Structure seamless steel pipe workpiece in the heating and cooling process, due to inconsistencies and center surface cooling rate and time to form a temperature difference, it will lead to uneven volume expansion and contraction stress, the thermal stress.

Wuhan, Hubei, China., May 25, 2015 – (PressReleasePoint) -Under thermal stress due to a temperature below the surface began to Heart Ministry, the Ministry of contraction is also greater than leaving the center core portion is pulled, when the end of the cooling, since the central portion finally cooled volumetric shrinkage can not freely leaving the surface pressure on core section tension. That is the role of thermal stress and finally to the workpiece surface under pressure and heart Ministry tension. This phenomenon is cooled velocity, material composition and heat treatment and other factors.

When cooled, the faster, the higher the carbon content and alloy composition, uneven cooling during plastic deformation under thermal stress generated by the larger, the final form of the residual stress is greater. On the other hand with the structural seamless steel pipe in the heat treatment process that is due to changes in the organization when the austenite to martensite, because the specific volume increase will be accompanied by a volume expansion of the workpiece, each part of the workpiece has a phase change, causing the volume of long big inconsistencies arising from the stress. The end result is a surface tissue stress tensile stress, the center compressive stress, and thermal stress exactly the opposite. The stress of the size of the workpiece in the martensite cooling rate zone factor, shape, chemical composition of the material.

Hot-rolled seamless steel tubes and cold drawn seamless or other sections, the production process requires heat treatment, heat treatment process as seamless steel pipe including the seamless annealed, seamless steel ball annealing, quenching seamless, seamless tempering, normalizing these types of seamless steel heat treatment. These models are used in heat treatment furnace bottom there are different, including: roller hearth furnace, walking beam furnace, car heaters and so on. Let’s take a brief two kinds of furnaces.

1, roller hearth furnace
Seamless steel heat treatment roller hearth furnace and billet heating and heat treatment of the slab roller hearth furnace is basically the same, but more accurate temperature control requirements. In order to ensure the transfer pipe along the axial roller when a predetermined temperature profile can be heated and cooled, the implementation of sub-control, which divided along the length of the furnace heating zone, soaking zone, quench zone, slow cooling section and so on. Now gradually in the direction of the development of continuous bright annealing furnace, the furnace has to radiant heat from the flame tube heating development trend, and pass into the protective gas. Long packet transmission furnace hearth roll along, sometimes furnace rollers can also be installed diagonally to make progress at the same time produce seamless steel rotary motion.

2, with a cover car heaters
When dealing with multi-species and small production, large diameter steel pipe, adopt intermittent trolley furnace. This stove also known as knee type furnace, which consists of trolley, trolley mobile devices, hoods, hoods lifting devices and other components, in fact, Car-furnace and bell furnace combination furnace. When the car pulled out, the seamless steel pipe pile in trolley, trolley feed the furnace, hood down to the trolley, and by sand-tight seal. By radiant tube heating furnace, pass protective gas furnace cover, this stove can be seamless bright annealing, the ball can also be processed and tempering.