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Characteristics Of Hot Rolled Steel And Normalized Steel
Jun 13, 2017

Hot Rolled Steel and normalized steel composition and performance (1) Hot Rolled Steel strengthening mechanism: solid solution strengthening, yield strength: 294 ~ 392MPa grade, alloy: C-Mn or Mn-Si system, the main alloying elements: Mn, Mn -Si, auxiliary alloying elements: V, Nb, to achieve the role of grain refinement and precipitation strengthening of the use of state: hot rolling typical steel: 16Mn, organization: fine ferrite + pearlite general composition range: C ≤ 0.2%, Si≤0.55%, Mn≤1.5%, in this range, the strength and toughness are very good, welding is also good, but if C> 0.3%, Si> 0.6%, Mn> 1.6%, welding Greatly worse. (2) normalizing steel It is reinforced by solid solution strengthening and diffusion phase strengthening, which is based on the hot-rolled steel with V, Ti, Nb through the formation of dispersed phase to further improve the strength, so its yield Strength is higher than hot rolled steel.

Hot Rolled Steel: carbon equivalent is relatively low, in addition to the ambient temperature is very low or steel plate thickness is very large, under normal circumstances the crack tendency is not large. Normalized steel: carbon equivalent does not exceed 0.5%, the hardening tend to hot rolled steel, but not serious, welding is acceptable, but for thick plate often need to warm up. When the carbon equivalent is greater than 0.5%, the tendency of hardening and cold cracking tends to increase. Preventive measures: strict control of line energy, preheating and post-weld heat treatment. * 2 reheat cracks 1) C-Mn and Mn-Si hot rolled steels are insensitive to reheat cracking, eg 16Mn; (2) some of the normalized steels contain strong carbide forming elements, but it is proven that Thermal cracking is not sensitive, such as 15MnVN; (3) normalizing + tempering steel, such as 18MnMoNb, 14MnMoV there is a slight reheat cracking sensitivity, can improve the preheating temperature and immediately after welding heat to prevent reheat cracking The

 (Such as Z-to-steel), improve the joint form and reduce the stress strain of the Z-direction of the steel plate, and use the welding material or the pre-stack with lower strength level under the premise of satisfying the requirement of using the product. Low-strength weld, the use of preheating and hydrogen reduction and other measures, are conducive to prevent layered tear. 2.4 layered tearing * 3 brittle welding of welded joints Hot Rolled Steel and normalized steel, there is overheating zone brittle problem, in addition, some of the low alloying elements in the steel, sometimes there will be thermal strain embrittlement problems. * (1) the embrittlement of the overheated zone ① austenite serious growth → Wei body, coarse martensite, mixed organization, M-A components, ② refractory melting point of the dissolved. ① Hot Rolled Steel welding line energy is too large: lead to slow cooling rate, the overheating area will grow due to grain growth or Wei's organization and so on to reduce the toughness; welding line energy is too small: due to overheating tissue martensite ratio Increasing the toughness to reduce, which is more obvious when the carbon content is high. * ② Hot Rolled Steel on the V, Nb normalized steel when the line energy is too large: will lead to superheat sedimentation phase solid solution, then V, Nb carbon, nitrogen compounds refinement of grain, inhibition of austenite length Large-scale effect is greatly weakened, the austenite grains in the superheated area grow significantly, and a series of unfavorable tissue changes may occur during the cooling process, such as weir, coarse martensite, and very low plasticity (ferrite , High-carbon martensite and bainite) and MA components, together with the superheat zone of metal carbon, nitrogen solid solution increased, resulting in reduced toughness and aging sensitivity increased overheating.