Steve Sells Posted January 11, 2009 Share Posted January 11, 2009 Introduction to Heat Treating simple steels. I would like to start off by stating that this is in the blade section because thicker items need different procedures than the thin cross sections we are dealing with in blades. Mill specs that come with an order of new steel are fine for dealing with cross sections that are inches of thickness, but leave the poor blade smith in the dark as to where to begin. Example of 1095, while fine with a water quench for a large tool, when we use it for a knife, it can crack with a standard water quench. In order for our newly made blade to hold an edge, we must get it hardened. Many have asked how to heat treat a blade. So here is a very basic primer on that process. When we finish forging our blade, we have a knife shaped object. To make it hard enough to hold an edge and actually be a blade, we use thermal treatments to change the molecular arrangement of the metal crystals. The following processes only work on steels with a carbon content of 30 points (0.30) or higher, if lower amounts of carbon are present the steel will not harden enough to make a difference. At room temperature steel is in a body centered cubic structure. The cubes of steel have an iron atom at each of the 8 corners of the cube, and one in the center of the box. This is called ferrite. By heating the steel we can change the arrangement of the carbon and iron, into a face centered cubic where iron is at the 8 corners, and carbon is on the six sides of the cube. This form is called austenite. The temperature that this occurs is close and slightly above the curie temperature. Lucky for us there are a few easy ways to identify this point. One is by using a magnet, as steels are non-magnetic at this phase transformation point. Also when you see the color from the glow of the hot metal, there will be a color shift, as the color progresses from orange into yellow from the added heat, at the curie point the color will shift back to a darker orange color as it changes state, then progress toward yellow again. This is very subtle, so trust the magnet. Then remove the steel from the heat, and slowly allow to cool. This is normalizing. It allows stress to relax in the blade. Many do this 3 times to cycle the steel for grain refinement as well to insure no warping. The next time we raise the steel to this curie point, we want to cool it fast enough to freeze the carbon atoms within the cubes of iron. Most of the time this will be done by quenching in Oil, tho some some lower carbon steels will need water to be fast enough, We are only dealing with simple steel here, so will not address air hardening or high alloy steels. When Quenching in a liquid, vapor pockets can form around the steel, so agitation in the form of a gentile up and down motion can break this up andd allow even cooling. Do not use a side to side or any fast motion as this can lead to warping. This quenching creates another form of steel known as martensite, where the carbon is trapped in the iron 'cube'. This is the hardest form steel can take, but it is also very brittle, so we must immediately temper this. I have had blades crack while waiting to temper, so heat the temper oven before you start to harden and you wont have this issue. Tempering relaxes the thermal shock we caused during the hardening process, all hardened blade should at least get a hour or more to relieve the stress. Most take only 320F or so, and I prefer 350F two times at two hours each, with a rest period of one day between. When we harden the blade, there may be retained austenite, rather a small amount of the austenite that has not yet converted to martensite. This will convert into martensite after some time as room temperature or lower, and that is the reason for a second temper cycle, to relieve that also. This is also one reason many use a sub zero quench, for advanced steel treatment, to force the change into martensite. Using a higher tempering temperature will result in a softer blade that takes more beating before breaking, but reduces the edge retention, as with the steel choices, its all a compromise, there is no one size fits all. for further References see PB 0078, and read "Metallurgy of Steel for Bladesmiths & Others who Heat Treat and Forge Steel", by Prof. John D. Verhoeven Quote Link to comment Share on other sites More sharing options...
Spears Posted April 1, 2010 Share Posted April 1, 2010 Beautifully written, I don't make blades but I used to work in tool and die. Thanks for posting. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted April 1, 2010 Share Posted April 1, 2010 I assume you posted this for comments; so: Could you add that the alloy should be a hardenable one to the beginning of that write-up? Also: "The temperature it occurs" is the austenitizing temp that happens to be *close* to the curie temp for *some* alloys; particularly the simple Fe-C ones. added, thank you for pointing that error out Quote Link to comment Share on other sites More sharing options...
brianbrazealblacksmith Posted April 2, 2010 Share Posted April 2, 2010 That has to be the best few sentences on heat treating that I have ever read. Excellent post, Steve! Quote Link to comment Share on other sites More sharing options...
Randy Jr. HHH Knives Posted April 19, 2010 Share Posted April 19, 2010 Im heat treating my first blade today, this has been very helpful thanks Steve! Quote Link to comment Share on other sites More sharing options...
NavySWCC37 Posted December 24, 2012 Share Posted December 24, 2012 fantastic article , Very informative and relevant to my situation and project. keep on rollin Quote Link to comment Share on other sites More sharing options...
cheftjcook Posted December 26, 2012 Share Posted December 26, 2012 Thank you, I printed a copy to keep in the shop. Quote Link to comment Share on other sites More sharing options...
Pug}{maN Posted December 27, 2012 Share Posted December 27, 2012 needed this today ! thanks... Quote Link to comment Share on other sites More sharing options...
Dan C Posted June 18, 2013 Share Posted June 18, 2013 When tempering in an oven I've saw where it was recommended suspending the knife via wire so it's not resting on metal. I don't have this option due to space, but wondered about setting the knife instead on a firebrick in the oven vs. a metal rack. Any preferences? Quote Link to comment Share on other sites More sharing options...
