When we choosing the best material for cutting tools used in CNC manufacturing, there is a type of typical metal – tool steel. With different types of tool steels, which one is your choice? In this article, we’ll focus on the definition and classification of tool steel, to learn about the characteristics and properties of each type.
Tool steel is a special type of carbon steel and alloy steel that primarily used for tooling purposes, due to its distinctive hardness, abrasion and deformation resistance, and the ability to hold a cutting edge at elevated temperatures. Tool steels are widely used for cutting, pressing, extruding, and coining metals and other materials.
There are six groups of tool steels: water-hardening, cold-work, shock-resistant, high-speed, hot-work, and special purpose. Thanks to Rohit Kamble, Here we get into four categories of tool steels.
When it comes to the designation of tool steel, you can recognize the class through the capital letter.
1. Cold work tool steel
The cold work tool steel is used for cold working of metals that are below its recrystallization temperature, they have some good hardness and wear resistance at low temperature but sometimes the steel can be used at high temperature, so at that temperature, we can find that they have relatively low hardness. Depending on the medium used for quenching purposes, cold work tool steels can be categorized into four types as below.
– Water hardening tool steel: have to be water quenched, poor hardenability, good impact & shock resistance, wear-resistance and low cost, used for blanking dies, threading dies, hammer, chisel, blade, carpentry tools, knives, etc., such as W1.
– Oil hardening tool steel: relatively better hardenability, less distortion, and less shrinkage during heat treatment, used for forming dies, cutting tools, gauges, etc., such as O2.
– Air hardening tool steel: high hardenability, less distortion, good wear resistance and depth of hardening, used for thread rolling, intricate die shapes and punches, such as A2.
– HCHC (high carbon high chromium) tool steel: very high hardenability, good hardness and wear resistance, used for forming dies, thread rolling dies, gauges, and cutting tools, such as D2. This type of tool is either oil quenched or air quenched.
2. Hot work tool steel
Hot work tool steel is mainly used for hot working such as drawing, forming, extruding, etc. In these processes, metal is worked at regressive above its recrystallization temperature. This type of tool steel has good strength, toughness, hardness, wear resistance at elevated temperatures. Generally they used from 0.35 to 0.65% of alloying elements. The hot work tool steel can be divided into three types according to the principle allowing element used.
– Chromium type hot work tool steel: such as H10
– Tungsten type hot work tool steel: such as H20
– Molybdenum type hot work tool steel: such as H41
3. High speed tool steel
High speed tool steels are used for operation in which the temperature can raise up to 550 ℃， it will require some high hardness, this type of steel gets high hardness up to some elevated temperature. These steels are widely used for cutting metals at high speed, such as in CNC machining, lathe machines will use the cutting tool that is made of high-speed steel. High-speed tool steel is capable for taking compressive load and for the tensile load. The high speed tool steel can be classified into two types based on its principle allowing element majorly.
– Tungsten high-speed steel: such as T1
– Molybdenum high-speed steel: such as M2
4. Special purpose steel
This type of tool steel is used for special purposes such as surface finish when we need high-quality surface finishes.
– Type L (Low alloy type): such as L1, interchangeable with oil hardening tool steel
– Type F (Carbon tungsten type: such as F1