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Moderator
Curtis Jacobson
Portland Oregon
(4576 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: Rover V8 porous block behind the liners
Posted by: Moderator
Date: August 27, 2009 07:40PM

There are a couple books I'd very strongly recommend to anyone with an interest in these subjects... actually, I'd recommend the whole set of Carroll Smith's books: "Prepare to Win", "Tune to Win", etc. They're all very readable and extremely informative, and at times I think Smith is quite funny in a sarcastic, tongue-in-cheek way.

In "Engineer to Win", Smith provides a whole course in metallurgy.

On page 79 he has a sub-heading called "Do It Yourself Heat Treating" and the whole message of that section can be paraphrased simply: "don't try this at home". I don't know... I haven't broken enough parts to have developed a lot of empirical knowledge, but my guru has told me not to use 4130 unless I heat treat it (page 63), and then he told me not to kid myself that I could heat treat it without potentially leaving stresses in the part. He goes into some detailed and specific warnings too, like this one: "Make sure there are no sharp edges or corners - inside or outside - ANYWHERE on the parts to be heat treated (they are guaranteed to come back glass hard and are virtually guaranteed to come back complete with 'quench cracks,' which WILL grow.)" and this one "With long straight pieces, make sure that they are HUNG in the oven, not just laid on the racks."


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Rover V8 porous block behind the liners
Posted by: BlownMGB-V8
Date: August 27, 2009 09:33PM

But... doesn't that advice simply fly in the face of, "don't try this at home..."?


TRip
Trip Anthony

(162 posts)

Registered:
08/18/2009 01:16AM

Main British Car:
1980 TR7 performance 4 cyl

Re: Rover V8 porous block behind the liners
Posted by: TRip
Date: August 28, 2009 02:16AM

I definitely won't be "trying this at home". I think though, that kind of the knowledge will come in handy when talking to a pro shop at their level and making sure they actually go about doing that sort of work right ie: hanging long straight pieces etc.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Rover V8 porous block behind the liners
Posted by: BlownMGB-V8
Date: August 28, 2009 09:24AM

This whole heat treatment business is a black art to most people, but the basics are pretty simple and it only starts to get complicated when you get very particular about straightness, surface finish, fine details and things like two stage hardening processes. For most general purposes it just isn't that complex. For instance, 4130 is not a particularly complex alloy and does not have a particularly high level of alloying elements added. A little chrome, a much smaller amount of molybdenum, a dash of carbon and near trace amounts of a few others. In most cases it is used in the annealed condition (soft). That's what you are doing after welding it, annealing or softening the metal in and adjacent to the welds. To anneal carbon steel and most alloys you simply raise the temperature of the metal enough to make the metal soft and cool it slowly enough that the grains do not freeze which is what creates the hardened state in the first place. As you heat it, more and more of the grains convert, (or "unfreeze") which is why tempering is effective in reducing brittleness. So, at anything over about 500 degrees or sometimes less you begin to reduce brittleness, beginning at any thin sections, corners and such and proceeding into thicker sections. This is why a heat soak in the oven is needed for complete through hardening or annealing of solid pieces. The heating creates a phase change in the grains or structure of the steel and rapid quenching freezes the grains in the changed state. Not all grains are converted (because quenching is not instantaneous) and subsequent heating allows more and more grains to revert. The reason sharp edges create stress risers is because the temperature goes up there the earliest and the most and likewise quenching is the most violent there. But likewise tempering has the greatest effect there, as does annealing. (the difference between tempering and annealing is one of degree only-- in both time and temperature)

So it's not exactly rocket science. Things like inert gas heat treat ovens just allow finer control of the process and prevent surface oxidation (as does wrapping in stainless foil) and if you think for a moment about that long bar on the floor of the oven you can see why it warps. It simply will not heat evenly. Nothing magical about it at all. Most parts either are too small to show warpage, are not critical, or will be ground afterwards. As for welding a cage, as long as the weld areas are annealed it will be fine. And the reason for trying not to get it too hot is not because it will weaken the steel, since it can't get any weaker than in it's fully annealed state anyway, but to keep from burning it which is basically surface oxidation. It is possible however to introduce impurities into the metal such as carbon and seriously screw up the surface texture both of which can weaken it, if it is heated to a near molten condition or held at an elevated temperature for an extended period. So a just barely visible glow is good enough.

