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Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate MikeHalloran (Mechanical)13 Aug 05 19:50You are aware that tool steel requires heat treating (in this case an elaborate cycle) to develop its best properties, right?
Mike Halloran
Pembroke Pines, FL, USA RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)13 Aug 05 23:29"You are aware that tool steel requires heat treating (in this case an elaborate cycle) to develop its best properties, right?"
Yes, I've made thousands of parts from H13 for molds and dies. I am just interested to know if there is something better at up to about 4 times the price. I am looking to save weight on there parts so if there is a stringer material, I want to consider it.
Thanks Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate ornerynorsk (Industrial)15 Aug 05 07:53Why not use 4140 at about $1 per pound? RE: Steel for rocker arms machined from plate NickE (Materials)15 Aug 05 08:53I agree with Norsk, the H11 and H13 tool steels have specific composition and heat treat for high red hardness. If your rocker arms are red hot you could be in trouble. I would depending on section thickness use either 4140 or 4340 with a quench and temper. You could easily get strength of 200ksi, if you need more strength you could try 300M and get 280ksi.
I think that with the section size you are going to need to get the required stiffness, you will likely have almost the same weight with any steel alloy. RE: Steel for rocker arms machined from plate Tmoose (Mechanical)15 Aug 05 13:08I think if I was making rocker arms for either valve trains of suspension the design would be driven first by stiffness, then by (fatigue) strength. Machining them from billet starts off on the wrong foot by scarificing grain optimization, but has the advantage of putting material right where it is needed. A surface process like shot peening does wonders for endurance/fatgue too. I wonder if the requirement for extreme heat treat could be designed out? RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)15 Aug 05 13:11" If your rocker arms are red hot you could be in trouble."
I doubt that the rocker arms will get as hot as 300F Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)15 Aug 05 13:18" I would depending on section thickness use either 4140 or 4340 with a quench and temper. You could easily get strength of 200ksi, if you need more strength you could try 300M and get 280ksi. "
I have a friend that makes billet crankshafts from these materials. He suggested that I look for something stronger.
I would gladly pay 5X the price of 4340 to get 10% more strength. Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate gearHTr (Aerospace)15 Aug 05 13:47More questions than answers: Is there any concern for vibration dampening that cast iron provides?
Can you use a S-grade or O-1 tool steel?
Regardless of material, machining from bar instead of plate would give better strength from grain flow.
RE: Steel for rocker arms machined from plate swall (Materials)15 Aug 05 14:02Motorsportdesign--keep in mind that in alloy steels, all of your realized strength comes from heat treating. Max hardness depends on carbon content. Tensile strength equates to max hardness with a 90% martensitic structure. Both H12 and H13 tool steels have .35 nominal carbon content, so you can't get as high a strength level as you can with 4140 or 4340. The main thing that all of the extra alloy does in tool steels is to help form 90% martensite at the center of the heaviest section. So, unless you are making huge rocker arms for a marine diesel, 4340 is all you need. If you have unlimited funds, consider Aermet 100 which is a maraging steel and has excellent fatigue properties. RE: Steel for rocker arms machined from plate NickE (Materials)15 Aug 05 16:29Grain direction is'nt going to be the limiting factor here. The limiting factor is stiffness. No matter what steel alloy you use you are going to be stiffness limited in your design.
This stiffness limiting requires that you use a specific geometry that uses teh 200GPa of modulus the most effectively. All steel alloys have roughly the same modulus. This modulus does not change significantly due to heattreatment or alloy composition. Going to higher strength materials is not going to reduce weight.
Try running a MatWeb search using modulus as the property to search by, get all metals with a modulus >40,000ksi. You'll notice that all thats left are beryllium, osmium, molyebdenum, iridium, rhenium, rhodium, and tungsten are in this grouping. These alloys are much more (>5x) expensive to purchase, not to mention working, machining etc...
Quote:"I would gladly pay 5X the price of 4340 to get 10% more strength."
Again, you are going to have a really hard time finding anything with tensile strength greater than the ultra-high strength alloy steels. (300M & 4340) Elgiloy at $160/lbs comes to mind. There are others, but again costs for the alloy itself can get extreme quickly, not to mention heattreating etc...
(I do know of a part that was manufactured by WireEDM in 3 dimensions from S7 tool steel. Then the part was hardened to HRc 59. I'm not sure how much they cost to make, we were trying to have it quoted and all we got was RTQ (refuse to quote)) RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)16 Aug 05 00:04Thanks for the input.
I will exmain the suggested materials.
I would prefer not to use an oil hardening steel as I think it may be possible to heat treat an air hardening steel piece with no need for after heat treat machining.
This rocker arm is used in similar application as the ones made by Jesel
Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)16 Aug 05 00:11I have used S7 before for some mold parts before. Standard practice in molds is to use S7 where the part may be required to flex some. Does anyone know the characteristics of S7? Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate NickE (Materials)16 Aug 05 15:42S7 can have really high strengths and still retain some impact toughness. I have been searching for standard tensile data on tool steels. Using a hardness to tensile strength conversion chart on my cube wall gives 340ksi UTS for 59HRc. That coupled with a charpy V-notch toughness of >12.5ft-lbs (I'm not exactly sure about that number though it just doesnt seem right, it is however from a Timken-Latrobe data sheet. Especially considering that Crucible's sheet gives a value of 125ft-lbs for the same test at HRC57.)
