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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Although these guidelines apply directly to landing gear components, they can be used to plan the overhaul rework of zteel high-strength steel components. This type of cracking most often occurs on surfaces that are both prone to corrosion and exposed to sustained tensile stresses while in service, such as the lower steeo of landing gear trucks, axles, and the surfaces of forward and aft trunnions.
This component developed extensive frictional heat damage in the upper bearing contact area as a result of improper clamp-up. 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.
When the entire face of a lug must be machined to remove damage, the new lug transition radii should be shaped and positioned in accordance with CMM requirements. syeel
Truck fractures most often occur at maximum ground loads such as after fueling or during preflight taxi. All portions of a component that are to be shot-peened should first be completely stripped; no cadmium residue should remain on the surface.
Bushings must be removed to stfel a thorough inspection of the base metal and to avoid bushing-to-bore interface degradation during bake cycles. Residual cadmium often is left on a part during overhaul processing to protect it from corrosion. Plating conditions and runout controls that are not in accordance with design standards.
When hydrogen remains in a component for an extended time, the microstructural damage that steek significantly degrades the mechanical properties of the steel.
Components steek of high-strength alloy steel generally weigh less and require less space to house than components made of lower strength alloys. Boeing can assist in this determination. Possible mechanical damage to a high-strength alloy steel component should be evaluated by the operator and repaired as needed. High-strength alloy steel components should be stripped completely during overhaul including removal of bushings and bearings in all structural components.
Discoloration of 44340m enamel, primer, or chrome or evidence of cadmium damage on sheel inner diameter of the axle may require the heat-damaged component be removed from service. Overheating affects components to various degrees; in some instances, only finish durability is degraded. This widespread reduction in metal hardness Rockwell-C hardness readings may indicate that the component cannot be salvaged. 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.
Components manufactured from steel alloys heat-treated above ksipsi should be reworked in accordance with guidelines in Component Maintenance Manuals CMM, and For example, figure 1 shows an outer cylinder clevis plated into the lug transition. Corrosion pitting also can lead to fatigue crack initiation depending on the component, the location of pitting, 4340j cyclic loading conditions. Slight or no discoloration of ateel enamel or primer may indicate the cadmium plating was not heated to the extent that cadmium embrittlement would be suspected.
This article discusses some factors that cause damage in service or during overhaul.
Bushings should not remain installed during overhaul unless retained by specific CMM requirements. The delay time between plating completion and baking start typically is observed.
In general, the best practice is to initiate baking as soon as possible following a plating operation. The intent is to remove eteel least amount of material possible while ensuring that all discrepant material is removed and the original design strength and durability are maintained.
Surface transitions into the lug hole and at the lug edges must have design transitions that 430m allow restoration of shot-peening on all reworked areas and permit complete seating of bushings without contacting hole edges. There are few options to restore these machined depressions to meet interface requirements.
The microstructural anomalies resulting from cadmium embrittlement can lead to component fractures in service. Overhaul should reflect the same careful, detailed review that occurred during the original design.
Operators usually recognize the benefits of using these steels; however, certain characteristics of the steels are not always given proper consideration during component maintenance or overhaul.
The pit then grows through the compressive layer, and the change in residual stress state and the pit geometry initiate stress corrosion cracking. Heat damage generally is removed by carefully machining the base metal. 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. To prevent excessive corrosion, thorough visual inspections should be performed on a regular basis to evaluate the condition of the protective finishes.
In most instances, these repairs involve rework of the base metal. All reworked surfaces must be shot-peened after removing material damaged by corrosion, heat, and deformation.
Through-thickness cracking also can lead to fatigue or stress corrosion cracking of setel base metal beneath the plating. Stress concentrations can lead to initiation of cracking by fatigue, stress corrosion, or hydrogen-assisted stress corrosion. Spot face transition radii need to be such that they can be shot-peened to the requirements of the adjacent surfaces. High-strength alloy steels are used widely in landing gear, flap track, flap support carriage, and flap actuating components on Boeing airplanes.
The following are examples of stress concentrations that can lead to cracking. Following proper rework practices and using Boeing-provided documents during maintenance and overhaul are necessary to achieve the benefits associated with high-strength alloy steel components and help ensure safe airplane operation.
High-strength alloy steel components also can be damaged by mishandling during shop rework e. If the plating runouts are blended or machined to remove the abrupt plating edge, the techniques must be well controlled to avoid damaging the adjacent base metal.
These situations often occur when components are Inadvertently strel in an oven.
Overheating will not alter the heat-treat conditions of the base metal if the temperatures are below the original tempering temperature.