Tool steels' dual personality

Author Edmund Isakov, Ph.D.
Published
October 01, 2009 - 12:00pm

Courtesy of Walter USA

Roughing H13 tool steel.

The guidelines for turning of tool steels include both tool- and part-making applications.

Metalcutting should be treated as an integrated system, which includes three equally important elements: workpiece, cutting tool and machine tool. Traditionally, end users pay more attention to the cutting tool, less to the machine tool (assuming it has adequate power to do the job) and, unfortunately, much too little attention to the workpiece. The information about a workpiece is often limited to the type of work material, such as steel, cast iron, aluminum alloy, etc. The most important mechanical properties of work materials, such as hardness and ultimate tensile strength, sometimes are not provided or not requested by customers. If this data is missing, the integrated system of metalcutting becomes incomplete. In such a situation, maximum cutting productivity cannot be calculated.

Tool steels are high-carbon, alloy and high-speed steels capable of being hardened and tempered. Traditionally, they are used to make tools for cutting, forming and shaping. Other applications include making parts where wear resistance, strength, toughness and hardness are essential for the specified performance, and cannot be achieved with carbon, alloy or stainless steels.

Classification of tool steels is based on the system developed by the American Iron and Steel Institute (AISI). This system arranges tool steels into categories, which are based on heat treatment, application or the major alloying elements. There are six major categories and 10 subcategories identified by letters followed by one or two digits.

In addition to AISI classification, tool steels are identified by designations in the Unified Numbering System (UNS) for metals and alloys, established by the Society of Automotive Engineers and the American Society for Testing and Materials. The UNS designation system consists of the letter T followed by five digits: the first three identify the tool steel category and the last two identify the grade of a tool steel category.

Six major categories, 10 subcategories and identifying symbols of tool steels are shown in Table 1.

Table 1: Tool steels classification.

Categories and subcategories of tool steels Identifying symbols
AISI UNS

Water-hardening

W

T723

Shock-resisting

S

T419

Cold-work (three subcategories):

   

Oil-hardening

O

T315

Air-hardening, medium-alloy

A

T301

High-carbon, high-chromium

D

T304

Special-purpose (two subcategories):

Low-alloy

L

T612

Mold

P

T516

Hot-work (three subcategories):

Chromium-base

H

T208

Tungsten-base

H

T208

Molybdenum-base

H

T208

High-speed (two subcategories):

Molybdenum-base

M

T113

Tungsten-base

T

T120

Machining parameters for turning of tool steels (cutting speed, DOC and feed rate) and respective coated carbide grades were adapted from the Machining Data Handbook, Volume 1 and provided in the same order as the tool steel categories listed in Table 1.

Water-Hardening Tool Steels

The water-hardening tool steels are essentially carbon steels with 0.6 to 1.40 percent carbon. They are the least expensive tool steels.

Three standard AISI (UNS) types of water-hardening steels are in production: W1 (T72301), W2 (T72302) and W5 (T72305). Types W3, W4, W6 and W7 steels are no longer in common use.

The water-hardening tool steels have a 100 percent machinability rating, as a basis for comparison with other groups of tool steels. When compared with free-machining AISI 1212 steel, the machinability rating of water-hardening steels is 40 percent.

The hardness of water-hardening tool steels at annealed condition is 150 to 200 HB.

The water-hardening steels are used for cutting tools (shear blades, reamers, taps and twist drills), fixtures and dies for blanking, coining and threading.

Machining parameters for standard grades of the water-hardening tool steels at the annealed condition are shown in Table 2.

Table 2: Machining parameters for water-hardening tool steels.

Grades and heat treatment Brinell hardness,HB DOC, in. Feed rate, ipr Cutting speed, sfm Coated carbide grades specification, ANSI/ISO

W1, W2, W5. Annealed

150 to 200

0.300

0.020

450

C6/P30, M30

0.150

0.015

550

C6/P20, M20

0.040

0.007

700

C7/P10, M10

Shock-Resisting Tool Steels

Shock-resisting tool steels have been developed to provide effective combinations of high hardness, high strength and high toughness, or impact fracture resistance. These steels were originally developed for springs and are still widely used for spring applications that require good fatigue resistance.

There are five standard AISI (UNS) types of shock-resisting tool steels: S1 (T41901), S2 (T41902), S5 (T41905), S6 (T41906) and S7 (T41907). S3 and S4 are no longer in common use.

The major alloying element is silicon, with amounts varying from 1.0 to 2.5 percent, depending on the S-type steel. Silicon provides resistance to softening during tempering to maintain a fracture-resistant microstructure.

