S355JR:Low Alloy High Strength Structural Steel

S355JR is a low-alloy high-strength structural steel that complies with the European standard EN10025. S355JR steel in China is a low-alloy high-strength structural steel with a hardness of 70-80B and a yield strength of 300-400MPa. S355JR steel plate grade indication. S: Indicates that the steel plate is European standard structural steel. 355: Indicates that the yield strength of the steel plate is not less than 355MPa. "J": Indicates the delivery quality of the steel plate. JR does not do impact, which corresponds to the national standard B grade. B grade does not do impact. , and later changed to normal temperature impact and 20 degree impact. S355JR is a low-alloy high-strength structural steel that complies with the European standard EN10025. S355JR steel plate implementation standard: implement EN10025 standard.

S355JR steel plate performance characteristics: Compared with ordinary carbon structural steel, it has higher yield strength and yield-to-strength ratio, better hot and cold processing formability, good weldability, lower cold brittleness tendency, notch and aging sensitivity, and It has good resistance to corrosion from the atmosphere and sea water.

S355J2 steel plate appearance requirements:First, the unevenness of single-rolled steel plates is specified according to the following two types of steel: Steel type L: steel plates with a specified minimum yield strength value not greater than 460 MPa that has not been treated by fire or fire tempering; Steel type H: specified minimum yield strength Values greater than 460 MPa, and all fire or quenched and tempered steel plates.

Second, the unevenness should be determined by measuring the maximum distance between the upper surface of the steel plate and the ruler. If the wave spacing (the distance between the two contact points of the ruler and the steel plate) is not greater than 1000 mm, use a 1000 mm long straight edge. For longer wave spacing use a ruler with a length of 2000 mm. For unevenness with a height not greater than 2 mm, it shall not be treated as a wave.

Mechanical properties of S355JR steel plate: hardness is 70-80B, yield strength is between 300-400MPa. For impact tests, the +20 degree impact energy requirement is no less than 27 kilojoules. Normalizing is to heat the workpiece to Ac3 (Ac refers to the end temperature at which all free ferrite is transformed into austenite during heating, usually between 727°C and 912°C) or Acm (Acm is hypereutectoid during actual heating The metal heat treatment process is 30~50℃ above the critical temperature line for complete austenitization of steel. After keeping the temperature for a period of time, it is taken out of the furnace and cooled in the air or by water spray, spray or air blowing. Tempering treatment means that the steel that has been quenched, hardened or normalized is cooled down at a certain rate after being immersed at a temperature lower than the critical temperature for a period of time. Annealing is a metal heat treatment process in which the metal is heated to a certain temperature, maintained for a sufficient time, and then cooled at an appropriate rate (usually slow cooling, sometimes controlled cooling). The quenching of steel is to heat the steel to a temperature above the critical temperature Ac3 (hypoeutectoid steel) or Ac1 (hypereutectoid steel), keep it warm for a period of time to make it fully or partially austenitized, and then cool it at a temperature greater than the critical cooling rate. A heat treatment process that rapidly cools to below Ms (or isothermally near Ms) to transform martensite (or bainite).

The role of chemical elements of S355J2 steel plate: Commonly used alloying elements can be divided into: solid solution strengthening elements (MRSi, A, Cr, Ni, MoCu, etc.) according to their role in the strengthening mechanism of steel; grain refining elements (A, NbxV , Ti, N, etc.), precipitation hardening elements (NbV, T, etc.) and phase change strengthening elements (MnSi, M cold). C: Pearlite or dispersed and precipitated alloy carbides are formed in the steel to strengthen the steel. In order to form a certain amount of carbon-nitride in microalloy steel, the carbon content only needs to be one. Carbon reduction can greatly improve the toughness and welding performance of the steel.

Mn A high Mn/C ratio is beneficial to improving the yield strength and impact toughness of steel. It can reduce the Y-a transformation temperature and facilitate the nucleation of acicular ferrite: it can increase the solubility of carbon-nitride forming elements in Y-Fe during the heating process, thus increasing the dispersion of carbides in ferrite. Amount of precipitation. Additionally, changes in the stress/strain characteristics of the steel due to high manganese can offset the strength losses of the Bauschinger effect.

S355JR steel plate uses:S355JR steel plates are commonly used in ships, boilers, pressure vessels, petroleum storage tanks, bridges, power station equipment, lifting and transportation machinery and other higher-load welded structural parts, large ships, bridges, power station equipment, medium and high-pressure boilers, and high-pressure vessels. , rolling stock, hoisting machinery, mining machinery and other large welded structural parts, used in various large-scale engineering structures and light-duty structures requiring high strength and large loads.