RU2256708C2 - Method of production of triblets of pilgrim-step rolling mills - Google Patents

Abstract

FIELD: metallurgy; pipe rolling.

SUBSTANCE: the invention is pertaining to the field of pipe rolling, in particular, to the methods of production of triblets of pilgrim-step rolling mills and may be used at production of triblets of pilgrim-step rolling mills for rolling of hot-rolled pipes of large and average diameters (273-550 mm). The method provides for casting of steel ingots, production of triblets out of the steel ingot blanks by, a heat treatment of the triblet ingot blanks, their mechanical working to obtain the finishing dimension with subsequent hardening by a roller run, casting of carbon steel ingots, application by surfacing on the ingot blanks of a heat-resistant and abrasive resistant layer and production of triblets out of the steel ingots by the pilgrim-step rolling, and in the process of operation after appearance of a net flame erosion cracks conduct a triblet multiple remachining till removal of the heat-resistant and abrasive resistant layer, application of a new heat-resistant and abrasive resistant layer by surfacing, machining till the finishing dimension and hardening by a roller running and determination of the thickness of the heat-resistant and abrasive resistant layer from the following equation Δ = A*µ* (l÷D/S*K), where: A - is the minimal thickness of the surfacing layer after the final mechanical working of a triblet and equaled to 10 mm; D - the maximal diameter of the pipes rolled on the given triblet, mm; S - the minimal wall thickness of the pipes rolled on the given triblet, mm; µ - a reduction ratio at rolling of ingots into the hollow triblet blanks and K - a coefficient equal to 0.02. The invention ensures production of triblets of pilgrim-step rolling mills for rolling of hot-rolled pipes of large and average diameters, usage as the basis of the triblet ingot blanks produced out of a carbon steel instead of alloyed steel, increased resistibility of triblets and as a result of it a decreased share of cost of the technological tools in the cost of production of pipes.

EFFECT: the invention ensures production of triblets of pilgrim-step rolling mills for rolling of hot-rolled pipes of large and average diameters, usage of carbon steel in production of triblet ingot blanks, increased resistibility of triblets, decreased share of triblets cost in the cost of the pipes production.

2 cl, 1 tbl

Description

The invention relates to pipe production, and in particular to a method of manufacturing a technological tool, and can be used in the manufacture of mandrels of pilgrim mills for rolling hot-rolled pipes of large and medium diameters (273-550 mm).

A known method of manufacturing the mandrels of pilgrim mills for rolling hot-rolled pipes of large and medium diameters, including casting ingots from steel grade SD1 (50XN) with a chemical composition according to GOST 4543-71, forging them into cylindrical billets (forgings) with a bite of 2.25-2.5 , rough machining with an allowance of 10-15 mm in diameter, taking into account the forging forgings during heat treatment, heat treatment of mandrel blanks, machining of mandrels to the final size, followed by hardening by rolling with a roller or grinding the surface and exp their ousting before the formation of a grid of high-wave cracks or longitudinal cracks (F.A. Danilov et al. Hot rolling of pipes, Metallurgy. Moscow. 1962, p. 355-356. Related report: 22-V-13-541- 73: "Development of manufacturing technology of mandrels of increased wear resistance and their introduction into production at ChTPZ", Dnepropetrovsk, 1975. TP 158-148-98 "Technological process for machining guides and work rolls of a piercing mill, mandrels and pilgrim rolls in workshop No. 1 of OAO" ChTPZ ").

The disadvantage of this method is that the mandrel breaks down according to the “wave” (corrugation), surface swing ring cracks and coarse longitudinal cracks, as well as their uneven abrasion along the length (loss of geometric dimensions). As a rule, when rolling pipes with a diameter of 377 and 426 mm on mandrels made of steel of grade SD1, the main type of defects is the “wave” (corrugation). "Wave" on the surface of the mandrels occurs at a distance of 1500-2000 mm from the mandrel lock. "Wave" is a plastic deformation of the surface layers of metal mandrels, which is caused by heating their surface to a temperature above 650 ° C and caused by prolonged contact of the sleeve tubes and mandrels or rolling of two or more sleeves on one mandrel without cooling. When rolling pipes with a size of 426 × 9 × 32000-35000 mm, the contact time of the mandrel with the sleeve tube is from 5.0 to 6.0 minutes. During this time, the mandrel in the area of 1500-4000 mm from the castle part is heated to 650 ° C. The mandrel has the highest temperature in the area from 2000 to 3000 mm from the mandrel castle, i.e. on the central part. The resistance of the mandrels on the "wave" is directly dependent on compliance with the instructions for their use.

Ring cracks are associated with poor-quality machining, the presence of stress concentrators (undercuts and grooves from incisors). Rough longitudinal cracks with depths from 1/3 to 3/4 of the radius of the mandrels are a consequence of the low values of the plastic properties and impact toughness of steel at cyclically changing temperatures.

