Cold-drawn Tubes Research Articles

Effect of Annealing Temperature on Microstructure and Properties of Cold Drawn Tube

The annealing process of an improved Q420 cold drawn tube was studied by using different annealing temperatures (430°C, 450°C, 470°C, 490°C and 510°C) with a same annealing holding time (3h). The effect of different annealing temperatures on the mechanical properties, microstructure and fracture features of the cold drawn tube was studied by means of tensile test, microstructure observation and scanning electron microscopy analysis. The results show that, annealing temperature has great influence on the strength and plasticity of the cold drawn tube. When the annealing temperature increased to 450°C, banded microstructure was mitigated and the pearlite is relatively dispersed. The tensile fracture morphology under the annealing temperature of 450°C has more dimples and deeper bremsstrahlung than other annealing temperatures. The best annealing process of the cold drawn tube was 450°C×3h. Under this annealing process, the cold drawn tube with good strength and toughness can be obtained.

Effect of heat treatment on property and residual stress of cold drawn tube

The change of strength, toughness and residual stress of Q690 cold-drawn tube were studied under (400˜;600)°C and heat preservation (1-3)h heat treatment. With the increase of temperature and the extension of the holding time, the strength and residual stress of the cold drawn tube gradually decreased, and the impact toughness increased first and then decreased. When holding at 550 °C for 2 hours, the impact toughness reached the highest 34.6J;the mechanical properties of cold drawn tubes were mainly affected by the reduction of internal stress and grain deformation caused by heat treatment.

Influential factor to dimensional precision of cold-drawn tubes

Elastic–plastic finite element analyses were carried out to sort out the influential factors on the dimensional precision of cold-drawn stainless steel seamless tube for energy industry. Good agreement was obtained between the predicted dimensions and the measured dimensions of tube after drawing experiment for validity check. Geometrical parameters of tools and geometry of parent tube have little influence on the geometrical precision of finished tube. Most influential factor on the geometrical precision of drawn tube is the temperature of tools. Observation and measurement on a production line showed that the temperature of tools increases according to the increase in the number of drawn tubes. Increase in the temperature of tool leads to the change in the geometry of drawn tube. A methodology for evaluating the thermal expansion of tools is shown to take it into consideration the designing procedure of cold-drawing process by using finite element analysis.

Optimization of heat treatment in cold-drawn 6063 aluminium tubes

The effect of heat treatment condition on mechanical properties and bendability of 6063 aluminium cold-drawn tubes was investigated. The standardized heat treatment presently used in manufacturing of cold-drawn tubes increases the cost and time of the process which ultimately reduces plant productivity. The effects of time, temperature, and furnace heating rate were studied in order to identify an optimized heat treatment for tubes with different cold work levels. Drawn from the as-extruded state, tubes were heat treated to under-aged, peak-aged, and over-aged conditions with time and temperature ranging from 1 min to 24 h and 130–200 °C, respectively. Mechanical properties were determined with full section tensile tests whereas tube bendability was evaluated on an industrial draw bending machine. These characteristics were evaluated in each condition in order to identify the heat treatment which allows conforming to 6063-T832 temper requirements and gives sufficient bendability. Moreover, bendability was successfully correlated to fracture strain measured during a uniaxial tensile test and a threshold value over which problem-free bending operation was determined.

Neutron and X-ray residual stress analysis of steel parts produced by cold forward extrusion and tube drawing

Deformation-induced residual stresses were studied by the examples of cold forward extrusion and tube drawing of ferritic steel parts. For analysing the volume stresses in the extruded rods, neutron diffraction was applied. Therefore, the interplanar spacing d { hkl} vs. sin 2 ψ up to sin 2 ψ = 1 were measured for the reflections {110}–{220}, {200}, {211} and {310}. In the case of the cold-drawn tubes, stress evaluation was performed at the outer surface of the specimens by means of X-ray diffraction taking d { hkl} vs. sin 2 ψ for the {200} and {211} reflections in both the axial and the tangential directions. For both metal-forming processes, the residual stress state is shown to depend in an obvious way on the degree of natural strain ϕ which is defined by the logarithmic ratio of initial and final cross-sectional areas. The results obtained are in good qualitative agreement with theoretical predictions of finite element calculations.

