Chinese Alloy Tool Steel Grades: Quenching Temperature and Hardness

Three numbers decide how a Chinese alloy tool steel is quenched. The temperature the tool is held at before it is cooled, the medium it is quenched into, and the hardness the grade is expected to reach at its minimum. The table below collects those three numbers for the alloy tool steel grades that appear most often on GB drawings and in orders from tool, die and mold shops.

What the three columns record

The quenching temperature is the austenitising temperature. The tool is soaked at that heat until the alloying elements are taken into solution, then cooled fast enough to miss the soft transformation products. A range is given rather than a single figure because the right point inside it depends on the section size of the tool, the furnace, and whether the grade is being treated for maximum wear resistance or for toughness.

The cooling medium is the quenchant the grade was tested in. Water removes heat faster than oil and is used on the shallow hardening carbon and low alloy tool steels, where a slow quench would leave the core soft. Oil is slower and is the normal medium for the alloyed grades, because a water quench on a fully hardened section of these steels will crack the tool. Where a grade takes two quench temperatures, the pair is a two stage schedule and both stages are shown.

The hardness column is the minimum Rockwell C value the quenched test piece reached. The minimum sign matters. It is a floor that the grade is expected to clear after quenching, not a target to aim at, and it says nothing about the hardness left after tempering, which is set by the tempering temperature that follows.

Grades and quench schedules

The table runs from the low alloy cold work grades at the top to the hot work and special grades at the bottom, in the order the source prints them. A dash in the temperature or medium column means the source publishes no quench schedule for that grade in this table, either because the grade is normally supplied pre-hardened or because its hardness is developed by a route other than a straight quench.

Quenching temperature, cooling medium and minimum hardness

Source, 刀具材料速查手册, Table 2-4, Alloy tool steel grades and hardness, printed pages 14 and 15. Every figure was read from a rendered image of the printed page and checked grade by grade. This is a reference summary of published practice and not an Aobo Steel specification.

Table notes. Four cells are printed defectively in the source and are reproduced above exactly as printed. The grade printed as 5CrMiMo is 5CrNiMo. The upper bound printed for 6Cr4W3Mo2VNb is 1600 °C and the upper bound printed for 5Cr4W5Mo2V is 150 °C, both of which read as truncated or transposed figures; the two temperatures for 6W6Mo5Cr4V are printed in descending order as 1180-1160 °C. Quench schedules for these four grades should be confirmed against the steelmaker’s own data sheet before the figures are used.

Reading the table in a workshop

The five grades in the table that carry a dash in both the temperature and the medium column are the higher alloyed cold work and hot work grades. Cr12Mo1V1 and Cr5Mo1V are close relatives of Cr12 and Cr12MoV, and the hot work grades 4Cr3Mo3SiV, 4Cr5MoSiV and 4Cr5MoSiV1 are usually ordered in the pre-hardened or annealed condition, with the hardening cycle taken from the steelmaker’s data sheet rather than from a general table. That is a difference in how the data is published, not a difference in whether the grade can be hardened.

The last row is the exception in the list. 7Mn15Cr2Al3V2WMo is an austenitic manganese tool steel that is hardened by solution treatment followed by ageing, not by a martensitic quench, and the medium shown is a water quench after solution treatment followed by an air cool after ageing. Its minimum hardness of 45 HRC is lower than the rest of the table for that reason, and it is chosen for non-magnetic tooling rather than for wear resistance.

Two practical cautions apply to every row. A quenched tool is not a finished tool. The hardness in the table is the hardness before tempering, and tempering will pull it down by a few points, so a grade quoted at 60 HRC minimum is tempered into the high fifties in normal practice. The second caution is that oil quench tables assume a still or mildly agitated oil bath at a controlled temperature. A cold, still bath on a heavy section will not reach the quoted hardness, whatever the table says about the grade.

Related reference data

Cr12MoV is the GB designation for the grade bought elsewhere as D2 tool steel and Cr12MoV tool steel, and Cr12 is the grade supplied as Cr12 tool steel. The oil hardening behaviour they share with 9SiCr comes from the same low alloy family, and the carbon and chromium ranges behind these quench temperatures are listed on the tool steel composition chart.

Compiled from 刀具材料速查手册, Table 2-4 on printed pages 14 and 15. Every figure was read from a rendered image of the printed page and checked grade by grade. The table is 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.