Learning Center What is a mineral?The most common minerals on earth Information for Educators Mindat Articles The Elements The Rock H. Currier Digital Library Geologic Time

Minerals by Properties Minerals by Chemistry Advanced Locality Search Random Mineral Random Locality Search by minID Localities Near Me Search Articles Search Glossary More Search Options

The Mindat Manual Add a New Photo Rate Photos Locality Edit Report Coordinate Completion Report Add Glossary Item

Mining Companies Statistics Users Mineral Museums Clubs & Organizations Mineral Shows & Events The Mindat Directory Device Settings The Mineral Quiz

Photo Search Photo Galleries Search by Color New Photos Today New Photos Yesterday Members' Photo Galleries Past Photo of the Day Gallery Photography

Discussions

💬 Home 🔎 Search 📅 Latest

╳Discussions

💬 Home 🔎 Search 📅 Latest

Groups

Recent Images in Discussions

Improving Mindat.orgHardness of steel overstated ?

29th Jun 2015 00:00 UTCReiner Mielke Expert

I read on a thread here that steel can be hardness 7.5 and then checking on line I saw reports of steel being 8.5. I checked the hardess of my cobalt drill bits against quartz and could not scratch it. I then checked several high quality files and none of them could scratch it. I think the claim of steel being harder than quartz is false. Does anyone have a piece of steel that can scratch quartz to prove this is true?

29th Jun 2015 01:44 UTCSteve Federico

Interesting question.....Steve

29th Jun 2015 07:04 UTCReinhardt van Vuuren

I'm sure it varies on what the iron mixture is, this past week I tried to drill a whole trough the casket of an old bicycle and that steel was so hard that non of my steel drill bits could drill trough it, I will try to remember to see if it scratches quartz when I get home tonight.

29th Jun 2015 07:47 UTCDavid Von Bargen Manager

There are a bunch of different alloys and you can also get particles of carbides forming in / on the surface of the steel.

http://www.daytonlamina.com/sites/default/files/dayton_tech-balancing.pdf

29th Jun 2015 14:23 UTCReiner Mielke Expert

Hello Reinhardt,

Cobalt alloy bits will drill through cast iron unless there happens to be something other than iron embedded in it. I can see coated steel being harder but then it is not the steel that is hard but the coating. I am thinking that part of the problem is in converting vickers hardness to Mohs, it is not a straight forward linear relationship. I suspect that those reported high hardness steels were not actually testing on minerals but mathematically converted to Mohs.

Hello David,

I can see if particles of carbides are embedded in the steel that it would scratch quartz, but then that is kind of like saying steel with particles of diamond embedded in it is hard steel isn't it? I suppose it all depends on the definition of "steel". To me it must be a homogeneous alloy and not a mixture to count as "steel".

29th Jun 2015 14:32 UTCDavid Von Bargen Manager

Mohs hardness is just a sort of semi-empirical hardness scale. With Vickers, at least you have a standardized test procedure.

29th Jun 2015 14:40 UTCReiner Mielke Expert

Hello David,

You are absolutely correct however there is nothing ambiguous about something being able to scratch a smooth quartz surface, either it can or cannot.

29th Jun 2015 14:49 UTCReiner Mielke Expert

Maybe I should have called this The Great Scratch Contest, scratch away and report your results! The prize ??? I'm scratching my head over that one. Wait I know, I will donate $20 to mindat in the name of the winner LOL.

29th Jun 2015 15:03 UTCSteven Kittleson

Hello,

Cronidur 30 steel alloy contains nitrides and is rated as one of the harder steel alloys.

TTFN and LLAP

29th Jun 2015 15:12 UTCWayne Corwin

Conversion Chart Absolute Hardness to Mohs

29th Jun 2015 15:32 UTCReiner Mielke Expert

Hello Steven,

My Cobalt drill bits will drill through Cronidur 30.

29th Jun 2015 15:39 UTCReiner Mielke Expert

Hello Wayne,

By absolute hardness do you mean as tested with a Sclerometer? The trouble is that the hardness of steel is not determined using a Sclerometer.

29th Jun 2015 15:44 UTCKelly Nash 🌟 Expert

Probably obvious, but I think all kinds of quite hard alloys were developed after the Mohs hardness scale came out in 1812. Whether there is one in widespread use now that can scratch quartz, I don't know, but wouldn't be surprised.

29th Jun 2015 16:59 UTCReiner Mielke Expert

Well Kelly find me one and if you do I will donate $20 to Mindat thanks to you. :-D

29th Jun 2015 18:08 UTCKelly Nash 🌟 Expert

Ah, I thought Siri could answer this, or google, but you may be right. Expect tungsten steel could go over 7 but can't find any confirmation. I imagine makers of oilfield drill bits have looked for this. Good luck.

