FI84369C - Maraging steel - Google Patents

Description

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Maraging steel

The invention relates to a certain type of maraging steel, its manufacture and use.

In general, the so-called maraging steels have been known 5 since the 1960s. Usually they have been used in customized products.

A maraging-type steel of a certain composition has now been invented, which can also be used in cast products, and in particular in cast products with a large cross-section.

The invention and some embodiments thereof are precisely defined in the claims.

Some embodiments of the invention are described in detail below.

15 Maraging-type steel is an iron-based alloy which is solution-annealed in the austenitic region and which, on cooling to room temperature, becomes martensitic. The martensite reaction is promoted by the rich alloying of the steel. Martensite is precipitated with intermetallic compounds by precipitation annealing at a temperature in the range of about 400 to 600 ° C. For intermetallic compounds, at least two of the following alloying elements are alloyed to the steel: cobalt, molybdenum and titanium. The strength and hardness of the steel is based on this separation process as well as the martensitic matrix. The carbon is an impurity and should have a content of not more than 0.05 S, preferably not more than 0.02%, in large castings preferably not more than 0.01%.

The concentrations of the alloying materials of the maraging steel used according to the invention are: 30 Ni 17 - 19%

Mo 4 - 6%

Co 10 - 13%

Ti <0.35 S.

The maximum concentrations of impurities are: 35 C <0.02%, Miel. <0.002%

Si <0.1%, Miel. <0.01%

Mn <0.1%, Miel. <0.05% P <0.01%, Miel. <0.005% 2 84369 S <0.01%, Miel. <0.001%

Cr <0.2%, Miel. <0.04%.

One of the most critical impurities is carbon, which, on slow cooling, forms large Ti (c, N) deposits on the grain boundaries, thus impairing toughness.

Steel is best made in the so-called. Using the VODC (Vacuum Oxygen Decarburization Converter) method. This achieves the required low concentrations of C, S, H, O and N.

10 The mechanical properties of steel are: tensile test

Re 2 1650 MPa (veto)

Re 2 2000 MPa (compression)

Rm J> 1730 MPa 15 As 2. 6% Z 2. 15%

Charpy V-notch impact test CVN 2 15 J at 20 ° C fracture toughness 20 KIC 2 80 MPaVm at 20 ° C

Rue 2. 140 MPaVm at 20 ° C.

Typical heat treatment temperatures are: homogenization approx. 1200 ° C solution annealing approx. 900 ° C 25 precipitation hardening approx. 450 ° C

Variations in precipitation time do not have a significant effect on mechanical properties.

The weldability of steel is also good with large cross sections. The mechanical properties of the welding area correspond to the properties of the 30 base materials. The best results are obtained when welding is performed before solution and precipitation hardening. The composition of the welding material is essentially the same as that of the parent metal. Preheating is not required. It is recommended to use low energy for welding.

35 Steel can be machined in a dissolved state. Then the machinability properties correspond to the properties of AISI 4340 martensitic steel hardened to the same hardness level (30 to 35 HRC).

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When hardened, the hardness of the steel is 50 to 53 HRC. In this mode, the machining speed per age of the machining tool is almost twice as high as with AISI 4340 hardened to the same hardness. However, with the steel 5 according to the invention, the machining does not normally have to be carried out by precipitation hardening, because the dimensional changes in the precipitation are very small, only about 0.05%.

In particular, machined parts with a large cross-section can be made of steel as follows: 1. A blank (hardness 280 to 320 HV) is produced from maraging steel as described above.

2. Coarse the blank.

3. Relieve stresses at 800-900 ° C, air cool. (Stress can occur, for example, in uneven machining.) 4. Perform the final machining.

5. Separation harden to final hardness (500-800 HV) at 450-500 ° C, air cooled.

6. Finishing is performed.

20 Compared to the same part production process using conventional ultra-hard tool steel, the following advantages are achieved: at least three machining or heat treatment steps are avoided, 25 - heat treatment costs are saved, - faster delivery times are saved, machining costs are saved deformations in heat treatment.

The uses of the steel according to the invention are in particular: aluminum die-casting tools, plastic injection molds and extrusion tools, sheet metal stamping and stamping tools , 5 - hydraulic equipment, springs, force transducers.

Claims (6)

1. Maraging steel is characterized in that it contains the following substances as alloys: Ni, Mo, Co and Ti, and that the concentrations of these alloys are: Maraging steel according to claim 1 for use as a material for castings. A maraging steel according to claim 2 for use as a material for castings with a large cross-section. Method for producing maraging steel, characterized in that the steel according to one of Claims 1 to 3 is produced in a VODC converter. A method for producing castings, in which a blank is made of steel, machined and hardened, characterized in that a blank is made of maraging steel according to one of claims 1 to 3. 5 Ni approx. 17 - 19% Mo approx. 4 - 6% Co approx. 10 - 13% Ti <approx. 0.35% and that the maximum concentrations of impurities C, Si, Μη, P, S and Cr are: C <about 0.02%, Miel. n. <0.002% Si <n. 0.1%, Miel. n. <0.01% Mn <n. 0.1%, Miel. n. <0.05% P <n. 0.01%, Miel. n. <0.005% 15 S <about 0.01%, Miel. n. <0.001% Cr <n. 0.2%, Miel. n. <0.04%. 5 84369 The method according to claim 5, characterized by the following steps: preparing a preform from the maraging steel according to any one of claims 1 to 3, coarse machining the preform, releasing stresses at about 800 to 900 ° C HV at a temperature of approx. 450-500 ° C. 6 84369