Now let's say you had access to a very large heat treat oven. In that case you could take your 4130 or 4140 chromemoly steel, weld up a cage, heat it, quench it, temper it (sometimes called "drawing it blue") and end up with a fully heat treated structure which would be much stronger than a standard cage. It would outperform the annealed cage in ever respect except one. It would be somewhat more susceptible to tearing of the steel due to the additional hardness. But it's yield strength would be so much higher that it pretty much eclipses that concern. The downside of course is cost. Also bear in mind that practically any carbon bearing steel can be made brittle, soft, or anything in between. It all depends on how you harden and temper it. So this is all just a tool to be used by those who have learned how, and the gas torch is the most basic tool in the arsenal.

Jim


Moderator
Curtis Jacobson
Portland Oregon
(4576 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: Rover V8 porous block behind the liners
Posted by: Moderator
Date: August 28, 2009 12:03PM

Suspension links are the most tempting place to use chrome moly.

But roll cages? I know of one MGB GT V8 race car with a chrome moly cage, but frankly I don't get it. If safety (or chassis rigidity) is your first concern and you want to make a cage stronger and stiffer, IMHO the best way to do so is to accept the weight penalty and use 1.75" diameter tubing instead of 1.5" diameter tubing. The individual tubes would be stiffer, but more importantly you'd benefit greatly from having more weld area at every single joint. Cages are normally built in situ. Even with a TR7 convertible, for example, it's going to be very tricky to build a cage outside of the car and then install it. Normally, one tube or hoop is installed before the next tube or hoop is even trimmed to length. Yes, you could possibly use your acetylene torch with a rosebud tip to carefully heat treat every joint of the entire cage, but it would be a real pain in the butt to do so. Getting to the back side of all those joints to evenly heat them all the way through, when they're blocked by the unibody sheetmetal? Mild steel is so much easier to deal with!


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Rover V8 porous block behind the liners
Posted by: BlownMGB-V8
Date: August 28, 2009 01:49PM

It's a good point Curtis, and really, the extra expense and effort only makes sense in an all out racing effort where every ounce of weight reduction counts, or where space is a factor. Then, if you can get at it to tig weld it, you can also follow behind with the rosebud to anneal it. Not much difference at all in terms of space needed and heat generated. Or if space is that tight, the cutting tip will do fine also, just don't hit the lever. It only has to be warmed well. At 400-500 degrees bare steel begins to color. Between that and 1100 it will go through the blue spectrum ending up a very light blue at around 650 degrees. By this point only the deep stresses remain, as the surface stresses have mostly been relieved. From that point until it begins to give off light as a very dim dull red glow, the rest of the stresses are relieved and the metal is fully annealed. It's important to recognize that this is a progressive process. It doesn't just fall of the proverbial cliff at 1100 degrees to the fully annealed state. Plus as already noted any projections or edges will get hot first and therefore get soft first. Inside corners will need the most attention. There is virtually no need to heat soak the metal as the tubing is thin enough that the inside will be at roughly the same temperature as the outside.

But let's take the case of the forward struts on the Jag IRS for the MGB-Roadmaster for an example. Those are made from heavy wall mild steel tube and are probably the weak point in the suspension. To make them a larger diameter would mean making a sharper bend for clearance to the inside of the bend which would make them weaker so it's a compromise set in a dilemma. Perfect application for chrome-moly wouldn't you say? Use the same dimension tube and roughly double the strength without changing the geometry. The entire link could then be heat treated without too much trouble at all.

