Overview

Alloy 17-4PH (UNS S17400), Type630, is a chromium-nickel-copper precipitation-hardening martensitic stainless steel with an addition of niobium. 17-4PH combines high strength and hardness with good corrosion resistance.

The alloy is furnished in the solution annealed condition(Condition A). It should not be used at temperatures above 572°F (300°C)or for cryogenic service. Optimal mechanical properties can be obtained by subjecting the alloy to age hardening heat treatments. Heat treatment in the 900°F (482°C) range produces the highest strength.

The corrosion resistance of Alloy17-4PH is comparable to 304stainless steel in most environments,and is generally superior to the 400series stainless steels. It is used in applications where the combination of moderate corrosion resistance and unusually high strength are required.Alloy 17-4PH can be easily welded and processed by standard shop fabrication practices. It is magnetic.

Limiting Chemical Composition, %

Iron..............................................................................................................................................................................................69.91-78.85

Nickel...............................................................................................................................................................................................3.00-5.00

Chromium...................................................................................................................................................................................15.00-17.50

Copper.............................................................................................................................................................................................3.00-5.00

Manganese.....................................................................................................................................................................................1.00 max.

Carbon.............................................................................................................................................................................................0.07 max.

Silicon..............................................................................................................................................................................................1.00 max.

Sulphur.............................................................................................................................................................................................0.03 max.

Phosphorus......................................................................................................................................................................................0.04 max.

Niobium plus Tantalum...................................................................................................................................................................0.15-0.45

Physical properties

Mechanical Properties

Corrosion resistance

The corrosion resistance of Alloy 17-4PH is comparable to 304 stainless steel in most environments, and is generally superior to the 400 series stainless steels. It is used in applications where the combination of moderate corrosion resistance and unusually high strength are required. Alloy 17-4PHhas corrosion resistance comparable to 304L in some chemical, dairy, food,paper and petroleum applications.Alloy 17-4PH in the solution-annealed condition should not generally be put in service. The alloy is subject to brittle fractures and more sensitive to chloride stress corrosion cracking than the aged material.If risks of chloride stress corrosion cracking are present the higher aging temperatures should be selected over 1022°F (550°C), preferably 1094°F(590°C). 1022°F (550°C) is the recommended tempering temperature in chloride service. 1094°F (590°C) is preferred in H2S media.Alloy 17-4PH is subject to crevice corrosion and pitting attack when exposed to stagnant seawater for a duration of time.

Heat treatment

Solution treatment — Grade 630 stainless steels are heated at 1040°C for 0.5 h, then air-cooled to 30°C. Small sections of these grades can be oil quenched.

Hardening — Grade 630 stainless steels are age-hardened at low temperatures to achieve the required mechanical properties. During the process, superficial discoloration occurs followed by shrinkage at 0.10% for condition H1150, and 0.05% for condition H900.

The table below shows the typical mechanical properties of grade 630 steels after solution treatment and age hardening:

Available Forms

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