Blackening of Fasteners by Quenching After Tempering

Typically shovels are produced by AUSTEMPERING.

Austempering involves a salt, not oil quench.

Bolts and shovels have different requirements and sections in use, hence different heat treatments.

milo

I may be wrong, but by heat treating shovels, I would think that they would have to be made of fairly thick steel. While heat treating will make the steel harder, it will also make it more brittle. I'm imagining trying to pry a rock or root out of the ground and having the shovel head break, kind of like having shovels made of cast iron, while much harder than steel, it would crack with the stress of shoveling.

This can be done.

Please bear in mind that a shovel requires different performances from different parts of the shovel blade.

The edge needs to be hard enough to be highly wear resistant but tough enough to withstand an impact on a hard rock edge without cracking. The body of the blade needs to be slightly wear resistant and yet springy enough to resist permanent deformation by someone using it as a crowbar or lever.

Differential tempering is difficult to achieve on a production line basis but it can be done.

There are many ways to blacken metal and I don't think that oil tempering will be the most cost effective or give the most satisfactory performance.

What size production run are you considering?

What size pieces are you proposing to harden and temper?

How skilled are your workforce and what equipment do they have to work with?

What quality level and price tag are you aiming your shovels at?

Sorry for all the questions but finding the right answers needs a clear brief.

BAB

Dear Friends,

Please do not mind my question, but how many of you have really worked with shovels or spades? the shovels are used for lifting and throwing loose earth or other material mostly in powder form, and

1. The complete surface of the blade comes in full contact with the material being handled,

2. Whole surface area at top as well as at bottom suffers friction in both directions,

3. The applied force is just enough to pierce it into the heap and generally at a tangent

4. the earth is loosened by digging or by wetting before the shovels are used.

So the requirements are,

a. The whole surface at top as well as at its bottom should be hard enough to resist the wear from sand and earth particles,

b. The hardness should be enough to resist bending at force,

c. Since the blade wears in its length and width, the core should be hard enough to function and to replace the edge,

d. The hardened depth achieved by Oil Quenching is only in micrones and will not cause the breakage on impact or leverage.

I think the Oil Quenching method is the best and long lasting one and it can be used on shovels and spades.

Regards.

rssahni,

We do not mind your questions at all. That is why we are here.

I put my self through college shovelling iron ore and coke spillage in the blast furnace department and docks at a large steel company before getting my degree. I had a shovel in my hand professionally for 7 years before i moved out of the labor gang. i continue to use shovels and spades in my gardening and snow removal here in Ohio.

I am well aware of how a shovel can be used, abused, and how it wears.

I also have 30 + years in metallurgy and quality. Hands on laboratory, heat treat, and manufacturing.

I have issues with a couple of your points:

3. The force is seldom "Just enough to pierce it into the heap" unless it is being operated by grudging slave labor. To penetrate the heap, the shovel is not "at tangent" by any common definition of what tangent means.

Frankly, any one who has ever shovelled from piles (which case you seem to describe by phrase "pierce the heap" as opposed to "dig a hole") knows that you don't pierce the heap. To efficiently shovel from a pile, you glide the shovel into the base along the ground (or deck plate) and lift slightly by pushing down on end of handle as a lever arm, using other hand as fulcrum, to let gravity and change in angle of repose of the heaped material fill the shovel, before adjusting ones grip and lifting. Have YOU ever used a shovel?

4. The earth is loosened by digging or wetting before the shovels are used.

Loosened by digging? Before the shovel is used ? HUH??? Why not let whatever magical force is 'loosening by digging' with out a shovel relocate the soil in space during that first loosening operation? Any one who wets earth to ease in shovelling has not compared weight of water with the weight of the material to be moved and deserves their perspiration. water weighs 8 pounds per gallon, why add this to the load to be shovelled? Very very very strange idea. Use a pick to break up hard material into shovelable particle size.

Requirements a. No problem, but this is not a big deal.

b. Resistance to bending is a function of section more than hardness. But you overestimate the need for resistance to bending as well. Frankly you want toughness not hardness. Hardness = Brittle behavior like a glass rod. MOST NOVICE ENGINEERS MISTAKE HARDNESS FOR TOUGHNESS. The real gift of steel is its "resilience" (the area under the stress- strain curve.)

c.Since shovel wears in length and width, the core should be hard enough to function and replace the edge. As you will see in the next section this will not be a big deal and does not argue exclusively for oil quenching.

d. The hardened depth achieved by oil quenching is only in micrones and will not cause the breakage on impact or leveraging. THis is utterly WRONG! Hardness is governed by steels hardenability and section. In the typical sections used for shovels, even medium carbon grades will through harden. As quenched , untempered martensite is in fact brittle as hell. You may think oil quenching is magic, but it is not. AUSTEMPERING is used for shovels because the process allows for the development of ideal properties of toughness as well as resistance to abrasion.

You are entitled to your opinion, but you came here asking for advice, which was freely given. Hardness is not the issue. Toughness is. Your thinking ignores fundamentals of hardenability, section and ductility and toughness.

Oil quench to get the pretty black color and you will fail in maximizing utility and worker safety.

Oil quenching without tempering is Malfeasance and endangers all by creation of unsafe tools.

milo.

Dear Mr Milo,

I accept that my comments were superficial and did not have the gravity of your knowledge with steels and heat treatment. Please write few words on health hazard caused 'during and after' surface hardening by oil quenching since it's much easier to learn from this forum.

I have copied and sent your comments along with my own to my two college going sons as a "lesson for inspiration" to succeed through struggles.

Regards,

Hi again rrsahni.

We didn't see it as struggles, we liked the work, We hated the unemployment. That was a struggle! For the company to finally accept a college degree after years of labor, that was a bit of a struggle. Its almost always politics.

My concern for "safety" was if the steel was oil quenched without proper tempering.

Quench and temper describes the full process. Oil quenched (without temper) describes a process that leaves untempered martensite in the steel. this is very brittle and can result in sudden failures.

Oil hardening without "tempering" will leave a microstructure of untempered martensite. Untempered martensite is very brittle and can shatter or spall upon shock or impact. So upon hitting a rock, (if digging) or upon over bending (if using to pry up something) an untempered Oil quenched through hardened steel section ican possibly splinter or send shards flying.

Tempering after the oil quench is necessary to Temper the martensitic structure that was formed by the oil quench to remove it's brittleness.

See the slides 10, 16 and 31 in the following to confirm the role of untempered martensite in the failure of rail steel after only 17 days of usage: http://www.ntsb.gov/events/2005/Tamaroa/board_meeting_presentation.pdf

Here is an explanation of the failure mechanism on a tool that mentions spalling as a result of transformation of retained austenite into untempered martensite:

"If, during service, some areas of the tool have to support excessive pressures, for example the shearing edge of circular slitting knives (see Figure 6), retained austenite may be transformed to martensite, with spalling at the edge as a result."

So I see the sudden unexpected failure of the shovel caused by untempered steel to potentially be: 1) loss of footing of laborer when shovel blade suddenly breaks; So he can fall, 2) flying slivers if parts of shovel break off upon hitting a very hard object;

3) spalling and slivers which might strike someone or enter their eye upon failure while using the blade and shovel as a lever (bending failure.)

I am certain that your sons will succeed given your continued mentoring and positive role model. In spite of what the professors may be teaching them away at college!

hope this is helpful.

milo

Soaking in hydrochloric acid (used to clean bricks) will do it. Found this out when cleaning shovels caked in dry mortar. Getting it hot ( but not hot enough to affect the temper ) and putting into old diesel engine oil, also will do the trick. A lovely lustre can be obtained using nitric acid. Why not paint?