Technical

Tool Steels

Properties, Comparisons, & Benefits

Choosing Tool Steels—Balancing Toughness, Wear Resistance, & Compressive Strength

Tool steels refer to a variety of carbon and alloy steels that are well-suited and widely used to make tools primarily used for perforating and fabrication. Tool steels are made to a number of grades for different forming and fabrication applications. The most common scale used to identify various grades of steel is the AISI-SAE scale.

In addition, each grade of tool steel has heat treatment guidelines that must be followed to achieve optimum results. (The heat treating processes for stamping applications are different from those used for cutting tools.)

Let's examine tool steel types (characteristics and features) and the heat treatment processes and options.

Tool Steel Characteristics

Tool steels are very different from steels used in consumer goods. They are made on a smaller scale with stringent quality requirements, and are designed to perform in specific applications, such as machining or perforating.

Different applications are made possible by adding a particular alloy along with the appropriate amount of carbon. The alloy combines with the carbon to enhance the steel's wear, strength, or toughness characteristics. These alloys also contribute to the steel's ability to resist thermal and mechanical stresses.

The chart shows some of the commonly used tool steels and their alloy content.

Side Effects

Each alloy element shown in the chart below contributes to a specific characteristic in the finished steel. It can also create an undesirable side effect, particularly when used in excessive amounts. In addition, alloys can react with each other–either enhancing or detracting from the desired results.

Tool Steels/Alloys

Typical Composition

Steel AISI JIS DIN C Mn Si Cr W Mo V
H13 H13 SKD 61 1.2344 0.40 0.40 1.00 5.25   1.35 1.00
S7 S7 * 1.2357 0.50 0.75 0.25 3.25   1.40  
A2 A2 SKD 12 1.2363 1.00 0.75 0.30 5.00   1.00 0.25
PM 1V * * * 0.55 0.40 0.50 4.50 2.15 2.75 1.00
D2 D2 SKD 11 1.2379 1.50 0.30 0.30 12.00   0.75 0.90
PM 3V * * * 0.80 0.30 1.00 7.50   1.30 2.75
M2 M2 SKH 51 1.3343 0.85 0.28 0.30 4.15 6.15 5.00 1.85
PS4 M4 SKH 54 * 1.42 0.30 0.25 4.00 5.50 5.25 4.00
PM 9V * * * 1.90 0.50 0.90 5.25   1.30 9.10
PS A11 * * 2.45 0.50 0.90 5.25   1.30 9.75
PM 15V * * * 3.40 0.50 0.90 5.25   1.30 14.50

Note: The steels shown above are a representative sampling of commonly used steels and their alloy content.
*No designation

 

Tool Steel Comparison

Tool Steel Comparison

 

Toughness

Toughness of tool steel is defined as the relative resistance to breakage, chipping, or cracking under impact or stress. Using toughness as the only criterion for selecting a tool steel, H13 or S7 (shown in the chart above) would be the obvious choice. However, all desired characteristics–and the needs of the job–must be considered when making your selection.

Tool steel toughness tends to decrease as the alloy content increases. Toughness is also affected by the manufacturing process of the steel. The PM (particle metallurgy) production process can enhance the toughness of the steel grade due to the uniformity of its microstructure.

Hardness also affects toughness. Any given grade of tool steel will have greater toughness at a lower hardness. The lower hardness, however, could have a negative effect on other characteristics necessary to achieve acceptable tool life.

Wear Resistance

Wear resistance is the ability of the tool steel to resist being abraded or eroded by contact with the work material, other tools, or outside influences such as scale, grit, etc. There are two types of wear damage in tool steels–abrasive and adhesive. Abrasive wear involves erosion or breaking down the cutting edge. Adhesive wear is experienced when the work piece material adheres to the punch point, reducing the coefficient of friction, which increases the perforating pressure.

Increased alloy content typically means increased wear resistance because more carbides are present in the steel, as illustrated in the chart.

Carbides are hard particles that provide wear resistance. The size and dispersion of the majority of carbides are formed when alloys, such as vanadium, tungsten, molybdenum, and chromium combine with carbon as the molten steel begins to solidify.

Greater amounts of carbide improve wear resistance, but reduce toughness.

Compressive Strength

Compressive strength is a little known and often overlooked characteristic of tool steels. It is a measurement of the maximum load an item can withstand before deforming or before a catastrophic failure occurs.

Two factors affect compressive strength. They are alloy content and tool steel hardness.

Alloy elements such as Molybdenum and Tungsten contribute to compressive strength. Higher hardness also improves compressive strength.

