MODELING OF CONTROLLED THERMO-MECHANICAL PROCESSING OF TUBES FOR ENHANCED MANUFACTURING AND PERFORMANCE

An integrated mathematical model to simulate seamless tube rolling processes has been developed at The Timken Company. The model is capable of simulating the thermal, deformation and microstructure evolution in the piercing, elongating and reducing/sizing and the austenite decomposition in the mill annealing and cooling operations. Finite difference schemes are employed to model cooling, reducing/sizing and stretch reducing, and finite-element schemes are employed to simulate piercing and elongating. The model predicts the thermal history, deformation, rolling load, torque, recrystallization and grain growth in hot tube rolling, austenite decomposition in cooling or annealing, and the final structure-properties. In this paper mathematical models which are employed to describe the thermal, deformation and microstructure evolution along with the modeling results are presented. The developed 'tube rolling mill in the computer' provides a powerful tool for engineers for product and process development, process control, process optimization and quality control.

Scheduling problem for hot-rolling seamless steel tube production

Taking the seamless tube plant of Baoshan Iron & Steel Complex in China as the background,we analyze the characters of hot rolling seamless steel tube:multi varieties,low volume,complicated production process,flexible production routes.Then integrated scheduling problem for hot rolling seamless steel tube production is studied,which covers two key points;order-grouping problem and solution method for flowshop/jobshop scheduling problem.On the basis of these two problems,integrated scheduling decision system is developed.The design idea,function flow sheet,data processing method,and functional module of visualized human-computer interactive scheduling system implemented in seamless steel tube plant of Shanghai Baoshan Iron & Steel Complex are described into detail.Compared with manual system,the performance of system shows the applicability and superiority in several criteria.

The PQF pass parametric design system of heavy calibre seamless tube

According to the characteristics of PQF continuous rolling pass,the relationship between spread coefficient,wall thickness coefficient and elongation are analyzed.The section shape of tube in each stand outlet,the efficient working radius and the rotational speed of each roll are obtained,therefore,the pass parametric design is completed.A thermal-mechanical coupled model of continuous rolling tube' s forming process is established by the three-dimensional elasto-plastic finite element method,the section shape and area of tube in each stand outlet are forecasted,which is used to modify the pass.The rolling force of each roller is predict too,which provides a guidance for pass design.In addition,a visual software of PQF pass parametric design system on heavy calibre seamless tube is generated with Visual Basic.The forming dimension of tube and the rolling force of each roller are successfully obtained,by simulating the forming process of a certain series heavy calibre seamless tube.This system posses practical utilization value.By using this system,the development cycle of new product can be shortened,the reliability of pass design can be improved,and the energy consumption of rolling mill and production cost can be decreased.

Quality prediction and control of tube hollow

The quality prediction of tube hollow model based on the variance staged multiway partial least square (MPLS) method was proposed.The key aspects of staged decomposition of the productive data,calculation of the variance value,modeling,and on-lined prediction in the variance-staged MPLS method were introduced.Based on the model,iterative optimal control method was used for quality control of tube hollow.The experimental results show that the obvious benefits of this method are low maintenance cost,good real time function,high reliability precision,and practical application to on-line prediction and optimization on the quality of tube hollow.

FE SIMULATION OF CENTER CRACK OCCURRENCE IN TUBE ROUNDS DURING TWO-ROLL ROTARY ROLLING PROCESS

With the aid of FE （finite element） code MSC.Superform 2005, 2-D coupled thermo-mechanical simulation of center-crack occurrence in round billet during 2-roll rotary rolling process was presented using Oyane ductile fracture criteria. A simple modeling is put forward based on the spiral motion of the workpiece as an essential characteristic in movement. The influence of the feed angle and the entry cone angle of the main roll on the process was taken into account in the modeling. The soundness for simplifying the 3-D rotary rolling into a 2-D problem was discussed. By adopting the parameters of Diescher piercer in 140mm mandrel mill of Bao Steel, the distribution and development of strain/stress were analyzed, and the eigen value of ductile fracture as well. The critical percentage of diameter reduction was obtained from the simulation. The result showed a good agreement with the experimental value, and therefore was of widely guiding significance to the practical process for rationally formulating the deformation parameters of steel tube piercing.

