Characterization of low-damage cutting of alfalfa stalks by self-sharpening cutters made of gradient materials

: The use of self-sharpening cutters can increase crop survival and regrowth by reducing the extent of stem damage incurred during the mowing stage and reducing the healing time at the harvest site. In this study, a self-sharpening cutter was prepared using a two-stage rare earth catalytic carbon – nitrogen – boron co-in ﬁ ltration process, and the self-sharpening and wear-resistant properties of the cutter were veri ﬁ ed by using metallographic organization testing, hardness testing, friction and wear performance testing, and the homemade tool wear test bench, and the low-damage cutting characteristics of the cutter were examined through ﬁ eld tests on alfalfa. The results show that the thickness of the penetration layer on the back face of a self-sharpening cutter made of gradient material is about 800 μ m, with a maximum hardness of 1,800 HV. The coe ﬃ cient of friction of the gradient material self-sharpening cutter is 67% lower than that of the commercially available 65Mn cutter. Gradient material self-sharpening cutter wear resistance is 2.15 times more than that of commercially available 65Mn cutter. The gradient material self-sharpening cutter reduces cutting damage by 11.42% compared to the commercially available 65Mn cutter. The application and promotion of self-sharpening cutting blades with gradient materials reduce alfalfa cutting damage, thereby improving reproductive yield.


Introduction
Cutter is a key harvesting component of harvesting machinery, and its performance will directly affect the operational efficiency and energy consumption of harvesting machinery.The main structural parameters of the cutter are wedge angle, slip angle, thickness, cutting edge height and width, etc.A performance [2].In addition, the harvesting machinery cutter is mainly prepared of carbon steel and manganese steel.These cutters, in the process of operation and crop stalks, soil, and stone chips, such as abrasive wear and adhesive wear [3], are very easily prone to passivation, chipping, and failure, resulting in reduced cutting performance and service life of the cutter [4].
In order to solve the problem of easy blunting of the cutter edge, a suitable thickness of the hardened layer can be infiltrated or coated on the back face of the cutter because the hardened layer on the back face is more wear-resistant than the cutter base material, the hardened layer is always convex, and the sharp edge can be maintained for a long time to form a self-sharpening edge [4][5][6][7].The formation principle of the self-sharpening edge is mainly to let the front face of the cutter produce different wear.The closer to the rear face, the less wear, so that the blade always protrudes.In recent years, many researchers and scholars have conducted a lot of studies on the preparation and classification of self-sharpening blades.Rostek et al. classified self-sharpening blades of semi-finished local steel [8]; Kakahy et al. prepared self-sharpening cutters applied to sweet potato harvester, which avoided damage to sweet potato tubers [9]; O'Dogherty concluded that the knife parameters linked to feed material properties can further provide a deeper understanding of the cutting forces [10]; Liu et al. developed a new chemically disordered multiphase tungsten high-entropy alloy, which improves the penetration performance by 10-20% compared to conventional tungsten alloys, and this study revealed the origin of the self-sharpening [11]; Jiang developed a 3D nanostructured coating inspired by the structure of sea urchins and sharks' teeth and used it to fabricate serrated self-sharpening knives to reduce surface contact and sliding friction at the interface between the tool and the workpiece [12]; Yuepeng et al. used three-layer plate vacuum composite rolling, rare earth catalytic carbon-nitrogen-boron co-infiltration process, and ultra-gravity combustion synthesis technology to prepare self-sharpening cutters, which proved to have good self-sharpening performance and wear resistance [13,14]; Xu et al. used laser cladding of Ni-based WC composite materials to prepare self-sharpening cutters, which had high hardness of cladding layer and good wear resistance, and met the requirements of self-sharpening edge of agricultural cutters [15].
The existing cutter mainly adopts an overall hardening treatment process for the cutting edge, and during the operation of the cutter, the cutting edge is seriously worn, resulting in rapid passivation of the cutting edge (Figure 1(a)), which leads to a decrease in the cutting performance of the cutter and an increase in alfalfa cutting damage.In order to solve the problem of easy passivation of the cutter edge, a hardened layer of suitable thickness can be infiltrated or coated on the back face of the cutter (Figure 1(b)), because the hardened layer on the back face has a higher abrasion resistance than the cutter substrate material, the hardened layer is always convex, which can keep a sharp edge for a long time and form a self-sharpening edge.Among them, the rare earth catalytic carbon-nitrogen-boron co-infiltration process can form a gentle hardness gradient change on the rear blade surface of the cutter so that it always stays sharp when cutting and colliding with the crop stalks, realizing lowdamage harvesting of the crop, thus enhancing the survival rate and regeneration rate.
The existing rare earth catalytic carbon-nitrogenboron process uses a section of the method of heating, but the thickness of the generated penetration layer is thin.Therefore, in this work, the self-sharpening edge cutter was prepared by a two-stage heating method coinfiltration process, and the self-sharpening edge cutter's self-sharpening and wear-resistant properties were verified by tissue analysis, hardness measurement, dry friction wear test, and design of the tool wear test bench, and the field test was carried out to check the low-damage cutting characteristics of the cutter on alfalfa.
2 Tests and methods First, use the DK7720 type wire cutting machine to cut the metal into small pieces, adhering to the GB/T 7925-2021 standard for the cutting process.Next, process these pieces using a metallographic specimen grinding and polishing machine to prepare the surfaces.After that, treat the specimens with a 4% nitric acid alcohol solution to etch them.This etching solution is primarily used to reveal the microstructure of the metals for analysis.Finally, examine and photograph the microstructure of the specimens using a Caikon-4XCE type metallographic microscope, following the GB/T 36591-2018 standard.The metallographic specimens were subjected to hardness test according to GB/T 4340.3-2012 standard using TH51 microhardness tester, whose loading time is set to 10 s and loading is set to 0.981 kN.Starting from the back blade surface of the cutter, as illustrated in Figure 2, measure the hardness at intervals set perpendicular to this surface.Continue these measurements along the direction of the back blade surface, conducting three repeated hardness tests at each interval of 150 μm parallel to the blade surface.Then, calculate the average hardness from these measurements using the method to minimize measurement errors.

