Flex testing

[SkagSig40]

I was wondering when you put a blade in a vice and flex it and it returns to true does it have any bad effect to the steel/blade like when you flex a blade and it takes a set? I guess what I'm trying to find out is if a blade does return to true is there any "internal" damage to the steel, is the steel weakend at all? I'm guesing not because truck springs (5160) flex and return to true over thousands of miles and never break. When a blade takes a set there is "internal" damage weakening the blade, right? Thanks for the input!

 

[Bruce Bump]

Chris, The temper that it takes to make a spring is different than a knife. Truck springs wont hold an edge because they are softer than a knife temper. A knife that is bent to 90 degrees wont return to true. The back is soft and the edge is hard. There is perfect spring temper in between somewhere. Ive never tried it but I bet a truck spring bent to 90 wont return to true either.

 

[raker]

All steel will flex some and there is a maximum degree of flex in all blades that will result in permanant deformation. The amount of flex will be different for the different steels that are heat treated differently. The amount of deformation in a given radius of bend will usually be constant for all steels in same condition of temper. If the knife was long enough, it would return back to true and there would be no permanant deformation of the steel even if you bent it in a circle (that would be a verry long blade). If it is slightly too hard, it will snap when it reaches a certain point. Even very hard blades will bend to some degree. Flexing the steel below the point of permanant deformation will, over a period of time, cause the steel to work harden and will gradually build up stresses in the steel to the point that it could develope cracks. An example is a 2 bladed boat prop that is designed for high speed. If the blades are not annealed after about 3 races, one of the blades will break off. This is due to the extreme flexing that the prop does. A knife will not go through any where near the amount of flexing that a prop will so we don't have to worry about that a lot. If it worries you, then it is always possible to temper the blade again to relieve the stress in the blade. If you used the knife a lot, maybe in 40 to 50 years.

 

[SkagSig40]

That makes sense! I was wondering this because I test out every knife I buy to be sure it will not fail in the field in normal use. I usually put the blade in a vice and try to flex it several times in both directions. I like thick blades for the extra strength and sometimes all my 175lbs will barley flex the blade and usually I'll get maybe 15 degrees of flex on most knives befor I stop. I'm usually happy with a blade going that far and springing back. I just was just thinking about this and hoping I wasn't doing any unseen damage to all my knives by flexing them during initial testing. Thank you for the input!