AISI S1 steel is the only grade that contains tungsten (1.5 to 3.0 percent). This steel is also referred to as tungsten chisel steel because it is used to make shock-resisting tools.

Shock-resisting tool steels have a machinability rating of about 75 percent compared to 100 percent for water-hardening tool steels.

The hardness of the shock-resisting tool steels at annealed condition is 175 to 225 HB.

Applications for these tool steels include heavy-duty blanking and forming dies, punches, chisels, shear blades, slitter knives, stamps, headers, piercers and forming tools.

Machining parameters for standard grades of the shock-resisting tool steels at the annealed condition are shown in Table 3.

Table 3: Machining parameters for shock-resisting tool steels.

Grades and heat treatment Brinell hardness, HB DOC, in. Feed rate, ipr Cutting speed, sfm Coated carbide grades specification, ANSI/ISO

S1, S2, S5, S6, S7. Annealed

175 to 225

0.300

0.020

400

C6/P30, M30

0.150

0.015

525

C6/P20, M20

0.040

0.007

675

C7/P10, M10

Cold-Work Tool Steels

Cold-work tool steels do not have the alloy content necessary to be resistant to softening at elevated temperatures. They are restricted in applications that require prolonged or repeated heating from 400° to 500° F (200° to 260° C). This category is divided into three subcategories (Table 1).

Oil-hardening tool steels derive their high hardness and wear resistance from their high carbon content of 0.85 to 1.55 percent and moderate contents of chromium, molybdenum, vanadium, tungsten and silicon.

There are four standard AISI (UNS) types: O1 (T31501), O2 (T31502), O6 (T31506) and O7 (T31507).

The most popular oil-hardening steel is O1. It has sufficient hardenability to produce adequate hardening and surface hardness depths, which extends service life. O1 steel has a slightly higher toughness than other oil-hardening steels and is the most widely available O-type steel. At 22 HRC, the tensile strength of O1 steel is 112 ksi compared with 108 ksi for O2 steel. At 31 HRC, the tensile strength of O1 steel is 133 ksi compared with 128 ksi for O7 steel. O2 steel exhibits the lowest dimensional changes on heat treatment. O6 steel contains free graphite in the microstructure to enhance machinability when making intricate dies. O7 is the most wear resistant oil-hardening steel and may be preferred for toolmaking applications.

The machinability rating of O6 is 125 percent, which means O6 steel is easier to machine than water-hardening tool steels. The machinability rating of other O-type steels is about 65 to 90 percent.

The hardness of oil-hardening tool steels at annealed condition is 200 to 250 HB.

All the oil-hardening tool steels are used for similar applications, including blanking, forming, thread-rolling, coining, molding, cold-trimming and drawing dies. These steels are also used to make reamers, taps, drills, small shear blades, slitting saws, circular cutters and hobs, spindles, gages, collets, broaches, burnishing tools, knurling tools and punches.

Air-Hardening, Medium-Hardening Tool Steels

Air-hardening steels achieve their performance characteristics because of combinations of high carbon (0.55 to 2.85 percent) and moderately high contents of other alloying elements, such as chromium, molybdenum, vanadium and nickel.

There are eight standard AISI (UNS) types of these steels: A2 (T30102), A3 (T30103), A4 (T30104), A6 (30106), A7 (30107), A8 (30108), A9 (30109) and A10 (30110). A5 tool steel is no longer in common use.

Air-hardening tool steels have high hardenability and a high degree of dimensional stability during heat treatment. They exhibit good wear resistance, fatigue life, toughness and deep-hardening qualities.

Air-hardening tool steels can be grouped as chromium grades containing 4.75 to 5.75 percent chromium and up to 1.0 percent manganese (types A2, A3, A7, A8 and A9), and manganese grades containing 1.60 to 2.50 percent manganese and 0.90 to 2.20 percent chromium (types A4, A6 and A10).

Chromium air-hardening types are more readily available and by far more widely used. The chromium types have higher wear resistance (at equivalent carbon contents) and greater hot hardness than manganese types. A9 steel is the toughest compared to other A-type grades, but also the least wear resistant. The manganese types, however, are less wear resistant and more difficult to machine.

The machinability rating of the medium-alloy, air-hardening steels are about 65 percent.

The hardness of air-hardening tool steels at annealed condition is 200 to 250 HB.

Applications of air-hardening tool steels include cold-forming dies, blanking dies, bending dies, forming rolls, drill bushings, knurling tools, muster dies and gages, and other uses that require low distortion in heat treatment and wear resistance.

High Carbon, High Chromium

The high-carbon, high-chromium tool steels are the most highly alloyed steels.

