Microstructure of Hadfield Steels (Robert Hadfield)

The steel constitutes a non-magnetic alloy made of iron, 1–1.4 wt% carbon and 10–14 wt% carbon, which has a considerable resistance to abrasion.
The first manganese austenitic steel, containing about 1.2 wt% carbon and12 wt% manganese, was produced by Robert Hadfield in 1882.
This high strength steel with good elasticity and excellent abrasion resistance is widely used in various industries such as cement, mining, road construction and railways [1–3].
This family of steel was named after Hadfield in honor of him. Having repeated experiments, Robert Hadfield demonstrated that a certain type of austenitic steels, in addition to high abrasion resistance, could have an excellent toughness.

1. Microstructure of Hadfield Steels Mr. MANICKAVASAHAM G, B.E., M.E., (Ph.D.) Assistant Professor, Department of Mechanical Engineering, Mookambigai College of Engineering, Pudukkottai-622502, Tamil Nadu, India. Email:[email protected] Dr. R.Narayanasamy , B.E., M.Tech ., M.Engg ., Ph.D., (D.Sc.) Retired Professor (HAG), Department of Production Engineering, National Institute of Technology, Tiruchirappalli-620015, Tamil Nadu, India. Email: [email protected] 1

2. The steel constitutes a non-magnetic alloy made of iron, 1–1.4 wt% carbon and 10–14 wt% carbon, which has a considerable resistance to abrasion. The first manganese austenitic steel, containing about 1.2 wt% carbon and12 wt% manganese, was produced by Robert Hadfield in 1882. This high strength steel with good elasticity and excellent abrasion resistance is widely used in various industries such as cement, mining, road construction and railways [1–3]. This family of steel was named after Hadfield in honor of him. Having repeated experiments, Robert Hadfield demonstrated that a certain type of austenitic steels, in addition to high abrasion resistance, could have an excellent toughness. Introduction 2

3. Following Robert Hadfield , Veladimir Lipsin pursued his research on the effect of manganese on this steel. The first factory to casting this steel began in 1892 in the United States. This steel, known as manganese austenitic steel or Hadfield steel, has been developed widely in the turn of the twentieth century due to its high abrasion resistance, good casting capability and high work hardening coefficients . Contd. 3

4. Effect of Base and Alloy Elements The Hadfield manganese steel is an alloy of iron, carbon and manganese, which, in its particular application, adds another alloying element to this steel. In the following, the effect of some important elements in the target steel is studied. Manganese is used as austenite phase stabilizer in Hadfield manganese austenitic steel and its role is to delay the austenite transformation at 700 ° C for 15 s. If in a steel with 13% manganese, it needs a transformation at 370 ° Cf or 48 h. Reduction of Mn from 13 to 10 wt%, practically increases the relative length to half of its normal value . 4

5. Lee and Choi [49] showed that with the increase of manganese in Fe- Mn alloys, the martensitic starvation temperature would be greatly reduced, so that in high manganese alloys a completely austenitic can be seen. Manganese is a carbide forming element and forms the Mn 3 C and (Fe, Mn ) 3 C carbides in the Hadfield manganese austenitic steel. Therefore , with increasing manganese from 10 to 14%, the amount of Mn 3 C and (Fe , Mn ) 3 C in the microstructure of Hadfield manganese austenitic steel increased and this leads to increased hardness and abrasion resistance in these alloys. Contd. 5

6. Of course, when Mn 3 C and (Fe, Mn ) 3 C are used as useful components in the microstructure of Hadfield manganese austenitic steel, they are distributed as a sedimentary dispersion in the austenite matrix. But if these particles are accumulated continuously in the grain boundaries (this usually happens after the casting), then they will be able to provide a Susceptibility to brittle fracture in this steel [44–47]. Contd. 6

7. Figure 1. A schematic of the effect of manganese content on the microstructure and mechanical properties of Hadfield manganese austenitic steel. The effect of manganese content on the microstructure and mechanical properties of Hadfield manganese austenite steel is shown in figure 1. Contd. 7

