On Sun, 13 Feb 2022 16:59:24 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

>On Sun, 13 Feb 2022 06:22:55 +0700, John B. <slocombjb@gmail.com>
>wrote:
>
>>On Sat, 12 Feb 2022 12:20:12 -0800, Jeff Liebermann <jeffl@cruzio.com>
>>wrote:
>>
>>>On Sat, 12 Feb 2022 07:04:21 -0800 (PST), Tom Kunich
>>><cyclintom@gmail.com> wrote:
>>>>This is so common that it is hard to get drill bits made of properly hardened steel. They are using high carbon steel that crystalizes and break off. And you have to buy a new one rather than sharpening the old.
>>>
>>>As usual, 100.0% wrong.
>>>
>>>It's hard to get inferior drill bits. Most if not all of what I see
>>>for sale is quite good quality. It is possible to find inferior drill
>>>bits if you look hard. Some of the junk in the hardware bargain bin
>>>probably qualifies. However, these don't "break off" when they fail.
>>>They are soft and bend a little before breaking. If you have a drill
>>>bit that "wobbles" from being bent, you have one of these.
>>>
>>>You can also accidentally purchase drill bits that are made for
>>>drilling in specialty material. Usually, these will have a strange
>>>looking point, lip, or edge. M35 Bits made for drilling titanium,
>>>cast iron, and stainless include cobalt in the recipe and tend to
>>>break if abused.
>>><https://www.azom.com/article.aspx?ArticleID=6169>
>>>Note that titanium plated drill bits are harder than cobalt. You can
>>>sharpen cobalt drill bits, but once the titanium layer is gone, forget
>>>about sharpening the bit.
>>>
>>>Most commodity drill bits are made from M2 tool steel:
>>><https://hudsontoolsteel.com/technical-data/steelM2>
>>><https://waldunsteel.com/products/m2-high-speed-steel/>
>>>M2 is 0.85% carbon. "High Carbon" between 0.6 to 1.0% carbon:
>>><https://en.wikipedia.org/wiki/Carbon_steel#Higher-carbon_steels>
>>>which puts M2 in the middle of the range making all commodity drills
>>>"high carbon steel".
>>>
>>>Also, please note that *ALL* steels are crystals. The various types
>>>are distinguished by their crystal structure.
>>>"Steels - The Structure of Engineering Steels"
>>><https://www.azom.com/article.aspx?ArticleID=399>
>>>M2 high speed tool steels are already crystalline. Using such steels
>>>do not crystallize the steel because it is are already crystallized.
>>>
>>>There are drill bits that are listed as "high speed steel", which are
>>>generally made only for drilling wood or plastic. Their major claim
>>>to fame is the low price. For example:
>>><https://www.harborfreight.com/power-tools/drill-driver-bits/high-speed-steel-drill-bit-set-13-pc-61723.html>
>>>These don't "break off" but rapidly become dull if used to drill
>>>through metal.
>
>>While I know that you are generalizing I would quibble with a couple
>>of statements.
>
>Sorry for the delay. I wanted to do some reading and ask a friend a
>few questions about these quibbles.
>
>>Cast iron, at least the commonly used term, refers to a
>>rather soft material, 150-200BH (Brinell hardness) to as high as
>>210-260 BH.
>>see http://www.iron-foundry.com/castings-hardness.html
>
>When I mentioned cast iron in my previous rant, it was in reference to
>using M35 cobalt drill bits to drill holes in cast iron:
> "M35 Bits made for drilling titanium, cast iron, and
> stainless include cobalt in the recipe and tend to break if abused."
>My main point was that there are specialty drill bits, with odd point
>angles considered to be best for drilling cast iron. I couldn't find
>any drill bits made from cast iron.
>
>"How to Drill Into Cast Iron"
><https://www.hunker.com/13403041/how-to-drill-into-cast-iron>
>
>I'm partial to using Rockwell hardness numbers, not Brinell, mostly
>because most of the metals I've dealt with use Rockwell.
><http://www.matweb.com/search/DataSheet.aspx?MatGUID=6291a24572754cae94ff365ed99b96f9&ckck=1>
> Metric English Comments
>Hardness, Rockwell B
> 40.0 - 800 40.0 - 800 Average value: 311
>Hardness, Rockwell C
> 11.4 - 65.0 11.4 - 65.0 Average value: 30.9
>
>Also, the numbers you supplied for the hardness of cast iron seem to
>be for the products made by the Dandong Foundry. The range of
>hardness for different cast iron formulations can vary from 130HB