There are five standard AISI (UNS) types of these steels: D2 (T30402), D3 (T30403), D4 (T30404), D5 (T30405) and D7 (T30407). D1 and D6 are no longer in common use.

Each type contains 11 to 13 percent chromium as the major alloying element. All grades are characterized by a high carbon content of 1.40 to 2.60 percent.

The machinability rating of the high-carbon, high-chromium tool steels is 40 to 60 percent.

The hardness of high-carbon, high-chromium tool steels at annealed condition is 200 to 250 HB.

Applications for these steels include spindles, hobs, cold rolls, slitting cutters, blanking dies, forming dies, coining dies, bushings, taps, broaches, sand-blast nozzles and plug and ring gages.

Machining parameters for standard grades of the cold-work tool steels at the annealed condition are shown in Table 4.

Special-purpose tool steels include two subcategories: low-alloy steels (L-types) and mold steels (P-types). A subcategory of carbon-tungsten steels, F-types, is no longer in common use.

Table 4: Machining data for cold-work tool steels.

Grades and heat treatment Brinell hardness, HB DOC, in. Feed rate, ipr Cutting speed, sfm Coated carbide grades specification, ANSI/ISO

O1, O2, O6, O7, A2, A3,

A4, A6, A8, A9, A10. Annealed

200 to 250

0.300

0.020

350

C6/P30, M30

0.150

0.015

450

C6/P20, M20

0.040

0.007

575

C7/P10, M10

A7, D2, D3, D4, D5, D7. Annealed

200 to 250

0.300

0.015

200

C6/P30, M30

0.150

0.010

275

C6/P20, M20

0.040

0.005

350

C7/P10, M10

           

Low-Alloy Steels

Low-alloy steels are similar to water-hardening tool steels, but have a greater alloy content, which increases wear resistance and hardenability compared to the water-hardening steels. Two AISI (UNS) types are manufactured and used: L2 (T61202) and L6 (T61206). L1, L3, L4, L5 and L7 steels are no longer in common use because of falling demand.

L2 steels are produced as medium-carbon (0.45 to 0.65 percent) and high-carbon (0.65 to 1.10 percent) grades. Both grades contain 0.70 to 1.20 percent chromium as a major alloying element. The other alloying elements are vanadium, manganese and silicon. Medium-carbon L2 also contains molybdenum.

The combination of strength and toughness of L2 steel provides fracture and shock resistance. This steel is used for making various blades, chisels, dies, gears, spindles, drive shafts and arbors.

L6 steel contains 1.25 to 2.00 percent nickel as the major alloying element and about the same amounts of chromium, vanadium, manganese, molybdenum and silicon as L2.

Typical tool applications of L6 steel are woodworking saws and knives, shear blades, blanking dies and punches. Nontooling applications include spindles, clutch parts, gears and ratchets.

The hardness of L-type tool steels at annealed condition is 150 to 200 HB.

Machining parameters for standard grades of low-alloy tool steels at the annealed condition are shown in Table 5 on page 61.

Table 5: Machining parameters for low-alloy tool steels.

Grades and heat treatment Brinell hardness, HB DOC, in. Feed rate, ipr Cutting speed, sfm Coated carbide grades specification, ANSI/ISO

L2, L6. Annealed

150 to 200

0.300

0.020

400

C6/P30, M30

0.150

0.015

525

C6/P20, M20

0.040

0.007

700

C7/P10, M10

Mold Steels

There are seven standard AISI (UNS) types of these steels in use: P2 (T51602), P3 (T51603), P4 (T51604), P5 (T51605), P6 (T51606), P20 (T51620) and P21 (T51621). P1 steel is no longer in common use.

P2 to P6 are low in carbon content with 0.05 to 0.15 percent and are usually supplied at low hardness to facilitate cold hubbing of the impression. (Hubbing is a technique for forming mold cavities by forcing hardened steel master hubs into the mold, replicating the cavities to be formed into softer die blanks.) They are then carburized to develop the required surface properties for injection and compression molds for plastics.

P20 (0.28 to 0.40 percent carbon) and P21 (0.18 to 0.22 percent carbon) are usually supplied in prehardened condition, so the cavity can be machined and the mold placed directly in service. The machinability rating of P2, P3 and P4 steels is 80 to 90 percent. Other machinability ratings are: 60 percent for P5, 40 percent for P6 and 65 percent for P20 and P21.

The hardness at annealed condition ranges from 100 to 150 HB for P2, P3, P4 and P5 steels; from 150 to 200 HB for P6 and P20 steels; and from 250 to 270 HB for P21 steel.

