Was at work the other day pondering how to spend my tax rebate and was thinking about different steels I'd like to try (I'm hopeless, right? :scared4
. It got my wondering "what exactly quantifies a tool steel?". Is it in the composition, what it was originally designed for or something else?
In simplest terms, anything that is ferrous (iron) based and can be treated in some way to allow it to perform as a 'tool' qualifies it as a 'tool steel'.
Doesn't mean it qualifies as a 'blade steel' though...
I think I've seen 01, D2 and whatever the TKC/Carbonext use referred to as "tool" steels among others. And on the same subject, what is a "High speed tool steel" a la the Tojiro powdered steel range and the Jin knives found at JKI?
Thanks in advance,
Josh
'Tool' steels that are also used for cutting blades have a general characteristic of being able to be made quite hard whilst still strong enough to perform the task.
Traditionally knives were made with a simple iron & carbon alloy. Easy to make, easy to use, works quite well for cutting stuff like food.
'Tool' steel was more often asked to do things that a simple knife steel wouldn't be able to stand up to for very long. Like cutting metal and composite materials, wood, leather, etc. So development of tougher, longer lasting steel was originally slanted toward cutting tools. Didn't take long for folks making knives to realize that if a piece of 'tool' steel can cut it's way through a slab of regular steel, then how long is it going to keep cutting carrots for?
Of course, cutting blades for steel, wood or food are different to each other in shape and desirable properties, but there is a lot of crossover and what will stay sharper for longer with dead tree will also stay sharper for longer with dead cow.
It's all pretty much the same stuff, the difference is what the cutting edge looks like (geometry wise) and how it's made and finished and also how it behaves after it leaves the workshop it was made in as well.
But, the cost of developing these steel was footed by tool makers/users originally, so that's why they get the name.
Also, High Speed Steel (HSS) and Powdered Metal (PM) are not the same thing. You can have HSS without it being PM, you have PM without it being HSS and you can have a PM-HSS as well.
High Speed Steel simply means that it can be used at higher speeds than 'normal' tool steel. Normal tool steels tend to lose their temper (hardness) at a fairly low temperature and if you're trying to cut away a lot of very tough material, heat buildup can be a real concern. If the cutting tool can stay hard at higher temperatures, then you can make it cut at faster speeds, hence the name 'high speed steel'. It simply allows the tool to cut at a faster rate because the tool won't go soft if it becomes hot, even up to red hot.
Unfortunately, this high temperature tolerance also means plain HSS won't take as keen an edge as 'normal' steels because of all the ingredients needed to make it 'HSS'. It'll take a good edge, but usually not a great edge (not easily anyway).
In situations where you want the improved edge life that HSS can provide even without the heat resistance, but you do need to be able to put a really keen edge on the blade, then PM-HSS can allow that as the ingredients that make up the steel have been made small, much smaller than is possible in regular 'melted' HSS which is why you'll see PM-HSS knives, but few (if any) regular HSS knives.
I hope that helps, and I tried to make it as simple as possible but it's a rather complicated subject and not easily explained.
Stu.