An Experimental Study of the Evolution of Yield Loci for Anisotropic Materials Subjected to Finite Shear Deformation

This paper presents a set of experimental results concerning the evolution of yield loci for anisotropic materials in the course of finite shear deformation history. Thin walled tubes of SAE 1020 steel are tested under triaxial loading conditions – tension, torsion and internal pressure, at room temperature. The specimens were prepared from cold-drawn tubes which had a prominent fibrous grain structure. They showed considerable amount of in-plane anisotropy and orthotropic yield properties with respect to the longitudinal and circumferential axes. The as-received specimens were further pre-strained by imposing simple shear which causes the change in orientations of these elongated polycrystalline grains. Our previous experimental results [1] have verified that the principal directions of the total stretch of the current grain shape match with the directions of orthotropy, and in this work, the subsequent yield loci for the pre-strained material are determined with respect to the new reference frame fixed along these directions of orthotropic symmetry. By utilizing the unique triaxial loading scheme of our servo-hydraulic testing system it has been possible to create the principal directions of a biaxial state of stress in a specified direction. The changes in the size and shape of the yield loci in the stress space are critically analyzed in this paper.

Deformation of cold-drawn tubes of Zr-2.5 wt% Nb after 7 years in-reactor

Small diameter tubes, 23 mm internal diameter, of Zr-2.5 wt% Nb alloy have been tested in-reactor at 570 K for 46000 h. The specimens were cold-drawn 10, 23 or 33% and stress relieved at 673 K. Half the specimens were in a high fast neutron flux and the other half of identical specimens were out-of-flux. Stresses on the specimens were biaxial from internal water pressure and hoop stresses ranged from 104 to 313 MPa. These long-term tests show that creep is fairly linear with time both in and out of flux, that creep rates increase with increasing cold-work, and that creep anisotropy is best predicted assuming 65% prism/35% basal slip.

Creep and Creep-Rupture Properties of the Nuclear Fuel Cladding Tube for Fast Breeder Reactor

For the design and fabrication of the experimental fast breeder reactor it is desirable to obtain the creep and creep-rupture properties of the domestic tubes of 316 stainless steel with nominal dimension of 5.6mm inside diameter and 0.35mm wall thickness, that will carry nuclear fuel.The creep rupture tests under internal gas pressure and creep and creep-rupture tests under uniaxial tension have been carried out on two kinds of these tubes, one of which was approximately 6% cold-drawn and the other was approximately 18% cold-drawn, in unirradiated and atmospheric conditions at test temperatures of 550°C, 600°C, 650°C and 700°C.The results obtained are summarized as follows:(1) The regression curves for the creep-rupture data obtained from the internal pressure tests and uniaxial tension tests showed points of bend at the pressure of 360kg/cm2 and stress of 30kg/mm2 when the Larson-Miller parameter method was applied.(2) Compared with ISO's and NRIM's data, the present data for uniaxial tension tests showed a little greater creep-rupture strength for 6% cold-drawn tubes and definitely greater creep-rupture strength for 18% cold-drawn tubes.(3) The creep-rupture strength of 18% cold-drawn tubes is generally greater than that of 6% cold-drawn tubes. However, the creep-rupture curves for the two kinds of tubes tended to approach each other when the temperature was raised from 600°C to 700°C and the test time was prolonged.(4) The data for creep-rupture tests under internal pressure nearly agreed with those for uniaxial tension tests at stresses less than 30kg/mm2, when the hoop stress of internally pressurized specimens was calculated by the mean diameter formula.

Straightening of cold-drawn tubes before heat treatment

Straightening of cold-drawn tubes before heat treatment