Chinobi Posted June 19, 2013 Share Posted June 19, 2013 theres not enough space to suspend from wire, but you can fit a firebrick in? :) if you have enough room to add clearance to the bottom could you make a thin trivet set or cradle of wire like a mini hammock to set the knife on, rather than hang from? Quote Link to comment Share on other sites More sharing options...
Dan C Posted June 19, 2013 Share Posted June 19, 2013 Thanks Chinobi, I realize now I need to change how I was approaching the question. Instead of hanging up and down it could be suspended horizontally so just the blade isn't making contact. Quote Link to comment Share on other sites More sharing options...
Rich Hale Posted June 19, 2013 Share Posted June 19, 2013 MAy want to try a couple of ways,,,I preheat my oven till it is the correct temp then lay blade on rack flat,,,if you choose to hang or prop it up think about wot you will use and how that may affedt time and temp. For instance a room temp fire brick with a slot to hold the blade will do wot you are thinking,,,,do you know how long the brick will take to come up to temp? Untill it does, the blade will not either.You could preheat the brick ot wotever or jusr add time to the process....wonder how much time? Heat treat oven makers sell a kind of rack..a flat ceramic with verticle rods spaced to hold several blades so the blade does not lay flat,,,I use mine when I heat blade for hardening,,, not tempering, And then I do that i leave the rack in while I preheat the oven before placing blade inside. Quote Link to comment Share on other sites More sharing options...
Dan C Posted June 19, 2013 Share Posted June 19, 2013 Good point on the pre-heating. I was thinking of welding a rack of sorts out of scrap steel that would hold the blade horizontally by the tang. Would that sort of contact if minimalized be a concern? Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted June 19, 2013 Author Share Posted June 19, 2013 for tempering, wire rack contact is not much of a concern, horizontal or vertical. Quote Link to comment Share on other sites More sharing options...
Doug_ Posted July 3, 2013 Share Posted July 3, 2013 Thank You For The Great Info Steve !!!! :D :D :D Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted December 23, 2015 Author Share Posted December 23, 2015 I wonder how many people wish they read this before they ruined their blades, trying to teach themselves with you tube? Quote Link to comment Share on other sites More sharing options...
Michael Cochran Posted December 23, 2015 Share Posted December 23, 2015 My guess is not enough. You know it's really hard to find these pinned topics like this with them tucked neatly in a logical location as they are. Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted December 23, 2015 Author Share Posted December 23, 2015 I have noticed over the years, most posting the simple questions dont look, the ones that have looked dont have to post lol Quote Link to comment Share on other sites More sharing options...
GIJosh Posted December 23, 2015 Share Posted December 23, 2015 Being new to blacksmithing (but not to common sense) I read all the stickies that I could when I first joined and still refer back to them. Not sure why so many don't do the same but my guess is that they have initial misconceptions about the complexity of blacksmithing to begin with due to movies and video games. As for myself, I could have never forged that last set of dragon scale armor of impending sarcasm nor my +5 mithril longsword of unavoidable mockery without doing some homework first. Quote Link to comment Share on other sites More sharing options...
Buchan Posted March 15, 2016 Share Posted March 15, 2016 Interesting reading, thanks Steve. Quote Link to comment Share on other sites More sharing options...
Frosty Posted March 15, 2016 Share Posted March 15, 2016 On 12/22/2015 at 3:17 PM, Steve Sells said: I have noticed over the years, most posting the simple questions dont look, the ones that have looked dont have to post lol Glenn: Is this in the "Gems and Pearls" thread? It's as true as most anything we read here. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Desmond Redmon Posted February 3, 2017 Share Posted February 3, 2017 A word, as someone who has asked questions that are answered in the forums (pinned or not). I asked because what is logical placement isn't obvious to those who don't know as much as the authors. After all it used to be that information was lost when the last person or copy died out, but now it's lost because it is buried in the masses of posts. That said I quit asking while I try to digest the pinned posts at least =-) Quote Link to comment Share on other sites More sharing options...
SLAG Posted February 3, 2017 Share Posted February 3, 2017 Steve, Your sage observation, namely, "I have noticed over the years, most posting the simple questions don't look, the ones that have looked don't have to post". bears a little suspicious relationship to the Latin, phrase "Reductio Ad Absurdum". Taken literally is there no need to post, no need for the forum? Somehow I do NOT think so. Regards, SLAG. Quote Link to comment Share on other sites More sharing options...
Frosty Posted February 3, 2017 Share Posted February 3, 2017 Dan: Your Latin phrase caused me to think a little. Here's an ancient Latin saying I just thought up. "Reducio Via Nauseum." Yeah YEAH I know, bolemia was an accepted practice back then and I'm sure has a proper Latin name. What fun's that though? Okay gang, back to your regular programming. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Marc1 Posted February 3, 2017 Share Posted February 3, 2017 "Reducio Via Nauseum?" err ... I have another one ... Latinus grossus facit tremare pilastros ... (*) Not that Reductio ad absurdum is any better. It may be spelled correctly but it's applied incorrectly. To say that those who post a simple question most of the time have failed to look for the answer, and that those who have found the answer need therefore not to ask a question, is a simple statement of fact and not an argument to prove or disprove anything much less the need for the forum to exist. Since we always talk about 'how to' perhaps the most pertinent latin quote would be this from the poet Virgilio "Vires acquirit eundo" or ... for the common man ... you gain strength (or you get better) as you go. * Maccaronic Latin makes the columns tremble ... (or rattles the building's foundations) Quote Link to comment Share on other sites More sharing options...
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