Kevin R. Cashen
Super Moderator
Although I am very careful to protect the privacy of my clients for whom I do consulting and testing, this research has so much educational value that I asked for permission to share some of the results with my knifemaking friends. I am currently involved in a project to help a quenchant manufacturer (not Parks or Houghton) develop some oils to specifically meet the demands of certain steels. The first goal is a very fast oil that will work for shallow hardening steels, so I am testing with a fast oil control.
Below you will see results from one of the first prototype formulations, starting at lower speeds, on 1095. 1095 is one of the toughest to thoroughly harden so I thought it would be a good challenge. The samples where ground from the same bar of steel, austenitized side by side with direct thermocouple monitoring in salts, and quenched side by side in identical quantities of oils and agitation, surrounded by a 125F bath to assure temperature. The results were then cross sectioned and roughly polished for metallographic examination (so please overlook the scratches). Micrographs were actually taken at 1mm increments from the edge but I only took a sampling to put this image on the web. After this the samples were then tested for Rockwell hardness at roughly 3mm increments.
The light background is martensite (the good hard stuff we want), the dark stuff, making it look like blue cheese, is fine pearlite (the soft stuff that quenching is supposed to avoid). Please be aware that at the edge both of these samples would have skated a file just fine, would have flexed over a brass rod all you want, and would even have cut a few 2x4” with little problem. But every little black patch represents a percentage of overall loss in strength, and long term edge retention.
Do be aware that that prototype oil would probably have held its own against many medium speed oils and was made by guys who’s business it is to make oils specifically for quenching and know what they are doing. This was a good oil but was still a first step in moving from medium to the fast speed, with a few adjustments that were yet needed to reach the goal, and many more tests in that process. But the speed factor is just one area among many to account for, long term stability, vapor points, interaction with the surface finish etc…
The real point of this post is that making a real quench oil isn’t all that simple and testing it is even less so, believe it or not these are just rough preliminary tests and not all that exhaustive. I hope this gives somewhat of an insight as to my perspective when I express my doubts about some of the homemade and improvised quenchants some folks feel work “just fine”, and I hope it gives food for thought to those who feel carefully considered quenchants are unnecessary.
Below you will see results from one of the first prototype formulations, starting at lower speeds, on 1095. 1095 is one of the toughest to thoroughly harden so I thought it would be a good challenge. The samples where ground from the same bar of steel, austenitized side by side with direct thermocouple monitoring in salts, and quenched side by side in identical quantities of oils and agitation, surrounded by a 125F bath to assure temperature. The results were then cross sectioned and roughly polished for metallographic examination (so please overlook the scratches). Micrographs were actually taken at 1mm increments from the edge but I only took a sampling to put this image on the web. After this the samples were then tested for Rockwell hardness at roughly 3mm increments.
The light background is martensite (the good hard stuff we want), the dark stuff, making it look like blue cheese, is fine pearlite (the soft stuff that quenching is supposed to avoid). Please be aware that at the edge both of these samples would have skated a file just fine, would have flexed over a brass rod all you want, and would even have cut a few 2x4” with little problem. But every little black patch represents a percentage of overall loss in strength, and long term edge retention.
Do be aware that that prototype oil would probably have held its own against many medium speed oils and was made by guys who’s business it is to make oils specifically for quenching and know what they are doing. This was a good oil but was still a first step in moving from medium to the fast speed, with a few adjustments that were yet needed to reach the goal, and many more tests in that process. But the speed factor is just one area among many to account for, long term stability, vapor points, interaction with the surface finish etc…
The real point of this post is that making a real quench oil isn’t all that simple and testing it is even less so, believe it or not these are just rough preliminary tests and not all that exhaustive. I hope this gives somewhat of an insight as to my perspective when I express my doubts about some of the homemade and improvised quenchants some folks feel work “just fine”, and I hope it gives food for thought to those who feel carefully considered quenchants are unnecessary.
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I do have to ask the question, was there a specific reason that 1095 was chosen as the test steel? 
