Hello. Nedzigon here!
People usually think of SUS304 or SUSXM7 when they think of stainless steel screw materials, but there are many other types of stainless steel with distinct properties. Perhaps your issues can be solved simply by changing the type of stainless steel of your screws. With that in mind, let's go over the main stainless steels used for screws.
Highly Corrosion-Resistant Austenitic Stainless Steel
A stainless steel containing chrome and nickel as its principal components’main property is its excellent corrosion resistance. The main austenitic stainless steels used in screws are described below.
SUS304 is the most standard austenitic stainless steel. When you add copper to SUS304, you get SUSXM7, which allows for improved cold working. Generally, austenitic stainless steel is said to be non-magnetic, but SUS304 can easily take on magnetic properties in cold working.
It will not stick to a magnet, but caution is needed when using equipment with very rigorous magnetic specifications.
＞＞Comparison of magnetic properties by material
SUS310S is an austenitic stainless steel with a high resistance to heat and oxidation due to a higher chrome and nickel content than SUS304.
SUS316L is an austenitic stainless steel with added molybdenum as well as nickel and chrome. The corrosion resistance of stainless steel comes from an oxide film (passive film) on the surface. Since molybdenum is effective in increasing the self-repairing function of this passive film when disrupted, it has a higher corrosion resistance than SUS304.
Incidentally, the "L" on the end indicates Low Carbon; reducing the carbon content has improved SUS316's poor inter-granular corrosion* properties.
SUS316L HiMo is an austenitic stainless steel with a tensile strength ranking of 10.9, equivalent to iron and steel screws. It is a superior stainless steel with higher corrosion and heat resistance than SUS316L, although its high price remains a sticking point.
High strength and magnetic detection enabled! Ferritic Stainless Steel
Martensitic Stainless Steel
Although martensitic stainless steel, typified by SUS410, has poor corrosion resistance compared to austenitic stainless steel, its best feature is that it can be hardened through heat treatment.
Taking advantage of this feature, it is often used for cutlery and tools, for example, as well as screws.
Ferritic Stainless Steel
When examining for corrosion resistance and strength, ferritic stainless steel lies midway between austenitic and martensitic steels. Ferritic stainless steel, like martensitic, possesses magnetism. This allows magnetic detection of contamination, and with a higher corrosion resistance than martensitic, it is effective in food processing machinery and so on.
SUS430 is typical of this type of stainless steel.
Combining the best of the austenitic and ferritic types! Duplex Stainless Steel
Duplex stainless steel fuses the two salient features of the austenite and ferrite varieties, bestowing on it the advantages of both the corrosion resistance of the austenitic type and the strength of the ferrite type.
＞＞Mechanical properties of duplex stainless steel screws
With its resilience to stress corrosion fractures and its remarkably excellent resistance to chloride corrosion, it is widely used in chemical plants and marine instruments among other areas.
Screw materials include other composites in addition to stainless steel as well, and each has its own characteristics. We look forward to discussing these another day.
But for today, please allow me to finish here.
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