RU2398892C1 - Procedure for surface strengthening of forming rolls - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: surface is treated with compressed scanning arc of direct action in argon. Also surface of forming rolls is strengthened with a pulse arc at current power 300-250 A, voltage 18-30 V superposing strips along spiral line at rate of arc travel along surface 1.0-1.3 m/min. A gap of 10-12 mm is maintained between a tungsten electrode and strengthened surface of the roll. Notably, electrode and strengthened surface of the roll are protected from oxidising with argon at its consumption 600-700 l/h.

EFFECT: upgraded quality of strengthened layer, raised resistance and operability of forming rolls.

2 tbl, 1 dwg

Description

The invention relates to ferrous metallurgy, in particular to the surface hardening of rolling rolls.

A known method of hardening a rolling roll, including mechanical turning of the roll, heating for surfacing at a speed of 50-100 ° C / h to a temperature of 250-300 ° C, arc surfacing at a density of 40-45 A / mm ² with a surfacing speed of 25-30 m / h and conducting holidays at a temperature of 300-400 ° C with exposure for 1.5-2 hours [1].

A significant disadvantage of this method is the significant duration of the hardening treatment due to several operations, as well as the insufficient durability and strength of the hardened layer of the rolling roll.

There is also known a method of heat treatment of rolling rolls, including induction heating for hardening, cooling and tempering of the roll [2].

A significant disadvantage of this method is the high complexity of the heat treatment of the rolls, as well as the insufficient depth and hardness of the hardened layer of the rolling roll.

Also known is a prototype method of surface hardening, including surface treatment with a compressed scanning arc of direct action in argon at a travel speed of 90-180 m / h, arc current of 200-300 A, with the imposition of hardened strips butt and overlap by 1 / 3- 1/2 width [3].

A significant disadvantage of this method is the insufficient depth and increased fragility of the hardened layer.

The desired technical results of the invention are to improve the quality of the hardened layer, as well as the durability and performance of the rolling rolls.

For this, a method for surface hardening of rolling rolls is proposed, which includes surface treatment with a compressed scanning arc of direct action in argon, and the surface of the rolling rolls is hardened by a pulsating arc at a current of 300-250 A, voltage of 18-30 V with overlapping of the helix lines at a speed moving the arc on the surface of 1.0-1.3 m / min, with a gap between the tungsten electrode and the hardened surface of the roll 10-12 mm, and the electrode of the hardened surface of the roll against oxidation is protected by argon m at a flow rate of 600-700 l / hour.

The inventive parameters are selected experimentally on the basis of the following assumptions that when the arc current is less than 250 A, the surface is not heated enough, as a result of this, a martensite structure of insufficient depth equal to less than 300 microns is formed. With a current strength of more than 300 A, a layer with a pronounced crystallization texture forms from the surface of the roll. At a voltage under which the non-consumable electrode is located, less than 18 V, the surface does not warm enough to perform the hardening process. At more than 30 V, the processed surface is melted. When moving the arc on the hardened surface at a speed of less than 1.0 m / min, the required depth is not hardened layer. At a movement speed of more than 1.3 m / min, surface underheating occurs and a hardened structure is not formed in the surface layer. When the gap between the tungsten electrode and the work surface is less than 10 mm, the work surface is melted, and when the gap is more than 12 mm, the surface is not heated enough to perform the hardening process. When the argon flow rate is less than 600 l / h, the arc breaks, and at more than 700 l / h the arc does not occur. To ensure a continuous hardened layer, arc movement over the surface along a helical line with the application of hardened sections is used.

The method of hardening the surface of the rolling rolls using electric arc hardening of the surface of the roll with a pulsating arc was implemented in an experimental setup (Figure 1) and consists in the following.

