Comparing grades of steel, S275 vs stainless 304 - Page 1
Forum section: electronics / general

author: Infraviolet
author_rank: Super Contributor
timestamp: June 30, 2023, 08:34:51 pm
content: I've been trying to find one specific parameter regarding two different steel alloys, namely to what extent a rectangular section bar would bend under a given load. I don't need exact numbers, just a comparison of how the two diferent alloys (stainless 304 and non-stainless S275) would behave. What sort of percentage difference would be expected, pretty neglibile or pretty major? Most of the websites I can find only compare stainless to other stainless, or non-stainless to other non-stainless, and a lot of the descriptions are more about special properties for temperature or environmental resistance than plain mechanical properties. As there doesn't seem to be much said about relative stiffness against bar/beam/plate bending does this mean that these two stel grades, and most other common grades, are pretty close in ability on this measure?I don't want to have all the metallurgical details, just a feel for what sort of proportion difference the two alloys would give.Thanks

author: Kleinstein
author_rank: Super Contributor
timestamp: June 30, 2023, 08:55:03 pm
content: For the elestic bending the property to look at is the elastic modulus (actually 2 moduli for tension and torsion). To a small degree there can be some magentic effect with the normal steel, that can change it modulus. The elastic modulus is not very sensitive to alloy details (unless the structure changes). So other normal steel instead for the S275 should do as well for the data.For the plastic deformation it is about the yield strength and in this case there is a problem with the 304 stainless: the yield stress does not only depend on the alloy, but also the heat treatment / work hardening done to it. The stainless steel can be relatively soft if annealed and relatively hard when cold rolled or similar treated. So chances are the comparison can go either way.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 30, 2023, 10:09:04 pm
content: Yeah, if elastic, you're after the elastic modulus. Which varies little between alloys of a given base metal, so don't worry about it too much -- look to geometry (can you make it taller? wider?) instead.A good resource is Matweb:https://www.matweb.com/search/DataSheet.aspx?MatGUID=59940161328c4f1aaf52a1f838c35184&ckck=1https://www.matweb.com/search/DataSheet.aspx?MatGUID=072da6c8d36c4c519a87c9b082c58cd3Evidently 304 is less. But yeah, not by much -- a few percent.Which is why, if you're doing an application that depends critically on stiffness, you look at a much more dramatic range of options. For example, aluminum or magnesium are common for aircraft parts (they're much less stiff per volume, but many times stiffer per weight; especially when there's enough space to form trusses and such); or carbide for high performance boring bars (heavy, and not really all that strong considering its brittleness, but extremely stiff -- just what you need to deliver cutting tool pressure deep into a hole).TimP.S. Congrats on the 666th

author: Infraviolet
author_rank: Super Contributor
timestamp: July 01, 2023, 01:54:20 pm
content: I'm putting two small "sheets" * of this steel either side of a D shaft, they both have holes in them through which screws run it to nuts placed on the other side. I tighten the screws hard and that holds one sheet against the flat of the D and one against the surved side opposite the flat. I found a company which can cheaply cut small pieces of appropriately thick steel to appropriate dimensions for this, they only do S275 and 304. Its a matter of picking which is less likely to deform when the screws are tightened, because if the sheet deforms too much it no longer grips the flat of the D. I'm having it done with relatively thick steel compared to the size of the D shaft and spacing between screw holes, so don't think this deformation is too likely, but as the part in either steel costs about the same want to pick whichever is going to be less subject to bending.*the area between the two screw holes can be thought of as a rectangular section solid bar of a certain width and thickness with a length equal to the distance between where the screw heads rest.

author: djsb
author_rank: Super Contributor
timestamp: July 01, 2023, 03:52:59 pm
content: Is youngs modulus the same as elastic modulus? When work hardening is mentioned I have always considered that to be work hardening of a metal when work is done on it i.e bending when it is COLD whereas case hardening is something done during a process of heating and quenching the metal after bending/working while it is HOT. Or do I misunderstand?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 01, 2023, 06:35:55 pm
content: Young's modulus is one particular elastic modulus. There are many ways to push and pull a solid (and many ways it can shrink or squeeze in response), so in general there is a sizable tensor (read: more complicated than a matrix) describing this relation. It would be strange, of course, to have a homogeneous solid that you pull on and instead of stretching, it... twists crosswise or something. The most common case is near isotropic, and tensile strain and stress for example are in the same direction, and this is Young's modulus.I suppose you can't get a thick enough sheet (or bar) and drill a hole in the edge, and clamp the shaft with a setscrew? Or a cylinder or bar with a shaft hole, cut across to open about the D section, then bolt a sheet/plate onto that?Mind that drilling, probably either of these, but 304 is certainly notorious, can be a challenge as it work hardens under the cutter.Tim

