Heat changes the physical or chemical structure of just about everything. Once most solids reach a certain temperature, they change their state.
You probably remember learning this during a science experiment in elementary school where you used water to explore solid, liquid, and gaseous states. In this lesson, you discovered that ice is just water in a solid state. Warm it up enough, and the ice will melt back to its liquid form. Continue to heat the liquid, and it will eventually become a gas in the form of steam.
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Ice changes from a solid to a liquid when it reaches a temperature known as the melting point. For water, that point is 32°F or 0°C. You’ll notice this is also the freezing point of water. At the melting/freezing point, a substance exists in a perfect equilibrium between melted and frozen. Cool things off a single degree, and the substance will begin to solidify. Heat it up, and the product will start to liquify.
Unlike water, other solids change directly into a gas through a process known as sublimation while still others decompose through another physical or chemical reaction.
Not metal, though.
When exposed to a high enough temperature, metals melt. They also soften when subjected to high heat that doesn’t reach the melting point. Soft metals are more malleable, meaning artisans and metal workers can bend them into beautiful or useful shapes.
All metal does not have the same melting point. Not even all grades of the same metal will melt at the same temperature.
Let’s talk specifically about stainless steel’s melting point.
If you are a metal worker or engineer who processes stainless steel in a high temperature setting, you need to know the melting point. Otherwise, you might turn a once useful piece of steel into a mess.
The melting point may not affect the users, but it matters to the workers. Melting and casting stainless steel depends on getting the temperature just right.
The melting point of steel isn’t only important to steelworkers who are crafting structural supports. It’s also critical to stainless steel that will be used to manufacture kitchen appliances or medical supplies.
With all these factors to consider, how do researchers pinpoint the exact melting point of an alloy?
They use something called the melting point determination principle. This principle relies on a material’s change in light conduction capacity to determine the melting point. A solid crystalline substance will move across five points of light conductivity, finally reaching a clear point at its liquid state.
Researchers use the capillary method to ascertain the melting point determination of an element or alloy. They pack a sample of the material into a thin-walled capillary melting point tube located next to a heat source and a precise thermometer. The researchers then increase the temperature at a rate of one degree Celsius each minute.
When the material inside the tube reaches a completely liquid state, the researchers record the temperature as the material’s melting point.
The melting point of steel ranges from 2500-2800°F or 1371-1540°C. Why a range? Why not just a single point on the thermometer?
Unlike a pure metal such as iron, steel is an alloy. Pure metals have a precise temperature, which is their melting point. Alloys, however, include multiple elements with different melting points. Therefore, alloys do not melt or freeze at a fixed temperature.
Steel is an alloy of iron and carbon. Stainless steel also includes chromium and usually nickel and other elements in its alloy. The addition of each new element lowers the overall melting point. This is called melting point depression.
Steel is a mixture of iron and carbon that can melt between 2500-2800°F or 1371-1540°C. The melting point of steel can vary because of the different elements it contains, which can cause melting point depression. Stainless steel has chromium, nickel, and other elements, which can lower its melting point even more.
Stainless steel’s melting point falls between 2550 and 2790°F or 1400 and 1530°C.
The melting point of a particular type of stainless steel depends upon its exact chemical composition. Each element brings its own melting point into the equation. The major elements composing stainless steel are iron, chromium, and nickel.
Pure iron has a fixed melting point of 1535°C, chromium of 1890°C, and nickel of 1453°C. Compare those numbers to the 1400-1530°C range for stainless steel.
Each grade of stainless steel has a slightly different mix of elements. Consequently, the exact melting point varies across different grades.
Stainless steel comes in five families and more than 150 grades. Only 15 of these grades are commonly used, however.
The two most popular grades of stainless steel are 304 and 316. Both grades are part of the austenitic stainless steel family, which includes about two-thirds of the stainless steel produced. Austenitic stainless steel features a face-centered cubic crystal structure, which remains constant across all temperatures from cryogenic to the melting point.
Stainless steel’s melting points can vary from a low of 1375°C for grade 316 steel to a high of 1510°C for grade 430. The most common grade, 304, has a melting point of 1400-1450°C.
High temperatures affect most metals’ tensile strength. When exposed to extreme heat, steel becomes more rigid and easier to bend. For stainless steel, this usually happens at about 1000°C.
Tensile strength matters to the user.
If you are making a steel basket that will hold heavy objects in an extremely hot environment, the tensile strength of that basket will determine how much weight it can bear. The same basket may hold twice as much weight at 800°C than it can carry at 1000 degrees. High temperatures could also damage the welded joints on the basket.
Besides the physical changes the melting point can induce, it also helps determine an object’s resistance to oxidation and sulfurization. Oxygen and sulfur will both destroy iron. Stainless steel resists oxidation and sulfidation because of its chromium content. But the inclusion of nickel, which has a relatively low melting point, diminishes the protective power of chromium and exposes the iron, and thus the stainless steel, to potential damage from oxygen or sulfur.
Consequently, the melting point is an important parameter to consider when choosing materials or fabrication techniques for stainless steel.
Find out more about the benefits and uses of stainless steel on our blog.
Kloeckner Metals is a full-line stainless steel supplier and service center. Kloeckner Metals combines a national footprint with the latest fabrication and processing technologies and most innovative customer service solutions.
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