Guest EMKnives Posted July 3, 2012 Share Posted July 3, 2012 So I finally got around to forging my first blades, and everything was going good until I decided to eat some scale off with vinegar... I left them in the vinegar over night and there was still some scale on them, so i left them in for another 2 nights and when I pulled them out and took a kitchen sponge to them I found that there was some serious cracking in the blades. I made them out of HF prybars by heating, straightening, annealing, forging, normalizing 3x, quenching 3x, and tempering 3x. I did not see cracks on the first or second day of vinegar but I did today. One of the blades is severly cracked, and the other one has only 1 visible crack. Sorta stumped on what is going on with these things. Quote Link to comment Share on other sites More sharing options...
pkrankow Posted July 3, 2012 Share Posted July 3, 2012 Need the whole story. What temperature did you normalize at, and quench from? What temperature control did you use? What quench medium did you use? How did you temper? What temperature did you temper to? The vinegar soak did not likely cause the cracks. I would guess too high of a temperature for the quench or too fast of a quench medium. I have broken things when everything is done right too. Phil Quote Link to comment Share on other sites More sharing options...
pete46 Posted July 3, 2012 Share Posted July 3, 2012 For mystery steel I anneal as my 1st step. At the very least normalize to releave stress from it's previous life. Quote Link to comment Share on other sites More sharing options...
Rich Hale Posted July 3, 2012 Share Posted July 3, 2012 Coil springs from a full size american car may be a better choice for blades.. I am not sure wot the carbon content is of those pry bars,,,,,,,, Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted July 3, 2012 Share Posted July 3, 2012 A few things I noticed is that some of those cracks seem to start at what looks like a hammer ding to my eye. Also quenching with rough scratches still present is an invitation for cracking. So did you forge at the correct temperature and *never* hit the metal too cold? What quench medium did you use and did you test a piece in that medium BEFORE you risked your blades? I'd guess you need to dress your hammer face better as some of the dings look to have sharp edges too. (And I too have run into "scrap" that will not make a blade as it cracked no matter what I did---I wondered if it actually had some proto-cracks from it's previous use.) Quote Link to comment Share on other sites More sharing options...
Guest EMKnives Posted July 3, 2012 Share Posted July 3, 2012 Ok, so I made these over the course of a few weeks. I heated them both to a medium red, 1300-1500ish, and got rid of any bends. I then got them back up to a red with hints of orange 1800-1900ish and then turned off the burners in my forge and let it cool over night. I did this twice for the smaller one and only once for the larger of the two. They were noticeably softer after doing this. For the forging, I tried to keep them in the red range and believe I only hit them once or twice when they were two cold. After I was happy with the rough forge I took both of them to a orangish red 1900 - 2000ish, and then let them cool to where I could grab them with a welding glove and not feel heat soaking through. The cooling was done in the forge after the burners have been turned off. Up to this point I think I was doing alright, I have a feeling I messed up on the heat treating temps. The first heat / quench I brought them to a redish orange and dropped them in 150ish degree veggi oil. They were non magnetic when I did this so assumed this was the correct temp for the metal. The second time I put a magnet to them and found that they were non magnetic much sooner than I thought. So the second and third times were quenched in veggie oil at a red that had much less orange in it than the first time. I was a bit pressed for time when I was doing the HT and did not have time to immediately put them in a my oven like I wanted. So after about 36hours, I came back and tossed them into a toaster over set to 475ish degrees 3 times, for 2 hours each. I let them cool to room temperature between being put in the over. Then the vinegar was used for almost 2 days. Here's the chart I was using for metal temps http://www.houseoffi...ingtemperature/. All my tool are new: ball pein, cross pein and anvil. I knew I needed to dress the sharp edges on my anvil but did not know a hammer required dressing. I was using the middle of the anvil and the horn and never landing a strike on the edge... or so I thought. Quote Link to comment Share on other sites More sharing options...
