Water hardening tool steels
W1 plain carbon tool steels are made in four grades of quality: Special, Extra, Standard and Commercial. Special (Grade 1) and Extra (Grade 2) conform to rigid macroscopic, microscopic or hardenability specifications, special being the highest quality. They are suitable for tools and dies requiring steels of uniform high quality. Standard (Grade 3) and Commercial grades are not always made in electric furnaces and meet less rigid processing requirements. They are suitable for many general-purpose applications or for short-run jobs. The standard carbon range is usually 0.95 to 1.1%.
W2 is a shallow hardening tool steel.
Due to its vanadium content, the grain is superior in toughness and resistance to fatigue compared to straight carbon tool steels thereby making it desirable for many types of impact tools.
W3 has higher vanadium content and this provides better toughness.
W4 (ASM composition C 0.6-1.4; Cr 0.25) - the chromium content increases the depth of hardness and reduces the danger of soft spots. A number of these steels were available in several carbon ranges.
W5 (ASM composition C 0.6-1.4; Cr 0.5) - a higher chromium content than W4 for increased depth of hardness.
W7 (ASM composition C 0.6-1.4; Cr 0.5; V 0.2) - the addition of vanadium to W5 provides more toughness because of the finer grain structure.
W8A - the molybdenum content provides deeper hardening, increased toughness, and red hardness.
Carbon steels have carbon as the principal control element generally in the range of 0.85% to 1.15%. When hardened, the surface becomes intensely hard providing good wear qualities.
Tools made from carbon steel can be sharpened to a keen edge with a high finish. Some special steels are made with the carbon content as low as 0.50% or as high as 1.50%.
The significant characteristic of carbon tools steels is that differential hardening results from heat treatment. This is better described as the “case” and “core” effect.
The case is a uniformly hard, outer area which is file hard in the as-quenched condition. The degree of hardness is in the range of 65-67 Rockwell C.
However, the core hardens to a lesser degree – about 40-45 Rockwell C. This core supplies support for the hard case. This also means that there is a limit to the amount of grinding or sharpening that can be done. If the hard case is ground away the cutting or wear resisting qualities are lost. But this seldom occurs in practice due to the small amount of metal removed.
The elasticity required to stand up under repeated stresses makes carbon tools steels useful in applications such as blacksmiths tools, cold chisels, hand punches, jeweller die blocks and cold forming tools. The intensely hard case which permits sharpening to a keen edge also make them valuable for tools such as knives, razors, shears, and wood chisels.
These steels require a fast quench to obtain maximum hardness. Therefore, they are quenched in water or a water solution such as brine.
Oil-hardening tool steels
SAE composition: C 1.2; Mn 0.25; Cr 0.2; V optional; and W 0.5. This group of steels was developed for maximum safety in hardening and minimum dimensional change after heat treatment.
They are preferred for tools or dies with adjacent thick and thin sections, sharp corners, or numerous holes. Tools and dies made from O1 will have good wearing qualities since the tungsten and higher chromium content gives improved wear resistance over the straight manganese grades. They have better wear resistance than the water-hardening grades but are not quite so good in shock resistance. Machining properties are good and material cost is relatively low.
The addition of a substantial amount of manganese plus small amounts of chromium and tungsten permits carbon tool steel to harden in oil. The “case-core” condition of the water hardening tool steels generally disappears and these steels will harden all the way through even in relatively large sections.
O1 (SAE composition: C 0.9; Mn 1.2; Cr 0.5; V 0.2 optional; W 0.5) - is an oil-hardening, non-deforming tool steel which can be hardened at relatively low temperatures. Tools and dies made from O1 will have good wearing qualities since the tungsten and higher chromium content gives improved wear resistance over the straight manganese grades. Typical applications include bushings, forming dies, forming rolls, and gauges.
O2 (SAE composition: C 0.9; Mn 1.6; Cr 0.55 optional; V 0.2 optional; Mo 0.3 optional) – the higher manganese content gives this steel slightly better cutting ability and non-deformation properties than O1. Toughness is considerably better and is the best of any of the oil-hardening group. Suitable for blanking, forming, trimming, and moulding dies, taps and threading dies, broaches, and reamers.
O6 (SAE composition: C 1.45; Mn 0.75-1.0; Mo 0.25) - is an oil-hardening cold work steel which has outstanding machinability resulting from small particles of graphitic carbon uniformly distributed throughout the steel. These particles increase resistance to wear and galling in service. For an oil-hardening steel, 06 holds size well during heat treating. Typical applications include pneumatic hammers, spinning tools, punches, stamps, gauges, wear plates, and cams.
O7 (ASM composition: C 1.2; Cr 0.75; W 1.75; Mo 0.25 optional) – better cutting ability than the other oil-hardening steels except D3 with high hardness and deep hardening. Suitable for taps, threading tools, drills, reamers, cutting tools for brass, and punches and dies for light stock.
Air-hardening tool steels
Air hardening tool steels represent an even better improvement over water hardening steels than the oil hardening types. The slower cooling in the hardening phase results in less intense strains with less distortion. While this is a notable characteristic, these steels are also more resistant to abrasion than the oil hardening types.
In general, the most important element in making these steels air hardening is molybdenum. Vanadium is introduced to prevent grain coarsening.
A2 (SAE composition: C 1.0; Mo 1.0; Cr 5.25; V 0.4 optional) - is an air-hardening tool steel containing five percent chromium. Replaces the oil hardening (O1 type) when safer hardening, less distortion and increased wear resistance are required. It is more difficult to machine than the oil hardening steels. Typical applications include thread roll dies, long punches, rolls, precision tools, gauges, coining dies, mandrels, shear blades and slitters.
