Vol. 43, No. 3, pp. 283-290 Published Year 2020
Studying the Effect of Duplex Quenching on Wear Behavior of
CK45
Lamyaa Khaleel Hasan
Electromechanical Engineering, University of Technology, Iraq *Email: [email protected], [email protected]
ABSTRACT: Attention has been given to the development of wear behavior for the CK45 steel by employing duplex quenching inter critical heat treatment which were investigated in this paper. The specimens were treated by single quenching and duplex quenching respectively. Single quenching was performed in α+γ region at 750, 800 and 850℃ and then quenching in oil. The duplex quenching was firstly heated at 900℃ and quenching in oil, and secondly the specimens reheated at 750, 800 and 850℃ and quenching in oil. Microstructure examination for the specimens single and duplex quenched was analyzed using optical microscope. Hardness test was done using Vickers hardness test. While wear test was done for the specimens (single and duplex quenching) using pin-on-disc machine by changing loads 5, 10, 15, 20 and 25N with sliding time 10 min, and at different sliding time 5, 10, 15, 20, 25and 30 min with constant load 15N.The results of this investigation show that the duplex quenching in oil decreasing wear art because of the martensitic volume fraction for duplex quenching higher than for single quenching, this in turn increases the Vickers hardness number.
KEYWORDS: inter critical heat treatment; duplex quenching; CK45 steel; hardness; wear. INTRODUCTION
The process that utilizing to improve the microstructure, mechanical properties and wear resistance of steel alloy is known heat treatment. Inter critical heat treatment as an important process using to improve low alloy Steel to obtain dual phase (DP) microstructure. This heat treatment involve heating steel alloy in the inter critical temperature range (α+γ) and then followed by quenching in a suitable quenching media in order to find the dual phase (α+γ) microstructure. The dual phase Steel microstructure consists of network of soft ferrite provides a good ductility with a hard martensite phase. However, increasing the inter critical heat temperature works on increasing the volume fraction of martnsite [1-3]. Dual Phase Steel (DPS) can be defined as an important class of high strength low alloy steel (HSLA). This type of steel has unparalleled specifications like continues yield behavior (i.e. there is no yield point) the tensile strength is high, elongation is high and the ratio of strength to weight also high. These properties correlated to the microstructure of DPS that contains a ductile phase (ferrite) with a hard materials phase [4]. The major employing for medium carbon low alloy steel are in the heavy machine, like coupling, axels, gears and crankshafts [5]. DPS is compound of ferrite and martesite that has a high strength steel. The structure of DSP can be gained by heating of the low steel alloy between Ac1 and Ac3 temperatures. DSP probably has a small quantity of pearlite and bainite phases. Then, it retained austinite depending on the quenching media, carbon content and cooling rate. Strength and ductility relationship is gaining by controlling of size, shape, the amount of the dispersion and the distribution of hard martensite in ductile ferrite matrix [6-7].
There are many researches published in this field such as Alfirano et al. [8]. They investigated the microstructures and hardness of low carbon steel. The specimens were heated at α+γ region at 775℃, 800℃ and 825℃ for 20 min, followed by quenching in water. The results of this work show that the volume fraction of martensite approaching 20% at 775℃.The highest value of the hardness was 373 VHN for inter critical temperature of 825℃, while the correlation between the inter critical temperature and time can be obtained from fγ/fe=1- exp (-ktn), the value of K=0.15 and n=0.461. Joshua T.O et al.[9] studied the mechanical properties of medium carbon steel after subjected to different inter critical temperature 760℃,770℃,780℃,790℃ and 800℃. The specimens have been immersed in many liquids like distilled water, water and palm oil. The main outcomes in current paper revealed that the hardness and strength values for the specimen quenched in distilled water was the highest, while the toughness and strength for the specimen quenched in palm oil was the highest. Wang et al. [10] investigated the effect of surface nano crystallization on wear rate and friction of low carbon steel. The paper outcomes have
improved the resistance of wear and friction because of the hard nano crystalline surface layer and in turn decrease micro cutting and plowing under loading. Adamzyk and Grajcar [11] studied the effect of different inter critical temperature on wear behavior for each one. Increasing of inter critical temperature worked on increasing the martensite volume fraction and enhanced the resistance of wear as a result.
In the present work, CK45 medium carbon steel was treated by heating intercritically. The influence of single quenching and duplex quenching on volume fraction of martensite, hardness and wear behavior was investigated. EXPERIMENTAL PROCEDURES
Materials and heat treatments
According in Table.1 chemical composition has been presented for CK45, while Table. 2 shows the heat treatments performed for the specimens which followed by tempering heat treatment at 200℃ for 1 hr
Table 1. CK45 Chemical composition
Element %C %Mn %Si %Cr %Ni %Mo %S %P %Fe
Actual value 0.46 0.65 Max 0.40 Max 0.40 Max 0.40 0_0.1 0_0.035 0_0.035 Remain
Table 2. Heat treatment for CK45 steel alloy.
R o u t.1 Sin g le q u en ch in g Sample A specimen as-received
B1 Quenched from temperature at 750 ̊C in oil.
B2 Quenched from temperature at 800 ̊C in oil.
B3 Quenched from temperature at 850 ̊C in oil.
R o u te. 2 Du p lex q u en ch in g
C1 Oil quenching at temperature 900 ̊C and 750 ̊C as two steps respectively.
