Hardtec is a registered brand name of an alloy known as KDS2000 made by Daido Steel (from by Nippon Steel). It is a proprietary stainless grade that has been developed to combine the high corrosion resistance of Austenitic grades like 304 and 316 AND has the hardness of heat treated Martensitic grades like 410 stainless steel. Hardtec has a chemistry very similar to 410 stainless steel; but also has 1% of Molybdenum added to it.
Molybdenum is the element that gives grade 316 its corrosion resistance improvement over grade 304. Marutex and YUS 550 are other material brand names of stainless grades similar to Hardtec.
Hardtec stainless offers high levels of corrosion resistance, the decline of which was previously unavoidable with heat-treated grades like 410.
There are other stainless steel self-drilling screw options on the market but they each have the following downsides:
All 304 and 316 grade screws have good corrosion resistance but these grades are an Austenitic type of stainless and cannot be hardened by heat treatment, therefore they are relatively soft and can only self-drill through very thin aluminium at best.
410 grade screws are a Martensitic grade of stainless steel and so are hardened by heat treatment making them excellent for self drilling into steel. However 410 has a low PRE value and as such a low level of corrosion resistance making 410 screws unsuitable for exterior coastal environments as they will rust and tea-stain easily.
Most 304 and 316 self drilling screws that can drill well are actually Bi-metal. That is they have a 304 or 316 head and body and a carbon steel tip. The tip might have a protective coating such as Ruspert or similar. These screws drill well and are ok if it is acceptable for the tip to rust away, but they are not fully stainless steel and the carbon steel tips risk rusting and bleeding.
Hardtec is stronger than both 304, 305 grades and 410 grade stainless steel.
Strength tests show that Hardtec screws have:
Hardness tests show that Hardtec has a surface hardness similar to that of grade 410 and 50% than that of 304, enabling it to self-drill into metal. It's core hardness is 88% greater than 304 and even 18% greater than Carbon Steel (SWCH18A).
Corrosion tests show that:
410 Screws have rust appearing after 48 hours of salt spray testing. Hardtec Screws have no rust appearing after 1000 hours of salt spray testing, the same as grade 305 stainless.
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