**2. Role of major alloying element in steel**

#### **2.1 Carbon**

The carbon steels are composed of carbon and iron by means of carbon up to 2.1 wt%. At the same time, when the carbon content increases, steel has the capability to become harder as well as stronger by heat treating, though it undergoes less

**189**

*Strengthening of High-Alloy Steel through Innovative Heat Treatment Routes*

ductility. In spite of heat treatment, a higher carbon content also decreases weldability. In carbon steels, the higher carbon content lowers the melting point. The classifications of carbon steel are on the basis of carbon content:

**Low-carbon steel**: carbon wt% is in the range of 0.05–0.30 (called plain carbon

**Medium-carbon steel**: 0.3–0.6% is the approximate carbon content [1]. It helps in balancing ductility and strength and also has superior wear resistance; it is

**High-carbon steel**: carbon content lies from 0.60 to 1.00% [1]. It has very high

**Ultrahigh-carbon steel**: it has carbon% between 1.25 and 2.0 [1]. It can be tempered to immense hardness. It is used in various purposes like axles, punches,

Mild steel, well known as plain carbon, is at present the common variety of steel as it is cost-effective and offers material properties for a lot of applications. It contains carbon wt% in the range of 0.05–0.30, building it more malleable and ductile. It has comparatively low tensile strength, other than being contemptible and simple to produce; surface hardness can be improved by carburizing. Due to its ductile nature, the failure from yielding is less risky, so it is best applicable (e.g., structural

~200 GPa [6]. Low-carbon steels include a smaller amount of carbon than other

Carbon steels that successfully experience heat treatment contain carbon in between 0.30 and 1.70 wt%. The impurities of different elements also have a considerable consequence on the superiority of the ensuing steel. Small amount of sulfur content makes steel brittle and crumble on operational temperatures. Manganese is added to enhance the hardenability of the steels. The name "carbon steel" can be employed in terms of the steel that is not stainless steel; in addition to it, carbon steel can be involved in alloy steels. Current modern steels are prepared with various mixtures of alloying elements to execute in various applications. The steel is alloyed along with additional elements, typically manganese, molybdenum (Mo), nickel, or chromium up to 10 wt%, in order to develop the hardenability. High-strength low-alloy steel has small additions (<2 wt%) of added elements,

Alloy steel reflects a category of steel facilitated with the addition of different elements. In general, all steels are referred to as alloy steel, while the plain steel is composed of iron added up to 2.06 wt% carbon. However, the term "alloy steel" commonly refers to steels that are alloyed with elements other than carbon. The total wt% of the alloying elements can be up to 20% to provide the material enhanced properties like better wear resistance, strength, or ductility. Low-alloyed

[5] and Young's modulus is

strength and is used for tools, edged tools, springs, and wires [4].

*DOI: http://dx.doi.org/10.5772/intechopen.91874*

used in automobiles [2, 3].

**2.2 Detailed study of low- and high-carbon steel**

steel). The density of mild or low steel is ~7.85 g/cm3

steels and are easy to handle as it is more deformable.

usually 1.5 wt% manganese, to offer extra strength.

**3. Alloying elements and their effects on steels**

steel) [1].

or knives.

*2.2.1 Mild- or low-carbon steel*

*2.2.2 Higher-carbon steels*

*Strengthening of High-Alloy Steel through Innovative Heat Treatment Routes DOI: http://dx.doi.org/10.5772/intechopen.91874*

ductility. In spite of heat treatment, a higher carbon content also decreases weldability. In carbon steels, the higher carbon content lowers the melting point.

The classifications of carbon steel are on the basis of carbon content:

**Low-carbon steel**: carbon wt% is in the range of 0.05–0.30 (called plain carbon steel) [1].

**Medium-carbon steel**: 0.3–0.6% is the approximate carbon content [1]. It helps in balancing ductility and strength and also has superior wear resistance; it is used in automobiles [2, 3].

**High-carbon steel**: carbon content lies from 0.60 to 1.00% [1]. It has very high strength and is used for tools, edged tools, springs, and wires [4].

**Ultrahigh-carbon steel**: it has carbon% between 1.25 and 2.0 [1]. It can be tempered to immense hardness. It is used in various purposes like axles, punches, or knives.
