The P91 PWHT Procedure

P91 martensitic steel is widely utilized for demanding applications, including supercritical power plants. It boasts high strength, thermal stability and corrosion resistance – characteristics which make it suitable for these tasks.

PWHTs are often required for grade 91 welds to reduce residual stresses and enhance toughness; however, this treatment can be time consuming and costly; thus this project explores alternative means of treating grade 91 welds using controlled deposition welding instead.

Modified Short-Circuit MIG

Contrary to conventional short-circuit transfer welding methods, this technique uses periodic contact between electrode and weld pool in order to transfer molten metal between them and thus reducing spatter generation and improving weld quality by preventing gas entrapment in the weld, making it especially suitable for applications where thickness matters.

This welding method also features low heat input, making it suitable for thin materials that could warp or distort under high temperatures. A wire electrode touches the workpiece multiple times per second before briefly shorting and extinguishing its arc – this cycle dissipates heat quickly while simultaneously decreasing metal transfer into the weld pool.

Modified short-circuit MIG welding comes with various current waveforms. Some offer more control settings than others, including lower wait phase current values and two step pulses. Furthermore, power decline rates during start/extinguish cycles have an impactful effect on instantaneous heat added to weld pools.

Pulsed MIG

Pulsed MIG welding is ideal for applications requiring greater control, such as applications that involve burn-through or distortion of finished products. With its ability to adjust peak current, background current, and pulse frequency settings, pulsed MIG allows welders to precisely manage heat input into an arc by controlling its heat input through peak current adjustment, background current control, and pulse frequency settings. This enhanced thermal control enables better quality finishes.

Additionally, it reduces heat-related issues associated with other welding processes, enabling operators to use larger wire diameters and faster travel speeds for increased productivity and avoiding any costly post-weld rework costs.

Pulsed MIG welding offers numerous advantages to industry, including improved weld quality, reduced distortion imperfections and higher precision when working with heat-sensitive materials. Some power sources even offer dual pulse options to take these advantages one step further – enabling welders to switch between procedure pre-sets more easily while decreasing training times for new welders.

Induction Heating

Induction heating uses electromagnetic induction to heat electrically conductive materials like metal. This non-contact method helps minimize cycle times and energy use, making it perfect for high production rates. Furthermore, operators can precisely control temperature to minimize distortion and warping in workpieces.

Induction heating can rapidly reach high temperatures, eliminating the need for warm-up and cool-down cycles and saving both time and money in industries with tight deadlines, such as aerospace and automotive manufacturing.

However, induction heating has limited penetration depth due to electromagnetic field produced by its coil heating only the surface of a part. While its frequency increases penetration depth increases slightly with frequency change; this may present challenges in applications requiring deeper penetration. Furthermore, induction requires expertise with regards to coil design and frequency settings that affect material behavior which makes this form of heating often more expensive than alternative methods of heating.

Processo di saldatura

P91 steel, while boasting an outstanding strength-to-weight ratio, is susceptible to hydrogen induced cracking and requires rigorous control of welding parameters in order to minimize it. Preheat and interpass temperatures must also be strictly maintained while its weldability “window” should remain small so as to allow quick refining and tempering times that will help minimize HIC.

Modified short-circuit MIG welding offers several advantages over TIG in this regard, with travel speeds three to four times faster and back purges often eliminated, saving both cost and gas consumption. Furthermore, using advanced waveforms may help eliminate root pass burn through for improved weld microstructure and tempering.