Carbide welding tool, cutter body material and quenching pro
2017/09/06 Hits：
The world's annual consumption of carbide cutting tools accounted for more than 55% of all tool consumption, including carbide welding tool due to outstanding cost advantages and good forming process has been widely used, especially in the medium diameter range and size Forming processing area occupies an important position. As the application of indexable tool in the country has not yet universal, welding tool in the total consumption of carbide cutting tools accounted for a higher proportion. Compared with other tools, carbide welding tool in the practical application of industrial use of the performance of the instability of the defect and further reduce the cost of competitive pressure.
In the high-speed, large cutting force processing conditions, the knife body, knife teeth cross-sectional area of the smaller welding tool will be the following problems: the new tool or wear in the normal range of the tool, the welding tool near the knife or knife break ; Tool body or knife teeth to produce distortion, so that the accuracy of the tool down, resulting in the parts were scrapped; in the normal tool wear range, tool life decreased; reduce the cost of the pressure mainly from the domestic carbide tool production increased prices caused by the decline The
Carbide welding tool blade material is mainly 45 steel, T10A, 9SiCr and W6Mo5Cr4V2.45 steel is mainly used for structural strength of the better cutting tool, the structure of the poor strength of the cutter and hole processing tool blade is mainly used Comprehensive performance better 9SiCr. T10, 9SiCr and W6Mo5Cr4V2 are carbon tool steel, alloy tool steel and high-speed steel, the price is higher than 45 steel more than 1 times, 9SiCr price is about 45 steel 3 times. As the blade is not directly involved in cutting, the theoretical performance requirements are low, and some manufacturers have used 40Cr instead of 9SiCr, to reduce costs, but in the end due to a serious knife body fracture and had to give up. Therefore, to improve the welding process, improve tool performance and stability, reduce product cost for carbide welding tool manufacturers and users have great practical significance.
Analysis of the causes of
Domestic tool manufacturers currently used carbide welding tool production process shown in Figure 1. After analysis, the problem may arise in the high-frequency welding carbide blade link. When using copper solder (commonly used), high-frequency welding of the welding temperature is usually between 900 ℃ -1000 ℃, hardened body in the welding process was secondary heating, the temperature has reached the normalizing temperature of steel, so welding (See Figure 2) or the entire head of the knife body (see Figure 3) was normalized, resulting in the part of the knife body hardness and strength dropped significantly. At the same time, the heat transfer, near the weld or the head of the knife part of the body will be heated, although the heating temperature is lower than the normalizing temperature, but enough to cause the part of the knife body in the high temperature tempering, so that part of the knife Body hardness and strength decreased. This can be verified in the form of a damaged tool, and the damage to the welding tool often occurs at the teeth or head near the weld.
In the welding process, 9SiCr knife body and 40Cr knife body are also normal and tempering, but the latter is more fragile. The reason should be 40Cr knife body hardness and strength drop lower, this analysis needs to be tested to verify.
The test uses a 4-tooth helical cutter, which is close to most practical rod-shaped tools, and eliminates the occasional factors that are prone to complex shapes. Knife body materials were used 9SiCr and 40Cr, carbide blade material for the YG8; process as mentioned above, respectively, after the knife body quenching and then welding carbide blade, 9SiCr cutter quenching hardness of 52-54HRC, 40Cr knife body Of the quenching hardness of 59-61HRC.
After the high-frequency welding with Rockwell hardness tester were the same two parts of the hardness of the same material parts (see Table 1), the results show that: the hardness of the two materials have a significant decline in the blade; Slit 1-2mm) is significantly greater than the hardness of the adjacent welds; 40Cr cutter body than 9SiCr knife body to reduce the magnitude of the larger, consistent with the previous analysis.
9SiCr Cr element in the main role is to improve the hardenability; Si element can improve the material hardenability and hardenability, but also refine the carbide and improve the distribution of carbides, thereby improving the wear resistance of materials, tempering stability Sexual and plastic deformation resistance. In addition, Si is to strengthen the ferrite element, can improve the hardness and strength of steel. As the 9SiCr itself can achieve higher than the 40Cr quenching hardness, and a higher tempering stability, so after being normalized and tempered, the hardness and strength decreased less.
Metallographic assays can further validate the above analysis. The microfabrication of the test milling head was cut along the direction of the vertical weld and the microstructure of the tooth profile near the weld was observed under a scanning electron microscope. Figure 4 and Figure 5 are two kinds of material cutting edge of the blade near the back of the metal structure of the photo. From the microstructure can be seen: 9SiCr cutter after quenching + welding after the microstructure is mainly martensite, and more uniform; and 40Cr cutter body after quenching + welding after the microstructure of ferrite + pearlite , The former hardness is higher than the latter. It can be seen that the main reason for the failure of the welding of cemented carbide welding tool is that the cutter body near the weld and its adjacent parts are normalized or tempered and caused by the decrease of hardness and strength. The 40Cr blade is larger than the 9SiCr Hardness, strength drop lower, higher proportion of breaking.
