Unsteady State Thermal Behavior of Industrial Quenched Steel Bar

Transcription

1 18th Wrld IMACS / MODSIM Cngress, Cairns, Australia July 29, Unsteady State Thermal Behavir f Industrial Quenched Steel Bar Prf. Dr. Haji Badrul Bin Omar, Prf. Dr. Mhamed Elshayeb and Abdlmanam. S.A. Elmaryami University Tun Hussein Onn Malaysia, Mechanical Engineering Department 864 Parit Raja, Batu Pahat, Jhr, Malaysia, badrul@uthm.edu.my, mhamed@uthm.edu.my and damer64@yah.cm Abstract: Heat transfer is very imprtant in steel industries because heating is an ecnmical way t alter a steel cmpnent s prperties t suit the end user s requirement. Heating interrupted by quenching is a well-knwn prcedure t treat steel cmpnents. Much wrk had been dne n changing the mechanical prperties f the steel cmpnent and little n the fundamental f the prcess, which is the heat transfer between the quenching medium and steel cmpnent. Theretically, we shuld be able t predict hardness at any pints f steel prvided that the relatinship between its cling rate and hardness and the temperature field and its evlutin with time are knwn. Nevertheless, based n metallurgy literature, steel such as ht rlled bar; the allwable hardness is 35HRC. In this paper, we will discuss the apprach f finite element sftware ANSYS Wrkbench. The ANSYS simulatin will be dne in 1-D, 2-D and three dimensinal. Beside that, the results will be verified by using ANSYS sftware. Frm the result, the hardness predictin can be used as a rugh guideline t assist the quality engineer prir t prductin by cmparing t a typical standard hardness value set. This will help t reduce the risk f trial and errr during prductin. In this manuscript we discussed the hardness predictin f the quenched bar is difference accrding t its quenching media which fr water have the highest value f 5.32 HRC, HRC fr statinary il and the lwest hardness is HRC fr salt bath. Hardness increase as cling rate increases. Once the cling temperature decreased, the steel bar will need t take lnger time t quench. This was caused the hardness f steel bar decreased. The effect f quenchants media gives variable f hardness f steel bar by accrding t its cling rate. As a cnclusin, this paper has fulfilled all the bjectives where the affected parameters have been identified t imprve the wrkability f steel bar during cling by using ANSYS sftware [1-D, 2-D and 3-D] wing t lwer cst, safer and reliable prcedure than experimental wrk. Keywrds: Heat treatment, Temperature distributin, Hardness, heat transfer, Ansys wrkbench sftware, Finite Element, Steel, Quenchant media 1. Intrductin This paper studied the thermal behavir f steel bar during quenching three dimensinal. Where, we fund that the temperature distributin btained by finite element methd and ANSYS Wrkbench are almst having the same results in ne [1-D] and tw-dimensinal [2-D] slutin as shwn in Figs.1. and 2 respectively. Therefre ANSYS Wrkbench can prduce the accurate result and it helps us save the time and mney t analyze the prblems. S, instead f wasting time and mney, the best alternative slutin is by ding the simulatin. Therefre we can easily calculate the hardness distributin during cling frm the temperature distributin histry by using Ansys Wrkbench Nde 1 (manual) Nde 2(manual) Nde 3(manual) Nde 1(ANSYS) Nde 2(ANSYS) Nde 3(ANSYS) Nde 1 (manual) Nde 2(manual) Nde 3(manual) Nde 4(manual) Nde 1(ANSYS) Nde 2(ANSYS) Nde 3(ANSYS) Nde 4(ANSYS) Fig.1. Cmparisn Result fr water quenchant (1-D) Fig.2. Cmparisn Result fr water quenchant (2-D) 1699

