abc® Aalco is a registered trademark of Aalco Metals Ltd
© Copyright: Aalco Metals Ltd, The Hersham Centre, Hersham Green, Hersham, Surrey KT12 4HP
All Data is indicative only and must not be seen as a substitute for the full specification from which it is drawn.
In particular, the mechanical property requirements vary widely with heat treatment, product form and product
dimensions. For more complete details please refer to the relevant specification –Specifications for Stainless Steel are
listed on a separate Datasheet.
Precipitation Hardening Stainless Steels
Precipitation hardening stainless steels
are chromium and nickel containing
steels that provide an optimum
combination of the properties of
martensitic and austenitic grades. Like
martensitic grades, they are known for
their ability to gain high strength
through heat treatment and they also
have the corrosion resistance of
austenitic stainless steel.
The high tensile strengths of
precipitation hardening stainless steels
come after a heat treatment process
that leads to precipitation hardening of
a martensitic or austenitic matrix.
Hardening is achieved through the
addition of one or more of the
elements Copper, Aluminium, Titanium,
Niobium, and Molybdenum.
The most well known precipitation
hardening steel is 17-4 PH. The name
comes from the additions 17%
Chromium and 4% Nickel. It also
contains 4% Copper and 0.3%
Niobium. 17-4 PH is also known as
stainless steel grade 630.
The advantage of precipitation
hardening steels is that they can be
supplied in a “solution treated”
condition, which is readily machinable.
After machining or another fabrication
method, a single, low temperature heat
treatment can be applied to increase
the strength of the steel. This is
known as ageing or age-hardening. As
it is carried out at low temperature, the
component undergoes no distortion.
Characterisation
Precipitation hardening steels are
characterised into one of three groups
based on their final microstructures after
heat treatment. The three types are:
martensitic (e.g. 17-4 PH), semi-austenitic
(e.g. 17-7 PH) and austenitic (e.g. A-286).
Martensitic Alloys
Martensitic precipitation hardening stainless
steels have a predominantly austenitic
structure at annealing temperatures of
around 1040 to 1065°C. Upon cooling to
room temperature, they undergo a
transformation that changes the austenite
to martensite.
Semi-austenitic Alloys
Unlike martensitic precipitation hardening
steels, annealed semi-austenitic
precipitation hardening steels are soft
enough to be cold worked. Semi-austenitc
steels retain their austenitic structure at
room temperature but will form martensite
at very low temperatures.
Austenitic Alloys
Austenitic precipitation hardening steels
retain their austenitic structure after
annealing and hardening by ageing. At the
annealing temperature of 1095 to 1120°C
the precipitation hardening phase is soluble.
It remains in solution during rapid cooling.
When reheated to 650 to 760°C,
precipitation occurs. This increases the
hardness and strength of the material.
Hardness remains lower than that for
martensitic or semi-austenitic precipitation
hardening steels. Austenitic alloys remain
nonmagnetic.
Strength
Yield strengths for precipitation-hardening
stainless steels are 515 to 1415 MPa.
Tensile strengths range from 860 to 1520
MPa. Elongations are 1 to 25%. Cold
working before ageing can be used to
facilitate even higher strengths.
X
abc® Aalco is a registered trademark of Aalco Metals Ltd
© Copyright: Aalco Metals Ltd, The Hersham Centre, Hersham Green, Hersham, Surrey KT12 4HP
All Data is indicative only and must not be seen as a substitute for the full specification from which it is drawn.
In particular, the mechanical property requirements vary widely with heat treatment, product form and product
dimensions. For more complete details please refer to the relevant specification –Specifications for Stainless Steel are
listed on a separate Datasheet.
Applications
Due to the high strength of precipitation
hardening stainless steels, most
applications are in aerospace and other
high-technology industries.
Applications include:
Gears
Valves and other engine components
High strength shafts
Turbine blades
Moulding dies
Nuclear waste casks
Heat Treatment
The key to the properties of precipitation
hardening stainless steels lies in heat
treatment.
After solution treatment or annealing of
precipitation hardening stainless steels, a
single low temperature “age hardening”
stage is employed to achieve the required
properties. As this treatment is carried out
at a low temperature, no distortion occurs
and there is only superficial discolouration.
During the hardening process a slight
decrease in size takes place. This shrinking
is approximately 0.05% for condition H900
and 0.10% for H1150.
Typical mechanical properties achieved for
17-4 PH after solution treating and age
hardening are given in the following table.
Condition designations are given by the age
hardening temperature in °F.
Cond.
