Ever since the beginning of this century, high speed steels have been one of the primary materials used in the manufacturing of cutting tools for the metalworking industry. Over the years, the popularity of various grades has shifted to technological advances. Early high speed steels were primarily of the tungsten variety. But during World War II, with tungsten scarce, molybdenum types were successfully developed to produce comparable results as obtained with tungsten. Since then, molybdenum types have gained popularity to the point where most high speed steel tools made today use the molybdenum steels.

The molybdenum high speed steels include a number of compositions. These range from the standard grades, such as M-2 and M-1 through the M-3's and M-4 with high carbon and high vanadium content to the super hard M-40 series. The tungsten high speed steels that have retained popularity over the years are T-5 and T-15.

In the last ten years, particle metallurgy techniques have added a new dimension to the high speed steel picture. Although there are a number of variations of this process, the basic procedure involves the compacting of millions of fine particles of steel, that are even in size and uniform in carbide distribution into a bar of tool steel.

The result of the procedure involves the compacting of millions of fine particles of steel, that are even in size and uniform in carbide distribution into a bar of tool steel.

Today, it is possible to obtain a powdered metal equivalent for almost any of the previously mentioned high speed steels. The biggest impact to date though has been in the T-15 material. But before we get into that, we should review the four basic properties generally used to compare various high speed steels.

These are:

• Red Hardness
• Wear Resistance
• Toughness
• Grindability

The retention of cutting edge strength at the high operating temperatures is called 'Red Hardness'.
High cutting speeds produce heat buildup at the cutting edges of the tools, often reaching 1000 degrees F. At these temperatures, insufficient hardness of a high speed steel will cause the cutting edges to deform, impairing cutting efficiency and requiring frequent resharpening.

WEAR RESISTANCE

In any cutting application, the work material constantly rubs against the tool edges resulting in an abrasive action that causes wear and impairment of cutting ability. Wear resistance is the relative ability to withstand such wear.

TOUGHNESS

Toughness is generally known as the ability to withstand shock and avoid premature breakage or chipping edges.

GRINDABILITY

Grindability is generally the last property reviewed in selecting of tool grade. However, the grindability of a material has a direct effect on the economics of tool manufacturing, whether you make or buy your tools, grinding time is expensive.

INTERRELATIONS OF PROPERTIES

As a general rule, these properties are not independent of one another. In many cases, improved characteristics in one property may be at the expense of certain other properties. In particular, wear resistance and grindability are opposing characteristics and red hardness and toughness are opposing characteristics. For example, wear resistance of a material is often measured by observing the wheel wear on grinding the different high speed steels-a greater magnitude of wheel wear signifies high wear resistance. In addition, hardness and toughness are opposites. Hardness often has to be compromised to avoid premature breakage or chipping cutting edges. This will become more evident as we study the charts.

A great many high speed steel comparison charts have been published by various sources. Each of these seem to be different from the next. In order to be as objective as possible, we solicited and compiled technical information from the following companies:

• Braeburn Alloy Steel Division
• Crucible Specialty Metals Div.
• Latrobe Steel
• Teledyne Vasco

M-2

M-2 is a general purpose high speed steel that is used in many applications. Our chart is organized using M-2 as our benchmark; for most comparisons of high speed steel start off with the question - "How does it compare to M-2?"

M-42

M-42 has a higher wear resistance and red hardness than M-3-2. It is almost tough as M-3-2 and its grindability is better M-3-2. Because of this, we have found that M-42 is preferred over M-3-2 in most cases. For this reason, M-42 tools and blanks are stocked while M-3-2 are not. Our designation for this material is "R", which refers to the fact that M-42 has the highest red hardness of any of the high speed steels generally used today.

CPM-20

CPM-20 is an alternative for M-42. It does everything as good as or better than M-42, and does not include hard-to-get cobalt. We substitute freely with M-42.

T-15 PM

T-15 has always been a good alternative to M-2 when additional wear resistance and red hardness are required. The chief problem with conventional T-15 has been that it is very difficult to grind and is relatively brittle. T-15 PM has solved that problem. As mentioned before, T-15 PM has the same components as conventional T-15, but it is manufactured in such a way that uniform carbide distribution and even particle size is obtained. The difference between conventional T-15 and T-15 PM is dramatic:

T-15 PM grinds far easier than conventional T-15 for form grinding and resharpening tools.

T-15 PM is much tougher than conventional T-15. It can withstand shock and is not nearly as brittle as conventional T-15.

T-15 PM still retains excellent high wear resistance and red hardness. In fact, we have designated T-15 PM as "W" because its wear resistance is superior to any of the materials shown.

HS 76

The most recent addition to our available materials. HS 76 offers even higher Red Hardness and wear resistance than T-15. Since this material is produced with the PM process, the grindability compares very closely to M-2. The tougher your part materials, the better HS 76 will perform. We suggest you try this on your next tough forming job.

Lester Detterbeck Enterprises, Ltd. has long been an advocate of proper Rockwell Hardness on Tool Steel. From our years of experience, and working with the High Speed Steel Manufacturer, we have developed what we feel are the optimal hardness ranges. The readings are checked on "C" scale and are as follows:

M-2..............63-65
CPM-20/M-42......65-67
T-15 PM..........65-67
HS 76............66-68

These Rockwell readings provide the best match of wear resistance, toughness and Red Hardness for each given steel. Lower reading may improve grindability slightly, but at a major loss of tool life. Typically these "higher" Rockwell readings can only be achieved by Heat Treating in a Salt Bath Style Furnace. LDE uses only Salt Bath Style Heat Treat so we may provide you with the best possible blanks and tools.

IN SUMMARY

The selection of the proper high speed steel is very important. Your effort reviewing the chart provided on this page will represent time well spent. Your order of LDE blanks and tools of the proper material with the optimal Rockwell Hardness will represent money well spent. Our objective is your profitable machining.