SU1186663A1 - Method oof reconditioning cld-rlling mill rolls - Google Patents

Abstract

1. METHOD OF RESTORING THE COLD ROLLING ROLLS, mainly weld heat-resistant steel, including tempering, in order to increase the resistance of the rolls by preventing delamination of the weld metal while maintaining the hardness of the deposited layer, tempering is carried out in the interval: the recrystallization temperature of the base metal tempering temperature weld metal. 2. The method according to claim 1, which is also distinguished by the fact that tempering is carried out after rolling with a roller 80-90% of the norm (L of the rolled metal.

Description

00 9e

9)

One CO 1 The invention relates to methods for improving the durability of cold rolling work rolls with a deposited working layer and can be used in cold rolling mills. The purpose of the invention is to maintain the stability of the rolls by preventing delaminations of the weld surface while maintaining the hardness of the weld layer. The use of high-temperature tempering during the operation of the deposited roll causes the p / gastically deformed metal to be more resilient than the appearance of recrystallization, the work hardening zone of the base metal fused to the weld metal is completely removed, while the structure of the metal and its properties become similar operation. High-temperature tempering completely removes the work hardening in the base metal in the fusion zone and restores its fatigue strength to its original values. Removing the work hardening zone prevents the nucleation of fatigue fracture foci and significantly reduces the likelihood of delamination. This eliminates the main cause of the rolls coming out of the building - hardening of the transition zone, due to which their resistance increases. The lower boundary of the proposed temperature range is limited by the temperature of the onset of recrystallization of the base metal (). The recrystallization processes proceed the faster, the higher the heating temperature. Therefore, the tempering tempering temperature is better to choose as high as possible, but not lower than the recrystallization temperature, since the use of a lower tempering temperature, lower than the recrystallization temperature, does not completely restore the original properties of the Fusion zone, as the heating temperature is low. and the return occurring at it somewhat increases the plasticity, but only recrystallization completely restores the initial plasticity (before work hardening) of the metal. Conducting an additional tempering of the working layer deposited with heat resistant steels of high hardness in the specified temperature range does not cause a decrease in hardness and also contributes to an increase in its fatigue strength. Increasing the tempering temperature above the tempering temperature of the deposited metal leads to a decrease in the hardness of the deposited heat-resistant steel of the surface layer. Hardness decreases due to decomposition of martensite, coagulation of carbides. A decrease in the hardness of the deposited layer in turn adversely affects the wear resistance of the mill rolls. The deposited rolls must be subjected to high-temperature tempering after rolling 80-90% of the metal rate, which is set for each case on the basis of statistical data on the resistance of the rolls. The limitation of the service life of the weld roll to tempering 80-90% of the rolled metal rate is explained as follows. When working with a roller less than 80% of the rate of the metal rolled on it, the failure of the deposited layer due to the detachment of the deposited layer is practically not observed. Therefore, premature roll-up of a roll reduces its overall service life. When a roll is being processed with more than 90% of the metal rolled on it, in some cases fatigue cracks form in the cold-worked layer. which are not eliminated during tempering and are further developed during operation during the first hours of operation. Example. The mill rolls (base metal ZOHGSA steel, deposited metal steel R18A10) cut out discs for fatigue tests with a thickness of 10-15 mm. Fatigue tests are performed on a rotating sample with a constant load applied. The compressive stress in the contact zone is 3500-4000 MPa. At the first stage of testing, the conditional norm of rolled metal is determined (the number of cycles until the deposited metal is peeled off). It is statistically established that, when hard-alloy rollers are rolled in, the deposited metal is peeled off after 5–10 loading cycles (jioijii; jH of the painted metal). To some single cases, detachments are observed after, 5 x

g

X 10 Cyclops loaded, i.e. after 90% of the conditional norm rolled. When loading with fewer cycles than 4.5-10 (90% of the norm), no detachment of the weld metal is observed.

Seven batches of discs are subjected to further fatigue tests. The first batch is subjected to rolling by carbide rollers until the appearance of deposition of deposited metal (l, 5-10 loading cycles). The remaining six batches of disks, after loading, corresponding to 80.80, 85.90, 80 and 85% of the conditional norm of rolled metal (table, batches 2-7), are subjected to tempering at different temperatures with an exposure of 1 hour, then they are run until destruction (peeling) of the deposited layer.

During testing, the hardness of the discs is controlled by their cross section. The hardness of the weld metal is 63-64 HRC, the main 28-30 HRC. During operation (work hardening), the hardness of the deposited metal increases to 64–65 HRC, and the hardness of the fusion zone increases to 35–36 HRC.

The test results are presented in the table.

Tests show that the use of high-temperature tempering in comparison with a known method in the temperature range: the recrystallization temperature of the base metal - the tempering temperature of the deposited metal (450-580 s, batch 35) leads to an increase in the resistance of the deposited disks 1.6-1.9 times

due to the increase in fatigue strength of the main metaplates (remove the work hardening of the AO of the initial values of hardness and plasticity) while maintaining the 5 high hardness of the weld.

layer (63.5-64.5 HRC). Recrystallization completely restores the properties of the fusion zone.

Holidaying with more

• A low temperature than the recrystallization temperature (batch 2) does not significantly improve the fatigue strength, since this does not eliminate the work hardening of the fusion zone. Some of the fatigue strength (by 10–20%) is explained by the return processes occurring at 250 and 400 ° C.

Conducting tempering at a high temperature than the tempering temperature of heat-resistant steel at maximum hardness results in the removal of work hardening and a sharp decrease in the hardness of the weld layer (to 48 5 49 HRC), which is unacceptable for cold rolling rolls.

Thus, the implementation of the proposed method provides a significant increase in the fatigue strength of the base metal and the resistance of the weld rolls of cold rolling mills by preventing delaminations of the weld layer while maintaining its high hardness. The increase in the cost of the deposited rolls allows, despite the introduction of additional heat treatment during the operation of the rolls, to reduce the consumption of the rolls by 1.6-1.9 times and significantly reduces the need for rolls and the cost of their production.

Controlled parameter

t tempering temp., C T1degree of deposited (surfaceIo) layer after tempering, HRC 64-65 64-65 64-65,5

Party

gp

I

7 (known) 64-65.6 63.5-64 48-49 64-65 35-36 32.5-34

- 80 J g 5-10 6-10 In some single instances, 95% of the norm of rolled metal is observed.

thirty

28

29

28 33-34

85

80

90

85

9-10 9.5-10 1.0 10 1.1-10 5.510 cracks and peeling after rolling

Claims (2)

1. METHOD OF RESTORING ROLLS OF COLD ROLLING MILLS, mainly deposited by heat-resistant steels, including tempering characterized in that, in order to increase the resistance of the rolls by preventing detachment of the deposited metal while maintaining the hardness of the deposited layer, tempering is carried out in the range: temperature * recrystallization of the base metal tempering temperature deposited metal. 2. The method of pop. ^ characterized in that the vacation is carried out after rolling with a roll of 80-90% of the norm of the rolled metal. > 118 666 3