author: Infraviolet
author_rank: Super Contributor
timestamp: July 01, 2023, 10:22:16 pm
content: "I suppose you can't get..."Unfortunately not, the way I'm able to get custom steel parts made reasonably cheaply is to get them laser cut out as 2D parts, if I wanted something 3d machined so as to have holes for screws going at 90 degrees to other holes then I'd be looking at vast price increases. Some day I'd like to build a CNC machine for doing this (to aluminium only, not steel, but with a properly shaped 3d machined part you aren't going to hav the sort of beding forces involved in doing this with 2d sheets), and I could rotate the workpiece in between making holes in one direction and then the other, but today is not that day.I've used the two "sheets" clamping method before, but for smaller shafts where the torque forces experienced were weaker and one could get away with pretty thin metal plates. I'm now trying to get a feel for which steel alloy would be the better choice for doing it for higher torques.Given s275 is not stainless, does that mean its the sort of thing which rusts fast even under benign indoor conditions? I've seen some cheap screws do that before, actual alloy used unknown. If the strengths are pretty similar, depending how each specific metal was actually treated, is 304 always the better choice even when not facing corrosive conditions?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 01, 2023, 11:00:52 pm
content: Don't have a drill press, even a hand drill? Drilling and tapping is very easy with even fairly meager tools.Also, if this is for mating shafts, or adding levers or what have you; have you looked at the various standard hardware for doing so? Flex couplers, U-joints, etc.Can also drill a hole then slot across it, and use a screw through the slot (into the slot plane) to clamp the shaft with leverage.It also seems surprising that a D-shaft would need strong alloys to mate with it; why not mild steel, or aluminum or plastic even..? And why these two alloys specifically, when there are other more common / better machinable alloys available; carbon steel (can be hardened), chrome-moly, etc.?Most steels are reasonably rust-resistant when kept dry, clean and lightly oiled. Rust requires three elements: moisture, electrolyte, and oxygen. It's an electrolytic reaction. Moisture can be as little as ambient humidity (how much, depends on the salts), and electrolyte can be as little as salt from sweaty fingerprints and ambient dust. Oxygen obviously is rather ubiquitous, but there are applications where it can be excluded, like boilers (some oxygen is normally dissolved in most water sources, which needs either pre-boiling, vacuum, sparging, or a deoxidizer treatment, and then is fine to cook ~forever).It's also stainless, not stainproof. After machining, it will normally be a bit prone to staining in use -- on environmental exposure, water, etc. The amount is mainly cosmetic, but obviously unsuitable for sanitary use, for example. A passivation step is required, basically partially dissolving the surface to expose fresh chromium (and thus oxide, which is the tough corrosion-resistant layer that actually does the job). Chemical mixes are available for this, usually based on hydrofluoric acid (yikes!!) or citric acid (phew..).And, the chrome oxide layer is only stable over conditions that it is; it's pretty stable at very high pH, but dissolves at low pH, along with the base metal; so, it's no good with, like, sulfuric acid.(It can also be oxidized to chromate at high pH, with subsequent risk of hexavalent chromium exposure; I don't think the production rate is anything to worry about. For example, food service regularly uses 10% NaOH to clean equipment. It might be relevant in certain industrial applications, or where trace amounts are harmful to a process or product.)(Trivalent chromium, as from acid attack, is not hazardous.)Tim

author: coppercone2
author_rank: Super Contributor
timestamp: July 02, 2023, 12:11:56 am
content: use citric acid it worksim not gonna say that its the best possible solution, but damn it works pretty good for crap you can dip your hands in and pour in a iced tea. And its cheap.But I mean for everyday stuff like knives and shop tools. If you are making stuff that is like automotive, marine.. then you might want the more advanced solutions, I can't vouch for that.