Fields of use

For heavy-duty gear wheels with a sufficiently high surface hardness on the tooth flanks and with a sufficient flexural strength due to the high strains in the tooth root and with a good impact resistance to protect against impact strains. At the same time, gear wheels that are produced from CV58Z exhibit a high level of wear resistance and are free from the tendency to pit. In the same way, this steel is suitable for other components, such as cam disks, etc.

Description

Normally, components with the described requirements are manufactured from a carburizing steel. For economic reasons, the gas hardening or inductive hardening of quenched and tempered steels is used, during which the tooth flanks are heated and quenched in the progressive feed process. However, this hardening only works flawlessly on spur gears with modules >6. Bevel gears and the areas situated beneath Module 6 can no longer be hardened with satisfactory results using this procedure.
From this realisation, the spin hardening procedure was developed to achieve flawless hardening results in this sector as well. However, the prerequisite was to develop a steel, which adopts a high surface hardness while having sufficiently high flexibility properties in order to flexibly absorb the impact strains that always occur during operation.

Properties

This is an oil hardening steel, meant for radial hardening. For this reason, it is mainly replaced by similar procedures, wherever water must be used for the quenching process.

The steel has the following average composition:
C            Mn         Cr          Mo          V            
0.60 %   0,90 %  1,00 %   0,20 %   0,07 %

The compliance with particular metallurgic conditions and the introduction of suitable testing methods are necessary to achieve consistent steel properties as a prerequisite for the radial hardening procedure.

CV 58 Z is supplied in an annealed state or in a hardened and tempered state.

Mechanical properties as delivered

Annealed to grainy cementite    Hardened and tempered:

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Higher strengths are possible, but not recommended for processing reasons. They are also not necessary as a strength of approx. 1470 N/mm2 is achieved in the tooth root during radial hardening. Some information for the treatment condition before radial hardening: In principle, the quenched and tempered state should be chosen for smaller wheels up to an external diameter of about 200mm and if the borehole is created through broaching (taper groove profile) or the teeth are produced through planing. The quench distortion is lower. The hardness is greater by about 2 - 3 HRC units with 62 - 64 HRC. In all other cases, annealed material can be used, as the heating time (bake-out and holding time) is already sufficiently long enough for larger wheels to guarantee flawless hardening results.

Heat shaping and heat treatment

*) with subsequent furnace cooling up to 600 °C

An evenness of the steel, as is required to achieve reproducible results, is guaranteed with CV 58 Z through special smelting and careful heat treatment.

Quench distortion

The quench distortion in the change of pressure angle and the major joint flash tends to be determined by measurements before and after the hardening. The result of such investigations in comparison with the 16 MnCr 5 steel shows that the quench distortion of CV 58 Z tends to be 45 or 30% less than for 16 MnCr 5.

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Radial hardening

With radial hardening, bodies of revolution are hardened around their circumference. In principle, the procedure is the same as stationary hardening with the difference that the workpiece rotates during the heating and quenching procedure. With this procedure, the gear wheel blank, which is in an annealed or pre-annealed state, is warmed locally and then quenched in oil. Objective: High surface hardness (wear resistance), high flexural strength, good impact resistance.

Hardness penetration zones

Characteristic hardness penetration states of a radially hardened and carburized gear wheel for the module 1.5.

With 16 MnCr 5 carburizing steel, you can clearly recognise the hard case and the soft core as two different joining zones. With CV 58 Z, you can also clearly observe the practically through-hardened joint of the actual tooth and its slow transition into the soft joint of the gear ring.

                           CV 58 Z radially hardened        16 MnCr 5 carburized