8. The amount of carbon in Hadfield manganese austenitic steel determines the yield strength and resistance to wear . With increasing carbon from 1 to 1.4 wt%, the yield strength and stiffness increase in these steels, while toughness and flexibility are greatly reduced. This is due to the formation of carbide deposits (especially Mn 3 C and (Fe, Mn ) 3 C carbides ) in austenite boundaries with increasing carbon content. In any case, because an increase in carbon up to 1.4 wt% increases the resistance to abrasion, it is often preferred to use the same amount of carbon. It is very difficult to obtain the austenitic structure of the carbide phase network in steels with carbon content of more than 1.4 wt %. Therefore , the increase in carbon over 1.4 wt% is rarely done. Contd. 8

9. As shown in figure 1, due to the high carbon content, the carbide deposits in the austenite boundaries are clearly visible in the Hadfield manganese austenitic steel [44–49]. When the carbon content reaches above 1.2 wt%, the amount of carbide deposits in the boundaries or austenite increases, so that the coarse deposits created in the austenite boundary create problems after casting and heat treatment. Because unsolved carbides in austenite after heat treatment reduce the toughness of this steel. It can, therefore, be said with certainty that the presence of carbide and ceramic compounds can greatly affect the properties of alloys and engineering components [24, 50, 51 ]. In general , carbon element has a definite effect on the mechanical properties of Hadfield manganese austenitic steel . Contd. 9

10. Contd. These impacts include: increasing the yield strength, increasing wear resistance, increasing tensile strength and increasing the relative length to a certain range of carbon and then reducing them with increasing carbon. In figure 2, the effect of carbon on mechanical properties of Hadfield steel has been shown. Figure 2. A schematic of effect of carbon content on mechanical properties of Hadfield steel. 10

11. The chromium element is added in the range of 1.5 to 2.5 wt% by weight to increase the strength of the sink to Hadfield steel. Chromium uptake results in the formation of complex carbides of (Fe, Mn , Cr) 23 C 6 in the grains and will greatly reduce the toughness of these steels. Basically, chromium is added to the Hadfield manganese austenitic steel to improve wear resistance. Since chromium is a strong carbide forming element, it produces a hardening in Hadfield steel by making carbides of the complex (Fe, Mn , Cr) 23 C 6 . It is because carbides are those particles that contribute to increase hardness in steels [24, 52]. Due to the role of chromium in the abrasion behavior of Hadfield manganese austenitic steel, a great deal of research has been devoted on the effect of this element on the wear behavior of Hadfield steel. Contd. 11

12. Agunsoye et al [52] compared the properties and the structure of the auxiliary manganese austenitic steel and high-chromium iron alloys, and their results indicate that in the heat treatment, Hadfield steel strength is higher than that of iron-chromium alloys . Mahallawi et al [53 ] investigated the effect of 1.7 to 2.3 weight percent chromium on the hardness and abrasion behavior of the Hadfield manganese austenitic steel. These researchers have reported that with increasing chromium content from 1.7 to 2.3 wt%, hardness and wear resistance increased but toughness decreased. As shown in figure 3, studies on the effect of chromium on the mechanical properties of Hadfield manganese austenite steel show that with increasing chromium, the hardening strength and hardness of Hadfield steel are increased. Contd. 12

13. But in excess of 1.8–2 wt% of chromium, tensile strength and elongation will be decreased. This is due to the formation of complex carbides of (Fe, Mn , Cr) 23 C 6 . Contd. Figure 3. A schematic of effect of chromium content on mechanical properties of Hadfield steel. 13

14. The use of titanium element to neutralize the effect of phosphorus in steel making has been considered. This element reduces the amount of austenite-soluble carbon by making stable carbides, and thus the mechanical properties of steel greatly affects. The presence of titanium improves the structure of the piece after solidification (due to its usefulness, the structure is fine -grained). By creating resistance to brittleness (in amounts less than 0.1 % by weight of titanium), the sensitivity to the heat treatment cycle in the piece is reduced and thus the piece protects the risk of cracking during the heat treatment. The use of titanium element for fine -grained structure and increase of hardness in this steel has been very efficient [54, 55]. Contd. 14

15. In the other studies by Srivastava and Das [54], it is reported that the Hadfield steel wear resistance can be improved by designing composites including Hadfield steel and titanium carbide reinforcing particles. It has been observed in various reports that the main reason for increasing the hardness in containing titanium steels is solid TiC particles. In figure 4, it is observed that the presence of titanium in the Hadfield manganese austenite steel increases the yield strength and hardening, but due to the formation of carbide and nitride deposits, it reduces the toughness and flexibility of Hadfield steel. Contd. 15

