The residual heat of the sprocket after forging is directly quenched

Test subjects and methods

test subject

The test object in this paper is a sprocket, and its parts structure is shown in Figure 1. The number of teeth of the sprocket is 21, the diameter of the index circle is about 650mm, the inner diameter is about 450mm, the thickness of the tooth is about 65mm, and the weight of the part is about 50kg.Its technical requirements: quenching and tempering treatment, hardness 229~302HB (dB: 3.5~4.0), metallographic structure grade 1~4, grain size ≥ grade 5.

experiment method

The original production process of the sprocket:Blanking → billet making → intermediate frequency heating → forging forming → trimming → quenching and tempering → magnetic particle inspection → grinding → surface quenching + low temperature tempering → magnetic particle inspection → machining.

Production process of sprocket waste heat quenching:Blanking → billet making → intermediate frequency heating → forging forming → trimming → residual heat quenching → high temperature tempering → magnetic particle inspection → grinding → surface quenching → low temperature tempering → magnetic particle inspection → machining.

The sprocket material is 40Mn2, which belongs to low hardenability quenched and tempered steel and alloy structural steel. Its main chemical composition is shown in Table 1.

Table 1 Main chemical composition of 40Mn2 steel (wt%)

element

C

Mn

P

S

Si

Ni

Cr

Cu

content

0.37 ~ 0.44

1.4 ~ 1.8

≤ 0.03

≤ 0.03

0.17 ~ 0.37

≤ 0.30

≤ 0.30

≤ 0.3

By consulting the "Heat Treatment Manual", it can be known that the material Ac3=766 ℃, and the quenching temperature is recommended to be 830-870 ℃.The initial forging temperature of this material in our factory is 1150±50℃. After two processes of forging forming and trimming, the temperature of 10 pieces after trimming is detected by an infrared thermometer. The temperature after trimming is about 950℃. The temperature is about 880~910℃, which is slightly higher than the recommended quenching temperature.

In this test, after forging with a 13t electro-hydraulic hammer from our factory, the edges are trimmed by the trimming press, and then transferred to the hook above the quenching tank through the slideway, and the designed quenching procedure is started to complete the quenching process (Fig. 2).The residence time of the parts in the quenching medium is 5 to 6 minutes.The quenching medium adopts ZY-747 PAG water-soluble quenching medium produced in Liuyang, Hunan.

After the sprocket is quenched by waste heat, it is transferred to the trolley furnace of the heat treatment branch in time for high temperature tempering, so as to avoid cracking due to excessive structural stress generated during the quenching process.

Test Results and Discussion

Quenching hardness test

SprocketAfter quenching with residual heat after forging, randomly select three pieces for quenching hardness inspection (three points are detected in the 120° direction of the tooth plane, and the testing equipment is HB-3000 Brinell hardness tester), and compare with the original process quenching hardness. The results are shown in Table 2.

Table 2 Comparison of quenching hardness of two processes

Serial number

Hardness after forging after heat quenching/HB

Conventional Quenching Hardness/HB

Technical requirements/HB

1

555, 534, 555

445, 387, 415

385 ~ 555

2

534, 555, 555

445, 415, 387

3

534, 514, 534

445, 415, 415

unevenness

±10

±29

Quenching hardness results show that compared with conventional quenching and tempering quenching,SprocketThe quenching hardness after forging is higher, because the high-density dislocations in the quenched martensitic structure after forging and the fine and dispersed carbide pinning dislocations precipitated during the forging deformation process, as well as the complete quenching, make it more common than conventional quenching. Has high quenching hardness (quenching hardness increased by more than 100HB).In addition, the dispersion of quenching hardness after forging is smaller than that of conventional quenching hardness.The main reason is that the residual heat quenching after forging improves the hardenability of the steel, reduces the depth of the decarburized layer caused by the secondary heating, and uniformly quenches and cools the single product in the PAG water-soluble quenching medium, as well as effectively and uniformly quenching the quenching medium. stirring, so that it has better hardness uniformity.