I am making some drill steels for single jack rock drilling competitions that I compete in. I am making them out of 1'' hex digging bars that are high carbon steel supposedly? I have made a few on a little lathe that I have but I am having trouble tempering them. I need the chisel end as hard as i can get it with out breaking and the end that i hit with the hammer to be hard enough not to mushroom. I tried one in a coal forge my buddy has. Heated the whole thing to cherry red then quenched the tip in water for about five seconds then pulled it out for about a minute then quenched the whole thing for about five to ten seconds then let air cool. When I struck it a few times with a hammer the chisel end shattered so its too hard I am thinking. This is all new to me so if anyone could give me some advice on how to temper these things i would be grateful. 

Did you temper it after you hardened it? You didn't mention any kind of temper so I'm guessing you went straight to using it after you quenched it. Once quenched the steel has a bunch of stress that needs to be relieved and it's much to hard and brittle to be used for anything.

Welcome to the site Stephen, add your location to your profile as you may be close enough to someone who can help show you how to achieve best results.

Although I can imagine what a digging bar is I don;t know what material it's made from or what you require for the rock drill, so I'll leave it to others to offer the correct advice.....however it seems to me you have hardened it and not tempered it....

No i guess not? I thought I was tempering it but i guess i just hardened it. How do you temper it after hardening? 

 

Strongly suggest you read the heat treating stickies in the knifemaking section!!!!

Do you want it to be really hard, or really tough?

I need them as hard as i can get them but not shatter with repeated blows from a 4 pound sledge . Here is a pic of the ones i have made so far the smallest one is the one that broke. the other three I heated to cherry red then quenched in oil for about five seconds. They seem too soft. 

Disappearing posts...

 

One of the rules is the steels cannot be hard faced. 

 

That's going to take some experimentation... Diferentialy temper with the cutting edge down in coolant or on a quench block (cooled aluminum) light straw is the color the old books say, that's 401f for the cutting edge, but idiots not backed with softer it's gunna break. Probably purple (540f) for the struck end (that's stone carving tool hard) and light blue (649f) for the rest of the tool (spring). Now this is a guess as to where to start. So this is were it's a pain. Bring it to no magnetic (red hot) and dribble a little table salt on it. If it melts it's hot enough. Quench till you can touch it. Heat in an oven till it is straw (400f +/-) now place it tip up and heat the middle till the tip reaches straw and flip and stick in a shallow bit of water and heat the middle till the struckend is purple. Quench, test and adjust. Practic and you can quench each end and let the heat run to the ends, but this is tricky

Thanks that's a lot of help.

 

One thing that would help is starting with a known steel that has some documentation about the heat treating method.  Otherwise you're trying to reverse engineer the hardening characteristics of the steel.  Maybe you'll want to buy a hunk of S7.  Its what jackhammer bits are made of and made to stand up to pounding.  With that digging bar, you don't know if it works best quenched in oil, water, or air (although I doubt air) and you don't know how to best temper it after the hardening.

dont know what steel you have,  didnt read anything about heat treating? good luck, I am off to my day job for another 12 installing some kind of wire

Your digging bars are more likely to be medium carbon steel.  Good steel for digging in dirt, not really the specialized alloy that would perform best for rock drilling! What you want is a steel with high impact and abrasion resistance!  Jack hammer bits are a likely salvage source!  

The partial quenching/tempering process that you seem to have attempted is quite skill dependent and really only makes sense for experts doing repetitive high volume work.  You'll do better with a full quench (I would use oil) followed by tempering.  LOTS of info in our archives here on quenching and tempering!  You have lots to learn, but that's the JOY of it all!  Drill into it!  Have FUN!!!

99 and 44/100% of jackhammer bits ARE NOT S SERIES STEEL.  That got put in some of the "junkyard steel lists" as Machinerys Handbook listed S series as a good alloy for jackhammer bits; well solid gold makes GREAT frying pans and Titanium makes great car bodies----you see any of those around?  A gentleman on this forum who's career was resharpening jack hammer bits said that out of the Million, (yes *million*)  ones he had re-worked only a handful were anything fancier than 1050; because 1050 would do an acceptable job and was way cheaper than high alloy steels.

Thanks for the correction.  I'll put that particular false fact that everybody knows out of my mind.  

Happy New Year Stephen,

You NEED to know what the steel is that you have, before you can begin the conversation of asking for HELP.

Digging Bar, could be anything. The Manufacture will not tell you, Trade Secret. If you purchase some new material, you will know what you have and you can do your research in the different quenching mediums and temperatures. Tempering is essential!!. Hardening and Tempering can be done together, when you learn what you are doing.

You are starting the learning process by learning what does not work. The School of Hard Knocks will teach you, if you don't take the time to study some of the pages that people have spent huge amounts of time posting on this Forum. Pack your lunch and beverage, sit down and read, and read some more, etc.

Enjoy the Journey, there is no simple answer.

Neil

S series tool steel can be bought from good steel suppliers as well as machine shop suppliers like  MSC, ENCO, McMaster Carr, as well as others.

Also check into professional heat treating. When I had my shop we used a company that had a few smaller furnaces, so their minimum rate was $50. $50 covered a lot of material, plus they had a 24 hr turn around. Great company, with knowledgeable tech guys that helped me out on the die sets I was making at the time.

 

Thanks. I am going try and get some o-1 . I reheated the steels to cherry red, quenched in water one of them got a hair line crack? Then I put them in the oven for 400 for a hr and re-quenched. Tried them out they work great. I didn't try the one with the crack. I am going to try a oil quench next.

O-1 gets very brittle, not sure how it will take the hammering. Make sure you have eye protection.  S-7 will probably be a better choice since it is formulated to take abuse.

Another note - the "O" in O1 stands for oil quenching.  You are asking for trouble by quenching it in water.  I'm surprised you just had one of them get a crack.  I've had some O1 even air harden a bit when making a knife from it.  Found it out the hard way when I tried to drill holes in the tang.  Also, O1 is supposed to soak for about 10 to 20 minutes before quenching.  It takes me a  while to play with the propane pressure, air, and a magnet to get a stable temperature for the soak.   You can get hard steel without the soak, but if you're trying to get the most out of it.........

Sounds like you have some more reading to do, could have saved you some trouble. All the info is on the site. From my limited experience it sounds like you want something on the tougher side not HARD, hard is brittle and your not looking for a durable shard cutting edge but a tool to take a pounding that is gonna hold up. 

Isn't S7 a couple of steps up in difficulty (forging, heat treatment, and machining) from the simpler steels? I'd think something like 1075 or O-1 would be a better choice in this case.

Yeah I am new to this so simpler is better for now.

 

The cutting edge has to be hard to pulverize the rock, but it has to be backed by tough or it will chip and fracture. That's why it will have to be diferentualy temperd. Ideally for a compitition you only need the very tip rock drill hard (just enough to not were down in drilling the prescribed hole) it would require dressing and heat treat for every compitition and experimintation and research to get the best combination of alloy, heat treatment and edge geometry.