Gas nitriding is a common method of creating a hard surface on steel. It works by diffusing nitrogen into the steel from a nitrogen-rich gas. The gas is usually ammonia (NH3), which is why this method is also referred to as ammonia nitriding.
Gas nitriding is a mature process which has been around for almost a century. It’s relatively easy to control the process parameters guiding the thickness and composition of the nitriding layer.
Steel that is gas nitrided can reach a surface hardness of more than 67 HRC for excellent wear resistance of the steel. It also gives the surface anti-galling properties, which is important in applications with poor lubrication.
The treated metal experiences a minimum of distortion and deformation and only minor changes in dimensions. Dimensional changes should be accounted for pre-nitriding to reach the desired measurements post-nitriding. Thanks to the low temperatures in the process the metal will not be subject to tempering which could make the steel softer.
The nitrided surface improves fatigue life and other fatigue-related properties such as notch sensitivity. An additional benefit is that gas nitrided steel generally becomes more resistant to corrosion.
Steel components that are surface treated with gas nitriding can withstand higher surface pressure and wear. Typical applications include crankshafts, camshafts, cam followers, valve parts, gears, screws, die-casting tools, forging dies, extrusion dies, firearm components, injectors and plastic-mold tools.
Laser hardening of tool steel can give high surface hardness that penetrates relatively deep into the material, typically up to 2 mm. Laser hardened surfaces become very smooth, which reduces friction and the risk for material sticking to the surface. Laser hardening is also called laser peening.
Induction hardening is a common process for the surface hardening of steel. The steel components are heated by means of an alternating magnetic field to a high temperature followed by immediate quenching. By quenching the heated part in water, oil, or a polymer-based liquid, the surface layer is altered to form a martensitic structure which is harder than the base metal.
Surface etching of metal is called chemical etching or photo etching. It is a subtractive metal machining process which uses chemistry to alter the surface geometry of a steel piece, for example when producing steel molds for making car interior panels.
Shot peening is a cold process which compresses the surface of the steel by striking it with round metallic, glass, or ceramic particles with a high enough force to create plastic deformation. Its main application is to avoid the propagation of microcracks in a surface.
By nitriding Toolox® you can reach a surface hardness of 58‑65 HRC for highly wear resistant applications with a long service life. By coating the nitrided surface through PVD it’s possible to achieve even greater hardness or resistance to corrosion. The high strength of Toolox® minimizes the risk of cracking and chipping of the surface layer.
All kinds of surface treatments work better on a homogenous steel with high surface quality and consistent properties. Toolox® engineering and tool steel from SSAB meet the strictest demands on suitability for gas nitriding and other surface treatment techniques.
|Y = SHardness (HV0.5)||1 = 15 h|
|X = Distance from outer surface (mm)||2 = 40 h|
|3 = 96 h|
|4 = 102 h|
|5 = 102 h + 102 h|