CPM 440V against 440C, D2 and CPM 10V, Wear Resistance and Toughness

What CPM 440V is

The source describes CPM 440V as a high vanadium, high chromium tool steel for applications that need high wear resistance and good corrosion resistance at the same time. Its composition is essentially that of T440C martensitic stainless steel, which is the tool-room name for 440C, with roughly 5.75 per cent vanadium and increased carbon added to raise the wear resistance. The vanadium is what does the work, because vanadium forms hard MC carbide, and the powder route is what makes that much vanadium possible in a steel that is also 17.5 per cent chromium. A conventionally cast steel at that vanadium level would be a carbide network rather than a usable tool steel. The composition of the grade is on the P/M tool steel composition chart.

Wear resistance and toughness compared

The table below puts the four materials side by side on the standard crossed-cylinder wear test and on Charpy C-notch toughness. Read the hardness column first, because the comparison is only fair where the hardnesses are close. CPM 440V is listed at 59 HRC and again at 56 HRC, D2 at 59 HRC, 440C at 56.5 HRC and CPM 10V at 60 HRC, so the group is within about three points of each other and the wear numbers can be compared directly.

Table 7. Comparative properties of CPM 440V, CPM 10V, conventional T440C and D2 tool steel

Source, ASM Handbook Vol.1, article P/M Tool Steels, Table 7. The wear figures are the crossed-cylinder test result in the units the source prints, 10⁷ MPa with a 10¹⁰ psi scale alongside. The second CPM 440V row is the same grade at a lower hardness, and the source lists no wear values for it. A dash means the source lists no value.

Reading the wear column

At 59 HRC, CPM 440V records 276 in the source’s wear unit. 440C at 56.5 HRC and D2 at 59 HRC both record 28. That is very close to a factor of ten in favour of the P/M stainless grade over both the conventional stainless steel and the cold work die steel it is usually compared with. CPM 10V, which is not a stainless grade, records 517 at 60 HRC, roughly eighteen times the 440C figure and about 1.9 times the CPM 440V figure. The ordering is what a shop would expect from the vanadium contents, and the numbers put a size on it: CPM 440V takes 440C corrosion resistance and buys about an order of magnitude of wear resistance with it, at the cost of about half the wear performance of CPM 10V.

Toughness, the other half of the table

The toughness column points the other way and it is worth being honest about it. CPM 440V is the least tough material in this table: 16.3 J at 59 HRC and 21.7 J at 56 HRC, against 35.3 J for 440C, 31.2 J for D2 and 35.3 J for CPM 10V. The stainless P/M grade is bought for wear resistance and corrosion resistance and it pays for them in impact energy, which is the normal trade for a steel that carries a large volume of hard carbide. The useful figure in the column is the pair of CPM 440V rows, because they show what the temper is worth. Dropping the grade from 59 to 56 HRC raises its impact energy from 16.3 to 21.7 J, so where the edge is likely to see impact rather than steady abrasion, tempering to the lower hardness is the cheaper fix than changing grade.

How to read the wear unit

The wear figure is not a hardness and it is not a wear rate in millimetres. It is the result of the crossed-cylinder test, in which two cylinders of the material are pressed against each other under load and the volume of material lost is measured, and the source reports it in units of 10⁷ MPa with a 10¹⁰ psi scale printed alongside. What matters for a buying decision is the ratio between the rows rather than the absolute number, because the test is a ranking test. A figure of 276 against 28 says the P/M stainless grade will outlast the conventional stainless grade by roughly ten to one in the same abrasive service, and that ratio is what a die life estimate is built from.

Two cautions belong with any crossed-cylinder number. The first is that the test measures abrasive wear at a fixed hardness, so a row has to be compared at the hardness it was run at, which is why the hardness column is printed next to the wear column. The second is that the test does not reproduce every wear mechanism. A tool that fails by adhesive pickup, by thermal fatigue or by chipping will not necessarily follow the ranking in this table, and that is the reason the toughness column sits beside the wear column rather than on another page.

Choosing between the four

CPM 440V is the grade for a tool that has to resist both wear and corrosion, which in practice means food and pharmaceutical tooling, plastic moulds that see corrosive polymers or washdown, and cutting or blanking tools for stainless and other corrosion-resistant stock. Where corrosion is not part of the problem, D2 at 59 HRC delivers the same wear figure as 440C with comparable toughness and costs less than either P/M grade, and D2 remains the reference cold work steel for that job. Where the job is long run abrasive wear with no corrosion exposure and the die can take the toughness penalty, CPM 10V is the higher performance choice. Where the tool is a conventional stainless application with no extreme wear demand, the ordinary 440C stainless grade does the work and the heat treatment for it is set out on the 440C stainless steel heat treatment page.

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.

The carbide size, crossed-cylinder wear and grindability data for the P/M family is collected on the P/M tool steel properties page, and the corrosion behaviour of the stainless grades is on the stainless steel corrosion resistance chart.

Source: ASM Handbook, Vol 1, Properties and Selection: Irons, Steels and High-Performance Alloys.