Q345D round steel – normalized
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Question: Is there a significant difference between the hot-rolled and normalized states of Q345D round steel? Is there a comparison of chemical composition and mechanical properties? I am overwhelmed with tears as I write this, filled with gratitude! :)
Q345D round steel is available in three forms: hot-rolled, forged, and cold-drawn. The specifications for hot-rolled round bars are 5.5–250 millimeters. Among them: small round bars with a diameter of 5.5–25 millimeters are mostly supplied in straight strands bundled together, and are commonly used as rebar, bolts, and various mechanical parts ； Round bars larger than 25 millimeters are mainly used for manufacturing mechanical parts and the billets for seamless steel pipes.
The concepts of hot rolling and normalizing do not refer to the same property; hot rolling is a state of steel processing, as opposed to the processing states of cold drawing and cold extrusion； Normalizing is a heat treatment method for steel, as opposed to tempering, annealing, and quenching
You can refer to GBT1591; both of the delivery states you mentioned fall under the same standard. If they are part of the same standard, then this delivery state does not affect the chemical composition, meaning the chemical composition remains the same. The so-called delivery condition can be understood as the final heat treatment process prior to leaving the steel plant. Normalizing is generally considered better than hot rolling; hot rolling is the process by which the steel sheet is shaped, while normalizing involves hot rolling followed by further heat treatment. However, the standards mentioned above do not separate the mechanical properties of the hot-rolled and normalized states. In my opinion, this is because the requirements for such materials are not strict or important, which is why no distinction is made
What are the specific differences between quenching and annealing?
The chemical composition and mechanical properties can refer to GB/T1591. Standardly speaking, hot-rolled Q345D and normalized Q345D are merely two heat treatment states. But in reality, the grains in the normalized state are finer, and the low-temperature impact toughness is higher. When the diameter of the steel rod is very large, hot rolling may not be sufficient to meet the requirements for low-temperature impact toughness. Of course, when the diameter of the steel bar is very large, normalizing may not be sufficient to meet both the requirements for tensile strength and low-temperature impact toughness; in such cases, normalizing + tempering or quenching + tempering is required.