What melting temperature means and why it matters
Melting temperature is the condition at which a metal transitions from solid to liquid at a specified pressure, typically standard atmospheric pressure. For alloys, melting often occurs across a temperature range rather than at a single point, reflecting a mix of solid and liquid phases. This property governs selection in casting, welding, heat treatment, and high-temperature service, because it sets the practical limits of temperature that a metal or component can withstand. In design and manufacturing, matching a metal’s melting behavior to process temperatures and service conditions helps control risks such as hot cracking, creep, and phase changes that affect strength and durability.
How melting point is defined and measured
Standard definitions and test conditions
Melting point is reported at standard pressure (one atmosphere, or 101.3 kPa) unless otherwise specified. For pure metals, this corresponds to the temperature at which solid and liquid phases coexist in equilibrium. Alloys exhibit a melting interval between the onset of liquid (solidus) and complete melting (liquidus). Test methods typically involve controlled heating of a sample while monitoring temperature and phase change, often using calibrated instruments under defined atmospheres to limit oxidation and contamination.
Key measurement methods
- Differential scanning calorimetry (DSC): measures heat flow associated with phase change to determine solidus and liquidus temperatures.
- Hot-stage microscopy: visually tracks sample behavior under heating, often combined with temperature measurement for confirmation.
- Dilatometry: detects dimensional changes at melting, useful for alloys and materials with pronounced expansion at phase transitions.
- Thermoanalytical methods are calibrated against certified reference materials to ensure comparability across labs.
Melting temperatures of common pure metals
The table below lists verified melting temperatures for widely used pure metals at or near one atmosphere. Values are rounded to the nearest degree Celsius for practical use and drawn from standard material data references to support consistent, repeatable decisions in design and processing.
| Metal | Melting Temperature (°C) | Melting Temperature (°F) | Source Type |
|---|---|---|---|
| Aluminum | 660 | 1220 | Standard reference |
| Copper | 1085 | 1984 | Standard reference |
| Gold | 1064 | 1947 | Standard reference |
| Iron | 1538 | 2800 | Standard reference |
| Lead | 327 | 621 | Standard reference |
| Magnesium | 650 | 1202 | Standard reference |
| Nickel | 1455 | 2651 | Standard reference |
| Silver | 962 | 1763 | Standard reference |
| Tin | 232 | 449 | Standard reference |
| Titanium | 1668 | 3034 | Standard reference |
| Tungsten | 3422 | 6192 | Standard reference |
| Zinc | 420 | 788 | Standard reference |
Melting temperature ranges for common alloys
Alloys melt over a temperature band, reflecting composition and microstructure. Knowing the solidus and liquidus temperatures is critical for casting, welding, and thermal processing to avoid defects and ensure sound joints. The following ranges are representative and can vary with specific grades and impurities.
| Alloy category | Typical melting range (°C) | Notes | Source Type |
|---|---|---|---|
| Carbon steel | 1425–1540 | Increases with carbon up ~0.8–1.0 wt% then decreases; higher grades shift range upward slightly. | Typical range |
| Stainless steel (304) | 1400–1450 | Austenitic alloy; range reflects Ni–Cr–Fe balance and minor elements. | Typical range |
| Brass (Cu–Zn) | 900–940 | Temperature decreases as Zn content increases; narrows melting can occur near eutectic compositions. | Typical range |
| Bronze (Cu–Sn) | 950–1050 | Solidus rises with Sn content; casting temperatures typically sit above the solidus to ensure flow. | Typical range |
| Aluminum alloys (e.g., A356) | 570–600 | Silicon-rich alloys melt near the lower end; Mg–Si systems show distinct solidus/liquidus separation. | Typical range |
| Titanium alloy (Ti–6Al–4V) | 1625–1680 | Slightly above pure Ti due to alloying; sensitive to oxygen and contamination during melting. | Typical range |
| Lead-free solder (Sn–Ag–Cu) | 217–235 | Eutectic-like behavior near ~217°C; selection depends on mechanical and thermal requirements. | Typical range |
Factors that shift melting temperatures
- Composition: Adding alloying elements generally lowers melting temperature compared to the pure metal, often introducing a melting range.
- Pressure: Melting points rise modestly with increasing pressure for most metals, a consideration in high-pressure processing environments.
- Grain structure and defects: Recrystallization, cold working, and grain boundaries can subtly influence local melting behavior, especially in highly strained materials.
- Rate of heating: Very fast heating can delay apparent melting onset (thermal inertia), while slow heating better reflects equilibrium temperatures.
- Environment and oxidation: Protective atmospheres or coatings prevent surface oxidation that can obscure true phase-change behavior during testing.
Practical implications in design and processing
In casting, pouring temperatures must remain above the liquidus but are often kept within defined windows to control shrinkage and porosity. For welding, the heat-affected zone and melt pool must stay within ranges that avoid hot cracking and detrimental phase formation. Heat treatments rely on precise temperature control relative to phase-change points to achieve desired microstructures. When specifying materials for high-temperature service, melting behavior—alongside creep resistance, oxidation tolerance, and thermal expansion—determines suitability and longevity.