>(mallable iron) to 550HB (Nickel hardened).
><https://en.wikipedia.org/wiki/Cast_iron#Table_of_comparative_qualities_of_cast_irons>
>For comparison, hardened tool steel is 600 to 900HB
>
>Of course, there's a catch. Some formulations of cast iron, with
>fairly high carbon content, contain tiny carbon "flakes" which are
>very soft. These "flakes" give the cast iron the consistency and
>strength of a sponge. The iron might be fairly hard, but the material
>will fracture if put under tension or shear stresses. The ability to
>control or eliminate these carbon flakes is why cast iron has a rather
>wide range of Rockwell C hardness (11.4 to 65.0). That is one reason
>why increasing the carbon content increases the hardness, where cast
>iron becomes harder and stronger, but also brittle and not so tough.
>Meanwhile, steel is not as hard and strong, but it is tougher.
>
>"What Is the Difference Between Cast Iron And Steel?"
><https://gallivantingcraftsman.com/what-is-the-difference-between-cast-iron-and-steel/>
>
>>And "High Speed Steel" does, or did, refer to a material commonly used
>>in steel cutting tools - drills, machine tool "bits", etc.
>> https://www.griggssteel.com/what-is-high-speed-steel/
>
><https://en.wikipedia.org/wiki/High-speed_steel>
>"High-speed steel (HSS or HS) is a subset of tool steels..."
>I'm not sure, but it seems that "high speed steel", "tool steel", and
>various mutations highlighting additives, such as "vanadium high speed
>steel" (found among the Grainger drill bits), have been taken over the
>manufacturers marketing departments. I previously mentioned this
>example:
><https://www.harborfreight.com/power-tools/drill-driver-bits/high-speed-steel-drill-bit-set-13-pc-61723.html>
>Notice that the description features "high speed steel" but also
>indicates that the drills are made for "general purpose drilling in
>wood". One might suspect that this is an oxymoron and certainly not
>"a material commonly used in steel cutting tools" (which incidentally
>isn't very clear if the steel refers to the cutting tool or the
>material being cut). I would much prefer to have something that
>follows a standard, instead of a marketing description:
>"SAE/AISI Carbon Steel Naming Conventions"
><https://www.azom.com/article.aspx?ArticleID=6151>
>
><https://en.wikipedia.org/wiki/Carbon_steel#AISI_classification>
>Low-carbon steel
>0.05 - 0.25% carbon (plain carbon steel) content.
>
>Medium-carbon steel
>Approximately 0.3 - 0.5% carbon content. Balances ductility and
>strength and has good wear resistance; used for large parts, forging
>and automotive components.
>
>High-carbon steel
>Approximately 0.6 - 1.0% carbon content. Very strong, used for
>springs, edged tools, and high-strength wires.
>
>Ultra-high-carbon steel
>Approximately 1.25 - 2.0% carbon content. Steels that can be tempered
>to great hardness. Used for special purposes like
>(non-industrial-purpose) knives, axles, and punches. Most steels with
>more than 2.5% carbon content are made using powder metallurgy.
>
>Drivel: Some manufacturers sell "high carbon stainless steel" to the
>knife making industry. The optimum recipe didn't quite meet the
>specifications for being called stainless steel (>13%), so they just
>changed the specification:
><https://agrussell.com/steel-articles/Stainless-Steel-vs-Non-stainless-steel-for-knife-blades>
>"According to ISSF (International Stainless Steel Forum) Stainless
>steel must contain a minimum of 10.5% Chromium rather than 13%. So you
>may find that the definition of stainless steel will differ slightly
>between America and other countries."

Well, you've go on for some lengths but to simplify cast iron is made
in various grades and compared to commonly used steels is relatively
soft... however... a cast iron casting usually has a "skin" of super
hard "steel", i,.e. high carbon iron, what because of rapid cooling is
extremely hard. But, if you take that same casting and stick it in a
furnace and anneal it, it will be the same hardness all the way
through, or maybe I should have said "softness" (:-)

As for "stainless". there are many, many, grades and types of
"stainless" see
https://www.tfgusa.com/types-of-stainless-steel/
--
Cheers,

John B.