Medium frequency induction heating machine is used in forging preheating and quenching of 65Mn steel plowshares

The plowshare is a typical basic part of agricultural machinery, with an average service life of approximately 0.5 farming seasons. At present, our country consumes millions of plowshares and tens of thousands of tons of steel every year. With the continuous improvement of the level of agricultural mechanization, the consumption of plowshares will increase year by year. Although relevant units in our country have conducted a lot of experimental research on the production technology and materials of plowshares, domestic plowshares have basically not deviated from the traditional production technology, and there is still a big gap compared with the more advanced levels.

There are two main failure modes of the plowshare: one is wear, if it is partially worn out, it will be scrapped; the other is that the impact-tough DZ type plowshare not only ensures the hardness required for its wear resistance (40-45HRC) after roll forging deformation heat treatment, And the strength and toughness are significantly improved.

1) Comparing the production process of traditional plowshares and DZ-type plowshares, the disadvantages of plowshares produced by traditional processes are: long production cycle, multiple processes, multiple heating times, low production efficiency, and many links that affect product quality. The plowshare produced by DZ type forging waste heat quenching only needs two heatings in the whole process, and the processing steps are reduced to 11.

Compared with the traditional processing technology, the DZ type plowshare that has been treated by forging waste heat quenching deformation heat treatment has advanced production equipment and technology, the production efficiency is increased by 4 times, the steel utilization rate is increased by 20%, the energy consumption is reduced by 55%, and the production cost is reduced by 34%. Product quality all meets the first-class requirements. The DZ type upland plowshare is a new type of plowshare with low resistance and self-sharpening blades. It has made fruitful improvements in terms of structure and heat treatment technical requirements without affecting interchangeability, such as changing only the edge quenching of traditional plowshares. For overall quenching, it fundamentally solves the problem of failure caused by local wear of non-quenched parts.

2) Roll forging and heat treatment process of DZ plowshare. The equipment used in production is a roll forging machine, a medium frequency induction heating furnace, a self-made calcium chloride solution quenching tank, and the 65Mn steel blanks for the plowshare are 18mm Trapezoidal blocks.

The intermediate frequency induction heating temperature of the plowshare blank is 1100 - 1120°C. The heating cycle (the time interval between two pushes of material into the intermediate frequency induction coil) depends on the specifications of the plowshare. It is roughly 10-30S, from the beginning of roll forging to before quenching. The whole process takes about 20 seconds. After medium-frequency induction heating, it is rolled through the roll forging machine three times within 10 seconds. After rolling, the thickness from the back to the blade is 8-3mm, and the deformation rate is 36%-83%. Then through trimming, hole and pressing, the temperature of the blade has dropped to about 800℃. Then the blade is rolled again, and the 3mm thick blade is extruded to 1.Smm, and then the residual heat quenching is performed. .

Since the thickness of the back of the workpiece is quite different from that of the cutting edge, that is, from the beginning of roll forging to the end of the last process before quenching, the cutting edge is about 760°C and the back is about 860°C. In order to ensure that the cutting edge can be hardened, the plowshare should be immersed in the quenching medium at a faster speed at this time. Because the temperature on the back is higher, in order to prevent the assembly square holes from cracking, the cooling time should not be too long, generally controlled at 4-6s, and tempering in time. 

Choosing the appropriate quenching medium is very important to reduce the deformation of the plowshare. Because the cross-section thickness of the plowshare blank after roll forging is quite different, whether the overall quenching deformation can be controlled within the allowable range (bending deformation allowed is 2mm) and whether the quenching hardness is uniform becomes the key to forging waste heat quenching. Practice has shown that selecting a CaCl2 aqueous solution with a density of 1. 30 - 1. 35g/cm3 as the quenching medium can meet the technical requirements. There are also some units that use triple nitrate or double nitrate quenching agent, which is also very effective.

3) The structure and performance of DZ type plowshare deformation heat treatment. After roll forging deformation heat treatment, the metallographic structure of the back, middle and edge parts are all tempered trotenite. As the amount of deformation increases (the deformation rate of the back is 56%, the middle part is 56%-83%, and the blade part is 83%), the number of stencils increases and the lath becomes thinner.

As the amount of deformation increases (from back to edge), the amount of lath martensite in the structure increases. Although the impact specimen is cut from the back 8mm (size 5mm x 5mm x 10mm without notch), the impact toughness of the specimen quenched by the residual heat of roll forging is still 10% higher than that of ordinary quenching without punching. , it can be inferred that the edge impact toughness will be higher, which is the main reason for the long life of the plowshare.