What is the difference between normalized and normalized + tempered supply conditions for 09MnNiDR material?

Normalizing, just like quenching, generates thermal microstructures and structural stresses that increase the brittleness of the material; it can also produce hardened microstructures, while tempering can eliminate these defects. ……As for specific applications, for example, in an environment subject to stress corrosion, normalizing followed by tempering would be necessary, I think… It’s just my personal opinion; I’ll wait for those more experienced experts

The purpose of normalizing is to refine the grain structure, improve toughness, and stabilize the mechanical properties of the steel, while the purpose of tempering is to relieve stress. During the cooling process in the normalizing process, since complete equilibrium cannot be achieved, it is not possible to obtain a fully balanced microstructure; internal stresses are inevitably present. The purpose of tempering is to eliminate these internal stresses. The thicker the steel, the more severe the imbalance becomes. Therefore, although the standards do not specify under what circumstances normalizing should be chosen and under what circumstances normalizing followed by tempering should be used, it is up to the designer to decide, taking into account factors such as the importance of the container, the operating conditions, and the thickness of the material.

Tempering serves more than just to relieve stress. For steels with high Cr and Mo contents, as well as high hardenability and hardness, the purpose of tempering is to reduce strength and hardness while increasing plasticity and toughness. Regarding quenching and tempering, steel that has been quenched cannot be used at all without high-temperature tempering. Tempering types include high-temperature tempering, medium-temperature tempering, and low-temperature tempering; the corresponding microstructures are tempered sorbite, tempered martensite, and tempered bainite, respectively. The tempering temperature is generally adjusted flexibly according to the required mechanical properties. The 09MnNiDR steel is not a highly hardenable material; when its thickness is not large, it can be supplied in the normalized state. As for when tempering is required, refer to clause 6.3.3 of standard GB3531-2014: when the thickness exceeds 60 mm, the steel plate can be normalized followed by rapid cooling, and then delivered after tempering. What this sentence means is that when the thickness is large, conventional air-cooled normalizing cannot ensure a sufficient cooling rate for the core area of the thick plate; as a result, the core structure ends up similar to that obtained through furnace cooling, and the grains of ferrite and pearlite formed become relatively coarse, which is detrimental to low-temperature impact strength. Therefore, accelerated cooling must be employed to ensure a sufficient cooling rate for the core material. While this approach helps maintain a proper cooling rate in the core, it also results in an excessively fast cooling rate on the surface of the thick plate, which can lead to the formation of hardened structures such as bainite. Hence, the tempering process here is intended to eliminate the residual stresses and hardened structures that arise on the surface of the thick steel plate due to the rapid cooling rate.

The expert on the 4th floor explained it extremely clearly.

Salute to the experts, thumbs up – that’s amazing!

Salute to the experts, thumbs up – that’s amazing!