Heat Treatment - hardening and tempering

Hello,

I am assisting a friend with the heat treatment of some large blades he has machined for an industrial/heavy duty wood chipper (as used to chip logs during tree surgery). The blades have been machined from tool steel (ground flat stock?) and are quite substantial from memory - perhaps 8" long, 2-3" wide and 1/2"+ thick.

I have access to an Industrial Electric Furnace which is capable of heating the items to 1200+ degrees C.

So:

1. What temperature to heat the items for, and for how long?

2. Once heated, presumably the items are then quenched in water to harden them?

3. Once cool, what temperature to heat the items to in order to Temper them, and for how long? And should they then be allowed to cool slowly or quenched as before.

Any other issues, tips, things to be aware of please?

Many thanks!

Brian

You might do well to seek advice from the British Blades Forum as well

Good luck

Get hold of a copy of 'Hardening Tempering and Heat Treatment ' by Tubal Cain

**LINK**

As with all TC's books it is worth it's weight in gold (well not quite, but you get my meaning)

Hi Brian, have look at these two links but definitely quench in oil NOT WATER, best if you can get some substitute for whale oil rather than "any old oil" If not probably a thin oil will be good enough but not motor oil it's generally too heavy.

I have seen these and 8" long seems rather large, most I have seen are 4/5" long X around 4" wide, in any case you will need a large container of oil I would suggest a minimum of 5 gallons better if it was more and depends on how many you are heat treating at a time ? Also remember they must go "edge first" into the oil not flat to minimise warping.

Tempering I would suggest 300 deg C soak for 30/40 mins at this temp and quench in oil. These need to be very tough with reasonable hardness.

John

**LINK**

**LINK**

Edited By JohnF on 30/05/2016 23:05:50

You certainly dont want HARD you need tough hard will shatter

To do the best heat treat you really need to be sure of the metal.

Ground flat stock is most commonly 01 and is a good blade material. You can't do better than follow the suppliers instructions for temperatures. You can, however, refine the grain, which is not often in the instructions and can significantly improve toughness.

If you can't find instructions, try this:

Heat to 870C and and cool in still air

Heat to 830C and cool in blown air.

Heat to 800C and cool in blown air.

Heat to 800C and quench in oil - any oil, veg oil, engine oil.

If you have tight temperature control at those high heats then you can soak for a while quite safely. I don't think you need to for a blade, but 5 or 10 mins should do it. The first heat is more important to soak than the last.

If you don't have good temp control, then don't soak at high temp for long - just get it to temp.

Temper at 220C for one hour - a bit longer if a really thick blade. Some O1 guides suggest a toughness peak at this temp - going a little higher can reduce toughness.

Heat treat may result in breakage.

8" long, 1/2" thick is outside my experience and longer soak times at high temp, and higher temper may be more appropriate - find the instructions!

If the 'tool steel' is not O1 then it may be air hardening and oil quench could be too risky. If in doubt, and you want to be safe, first 'quench' in air and see if a file skates on the surface... if not then quench in oil. Repeating heat treat is OK, quenching too slowly does no harm - it just doesn't get hard. Quenching too fast will result in breakage.

Edited By jaCK Hobson on 31/05/2016 08:35:44

Edited By jaCK Hobson on 31/05/2016 08:39:13

Edited By jaCK Hobson on 31/05/2016 08:43:36

I imagine they have fixing holes which might cause additional cracking problems. The home garden ones are mild steel or similar so there is no chance of shattering on stones and can be file sharpened. I wonder if commercial ones are the same and aim to cut by brute force rather than a finely honed edge so ' as supplied' state might do.

Edited By Bazyle on 31/05/2016 13:10:49

If you have a number of these to do (it being industrial sized) you will be surprised at the cost of commercial heat treating - I use Wallwork and they charge by weight. They will give you them back in exactly the condition you ask for and will often be able to advise what treatment is best for the material and use.

Mark

I go along with Mark C use a professional service, it could work out cheaper in the long run. I have worked in several toolroom's where we had access to ovens for heat treating various odds and ends, but anything of any size would be sent to the hardening shop (either in house or outside) I would not attempt this even with my experience and lack of access to proper equipment. Remember if anything go's wrong with one of the blades in the machine whilst it is running the result could be catastrophic to both the machine and possibly anyone in the near vicinity.

When you say "tool steel", you need to be a bit more specific. The supplier should be able to give you a more technical specification as well as the recommended procedure for hardening and tempering whatever he has sold you. There are many dozens of tool steels with widely differing requirements, some very challenging to implement in a home workshop. Ideally you'd consider this before purchasing said steel....

I don't mean to hijack this thread but I require some advice on hardening two commercial gears 50t x 1.5 module made from en8.

I would think it would be beyond my home workshop facilities so is there any reasonable firms near York that could harden them for me.

They might be ok for the short while they are running at about 7000rpm but are under a bit of shock loading due to opening a valve with a great amount pressure on it but would rather err on the side of caution and have them toughened to buy already hardened gears was expensive.

Edited By Windy on 31/05/2016 14:22:08

You might think that 8" x 2"/3" x 1/2" is big, a local lad has built one a little bigger, its built on a large truck, the hydraulics are driven by a 300hp V8 diesel engine, first you put the log in length wise(about 3 meters long x up to 1 meter dia), that splits the log in about a dozen bits, this lot gets turned side ways, and chopped into firewood lengths, whole job about 2 miniutes. I think the steel used is something like 4140 with Stellite hard facing weld on it. Ian S C

Ian,

i did think GP was possibly a bit odd for an industrial machine. First thought was tough grade of carbide and then if an edge was required a cold working tool steel perhaps? I tend not to think of GP as tool steel.

Mark

Gauge plate or Flat Ground Stock etc. is definitely what they call 'tool steel', I think from memory its basically an 01 steel packaged in convenient ground sizes.

Tony

Tony,

I did not say it was not tool steel, I just don't think of it as tool steel given the modern materials that abound. I tend to think of it mainly for use as its name suggests or for parts of a tool that need to be hard but do not do any cutting or forming etc.

Most modern tool steels tend to be powder met materials and offer significant benefits for tool applications. I am thinking of cold blanking/fine blanking and forming operations such as deep drawing and coining etc.

Mark

I agree with MarkC and Dusty that you should use a professional heat treat service. They use a controlled atmosphere furnace that prevents scaling and decarburization. As long as they know what steel they are dealing with they can deliver your parts to the exact hardness you specify.

Many thanks for all the helpful replies; cooling in oil may prove to be the show stopper, since the furnace is located in a lab environment rather than a workshop - large (5L+) quantities of oil plus the risk of fumes etc. will prove problematic.

Over to Plan 2....

Kind Regards,

Brian

This guide shows it as pretty straightforward to harden and temper, except the requirement for tempering for is two hours minimum!

Neil

www.westyorkssteel.com/files/en8.pdf