MTC utilizes powder metallurgically based hot isostatic pressing (PM HIP) technology for its near-net shape products.
How it works
The basic idea is simple. Place fine metal powder in a gas-tight steel capsule, heat to elevated temperature (but below melting point), apply isostatic gas pressure and you get a very strong, solid, 100% dense shape with practically no inclusions. The encapsulated powder can be HIPed to produce Near-Net Shapes (NNS) of virtually any geometry. Not only does this offer more design freedom than forging or casting, it reduces the risk of hydrogen-induced stress cracking (HISC) in duplex stainless steels, since the process results in a material with very fine microstructure. It also eliminates the risk of any defects like cracks, porosity or stringers. By avoiding time-consuming welding and inspections in the forging-machining process, or weld repair in the casting process, you reduce risk and lead-time costs.
The production process from the melt to the finished product takes place in four stages.
1. Melting and atomization
The melt produced in an induction furnace is tapped into an induction-heated ladle where further alloying elements can be added in a protective atmosphere. The ladle also permits stirring and temperature control of the melt throughout the process.
When the melt is tapped from the bottom of the ladle it is discharged directly into the atomization chamber. The molten steel is broken up by jets of inert gas and the atomized melt solidifies into small spherical particles of high purity and low oxygen content and with a diameter less than 500 micron. The powder is stored under inert gas hermetically-sealed vessels.
The powder is canned in capsules of mild steel, which are produced by sheet metal forming and welding. The capsule is designed to give the fully dense end product to the desired shape. Compound products can be produced by designing capsules with separate compartments for different powders, enclosing parts of solid material together with powder or by other proprietary processes.
3. Hot isostatic pressing (HIP)
The evacuated and sealed capsules are placed in a hot isostatic press where they are subjected to high pressure and temperatures. The hot isostatic pressing parameters are predetermined to give the material full density.
4. Post treatment
Depending on the type of material and the application, the PM HIP products will be heat treated, machined and subjected to various types of quality control, such as ultrasonic inspection, dye penetrant testing, testing of mechanical properties.
The mild steel sheet used in the can remains on the product after the hot isostatic pressing and heat treatment and is either removed by machining or pickling.
Materials, product size and weight range
MTC products produced by powder metallurgically based hot isostatic pressing (PM HIP) are available in a wide range of materials, for example:
- Austenitic stainless steels
- Duplex stainless steels
- Martensitic steels
- Metal matrix composites (MMC)
- Nickel alloys
- Tool steels
The maximum dimension after hot isostatic pressing is a diameter of 1800 mm and a height of 3550mm The maximum weight for a single HIP product is approximately 25 tonnes.