How To Classify The ASTM Tool Steel?

We know ASTM tool steel start from letter, such as H12, A2, D2, O2, S7, L2, F2 and P20 etc, do you know how to classify them? What’s the difference among them?

1: Hot work tool steels, Identification H:

1): Types H10 to H19 are characterized by a controlled chromium content along with other alloying elements. The first four, containing molybdenum, offer excellent toughness and and high hardenability and are frequently used in cold work applications requiring toughness at relatively high hardness levels.

2): Types H21 to H26 are characterized by a controlled tungsten content along with other alloying elements. These steels offer greater resistance to the softening effect of elevated service temperatures but exhibit a lower degree of toughness.

3): Types H41 to H43 are low-carbon modifications of molybdenum high speed tool steels and have characteristics similar to the tungsten types.

2: Cold work tool steels, Identification A, D and O：

1): Types A2 to A10 cover a wide range of carbon and alloy contents but al have high hardenability and may be hardened in air. The low carbon types A8 and A9 have less wear resistance but offer greater toughness than others in this group. Type A7, wigh high carbon and vanadium, offers exceptional wear resistance but at a very low level of toughness.

2): Types D2 to D7 are characterized by high carbon and high chromium contents and exhibit high resistance to abrasion. The types containing molybdenum may be hardened in air and offer a high degree of dimensional stability in heat treatment.

3): Types O1 to O7 are low-alloy types that must be hardened by quenching in oil. Sizes over about 2 in.(50mm) in cross section usually exhibit lower interior hardness.

3: Shock-Resisting steels, Identification S:

Types S1 to S7 vary in alloy content but are intended for shock-resisting applications.

4: Special-purpose tool steels, Identification L and F:

1): Types L2 to L6 are low-alloy steels with a wide range of carbon content. The low-carbon types are generally used for structural applications requiring good levels of toughness, while the high-carbon types may be used for short-run tools.

2): Types F1 to F2 are high-carbon steels with varying tungsten content used primarily for relatively short-run fine edge cutting tools.

5: Mold steels, Identification P:

1): Types P2 to P6 are very low-carbon steels and must be carburized after machining or hubbing.

2): Types P20 and P21 are usually supplied in the prehardened condition and can be placed in service directly after machining.

If we know above information, we can identify the tool steel with grade number easily.