Applied basics of sodium cyanide case hardening for steel.
I work as a managing engineer at a concrete block plant located in central Mexico. My degree is in industrial engineering and I did some graduate studies in the US in mechanical engineering.
Right now I am facing the problem of having to make our own block molds in order to save money. All our molds come from developed nations and are expensive. The block is sold here for about half the price. The basic structure of the molds represents no problem, structural steel can be found here easily. My problem is that there is no quality white cast iron for the wear parts. To get around the problem, we are looking at what is available concerning materials and hardening processes. There is available 4140, 8620 and 9840 steel in plates in the area and we would like to use a case hardening process to replace the stock white cast iron wear parts. If our own made parts last half the time as the stock parts I think it still would be a bargain. We thought of using nitrogen gas or carbon monoxide gas but the small oven we have access to does not have an inlet port for gas and we don't know much about the process. We decided that the sodium cyanide process would be the easiest way but still we don't know how to actually do it. Specifically, we don't know wether to dissolve the cyanide in water and inmerse our red hot parts in it or to splatter the cyanide on top of the parts before placing them in the oven or maybe splatter the parts with the cyanide after being in the oven.
I understand this requires a lot of experimenting with temperatures and times and we are most excited about it, but I would like to ask the audience for some tips and short cuts that can save a little time. Is the sodium cyanide process the best for us? Could we put a nitrogen gas tube or carbon monoxide tube through a partially open oven door with the parts inside?
Our main problem has been access to books and literature. What we have is related to materials science and does mention the process but without any specifics. I plan to order a couple of books from ASM but they are expensive and take a few weeks to clear customs. I've also looked on the web and found a few good things but still I'm missing the basics of the process.
Thanks for having this page and thanks in advance for the help.Salvador Velasco
- Toluca, Edomex, Mexico
Good afternoon, Mr Velasco:
Carburizing steel is a process where you diffuse carbon into the surface of the steel. It is highly temperature dependent. At temperatures below 1500 degrees F, the carbon diffusion into the steel will be so slow that it won't be practical. Immersing red hot parts in an aqueous cyanide solution won't provide a carburized surface and sounds like a dangerous practice. At one time, molten cyanide salt processes were a popular method of carburizing, but safety and environmental issues forced almost all heat treaters to get rid of them. If you are still interested in fabricating your own molds, I would recommend trying to find a reputable heat treat shop to do the carburizing for you. Heat treating, like plating, is not as simple as it looks on paper.Steve Bizub
- St Louis, Missouri
April 24, 2009
Heat treatment is relatively easy using carburizing salts
(mixture-70% sodium cyanide to 30% barium chloride by weight)
- Mataram, Indonesia