Major applications of mold steels are for moldmaking with cavities for plastics molding and die casting of metals that melt at low-temperatures, such as tin, zinc and lead alloys.

Machining parameters for standard grades of mold tool steels at the annealed condition are shown in this article’s full version at www.ctemag.com (see Articles Archive Index).

Hot-Work Tools Steels

The hot-work tool steels represent the H-type category designated by the AISI. They have been developed to withstand the combination of heat, pressure and abrasion wear associated with operations. There are three subcategories of these steels, as shown in Table 1.

Chromium-base steels contain 3.00 to 5.50 percent chromium as a major alloying element. There are six standard AISI (UNS) types of these steels: H10 (T20810), H11 (T20811), H12 (T20812), H13 (T20813), H14 (T20814) and H19 (T20819). H15 and H16 steels are no longer in common use.

The machinability ratings are 55 to 65 percent for H11 and H12, 45 to 55 percent for H13 and 60 to 70 percent for H19.

The hardness of the chromium-base steels is 150 to 250 HB at annealed condition. These steels exhibit a hardness of 325 to 375 HB when quenched and tempered.

Typical applications of chromium hot-work steels include dies for aluminum, zinc and magnesium castings; forging dies; punches, piercers, mandrels, hot-extrusion tooling, shear blades and hot-work dies.

Machining parameters for standard grades of chromium-base, hot-work tool steels at the annealed, quenched and tempered condition are shown in this article’s full version at www.ctemag.com.

Regarding chromium-base tool steels, Terry Ashley, training manager for Walter USA, Waukesha, Wis., said: “In the Walter USA machine shop, we use the H13 grade for special and standard products. Our facility is responsible for the design and manufacture of inch product specials and inch drill standards and specials. All of the indexable drills and most of the special tools we manufacture are made using H13 steel. This includes special milling cutters and integral taper shank tools, special drills and multipocketed, multipurpose special tools and cartridges. We turn it, mill it, drill it, tap it and grind it. Mostly, we machine it in the annealed condition and then harden it. Occasionally, we machine it after it’s hardened to 43 to 47 HRC. Generally, we only finish the heat-treated material. We’ve tested competitive grades and our own grades and settled on the following turning parameters and tool characteristics in our shop.”

Rough turning of H13, annealed

Speed: 650 sfm

Feed: 0.013 ipr

DOC: 0.125 " to 0.200 "

Insert: CNMG 432

Grade: Tiger-tec WAK 20 (thick aluminum-oxide coating, K20 grade)

Geometry: NM5

Tool life: equal to or greater than 1 hour in the cut (1 to 2 days production)

Finish turning of H13, annealed

Speed: 650 sfm

Feed: 0.005 to 0.007 ipr

Finish : finer than 63 rma

DOC: 0.032 " (average)

Insert/geometry: DNMG 441 NF3 and VCMT 331 PM5

Grade: Tiger-tec WPP 10 (thick Al2O3 coating, P10 grade)

Geometry: NF3

Tool life: 3 to 4 days production

Finish turning of H13, heat treated (sometimes interrupted cuts)

Speed : 500 sfm

Feed: 0.005 to 0.007 ipr

DOC: 0.032 " (average)

Finish : finer than 63 rma

Insert/geometry: CNMG 432 NM6

Grade : Tiger-tec WPP 20 (thick Al2O3 coating, P15 grade)

Tool life: 1.5 days production

The cutting speed data shown in Tables 2 to 5 are starting-point recommendations. Please notice that carbide grades listed under the ANSI and ISO codes and the corresponding grades listed by various manufacturers are not equivalent.

Because of contemporary cutting tools with advanced coating compositions and improved geometries and modern lathes, cutting speed can be increased 20 to 40 percent to achieve higher productivity. However, the machine tools’ available power should always be considered.

Table 6: Machining data for mold tool steels.

Grades and heat treatment Brinell hardness, HB DOC, in. Feed rate, ipr Cutting speed, sfm Coated carbide grades specification, ANSI/ISO

P2, P3, P4, P5, P6. Annealed

100 to 150

0.300

0.020

475

C6/P30, M30

0.150

0.015

625

C6/P20, M20

0.040

0.007

775

C7/P10, M10

P20, P21. Annealed

150 to 200

0.300

0.020

475

C6/P30, M30

0.150

0.015

600

C6/P20, M20

0.040

0.007

750

C7/P10, M10

           

Table 7: Machining data for chromium-base, hot-work tool steels.

Grades and heat treatment

Brinell hardness, HB

DOC, in.

