Or why high-alloyed heat resistant steel is better than ordinary.
There is no secret that many consumer properties of stoves strongly depend on the metal of which they are made. However, casual buyer sometimes hardly understands the meaning and importance of a "stainless alloy heat-resistant steel," of which selected stove are allegedly cooked.
To answer this question, let's consider terms and definitions.
Steel is a metal alloy consisting mostly of iron, in addition to small amounts of carbon, depending on the grade and quality of the steel. Alloy steel is any type of steel to which one or more elements have been intentionally added, besides carbon, to produce a desired physical property or characteristic. Common elements which are added to make alloy steel are molybdenum, manganese, nickel, silicon, boron, chromium, and vanadium.
Alloy steel is often subdivided into two groups: high alloy steels and low alloy steels. Most agree that any steel that is alloyed with more than eight percent of its weight being other elements beside iron and carbon, is high alloy steel. Low alloy steels are slightly more common. The physical properties of these steels are modified by the other elements, to give them greater hardness, durability, corrosion resistance, or toughness as compared to carbon steel. To achieve such properties, these alloys often require heat treatment.
In all types of alloy steel, the alloying elements tend to form either carbides or compounds, rather than simply being uniformly mixed in with the iron and carbon. Nickel, aluminum, and silicon are examples of the elements that form compounds in the steel. Tungsten and vanadium will form carbides, both of which increase the hardness and stability of the finished product.
Alloying elements are added to achieve certain properties in the material. As a guideline, alloying elements are added in lower percentages (less than 5%) to increase strength or hardenability, or in larger percentages (over 5%) to achieve special properties, such as corrosion resistance or extreme temperature stability.
Major effects of alloying elements for steel
To answer this question, let's consider terms and definitions.
Steel is a metal alloy consisting mostly of iron, in addition to small amounts of carbon, depending on the grade and quality of the steel. Alloy steel is any type of steel to which one or more elements have been intentionally added, besides carbon, to produce a desired physical property or characteristic. Common elements which are added to make alloy steel are molybdenum, manganese, nickel, silicon, boron, chromium, and vanadium.
Alloy steel is often subdivided into two groups: high alloy steels and low alloy steels. Most agree that any steel that is alloyed with more than eight percent of its weight being other elements beside iron and carbon, is high alloy steel. Low alloy steels are slightly more common. The physical properties of these steels are modified by the other elements, to give them greater hardness, durability, corrosion resistance, or toughness as compared to carbon steel. To achieve such properties, these alloys often require heat treatment.
In all types of alloy steel, the alloying elements tend to form either carbides or compounds, rather than simply being uniformly mixed in with the iron and carbon. Nickel, aluminum, and silicon are examples of the elements that form compounds in the steel. Tungsten and vanadium will form carbides, both of which increase the hardness and stability of the finished product.
Alloying elements are added to achieve certain properties in the material. As a guideline, alloying elements are added in lower percentages (less than 5%) to increase strength or hardenability, or in larger percentages (over 5%) to achieve special properties, such as corrosion resistance or extreme temperature stability.
Major effects of alloying elements for steel
Element Bismuth Boron Chromium Copper Lead Manganese Molybdenum Nickel Silicon Sulfur Titanium Tungsten Vanadium | Percentage - 0.001–0.003 0.5–2 4–18 0.1–0.4 - 0.25–0.40 >1 0.2–5 2–5 12–20 0.2–0.7 2 >2 0.08–0.15 - - 0.15 | Primary function Improves machinability A powerful hardenability agent Increases hardenability Increases corrosion resistance Corrosion resistance Improves machinability Combines with sulfur and with phosphorus to reduce the brittleness. Also helps to remove excess oxygen from molten steel. Increases hardenability by lowering transformation points and causing transformations to be sluggish Stable carbides; inhibits grain growth. Increases the toughness of steel, thus making molybdenum a very valuable alloy metal for making the cutting parts of machine tools and also the turbine blades of turbojet engines. Also used in rocket motors. Toughened Increases corrosion resistance Increases strength Spring steels Improves magnetic properties Free-machining properties Fixes carbon in inert particles; reduces martensitic hardness in chromium steels Also increases the melting point. Stable carbides; increases strength while retaining ductility; promotes fine grain structure. Increases the toughness at high temperatures |
The heat resistant (resistant to scaling) metallic material is the material with an ability to resist chemical degradation when its surface is exposed to air at high temperatures.
This property - heat resistance - along with resistance to creep and rupture determines the heat resistance, i.e. the ability of materials withstands the mechanical stresses at high temperatures without significant deformations. Typically, heat-resistant materials are very expensive and are used for the manufacture of steam and gas turbines, the external parts of supersonic aircraft, their covers and defenses, etc.
