2020 Volume 60 Issue 11 Pages 2586-2595
The TiC-reinforced low alloy abrasion resistant martensitic steel was developed to improve the wear resistance without increasing hardness through traditional melting and casting technology and subsequent hot rolling and heat treatment processes. The new wear resistant steel was reinforced with micron- and nano-sized TiC particles. The phase diagram calculated by Thermal-Calc software indicated that micron-sized TiC particles precipitates towards the end of solidification. The hot rolling process changed the distribution of initial micron-sized TiC particles and transformed it from a segregated distribution to a uniform distribution. Amounts of nano-sized precipitation was obtained via pre-tempering treatment, which remarkably improved the three-body abrasive wear performance of TiC reinforced steel at the expense of a little ductility and toughness. The steel reinforced with only micron-sized TiC particles, whose wear resistance was 1.35 times that of conventional abrasion resistant steel (NM500). However, the steel reinforced with micron- and nano-sized TiC particles, whose wear resistance increased to 1.5 times that of NM500. The wear mechanism of conventional steel was micro-cutting/micro-ploughing, while the wear mechanism of TiC-reinforced steel was spalling and fatigue, because the micro-cutting was efficiently resisted by TiC particles.
High-manganese steel is the earliest wear-resistant steel, while low-alloy abrasion-resistant steel is currently the most widely used low-cost wear resistant plate.1,2,3,4,5) The low-alloy abrasion-resistant steel, its matrix is martensite, is less restricted by the working conditions unlike high-manganese steel, which can be used in a variety of working conditions such as high-stress conditions and low-stress conditions.6,7) The wear resistance of low-alloy abrasion-resistant steel corresponds to the hardness of martensitic matrix, thus the high-grade low-alloy abrasion-resistant steels tend to higher hardness.8,9) Due to the limited by current welding and processing technology, although high-grade low-alloy wear-resistant steels have been successfully developed for some time, they have been used in very few working conditions. Therefore, researchers intend to develop a super wear-resistant steel with lower hardness, high wear resistance and good serviceability to break the existing awkward situation.
In recent decades, metal matrix composites (MMCs) have received widespread attention due to their superior comprehensive properties and special properties such as high specific modulus and strength, excellent high-temperature properties, and enhanced wear resistance.10,11,12,13,14) However, manufacturing processes of MMCs such as stir casting, powder metallurgy, spray forming, liquid metal infiltration and in situ methods are complex and expensive, and it has not yet been able to produce industrially.15,16,17,18,19) Previous works indicate that the wear resistance of MMCs was significantly enhanced due to the second particles.20,21,22) Thus the concept of MMCs was introduced into low-alloy abrasion-resistant steel, the super abrasion-resistant steel reinforced with self-generated TiC particles was developed through the traditional melting and casting technology.23,24,25) And the three-body abrasion wear resistance of super abrasion-resistant steels were improved to 1.8 times that of the conventional low-alloy abrasion-resistant steels under same hardness. The micron-sized TiC particles can resist micro-cutting and protect matrix from wear, but the role of nano-sized TiC precipitation remains to be studied.
In this study, the low-alloy abrasion-resistant steel reinforced with TiC particles was prepared using melting and casting technology. The billets were hot rolled and heat treated with three different processes, three plates containing nano-sized TiC precipitation with different size and quantity were obtained. The microstructures, mechanical properties and wear resistance of three plates were studied to determine the role of nano-sized TiC precipitation on TiC-reinforced abrasion-resistant steel. In addition, the solidification phase diagram of TiC-reinforced wear-resistant steel was calculated using Thermo-Calc software to study the precipitation process of micron-sized TiC. And the morphologies of the worn surfaces were observed by SEM to analyze the wear mechanism of TiC-reinforced abrasion-resistant steel.
The chemical composition of the TiC-reinforced steel in weight percentage is 0.30C, 0.30Si, 0.60Mn, 0.57Ti, 1.00Cr, 0.32Mo and balance Fe. The TiC-reinforced steel was melted by a 150 kg vacuum electromagnetic melting furnace, and casted into a round ingot, because Ti is very active and easily oxidized at high temperatures. And then the TiC-reinforced steel was forged into 100 × 100 × 120 mm billets. The ingots were heated to 1200°C and hold 3 h for solution treatment before hot rolling. The billets were hot rolled to 12 mm thickness plates by two-stage controlled rolling and ultra-fast (~100°C/s) cooled to room temperature.26) Then the plates were heat treated through three different process. (1) Direct Quenching: the first plate was reheated to 880°C and hold 20 min, then water quenched to room temperature (as 880Q). (2) Pre-tempering + quenching: the second plate was heated to 550°C and hold 40 min, then heated to 880°C and hold 20 min, finally water quenched to room temperature (as 550PT+880Q). (3) Pre-tempering + quenching: The third plate was heated to 650°C and hold 40 min, then heated to 880°C and hold 20 min, finally water quenched to room temperature (as 650PT+880Q). Schematic drawing of the rolling and heat treatment procedure is shown in Fig. 1.
