630 stainless steel pipe has been used for a variety of applications including oil field valve parts, chemical process equipment, aircraft fittings, fasteners, pump shafts, nuclear reactor components, gears, paper mill equipment, missile fittings, and jet engine parts. 630 shows excellent resistance to oxidation up to approximately 1100oF (539oC).
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.
630 has withstood corrosive attack better than any of the 400 series hardenable stainless steels, and, in most corrodents, its corrosion resistance closely approaches that of stainless type 304.
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.
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.
The compositional ranges of grade 630 stainless steels are displayed below:
Table 1. Composition ranges for grade 630 stainless steels
The table below outlines the mechanical properties of grade 630 stainless steels:
Table 2. Mechanical properties of grade 630 stainless steels
||Tensile Strength (MPa)
||Yield Strength 0.2% Proof (MPa)
||Elongation (% in 50mm)
|Rockwell C (HR C)
*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.
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)
|Specific Heat 0-100°C
Grade Specification Comparison
The typical grade specifications of 630 stainless steels are tabulated below:
Table 4. Grade specifications for grade 630 stainless steels
Possible Alternative Grades
The following table lists the possible alternative grades to 630 stainless steels:
Table 5. Possible alternative grades to 630 stainless steels
||Reasons for choosing 17/4PH (630)
||431 Has higher toughness than 17/4PH. Better availability in some sizes.
||Free-machining martensitic stainless steel - better for repetition machining. Lower cost.
||Higher corrosion resistance of 316 to resist more severe environments, but with much lower strength than 17/4PH.
||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.
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.
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
||Typical Hardness Rockwell C
||Tensile Strength (MPa)
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.
Photo of Products
Some of the major applications of grade 630 stainless steels include:
- Engine components
- High strength and boat propeller shafts
- Plastic moulding dies
- Valves and gears