Gradient material self-sharpening cutter preparation method
The cutter is an important cutting part in the mowing machine, the more complex the structure of the cutter, the higher the cost of the cutter.In order to reduce the cost of the mowing machine, a relatively simple structure of the flat cutter is used, and the initially selected structure of the cutter is shown in Figure 3.
The base material of the rare earth catalytic carbonnitrogen-boron co-infiltration cutter is 40Cr, and its chemical composition is shown in Table 1.
The material is medium carbon alloy steel, low price, has good comprehensive mechanical properties, and has good low-temperature impact toughness to meet the requirements of the preparation of rotary lawn mower cutter.Among them, Cr element can promote the infiltration of nitrogen elements in the formation of alloy carbide.Mn element can improve the strength of the material, promote the infiltration of carbon elements, and help to generate a thicker carbon and nitrogen co-infiltration layer, so 40Cr is selected as a rare earth catalytic carbon-nitrogen-boron co-infiltration cutter base material.
Commercially available cutters usually use 65Mn as the base material, and its chemical composition is shown in Table 2.
According to the existing rare earth catalytic carbonnitrogen-boron co-infiltration cutter preparation process, the infiltration agent composition is as follows [7]: rare earth accounted for 5%, boron and carbon-nitrogen co-    Due to the use of one-stage heating method of rare earth catalytic carbon-nitrogen-boron co-infiltration of the thickness of the infiltration layer is relatively thin, in order to further improve the thickness of the infiltration layer, can extend the holding time and increase the temperature of the co-infiltration, so the following respectively, the first section of low-temperature carbon-nitrogen coinfiltration of the temperature and the holding time of the factors such as the three levels of single-factor test, to determine the optimal conditions of the process.

Single factor test with different low-temperature carbonitriding temperatures
Taking the low-temperature carbonitriding temperature as a variable, the three levels of 570, 600, and 630°C were taken and held for 6 h.Then, a temperature of 800°C was maintained for 6 h, and finally oil quenching was performed at 850°C and tempering was done at 200°C.The hardness curve of the cutter was measured using a hardness tester, as shown in Figure 4.
From Figure 4, it can be found that beyond 75 μm, at the same distance, the hardness increases and then decreases with the increase in the co-diffusion temperature.When the temperature is lower, the rate of ammonia generation and the efficiency of carbon and nitrogen co-diffusion are lower.When the temperature is higher, the rate of ammonia dissipation in the infiltration tank increases, and the infiltration of nitrogen decreases.At 600°C, when the carbonitriding rate is moderate, the ammonia reaction is adequate, and the hardness of the carbonitriding layer is higher under this condition.

