Just for the record, 300-500C molten lye is hazardous and proper PPE and work practices are needed to handle it safely. I have tested it with zero issues, but I have several years of experience on chemistry and handling hazmat chemicals.
As marquenching is commonly carried out in hot oil up to 200C, and above that, and with austempering, a mixture of sodium and potassium nitrate has been used.
However, I figured out one potential alternative for this process: molten lye. A mixture of sodium and potassium hydroxide form an eutectic that melts at around 160-180C, and will remain stable up to 450-500C, so it would suit ideally for temperatures above 200C, and it appears to have pretty good quenching rate.
There is one patent that crosses this same idea, although it does not address any of the austempering or marquenching, but is more about surface finish and preparation of the parts for further processing. It indicates, though, that at least someone, somewhere has found molten caustics as an option for their needs.
There is also this research paper, which tests 1045 to caustic bath. It indicates that caustic bath cut with some water has great quenching capacity.
I have tested out this stuff myself. I never had nitrates in large enough amounts and purifying them appears too valuable for me to be used for consumable quench bath, and also, nitrates being strong oxidizers, can get unstable if hotspots are formed, from insufficient stirring or too large hot parts introduction, and it can cause violent reactions up to explosive nature. Hence I figured out a molten caustic, which can be readily bought cheap as granules in both sodium and potassium, could be an alternative, and it is chemically stable in temperatures needed for marquenching and austempering and it can not cause violent reactions similar in nature of nitrates, as long as the parts introduced do not contain large deposits of organics(except pure carbon), water or oil, which they don't really do once heated red hot. Obviously caustics are corrosive by their nature, and while molten hot, as with most chemical reactions, they procceed the faster the hotter they are, the stuff will literally melt skin if a splash occurs, however you will not want anything on your skin that is 200-600C and liquid, so there's that. Caustics are also nontoxic and do not have any bioaccumulative properties as they contain only basic alkali metals and a hydroxide ion, which readily reacts to form an alkali salt and water.
Parts introduced in it seem to quench really fast, the sound it makes is more like sharp, prompt hissing, almost like a swift steam crack, which subsides at once, similar to 10% lye water quench but even faster, although I haven't yet tried it on larger parts. One thing I have thought actually if it might cool the parts down actually too fast, and I'm not sure if quenching can be too fast when performed for austempering or marquenching, as martensite formation will not begin at any moment until temperature has stabilized and the part is removed from the bath.
After that, the bath just sits doing absolutely nothing, it doesn't smell, smoke, boil, steam or anything at all. The induction plate I have can not get the pot hotter than 300C, but it happens to be just nice for my needs. I have performed the small scale tests with 2L bath size on my kitchen desk multiple times with zero issues.
The parts I have obtained have presented higher toughness than comparable quenched and tempered workpieces, and it took a lot more effort to snap a 115CrV3 rod that was lye bath treated than through conventional QT, at hardness level around 56, according to TDS isothermal curve data. I don't have measuring equipment, so I can't give exact data. The parts come out dull dark gray.
The question is, does anyone have any information or references regarding this method? I would be most interested if someone else has thought about this as well. Most of the parts I treat are for lower hardness than blade uses, but the heat treatment science in general has a lot of cross sectional area with bladesmithing.
As marquenching is commonly carried out in hot oil up to 200C, and above that, and with austempering, a mixture of sodium and potassium nitrate has been used.
However, I figured out one potential alternative for this process: molten lye. A mixture of sodium and potassium hydroxide form an eutectic that melts at around 160-180C, and will remain stable up to 450-500C, so it would suit ideally for temperatures above 200C, and it appears to have pretty good quenching rate.
There is one patent that crosses this same idea, although it does not address any of the austempering or marquenching, but is more about surface finish and preparation of the parts for further processing. It indicates, though, that at least someone, somewhere has found molten caustics as an option for their needs.
There is also this research paper, which tests 1045 to caustic bath. It indicates that caustic bath cut with some water has great quenching capacity.
I have tested out this stuff myself. I never had nitrates in large enough amounts and purifying them appears too valuable for me to be used for consumable quench bath, and also, nitrates being strong oxidizers, can get unstable if hotspots are formed, from insufficient stirring or too large hot parts introduction, and it can cause violent reactions up to explosive nature. Hence I figured out a molten caustic, which can be readily bought cheap as granules in both sodium and potassium, could be an alternative, and it is chemically stable in temperatures needed for marquenching and austempering and it can not cause violent reactions similar in nature of nitrates, as long as the parts introduced do not contain large deposits of organics(except pure carbon), water or oil, which they don't really do once heated red hot. Obviously caustics are corrosive by their nature, and while molten hot, as with most chemical reactions, they procceed the faster the hotter they are, the stuff will literally melt skin if a splash occurs, however you will not want anything on your skin that is 200-600C and liquid, so there's that. Caustics are also nontoxic and do not have any bioaccumulative properties as they contain only basic alkali metals and a hydroxide ion, which readily reacts to form an alkali salt and water.
Parts introduced in it seem to quench really fast, the sound it makes is more like sharp, prompt hissing, almost like a swift steam crack, which subsides at once, similar to 10% lye water quench but even faster, although I haven't yet tried it on larger parts. One thing I have thought actually if it might cool the parts down actually too fast, and I'm not sure if quenching can be too fast when performed for austempering or marquenching, as martensite formation will not begin at any moment until temperature has stabilized and the part is removed from the bath.
After that, the bath just sits doing absolutely nothing, it doesn't smell, smoke, boil, steam or anything at all. The induction plate I have can not get the pot hotter than 300C, but it happens to be just nice for my needs. I have performed the small scale tests with 2L bath size on my kitchen desk multiple times with zero issues.
The parts I have obtained have presented higher toughness than comparable quenched and tempered workpieces, and it took a lot more effort to snap a 115CrV3 rod that was lye bath treated than through conventional QT, at hardness level around 56, according to TDS isothermal curve data. I don't have measuring equipment, so I can't give exact data. The parts come out dull dark gray.
The question is, does anyone have any information or references regarding this method? I would be most interested if someone else has thought about this as well. Most of the parts I treat are for lower hardness than blade uses, but the heat treatment science in general has a lot of cross sectional area with bladesmithing.
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