FTM 103: Can Stainless Steel be Magnetic?

Fastener Training Minute 103: Can Stainless Steel be Magnetic

This edition of the Fastener Training Minute with Carmen Vertullo was originally published March 17, 2016 as “can stainless steel be magnetic?” during episode 103 of Fully Threaded Radio.

Well, this is Carmen Vertullo with your Fastener Training Minute coming from the Carver FACT Center in San Diego. And of course representing the Fastener Training Institute. First, I want to tell you how excited I am about just finishing our first training program at the Carver FACT Center. It was about hydrogen embrittlement testing for fasteners. We had 13 students and we did two days of Hands-On testing. We also had Salim Brahimi join us by GoToMeeting on the big screen. He presented some information about the Bay Bridge and some other hydrogen embrittlement case studies. Everybody in the class got the experience hands-on Rockwell hardness testing, and hydrogen embrittlement testing and we had a great class.

So, to every student, if you’re listening to this, I just want to thank you for attending. Every one of you brought valuable input to the class. We had manufacturers and suppliers and we had a plating shop end-users. It was just a fantastic program and we hope to do it again soon possibly in Cleveland. So be looking for that. Anyway, this is the Fastener Training Minute and not the Carver FACT Center advertisement minute.

I just had an interesting question today by email. One of our CFS students asked me exactly what kinds of stainless Steels are magnetic and which ones are not. Well when we come back I’ll tell you this is Carmen Vertullo the Fastener Training Minute.

The question was: which stainless steels are magnetic and which ones are not and how can we tell? Well, first off when we talk about magnetism there’s kind of two varieties. One thing is is the thing actually magnetic and other words, would it pick up something that was made out of steel or iron, or secondly, is it susceptible to a magnetic field? That is, if we bring a magnet towards it would it be attracted to it? When we talk about stainless steel being magnetic we’re generally talking about would it be attracted to a magnet? Well, we generally think that being non-magnetic is one of those properties of stainless steel, and it is for some of the stainless steels that we generally call the 300 Series or 18/8. The 300 Series are austenitic stainless steels and they are generally non-magnetic.

However, if we get a really strong magnet like one of these neodymium magnets, it will jump right on almost any stainless steel. So if you want to test for magnetism get yourself one of those magnets, you can pick them up at a hobby store or McMaster-Carr. Did I say McMaster-Carr? I love those guys, they’re very cheap couple of bucks. And that’s a good thing to have around so other stainless.

Besides the 18/8 stainless or the 300 Series stainless, are the 400 Series stainless ,which are the ferritic stainless steels, including 17-4 pH. Some of these can be quite magnetic, almost the same as steel. You can hardly tell the difference. So we’re not usually too concerned about those.

The problem occurs when an end user uses a magnet to inspect their stainless steel fasteners and it sticks to the magnet and they think it’s not stainless. Well, what happens to these austenitic stainless steels when they are work hardened such as when we roll a thread on them,  is that work hardening tends to make the material magnetic. It aligns the molecules up in such a way that that happens. If we wanted to remove that magnetism one way we could do it is by annealing the material and we can easily demonstrate this. take a small screw like a small set screw or small socket screw #4-32, it’ll jump right on the one of those super magnets. Heat it red hot with a cigar lighter or something like that and try it again. It’ll be totally annealed and no longer magnetic. If you wanted to continue the test, take that same screw, smash it flat with a hammer, which would be a form of work hardening, and then that material will be magnetic again.

So don’t despair when your customer wants to reject your stainless steel material because it’s magnetic. There are ways to prove it is stainless and there are ways to train your customer.

This is Carmen Vertullo with the Fastener Training Minute coming to you from the Carver FACT Center and the Fastener Training Institute.

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