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	PRODUCT DATA of 18 Ni Maraging steel, 250 grade

Material

18 Ni Maraging steel, 250 grade

General Information

The high-strength maraging steels are hardened by a reaction that does not involve carbon. Instead, they are strengthened by the precipitation at 480 C of intermetallic compounds in a low martensitic matrix. Carbon is considered an impurity in these alloys and is kept as low as commercially feasible (<0.03%)

Processing and Assembly

In the solution annealed condition (as supplied to the customer), they are very tough, relatively soft (30/35 HRc ), and therefore, readily machined and formed. After machining or forming, a precipitation hardening (aging) process, which requires no protective atmosphere and relatively low furnace temperatures, raises the hardness to a level sufficient for many tooling applications. For optimum strength and toughness, carbon, silicon, manganese, sulfur and phosporous should be held at low levels. An important aspect of maraging steels is that martensite is formed at all cooling rates and thus in all section sizes. The usual concepts of hardebility do not apply to maraging steels. Standard annealing and aging cycle: Annealed for one hour at 815° C, air cooled and aged at 480° C for three hours

Effects of Space environment

Vacuum poses no special problems. All metals in contact under vacuum conditions or in inert gas have a tendency to cold weld.

Chemical Composition

0.03C-18.5Ni-7.5Co-4.8Mo-0.4Ti, rem Fe

Name of Manufacturer

Aubert and Duval 22, rue Henri-Vuillemin • 92230 Gennevilliers - France 33 (0)1 55 02 58 00 33 (0)1 55 03 58 01 dircom@aubertduval.com www.aubertduval.com Corus Postbus 10000, 1970 CA IJmuiden, The Netherlands +31 (0) 251 499111 +31 (0) 251 470000 feedback@ corusgroup.com www.corusgroup.com

	EXPERIENCE IN PRACTICE

Development Status

Commercial Product

Equivalent Designations

Maraging 250; Maraging C250; Vascomax C250, Marval 18, c-250

Space Experience

Limited

	PHYSICAL PROPERTIES

Specific Gravity

8

Phase changes

Alloy transforms to martensite on slow cooling from annealing temperatute. Ms=230 C and Mf=150 C approximately. These temperatures depend on the exact alloy composition. Austenite reversion occurs on overaging which depends on time and temperature and on composition.

Magnetic Properties

Ferromagnetic

Relative Permeability

77.5 Remark: at 200 oersteds

	ELASTIC PROPERTIES

Tensile Modulus

180 GPa Remark: 12 mm Plate CVM anneal 815 C+ 482 C for 3 hrs aged

Poisson Ratio

0.32

	ELECTRICAL PROPERTIES

Electrical Volume Resistivity

1.38e-7 to 2.36e-7 ohm.m

	THERMAL PROPERTIES

Thermal Conductivity

25.6 W/m.K

Thermal Expansion Coefficient

10.1 μstrain/°C

Specific Heat

0.293 J/g.K

	RELEVANT PROPERTIES FOR USE IN SPACE COMMUNITY

Corrosion/Thermal

Maraging steels corrode substantially in tap water, some neutral salt solutions and in some inorganic and organic acids. They should be protected from exposure to corrosive solutions by a suitable coating. Cathodic protection is not recommended due to the danger of hydrogen embrittlement.

Atmospheric Corrosion

Atmospheric environments such as industrial and marine atmospheres, corrode the maraging steels 12 to 25 um per year.

Stress Corrosion Status

Low Resistance to SCC: Table 3 Remark: Not for primary structural items Remark: Requires Stress corrosion evaluation form Remark: acc. to ECSS-Q-ST-70-36C Data Quality: Design Data

EMF vs SCE

-0.31 V Remark:in aged condition, in 3.5%NaCl Data Quality: Design Data

Machinability

This alloy is machined most easily in the solution treated condition. Because of its dimensional stability, machining prior to aging should be considered.

Welding

This alloy is weldable in both the solution annealed and fully heat treated conditions. Heat input to the weld area should be minimized in order to minimize the amount of reverted autenite in the heat affected zone. In general avoid prolonged times at elevated temperatures - do not preheat - keep interpass temperatures below 120 C - use minimum possible weld energy input - avoid conditions causing low cooling rates

Brazing

There are no brazing problems unique to this steel. Temperatures in the austenite reversion range should avoided Temperatures above 980 C result in grain coarsening Excellent vacuum, very dry reducing atmospheres to minimize the presence of oxides

Plating

This steel can be nitrided.

	SPECIAL RECOMMENDATIONS

Special Recommendations

The yield strength and toughness of aged material will vary from heat to heat within the specified composition limits. It is recommended that for critical applications the aging response regarding strength and toughness is determined for each heat.