What thickness of steel plate is suitable for flame cutting?

Flame cutting relies on a preheating flame to bring the steel to its ignition temperature, followed by a high-pressure oxygen stream that triggers an oxidation reaction to perform the cut. This principle imposes two inherent limitations: for very thin plates, the heat input can cause warping and edge collapse; for very thick plates, challenges arise regarding preheating penetration and maintaining the perpendicularity of the cut edge. In practical production, flame cutting is generally avoided for materials under 5mm; it is most efficient for thicknesses between 20mm and 50mm, and it remains the primary—often only—viable option for thicknesses exceeding 100mm.
 
The optimal processes for various thickness ranges are generally as follows:
Below 3mm: Laser cutting or shearing. Fiber laser cutting offers high speed, narrow kerf, and minimal deformation for thin sheets; for standard, regularly shaped parts produced in batches, shearing is a more cost-effective solution.
3–10mm: Fiber laser cutting is the dominant method. It achieves speeds of over ten meters per minute with a precision of ±0.05–0.1mm, allowing parts to be used immediately after cutting. In this range, flame cutting is slow, causes significant deformation, and is ultimately more expensive.
10–25mm: Medium-to-high-power laser cutting (6–12kW) remains advantageous, providing high-quality cut surfaces that require no secondary processing. If precision requirements are lower and the parts consist primarily of linear contours, CNC plasma cutting is a more economical choice.
25–50mm: This is the transition zone between laser and flame cutting. In this range, flame cutting offers stable speeds, low costs, and the ability to create bevels, making it the primary process for structural components, flanges, and heavy-plate blanking.
50–100mm: Flame cutting is essentially the only viable option. It requires the use of larger cutting nozzles and longer preheating times, with careful attention paid to kerf compensation and the perpendicularity of the cut.
Above 100mm: For extra-thick plates, flame cutting requires specialized, large-scale CNC equipment, with cutting speeds potentially as low as a few dozen millimeters per minute. If extremely high precision is required, waterjet cutting or subsequent mechanical machining may be considered. There are three key factors in the flame cutting of thick plates: preheating before cutting (materials with high carbon content or thick plates require preheating to 100–150°C to prevent cracking), maintaining a consistent distance between the cutting nozzle and the plate surface, and ensuring an oxygen purity of at least 99.5%. By mastering these aspects, the cut surface quality for plates thicker than 50 mm can reach a level that requires no further machining.