There is also known a method of manufacturing mandrels of pilgrim stems from steel grade SD2 (25X2M1F), having the following content of elements: carbon - 0.24-0.32%, manganese - 0.3-0.6%, silicon - 0.15-0, 40%, chromium - 1.6-1.9%, molybdenum - 0.6-0.9%, vanadium - 0.15-0.25%, nickel - up to 0.5%. Dorn made of this steel is more wear resistant. Their resistance is 1.2-1.3 times higher than that of steel СД1 (Report on the topic: 23-V-13-81 / 19-72 / П2 - and ПП "Search for steels with increased heat resistance and development of the composite structure of pilgherthorn". Ural Research Institute of the Pipe Industry, Ufa Aviation Institute, Chelyabinsk Tube-Rolling Plant, Chelyabinsk, 1972).

However, the known method also has disadvantages. Dorn with a carbon content of 0.24-0.32% fail mainly due to the appearance of hot cracks on their surface, as well as uneven abrasion along the length (loss of geometric dimensions). Hot cracks occur as a result of thermal and structural stresses in the surface layer of the doruns, which are heated by contact with hot sleeves-pipes to a temperature Ac1-Ac3 (650 ° C and above). The formation of a network of high-level cracks is the result of irreversible structural changes (shear deformations inside the grain, grain crushing, void formation, deformation along grain boundaries and the formation of submicroscopic discontinuities and damage to the surface layer). Thermal fatigue damage to the surface is the cause of the first foci of destruction, initiating the further development of cracks. With an increase in the number of heating and cooling cycles, the number and size of cracks increases, the cracks connect and intertwine, forming a so-called “grid”. The formation of a grid of hot cracks on the surface of the mandrels accelerates the abrasion and tearing of metal particles. Intensive oxidation of the metal and the processes of their wedging occur in cracks. The decisive influence on the life of the mandrels is exerted by the intensity of the development of the grid of widening cracks into larger ones, which are a rejection sign of mandrels.

The closest technical solution is a method of manufacturing and operating mandrels of pilgrim mills for rolling hot-rolled pipes of large and medium diameters, including the production of a conical electroslag ingot from SD2-Sh steel and its subsequent radial forging on a cylindrical billet having a locking and working parts, and forging its working parts are carried out with a linear increase in forging in the direction of the castle part with a ratio of the maximum forging to a minimum of 1.26-1.56, annealing the workpieces and drilling holes diameter of 100-105 mm (RF Patent No. 2055660 dated 03/10/96, Bull. No. 7, p. 34 and A. V. Safyanov, L. M. Kleiner, L. D. Pilikina and others. "New technology production of hollow mandrels of pilgrim mills ", Steel, No. 9, p. 55-56, 1997).

However, the known method also has disadvantages. The resistance of the mandrels increased by 1.2-1.4 times in comparison with the existing one, but they also fail due to longitudinal cracks and a grid of high cracks, and their cost in the cost of pipes is from 2.5 to 3.0%.

The technical result of the method is to increase the resistance of mandrels for rolling hot-rolled pipes of large and medium diameters, reduce their cost by replacing steel 25X2M1F with steel 20 for manufacturing mandrel blanks, followed by multiple application (type SV30X25N16G7) of a heat-resistant wear-resistant layer by welding and subsequent break-in. The technical result is achieved by the fact that in the known method of manufacturing mandrels of pilgrim mills for the production of hot rolled pipes of large and medium diameters, including casting ingots from steel, obtaining mandrel blanks, heat treatment of mandrel blanks, machining mandrels to the final size, followed by hardening by rolling with a roller, ingots cast from carbon steel, a heat-resistant wear-resistant layer is deposited on the surface of the ingot by surfacing and the mandrel blank is obtained from the ingot by sawing Ream rolling and in operation after the appearance of the grid razgarnyh produce multiple fractures regrinding mandrel prior to removal of heat resistant wear layer, applying a new heat-resistant wear layer by welding, machining to finished size and hardening the roller burnishing, while a heat-resistant wear layer thickness is determined from the expression

Δ = A * μ * (1 + D / S * K),

where A is the minimum thickness of the deposited layer after machining of the mandrel, equal to 10 mm;

D is the maximum diameter of the pipes rolled on this mandrel, mm;

S is the minimum wall thickness of the pipes rolled on this mandrel, mm;

μ is the drawing coefficient when rolling ingots into hollow mandrel blanks;

K is a coefficient equal to 0.02.

