About Stainless Steel

Definition of stainless steel

Stainless steel usually refers to the steel owning ability to resist the corrosion of air, water, acid, alkali salt or other media. According to the different alloy composition, the emphasis is on rust and resistance Acidic. Although some steels have stainless properties, they are not necessarily acid-resistant, but acid-resistant steels usually have stainless properties.

Classification of stainless steel

l According to structure: Austenitic stainless steel, Martensitic stainless steel, Ferritic stainless steel, Duplex stainless steel;
According to the main chemical elements: Chromium stainless steel, Chromium nickel stainless steel, Chromium nickel molybdenum stainless steel, ultra-low carbon stainless steel. (Mainly used for the production of fasteners is Austenitic stainless steel, further more, it is also referred to Austenitic stainless  steel as usually stainless steel in people’s daily life.)

Steel grades and characteristics of Austenitic stainless steel

Non-magnetic under normal conditions, slightly magnetic after cold processing; At various temperatures, the austenitic structure can be maintained without phase change, so it cannot be used for heat treatment Harden it. However, cold processing can harden it and increase its strength. Austenitic stainless steel mainly has the following types of steel:

 

 

Since 2003, in response to the high price of stainless steel raw materials around the world, there has been a class of cheap and economical non-embroidered steel (containing nickel) commonly known as "low nickel" in the domestic market. Ni1.5 ~ 4.5 Austenitic 200 series stainless steel), the price is about 15% ~ 40% lower than 304 stainless steel. Corrosion and rust prevention ability is relatively low,Steinway products all are Austenitic 304 or 316 stainless steel products.


Remark
:

1) GB1220-92;

2) Taiyuan Steel steel wire rod technical conditions;

3) According to the business information of a private steel mill in China.

Chemical composition of Austenitic stainless steel

 

Remark:

1) If the nickel content is less than 8%, the minimum content of manganese must be 5%. 2) When the nickel content is greater than 8%, the minimum content of copper is not limited. 3) For example ,when chromium content is less than 17%, the minimum nickel content is 12%. 4) For Austenitic stainless steel with a maximum carbon content of 0.03%, the nitrogen content can reach up to 0.22%. 5) For larger diameter products, in order to achieve the specified mechanical properties, there may be a higher carbon content in the manufacturer's instruction manual, but it should not be exceeded for Austenitic steel 0.12%.

Mechanical properties of Austenitic steel bolts, screws and studs (Standard: ISO 3506,GB/T 3098.6)


Austenitic steel bolts and screws failure torque M1.6-M16(coarse thread) (standard: ISO 3506, GB/T 3098.6)


Mechanical properties of austenitic stainless steels at high temperatures and suitability at low temperatures 

(standard: ISO 3506, GB/T 3098.6)

If the bolt, screw or stud is calculated to be suitable, the matching nut will also meet the requirements. (The following data is indicative only)
1. Mechanical properties at high temperature
The ratio of the yield point σ S  at high temperature and the specified non-proportional elongation stress σ po2 to the value at room temperature (expressed in %) is shown in Table 1:

 

Table 1   σ S and σ po2 affected by temperature

   

2.    Suitability at low temperatures
The suitability of stainless steel bolts, screws and studs at low temperatures is shown in Table 2

 

Table 2   Suitability of stainless steel bolts, screws and studs at low temperatures (Austenitic steel only)


 

Magnetic properties of Austenitic stainless steel

(Standard: ISO 3506, GB/T 3098.6)

All Austenitic stainless steel fasteners, usually non-magnetic; after cold working, some magnetism may be obvious.
The characteristics of the ability of various materials to be magnetized also apply to stainless steel. Only in a vacuum is it possible to be completely non-magnetic. Measurement of the permeability of a material in a magnetic field is relative to the material in vacuum permeability μr. If μr is close to 1, the material has a low permeability.
For example:
A2: μr≈1.8 A4: μr≈1.015 A4L: μr≈1.005 F1: μr≈5
The strength of magnetism is closely related to the alloy composition of steel:
Magnetic formula: : MD30=551-462 x (C+N)-9.2 x Si-8.1 x Mn-13.7 x Cr-29 x (Ni+Cu)-18.5 x Mo The smaller the value, the smaller the magnetism.