2 2. Prblem and Slutin In manufacturing prcess, the material is in sme way thermally and mechanically affected. Thus the effect n steel bar will be studied in rder t determine the parameters f cling prcess. After knwing the thermal effects and behavir f steel bar, cntrlling the cling prcess becmes essential. The cntrl f cling depends n the heat transfer between steel bar and the quenching medium such as water, statinary il, and salt bath. After knw the heat transfer utput data such as changes in thermal behavir accrding t time has been btained, we can btain a specific cling time fr the prcess. If the cling time is t lng, the steel bar will becme lw ductility. Cnsequently, it is pssible t develp a virtual labratry fr cling prcess using mathematical mdel and cmputer simulatin t increase the prductivity and reliability f steel bar, whilst minimizing the csts and risk assciated with the trial and errr. Anther pssible methd f studying the thermal behavir wuld be t study the hardenability f steel. The ability f steel t frm martensite n quenching is referred t as the hardenability and thrugh this prperty ne can knw the thermal behavir f the prduct during quenching as well. The use f TTT (Time-Temperature Transfrmatin) diagrams culd prvide a gd starting pint fr an examinatin f hardenability, but as they are statements f the kinetics f transfrmatin f austenite carried ut isthermally, they can nly be a rugh guide. Besides the temperature distributin, anther prperty that can be btained frm the cling time is the hardness f the prduct. The hardness f the prduct wuld be the measure f the effectiveness f the quenching prcess and can be determined using the several tests, such as the Grssman test and the Jminy end quenched test data via ASTM E14. In the Grssman test, the transverse sectins are metall-graphically examined t determine the particular bar which has 5% martensite at its centre. The diameter bar is designated at its critical diameter. A less elabrate apprach wuld be the Jminy test in which a standardized rund bar is used. It has been knwn after cling prcess, steel will becme very hard and lw wrkability. Cling time can be cmputed frm temperature behavir. Using Bz s methd and with the availability f cling time frm temperature histry, we can predict the hardness f quenched steel bar. This simulated hardness can be used as a guideline t make the quality f steel bar. 3. ANSYS Simulatin f Steel Bar during Quenching in Three-Dimensinal Data Input: Material : AISI 414, Dimensin :.125m radius and.1m length, Thermal cnductivity 28.2 W/m. C, Steel bar temperature : 5 C, Cling water temperature : 4 C Quenchants types : (Water, statinary il and salt bath), Film cefficient : 65 W/m 2. C, Elements : 722 and End time : 1.67min 3.1. Water Quenchants: This is repeated fr step.8, 1.2, 1.6 and 2 (s) the results shwn in table.1. and Fig.4. shws temperature histry until 1 secnd, water cled 3-D Steel Bar ½ f Steel Bar t(s) Nde 1 Nde 2 Nde 3 Nde 4 (ºC) (ºC) (ºC) (ºC) Fig.3. Result fr 5 ºC Steel bar and 4 ºC at time step.4 secnd. Table.1. Result frm ANSYS sftware in three-dimensinal Frm fig.4. Temperature will reach abslute 4 ºC after 1s. Each nde has the same value f temperature due t its crdinate that lcated at the end f steel bar. Basically temperature is difficult t archive equilibrium value when it s cme t heating r cling. Heat is remved very slwly where biling ceases and heat is remved by cnvectin int the liquid. Temperature will highly decrease when the steel bar suddenly immersed int water which this explained the behavir f biling phase which the stable vapr film will eventually cllapses and cl quenchant cmes int cntact with the ht metal surface resulting in nucleate biling and high heat extractin rates. 5 Nde 1 45 Nde 2 Nde 3 4 Nde 4 Nde 5 35 Nde 6 Nde 7 3 Nde Fig.4. Temperature histry until 1 secnd, water cled 17