Tool Steel Benefits

  • H13–54 HRC
    • Popular hot work mold steel
    • Good balance of toughness, heat check resistance, & high temp. strength
    • Moderate wear resistance
  • S7–57 HRC
    • High impact resistance at relatively high hardness
    • Very high toughness to withstand chipping and breaking
  • A2–62 HRC
    • Good toughness
    • Moderate wear resistance
    • Combination of properties and low cost make it well suited for a variety of tooling applications
  • PM 1V–60 HRC
    • Very high impact toughness
    • High heat resistance
    • Good wear resistance
  • PM 3V–60 HRC
    • High toughness
    • Wear-resistant
    • Maximum resistance to breakage and chipping in a wear-resistant steel
  • D2–61 HRC
    • High carbon, high chromium
    • Good wear resistance
    • Moderate toughness
  • M2–62 HRC
    • Tungsten-molybdenum high speed steel
    • Very good wear resistance
    • Good toughness
  • PM M4 (PS4)–62 HRC
    • Excellent wear resistance
    • High impact toughness
    • High transverse bend strength
  • PM 9V–56 HRC
    • Good toughness and wear resistance
    • Resists cracking
    • Not for applications requiring high compressive strength
  • PM 10V (PS)–63 HRC
    • Extremely high wear resistance
    • Relatively high impact toughness
    • Excellent candidate to replace carbide in cold work tooling applications
  • PM 15V–62 HRC
    • Exceptional wear resistance, second only to carbide.
    • An alternative to solid carbide where carbide fails by fracture or where intricate tool design makes carbide difficult or risky to fabricate.

In-house Metallurgical Lab—Solutions-based Testing & Analyses

Dayton's in-house metallurgy lab is designed to develop new products and to test and analyze the quality and viability of materials used in the manufacture of Dayton products. Laboratory services include: hardness testing; metallography (e.g., coating thickness); and failure analysis.

Metallurgical Lab

Equipment includes a high-resolution scanning electron microscope used to evaluate metal structures and a full complement of high-tech equipment used for specimen preparation, routine testing, microscopy, heat treatment evaluation, and failure analysis.

Metallurgical Services

  • Micro Structure Analysis
  • Stereoscopic Analysis
  • Material Qualification
  • Metallurgical Qualification
  • Surface Treatment Analysis
  • Conventional Hardness Testing
  • Micro Hardness Testing
  • Wear Analysis
  • Failure Mode Analysis
  • Scanning Electron Microscopy

Dayton's metallurgy lab utilizes leading-edge equipment, employs professional, experienced metallurgists; and is the first full-service laboratory of its kind in the industry.

Heat Treating–Optimizing Tool Steel Properties

Heat treatment involves a number of processes that are used to alter the physical and mechanical properties of the tool steel. Heat treatment–which includes both the heating and cooling of the material–is an efficient method for manipulating the properties of the steel to achieve the desired results.

A vacuum furnace is used to heat the metals to very high temperatures and allow high consistency and low contamination in the process. Each grade of tool steel has specific heat treating guidelines that must be followed to acquire optimum results for a given application. Unlike cutting tools, the nature of the stamping operation places a high demand on toughness. Thus, a specific steel grade used as a tool steel for stamping must be heat treated differently than one used in a cutting tool.

Tool steel heat treatment processes include: material segregation; fixturing; pre-heating; soaking; quenching; and tempering. The following procedures are general guidelines for tool steel heat treatment. Certain steels require different timing, preheating and soaking temperatures, and number of tempers, e.g., M2, PM-M4, & CPM-10V.

Material Segregation & Fixturing

Segregation by size is extremely important because different individual sizes require different rates in preheat, soak, and quench. Fixturing ensures even support and uniform exposure during heating and cooling.

Pre-heating & Soaking

During pre-heating, both cold-work & high speed tool steels are evenly heated to prevent distortion and cracking. Soaking (austenitizing) is done for a specific time to force some of the alloy elements into the matrix of the steel.

Quenching

Quenching is the sudden cooling of the parts from the austenitizing temperature through the martensite transfer range. The steel is transformed from austenite to martensite, resulting in hardened parts.

Tempering

Untempered martensitic steel is very hard, but too brittle for most applications. Tempering is heating the steel to a lower-than-critical temperature to improve toughness. Tool steels are typically tempered at temperatures between 400° - 1000°F.

Cryogenics

Cryogenics is a process that aids in transformation of austenite to martensite, ensuring greater hardness results and reduced internal stresses. This process takes place at temperatures between -150° and -310°F and will vary in duration, depending on the size of the parts.

