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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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 to the original design requirements.

4340M / 300M VAR Cr-Ni-Mo-V Aircraft Quality Alloy Steel

stel Figure 17 is a scanning electron microscope view of a typical hydrogen embrittlement crack where separation occurs along grain boundaries. For example, when a coating such as chrome or nickel plating is applied to surfaces to prevent wear or corrosion, the coating must exhibit proper runouts that terminate before the tangent of fillet radii, edges, or other shape changes. This component developed extensive frictional heat damage in the upper bearing contact area as a result of improper clamp-up.

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. 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.

This damage generally is shallow and can be removed by machining. These characteristics, including sensitivity to corrosion pitting, susceptibility to microstructural damage resulting 43440m embrittlement, and notch sensitivity, can lead to rapid crack growth in some load environments. Bushings must be removed to permit a thorough inspection of 440m base metal and to avoid bushing-to-bore interface degradation during bake cycles. Corrosion pitting also can lead to fatigue crack initiation depending on the component, the location of pitting, and cyclic xteel conditions.

  BS EN50131 PDF

Proper use of special plating techniques, such as conforming anodes and robbers, can control plating thicknesses and runouts. High-strength alloy steels are used widely in landing gear, flap track, flap support carriage, and flap actuating components on Boeing airplanes.

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. In most instances, these repairs involve rework of the base metal. The part was subsequently shot-peened, and new protective finishes were applied over the residual active corrosion.

300M High Strength Low Alloy Steel

Exposed to elevated temperatures with some finishes intact or bushings installed. The following are examples of stress concentrations that can lead to cracking. After hydrogen-generating operations, relief bake delay time limits must be observed to ensure complete hydrogen removal.

Removing visible surface corrosion before pitting begins such as during a C-check helps prevent conditions that can lead to crack initiation.

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: Improper blending can remove the required shot-peened layer or create undercuts or grooves at the edge of the plating that can cause cracking in service.

Transitions or radii that are sharper than original design.

Aero 22 – Maintenance of High-Stregth Alloy Steel Components

Figure 16 shows a flap track that cracked because of hydrogen embrittlement flight cycles after overhaul. SOPM and CMMs, and provide guidelines that indicate when chrome must be removed during overhaul. Plating into a transition radius transition or undercut will create a stress concentration that can cause crack initiation. Using high-strength alloy steel for component design provides an opportunity to do the same job with less material.


Inspection of Aircraft Landing Gear Components by Barkhausen Noise Measurement

Other steels in use, including 9Ni-4Co Possible mechanical damage to a high-strength alloy steel component should be evaluated by the operator and repaired as needed. The decision to use high-strength alloy steels is based on weight and economic factors.

Residual cadmium often is left on a part during overhaul processing to protect it from corrosion. This also optimizes wing shape and reduces the potential need for bulging aerodynamic surfaces, which in turn reduces drag and increases airplane performance. Abusive machining and grinding operations during manufacture or overhaul. Exceeding shot-peen requirements is better than leaving areas without shotpeening. For example, figure 1 shows an outer cylinder clevis plated into the lug transition.

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.

These components provide structural benefits e. Many landing gear, flap track, flap carriage, and other flap actuating components on Boeing airplanes are made of high-strength alloy steels, such as M, Hy-Tuf, M, and M.

These high-strength materials provide significant structural benefits and can result in a weight savings.

This resulted in crack initiation and propagation while in service and the eventual fracture of the component. Truck fractures most often occur at maximum ground loads such as after fueling or during preflight taxi. This damage, which occurs on a more frequent basis, is caused by vertical motion against the lower bearing surfaces. Exposure to high temperatures during overhaul bake cycles.

Heat damage generally is removed by carefully machining the base metal. When grinding chrome to finish dimensions, overheating the base metal can create UTM and OTM formations under the chrome.