Nov 13 2012
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
Machinability
Forming
Welding
Heat Treatment
Forging
Cold Working
Annealing
Tempering
Applications
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 |
Thermal Properties
The following table shows the thermal properties of H11 tool steels.
| Properties |
Metric
|
Imperial |
| Thermal expansion (@20-100ºC/68-212ºF) |
11.9 x 10-6/ºC |
6.63 µin/in°F |
| Thermal conductivity (@100ºC/212ºF) |
42.2 W/mK |
292.9 in/hr.ft².°F |
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.