Boronizing

boronizing, also called Boriding, is the process by which boron is introduced to a metal or a metal alloy. It is a type of surface hardening thermo chemical heat treatment process. Boronizing is generally done by diffusing boron atoms into the surface of the part to be treated at high temperatures. This results in a hard, low-friction, wear-resistant boronized surface made of FeB/FeB2 . The resulting case layer has a hard, slippery surface capable of performing at higher temperatures than most surface treatments. Boronizing is used to improve the life and performance of metal components. 
The boronizing process is Suitable for a broad range of materials.

The boron diffusion process is a two-step reaction. The first step is a reaction between the boron-yielding substance or compound and the part, which is a function of time and temperature. This results in a thin, dense boride layer. This reaction is followed by diffusion, which is a faster process. Boronizing here at Wear Cote Technologies is often used on steel, but is applicable to a variety of alloys and cermet materials,  Practically any ferrous material can be boronized, as well as many Ni, Ti & Co alloys.  However, it is important to note, the higher the content of alloy elements, the slower the diffusion rate. The micro-hardness of the diffused layer will vary depending on the base material. For example, FeB/FeB2layers will have a micro-hardness in the range of 1600-1900 HV. Other elements, such as Ni, Ti and Co, will produce a different hardness range, some even higher than FeB/Fe2B. The FeB layer, while harder, is more brittle and more prone to fracture upon impact.

The thickness of the boride layers varies according to:

WCT B-Cote boronizing literature  

• Temperature

• Treatment time

• Material

·      Strengthens resistance to corrosion

·      Strengthens resistance to acid (especially Hydrochloric acid)

·      Strengthens resistance to abrasive wear

·      Decreases coefficient of friction (0.4)

·      Increases surface hardness (1500HV to 2300HV in general)

The surface boride may be in the form of either a single phase or a double phase boride layer. With ferrous materials, the boride layers attain a hardness of between 1500HV to 2300HV. Boronized metal parts are extremely wear resistant and will often last two to five times longer than components treated with conventional heat treatments such as Hardening, Carburizing, Nitriding, Nitrocarburizing.

A monophase Fe2B layer with a tooth-shaped morphology is generally suitable for industrial application because of the difference between the specific volume and coefficient of thermal expansion of boride and the substrate. Boron rich upper phase FeB (containing approximately 16. 23 wt. % B) is not desirable because FeB is more brittle and less tough than Fe2B (containing approximately 8. 83 wt. % B) . The boronizing results in some considerable improvements in the surface such as resistance to wear, fatigue, corrosion, and high temperature oxidation.