Single factor test with different low-temperature carbonitriding holding times
The low-temperature carbonitriding holding time was taken as the variable.Samples were subjected to carbonitriding for durations of 4, 6, and 8 hours at a temperature of 600°C.Following this, the samples were held at 800°C for 6 hours.Finally, the treatment concluded with oil quenching at 850°C and tempering at 200°C.The hard curve of the cutter was measured using a hardness tester, as shown in Figure 5.As can be seen from Figure 5, at the same 75 μm beyond the distance, the same distance, the hardness increases with the increase in insulation time, with insulation time of 6 and 8 h of the seepage layer thickness is basically the same about 800 μm, in 600 μm after the two hardness curve tends to be the same, continue to extend the insulation time to increase the thickness of the seepage layer of the role of the smaller, carbon-nitrogen infiltration insulation of 8 h for the preferred conditions.Therefore, rare earth catalysed carbon-nitrogen-boron co-infiltration heat treatment process of the two-stage heating method heat treatment process is determined.Initially, the material is treated at 600°C for 8 hours to facilitate low-temperature co-infiltration of carbon and nitrogen.This is followed by a continuation at 800°C for 6 hours, during which carbon, nitrogen, and boron are co-infiltrated using rare earth catalysts.The process concludes with the material being heated to 850°C for oil quenching and then tempered at 200°C.

Analysis of frictional wear and wear resistance of self-sharpening cutter made of gradient materials
In accordance with the requirements of the standard GB/T 7925-2021, the cutter was cut into a specimen block using a wire cutter, and the mass of the specimen block m 1 was weighed.The use of 45 steel friction ring on the rear blade surface of the cutter, according to GB/T 3960-2016 standards for line contact dry friction wear test, and the parameters of the MMS-2A screen display friction wear tester were set, with its loading load set at 100 N, rotational speed at 200 rpm, torque at 15 N•m, and friction time of the specimen set at 75 min.After completion of the test, the specimen block was cleaned, dried, and weighed for m 2 .
The wear resistance and self-sharpening performance of the cutter need to be verified by field wear test, but the field test needs to cut a large area of pasture, which costs a lot of manpower and material resources.So, in order to reduce the cost of the study and the time spent, as well as not to be limited by the season, the wear resistance and selfsharpening performance of the cutter were verified by wear test using a homemade cutter wear test bench, the structure of which is shown in Figure 6.The machine has a motor speed of 2,880 rpm, motor power of 1.5 kW, a large pulley diameter of 130 mm, and a small pulley diameter of 90 mm.
When using alfalfa grass for abrasives, the change in cutter wear was not significant, so to shorten the duration of the wear test, soil was used instead of alfalfa in this work.The soil used was collected from the Technology Demonstration Base of Pasture Innovation Team of Shandong Agricultural University.The volumetric weight was determined using the ring knife method, and the result was 2,480 kg•m −3 .The moisture content of the soil was determined using the drying method, and the result was 11.63%.The percentage of soil with different particle diameters was measured as 7.32, 6.32, 40.19, and 46.17% for soil larger than 2, 1-2, 0-1 mm, and less than 0.25 mm, respectively, using a standard split-sample test sieve.The wear test for the cutters involves operating them continuously for 5 h.The weight of each cutter is measured at 1 h intervals during this period to assess wear.

Field experiment
For a multi-crop forage crop like alfalfa, the amount of postharvest regrowth is extremely important for the entire year's alfalfa yield.When alfalfa is harvested with blunt Low-damage cutting of alfalfa stalks by self-sharpening cutters  5 cutting knives, it leads to tearing of alfalfa cuts, destruction of fibrous tissues, loss of water and nutrients from the healed cuts, and increased pulling force upward on the alfalfa stalk, which can lead to loosening of alfalfa roots.The self-healing process of alfalfa stalks is seriously impeded, thus affecting their regeneration process, prolonging the regeneration cycle, reducing the amount of reproduction and even death.Therefore, it is extremely important to have low damage characteristics of the cutter for alfalfa reproduction when harvesting alfalfa.
To verify the low-damage performance of the gradient material self-sharpening cutter, alfalfa was mowed at the same harvesting height using a gradient material self-sharpening cutter and a commercially available 65Mn cutter.After the alfalfa was mowed, two test areas of 1 m 2 were selected, and the alfalfa fields were watered regularly to ensure that the alfalfa fields had the same degree of wetness and dryness.Three randomly selected alfalfa plants in each test area were measured at 1-week intervals, and the average regenerated plant heights of the mowed alfalfa plants were recorded and calculated for a total of 3 weeks.

