Faberware Millennium cookware hydrogen cracking

Tom's full forensic walkthrough of the case. Farberware came to him through the MIT Industrial Liaison Program after Millennium Cookware pots shipped to Japan developed cracks running parallel to the drawing axis during the voyage. Tom used a magnet to demonstrate that 301 stainless deep-drawing had transformed the FCC austenite to BCC martensite (TRIP behavior), creating the cathode for hydrogen embrittlement. Source of hydrogen identified as the argon-5% hydrogen atmosphere used to spray-deposit the stainless steel powder substrate for the Teflon coating. Tom uses the case to teach: (1) that 70% of metallurgists conflate stress corrosion cracking with hydrogen embrittlement, (2) that the distinction is anode (SCC) vs. cathode (HE), and (3) that delayed cracking with stainless on a bench is the diagnostic giveaway for hydrogen.

Let's talk about plain old deep drawing. [Tom produces a set of progressively drawn cups.] Here's my set of deep draws, where you go from a round circular blank and you do the first draw, the second draw, third draw, fourth draw. These have all been cut off the end. Backofen's dead, I can't find out where those came from. Farberware is the company — they came to me 15 years ago through the MIT Industrial Liaison Program. They said, "We make these very expensive pots called Millennium Cookware, and we've shipped them to Japan, and lo and behold, when they get to Japan they're cracked."

First of all, what did I know? They didn't have cracks when it left Brooklyn. A couple of weeks later he gets to Japan and it had cracks. It's hydrogen cracking. I didn't tell them that, but I knew it was hydrogen cracking. It's delayed cracking. We caught delayed cracking — it's the only thing I know that shows up a few days, a few weeks later.

Two-part teaching unit using the pot as prop. (1) The aluminum/stainless cold-bonded base illustrates that a deliberately weak bond (10% bonded area) is correct design for dissimilar-CTE joints — porosity accommodates thermal strain. (2) The plasma-sprayed inner surface for Teflon adhesion introduced hydrogen (95% argon / 5% hydrogen gas), which caused delayed cracking after shipping from Brooklyn to Japan. Martensite transformation in deformed 304 stainless was the susceptible microstructure.

Another type of mechanical interlocking — several of you who've taken parts of the class before have seen this prop. [Tom produces a piece of Millennium cookware.] This is Millennium cookware by Farberware. It illustrates a number of things. It illustrates forming, if you take my deformation processing course. It's actually an example of cold bonding. They have a layer of aluminum at the bottom of the stainless steel. They draw the stainless steel, they heat up the aluminum in a furnace, they put the pot over a die — a guy by hand takes some tongs, puts the aluminum on top, and there's a steel die holding it, and a 5,000-ton press comes down, goes wham, and just with pure normal pressure bonds it. There's a little bit of shear, because this thing does have some rounded edges after it comes out of the die.