强化理论与技术

摘要：当前钢铁材料的强化理论体系主要包含四大机制：固溶强化、晶界强化、位错强化和析出强化。固溶强化是通过引入点缺陷阻碍位错滑移的强化机制，主要分为两类：一类是以C、N等间隙原子为主的间隙固溶强化，另一类是以Ni、Cr、Mo等合金元素为主的置换固溶强化；晶界强化通过细

世界金属导报

钢铁材料的强化本质在于通过微观组织调控实现对位错运动的有效抑制，从而增强材料的抗变形能力。

1 主要强化机制

当前钢铁材料的强化理论体系主要包含四大机制：固溶强化、晶界强化、位错强化和析出强化。固溶强化是通过引入点缺陷阻碍位错滑移的强化机制，主要分为两类：一类是以C、N等间隙原子为主的间隙固溶强化，另一类是以Ni、Cr、Mo等合金元素为主的置换固溶强化；晶界强化通过细化晶粒增加晶界数量，利用晶界对位错滑移的阻碍作用实现强化；位错强化依赖塑性变形或相变引入的高密度位错结构，通过位错间的相互作用抑制后续变形过程中位错的运动；析出强化则通过第二相粒子（如MC、M2C、NiAl、Ni3Ti等）在变形过程中与位错产生的切过或绕过机制，阻碍位错的运动，提高材料强度。四种强化机制的计算公式和理论强化量如表1所示。

2 协同强化实现高性能

上海大学高性能钢铁材料团队采用高位错密度的马氏体基体和组织中均匀析出的亚微米级ε-carbides实现协同强化，使材料强度提高至1800-1900MPa，冲击韧性（U型缺口）保持70J，主要原因是马氏体板条界面处的薄膜奥氏体提高了钢的韧性，见图1。

3 双析出钢的研发与创新

研究团队在传统二次硬化超高强度钢中创新性引入NiAl金属间化合物，并通过高纯净度冶炼和组织均匀化控制技术，研制出2200MPa级和2400MPa级双析出钢（图2），正在研制2800MPa级钢。

2400MPa级钢在510℃时效后的组织和析出相如图3所示。时效后，钢中的组织为高位错密度的板条马氏体，马氏体基体中均匀析出数量密度为14.5×1023m-3的NiAl和2.2×1023m-3的M2C，其中2400MPa级钢中M2C的数量密度达到单M2C析出体系AerMet100钢的3倍。在Co元素的协同作用下，马氏体基体中析出等效半径为0.5-20nm、数量密度大于1023m-3的NiAl和M2C，这些纳米相与位错的交互作用，为钢增加了超过1000MPa的屈服强度。

NiAl与M2C的协同析出机理如图4所示。时效过程中，低错配度和低形核能的NiAl相优先在基体中高密度弥散析出，为M2C提供形核点，促进M2C形核。这种协同析出效应不仅使M2C数量密度显著提升，还通过两相间的相互阻碍长大作用抑制双析出的粗化，提升析出强化量。高位错密度的马氏体基体以及纳米级NiAl与M2C的双析出是2400MPa级钢强化的来源。

（汪杨鑫胡春东）

Strengthening Theories and Technologies

Yangxin Wang, ChunDong Hu, Han Dong

Strength enhancement remains a perpetual theme in steel material research and development. Its intrinsic mechanism lies in effectively suppressing dislocation motion through microstructural regulation, thereby improving the resistance to deformation. The current theoretical framework for steel strengthening primarily comprises four mechanisms: solution strengthening, grain boundary strengthening, dislocation strengthening, and precipitation strengthening. Solution strengthening operates through point defect-induced obstruction of dislocation glide, categorized into two types: Interstitial solid solution strengthening (dominated by C, N interstitial atoms); Substitutional solid solution strengthening (mediated by alloying elements such as Ni, Cr, Mo). Grain boundary strengthening achieves strengthening via grain refinement to increase grain boundary density, utilizing the hindrance of dislocation glide by boundaries. Dislocation strengthening relies on high-density dislocation structures introduced through plastic deformation or phase transformation, where mutual interactions between dislocations impede subsequent dislocation motion. Precipitation strengthening employs second-phase particles（such as MC, M2C, NiAl, Ni3Ti）that interact with dislocations through either shearing or bypassing mechanisms during deformation, effectively obstructing dislocation movement and enhancing strength. The computational formulas and theoretical strengthening contributions of these four mechanisms are summarized in Table 1.

The High-Performance Steel Materials Team at Shanghai University has achieved synergistic strengthening by employing a high-dislocation-density martensitic matrix combined with uniformly dispersed submicron-sized ε-carbides within the microstructure. This strategy results in ultimate tensile strengths of 1800-1900 MPa while retaining an impact toughness of 70 J (U-notch). Additionally, the presence of filmy austenite at the martensite lath interfaces contributes to enhanced toughness in the steel (Figure 1).

The research team has innovatively introduced NiAl intermetallic compounds into conventional secondary hardening ultrahigh-strength steels. By employing high-purity melting and microstructural homogenization techniques, dual-precipitation steels with tensile strengths of 2200 MPa and 2400 MPa have been successfully developed (Fig. 2), and efforts are currently underway to design a 2800 MPa grade steel.

The microstructure and precipitates of the 2400 MPa-grade steel after aging at 510 °C are shown in Figure 3. Following aging, the microstructure consists of lath martensite with a high dislocation density. Within the martensitic matrix, NiAl and M2C precipitates are uniformly distributed, with number densities of 14.5×1023 m-3 and 2.2×1023 m-3, respectively. Notably, the number density of M2C in the 2400 MPa grade steel is approximately three times that of AerMet100 steel, which features a single M2C -precipitation system. Under the synergistic effect of Co, both NiAl and M2C precipitates exhibit equivalent radii ranging from 0.5 to 20 nm and number densities exceeding 1023 m-3. The strong interactions between these nanoscale precipitates and dislocations contribute to a yield strength increment of over 1000 MPa.

The synergistic precipitation mechanism of NiAl and M2C is illustrated in Figure 4. During aging, NiAl precipitates characterized by low lattice misfit and low nucleation energy, preferentially form with high number density within the matrix, providing heterogeneous nucleation sites for M2C and thereby promoting its precipitation. This synergistic effect not only significantly increases the number density of M2C, but also suppresses the coarsening of both phases through mutual growth inhibition, enhancing the overall precipitation strengthening contribution. The high dislocation density of the martensitic matrix, combined with the nanoscale dual precipitation of NiAl and M2C, serves as the primary source of strengthening in the 2400 MPa grade steel.