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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The decision to use high-strength alloy steels is based on weight and economic factors. However, long-term exposure to the solution or material still may adversely affect finishes. The delay time between plating completion and baking start typically is observed. Boeing documentation describes the methods for detecting base metal damage while in service and during overhaul.
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.
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.
M Alloy Steel (M) | TW Metals
Several in-service fractures have been attributed to improper plating technique, poor-quality plating, improper runout conditions, and 4340n metal damage caused by poor blending or machining control.
Figure 16 shows a flap track that cracked because of hydrogen embrittlement flight cycles after overhaul. This widespread reduction in metal hardness Rockwell-C hardness readings may indicate that the component cannot be salvaged. In this article, cadmium plating means cadmiumtitanium or LHE cadmium plating.
When removing damaged material from part surfaces during rework, the new transitions or radii 3440m not cause an unacceptable increase in stress concentration at the location or degrade the original design features.
However, when thick plating deposits or multiple plating operations stdel performed on a single component, the total time between initial plating start and baking start is a key factor when determining the maximum delay time allowed. The use of high-strength alloy steel parts is economical because it reduces weight, thereby allowing for more efficient aerodynamic surfaces and providing the potential for increased payload and fuel.
300M/4340M UNS K44220
In some cases, internal residual stresses are sufficiently high to cause cracking even before the part is installed. Spot face transition radii need to be such that they can be shot-peened to the requirements of the adjacent surfaces.
All deformed material must be removed before refinishing; deformed high-strength steel alloy components must not be straightened. See SOPMs and Airline personnel should follow proper maintenance procedures and Boeing-provided rework practices, checklists, and planning guidelines during maintenance and overhaul of these components. Exposed to elevated temperatures with some finishes intact or bushings installed.
The sequence of rework operations is provided in CMMs, and SOPM and CMMs, and provide guidelines that indicate when chrome must be removed during overhaul. Contact Boeing for assistance with questions about repairing or salvaging high-strength alloy steel components that appear to have been damaged by overheating.
The following are examples of stress concentrations that can lead to cracking. If the damage is local and widespread deformations are not evident, repair may be similar to that required for corrosion and pitting. However, the component still may require special consideration or rework because.
Organic coatings or sealants may crack or become brittle or discolored wide range of temperatures. This can reduce the possibility of chrome chicken-wire cracking and poor runout details. Axle heat damage caused by a wheel bearing fracture may lead to such a condition.
The microstructural anomalies stel from cadmium embrittlement can lead to component fractures in service. The degree to which the mechanical properties are changed depends on the temperature and duration of exposure.
In these cases, the cracks can propagate to the critical length and result in ductile fracture of the component. During overhaul, many landing gear components are completely stripped to replace nickel and chrome plating.
Aircraft Alloy Steel 300M / AISI E4340 Mod (AMS 6417 / AMS 6419)
Boeing also is developing supplemental, specialized techniques, such as the Barkhausen inspection, to detect base metal heat damage under chrome plating or other protective finishes. Using high-strength alloy steel for component design provides an opportunity to do the same job with less material. Determining whether cadmium has migrated into the grain boundaries of cadmium-plated, high-strength alloy steel components requires destructive stfel of the components.
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. 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. As the pit forms, it damages the shot-peened layer locally at the surface.
For example, embrittlement relief baking must begin 10 hr after sulfamate-nickel plating is completed or within 24 hr after plating begins, whichever stteel in the shortest overall bake delay. Stress concentrations can be created by mechanical damage that compromises the protective finishes and alters the compressive shot-peen layer.
For example, the trailing edge of the wing is relatively shallow. The elevated temperatures reached during hydrogen embrittlement relief baking, which is performed directly after stripping or plating operations during overhaul, effectively remove hydrogen generated during these operations.
Afterward, another temper etch inspection is done to ensure that the machining did not create more heat damage. 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. In most instances, these repairs involve rework of the base metal. 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.
After hydrogen-generating operations, relief bake delay time limits must be observed to ensure complete hydrogen removal. Key benefits of proper rework and maintenance practices include the possibility of extending the gear or component overhaul intervals time between overhaul. 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.