Timing between normalizing and quenching

[Chris Pariso]

Hey all, 

I have a piece of 5160 (purchased as such - not scrapped leaf spring) that I am making a small hiking/utility blade out of for my wife. For all the reading and research I've done on the heat treating process, there is one thing that I have not yet found a definitive answer on: if I do three cycles of normalizing, would there be any detriment to the steel if I did not immediately follow it up by heating and quenching it? That is, if I wait to do the quenching until a few hours later (when it's dark enough to see the color of the steel), or a few days later, would I be introducing any potential issues into the final product? 

Worth noting: I'm a complete novice in the entire blacksmithing world, operating with the simplest of equipment, and learning as I go (well, trying to learn *before* I go). I know sending the steel out for heat treat is optimum, but by that rational, purchasing the knife would be better than making it. I appreciate any thoughts or advice you're willing to share! 

[Steve Sells]

no problem, harden now or later,  wont effect it

 

[JHCC]

My understanding is that the critical timing issue is between hardening and tempering, as the stresses of the former need to be relieved by the latter before they cause cracking. Since normalizing is a stress-relieving procedure, you're not setting up anything that would cause issues.

[Chris Pariso]

Steve and JHCC,

That is exactly what I was hoping to hear - thank you!

Also, this went from asked to answered in under 3 minutes... that has to be close to a record, right?

[JHCC]

Yes, that took an unconscionably long time. Our apologies.

Welcome to IFI, by the way. If you haven't yet, please READ THIS FIRST!!!

[Chris Pariso]

JHCC, 

The answer was what I hoped it would be, so all is forgiven. Once the project is all said and done, I'll be sure to let everyone know how it came out.

[Lou L]

Chris, nice to see another denizen of CT on here.  Have you joined the CT Blacksmith Guild?

Good luck on the knife.  Please do keep us in the loop.  A word of advice from my own recent experience:

  The color of the 5160 when it is at quenching temp is not as bright as you might think.  If you watch videos of people doing it you can be tricked by the camera’s color management or by the fact that many people quench well past the right temp.  I aimed for about 100 degrees past non-magnetic and used color as well.  If you have left over steel try it a few times with scrap to get a feel for it.

Lou

[Latticino]

Also don't dawdle on the way to the quench tank, you need the quick cooling from the fluid to get under the nose in time.  If using canola, which will work great for a deep hardening steel like 5160, preheat to 120 -140 deg F.

[Chris Pariso]

Lou - New England represent! I'm in CT by way of New Hampshire, and happy to run into anyone from the North East. I haven't yet joined the guild, as I just finished setting up my forge about three weeks ago (bought everything as a gift for my first Father's Day). Good to know about the color of 5160, too - I plan on giving the heat treat a shot some time this week, so I'll definitely keep that in mind.

 

Latticino - Canola was the plan, and thank you for the advice on speed and preheat temps. I spent about 11 years as a professional baker/pastry chef, so getting everything prepped and ready to go before the oven (forge) is kicked on is standard procedure for me. Mise en place is just as important in the smithy as the kitchen, I'm finding.

[Lou L]

Let us know how it went.  

I just had a quench fiasco myself two days ago.  The knife was too darn long, the coal fire was too old and dirty and I was too impatient.  I should have cleaned out the fire pot and built up a nice large ball of heat.  Instead I frustrated myself for a half hour trying to get even heat  along the length of the blade....and then rebuilt the fire.  It was the single most powerful inspiration for building a propane forge!  I seriously had to keep reminding myself, “3000 years worth of smiths have done it this way...you can do it too.”  

Once is set myself up for success it worked out.  I think....

[ThomasPowers]

You were missing the 3000 years of having assistants keeping the fire tuned for you...

Of course in the "early years" they were not heat treating their blades---but a good 2000 years none the less..."The Celtic Sword", Radomir Pleiner,  has an interesting look at the metallography of ferrous Celtic blades showing all the fun they had trying to figure out alloy and heat treat in those days.

[Chris Pariso]

Lou -

I didn't want my wife's gift to be the first piece of steel I attempted to heat treat, so I spent part of yesterday pounding out a utility blade for myself to use as a tester. After I was done hammering it, I normalized three times, then started filing/grinding to get the final profile. That finished up around 10am, and I waited until about 8pm that night to do the quench. Heated to what looked like the right temp, held it there for a few minutes, and quenched in 130f canola oil. I did this twice, then immediately tempered at 385f for one hour. No bends, warps, cracks, or anything else that I could see, and a file I used earlier to clean up the profile skated right off of it once everything was said and done. Granted, this is a single data point, but it seems like waiting between normalizing and quenching/tempering wasn't an issue at all. Of course, this is also the first time I've taken a piece of metal from stock to knife, and the first time I've heat treated anything, so it could just be beginners luck!

Either way, after a quick paracord wrap and some time on the whetstone, I have myself a new beater utility knife that I'm pretty happy with. Going to take lessons learned from this one, and try to finish my wife's blade this weekend. Thanks again to everyone for the advice!

[ThomasPowers]

Why quench twice? Usually you normalize multiple times to refine grain; harden once and temper multiple times.

