Jethete M448 traces back to Firth-Vickers 448, a stainless steel documented in period ASM Alloy Digest technical literature from the same Sheffield producer responsible for the better-known Jethete M152 and Jethete X-series martensitic grades. Unlike its Jethete PH-martensitic siblings, the verified reference source for grade 448 characterizes it as a ferritic-type stainless steel valued for high oxidation resistance and retained strength at elevated temperature, with good creep resistance reported in roughly the 1020-1200°F (550-650°C) range. That places it in a different metallurgical family from M152, X19, and X20 — it is not a nitrogen-bearing, precipitation/creep-resisting martensitic alloy, but a high-chromium ferritic grade selected primarily for oxidation and scaling resistance in continuous elevated-temperature service.

Because this is a genuinely less-documented trade name, a fully verified modern composition table and current governing specification could not be confirmed from publicly available technical sources at the time of writing. If M448 is called out on a drawing, confirm the exact British Standard/DTD reference and mill chemistry directly — do not assume interchangeability with the martensitic Jethete grades based on the shared "Jethete" branding alone.

No independently verifiable modern UNS, DIN/Wnr., or AISI cross-reference for M448 was found in publicly accessible technical sources. Confirm the governing specification from the engineering drawing or mill certificate.

A verified, source-backed composition table for M448 specifically could not be confirmed and is intentionally omitted rather than published as an estimate. As general family context, high-chromium ferritic heat-resisting stainless steels of this era and service class are typically low-carbon, low-nickel alloys in the 17-27% chromium range with silicon additions for scaling resistance — request the mill certificate for exact values.

Ferritic heat-resisting stainless steels in this class generally machine more predictably than austenitic or martensitic PH grades — they do not work-harden as aggressively, and cutting forces are moderate compared to a hardened-and-tempered martensitic alloy of similar chromium content. The main challenge is abrasive flank wear from the high chromium carbide content and, on some heats, coarse grain structure from high-temperature service history, which can produce an inconsistent surface finish if the tool is not kept sharp.

Positive-rake, sharp inserts with steady feed rates give the best results; avoid light, dwelling passes that glaze the surface. Coolant helps manage the heat concentration typical of any stainless grade with low thermal conductivity and assists in evacuating chips. As with any unfamiliar or historic specification, a test cut on the actual certified stock is strongly recommended before committing to production speeds.

Representative starting values for a ferritic heat-resisting stainless in the annealed condition — confirm actual hardness before finalizing.

Turning

Parting / Grooving

Milling