I think that one problem you may encounter when investigating tool steels for non-tool parts/components is the lack of valid data regarding these uses. It'd be nice to know the yield strength of HRc50 A2 for example.
good luck. RE: Steel for rocker arms machined from plate unclesyd (Materials)17 Aug 05 10:15You can usually find all the physical data you need on tool steels if you look in the older mills technical data books , like Bethlehem, Vanadium Alloy, etc. The data is still around but getting the information has become a pain in rear.
You would normally look at the trade names of the different steels, like Bethlehem's S7 is called Bearcat. Bearcat has the highest impact strength of any of the older tool steels.
I'm trying to get my old books on tool steels returned. RE: Steel for rocker arms machined from plate Rob45 (Automotive)17 Aug 05 10:51In examining the Jesel rocker arms, I see they're made of aluminum, suggesting that for example ultimate tensile strength of the material isn't the major design criterion.
It would seem that if you wanted to approximate the Jesel rocker arm shape in steel, you could use just about any steel.
Unless I'm missing something here... RE: Steel for rocker arms machined from plate NickE (Materials)17 Aug 05 13:10Quote:"In examining the Jesel rocker arms, I see they're made of aluminum, suggesting that for example ultimate tensile strength of the material isn't the major design criterion."
Also this suggests that I was also wrong in stating that the design is limited by stiffness. Obviously stiffness and strength are important, however it seems from reviewing the site that the geometry creates the required stiffness, and that 2024 is strong enough also.
The way I would try to re-design is by optimizing the geometry for the stiffer steel. Then you coudl adjust shape a bit to modify the actual strength. Then you could use thsi to do a material selection. Although I doubt this will reduce the weight below that of the aluminium rockers. RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)17 Aug 05 14:24The life of the aluminum rockers is very short. Some people are making stell rockers at about the same weight that are lasting at least ten times longer that the aluminum rockers.
The reason that I need the strongest material that is practically affordable and machinable is to allow a reduced weight design.
Here is an example of a steel rocker.
Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate NickE (Materials)17 Aug 05 15:02Ahhh that makes more sense, then why didn't you say that you were trying to improve fatigue performance. That is definately governed by UTS. I think that 300M is going to be a good choice. Also you might want to try A2/D2/S7 or other air hardening toolsteel. Just remember: dimensions change on heattreat. A final grind is definately going to be important for tight dimensional tolerances. RE: Steel for rocker arms machined from plate icrman (Automotive)19 Aug 05 06:35Why not just go with a rocker from a manufacture like Comp cams? They are supposed to be lighter than the Al ones.
Remember the harder the alloy steel the greater the notch sesitivity. Meaning if there is a small imperfection like an inclusion or stress riser of some sort, its gona break.
RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)19 Aug 05 12:37"Why not just go with a rocker from a manufacture like Comp cams? "
Those rockers are considered junk for serious competition engines. They are investment castings so they are not nearly as strong as a piece the same size made from bar or plate. Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate icrman (Automotive)21 Aug 05 01:35I didn't know that. Thanks for the info. I agree with you about investment castings.
Anyway I also go with the 4340 camp. Not a good place for tool steel. RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)21 Aug 05 11:32"Not a good place for tool steel."
Why do you say it's not a good place for tool steel?
I will have to remachine the critical features after heat treating if I use 4340. Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate icrman (Automotive)22 Aug 05 03:51If I understand correctly it is a micro structure, and fatique resistance deal.
Just rough machine your parts, do the heat treat, and finish machine them. How high are you going? 160ksi? RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)22 Aug 05 12:33I would like to make them as hard as possible maybe 58RC if I use tool steel. Having made crankshafts from 4340 there are some problems that I experienced that I would need to avoid for the rocker arms.
The threads can't be tapped practically after heat treat if I go above 40RC. If I tap them before heatreat the threads are rusty not smooth enough for a rocker arm.
My experience in air hardening heat treat has been much better in this regard.
Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate NickE (Materials)22 Aug 05 16:39First the dimensional change cna vary depending on what austenitize/quench/temper/NxTemper is used. S7 tempered to make 58HRc is going to change size by+0.025%. D2 is going to change size by-0.02% And A2 +0.075%. (Again the preceeding data is from TimkenLatrobe data sheets.)
Second: YOu might be able to find a heat treater who can process your parts in an inert atmosphere start to finish. This will give a much cleaner final part with little scale.
I still dont see how you are going to reduce weight with higher strenght material though. Care to enlighten me anyone?
RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)22 Aug 05 18:36"I still dont see how you are going to reduce weight with higher strenght material though. Care to enlighten me anyone?"
Because the cross section required to accomplish the same strength is less when higher strength material is used. This seems rather obvious to me, is there something more to your question that I am amissing?