Comparison of cutter organization and performance
Since the organization of materials impacts their properties, we conducted a study of the microstructures of two cutters to better compare their performance characteristics.The microstructure of the cutter, magnified 100 times, is displayed in Figure 7. Figure 7, illustrates that the surface of the gradient material self-sharpening cutter blade features a bright, dense boron layer about 75 μm thick.This boron layer is tightly embedded into the base material, which consists of a knitted martensite structure.In contrast, the commercially available 65Mn cutter has a uniform martensite structure and lacks a hardened layer on the blade surface.Due to the gradient material self-sharpening cutter's rear cutter face, the existence of a seepage layer increases the wear resistance of the rear cutter face, so that the wear resistance of the self-sharpening cutter's rear cutter face is good.
The hardness of the cutter is positively correlated with the wear resistance, and the hardness can be used to judge the superiority of the cutter's wear resistance and selfsharpening performance; for this reason, the hardness test was carried out on two kinds of cutters, and the hardness curves are shown in Figure 8.
As can be seen from Figure 8, with the increase in distance from the rear blade surface, due to the presence of gradient material self-sharpening cutter boron layer and carbon-nitrogen co-penetration layer, resulting in a gradient decrease in the hardness of the cutter, the hardness of the cutter is gradually reduced from about 1,800 HV to about 490 HV, which can be judged to be due to the gradient material with self-sharpening performance.In the commercially available 65Mn cutter for a single martensitic organization, the hardness is basically maintained at 650 HV or so; the edge of the overall hardening, as reflected by the hardness curve, does not have a self-sharpening performance.

Comparison of friction coefficient and abrasion resistance of cutter back face
The frictional coefficient of the rear blade surface of the cutter not only affects the wear resistance of the cutter but also can judge whether the cutter has a self-sharpening performance.For this reason, the friction and wear performance test is conducted on the sample of the rear blade of two kinds of cutters, and the test results are shown in Figure 9.
Figure 9 shows that the friction coefficient on the rear surface of both cutters rises quickly for approximately 200 seconds before reaching a stable level.Mainly dry friction at room temperature, the first 200 s or so is the contact phase, where the specimen and the counter-abrasive ring are actually in microconvex body contact [16], and the friction coefficient increases rapidly to a great extent when the tips of the convex peaks of the surface profile are in direct contact [17].In the continuous long time friction process, the temperature gradually increases, the specimen surface forms a layer of oxide film, the surface becomes smooth, the friction coefficient tends to stabilise, the specimen enters the smooth friction stage [18].The friction coefficient of the commercially available 65Mn cutter is stabilized at about 0.42, while the friction coefficient of the self-sharpening cutter of the gradient material is stabilized at about 0.14, i.e., the coefficient of friction of the gradient material self-sharpening cutter is 67% lower than that of the commercially available 65Mn cutter.
In order to investigate the amount of change in the wear of the two cutter back blade samples after the dry friction test, the two cutter samples were weighed before and after the end of the test, and the histogram of the mass change is shown in Figure 10.
From Figure 10, it is found that after 75 min friction wear test, the gradient material self-sharpening cutter sample lost 0.0031 g, and the 65Mn cutter sample lost 0.0309 g.It can be seen that the gradient material self-sharpening cutter's rear blade surface has good wear resistance, and the wear resistance is better than that of the commercially available 65Mn cutter.The gradient material used in the self-sharpening cutter exhibits a decrease in hardness from one end to the other.Additionally, the rear surface of the blade demonstrates good wear resistance.These observations preliminarily confirm that the gradient material self-sharpening cutter possesses inherent selfsharpening characteristics.

