*4.1.2 High-alloy steels*

In high-alloy steel, the entire alloying element content is above 10 wt%. In stainless steels, the principally alloying element is Cr (≥11 wt%). It is greatly resistant to corrosion. Nickel and molybdenum addition adds to corrosion resistance. An important property of the highly alloyed steel is the capability of alloying elements to promote the creation of a certain multiple phases and stabilize it. These elements are grouped into four major classes as discussed in the previous section: (1) austenite-forming, (2) ferrite-forming, and (3) carbide-forming.

Some varieties of the high-alloy steels are the following:


**193**

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

W, and Cr. These elements have wear resistance, high strength, and toughness but have low ductility. One of the primary heat treatments provided for tool steel is tempering that requires cautious preparation. Various complex tool steels like the high-speed steel need twice over tempering to convert austenite to martensite completely. High-speed steel (18 wt%W, 4 wt%Cr, 1 wt%V, 0.7 wt%C, 5–8 wt%Co, rest Fe) suits best for high-speed machining purpose, owing to secondary hardening. Besides, high-temperature annealing is performed with majorly ferritic structure to achieve a maximum bending strength of 4700 MPa. These types of steels achieve utmost hardness after first tempering, which is followed by second tempering that lowers the hardness to the desired working level. In some cases, the third temper is needed for secondary hardening of steels to make sure that some new martensite produced as a consequence of austenite conversion in tempering is efficiently tempered. This is a subject of individual selection and includes minimum

c.High-entropy alloy steel: the essential elements of the high-entropy steels are Fe, Co, Ni, Cr, Cu, and Al. The cast microstructure expands from FCC to BCC phase along with the increase in Al content. The hardness in BCC phase is greater than FCC phase; in addition to it, the corrosion resistance is also superior in BCC phase. Some of the high-entropy alloy steels like Al-Fe-Cr-Co-Ni-Ti alloy coating was equipped by laser cladding, and the effects of annealing temperature (873, 1073, and 1473 K) on structure and its properties were studied. The consequences illustrate that the intermetallic precipitation compounds in the coating are efficiently repressed through laser cladding by means of fast solidification, and the microstructure of the coating forms dendrite structure of BCC, having superior hardness (~698 HV). As a result, the grain size of the coating rises somewhat, and the microhardness reduces slightly, following various annealing temperatures at a range of 1073–

1373 K. This specifies that the elevated temperature stability of the structure and microhardness of the coating are superior. Al and Fe are improved in dendritic boundary, while Co, Ni, Ti, and Cr are enhanced in interdendritic boundary. In addition, the degree of segregation rises with the enhancement

<1 wt%C, <3 wt%Si, <3 wt%Al, rest Fe) high-temperature thermomechanical heat treatment provides a strength greater than1000 MPa. The examination of the solution heat treatment of hot-rolled TWIP steel of the three various compositions (Fe-30Mn-3Si3Al, Fe-25Mn-4Si-2Al, and Fe-30Mn-4Si-2Al) reflected that prolonging the time of holding temperature can enhance the elongation through no change observed in strength. Prolonging the holding time facilitates both the production of additional annealing twins to amplify their areas of boundary and the boost in the number of twin boundaries that

e.Hadfield steel: in Hadfield steel (11–14 wt%Mn, 1–1.4 wt%C), a fully austenitic phase is obtained with a strength level of 1000 MPa. High-alloy tool steel (5 wt%Mo, 6 wt%W, 4 wt%Cr, 0.3 wt%Si, 1 wt%V, rest Fe) is provided with austenitizing, quenching, and tempering treatment to achieve a maximum hardness of 1200–1400 HV. The heat treatment processing of Hadfield manganese steel means dissolving the carbide precipitates at higher temperature,

d.Twinning-induced plasticity (TWIP) steel: in TWIP steel (>20 wt%Mn,

are favorable for the corrosion resistance creep and fracture.

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

extra cost.

of annealing temperature.

