Hydrogen Shroud


During some of my time at Iscor, I had been studying the effects of hydrogen on armour plate steel, and the means to try and get rid of it. That’s why the following experiment is rather odd, firstly because it didn’t yield the expected result, and secondly because no action followed once I realised what had actually happened. Here’s what happened.

I had been doing a literature survey, and done some trials and FEA analysis to find means of getting hydrogen out of solid steel, but the next planned trial was rather hard to get through the system: it was my intention to INCREASE the hydrogen content of one ingot and see how the properties would be affected. In order to do so, I had a cylinder of argon enriched with 5% hydrogen (the highest concentration you could go without a major danger of explosive flammability) which I intended to aim at the liquid steel flow at the time it was poured into the ingot mould.

It took quite a bit of arguing my case before I could convince the powers-that-be to allow me to perform an action that would possibly affect the steel properties for the worst. That’s why the actual trial took place quite late in the day, and once I had already moved on to my next project, which concerned itself with the cleanliness of tinplate steel. And when it ended in what looked like a damp squib, no-one took any notice, and possibly valuable lessons were not learned.

The way the hydrogen was being injected into the steel was by means of a gas shroud, i.e. a ring was placed at the bottom of the ladle where the liquid steel was poured from so that the liquid steel stream was surrounded by a mantle of argon enriched with hydrogen, and the idea was that some of the hydrogen would be absorbed in the liquid steel before it collected in the ingot mould.

The result ? Instead of an enrichment I had actually achieved a LOWER hydrogen content in the targeted ingot. Relief all round that they wouldn’t have to downgrade or scrap an expensive ingot, and me scratching my head, not quite sure what had happened. It was only on later reflection that I realised what had happened: molecular hydrogen gas probably does not split into its individual hydrogen atoms, and as such never entered the liquid steel. What I HAD actually done was to exclude another source of hydrogen, which is dampness in the air.

Consider the mechanism when a water molecule meets liquid steel, especially a turbulent stream when pouring into a mould : water’s oxygen atom readily reacts with iron to form FeO, thereby creating two free hydrogen atoms which can then enter the steel at the same time the oxygen reacts with the steel. The lesson that should have been learnt was that you should try and prevent hydrogen entering the liquid steel at the time you pour it into the mould by applying a gas shroud. Plain argon would have done the job, the hydrogen enrichment being totally unnecessary.

Surely preventing the steel from entering the steel in the first place is far better than attempting to diffuse hydrogen out of solid steel at a later stage. But somehow my realisation of what had happened came too late, and the hydrogen project had already been closed. I still don’t know why I didn’t bring it up with my boss though, because at that time I was still in the same department.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s