The Vacuum Furnace

Furnace Illustration

  1. The process starts by removing the atmosphere creating a vacuum and electrically heating the parts in the hot zone.
  2. After the parts are properly heated (austenitized) the system is backfilled with nitrogen. Nitrogen is used as a means of conducting heat away from the parts. A large turbine blower forces room temperature nitrogen across the parts, cooling (quenching) them through the martensite transfer range.
  3. Hot nitrogen exits the hot zone through gates at the front and rear of the chamber.
  4. The nitrogen circulates through a heat exchanger where it is cooled.
  5. The cooled nitrogen is recirculated over the parts until they reach room temperature.

Dayton maintains a state-of-the-art heat treatment facility, including support equipment and systems monitored by our in-house metallurgist.

Dayton's Engineered Clearance

Punch-to-die Clearance: What Works & What Doesn't?

Punch-to-die clearance (Δ) is the space between the cutting edge of the punch and the cutting edge of the die button, which is determined by the thickness and the type of material being punched.

Optimizing the die clearance is one of the most important steps to punching success. Too large or too tight, an improper clearance can lead to poor edge quality, reduced tool life, and more.

Part Material

The material being punched has a polycrystalline structure with a pre-determined fracture plane. When the punch penetrates the material originating at the cutting edges of the punch and die button on both the upper and lower surfaces of the material, it produces fracture–and pushes it into the die button. When the die button has the correct clearance, these upper and lower fractures connect. This frees the slug and releases the punching force.

Considerations

A common mistake is to specify a too-tight clearance, assuming it will improve the edge quality. This is not the case. When the die clearance is too tight, the upper and lower fractures essentially miss each other. Secondary cracks and/or double breaks are created.

In addition, with tight clearances the material has a higher tendency to grab the punch, thereby increasing the stripping force on the punch. Excessive stripping forces will result in abrasive wear and diminished punch and die button life. In general, increasing the clearance percentage will result in better hole quality and smaller burrs. However, it can increase the tendency for rollover and slug pulling.

For instance, the figure below shows the effect of clearance on roll-over and shear zones. Roll-over is minimized with tighter clearance, but results in uneven burnish and breakage. The opposite is observed with Dayton's Engineered Clearance.

This change in hole quality is critical for holes where a secondary operation is performed.

Slug Inspection

Slugs are a mirror image of the hole, and can tell you if the clearance is appropriate for the application.

The slug at the top has a rough fracture plane, a small burnished land area, and excessive burr, indicating a too-large clearance.

The slug in the middle shows an irregular fracture plane, an uneven burnished land, and secondary shear, indicating a too-small clearance.

The slug at the bottom shows the optimal die clearance–a consistent burnished land that is approximately one third of the material thickness and an even fracture plane in line with the land.

Increasing Punch-to-die Clearance

Perforating a Hole

Punching (or perforating) a hole seems a relatively simple process. It is, however, a multiple step operation (shown below), and best product quality results can be obtained by optimizing the punch-to-die clearance.

If the clearance between the punch and die button is too tight, the pressure can cause the slug to expand and jam in the die button. It will cause excessive wear, and can cause breakage and chipping of the punch–and result in slug pulling or jamming (stacking).

Industry Standard Clearance

A long-time industry "rule of thumb" used by die makers for the clearance between the punch and the die button is 5% of the stock thickness per side. This provided an acceptable burr height and slug control.

Extensive research and testing have shown that a significant increase in punch-to-die clearance can reduce burr height, increase the life of the punch, and improve hole quality–all good reasons to consider Dayton Engineered Clearance as the new industry standard.

The Dayton Engineered Clearance

The Dayton Engineered Clearance, considered by many as the "new" standard, offers a wider range of clearances, reaching as high as 28% Δ. ( Δ = clearance per side.)

The clearance itself depends on the stock thickness, the tensile strength, and the type of material–all driven by the requirements of the specific job.

A regular clearance of 5% per side can produce a hole 0.0001" or smaller than the point of the punch. This creates a press-fit condition on the point during withdrawal, causing excessive wear on the punch and the die button. The Dayton Engineered Clearance produces a hole that is larger than the point of the punch, thus eliminating as much as two-thirds of the wear on the punch.

Optimization

Optimum benefits from The Dayton Engineered Clearance can be achieved by utilizing a Dayton product called a Jektole® Punch. The Dayton Jektole® Punch employs a built-in, spring-loaded ejector with a side vent hole, which helps reduce slug pulling by not allowing the slug to stick to the face of the punch. Thus, optimum punch performance and product quality are achieved.

Dayton Jektole® Punches are used with all types of materials and applications (including high-speed, high-volume punching), and are a key part of the Dayton Engineered Clearance.

Dayton Jektole® Punches, utilizing the tested and proven Dayton Engineered Clearance standard, prevent slug pulling, breakage, and chipping, and help improve punch performance and product quality.