Feed rate, ipr

Cutting speed, sfm Coated carbide grades specification, ANSI/ISO

H10, H11, H12, H13, H14, H19.

Annealed

150 to 200

0.300

0.020

350

C6/P30, M30

0.150

0.015

425

C6/P20, M20

0.040

0.007

550

C7/P10, M10

200 to 250

0.300

0.020

300

C6/P30, M30

0.150

0.015

400

C6/P20, M20

0.040

0.007

525

C7/P10, M10

Same grades. Quenched and tempered

325 to 375

0.150

0.015

200

C6/P20, M20

0.040

0.007

250

C7/P10, M10

Tungsten-Base, Hot-Work Steels

Historically, the tungsten-base steels were the first steels for hot-work tooling. These steels contain 8.5 to 19.0 percent tungsten and are available in six standard AISI (UNS) types: H21 (T20821), H22 (T20822), H23 (T20823), H24 (T20824), H25 (T20825) and H26 (T20826). H20 steel is no longer in common use.

Tungsten-base steels have greater hot hardness than any category of hot-work steels and therefore have excellent resistance to softening and washing of dies during operations at elevated temperatures.

The machinability rating for type H21 steel is about 40 to 50 percent.

The hardness of tungsten-base, hot-work steels at annealed condition is 150 to 250 HB.

Applications of these steels include extrusion dies for brass, bronze and steel; hot-press dies, drawing and hot-swaging dies; shear blades and punches.

Molybdenum-Base, Hot-Work Steels

As a result of wartime shortages of tungsten, a few grades of molybdenum hot-work steels were developed. The properties of these steels were intermediate to the chromium- and tungsten-base steels, but the use of molybdenum-base steels gradually has declined. Only AISI (UNS) H42 (T20842) steel is available and used as an alternative to the tungsten-base tool steels when cost is considered. H42 steel contains 4.5 to 5.5 percent molybdenum as a major alloying element. H41 and H43 steels are no longer in common use.

The hardness of molybdenum-base H42 steel at annealed condition is 150 to 250 HB.

Machining parameters for standard grades of tungsten- and molybdenum-base, hot-work steels at the annealed condition are shown in Table 8.

Table 8: Machining data for tungsten- and molybdenum-base, hot-work tool steels.

Grades and heat treatment Brinell hardness, HB DOC, in. Feed rate, ipr Cutting speed, sfm Coated carbide grades specification, ANSI/ISO

H21, H22, H23, H24, H25, H26, H42. Annealed

150 to 200

0.300

0.020

325

C6/P30, M30

0.150

0.015

425

C6/P20, M20

0.040

0.007

550

C7/P10, M10

200 to 250

0.300

0.020

300

C6/P30, M30

0.150

0.015

400

C6/P20, M20

0.040

0.007

525

C7/P10, M10

High-Speed Tool Steels

HSS have dual destinies: They were developed first to make cutting tools, but today are also used to make various parts.

The high-speed tool steels are divided into subcategories M (molybdenum-base) and T (tungsten-base) steels (Table 1). Both HSS subcategories are equivalent in performance; the main advantage of molybdenum-base steels is their initial cost, which is about 40 percent lower than tungsten-base steels. The molybdenum-base steels are more widely used than tungsten-base steels.

Molybdenum-Base HSS

The molybdenum-base HSS constitute more than 95 percent of all HSS produced in the U.S. There are 20 standard AISI (UNS) types of these steels: from M1 (T11301) to M62 (T11362). Molybdenum content varies from 3.25 to 11.00 percent. M6, M8, M15 and M45 steels are no longer in common use.

All grades contain moderate amounts of chromium and vanadium, and 19 grades (excluding M10) contain substantial amounts of tungsten (1.15 to 10.50 percent). Twelve grades, from M30 (T11330) to M48 (T11348), contain substantial amounts of cobalt (4.50 to 12.25 percent).

Those steels with higher carbon and vanadium contents generally offer improved abrasion resistance.

The maximum hardness that can be obtained for the molybdenum HSS varies with compositions. For steels with carbon contents under 1.0 percent (M1, M2, M10, M30, M33, M34, M35 and M36), the maximum hardness is 65 HRC. For those with carbon contents from 1.0 to 1.4 percent (M3, M4 and M7), the maximum hardness is about 66 HRC. Maximum hardness of the high-carbon (1.1 to 1.5 percent) and high-cobalt (4.75 to 12.25 percent) steels (M41, M42, M43, M44, M46 and M48) exceeds 68 HRC.

The machinability rating for the M2 and M7 steels is about 60 percent and 35 to 45 percent for the other M-type steels.