A rolling roll (1) was installed in the chuck of the headstock (2) of the rolling mill machine (3). The quenching head (4) was installed and fastened on a support (5) of a roll-forming machine (3). By transverse movement of the support (5), a gap was established between the tungsten electrode (6) of the quenching head (4) and the machined surface of the caliber (7) of the rolling roll (1). Between the surface of the roll (1) and the tungsten electrode (6), which is energized, an electric arc of reverse polarity was excited by a high-frequency spark discharge. To protect the tungsten electrode (6) and the heated surface of the roll (1) from oxidation, an inert argon gas was introduced into the arc gap. To disperse the thermal arc, to regulate the shape and area of the heating spot on the surface of the roll (1), electromagnetic control of the arc was used. The regulation of the thermal cycle in the surface layer of the roll (1) was carried out by changing the voltage and arc current, the shape and speed of movement of the heating spot along the surface of the roll (1). Hardening of the surface was carried out by moving the heating spot along the surface of the roll (1) with the imposition of hardened sections along a helix.

The method is implemented in an industrial environment for hardening the rolls of the finishing stand of a rail and beam workshop on a roll mill model 1K826. An electric arc of reverse polarity was excited between the surface of the roll and the energized tungsten electrode by means of a high-frequency spark discharge. To protect the electrode and heated metal of the roll from oxidation, an inert argon gas was introduced into the arc gap. To disperse the thermal power of the arc, to regulate the shape and area of the heating spot on the surface of the roll, electromagnetic control of the arc was used. The regulation of the thermal cycle in the surface layer of the roll was carried out by changing the voltage and arc current, the shape and speed of movement of the heating spot along the surface of the roll. Hardening of the surface with a given area was carried out by moving the heating spot along the surface of the roll with the application of the hardened sections in a straight or helical line.

The inventive method was used when hardening the rolls of the finishing stand of the rail and beam workshop for rolling the channel No. 22U and No. 40U.

The necessary hardened layer was obtained by changing the arc current strength from 250 to 300 A, voltage from 18 to 30 V, arc movement speed from 1 to 1.3 m / min, and also adjusting the gap between the electrode and the hardening surface from 10 to 12 mm. In this case, the argon flow rate was varied from 600 to 700 l / h.

The inventive method of hardening provided on the rolls obtaining a hardened layer with a depth of 460-500 microns with a hardness of 7500-8000 MPa. At the same time, the roll resistance on the channel No. 40U increased from 1,500 tons to 2,500 tons, on the channel No. 22U - from 500 tons to 800 tons. Reduced roll consumption by 2.5 kg / t.

The technological parameters of hardening treatment are given in table 1. The results of the study of the depth and hardness of the hardened layer are given in table 2.

Table 1 No. p / p Current strength, A Voltage Clearance mm Argon consumption, l / h Speed of movement, m / min one 250 eighteen 10 600 one 2 260 twenty eleven 650 1,2 3 280 25 12 690 1.25 four 300 thirty 10 700 1.3 prototype 200-300 - - - 1.3-1.5

table 2 No. p / p The depth of the hardened layer, microns Microhardness, MPa one 490 7800 2 460 7500 3 480 8000 four 500 8000 prototype 600-970 9000

Information sources

1. Patent RU 2339469 C2.

2. Patent RU 2163644.

3. Surface hardening of nodular cast iron with an electric arc of direct action. // Izv. university. Ferrous metallurgy. 1994. No. 10. S.48-49.

Claims (1)

The method of surface hardening of rolling rolls, including surface treatment with a compressed scanning arc of direct action, excited between a tungsten electrode and a hardened surface at a current strength of 300-250 A with overlapping stripes along a helix, protecting the electrode and hardened surface of the roll from argon oxidation, characterized in that hardening of the surface of the rolling rolls is carried out by a pulsating arc at a voltage of 18-30 V, the speed of movement of the arc on the surface of 1.0-1.3 m / min with a gap between the electrode and the reinforced surface with a roll surface of 10-12 mm and with an argon flow rate of 600-700 l / h.

Images