Use of Sodium Hydroxide (NaOH) or Lye or Caustic Soda for Heat Treatment of Metal

Hi All,

I am a professional heat treater and I have a peculiar query. I am basicall= y doing heat treatment of High Speed Steel (HSS). Now the thing is in HSS h= eat treatment we do a process of QUENCHING (600 Deg Celcius) which is done = after AUSTENISING (1200 deg Celcius).

Now we are currently using a SALT of Barium Chloride mixed with heavy quant= ities of Calcium for Austenising but the problem with this salt is that is = very corrosive. Now we wanted to change this salt to a less corrosive salt = and someone told us to use NaOH which has a melting point of 300 deg C and = melting point of 1200 deg C.

Now my question is tat is NaOH good for Quenching process, what is the maxi= mum temperature at which it is used without causing much of health hazards.

The temperature range required for this salt is 600~700 deg C.

Can any one let me know is the use of NaOH good or bad?

What precautions should be taken by the operators to avoid any mishap?

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I can't give you the operating temperature, but I can tell you that sodium hydroxide - whether molten or dissolved in water - is quite dangerous stuff. It's one of the MOST caustic substances around that you can legitimately lay your hands on. If barium chloride is too caustic, you'll find sodium hydroxide to be most exceedingly so.

Most of the old quenching/color bluing formulae I've seen use molten potassium nitrate. As a molten substance, it's quite a vigorous oxidizer, and will leave a significant oxide coating on the metal. OTOH, although it is a significant fire hazard in the presence of any organics, it's safer generally than sodium hydroxide.

If it's not so much the quenching, but the bluing effect you're after, there are some good color blues that use barium carbonate (poisonous, not not the least caustic).


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Lloyd E. Sponenburgh

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