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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One type of rework or overhaul, sulfamate-nickel plating, is common on shock strut cylinder diameters and is used to repair lug faces to design dimensions as follows: Local blends stele 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. Slight or no discoloration of the enamel or primer may indicate the cadmium plating was not heated to the extent that cadmium embrittlement would be suspected.

Discontinuous shot-peening can lead to crack initiation at the tensile surface stresses adjacent to edges of abrupt compressive layer runouts no fadeout. These cracks may result in a fracture or scrap of a component when found while in service or during overhaul.

Inspection of Aircraft Landing Gear Components by Barkhausen Noise Measurement

If the plating runouts are blended or machined to remove the abrupt plating edge, the techniques must be well controlled to avoid stee, the adjacent base metal. Plating conditions and runout controls that are not in accordance with design standards. Although high-strength alloy steels are hard and resist dents, scratches, and nicks, stress concentrations caused by mechanical damage can dramatically reduce the service life of a component.


Landing gear truck fractures have occurred in service because of corrosion on the inner diameter of the main gear truck beam figs.

300M Alloy Steel (4340M)

Salvage was not possible. This section provides guidelines for reworking high-strength alloy steel components and describes some of the implications of improper rework procedures. High-strength alloy steels referenced in this article generally have been heat-treated above ksi [, psi]; most have been heat-treated above ksi.

Most can be attributed to a lack of familiarity with high-strength alloy steels. Boeing can assist in this determination.

Any rework or repair must not increase stress concentrations that degrade component durability. 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.

M (Modified) Steel | Rickard Metals

Discoloration of the enamel, primer, or chrome or evidence of cadmium damage on the inner diameter of the axle may require the heat-damaged component be removed from service. After overhaul operations steeo completed, the component is returned to service in accordance with CMM requirements.

For example, embrittlement relief baking must begin 10 hr after stefl plating is completed or within 24 hr after plating begins, whichever results in the shortest overall bake delay.

Operators also will benefit from the enhanced reliability and durability 4340j high-strength alloy steel components on their airplanes. This can reduce the possibility of chrome chicken-wire cracking and poor runout details.

When hydrogen remains in a component for an extended time, the microstructural damage that develops significantly degrades the mechanical properties of the steel. Any visible evidence of chrome plate distress can indicate the likelihood of base metal heat damage. UTM formations may be accompanied by heat-induced cracking within these overheated areas that, if left in place, can propagate while in service.


The resulting damage also could precipitate crack initiation and removal of the part from service. Figures steeel and 15 show a fracture resulting from an arc burn that developed during LHE stylus cadmium plating.

Through-thickness cracking also can lead to fatigue or stress corrosion cracking of the base metal beneath the plating. If these components have been overheated, salvage may not be possible.

Special attention is given to protective finish runouts adjacent to stress concentration details. Corrosion pits are stress concentrations. When locally machining out corrosion strel damage during overhaul, a gradual transition into the reworked depression is necessary.

Improper rework practices can result in unscheduled maintenance or surface damage that causes crack initiation. This will help operators achieve the benefits associated with high-strength alloy steels and avoid potential safety issues resulting from damage caused by stesl concentrations, detrimental surface conditions, corrosion, improper processing, or other factors.

For example, figure 1 shows an outer cylinder clevis plated into the lug transition. Possible mechanical damage to a high-strength alloy steel component should be evaluated by the operator and repaired as needed. When properly maintained and overhauled, high-strength alloy steel components demonstrate high levels of service reliability.

These fractures may be caused by a combination of degraded protective strel on the truck inner diameter, poor drainage, and contact with the corrosive chemicals in washing solutions or deicing compounds.