Review of research developments of 12Cr1MoVG heat resistant steel in China

In this paper, we review the evolution of 12CrlMoV steel standards at home and abroad, analyze the effects of various elements and determine their optimal contents in steel. The influence of heat treatment and microstructure on the creep strength of 12CrlMoV steel is investigated. Statistical results from conventional mechanical properties, ductile-brittle transition temperature, high temperature oxidation resistance, aging, instant high temperature properties, and creep are introduced. The results show that the chemical composition and heat treatment process of 12CrlMoVG steel identified in the GB 5310 - 2008 standard is appropriate, resulting in a steel with higher creep strength and good comprehensive properties.

Comprehensive Control on Microstructures and Properties of Medium Carbon V-N Microalloyed Steel Seamless Oil-Well Tubes of Hot-Rolling Non-Quenched/Tempered

The relationship between microstructures and mechanical properties of a medium carbon V-N microalloyed steel used for N80 seamless oil-well tubes of hot rolling non-quenched/tempered (non-Q and T) was investigated.The results have shown that volume percentages of upper bainite,modified bainite and ferrite have a decisive influence on impact energies of steel tubes.When the total volume percentage of bainite is larger than 5%,the impact energy of tubes can not satisfy with the industrial criteria.Moreover,if the total volume percentage of bainite is smaller than 5%,then the impact energy of steel tubes enhances with volume percentage of ferrite increasing.The final microstructures have closely relation with tube billet quality,controlled cooling temperature after tube rolling and cooling method after stretch-reduction-diameter.High quality of medium carbon V-N microalloyed steel for non-Q and T oil-well tubes can be produced through comprehensive control of microstructures and mechanical properties in sub-procedures,especially for tube billet quality and controlled cooling parameters.

Chemistry and Process Optimization of V-Microalloyed N80-Class Seamless Casing Tube

The complex effects of different nitrogen （N） contents and thermal routines on the microstructure and mechanical properties of 33Mn2V steels for N80-Class seamless casing tube application were investigated using Gleeble simulation technique. The results showed that the N additions of 0. 014 %- 0. 021 % in the steels for the in-line normalization process （ILNP） increased the strength while the toughngss remained at a high level as compared with the steel with N content of 0. 005 %. It was also revealed that the N addition of 0. 021%could enhance the performance combination of strength and toughness in the steels by using 700 ℃ as the cooling interrupted temperature （CIT） for the non in-line normalizing process （NILNP）. It was further evidenced that the toughness was improved at expense of strength to some degree in all the steels by decreasing reheating temperature for the ILNP, while an increase of CIT for NILNP severely impaired the toughness and slightly improve the strength in the high-N steel with N content of 0. 021%. This can be attributed to the dissolution and precipitation behavior of V（C,N）. The optimization of V （C,N） precipitation could be achieved by enhancing N. The precipitation of V（C, N） in austenite was promoted by cooling to a certain temperature lower than the A,1 for the ILNP. The V（C,N） particles formed in austenite contrib- uted to grain refinement by the VN-induced nucleation of intragranular ferrite, but as a result the effect of precipitation on strengthening would become weaker due to a decrease of the precipitation of V in ferrite.

Effect of Martensite Morphology on Impact Toughness of Ultra-High Strength 25CrMo48V Steel Seamless Tube Quenched at Different Temperatures

A 25CrMo48V steel for ultra-deep oil/gas well casings was quenched at 900-1 200 ℃ and tempered at 650 ℃. The lath martensitic structures were characterized by optical microscope （OM）, field emission scanning electron microscopy （FESEM）, electron backscattering diffraction （EBSD） and transmission electron microscopy （TEM）, and the transverse impact energy at 0 ℃ was measured from the as-quenched and tempered specimens. The results show that with the quenching temperature decreased, the prior austenite grain, martensitic packet and block are refined, while the lath width seems to remain unchanged. The enhancement of impact toughness with the decreasing quenching temperature can be attributed to refinement of the martensitic structure with high-angle boundaries, and the block is the minimum structure unit controlling impact toughness. The transverse impact energy [ECVN （0 ℃） ≥100 J] required for seamless casings with ultra-high strength （Rp0.2≥932 MPa） has been finally achieved with the experimental steel quenched at 900-1 000 ℃ and tempered at 650 ℃.

