I didn't have any trouble with the first knife I made but the last several have all given me trouble when I go to try to drill the pin holes. My process is to forge the shape, bring it back up to a yellow heat and "normalize" it in vermiculite. The next day I do my basic shaping and try to drill the holes but I've thrashed several drill bits now on clearly hardened metal. I thought the normalization step would reduce the hardness of the metal to make it easier to drill. Am I doing it wrong? Any advice is greatly appreciated!

Cooling it slowly in vermiculite is annealing the stock and should make it easier to drill. What type of steel is it? Some steels are air hardening.

Pnut

More to the point than definition of terms is you anneal and normalize from "cherry red", not a yellow. This is called "critical temp". Critical temp is just after it loses its magnetism.

Also, bring it up to "critical temp", dont bring it down to "critical temp'. This means do it on a rising heat

24 minutes ago, pnut said:

Cooling it slowly in vermiculite is annealing the stock and should make it easier to drill. What type of steel is it? Some steels are air hardening.

Pnut

It's 5160.

What pnut and anvil said. 

15 minutes ago, anvil said:

More to the point than definition of terms is you anneal and normalize from "cherry red", not a yellow. This is called "critical temp". Critical temp is just after it loses its magnetism.

Also, bring it up to "critical temp", dont bring it down to "critical temp'. This means do it on a rising heat

So what happens if I anneal from above the critical temp? I though the purpose of annealing was to remove the stresses from the metal by bringing it above the plasticity state. 

extra grain growth

What happens is the results you got more times than not.

There are two very important points when heat treating. 

1: proper temp

2: proper time at that temp.

2 hours ago, PhillyAlchemist said:

So what happens if I anneal from above the critical temp

You may get lamillar (sp?) annealing which can result in excessive grain growth, as Steve indicates, as well as lamillar plates of extremely hard iron carbide in the soft steel matrix.  Hit one of those plates and your drill bits will scream bloody murder before dulling. 

For maximum "softness" you need spheroidal annealing.  

Here is his specific direction for proper 5160 annealing:   "Annealing: For a predominately pearlitic structure, heat to 1525 °F (830 °C), then cool rapidly to 1300 °F (705 °C), then cool to 1200 °F (650 °C) at a rate not exceeding 20 °F (11 °C) per hour; or heat to 1525 °F (830 °C), cool rapidly to 1250 °F (675 °C), and hold for 6 hr. For a predominately spheroidized structure, heat to 1380 °F (750 °C), cool rapidly to 1300 °F (705 °C), then cool to 1200 °F (650 °C) at a rate not exceeding 10 °F (6 °C) per hour; or heat to 1380 °F (750 °C), cool rapidly to 1250 °F (675 °C), and hold for 10 hr."

Notice that there is a distinct difference in the process used to create the most stress free steel (pearlite) as opposed to the easiest to machine (spheroidal).

 

 

Note that some alloys not listed as air hardening will air harden in knife sized cross sections. Also note that small items may need a heat donor to go into the annealing mixture to slow down the temperature drop and get a good blacksmith anneal.

If you find that you have trouble drilling holes after an attempt at annealing or normalizing you probably didn't get the process right.  However, if you still want to drill the holes, bring the portion you want to drill into to a dull red (still magnetic) and then let it air cool or you can cool it slower if you want.  This would be considered a sub-critical annealing process and should easily soften 5160 enough for drilling.

1 hour ago, ThomasPowers said:

Also note that small items may need a heat donor to go into the annealing mixture to slow down the temperature drop and get a good blacksmith anneal.

I have a dedicated hunk of scrap that I use both for this and to preheat the oil in my quench tank. It's a bundle of seven 8' lengths of 1/2" round welded into a big hexagon (a failed attempt at a project that was rapidly abandoned) with a hook on one end both for retrieval and for hanging off the edge of my coal forge.

On 9/13/2019 at 8:00 AM, PhillyAlchemist said:

So what happens if I anneal from above the critical temp?

The thing to remember is all these specs and graphs is a means of Predicting what will happen to a specific piece of steel at a given temp and for a specific time. The farther off from these specs, the less likely you are to meet these predictions.