Deck screws

[Osvaldo Cristo]

It was the first time I purchased some deck screws, as stated on the box label. It also states the material is stainless steel. Made in Taiwan. It looked great as I got them at a reasonable price...

...but I found something odd when I arrived at my workshop: my strong magnet barely provoke reaction when close and even contacted with a such screws. They are practically amagnetic. It is strange as it would be mainly iron...

I would appreciate if you that are consumer for deck screws could explain me why Asian stainless steel is different from my other stainless steel experience.

Thanks in advance.

[Lee Schierer]

Only some stainless in the 400 series is magnetic and can also be hardened. Most 300 series stainless steels are non-magnetic. Your screws are likely a 300 series stainless. They are still stainless steel and they should work okay, but may be softer than steel screws.

The following types of stainless steel are typically magnetic:

Ferritic Stainless Steels such as grades 409, 430 and 439
Martensitic Stainless Steel such as grades 410, 420, 440
Duplex Stainless Steel such as grade 2205

[Doug Garson]

There are several types of stainless steel, they have different properties and uses. Does the box say what grade of stainless steel?

A basic stainless steel has a 'ferritic' structure and is magnetic. ... However, the most common stainless steels are 'austenitic' - these have a higher chromium content and nickel is also added. It is the nickel which modifies the physical structure of the steel and makes it non-magnetic.

[Osvaldo Cristo]

There are several types of stainless steel, they have different properties and uses. Does the box say what grade of stainless steel?

[...]
It is the nickel which modifies the physical structure of the steel and makes it non-magnetic.

It is a surprise for me. I knew usually stainless steel contains nickel but it is the first time I read nickel can change so dramatically the properties of a iron alloy. Thanks both of you to educate me.

[Osvaldo Cristo]

Only some stainless in the 400 series is magnetic and can also be hardened. Most 300 series stainless steels are non-magnetic. Your screws are likely a 300 series stainless. They are still stainless steel and they should work okay, but may be softer than steel screws.

The following types of stainless steel are typically magnetic:

Ferritic Stainless Steels such as grades 409, 430 and 439
Martensitic Stainless Steel such as grades 410, 420, 440
Duplex Stainless Steel such as grade 2205

Very comprehensive answer. Thank you very much! Now I got it.

[Frank Pratt]

You want to be careful when using SS screws. The are much weaker than conventional steel construction screws.

[Osvaldo Cristo]

Only some stainless in the 400 series is magnetic and can also be hardened. Most 300 series stainless steels are non-magnetic. Your screws are likely a 300 series stainless. They are still stainless steel and they should work okay, but may be softer than steel screws.

The following types of stainless steel are typically magnetic:

Ferritic Stainless Steels such as grades 409, 430 and 439
Martensitic Stainless Steel such as grades 410, 420, 440
Duplex Stainless Steel such as grade 2205

Humm... just wandering, could the navy to use series 300 stainless alloys to construct mine hunter vessels?

[Lee Schierer]

Humm... just wandering, could the navy to use series 300 stainless alloys to construct mine hunter vessels?

No 300 series stainless is prone to stress corrosion cracking in the presence of chloride (salt).

[Bill Dufour]

The navy could use fiberglass for hulls but the engine and pumps/radios would still be magnetic.
My father worked with a guy who was in the US navy during world war 2. They took a millionaires sailing yacht and removed the radio, engine, generators etc. basically anything metal was removed. Since he had been in the sea scouts he was in charge of a small crew. They based in Bermuda? and sailed around for two weeks or so, until the food ran out, looking for mines. If they saw any they were supposed to shoot it with a rifle they had on board. He did this for about one year and never saw anything.
After the war was over the engines etc were reinstalled and the boat was given back to the owner. He would not have been allowed to sai lit to sea during the war anyway.
Bill D

[Osvaldo Cristo]

No 300 series stainless is prone to stress corrosion cracking in the presence of chloride (salt).

...so it does not look a good material for deck screws, no? It is common to have decks around swimming pools and at beach homes.

[Tom M King]

My favorite deck screws are Deckmate with "Star Drive" heads. Star Drive is actually a T25 TORX.

What I don't like about stainless screws for decking is that they are soft. The softness means that if you hit a knot, or some hard spot in a board, or joist, the driver bit will cam-out the head, leaving you to have to use Vise-Grips to back the screw out, and then try another one. Also, when the time comes that you might be able to turn a deck board over, the percentage of the stainless screws you can get back out is not high.

The T25 Deckmates can be backed out any time in the future, and the finish lasts as long as the deck boards do.

[Jim Koepke]

My favorite deck screws are Deckmate with "Star Drive" heads. Star Drive is actually a T25 TORX.

With the help of my grandson we built two decks using Deckmate screws. Not a single problem.

My use of Stainless Steel deck screws with Robertson drive (square drive) always seems to have problems with the socket stripping.

jtk

[Frank Pratt]

Just a side note with regards to camming out of the screw head; an impact driver, as opposed to a drill, will help tremendously in that regard.

Torx are good, but the screw won't stay on the bit nearly as well as with Robertson. With decent screws & driver bits, camming out will never be a problem with Robertson drive.

[Aaron Rosenthal]

I've built many a deck using 300 series SS screws, and the best way I found to keep the cam out issue at bay was:
Pre-drill with an appropriate drill/countersink unit;
Bees way the thread (paraffin also works, but too dangerous);
Use the impact driver to run the screw into the pre-drilled hole;
Repeat another 10,000 times.
I have found one issue with the stainless is the small heads: after 8-10 years, the wood movement loosens them up.

[Frank Pratt]

Bees way the thread (paraffin also works, but too dangerous)

How is paraffin too dangerous?