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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Improper rework and overhaul practices may result in loss of finish, corrosion, and damage to or alteration of the 4430m metal, which may require unscheduled maintenance between overhauls. Components manufactured from steel alloys heat-treated above ksipsi should be reworked in accordance with guidelines in Component Maintenance Manuals CMM, and If the damage is local and widespread deformations are not evident, repair may be similar to that required for corrosion and pitting.

300M High Strength Low Alloy Steel

This type of cracking most often occurs on surfaces that are stele prone to corrosion and exposed to sustained tensile stresses while in service, such as the lower surface of landing gear trucks, axles, and the surfaces of forward and aft trunnions. The decision to use high-strength alloy steels is based on weight and economic factors.

Processes that must be followed with relief baking include chrome, sulfamate-nickel, and LHE cadmium plating; stripping operations; and many nital etch inspections. Shop procedures such as magnetic particle inspection and LHE cadmium stylus plating can cause arc burns if appropriate precautions are not maintained during processing. Removing or damaging the shot-peened layer can reduce the protection that this compressive layer provides against fatigue and stress corrosion crack initiation.

When removing damaged material from part surfaces during rework, the new transitions or radii should not cause an unacceptable increase in stress concentration at the location or degrade the original design features.

Common techniques include detailed visual inspections and other nondestructive inspection methods, such as magnetic particle inspection MPI and fluorescent penetrant inspection FPI.

This includes repairing damaged finishes to prevent corrosion and ensuring that solvents and materials that come in contact with the finishes do not result in premature degradation and unscheduled component removal. SOPM and CMMs, and provide guidelines that indicate when chrome must be removed during overhaul. 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.


Corrosion pitting also can lead to fatigue crack initiation depending on the component, the location of pitting, and cyclic loading conditions. Figure 16 shows a flap track that cracked because of hydrogen embrittlement flight cycles after overhaul. These situations often occur when components are Inadvertently overheated in an oven.

Aero 22 – Maintenance of High-Stregth Alloy Steel Components

Airline personnel who participate in component rework, maintenance, and overhaul tasks should be familiar with the properties of high-strength steels and understand the negative effects that can result from. As the pit forms, it damages the shot-peened layer locally at the surface. The following are examples of stress concentrations that can lead to cracking. These cracks may result in a fracture or scrap of a component steeel found while in service or tseel overhaul.

There are few options to restore these machined depressions to meet interface requirements. For example, embrittlement relief baking must begin 10 hr after sulfamate-nickel plating is completed or within 24 hr after plating begins, whichever results in the shortest overall bake delay. Local blends on inner cylinder outer diameter surfaces and outer cylinder inner diameter surfaces often are filled with sulfamate-nickel plating to restore them to dimensions that are suitable for subsequent chrome plate application.

Figures 8 and 9 show a severe grinding burn on a main landing gear axle that resulted in a fracture. Airframe space for gear components may be reduced because of smaller diameter shock strut components, smaller pins reduced space for jointssmaller diameter trucks and axles, and, in some instances, smaller drag brace, side brace, and attach fittings.

This also optimizes wing shape and reduces the potential need for bulging aerodynamic surfaces, which in turn reduces drag and increases airplane performance. These fractures may be caused by a combination of degraded protective finishes on the truck inner diameter, poor drainage, and contact with the corrosive chemicals in washing solutions or deicing compounds.

For example, the trailing edge of the wing is relatively shallow. Contact Boeing for assistance, if needed. High-strength alloy steels are used widely in landing gear, flap track, flap support carriage, and flap actuating components on Boeing airplanes.

300M/4340M UNS K44220

430m 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. Personnel must ensure that materials used for activities such as cleaning and deicing conform to Boeing document D requirements and will accomplish the intended task verified by the material provider or operator.


Abusive machining and grinding operations during manufacture or overhaul. Some heat damage is so severe that the heat-treat condition of material is altered in adjacent areas.

The sequence of rework operations is provided in CMMs, and Possible mechanical damage to a high-strength alloy steel component should be evaluated by the operator 44340m repaired as needed.

See SOPMs and When the entire face of a lug must be machined to remove damage, the new lug transition steeo should be shaped 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. The part was subsequently shot-peened, and new protective finishes were applied over the residual active corrosion.


Visual evidence of chicken-wire cracking after chrome grinding indicates poor chrome quality and also may indicate the possibility of base metal heat damage. Heat damage generally is removed by carefully machining the base metal. Chicken-wire cracking noted in SOPM indicates that the chrome should be stripped and replated.

Through-thickness cracking also can lead to fatigue or stress corrosion cracking of the base metal beneath the plating. Surface transitions into the lug hole and at the lug edges must have design transitions that will allow restoration of shot-peening on all reworked areas and permit complete seating of bushings without contacting hole edges.

Key benefits of proper rework and maintenance practices include the possibility of extending the gear or component overhaul intervals time between overhaul.

M High Strength Low Alloy Steel,M alloy steel bar suppliers | Shew-E Steel Pipe

Some cleaners and chemicals may accelerate finish degradation and lead to corrosion. Finer surface finishes also may be needed to eliminate unnecessary stress concentrations, especially in areas of machined radii or undercuts. As a rule, if material removal exceeds 0. All portions of a component that are to be shot-peened should first be completely stripped; no cadmium residue should remain on the surface.

Exposure to high temperatures during overhaul bake cycles. Bushings must be removed to permit a thorough inspection of the base metal and to avoid bushing-to-bore interface degradation during bake cycles.

Typically, hydrogen embrittlement cracks propagate rapidly once loads are applied to the part. For example, figure 1 shows an outer cylinder clevis plated into the lug transition.

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