Hardening
Temp and
time
Hardness
(Rockwell
C)
Tensile
Strength
(MPa)
A Annealed 36 1100
H900
482°C, 1
hour 44 1310
H925
496°C, 4
hours 42
1170-
1320
H1025
552°C, 4
hours 38
1070-
1220
H1075
580°C, 4
hours 36
1000-
1150
H1100
593°C, 4
hours 35 970-1120
H1150
621°C, 4
hours 33 930-1080
Typical Chemical Composition
17-4 PH
C 0.07%
Mn 1.00%
Si 1.00%
P 0.04%
S 0.03%
Cr 17.0%
Ni 4.0%
Cu 4.0%
Nb+Ta 0.30%
Typical Mechanical Properties
Grade 17-4PH Annealed
Cond
900
Cond
1150
Tensile
Strength (MPa)
1100 1310 930
Elongation A5
(%)
15 10 16
Proof Stress
0.2% (MPa)
1000 1170 724
Elongation A5
(%)
15 10 16
Typical Physical Properties
Property Value
Density 7.75 g/cm3
Melting Point °C
Modulus of Elasticity 196 GPa
Electrical Resistivity 0.080x10-6 Ω.m
Thermal
Conductivity
18.4 W/m.K at
100°C
Thermal Expansion 10.8x10
-6 /K at
100°C
Alloy Designations
Stainless steel 17-4 PH also corresponds to
the following standard designations and
specifications:
Euronorm UNS BS En Grade
1.4542 S17400 - - 630
X
abc® Aalco is a registered trademark of Aalco Metals Ltd
© Copyright: Aalco Metals Ltd, The Hersham Centre, Hersham Green, Hersham, Surrey KT12 4HP
All Data is indicative only and must not be seen as a substitute for the full specification from which it is drawn.
In particular, the mechanical property requirements vary widely with heat treatment, product form and product
dimensions. For more complete details please refer to the relevant specification –Specifications for Stainless Steel are
listed on a separate Datasheet.
Corrosion Resistance
Precipitation hardening stainless steels
have moderate to good corrosion resistance
in a range of environments. They have a
better combination of strength and
corrosion resistance than when compared
with the heat treatable 400 series
martensitic alloys. Corrosion resistance is
similar to that found in grade 304 stainless
steel.
In warm chloride environments, 17-4 PH is
susceptible to pitting and crevice corrosion.
When aged at 550°C or higher, 17-4 PH is
highly resistant to stress corrosion cracking.
Better stress corrosion cracking resistance
comes with higher ageing temperatures.
Corrosion resistance is low in the solution
treated (annealed) condition and it should
not be used before heat treatment.
Heat Resistance
17-4 PH has good oxidation resistance. In
order to avoid reduction in mechanical
properties, it should not be used over its
precipitation hardening temperature.
Prolonged exposure to 370-480°C should
be avoided if ambient temperature
toughness is critical.
Fabrication
Fabrication of all stainless steels should be
done only with tools dedicated to stainless
steel materials or tooling and work surfaces
must be thoroughly cleaned before use.
These precautions are necessary to avoid
cross contamination of stainless steel by
easily corroded metals that may discolour
the surface of the fabricated product.
Cold Working
Cold forming such as rolling, bending and
hydroforming can be performed on 17-4PH
but only in the fully annealed condition.
After cold working, stress corrosion
resistance is improved by re-ageing at the
precipitation hardening temperature.
Hot Working
Hot working of 17-4 PH should be
performed at 950°-1200°C. After hot
working, full heat treatment is required.
This involves annealing and cooling to room
temperature or lower. Then the component
needs to be precipitation hardened to
achieve the required mechanical properties.
Machinability
In the annealed condition, 17-4 PH has
good machinability, similar to that of 304
stainless steel. After hardening heat
treatment, machining is difficult but
possible.
Carbide or high speed steel tools are
normally used with standard lubrication.
When strict tolerance limits are required,
the dimensional changes due to heat
treatment must be taken into account
Welding
Precipitation hardening steels can be readily
welded using procedures similar to those
used for the 300 series of stainless steels.
Grade 17-4 PH can be successfully welded
without preheating. Heat treating after
welding can be used to give the weld metal
the same properties as for the parent
metal. The recommended grade of filler
rods for welding 17-4 PH is 17-7 PH.
Supplied Forms
17-4 PH is typically supplied by Aalco in the
following forms:
Round bar
Hexagonal bar
Billet
This information is based on our present
knowledge and is given in good faith. However,
no liability will be accepted by the Company is
respect of any action taken by any third party in
reliance thereon
As the products detailed may be used for a wide
variety of purposes and as the Company has no
control over their use; the Company specifically
excludes all conditions or warranties expressed
or implied by statute or otherwise as to
dimensions, properties and/or fitness for any
particular purpose. Any advice given by the
Company to any third party is given for that
party’s assistance only and without liability on
the part of the Company.
Any contract between the Company and a
customer will be subject to the Company’s
Conditions of Sale. The extent of the Company’s
liabilities to any customer is clearly set out in
those Conditions; a copy of which is available on
request.