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 damage generally is shallow and can be removed by machining. Solid-metal embrittlement by cadmium can occur at temperatures below the cadmium melting point. UTM formations may be accompanied by heat-induced cracking within these overheated areas that, if left in place, can propagate while in service. Several in-service fractures have been attributed to improper plating technique, poor-quality plating, improper runout conditions, and base metal damage caused by poor blending or machining control.

Chicken-wire cracking noted in SOPM indicates that the chrome should be stripped and replated. Plating conditions and runout controls that are not in accordance with design standards. Discontinuous shot-peening can lead to crack initiation at the tensile surface stresses adjacent to edges of abrupt compressive layer runouts no fadeout.

This 43440m can be used successfully to screen components with suspect damage. These situations often occur when components are.

The sequence of rework operations is provided in CMMs, and In general, the best practice is to initiate baking as soon as possible following a plating operation. For example, the trailing edge of the wing is relatively shallow.

300M High Strength Low Alloy Steel

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. Testing to these requirements will determine whether a cleaner or chemical is detrimental to wteel finishes or base metal.


The delay time between plating completion and baking start typically is observed.

Therefore, surface damage detection is important during overhaul and on components in service. Common techniques include detailed visual inspections and other nondestructive inspection methods, such as magnetic particle inspection MPI and fluorescent penetrant inspection FPI.

M (Modified) Steel | Rickard Metals

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. Corrosion pitting also can lead to fatigue crack initiation depending on the component, the location of pitting, and cyclic loading conditions.

Other steels in use, including 9Ni-4Co Removing or damaging the shot-peened layer can reduce the protection that this compressive layer provides against fatigue and stress corrosion crack initiation. Airline personnel should follow proper maintenance procedures and Boeing-provided rework practices, checklists, and planning guidelines during maintenance and overhaul of these components.

Refer to the Aircraft Maintenance Manual for materials specified for aircraft cleaning and deicing.

M / E Mod Alloy Steel (AMS / AMS )

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

Processes that must be followed with relief baking include chrome, sulfamate-nickel, and LHE cadmium plating; stripping operations; and many nital etch inspections. If the plating runouts are blended or machined to remove the abrupt plating edge, the techniques must be well controlled to avoid 43400m the adjacent base metal.

300M/4340M UNS K44220

Exposure to high temperatures during overhaul bake cycles. This widespread reduction in metal hardness Rockwell-C hardness readings may indicate that the component cannot be salvaged. Boeing documentation describes the methods for detecting base metal damage while in service and during overhaul. These situations often occur when components are Inadvertently overheated in an oven. When removing damaged material from part surfaces during rework, the new transitions or radii should not cause an unacceptable increase in stress concentration at the location or degrade the original design features.


Boeing SOPM guidelines should be followed for the rework of any component and for all types of plating or coating. Components manufactured from steel alloys heat-treated above ksipsi should be reworked in accordance with guidelines in Component Maintenance Manuals CMM, and When grinding chrome to finish dimensions, overheating the base metal can create UTM and OTM formations under the chrome.

Figure 16 shows a flap track that stteel because of hydrogen embrittlement flight cycles after overhaul. 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. When hydrogen remains in a component for an extended time, the microstructural damage that develops significantly degrades the mechanical properties of the steel.

In some cases, internal residual stresses are sufficiently high to cause cracking even tseel the part is installed. When the component is removed for overhaul, all evidence of corrosion must be removed and finishes restored to design requirements or better.

Both conditions can be detected by a temper etch i. These components provide structural benefits e. Plating into a transition radius transition or undercut will create a stress concentration that can cause crack initiation. When locally machining out corrosion or damage during overhaul, a gradual transition into the reworked depression is necessary.

Design finishes are restored and new bushings with design interferences and dimensions are installed because bushing wear limits do not apply during overhaul.