An Evaluation of Blacksmithing Steel Types, Applications & Forging Benefits
In the metalworking process, selecting the proper material to work with is a crucial step towards creating a piece that you can be proud of. But the sheer variety of choices available can turn this into quite a daunting and time-consuming endeavor, with countless alloys and grades of metal all striving for your attention. However, by familiarizing yourself with a few key categories of material that are widely used in metalworking, you can narrow down your choices immensely and make the selection process that much easier on yourself.
Here, we’ve created a detailed breakdown of some of the more common types of steel that you may encounter, as well as the advantages and disadvantages of each type.
1) Carbon SteelsThe most common variety of steel, by far, is carbon steel. Broadly speaking, carbon steels typically contain no more than 2% alloying elements. As defined by the American Iron and Steel Institute (AISI), carbon steel has no minimum specified content for elements such as titanium, nickel, chromium, or any other type of element that may be added for the purpose of achieving alloying qualities. More specifically, carbon steel has a maximum copper content of 0.60%, a maximum manganese content of 1.65%, and a maximum silicon content of 0.60%.
Composition of Carbon Steels (Low-Medium-High)
- Low to mild carbon steels are composed of 0.30% carbon. This group of steels is the largest of the three. Low carbon steels can have a variety of shapes and structures, making them suitable for many different applications, such as railings, hooks, and other fixtures. Low carbon steels can be flat metal sheets or support beams.
- Medium carbon steels contain between 0.31% and 0.60% carbon. The higher carbon content makes this type of steel stronger than low carbon steel, but more resistant to changes in shape. Metal hardware, like nuts and bolts, is often made with medium carbon steel, as well as rail products, gears, and hammers.
- High carbon steels have over 0.61% carbon content. Due to their relatively high carbon content and impurities, they are the hardest to deform and are very brittle. Consequently, the toughness of high carbon steel makes it a great material for knives, swords, nails, and other metal-cutting tools. There also exists a category known as ultra high carbon or tool steel, containing up to 2.00% carbon content in addition to other alloying elements, which will be covered in its own separate section of this article.
Forging Temperature of Carbon Steels
The temperature at which carbon steel can be deformed through blacksmithing is dependent upon its carbon content. Steel changes color according to the temperature to which it is heated. These steels require a temperature between 2200° F and 2300° F for hand forging, but it should be noted that the maximum workable temperature generally decreases with greater carbon content. As a blacksmith, you can often gauge this temperature by observing the changing color of steel during heating in a shaded room. While, this method is not 100% accurate, it can provide some insight into the formability of the material. Although carbon steel may be shaped through hot forging, it does not usually require any heat treatment.
Advantages & Disadvanatges of Carbon Steels
Carbon steels are clearly widely versatile in their applications to metalworking. This trait is further reinforced by the fact that carbon steel is extremely easy to get your hands on, as it is stocked at most metal retailers and can even be found in general home improvement stores. Its ubiquity in industrial applications also means that carbon steel can also be sourced from recycled material, though caution should be exercised, as the makeup of recycled steel cannot always be easily determined. Certain materials, such as zinc and lead, among others, can be present is recycled steel, and release harmful fumes when burned off in a forge. Always err on the side of caution when using material whose origins cannot be determined with certainty.
2) Alloy Steels
Steel is already an alloyed metal, but alloy steel is a very specific designation of steels. Alloy steel contains elements that are intentionally added to influence the properties of steel, such as hardenability, ductility, formability, and resistance. Some of the alloying elements used to make alloy steel are chromium, manganese, nickel, tungsten, or vanadium.
Composition of Alloy Steels (Low-High)
There is high alloy steel and low alloy steel. High alloy steel is typically classified as containing more than 10% of alloying elements that are not carbon or iron. Low alloy steel usually has less than 0.2% carbon content and its alloying elements make up less than 10% of its composition. Alloy steels are easy to process, inexpensive to produce, and can be readily heat-treated and mechanically-treated. Most alloy steels require heat treatment in order to enhance their properties.
Each alloying element has a different effect on the steel to which it is added. Chromium adds hardness, increases toughness, and increases wear resistance of steel. Manganese increases surface hardness, strain resistance, shock resistance, and high-temperature strength. Nickel increases strength, toughness, resistance to corrosion, and resistance to oxidation. Tungsten adds hardness and enhances the grain structure of the metal, improving heat resistance. Vanadium increases strength, toughness, shock resistance, and corrosion resistance.
