In the market of stainless steel, there are two common stainless steel grade, that is SUS 201 and SUS 304 with the default information is stainless steel SUS 201 suction magnets mild and rusty, stainless steel SUS 304 does not suck magnets and non-rusty, Is the information correct?
With the default information is SUS 201 stainless steel is suction magnets mild and rusty, SUS 304 does not suck magnets and non-rusty, whether this information is correct or not?
To understand more about the two basic properties of stainless steel, we need to find out what the suction magnets and not rusty (ability against Oxidation and corrosion).
The first, we find out chemical composition of stainless steel SUS 201 and SUS 304
Chemical composition of stainless steel SUS 201 and SUS 304 (by weight) according to Japanese standard JIS
|SUS 201||≤ 0.15||≤ 1||5.5 – 7.5||≤ 0.06||≤ 0.03||16 – 18||3.5 – 5.5||–||≤ 0.25|
|SUS 304||≤ 0.08||≤ 1||≤ 2||≤ 0.045||≤ 0.03||18 – 20||8 – 10.5||–||–|
Ability corrosion (antirust) of stainless steel is mainly due to the percentage of Cr, Ni, Mo. When chromium (nickel) in steel alloy is exposed to air, a very thin layer of chromium oxide (nickel oxide) appears on the surface of the material, which is so thin that it cannot be seen with the naked eye. The metal surface is still shiny. However, they didn’t affected by the water and the air so it protect the steel layer below. Mo-lip-đen (Mo) is made stainless steel more resistant to corrosion in acidic environments.
Classification of stainless steel by phase organization
According to the phase organization (lattice type) stainless steel is divided into four categories:
- wo-phase stainless steels (duplex) are type 0.1-0.4% C and 13% Cr with two – phase organization is ferit (high Cr soluble) and bit Cr.
- Single phase ferrit stainless steels have a ferrite phase with 13% Cr and C <0.08% or with 0.1-0.2% C but with 17-25% Cr.
- Austenite Single phase stainless steel have high Cr (16-18% Cr) and high Ni (> 6% Ni). It is also named 18-8 (Cr> 18% and Ni> 8% ).
- Stainless steel persistence detail phase is a steel, that is included components and organization same as a Austenite but the Cr and Ni is low than but has been added Al, Cu, Mo and a Austenite is not stability.
|Stainless Steel with phase group||Magnetic (magnet attraction)||Corrosion|
|Persistence detail phase||Yes||Medium|
Capability of magnetism is due to the arrangement of stainless steel crystal (phase organization) decision.
Based on the chemical composition and classification of the steel group we see SUS 304 belong to the group of single phase stainless steel OSTEIT and SUS 201 belongs to the group of stainless steel single phase ferrit.
Thus, “stainless steel SUS 201 suction magnets mild and rusty, stainless steel SUS 304 does not suck magnets and non-rusty” is true but not enough because. These properties just right ingot steel out of the metallurgical plant is properly processed according to the process to achieve the desired steel organization. Stainless steel products to the consumer must go through many stages of processing such as rolling, torn, folding, grinding, welding … the thermal impact and mechanical impact in the process if not solved (usually handle by heat), SUS 304 stainless steel will be changed Ôstenit-phase lead to ability the stainless steel SUS 304 is magnetism so SUS 304 stainless steel is still suctioned but anti-corrosive stainless steel SUS 304 is still intact due to the process does not change the chemical composition of stainless steel SUS 304.
Cause stainless steel is suction magnets
The cause of stainless steel products is magnet attraction is due to the magnetic induced due to strong and concentrated deformation, Usually magnetic will arise at angular or inflection points. with uncoated rolls or stainless steel pipes will not encounter the above cases. With stainless steel bending to some degree will still be magnetized.
Magnetic arising in the process of cold processing: Rolling, Slitting, … At the processing sites, stainless steel is heavily impacted, the surface is deformed, along with the lattice at this location will change to be magnetic. This phenomenon will decrease over time.
With decoration rectangle pipe products, the pipe will be infected Magnetic mildly magnetism and concentrated in the corner because the corner is where the most damage and deformation, the thicker and smaller rectangle pipe, Magnetic is the greater.
With the round product due to no angle, the distribution force is evenly distributed on stainless steel so it is difficult to generate magnetism.
In the process of production is incurred magnetism from the normal, the austenitic current is not magnetic but after cold rolling, the surface deformation phase change to Magnetic should appear from the lightweight. Austenitic ducts are also susceptible to mild magnetic infections.
Conclusion: So Stainless Steel Products That use magnets lead to corner points, edge, bending Points is transformed, this is fully normal. This magnetism will be born and will fall in time, no effect the quality of stainless steel products.