Tag : surface hardening

Laser cladding fundamentals

Using a laser to deposit a rugged clad surface on wear-prone components can be relatively inexpensive and can yield highly effective results.

Cladding is the association of layers of metals of different natures by molecular interpenetration of the surfaces in contact. Limited diffusion of the surface material is a characteristic of clad products and differentiates them from products metalized in other manners, such as normal electroplating. Large scale cladding processes include pouring molten cladding metal onto a basic metal followed by rolling or simple hot-rolling of the cladding metal to ensure efficient welding to the basic metal. Smaller-scale cladding methods include superimposing the cladding material (nickel, chromium, etc.) by a thermal process to ensure welding. In these methods the cladding metal is applied to the basic metal by heat treatment at the appropriate temperature.

Cladding is a highly flexible technique for developing a tough corrosion and erosion resistant surface to metal surfaces. Laser cladding is simply a finely-tuned technology for heating the cladding and substrate materials to the proper temperature. It involves depositing a hard material, usually in the form of powder, onto a surface to enhance the wear and corrosion resistance of the substrate material. The process is actually fairly simple: A laser beam melts a very thin layer of the work piece, some cladding alloy is added to the melt pool, and this surface freezes to the work piece with a metallurgical bond. The resulting thin surface has all the desirable properties of a wear coating without significant changes to the substrate material. The result is a highly effective and economic hardened surface that can extend the life of the component.

Laser cladding offers one of the most cost effective ways of developing a wear- or corrosion-resistant surface layer to components in repair and life-extending maintenance. It is used to build up worn surfaces, repairing components, and to produce low volume parts.

BMR Group has more expertise and experience with laser materials processing than any other company in the industry. If you want to know anything about how this technology can help your operational up time and pad your bottom line, call one of our technical specialists at 260-635-2195 or email info@bmrgroup.net.

Laser heat treating fundamentals

Laser heat treating can provide an exceptionally hard surface on certain types of steel that helps resist wear…and the risk of distortion is virtually zero!

In surface heat treating of steel, the surface of a piece of steel is hardened by heating it to a suitable temperature at which it begins to change its internal structure, and then causing it to cool rapidly. This process is referred to as transformation hardening, because the surface of the metal is transformed to another state. In laser heat treating the concentrated light energy emitted by the laser is converted into heat energy when absorbed by the metal, causing the transformation.

The transformation involved when steel is hardened is actually a change in the arrangement of the atoms in the metal. Technical people involved in heat treating sometimes referred to this as a change in the “crystallographic lattice network” of the metal. That may give you a good word picture of what actually happens. This change occurs at critical transformation temperatures both when the metal is being heated and as it is cooled. The transformation temperature is the temperature above, or below which solid state transformation takes place.

The exact temperature depends on the alloy composition of the steel being treated The changes, and the structures they produce in the metal, all take place while the metal is in the solid state. That is. the metal is not actually melted, because transformation occurs before the surface reaches the melting temperature. After the metal surface is heated, it has to cool at the critical cooling rate, which is the rate at which the heated material is cooled from the transformation temperature to a lower temperature .

In conventional heat treating, high cooling rates are achieved after the heating process by chilling, or quenching the work piece with oil, water or forced air. In most laser heat treating applications the material is allowed to “self-quench ” or cool? in ambient air. That is possible with laser heat creating because the area heated at any one instant is so small.

The transformed area of the steel is called martensite, and it is the iron-carbon structure that is produced upon a very rapid cooling to the martensite transformation temperature. Martensite is the structure that produces the high hardness in ferrous materials The greater the degree of martensite formation, the higher the hardness. Typical heat treatments for most industrial applications result in hardness of 56 – 62 points of the Rockwell C scale.

Normally, 0.4 per cent carbon content is the minimum that can be successfully hardened to this range by any heat treating method, and laser heat treating is no exception to this rule The big advantage the laser provides is uniformity and precise control of the depth of hardened area.

BMR Group has more expertise and experience with laser materials processing than any other company in the industry. If you want to know anything about how this technology can help your operational up time and pad your bottom line, call one of our technical specialists at 260-635-2195 or email info@bmrgroup.net.