The diffusion of nitrogen into the surface layers of low carbon steels at elevated temperature. The formation of nitrides in the surface layer

creates increased mechanical properties.

Beth Blumhardt – Brent Fogal – Greg Mooren – Jana Young

•Benefits of Nitriding

•Types of Nitriding

•Future of Nitriding

•Process Determination•CVD Reaction•Deposition Process•Diffusion Depth

•Process Results

•Principal Reasons for Nitriding are:

•Obtain High Surface Hardness

•Obtain a Resistant Surface

•Increase Wear Resistance

•Increase Tensile Strength and Yield Point

•Improve Fatigue Life

•Improve Corrosion Resistance (Except for Stainless Steels)

•Improves Mechanical Properties•Surface Hardness•Corrosion Resistance

•Chemical Reaction•Nitrogen & Iron•Core Properties Not Effected

•Temperature Range•495 - 565 ºC•Below Tempering Temperature

• White Layer By-Product•Thin•Hard Iron Nitride

•Process methods for nitriding include:

•Gas

•Liquid

•Plasma

•Bright

•Pack

***Lots of more nitriding methods for specific applications***

http://www.nitriding.co.uk/np01.htm

•Gas methods:

•Case-Hardening Process

•Nitrogen Introduction•Surface of a Solid Ferrous Alloy

•Suitable Temperature•Between 495 and 565°C (for Steels)

•Nitrogenous Gas•Ammonia

Liquid nitriding:

•Thermo-chemical Diffusion Treatment

•Hardening Components With Repeatability. 

•Salt Bath, at Less Critical Temperatures.

•Preserves Dimensional Stability•Corrosion Protection

•Exhibit Long-Term Resistance to Wear, Seizure, Scuffing, Adhesion and Fatigue.

•Vacuum Chamber•Pressure = 0.64 Pa

•Pre-Heat Cycle•Surface Cleaning

•Ion Bombardment

•Control Gas Flow•N, H, CH4

•Ionization by Voltage

•Blue-Violet Glow

•Wear Resistant Layerhttp://www.milwaukeegear.com/nitrid.htm

•Replacing Liquid Nitriding •Environmental Effects•Ease of Control•More Complex Substrates•Performed at Lower Temperatures•Creates Higher Residual Stress

http://www.northeastcoating.com/

Gas Nitriding

•How do the variables of nitriding steel affect the process and the mechanical properties of the surface?

•The following variables were investigated:

•Time

•Temperature

•Gas Velocity

•Develop Process Model

CVD Process

CVD Equations

CVD Reaction

CVD Process

The Following Variables Were Used in The Calculation of C surface η(T) ρ(T) D(T) δ(T,v) hmass(T,v)

Surface Composition

Case Depth

Case Depth

Case Depth

•Time Effects•Increase Diffusion Depth

•Temperature Effects•Surface Composition•Deposition Efficiency•Diffusion Rate•Diffusion Depth

•Gas Velocity Effects•Surface Composition•Replenishes Nitrogen Gas•Minimizes Stagnant Layer Thickness

•Microstructural Effects•Processing Temperature•Surface Microstructure

•Mechanical Property Effects•Improves

•Surface Hardness•Wear Resistance•Corrosion Resistance•Fatigue Life•Yield Strength

•Lowers•Ductility•Fracture Toughness