Rob Browne Posted August 3, 2009 Share Posted August 3, 2009 First I do not consider myself a "bladesmith" in any way. I make the odd knife for the kitchen or workshop and that is it so my question is just from curiosity. A few weeks ago there was a link to a video posted that showed a sword made and at the end the maker flexed it and really bent it and it sprung straight back to shape. If the sword had a differential temper to have a springy "body" and a hard edge why doesn't the hard edge break off when the sword is flexed? Once again, this is for interests sake only on my part. Thanx Quote Link to comment Share on other sites More sharing options...
Charlotte Posted August 3, 2009 Share Posted August 3, 2009 Good question. I'd guess that the heat treatment which left the spine soft also softened the edge enough that it was not brittle hard. I know that in the blade testing for master knife making they bend knives to a right angle and require them to have a certain degree of return and limit the amount of damage to the cutting edge from that treatment. Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted August 3, 2009 Share Posted August 3, 2009 (edited) The ABS test is designed to show one knows how to control the heat treat of the chosen steel. Nothing wrong with making a blade to flex 90 degrees, but it is not needed for most. I rarely make a sword too hard at the edge anyway. On a side note: Very few people are able to sharpen a 3 foot long razor safely, even fewer are able to use a razor sharp sword safely. Edited August 4, 2009 by mod07 Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted August 3, 2009 Share Posted August 3, 2009 The cross section and taper of a sword blade affects how it flexes a whole lot as well. In the Army Museum in Spain they have a Toledo sword blade that is bent into a spiral and embedded in a block of wood as it will spring back true! Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted August 3, 2009 Share Posted August 3, 2009 (edited) I made a lot of highly abused products (demolition tools) and came to have a great deal of respect for straight high carbon steel (1095 in my case) and it's really unique properties. When carbon steel it hardened it expands. This can be seen readily in the quenching of a Samuri sword. It goes into the quench straight and comes out with a graceful curve. By using clay on the backside they achieve hardening only on the edge. When a straight carbon steel is quenched "overall" it only is able to harden to a shallow depth. This means that only the surface has expanded which puts the core is tremendous tension. (these forces can lead to cracking before tempering). So now we have a near "compound" material with the core it tension and shell in compression. A near ideal situation for a structural piece. Have you ever paid attention to concrete pilings being driven? How the heck can brittle ol' concrete flex like that? It's amazing to see. Well, they have tension cables running through them placing the concrete under compression. When they are subjected to a bending force the surface cannot be put in tension until that compressive force is relieved, otherwise it would crack. You see where I'm going with this, right? The EXACT same physics applies to our carbon steel with it's core in tension and the shell in compression. You can't produce tension on the surface that would cause cracking until you've relieved all the compression it's under from the core. This greatly extends the range of flexure that the blade can take without cracking or "taking a set". S.T.O.C.K. from Edited August 3, 2009 by nakedanvil Quote Link to comment Share on other sites More sharing options...
Rob Browne Posted August 3, 2009 Author Share Posted August 3, 2009 Thanks for the feedback. I'll have to read Grant's answer a few times to gete my head right around it though :) Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted August 4, 2009 Share Posted August 4, 2009 shallow hardening means a lot more hardening difference with a large cross section as with a hammer or anchor, than in thin cross sections as with a blade, its all relative. Quote Link to comment Share on other sites More sharing options...
AndrewOC Posted August 4, 2009 Share Posted August 4, 2009 The historic fencers i know that meet at Denistone (one comes from your way too, Rob) prefer flex/bending to edge holding. A lot safer (fewer chips and breaks) and the edge cops a real hiding in bouts. Soo i imagine differential hardening is not a priority there. Grant; i've never seen concrete pilings being (pile) driven, does the upper end free from the ground wave around? Is this the flex you refer to? In Aus i've heard of 'pre-stressed' concrete members; is this the same as the cable reo in the piles you refer to? Regards Andrew O'C Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted August 4, 2009 Share Posted August 4, 2009 Concrete pile: No, but when the stand them up to drive they sag incredibly and when thy're driving them the middle is "twanging" all over. Yes, most precast concrete member are done that way. Quote Link to comment Share on other sites More sharing options...
Charlotte Posted August 4, 2009 Share Posted August 4, 2009 In south Louisiana almost everything is on pilings. It is amazing to watch concrete being done than way. Our Interstate highways in and around New Orleans are set on driven concrete pilings. The thing that is most astonishing is that the end that get the pounding doesen't crumble. It takes a beating sure but not like you think it might. Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted August 5, 2009 Share Posted August 5, 2009 There's actually a pretty good steel cap on them for welding on more section if needed, although they make them in incredible lengths, like 80 - 100 feet. I have see them break when driving, more like explode! No doubt due the internal compression. Quote Link to comment Share on other sites More sharing options...
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