S5 Tool Steel Heat Treatment

S5 in the shock-resisting group

S5 belongs to the shock-resisting group, the grades a shop reaches for when a tool takes repeated heavy impact and edge holding matters less. The card hardens it in oil from 1725 °F (940 °C), and the silicon at 1.90% on the card is what lifts the elastic limit, while the manganese at 0.90% carries the hardenability through the oil quench. S1 and S7 sit in the same group and go into the quench in the same way.

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 tool cut from a new heat of steel is worth running as a trial before the cycle goes onto a production tool.

Chemistry of S5

Elements the reference card lists, percent

Source, heat treating reference information for S5, printed page 196.

The card prints one figure for each element rather than a specification range. Tungsten, cobalt and sulfur appear on the card with no figure against them and are left out of the table rather than shown as a zero.

Carbon at 0.60% with silicon at 1.90% and manganese at 0.90% is the combination that makes S5 a shock steel, one that bends under impact instead of cracking. Chromium at 0.20% and molybdenum at 1.30% give the hardenability that lets an oil quench reach through the section, and vanadium at 0.30% holds grain size through the hardening temperature. The card lists tungsten, cobalt and sulfur with no figure against them, so those rows are left out of the table rather than printed as a zero. 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 S5

Preheat, hardening temperature and quench

Source, heat treating reference information for S5, printed page 196.

The card attaches no size condition to the preheat, so the step is not marked as one that only larger sections need. It prints one hardening temperature and one quench medium for the grade, with no air or salt alternative alongside the oil quench.

The preheat of 1200 °F (650 °C) takes the section through the range where the steel takes a shock least well, and the card attaches no size condition to it, so the step applies to every load rather than only to heavy sections. The hardening temperature of 1725 °F (940 °C) is followed by an oil quench, with no air or salt alternative printed beside it. On a shock grade the oil is the middle road between water and air, fast enough to reach the hardness the tempering table starts from and slow enough to leave the section in one piece.

Tempering response of S5

Hardness left by each tempering temperature

Source, heat treating reference information for S5, printed page 196.

The card steps the tempering temperatures by 100 °F from 300 °F to 1200 °F and prints one Rockwell C figure on each row, with no row at 500 °F or 700 °F. The first row is the hardness as quenched, before any temper.

As quenched the grade sits at 61 HRC and the line falls from there, with no secondary hardening peak to search for. The first temper at 300 °F (150 °C) leaves 60 HRC, 800 °F (425 °C) leaves 52 HRC and the last row at 1200 °F (650 °C) leaves 41 HRC. A shock tool is usually tempered in the upper half of the table, where the hardness given up buys toughness, and the twenty point fall from the as-quenched hardness to the last row is what makes that choice a wide one.

Related reference data

The grades that sit around S5 in the shock-resisting group are set out on the tool steels for chipping resistance page, and the impact toughness the group is bought for is charted on the tool steel impact toughness chart. Tempering bands alone are on the tool steel tempering chart, hardening and tempering bands across every group are on the tool steel hardening and tempering chart, and the composition ranges of the S series are on the tool steel composition chart. Stock sizes of the shock-resisting grades are on the S1 tool steel page and the S7 tool steel page.

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 S5 come from the heat treating reference information on printed page 196.