Rich Hale Posted July 3, 2012 Share Posted July 3, 2012 Tempil sticks are sold in welding shops, you wipe them accross a piece of hot metal and each one is marked as to wot color the stick will make a mark like a crayon. if the metal is too cold for the stick it will not mark or leave a rough mark. From that you calibrate your eye to see wot temp is for a piece of steel you have heated. Simply put: a stick marked 1500f, heat metal and keep checking til stick wipes a mark..remember that color..It is the temp marked on the stick..Now if you know wot temp you wish to forge or heat treat at yoiu can start the forging session at a known heat. And keep it in that range. Putting it back in the forge is up to you. Temp; control of forging is a really big deal. Same with heat treat colors..get a sltick to guide you for the metal you are working with. Use that stick to become familiar with the color at that temp and then reheat to make up for lost heat while checking and then into the quench. You will not likely need many sticks to cover the ranges you will work with. This help adjust to the ambient light. In shade or sun this will tell you real close as to temps of hot metal. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted July 3, 2012 Share Posted July 3, 2012 In the 30+ years I have been smithing I don't recall *ever* seeing a new commercial hammer that didn't require dressing for use in smithing. Now you can sometimes find old ones "pre-dressed" and many of the custom hammers come properly dressed. Too hot could be a problem but 36 hours between quenching and tempering!!!!!!!!!!!!!!! I get nervous if it's longer than 15 minutes. If you can't get to tempering ASAP don't do the hardening! I had one student leave a hardened but untempered blade on his workbench overnight and came the next morning to find it in 3 pieces. So a target rich environment as to issues that could cause problems. Do you have a mentor; or are you winging this on your own? Quote Link to comment Share on other sites More sharing options...
bigfootnampa Posted July 3, 2012 Share Posted July 3, 2012 The hammers DO need to be dressed. You cannot get by with hitting the metal when it is too cold... even ONCE could create a problem. You will have better success if you anneal immediately after quenching. 36 hours or even ONE hour later could be disastrous. You have several issues to address and I expect that by the time you get those fixed you'll be having more success. Quote Link to comment Share on other sites More sharing options...
Rich Hale Posted July 3, 2012 Share Posted July 3, 2012 Anneal immediately after quenching? i do not do that at all..Is there an off chance you mean to temper after quench,,,? That I do.! Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted July 3, 2012 Share Posted July 3, 2012 Yah that's a typo *temper* immediately after quenching. Quote Link to comment Share on other sites More sharing options...
pkrankow Posted July 4, 2012 Share Posted July 4, 2012 If nothing else put a strong magnet on a thin copper wire, and hang it up. If the magnet is attracted to the steel, it has not reached 1450F, if it swings naturally then it has reached 1450F and become non-magnetic. The problem with this is the steel remains non-magnetic till it drops below about 800F, so you only get to examine the temperature once going up. You can normalize, anneal, or harden many steels from at or just above non-magnetic. I use a ceramic donut magnet from Radio Shack and a strand out of an old network or phone cable. I hang it from the handle of my hand truck, since I had to move the anvil and such all out onto the driveway. Most store bought hammers have horrible swirl marks on the faces, and hard corners. Remove the swirls and dress to a "watch glass" in profile. Phil Quote Link to comment Share on other sites More sharing options...
jmccustomknives Posted July 4, 2012 Share Posted July 4, 2012 Wow, I don't think I've ever seen one crack that way. Pry bars are usually going to be a medium carbon steel, with modern ones being like an 8630 or the like. Not exactly the best for bladesmithing. Break one, I know that isn't what you want to do but it will go a long way to tell you what you did wrong. If the grain is real rough that usually means you overheated the steel before quench. A fine grain means you got the quench right but you may be using too fast of a quenchant. I've never used a chrome moly steel for forging, if anyone here has mabe they've had cracking issues. One other thing is overheating in the final forge. A lot of smiths will quench right out of the forge, I prefer to clean the blade up. You do it that way and any cracks that might be there will show up before the quench plus any deep hammer marks will be found before they can cause a stress riser. Quote Link to comment Share on other sites More sharing options...
