Cutting of high-performance austenitic stainless steels – waterjet, plasma and laser cutting

2024-04-26 16:34:41

Water jet cutting

Water jet cutting uses a nozzle to produce a high-pressure water jet carrying fine abrasive particles for cutting. This method is very effective for cutting both metallic and non-metallic materials. The process uses high-capacity pumps and has very high water and electricity requirements. This method can cut thick stainless steel (>100mm) without generating a heat-affected zone (HAZ) or changing the metallurgical structure of the workpiece. Although the quality of water jet incision is good, when the cutting section is thick, the bevel angle of the section will be larger. It is not economical to cut thin steel plates using this method, but by stacking multiple thin steel plates, multiple workpieces can be cut at one time.

Plasma cutting

Plasma cutting is the most commonly used method for cutting all grades of austenitic stainless steel medium-thick plates with a thickness above 25mm. The design of the plasma gun significantly improves accuracy and cut quality, making it an ideal process for cutting straight lines or special shapes. In some cases, plasma cut cuts are of such good quality that they can be used directly without further processing or as welded joints. Since plasma cutting does involve high temperatures and localized melting of the metal, the corrosion resistance of the cut is reduced. The portable plasma cutting machine can cut formed workpieces or specimens. Underwater plasma cutting reduces smoke and dust.

In plasma cutting, the stainless steel grade and cutting thickness are important factors that must be considered when selecting plasma gas. Avoid using oxygen-containing gases, as oxygen will cause the formation of a chromium oxide layer on the surface, thereby depleting the chromium below the surface and reducing corrosion resistance. Slight discoloration of the cut surface indicates chromium oxidation. If severe discoloration occurs, subsequent pickling or edging will be required to restore corrosion resistance. The certified purity of nitrogen auxiliary gas must reach at least 99.95%, with a maximum oxygen content of 200ppm. In addition to N2, other gases commonly used for stainless steel plasma cutting are mixed gases of N2 and H2 or Ar and H2.

Variables such as gas flow rate, arc current, nozzle design, cutting speed, etc. all affect the width, shape, and quality of the cut. For different grades and thicknesses of stainless steel, the plasma cutting equipment manufacturer should be consulted for specific recommendations.

Laser cutting

In laser cutting, a laser beam melts the material while a jet of nitrogen blows the molten away from the cut. Nitrogen prevents oxidation and loss of corrosion resistance. When laser cutting stainless steel, the nitrogen pressure is greater than the oxygen pressure when cutting carbon steel. In order to effectively blow away the molten metal, the nitrogen pressure needs to increase as the thickness of the material increases. Compared with plasma cutting, laser cutting is faster, has narrow kerf width, and has high quality kerfs. It can usually be used directly without further processing of the kerfs. Compared with plasma cutting, the disadvantage of laser cutting is the limited cutting thickness. Current laser cutting equipment can only cut stainless steel with a maximum thickness of no more than 12 mm. Laser cutting machines can cut high-performance austenitic stainless steel and standard austenitic stainless steel to final size without the need for additional machining. There is only a small difference in the laser cutting properties of high-performance and standard austenitic stainless steels.

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