ISO 4957 Tool Steel Grades: Composition, Hardness and Equivalents

The four families of ISO 4957

ISO 4957 sorts tool steels by end use rather than by chemistry alone. The four families are non-alloy cold-work, alloy cold-work, alloy hot-work and high-speed tool steels. The dividing line between cold work and hot work is a working temperature, below or above about 200 °C, and the high-speed grades are the ones that hold their hardness up to roughly 600 °C. Anything the standard does not recognise as one of the four families is simply not an ISO 4957 tool steel.

Grade counts and carbon ranges as set by ISO 4957:1999. The carbon range is the span across the family, not the range of any one grade.

Chemical composition of the ISO 4957 grades

Table 1 of the standard gives a composition range for every grade, together with the German EN 10027-2 number and the nearest Japanese JIS grade. The ranges are the specification limits, so a heat that sits anywhere inside them is to the standard. Where a cell is empty the element is not specified for that grade.

Chemical composition of tool steels to ISO 4957:1999, with the comparable EN 10027-2:1992 and JIS grades, reproduced from Table 1 of the standard. Values are percent by mass. The JIS column is blank where the standard lists no direct comparable.

Hardness and hardening schedule of the ISO 4957 grades

Table 2 of the standard pairs each grade with the hardness its heat treatment develops. The annealed hardness is given as a maximum in HB, and the hardened hardness as a minimum in HRC, with the hardening temperature, the quenching medium and the tempering temperature that produce it. The hardened hardness is the figure to quote when a drawing calls up a working hardness.

Hardness and hardening method for tool steels to ISO 4957:1999, reproduced from Table 2 of the standard. The quenching medium letters are air, oil and water; the tempering temperature is a guide to the schedule that reaches the listed minimum hardness, and a higher or lower temper moves the hardness of the work.

How to read an ISO 4957 name

An ISO name carries the alloy in it. A leading X means a tool steel alloyed above about 5 percent total, and the number that follows is the carbon content in hundredths of a percent, so X40CrMoV5-1 is a chromium-molybdenum-vanadium tool steel at about 0.40 percent carbon with about 5 percent chromium and 1 percent molybdenum. A name without the X is a lower alloy grade, where the first number is the carbon in hundredths of a percent. The HS grades use a fixed three-number pattern instead, tungsten, molybdenum and vanadium in that order, so HS6-5-2 is about 6 percent tungsten, 5 percent molybdenum and 2 percent vanadium.

The names do not answer the question a buyer usually has, which is what the grade is called where the tool is made or sold. A few of the ISO grades map onto an AISI grade cleanly, and those are the ones below. Where a whole range of equivalent names is needed, the cross reference is on the tool steel equivalent grades page.

The ISO 4957 names whose AISI equivalent is in common use, with the EN 10027-2 number as the standard prints it. Grades outside this short list are better matched on the equivalent grades page than by letter.

Where this sits in a tool steel enquiry

The ISO name is the order document, and the AISI or the DIN name is what gets quoted back, so the two have to be reconciled before a heat is promised. The grades above that customers ask for most often are covered in more depth on their own pages. Start with equivalent grades, H13 across the standards, cold work tool steels, hot work tool steels and high speed steels. The composition the standard allows for each AISI grade is on the tool steel composition chart, and the processing and service ratings are on the AISI tool steel properties chart and the processing and service characteristics chart.

Source, ISO 4957:1999 (BS EN ISO 4957:2000), Tool Steels, Tables 1 and 2, as reproduced in Handbook of Mechanical Alloy Design (G. E. Totten, L. Xie and K. Funatani, eds.), Marcel Dekker, 2004, Chapter 4 (Yang and Collins), pages 189 to 192.