Dorn during operation are subjected to repeated cyclic heating and cooling. In addition to the thermal effects, the mandrels are subjected to pressure from the rolls of the pilgrim mill and longitudinal tension caused by the frictional forces of the deformable metal during rolling and extraction of the mandrels from the pipes by the feeding apparatus. Due to the inconstancy of the deformation zone during one revolution of the rolls, the pressure on the mandrel and the effect of friction forces are constantly changing. The complexity of the working conditions of the mandrels consists in their prolonged contact with heated plastically deformable metal, the absence of cooling during deformation, large temperature differences of the working surface of the mandrels in one cycle of their operation (cooling to a temperature of 180-200 ° C in a bath with water and grease, heating during rolling and operation for 3.5-6.0 minutes at a temperature of 500-650 ° C). The combined actions of high temperatures and pressures lead to a quick failure of the mandrels, mainly along the grid of high-level cracks. High cracks on the surface of the mandrels begin to appear after 0.80-0.85 from their initial resistance, which subsequently begin to progress, grow both qualitatively and quantitatively, i.e. in breadth and inland. At this point, the mandrel is forcibly removed from service and ground until the deposited heat-resistant wear-resistant layer is removed. After regrinding, a new heat-resistant wear-resistant layer with a thickness of Δ ₁ is applied to the mandrel, machined to the final size, followed by grinding or hardening by rolling with a roller and the mandrel is returned to the production cycle. After regrinding and applying a new heat-resistant wear-resistant layer, the mandrel is exploited until the appearance of the network of high-crack cracks. The work cycle is repeated, that is, they are removed from the technological process, grind until the heat-resistant wear-resistant layer is removed, a new heat-resistant wear-resistant layer is applied, the machining is performed to the final size, followed by roller hardening.

Thus, the mandrels are operated until failure for reasons not related to high-cracking (breakage of the mandrel, wear of the lock, etc.).

A comparative analysis of the proposed solution with the prototype shows that the claimed method of manufacturing mandrels of pilgrim mills for the production of hot-rolled pipes of large and medium diameters differs from the known one in that ingots are cast from carbon steel, a heat-resistant wear-resistant layer is deposited on the surface of the ingot and a mandrel blank is obtained from the ingot by means of a pilgrim rolling, and during operation, after the appearance of a grid of hot cracks, the mandrel is repeatedly regrind until heat is removed Toyko wear layer, applying a new heat-resistant wear layer by welding, machining to finished size and hardening the roller burnishing, while a heat-resistant wear layer thickness is determined from the expression

Δ = A * μ * (1 + D / S * K),

where A is the minimum thickness of the deposited layer after machining of the mandrel, equal to 10 mm;

D is the maximum diameter of the pipes rolled on this mandrel, mm;

S is the minimum wall thickness of the pipes rolled on this mandrel, mm;

μ is the drawing coefficient when rolling ingots into hollow mandrel blanks;

K is a coefficient equal to 0.02.

Thus, the claimed method meets the criteria of the invention of "novelty."

Comparison of the proposed method for the manufacture and operation of mandrels, not only with the prototype, but also with other technical solutions in the art, did not reveal the signs that distinguish the claimed solution from the prototype, which allows us to conclude that the criterion of "significant differences".

