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低合金高强度铸钢具有与相应锻钢同样的优点:主要是优异的强韧性和良好的可焊性。要获得低合金高强度铸钢所可能获得的突出的机械性能,成份与显微组织的控制必不可少。奥氏体晶粒细化,铁素体晶粒细化、奥氏体控制转变(通常主要转变为铁素体)以及这些参数与氧化物、碳化物和碳氮化合物析出的相互作用,均可影响所得到的特定强韧性。列举了Mn—Mo—Nb—V系铸钢的组织与性能,以阐明不同热处理的优点和截面尺寸的作用。针状的铸态组织可分别获得高达795兆帕和660兆帕的抗拉强度和屈服强度,经长期时效后还可保持。二次奥氏体化的热处理,在仍具有较高的强度时,常显著改善韧性。例如,一种0.10C—0.006N—0.04Nb—0.06V—1.65Mn—0.4Mo合金铸钢,在正火和时效状态下主要为细晶粒的多边形铁素体组织,具有192HB的硬度,620兆帕的抗拉强度,460兆帕的屈服强度,29％的廷伸率,67％的断面收缩率和39焦的-40℃夏氏V形缺口冲击能(CVN)。正火和时效前的均匀化处理减少偏析、细化晶粒并在保持同样高的韧性水平下提高硬度。低合金高强度铸钢潜在应用范围极广,尤其是在既保持强度、韧性和可焊性,又要提高具有可比屈服强度的钢的高温强度和降低合金化成本的场合。目前,低合金高强度铸钢大都用于近海采油工业中采油平台的接头和结节类部件,以及蒸汽和天然气压缩系统中的壳体和承压件。不过,在铁路工业和矿物输送系统中的新应用也正在掘起,因为设计师门认识到这些铸钢件能有效应用于焊接组件之中,以减少复杂焊缝的数量和减少结构连接处的应力集中。
Low alloy high strength cast steel has the same advantages as the corresponding forged steel: mainly excellent toughness and good weldability. In order to obtain the outstanding mechanical properties that may be obtained with low alloy high strength cast steel, the control of composition and microstructure is essential. The austenite grain refinement, ferrite grain refinement, austenite controlled transformation (usually predominantly ferrite) and the interaction of these parameters with the precipitation of oxides, carbides and carbonitrides may either Affect the resulting specific strength and toughness. The microstructure and properties of Mn-Mo-Nb-V cast steel are listed to clarify the advantages of different heat treatments and the effect of cross-sectional dimensions. Needle-like as-cast structures achieve tensile and yield strengths of up to 795 MPa and 660 MPa, respectively, and are retained after long-term aging. Secondary austenitizing heat treatment, when still having high strength, often significantly improves toughness. For example, a 0.10C-0.006N-0.04Nb-0.06V-1.65Mn-0.4Mo alloy cast steel, mainly fine grained polygonal ferrite structure under normalizing and aging conditions, has a hardness of 192HB, 620 Tensile strength at MPa, yield strength at 460 MPa, Tensile elongation at 29%, reduction in area at 67% and Charpy V-notch impact energy (CVN) at 39 ° C at -40 ° C. Homogenization before normalizing and aging reduces segregation, grain refinement and increases hardness while maintaining the same high level of toughness. Low-alloy, high-strength castings offer a wide range of potential applications, especially where high-temperature strength and reduced alloying costs are achieved while maintaining strength, toughness and weldability. Currently, most low-alloy high-strength cast steels are used in joints and nodular components in oil recovery platforms in offshore production, as well as in housings and pressure components in steam and natural gas compression systems. However, new applications in the railway industry and in mineral delivery systems are also emerging as designers have realized that these castings can be effectively used in welded assemblies to reduce the number of complex welds and reduce the number of Stress concentration.