Weldability. CTU in Prague Faculty of Mechanical Engineering

Transcription

1 1st semester 2015/2016 Weldability CTU in Prague Faculty of Mechanical Engineering Ing. Petr Vondrouš, PhD., IWE

2 Hodnocení svařitelnosti Welding and weldability Welding is heating locally material to a high temperature, and is possibly accompanied by this detrimental phenomena. Then is stress in the weld, stress concentration Welding have influence on structure safety, on prize AREA Causes Change of properties Defects, where Heated Phase changes Annealing, recrystalization, precipitation, grain coarsening, segragation Change of mech. Properties in HAZ Molten Fast segregation Non homogeneous properties in WM, HAZ Soliidification cracks in WM, HAZ Fast cooled Metastable phases Change of mechanical properties - martenzite, retained austenite. Loss of ductility, Cold cracks ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování

3 Knowledge of Material weldability Change of material properties due to weld thermal cycle. Influence of Chemical compostion. Material production method Heat treatment If materials have different properties, then their weldability will differ. Imagine welding such semiproducts Shrinkage Segragation

4 Weldability (joinability) -definition Technologist view Weldability is technological property of material, an ability of material to be welded. Explanation from ISO/TR 581 Component is weldable by a process if metallic continuity can be obtained by suitable procedure. Weld shall also comply requirments in regard of metallurgical and mechanical properties. Explanation of AWS Capacity of metal to be welded under fabrication conditions into suitably designed structure to perform inteded service. Often is used to determine welding process and to compare materials. Weldability is not easy to be quantified. Weldability is similar to quality in broad meaning.

5 Material Arc welding Oxyacetylene welding Weldability by process[1] Electron beam welding Resistance welding Brazing Soldering Adhesive bonding Cast iron C R N S D N C Carbon steel and low-alloy steel Stainless steel Aluminum and magnesium Copper and copper alloys Nickel and nickel alloys R R C R R D C R C C R R C C C C C C C S R C C C C R R C R C C R R C C Titanium C N C C D S C Lead and zinc C C N D N R R Thermoplasti c N N N N N N C Thermosets N N N N N N C Elastomers N N N N N N R Ceramics N S C N N N R Dissimilar D D C D D/C R R

6 ABLE 1. Metallurgical compatibility of metal pairs: etals: Al: aluminum; Ag: silver; Au: gold; Cu: copper; Pt: platinum; Ni: nickel; e: iron; Ti: titanium; and W: tungsten. ey: C: Complex structures may exist; X: Intermetallics compounds formed ndesirable combination; S: Solid solubility exists in all alloy ombination; D: Insufficient data for proper evaluation; and N: No data available rom

7 Weldability according to ISO/TR 581 Weldability is governed by 3 factors, each of them can be decisive.

8 From - Weldability Of Thermo-Mechanically Rolled Steels Used In Oil And Gas Offshore Structures Joshua Omajene, Jukka Martikainen, Paul Kah

9 Weldability evaluation What can be the customer demand on weld product quality? strength safety production volume precision assembly price lead time What is your demand on these welded structures? balcony flower pot holder IKEA clothes holder weekend bugy student formula production car ship bridge

10 Weldability evaluation Weldability is very complex property, all is interrelated. The best to evaluate weldability, i.e. fulfillment of all demands on welded structure, is to create the structure and test it. Yet is it possible and meaningful? Testing of balcony flower pot holder - evaluation not needed IKEA clothes holder rigid testing done, needed weekend bugy- evaluation not needed student formula-needed production car rigid testing done, pre-production series ship testing needed, yet not full scale bridge testing needed, yet not full scale Testing of weldability must be simplified, yet with good results, secure. Different levels of quality requirements are to be fulfilled acc. to product.

11 Weldability evaluation Testing of weldability must be simplified, yet with good results, secure. How to do it? not needed easy, highest risk when needed 1. Theoreticaly from past experience, books in library- past experience, calculation of material composition, CCT, CET 2. Practically by welding On simplified piece- normalized weldability tests weld ductility, tensile test On representative piece - normalized weldability tests On piece to be welded- welding process qualification Ad. 1. Much experience summarized into simply to apply calculations summarized in norms, material composition,cct, CET e.g. C-Mn steels have excellent weldability upto C=0,2 %, CE=0,45 %, preheat only for thick sheets (30 mm), suitable for all welding methods Serves for TECHNOLOGY PREPARATION, For very simple tasks

12 Practical weldability evaluation normalized weldability tests weld ductility, tensile test For new materials, complicated ones where research must be done as data do not exist. Serves for RESEARCH and process qualifications On piece to be welded- welding process qualification of DEMANDING PRODUCTS

13 Scientific approach Knowledge of CCT, cooling speeds enables knowing phases, properties It needs precise measurement and know how Experience of many experiments summarized into simply to apply general calculations summarized in norms

14 Material weldability Steels C-Mn HSLA Cr-Mo, Cr-Mo-V Quenched and tempered steels Thermomechanically treated steel High alloy steel Stainless Al alloys Ni alloys Ti alloys If materials have different chemical, mechanical, physical properties, then their weldability will differ.

