Both normalized SAE-AISI and SAE-AISI M steel are iron alloys. There are 10 material properties with values for both materials. Properties with values. M is a low alloy, vacuum melted, steel of very high strength and toughness. It is a modified steel with silicon, vanadium and slightly greater carbon and. M high strength low alloy steel. M (M) is a through hardened low- alloyed with very high strength. It is a modified AISI with silicon, vanadium.

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These characteristics, including sensitivity to corrosion pitting, susceptibility to microstructural damage resulting from embrittlement, and notch sensitivity, can lead to rapid crack growth in some load environments.

Rework or overhaul of components should not introduce stress concentrations, or otherwise increase stresses, which can reduce the service life of a component below that of the original design configuration.

Ultrasonic or eddy current inspections also may be useful for in situ inspections. Spot facing on lugs is controlled to have a generous radius at the transition to the adjacent surface and usually is kept at the minimum depth necessary to clean up the damaged surface.

This widespread reduction in stee, hardness Rockwell-C hardness readings may indicate that the component cannot be salvaged. Improper rework and overhaul practices may result in loss of finish, corrosion, and damage to or alteration of the base metal, which may require unscheduled maintenance between overhauls.

When the entire face of a lug must be machined to remove damage, the new lug transition radii should be stele and positioned in accordance with CMM requirements. The planning flowcharts in CMMs, and are value-added guidelines for planning the rework of any high-strength alloy steel component on a Boeing airplane.


Local blends on inner cylinder outer diameter surfaces and outer cylinder inner diameter surfaces often are filled stewl sulfamate-nickel plating to restore them to dimensions that are suitable for 43440m chrome plate application. Less severe friction-induced heat damage can be found on inner cylinders during component overhaul.

Corrosion pitting also can lead to fatigue crack initiation depending on the component, the location of pitting, and cyclic loading conditions. However, long-term exposure to the solution or material still may adversely affect finishes.

M/M UNS K – Landmark Metals

For example, the trailing edge of the wing is relatively shallow. Salvage was not possible. Components made of high-strength alloy steel generally weigh less and require less space to house than components made of lower strength alloys.

Operators should ensure that cleaners and chemicals are tested before use in accordance with Boeing document D6Evaluation of Airplane Maintenance Materials.

Figure 17 is a scanning electron microscope view of a typical hydrogen embrittlement crack where separation occurs along grain boundaries. The resulting damage also could precipitate crack initiation and removal of the part from service.

Heat damage generally is removed by carefully machining the base metal. Overheating affects components to various degrees; in some instances, only finish durability is degraded. These parts often are selected for placement in limited-space envelopes e.

300M/4340M UNS K44220

Operators also will benefit from the enhanced reliability and durability of high-strength alloy steel components on their airplanes. Proper design will reflect generous fillets, gradual changes of shape, and the use of relief grooves in areas of high stress.

Abrupt changes in sections, holes, and sharp-cornered keyways should stwel avoided.


Chicken-wire cracking noted in SOPM indicates that the chrome should be stripped and replated. Any visible evidence of chrome plate distress can indicate the likelihood of base metal heat damage. Damage should be repaired soon after it is found.

Boeing can assist in this determination.

Some cleaners and chemicals may accelerate finish degradation and lead to corrosion. Using high-strength alloy steel flap tracks, flap carriages, and flap actuating components reduces 43440m profile and decreases spatial envelope requirements while meeting or improving aerodynamic requirements. High-strength alloy steel components should be stripped completely during overhaul including removal of bushings and bearings in all structural components.

For example, if an axle fractures as a result of chrome-grinding heat damage during manufacture or overhaul, the Barkhausen inspection allows other suspect components to be screened without first performing a chrome strip and temper etch e. These components provide structural benefits e.


If these components have been overheated, salvage may not be possible. Finer surface finishes also may be needed to eliminate unnecessary stress concentrations, especially in areas of machined radii or undercuts. All deformed material must be removed before refinishing; deformed high-strength steel alloy components must not be straightened.

This allows a thorough inspection of the base metal a primary component overhaul requirement and ensures that all finishes, including the LHE cadmium plating and conversion coating, are restored 43400m the original design requirements.