A4 (ASM composition: C 1.0; Mn 2.0; Cr 1.0; Mo 1.0) – low hardening temperature of the steel is combined with good toughness, though wear resistance is lower than the other non-deforming steels. Rockwell hardness is C.59-61. Suitable for punches, blanking and forming dies, and gauges.
A5 is an air-hardening, medium-alloy, cold work steel for tools, resembling A4 but containing typically 1.0% carbon, 3.0% manganese, 1.0% chromium and 0.25% molybdenum.
A6 tool steel is like A4 but with 0.7% carbon, 2.0% manganese, 1.0% chromium, and 1.0% molybdenum.
A7 tool steel (composition: C 2.25; Cr 5.25; V 4.5; Mo 1.0) is like A2 but is highly wear-resistant and more so than many other tool steels. It has useful resistance to softening at elevated temperatures and is suitable for complicated dies, thread rolling dies and slitters. Relatively free from distortion.
If you have any comments or questions please contact the author via email at secretary@tttg.org.au.
References
ALLEGHENY LUDLUM STEEL CORPORATION Tool Steel Handbook. Allegheny Ludlum Steel Corp, PA, USA, 1951
ANSTIS, Ralph Man of Iron – Man of Steel: The lives of David and Robert Mushet. Albion House, Coleford, 1997
ATLAS STEELS LTD The Selection and Treatment of Tool and Machinery Steels. Atlas Steels Ltd, Canada, 1960
BECKER O M High-Speed Steel: the development, nature, treatment, and use of high-speed steels, together with some suggestions as to the problems involved in their use. McGraw-Hill, New York, 1910
BETHLEHEM STEEL CO Bethlehem Tool Steels. Catalog 257-A, Bethlehem Steel Co., Bethlehem, PA, USA, 1954
BRADY, George S Materials Handbook. McGraw-Hill, New York, 5th edition, 1944
CARPENTER STEEL CO Carpenter Matched Tool and Die Steels. The Carpenter Steel Co, Reading, PA, USA, 1955
COMMERCIAL STEELS (Australia) LTD English Steel Corporation Products – Steels. Commercial Steels Ltd, Sydney, no date
COMMONWEALTH STEEL CO LTD Comsteel Alloy and Tool Steels. Commonwealth Steel Co Ltd, Waratah, NSW, Australia, no date (c.1965)
CRUCIBLE STEEL COMPANY OF AMERICA The Crucible Steel Pocket Data Book. Crucible Steel Co., Pittsburgh, USA, 1959 (ADV 176-100M-3/59)
CRUCIBLE STEEL CORPORATION Crucible Rex High Speed Tool Bits - Price List. Crucible Steel Corp, Pittsburgh, PA, USA, July 1968
CRUCIBLE SPECIALTY METALS DIVISION Crucible Steel and High Speed Steel Selector. Colt Industries, Syracuse, New York, USA, no date
CRUCIBLE STEEL COMPANY Tool Steel …. For the Non-Metallurgist. Crucible Steel Co, Pittsburgh, PA, USA, no date
CTMA Classification and Identification of High Speed Steels and Cemented Carbide Cutting Grades. Cutting Tool Manufacturers Association, Birmingham, USA, 1980
CUTTING TOOL MANUFACTURERS ASSOCIATION Classification and Identification of High Speed Steels and Cemented Carbide Cutting Grades. CTMA, 1st edition, Birmingham, MI, USA, 1980
DELORO STELLITE LTD Machining with Stellite. Deloro Stellite, Swindon, England, 1963, Brochure B14E
DIRKS, H B High Speed Tool Steels. Thesis submitted in part fulfilment of the degree of Mechanical Engineer, University of Illinois, 1905
EAGLE & GLOBE STEEL CO LTD Balfour’s Hints on Steel. The Eagle & Globe Steel Co Ltd, Sheffield, England, no date
FIRTH STERLING INC Catalog 55R. Firth Sterling Inc, Pittsburgh, PA, USA, 1956
GILL, J P High Speed Steel: Its history, development, manufacture, metallography and constitution, including an extended bibliography. Thesis submitted in part fulfilment for the degree of Master of Science in Metallurgy, Missouri School of Mines, 1922
GILLETT, H W and E L MACK Preparation of Ferro-Uranium. Technical Paper 177, Bureau of Mines, Washington, USA, 1917
Le GRAND, Rupert The New American Machinist’s Handbook. McGraw-Hill, New York, 1955
SEED, Alec T Pioneers for a Century 1852-1952: A history of the growth and achievement of Samuel Osborn & Co Ltd Clyde Steel Works Sheffield. Samuel Osborn & Co Ltd, Sheffield, England, 1953
STANDARD ALLOYS CO URANIUM IN STEEL: The history and function of this element in the making of Uranium steels, with analytical methods and test charts. Standard Alloys Company, Pittsburgh, 1921
THE AUSTRALIAN INSTITUTE OF METALS Handbook. AIM, 1966 edition, Melbourne, Australia
TIMKEN Practical Data for Metallurgists. The Timken Company, 15th edition, 2006
TOWNSEND, A S “Tool Steels and the Development of High Speed Steel”, in Transactions of the American Society of Steel Treatment. Vol. 21, Jan-Dec 1933, pp.769-795
WOLDMAN, Norman E and Albert J DORNBLATT Engineering Alloys. American Society for Metals, 1936
WREGE, C D & R G GREENWOOD “Frederick W Taylor and Industrial Espionage: 1895-1897”, in Business and Economic History. Second Series, Volume 15, 1986.
For the start of the series: Tool Steels: A Brief History — Part 1 Introduction