Questions regarding auto/light truck wheel lug nuts

After replacing all of the rubber brake lines, caliper pads, pressure flushing the brake system, and replacing the front wheel sealed bearing hubs with new units on an old Nissan Xterra, I decided to replace all of the wheel lug nuts since most of them were pretty banged up as original 2007 factory parts.

Having had good luck previously with lug nuts from Gorilla Automotive products for my F150, I decided on the product I wanted, but it comes in two varieties; regular and heat treated. Since I'd never heard about heat treated lug nuts before, I called the company to ask them some questions. Since they had zero answers and didn't know anything about their own product regarding their heat treated lines, here are the questions I have about "heat treated" lug nuts:

1. What is the purpose of heat treating lug nuts in general, besides the obvious of heat treating steels in general.

2. Do the heat treated versions of the lug nuts only harden the surface, to minimize damage from over eager tire mechanics using air wrenches ?

3. Does the heat treat extend through the entire nut to the interior where the nut threads engage the wheel stud threads ? And if so, is the hardness of the lug nut equal to the hardness of the wheel stud, which could damage the threads of the stud itself from an over eager or careless tire mechanic with an air wrench ?

4. Are the heat treated variety of lug nuts compatible with factory aluminum wheels ? In other words does the harder steel surface of the nut create any excessive deformation issues with the 60 deg conical seating surface of the wheel factory aluminum wheel itself ? Are the harder lug nuts normally intended only for steel wheels ? I could see the point for heat treating lug nuts for work trucks, buses, big rigs, and large machines in factories, earth moving and mining etc., but for regular factory automobiles and light trucks used for driving to work and hauling plywood ?

Where there you go, weird I know. But there is nothing on the internet about heat treating lug nuts specifically, which I thought unusual.

If you know the answers, or may speculate one way or the other, I'd appreciate it, since I need to get this vehicle back on the road, I've had it on stilts for a few weeks and I'm running behind, only working on it after work and in good weather, time permitting.

As usual any information and advice appreciated.

JDM Lug Nuts Heat Treating Process



https://www.google.com/url?sa=...COpmUG4NPfbFBl4rVHAU

Good video. I would agree with everything he said.

As for your questions - while there are all kinds of hardening, let’s consider two. One is case hardening where just a thin outside layer is hardened and the inside is still soft. Something like this is done for some kitchen knives. Outside hard for sharpening, softer inside to allow flex. It is not good for lug nuts and is likely not even available that way.
The second is “through hardening” where the entire part is hardened the same amount through the entire piece. That is what the video talked about. If you are shopping for hardened lug nuts, this is what you are finding and paying for. The other lug nuts would would be of a “good” steel (again, there are hundreds of kinds of steels) but they won’t hold up as well as hardened ones. The “unhardened”, (ie soft) nuts are cheaper because you are not paying for the steel and the process of hardening. Again, those will still be pretty good steel, just not as good as the hardened ones. Millions of cars are on the road today with those nuts.
The lugs that the nuts screw on to will be a pretty good steel too. It would be a poor manufacturer that would make cheap studs, use them on cars and risk legal liability.
If you buy the better nuts, what will happen as far as wear on other parts? Studs could strip, but it is likely the nuts will not ever strip. (Stud stripping is pretty unlikely too). Will they damage the aluminum wheels? As long as the finished surface quality (on the nuts) matches or exceeds that of the original nuts, there will be little or no damage because of the hardness.
The hardened nuts will likely hold up very well to “over eager shop mechanics with power tools”. Actually the nuts should be exceptional in this case. What I do after the shop has had my wheels off and on is, when at home, go around and loosen up the nuts. Often these guys overtighten the nuts (impact wrenches can do that) and with a flat at the side of the road you will never get that tire off. I loosen them and retighten by hand to whatever the factory recommends. As an aside, there are impact wrenches that can torque to a specific value. Whether this has been done, and recently tested, is the question.
Stud hardness vs. nut hardness? Identical hardnesses are possible but not likely. It would be a standard that would increase the cost unnecessarily. In industry the cheaper to replace part is often the sacrificial part. A nut is cheaper, easier to replace than a stud. Of the two then the stud would be “tougher”, to last longer.

Opinion time? Both nuts are likely to work well, with reasonable care, for a very long time. If you want a bit more insurance, buy the hardened ones.

Finally, I am not an engineer. I have some years in as a teacher/professor, teaching metals and metal working to future shop teachers. I am sure we have some engineers that might find some holes in my reasoning. Please bring my errors to light, so we can all benefit.

The video guy is saying the right things, but you should always use the lug nut specified by the manufacturer, whatever its material properties and heat treat are. This should not be a consumer level choice, given the significant differences between "soft" and hardened nuts.

Factory lug nuts have a specified tensile strength and proof load, and the torque spec takes this into account. Changing the nut (or stud) changes the required torque to keep the nut from backing off, and this also brings the wheel material into the equation since it is part of the clamping load calculation.

And make sure you get ones that are all one piece. My F150 had two part lug nuts and could cause swelling due to the dis-similar metals rendering your factory tire tool useless on the side of the road.

I recently replaced mine for $75. The new ones are triple nickel plated and guaranteed.

I got them from https://www.cjponyparts.com/ fast delivery.