Jim


TRip
Trip Anthony

(162 posts)

Registered:
08/18/2009 01:16AM

Main British Car:
1980 TR7 performance 4 cyl

Re: Rover V8 porous block behind the liners
Posted by: TRip
Date: August 28, 2009 04:28PM

In regards to things built in-situ like a roll cage, if you can't heat treat the entire cage - unless you put the whole car chassis in an oven (don't think that's feasible?) - Don't you have to hand "heat soak" the entire tubing length not just the weld points. Are the tubes "pre-heated" and doesn't the high welding heat radiate out along the tube causing other issues?


Trip



BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Rover V8 porous block behind the liners
Posted by: BlownMGB-V8
Date: August 29, 2009 10:47PM

You're missing the point Trip. As supplied, the tube is annealed, which means that it is as soft as it ever gets. In order to be hardened it has to be heated, in the case of 4130 probably in excess of 1500 degrees F which would be a bright red and then it is quenched. The only area that ever gets that hot is in the weld zone so that is the only area that is in any danger of being hardened. Therefore that is the only area that has any need of being annealed back to the soft condition.

Annealed 4130 is considerably stronger than mild steel tubing, but is still reasonably ductile. It therefore allows a lighter construction. Only an extreme racing application could ever justify the use of a fully hardened 4130 cage, and that would be a full custom tube chassis. A stock body would never be used due to it's weight.

Jim


TRip
Trip Anthony

(162 posts)

Registered:
08/18/2009 01:16AM

Main British Car:
1980 TR7 performance 4 cyl

Re: Rover V8 porous block behind the liners
Posted by: TRip
Date: August 29, 2009 11:09PM

Okay, now I understand. Heated to 1500=Hard=brittle. Thanks for the clarification, Jim. I definitely don't have any delusions of turning my home-built project into a full race car but it's fantastic to have the understanding and knowledge, though. I can see how a custom body ie. in pro-drag car could be used with a fully hardened cage.

Thanks again

Trip


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Rover V8 porous block behind the liners
Posted by: BlownMGB-V8
Date: August 30, 2009 06:35PM

Close Trip. Heated and then Quenched to harden. If just allowed to cool it will not get hard. Welds get hard because they are quenched by the cold steel immediately surrounding them. If preheated before welding they will not quench and will not need to be annealed. If quenched intentionally the steel will then need to be "tempered" or "drawn" in order to reduce brittleness in most cases.

Mild steel or the most common low carbon alloy used for tubing, 1018 steel, has about 60-65,000 psi of tensile strength. It cannot be hardened significantly without the introduction of extra carbon, such as is done in case hardening, by heating the metal and introducing a carbon bearing material to it while it is in a state that will allow it to absorb the carbon. But this is a very valuable and useful property that is used quite commonly to create a hard shell or cutting edge. This steel has a .18% carbon content and no other significant alloying materials, hence the 1018 designation.

By contrast 4130 chromemoly has .30% carbon and as annealed has 115,000 psi of tensile strength, nearly double that of 1018 steel. If hardened and drawn to 400 degrees it has 236,000 psi of tensile strength, nearly four times that of 1018. In that condition as pointed out above it will tear upon deformation at a less extreme angle than the annealed metal or 1018 also, but it is also quite clear that it will take four times the force to bend it in the first place. Also since it is a medium carbon alloy it is not particularly brittle. Cracks and work hardening are only a concern if stress risers are allowed in the construction, provided it is evenly hardened and tempered.

As such it's easy to see why it is such a widely used alloy in the auto industry, being very common in things like spindles, shafts, suspension links and much more. Any time you see a suspension part and wonder at the small cross section considering the loads it carries, it's a pretty good bet it is heat treated chromemoly, usually either 4130 or 4140. And it may interest you to know, that as a medium carbon alloy steel, in the fully hardened state it can still be machined.

Jim


Moderator
Curtis Jacobson
Portland Oregon
(4576 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: Rover V8 porous block behind the liners
Posted by: Moderator
Date: August 30, 2009 07:24PM

Where are these numbers coming from? They simply don't match "Engineer to Win", which is still sitting on the edge of my desk. (I've been working on an article about a Formula 5000 racecar this week, and Smith's books are especially full of insight into those designs.)

