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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For example, figure 1 shows an outer cylinder clevis plated into the lug transition. Both conditions can stesl detected by a temper etch i. Figures 8 and 9 show a severe grinding burn on a main landing gear axle that resulted in a fracture. UTM indications show white during temper etch inspections and often are found within patches of OTM, which show dark gray to black during temper etch inspection.

In general, the best practice is to initiate baking as soon as possible following a plating operation. Spot face transition radii need to be such that they can be shot-peened to the requirements of the adjacent surfaces. Less severe friction-induced heat damage can be found on inner cylinders during component overhaul. For example, the trailing edge of the wing is relatively shallow. However, the component still may require special consideration or rework because.

There are few options to restore these machined depressions to meet interface 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.

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. Finer surface finishes also may be needed to eliminate unnecessary stress concentrations, especially in areas of machined radii or undercuts.

If these components have been overheated, salvage may not be possible. The use of high-strength alloy steel parts is economical because it reduces weight, thereby allowing for more efficient aerodynamic sfeel and providing the potential for increased payload and fuel. Setel procedures such as magnetic particle inspection and LHE cadmium stylus plating can cause arc burns if appropriate precautions are not maintained during processing.


UTM formations may be accompanied by heat-induced cracking within these overheated areas that, if left in place, can propagate while in service.

300M/4340M UNS K44220

Organic coatings or sealants may crack or become brittle or discolored wide range of temperatures. If the damage is local and widespread deformations are not evident, repair may be similar to that 4340k for corrosion and pitting. The sequence of rework operations is provided in CMMs, and When grinding chrome to finish dimensions, overheating the base metal can create UTM and OTM formations under the chrome.

Wteel 17 is a scanning electron microscope view of a typical xteel embrittlement crack where separation occurs along grain boundaries.

Figures 14 and 15 show a fracture resulting from an arc burn that developed during LHE stylus cadmium plating. 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.

The degree to which the mechanical properties xteel changed depends on the temperature and duration of exposure. High-strength alloy steels are used widely in landing gear, flap track, flap support carriage, and flap actuating components on Boeing airplanes. All reworked surfaces must be shot-peened after removing material damaged by corrosion, heat, and deformation.

When a surface is machined or ground to remove damage, the reworked area should be shot-peened with proper overlap onto the existing shot-peened surface. Abusive machining and grinding operations during manufacture or overhaul.

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

Salvage was not possible. Figures 6 and 7 show service-induced heat damage on the inside diameter of a main gear outer cylinder. Similar grinding burns also have led to the fracture of flap carriage spindle journals figs.

The heat damage led to cracking through the cylinder wall.


Any rework or repair must not increase stress concentrations that degrade component durability. In most instances, these repairs involve rework of the base metal. Removing corrosion and restoring worn interfaces on a periodic basis are the main emphases of high-strength alloy steel component overhaul steeel. The microstructural anomalies resulting from cadmium embrittlement can lead to component fractures in service. In service, fatigue cracking initiated at the plating runout led to lug fracture.


These parts often are selected for placement in limited-space envelopes e. High-strength alloy steels can experience rapid crack propagation from stress corrosion under certain loading conditions.

The new plating deposits frequently are thicker than the original design configuration and deterioration of the plating adhesion.

These situations often occur when components are Inadvertently overheated in an oven. In addition, airline personnel need to understand the importance of maintaining component finishes while in service in situor on the airplane. After overhaul operations are 4304m, the component is returned to service in accordance with CMM requirements.

Design finishes are restored and new bushings with design interferences and dimensions are installed because bushing wear limits do not apply during overhaul. They need to understand the importance of maintaining component finishes while in service, follow proper rework practices, and use Boeing provided maintenance procedures, planning guidelines, and checklists during scheduled maintenance and overhaul processes. 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.

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. Figure 16 shows a flap track that cracked because of hydrogen embrittlement flight cycles after overhaul. 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.

However, long-term exposure to the solution or material still may adversely affect finishes. This damage, which occurs on a more frequent basis, is caused by vertical motion against the lower bearing surfaces. Overhaul should reflect the same careful, detailed review that occurred during the original design.