mystery steel woes (coil spring)

[Myles Mulkey]

Hey forumites, I have had a bad day. Maybe you guys can help me figure out where I went wrong. I've been working on pocket knives for my groomsmen (getting married in a month!), and I have had nothing but trouble from these knives the whole time. They were butt welded wrought and quarter inch coil spring (no idea where from, it's been sitting around forever). They ended up super teeny tiny, but I figured they would be alright as pocket knives. But I got a bad surprise this evening.

 

I decided to etch the one I polished earlier this evening while I had the time. When I pulled it out of the etch, I noticed a small, straight crack running perpendicular to the edge. As I looked up and down the edge, I counted nine cracks, spaced closer together towards the tip. Absolutely ruined. Have to start all over. I fear the rest of this batch will end up the same way.

 

Now, I've cracked blades before when quenching in water, but these were oil quenched. They were normalized three times, and they looked fine when they came out of the quench. But they obviously weren't fine. I just don't know where I went wrong. I quenched at non-magnetic. These were thin blades and they cooled quickly when taken out of the fire, but I took care not to forge too cold. They were tempered to a damn light blue color; too soft really. What happened??? Why the cracks??? I bent it to almost 90 degrees before the steel broke along one of the cracks. Grain looks fine. What did I do?

By the way, when I forge the replacemets, I'm making them thick and wide and out of predictable, non-alloy steel. No more of this "sleek, never know it's in your pocket" stuff. BIG, STRONG, GRRRRR haha

[Freya W. Ward]

Leaf and coil springs can develop small cracks over their life as car parts. That might be what happened here. That's why I avoid the stuff now

[ryanwrath]

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what freya said. I have quenched many hundreds of different mystery spring type steels in oil, always with used steel its a crap shoot.......ONe interesting thing to note: i do A LOT of air arc metal removal and there is some dynamic i do not know how to explain techniquely.........but under the air arc, i can trace and root out hairline stress fractures that the naked eye cannot see, only revealed by xray..........if this has to do with the intense light, and how it is refracted into my eyeball or some other mechanice i dont know, but it is a stark naked look at metal that has been incredibly stressed into oblivion and beyond...........all that to say, old, used, tired steel is just that: old, tired, used steel......the brightside is depending on your knowledge you know how to make it young and new again........

[Jeroen Zuiderwijk]

With used steels, avoid anything that endured many cycles of (high) loading during its lifetime, as they can protentially be full of fatigue cracks. Most cracks will be microscopic, but they are there. So car springs, axles etc. are best to be avoided. It's too bad, because I frequently find bits of coil springs along the road, great shape and steel to make small knives, but unfortunately not suitable due to fatigue cracks (which is exactly why they broke off in the first place).

[Myles Mulkey]

Ah well that makes sense. Thanks everyone! I will avoid this kind of thing from now on.