Schematic drawing of the rolling and heat treatment procedure. (Online version in color.)
Sample (8 × 10 ×12 mm) was cut from the ingot to observe the initial morphologies of TiC particles obtained during solidification. Metallographic samples (8 × 10 ×12 mm) were cut from three plates to observe the morphologies of TiC particles after rolling and the microstructures of the TiC-reinforced steels under different heat treatments. TEM samples (Φ 3 mm × 800 μm) for observing nano-sized TiC precipitation, hardness samples (20 × 20 ×12 mm), tensile testing samples (sample geometry A25), Charpy-V impact testing samples (10 × 10 ×55 mm), three-body abrasion wear testing samples (75 × 25.5 × 7 mm) were also cut from three plates. The samples for abrasion wear testing and impact testing were cut along the rolling direction, whereas the samples for tensile testing were perpendicular to the rolling direction.
2.2. Microstructure ExaminationThe metallographic samples were mechanical grinded and polished, and the morphologies of initial TiC particles in ingot and TiC particles in plates after hot rolling were observed using the non-erosion samples by scanning electron microscopy (SEM; ZEISS ULTRA-55) at 15 kV. Then the Metallographic samples were etched with 4% nital (4 ml HNO3 + 96 ml ethanol), and the microstructures of TiC-reinforced steels under different heat treatments were also observed using SEM. As for nano-sized TiC precipitation, it was observed using 3 mm diameter samples by transmission electron metallography (TEM; FEI Tecnai G2 F20) at 200 kV, before which the 3 mm diameter samples were ground to ~45 μm thickness and electrolytically jet-polished at a potential of 32 V and −25°C, in an electrolyte containing 8% perchloric acid and 92% ethanol. In order to analyse the grain size of TiC-reinforced steels under different treatments, electron back-scattered diffraction (EBSD) analyses were performed by this SEM equipped with an EBSD attachment (Oxford Instruments, INCA Crystal). The samples were treated by electropolishing to eliminate mechanical stress at the surface.
2.3. Mechanical Property TestsThe hardness samples of three plates were mechanical grinded and polished before tests, and Vickers hardness was measured using macro-hardness tester (KB3000BVRZ-SA) under a load of 10 kg. The hardness of every samples was tested 10 times under room temperature, and the average of 10 measurements was taken as the final result. The tensile tests were performed on an AG-X 100 kN tensile testing machine with a crosshead speed of 1 mm/min under room temperature. Cylindrical Tensile testing samples with 5 mm diameter and 25 mm gauge length were prepared as per the GB/T 228.1-2010 Chinese standard. The Charpy impact tests were conducted using a SANS ZBC2452-B pendulum impact testing machine at −20°C temperature. Fracture morphologies of tensile and impact testing specimens were observed using a FEI Quanta 600 SEM.
2.4. Dry Sand Rubber Wheel Abrasion Wear Test (ASTM G65)In order to study the three-body abrasive wear resistance of TiC-reinforced steels under different treatments, abrasive wear tests were performed using a commercially made, dry sand/rubber wheel wear testing machine (model MLG-130, manufactured by the company of Chengxin, the location of company is Zhangjiakou, Hebei, China). The commercial conventional low alloy abrasion resistant steel NM500 with Vickers hardness of 540 was selected as contrast steel, whose composition in weight percentage is 0.28C, 0.31Si, 1.0Mn, 0.013Ti, 0.30Mo and balance Fe.25) The experimental process is performed according to ASTM standard test method G65 Procedure B.27) The experiments were carried out at room temperature, and each test of three plates were conducted three times and data were treated using statistical analysis. Equipment parameters and experimental parameters are shown in the Table 1. The samples of abrasion wear tests were weighed to calculate the wear mass loss using an electronic balance (SECURA225D-1CN) before and after the tests, before that the samples were carefully cleaned and removed unattached abrading particles. Then the morphologies of the worn surface of samples was observed using FEI Quanta 600 SEM.
