Stainless Steel Corrosion Resistance Chart
Corrosion resistance score for 48 stainless and tool steel grades, worked out from the chromium, molybdenum, tungsten and nitrogen left in solution. A reference summary of published practice and not an Aobo Steel specification.
What the corrosion resistance score measures
Rust resistance in a stainless steel comes from the chromium that is left in solution in the matrix. Alloy that is tied up in carbide protects nothing, which is why two grades with the same chromium content can sit far apart on this scale. The score in the table is the corrosion resistance equation that the source developed from its own corrosion testing, chromium plus 1.6 times molybdenum plus 0.8 times tungsten plus 6 times nitrogen, applied to the alloy that is in solution at the austenitizing temperature listed beside the grade. The contribution from molybdenum, tungsten and nitrogen is capped, so a grade cannot pass the ceiling on a large addition of one of them alone.
The dividing line the source uses for the word stainless is a score of 11. A grade at 11 or above passed the corrosion test that separates a stainless steel from a tool steel, and a grade below it will rust in the same service even when its chromium number looks healthy on a mill certificate. That single number is the practical reason a mold shop reaches for 420 or 440C when the plastic or the coolant is aggressive, and stays with D2 or A2 when it is not. It is also the reason a grade can be sold as stainless and still pit on a wet machine.
Corrosion resistance of 48 stainless and tool steels
Composition and corrosion resistance score by grade
| Steel | Austenitize (°F) | Cr (%) | Mo (%) | W (%) | N (%) | Score |
|---|---|---|---|---|---|---|
| Vanax | 1975 | 14.6 | 1.1 | – | 0.2 | 17.3 |
| LC200N | 1875 | 14.1 | 0.9 | – | 0.28 | 17.0 |
| M390 | 2100 | 13.5 | 0.9 | 0.4 | – | 15.2 |
| S110V | 2150 | 12.5 | 1.7 | – | – | 15.1 |
| BD1N | 1925 | 13.0 | 0.4 | – | 0.13 | 14.3 |
| 440A | 1900 | 13.7 | 0.3 | – | – | 14.2 |
| 14C28N | 2000 | 13.4 | 0.0 | – | 0.11 | 13.9 |
| S45VN | 1950 | 11.1 | 1.7 | – | – | 13.7 |
| N690 | 1925 | 12.3 | 0.8 | – | – | 13.5 |
| BD1 | 1900 | 12.6 | 0.4 | – | – | 13.3 |
| VG-10 | 1975 | 11.7 | 0.9 | – | – | 13.1 |
| S35VN | 1950 | 10.4 | 1.7 | – | – | 13.0 |
| 420 | 1900 | 13.0 | 0.0 | – | – | 13.0 |
| Super Gold2 | 2000 | 10.4 | 2.4 | – | – | 13.0 |
| Elmax | 1975 | 11.6 | 0.8 | – | – | 12.9 |
| S30V | 1950 | 10.2 | 1.7 | – | – | 12.8 |
| AUS-6 | 1925 | 12.5 | 0.2 | – | – | 12.8 |
| S125V | 2125 | 10.2 | 1.6 | – | – | 12.8 |
| 420HC | 1900 | 12.5 | 0.0 | – | – | 12.5 |
| 440C | 1875 | 12.0 | 0.3 | – | – | 12.5 |
| Niolox | 1925 | 10.8 | 1.0 | – | – | 12.4 |
| S90V | 2125 | 11.1 | 0.8 | – | – | 12.4 |
| Nitro-V | 1900 | 11.5 | 0.0 | – | 0.11 | 12.0 |
| AUS-8 | 1925 | 11.7 | 0.2 | – | – | 12.0 |
| 8Cr13MoV | 1925 | 11.7 | 0.2 | – | – | 12.0 |
| 154CM | 1950 | 9.4 | 2.7 | – | – | 12.0 |
| AEB-L | 1950 | 11.7 | 0.0 | – | – | 11.7 |
| S60V | 2050 | 11.1 | 0.3 | – | – | 11.6 |
| 19C27 | 2000 | 11.5 | 0.0 | – | – | 11.5 |
| XHP | 1925 | 9.7 | 0.6 | – | – | 10.6 |
| A8 Mod | 1875 | 7.5 | 1.3 | – | – | 9.6 |
| 3V | 1975 | 7.5 | 1.1 | – | – | 9.3 |
| CruWear | 1950 | 6.5 | 1.3 | 0.9 | – | 9.2 |
| ZDP-189 | 1875 | 7.0 | 0.6 | 0.3 | – | 8.2 |
| K190 | 2000 | 6.4 | 0.7 | – | – | 7.5 |
| D2 | 1850 | 6.5 | 0.6 | – | – | 7.4 |
| Maxamet | 2100 | 4.7 | 0.0 | 4.3 | – | 7.3 |
| Vanadis 8 | 2000 | 4.6 | 2.0 | – | – | 7.2 |
| Vanadis 4E | 1875 | 4.5 | 2.1 | – | – | 7.1 |
| M2 | 2100 | 4.3 | 2.4 | 2.3 | – | 6.9 |
| K390 | 2000 | 4.1 | 2.0 | 0.4 | – | 6.7 |
| M4 | 2100 | 4.0 | 2.0 | 3.9 | – | 6.6 |
| 10V | 2000 | 5.2 | 0.7 | – | – | 6.3 |
| A2 | 1775 | 3.8 | 0.9 | – | – | 5.3 |
| 52100 | 1500 | 1.0 | 0.0 | – | – | 1.0 |
| 5160 | 1525 | 0.8 | 0.0 | – | – | 0.8 |
| O1 | 1475 | 0.5 | 0.0 | 0.1 | – | 0.5 |
| 1095 | 1475 | 0.0 | 0.0 | – | – | 0.0 |
Source, corrosion resistance of knife steels, Table 15.1 on the source.
