T1, T5 and T15 Tungsten High Speed Steel Tempering Chart
The hardness each tempering temperature leaves on the three tungsten high speed steels T1, T5 and T15, with the hardening window and the quench medium that go with them, set out as the source publishes it. A reference summary of published practice and not an Aobo Steel specification.
The three tungsten grades
The T series is the tungsten branch of the high speed steels. T1 carries 18% tungsten and no cobalt, T5 keeps the tungsten and adds 8% cobalt, and T15 trades tungsten for vanadium and cobalt. The source describes T1 as the first of the tungsten grades, with good toughness and heat resistance, T5 as an outstanding wear resistant tungsten steel with better wear resistance than M42 but not readily available in all sizes in the market, and T15 as a combination of tungsten, cobalt, high carbon and vanadium that gives maximum wear resistance.
The shape of the curve is the point of the group. Hardness holds within two points of the as quenched figure all the way to 1050 °F (565 °C), peaks at 950 to 1000 °F (510 to 540 °C), and then falls away as the temper goes higher. That peak is the secondary hardening the group is bought for, and it is where the source marks the optimum temper for all three grades.
Tempering chart for T1, T5 and T15
Hardness left by each tempering temperature
| Temper, °F | °C | T1, HRC | T5, HRC | T15, HRC |
|---|---|---|---|---|
| As quenched | No temper | 65 | 65 | 65 |
| 900 | 480 | 66 | 67 | 67 |
| 950 | 510 | 68 | 67 | 67 |
| 1000 | 540 | 67 | 66 | 67 |
| 1050 | 565 | 66 | 66 | 66 |
| 1100 | 595 | 62 | 64 | 64 |
| 1150 | 620 | 58 | 60 | 60 |
| 1200 | 650 | 52 | 56 | 56 |
Source, heat treating reference information for T1, T5 and T15, printed pages 197 and 198.
The source prints the 1150 °F line for T15 as 1150F/620°C, without the degree symbol. The line is shown here as published and the temperature is the one the rows around it give.
The selection chapter of the same source prints a second tempering set for these grades on a different basis and marks 1000 °F (540 °C) as the optimum temper for all three, giving T1 at 64 HRC, T5 at 64 HRC and T15 at 67 HRC at that temperature. That set runs from 900 °F (480 °C) and stops at 1200 °F (650 °C) for T1 and at 1150 °F (620 °C) for T5 and T15.
Above the peak the trade is hardness against toughness. The guidance the source gives for the family is not to draw a grade back to a higher temperature for toughness, because the wear resistance goes with it, but to move to a grade that takes the shock at its own optimum temper. A punch that keeps fracturing is a steel selection problem before it is a tempering problem.
Hardening the tungsten grades
Preheat, austenitizing temperature and quench
| Step | T1 | T5 | T15 |
|---|---|---|---|
| Preheat | 1500 °F (815 °C) | 1500 °F (815 °C) | 1500 °F (815 °C) |
| Austenitize | 2250 °F (1230 °C) | 2350 °F (1290 °C) | 2250 °F (1230 °C) |
| Quench | Oil or salt | Oil or salt | Oil or salt |
Source, heat treating reference information for T1, T5 and T15, printed pages 197 and 198.
The reference section gives one preheat and one austenitizing temperature for each grade and oil or salt as the quench. T5 is the one grade of the three that is austenitized 100 °F (55 °C) above the other two.
The reference block that carries the tempering table also gives the hardening window. All three grades preheat at 1500 °F (815 °C). T1 and T15 austenitize at 2250 °F (1230 °C) and T5 at 2350 °F (1290 °C), and all three quench in oil or in a salt bath. The high speed group is the one that most needs a quick rise from the preheat to the austenitizing temperature, which is why the source recommends a second furnace or a salt bath for it, and the temper follows as soon as the part is cool enough to handle.
Chemistry of the three grades
Carbon and alloy content, percent
| Grade | C | Mn | Si | Cr | Mo | V | W | Co |
|---|---|---|---|---|---|---|---|---|
| T1 | 0.75 | 0.30 | 0.30 | 4.00 | 0.70 | 1.00 | 18.00 | — |
| T5 | 0.80 | 0.30 | 0.30 | 4.00 | 0.80 | 2.00 | 18.00 | 8.00 |
| T15 | 1.50 | 0.30 | 0.30 | 4.00 | 0.50 | 5.00 | 12.00 | 5.00 |
Source, heat treating reference information for T1, T5 and T15, printed pages 197 and 198.
All three lines are printed as single figures in the reference section, not as the specification ranges. The ranges for the same three grades are on the tool steel composition chart.
T1 carries 0.75% carbon, 4.00% chromium, 1.00% vanadium and 18.00% tungsten. T5 carries 0.80% carbon, 2.00% vanadium, 18.00% tungsten and 8.00% cobalt. T15 carries 1.50% carbon, 5.00% vanadium, 12.00% tungsten and 5.00% cobalt. Manganese and silicon sit at 0.30% in all three and the cobalt line is empty for T1. The three lines are printed as single figures in the source, not as the specification ranges published for these grades.
Related reference data
Tempering bands across the whole grade range are on the tool steel tempering chart, and the austenitizing and tempering bands together are on the tool steel hardening and tempering chart. The specification ranges and UNS numbers for the three grades are on the tool steel composition chart, double and triple tempering practice for the group is on the M2 tool steel heat treatment guide, soak rates by section are on the tool steel soak time chart, and the machinability ratings for T1 and T15 are on the tool steel machinability rating chart.
Reference data compiled from Heat Treatment, Selection, and Application of Tool Steels (William E. Bryson, second edition, Hanser). The chemistry, hardening window and tempering table for T1, T5 and T15 come from the heat treating reference information on printed pages 197 and 198, and the grade notes from the tool steel selection chapter on printed pages 158, 161 and 162.