Chuck_Steak Posted July 6, 2012 Share Posted July 6, 2012 Hey Guys, I wanted to throw my 2C in on this discussion. By the failure circumstances, i'm going to say they failed due to Hydrogen Embrittlement (HE). Hydrogen embrittlement occurs when a susceptible material containing absorbed atomic hydrogen is subjected to a sustained static tensile stress. Steels at hardnesses greater than approximately 30 Rockwell C are susceptible to hydrogen embrittlement, with the susceptibility increasing with increasing hardness. The sustained static tensile stress is likely the result of the residual stresses from the heat treatment procedure. (Most likely it was done properly, but residual stresses are going to be present). The absorbed hydrogen is the result of the vinegar cleaning. HE cracking typically occurs within approximately 48 hours of the introduction of the hydrogen (In this case, 2 days after the start of the vinegar cleaning), so the timing is pretty much right. HE is well known in the plating industry because Grade 5 and Grade 8 fasteners are heat treated to high enough hardnesses to be susceptible. In that case the acid is from the electroplating process, however, Hydrogen can be absorbed from pickling or other acid cleaning processes. To prevent hydrogen embrittlement, a hydrogen relief baking treatment is usually specified, which is typically performed at 400F for 4 hours, within 4 hours of the introduction of the hydrogen. So if you acid cleaned the parts for a couple hours, you would then bake the part out to diffuse the hydrogen from the microstructure. If the part is in the acid for two days, then you don't really have a chance to bake the part out. If you still have the failed part, PM me, I could take a look at it on our SEM and tell you whether it was hydrogen or a quench crack or something different, assuming the fracture features weren't completely destroyed by the cleaning process after the cracks occurred. Basically I'd just open up one of the cracks and see what the fracture morphology looks like. Heck, as long as I was messing around, I'd probably polish and etch a cross section and show you what your microstructure looks like. Quote Link to comment Share on other sites More sharing options...
2Tim215 Posted July 6, 2012 Share Posted July 6, 2012 The hydrogen thing is interesting and poses some questions. Would all or most acids do this? If so the why would it only affect certain steel types? The cracks as posted in the pics are so similar to those I used to experience when I first started forging steels like 52100. Steels that DON"T like anything above critical and the problem with unknown steels is that you don't know what their critical temp range is. Pry bars are not always a med carbon steel and I have seen many that are alloy steels specifically for their flexibility and durability. These alloys can have Cr/Ni/Mg is differing amounts that can cause havoc in forging. High amounts of Mg and Cr especially. 52100 has: Manganese .25-.45 Chromium 1.30-1.60 When I first started forging knives I also tried unknown steels and though it was a good learning curve it's better and cheaper to buy known steels that work. The time and effort spent working behind a forge is not worth it if it fails when you have steels like 5160/O1 etc readily available. If these are not in your area the stick to known leaf springs (EN 45 and 5160) they make excellent knives. What takes the average forger two hours with "friendly" steels to forge a blade can take me up to 8 hours to forge 52100 with the normalizing and annealing cycle I follow and because of this I have never experienced cracks like that again nor have I had a blade fail. Quote Link to comment Share on other sites More sharing options...
HWooldridge Posted July 7, 2012 Share Posted July 7, 2012 Retained austenite...try a subzero quench to convert the austenite to martensite. I'm not a knifemaker but have been involved in a lot of commercial heat treating experiences over the years and have learned internal stress leads to all sorts of problems. You also have the potential for notch effect so that any microscopic crack or corner can propagate into a visible defect while under stress. Quote Link to comment Share on other sites More sharing options...
Guest EMKnives Posted July 8, 2012 Share Posted July 8, 2012 Got some running around to do today for sure! Going to grab some Temp sticks, pickup some steel (1095 and 5160), grab an old electric kitchen oven and then break the larger of the two knifes to check that grain structure. Any ideas on how to break it safely btw? Also thanks for the help on this guys, I really appreciate it. Quote Link to comment Share on other sites More sharing options...
pkrankow Posted July 8, 2012 Share Posted July 8, 2012 Wrap in heavy rag, like denim or canvas, use several layers and not too tight. Clamp in vise. Hit with hammer. The wrappings are no guarantee that pieces won't go flying, so wear eye protection and other PPE. Phil Quote Link to comment Share on other sites More sharing options...
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