Advantages & Disadvanatges of Alloy Steels
Since alloy steel is generally harder, stronger, more ductile, and more resistant to corrosion than regular carbon steel, its applications are typically more demanding. Among these applications are the aerospace and power industries, which typically require high quality, durable materials. The improved magnetic properties of alloy steels also make them an attractive choice for electric products. The building and construction industry also uses alloy steel for supporting large structures because of its increased strength-to-weight ratio.
3) Stainless Steels
Carbon steel may be a strong metal, but it is very susceptible to corrosion. A form of steel that is resistant to corrosion is stainless steel. Stainless steel was discovered in the early 20th century and it is composed of at least 10% chromium, making it a high alloy steel. Chromium is an alloying element that reacts with atmospheric gases to produce chromium oxide. This oxide layer acts as a self-repairing, passive layer on the surface of the steel, which prevents any rusting or staining from taking place. As a result, stainless steel has a lustrous appearance when compared to the dull finish of regular carbon steel. In fact, it is often used in a decorative manner because of its attractive surface finish.
Composition of Stainless Steels
There are actually four groups of stainless steels: ferritic, austenitic, martensitic, and duplex. Stainless steels can be classified by different grades within these groups.
- Ferritic stainless steels are magnetic and have a very high chromium content, up to 27% of its total composition.
- Austenitic stainless steels also have an 8% nickel content in addition to their high chromium content. This type of stainless steel is often used to make equipment for the food and medical industry. It is considered a relatively tough metal at ambient temperatures.
- Martensitic stainless steels are also magnetic and contain up to 1% molybdenum. Their high ductility makes them easy to form into different shapes. Martensitic stainless steels are commonly used to make blades and machine parts.
- Duplex stainless steels are a mix of ferritic and austenitic stainless steels. They have a high chromium and molybdenum content, making them stronger and tougher than ferritic and austenitic stainless steels on their own. Duplex stainless steels are used to make a lot of chemical and food processing equipment because of their ability to withstand harsh environments.
Forging Temperature of Stainless Steels
Its compatibility with different substances makes it an especially attractive material for use in chemical processes conducted at elevated temperatures. Depending on its grade, stainless steel can be used in temperatures ranging from 1700ºF to 2100ºF. Nickel and molybdenum can also be added as alloying elements to enhance the formability of stainless steel. Forging stainless steel can further enhance the quality of the material. The mechanical properties of stainless steel are improved through the forging process by creating a stronger, more resistant material. Stainless steel forgings generally have a greater strength-to-weight ratio than the starting workpiece.
Advantages & Disadvanatges of Stainless Steels
Although stainless steel has a lower thermal conductivity than carbon steel, it is widely used in domestic appliances and industrial applications due to its high resistance to corrosion and oxidation. Outside of industrial applications, stainless steel is most commonly used in cutlery and kitchenware, as well as in the creation of automotive exhaust systems. Like carbon steel, it is also easily sourced, with wide availability at industrial supply and home improvement stores.
4) Tool Steels
The purpose of tool steels can be inferred from their name. They are mostly used to make tools that cut or form other metal products. Tool steels must be tough, heat-resistant, and wear-resistant because of their demanding applications. Tool steels are a combination of carbon and alloy steels. They may contain molybdenum, cobalt, tungsten, or vanadium as alloying elements to promote the durability of the tool material.
Composition of Different Tool Steels
There are six different classes of tool steels: water-hardening, cold-work, hot-work, shock-resisting, high speed, and special purpose tool steels.
1) Water Hardening Tool Steel
Water hardening tool steel is tool steel at its most basic: very high carbon steel with few other additions. Unsurprisingly, this category of tool steel is so named due to the fact that can be quenched simply with water, although this makes the material prone to warping and cracking during the quenching process. Its other primary drawback is a low resistance to high temperatures, and any items made using this material may begin to experience some softening above 300° F. However, this also means that water hardening tool steel can be forged by hand at comparatively low temperature ranges, with the ideal temperature window ranging from 1550° F to 1900° F.
As an added bonus, water hardening tool steel is relatively inexpensive in comparison to other types of tool steel. As with other tool steels, they are difficult to find at general retailers and often must be sought out at metal retailers or industrial supply warehouses. They are most often used for cutlery, embossing taps, and a variety of hand operated metal cutting tools.
2) Cold Work Tool Steel
First introduced in the 1860’s, cold work tool steel was the earliest form of tool steel developed, the fruit of famed metallurgist Robert Mushet’s efforts to create steel that could be hardened without quenching in water. Mushet’s initial creation underwent hardening simply by air, but later varieties of cold work tool steel were quenched in oil, and both methods reduce the risk of cracking that is common with water hardening tool steel. Small additions of tungsten, chromium, manganese, or molybdenum improve the hardness, wear resistance, and high temperature ability of these materials.
