Heat Treating Equipment

Achieve and Maintain Temperature Specifications with Heat Treating

Heat treating is a critical part of the manufacturing process as nearly every metal must undergo some form of heat treatment. During the heat treating process, metals are heated and cooled under tight controls to improve their properties, performance and durability. It is an extremely versatile process with the ability to soften metal to improve formability, make parts harder to improve strength, create a hard surface on soft components to increase abrasion resistance or add a corrosion-resistant skin to protect parts that would otherwise corrode. While iron and steel are the most commonly heat treated materials, alloys made of aluminum, copper, magnesium, nickel and titanium can also be heat treated.

The heat treating process follows three steps:

• Heating the material to a specified temperature at a given rate
• Holding that temperature for the appropriate timespan
• Cooling the materials according to the prescribed methods

 

Efficient Methods for Heat Treating

Induction Heating

Induction heating is a fast time-to-temperature, accurate method of preheating and post-weld heat treatment (PWHT) delivering accurate temperature measurements and records along with a precise ability to maintain weld temperatures. In induction heating, a power source supplies alternating current (AC) through an induction heating cable which is wrapped or coiled around a magnetic material (pipe, column, etc.). As a result, the coil generates an alternating magnetic field, reversing directions when the current switches direction (alternates). This creates an Electro-Magnetic Frequency (EMF) heating effect to occur to the coiled object (only in magnetic materials such as iron, nickel, cobalt, etc.). The part becomes its own heating element and heats from within making it a very efficient heating method since little heat is lost in the process.

Check out the induction heating equipment Red-D-Arc has available for rent, lease or purchase:

Resistance Heating

Resistance heating is a versatile and efficient way to achieve any heating application with excellent temperature uniformity across the metal. During the resistance heating process, an electric current passes through a conductive material (the wire), and generates and releases heat. The wire then transfers heat to the flexible ceramic heating elements,  known as chiclets or beads, which are in direct contact with the base material providing a stable, uniform heating process required for code work and critical applications.

Check out the resistance heating equipment Red-D-Arc has available for rent, lease or purchase:

What is Preheating and Why is it Important?

Preheating is defined as the application of heat to a base metal prior to welding and the desired temperature maintained throughout welding till the weld joint is complete. Preheating the weld joint and surrounding area serves a dual purpose: to reduce the amount of H₂O or moisture in the base metal prior to welding, and to slow the cooling rate of a finished weld and base metal. This is accomplished by heating the base material to a temperature typically between 200-600°F depending upon the type of material and thickness, which is determined by the applicable welding code.

Sudden heating of the weld area abutting the cooler base metal can cause stresses in the neighboring area between the weld and base material (called the Heat Affected Zone or HAZ) due to the rapid cooling. The microstructure and properties in the HAZ region change so that they differ to that of the weld and the base material. These changes can be detrimental depending on the material, and can lead to hydrogen induced cracking, higher or lower strength, reduced corrosion resistance or lower toughness. Typically, if a failure is going to occur, it will be in the HAZ.

Hydrogen induced cracking can be slow to take effect, and visible cracks may appear hours or days after the weld has been completed, which may result in costly repairs and downtime. Hydrogen easily migrates and tends to diffuse out of the weld zone and park along discontinuities that are present in the microstructure. Once enough hydrogen starts to group up it can cause stresses in the microstructure that lead to cracking.

The welding process, filler metal, and moisture in the base material are the main contributors to hydrogen being present in the weld. Using low-hydrogen filler metals and proper preheat methods will help minimize available hydrogen. Preheating the adjacent base material of a weld joint will allow the weld puddle to cool slower, which in turn allows the hydrogen to diffuse out and not become trapped in the weld.  Induction and resistance heating methods provide the most consistent heating control and will ensure that the interpass heating is maintained throughout the duration of the weld. These methods also allow for controlled cooling at the end cycle or to transition directly into a post-weld heat treatment if required.