Comparison of wear resistance between cutters and their wear amount
To evaluate and enhance the wear resistance of the gradient material self-sharpening cutter relative to the commercially available 65Mn cutter, a wear test was conducted   Low-damage cutting of alfalfa stalks by self-sharpening cutters  7 using a homemade tool wear test bench on specimens of both cutters.The initial weights of the cutters were recorded, and subsequent measurements of their mass were taken at one-hour intervals to track wear.The results of these measurements are displayed in Figure 11.The initial weights of the two cutters were 103.0858 g and 103.0021 g, which were inconsistent but did not affect the accuracy of the whole wear test and the measurement error could be ignored.
As can be seen from Figure 11, the wear amount of the two kinds of cutters increases gradually with the test time.After 5 h test, the wear amount of the self-sharpening cutter of gradient material is 2.1148 g, the wear amount of the commercially available 65Mn cutter is 4.5433 g, i.e., the wear amount of the commercially available 65Mn cutter is 2.15 times more than that of the wear amount of self-sharpening cutter of gradient material.Figure 12 shows the morphology of two cutters after wear; the left cutter is a 65Mn cutter, and the right cutter is a self-sharpening cutter of gradient material.
As can be seen from Figure 12, the wear of the commercially available 65Mn cutter produces a larger arc angle, while the gradient material self-sharpening cutter wear arc angle is smaller, the radius of curvature of the edge of the commercially available 65Mn cutter is significantly larger than that of the edge of the gradient material self-sharpening cutter.The closer the radius of curvature of the cutting edge to the tip of the knife, the larger the radius of curvature of the cutting edges, this is mainly because the closer the tip of the knife, the higher the linear velocity, and the friction is relatively serious.
From the above friction wear and abrasion resistance test, it can be seen that the gradient material self-sharpening cutter has good abrasion resistance on the rear blade surface, and the abrasion resistance is better than the commercially available 65Mn cutter.This is mainly due to the presence of an infiltration layer on the surface of the blade after self-sharpening, which reduces the hardness gradient of the blade.As the distance from the rear blade surface decreases, the hardness increases and wear decreases.This gradual abrasion process during cutting ensures that the blade remains sharp for an extended period [19][20][21][22].

Analysis of stubble and regeneration plant height after cutting of alfalfa stalks
To verify the low-damage cutting performance of the gradient material self-sharpening cutter for crop stalks, alfalfa was mowed at the same height using a commercially available 65Mn cutter and a gradient material selfsharpening cutter, respectively, and the alfalfa stubbles were observed, and alfalfa regeneration heights were measured in the first 3 weeks.

Field mowing test with commercially available 65Mn cutters
The changes in alfalfa stubble and alfalfa regrowth in the first 3 weeks using a commercially available 65Mn cutter are shown in Figure 13, and the results of plant height measurements of regrowing alfalfa in the first 3 weeks are shown in Table 3.
As can be seen in Figure 13, the alfalfa stubble was severely torn, the skin cracked, and the stubble height  was uneven, mainly because the commercially available 65Mn cutter blade was hardened as a whole, and in the process of cutting alfalfa, the cutter blade was blunted, which led to a significant reduction in cutting performance.Due to the serious damage to alfalfa, resulting in the loss of alfalfa moisture and nutrients, the alfalfa stalks withered and died in large quantities after 1 week.For the calculation of the experimental data in Table 3, the average value of alfalfa regeneration plant height was 12.0 cm after 1 week of growth, the average value of alfalfa regeneration plant height was 31.4 cm after 2 weeks of growth, and the average value of alfalfa regeneration plant height was 42.9 cm after 3 weeks of growth.

Field mowing test of self-sharpening cutter with gradient material
The stubble condition of alfalfa mowed with a gradient material self-sharpening cutter and the change in plant height of regenerated alfalfa during the first 3 weeks are shown in Figure 14.Measurements of plant height for the first 3 weeks of regenerated alfalfa are shown in Table 4.
From Figure 14, it can be found that the gradient material self-sharpening cutter cuts alfalfa with flat stubble and no significant damage.According to the test data in Table 3, the average height of the regenerated plants of alfalfa after 1 week of growth was 20.5 cm, the average height of the regenerated plants of alfalfa after 2 weeks of growth was 39.7 cm, and the average height of the regenerated plants of alfalfa after 3 weeks of growth was 47.8 cm.This is because the low cutting damage and even stubble of alfalfa shorten the healing time of the cutting site, resulting in good growth conditions and higher plant height of the  regenerated alfalfa.The average regrowth height of alfalfa in the first 3 weeks after mowing with the two cutters calculated above was tested for comparison, as shown in Figure 15.
Figure 15 shows that the height of alfalfa plants 3 weeks after mowing with the gradient material self-sharpening cutter was greater than the height of alfalfa plants mowed with the commercially available knife.The main reason is that the gradient material self-sharpening cutter can keep the sharp edge for a long time, which significantly reduces the cutting damage to the alfalfa, and the regenerated alfalfa grows better and taller.
Alfalfa plant height slowed down 2 weeks after alfalfa mowing, mainly because alfalfa reaches the first flowering stage, and alfalfa height basically does not change much [23].Therefore, judging the degree of alfalfa damage by the height of the regenerated alfalfa plant after 3 weeks, the cutting damage of the gradient material self-sharpening cutter on alfalfa was elevated by 11.42% compared with that of the commercially available cutter, which proved that the gradient material self-sharpening cutter had a low-damage cutting performance.The research prepared self-sharpening sharp cutter base material for 40Cr, compared with the commercially available 65Mn cutter, the production cost increased only 25%, but the service life was increased by 2.15 times, while reducing the number of times of cutter replacement of forage harvesting machinery, improve the operational efficiency, reduce the operational energy consumption, and can achieve significant economic benefits.It should also be noted that the results of this study show that the selfsharpening sharp cutter prepared by rare earth carbonammonia-boron co-infiltration realizes low damage cutting of alfalfa stalks, significantly shortens alfalfa regeneration cycle, and improves the average annual yield and quality of forage, which are potential economic and social benefits that will be gradually manifested with the promotion of this technology.