The hardness of molybdenum-base HSS at annealed condition varies from 200 to 250 HB and from 225 to 275 HB (steel grades are shown in Table 9), depending on combinations of alloying elements and their amounts.

M1, M2, and M3 steels are used for manufacturing cutting tools, such as twist drills, reamers and taps.

M7 and M10 steels are used for blanking and trimming dies, shear blades, thread rolling dies, broaches and punches. Cutting tools made of M40 of molybdenum steels exhibit top efficiency on difficult-to-machine aerospace-grade materials, such as titanium and nickel-base alloys.

There are seven standard AISI (UNS) types of the tungsten-base HSS: T1 (T12001), T2 (T12002), T4 (T12004), T5 (T12005), T6 (T12006), T8 (T12008) and T15 (T12015). Tungsten content varies from 11.75 to 21.00 percent. T3, T7 and T9 HSS are no longer in common use.

Tungsten-Base HSS

The tungsten-base steels (excluding T1 and T2 grades) contain a wide range of cobalt (4.25 to 13.00 percent) and have greater red hardness and good wear resistance, but slightly less toughness than those grades without cobalt.

The hardness of tungsten-base steels at annealed condition varies from 200 to 250 HB for T1, T2 and T8 grades and from 225 to 275 HB for T4, T5, T6 and T15 grades, depending on combinations of alloying elements and their amounts.

Applications for tungsten-base steels include milling cutters, drills, taps, reamers, gear cutters, broaches, hot-forming punches and dies, blanking dies, slitters, trim dies, powder-compacting dies, cold-extrusion punches, thread-rolling dies, ball and roller bearings and saw blades.

Machining parameters for standard grades of molybdenum-base and tungsten-base high-speed tool steels at the annealed condition are shown in Table 9. CTE

About the Author: Edmund Isakov, Ph.D., is a consultant and writer. He is the author of several books, including “Engineering Formulas for Metalcutting” (Industrial Press, 2004) and “Cutting Data for Turning of Steel” (Industrial Press, 2009). He can be e-mailed at edmundisakov@bellsouth.net or reached at (561) 369-4063.

Table 9: Machining data for molybdenum- and tungsten-base high-speed tool steels.

Grades and heat treatment Brinell hardness, HB DOC, in. Feed rate, ipr Cutting speed, sfm Coated carbide grades specification, ANSI/ISO

M1, M2, M10, T1, T2, T8. Annealed

200 to 250

0.300

0.020

325

C6/P30, M30

0.150

0.015

425

C6/P20, M20

0.040

0.007

525

C7/P10, M10

M3 (class 1), M4, M7, M30, M33, M34, M36, M41, M42, M43, M44, M46, M47, T4, T5, T6.

Annealed

225 to 275

0.300

0.020

300

C6/P30, M30

0.150

0.015

400

C6/P20, M20

0.040

0.007

500

C7/P10, M10

M3 (class 2) and T15. Annealed

225 to 275

0.300

0.020

225

C6/P30, M30

0.150

0.015

300

C6/P20, M20

0.040

0.007

325

C7/P10, M10

Related Glossary Terms

  • Brinell hardness number ( HB)

    Brinell hardness number ( HB)

    Number related to the applied load (usually, 500 kgf and 3,000 kgf) and to the surface area of the permanent impression made by a 10mm ball indenter. The Brinell hardness number is a calculated value of the applied load (kgf) divided by the surface area of the indentation (mm2). Therefore, the unit of measure of a Brinell hardness number is kgf/mm2, but it is always omitted.

  • alloying element

    alloying element

    Element added to a metal to change its mechanical and/or physical properties.

  • alloys

    alloys

    Substances having metallic properties and being composed of two or more chemical elements of which at least one is a metal.

  • burnishing

    burnishing

    Finishing method by means of compressing or cold-working the workpiece surface with carbide rollers called burnishing rolls or burnishers.

  • carbon steels

    carbon steels

    Known as unalloyed steels and plain carbon steels. Contains, in addition to iron and carbon, manganese, phosphorus and sulfur. Characterized as low carbon, medium carbon, high carbon and free machining.

  • cutting speed

    cutting speed

    Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).

  • die casting

    die casting

    Casting process wherein molten metal is forced under high pressure into the cavity of a metal mold.

  • extrusion

    extrusion

    Conversion of an ingot or billet into lengths of uniform cross section by forcing metal to flow plastically through a die orifice.

  • fatigue

    fatigue

    Phenomenon leading to fracture under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material. Fatigue fractures are progressive, beginning as minute cracks that grow under the action of the fluctuating stress.

  • fatigue life

    fatigue life

    Number of cycles of stress that can be sustained prior to failure under a stated test condition.

