Chemical Formula
Fe, <0.07% C, 15-17.5% Cr, 3.0-5.0% Ni, <1.0% Mn, <1% Si, <0.040% P, <0.03% S, 3.0-5.0% Cu, 0.15-0.45% Nb+Ta
Introduction
Grade 630 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.
Key Properties
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.
Production Introduction
Composition
The compositional ranges of grade 630 stainless steels are displayed below:
Table 1. Composition ranges for grade 630 stainless steels
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 |
Mechanical Properties
The table below outlines the mechanical properties of grade 630 stainless steels:
Table 2. Mechanical properties of grade 630 stainless steels
Condition | 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 |
*These values are specified for ASTM A564 and they apply only to certain size ranges. The specification should be consulted for the complete details of these properties. Condition 900 is aged at 900°F (482°C), Condition 1150 is aged at 1150°F (621°C). Solution treatment is at 927°C and cooled as required.
Physical Properties
The physical properties of grade 630 stainless steels are given in the following table:
Table 3. Typical physical properties of grade 630 stainless steels
Grade | Density (kg/m3) | Elastic Modulus (GPa) | 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 |
Grade Specification Comparison
The typical grade specifications of 630 stainless steels are tabulated below:
Table 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 |
Possible Alternative Grades
The following table lists the possible alternative grades to 630 stainless steels:
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). |
Production Introduction
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