But before i continue on i need to carlify when i'm talking ab9out toughnes. When i think about toughness i think of it as impact/notch toughness at low temperature (you probably don't have to worry about that like i do as we have to worry about impact/notch toughness at -40*C), correct me if i'm wrong but you seem to refer to it more as fatigue, or a time thing of a part over time correct? If so we're talking about 2 different things (well kinda anyway
)
Toughness is basically a measure of the energy a material can absorb up to failure. This means what it absorbs from the time it loads, through it's elastic range, into into plastic deformation, and ultimately failure. It is directly proportional to yield strength and ductility. Fracture toughness deals with the ability of a material to resist crack propogation.
Now, I'm not talking about
fatigue. I am talking about
toughness. You are really talking about
fracture toughness and toughness. Three totally different things. Toughness is the total area under the stress strain curve. Fracture toughness is a material constant. Fatigue is a whole different discussion. Impact and notch toughness is related to toughness, but they're their own little ideas, but the higher a material's toughness is the better its impact strengh and notch toughness will be. So I'm talking about what you're talking about when I say toughness, and the thing is, 4130 N used right is actually more resistant to failure than 1020 in impacts and energy absorbtion.
Bringing in temperature is different. I'm talking at typical naturally occuring temperatures we race, wheel, and fly in. There is this ductile to brittle transition thing, but I don't care about that because that doesn't happen at the temperatures cages and chassis are used in. Temperature no doubt can have an effect on these numbers, and I can't comment on what happens at very low service temperatures as I have not studied or experienced the phenomenon much.
also, for comparission sake lets use a 1040 vs. 4340, as the max achievable UTS is very close to the same (the carbon content is what has the gretest effect on a number of properities including the UTS), and thus we're only comparing the alloying content differences.
Somewhat close, yes. But that alloying is what can do neat things with the carbon and steel's microstructure to increase the material's strength.
Yeah here we're talking about 2 different things, i should've clarified more i guess. Yes 4130/4340 (new comparo remember
) is ductile, but hardenability of the alloy allows the formation of martensite in varing amounts (i think it hits hrc 25ish air cool after taken above the critical temp, and that is getting up there, but still a long ways to go to steel's max hardness of 65, but a 4340 can hit that with a water quench), and under high impact at lower temps the 1020/1040 will perform better the 4130/4340 because of the martensitic stucture and its shitty toughness properities (think of a rubber band being stretched to its max, doesn't take a lot more to break whereas a nonstretched rubber band takes a lot).
Not always the case. It depends on what exactly you've done to each material. And this is beyond the scope of the 4130/1020 we're talking about. This is getting into something much more in depth and now we're talking heat treat. But no, 1040 does NOT outperform 4340. Simply enough, if 1040 could it would be making the higher end axle shafts and gears and not 4340 and 300m and Aermet. You can do fun stuff to make the toughness of 4340 much better than typical 1040. While I love 1040, 4340 can always be made tougher and stronger. The process for maximizing the properties of each is not the same, but that's cause they're not the same material. So 4340 is TOUGH AND CAN RESIST IMPACTS BETTER THAN 1040. But you must know how to get it to that state. Does this make sense.
Brittleness is a term that's misused imo. Just cause something CAN have brittle properties, it doesn't mean it's worthless and shatters under impact. Brittle materials are ceramics and concrete and junk like that. Almost all steels are very ductile comparitively. The bad thing brittleness properties cause is a sensitivity to IMPERFECTIONS. That's where you must be careful and why a "catastrophic" failure is likely to occur. Handled correctly, materials that are called "brittle" are often the strongest and toughest.
But i do agree with what you said, i believe too that isn't that also refered to young's modulas of elasticity (sp?)
No. Not at all. Modulus of elasticity is the measure of strain to stress of a steel IN ITS ELASTIC RANGE in tension. Because this relationship with steels is linear the modulus of elasticty is the slope of the stress/strain curve in the elastic range. That's all. It is a material constant and is the same for all steels.. (about 29,000,000 psi) It is a measure of a material's stiffness and is used in calculations to help determine things like deflection, stiffness, strain, etc. Doesn't have anything to do with the material's strength. Just its resilience.
The diagrams i'm thinking about probably isn't the phase diagram you're thinking about (it's the one that shows how much martensite, pearlite, bainite, etc, and the rates of cooling you need to achieve those grain structures, are you thinking of the diagram that show austenite, iron carbides, ferrite, delta ferrite, etc?) But these diagrams show that if you cool at a such and such rate what structure you will get (say martensite or pearlite), and this structure, martensite for example, correlates to what kind of uts you will get, but it kinda of sorta related hear, like if you compare 1040 to 4340 you will see that the 4340 get a 100% martensitic structure before the 1040 will, but you can still get the 100% martensite, but the cooling rate will be so quick you will probably warp the crap out of the plate trying to get it.
