5CrMnMo Tool Steel Heat Treatment and Properties
5CrMnMo is the manganese economy substitute for 5CrNiMo, and it is ordered for hammer and press forging dies by the tonnage of the hammer it has to stand rather than by a single hardness number. This page collects the composition, the critical points, the forging range, the annealing, hardening and tempering cycles and the mechanical property data for 5CrMnMo, so a die shop can set a process sheet from one sheet of paper.
Where 5CrMnMo sits in the hot work family
5CrMnMo is a low alloy hot work die steel in which manganese carries part of the hardenability that nickel carries in 5CrNiMo. Both grades are built around a 0.5 percent carbon level with chromium and molybdenum for temper resistance, and both are supplied in the annealed condition for a forging die that will be machined, hardened and tempered in the die shop. The manganese substitution lowers alloy cost and raises strength, and it also lowers hardenability and toughness, which is why the grade is specified for the small and medium dies in a forging plant and 5CrNiMo for the large blocks.
Composition
The chemistry below is the GB/T 1299-2000 specification printed for the grade. A supplier certificate that sits outside these ranges is not the same grade, whatever the mill calls it.
| Grade | C | Si | Mn | Cr | Mo | P | S |
|---|---|---|---|---|---|---|---|
| 5CrMnMo | 0.50-0.60 | 0.25-0.60 | 1.20-1.60 | 0.60-0.90 | 0.15-0.30 | 0.030 max | 0.030 max |
Source, 实用模具材料与热处理速查手册, Table 5-24, 5CrMnMo steel chemical composition (GB/T 1299-2000), mass fraction in %. Printed page 225. The source prints the phosphorus and sulfur limits as 0.030 max. This is a reference summary of published practice and not an Aobo Steel specification.
Critical points
The critical points set the window for every cycle on this page. Ac1 and Ac3 bound the heating range for austenitizing, Ar1 marks the temperature at which ferrite and pearlite begin to form again on cooling, and the martensite start temperature at 220 °C is the reason the quench is interrupted at 150-180 °C rather than taken to room temperature.
| Critical point | Ac1 | Ac3 | Ar1 | Ms |
|---|---|---|---|---|
| Temperature, approximate, °C | 710 | 760 | 650 | 220 |
Source, Table 5-25, 5CrMnMo steel critical point temperatures, printed page 225.
Forging
Forging is the first place a 5CrMnMo die is lost, because the grade hardens in air and is prone to white spots and cracking if it is left to cool in still air after the last blow. The practice below keeps the finish above the Ar1 temperature and puts the whole section into a slow cool as soon as the hammering stops.
| Item | Heating temperature, °C | Initial forging temperature, °C | Final forging temperature, °C | Cooling |
|---|---|---|---|---|
| Steel ingot | 1140-1180 | 1100-1150 | 800-880 | Slow cooling, pit or sand |
| Steel billet | 1100-1150 | 1050-1100 | 800-850 | Slow cooling, pit or sand |
Source, Table 5-26, 5CrMnMo steel forging practice, printed page 225. The source note adds that the forging must be cooled slowly after forging, and that a large die is held in a furnace at about 600 °C, then cooled to 150-200 °C before it is taken out for air cooling.
Heat treatment
The heat treatment section of the grade card is short because the cycles overlap. A forging die is annealed to make it machinable, hardened in oil, and tempered to the hardness the die face needs, with a separate higher temper for the shank so that the dovetail stays tough.
Annealing, before machining
| Plan | Process parameters |
|---|---|
| General annealing | Heat to 760-780 °C, hold 2-4 h, cool in the furnace to below 500 °C and take out for air cooling. Hardness after annealing 197-241 HBW. |
| Isothermal annealing after forging | Heat to 850-870 °C, hold 2-4 h, cool in the furnace to 680 °C, hold 4-6 h, cool in the furnace to below 500 °C and take out for air cooling. Hardness after annealing 197-241 HBW. |
Source, Table 5-27, 5CrMnMo steel preliminary heat treatment, printed page 226.
Hardening
| Quenching temperature, °C | Quenching medium | Medium temperature, °C | Operation | Hardness HRC |
|---|---|---|---|---|
| 820-850 | Oil | 150-180 | Cool to 150-180 °C, small dies air cool, medium and large dies are tempered immediately | 52-58 |
Source, Table 5-28, 5CrMnMo steel recommended hardening practice, printed page 226. The source notes that medium and large dies take the upper end of the heating range and small dies the lower end, and that the die is pre-cooled in air to 740-760 °C before the oil quench.