Conclusion
In this work, in order to enhance the thickness of the boron layer on the cutter back face, on the basis of the existing one-stage heating method of rare earth catalyzed carbon-nitrogen-boron co-infiltration process, the two-stage heating method is proposed.(1) A two-stage heating method was identified: the low-temperature carbon-nitrogen co-infiltration (600°C for 8 h), followed by high-temperature rare earth catalyzed carbon-nitrogen-boron co-infiltration (800°C for 6 h), and then finally, the oil is quenched at 850°C, and the tempering is done at 200°C.(2) On the basis of this process, 40Cr was selected as the base material for the preparation of a self-sharpening cutting edge.(3) The friction coefficient of the self-sharpening cutter of the second-gradient material was stabilized at about 0.14, while the friction coefficient of the commercially available 65Mn cutter was stabilized at about 0.42, as obtained by the dry friction test.(4) As verified by the tool wear test, the gradient material self-sharpening cutter has good self-sharpening performance, and the wear resistance is 2.15 times higher than that of the commercially available 65Mn cutter.(5) A field comparison test was conducted to determine the degree of alfalfa damage by the height of alfalfa regrowth after 3 weeks, and the gradient material self-sharpening cutter reduced the cutting damage by 11.42% compared with the commercially available 65Mn cutter, and the lowdamage harvesting performance of the gradient material self-sharpening cutter was significantly improved.In conclusion, self-sharpening cutters made of gradient materials are valuable in reducing mowing damage and thus increasing reproduction.

Figure 1 :
Figure 1: Cutting edge wear and hardening layer of the back cutter face.(a) Schematic diagram of edge wear.(b) Schematic of the hardened layer on the back face.

Figure 4 :
Figure 4: Hardness curves and indentation morphology of boron nitride cutting tools carburized for 6 h at different carbonitriding temperatures.

Figure 5 :
Figure 5: Hardness curves and indentation morphology of carbonnitrogen-boron cutting tools with different carbonitriding holding times at a heating temperature of 600°C.

Figure 7 :
Figure 7: Two kinds of cutter edge microstructure morphology.(a) Self-sharpening cutting edge for gradient materials.(b) Commercially available 65Mn cutter edge.

Figure 10 :
Figure 10: Histogram of the mass change of the tool face after two tool specimens.

Figure 11 :
Figure 11: Mass change curve of two kinds of cutter.

Figure 12 :
Figure 12: The morphology of the two cutters after wear.

Figure 13 :
Figure 13: Changes in alfalfa stubble and regrowth height in the first 3 weeks of mowing with commercially available 65Mn cutter knives.

Figure 14 :
Figure 14: Changes in the height of alfalfa cut stubble and regrowth in the first 3 weeks of mowing with self-sharpening cutters of gradient materials.

Figure 15 :
Figure 15: Average plant height changes of alfalfa regeneration in the first 3 weeks after mowing.

Table 1 :
Main components and content of 40Cr (wt%)

Table 2 :
Main components and content of 65Mn (wt%)

Table 3 :
Plant height measurements of regenerated alfalfa in the first 3 weeks after mowing with commercially available 65Mn cutters

Table 4 :
Results of plant height measurement in the first 3 weeks after cutting after optimization of alfalfa cutting machine