Nitriding Pvd And Hard Chrome On Mold Steels - China

A tool that fails at the gate after a few weeks of glass-filled nylon is rarely asking for a coating.

It is asking for a diagnosis.

The sequence is familiar: the moulder sees wash-out at the gate, a coating supplier quotes a chromium nitride film, the film is applied to a 30 HRC P20 insert, and the tool fails again — this time with the added complication that the spalled film has taken polished steel with it and the gate is rougher than it was at the start.

No one in that chain acted in bad faith.

The moulder asked for a coating rather than for wear resistance, and the coater quoted a film rather than a system.

Surface treatments are sold as upgrades, and in a narrow sense they are: each one raises the hardness or lowers the friction of the surface it is applied to.

But each is an answer to a particular mechanism — abrasion, adhesion, corrosion, release — and each is bounded by the steel underneath.

Nitriding changes the steel itself.

PVD deposits a film two to five micrometres thick.

Hard chrome electrodeposits a metallic barrier twenty-five to fifty micrometres thick.

The three fail for different reasons, repair differently, and demand different things from the substrate.

This article separates what each treatment actually buys from what it is credited with, and describes the situations in which the coating is neither the problem nor the solution — where the money would be better spent on the steel.

Three treatments, three relationships with the substrate The distinction that matters most is metallurgical rather than commercial.

Nitriding is a diffusion treatment.

Nitrogen enters the steel at 450–560 °C and reacts with alloying elements to form nitrides and a hard diffusion zone.

The case is not an addition to the steel; it is the steel, chemically modified.

It cannot delaminate, because there is no interface at which to delaminate, and for the same reason it cannot be stripped.

Its hardness falls gradually with depth instead of ending at a boundary.

PVD is a deposition process.

Atoms of chromium, titanium, aluminium or carbon are condensed onto a surface in a vacuum to build a film 2–5 µm thick.

There is a real interface, and everything that happens in service depends on what that interface can survive.

The film has no independent structural strength; it is a surface layer carried by the substrate.

Hard chrome is an electrodeposit.

Chromium is reduced from an electrolyte onto the cathode, building a metallic layer typically 25–50 µm thick.

It is thick enough to act as a barrier and hard enough, at 850–1100 HV, to resist wear, but it is deposited with an inherent crack network and it is electrochemically noble relative to steel.

That last property shapes how it fails, and it is the reason a small defect in chrome can do more damage than no chrome at all.

Those three sentences predict most of the practical differences that follow.

Nitriding: a case, not a coating Gas, salt bath and plasma are not interchangeable Gas nitriding holds the part in dissociated ammonia at 500–540 °C for 20–60 hours.

Nitrogen diffuses in slowly, which is what produces a deep, gradual case; it is also why the process is measured in days rather than hours and why it is usually the last operation before production.

Salt-bath nitrocarburising runs hotter, around 570–580 °C, in a cyanate-based salt, and finishes in one to four hours.

It produces a thin, hard compound layer — the familiar grey or black skin — over a modest diffusion zone.

It is fast and gives useful wear resistance plus some corrosion resistance, but the compound zone is porous, the process carries salt drag-out and disposal obligations, and the higher temperature is less kind to pre-hardened molds.

Company Contact:

• Posted By: Hubei Keyspark Special Steel Co., Ltd.

• Phone: +8615024056480

• Address: 30 Huahu Avenue, Huangshigang District, Huangshi , Hubei , China

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• Website: https://keysparksteel.com

• Business Description: Hubei Keyspark Special Steel Co., Ltd. is an integrated special steel manufacturer in Huangshi, Hubei, China.
  
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