29th Jun 2015 21:11 UTCReiner Mielke Expert

Hello Kelly,

Modern drill bits us tungsten carbide or diamonds. Other than a matrix, they gave up using steel for that a long time ago.

30th Jun 2015 03:31 UTCDoug Daniels

To further confuse the issue....are you using just a rotary drill, or a percussion drill?

30th Jun 2015 04:55 UTCJason Bennett

Because steel is often coated as mentioned above, could it be that what was actually tested was not steel scratching quartz, but quartz scratching steel?

Have you tried scratching any of your different steels with a quartz point Reiner? That might be where the conjectured hardness values come from...

Jason

30th Jun 2015 11:53 UTCBela Feher Expert

Ferrite, austenite: HRC = 10-15, HV = 196-213, Mohs = ca. 3-3.5

Pearlite, upper bainite: HRC = 40-45, HV = 392-446, Mohs = ca. 4.5

Lower bainite: HRC = 58-60, HV = 653-697, Mohs = ca. 5.5

Martensite: HRC = 65-66, HV = 832-865, Mohs = ca. 6

30th Jun 2015 14:45 UTCReiner Mielke Expert

Hello Doug,

I am not using any drill just dragging a drill bit across the face of a quartz fragment.

Hello Jason,

Why would one expect a different result from quartz on steel rather than steel on quartz? Here is one site (there are others) for example that claims hardness 7-8 for steel http://www.jewelrynotes.com/the-mohs-scale-of-hardness-for-metals-why-it-is-important/. How they determined that I don't know.

Thank you Bela! That would seem to settle this but one could still argue that the conversion to mohs is incorrect? However I think Mindat is not likely to get a donation from this thread. LOL

30th Jun 2015 15:44 UTCJolyon Ralph Founder

This is a highly pointless debate in my opinion.

I have long been of the opinion that assigning arbitrary mohs values to items such as "a steel file" or a "copper penny" is just asking for trouble as there is so much variation (not least that copper pennies are now something completely different).

Mohs testing should be used based on known constants and none of these things are constant.

The best thing we can say from this is "Do not use metal objects for hardness tests unless they are part of a known and calibrated testing set"

30th Jun 2015 16:38 UTCReiner Mielke Expert

The debate is not pointless. What I am trying to find out is if there is any steel harder than quartz, no more no less. The reason this is important is that for many years of logging core I have found it very fast and easy to distinguish white quartz , feldspar and carbonate by using a nail and a file. The nail will scratch carbonate but not the others, the file will scratch feldspar and carbonate but not the quartz. Now all of a sudden it comes to my attention that apparently hardened steel can be harder than quartz which could create a serious problem for me. I want to be sure that is not true, thus this thread.

30th Jun 2015 16:47 UTCDavid Von Bargen Manager

The hardness of steel can also be affected by annealing and work hardening it has undergone. You can conceivably change hardness on how something was treated. The simplest thing for your testing is to try your steel implement is to try and scratch a piece of quartz. If it doesn't scratch, you are OK.

30th Jun 2015 17:06 UTCWayne Corwin

Reiner

If what you have been using works, keep them with you. ;-)

30th Jun 2015 17:30 UTCReiner Mielke Expert

I would also like to add that I think it is important to stop disinformation which the claim of steel being harder than 7 seems to me to be.

30th Jun 2015 17:55 UTCJolyon Ralph Founder

David hit the steel nail right on the head. Figuring out whether a steel implement can scratch quartz or not shouldn't be beyond the skill of any competent mineralogist :)

30th Jun 2015 18:40 UTCReiner Mielke Expert

Hello Jolyon,

That is true, but do you check every glass of water you drink to see if it has arsenic in it before you drink it? I have at times assumed the file I was using was softer than quartz without first determining if it was because I was not expecting it to not be, just like you would not expect your glass of water to have arsenic in it. So if in fact a file can never be harder than quartz then I will never have to worry about it. Of course you on the other hand can probably not assume anything about your glass of water LOL.

1st Jul 2015 03:41 UTCJason Bennett

Reiner:

I was thinking along the lines of Cr-doped steel. From my understanding (and I may be completely wrong) the idea of Chrome steel is that the Cr oxidises at the surface of the steel forming atomic-scale layers from Cr-oxide, something like Eskolaite maybe (http://www.mindat.org/min-1411.html) which has a hardness 8-8.5. Looks like most Cr minerals have a high hardness.

