A10 Tool Steel Heat Treatment

A10 in the air-hardening cold work group

A10 sits in the air-hardening cold work group of the A series, next to A2 and A6, and it is the graphite that marks it out from them. The card carries 1.35% of carbon, 1.80% of manganese and 1.25% of silicon, with 1.80% of nickel and 1.50% of molybdenum, and it prints graphite as a row of its own at 0.35%. Chromium, vanadium, tungsten, cobalt and sulfur are listed on the card with no figure against them. The three tables below print what the card prints and nothing else.

The card is shop reference information rather than a specification. It prints one preheat step, one hardening temperature and one quench medium, then a tempering table with a single hardness figure on each row and no tolerance band anywhere. A first run of parts from a new heat of steel is worth treating as a trial before the cycle goes onto production work.

Chemistry of A10

Elements the reference card lists, percent

Source, heat treating reference information for A10, printed page 183.

The card prints one figure for each element rather than a specification range. Chromium, vanadium, tungsten, cobalt and sulfur are listed on the card with no figure against them, so those rows are left out of the table instead of being printed as blanks. Graphite is the free graphite the card prints for the grade, which is what gives the grade its name.

Carbon at 1.35% is at the high end of the A group, and manganese at 1.80% and silicon at 1.25% are printed as single figures rather than ranges. Nickel at 1.80% and molybdenum at 1.50% follow, and graphite at 0.35% is the free graphite the card prints for the grade, which is what makes A10 a graphitic tool steel. Chromium, vanadium, tungsten, cobalt and sulfur carry no figure on the card, so those rows are left out of the table. Composition data in the table is for general reference only, actual values vary by standard, mill and heat number, so confirm the figures against the material test certificate of the heat or ask Aobo Steel.

Hardening A10

Preheat, hardening temperature and quench

Source, heat treating reference information for A10, printed page 183.

The card prints one preheat step, one hardening temperature and one quench medium for the grade, with no section-size condition against any of them, so the figures stand for the load as written. The hardening temperature the site lists for A10 in the hardening and tempering temperature chart is 1450 to 1500 °F (790 to 815 °C), and the single figure on this card sits inside that range.

The preheat of 1200 \°F (650 \°C) brings the load up before the austenitizing temperature, and the card prints no condition against it, so the step stands for every load. Hardening runs at 1475 \°F (800 \°C) into an air quench. Air is the slowest of the usual quench media, which is what keeps A10 in the air-hardening group and keeps distortion down on thin sections. The hardening and tempering chart on the site gives the grade a window of 1450 to 1500 \°F (790 to 815 \°C), and the single figure on this card sits inside it. A shop running outside that window is working beyond what the card prints.

Tempering response of A10

Hardness left by each tempering temperature

Source, heat treating reference information for A10, printed page 183.

The card prints one Rockwell C figure on each row. Unlike some cards in the same set, this one carries a figure on the as quenched row, 62 HRC, so that row is shown with no tempering temperature against it. The temperatures run to 1000 °F (540 °C) and the hardness falls from the first row downwards with no second rise.

This card carries a figure on the as quenched row, 62 HRC, so the table starts there. The line falls to 61 HRC at 300 \°F (150 \°C), holds 60 HRC across 400 \°F and 500 \°F, and reaches 51 HRC at 1000 \°F (540 \°C), with no second rise anywhere on the curve. Tempering in the 300 \°F to 600 \°F band therefore holds the part between 59 and 61 HRC, inside the 55 to 62 HRC working range the site lists for the grade, and every step above that trades hardness away for toughness and stress relief. The card prints one figure on each row and says nothing about the number of tempering cycles, so treat the line as the response of the grade and settle the cycles with your heat treater before the parts go into service.

Related reference data

The heat treatment of the grade A10 is grouped with is on the A2 tool steel heat treatment page, and what the air quench means for the group is described on the air-hardening tool steel page. Chemistry ranges for the whole A series sit on the tool steel composition chart and the hardening and tempering temperatures on the tool steel hardening and tempering chart. The supply condition of the cold work group is on the cold work tool steels page, the grade itself is on the A2 tool steel page, and tempering bands across every tool steel group are on the tool steel tempering chart.

Reference data compiled from Heat Treatment, Selection, and Application of Tool Steels (William E. Bryson, second edition, Hanser). The chemistry, the hardening cycle and the tempering response for A10 come from the heat treating reference information on printed page 183.