H11

H11 Die Steel

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Product Description

H11 Hot Work Die Steel

Equivalent grades: SKD6/4Cr5MoVSi

Introduction

Chromium hot-work tool steels are designated as group H steels according to the AISI classification system. This series of steels start from H1 to H19. The most commonly used chromium hot-work steels are H11, H12, and H13, which can be air hardened in 150 mm thick sections. The steels are subjected to minimal distortion during hardening due to their balanced alloy content. The tools produced from chromium hot-work steels can be cooled using water without damage as these steels have low carbon and alloy contents.
This article will give an overview of H11 chromium hot-work steels, which have low carbon content and good toughness. These steels can be deep hardened by heat treatment and air-quenching.

Chemical Composition

The following table shows the chemical composition of H11 tool steels.

 Element  Content (%)
 Carbon, C  0.33-0.43
 Manganese, Mn  0.20-0.50
 Silicon, Si  0.80-1.20
 Chromium, Cr  4.75-5.50
 Nickel, Ni  0.3
 Molybdenum, Mo  1.10-1.60
 Vanadium, V  0.30-0.60
 Copper, Cu  0.25
 Phosphorous, P  0.03
 Sulfur, S  0.03
 Iron, Fe  Balance

Physical Properties

The physical properties of H11 tool steels are given in the following table.

 Properties  Metric  Imperial
 Density  7.81 g/cm3  0.282 lb/in3
 Melting point  1427°C 2600°F

Mechanical Properties

The mechanical properties of H11 tool steels are tabulated below.

 Properties  Metric  Imperial
 Hardness, Rockwell C (air cooled from 982°C, 45 mins)  52.5  52.5
 Hardness, Rockwell C (air cooled from 1010°C, 45 mins)  56  56
 Hardness, Rockwell C (air cooled from 1038°C, 45 mins)  57  57
 Modulus of elasticity  207 GPa  30000 ksi
 Modulus of elasticity (@538°C/1000°F)  159 GPa  23000 ksi
 Modulus of elasticity (@204°C/400°F)  190 GPa  27500 ksi
 Charpy impact (V-notch; air cooled from 1010°C;535°C temper temperature)  13.6 J  10.0 ft-lb
 Charpy impact (V-notch; air cooled from 1010°C;650°C temper temperature)  27.1 J  20.0 ft-lb
 Charpy impact (V-notch; air cooled from 1010°C;370°C temper temperature)  33.9 J  25.0 ft-lb
 Machinability (1% carbon steel)  75.0 – 80.0%  75.0 – 80.0%
 Poisson’s ratio  0.27-0.30 0.27-0.30

Other Designations

Other designations that are equivalent to H11 tool steels include:

 AFNOR Z 38 CDV 5  AMS 6485  SAE J438
 DIN 1.2343  AMS 6487  SAE J467
 UNI KU   AMS 6488  UNS T20811
 JIS SKD6  ASTM A681  AISI 610
 B.S. BH 11  FED QQ-T-570  ASTM A579
 AMS 6437  SAE J437 MIL S-47262

Fabrication and Heat Treatment

Machinability

The machinability rate of H11 tool steels is nearly 75% of that of the W group tool steels.

Forming

H11 tool steels are formed by using conventional methods, machining and forging.

Welding

H11 tool steels can be readily welded by conventional methods.

Heat Treatment

H11 tool steels are preheated to 816°C (1500°F). Then the steels are directly heated by increasing the temperature to 1010°C (1850°F) followed by holding for 15 to 40 mins. The steels are then air-quenched.

Forging

H11 tool steels are forged at 1121°C (2050°F). For this type of steels, forging below 899°C (1650°F) is not preferable.

Cold Working

Cold working may be carried out on H11 tool steels using conventional methods.

Annealing

H11 tool steels are annealed at 871°C (1600°F) and slowly cooled at 4°C (40°F) in the furnace.

Tempering

Tempering is carried out on H11 tool steels at temperature ranging from 538 to 649°C (1000 to 1200°F) to obtain Rockwell C hardness of 54 to 38. Double tempering can also be performed in these steels every one hour at the preferred tempering temperature.

Applications

H11 tool steels are suitable for designing highly stressed structural parts such as aircraft landing gear.