Pure Molybdenum

Recrystallisation & hot strength

Metallurgical condition as supplied Required by the standard

Unless the purchase order states otherwise, products are supplied wrought and stress relieved (SR). RX has to be called out.

The two tempers: SR = stress-relieved, RX = essentially fully recrystallized. Each carries its own set of minima, and the two sets must not be mixed.

Stress-relieved versus recrystallised Required by the standard

Recrystallisation costs pure molybdenum strength, which is why each temper has its own set of minima. On recrystallisation the specified yield strength falls from 450 to 240 MPa (about −47%) and the tensile from 515 to 415 (about −19%), while elongation rises from 10% to 20%. The hardness limit likewise changes from a 210-260 DPH band to 200 max.

⚠ The two diameter bands do not line up exactly: the SR row is 1.125-1.875 in (28.6-47.6 mm), the RX row is under 2 in (<50.8 mm). That is how the standard bands them, not something assembled here; read the pair as the same size class, not as before-and-after measurements on one bar.

The engineering consequence: once a molybdenum part is taken above its recrystallisation temperature in service, strength drops by roughly this much and does not come back. The design temperature has to sit below the recrystallisation temperature, not below the melting point.

Thermal-stability reheat test Required by the standard, conditionally

If the purchase order specifies it, the material must still meet the tensile minima after reheating in a protective atmosphere to the specified temperature for 30 min.

⚠ This is done only when the purchase order specifies it, which is why the basis is recorded as conditional. If you want the guarantee you have to write it into the order; otherwise the mill does not run the test and the certificate will not carry it.

The criterion is not "does not recrystallise" but "still meets the tensile minima after 30 min of reheating" — an acceptance test for recrystallisation resistance, which is harder evidence than a bare recrystallisation temperature.

For 360, 361 and 365 rounds 1.875 in (47.6 mm) diameter and below, the annealing temperature is 1550 °F (850 °C) — a lower temperature for the smaller sizes, which carry more prior deformation and recrystallise more readily.

Protective annealing atmosphere Required by the standard

Not permitted — Nitrogen is not an acceptable atmosphere for annealing molybdenum or molybdenum alloys.

⚠ The outright prohibition on nitrogen is unusual for an ASTM specification and worth listing on its own: at temperature, nitrogen forms nitrides with molybdenum and embrittles the surface. Many shops treat nitrogen as a general-purpose cheap inert gas; on molybdenum that is simply wrong.

All four acceptable atmospheres carry a purity threshold — argon and helium at the 5 ppm oxygen level, vacuum down to 0.0133 Pa. A protective atmosphere that misses its purity spec is not protective.

Chemical composition

Nominal: elements given only as a maximum are counted at the cap; the balance takes the remainder.

Mechanical minima by form

Guaranteed values differ by form, size and delivery condition; quotations confirm the specification, form, size and condition.

Where this grade is recommended

Matched in 16 service conditions; ranks and scores computed from the condition-scoring matrix.

Top 12 by score shown; 4 more matched conditions — browse them by industry in the selector. Open the selector →

Designations & equivalents

Cross-references are common near-equivalents for search and shortlisting; substitution across standards requires clause-by-clause verification. All grades in one cross-reference table →

Applicable standards

Name the standard and its edition on the order.

Frequently asked questions

Same series

Download PDF datasheet

Supply & enquiry

Tube & pipeφ1 – 219 × 0.25 – 25 mmPlate4.76 – 80 mmBarφ8 – 300 mmWire & filler metalsφ0.01 – 8 mm