  • fatigue resistance

    fatigue resistance

    Ability of a tool or component to be flexed repeatedly without cracking. Important for bandsaw-blade backing.

  • feed

    feed

    Rate of change of position of the tool as a whole, relative to the workpiece while cutting.

  • gang cutting ( milling)

    gang cutting ( milling)

    Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.

  • gang cutting ( milling)2

    gang cutting ( milling)

    Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.

  • hardenability

    hardenability

    Relative ability of a ferrous alloy to form martensite when quenched from a temperature above the upper critical temperature. Hardenability is commonly measured as the distance below a quenched surface at which the metal exhibits a specific hardness (50 HRC, for example) or a specific percentage of martensite in the microstructure.

  • hardening

    hardening

    Process of increasing the surface hardness of a part. It is accomplished by heating a piece of steel to a temperature within or above its critical range and then cooling (or quenching) it rapidly. In any heat-treatment operation, the rate of heating is important. Heat flows from the exterior to the interior of steel at a definite rate. If the steel is heated too quickly, the outside becomes hotter than the inside and the desired uniform structure cannot be obtained. If a piece is irregular in shape, a slow heating rate is essential to prevent warping and cracking. The heavier the section, the longer the heating time must be to achieve uniform results. Even after the correct temperature has been reached, the piece should be held at the temperature for a sufficient period of time to permit its thickest section to attain a uniform temperature. See workhardening.

  • hardness

    hardness

    Hardness is a measure of the resistance of a material to surface indentation or abrasion. There is no absolute scale for hardness. In order to express hardness quantitatively, each type of test has its own scale, which defines hardness. Indentation hardness obtained through static methods is measured by Brinell, Rockwell, Vickers and Knoop tests. Hardness without indentation is measured by a dynamic method, known as the Scleroscope test.

  • high-speed steels ( HSS)

    high-speed steels ( HSS)

    Available in two major types: tungsten high-speed steels (designated by letter T having tungsten as the principal alloying element) and molybdenum high-speed steels (designated by letter M having molybdenum as the principal alloying element). The type T high-speed steels containing cobalt have higher wear resistance and greater red (hot) hardness, withstanding cutting temperature up to 1,100º F (590º C). The type T steels are used to fabricate metalcutting tools (milling cutters, drills, reamers and taps), woodworking tools, various types of punches and dies, ball and roller bearings. The type M steels are used for cutting tools and various types of dies.

  • high-speed steels ( HSS)2

    high-speed steels ( HSS)

    Available in two major types: tungsten high-speed steels (designated by letter T having tungsten as the principal alloying element) and molybdenum high-speed steels (designated by letter M having molybdenum as the principal alloying element). The type T high-speed steels containing cobalt have higher wear resistance and greater red (hot) hardness, withstanding cutting temperature up to 1,100º F (590º C). The type T steels are used to fabricate metalcutting tools (milling cutters, drills, reamers and taps), woodworking tools, various types of punches and dies, ball and roller bearings. The type M steels are used for cutting tools and various types of dies.

  • knurling

    knurling

    Chipless material-displacement process that is usually accomplished on a lathe by forcing a knurling die into the surface of a rotating workpiece to create a pattern. Knurling is often performed to create a decorative or gripping surface and repair undersized shafts.

  • machinability

    machinability

    The relative ease of machining metals and alloys.

  • machinability rating

    machinability rating

    A relative measure of the machinability of a metallic work material under specified standard conditions. Machinability rating is expressed in percents, with the assumption that the machinability rating of AISI 1212 free-machining steel is 100 percent. If machinability ratings of work materials are less than 100 percent, it means that such work materials are more difficult to machine than AISI 1212 steel; and vice versa if machinability ratings are greater than that for AISI 1212 steel.

  • mechanical properties

    mechanical properties

    Properties of a material that reveal its elastic and inelastic behavior when force is applied, thereby indicating its suitability for mechanical applications; for example, modulus of elasticity, tensile strength, elongation, hardness and fatigue limit.

  • metalcutting ( material cutting)

    metalcutting ( material cutting)

    Any machining process used to part metal or other material or give a workpiece a new configuration. Conventionally applies to machining operations in which a cutting tool mechanically removes material in the form of chips; applies to any process in which metal or material is removed to create new shapes. See metalforming.

  • microstructure

    microstructure

    Structure of a metal as revealed by microscopic examination of the etched surface of a polished specimen.

  • milling

    milling

    Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

  • milling machine ( mill)

    milling machine ( mill)

    Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.

