416 stainless steel is a martensitic stainless steel grade with most of the free-machining properties, It has the highest machinability of any stainless steel at about 85% of that of free-machining carbon steel. Martensitic stainless steels were designed to be hardenable by heat treatment and also corrosion resistant. Although stainless steel 416 and other martensitic stainless steels are not as resistant as austenitic or ferritic stainless, they still demonstrate good corrosion and oxidation resistance and high strength in hardened and tempered conditions.
Stainless Steel 416 is magnetic, highly machinable and is known for being wear-resistant. Other characteristics include non-seizing and non-galling properties, resistance to mildly corrosive environments, and reasonable strength in the tempered and hardened state. Stainless Steel 416 is not approved for use in high-sulfur environments. To be the first “free machining” stainless, Stainless Steel 416 can be easily turned, tapped, broached, drilled, reamed, threaded and milled per various machine manufacturer’s recommendations for various suitable tool speeds, feeds and types.
The machinability can be improved by adding sulphur, which leads to the formation of manganese sulphide inclusions. The addition of sulphur also reduces the formability, weldability and corrosion resistance of 416 steels to below that of grade 410. Because of their high machinability and low cost, grade 416 steels are available in highly tempered, hardened or unhardened forms.
416 Stainless Steel Composition
| Grade | C, max | Mn, max | Si, max | P, max | S, min | Cr | Mo, max |
|---|---|---|---|---|---|---|---|
| 416 | 0.15 | 1.25 | 1.00 | 0.06 | 0.15 | 12-14 | 0.6 |
416 Stainless Steel Mechanical Properties
| Tempering Temperature (°C) | Tensile Strength (MPa) | Yield Strength 0.2% Proof (MPa) | Elongation (% in 50mm) | Hardness Brinell (HB) |
|---|---|---|---|---|
| Annealed * | 517 | 275 | 30 | 262 |
| Condition T ** | 758 | 586 | 18 | 248-302 |
| 204 | 1340 | 1050 | 11 | 388 |
| 316 | 1350 | 1060 | 12 | 388 |
| 427 | 1405 | 1110 | 11 | 401 |
| 538 | 1000 | 795 | 13 | 321 |
| 593 | 840 | 705 | 19 | 248 |
| 650 | 796 | 670 | 17.5 | 253 |
* Annealed properties are typical for Condition A of ASTM A582.
** Hardened and tempered Condition T of ASTM A582 – Brinell hardness is specified range, other properties are typical only.
# Tempering of this steel at temperatures of 400 to 580°C should be avoided due to low impact resistance.
416 Stainless Steel Physical Properties
| Grade | Density (kg/m3) | Elastic Modulus (GPa) | Mean Coefficient of Thermal Expansion (μm/m/°C) | Thermal Conductivity (W/m.K) | Specific Heat 0-100°C (J/kg.K) | Electrical Resistivity (nΩ.m) | |||
|---|---|---|---|---|---|---|---|---|---|
| 0-100°C | 0-315°C | 0-538°C | at 100°C | at 500°C | |||||
| 416 | 7800 | 200 | 9.9 | 11 | 11.5 | 24.9 | 28.7 | 460 | 570 |
Equivalent Grades
| Grade | UNS No | Old British | Euronorm | Swedish SS | Japanese JIS | ||
|---|---|---|---|---|---|---|---|
| BS | En | No. | Name | ||||
| 416 | S41600 | 416S21 | 56AM | 1.4005 | X12CrS13 | 2380 | SUS 416 |
Corrosion Resistance
Grade 416 steels are highly resistant to acids, alkalis, fresh water and dry air. However, they are less corrosion resistant than non-free-machining steels, austenitic grades and grade 430 Ferritic alloys with 17% chromium. These steels are hardened to obtain maximum corrosion resistance and smooth surface. 416 free-machining grades with high sulphur content are inappropriate for chloride and marine environments.
Heat Resistance
Scaling resistance of grade 416 steels under intermittent conditions can be extended up to 760°C, and up to 675°C under continuous operations. Considering the sustainability of mechanical properties, 416 steels should not be employed at temperatures greater than the standard tempering temperatures.
Heat Treatment
Full Annealing – Grade 416 steel can be annealed at temperatures of 815 to 900°C for ½ h. This process is followed by cooling at 30°C for an hour and air-cooling.
Sub-Critical Annealing – Grade 416 steel is heated to 650 to 760°C and air-cooled.
Hardening – This process involves heating grade 416 steels to 925 to 1010°C, oil quenching and tempering to improve mechanical properties. Tempering should not be carried out at temperatures ranging from 400 to 580°C, owing to poor ductility of grade 416.
Welding
Grade 416 steel exhibits poor weldability. Welding can be carried by pre-heating 416 steels to 200 to 300°C, followed by re-hardening, annealing or stress relieving at 650 to 675°C.
Grade 410 low hydrogen electrodes can be used for welding purposes. Grade 309 filler rods can also be used for materials that require moderate hardening.
Machining
Grade 416 steels offer the highest machinability of any stainless steel in their sub-critical annealed condition.
Forms
Bar specifications: diameters from 10mm to 300mm, lengths from 2m to 6m.
Wire specifications: can be supplied as straight bars or coiled rounds with diameters from 5.5mm to 25mm.
Plate/strip specifications: including foil, thin, medium, thick and extra thick plates, with thicknesses ranging from under 0.2mm to over 60mm.
Surface Finish: The surface of 416 stainless steel can be finished in a variety of ways, including bright, 2B, BA (6k) mirror, 8K mirror, brushed, and frosted.
Applications
- Medical instruments: AISI416 stainless steel is a medical-grade stainless steel material, due to its good corrosion resistance and high strength, it is often used in the manufacture of medical equipment, such as scalpels, surgical scissors and so on.
- Chemical equipment: AISI416 stainless steel is also widely used in the chemical industry. Due to its corrosion and heat resistance, it is used in the manufacture of chemical equipment such as reactors and storage tanks.
- Food processing equipment: AISI416 stainless steel meets the food safety standards, so it is often used in the manufacture of food processing equipment, such as knives, cutlery and so on.
- Building structure: AISI416 stainless steel has high strength and good corrosion resistance, so it is also used in building structures, such as bridges, building support structures and so on.