16. Figure 4. A schematic of the effect of Ti content on the mechanical properties of Hadfield steel. Contd. The element of vanadium is very strong carbide forming. Therefore , this element is added to Hadfield steel to increase the yield strength and hardness. Moghadam et al [56] studied the wear properties of Hadfield steel. Moghaddam and his colleagues showed that adding vanadium to manganese steels increases the hardness of the manganese austenite steel. 16

17. The researchers used the XRD analysis to investigate the cause of the incident, which is the result of their review of the formation of the V 8 C 7 carbide . Moghadam and his colleagues have reported the hardness superiority of vanadium-containing manganese steels to Hadfield manganese steel because of formation of vanadium carbide particles ( V 8 C 7 ). Contd. 17

18. Contd. One of the main reasons for the use of aluminum in steels is the effect of deoxidation of this element. For this reason , the researchers studied the effect of aluminum on the properties and microstructure of Hadfield manganese steel. The researchers found that the addition of aluminum to Hadfield manganese steel resulted in a reduction in the amount of grain- boundary carbides in the casting structure and the morphology of the carbides from the continuous state and into a discontinuous form. Also , the addition of aluminum to Hadfield steel leads to an increase in the solubility of carbon in the austenite crystal network and the grain size of austenite, which does not change significantly with annealing heat treatment cycle [57]. 18

19. Contd. Tian and Zhan [58] showed that increasing the amount of aluminum in manganese steels increased the driving force required for austenite transformation to martensite in these steels, and it also reduces the formation temperature of martensite ( M s ). As a result, aluminum will stabilize the austenite phase compared to martensitic in manganese austenitic steels. 19

20. Silicon is a carbide forming element and is usually added to steel to increase its hardness and wear resistance. In Hadfield manganese steels containing 1 wt% silicon, there is no needle-shaped carbide, but if the amount of silicon is 0.5 wt%, then needle-shaped carbides are observed. But in general, the amount of 0.8 wt% silicon gives the best fluidity and casting properties to manganese steels. If the amount of silicon is exceeded, a percentage of the weight of the piece will tend to be brittle. In various standards, the use of Hadfield steel parts, the amount of silicon and other alloying elements is determined and depending on the manufacturer’s and customer’s agreement , they may have a different range. Contd. 20

21. For example, the amount of silicon for the centerpiece of the needle rail should not exceed 1 wt%, and it is recommended in the Hadfield parts in the cement industry that the amount of silicon is less than 1%by weight [61, 62]. Figure 5 shows the effect of the amount of silicon on the mechanical properties of the Hadfield manganese austenite steel. As seen from this figure , up to 1 wt% by weight of silicon, tensile strength, yield strength and hardness increased, but due to the formation of SiC particles in the microstructure , the flexibility of the Hadfield manganese austenite steel decreases. Contd. 21

22. Figure 6. A schematic of effect of silicon content on mechanical properties of Hadfield steel. Contd. 22

23. Microstructure of Hadfield Steels A schematic of the microstructure of Hadfield manganese austenitic steel. 23

24. Contd. As-cast microstructure of Hadfield steel; austenitic matrix with precipitates of alloyed cementite ; nital etching [1] 24

25. Material microstructure of the X120Mn12 steel in the as-delivered state. Microstructure of coarse-grained austenite with twins. Etched state. LM. Contd. 25

26. Contd.  Microstructure of the X120Mn12 steel after isothermal annealing at 510 °C and cooling with the furnace. Visible heterogonous growth of new pearlite grains and needle-like precipitations at the grain boundaries of the former austenite, which are also the site of the nucleation of “thin” carbides. Etched state. SEM (BSE). 26

27. Contd. Microstructure of the X120Mn12 steel after isothermal annealing at 510 °C and cooling with the furnace. Brightfield image of a “thin” carbide about 0.35-μm thick at the grain boundary of the former austenite and a fine pearlite colony growing on it. TEM. 27

28. Contd. (a) Thin M3C carbide plates in the austenite matrix. (b) Diffraction pattern obtained from the grain of austenite with zone axis [001¯001¯] showed in (a). TEM. 28

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32. References : Sabzi , M., & Farzam , M. (2019). Hadfield manganese austenitic steel: a review of manufacturing processes and properties. Materials Research Express, 6(10), 1065c2. Authors of Technical articles and Scopus Journals are Acknowledged. 32

33. Thank You 33