| Experimental parameters | Applied load | Rotation speed | Size of abrasive | Revolutions of rubber wheel | Sliding distance |
| 45 N | 200 r/min | 212–425 μm | 2000 r | 1436 m | |
| Equipment parameters | Diameter of rubber wheel | Hardness of rubber wheel | Sand flow rate | ||
| 228.6 mm | 60 Shore A | 300 g/min |
The phase diagram of TiC-reinforced steel was calculated using Thermo-Calc software based on the actual composition. Figure 2(a) reveals the phase diagram of TiC-reinforced steel at the temperature range of 1300–1600°C. Different colored lines indicate the start and end of different phases. When the temperature is above 1550°C, the experimental steel is liquid. TiC has higher solubility in the liquid at high temperature, and it is difficult to precipitate in the liquid when the mass fraction of Ti and C is 0.57% and 0.30%, respectively. As solidification progresses, the liquid gradually decreases owing to the precipitation of δ phase and the peritectic reaction of L + δ → γ, and the mass fractions of Ti and C in the remaining liquid gradually increase. TiC will precipitate from the liquid when the actual solubility of Ti and C in the remaining liquid is greater than its equilibrium solubility, and the greater the mass fraction of C, the higher the mass fraction of TiC particles, which also reduces the temperature at the end of solidification.28,29) The precipitation of micron-sized TiC particles can be considered a eutectic reaction L → (γ + TiC)eutectic, whose solidification path can be expressed as L → L + δ → L + γ → L + γ + (γ + TiC)eutectic →γ + (γ + TiC)eutectic, thus the TiC particles precipitate towards the end of solidification.30) The precipitation temperature of TiC particles is hardly affected by the mass fraction of C, which is about 1460°C. The morphologies of initial micron-sized TiC particles observed by SEM is shown in Fig. 2(b). Initial micron-sized TiC particles distributes in the matrix, which seems like grain boundaries, and our previous research results indicate that it has a TiC structure.23) TiC particles precipitated towards the end of solidification, the remaining unsolidified liquid gathered between the dendrite of the solid phase, TiC precipitated from the remaining liquid, thus the distribution of the initial TiC particles seems like grain boundaries. The shapes of initial micron-sized particles are mainly long strips, lamellar and granular.
Phase diagram calculated of TiC-reinforced steel (a) and morphology (b) of initial micron-sized TiC particles. (Online version in color.)
Under high temperature conditions, TiC-reinforced steel had good fluidity, and redistribution of initial micron-sized TiC particles occurred during hot rolling. The morphologies of TiC particles in plates after hot rolling is shown in Fig. 3(a). The distribution of TiC particles is significantly changed, and the TiC particles relatively uniformly distribute in the matrix. The space between micron-sized TiC particles is reduced, and matrix is protected by TiC particles more comprehensively. Ni22) argued that uniformly distributed micron-sized TiC particles can not only improve the mechanical properties of the steel, but also enhance its wear performance. In order to characterize the particles more intuitively, the size of micron-sized TiC particles in 10 SEM figures was counted using Image-Pro Plus software. The main shapes of micro-TiC particles are long strips, lamellar, and granular. Therefore, only the lengths of micro-TiC particles were counted, and the histogram of the distribution frequency of TiC particle size is shown in Fig. 3(b). The statistical results show that the sizes of most micron-sized particles in the plates of TiC-reinforced steels are in the range of 1–6 μm, whose 40% are in the range of 1–2 μm, and the larger the sizes of particles, the less their quantity.
Morphologies and sizes distribution frequency of micron-sized TiC particles in plates. (Online version in color.)
The microstructures of NM500 and TiC-reinforced steels under different heat treatments are shown in Fig. 4. The microstructures of 880Q, 550PT+880Q and 650PT+880Q are ultra-fine martensite, and there are some micron-sized TiC particles distribute on the martensitic matrix. However, the microstructure of NM500 is lath martensite without micron-sized particles. The EBSD images (as shown in Fig. 5) evident that the grain size of 550PT+880Q is similar to that of 650PT+880Q, which is slightly smaller than that of 880Q. Nano-sized TiC precipitation can effectively refine the grains of primary austenite. However, when the nano-sized TiC exceeds a certain amount, the grains will not be further refined. And excessive nano-sized precipitation is disadvantageous to the ductility and toughness of steel.31,32)
Microstructures for NM500 (a), 880Q (b), 550PT+880Q (c) and 650PT+880Q (d).
EBSD images for 880Q (a), 550PT+880Q (b) and 650PT+880Q (c). (Online version in color.)
