granular materials such as steel particles, etc. It is done under control due to the dangers in the process stage, and an air vacuum unit, protective equipment and appropriate ventilation is used.