Regarding cutting stainless steel

The wrong tool is being used; oxygen-acetylene cutting is generally employed. So how is stainless steel cut with oxygen? Since a chromium trioxide oxide layer is formed on the surface of stainless steel, and this oxide layer has a high melting point, we use flammable iron powder to melt it in order to enable cutting. 1. Basic principle of iron powder flame cutting: Iron powder flame cutting is a cutting method used for cutting stainless steel, cast iron, and high-carbon heat-resistant steel in cases where an oxygen-acetylene flame cannot be utilized for such cutting; it operates on the basis of the principles of oxygen-acetylene flame cutting, but in a simulated manner. First, the oxygen-acetylene torch is converted into a powder feeding device, with cutting powder being sprayed onto the cutting line to assist combustion and melting, thereby increasing the oxidation reaction during cutting. The methods for this modification will be thoroughly explained in the teaching material. The temperature generated when iron powder burns in oxygen is generally around 2000°C. During cutting, an oxygen stream is introduced to preheat the workpiece being cut; in this process, the iron powder undergoes a vigorous oxidation reaction within the flame, releasing large amounts of heat. By continuously feeding iron powder, the cutting process proceeds, with melting occurring at the cut edge and slag being formed simultaneously. This allows the heat from the upper part of the workpiece to be transferred to the lower part of the cut edge, enabling successful cutting. 2. Iron powder flame cutting method: The iron powder flame cutting method is essentially similar to the oxygen-acetylene cutting method used for low-carbon steel; the difference lies in the fact that a device is installed at the top of the cutting torch, whereby the cutting powder is delivered simultaneously with the cutting oxygen. Before cutting, adjust the mixture of acetylene and oxygen first so that the flame becomes a neutral flame. Turn on the shunt switch on the powder feeding device to allow oxygen flow into the powder feeding chamber; the cutting powder is then sprayed onto the workpiece through the nozzle. Preheat the workpiece first, and once the preheating temperature reaches the level necessary for combustion, start cutting. 3. Characteristics of flame cutting of stainless steel using iron powder: Compared with plasma cutting, the method of cutting stainless steel with iron powder flame cutting offers advantages such as lower equipment costs, energy savings, simpler equipment, ease of operation, and wide applicability. Taking two different cutting methods as examples, let’s look at their power-saving data. Powder flame cutting: As can be seen from the table, using iron powder flame cutting instead of plasma cutting results in energy savings. Furthermore, in terms of removing burrs from the cut edges, using iron powder flame cutting on iron oxide makes it easy to eliminate residues, whereas plasma cutting requires carbon arc gas gouging to remove the slag. From this perspective, it also helps to save electrical energy. Secondly, compared to the other cutting method, iron powder flame cutting offers greater flexibility; it can be moved to the desired cutting location as needed, just like when using an oxygen-acetylene flame to cut carbon steel. Moreover, it can cut at various locations; for example, when holes need to be made in an already assembled stainless steel cylinder or in semi-finished products of other shapes, iron powder flame cutting allows for cutting holes of any shape at any position. It is also convenient for removing parts that overlap during assembly, whereas plasma cutting can only be used at fixed locations. A comparison of the quality of two different methods for cutting stainless steel shows that the surface quality of the cut seams and their microstructural characteristics are essentially the same. Taking 40-mm stainless steel cutting as an example, two different cutting methods were used, and the seam width in both cases was 4–5 mm. In terms of the surface finish of the seam, oxy-fuel cutting yielded a quality about one level lower than plasma cutting; however, oxy-fuel cutting provided better verticality for the seam surface. From the metallographic perspective, the microstructure of the edges obtained by both cutting methods is austenitic. It’s just that the width of the heat-affected zone varies slightly. The width of the heat-affected zone in plasma cutting ranges from a minimum of 0.237 millimeters to a maximum of 0.316 millimeters ； The width of the heat-affected zone in iron powder flame cutting ranges from a minimum of 0.158 millimeters to a maximum of 0.432 millimeters. There were no abnormalities in the infiltrates obtained by cutting using the two different methods ； The microhardness at the cut seams is uniform, and the cut seam processing performance is good. V. Vibratory cutting method for stainless steel: Stainless steel cannot be cut continuously using an oxygen-acetylene flame, as a high-melting-point chromium trioxide film forms on the surface at the cut site, preventing further combustion of the metal beneath it. To enable continuous gas cutting, it is necessary to break this film; vibration gas cutting utilizes vibration to break the chromium trioxide film. For stainless steel vibration cutting, a standard G01-300 type cutting torch is used; the preheating flame is of the neutral type. It is larger and more concentrated than the flame used for cutting carbon steel, and the oxygen pressure required for cutting is 15–20% higher. During cutting, first preheat the edge of the workpiece with a flame; once it reaches a red, molten state, open the cutting oxygen valve. Slightly raise the cutting torch, and the slag will flow out from the cut area. At this point, move the torch back and forth as well as up and down by a certain amount to enable continuous gas cutting. The frequency of the mouth-cutting movement is about 80 times per minute, with an amplitude of 10–15 mm. The high temperature of the flame is used to break down the oxide layer at the cut site, allowing the metal to continue burning; meanwhile, the impact grinding effect caused by the back-and-forth and up-and-down vibrations of the oxygen flow within the flame is utilized to remove the slag, thereby achieving continuous gas cutting

Can’t a grinding wheel cut stainless steel? ——Joke! You’ve been tricked! But strictly speaking, plasma cutting should be used to ensure that the microstructure of the stainless steel is not damaged!

I have worked on on-site installation projects; for cutting stainless steel, plasma cutting is the method to use. Grinding wheels can be used for cutting very thin sheets of stainless steel, but not for thicker ones. If the cut surface is not very long, and you don’t have a plasma cutter, you can use 304 welding rods, increase the current to make a cut, and then use an abrasive disc to smooth out the cut surface. This is also a method that was developed on the spot.

Stainless steel pipes with a diameter of 50 mm or less are easy to cut with grinding wheels. Where can’t it be cut! But it’s usually ion cutting.

There shouldn’t be any problem; it’s not likely that there’s an issue with the cutting disc. Check that aspect, and it’s better to use plasma cutting. Using electric welding or cutting methods will definitely cause problems.

Oxy-acetylene cannot be used for cutting stainless steel; different cutting methods must be employed depending on the type of workpiece being processed. Generally, those smaller than 50mm can be cut using a grinder or cutter; if the processing conditions do not require heat treatment, they can also be cut with high-current welding. When it exceeds 50 mm, specialized equipment for ring cutters or plasma cutting can be used, as well as graphite cutters. The above cutting methods are only applicable to new pipes; for high-pressure pipelines and those with strict heat-treatment requirements, cold cutting must be used to prevent excessive heating at the weld site, which could affect their performance.