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Introduction
Grade 630(17-4ph) stainless steels are martensitic stainless steels that are precipitation hardened to achieve excellent mechanical properties. These steel achieve high strength and hardness following heat treatment. The heat and corrosion resistance of grade 630 are similar to that of grade 304 steels. This grades is also commonly referred to as grade 17-4PH.
One of the key benefits of this grade is that it is available in solution treated conditions, at which they can be easily machined and age-hardened to attain high strength. The age treatment of grade 630 is carried out at low temperatures, to avoid significant distortion. Therefore, this grade is used for applications such as the manufacture of long shafts that do not require re-straightening after heat treatment.
17-4pH Steel Tube Composition
The table below provides the compositional ranges of grade 17-4pH stainless steels:
Composition ranges of grade 17-4ph stainless steels
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17-4pH Steel Tube Grade Specification
| Grade | UNS | DIN | EN | AMS | ASTM | JIS | |
| 630 | S17400 | - | 1.4542 17-4 PH | SUS 630 | |||
Possible Alternative Grades
The following table lists the possible alternative grades to 630 stainless steels:
Possible alternative grades to 630 stainless steels
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17-4pH Steel Tube Characteristic
Corrosion Resistance
Grade 630 stainless steels have good corrosion resistance in many environments. They exhibit improved resistance against stress corrosion cracking, if aged at 550°C or more. However, grade 630 steels are less resistant to solution treated Condition A, and hence these steels, even with considerable hardness, should not be used in this condition.
Heat Resistance
Grade 630 stainless steels have good resistance to oxidation. However, long-time exposure of grade 630 to temperatures of 370 to 480°C should be avoided, to prevent loss of toughness at ambient temperature. These grades should not be used at temperatures above age-hardening temperature, to avoid reduction of hardness and mechanical properties of the metal.
17-4pH Steel Tube Processing method
Heat Treatment
Solution treatment (Condition A) - 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:
Typical mechanical properties of grade 630 steels achieved after solution treating
Cond. | Hardening | Typical Hardness Rockwell C | Tensile Strength (MPa) | |
Temp (°C) | Time (h) | |||
A | Ann | - | 36 | 1100 |
H900 | 482 | 1 | 44 | - |
H925 | 496 | 4 | 42 | 1170-1320 |
H1025 | 552 | 4 | 38 | 1070-1220 |
H1075 | 580 | 4 | 36 | 1000-1150 |
H1100 | 593 | 4 | 35 | 970-1120 |
H1150 | 621 | 4 | 33 | 930-1080 |
Welding
Grade 630 stainless steels can be welded using all conventional methods, and they do not require pre-heating. Care should be taken in designing and welding of high strength steels to prevent weldment stresses.
Machining
Grade 630 stainless steels can be machined in their solution-treated condition. They have machining rates similar to that of grade 304 steels.
17-4pH Steel Tube Applications
- Valves and gears
- Oil field equipment
- Propeller shafts
- Pump shafts
- Valve spindles
- Aircraft and gas turbines
- Nuclear reactors
- Paper mills
- Chemical processing equipment