Isothermal hardening, when cracking risk is high
| Plan | Process parameters |
|---|---|
| I | Heat to 840-860 °C and hold in 160-180 °C nitrate salt in a stepped stop, so that part of the austenite transforms to martensite, then transfer to 280-300 °C nitrate salt and hold 2-3 h. |
| II | Heat to 840-860 °C and quench into oil, and when the die surface has cooled to 150-200 °C transfer it still warm to the isothermal bath and hold at 280-300 °C for 2-3 h. |
Source, Table 5-29, 5CrMnMo steel isothermal hardening practice, printed page 226. The source notes that the structure after either route is martensite plus lower bainite plus retained austenite, that tempering converts it to tempered lower bainite, and that the route lowers the cracking risk and raises die life.
Tempering, by part of the die
| Part of the die | Die size | Tempering temperature, °C | Heating medium | Hardness HRC |
|---|---|---|---|---|
| Working part | Small forging die | 490-510 | Gas furnace or electric furnace | 41-47 |
| Working part | Medium forging die | 520-540 | Gas furnace or electric furnace | 38-41 |
| Shank, dovetail | Small forging die | 600-620 | Gas furnace or electric furnace | 35-39 |
| Shank, dovetail | Medium forging die | 620-640 | Gas furnace or electric furnace | 34-37 |
Source, Table 5-30, 5CrMnMo steel recommended tempering practice, printed page 226. The source note adds that the die is normally tempered twice, and that each temper is followed by an oil cool to suppress temper embrittlement.
Tempering temperature against room temperature mechanical properties
| Tempering temperature, °C | 200 | 300 | 400 | 450 | 500 | 550 | 600 | 650 |
|---|---|---|---|---|---|---|---|---|
| Hardness HRC | 57 | 52 | 47 | 44 | 41 | 37 | 34 | 30 |
| Tensile strength Rm, MPa | – | – | – | 1630 | 1600 | 1430 | 1260 | 1120 |
| Impact energy aK, J/cm² | – | – | – | 19 | 20 | 27 | 42 | 30 |
| Elongation A, % | – | – | – | 5.5 | 7.5 | 9.5 | 10 | 11.5 |
Source, Table 5-31, 5CrMnMo steel tempering temperature against room temperature mechanical properties, printed page 227. The source note states the specimens were oil quenched from 840 °C. The source prints a dash where no value is given.
High temperature hardening and tempering
| Process | Process parameters |
|---|---|
| High temperature hardening and tempering | Harden at 890-900 °C, oil quench, hardness 61.5 HRC. Temper at 420-550 °C, twice. |
Source, Table 5-32, 5CrMnMo steel high temperature hardening and tempering practice, printed page 227. The source note states that high temperature hardening produces a fine lath martensite with better strength and toughness, and that above 900 °C the impact toughness begins to fall.
Mechanical properties and service limits
5CrMnMo is a traditional hot forging die steel whose strength, wear resistance and scaling resistance are good, and it is the lower alloy, manganese bearing relation of 5CrNiMo. Two limits follow from the substitution. Its hardenability is lower, so a large block will not harden through and the grade is specified for dies up to about 400 mm on the side. Its fatigue strength is also somewhat lower, so a die that sees a long running thermal cycle is better made in a higher alloyed grade. Where a die of this size needs more toughness than the air melted steel gives, the usual route is the electroslag remelted version of the same grade.
Typical applications
The grade is used for hammer forging dies, press forging die blocks and shallow impression dies in small and medium sizes, and for other small hot work dies that work below 500 °C. It is a common choice for dies below a three tonne hammer. It is not the grade for a large die block, a long running hot extrusion tool, or a die that has to hold hardness above 500 °C, and those applications move to the chromium hot work grades. The closest cross reference is 5CrNiMo, which shares the composition family and adds the nickel that carries hardenability through a large section, and the air hardening family that includes L6 tool steel sits alongside both.
Related reference data
The hardness this grade keeps as the die runs hot is set out on the tool steel hot hardness chart, which is the number that decides whether a forging die softens in service, and the hardness the grade reaches after each tempering temperature is compared across grades on the tool steel tempering chart.
Compiled from 实用模具材料与热处理速查手册, Tables 5-24 to 5-32, printed pages 225 to 227. Every figure was read from the searchable text layer of the file and checked table by table against the printed values. The tables are a reference summary of published practice rather than an Aobo Steel specification, so confirm the grade and the heat treatment cycle before the data is written into a process sheet.