ASTM A693 630 Stainless Steel Sheet: Composition, Heat Treatment and Properties
Dec 05, 2025
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Overview: 630 Precipitation-Hardening Stainless Steel
630 (UNS S17400), commonly known as 17-4 PH, is a martensitic precipitation-hardening stainless steel that combines high strength and hardness with good corrosion resistance. The material is delivered in the solution-annealed condition and reaches its final properties through an aging heat treatment, which precipitates copper-rich particles in the martensitic matrix. This article covers the standards that govern 630 sheet: ASTM A693 for precipitation-hardening sheet, strip and plate, AMS 5643 for bar, forgings and other wrought forms, and ASTM A484 for the general requirements of stainless steel bars, billets and forgings. The European designation is 1.4542 (X5CrNiCuNb16-4) and the Japanese designation is SUS630.
Chemical Composition
The composition limits below follow ASTM A693.
| Element (wt %) | 630 (S17400) |
|---|---|
| Carbon, max | 0.07 |
| Manganese, max | 1.0 |
| Silicon, max | 1.0 |
| Phosphorus, max | 0.040 |
| Sulfur, max | 0.030 |
| Chromium | 15.0-17.5 |
| Nickel | 3.0-5.0 |
| Copper | 3.0-5.0 |
| Niobium plus Tantalum | 0.15-0.45 |
Copper is the precipitation-hardening element; niobium and tantalum refine the grain structure and contribute to strength, while the chromium level provides corrosion resistance comparable to the 400-series martensitic grades.
Heat Treatment Conditions
630 is solution annealed at about 1038°C and rapidly cooled, then aged at an elevated temperature to develop strength. The aging temperature controls the balance of strength and toughness; lower aging temperatures give higher strength.
| Condition | Aging treatment |
|---|---|
| Condition A | Solution annealed, no aging |
| H900 | 482°C, 1 hour, air cool |
| H925 | 496°C, 4 hours, air cool |
| H1025 | 552°C, 4 hours, air cool |
| H1075 | 579°C, 4 hours, air cool |
| H1100 | 593°C, 4 hours, air cool |
| H1150 | 621°C, 4 hours, air cool |
Mechanical Properties by Condition
Minimum values for sheet, strip and plate per ASTM A693.
| Property | H900 | H1025 | H1150 |
|---|---|---|---|
| Tensile strength, min (MPa) | 1310 | 1070 | 930 |
| 0.2% yield strength, min (MPa) | 1170 | 1000 | 725 |
| Elongation in 50 mm, min (%) | 10 | 12 | 16 |
Hardness follows the same pattern, reaching about 44 HRC in H900 and decreasing to about 31-33 HRC in H1150. Condition A is the softest state and is intended for forming and machining before aging; after fabrication the part is aged to the required condition, with a maximum size change of roughly 0.1% that should be considered in final dimensions.
Corrosion Resistance and Applications
630 offers corrosion resistance similar to Type 430 in most environments and superior resistance to the hardenable 400-series martensitic grades. It is used where high strength, hardness and moderate corrosion resistance are required in one component: pump shafts and impellers, valve stems, fasteners, gears, shafts in food and chemical processing, paper mill equipment, aerospace structural components, and fasteners for offshore and marine hardware. For severe seawater service, the alloy can be used in lower hardness conditions, but more corrosion-resistant precipitation-hardening grades should be considered for long-term chloride exposure.
Frequently Asked Questions
What does H900 mean? H900 is an aging condition: the material is aged at 482°C for one hour and air cooled, giving the highest strength level of the standard conditions.
Is 630 stainless steel magnetic? Yes. It has a martensitic structure in the aged conditions and is magnetic.
What is the difference between ASTM A693 and AMS 5643? ASTM A693 covers precipitation-hardening sheet, strip and plate, while AMS 5643 covers bar, wire, forgings and other wrought forms of the same alloy.
Can 630 be welded? Yes, it can be welded by conventional processes; the part is aged after welding to restore full mechanical properties in the weld and heat-affected zone.
What is the EN equivalent of 630? EN 1.4542 (X5CrNiCuNb16-4); the JIS designation is SUS630.
What hardness can 630 reach? In the H900 condition, hardness is typically about 44 HRC; higher aging temperatures reduce strength and hardness while improving toughness.
Frequently Asked Questions
Q1. What is the chemical composition of 630 (UNS S17400)?
Carbon 0.07 max, chromium 15.0-17.5, nickel 3.0-5.0, copper 3.0-5.0 and niobium plus tantalum 0.15-0.45 per ASTM A693.
Q2. How does the aging temperature affect 630?
Lower aging temperatures give higher strength; H900 at 482 C for one hour gives the highest strength, while H1150 at 621 C gives lower strength but better toughness.
Q3. What is Condition A?
The solution-annealed condition (about 1038 C) with no aging, which is the softest state intended for forming and machining before the final aging treatment.
Q4. Where is 630 used?
Pump shafts and impellers, valve stems, fasteners, gears, food and chemical processing equipment, paper mill equipment and aerospace structural components.
Q5. What dimensional change occurs during aging?
A maximum size change of roughly 0.1 percent, which should be considered in final dimensions.
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