Machinability - The ease of metal removal during machining, the tool life obtained, the surface finish obtained, or any combination of these three.

Machine Straightening - Straightening metal bars by rolling in a straightening machine.

Macroetch Test - Deep etching steel in a hot acid solution to evaluate soundness and homogeneity without magnification.

Magnaflux Test - A method of detecting cracks, laps, and other defects by magnetizing the steel and applying fine magnetic particles (dry or suspended in solution). Presence of a surface or subsurface defect is indicated by a particle pattern.

Magnetic-Analysis Inspection - A nondestructive method of inspection for determining the existence and extent of possible defects in ferromagnetic materials. Finely divided magnetic particles, applied to the magnetized part, are attached to and outline the pattern of any magnetic leakage fields created by discontinuities.

Malleability - The property of a metal to deform when subjected to rolling or hammering. The more malleable a metal is, the easier it can be deformed.

Malleabilizing - An annealing operation performed on white cast iron for the purpose of partially or wholly transforming the combined carbon to temper carbon, and in some cases to remove completely the carbon from the iron by decarburization.

Matrix - The ground mass or principal substance in which a constituent is embedded.

McQuaid-Ehn Test - A test for revealing grain size of steel by heating above the critical range in a carbonaceous medium. This causes grains to be outlined sharply when polished, etched and viewed under a microscope. Grain sizes range from No. 8 (finest) to No. 1 (coarsest).

Mean Dimension - The average of minimum and maximum mill tolerances; generally used in connection with tubing on O.D., I.D., or wall dimension.

Mechanical Properties - Properties of a material that reveal the reaction when force is applied, or that involve the relationship between stress and strain, such as modules of elasticity, tensile strength and fatigue limit. The term "mechanical properties" is preferred to "physical properties".

Merchant Bar Quality Steel - A standard steel, free from visible pipe, widely used for general production and repair work, bracing, machine parts, welding jobs, etc. It is not particularly recommended for forging, heat-treating or complicated machine operations.

Microscopic - Extremely small-not large enough to be seen with the naked eye.

Microstructure - The structure of metals as revealed by examination of polishes and etched samples with the microscope.

Mill Edge - Replaces "band edge"; see "Edge Condition".

Modules of Elasticity - Within the proportional limit, if the stress (in lbs. per sq. inch) is divided by the strain (stretch in inches per inch) a value will be obtained which is called the modules of elasticity of the material. This value for steel is about 30,000,000.