The score is the corrosion resistance equation that the source developed from its own corrosion testing, chromium plus 1.6 times molybdenum plus 0.8 times tungsten plus 6 times nitrogen, applied to the alloy that is in solution at the austenitizing temperature listed for each grade, with the contribution from molybdenum, tungsten and nitrogen capped. Every grade is assumed to have been given a low temperature temper. A score of 11 or higher is the line the source uses for the word stainless. A reference table only, it is not an Aobo Steel specification.
How the grade families score
The martensitic stainless grades sit at the top of the range a tool room actually buys from. 440A scores 14.2, 420 scores 13.0 and 440C scores 12.5, so the three grades that carry most mold, cutlery and pump work are separated by under two points, and what separates them in service is hardness and carbon rather than rust resistance. 420HC scores 12.5 on the same chromium as 420, and AEB-L and 19C27 score 11.7 and 11.5 on lower carbon. All of them clear the line at 11.
The cold work and high speed tool steels sit in the middle and below. D2 scores 7.4 and A2 scores 5.3, both well under the line, so a D2 die rusts on a wet machine even though it carries 12 per cent chromium, because most of that chromium is held in carbide and the matrix is left short. M2 and M4 score 6.9 and 6.6 with less chromium and more tungsten and molybdenum, and 52100, 5160, O1 and 1095 score 1.0 or less on under 1 per cent chromium. On this chart those four are carbon steel with better manners.
The nitrogen and powder metallurgy grades take the top of the table. Vanax and LC200N score 17.3 and 17.0 on chromium close to 440A plus nitrogen in solution, and M390 and S110V score 15.2 and 15.1 on chromium with molybdenum beside it. None of the four is general tool room stock, and the pattern they set is the useful part. Nitrogen and molybdenum in solution lift the score faster than chromium does, which is why a mold steel specified for a wet or chemically aggressive job is selected on the whole analysis rather than on the chromium number alone. Two grades with 12 to 13 per cent chromium can sit four points apart.
What moves the score in service
Three heat treatment decisions move the score more than the grade sheet does. Austenitizing temperature sets how much chromium, molybdenum and tungsten go into solution, and the temperature listed for each grade is the midpoint of the range a datasheet gives, so hardening at the bottom of the range leaves alloy in carbide and returns a lower score. Tempering above the secondary hardening range precipitates chromium carbide and takes chromium back out of solution, which is why a low temperature temper is assumed for every grade in the table. Retained austenite holds carbon and alloy that would otherwise be in the matrix, and it lowers the score until a cold treatment or a second temper breaks it down.
Read it as a ranking of the alloy in solution rather than a corrosion rate. The score says which grades are worth considering for a wet or chemically aggressive job and which ones are not, and the grade datasheet still decides the hardness, the toughness and the finish that the part needs.
Related reference data
Composition ranges for the stainless grades are on the stainless steel composition chart, and hardness, tensile and impact data for the same family are on the martensitic stainless steel properties chart. The grades we hold and ship are 420 stainless steel and 440C stainless steel. Where the score comes from in the microstructure is covered on the tool steel carbide types page, and grade selection for a mold that sees moisture or an aggressive resin is on the plastic mold steel selection page. Surface treatments that restore corrosion resistance after machining are on the tool steel surface treatment page, and the same question for the cold work grades is on the D2 versus 440C comparison.
Source: Knife Engineering, Steel, Heat Treating, and Geometry (Larrin Thomas).