Scratching a surface of Cr-steel would be like scratching a surface of Cr-oxide, hence the high hardness. If you tried the other way around, then the sharp/angular point you are using might shear at the surface, and you are trying to scratch with 'fresh' steel, which has hardness much less as you point out above.

For something that is not a single crystal, or homogenously amorphous, I always thought that testing for hardness was a moot point (as Jolyon mentions) because you are not testing for hardness of the mineral, but strength of the intragranular bonds.

Jason

1st Jul 2015 09:16 UTCJolyon Ralph Founder

I am not a metallurgist so I really don't have a clue about the composition of steel files and whether there is a chance that some could scratch quartz.

But this uncertainty probably rules out using a steel file for this kind of test unless you have previously checked it with a known piece of quartz.

Moral of the story - keep a piece of feldspar in your pocket.

1st Jul 2015 10:49 UTCDavid Von Bargen Manager

Moral could also be to use a cheap steel file for testing. It is unlikely to be of sufficient quality to scratch quartz. Other is to spend money on a file with a known hardness (they do make them for testing)

Brinell test blocks go to 550 (vickers 580)

Rockwell C HRCN 63 (Vickers 772)

Test file - Vickers 832

http://www.flexbar.com/shop/pc/Hardness-Testers-and-Accessories-c26.htm

http://www.minersoc.org/pages/Archive-MM/Volume_28/28-206-718.pdf

quartz 1100-1200 Vickers.

Powder metal.

https://nanosteelco.com/images/uploads/resources/NSB_72_tech_data.pdf

Hardness Vickers 1 1096 HV

1st Jul 2015 13:56 UTCReiner Mielke Expert

Hello Jason,

I doubt if that is a factor. For example the only thing that keeps aluminum from rapidly corroding in air is the instant formation of a protective thin layer of corundum but that does not make it scratch resistant.

Thanks David, That just goes to show that steel is not harder than quartz.

2nd Jul 2015 05:13 UTCJason Bennett

Hmm, the aluminium is a good point Reiner.

I guess it's back to the drawing board, as long as the board isn't quartz, and the pen isn't steel.

Jason

2nd Jul 2015 05:39 UTCRyan Allen

Hey folks, havent posted much lately as im working nightshift. Sending this from my phone so i apologize for any spelling/grammer issues. Im a heat treatment tech and changing the hardness of steel is my business. Even high carbon steel would be considered soft stuff compared to the new chrome alloys. The hardest stuff i have dealt with in the last 15 years is a material we call P91 its a chrome alloy with molibdinum and is still considered steel. We dont use mohs scale and most of the hardness tests i do are done via a mic 10 or old school tella brinell. I can change the hardness of any kind of steel via heat treatment. Stainless is a whole different entity and most heat treatments have the opposite effect on stainless as carbon steel. Ill try and round up a piece of scrap p91 and do a scratch test on some material when i get home. I can make the same piece of steel as soft as wood or so hard it will shatter like glass if dropped by adjusting the heating ramp rates and soak temperatures during a post weld heat treatment. Not sure if this any help but ill see what i can drum up out of the bone yard of this gas plant for some R&D.

2nd Jul 2015 14:20 UTCReiner Mielke Expert

Hello Ryan,

If anyone can settle this question it sure sounds like you will be the one. Looking forward to what you find out. Thanks

7th Jul 2015 00:40 UTCDon Saathoff Expert

Since I run the "Mineral Group Meeting" connected with the local rock club I occasionally get to talk about field ID. In one session I had the interested individuals bring their pocket knives to a meeting where we tested the hardness of the blades against Moh's reference specimens. The blades ranged from between 4 & 5 to between 5 & 6 (I don't use 4.5 or 5.5). My great-grandfathers whittling (sp) was the upper end of the range between 5 & 6. None could scratch quartz!!

Don S

16th Jul 2015 06:16 UTCRyan Allen

Well ive tried p91, inconel, tungsten welding stingers and carbon steel. None would scratch quartz in their normal form. I did come across some 9% chrome alloy that they had used carbon gouging rods on. The resulting slag would scratch quartz. So im pretty sure that many of the alloys could be hardened to this level by hitting steel with a torch until glowing bright red then water quenching and repeating. By the time you made a knife blade hard enough it would be so brittle you could easily snap it off with your fingers. At this point you have induced so much martinsite that i would no longer classify it as a steel. So as it stands i would answer no you cannot scratch quartz with "steel".

16th Jul 2015 14:17 UTCReiner Mielke Expert

Thanks Ryan,

I think that settles it. Now I don't have to worry about that anymore.:-)

Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 19, 2024 03:19:19

Go to top of page