A method of manufacturing a superheater tubes of alloy steels

 

The invention relates to the production of steel pipes by the method of hot deformation and can most effectively be used in the manufacture of pipes of alloy steels for steam boilers and pipelines. The technical result is to reduce the duration of the heat treatment and the guarantee of quality indicators (mechanical properties, strokefest) metal pipes. The technical result is achieved in that in the method of manufacturing a superheater tubes of alloy steels, including multi-stage hot deformation, rapid cooling and subsequent heating to a temperature of 10-30oWith lower temperature at the start of phase transformation (A1before the last stage of deformation and the final deformation at this temperature, the cooling is produced at a rate of over 75oC/min, but less than the critical speed, providing a purely martensitic transformation and not higher than the temperature corresponding to the point A1- 350oWith this grade of steel at this temperature is the exposure duration of not less than 30, and after heating also made the exposure time of at least 10 min and the final release of trueforall and most can be effectively used in the manufacture of pipes of alloy steels for steam boilers and pipelines.

Superheater tubes manufactured according to known technology, is not guaranteed in the structure in terms strokefest" (acceptance criterion) and require long-term treatment. The proposed method allows to eliminate or significantly reduce these drawbacks.

A known method of manufacturing a superheater tubes, including deformation at a temperature of 1000-1200oAnd then double the heat with separate heating, consisting of normalizing and tempering (Bernstein, M. L., Ruhstadt A., "the Metallography and heat treatment of steel". Reference 3 so, M, metallurgy, 1983, I. 3, S. 102-108).

The disadvantage of this method is the long duration of the double heat treatment.

The closest to the technical nature of the proposed method is a method of hot plastic deformation of materials, including heating to a high temperature, high plasticity and speed plastic deformation, and between stages of deformation, the cooling speed of not less than 20oC/sec to a temperature of at 240-450oWith lower temperature before pearlite transformation, and is heated to a temperature of at 10-100oWith lower temperature maculalutea in metal properties, determined by the requirements of TU-14-3-460-75 "seamless steel Tubes for steam boilers and pipelines after single (vacation) heat treatment, but only after normalization with vacation time-consuming.

The objective of the invention is the reduction in the duration of the heat treatment and the guarantee of quality indicators (mechanical properties, strokefest) metal pipes.

The task is achieved in that in the method of manufacturing a superheater tubes of alloy steels, including multi-stage hot deformation, rapid cooling and subsequent heating to a temperature of 10-30oWith lower temperature at the start of phase transformation (a1before the last stage of deformation and the final deformation at this temperature, the cooling is produced at a rate of over 75oC/min, but less than the critical speed, providing a purely martensitic transformation, and not above the temperature corresponding to the point A1- 350oC for the grade of steel at this temperature is delay for at least 30 seconds, and after warming up, so is the exposure duration for at least 10 minutes and a final vacation pipes.

Accelerated cooling gap (metal cooling rate of at least 75oC/ min) and the receipt of a sufficient number of bainite (not less than 30%) to achieve after the holidays, the required level of mechanical properties. Excerpt after cooling, a duration of at least 30 seconds required to pass the intermediate transformations in steel, and the upper limit of the shutter speed is limited only by the rate of rolling tubes.

The extract at a temperature of 10-30oWith temperature below the pearlite transformation is actually a vacation pipes. But, since the required duration of the leave (in some cases) high (depending on the brand of steel from 1 hour to 10 hours), then fully to realize it is not possible, and in this case is inappropriate, since it is known that cyclic vacation total expenses less time than when single. That is, the shutter speed after heating in combination with further deformation and cooling represents one cycle of a vacation. The second cycle is carried out with separate heating out of the technological process of hot deformation. Based on the research conducted by the authors, the minimum shutter speed should be 10 minutes, because at lower temperatures the reduction in the duration of poslepozharnaya performance of tube Assembly.

Determining boundary parameters and the estimation of their values was performed on the nozzles in laboratory conditions for steels MP and MF. The results are shown in table 1.

A specific implementation of the method was tested in the experimental rolling and heat treatment of boiler tubes size h mm of steel HF and mn TPA 50-200 Volzhsky pipe plant with three-roll raschetnym mill. The firmware and the rolling of the pipes was carried out at a temperature of 1100-1200oC. After removal of the mandrel tube was cooled in a stream of cooler (air / water mixture) to a temperature of 350-400oWith, then transported into the furnace walking beam. Transportation time (shutter speed when the cooling temperature) was maintained at 35-40 sec. Next, the tube was heated in a furnace to a temperature of 730-750oC and kept for 12 min, after which the calibration was performed in a three-roll mill helical rolling, cooling in still air to room temperature and leave.

Simultaneously let go of the pipe, laminated by known techniques without prior normalization.

The results of the control of mechanical properties and state of the microstructure (strokefest) are shown in table 2.

The holiday was established to Sinai operations - normalization and reduction of the time vacation in metal pipes is achieved the desired set of mechanical properties and structural state.

Claims

A method of manufacturing a superheater tubes of alloy steels, including multi-stage hot deformation, rapid cooling and subsequent heating to AU1-(10-30)With that exposure, calibration and vacation, characterized in that the accelerated cooling is produced at a rate of over 75C/min, but less than the critical speed to a temperature not exceeding AU1-350With a shutter speed of at least 30 s and at a temperature AU1-(10-30)C carry out an extract of at least 10 minutes

 

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FIELD: rolled tube production, namely method for making pilger mill mandrels from heat resistant steel for rolling hot rolled tubes.

SUBSTANCE: method for making mandrels used for rolling hot rolled tubes with large and mean diameters in range 273-550mm comprises steps of casting ingots of hear resistant steel; forging cylindrical solid or hollow blanks, roughly working of them, performing heat treatment and finishing mandrels at forming conicity 1 - 2 mm on length of their working portion while taking into account designed linear expansion coefficient during rolling process; determining diameter size by means of expression δ = dn - Δ/1 + αĚt. One portion of mandrel from lock along length of half of working portion of mandrel is in the form of cone with diameters of cone bases determined form given expression and second portion is in the form of cylinder or truncated cone whose diameters are determined according to next expression

EFFECT: lowered lengthwise thickness difference of tubes.

3 cl, 1 dwg, 1 tbl

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