(from the chart on page 66 of Engineer to Win)
cold-rolled 1018 sheet and tube: ultimate tensile strength = 82,000psi
cold worked and annealed 4130 sheet and tube: ultimate tensile strength = 95,000psi

(from pg 63)
Quote:
The other side of the 4130 coin, often unknown to (or at least unappreciated by) the racer is that it possesses poor deep-heat-treating characteristics and has an inborn dislike of varying cross-sections. These characteristics make 4130 a poor choice for machined or forged parts. It doesn't machine very well at least in the normalized condition - too gummy. Those people who make hubs, steering knuckles and the like from 4130 are kidding themselves - and their customers. It doesn't make very good shafts either, as in drive shaft, or axle, or torsion bar.

4140 is better for deep hardening and machining, but harder to weld... To get to 236,000psi, we're talking about "4340 modified" (i.e. alloys with vanadium) and big budgets.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Rover V8 porous block behind the liners
Posted by: BlownMGB-V8
Date: August 30, 2009 10:50PM

Curtis, those numbers are from Machinery's Handbook, 20th edition, 1978. (Current edition is 28th and 100 years in print) I think you'd have to agree that they've had ample time to error check their information, and based on practical experience I would have to agree that the roughly double and quadruple numbers are at least in the ball park. I don't know if Carroll Smith has done any actual tensile strength testing to base his numbers on, or if he is using manufacturer's numbers or what, but 82K sounds awfully high for 1018 and only a roughly 15% increase in strength between 1018 and 4130 just doesn't sound realistic.

But, plate, bar, structural and tube often have different characteristics and different sources can vary widely on their testing results so there's no point in arguing the specifics. The point is that an alloy steel (pick your favorite, there are so very many of them) is going to be noticeably stronger than a low carbon steel and a heat treated alloy is going to be noticeably stronger than it's annealed brother. If you want ultimate strength, a hardened electric arc remelt cobalt alloy is hard to beat, but you can always find a way to spend yet more money. If that 235K number seemed high, recall that it was at a 400 degree draw. Hotter draws yield lower tensile numbers and this has a great deal to do with the variations we are talking about. Commercial 4130 HT or 4140 HT are going to be drawn to a higher temperature than that, but if you'll recall, we were discussing a custom heat treat for an entire cage so we can specify the draw we want to use.

For truly accurate results there is no substitute for a reliable supplier and in-house testing. Since most of us don't have that luxury we have to make do with what is commercially available and the results often vary widely. Thankfully once we are accustomed to a given product we can usually spot a different material very quickly, but within the range of noticeable differences there are going to be some pretty significant variations in all commercial supplies, and that's what good quality control is all about. If you don't like the characteristics of what you are getting it's pretty easy to change the specification. If you don't like the way 4130 or 4140 machines, there are free machining varieties available. If you aren't happy with it as a shaft material, pick one you like better. It's not like there was only one choice or something. But just because one guy doesn't like a particular alloy that doesn't make it a bad alloy either. Could just be the way he's using it, or the particular variety of it he's been using, or the draw temperature of the stock he's gotten, or a hundred other things. Just because a change in the material worked for him doesn't mean everyone else who is using it is wrong either, maybe they are all using a leaded alloy for increased machinability. Or maybe they are using stock supplied in heat treated form, which machines very well with carbide tooling and leaves a nice finish.

What really matters is the end result, and the time and money it took to get there. Alloy steels wouldn't be around unless they served that need very well indeed. But they aren't the solution for everything and sometimes black iron pipe is just the ticket. I just wouldn't build a roll cage out of it unless that was a last resort, Mad Max sort of situation. And then I'd build it beefy.

Jim


TRip
Trip Anthony

(162 posts)

Registered:
08/18/2009 01:16AM

Main British Car:
1980 TR7 performance 4 cyl

Re: Rover V8 porous block behind the liners
Posted by: TRip
Date: September 01, 2009 01:34PM

Wow, this is an AMAZING wealth of knowledge! I'm going to be reading your posts over many times so I can absorb all the finite details.

Trip

PS. I'm also reading your other posts RE: welding.

Thanks for sharing your insights with me, everyone!
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