This property - heat resistance - along with resistance to creep and rupture determines the heat resistance, i.e. the ability of materials withstands the mechanical stresses at high temperatures without significant deformations. Typically, heat-resistant materials are very expensive and are used for the manufacture of steam and gas turbines, the external parts of supersonic aircraft, their covers and defenses, etc.
Chromium creates a surface’ passive film, which is not prone to oxidation to the limiting temperature, called the beginning of scaling. The higher is the temperature of scaling, the lower is the possibility of intensive oxidation of heated metal surfaces, i.e. that unpleasant phenomenon, which is called "burning of oxygen."
Perhaps the most well-known alloy steel is stainless steel. This is a steel alloy with a minimum of 10% chromium content. Stainless steel is more resistant to stains, corrosion, and rust than ordinary steel. It was discovered in 1913 by Harry Brearley of Sheffield, England. Stainless steel has also been appropriated for many famous architectural designs, such as the Chrysler Building in New York City.
Perhaps the most well-known alloy steel is stainless steel. This is a steel alloy with a minimum of 10% chromium content. Stainless steel is more resistant to stains, corrosion, and rust than ordinary steel. It was discovered in 1913 by Harry Brearley of Sheffield, England. Stainless steel has also been appropriated for many famous architectural designs, such as the Chrysler Building in New York City.
Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steel rusts readily when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide, and due to the greater volume of the iron oxide this tends to flake and fall away. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion by blocking oxygen diffusion to the steel surface and blocks corrosion from spreading into the metal's internal structure, and due to the similar size of the steel and oxide ions they bond very strongly and remain attached to the surface.
So, key property is the heat resistance, it can be ensured only when high-alloy steel chromium content of the mass fraction is 10% and more. In metallurgy, stainless steel is also known as Inox steel or Inox from French ”inoxydable”. Steels used in the manufacture of stoves, marketed under the trademark TERMOFOR, content either 13% or even 18% of chromium. That’s a key!
Steel used in the manufacture of stoves INDIGIRKA contents 13% of chromium and has a starting temperature of scaling at least 7500 C or 13800 F. Summarize, the stove INDIGIRKA is really made of heat-resistant, high-alloy, corrosion-resistant stainless steel.
Steel used in the manufacture of stoves INDIGIRKA contents 13% of chromium and has a starting temperature of scaling at least 7500 C or 13800 F. Summarize, the stove INDIGIRKA is really made of heat-resistant, high-alloy, corrosion-resistant stainless steel.
That 13-percent chromium content provides such property of wood burning stoves as heat resistance and, consequently, a decrease in the thickness of the walls of the furnace while maintaining its resource. This in turn provides a "reactive" convectional heating. However, even at the highest temperature in the room one can breathe freely and easily, because due to the high temperature of the beginning of scaling oxygen does not react with the walls of the oxidation furnace.
Now we want to talk about the another stereotype, as a representation of stainless steel in the form of a shiny mirror surface. In fact, the shiny surface used for domestic stainless steel products is reached with more special operation to remove dark oxide film from the surface of the sheet. This operation is costly and is not necessary in the manufacture of wood burning stoves.
TERMOFOR believes that customers should only pay for those special properties of the steel which are needed for use in wood-burning stoves.
It should be noted that the storage of stoves in damp, moisture conditions on unpainted stainless steel surfaces sometimes causes the appearance of traces of surface corrosion, not leading to the deterioration of its properties and consumer resource.
In conclusion, Termofor wants to give an advise:
Market sells a large number of stoves, and their manufacturers often claim that their products are made of heat-resistant or stainless steel. Ask the dealer about steel composition and look for the percentage of chromium in the official documents of the manufacturer. If the answer is incomplete, or indefinite, or documents are not available – that’s a lucky day for a buyer with number 13. At best, you can buy a furnace of low alloy steel, but not necessarily of heat-resistant steel, at worst - of cheap "black" steel.
Now we want to talk about the another stereotype, as a representation of stainless steel in the form of a shiny mirror surface. In fact, the shiny surface used for domestic stainless steel products is reached with more special operation to remove dark oxide film from the surface of the sheet. This operation is costly and is not necessary in the manufacture of wood burning stoves.
TERMOFOR believes that customers should only pay for those special properties of the steel which are needed for use in wood-burning stoves.
It should be noted that the storage of stoves in damp, moisture conditions on unpainted stainless steel surfaces sometimes causes the appearance of traces of surface corrosion, not leading to the deterioration of its properties and consumer resource.
In conclusion, Termofor wants to give an advise:
Market sells a large number of stoves, and their manufacturers often claim that their products are made of heat-resistant or stainless steel. Ask the dealer about steel composition and look for the percentage of chromium in the official documents of the manufacturer. If the answer is incomplete, or indefinite, or documents are not available – that’s a lucky day for a buyer with number 13. At best, you can buy a furnace of low alloy steel, but not necessarily of heat-resistant steel, at worst - of cheap "black" steel.