Precipitation Hardened Stainless Steels

Precipitation Hardened Stainless Steels

Overview

Austenitic or martensitic steels modified by additions which allow the precipitation of intermetallic compounds at aging temperatures. After age-hardening, this can result in very high-strength steels.

Strengths

Very high strength compared to other stainless steels. Good corrosion resistance, ductility, and toughness.

Limitations

Complicated heat treatments are necessary to achieve the required properties. Some of the most expensive stainless steels.

Typical uses

Gears, fasteners, cutlery, aircraft and steam turbine parts, processing of potentially corrosive liquids, structural uses in corrosive environments.

Compositional summary

Fe/11-18Cr/3-11Ni with varying additions of Cu, Mn, Mo, Al, Si, C, N, P, S, Ti, Nb, Ta
Material familyMetal (ferrous)
Base materialFe (Iron)

Microstructure

Austenite (fcc) and martensite (body-centered tetragonal).

Effect of composition

Ti, Nb, and Al are added to assist age-hardening. Small quantities of Mo improve mechanical properties and corrosion resistance.

Processing properties

Available forms

Sheet, strip, bar, plate, foil, most wrought forms.

Forming

Cold-working prior to aging can result in even higher strengths.

Machining

Can be machined but only in the soft condition- this works well as subsequent aging induces little or no distortion.

Heat treatment

Heat treatments are complicated; they must be solution-treated and then undergo one or more aging treatments. Aging for too long, known as overaging, can reduce strengthening as the precipitates coarsen to such an extent that dislocations can bow around them. However, it is sometimes used for increased cold formability.

Joining

Reasonable weldability but a post-welding heat treatment is required to restore or improve mechanical properties.

Precipitation Hardened Stainless Steel Grades

CAST

15-5PH (martensitic)

15-5PH, cast, H935

17-4PH (martensitic)

17-4PH, cast, H1000
17-4PH, cast, H1100
17-4PH, cast, H900

ASTM CB-7Cu (martensitic)

ASTM CB-7Cu, cast, aged at 480°C
ASTM CB-7Cu, cast, aged at 495°C
ASTM CB-7Cu, cast, aged at 550°C
ASTM CB-7Cu, cast, aged at 580°C
ASTM CB-7Cu, cast, aged at 595°C
ASTM CB-7Cu, cast, aged at 620°C

WROUGHT

15-5PH (martensitic)

15-5PH, H1025
15-5PH, H1075
15-5PH, H1100
15-5PH, H1150
15-5PH, H1150M
15-5PH, H900
15-5PH, H925

17-4PH (martensitic)

17-4PH, H1025
17-4PH, H1075
17-4PH, H1100
17-4PH, H1150
17-4PH, H1150M
17-4PH, H900
17-4PH, H925

17-7PH (semi-austenitic)

17-7PH, TH1050

AM-350 (semi-austenitic)

AM-350, SCT 850

AM-355 (semi-austenitic)

AM-355, SCT 1000
AM-355, SCT 850

Custom 450 (martensitic)

Custom 450, H1000
Custom 450, H1050
Custom 450, H1100
Custom 450, H1150
Custom 450, H900
Custom 450, H950
Custom 450, ST

Custom 455 (martensitic)

Custom 455, H1000
Custom 455, H950

Custom 465 (martensitic)

Custom 465, H1000
Custom 465, H950

FV520 (martensitic)

FV520, hardened at 450°C (BS S145)
FV520, primary and secondary hardened at 450°C (BS S144)
FV520, primary and secondary hardened at 540°C (BS S143)

PH 13-8Mo (martensitic)

PH 13-8Mo, H1000
PH 13-8Mo, H1025
PH 13-8Mo, H1050
PH 13-8Mo, H1100
PH 13-8Mo, H1150
PH 13-8Mo, H950

PH15-7Mo (semi-austenitic)

PH15-7Mo, TH1050