Carbon Tool Steel Temper Chart
The carbon content behind each named carbon tool steel temper, from die temper at 0.70 percent carbon to razor temper at 1.40 percent, with the tools each level was sold for and how far the steel can be welded. A reference summary of published practice and not an Aobo Steel specification.
What the temper names meant
Before grade designations were standardised, carbon tool steel was bought and sold by temper. In the trade temper was the noun for the natural degree of hardness a bar carried from its carbon content, so a bar sold as shear blade temper and a bar sold as razor temper were the same family of plain carbon steel at two different carbon levels. The maker stamped or labelled a bar with the purpose it suited, which is why the older catalogues read as a list of tools rather than a list of numbers.
These were plain carbon steels. The source puts the limit at rarely more than 0.4 to 0.6 percent in total of any element other than iron and carbon. Alloying additions later took over the job carbon had done on its own and the temper names fell out of use, and the carbon ladder behind them still describes the same material. The water hardening carbon grades still sold today as W1 span the same range, roughly 0.60 to 1.40 percent carbon.
Carbon content and the tools each temper was sold for
Temper, approximate carbon and the tools each level was sold for
| Temper | Approximate carbon (wt %) | Used for | Weldability |
|---|---|---|---|
| Die temper | 0.70-0.75 | All kinds of dies for deep stamping, pressing, and drop forgings, mining drills to harden only | Easily weldable |
| Smith’s tool temper | 0.80-0.85 | Large punches, minting and rivet dies, nailmakers’ tools, hammers, hot and cold sates, snaps and boilermakers’ tools, various smiths’ tools, large shear blades, double-handed chisels, caulking tools, heading dies, masons’ tools, and general welding purposes | Not stated in the source |
| Shear blade temper | 0.90 | Punches, large taps, screwing dies, shear blades, table cutlery, circular and long saws, heading dies | Weldable |
| General purposes temper | 0.90-0.95 | Taps, small punches, screwing dies, saw webs, needles, and all general purposes | Weldable |
| Axe temper | 0.95-1.05 | Axes, chisels, small taps, miners’ drills, jumpers to harden and temper, plane irons | Weldable with care |
| Cutlery temper | 1.0-1.1 | Large milling cutters, reamers, pocket cutlery, wood tools, short saws, granite drills, paper and tobacco knives | Weldable with very great care |
| Tool temper | 1.2-1.3 | Turning, planing, slotting and shaping tools, twist drills, mill picks, scythes, circular cutters, engravers’ tools, surgical cutlery, circular saws for cutting metals, bevel and other sections for turret lathes | Not weldable |
| Razor temper | 1.3-1.4 | Razors, barrel boring bits, special lathe tools for turning chilled rolls | Not weldable |
Source, the table of tempers on printed page 10 of The Heat Treatment of Tool Steel (Harry Brearley), which is PDF page 28 of the copy consulted.
Carbon figures are the approximate content of the finished bar as the source prints them and are not a specification for any single grade. The source prints no weldability note against Smith’s tool temper. Its note on tool temper reads that the steel can still be welded to itself with a suitable flux and careful handling, and that this applies to ordinary shop methods only.
How to read the ladder
Read the table from the top down and three things move together. Carbon rises from 0.70 to 1.40 percent, hardness and wear resistance rise with it, and the tools listed at each level get finer and more demanding. Die temper at the top of the table is the toughest level of the group and is the one sold for deep stamping, pressing and drop forging work, where the tool has to absorb impact. Tool temper and razor temper at the bottom are the cutting levels, sold for edges that must hold up without support, and they are the levels that will not tolerate a repair.
The weldability column is the practical test of where a bar sits on the ladder. A die temper bar can be welded by ordinary shop methods, cutlery temper needs very great care, and from tool temper upward the ordinary methods do not apply. A cracked tool can therefore be repaired by welding at the low carbon end of the table and cannot at the high carbon end, which decides whether a large die or punch is worth repairing or has to be replaced.
Composition data is for general reference only. Actual values vary by standard, mill, and heat number. Confirm against the material test certificate (MTC) or contact Aobo Steel.
Related reference data
The temperatures these grades are tempered at are on the tool steel tempering chart, and the colours the oxide film takes at those temperatures are on the steel heat treatment color chart. The water hardening carbon grade in the same range is covered on the W1 tool steel heat treatment page, and the alloy grades that replaced these tempers are listed in the tool steel composition chart.
Compiled from The Heat Treatment of Tool Steel (Harry Brearley), the table of tempers on printed page 10. The figures are reproduced from the published table and are a reference summary rather than an Aobo Steel specification.