Tool Steels – Low Alloy Special-Purpose Tool Steels

Topics Covered

Introduction

According to the American Iron and Steel Institute (AISI) classification system, low alloy special-purpose steels are designated Group L steels. Low alloy special-purpose steels contain small quantities of chromium, nickel, vanadium, and molybdenum. In the past, the low alloy special-purpose steels comprised seven grades of steels, but due to decrease in demand only two types of Group L steels - L2 and L6 - are in use today.

The L-series steels are similar to water-hardening tool steels but contain a fairly higher amount of alloy content. The greater alloy content of Group L steels enhances wear resistance and thus tool life, and increases hardenability.

Characteristics

The low alloy special-purpose steels are nearly as tough as the shock resisting steels. The L steels are easy to normalize after forging or hot working. It is better to relieve stress before hardening so as to minimize distortion of the steel. Tempering process can be performed as soon as the steel is heated up to 50 to 80°C (125 to 180°F). Double tempering helps in nullifying the effects of retained austenite. Water or brine quenching is ideal for parts (e.g., rolling-mill rolls) made using L-type steels.

L2 - Tool Steels

The L2 type low alloy special-purpose tool steel contains chromium and vanadium for fine grain size and enhanced hardenability. L2 tool steel is available in several carbon levels ranging from 0.50 to 1.10%. The L2 steel with 0.50% C and 13 mm (0.5 in.) thickness can be hardened to about 57 HRC when oil quenched. However, thicker sections of L2 are often water-quenched.

L6 - Tool Steels

The L6 type low alloy special-purpose tool steel contains 0.70% carbon with as-quenched hardness of nearly 64 HRC. The alloying elements present in the L6 type are chromium, molybdenum, and 1.50% nickel to enhance toughness. Hardness above 60 HRC can be maintained for sections of 75 mm (3 in.) thickness. Higher levels of hardenability allow the L6 steels to be oil-quenched, which minimizes the dimensional changes that occur during hardening.

Composition

The composition of L2 and L6 tool steels is tabulated below.

^a Present in a number of carbon ranges
^bOptional

Applications

The L-series tool steels find applications in the following areas:

• Machine parts - Arbors, chucks, cams, and collets
• Special applications requiring dependable strength and toughness.