Solution treatment is a core process for optimizing the microstructure and properties of stainless steel plates. It involves heating to high temperatures to fully dissolve carbides and alloying elements into the austenite matrix, followed by rapid cooling to solidify a uniform solution-treated microstructure. During this process, fluctuations in the solution treatment temperature have a significant impact on grain size and mechanical properties. Essentially, temperature changes alter the atomic diffusion rate, grain boundary migration ability, and phase transformation kinetics, thereby regulating the nucleation and growth behavior of austenite grains.
As the solution treatment temperature increases, the thermal activation energy of atoms strengthens, and the grain boundary migration rate accelerates, causing austenite grains to grow rapidly by engulfing surrounding smaller grains. This grain coarsening phenomenon is particularly pronounced at high temperatures. For example, when the temperature exceeds a critical value, the grain growth rate increases exponentially, the grain boundary area decreases significantly, and the microstructure uniformity declines. Conversely, if the solution temperature is too low, atomic diffusion is insufficient, carbide dissolution is incomplete, the austenite nucleation density decreases, and although the grain size is small, its distribution is uneven. Undissolved carbide or ferrite phases may remain in localized areas, forming microstructural defects.
Variations in grain size directly affect the mechanical properties of stainless steel plates. Fine, uniform austenitic grains improve the yield strength and tensile strength of the material. This is because grain boundaries, acting as barriers to dislocation movement, effectively hinder the propagation of slip bands during plastic deformation, thereby enhancing the material's resistance to deformation. Simultaneously, fine-grained structures increase crack propagation paths, improving fracture toughness and reducing the risk of brittle fracture. However, when the solution treatment temperature is too high, leading to grain coarsening, the grain boundary area decreases, the dislocation pile-up effect weakens, and the material strength declines. Furthermore, coarse-grained structures are prone to stress concentration under stress, reducing the resistance to crack initiation and propagation, resulting in deteriorated toughness.
Fluctuations in solution treatment temperature also affect the corrosion resistance of stainless steel plates. While high-temperature solution treatment can promote carbide dissolution and reduce chromium-depleted areas between grains, excessively high temperatures leading to grain coarsening can actually reduce the grain boundaries' resistance to corrosive media. For example, coarse-grained structures exhibit an increased tendency for carbide precipitation at grain boundaries, making them more susceptible to pitting corrosion or stress corrosion cracking in chloride-containing corrosive environments. If low-temperature solution treatment fails to completely dissolve carbides, the remaining Cr₂₃C₆ phase will form chromium-depleted zones, significantly reducing the material's resistance to intergranular corrosion.
Stainless steel plates with different compositions exhibit varying sensitivities to solution temperature fluctuations. For example, austenitic stainless steels containing stabilizing elements (such as titanium and niobium) can broaden their solution temperature window by forming TiC or NbC to inhibit grain growth. However, high-carbon martensitic stainless steels require strict temperature control during solution treatment to avoid austenite grain coarsening, which would lead to excessively high residual austenite content after quenching, affecting hardness and wear resistance. Furthermore, the solution treatment of duplex stainless steels must balance the ferrite and austenite phases; temperature fluctuations may disrupt the phase ratio, resulting in an imbalance between mechanical properties and corrosion resistance.
To optimize the performance of stainless steel plates, the solution temperature must be precisely controlled based on the material composition and application scenario. For example, 316LN stainless steel used in nuclear power plants requires a grain size higher than the ASTM standard, and its solution treatment temperature must be strictly limited to a specific range to avoid excessive grain growth affecting high-temperature creep performance. Food-grade 304 stainless steel, on the other hand, needs to balance strength and corrosion resistance, achieving a fine and uniform austenitic structure through medium-temperature solution treatment.
Fluctuations in solution treatment temperature have a profound impact on the grain size and mechanical properties of stainless steel plates by regulating atomic diffusion, grain boundary migration, and phase transformation behavior. Reasonable control of the temperature range is key to optimizing the overall performance of the material, requiring systematic process optimization combining composition design, microstructure evolution, and service conditions.