The nano-sized TiC precipitation in 880Q, 550PT+880Q and 650PT+880Q was observed using TEM, and its size distribution frequency was also counted. Figures 6(a)–6(c) show the TEM figures of TiC-reinforced steel plates under different treatments, previous works have shown that the spherical carbides in TEM figures had the FCC structure, which were nano-sized TiC precipitates.23,24) A little nano-sized TiC precipitation is observed in 880Q and the size is smallest. However, the number and sizes of nano-sized TiC in 550PT+880Q and 650PT+880Q gradually increase, and 650PT+880Q has the most and largest nano-sized TiC precipitation. Pre-tempering significantly increases the quantity of nano-sized precipitation in the martensite matrix. This is because that lots of nano-sized TiC precipitates during pre-tempering, and finally retains in the martensite matrix obtained by quenching.33) In addition, there are some rod-shaped ε-carbides formed by self-tempering in 880Q, while 650PT+880Q has almost no ε-carbides. This may be because lots of TiC precipitate during the pre-tempering process and reduce the solution C in the matrix, so that ε-carbides form difficultly. The size and density of nano-sized TiC precipitation were measured using Image-Pro Plus software, and the results are shown in Figs. 6(d)–6(e). The size of nano-sized TiC precipitation in 880Q is main in the range of 1–4 nm. When the pre-tempering temperature is 550°C, the sizes of nano-sized TiC precipitation increase to 2–6 nm, and the density of nano-sized TiC precipitation is 789 μm−2. As the pre-tempering temperature increases to 650°C, the sizes of the nano-sized TiC precipitation in 650PT+880Q further increase to 3–8 nm, and the density of nano-sized TiC precipitation is 987 μm−2. Pre-tempering not only greatly increases the quantity of nano-sized TiC precipitates, but also increases the sizes of the TiC precipitates.
Morphologies of nano-sized TiC precipitation in 880Q (a), 550PT+880Q (b) and 650PT+880Q (c) and size distribution frequency of nano-sized TiC precipitation in 550PT+880Q (d) and 650PT+880Q (e). (Online version in color.)
Figure 7 reveals the mechanical properties of 880Q, 550PT+880Q and 650PT+880Q, as can be seen, the mechanical properties of TiC-reinforced steel vary with the quantity of nano-sized TiC precipitation. The tensile strength of the 880Q, 550PT+880Q and 650PT+880Q gradually decreases from 1504 MPa to 1489 MPa, to the opposite, the yield strength of the 880Q, 550PT+880Q and 650PT+880Q increases from 1089 MPa to 1127 MPa, as shown in Fig. 7(a). The quantities of nano-sized TiC precipitation in TiC-reinforced steels increases with pre-tempering temperature increasing, and nano-sized precipitation has a positive impact on the yield strength of the steels. However, the precipitation strengthening also weakens solution strengthening of the TiC-reinforced steels, which has unfavorable effect on the tensile strength. Local strain concentration is prone to occur at the nano-precipitates, so that early cleavage cracking occurs in advance. Thus, the elongations of 880Q, 550PT+880Q and 650PT+880Q decrease from 9% to 8% with the temperature of pre-tempering increasing. The impact energy and Vickers hardness of TiC-reinforced steels under three different treatments are shown in Fig. 7(b), the variation of impact toughness and hardness of the 880Q, 550PT+880Q and 650PT+880Q is similar. 880Q has a good combination of high hardness and good impact toughness, Vickers hardness up to 508, and the impact energy is 41 J. However, as the pre-tempering temperature increases, the hardness and impact energy of 550PT+880Q and 650PT+880Q decrease. The 650PT+880Q with the most nano-sized TiC particles expresses the lowest hardness and impact energy. Amounts of nano-sized TiC precipitates from the matrix of 650PT+880Q, reducing the content of solid solution C in martensite, which decreases the hardness of the martensitic matrix, and the excessive precipitation of nano-sized TiC is detrimental to the toughness of the steel.
Tensile properties (a), impact energy and Vickers hardness (b) of TiC-reinforced steels under different treatments. (Online version in color.)
