Stainless steel (stainless steel) attached to the name of a British steel industry experts are Harry Brearley. When in 1913, he invented a special type of steel with high wear resistance, by reducing the carbon content down into components for chromium steel (0.24% to 12.8% C and Cr).
Then steel company Krupp in Germany continues to improve this steel by adding nickel to steel elements to improve corrosion resistance to acids and easy processing softer.
Based on this discovery that the two types of steel grade 400 and 2 300 was born just before World War First. 20 years of the 20th century, a British steel industry experts as Mr. W. H Hatfield continued research and development of the idea of stainless steel.
By combining the different ratio between nickel and chromium in the steel sectors, he has introduced a new type of stainless steel 18/8, who 8% Ni and 18% Cr, is the familiar steel grade 304 of today.
He is also the inventor of the 321 steel by adding titanium to steel composition ratio above 18/8.
Resistant to oxidation from the surrounding air temperature of stainless steel typically is due to the ratio of chromium present in the alloy (minimum of 13% and up to 26% in the case of work in harsh working environments).
Oxidized state of chromium oxide of chromium is commonly (III). When chromium alloy steel in contact with air is a very thin layer of chromium oxide III appeared on the surface of the material; This thin layer that can not be seen with the naked eye, which means that the metal surface is still shiny.
Stainless steel 201 , stainless steel 304 , stainless steel 430
When these objects made of stainless steel linked together with forces acting as bolts and rivets, the oxide layer may be flying their lost positions at which they are connected together. When disassembled them out, you can see the corrosion that position.
Nickel as well as lip-black modules and vanadium also features stainless oxidation similar but not widely used.
Besides chromium, nickel and lip-black modules and nitrogen oxidation also features similar rust. Nickel (Ni) is a common ingredient to enhance ductility, ductile, shaping properties of stainless steel.
Lip-black module (Mo) made of stainless steel with high corrosion resistance in acidic environments. Nitrogen (N) create stability for stainless steel at a temperature of minus (Cryogenic).
The participation of the various components of chromium, nickel, lip-black module, nitrogen leads to the different crystal structures generate different physical properties of stainless steel.
According to those presented above, we can see the marks of their 4xx steel martensite and ferrite stainless steel, the steel grade 2xx and 3xx of austenite stainless steel.
In theory, the original austenite steel group completely nonmagnetic (not magnet) but, according to the presentation above, austenite steel groups transformed sharply hard when cold plastic deformation due to the transition from austenite into deformation martensite (martensite phase which is magnetic).
So, in fact, used magnets to distinguish the stainless steel grade, especially to distinguish the marks 2xx and 3xx, you can say is impossible. To distinguish the most accurate method can only analyze the chemical composition (but more expensive) or based on the method of identification according grinding sparks (dependent on experience).
Distinguishing 430 stainless steel, 201 stainless steel and 304 stainless steel
* Steel group 4xx: because in the composition containing more Cr and Ni should hardly be formed when grinding rays and orange flowers with dark fire, end the shape of a flower blooming. Strongly magnetic than 2xx and 3xx marks
* Steel group 2xx: Partly Ni Mn should be replaced with the same thickness at the label if 3xx, breaking or bending when it feels harder. When grinding, beam bright orange, thick sparks, fire flowers much more wings (compared to 3xx)
* Steel group 3xx: When grinding, the beam has orange petals of little flames, sparks along with the flashing blip.