Sow Molds & Dross/Drain pans · casthouses, remelt & recovery

Proper Heat Treatment for Sow Molds: Hardness, Elongation, and Wash

Written by

FerroTech Castings

in

Heat treatment is not optional paperwork

Chemistry chooses the steel class. Heat treatment (HT) sets how that steel behaves in your plant—hardness, toughness, and the ability to stretch a little (elongation) under repeated thermal shock.

For aluminum sow molds, that balance is critical. Every pour loads the cavity; every cool-down pulls heat through the mold wall. Higher casts per day with forced air or water cooling is a different thermal duty than a slow, still-air cool—and those duties need different HT targets. Ordering “a mold” without naming cooling method and cast frequency asks the steel to guess your process.

FerroTech Castings LLC (FerroTech / FTC) coordinates manufacturing of sow molds and drain pans for the worldwide aluminum industry. We deliver a full engineering drawing with customer specifications and the required heat treatment, then quote and ship against that drawing, the specification, and the purchase order. Technical expertise means matching metal class and HT to duty—not a one-hardness catalog part.

Hardness in plain language

Heat treatment rearranges crystal structure and carbon distribution so the same chemistry can deliver different mechanical results. At a high level (not a furnace recipe):

Concept Layman meaning
Hardness How strongly the surface resists indentation and wear
Strength How much load the steel can carry before it yields or breaks
Toughness Ability to absorb energy before fracture
Elongation / ductility Ability to stretch a little without cracking
Normalizing Heat, then cool in air—common balanced strength/ductility route
Quench + temper Rapid cool (water/oil) to harden, then reheat to restore toughness while keeping useful strength

Industry guidance for carbon and low-alloy steel castings is consistent: raising strength and hardness generally reduces ductility and toughness. Quenching can produce a hard structure; left as-hardened it is often too brittle for service. Tempering “softens” that extreme just enough to regain fracture resistance. Asking for maximum hardness without checking elongation is asking for cracks. Molds under thermal cycling need a specified balance, not a hardness trophy.

Too hard → little elongation → cracks show up fast

When HT pushes hardness too high for the duty, elongation drops. The mold wall cannot flex enough under each pour–cool expansion cycle. Stresses that a tougher condition would absorb open into cracks—often sooner than “months on the floor” suggested.

Hot-work mold research on tool steels under aluminum thermal cycling shows the same pattern: above an optimum hardness band, toughness falls and gross cracking risk rises; below it, surface damage worsens. Sow molds are not H13 die inserts, and we do not claim one Rockwell number for every FTC mold. The layman principle still holds: too hard and the steel snaps instead of yielding a little. High-frequency casting with forced-air or water cool steepens those temperature swings—exactly when low elongation gets expensive.

Too soft → wash from higher casting frequency

The other failure is quieter at first. When HT leaves the steel too soft for cast rate and cooling intensity, contact zones lose metal faster under molten aluminum and cleaning cycles. Plants call that wash or washout—thinned walls, lost dimensional control, early changeouts.

Higher casts per day with forced cooling accelerates that wear. A hardness that looked fine for slow air cool and few pours per day can wash out when the line ramps frequency. Softer surfaces may resist cracking briefly, then fail because cavity life in cycles of pours collapses.

The specification problem is two-sided:

  • Too hard → cracks develop quickly (low elongation / toughness)
  • Too soft → wash accelerates with increased casting frequency

“Harder is always better” and “softer is always safer” are both wrong. The answer is the hardness–toughness window for your cooling method and cast rate.

Forced air / water cool vs slow air cool — different HT

Duty is part of the HT brief.

Cooling / rate pattern What the mold sees HT implication (process-level)
Slow, still-air cool; low casts/day Gentler thermal gradients Often a milder harden-and-temper target if chemistry matches
Forced air or water cool; high casts/day Steep heat-in / heat-out cycles HT tuned for thermal fatigue + wash resistance—not max hardness, not under-hard

Cooling method changes how fast heat leaves the wall; casts per day multiplies how often that cycle repeats. Same sow drawing, different coolers → different HT job. Capture cooling and frequency before quote, with alloy class and washout history—the same process capture FTC uses for chemistry.

HT depends on low, medium, and high alloy materials

Heat treatment does not float free of chemistry. Alloy class (low / medium / high—or standard vs mid and higher duty bands) changes hardenability: how deeply and uniformly the steel responds to quench severity and section thickness.

In general steel-casting practice:

  • Lower-alloy materials often need closer matching of quench severity and section size to develop the intended structure through the wall.
  • Medium and higher-alloy materials can reach higher strength/hardness and better hardenability in thicker sections—but elongation and toughness still fall as hardness rises, so temper practice matters more, not less.
  • The right HT for a low-alloy / standard duty will not automatically suit a mid or high-alloy mold for aggressive washout duty—and the reverse is also true.

FTC does not publish proprietary chem formulas or invent unverified grade numbers here. We work from your process needs, duty history, and any chemistry or microstructure data you hold—or help you assemble enough to define clean mold-metal and HT specs on the engineering drawing. A wide range of chemical specifications and related heat treatments is available. What ships is what the drawing, the specification, and the PO call out—not a generic “shop hardness.”

What to put on the pre-quote note

Before you ask for a hardness number, list:

  1. Casts per day (or per week) and whether the line is near-continuous
  2. Cooling method: slow air vs forced air vs water
  3. Alloy class: low / medium / high (or prior standard vs mid history)
  4. Last mold failure mode: cracking, wash, or both
  5. Size family (e.g. LP1500, LP2000, LP1850) and any existing HT notes

That list usually separates a durable HT callout from an expensive guess—and keeps mold life measured in cycles of pours, not vague calendar days (see LP1500 / LP2000: Measure Mold Life in Cycles of Pours, Not Days). For the full list of what to send with a drawing, use the Pre-Quote Technical Checklist.

Next steps

When you are ready to tie heat treatment to real process duty:

  • Review ready-stock options on Inventory (including ready-stock Qty-15 FTC-LP1850 when that size fits)
  • Start an Online DRAFT Quote with size, cooling method, cast rate, and alloy-class inputs

Bring cooling method and failure history. We will help you set chemistry and heat treatment on the drawing before anything ships.

Related pages

Sources (general metallurgy — not FTC proprietary practice)

More posts