Tensile fracture morphologies of TiC-reinforced steels under different treatments observed by SEM is represented in Fig. 8, it can be seen that there are visible shear lip zones on the tensile fracture surfaces, and the macro tensile fracture morphologies are characterized by ductile rupture. The middle zones of the tensile fracture surfaces are mixed zones of fibrous and radiation zones, which show slight delamination. Delamination is a characteristic of the presence of amount of micron-sized carbides in TiC-reinforced steels. Figures 8(a1)–8(c1) show that the local morphologies of mixed zones indicate that amounts of large and small dimples distribute in the mixed zones, micron-sized TiC particles appear at the bottom of the large dimples. Delamination is formed through many large dimples joining together. The primary austenite grains of the TiC-reinforce steels are fine, so there are a large number of small dimples in the mixing zones. The small dimples can reduce the impact of the small micron-sized TiC particles on the ductility and hinder the crack propagation, so that the TiC-reinforced steels maintain good ductility with lots of micron-sized particles.
Tensile fracture morphologies of 880Q (a, a1), 550PT+880Q (b, b1) and 650PT+880Q (c, c1).
The Charpy impact fracture surfaces of TiC-reinforced steels under different treatments were observed by SEM to analysis the reason of good toughness. Figures 9(a)–9(c) represent the macro morphologies of impact fracture surfaces, which exhibit the characteristics of ductile fracture, but the shear lips and fibrous zones are small. The Charpy V-mouth impact samples were used in impact tests leading to localized areas of fibrous zones. A crack source is artificially set on the sample surface in advance, and the impact energy is mainly the energy absorbed by the crack during the propagation through the entire section. Figures 9(a1)–9(c1) show the enlarged views of radiation zones on fracture surfaces of 880Q, 550PT+880Q and 650PT+880Q, which indicate that the radiation zones are full of small dimples, but the dimples are shallow. The grains of the TiC-reinforced steel is relatively fine, the grain boundary area is larger, and the grain boundaries can hinder crack growth, which causes the crack to change direction to form tearing edges during the propagation process, so the energy absorbed by the crack propagation increases. The sizes of the nano-sized TiC precipitation in 550PT+880Q and 650PT+880Q are less than 10 nm, and the damage to the toughness is small. It is inevitable that nano-sized TiC precipitates on the grain boundaries, which weakens the effect of the grain boundaries on crack prevention. So, the sizes of dimples in Fig. 9(b1) are relatively large, and tearing edges are relatively few. Therefore, impact energy of 550PT+880Q and 650PT+880Q is lower than that of 880Q.
Impact fracture morphologies of 880Q (a, a1), 550PT+880Q (b, b1) and 650PT+880Q (c, c1).
The dry sand/rubber wheel wear tests were performed under room temperature to study the wear resistance of TiC-reinforced steels under different treatments. And the wear resistance of 880Q, 550PT+880Q and 650PT+880Q was compared with that of commercial conventional low alloy abrasion resistant steel NM500. The wear mass losses during wear and relative wear resistance of TiC-reinforced steels and NM500 are shown in Fig. 10. The wear mass loss of NM500 is the largest, up to 0.8 g, while the mass losses of TiC-reinforced steels are much lower than that of NM500, less than 0.6 g. The relative wear performance of TiC-reinforced steels is the ratio of the mass loss of NM500 to the mass losses of 880Q, 550PT+880Q and 650PT+880Q. As a matter of course, the relative wear performance of NM500 is 1, while the relative wear performance of 880Q, 550PT+880Q and 650PT+880Q are 1.35, 1.43 and 1.48 respectively, which indicates that TiC-reinforced steels with different quantities and sizes of nano-sized TiC precipitates exhibit different wear properties. 880Q has the smallest number of nano-sized TiC precipitates and the size of TiC precipitates is also smallest, whose wear performance is only 1.35 times that of NM500. While 650PT+880Q has the largest number of nano-sized TiC precipitates and the size is relatively large, whose wear performance is as high as 1.48 times that of NM500. At the same time, even if the matrix of TiC-reinforced steel contain few nano-sized TiC precipitates (880Q), the wear performance is also much higher than NM500. This is mainly due to the micron-sized TiC particles, the most important wear-resistant phase of TiC-reinforced steels, which can resist micro-cutting and protect matrix from wear.20)
Mass losses and relative wear resistance of NM500 and TiC-reinforce steels. (Online version in color.)
