exactly what is hss?

[thomas harris]

I have some A-2 air hardening steel. It is annealed right now. If you heat it and let it cool in air it'll be rock-hard. Is this a type of hss. If not what exactly is hss. Does it have a special name/letter abbreviation? Just curious, as it's something used in many production cutting methods routinely.

[JimGlass]

A-2 is a wonderful tool steel but it is not a high speed steel. Different tool steels have different alloys which effects their cost and how they are used.

High speed steel has tungsten it. If I remember correctly tungsten has the highest melting point of any known metal. Tungsten gives high speed steel the ability to remain hard even when red hot. Other tool steels would loose hardness if heated red hot.

Before high speed tool steel came along machinist only had high carbon steel tools. Imagin how much better the high speed steel must have been over the high carbon steel. Similar to comparing HSS to carbide

JIm

[thomas harris]

A-2 is a wonderful tool steel but it is not a high speed steel. Different tool steels have different alloys which effects their cost and how they are used.

High speed steel has tungsten it. If I remember correctly tungsten has the highest melting point of any known metal. Tungsten gives high speed steel the ability to remain hard even when red hot. Other tool steels would loose hardness if heated red hot.

Before high speed tool steel came along machinist only had high carbon steel tools. Imagin how much better the high speed steel must have been over the high carbon steel. Similar to comparing HSS to carbide

JIm

Makes sense, as tungsten is used for tig welding electrodes and light filimants. So the air quechned steels maintain hardness AFTER heating, but soften DURING the heating proces more than hss?

[SteveM]

Also, IIRC, the HSS does not anneal after cooling down from red hot (at least not like carbon steel).

Wikipedia has an entry for it:
http://en.wikipedia.org/wiki/High_speed_steel

Steve

[geraldvowles]

Could it be that older lathes ran at lower RPM because HSS was not available? If that's the case, it would seem logical that there would be no reason not to put a bigger pulley on the motor shaft as long as the bearings were right for the job, assuming one cared about speed at all.

Or was it more an issue of productivity demands that's pushed the speeds up I wonder. - Gerry

[JimGlass]

lower RPM because HSS was not available?

High speed steel had not been invented yet. Carbide tooling came along even later.

I wish I could invent a cutting tool better than carbide.

So the air quechned steels maintain hardness AFTER heating, but soften DURING the heating proces more than hss?

Not sure I understand the question. I may shoot myself in the foot but here it goes. Heat treatable steels need to be heated to a critical point or transfermation temperature then quenched before any change takes place in hardness. After quenching the steel will be at full hardness but will also be brittle. After quenching the steel needs to be tempered or drawn back. In other words, some of the hardness is removed to make the steel less brittle but with increased toughness. Tempering or drawing requires reheating the quenched steel to 500 to 900*F then slow cooling in still air. Heating the steel to higher temps draws the hardness away even more. Eventually, overheating the steel removes most of the usefull hardness. Either way the steel will loose performance in use.

A-2 hardens at 1725-1800*F approx. and is then drawn back to a usable hardess. High Speed tool steels hardens at 2200*F and is then drawn back. The tungsten in HSS makes the hardness take place at the high temperature. This same high temperature also keeps HSS hard at elevated temperatures. The tempering temperatures for HSS are much higher than A-2.

Jim

[thomas harris]

Yes, that explains all. I knew of tempering, but was wondering if the air hardening steels were tempered near the same as hss, with the main exception being hss maintains near full strength at high operation temps. I guess it doesn't really matter with a cutting tool, because if it softens during use the forces on it will instantly dull it before it air quenches itself back to hardness.

[emchd]

I have some A-2 air hardening steel. It is annealed right now. If you heat it and let it cool in air it'll be rock-hard. Is this a type of hss. If not what exactly is hss. Does it have a special name/letter abbreviation? Just curious, as it's something used in many production cutting methods routinely.

In a nut shell, HSS is used to make cutting edges. Most often in woodworking machinery applications. I am currently looking for some HSS to make some MAKA chisels. These chisels ossicalte back and forth about 2200 cycles per minute and cut very clean square and square bottomed holes in wood. As with most woodworking tooling, the edge is razor sharp and the mimium surface area around the edge allows frictional heating to become an issue. This prematurely dulls the cutting tool. Its also why machines like shapers and planers must be run at the fastest reasonable feed rates. Slow feed rates reduce the chip load which is essential to removing unecessary heat from the edge. Dont do this, and your tooling gets dull quick and you burn woods like maple and cherry.

Basicly, as I remember, A-2 is a chrome based tool steel with excellent abrasive resistance whereas HSS is tungston based which means it can maintain hardness at very high elevated temperatures.

The two most popular HSS steels are M-2 and T-1. My jointer and planer knives are T-1. Most steel based shaper knives are still M-2.