[Chris Pariso]

Thomas,

From the reading I had done, multiple quenches could help overcome some of the potential shortcomings from not having a time/temp controlled furnace for soak the metal at its critical temp. That said, it seems like everyone has their own secret sauce for heat treating any given steel, so I figured I would end up trying and testing a number of different processes before I found a winning combination. Take detailed notes, fire, and adjust.

That said, I will definitely try what you said for my wife's blade. When tempering multiple times, do you pull the piece out of the oven, let it cool to room temp, then pop it back in for another hour? Or is the wait between heats longer?

[ThomasPowers]

For tempering cooling to ambient is fine.

The idea of multiple tempering cycles is that the percentage of the steel that converts is not 100% so if each cycle takes care of say 90% then 1 cycle 90%  converted : leaving 10%; two cycles 99:1, 3 cycles 99.9 : .1 and diminishing returns...

As I recall multiple hardenings tend to make an alloy react as a more shallow hardening steel; which may not make a difference depending on your alloy. 

Any of the metallurgists here feel free to correct me; been a long time and a little TBI  since MatSci in college; in the late 1970's...

[Lou L]

I read an article by Ed Caffrey in which he purported that there was a benefit in strength and sharpness of knives made of 5160 when triple quenched.  He claimed to have made samples using identical methods in heat treatment ovens and quenched knives up to four times.  He then tested them and had the grain analyzed by a metallurgist.  He found a 15% improvement with three quenches and no benefit to the fourth.  He left the knife in the oil each time and came back to it the next day.  I’ve also read other people arguing that the idea was nonsense.  I’ve tried finding the article just now but couldn’t.  If there is interest I will keep looking.

For knuckleheads like me, in their simple home forge, the odds of getting those proposed benefits are highly unlikely.  We are, after all, essentially guessing at proper temperatures.

Chris, I’d seriously suggest you use a magnet to check for when the steel goes non-magnetic as your target temperature is just 100 degrees higher than that.  It gives you a good basis for the type of guesswork we are doing and helps identify the right colors so that, one day, we can be accurate going by eye alone.

Thomas, I seriously could have used those people managing my fire for me, but it was my failure alone.  I knew it was on its last legs and thought I could get away with it and then shut the forge down.  The easy path is always the hardest.

[Chris Pariso]

Lou,

I think one of the things that I read was referencing that article by Caffrey - the information matches what I was seeing. I completely agree, too, that backyard setups like ours probably can't reach the full potential of a test done under (essentially) laboratory conditions. Oh, and I did use a magnet to identify the color, as close as I could tell, when the steel became non-magnetic, then took it just slightly brighter. Between that, and looking at the changes in color between temperatures on a scale that I looked up, I was able to gauge things (I know color scales on a screen can be inaccurate, so I was more focused on change in shade/brightness from one temp to another, rather than the actual color shown on the scale).

 

Thomas,

Thank you for the info. Now a day later, would I still be able to unwrap the blade and put it into the oven for two more tempering cycles, or does that have to be done immediately after hardening to have the desired effect?

[ThomasPowers]

Anytime after.

[Lou L]

Chris, I’m “color impaired” which is the correct term for what people usual call lcolor blind”.  Basically, I can’t see a number of wavelengths in blue, green, and red.  I always doubt what colors I’m seeing.  Still, when I turn off the lights in the shop, I feel I’m getting good at determining the colors of the steel.  I’ve seen those co.or scales but pretty much wrote them off because of my eyes.  You just reminded me of that option and I think I need to go ahead and get a proper one.  I will look into buying one because I don’t trust my printer and I want it laminated.  Thanks for the idea whether you intended to give it to me or not.

I just did only one tempering cycle on the last knife two days ago because my wife was none too pleased with me two days ago.  It’s been super hot and humid here and I use the oven in the kitchen.  A second tempering was not in the cards!

Good luck on yours!

Lou

[JHCC]

20 minutes ago, Lou L said:

I just did only one tempering cycle on the last knife two days ago because my wife was none too pleased with me two days ago.  It’s been super hot and humid here and I use the oven in the kitchen.  A second tempering was not in the cards!

This is why so many blademakers keep a toaster oven in the shop. I've been experimenting with tempering tongs, myself.

[Lou L]

I have our last toaster oven in storage.  I was hoping to dismantle it, add firebrick walls, and install a cheap thermocouple.  Once again my flights of fancy inhibit progress!

[Chris Pariso]

Toaster oven isn't a bad idea at all... Now, is there any danger of the knife being too close to the heating coils in a small toaster oven, and being brought to a temp a lot higher than what it should be for tempering?

[JME1149]

You could always put a piece of pipe in the toaster oven and preheat that, then place the blade inside the pipe for the temper cycle.

[Chris Pariso]

JME - ahh, basically adding an insulating layer to protect it from the direct heat... I like it. I might have to swing by the store on my way home, and get a cheap toaster/temper oven. I know my wife would appreciate not having the oven on for several hours at a stretch, especially in this heat! Thanks for the tip!

[Latticino]

In my experience, thermal mass inside a toaster oven is the key to the stability that you want.  Ideally the thermal mass should be in actual contact with the stock being tempered.  One trick I like is to use a shallow pan filled with sand.  Heat that to tempering temperature in the toaster first,  then put your piece into it for the hour soak inside the oven.