9Mn2V Tool Steel Heat Treatment and Properties

Where 9Mn2V sits in the cold work family

9Mn2V is the Chinese grade that matches AISI O2 and German 90MnV8. It contains no chromium and no nickel, which is why it is the low cost end of the oil hardening family, and it carries about 0.9 percent carbon with manganese for hardenability and vanadium to keep the grain fine. The trade off is size and temperature. The oil quench critical diameter is only about 30 mm, so the grade hardens through in small sections and not in a large block, and its resistance to softening on tempering is poor: above 250 °C the hardness falls away quickly, which is the same message the tempering curve on this page carries. Where a die needs to hold hardness at a working temperature, or needs to harden through a thick section, the chromium grades are the right family instead: D2 for wear resistance with some hot hardness, and 5CrNiMo when the section is large and the tool is a forging die rather than a cold work die.

Composition

The chemistry below is the GB/T 1299-2000 specification printed for the grade, with the AISI equivalent on the second row for comparison. A certificate that falls outside these ranges is not this grade, whatever the mill calls it.

Source, 实用模具材料与热处理速查手册 (王邦杰), Table 4-83, printed page 102, per GB/T 1299-2000, mass fraction in percent. One value is printed inconsistently in the source: the silicon limit of 9Mn2V is printed as 0.040 max, while the same page prints 0.40 max for 9CrWMn and 0.20-0.40 for AISI O2. The value is published here exactly as printed, and a silicon limit of 0.40 max is what the grade is normally bought to. Reference summary of published practice, not an Aobo Steel specification.

Critical points

These temperatures set every cycle on the page. Ac1 and Accm bound the austenitizing range, and the low martensite start temperature of 125 °C is the number that decides the quench: it is why the grade can be interrupted in oil or stepped into a salt bath, and why a shop that quenches to room temperature in one go distorts small gauges. The 150-200 °C tempering window sits only just above Ms, so the part is tempered while it is still finishing its transformation, which is the normal route for a gauge that has to keep its size.

Source, 实用模具材料与热处理速查手册 (王邦杰), Table 4-84, printed page 102.

Forging

The forging ranges below are for ingot and for billet. The finish is kept above the Ar1 temperature and the part goes straight into a slow cool, because 9Mn2V hardens in air and a forged tool left on the floor will crack in the section change.

Source, 实用模具材料与热处理速查手册 (王邦杰), Table 4-85, printed page 103.

Heat treatment

The cycle for the grade is short. Forge, anneal to a machinable 229 HBW, rough machine, harden from the 780-820 °C window in oil, then temper in the 150-200 °C window to hold 60-62 HRC. The parts that have to hold size to a few microns take the stepped route rather than the plain quench.

Annealing, before machining

Source, 实用模具材料与热处理速查手册 (王邦杰), Table 4-86, printed page 103.

Hardening

Source, 实用模具材料与热处理速查手册 (王邦杰), Table 4-87, printed page 103. The hardness cell is printed as ≥62.

Tempering

Source, 实用模具材料与热处理速查手册 (王邦杰), Table 4-88, printed page 103.

Tempering temperature against hardness

Source, 实用模具材料与热处理速查手册 (王邦杰), Table 4-89, printed page 103. The source note reads: oil quenched from 790 °C, tempered 2 h. The source prints 250 °C twice (ten temperature cells for ten hardness values); the duplicate is reproduced here as printed rather than silently replaced.

Mechanical properties and service limits

9Mn2V has better hardenability than a plain carbon tool steel and hardens with little distortion, which is what the grade is bought for. The vanadium content refines the grain and lowers the sensitivity to overheating, and the carbides are fine and evenly distributed, so the combination of strength and toughness is good for a low alloy steel. Two limits follow. The first is tempering resistance: the grade should not be used where the tool runs hot, and 200-250 °C is a window to avoid rather than a tempering range to use, because that is where low temperature temper embrittlement sits. The second is section size, which the 30 mm oil quench critical diameter makes plain. Where a die is larger than that, or sees a long thermal cycle in service, the higher alloyed cold work grades are the correct choice.

Typical applications

The grade is used for precision gauges and samples, for the small punching and blanking dies, cold pressing dies, engraving dies and blanking tools that a plain carbon tool steel cannot hold, and for plastic mould parts. A shop example that is worth copying is a fine blanking die made in 9Mn2V: preheat at 600 °C, austenitize at 790 °C, quench into nitrate salt held at 180-190 °C, then temper at 200 °C for 2 h. The die comes out at 59-61 HRC with the size held, and the reported life on that job was 950,000 parts. That cycle is the reason the grade is specified where a gauge or a fine blanking tool has to stay straight rather than where it has to survive abrasion.

Related reference data

The hardness the grade keeps as the tool runs warm is compared with the other tool steels on the tool steel hot hardness chart, and the hardness after each tempering temperature is compared across grades on the tool steel tempering chart. The oil hardening carbon grades that sit either side of this one are collected with O2, which is the closest AISI equivalent, and D2, which takes over where more wear resistance is needed.

Compiled from 实用模具材料与热处理速查手册 (王邦杰), Tables 4-83 to 4-89, printed pages 102 to 103. Every figure was read from the searchable text layer of the book and checked table by table against the printed values, and two printing defects in the source are disclosed above rather than corrected silently. 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.