Improvement Test and Effect Evaluation of Quenching Process
3.1 process improvement test program
As mentioned above, the secondary heating of high-frequency welding is not only the main reason for the performance of cemented carbide welding tool, but also the main obstacle to realize the tool body of 40Cr material instead of 9SiCr. To avoid process defects, only to re-hardened the body, or the quenching process on the welding, it is clear that the latter than the former more cost savings.
Using 9SiCr for the body material and did not play its role as alloy cutting tool steel red hardness and wear resistance. 40Cr after heat treatment has a high overall mechanical properties, better than 45 steel hardenability and close to the price, commonly used in manufacturing to withstand high load, impact resistance of the shaft parts. By the impact of the welding process, the original process with 40Cr for the body when the material did not give full play to the potential, so the new process program using 40Cr for the body material is theoretically feasible. However, the method of post-weld quenching may also cause other defects, such as quenching of the heating and cooling process, resulting in weld strength and blade hardness reduction and blade cracking and shedding.
At the same temperature, the linear expansion coefficient of the cemented carbide (blade) and steel (arbor) is very different, which is 1 / 3-1 / 2 lower than that of the steel, and the thermal conductivity of the cemented carbide is also lower than that of the steel. Quenching heating and cooling process, the two materials, the degree of thermal expansion and contraction is quite poor. After welding the blade and the knife body solidified into one, then the blade and the knife between the free shrinkage is limited, the blade and the knife body will be pulled, the role of compressive stress. As the carbide blade brittle, the ability to withstand stress is less than steel, blade cracks, so the main factors affecting the crack is quenching temperature, heating rate and cooling rate.
105 # solder equivalent to Cu-40Zn alloy. The results show that 105 # brazing filler metal is slow after brazing, obtain α + β 'structure, improve the cooling rate after brazing to obtain a single β' phase, β 'phase brittleness, will reduce the weld strength [1] The It can be seen that the blade crack and weld strength are related to the cooling rate, and the quenching cooling rate is mainly determined by the quenching medium.
The new process plan must be verified by the test in order to promote the production site. Test tool is still used in complex structure, the most widely used in industrial production of spiral end mills, blade material selection of tungsten cobalt class YG8. As the melting temperature of silver solder is lower than the quenching temperature of steel, the melting temperature of nickel solder is higher than the oxidation temperature of cemented carbide, copper prices are cheaper, so the choice of 105 # copper solder.
Table 2 is a different heat treatment process. Select the specific quenching process to consider the main quenching temperature, holding time, quenching medium and tempering temperature. Among them, different tempering temperatures correspond to different final hardness and other mechanical properties, as desired. In addition to mining machinery need to impact the use of medium temperature tempering, the general use of low temperature tempering around 200 ℃. Quenching medium were selected commonly used oil and salt water, quenching temperature selection 860 ℃, 790 ℃ and 950 ℃ third gear respectively corresponding to conventional quenching, sub-temperature quenching and zero insulation quenching or direct quenching after welding (105 # copper melting point is 909 ℃ , The welding temperature is about 950 ℃). Conventional quenching and sub-temperature quenching time for 30 minutes, zero insulation or welding quenching does not require insulation [2-4]. Sub-temperature quenching and zero insulation can reduce the heating time, reduce energy consumption, direct quenching after welding to avoid secondary heating, can be used for drill head, pick and head and other single-head tool.
Table 2 different heat treatment process program
3.2 Evaluation of process improvement test results
The experimental evaluation mainly examines the hardness and defects of the tool body in two aspects, the former evaluation of whether to solve the existing problems, which prevent the emergence of new defects, the test results in Table 3. As can be seen from Table 3:
(1) 40Cr die hardness of more than 40HRC, which brine cooling medium quenching hardness slightly higher than the oil, sub-temperature quenching hardness lower than the other two quenching temperature, but also reached the national standard on the hardness requirements of the handle 40- 45HRC, should be available.
(2) The hardness of the cemented carbide varies little, and the hardness decreases at 0.6HRA at a higher quenching temperature of 950 ° C, and the hardness increases at the other two lower quenching temperatures. The study shows that the hardness of the cemented carbide can be increased by about 3% -9% [5], but at the same time the carbide at 950 ℃ has begun to oxidize, the surface of WC and Co oxidation reaction to produce oxides, of which WC loss of more than Co lead to decreased hardness [6], other quenching temperature due to no oxidation and a slight increase in hardness. In short, the quenching temperature as far as possible under the control of 950 ℃, the hardness requirements of the use of non-harsh occasions, or suitable for the use of welding quenching heat treatment of single-tooth cutter, the quenching temperature can reach 950 ℃.
(3) weld strength and blade cracks. Quenching medium for the salt water, no matter what kind of quenching temperature will appear blade cracks and sharpening off, the reason should be brine cooling rate too fast. When the quenching temperature reaches 950 ° C, the solder dissolves and the blade moves relative to the position of the blade due to the temperature above the melting point of the 105 # copper solder. It can be seen that the quenching medium after welding quenching process can not use water, and 45 # steel in the oil quenching when the poor permeability is not recommended. The quenching temperature must be controlled below 900 ° C, preferably not more than 950 ° C (except for direct quenching after welding).