Method for Improving Transverse Wall Thickness Precision of Seamless Steel Tube Based on Tube Rotation

The tube rotation method （TRM） refers to the rotational movement of steel tube about its axis as well as translation in rolling direction in stretch reducing rolling process. The influence of the TRM on transverse wall thickness precision of seamless steel tube was studied. Thickness distribution of the TRM was obtained by superimposing the thickened amount of single pass rolling. Results show that the TRM can effectively improve the evenness of thickness distribution. In order to analyze the influence mechanism of the TRM, the finite element method was adopted to simulate the thickness distribution in stretch reduction process. Results show that the TRM changes the roundtrip flow between two fix places of conventional stretch reducing and inhibits the directional accumulation of metal. In addition, the TRM has a correction effect on thickness cusp. All these advantages of the TRM help to improve the transverse wall thickness precision of seamless steel tube.

Influence of Heat Treatment on Hydroformability of TRIP Seamless Steel Tube

A low-carbon TRIP seamless steel tube, which is expected to be used in the hydroforming process, was successfully fabricated using piercing, cold-drawing and two-stage heat treatment process. The two-stage heat treatment is one crucial step because it significantly affects the microstructure and mechanical properties of TRIP seam less steel tube. In order to obtain the TRIP seamless steel tube with high hydroformability, several different heat treatment processes were conducted. The effects of heat treatment conditions （intercritical annealing （IA） and isothermal bainite treatment （IBT）） on the TRIP seamless steel tube hydroformability which was determined by free hydraulic bulge test were analyzed. Two different internal pressure boosting velocities of 0.2 and 0.5 MPa/s of free hydraulic bulge tests were adopted to determine the effective stress vs. effective strain curve of TRIP seamless steel tube. The results showed that for the predetermined IA condition, the maximum bulge height increased, but the maximum burst internal pressure decreased, with the increase of IBT holding time from 4 to 6 rain. For the predetermined IBT condition, the maximum bulge height decreased, but the maximum burst internal pressure increased, with the increase of IA holding time from 5 to 10 rain. By analyzing the free hydraulic bulge test results, it was found that the maximum bulge heights of TRIP seamless steel tubes with the internal pressure boosting velocity of 0.5 MPa/s were higher than those when the internal pressure boosting velocity was 0.2 MPa/s. This means that an appropriate deformation rate should be chosen to obtain the optimal hydroformability of TRIP seamless steel tube. In addition, the effective stress vs. effective strain curves of TRIP seamless steel tubes were ohtained with free hydraulic bulge test.

Modeling and Optimization for Piercing Energy Consumption

Energy consumption is an important quality index in the production of seamless tubes. The complex factors affecting energy consumption make it difficult to build its mechanism model, and optimization is also very difficult, if not impossible. The piercing process was divided into three parts based on the production process, and an energy consumption prediction model was proposed based on the step mean value staged multiway partial least square meth- od. On the basis of the batch process prediction model, a genetic algorithm was adopted to calculate the optimum mean value of each process parameter and the minimum piercing energy consumption. Simulation proves that the op- timization method based on the energy consumption prediction model can obtain the optimum process parameters effectively and also provide reliable evidences for practical production.

Numerical Simulation of Steel Tube Induction Heating During Quenching Process

Induction heating process of steel tube using of intermediate frequency is characterized by short time,precise temperature control and environment friendly.It has been widely applied to the quenched steel,bent pipe,etc.In this paper,induction heating process for a typical variety of seamless steel tube,in particular the heating section different frequency combination is studied by numerical stimulation.The temperature field has been calculated during the entire heating process of tube.The optimum operating parameters of induction heating has been suggested which in turn provides an important reference data to the research of seamless steel tube induction quenching.