AL 4750, also marketed as High Perm 49, is a 48% nickel-iron soft-magnetic alloy rather than a hot-strength superalloy. It is governed by ASTM A753 Alloy 2 (UNS K94840), and is also produced to MIL-N-14411 Compositions 3 and 4, AMS 7718, and IEC 404-8-6 Alloy Class E3. Note: reference materials sometimes cite this specification as "ASTM B753" - that designation could not be verified and appears to be an error; the correct, ASTM-listed standard for this alloy family is ASTM A753.

The defining feature of AL 4750 is its balance of high saturation flux density (roughly 16,000 gauss / 1.6 tesla) with high magnetic permeability and low core loss after proper hydrogen annealing. It is used in laminated cores for instrument transformers, magnetic shields, and cores for electronic and communications equipment where high permeability at low magnetizing force improves device efficiency. This places AL 4750 in the same general nickel-iron family as other high-nickel alloys covered in this library, but its application and processing are driven by magnetic performance, not by high-temperature structural strength.

Because it is not precipitation-hardened and carries no significant chromium, molybdenum, or cobalt additions, AL 4750 does not exhibit the retained hot hardness or extreme work-hardening behavior of true nickel-base superalloys such as Inconel or Hastelloy grades. Shops that have machined Monel or 300-series stainless will recognize its general behavior more readily than shops used to age-hardened superalloys.

AL 4750 is a soft, ductile, single-phase nickel-iron alloy, and its machining behavior is closer to that of an austenitic stainless or Monel-type alloy than to an age-hardened nickel superalloy. In the fully hydrogen-annealed condition used to develop its magnetic properties, hardness runs as low as roughly 62 HRB, which makes the material soft and gummy rather than hard and abrasive. In the cold-drawn condition it work-hardens more noticeably and reaches roughly 100 HRB.

Thermal conductivity is moderate-low (on the order of 13 W/m-K), similar to austenitic stainless steel, so heat does concentrate somewhat at the cutting edge compared with plain carbon or low-alloy steels. Combined with the alloy's ductility, this creates a tendency toward built-up edge and smearing at low cutting speeds and light feeds, rather than the rapid, aggressive work hardening seen in precipitation-hardened superalloys. AL 4750 does not retain significant strength or hardness at elevated temperature the way true superalloys do, since it has no chromium-carbide or gamma-prime strengthening.

Practical countermeasures are similar in kind, if not in severity, to those used on true nickel superalloys: sharp, positive-rake cutting edges to shear rather than plow the material, a feed rate sufficient to avoid rubbing and edge smearing, rigid workholding to limit deflection in this relatively soft material, and adequate coolant to control heat and flush chips. Overall, AL 4750 is meaningfully more machinable than the Ni-Cr-Mo and Co-Cr-W superalloys elsewhere in this library.