Producing process of large-diameter core rod for rolling of mandrel pipe mill

Abstract

The invention discloses a producing process of a large-diameter core rod for the rolling of a mandrel pipe mill, which has the advantage of prolonging the service life of the core rod. The producing process comprises the following steps of: steel raw material selecting, steel ingot smelting, core rod blank forging, primary aligning, surface rough turning, quenching and tempering, secondary aligning, and finish turning. After the rough turning is completed, the oxidization black scale on the depressed position of the core rod surface is removed before quenching and tempering. As the oxidization black scale is removed, the quality of the subsequent quenching and tempering can be ensured, the influence of oxidization black scale on the core rod quality is prevented, and the service life of the produced core rod is greatly prolonged; by restoring the cracks on the surface of the core rod by supplementary welding, the finished rate of the core rod is enhanced; as the secondary hardening treatment is adopted in the quenching and tempering process, the tempering stability of the core rod is increased, the friction resistance of the steel pipe in rolling is decreased, and the invention is especially suitable for producing large-diameter core rods.

Description

technical field [0001] The invention relates to a rod body production process, in particular to a large-diameter mandrel production process for continuous pipe mill rolling. Background technique [0002] At present, seamless steel pipes play a very important role in my country's national economic construction. Seamless steel pipes are widely used in petroleum, military industry, shipbuilding, machinery, automobiles, gas fluid transportation and other industries. The stop mandrel is one of the important tools for seamless steel pipe rolling. During the rolling process of the steel pipe, the stop mandrel is penetrated into the extension billet and sent to the rolling mill for rolling. During the rolling process, the mandrel on the one hand The steel pipe is rolled under the action of extrusion force and thrust, and on the other hand, it is limited by the action of power, and the mandrel is kept limited during the rolling of the steel pipe. After rolling, the mandrel is drawn ...

AI Technical Summary

Problems solved by technology

However, if this production process is used to produce a large-diameter stop mandrel (such as a stop mandrel with a diameter of 358.1 mm), after the mandrel forging is completed, if the large-diameter mandrel remains relatively small like the small-diameter mandrel A large machining allowance will make the effect of quenching and tempering treatment poor (because the diameter is too large, it cannot be hardened during quenching), resulting in poor quality of the finished product; if a small machining allowance is left, although the quenching and tempering treatment It is easy to harden to the core of the mandrel. However, in rough turning and finishing turning, the turning allowance is not easy to control, especially in the rough turning process, it is easy to turn too much and the final product diameter is smaller than the required size. , it can only be changed to a small-sized mandrel or scrapped directly; if there is less turning during the rough turning process to ensure the finished product size, since the mandrel has a certain curvature, there will be a lot of mandrel surface after the rough turning is completed. The concave part cannot be turned, and there is oxidized black skin in the concave part, which affects the quality of subsequent quenching and tempering treatment (①The existence of oxidized black skin covers the cracks under the black skin, which is easy to cause cracks to expand during quenching of the mandrel and cause the entire core to be damaged. The rod is scrapped; ②The existence of oxidized black skin reduces the quenching cooling rate of the quenching liquid on the workpiece during quenching, resulting in the local organization not meeting the requirements), which will also affect the product quality and the service life of the mandrel

Mandrels are prone to cracks during processing. If the cracks extend to within the diameter of the finished mandrel, it will also affect the service life of the finished mandrel. To eliminate the cracks, it is necessary to continue turning (causing the diameter to be smaller than the required finished product diameter), it will also cause the mandrel to be scrapped or changed to a small-sized mandrel after the subsequent finishing car is completed, resulting in a decrease in the yield

In addition, in the quenching and tempering treatment of the existing mandrel processing, the mandrel is generally placed on the support platform in the heat treatment furnace for quenching and tempering treatment, and the mandrel is placed directly on the support platform (i.e. the core The rod line contacts the support platform), and during quenching and tempering treatment, due to the heat expansion of the mandrel, there is a large friction between the mandrel and the support platform, which is easy to cause a large bending deformation of the mandrel, which will also affect the quality of the product. Quality, reduce the service life of mandrel