Choosing the Correct Tool Steel
To begin choosing the correct tool steel, some assumptions are usually made. Many tool engineers will assume that D-2 is the standard tool steel. This assumption is made based on the fact that D-2 has been so widely accepted during the past 60 years. D-2 has been successfully used as a starting point in many industries because it offers a well-balanced combination of required properties. Since it is so widely accepted, it is easy for tool engineers to visualize which tool steel will provide the needed properties.
Most tool steel producers publish some type of chart, graph or table similar to the one pictured in Fig. 1 below. In most cases, this graph will use D-2 as the standard tool steel grade and references will be made to D-2 (i.e. PM M-4 has twice the wear resistance as D-2). These graphs will generally show the relationship of D-2 and other tool steel grades.
In the graph in Fig 1, we see 13 common tool steel grades depicted. All of these grades have varying levels of wear resistance and toughness. The hardness of each grade is not depicted. However, the normal operating hardness is assumed for most typical applications. For example CPM® 10V® is normally used in the range of HRC 60-62, so the data depicted is based on that hardness. Some consideration will need to be made about the limitation of the hardness of these indicated grades. H-13 and CPM® 9V® will only achieve a maximum hardness of RC 55 which may be too soft for some applications. PM M-4 and Vanadis® 4 can be used as high as RC 65 in hardness. The rest of the indicated grades are typically used in the hardness range of RC 58-62.
Using the graph in Fig 1, a tooling engineer will ask “Will D-2 provide the necessary properties for my tooling application?’ The engineer will then compare D-2 to the requirements of the new tooling application. Will D-2 provide the necessary toughness? Will D-2 provide the necessary wear resistance? If D-2 doesn’t provide the necessary level of each of the required properties, then the tooling engineer will move in one direction or the other on the chart to achieve the desired amount of toughness or wear resistance.
We can separate the graph in Fig 1 into 2 graphs. One graph shows the toughness and one graph shows the wear resistance of the common tool steels.
As we look at the chart in Fig 2, we can see the toughness of D-2 in relationship to many common tool steel grades. To gain better toughness than D-2, the tooling engineer would move to the right on the chart. For a little better toughness, he might choose M-2, Cru-Wear® or CPM® 10V®. Grades like CPM® 9V®, Vanadis® 4 and CPM® 3V® would offer a substantial increase in toughness. Whereas, CPM® 1V®, S-7 and H-13 will offer the toughness required for extreme demands.
The toughness of CPM® 15V® is located to the left of D-2, so its toughness is less than D-2 and would not be an upgrade from D-2.
The chart in Fig 3 shows the comparative wear resistance of the same tool steel grades as indicated in Fig 1 and 2. The wear resistance chart increases from right to left. D-2 is shown in the fifth position from the right. Moving to the left, we see that Cru-wear®, M-2, CPM® 3V®, Vanadis® 4 and PM M4 offer a moderate increase in wear resistance compared to D-2. The grades CPM® 9V®, CPM® 10V® and CPM® 15V® offer a significant increase in wear resistance over D-2. A large volume of vanadium in the alloy content contributes to the wear resistance of these 3 grades. Since CPM® 1V®, A-2, H-13 and S-7 are to the right of the D-2, the wear resistance of these grades are less than D-2. We could expect tools made of these grades to wear out sooner than the D-2 tool.
There is no perfect tool steel grade, only the perfect one for the application. Some trade-offs may be necessary to achieve satisfactory results, but by using D-2 as the assumed starting position, the correct grade can be chosen. The combined chart in Fig 1 is a typical comparison chart used by tooling engineers in choosing the correct tool steel.
Consult with your tool steel service center for assistance in choosing the proper tool steel grade for your application. Your tool steel supplier should be knowledgable about the grades, applications, hardness, toughness and wear resistance required. Your tool steel service center should also be experienced in machining, grinding and heat treating tool steel, as well as the design of the tools and the problems that the tools may encounter during use.
For more specific information about tool steel grades, refer to the individual data sheets for each grade. Data sheets provide more detailed information such as typical applications, heat treating, machining, and grinding. These
may also help in choosing the right tool steel.
CPM®, 1V®, 3V®, 9V®,10V®, 15V® and Cru-Wear are registered trademark of Crucible Industries, LLC
Vanadis® is a registered trademark of Uddehlom