  • red hardness

    red hardness

    Ability of a cutting tool material to withstand high temperatures at the point of cut without softening and degrading.

  • sawing machine ( saw)

    sawing machine ( saw)

    Machine designed to use a serrated-tooth blade to cut metal or other material. Comes in a wide variety of styles but takes one of four basic forms: hacksaw (a simple, rugged machine that uses a reciprocating motion to part metal or other material); cold or circular saw (powers a circular blade that cuts structural materials); bandsaw (runs an endless band; the two basic types are cutoff and contour band machines, which cut intricate contours and shapes); and abrasive cutoff saw (similar in appearance to the cold saw, but uses an abrasive disc that rotates at high speeds rather than a blade with serrated teeth).

  • shank

    shank

    Main body of a tool; the portion of a drill or similar end-held tool that fits into a collet, chuck or similar mounting device.

  • shaping

    shaping

    Using a shaper primarily to produce flat surfaces in horizontal, vertical or angular planes. It can also include the machining of curved surfaces, helixes, serrations and special work involving odd and irregular shapes. Often used for prototype or short-run manufacturing to eliminate the need for expensive special tooling or processes.

  • stainless steels

    stainless steels

    Stainless steels possess high strength, heat resistance, excellent workability and erosion resistance. Four general classes have been developed to cover a range of mechanical and physical properties for particular applications. The four classes are: the austenitic types of the chromium-nickel-manganese 200 series and the chromium-nickel 300 series; the martensitic types of the chromium, hardenable 400 series; the chromium, nonhardenable 400-series ferritic types; and the precipitation-hardening type of chromium-nickel alloys with additional elements that are hardenable by solution treating and aging.

  • tap

    tap

    Cylindrical tool that cuts internal threads and has flutes to remove chips and carry tapping fluid to the point of cut. Normally used on a drill press or tapping machine but also may be operated manually. See tapping.

  • tempering

    tempering

    1. In heat-treatment, reheating hardened steel or hardened cast iron to a given temperature below the eutectoid temperature to decrease hardness and increase toughness. The process also is sometimes applied to normalized steel. 2. In nonferrous alloys and in some ferrous alloys (steels that cannot be hardened by heat-treatment), the hardness and strength produced by mechanical or thermal treatment, or both, and characterized by a certain structure, mechanical properties or reduction in area during cold working.

  • tensile strength

    tensile strength

    In tensile testing, the ratio of maximum load to original cross-sectional area. Also called ultimate strength. Compare with yield strength.

  • thread rolling

    thread rolling

    Chipless, cold-forming material-displacement process where a rolling head is pressed into the workpiece to create threads. The material is stressed beyond its yield point, which causes it to be deformed platically and permanently. There are three basic types of rolling heads: axial, radial and tangential.

  • threading

    threading

    Process of both external (e.g., thread milling) and internal (e.g., tapping, thread milling) cutting, turning and rolling of threads into particular material. Standardized specifications are available to determine the desired results of the threading process. Numerous thread-series designations are written for specific applications. Threading often is performed on a lathe. Specifications such as thread height are critical in determining the strength of the threads. The material used is taken into consideration in determining the expected results of any particular application for that threaded piece. In external threading, a calculated depth is required as well as a particular angle to the cut. To perform internal threading, the exact diameter to bore the hole is critical before threading. The threads are distinguished from one another by the amount of tolerance and/or allowance that is specified. See turning.

  • titanium nitride ( TiN)

    titanium nitride ( TiN)

    Added to titanium-carbide tooling to permit machining of hard metals at high speeds. Also used as a tool coating. See coated tools.

  • tool steels

    tool steels

    Group of alloy steels which, after proper heat treatment, provide the combination of properties required for cutting tool and die applications. The American Iron and Steel Institute divides tool steels into six major categories: water hardening, shock resisting, cold work, hot work, special purpose and high speed.

  • turning

    turning

    Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.

  • wear resistance

    wear resistance

    Ability of the tool to withstand stresses that cause it to wear during cutting; an attribute linked to alloy composition, base material, thermal conditions, type of tooling and operation and other variables.

Author

Edmund Isakov, Ph.D., is a consultant, writer and frequent CTE contributor. He is the author of the books “Mechanical Properties of Work Materials” (Modern Machine Shop Publications, 2000); “Engineering Formulas for Metalcutting” (Industrial Press, 2004); “Cutting Data for Turning of Steel” (Industrial Press, 2009); the CD-ROM “International System of Units (SI)” (Industrial Press, 2012); and the software “Advanced Metalcutting Calculators” (Industrial Press, 2005). For more information, call (561) 369-4063 or visit www.edmundisakovphd.com. 

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