For example, the design of an mild steel rocker will be much more bulky than a tool steel design because mild steel is not as strong as tool steel.
Imagine something basic like a bolt, an mild steel bolt would have to be much larger than a tool steel bolt to acomplish the same strength.
Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate NickE (Materials)23 Aug 05 08:55Yes, I do understand that lower strengths means that thicker sections must be used to withstand the same stresses. Although strength aside the stiffness of a mild steel rocker and a tool steels rocker with the same geometry is going to be the same.
It appears to me that at some point the section size is going to be too small to retain the stiffness required to perform the function. Admittedly geometry can be used to overcome this, but at some point there is no way to reduce weight any further without going to a stiffer material.
It seems that EPD's design is lighter than the aluminium ones and is a highly optimized design, are they that expensive that manufacturing your own is of any benefit?
good luck. Nick
I love materials science! RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)23 Aug 05 10:54"It seems that EPD's design is lighter than the aluminium ones and is a highly optimized design, are they that expensive that manufacturing your own is of any benefit?"
I intend to compete with EPD with a similar but slightly improved design. Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate icrman (Automotive)23 Aug 05 14:50I know we have some better materials these days. But
from the information I have studied. The harder the steel is, the lower the resistance to fatique. And a rocker arm is something that you want to have a fairly high fatique resistance on. And especially if you are planning on a thin cross section. That means you will have higher stresses. You relize most of the stress is carried on the surface of the structure, and this is the reason shot peening improves fatique resistance.
It sounds like it is something you are going to have to experiment on. I think your on the right track. There isn't much available as far as a "good" rocker arm.
RE: Steel for rocker arms machined from plate NickE (Materials)23 Aug 05 15:44icrman- As hardness goes up so does Ultimate tensile strength.
Excepting impact loading, which may occur, I know very little about rocker arm loading conditions, higher tensile strength indicates longer fatigue life.
RE: Steel for rocker arms machined from plate patprimmer (Publican)23 Aug 05 17:32FEA can be quite economical these days.
You could test several designs in several materials that way, and remove any material that does not contribute to strength, and also eliminate hard and soft spots that cause stress concentrations. Regards
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RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)23 Aug 05 19:42"FEA can be quite economical these days."
Yes, I used FEA to remove weight anywhere that I could. Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate unclesyd (Materials)23 Aug 05 22:21There is a tool steel that we used for services quite similar to a rocker arm that took a lot of impacts and was subject to potential wear.
The material was S-7 and in particular Bearcat made by Bethlehem Steel. I'll try to dig up my information on it. In it's day it had the highest impact properties of any tool steel available. In fact the standard CHARPY impact specimen wouldn't break under maximum load.
This material was used in all pneumatic tools for years, both as the anvil and hammer along with a few other parts.
We also use D2 in all our gear pumps where the teeth were highly loaded and the material being pump was fairly abrasive. The beauty of D2 was very predictable with size changes when heat treating small sections. RE: Steel for rocker arms machined from plate motorsportsdesign (Automotive)(OP)24 Aug 05 01:07Yes, I am also looking into S7, I have heard of D2 but i have never seen it or machined it that I know of. I will check it out tonight. Jonathan T. Schmidt
RE: Steel for rocker arms machined from plate patprimmer (Publican)24 Aug 05 06:23Then you should be able to analyse the stress levels and the number of required cycles and using the steel suppliers data, you can estimate weight, deflection in use and number of cycles before cracks develop. Regards
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RE: Steel for rocker arms machined from plate unclesyd (Materials)24 Aug 05 08:54One thing not generally mentioned about using tool steels for mechanical components is one particular aspect of the heat treatment.
Look at the heat treating curves for each steel and if the material has a secondary hardening temperature use the material at or either slightly on either side of the secondary hardening peak.
To assure maximum wear resistance of a tool steel you will need to get the hardness above Rc 58.5.
You can use as cryogenic treatment as part of the heat treating process if possible. This will ensure maximum stability with a minimum number of tempers. On some tool steels and under certain conditions we have also seen greatly improved wear properties along with the increased stability. RE: Steel for rocker arms machined from plate Tmoose (Mechanical)28 Aug 05 15:20 -to-steel.com/Articles/Art137.htm
"The results indicate that below a tensile strength of about 200,000 psi (1400 MPa) the fatigue limits of quenched and tempered low-alloy steels of different chemical composition are about equivalent when the steels are tempered to the same tensile strength. This generalization holds for fatigue properties determined in the longitudinal direction of wrought products. However, tests have shown that the fatigue limit in the transverse direction of steel forcing may be only 60 to 70 percent of the longitudinal fatigue limit. "
-4-29.pdf
The endurance limit is not a true property of a material, since other significant influences such as surface finish cannot be entirely eliminated. However, a test values (Se') obtained from polished specimens provide a baseline to which other factors can be applied. Influences that can affect the endurance limit include:
Surface Finish
Temperature
Stress Concentration
Notch Sensitivity
Size
Environment
Reliabi