Chromium and molybdenum both individually increase the hardenability of low alloy steel. Important synergistic effects, not yet fully defined, can also occur when Cr and Mo are used in place of single elements.
Chromium brings resistance to corrosion and oxidation, high temperature strength and abrasion resistance. Molybdenum helps maintain a specified hardenability and increases high temperature tensile and creep strengths. These grades are generally heat-treated to specified properties.
Grade Designation: 41XX, PSXX (formerly EX grades)
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Chemical Composition Ranges
and Limits Charts.