3 3.2. Statinary Oil Quenchants: Stee Figure.5. Ndes crdinates fr 3-D statinary il quenchant. ½ f Steel 3-D Nde 1 Nde 2 Nde 3 Nde 4 Nde 5 Nde 6 Nde 7 Nde 8 Frm Fig.6. temperature will reach abslute 4 ºC after 49 secnd (8.17 minute). Each nde has the same value f temperature due t its crdinate that lcated at the end f steel bar. Quenching il has different value f heat transfer cefficient if cmpared t heat transfer cefficients fr water; this will give different value f cling rate thus resulting difference hardness value. Similar with water case study, value fr cling rate are appraching zer at the end f the quenching prcess Figure.6. Temperature versus time fr statinary il quenchant 3.3. Salt Bath Quenchants Steel ½ f Steel Bar 3-D Nde 1 Nde 2 Nde 3 Nde 4 Nde 5 Nde 6 Nde 7 Nde 8 15 Figure.7. Ndes crdinates fr 3-D salt bath quenchants 1 5 Frm Fig.8. temperature will reach abslute 4 ºC after 236 secnd (39.3 minute). Each nde has the same value f temperature due t its, crdinate that lcated at the end f steel bar. Salt bath has different value f heat transfer cefficient if cmpared t heat transfer cefficients fr water and il; this will give different value f cling rate thus resulting difference hardness value which will be discuss in the next chapter. Similar with water and il case study, value fr cling rate are appraching zer at the end f the quenching prcess, and Fig.9. shws Cling curves quenching in water, il, and salt. A plt f temperature vs. time fr AISI 414 steel bar, quenched in different fluids, is shwn in figure.9. The steel bar quenched in water has the highest cling rates and the bushing quenched in salt bath has the lwest cling rate. Water has the fastest cling time due t its largest heat transfer cnvectin cefficients while salt bath has the smallest heat transfer cnvectin cefficients cmpared t statinary il. This variable end time can prvide different type f hardness and ductility. Figure.9. Cling curves quenching in water, il, and salt Discussin The result when changing the quenchants media frm water t statinary il and salt bath with the cmparisn f result between each quenchants. Frm the result, we can say that ANSYS sftware and Finite Element Methd Temperature (^C) Figure.8. Temperature versus time fr salt bath Cling curves in quenching 15 steel in water, il, and salt Wat er Stat inary Oil Salt Bath

4 manual calculatin are in gd agreement. S, instead f wasting time and mney, the best alternative slutin is by ding the simulatin. 4. Hardness Predictin Hardenability is defined as the ability fr a ferrus ally t frm martensite when quenched frm its austenizing temperature. Theretically, hardness f a particular ally is a functin f its cling rate. Thus, knwing the relatinship between the cling rate and hardness fr a particular ally shuld enable us t predict the hardness at a material pint in a cmplicated part, prvided that the temperature field and its evlutin with time are knwn. Hwever, the experiment shws that this predicted hardness is a lt greater than actual hardness. we need t knw the cling time, t c, frm 8 C t 5 C fr a starting temperature f steel bar 1 C. This is the time relevant fr structure transfrmatin in mst structural steel. After get the cling time, calculate the cling rate, Jminy distance, Hardness f Rckwell C (HRC) and Vickers Hardness (HV) Jminy Distance versus Cling Time One standard prcedure that is widely utilized t determine hardenability is the Jminy end quench test as shwn in Fig.1. Since each distance alng the quenched bar is equivalent t a certain actual cling rate, ne culd just as well plt HRC hardness versus cling rate as HRC hardness versus J-distance. This is exactly what is dne n the ASTM graph paper. Cling Time, = t t (4.1) Cling t c T Rate, ROC = 5 C T 8 C t c 8 C 5 C Jminy distance versus cling time curve was regressed int the fllwing plynmial equatins (4.3) (4.5) by Yeh Chuan Shuan [2] via using Muller methd. The J-distance can be determined frm these equatins based n its cling time. Fr ( t c 12.86): J-distance = -.57(t c ) (t c ) (4.3) Fr (12.86 < t c 43.55): J-distance = -.25(t c ) (t c ) (4.4) Fr (43.55 < t c ): J-distance =.1(t c ) (t c ) (4.5) Where: J-distance =Jminy Distance and t c = Cling Time 4.2. Hardness versus Jminy Distance The Jminy distance is input int hardness versus Jminy distance curve t get the hardness value. The hardness versus Jminy Distance curve was regressed by Yeh (C.S Yeh, 22) using Muller methd. Fr (mm J-distance<13.5mm): HRC=.215(J-distance) (J-distance) (4.6) Fr (13.5mm J-distance<51.mm): HRC=.44(J-distance) (J-distance) (4.7) Where: HRC = Rckwell Hardness C and J-distance = Jminy Distance 4.3. Hardness Cnversin The cnversin f Rckwell Hardness C (HRC) t Vickers Hardness (HV) can be dne thrugh calculatins which were dne by Yeh Chuan Shuan [2] via using regressed plynmial equatin. Fr 29 HRC and belw: HV =.627 (HRC) (HRC) (4.8) Fr 29 HRC 68: HV =.3199 (HRC) (HRC) (4.9) Where: HV = Vickers Hardness and HRC = Rckwell Hardness C Figure.1. Jminy end quench test Result f J-distance, Rckwell Hardness C and Vickers Hardness The sensitivity analysis f this paper was dne in unsteady state cnditin, s we can predict the J-distance, Rckwell Hardness C and Vickers by assumed the cling time via using the equatins (4.1)-(4.9). Table belw shws the relatin amng them. (4.2) 172

5 Table.2. The result f J-distance, HRC and HV Cling Cling J-distance Time, t(s) Rate ( C/s) (mm) HRC HV Discussin Cling Rate (Deg/s) Hardness (HRC) Cling Rate (Deg C/s) versus Jminy Distance (mm) Jminy Distance (mm) Hardness (HRC) versus Cling Rate (Deg/s) Cling Rate (Deg C/s) The relatin between the cling rate, J-distance and the hardness. Fig.11. shws that when the distances f Jminy quench end increase, the cling rate will decrease. This means that the surface f quench end have faster cling rate than the center. While Fig.12. shws that hardness f the Jminy quench bar increase when the cling rate increase. Fig.13. shws that the hardness near t the surface f the quench bar is higher, the center is lwer. S the micrstructure at the surface f quench bar will als be harder rather than center Calculatin fr hardness predictin fr starting temperature f 1ºC, water Hardness can be calculated via using the equatins (4.1)-(4.9). The cling time fr steel bar t achieve 5ºC frm 8ºC initial temperature f 1ºC can be determine frm three-dimensinal case ANSYS 1. sftware. i) Cling Time t c = t 5 C t 8 C = = Sec ii) Hardness (HRC) Hardness (HRC) versus Jminy Distance (mm) Jminy Distance (mm) Cling Rate Cling Rate, ROC = (T 8 C T 5 C ) / t c = [ O C O C] / Sec Thus ROC = O C / Sec iii) Jminy Distance: fr ( t c ) J-distance = -.57(t c ) (t c ) =.8261 mm iv) Hardness: fr ( mm J-distance 13.5mm ) HRC =.215 (J-distance) (J-distance) = 5.32 v) Hardness Cnversin HV: fr 29 HRC 68 HV =.3199(HRC) (HRC) = Figure 11. Graph cling rate versus Jminy Distance Figure 12. Graph hardness (HRC) versus cling rate (C /s) Figure.13. Graph hardness (HRC) versus Jminy Distance (mm) 173

6 4.7. Calculatin fr hardness predictin fr starting temperature f 1ºC, il i) Cling Time t c = t 5 C t 8 C = = 5.6 Sec ii) Cling Rate Cling Rate, ROC = (T 8 C T 5 C ) / t c = [ O C 5,53 O C] / 5.6 Sec Thus ROC = 53.4 O C / Sec iii) Jminy Distance: fr ( t c ) J-distance = -.57(t c ) (t c ) = mm iv) Hardness: fr ( mm J-distance 13.5mm ) HRC =.215 (J-distance) (J-distance) = v) Hardness Cnversin HV: fr 29 HRC and belw HV =.627(HRC) (HRC) = Calculatin fr hardness predictin fr starting temperature f 1ºC, salt bath i) Cling Time t c = t 5 C t 8 C = = Sec ii) Cling Rate Cling Rate, ROC = (T 8 C T 5 C ) / t c = [84.9 O C O C] / Sec Thus ROC = 7.17 O C / Sec iii) Jminy Distance: fr ( t c ) J-distance = -.25(t c ) (t c ) = mm iv) Hardness: fr ( 13.5mm J-distance 51,mm ) HRC =.44 (J-distance) (J-distance) = v) Hardness Cnversin HV: fr 29 HRC and belw HV =.627(HRC) (HRC) = Table.3. The result f J-distance, HRC