Tool Steels - Tungsten Hot Work Steels

Topics Covered

Introduction
Overview
Properties
Composition
Applications

Introduction

Hot work tool steels are steels capable of withstanding high abrasion, heat and pressure conditions that prevail in manufacturing units that perform processes such as forming, shearing and punching of metals at high temperatures of 480 to 760°C (900 to 1400°F). These steels have wear resistance up to 540°C (1000°F).

Hot work tool steels are designated as group H steels and they have 0.35% to 0.45% carbon, 6% to 25% chromium, with vanadium, molybdenum, and tungsten as the other alloying elements. Tungsten is primarily used in hot forming tool steels due to its high temperature strength, toughness and resistance to grain growth.

Overview

Tungsten hot-work steels constitute the H21 to H26 types of hot work steels. These steels have similar characteristics as those of other of high-speed steels. The hot work steel type H26 has low carbon content when compared to that of T1 high speed steel. The primary alloying elements of tungsten hot-work steels include tungsten, carbon, chromium and vanadium.

Properties

Tungsten hot work steels have high alloy content, which enhances their heat resistance. The high alloy content also makes the tungsten steels brittle and unsuitable for the water-cooling process. Breakage of tungsten hot work steels can be reduced if they are preheated to operating temperatures prior to use. Tungsten steels have normal working hardness of 45 to 55 HRC. Thermal shock resistance and toughness of these steels can be improved by reducing the carbon content. In such cases, it is necessary to adjust the tungsten and vanadium content also as these two reduce the hardenability of steel by trapping large amount of carbon in the form of carbides.

Scaling can be reduced by quenching tungsten hot-work steels in oil or hot salt. Tungsten hot-work steels are resistant to distortion when they are air- hardened, and have higher hardening temperature when compared to chromium hot-work steels.

Composition

The following table shows the composition limits of tungsten hot-work steels.

Designation Compositiona, %
AISI UNS C Mn Si Cr Ni Mo W V Co
H21 T20821 0.28-0.36 0.15-0.40 0.15-0.50 3.00-3.75 0.30 max - 8.50-10.00 0.30-0.60 -
H22 T20822 0.30-0.40 0.15-0.40 0.15-0.40 1.75-3.75 0.30 max - 10.00-11.75 0.25-0.50 -
H23 T20823 0.25-0.35 0.15-0.40 0.15-0.60 11.00-12.75 0.30 max - 11.00-12.75 0.75-1.25 -
H24 T20824 0.42-0.53 0.15-0.40 0.15-0.40 2.50-3.50 0.30 max - 14.00-16.00 0.40-0.60 -
H25 T20825 0.22-0.32 0.15-0.40 0.15-0.40 3.75-4.50 0.30 max - 14.00-16.00 0.40-0.60 -
H26 T20826 0.45-0.55b 0.15-0.40 0.15-0.40 3.75-4.50 0.30 max - 17.25-19.00 0.75-1.25 -

aExcept group W, all steels contain 0.03 max S, 0.03 max P and 0.25 max Cu; group W contain 0.025 max S, 0.025 max P, and 0.20 max Cu. As mentioned, amount of sulfur may be increased from 0.06% to 0.15% to enhance the machinability of group A, M, T, H and D steels..

Applications

Tungsten hot work steels find applications in the following areas:

  • Manufacturing mandrels and extrusion dies for high temperature applications, such as extrusion of brass, nickel alloys, and steel
  • Hot-forging dies of rugged design.

Comments

  1. Mahmoud Yehia Mahmoud Yehia Egypt says:

    High tungsten hot work tool steels are avoided as possible from hot forging application, especially the drop forging type, this is due to its low toughness

  2. Mahmoud Yehia Mahmoud Yehia Egypt says:

    Special Steel Materials are of a great importance for all branches in all industries.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoM.com.

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