Maraging steel is a kind of low carbon martensite as substrate, the intermetallic compounds by aging precipitation hardening ultra-high strength steel. Differs from the conventional high strength steel, it is not made of carbon but by dispersion analysis of intermetallic compounds out reinforcement, making it has a prominent advantages: simple and convenient heat treatment process, this is due to the martensitic transformation is not affected by the influence of cooling rate, there will not be like quenching tempering steel hardenability of problems commonly, heat treatment deformation is small, processing property and welding performance is very good.
The significant characteristic of maraging steel is still under ultra high strength with good plasticity and excellent fracture toughness, which makes it not only can replace the traditional high strength steel, and in some important areas for other application materials will be hard to replace. Such as the preparation of rockets and missiles that can be used for thin shell, under the premise that keep meet the application requirements of strength increase payload; It has a very stable performance, even in high temperature and happened after aging, the softening process is very slow. These alloys in high temperature still keep good performance, and the highest working temperature over 400 ℃. This guarantees that the rockets or warhead shell outside keep good strength in the process of flight.
Maraging steel reinforcement process is a solid solution strengthening, phase transformation strengthening, aging strengthening factors such as the result of comprehensive action. Solid solution strengthening to improve the strength of the maraging steel by 100 ~ 250 MPa, contribution is smaller. But with solid solution treatment can eliminate the residual stress of the forging rolling and composition segregation, dissolve precipitate at the same time, lays the foundation for subsequent aging of intensive. , i.e., the phase transformation strengthening organization in austenite to martensite transformation hardening that occurs, to raise the intensity of 500 ~ 600 mpa, phase transformation of martensite in the organization has the extremely high density dislocation substructure, is a major cause of improving strength, as well as the subsequent precipitation strengthening have created favorable conditions. Aging hardening is the main means to improve strength maraging steel, can make its strength increased about 1100 MPa. In the process of heat treatment by Co, Mo, Ti alloy elements such as precipitation from the supersaturated solid solution (martensite) intermetallic compound as the second phase particle to implement strong. In the process of aging, the grain boundary, phase boundary and dislocation line defect precipitate fine dispersion of intermetallic compounds.
It should be noted that special fine-grain strengthening is a kind of maraging steel can not only improve the strength, can improve toughness reinforcement method. On the grain refinement way, basically have cycle phase change refining process and deformation heat treatment process.
Cycle phase change heat treatment process is to austenite transformation product repeatedly heating, recrystallization, austenitizing, loop phase change, make the austenitic grain refinement, fully, in turn, tiny lath martensite transformation of tissue, thus improve the strength, plasticity and toughness. For example, on 3 j33 for 4 cycles of maraging steel after heat treatment, grain size by about 220 microns reduce to 15 microns, the formation of fine martensite structure. Experiments show that under the same aging procedures, high temperature solid solution plus aging treatment of metal with a high temperature solid solution + variable temperature cycle phase change, aging treatment of metal performance comparison, the mechanical properties of the latter is superior to the former.
Martensite deformation process between the solid solution and aging treatment, can also be used in solid solution treatment before, the former increases the dislocation density, the latter can refine austenite grain size. According to the report, about 18 ni7co5mo0. 1 to 90% ti cold rolling deformation and aging treatment can make the yield strength increases by about 547 MPa, while keeping the material toughness.