Tool Steel Heat Treatment Temperature Ranges and Reference Points
The temperature ranges tool steel is hardened, annealed, carburized, nitrided and stress relieved at, with the heat sources above them and the subzero range below, from a tool and die shop handbook. A reference summary of published practice and not an Aobo Steel specification.
How to read the table
These are the temperatures that come up across tool and die work, collected in one place so the hardening, annealing and surface treatment ranges can be read against the heat sources that produce them and against the cold end they are measured from. Every figure is printed in degrees Fahrenheit with the book’s own conversion in degrees Celsius beside it. They are ranges for a group of grades rather than settings for one heat, and where a grade sits inside a range is set by its alloy content and by the section being treated.
Temperatures for various operations and conditions
| Operation or condition | °F | °C |
|---|---|---|
| Tungsten arc | 11,600 | (6,427) |
| Iron welding arc | 10,800 | (5,982) |
| Oxyacetylene flame | 6,300 | (3,482) |
| MAPP gas | 5,301 | (2,927) |
| Propane flame | 5,300 | (2,927) |
| Oxyhydrogen | 5,072 | (2,800) |
| Laboratory burner | 3,360 | (1,849) |
| Iron melts (liquid) | 2,800 | (1,538) |
| Welding and steel melting | 2,400 | (1,316) |
| High speed hardening | 2,100–2,400 | (1,149–1,316) |
| Alloy tool steel hardening | 1,500–1,900 | (816–1,038) |
| Carburizing range | 1,700–1,800 | (927–982) |
| Flame hardening range (4140 / 4150) | 1,550–1,600 | (843–871) |
| Annealing range | 1,400–1,700 | (760–927) |
| Carbon steel hardening | 1,350–1,550 | (732–843) |
| Stress relieving | 400–1,200 | (204–649) |
| Nitriding range | 900–1,000 | (482–538) |
| Blue brittle range | 600–800 | (316–427) |
| Water boils | 212 | (100) |
| Ice melts | 32 | (0) |
| Zero Fahrenheit | 0 | (-18) |
| Dry ice | -120 | (-84) |
| Subzero treatment | -320 to 0 | (-196 to -18) |
| Absolute zero | -460 | (-273) |
Source, Table 8-1, temperatures for various operations and conditions, printed page 153 of Tool and Die Making Troubleshooter (Richard M. Leed), PDF page 170 of the copy consulted. The book credits Bethlehem Steel Corp., 1936.
MAPP gas in the table is the liquefied petroleum and methylacetylene-propadiene mixture the book names, and the flame hardening range is quoted there for 4140 and 4150, which are printed as a reference point rather than as tool steels. Degrees Celsius are the book’s own conversions, shown in brackets exactly as the source prints them.
Where the tool steel heat treatment ranges sit
The ranges a tool steel buyer is usually quoted for are the ones in the middle of the table. Alloy tool steel is hardened between 1,500 and 1,900 °F (816 and 1,038 °C), while the high speed grades need 2,100 to 2,400 °F (1,149 to 1,316 °C) before their carbides go into solution. Annealing sits below the hardening range at 1,400 to 1,700 °F (760 to 927 °C), carburizing at 1,700 to 1,800 °F (927 to 982 °C), nitriding at 900 to 1,000 °F (482 to 538 °C), and stress relieving spans a wide band from 400 to 1,200 °F (204 to 649 °C). The blue brittle range at 600 to 800 °F (316 to 427 °C) is the band where a tempered part gives up impact toughness, which is why a temper is often run below it or well above it.
The grade by grade figures behind those ranges are on our pages for the tool steel hardening and tempering chart, the annealing and normalizing temperatures and the tool steel heat treatment guide.
Which grades the ranges cover
The high speed range belongs to M2 tool steel and the other molybdenum high speed grades, the alloy tool steel range covers the cold work grades such as D2 tool steel and the air hardening family, and the hot work grades such as H13 tool steel are hardened inside that same band and then tempered for hot hardness. The hardening temperature a given grade is run at, and the soak that goes with it, are on our tool steel catalog grade pages.
The top of the table, the heat sources
The first rows are temperatures a heat source reaches rather than a treatment a furnace is set to. A tungsten arc runs at 11,600 °F (6,427 °C) and an oxyacetylene flame at 6,300 °F (3,482 °C), both well above any hardening range, which is why a torch or an arc melts the surface of a die long before the part itself reaches temperature. Iron melts at 2,800 °F (1,538 °C), and that figure is the practical ceiling for any operation where the steel is meant to stay solid.
The cold end and subzero treatment
Dry ice sits at -120 °F (-84 °C) and a subzero treatment runs from -320 to 0 °F (-196 to -18 °C), below the dry ice it replaced. Absolute zero, -460 °F (-273 °C), is printed at the foot of the table because it is the floor the scale is built on rather than a temperature a shop works at. The subzero step in a tool steel cycle continues the transformation the quench interrupted, and our page on cryogenic treatment of tool steel covers when it is used and what it does to the retained austenite.
Compiled from Tool and Die Making Troubleshooter (Richard M. Leed), Table 8-1 on printed page 153, with the surrounding discussion of hardening, soaking and heat colours on printed pages 152 to 155. The figures are reproduced from the published table and are a reference summary rather than an Aobo Steel specification, so treat them as the ranges the trade works inside rather than as a heat treatment instruction for a particular part.