C2 Oil quenching at temperature 900 ̊C and 800 ̊C as two steps respectively
C3 Oil quenching at temperature 900 ̊C and 850 ̊C as two steps respectively
Microstructure examination
The CK45 has been characterized by microscope for microstructure. the preparation of specimens were done by grinding process in addition to SiC emery papers at grit sizes 320 μm, 500 μm and 1000 μm respectively, and then the specimens polished with alumina suspension followed by etching in nital solution (2% HNO3 acid +98% alchohol).
Hardness test has been carried out using Vickers hardness apparatus according to ASTM E-384 standard. Many readings have been considered (at least four readings) before calculating the average reading for each position in the specimen surface in order to achieve the average diameter of the indentation. The equation below has employed to calculate the Vickers hardness number [14].
V.H.N= 1.8544 x (𝑑𝑎𝑣𝑒)𝐹 2 (kgf/ mm2) (1) Where:
F: is applied force (100 kgf)
dave: is average indentation diameter (mm) Wear lest
Dry sliding wear test was performed using pin-on-disc machine according to ASTM G99 standard. Wear test was performed under two variables as following:
1. Study the effect of normal load 5, 10, 15 and 20 N on wear rate at constant time 15 min. 2. Study the effect of sliding time (5, 10, 15 and 20 min) on wear rate at constant load 15N. In order to estimate the rate of wear, the equation below was used:
W.R = ∆𝑤
2𝜋.𝑟.𝑛.𝑡 (2)
Where:
∆w: the change in weight of the specimen
∆𝑤 =𝑤1−𝑤2
2𝜋. 𝑟. 𝑛. 𝑡 is referring to the distance of sliding (cm)
r refers to the radius calculated that measured from the center of specimen to the center of disc n refers to rotational speed of the disc (480 rpm )
t is refereeing to the test time (min) RESULTS AND DISCUSSION Microstructural analysis
Figure 1. shows the images of the specimens for single and duplex quenching. The microstructure of the specimen as- received consists of ferrite phase and pearlite phase.
For the specimens single quenched consisting of ferrite and island of martensite, the amount of martensite depended strongly on the amount of austenite before the trans formation [15].
While for duplex quenching, during heating the specimens at austenizing temperature (900℃) and quenching in oil, the austenite will be transform to martensite. During the second quenching by heating the specimen at different inter critical temperature (750℃, 800℃ and 850℃) and then quenching in oil; the martensite will be formed at the grain boundaries of ferrite grain as shown in Fig 1.
As-received (200X)
750 ̊C (single quenching) (200X) 800 ̊C (single quenching) (200X) 850 ̊C (single quenching) (200X)
750 ̊C (duplex quenching) (200X) 800 ̊C (duplex quenching) (200X) 850 ̊C (duplex quenching) (200X) Figure 1. Photomicrographs of the specimen's microstructure before and after inter critically heat treatments at
750 ̊C, 800 ̊C, and 850 ̊C.
Moreover, at the surroundings of martensite, the plastic deformation has been observed due to observe the small grains of recrystallized ferrite that led to the martensite transformation [11].
Optical images showed increasing in the heat treatment temperature and led to the volume fraction of martensite increasing [11, 16] as shown in Table 3.
Table 3. Volume fraction of Martensite %
Sample Volume fraction of Martensite %
M 𝛼 M 𝛼 𝛼 p
Hardness test
Table 4. revealed that an increasing in the of heat treatment temperature worked on increasing the volume fraction of martensite, and then increased the hardness [11], it is attribute to the martensite enrich with carbon and then increase the hardenability of steel alloy. But the martensite with lower carbon causes the decreasing in hardenability [11] as shown in Fig 2. This result agreed with [6].
Figure 2. Hardness versus the inter critical heating temperature Wear Test
Figure 3. show that wear rate increases with increasing applied load. This is attributed to raise the temperature of the surfaces and then causes to form oxide films at the surface of the specimen. More applied load more oxide films, and then decreasing the contact between the specimens and rotating disc, thus decreasing wear rate [17]. Increasing the applied load causes micro cutting and plowing of oxides and abrasive particles form the surface of the specimen. As the load increases, plastic deformation caused by sliding action and then spilling loss will happen as a result of work hardening.
Figure 3. Wear rate versus the applied load for single quenching and duplex quenching.
From Figure 4. It has been observed that the increasing sliding time leads to increase wear rate, because of raising surface temperature which in turn form oxide layer on the specimen surface. Most oxide layers as a result of sliding the specimen on rotating disc, and then the contact between them will reduce and lowering wear rate, thus leads to transition from mild wear to server wear [17].
Figure 3 and Figure 4 show that duplex quenching improve wear resistance, this result is agreed with [18], it is due to higher hardness associated with homogeneous distribution of fine microstructure of ferrite and martensite obtained by duplex quenching [6]. It is expected that the improvement in the hardness result in improving of wear resistance [10], so that the enhancement of wear resistance for the specimen duplex quenched from temperature 900℃ and 850℃.
Figure 4. Wear rate versus the time for single quenching and duplex quenching. CONCLUSIONS
The results of this work have shown that:
1- Martensite is homogeneously distributed in ferrite for duplex quenching. Increasing the volume fraction of martensite worked on increasing the inter critical temperature.
2- A high hardness is resulted due to duplex quenching with higher volume fraction of martensite. 3- Increasing applied load and sliding time lead to increase wear rate.
4- The wear rate is decreased in duplex quenching due to fine martensite and fine ferrite. REFERENCES
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