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Stainless steels are alloys and therefore do not melt and freeze at a fixed temperature, as do metallic elements, but over a temperature range, depending on the chemical composition of the steel. Thus on heating, alloys start to melt at temperature known as the solidus and become completely molten at the liquidus temperature.
Most alloying additions made to iron tend to suppress, (lower), the liquidus of the resulting alloy. Pure iron (Fe) has a fixed melting point of 1535°C, chromium (Cr) 1890°C and nickel (Ni) 1453°C compared with a range of 1400-1450 °C for type 304 stainless steel.
Melting ranges are very important to the steelmakers as the success of the melting and casting operations depends on the correct selection of temperature. Once solidified and primary processed (rolling or forging) by the steelmaker, the melting temperature has little significance to designers, engineers and steel users.
Although melting temperature does influence elevated temperature properties, such as creep strength, this is only of interest to researchers.
Data on creep strength at various service temperatures is available.
Melting range does not directly affect the oxidation resistance of individual heat resisting stainless steels. This is linked more closely to chromium content and is illustrated by comparing 304 and 310 types. Maximum service temperatures in air for stainless steels
Both have the same melting range of 1400-1450°C, but the maximum service temperatures in air atmospheres are 870°C for 304 type and 1050°C for 310 type.
The following table, taken from the
ASM Specialty Handbook ‘Stainless Steels’
shows the melting ranges in degrees C (°C) of some of the common stainless steel grades, grouped in their melting ranges for comparison.
Data for grades marked ‘1’ is taken from Outokumpu Stainless data sheets.
|Melting Range, oC||Steel Grades|
|1325-1400||1.4547 (254SMO) 1|
|1370-1480||440A, 1.4125 (440C)|
|1375-1400||1.4401 (316), 1.4404) 316L|
|1400-1425||1.4886 (330), 1.4541 (321), 1.4550 (347)|
|1400-1450||1.4372 (201), 1.4301 (304), 1.4307 (304L), 1.4303 (305), 1.4833 (309), 1.4845 (310)|
|1480-1530||409, 410, 416,|