The method was tested on a pipe-rolling installation with pilgrim mills 8-16 "OAO" ChTPZ ". Two new mandrels with a diameter of 409/410 and 309/310 mm, manufactured using the existing and proposed technologies, were assigned to the production. Data on the durability of the mandrels of pilgrim mills made according to the existing and proposed technologies are shown in the table. The table shows that the average statistical resistance of mandrels with a diameter of 409/410 mm, manufactured and operated by the existing method, is 1100 tons of pipes with a size of 426 × 9 mm, and mandrels with a diameter of 309/310 mm - 800 tons of pipes with a size of 325 × 9 mm Dorn according to the new method was made according to the following technology: a central hole with a diameter of 150 ± 5.0 mm was drilled in ingots of art. 100 ± 5.0 mm, then a heat-resistant wear-resistant layer (SV30X25N16G7) with a thickness of 60.0 and 55.0 mm, respectively, was deposited onto these ingots by the welding method. The ingots were heated in methodological furnaces to a temperature of 1270-1280С. Ingots 630x100 in size were sewn in a piercing mill into sleeves 600x215x2600 mm in size on a mandrel with a diameter of 200 mm and rolled on a pilgrim mill in hollow mandrel blanks of 430 × 120 × 5500 mm in diameter on a mandrel with a diameter of 189/190 mm. Ingots 540 × 150 × 2000 mm in size after heating without piercing were fed to a pilgrim mill and rolled into mandrel blanks of 330 × 100 × 5850 mm in size on mandrels with a diameter of 129/130 mm. After rolling, the mandrel blanks were subjected to heat treatment, dressing, and machining to a final size of 309/310 and 409/410 mm, respectively. On a mandrel with a diameter of 409/410 mm, manufactured according to the existing technology, 1,185 tons of pipes 426x9 in accordance with GOST 8732 were rolled, and on a mandrel with a diameter of 309/310 mm - 865 tons of 325 × 9 oil pipes in accordance with GOST 8732. Both mandrels failed. on a grid of high cracks. On a mandrel with a diameter of 409/410 mm, manufactured using the new technology, 1350 tons of pipes 426 × 9 in accordance with GOST 8732 were rolled to the first regrinding. A grid of high-grade cracks began to appear on the surface of the mandrel. Dorn was removed from the technological cycle and regrind. During regrinding, the deposited heat-resistant wear-resistant layer was removed, and then a new heat-resistant wear-resistant layer with a thickness of 20.1 mm was applied, taking into account the allowance for machining. After surfacing of the heat-resistant wear-resistant layer, final machining was performed, and the surface of the mandrel was hardened by rolling by a roller. Then, on a mandrel with a diameter of 409/410 mm, after the first regrinding and surfacing of a new heat-resistant wear-resistant layer, 1035 tons of pipes of size 426 × 9 in accordance with GOST 8732 were rolled. On the surface of the mandrel, a network of high-grade cracks began to appear. Dorn was removed from the technological cycle and again regrind. During regrinding, the deposited heat-resistant wear-resistant layer was removed, and a new layer with a thickness of 19.8 mm was applied. After surfacing of the heat-resistant wear-resistant layer and final machining, the surface of the mandrel is hardened by rolling by a roller. Then, 1,100 tons were rolled on this mandrel. After the third regrinding and surfacing, 1075 tons of pipes were still rolled on this mandrel. A similar process sequence was carried out on a mandrel with a diameter of 309/310. The table shows that the resistance of the mandrel with a diameter of 309/310 mm, manufactured and operated by the new technology, is 3515 tons, that is, the resistance increases by 4.06 times, compared with the mandrel manufactured by the existing technology. Dorn went through three regrindings and surfacing with subsequent machining and rolling (hardening) of the working surface with a roller. After repair of the mandrel lock (surfacing and milling of the cheeks), the mandrel will be used for further pipe production. On a mandrel with a diameter of 409/410 mm, manufactured by the proposed technology, 4560 tons of pipes with a size of 426 × 9 mm were rolled, i.e. its durability increased by 3.85 times, compared with a mandrel made using existing technology. The mandrel can be used for further work after surfacing and milling of the lock, as well as the fourth regrinding and surfacing of the working surface.

Thus, on a mandrel with a diameter of 309/310 mm, manufactured and operated according to the existing technology, 865 tons of 325 × 9 mm pipes were rolled (the mandrel failed according to the grid of high-grade cracks), and on the mandrel manufactured and operated by the proposed technology, after three regrinds and surfacing of a wear-resistant heat-resistant layer, 3515 tons of pipes are rolled, i.e. resistance increases by 4.06 times. On a mandrel with a diameter of 409/410 mm, manufactured and operated according to the existing technology, 1,185 tons of pipes 426 × 9 in size were rolled. Dorn failed on a grid of high cracks. On a mandrel with a diameter of 409/410 mm, manufactured and operated according to the proposed technology, 4,560 tons of pipes 426 × 9 mm in size were rolled for 3 regrinding and surfacing resistance of the mandrel increased by 3.85 times. The mandrel can be used in work after repair (surfacing) and milling of mandrel locks, as well as regrinding and surfacing on the working surface of a new heat-resistant wear-resistant layer.

Using the proposed method for the manufacture of mandrels of pilgrim mills for the production of hot-rolled pipes of large and medium diameters allows the use of carbon steel ingots (st.20) instead of alloyed (25X2M1F) as the basis for mandrel blanks, to significantly increase their resistance, and therefore reduce the share of the cost of the technological tool cost of pipes.

Claims (2)

1. A method of manufacturing the mandrels of pilgrim mills for the production of hot-rolled pipes of large and medium diameters, including casting ingots from steel, producing mandrel blanks, heat treatment of mandrel blanks, machining mandrels to the final size, followed by rolling hardening by a roller, characterized in that the ingots are cast from carbon steel, a heat-resistant wear-resistant layer is deposited on the surface of the ingot by surfacing and the mandrel blank is obtained from the ingot by means of pilgrim rolling, and in the process service, after the appearance of a grid of hot cracks, the mandrel is repeatedly regrind until the heat-resistant wear-resistant layer is removed, a new heat-resistant wear-resistant layer is deposited by surfacing, machining to the final size and hardening by rolling with a roller. 2. The method according to claim 1, characterized in that the thickness of the heat-resistant wear-resistant layer is determined from the expression Δ = A · μ · (1 + D / S · K), where A is the minimum thickness of the deposited layer after machining of the mandrel, equal to 10 mm; D is the maximum diameter of the pipes rolled on this mandrel, mm; S is the minimum wall thickness of the pipes rolled on this mandrel, mm; μ is the drawing coefficient when rolling ingots into hollow mandrel blanks; K is a coefficient equal to 0.02.