Stainless Steel Grade 416 and its highest machinability

Stainless Steel Grade 416 and its highest machinability

Grade 416 has the highest machinability of any stainless steel, at about 85% of that of a free-machining carbon steel. As for most other free-machining steels the improvement in machinability is achieved by addition of sulphur which forms manganese sulphide inclusions; this sulphur addition also lowers the corrosion resistance, weldability and formability to below that of its non-free machining equivalent Grade 410.

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Grade 416 is sometimes used in the unhardened or hardened and highly tempered condition because of its low cost and ready machinability.

Martensitic stainless steels are optimised for high hardness, and other properties are to some degree compromised. Fabrication must be by methods that allow for poor weldability and usually also allow for a final harden and temper heat treatment. Corrosion resistance is lower than the common austenitic grades, and their useful operating temperature range is limited by their loss of ductility at sub-zero temperatures and loss of strength by over-tempering at elevated temperatures.

Corrosion Resistance of Stainless Steel Grade 416

Grade 416 has useful resistance to dry atmospheres, fresh water and mild alkalies and acids, but less resistant than the equivalent non-free-machining grades. Less corrosion resistant than the austenitic grades and also less than 17% chromium ferritic alloys such as Grade 430. High sulphur content free machining grades such as 416 are totally unsuitable for marine or other chloride exposure.

Maximum corrosion resistance is achieved in the hardened condition, with a smooth surface finish.

Consult Atlas Technical Assistance for specific environmental recommendations.

Heat Resistance  of Stainless Steel Grade 416

Fair resistance to scaling in intermittent service up to 760°C and up to 675°C in continuous service. Not recommended for use in temperatures above the relevant tempering temperature, if maintenance of mechanical properties is important.

Heat Treatment Full Annealing  of Stainless Steel Grade 416

Heat to 815-900°C for ½ hour per 25mm of thickness. Cool at 30°C per hour maximum to 600°C and air cool.

Sub-Critical Annealing  of Stainless Steel Grade 416

Heat to 650-760°C and air cool.

Hardening  of Stainless Steel Grade 416

Hardened by heating to 925-1010°C, quenching in oil, and tempering to suit the mechanical requirements. See accompanying table.

Note: The tempering range 400-580°C should be avoided, due to poor ductility.

Welding  of Stainless Steel Grade 416

Grade 416 has poor weldability. If welding is necessary ... use Grade 410 low hydrogen electrodes. Pre-heat to 200-300°C. Follow immediately with annealing or re-hardening, or a stress relief at 650-675°C.

A better option if the weld is not required to be hard is to use a Grade 309 austenitic stainless steel filler rod.

Machining  of Stainless Steel Grade 416

Grade 416 offers exceptionally good machinability, the highest of any of the commonly available stainless steels. Best machinability is in the sub-critical annealed condition.

Typical Applications  of Stainless Steel Grade 416

Valve parts, pump shafts, automatic screw machined parts, motor shafts and washing machine components. Bolts, nuts, studs and gears.

Specified Properties  of Stainless Steel Grade 416

These properties are specified for bar product in ASTM A582/A582M. Similar but not necessarily identical properties are specified for other products such as wire and forgings in their respective specifications.




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