Standard BS 4659:1971 groups tool steels into six types:

1. high speed,
2. hot work,
3. cold work,
4. shock resisting,
5. special purpose and
6. water hardening.

The designations follow the AISI with the addition of B. Thus BTI and BMI designates high speed steel of tungsten and molybdenum grades respectively.
Non-Shrinking Steels

This term refers to steels which show little change in volume from the annealed state when hardened and tempered at low temperatures. Usually the following volume changes occur.

Pearlitic	austenitic state, contraction
austenitic	martensitic state, expansion
martensitic	sorbitic state, contraction

In non-shrinking steels the volume changes counterbalance each other, and such steels are required for master tools, gauges and dies which must not change size when hardened after machining in the annealed condition. The cheapest non-shrinkage steel contains 0,9% carbon and about 1,7% manganese. A better steel is,

C, 1.0; Mn, 0.95; W, 0.5; Cr, 0.75; V, 0.2

Both steels are oil quenched from 780° to 800°C and tempered 224-245°C. High carbon 5% and 12% chromium steels are also used for non-distortion.
Finishing Tool Steel

While high-speed steels are very efficient with heavy cuts and high speeds they are incapable, at slow speeds and lighter cuts, of holding the keen edge necessary for obtaining a very smooth finish on certain articles. Special steels have been produced for this purpose, known as finishing steels, which are capable of retaining a keen cutting edge for much longer periods than carbon steel used under similar conditions. The usual type has the approximate composition:

C, 1.1 to 1.4; W, 4; Cr, 0.7 to 1.5; V, 0.3

After preheating to 650°C it is water hardened at 820-840°C and immediately tempered at 150-180°C. Anneal at 750°C. Tungsten steels containing 1 to 5,5% and 1 to 1,3% carbon are used for twist drills, taps, milling cutters, drawing dies and also tools for rifling gun barrels, boring cylinders and expanding tubes, which require long continuous cutting without interruption for regrinding. They are tempered at 200-230°C.

Cold Die Steels

The standard oil hardening die steels contain 1 C, 1 Mn, 0,3-1,6 W, 0,5 Cr, hardened from 800°C and immediately tempered at 170-250°C. For cold obtrusion punches high-speed steels are satisfactory, e.g. 6W6 Mo.
High carbon-chromium (A)

C	Cr	Mn	Si	Harden °C	Temper °C
2	13	0-25	0-6	OQ 950 or AC 1000	480-2 hrs

This steel has good resistance to oxidation at elevated temperatures, high hardness and good wearing properties. lt is suitable for intricate sections, dies for blanking, coining, toller threading and drop forging hard materials. The structure is martensitic on cooling in air but the carbides can be precipitated and the steel softened by very slow cooling from 840°C.
High Tungsten-Chromium Steel

C	Mn	W	Cr	V	Mo	Harden,°C	Temper,°C	Anneal, °C
0,3	0,3	10	3	0,3	0,3	OQ 1150	570	850

This is the best type of steel for hot work except where resistance to scaling or oxidation is important. lt is used for hot-drawing, hot-forging, extrusion dies and dies for die casting aluminium, brass and zinc alloys. Die-casting die steels often fall through surface cracking caused by cyclic expansion and contraction, aggravated by the erosive action of the molten metal. Increased die life necessitates regular maintenance and careful preheating before use.

Sensitivity of die steels to distortion during heat-treatment is largely affected by directionality and particle size of the carbides in the microstructure. Expansion is greatest in the direction of carbide stringers. Fine random distribution of carbides are therefore desirable. For die casting and extrusion dies molybdenum containing 0,5 Ti + 0,08 Zr is useful in critical applications. Thermal conductivity, resistance to thermal shock and attack by molten metal is high and no heat treatment is required. Nimonic 80(a) and 90 have also been used satisfactorily for dies and inserts. Die block steels for drop forging have been standardised into four type. These are:
1) 0,6 carbon steel,
2) 1% nickel, 0,6 C,
3) 1,5 Ni, 0,7 Cr, 0,6 C,
4) 1,5 Ni, 0,7 Cr, 0,6 C, 0,25 Mo.

Hardness ranges from 425/455 for dies with shallow impressions to 298/355 for very large forgings.