H11 Hot Work Die Steel
Equivalent grades: SKD6/4Cr5MoVSi
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.
The following table shows the chemical composition of H11 tool steels.
The physical properties of H11 tool steels are given in the following table.
|Density||7.81 g/cm3||0.282 lb/in3|
The mechanical properties of H11 tool steels are tabulated below.
|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%|
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
The machinability rate of H11 tool steels is nearly 75% of that of the W group tool steels.
H11 tool steels are formed by using conventional methods, machining and forging.
H11 tool steels can be readily welded by conventional methods.
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.
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 may be carried out on H11 tool steels using conventional methods.
H11 tool steels are annealed at 871°C (1600°F) and slowly cooled at 4°C (40°F) in the furnace.
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.
H11 tool steels are suitable for designing highly stressed structural parts such as aircraft landing gear.