Another engineering / metallurgy question

[Al_C]

Based on what I've seen on other on-line sources, there are a variety of opinions on this one. I suspect that may be the same here, but I have a greater degree of confidence in this group...

So here's the first-time builder, non-engineer situation: I have some hot-rolled mild steel, 1/4" thick. I want to put a 45 degree bend in it. It will be part of my engine lift bracket. My options are a) put it in a vice and whack the crap out of it with a hammer, or b) heat it up and whack the crap out of it. Judging from my success so far, the (a) option is not all that it's cracked up to be.

Question: If I heat this steel prior to bending, will I weaken it to any significant degree? At most, it will need to support a few hundred pounds, but I'd rather not be surprised when the engine is suspended over the frame.

[wareaglescott]

Dont know squat about metallurgy but I used 1/4" steel with the heat and bend method for my lift plates. Had no problems lifting the motor. Of course whether I had 90% safety margin on the load capacity or .001% I have no idea. So with that this advice is about useless other than to say the heat and bend was quite easy!

[NAZ]

I won't give engineering advice over a forum but I will tell you that if it was me I'd have no problem heating and bending A36 HRS and let it air cool. I'd have no problem using ¼" x 1 ¼" or wider for motor lifting tabs. I would expect A36 to have a tensile strength of 58 ksi and have no problem lifting even an old school hemi using four chains and tabs fabricated out of ¼ x 1 ¼ A36.

[DaveS53]

Using 1/4" thick metal would generally be huge overkill, unless it's important that the 45 degree angle not deflect much under load. Bend it any way you want.

As a demonstration to someone who criticized my welding, I TIG welded a 1/8" x 1" piece of bar stock to a 1" square steel tube and lifted the whole front of my car with it. The bar stock would not yield under several times that load. This was also a demonstration of the strength of a threaded connection. The 3/8-16 threaded steel eye is screwed into a 1/8" wall thickness tube that I drilled and tapped to show how few threads are needed to withstand a substantial load. Notice that the load caused a significant bend in the lower 1" square steel tube, due to the long span. Some people may think that a 3/8-16 thread tapped into the 1/8" thick wall of a frame would not withstand much of a load. They would be wrong.



A load leveler is a nice thing to have when installing an engine and transmission. You can adjust the angle easily. That's 3/8" all thread rod spanning between the lifting bars that are much larger than needed, at 3/16" x 1-1/2".

[rich grsc]

Its cold rolled, you won't bend it in a vice unless you heat it. There is no way you are going to weaken it enough to have any concern, it will lift several engines with no problems.

[Al_C]

Thank you! Problem solved. The piece I'm bending will connect the load leveler and the block. We're good to go.

[initiator]

I took the cold whacking route. A lot of work with a sledge, should've heated it. I ended up cold-working it by not heating it, which makes it stronger but more brittle. Heating it anneals the steel, which makes it easier to bend without cracking.

1/4" steel in any reasonable width is more strength that you'll need for about any task you can do at home. Plenty of margin for lifting an engine. I used it because there's no kill like overkill.

[Gumball]

Not an engineer, but wouldn't a water or oil quench while hot (once bent) heat treat the metal and return the strength?

[DaveS53]

Not an engineer, but wouldn't a water or oil quench while hot (once bent) heat treat the metal and return the strength?

You have to be able to accurately measure and control the temperature and rate of cooling after reaching a specific temperature to perform a reliable heat treat. The size of steel stock being used is so large that it doesn't matter if the steel's strength is reduced to the annealed condition.

As an example, the small 1/8" x 1" bar stock that's holding up the front of my car could hold up to 6,000 lbs, even if the steel is in the annealed condition with a yield strength of 50,000 lbs/ square inch.

http://www.anvilfire.com/article.php...attreating.htm

[initiator]

Agreed - both the temperature and cooling rate are critical for successful heat treat. Wikipedia has a good high-level overview if you're curious.

[lance corsi]

Hardness is largely determined by the carbon content of the steel and the critical temps reached during the heat treat process, and the quench. Low carbon steel generally cannot be heat treated, except for surface treatment like carburizing, which augments the amount of carbon just on the surface. This process can impart wear resistance without thru hardening.
I do know that bending steel without heat will send your soul to hell! Better fire up the torch!

[dallas_]

Your question has been answered, but I'll just add this.
Get Carroll Smith's book "Engineer to Win". Great resource for an introduction to materials for car builders.