*Welding - Modern Topics*

cobalt, boron, and copper.

*4.1.1 Low-alloy steel*

*4.1.2 High-alloy steels*

Mo 0.40% or 0.52% C, rest Fe

(3) carbide-forming.

**4.1 Categorization of alloy steel and their heat treatments**

structural shapes, sheets, etc. [2, 3, 5, 6, 10–12].

Mo 0.20% or 0.25% or 0.25% Mo or 0.042% S, rest Fe

Ni 1.82%, Cr 0.50% to 0.80%, Mo 0.25% Cu, rest Fe

Some of the compositions of low-alloy steels are the following:

Cr 0.50% or 0.80% or 0.95%, Mo 0.12% or 0.20% or 0.25% or 0.30%, rest Fe

In high-alloy steel, the entire alloying element content is above 10 wt%. In stainless steels, the principally alloying element is Cr (≥11 wt%). It is greatly resistant to corrosion. Nickel and molybdenum addition adds to corrosion resistance. An important property of the highly alloyed steel is the capability of alloying elements to promote the creation of a certain multiple phases and stabilize it. These elements are grouped into four major classes as discussed in the previous section: (1) austenite-forming, (2) ferrite-forming, and

Several low-alloy steels underwent normalizing and tempering in the manufacturing industries; however there is an increase affinity to a quenching and tempering action. Low-alloy steels are weldable, but pre-welding or post-welding heat treatment is essential to evade weld zone cracking issues.

a.Stainless steels: Fe-18Cr-8Ni-1Mn-0.1C characteristically is γ-alloy. It stabilizes austenite for its rising temperature range, where austenite subsists. It elevates the austenite-forming temperature (A1) and reduces the A3 temperature. Mostly, this type of steels underwent solution annealing type of heat treatment primarily specified for austenitic stainless steels. The main requirement for this treatment is to dissolve all the precipitated phases, mainly chromium-rich carbides, where the precipitate of M23C6 occurs in the range of 673–1173 K. For other stainless steels, it is recommended to maintain the solution annealing

b.Tool steel: it provides necessary hardness with simpler heat treatment and retains hardness at high temperature. The primary alloying elements are Mo,

Some varieties of the high-alloy steels are the following:

temperature in the range of 1273–1393 K.

Alloy steels are categorized into low- and high-alloy steels. High-alloy steels would be more than 10 wt% of alloying elements in steel groups [1, 5, 8, 9]. The majority of alloy steels lie under the group of low alloy. The most common alloy elements include chromium, manganese, nickel, molybdenum, vanadium, tungsten,

Low-alloy steels are a group of ferrous materials that show improved mechanical properties compared to plain carbon steels, because of the alloying elements such as nickel, molybdenum and chromium. Through the development of specific alloys, low-alloy steel provides desired mechanical properties. Microstructure consists of ferrite and pearlite. Its properties are relatively soft and weak, although they have high ductility and toughness. Its various applications are auto-body components,

**192**

W, and Cr. These elements have wear resistance, high strength, and toughness but have low ductility. One of the primary heat treatments provided for tool steel is tempering that requires cautious preparation. Various complex tool steels like the high-speed steel need twice over tempering to convert austenite to martensite completely. High-speed steel (18 wt%W, 4 wt%Cr, 1 wt%V, 0.7 wt%C, 5–8 wt%Co, rest Fe) suits best for high-speed machining purpose, owing to secondary hardening. Besides, high-temperature annealing is performed with majorly ferritic structure to achieve a maximum bending strength of 4700 MPa. These types of steels achieve utmost hardness after first tempering, which is followed by second tempering that lowers the hardness to the desired working level. In some cases, the third temper is needed for secondary hardening of steels to make sure that some new martensite produced as a consequence of austenite conversion in tempering is efficiently tempered. This is a subject of individual selection and includes minimum extra cost.


followed by fast cooling to attain austenitic carbide-free grains which is desired to be the preferred microstructure for the commercial applications.