But we're not talking about this per-se. We're not talking about achieving this hard structure with 1040. We're just worried what happens with a slow air cool after welding. And I talked about this a bit earlier. And this goes along with the other things I've been saying.
The first part is more related to material strength and not toughness, and what type of condition does that need to happen in cause in all the charpy testing i've done (low temp) i never came across that?
No, I was talking exactly about toughness. Material strength is going to be a part of toughness as they're directly proportional if ductility is the same.
The Charpy test is great, but it's just yet another measure of toughness. You need to just look at some elogation numbers and tensile strengths to figure about how well a material will perform in that test.
Here is my point:
1020 specs (normalized): 50,000 psi yield / 63,000 psi ultimate / elongation at break 35%
4130 specs (normalized): 63,000 psi yield / 97,200 psi ultimate / elongation at break 25%
Ok, so they're pretty damn similar when it comes to the yield point. 13ksi is a bit, but not a huge different. You will see 1020 is very ductile (35%). BUT 4130 is also very ductile when normalized (25%). Overall toughness here is definitely going to go to 4130 because look at the gap between yield and ultimate. So what I'm saying is material wise, 4130 will permanetly change shape with a load 13,000 psi greater than 1020.. Now 1020 will fail when the load reaches only 63,000 psi and will have "stretched" 35%. 4130 on the other hand will not ultimately fail until the load reaches 97,000 psi! This is impressive. It will strech 25% when it does fail. So do you see the advantage?? While 1020 is more ductile, it is NOT tougher. 4130 absorbs more energy. Which do you want surrounding you in a horrid crash if the need arised? (Rhetorical question just to make one think.)
Now it is important with a build to not load weak spots heavily in order to let the rest of the material work up to that 97ksi load point. This goes back to the engineering, design, manufacture, experience thing.
1020 is GREAT stuff as you see above. Very often DOM is NOT quality 1020 and much weaker 1010 or something. My example is using the run of the mill 4130 as supplied and top of the line mild steel DOM. Often DOM is supplied as rolled and not normalized. Still, mild steel DOM is very adequate, so what does that say about typically supplied 4130 N?
Now what I've given above is a VERY simplified example and negates some factors, but it explains the concept behind the advantages and toughness and ductility and what we've been talking about. However, you better know how to use those advantages or else you help give the 4130 structures their bad name which occurs from uninformed people or poor building and design.
I agree
the welding thing will depend more or less on the size/thickness of the part as your really thick parts can cool small welds alot quicker than what a normalized plate was.
Sure, lots of things effect cooling rates.
yeah you need a controled furnace environment for it to be benefical. But a quench and temper (i'm assuming a water quench, correct me if i'm wrong as then what i'm about to say won't be true) is something i'd avoid as you material would become for what i consider to be to hard for a tube stucture (say a roll cage)and you will see cracking happening more and more before a tube will deform, and thats due to a 100% martensitic structure which although has wicked strength, its impact toughness is not very good.
Nope, see above about 4340 for axle shafts. Think about it. It will happen, has happened, and I hope to experiment with it some day. I'm going to stop now as I've given away too much information as is.
And yes that is a very expensive way to do something espically when good design practices can prove to be just as benefical (may not be as light though).
Good point with er70s-2 lessening the hardenability of the weld, but you should not have to add excessive reiforcement for the weld to as strong, i would much prefer the er80s-d2 over the er70s-2, as the strength of the filler is closer with the strength of the 4130/4340 base material, and yes you should always match the filler to your base using the approiate methods.
Your thinking is the same trap lots of other people fall into. You DO need more-than-textbook reinforcement in this situation as it's a special case with the way we do things and use the material. However, er80s-d2 is common and has worked well for many folks, including myself. But.......
Yeah i could to, and i too much perfer mild steel dom, and yes its a great tool, but the break in half thig, i to see where you're coming from with it and agree, but there are some properities with it that are why i'm not a fan of the people that doesn't understand the properities of it using it.
If everyone continues to use good DOM they will be more than happy. Quality DOM is GREAT stuff and works perfectly for most every application. Look at NASCAR. Those cars are very tough. They are mild steel DOM. 4130 is a "special" thing.. That is all. :grinpimp: