Allotropic transformation of steel

钢的工程性能的影响与其同素异构转变有关。钢的同素异构转变是它从饱和晶系中形成低温晶系的转变，以消除结构缺陷，加强它的性能。转变从饱和晶系到低温晶系的过程称为退火或马氏体转变(Martensitic transformation)。 钢的同素异构转变涉及到各种步骤和性能问题，包括形状变化，硬度的改变以及材料的微观形貌，如晶界和结构等。同素异构转变可能会影响钢的性能，特别是其强度和硬度，因此需要进行钢的同素异构转变以改善特定性能要求。

钢的同素异构转变受到环境温度和组成的影响。转变温度越低，细粒晶系变化贡献到钢的性能的可能性越大，因此，低温晶系的表现也会更好。如果组成和环境条件适当，马氏体转变可以改善钢的性能，比如弹性模量、抗拉强度、硬度、抗弯强度和开裂抵抗力等。因此，同素异构变化可能会影响材料的结构和性能，促使它们变得更加抗拉强。

In engineeringperformance of steel is particularly dependent on its solid-solution-variant transformation. The solid-solution-variant transformation of steel is the transformation of itfrom a saturated crystalline form to a low-temperature form in order to eliminate structure defects and to enhance its performance. The transformation from saturated crystallineto low-temperature crystalline form is referred to as annealing or Martensitic transformation.

The solid-solution-variant transformationof steel involves several steps and performance issues, including shape changes, hardness changes, and microstructures such as grain boundaries and structures. The solid-solution-variant transformation can affect the performance of steel, particularly its strength and hardness, requiring solid-solution-variant transformation to improve specific performance requirements.

The solid-solution-variant transformationof steel is affected by environmental temperature and composition. The lower the transformation temperature is, the greater the possibility that fine-grained crystalline changes contribute to the performance of steel, so the performance of low-temperature crystallines will be better. If the composition and environmental conditions are appropriate, the Martensitic transformation can improve the performance of steel, such as elastic modulus, tensile strength, hardness, bend strength, and fracture resistance. Thus, solid-solution-variant transformation may affect the structure and properties of materials, prompting them to become more tensile.

此外，钢的同素异构转变还影响铸造行为，强度和尺寸精度等因素。金属固溶同样影响定向凝固性，有利于增强钢的抗疲劳性能。同素异构转变还有助于缩短铸造过程，强化抗碎裂能力。此外，同素异构转变有助于改善铸件的强度，尺寸精度，减少缺陷的数量等。

另外，同素异构转变也将影响钢外表面的微观结构和外观。例如，软化表面会导致钢表面的磨损损伤。而热处理可以减少外表面的感温和磨损损伤，有助于改善零件的展开性。

In addition, the solid-solution-variant transformation of steel also affects casting behavior, strength, and dimensional accuracy factors. The metal solid solution similarly affects directional solidification, which is conducive to enhancing the fatigue performance of steel. Solid-solution-variant transformation also helps to shorten casting processes and strengthen fracture resistance. In addition, the solid-solution-variant transformation helps to improve strength, dimensional accuracy, and reduce the number of defects of castings.

Furthermore, solid-solution-variant transformation will also affect the macrostructure and appearance of the steel surface. For instance, softening the surface can result in wear and damage to the steel surface. Heat treatment can reduce the thermal sensation and damage to the surface, which helps improve the unfoldability of the part.

The Bainite Transformation of Steel

The bainite transformation, also known as bainitic transformation, is a type of phase transformation that takes place in steels during cooling. It orders atoms differently to achieve its unique structural properties. The transformed steel contains thin ribbons of ferrite and ultra-fine, needle-like particles of carbon-enriched iron (cementite). The overall composition of the bainite remains dominated by that of the initial austenite.

Bainite typically forms when steel is cooled at rates lying in between those used to form ferrite and pearlite. At rates fast enough to produce ferrite, most of the transformation usually occurs before the carbon concentration drops below the eutectoid level, avoiding the formation of pearlite. Cooling at slower speeds enables the majority of the transformation to occur in the lower-carbon environment.

Bainite formation is considered to occur in two stages. In the first stage, known as the nucleation stage, the solid solution of austenite rapidly decomposes into a supersaturated solid solution of ferrite and carbides. In the second stage, or the growth stage, the ferrite and carbides slow but eventually complete the transformation. This growth is often hindered and can sometimes cannot take place at all, ultimately leading to the formation of pearlitic microstructure instead.

Besides providing toughness, bainite also contributes to the strength of steel, as it requires little energy to form. The transformation also has some unique, beneficial mechanical properties. However, the uniform hardness of bainite can sometimes make it unsuitable for producing a desired range of mechanical properties. In such cases, the bainite can be tempered to enable the accomplishment of desired characteristics.

In conclusion, the bainite transformation is a unique form of phase transformation that occurs when steel is cooled quickly. It forms ribbons of ferrite and needle-like particles of cementite, and it can be used to produce desirable mechanical properties in steel.