Improve Your Productivity: Select the Proper Clearance

The two charts below show the Dayton Engineered Clearance for various steels and other materials. In the Ferrous Materials chart, both the tensile strength and the hardness ratings are shown. Tensile strength is presented as MPa, along with the appropriate KSI (Kilogram per Square Inch or PSI x 1000) conversion. Hardness values are shown in HB (Brinnel Rating Scale) or HRC (Rockwell Rating Scale), whichever applies.

The punch-to-die clearance depends on the thickness, type, and strength of the material. The Dayton Engineered Clearance offers a wider range of clearances, thus allowing you to optimize the performance of your materials.

How To Select The Proper Clearance

  1. Identify your grade of material on left side of chart.
  2. Identify the tensile strength of the material from the last row of the chart.
  3. If the material is HSS, AHSS, UHSS, or Aluminum, look up the thickness scaling factor based on the material thickness (see chart below)
  4. Multipy the recommended clearance from the chart with the scaling factor table.
    Examples:
  • SAE Grade 280B (Bake Hardenable), Tensile strength 421 MPa. =10-11% Δ per side of Material Thickness
  • SAE Grade 800 DL (Dual Phase), Tensile strength 860 MPa, Material Thickness=2.0mm (14% x 1.20 scaling factor). =16-17% Δ per side of Material Thickness.

Ferrous Materials–Engineered (Jektole®) Die Clearance, Tensile Strength, and Approximate Hardness Values

Other Materials–Engineered (Jektole®) Die Clearance and Tensile Strength

The ranges shown above are the result of more than 10,000 clearance tests performed by Dayton Progress on actual customer provided materials. The optimum clearance will vary, depending on your requirements for burnish length, burr height, and tool life. See the next page to find out how to have your material tested by Dayton Progress.

Jektole® Clearance Testing–Exclusively from Dayton

Clearance Testing

Dayton Progress has performed extensive research, completing and validating more than 10,000 clearance tests. The Dayton Engineered Clearance does, in fact, offer many positive benefits:

  • Reduces punch wear by reducing the force required to strip the punch
  • Produces less burr/reduces the need for grinding
  • Reduces downtime from re-grinding
  • Reduces total punch and PM costs
  • Requires less press tonnage
  • Increases bottom line profit

 

Customer Clearance Testing

Customer clearance testing–an exclusive Dayton Progress testing service–is available to any company interested in using the Dayton Engineered Clearance. In the test, a series of .188" diameter holes are punched, using varying clearances to determine the optimum clearance for a given material. The chart shows typical test results.

The Process

  1. Provide Dayton Progress with four samples of your material. Samples must be 25 mm (1") x 100 mm (4") up to 4.8 mm thickness; burrs removed; flat; and free of holes and material spurs. Note: Depending on the material tensile strength, the maximum thickness could be lower than 4.8 mm (.188").
  2. Test results are analyzed and recorded on data sheets, showing clearance ranges and corresponding hole characteristics.
  3. After the samples and data sheets are returned, select the clearance based on hole size and burr height. If you desire a specific hole characteristics (e.g., more burnish length), select the clearance to meet your requirements by examining the test strip.

Clearance Test Sample

Jektole® vs. Regular Clearance

The bar graph above illustrates the dramatic differences in individual test results for both the standard 5% Δ clearance and the Dayton Engineered Clearance. Under similar test conditions, the standard 5% Δ clearance requires 41 hours of maintenance per million parts, while the Dayton Engineered Clearance requires 12.5 hours of maintenance per million parts!

Contact your nearest Dayton representative for Jektole® Clearance Testing.

PreviewAttachmentSize
Dayton's Engineered Clearance brochure661.65 KB

Birth of a Hole

The dynamics of the perforating process is often considered to be a simple two step process of driving a punch through a piece of sheet steel and then withdrawal of the punch from the hole.

There are in fact six steps to perforating a hole. Each step contains elements critical to the overall process. An understanding of these steps will assist in the selection of die construction, tool steels, and punch to die clearance.

PreviewAttachmentSize
Birth of a Hole826 KB

Stamping Basics

This report defines basic stamping terminology and illustrates basic stamping functions. We explore the common types of die construction, compare stripper design options, and analyze common die operations.

 

PreviewAttachmentSize
Stamping Basics1.42 MB

High Speed Stamping

This report addresses the special concerns of high-speed stamping. We define high-speed stamping and discuss operating factors - such as the effects of die clearance and methods of slug control - that will help improve your stamping operation. We explore tool steel and selecting the proper surface treatment for your application. We further describe how stripper design affects your high-speed stamping operation. Finally, we discuss application problems and possible solutions.

 

PreviewAttachmentSize
High Speed Stamping2.51 MB
Syndicate content