Stainless Steel

Description

Stainless steel alloy usually contains iron, chromium, manganese, silicon, carbon, and sometimes nickel and molybdenum. This material is used in almost every industry and technology (like CNC machining and milling) as it's both strong and has good corrosion resistance. However, after sustained contact with water, it can eventually corrode. Stainless steel has lots of different types (grades) that each has various properties depending on the additives they contain, though a minimum of 10.5% of chromium is a must. The main grades of stainless steel are:

• 304 - most common grade that has 18% Chromium and 8% Nickel;
• 316 - another very widespread grade, that unlike 304, thanks to molybdenum (about 2%) has an additional solarium and chloride acid resistance;
• 316L - is an extra-low carbon version of the 316 steel alloy. This version minimizes deleterious carbide precipitation during welding and is often used for metal 3D printing;
• Other 300 grades - overall, a family of 300 series stainless steel is generally non-magnetic and not heat treatable. These steels are resistant to corrosion and keep strength in a wide range of temperatures;
• 410 - general purpose martensitic stainless steels containing 11.5% chromium;
• 420 - is a martensitic higher carbon version of type 410. This material is often hardened and polished to achieve the best corrosion resistance;
• Other 400 series grades - exhibit great toughness and strength, however, have lower corrosion resistance. These steels are magnetic and can be heat treated to increase hardness;
• 17-4 PH - is martensitic precipitation hardened stainless steel. In its composition, there is around 15–17.5% chromium and 3–5% nickel, as well as 3–5% copper. This material provides high strength paired with good corrosion resistance. It is also magnetic and heat treatable.

Machined stainless steels have, on average, quite shiny silver surfaces, which can be treated in many ways, including powder coating, polishing, and blasting.

3D printing with stainless steel

3D printing with stainless steel is available in several different technologies from powdered or extruded material.

316L is one of the most popular stainless steel grades used in 3D printing. This material has better mechanical properties thanks to the high temperature gradient and fast rate of solidification, though some printers are able to print with 17-4 PH as well.

• Selective Laser Melting (SLM) 3D printing with stainless steel - the powdered material gets melted together layer by layer resulting in a final part. Compared to machining, parts appear a bit weaker and more porous. However, through 3D printing, it is possible to achieve more complicated geometries and structures of metal, which would be impossible to machine or form with other manufacturing methods. SLM is suitable for prototypes and small batches of parts from stainless steel.
• Direct metal laser sintering (DMLS) - instead of melting the powder, this technology only fuses the grains together. Though it is possible to form good and strong parts, they would appear a bit more grainy and porous than SLM ones. Aside from this difference, the two technologies are quite similar and can be used for mechanical and functional stainless steel parts.
• Metal FFF - this 3D printing technology utilizes metals formed into filament strings rather than powders. Layer by layer it heats the filament up and lays it down in a pattern much like common plastic printers. To solidify the layers better and provide strength to a piece, the 3D printed part is then washed and sintered.

CNC machining of Stainless Steel

Stainless steels are easy to machine on CNC mills and lathes to good mechanical tolerances with great repeatability. Machined stainless steel parts are suitable for many applications and can be manufactured to ISO standards.

The huge advantage of machining with this material is that stainless steel exhibits so-called self-repairing, which means the surface repairs itself from scratches due to chromium content in the stainless steel.

Laser Cutting of Stainless Steel

Stainless steels for laser cutting are available in different forms such as angles, beams, tubes, and more. Laser cut steels have precise edges and small radii, they appear highly refined.

Metal Forming of Stainless Steel

Forming or stamping of stainless steels is sometimes chosen for repetitive better production rates, especially for thick-gauge steels. For elongated, shallow or simple stainless steel shapes it is possible to perform a fluid cell forming process. Steel would go under high pressure to form it in geometry with tight tolerances. The main advantage is that several high-quality parts can be formed at one time. Additionally, the forming process causes lower surface abrasion, reducing post-processing.

Common Uses

• ​Architecture;
• Aerospace;
• Food industry;
• Automotive;
• Engineering;
• Firearms;
• Medical devices and components;
• Marine;
• Tanks;
• Advertisement;
• Jewelry and decoration.

Advantages

• Corrosion resistance;
• Chemical resistance;
• Good strength;
• Durability;
• Heat resistance;
• High tensile strength;
• Good wear resistance;
• Cleanability.

Disadvantages

• Relatively high costs;
• Can be difficult to weld;
• Can be hard to use and to size in the jewelry industry due to rigidity and stiffness.