Stainless Steel Grade 630 Composition Specification (%)

Stainless Steel Grade 630 Composition Specification (%)

Grade 630 martensitic precipitation hardening stainless steel has a combination of high hardness and strength after suitable heat treatment. It also has similar corrosion and heat resistance to Grade 304. The terms "Type 630" and "17-4PH" refer to the same grade.

Stainless steel Gears, image credit:

The great benefit of this grade (and of other precipitation hardening grades of stainless steel) is that they are generally supplied in the solution treated condition, in which they are just machinable, and then can be age hardened to achieve quite high strengths. This aging treatment is so low in temperature that there is no significant distortion. These grades are therefore well suited to production of long shafts, which require no re-straightening after heat treatment.

Corrosion Resistance of Stainless Steel Grade 630

Good resistance to a wide range of corrosive environments; approaching that of Grade 304 stainless steel. Like 304, this grade is subject to pitting and crevice corrosion in warm chloride environments. Grade 630 has been used for boat shafting for fresh water, and in sea water with the addition of cathodic protection.

Highly resistant to stress corrosion cracking if aged at 550°C or higher. Higher aging temperatures give better SCC resistance. Grade 630 is resistant to sulphide stress cracking (SSC) if highly aged; NACE MR0175 permits the use of 630 but only in a double age hardened condition (refer to MR0175 and ASTM A564M).

In solution treated Condition A the grade has lower resistance to stress corrosion cracking, and lower ductility compared to aged conditions. It should not generally be used in the solution treated condition, even if the hardness is considered satisfactory.

Consult Atlas Technical Assistance for specific environmental recommendations.

Heat Resistance of Stainless Steel Grade 630

This grade has good oxidation resistance, but to avoid reduction of its mechanical properties and hardness it should not be used above its age hardening temperature. Prolonger exposure in the range 370-480°C should be avoided if ambient temperature toughness is critical.

Heat Treatment of Stainless Steel Grade 630

Solution treatment (Condition A)

Heat at 1040°C for ½ hour and cool to 30°C maximum in air. Oil quenching may be used for small non-intricate sections.

Hardening (Aging) of Stainless Steel Grade 630

After solution treatment a single low temperature "age hardening" treatment is employed to achieve required properties, as below. This treatment results in no distortion and only superficial discolouration. A slight decrease in size (shrinkage) takes place during the hardening; this is approximately 0.05% for Condition H900 and 0.10% for H1150.

Typical mechanical properties achieved after solution treating and then age hardening at the indicated temperatures are as in the table in the following page. The Condition is designated by the age hardening temperature in °F (Condition A is solution treated, ie not aged).

Welding of Stainless Steel Grade 630

Grade 630 can be successfully welded by all standard methods. Preheating is not necessary. Properties comparable to those of the parent metal may be achieved in the weld metal by post-weld heat treatment. As for other high strength steels precaution should be taken in design and welding procedures to avoid concentration of weldment stresses.

Machining of Stainless Steel Grade 630

This steel is usually supplied in the solution treated condition, in which it can be machined. Machinability is similar to Grade 304.

Typical Applications of Stainless Steel Grade 630

Gears, bolts and valve components. Plastic moulding dies. High strength pump shafts and boat propeller shafts. Engine components. In general applications where some level of corrosion resistance is needed in conjunction with high strength or hardness.

Specified Properties of Stainless Steel Grade 630

These properties are specified for bar products in ASTM A564/A564M; round bar is the most commonly available product form for this grade. Similar but not necessarily identical properties are specified for other products such as plate and forgings in their respective specifications.

Composition Specification (%) of Stainless Steel Grade 630