15 Weldability of steels C-Mn excellent weldability upto C=0,2 %, CE=0,45 %, preheat only for thick sheets (30 mm), suitable for all welding methods HSLA Cr-Mo, Cr-Mo-V low alloy, oxidation, corrosion resistence, good weldability, but high hardenability (in air), preheat or PWHT needed, control of q, temper embittlement Quenched and tempered steels already in heat treated state, structures will be effected, stress relieve, critical preheating, excess heat input, stringer beads, low hydrogen, HAZ can transform to martensite, bainite, oxy fuel cutting problematic, grinding, gouging Thermomechanically treated steel High alloy steel Stainless Tool steels martensitic, austenitic, feritic, duplex

16 Influence of Chemical composition over time summarized into Practical recommendations and calculations: Norm ISO places materials into weldability groups Steels have 11 groups, every group has different weldability issues Norm 1011 Recommendations for fusion welding CET carbon equivalent combined influence of elements on cold cracking Preheat temperature Hot cracking factor sensitivity to segregation and solidification cracking Lamellar tearing factor Weldability is often judged by susceptibility to certain detrimental phenemona, i.e. cold cracking, hot cracking

17 Metallic_Materials_Grouping_System.pdf

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19 Carbon equivalent for ferittic steels In ČSN EN is presented CET for method B: CET C Mn Mo 10 Cr Cu 20 Suitable for steels 1-4 acc. to ISO/TR wt.% C (0,05-0,25 wt. %), Si (max. 0,8 wt. %), Mn (0,5-1,9 wt. %), Cr (max. 1,5 %), Cu (max. 0,7 %), Mo (max. 0,75 %), Nb (max. 0,06 %), Ni (max. 2,5 %), Ti (max. 0,12 %), V (max. 0,18 %) a B (max. 0,005 %). Ni 40 Limiting thickness

20 Carbon equivalent In ČSN EN 1011 is presented CET for method B, recommended manily for HSLA steels: CET C Mn Mo 10 Cr Cu 20 Tp = TpCET + Tpd + TpHD + TpQ. [ C] wm.% Tp = 697*CET tanh (d/35) + 62*HD^0.35 +(53*CET-32)*Q-330 Ni 40

21 Carbon equivalent IIW/IIS and EN (method A) recommend for ferittic C- Mn steels: C (0,05-0,25 wt. %), Si (max. 0,8 wt. %), Mn (max 1,7 wt. %), Cr (max. 0,9 %), Cu (max. 1 %), Mo (max. 0,75 %), Ni (max. 2,5 %), V (max. 0,2 %). wt.% C e ( IIW) C Mn 6 Cr Mo V 5 Ni Cu 15 Usable for CE=0,3-0,7, not suitable for B steels If it is till 0,45 % thickness 4 mm, 0,4 % thickness 6,5 mm 0,35 % thickness 25 mm, 0,3 thickness 50 mm Steel can be welded without preheat.

22 Preheat calculation Seferian calculation Seferian : T p 350. C 0,25 p [ C] C p C c C s C c 360C 40( Mn Cr) 20Ni 28Mo 360 C 0,005. s. s C c s = thickness Suitable for carbon and low alloy steels with C > 0,1 %

23 Preheat calculation Ito + Bessya T p Pw 392 [ C] Kde : Pw Pcm H 60 K Si Mn Cu Cr Ni Mo V Pcm C 5B H = diffusible H [ml 100 g] K = weld stiffness = 69.s butt weld (66.s fillet weld) s = thickness [mm]

24 Hot cracking sensitivity EN 1011 recommends using UCS-unit of crack susceptibility U. C. S. 230 C 190 S 75P 45Nb 40Ni 12Si 5,4Mn 1 Usable for steels with composition max. C = 0,23 wt.%, S = 0,05 %, P = 0,045 %, Si = 0,65 %, Mn = 1,6 %, Nb = 0,07 % results: UCS < 10 low risk of solidification crack USC > 30 high risk of solid. crack Other sources show other parameters to show probability of solidification cracking, e.g. HCS H. C. S. Si Ni C.( S P ) Mn Cr Mo V 3

25 Other possible calculations Lamelar tearing factor Reheat cracking Diagrams.

26 Normalized tests of welds ČSN EN ISO Destructive tests on welds in metallic materials Cold cracking tests for weldments- Arc welding ČSN EN ISO Destructive tests on welds in metallic materials Hot cracking tests for weldments- Arc welding ČSN EN ISO 9017 Fracture test ČSN EN ISO Macroscopy ČSN EN ISO 9015 Hardness ČSN EN ISO Destructive tests on welds Impact test ČSN EN ISO 4136 Destructive tests on welds Bend test ISO 18278,18595 Resistance spot welding weldability

27 Welding procedure qualification ČSN EN ISO Specification and qualification of welding procedures for metallic materials - General rules ISO Specification and qualification of welding procedures for metallic materials - Welding procedure specification from arc, gas welding upto laser hybrid welding ISO Qualification based on tested welding consumables ISO Qualification based on previous welding experience ISO Qualification by adoption of a standard welding procedure ISO Qualification based on pre-production welding test ISO Specification and qualification of welding procedures for metallic materials - Welding procedure test - from Arc and gas welding of steels, Ni up to laser welding, resistence welding, cladding.