416 Stainless Steel Heat Treatment

416 in the martensitic stainless family

416 is the free machining grade of the 12 to 14 percent chromium martensitic family. It carries the same 0.15 percent carbon as type 410, which puts the hardness ceiling at the same low figure, and the two grades sit at the bottom of the family together. The difference between them is machinability. Sulfur is taken up to 0.15 percent as a deliberate addition, manganese is raised to 1.25 percent to carry that sulfur, and molybdenum is added at 0.60 percent, which the 410 card does not list with a figure at all. Those three figures are the reason 416 turns and drills like a free cutting grade while 410 does not, and they are also the reason the grade is taken for parts such as valve bodies, pump shafts, bushings and mold components that need corrosion resistance together with a machined finish.

The card is shop reference information rather than a specification. It prints one preheat step, one hardening temperature and two quench media, then a tempering table in Brinell hardness with a single figure on each row and no tolerance band anywhere. A first run of parts from a new heat of steel is worth treating as a trial before the cycle goes onto production work.

Chemistry of 416

Elements the reference card lists, percent

Source, heat treating reference information for type 416 stainless steel, printed page 200.

The card prints sulfur as a maximum of 0.15 percent. Sulfur is the deliberate free machining addition in this grade, and the ASTM range writes the same figure as 0.15 min, which is the form the stainless steel composition chart on this site carries. Vanadium and tungsten are listed on the card with no figure, so those rows are left out rather than printed blank. Composition data is for general reference only, actual values vary by standard, mill and heat number, so confirm against the material test certificate of the heat or ask Aobo Steel.

Chromium at 13.00 percent is the highest figure in the martensitic stainless cards and it is the element the corrosion resistance rests on. Sulfur at 0.15 percent is five times the 0.03 percent the card prints for 410, and it is the element that does the work in this grade, since sulfur forms manganese sulfide inclusions that break the chip and let a machinist run heavier feeds on the same tool. Manganese at 1.25 percent is raised along with it because manganese is what holds that sulfur in the steel as a sulfide. Molybdenum at 0.60 percent carries a figure on this card, where the 410 card lists the element with no figure against it. Carbon at 0.15 percent is the same as 410 and it is the figure that caps the hardness. Phosphorus at 0.06 percent and sulfur at 0.15 percent are printed as maxima, and the sulfur row is worth a second look with your supplier, for the reason set out under the table. Composition data in the table is for general reference only, actual values vary by standard, mill and heat number, so confirm the figures against the material test certificate of the heat or ask Aobo Steel.

Hardening 416

Preheat, hardening temperature and quench

Source, heat treating reference information for type 416 stainless steel, printed page 200.

The card prints one preheat step, one hardening temperature and two quench media for the grade, with no section size condition against any of them, so the figures stand for the load as written.

The cycle is the one the card prints for 410 as well. The load goes in at 1200 °F (650 °C) for the preheat, then up to 1850 °F (1010 °C) for austenitizing, followed by an air or an oil quench. Air is the slower of the two media and the one to take on thin sections where distortion has to be held down, while oil is used where the section is heavy enough to need faster cooling. Two grades with the same carbon content harden on the same cycle, so the difference between them shows up in the tempering table rather than here. A 416 part leaves the quench at about 210 Brinell, close to the 220 the card prints for 410 and well below what a die or a cutting edge needs, which is why the grade is taken for corrosion resistant hardware rather than for tooling that has to hold an edge. One hardening temperature is printed, so a shop running a different austenitizing window is working outside what the card gives.

Tempering response of 416

Hardness left by each tempering temperature

Source, heat treating reference information for type 416 stainless steel, printed page 200.

The card prints 210 BHN for the as quenched condition and 210 BHN again after a 300 °F (150 °C) temper, so the first step of the line is flat. The hardness is printed in Brinell on the card rather than in Rockwell C, and no tolerance band appears against any row.

The line climbs where the 410 line holds flat. 416 leaves the quench at 210 Brinell and gains 5 points at 400 °F (205 °C), another 5 at 500 °F (260 °C) and 5 more at 600 °F (315 °C), reaching 225 Brinell. From 700 °F (370 °C) to 900 °F (480 °C) the card prints 230 Brinell on all three rows, which is the peak of the curve and 20 points above the as quenched figure. That rise happens in the temper rather than in the quench, so a shop that needs the higher figure has to take it from the tempering cycle. At 1000 °F (540 °C) the reading falls to 178 Brinell, the lowest figure on the card, and that is the point at which the temper has gone past the range in which the part keeps its strength. The card prints one figure on each row and says nothing about the number of tempering cycles, so treat the line as the response of the grade and settle the cycles with your heat treater before the parts go into service.

Related reference data

416 sits with the other martensitic stainless grades on this site. The grades beside it in carbon are set out on the 410 stainless steel heat treatment page, the 420 stainless steel heat treatment page, the 440A stainless steel heat treatment page and the 440B stainless steel heat treatment page. Mechanical property rows for 416 and 416Se sit on the martensitic stainless steel properties chart, chemistry for every grade is on the stainless steel composition chart, and the tempering bands across the tool steel groups are on the tool steel tempering chart. The supply condition of the corrosion resistant grades we hold is on the 420 stainless steel page.

Reference data compiled from Heat Treatment, Selection, and Application of Tool Steels (William E. Bryson, second edition, Carl Hanser Verlag, 2009). The chemistry, the hardening cycle and the tempering response for type 416 come from the heat treating reference information on printed page 200.