What Is P355M Steel
P355M, material number 1.8821, is a weldable fine-grain structural steel specified in EN 10028-5 for pressure purposes, delivered in the thermomechanically rolled condition. The P indicates pressure application, 355 the minimum yield strength in megapascals, and M the thermomechanical rolling treatment with impact testing at minus 20 degrees C.
Carbon Content Range
The carbon content of P355M is limited to 0.14 percent maximum by heat analysis. This low carbon level is fundamental to the grade's weldability, allowing fabrication without complex preheating and usually without post-weld heat treatment, while the strength is developed through thermomechanical rolling and microalloying rather than carbon content.
Complete Chemical Composition
Heat analysis limits are silicon 0.50 percent, manganese 1.60 percent, nickel 0.50 percent, phosphorus 0.025 percent, sulfur 0.010 percent, molybdenum 0.20 percent, vanadium 0.10 percent, nitrogen 0.015 percent, niobium 0.05 percent, titanium 0.05 percent, and aluminum 0.020 percent, with combined chromium, copper, and molybdenum limited and combined vanadium, niobium, and titanium limited to preserve toughness.
Mechanical Properties
The minimum yield strength is 355 MPa for thicknesses up to 40 mm and 345 MPa for 40 to 63 mm, with a tensile strength of 450 to 610 MPa and a minimum elongation of 22 percent. Impact energy is 27 J transverse at minus 20 degrees C, 40 J at 0 degrees C, and 60 J at plus 20 degrees C.
Production and Processing
Thermomechanical rolling controls the rolling temperature and deformation schedule, followed by accelerated cooling to refine the grain size, eliminating the need for subsequent normalization and shortening production cycles. The plate welds by SMAW, GMAW, SAW, and FCAW with preheating of 50 to 100 degrees C, forms hot at 800 to 900 degrees C or cold for thin and medium thicknesses, and machines well with standard tooling.
Applications
P355M is used for pressure vessels and storage tanks in the oil and gas industry, boilers and heat exchangers in power plants, large-diameter pipes and pipeline components, offshore structures, and thick-walled fabrications requiring high strength, good weldability, and low-temperature toughness.
Frequently Asked Questions
Q: What is the maximum carbon content of P355M?
A: 0.14 percent by heat analysis.
Q: What does the M in P355M mean?
A: Thermomechanically rolled delivery with impact testing at minus 20 degrees C.
Q: What standard specifies P355M?
A: EN 10028-5.
Q: Does P355M require normalization?
A: No, thermomechanical rolling with accelerated cooling replaces normalization.
Q: What is the yield strength of P355M?
A: 355 MPa minimum for thicknesses up to 40 mm.
Q: What applications use P355M?
A: Pressure vessels, storage tanks, boilers, large-diameter pipes, and offshore structures.
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