1075 and 1095 Comparison

INTRODUCTION

My name is Dan Maragni and I am responsible for the change from 1095 steel to 1075 steel at Ontario Knife Company and here is the story and reasoning behind the decision.

I have been an independent contractor working at Ontario Knife Company since 2007 and work as a technical consultant specializing in heat treatment, knife design and training.  I was responsible for updating their heat treatment facility with digitally controlled salt pots, designing their impeller agitated quench tank and monitoring the heat treatment processes.

I have have been a dedicated student of the blade all my life and began my career as a bladesmith in the mid-1970s working with an extremely knowledgable and talented artist and smith named Phillip Baldwin who I met in high school.  Phill introduced me to the use of W-1 for a blade steel and everything I ever learned about smithing blades I learned from him (Phill made his first “Damascus”/folded steel blade in 1969).  Phill and I began working together while we were attending college over the summer and winter breaks. Phill and I had a complimentary roles in our work together- he was the bladesmith and smithing teacher and I was the researcher although there was little research material available on bladesmithing at the time.

I became a full time bladesmith in 1980.

PHYSICAL TESTING

In about 1979 I met Jimmy Fikes at a course Phill and I were teaching at Peter’s Valley Crafts and he introduced me to Don Fogg and Jim Schmidt.  I was unbelievably lucky to be exposed to the ideas and work of these incredible bladesmiths especially this early in my career.  In 1980 Jimmy invited me to speak at the first “Ashokan Hammer-In” on heat treatment which resulted in a long, boring lecture on my part.  As bladesmiths making functional tools at the time we were understandably interested in how our blades would perform and needed to come up with a way to determine how functional our blades were.  Ultimately we came up with a series of cutting and strength tests involving manila rope (especially tough on brittle edges with large carbides), hard and soft wood and flexing blades often with “cheater bars”.  Not only did this show us how our blades performed but if our blades were improving over time.  For the first few years we were all bringing blades to the Ashokan Seminar and testing them often to their limits and the performance of the blades increased in leaps and bounds (I remember piles of rope fragments and wood chips strewn all over).  Although it may seem obvious I have always felt that you learn more about a blade when cutting with it than not cutting with it. I also started looking at other steels which might improve my blades and my research ultimately led me to W-2, a slightly tweaked version of W-1 which had benefits in heat treating.  Remember, at this time we were all heat treating our blades in coal forges judging temperatures by eye and I felt that I needed every advantage I could get (Phill and I had also figured out a way to create a hamon on our blades which showed if our edges got completely hard and was a great quality control technique).

CARBON V™

In the late 1980s I met Lynn Thompson at the Costa Mesa Knife Show in California and he noticed that I made knives from “Damascus Steel”.  “Damascus Steel” at the time had a reputation in the literature as being the highest performance steel available although mine and others testing was showing that the high carbon steels out performed them quite consistently.  (“Damascus Steel” is not really a steel but rather a technique and varied greatly from smith to smith depending on the choice of steels and the ability of the smith.). Lynn was determined to make the best performing knives and I suggested making them of carbon steel which was more consistent and readily available.  He bought into the idea and sometime in the early 1990s I was overseeing the domestic production of what was ultimately to become the Trailmaster.  The first thing I did was take samples of some blades to a metallurgist and he did some micros and I did some physical testing.  We both found that the performance of the blades could be improved and I had the heat treatment tweaked (changed the austenitizing temperature, soak time and tempering temperature).  I then selected the heat treatment that produced the microstructure that resulted in the best cutting and toughest blades.  I continued to work for Cold Steel as a technical consultant and supervisor of domestic production until 2006 when Camillus Cutlery Company closed.

1075 and 1095

In the mid 1990s I modernized my shop getting digitally controlled kilns and building an impeller agitated quench tank with a “J-Tube” to concentrate and direct the flow of the oil.  I was interested in making longer blades and my research into metallurgy and the metallurgy of ancient swords was revealing that I should be looking at other steels to maximize the toughness of the blades.  I began experimenting with steels that would develop more tough lath martensite than brittle plate martensite (1060, 1075, 5160 and 6150) and using the same procedures  I developed for Carbon V were used to maximize the heat treatment of these steels. One of the findings which surprised me the most was that these lower carbon and alloy steels cut as well or slightly better than than steels with carbon contents at 0.95-1.00%.  I was aware that the literature always said that the excess carbon in steel which had over 0.6% would produce more carbides which increased abrasion resistance and resulted in better edge retention. But the literature was not focussed on the metallurgy of blades (unlike what is available today) and the edges of most tools have a very different configuration and is subject to very different stresses than the edge of a knife.

For me the worst of all failures for a blade is for it to break. Once a blade breaks it is rendered pretty much unusable.  My research into ancient swords confirmed this bias of the ancient smiths and a great example of this is the Japanese sword (laminations, differential heat treatment, creating compressive stresses along the edge). Yoshindo Yoshihara the traditional Japanese swordsmith whose uses a kobuse laminate for his blade construction prefers steel with a carbon content of 0.7% for the outside/edge steel.  Sword edges must be very tough and the choice of 0.7% C (his brother prefers 0.6% C) is revealing.

CHEMISTRY

Lath martensite forms in carbon steel at carbon contents at 0.6% and below, plate martensite forms at carbon contents of 1.0% and above and in between these carbon contents the martensite is a mixture of the two types.  When quenched carbon steels will pretty much reach “full” hardness with a carbon content of 0.6% and the remaining carbon will form carbides.  1075 is less likely to form as much retained austenite as 1095 as the Mf (martensite finish temperature) decreases with increasing carbon content (the Mf is below room temperature for steels containing more than 0.8% carbon).  If the steel does not reach the Mf temperature when quenched the austenite will not transform to martensite and remains “soft” and there is the possibility the austenite will ultimately  transform to untempered martensite. 1095 also exhibits micro cracking when quenched due to the greater amount of expansion in the martensitic transformation which is typical of higher carbon content steels (as carbon content increases above 0.75% so does the amount of micro cracking).  1075 also has a higher manganese content than 1095 which results in a slower critical cooling rate and minimizes the chance that you will clip the nose of the pearlite curve in the quench and wind up with a mixture of martensite and pearlite in the finished blade. The finished structure of a blade should be tempered martensite and having a mix with retained austenite and pearlite is not an optimal structure.

HEAT TREATMENT

As we all know even the best steel can be compromised by a poor heat treatment and heat treating can only allow you to optimize the performance characteristics of the steel. 1075 is a lot less sensitive than 1095 in heat treatment (slower critical cooling rate) and resultant structure has less micro cracks and retained austenite than 1095 which results in a stronger blade.

SUMMARY

By replacing 1095 with 1075 Ontario has selected a steel that is readily available, responds better to heat treatment resulting in a blade with less retained austenite and less micro cracking. The physical testing also shows the blades in 1075 are tougher and hold an edge as well or better than 1095.

Toshishiro Obata, the Japanese tameshigiri champion, was known to say that a sword should have these characteristics

                           “Be Strong, Be Sharp, Be Beautiful”

While the third characteristic is determined by an aesthetic sense and is not so easily defined the goal at Ontario is to create blades that are a combination of the first two.