Marquench

Bruce Bump

Bruce Bump

Joined
Dec 2, 1999
Messages
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This weekend I made a 1 gallon coffe can forge with castable refractory and a junk yard 12volt blower. I used a stainless steel pipe with a bottom welded on so I can pour salts (barium cloride) in it and heat it to 1500 degrees in the little forge. I used my pyrometer and set a thermocouple in a ceramic tube inside the melted salts to monitor and I can adjust the temperature to maintain the 1500 deg. While this was heating up I warmed my Nitre Blue salts on a Coleman cookstove and probed it with a brownells bluing thermometer. I got it adjusted and maintained 500-550 deg. All this trouble just to heat-treat the hammer spring for my pistol/folder. After breaking 3 of them because of improper HT I decided to get more serious. I used a formed piece of 1095 that Dan Gray sent to me free..Thanks Dan.. and attached it to a wire and put it in the hot salt for 5 minutes and quickly quenched it in the 5oo deg. bluing salts for about 10 minutes and cooled it in water. I believe this is called "Marquenching" Please correct me if I did anything wrong. The spring seems to work fine but I havent pulled the hammer all the way back yet. Im too afraid it will snap like the others! I am going to polish it more so to remove any stress risers where a break could start. I also want to give it a hardness test.

Now my question...What is a 1095 spring hardness? Im using a Rockwell Tester on C scale
 
I seem to recall a hardness around 46 or 48 rc. I do know that the temper color is a bright blue (I'm sure you know that). In my Dixie Gun Works cat. there is a how to on 1095 springs and it says to make sure you are not folding with the grain. I assuming you are making a flat spring.
 
To follow up on my first post, I looked up what I had read before on 1095 and it said to heat to 1470 quench in oil and temper in between 740 and 810. And it stressed to fold againist the grain. So I was wrong in the final oxide color.
 
There is alot I need to learn about Marquenching but I may have done it right with the 500-550 degress. I think it should get me the 48-51 rc hardness Im looking for. I will check it with a rockwell tester today and let you know how it came out. It is a flat piece of 1095 and has been fashioned into a trigger guard (rounded) for my pistol/folder. Im not folding against the grain but I hope there is a grain because it is stock removal instead of forged.

One real advantage of the hot salts is so the steel doesnt get overheated and grow grain. Over-heating is a real flaw causing a spring or knife edge to break even if it was tempered correctly. If this one doesnt work Im going to try oil quenching from the salts and oven tempering.

Thanks for the help so far guys.
 
I checked the hardness of the spring at the college. It was 59 rc. That is way too hard so I tempered it in my even heat oven at 600 deg. for 40 min. and it tested 54-55rc. Still to hard. Remember I wanted 48-51rc. I took it home and threw it back in the oven at 695deg. for 40 min. and it tested at 49-51 rc. See that wasnt so bad was it? Only 2 full days to make a spring. Geez.
 
Hey Bruce, thats neat, I can't wait to start fooling around with marquenching. What happens when you marquench, as you found out, is that you cause a much more stable form of untempered martensite to form. The martensite doesn't form until the steel cools down from the 400 to 500 degree quench. Cooling in water was probably unnecessary and more than likely just caused martensite to form faster. Kevin Cahen talked to me a bit at Blade this year about marquenching, he claimed (and I've heard it from others) you can drop an untempered marquenched blade on the floor without breaking or cracking it.

Bainite might be a better state for your spring if you still have trouble with it. As I understand it, that would be quenching the steel in a quench heated to around 900 degrees, since you miss the nose of the curve martensite never forms but bainite does. Bainite is supposed to be incredibly tough and is used in many industrial spring applications.
 
Bruce, These two terms represent similar processes but with different results. A mar-quench or interruped quench is the process of quenching into a heated medium such as salts using quench temperatures BELOW THE MARTINSITE START line. Mstart is around 465F(I dont have the HT guide in front of me) for 1095. This process lets you transform to martinsite in a gentler manner than shocking the steel like a normal quench. It also provides a short window of time to straighten or adjust the marquenched part befor it completely hardens and transforms to martinsite.

Martempering is the process where the austentized steel is quenched into a medium that is heated ABOVE the martinsite start line. This process is used to obtain the formation of Banite. This process requires that the part be held at the martempering temperature for a certain length of time. Usually at least 1 hour. There has been some conroversy whether a super long hang time (weeks or months) will tend to create more banite. There are both lower and upper banite, The closer to the martinsite start line the martempering occurs the harder(Rc) the banite(lower banite). Martempering at higher temps creates less hardness, leading up to upper banite. uper banite does not have the same qualities(strength and durability) that lower banite is praised for. Lower banite will register up to the high 50'sRc but does not act like martinsite at these hardnesses. So don't just judge it by Rc. also there is no need to temper lower banite because tempering at a temperature lower than the Ms will not affect the structure.

A real good local source of info would be Bob Kramer, He has done as much martempering as anyone I know of (except Howard C) hope this helps Matt
 
Matt, Thanks alot. Now I know I need to learn more. I thought that if I could get the hardness down in the spring temper range it would be spring steel. I think I need a book on the subject but have never found one on Marquench/temper. What is the HT guide you speek of? Is it avail?

I did talk with Bob Kramer on this subject while in Ephrata at Planet Builders. He got me this far.

BTW, I tested the hammer spring and it works great.

Thanks, Bruce
 
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