The designation CRES stands for Corrosion Resistant (Stainless) Steel. This steel does not stain, corrode, or rust as easily as ordinary steel. However, it is not completely stain-proof. Also, it stands as corrosion-resistant steel when the alloy type and grade are not detailed, particularly in aviation. This article discusses the properties of CRES material, applications, and alternatives.
Stainless steel’s corrosion resistance attributes to its chromium content. In fact, stainless steel contains a minimum chromium content of around 10.5 percent. The chromium in the alloy generates a self-healing transparent oxide layer. The oxide layer’s self-healing properties ensure that corrosion resistance maintains regardless of production processes. Even if the material’s surface is sliced or damage, it self-heals and continues to be corrosion resistant.
Some stainless steel grades can resist scaling at high temperatures while maintaining high strength. At cryogenic temperatures, mechanical properties are well preserved.
CRES material can be cut, welded, shaped, machined, and fabricated using the same procedures and equipment as other steels. For example, modern means of cutting include laser cutting, waterjet cutting, power scissors, and plasma arc cutting, in addition to sawing.
Material hardening of CRES occurs when engineers desire higher strength properties. Thus, this hardening process allows for thinner materials, resulting in lower weights and prices. Depending on the cycle, heat treatment alllows for stronger, more flexible, and/or stress-relieved material.
CRES material offers a variety of surface treatments. Post manufacturing operations provides the desired finish. Due to the lack of corrosion experienced by CRES material, the most common surface treatment typically involves sandblasting. CRES material typically requires a less harsh form of blasting than conventional carbon steel. Thus, this blast operation is often called “sugar blasting”. Additionally, common manufacturing operations such as pickling, passivation do not see common use in CRES material.
Hygiene and Ease of Cleaning
CRES provides a non-toxic, easy-to-clean material. As a result, CRES is the preferred material for usage in hospitals, kitchens, food, beverage, and pharmaceutical manufacturing facilities.
Long Life Cycle
Because of its endurance and resistance to corrosion, CRES outlasts many rival items. CRES frequently provides the least expensive option in a life cycle cost comparison due to its low maintenance qualities.
CRES is fully recyclable. In fact, new stainless steel typically contains between 50 and 80% recycled material. Scrap stainless steel can be stored without degradation to its value as a raw material.
Magnetic permeability is the ability of a material to attract a magnet. The austenitic grades of CRES are the only stainless steel grades that are not magnetic. Cold working can induce limited magnetism in austenitic grades other than 310 and 316 stainless steel.
Yield strength of CRES depends on the alloying element. These alloying elements include carbon, chromium, nickel, molybdenum, vanadium, and tungsten.
Ductility usually measures as the % elongation before fracture during tensile testing. Annealed austenitic CRES material provides exceptionally high elongation. Typical figures range from 60 to 70%.
The stainless steel alloy’s exceptional tensile strength of around 621 MPa or 90 KSI makes it stand out. Grade 304 can also withstand temperatures of up to 870°C.
CRES is a highly flexible material. The use-cases differ from one industry to the next. Common use cases range from culinary to aircraft.
- Kitchen sinks
Surgical tools and medical equipment
- Surgical implants
- Temporary crowns (dentistry)
- Monuments and sculptures
- Airport roofs
Automotive and aerospace applications
- Rail cars
The most common alternative to a corrosion-resistant material is carbon steel with some kind of coating. This coating may include powder coating, conventional paint, epoxy, and galvanization.
Powder coating is a dry coating procedure commonly used on industrial equipment as a metal finish. The powder coating produces a barrier that protects against rust and other sorts of corrosion. Like many other natural metals, steel rusts over time when exposed to moisture and oxygen. So, powder-coating generates a protective barrier that prevents rust from forming on the metal.
Another alternative is conventional paint. Paint mechanically bonds to a surface and provides a barrier film between steel and the environment. A paint system involves several layers of coating, and sometimes, different formulations of paint. The formulation depends on the type of environment in which the structure is placed. When paint applies to metals, electrolytes should not touch the metal structure.
Because of its ability to harden and produce a lasting protective barrier around the metal, an epoxy coating provides a superior option to other corrosion prevention treatments. Moreover, the coating applies as a liquid and then hardens to a high degree of durability. It is ideal for manufacturing resins and glues because of this property.
Lastly, galvanization is the process of immersing iron or steel in a bath of molten zinc to produce a corrosion-resistant, multi-layered coating of zinc-iron alloy and zinc metal. While the steel engages in the zinc, a metallurgical reaction occurs between the iron and the molten zinc. This reaction is a diffusion process, so the coating forms perpendicular to all surfaces creating a uniform thickness throughout the part.