How to tell the quality of stainless steel can be an uphill task without the right information. It is even cumbersome when you are importing stainless steel sheets, plates, rods, tubes, or pipes in bulk for your fabrication needs.
The best part – this article explores various you can use to determine stainless steel quality.
Method 1: Stainless Steel Visual Inspection
Stainless Steel Sheet Color
Although this process is not accurate, it can help you identify stainless steel.
In most cases, stainless steel is inherently silver or silver-grey. However, this may vary depending on the stainless steel surface finishing.
Usually, depending on the stainless steel surface finish, the color may vary slightly. Again, it makes it difficult to conclusively determine the stainless steel quality.
|Key Alloying Elements Determining Color Variation
|Possible Color Effects
|Chrome-nickel stainless steel after pickling
|Chrome stainless steel after pickling
|Chrome-nitrogen-manganese stainless steel after pickling
As you can see, there is a slight variation in the stainless steel color.
Furthermore, if you are importing stainless steel material from a reputable manufacturer, they will have labels. These labels indicate the stainless steel grade.
Again, through these labels, you can determine the best quality of stainless steel for your application.
In short – visually inspecting stainless sleet will give you a “rough” idea of whether the metal is good quality or not. It is not accurate.
Using Magnet to Check Stainless Steel Quality
Whether the magnetism of stainless steel determines the quality or not is also an interesting factor to evaluate. Remember, stainless steel composition has both magnetic and non-magnetic elements.
Besides, stainless steel exists as:
- Austenitic stainless steel
- Ferritic stainless steel
- Martensitic stainless steel
- Duplex stainless steel
Even as you try to distinguish stainless steel qualities of grades using magnets, the process has some drawbacks. Therefore, making accurate deductions on the qualities of stainless steel is virtually impossible.
Still, here are critical factors to note when using magnetism to determine the quality of stainless steel:
- Ferritic stainless steels are magnetic
- Martensitic stainless steels are magnetic
- Duplex stainless steels are magnetic
- Austenitic stainless steels are generally non-magnetic
However, there is a limit when dealing with austenitic stainless steel. The non-magnetic property only holds when they are in a softened state.
With this knowledge, you can separate softened austenitic SS from other stainless steel grades. But remember, you will not know the chemical composition of each austenitic stainless steel.
Additionally, cold-working austenitic SS will make them partially magnetic. Of course, partial ferromagnetism will be unevenly distributed. A similar phenomenon is common through special thermal treatment.
Verdict: With magnetism, you can only confirm is stainless steel is austenitic or not.
Testing Stainless Steel Quality using Mechanical Methods
Stainless Steel Mechanical Properties
There are certain mechanical techniques you can use to examine the qualities of stainless steel. Theoretically, each metal has specific mechanical properties such as tensile strength, hardness, elongation, or modulus of elasticity.
So at this point, you will conduct some tests. Through these tests, you determine whether the stainless steel quality meets the recommended mechanical properties.
Let’s look at a few tests:
- Hardness – austenitic stainless steel has>165 Brinell while martensitic SS has> 280 Brinell, and Ferritic varies from 180 to 250 Brinell. Remember, these values are applicable after heating stainless steel grade to 1800oF followed by water quenching.
- Heating martensitic stainless less makes the grades more scratch resistant. However, this test does not confirm whether it is a low or high-carbon steel.
- Tensile test – it is a destructive you will use to determine the mechanical properties of stainless steel
Stainless Steel Dimensional Inspection
Dimension is an integral quality aspect when analyzing stainless steel. For example, for sheet metal sheets, you can check the thickness, length, and width.
The best quality of stainless steel should have uniform dimensions with acceptable tolerances. You can coordinate measuring machines (CMM) or other tools like vernier calipers.
Stainless Steel Gauge
Check Qualities Of Stainless Steel through Chemical Reaction
Before you start any chemical reaction, you should ensure the surface is free from:
You can perform several tests, whose outcome can detect stainless steel. However, they may not conclusively give specific quality.
|Chemical Reaction Testing Stainless Steel Quality
|Observation on Determining Quality of Stainless Steel and Grade (Where Possible)
|Reaction with water after prolonged exposure
|Rubbing with copper sulfate
|Effects of sulphuric acid
Testing Alloying Elements in Stainless Steel
The best quality of stainless steel should have standardized chemical composition. Unfortunately, analyzing the chemical composition of various elements is not an easy task.
The best part – it gives accurate information about the stainless steel qualities of grades. In today’s industrial setups, Spectro metal analyzers play integral roles when it comes to this analysis.
Through Spectro metal analyzers, you can classify various stainless steel grades. Among the machines you can use to analyze stainless steel grades are:
- Inductively coupled plasma spectrometry (ICP)
- Optimal emission spectrometry (OES)
- Spark spectroscopy
- X-ray fluorescence (XRF)
Metal Alloy Analyzer
With these instruments, you can estimate the chemical composition of stainless steel.
Clearly, to check the quality of stainless steel, you need a clear framework on how to test the various mechanical and chemical variables.
In most cases, stainless steel manufacturing companies will handle this for you. For all your stainless steel from China, contact Tuolian now.
Choosing Stainless Steel Grades – Source: Tuolian
Stainless Steel Grade Sorting – Source: BSSA
Sorting Stainless Steel – Source: AZO Materials
Stainless Steel Identification Tests – Source: Engineering Toolbox
Testing Stainless Steel Quality – Source: EDM
Stainless Steel Quality Control – Source: Stainless Steel Casting