In order to investigate the wear mechanism of conventional low alloy abrasion resistant steel and TiC-reinforced steels with different treatments under three-body dry sand/abrasion wear, the wear surfaces of NM500, 880Q, 550PT+880Q and 650PT+880Q were observed using SEM. The morphologies of wear surface (Fig. 11(a)) indicate that the characteristic morphologies of the wear surfaces of NM500 is deep and long grooves and slight plastic deformation, and the main wear mechanism is micro-cutting.34) The wear surfaces of TiC-reinforced steel containing few nano-sized precipitation (880Q) are more flat, as shown in Fig. 11(b), the grooves are shallower and there is a blocked groove on the wear surface. The micro-cutting wear mechanism was effectively resisted by micron-sized TiC particles,24,35,36) so the main wear mechanism of TiC-reinforced steels is fatigue spalling. The effect of nano-sized TiC precipitation on wear mechanism was investigated through observing the wear morphologies of 880Q, 550PT+880Q and 650PT+880Q (Figs. 11(b)–11(c)). Fractured sand tips also appear on the wear surfaces of 550PT+880Q and 650PT+880Q, but the grooves caused by fractured sand tips gradually become shallow and short. In addition, the more nano-sized TiC precipitates in TiC-reinforced steel, the fewer shallow grooves, and the flatter wear surfaces. However, the fatigue pits exhibit an increasing trend. One of the main causes is that the wear mechanism transforms from micro-cutting to fatigue shedding. Another contributing factor is that the main movement of sands changes from sliding to rolling owing to that nano-sized precipitation distributed on the wear surface increased the sliding resistance.
Wear surface morphologies of NM500 (a), 880Q (b), 550PT+880Q (c) and 650PT+880Q (d).
Longitudinal sections of wear surfaces were also observed to understand the effect of micron- and nano-sized TiC particles on the wear mechanism. Figure 12 reveals that the wear subsurface does not undergo significant plastic deformation because the wear surfaces are mainly affected by the shear force of the rubber wheel. The wear surface of NM500 is undulated, indicating that it is subject to heavy wear. The wear surface of 650PT+880Q is relatively flat and two micron-sized TiC particles appear on wear surface. The 650PT+880Q is protected by micron-sized particles and strengthened by nano-sized precipitation. Supposing that TiC-reinforced steel is a gravel road, then micron-sized TiC particles are gravels that protect the cement matrix from wear. As for the precipitation of nano-sized TiC precipitation, it is the small grits in the cement matrix, which strengthens the matrix and enhances the support effect on gravels, so that the gravels can protect matrix better.
Longitudinal section morphologies of NM500 (a) and 650PT+880Q (b).
The schematic diagram of wear mechanism for the TiC-reinforced steels and NM500 is revealed in the Fig. 12. Conventional low alloy abrasion resistant steel contains no second phase that can prevent sand tips from sliding on the wear surface, thus the sand tips lead to deep grooves on the wear surface, as shown in Fig. 13(a). However, there are amount of micron-sized particles in 880Q, which can effectively resist micro-cutting, thereby making the grooves remarkably shallower (Fig. 13(b)). 650PT+880Q contains a large number of nano-sized precipitation, which effectively strengthens the martensite matrix and makes the grooves further shallower compared to 880Q (Fig. 13(c)). In addition, nano-sized precipitation also enables micro-sized TiC particles to be well supported, which is beneficial to wear performance.37) Therefore, with the increase of nano-precipitation in TiC-reinforced steels, the wear resistance is gradually enhanced.
Wear mechanisms of NM500 (a), 550PT+880Q (b) and 650PT+880Q (c) under dry sand/rubber wheel abrasion wear. (Online version in color.)
(1) The micron-sized TiC particles precipitated towards the end of the solidification, and the initial micron-sized TiC particles distributed like grain boundary, hot rolling changed the distribution of the initial micron-sized TiC particles and enabled them to uniformly distribute in the matrix.
(2) The microstructures of the TiC-reinforced low-alloy abrasion-resistant steels consisted of micron-sized TiC particles, nano-sized TiC precipitation and martensitic matrix after heat treatments. Nano-sized TiC mainly precipitated during pre-tempering, whose size and quantity were related to the temperature of pre-tempering.
(3) Although the precipitation of nano-sized TiC slightly reduced ductility and toughness of TiC-reinforced steels, the three-body wear resistance was improved to 1.5 times that of conventional wear resistant steel (NM500).
(4) During abrasive wear, the main wear mechanism of NM500 is mico-cutting, while the micro-cutting was effectively resisted by micron-sized TiC particles distributed in TiC-reinforced steels. Nano-sized precipitation strengthened the martensitic matrix, and improved the support of the matrix on micron-sized TiC, thereby the wear resistance was improved.
The authors acknowledge support from the National Basic Research Program, China (No. 2017YFB0305100), National Natural Science Foundation of China (No. 51874089, U1960112, 51504064), and Fundamental Research Funds for the Central Universities, China (No. N180715002, N2007002).
