When we talk about the ‘specifications of stainless steel’, we are referring to the family and the grade in which a particular metal is part of.
Just like steel, stainless steel is an alloy which means that it consists of different materials. When steel has a chromium content of more than 10.5% it is considered to be ‘stainless’.
It is this chromium that gives stainless steel its characteristic ‘stainless’ finish. This is because when chromium is combined with oxygen it forms a thin, sealed, fixed-adhering, chromic-oxide layer – the so-called passive layer – which in turn gives stainless steel its distinctive corrosion resistance.
The specifications of stainless steel lead to the many useful properties and benefits of this popular metal that in turn make it such a versatile and popular metal in many different industries.
Let’s look a bit more closely at the specifications of stainless steel and what they mean.
Stainless Steel Families
To understand the specifications of stainless steel, you need to first look at the families and grades of stainless steel.
While all stainless steel has a chromium content of more than 10.5%, there are numerous combinations of various metals marketed as stainless steel today.
These various stainless steels do share some characteristics, so understanding the different types available is an important step in choosing the right metal for your project.
Stainless steel falls into four distinct families:
- Austenitic Stainless Steel
- Ferritic Stainless Steel
- Duplex Stainless Steel
- Martensitic & Precipitation Hardening Stainless Steel
We give more information on these ‘families’ of stainless steel here.
Stainless steel grades
Within the ‘families’ mentioned above, there are various grades that help to define specific properties of the alloy such as toughness, magnetism, corrosion resistance and alloy composition. There are different ways of identifying these grades and several different systems around the world.
To receive a specific grade designation, an alloy must adhere to a strict set of requirements set down by the organisation that is maintaining that standard.
One of the ‘oldest’ ways of identifying a grade of stainless steel was conceptualised by the Society of Automotive Engineers (SAE). Theirs is a three-digit identifier, and an example of this is 304 stainless steel.
If we refer back to the main ‘families’ of stainless steel, then the following is true of the SAE Grades:
- Austenitic is one of the most widely used and popular type of stainless steel and the grades within this group include 304 (1.4301) and 316 (1.4404)
- The common stainless steel grades found within the ferritic family include 409 (1.4512) and 430 (1.4016).
- The martensitic popular grades are 410 and 420 (1.4021)
Some of the other grading systems are as follows:
- The American Society for Testing and Materials (ASTM) Unified Number System (UNS) – a six-character identifier
- American Iron and Steel Institute (AISI) Steel grades – a four-digit number identifier
- British Standards (BS)
- International Organization for Standardization (ISO)
- Japanese Industrial Standards (JIS)
- European Standard (EN)
- German Standard (DIN)
- Chinese Standard (GB)
Example of the specifications of stainless steel
Let’s look closer at an example of a stainless steel. Here at Special Metric Materials, we have a large stock of 304 Stainless steel and this metal, by the SAE standard must contain:
- 18% to 20% Chromium.
- 8% to 10.5% Nickel.
- 0.08% Carbon.
- 2% Manganese.
- 0.75% Silicon.
- 0.045% Phosphorus.
- 0.03% Sulfur.
- 0.1% Nitrogen.
This particular metal could also be graded via the following identifiers:
- EN number: 1.4305
- EN name: X8CrNiN18-9
- UNS: S30400
- DIN: X5CrNi18-9, X5CrNi18-10, X5CrNi19-9
- BS: 304S 15, 304S 16, 304S 18, 304S 25, En58E
- JIS: SUS 304, SUS 304-CSP
Due to the vast number of standards and grading systems, it can sometimes be difficult to obtain much information about a certain alloy’s unique composition from its grade.
If you’re not sure which grade of steel you need, or what the composition requirements are, the following websites can be very helpful:
- SAE and UNS Chemical Compositions & Mechanical Properties
- BS EN Stainless Steel Compositions
- MatWeb Metall Alloy UNS Number Search
Special Metric Materials products
Two of the most popular product lines we have in stock at Special Metric Materials are ISO Stainless steel Tube and Tru-Bore® Metric Tube. Read on to find out more about the specifications of these metals.
ISO Stainless Steel Tube: ISO stainless steel tube is an essential piping product utilised across many different industries, including the renewable energy sector and building services.
- Special Metric Materials stocks and supplies ISO stainless steel tube for Pressure Purposes, produced in accordance with EN 10217-7, with a weld factor z = 1.0. We can supply ISO stainless steel tube, pickled, in 6m random lengths, with Plain Ends (PE).
- Tolerances of our ISO stainless steel tube are in accordance with EN ISO 1127. The design pressures are calculated in bar according to: EN 13480, EN 10217-7 or EN 10296-2, T = 20 °C, actual weld factor z.
- Special Metric Materials can supply ISO stainless steel tube in the following Grades: 304L (1.4307), 316L (1.4404) & 316L High Moly (1.4432).
TRU-BORE® Metric Tube: Tru-Bore® Metric Tube (Tru-Bore® is a registered trademark of OSTP) is a type of piping used in many different types of industries, from pulp and paper, to chemical, petrochemical, water & wastewater treatment.
- Special Metric Materials stocks and supplies stainless steel Tru-Bore® metric tube for Pressure Purposes, produced in accordance with EN 10217-7, with a weld factor z = 1.0.
- We can supply welded tubes, pickled, in 6m random lengths, with Plain Ends (PE). Tolerances of our stainless steel Tru-Bore® metric tube are in accordance with EN ISO 1127.
- The design pressures are calculated in bar according to: EN 13480, EN 10217-7 or EN 10296-2, T = 20 °C, actual weld factor z.
- Special Metric Materials can supply stainless steel Tru-Bore® metric welded tube in the following Grades: 304L (1.4307), 316L (1.4404) & 316L High Moly (1.4432).
Speak to the Special Metric Materials team today to find out more about the specifications of stainless steel and to get help with your next project.
