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Thread: Turning High Tensile Steel.
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29th Nov 2018, 09:07 AM #16Most Valued Member
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29th Nov 2018, 10:32 AM #17
given that it's 40 years since I last did any work using bolted joints, what I recall could be wrong
high tensile bolted joints are not really "bolted together". When a HT bolt is "done up" it is streteched along its length. The elastic properties of the steel convert this stretching into a clamping force that acts to increase the friction between the plates being bolted together. It is this friction between the plates that gives the joint its strength, not the properties of the bolt itself. A HT bolted joint fails when the joined plates move (slip) relative to each other. I don't recall how much strength the bolt by itself added to the joint, but do recall that if the bolts weren't fully tightened (i.e. stretched) the bolts would sheer (i.e. break) relatively easily.
a joint bolted with mild steel bolts gets its strength from the toughness of the shank of the bolt and the properties of the metal plates. The joint fails when the bolt bends too much or the plate buckles against the shank of the bolt. The primary purpose of the nut on a mild steel bolt is to stop the bolt itself falling out of the bolt hole. A mild steel bolt will hold two pieces together, but will not clamp them hard enough that friction between the pieces becomes a significant factor.
placing a mild steel nut on a HT bolt is a No-No because the threads in the mild steel nut are too weak to allow the bolt to be correctly torqued.
I also recall that a mild steel bolt and HT nut are also a No-No, but I don't remember why.
looking at an engine or trailer component, for a HT bolt to be effective, the threaded part of the casting or trailer would need to be the right strength, otherwise the HT bolt can not be tightened to the correct torque.
You can look up recommended tightening torques here http://www.westcoastfasteners.com.au...20handbook.pdf
On first reading it looks as though a properly tightened HT bolt needs 5x the tightening torque of a mild steel bolt.regards from Canmore
ian
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29th Nov 2018, 06:02 PM #18China
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Thanks for the replies, just about to repair a mates trailer and he was fairly insistent that HT bolts were the go, I think I will stickwith the mild steel and explain that if you drive off with the jockey wheel down even with HT bolts it is still going to wreck everything
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3rd Dec 2018, 08:14 PM #19
When buying 4140 don't buy the soft annealed stuff. Think its called black or hot rolled .
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3rd Dec 2018, 08:43 PM #20Most Valued Member
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