Equivalent Grades: 18Ni300, Maraging 300, C300,3J33, martensitic aging steel
Maraging is a series of martensitic aged steels with a nickel content of 18% and enhanced properties through the addition of cobalt. The steel grades in this series have excellent mechanical properties, processing performance, and heat treatment performance.
Maraging300 is an ultra-high strength steel based on carbon free (or micro carbon) martensite that can produce intermetallic compound precipitation hardening during aging. Unlike traditional high-strength steel, it does not require carbon but relies on the dispersion and precipitation of intermetallic compounds for strengthening. This gives it some unique properties: high strength and toughness, low hardening index, good formability, simple heat treatment process, almost no deformation during aging, and excellent welding performance. Therefore, martensitic aging steel has been widely used in departments that require this characteristic.
Production process:
The main production processes include smelting, hot processing, cold processing, welding, heat treatment, and surface treatment.
Smelting:
The dual vacuum smelting process of vacuum induction furnace melting and vacuum consumable furnace remelting is generally adopted. For steel grades with strength levels below 1500MPa, non vacuum smelting or non vacuum smelting with electroslag remelting process can be used. However, for steel grades with high strength and important applications, the dual vacuum smelting process must be adopted. During vacuum self consumption remelting, the current and molten pool temperature should be strictly controlled to avoid severe dendritic segregation of the steel ingot.
Hot working:
Maraging steel has good thermoplastic properties at high temperatures, and its hot workability is roughly the same as that of 1Crl8Ni9Ti. For steel grades with high titanium and molybdenum content, microsegregation of these elements is prone to occur during ingot solidification, and anisotropic banded microstructures are formed after hot working. The effective measure to reduce or eliminate microsegregation is to select the appropriate ingot size and conduct sufficient high-temperature homogenization treatment during hot working. In order to prevent high-temperature slow cooling brittleness caused by the precipitation of Ti (C, N) and other compounds along the austenite grain boundaries, it is necessary to avoid slow cooling or staying in the temperature range of 1100~750C for the workpiece after hot processing. In order to obtain fine grains and better mechanical properties, final forging should be completed at a lower temperature (950-850C) with a larger deformation amount (greater than 25%).
Cold working:
The cold workability is very good in the solid solution state. Drawing, cold rolling, bending, deep drawing and other processing are all easy to carry out. The work hardening index of steel is 0.02-0.03, which is one order of magnitude lower than that of ordinary steel. Therefore, during the processing, cold processing with a deformation of over 90% can be carried out without the need for softening and annealing.
Welding:
Good weldability is one of the advantages of maraging steel. Almost all welding processes are applicable. The composition of the welding wire is basically the same as that of the welded steel, and there is no need to preheat before welding. Without treatment after welding, there will be no cracks. After direct aging, the joint coefficient can exceed 90%.
Heat treatment:
The simple heat treatment process is another important advantage of martensitic aging steel. After hot processing, Maraging300 should undergo solution treatment before cold processing and aging strengthening. The purpose is to dissolve the remaining sediment after hot processing.
Chemical composition of Maraging martensitic aging steel:
Heat treatment of Maraging martensitic aging steel:
The solid solution temperature is 815-830 ℃, oil cooled or air cooled (heating time: salt bath furnace 1min/mm, air furnace 2-2.5min/mm), and the hardness is 28HRC.
The aging temperature of Maraging250 and Maraging300 steel is 480 ℃, the holding time is 3 hours, and the hardness is 43HRC; Insulation for 6 hours, with a hardness of 52HRC.
The aging temperature of Maraging350 steel is 510 ℃, the aging time is 6 hours, and the hardness is 57-60HRC.
Nitriding treatment of Maraging martensitic aging steel:
Gas nitriding process for Maraging300 steel:
The nitriding temperature is (455 ± 10) ℃, and the insulation time is 24-28 hours.
