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17-4 Precipitation Hardening also known as Type 630 is a chromium-copper precipitation hardening stainless steel used for applications requiring high strength and a moderate level of corrosion resistance. High strength is maintained to approximately 600 degrees Fahrenheit (316 degrees Celsius).
General Properties
Alloy 17-4 PH is a precipitation hardening martensitic stainless steel with Cu and Nb/Cb additions. The grade combines high strength, hardness (up to 572°F / 300°C), and corrosion resistance.
Mechanical properties can be optimized with heat treatment. Very high yield strength up to 1100-1300 MPa (160-190 ksi) can be achieved.
The grade should not be used at temperatures above 572°F (300°C) or at very low temperatures. It has adequate resistance to atmospheric corrosion or in diluted acids or salts where its corrosion resistance is equivalent to Alloy 304 or 430.
| Applications | Standards |
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Corrosion Resistance
Alloy 17-4 PH withstands corrosive attacks better than any of the standard hardenable stainless steels and is comparable to Alloy 304 in most media.
If there are potential risks of stress corrosion cracking, the higher aging temperatures then must be selected over 1022°F (550°C), preferably 1094°F (590°C). 1022°F (550°C) is the optimum tempering temperature in chloride media.
1094°F (590°C) is the optimum tempering temperature in H2S media.
The alloy is subject to crevice or pitting attack if exposed to stagnant seawater for any length of time.
It is corrosion resistant in some chemical, petroleum, paper, dairy and food processing industries (equivalent to 304L grade).
If you would like to know more about 17-4PH stainless steel then click 17-4PH Technical Data.
The properties mentioned below pertain to commonly available grade 630 bar products in ASTM A564. The specifications may not be similar to other forms such as forgings and plates.
Composition Composition of 17-4PH stainless Steel
The compositional ranges of grade 630 stainless steels are displayed below:
| Grade | C | Mn | Si | P | S | Cr | Ni | Cu | Nb+Ta | |
| 630 |
min. max |
- 0.07 |
- 1 |
- 1 |
- 0.04 |
- 0.030 |
15 17.5 |
3 5 |
3 5 |
0.15 0.45 |
Table 2. Mechanical properties of grade 630 stainless steels
| dition | Tensile Strength (MPa) | Yield Strength 0.2% Proof (MPa) | Elongation (% in 50mm) | Hardness | |
| Rockwell C (HR C) | Brinell (HB) | ||||
| Solution Treated | 1105 typ | 1000 typ | 15 typ | 38 max | 363 max |
| Condition 900 | 1310 min | 1170 min | 10 min | 40 min | 388 min |
| Condition 1150 | 930 min | 724 min | 16 min | 28 min | 277 min |
The physical properties of grade 630 stainless steels are given in the following table:
Table 3. Typical physical properties of grade 630 stainless steels
| Mean Co-eff of Thermal Expansion (µm/m/°C) | Thermal Conductivity (W/m.K) |
Specific Heat 0-100°C (J/kg.K) |
Elec Resistivity (nΩ.m) |
||||||
| 0-100°C | 0-315°C | 0-538°C | At 100°C | At 500°C | |||||
| 630 | 7750 | 197 | 10.8 | 11.6 | - | 18.4 | 22.7 | 460 | 800 |
The typical grade specifications of 630 stainless steels are tabulated below:
able 4. Grade specifications for grade 630 stainless steels
| Grade |
UNS No |
Old British | Euronorm |
Swedish SS |
Japanese JIS |
||
| BS | En | No | Name | ||||
| 630 | S17400 | - | - | 1.4542 | X5CrNiCuNb16-4 | - |
SUS 630 |
Table 5. Possible alternative grades to 630 stainless steels
| Grade | Reasons for choosing 17/4PH (630) |
| 431 | 431 Has higher toughness than 17/4PH. Better availability in some sizes. |
| 416 | Free-machining martensitic stainless steel - better for repetition machining. Lower cost. |
| 316 | Higher corrosion resistance of 316 to resist more severe environments, but with much lower strength than 17/4PH. |
| 2205 | Much better corrosion resistance than 17/4PH, with a lower strength (but not as low as 316). |
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.
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:
Table 6. 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 |
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.
Grade 630 stainless steels can be machined in their solution-treated condition. They have machining rates similar to that of grade 304 steels.
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