Cold work tool steel should be forged at temperatures between 1575° F and 2000°F, with air hardened varieties requiring slightly higher temperatures than their oil hardened counterparts. This class of steels has wide commercial applications, including punches, dies, and machine parts such as camshafts and bushings, but in a hobbyist setting they are also commonly used for blades and woodworking tools
3) Shock Resisting Tool Steel
Like many of the other categories of tool steel, shock resisting tool steel contains elements of molybdenum, chromium, and manganese, which provide added strength and hardness. Where this type of steel differs, however, is its inclusion of silicon, which lends the material a high degree of resistance to deformation due to impact forces. They are also highly resistant to wear, making them ideal candidates for use in chisels, punches, and even springs.
For the purposes of forging by hand, the ideal temperature range for this class of materials lies between 1800° F and 2000° F, and it must be brought up to temperature gradually. Moreover, forging should not be performed anywhere below 1600° F. After the forging process has been completed, shock resisting tool steels must be cooled down rather slowly and uniformly in order to minimize the degree of stress that the metal is subjected to. For this reason, items made using this material are often allowed to cool within the confines of a furnace.
4) High Speed Tool Steel
The invention of high speed tool steel has its roots in Robert Mushet’s earlier work with cold work tool steel. Around the turn of the 20th century, metallurgists at Bethlehem Steel carried out painstakingly thorough experiments on existing types of high quality steel, including Mushet’s tool steel, heat treating them at much higher temperatures than was the generally accepted norm. The end result was a material with very high temperature resistance, which is now known as high speed tool steel.
This category of tool steel derives its attributes from a combination of tungsten and molybdenum, at a combined total of approximately ten percent. Their primary usage is in cutting tools such as drills, taps, milling cutters, gear cutters, and saw blades, where their ability to withstand the heat generated by friction allows the tools to withstand cutting at a high rate of speed, hence the name of this category of tool steel. Other common applications include woodturning tools and high quality hand tools. As a trade off, high speed steel has a narrow temperature range at which it can be forged, as it is happiest between 1900° F and 2050° F. As with shock resisting steel, it must be heated to this range slowly and uniformly, and not worked at temperatures below 1600° F. Gradual cooling after forging process is complete is also a requirement.
5) Hot Work Tool Steel
Last but not least comes hot work tool steel. As its name implies, this material is primarily used to form tools for very high temperature applications. Tools created from this resilient metal are known for their use in industrial applications such as pressure die casting, as well as more casual applications such as glass work and metal forging.
Hot work tool steels derive their characteristic resistance to high temperatures from their low carbon content, usually no more than 0.6%, coupled with an extremely high chromium, tungsten, or molybdenum content, to the tune of 6% to 25%. Be aware, however, that some grades of hot work tool steel are susceptible to cracking if exposed to water while at high temperatures, particularly those varieties with high tungsten content. In general, though, most hot work tool steels display excellent resistance to thermal shock and high temperature deformation and wear. Unsurprisingly, they also demand very high temperatures for hand forging, in the range of 1700° F to 2100° F.
6) Special Purpose Tool Steels
Special purpose tool steels generally have a higher alloy content. This higher alloy content increases their wear resistance and hardenability when compared to water-hardening tool steel. Since there is such a wide range of tool steels, selecting the type of tool steel to be used in a particular applications is very important. Factors such as temperature, hardness, resistance, and cost should all be taken into account.
5) Scrap Steels
Steel is a highly recyclable product. In fact, it is the most recycled material on the planet. Since the physical characteristics of steel to not deteriorate throughout the recycling process, it recycling it is a very efficient process. Recycling steel actually emits 80% less carbon dioxide than the production of new steel. This characteristic makes the steel industry incredibly sustainable, allowing for the conservation of energy and raw materials.
In order to recycle steel, it must be sorted at a recycling center. Scrap metal or steel is properly separated and sorted to ensure that the end material is made up of high quality metal. Once the metal is sorted, it must be compacted to reduce the volume of the sorted material. At this point, the compacted metal can be shredded into smaller pieces. These smaller pieces of metal are easier to process, lowering the amount of carbon emissions. These pieces of metal are then smelted and converted to liquid steel. The liquid steel is then refined by using an appropriate purification method. After the material is refined, it is transferred to a cooling chamber for solidification. Recycled steel is typically used a structural steel. It can be fashioned into beams and pipes in different sizes for a variety of industrial applications.