Research On Seamless Techniques And Equipment Development For Medium Or Small Caliber HFW Tubes

Because of its accurate size,uniformity and few defects of base material and low cost,the high-frequency welded(HFW)tube is applied wider and wider.However,different part of the HFW joint undergoes different heating and deformation history during the welding process,resulting in the non-uniformity of the joint.The microstructure and mechanical properties of Q235B and 26MnB5 HFW joints before and after normalizing were studied.It shows that the non-uniformity of HFW joints is mainly attributed to nonuniform grain size and consequently different mechanical properties.The method to eliminate this kind of non-uniformity is thermomechanical treatment.Therefore,isothermal compression experiments were carried out on Gleeble thermal simulation machine in order to know the microstructure evolution mechanism of Q235B and 26MnB5 HFW joints.The results show that the dominant softening mechanisms of Q235B welded joints are ferrite strain-enhanced transformation(800 ?)and austenite dynamic recrystallization(850-1000 ?).As for 26MnB5 welded joints,Dynamic recrystallization(920-1000?)and dynamic recovery(880 ?)of austenite are the dominant microstructure softening mechanisms.Different part of HFW joint has different microstructural revolution characteristics.For Q235B welded joints,zone? has more fraction of Ferrite and the same grain size compared with zone?,while Zone ? has less Ferrite and coarser grain.For 26MnB5 welded joints,grain size of Austenite gets larger and uniformity gets worse from zone ? to?.Statistical examinations of grain size show that the deformation temperature of Q235B HFW joint should be less than 900 ?,and the strain and strain rate should be more than 0.43 and 0.1s-1,respectively.The 26MnB5 HFW joint should not deformed at high temperature and low strain rate condition(0.01s-1,960-1000?)and low temperature and high strain rate condition(10s-1,880?).Swing multi-directional rolling process was proposed.The motion of dies and rolling mechanisms were studied in this work by Matlab/Simulink sofeware and theoretical analysis,respectively.Biting conditions,the rolling central angles and rolling force formula in the deformation zone are obtained.The calculated rolling force is compared with the simulation results and the results from literature.The three results show the same changing trend.All the three peak forces appear in the wall-reducing stage,which proves the reliability of theoretical study.The swing multi-directional rolling process was modelled by ABAQUS/Explicit software.The distribution and variation of workpiece stress field,strain field,temperature field,velocity field and die load are obtained.It shows that there are three forming stages for every cross-section,that is diameter-reducing,wall-reducing and sizing stage.In diameter-reducing stage,outside surface of workpiece which contact with die opening zone tend to produce stress and strain concentration.In the wall-reducing stage,rolling force gets its peak value.In the sizing stage,maximum strain reaches 0.7.The influence of key process parameters on the rolling process was analyzed.The results show that,increasing the feed amount and heating temperature and adopting the rolling process with mandrel will improve the PEEQ of workpiece,but the increasing of feed amount and adopting of mandrel will lead to the rise of the peak value of the die load and the axial force of the push block,which may require greater capacity of the rolling and driving part.The eccentric speed has no direct influence on PEEQ of workpiece and the load of the die and push block.But improper eccentric speed will affect the rolling efficiency and the deformation temperature of the workpiece negatively.Based on researches above,swing multi-directional rolling equipment was designed and manufactured in this work.The equipment includes rolling part,driving part,heating part and feeding part.Dies are designed based on the principle of large deformation when reducing diameter and small deformation when reducing wall-thickness,which can optimize the rolling force distribution.The practical rolling on Q235B and 26MnB5 HFW tubes was implemented using swing multi-directional rolling equipment.It shows that under the deformation condition of 20mm/(2s)feeding amount and 55mm sizing diameter of mandrel(M55),the outer diameter deviation of rolled products is less than 0.2mm and the ellipticity deviation is less than 0.1mm,and the surface quality is good.After rolled at the condition of deformation temperature 950? and M55 for Q235B HFW tubes,the grain size of zone ? and zone ? is 9.2?m and 9.8?m,respectively.The joint and base both possess good comprehensive mechanical properties.After rolled at 1000?,M55 for 26MnB5 tubes,area ratio and average size of pearlite in zone ? and base are 49.25%?38.3pm and 47.69%?27.1?m,respectively.Rolled samples tend to have higher strength and lower elongation compared with normalized samples.