and HV fr different types f quenchant. Quenchants Cling Time, t c Cling Rate J-distance (s) ( C/s) (mm) HRC HV Water Statinary Oil Salt Bath Discussin Hardness increases as cling rate increases. Theretically, we shuld be able t predict hardness at any pints n an ally prvided that the relatinship between its cling rate and hardness and the temperature field and its evlutin with time are knwn. Nevertheless, based n metallurgy literature, steel such as ht rlled bar; the allwable hardness is 35HRC. 5. General Discussin The result f the sensitivity analysis n the quenched bar was simulated in three dimensinal mdel. The predicted hardenability f steel bar n varius cling time fr water quenchants was discussed. In rder t increase a prductivity and wrkability f steel bar by quenching, the hardness f steel bar must belw the 35HRC. 6. Cnclusin 1. The hardness predictin f the quenched bar is difference accrding t its quenching media which fr water have the highest value f 5.32 HRC. Hardness increase as cling rate increases. Nevertheless, based n metallurgy literature, steel such as ht rlled bar; the allwable hardness is 35HRC. 174

7 2. Frm the result, the hardness predictin can be used as a rugh guideline t assist the quality engineer prir t prductin by cmparing t a typical standard hardness value set. This will help t reduce the risk f trial and errr during prductin. 3. As a cnclusin, this paper has fulfilled all the bjectives where the affected parameters have been identified t imprve the wrkability f steel bar during quenching. 7. Recmmendatin fr Further papers There are many ptential future wrks which can be carried ut t mdify r expand the mdels. The fllwing are recmmended fr further manuscripts: i. We have t change the ther parameter s that we can achieve allwable hardness fr quenched steel bar. ii. iii. iv. Applying temperature histry n different type f heat treating, such as nrmalizing, annealing, stress relieving, and surface hardening. Cntinue t study the alternative methds f quenching such austempering, martempering, isthermal quenching, Aus-bay quenching, Spray quenching, Fg quenching, Cld die quenching, Press quenching, Vacuum quenching, Fluidized bed quenching, HIP quenching, Ultrasnic quenching, and Quenching in electric and magnetic fields. Perfrm the Jminy end quenched test experimentally t get the hardness fr the Jminy distance mre than 51mm. v. Extending the mdel t ther shape f steel bar such as square, rectangular and triangular steel bar. vi. Applying bending and grinding t steel bar t see the effect f stress relief due t heat treating f steel. REFERENCE El-shayeb, M., Al-Habbali, Sa ad and Bibby M.J. (1997). Hardness Predictin f A Weld (Three Dimensinal Mathematical Mdel). Jurnal f Institutin f Engineers, Malaysia 58(2) Yeh, Chuan Shuan. (22). Thermal Behavir f Steel Bar during Quenching. University Malaysia Sabah: Thesis Degree f Master f Science (Mechanical Engineering). Rthe H. and Siegmund H. (1995). Temperature Cntrlled Rlling Of Wire And Bar. Technical Paper - Originally Written Fr The 1995 AISE Annual Cnventin Prgram And Irn And Steel Expsitin, Pittsburgh, Pennsylvania, USA. September 25-28, Hamuda A.M.S., Sulaiman S. and Lau, C.K. (21). Finite Element Analysis n the Effect f Wrkpiece Gemetry n the quenching f ST5 Steel. Jurnal f Material Prcessing Technlgy (119) Hamuda A.M.S., Sulaiman S. and Lau, C.K. (21). Finite Element Analysis n the Effect f Wrkpiece Gemetry n the quenching f ST5 Steel. Jurnal f Material Prcessing Technlgy (119) M a, Y., Wng, G. and Wang, B.(1997). Numerical and Experiment Study f the Behavir f Rail under Different Cling Rates. Jurnal f Material Prcessing Technlgy 63 (1997) Bz, S. (1998). Numerical Simulatin f As-quenched Hardness in a Steel Specimen f Cmplex Frm. Cmmunicatins in Numerical Methd in Engineering