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Uncoated Plain Carbon Steel Material Variables

Uncoated Plain Carbon Steel Material Variables. Uncoated Plain Carbon – Material variables. Learning Activities Look up Keywords View Slides; Read Notes, Listen to lecture Do on-line workbook. Lesson Objectives When you finish this lesson you will understand:

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Uncoated Plain Carbon Steel Material Variables

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  1. Uncoated Plain Carbon Steel Material Variables

  2. Uncoated Plain Carbon – Material variables • Learning Activities • Look up Keywords • View Slides; • Read Notes, • Listen to lecture • Do on-line workbook • Lesson Objectives • When you finish this lesson you will understand: • the relationship between steel manufacturing variables and spot weldability Keywords Chemistry, Carbon Equivalent, Steel Cleanliness, Surface Condition, Solid State Bond, Thickness

  3. Process Parameters: Weld Current Weld Time Hold Time Upslope/Downslope Pulsing Electrode Force Postweld Temper Electrode Designs Material Parameters: Chemistry Cleanliness Surface Condition Material Processing Thickness Material Variables

  4. Chemistry To avoid weld problems: C < 0.10% + 0.3 t Material Thickness 1000 Thin Material = 100% Martensite (interface tears) 800 600 Maximum Hardness, DPH Thick Material = Slower Cooling= Ferrite + Pearlite 400 200 0 0 0.2 0.4 0.6 0.8 1.0 Carbon Content, % [Reference: Welding in the Automotive Industry, p.153, D. W. Dickinson ]

  5. Weldability Lobes for Uncoated Mild & Interstitial-Free Steel 15 IF Steels have lower bulk Resistance Mild Steel 10 IF Weld Time (Cycles) 5 Interstitial Free Steel Mild Steel [Reference: “Challenges in Welding New Sheet Steel Products”, Gould & Kimchi] 0 6 7 8 9 10 11 12 Welding Current (kA)

  6. Chemistry (CONT.) (Centerline Cracking) 0.20 0.15 Spot Weld Failure 0.10 P + 3S, % Acceptable Spot Weld 0.05 0 0 0.05 0.10 0.15 0.20 0.25 0.30 C, % [Reference: Welding in the Automotive Industry, p.154, D. W. Dickinson ]

  7. Base Metal Microstructures for Killed Plain Carbon and Rephosphorized Steels Since P in solution = Very little difference in microstructure 100/110 HV 140/170 HV Result: Hardness & Centerline Cracking [Reference: “Spot Weldability of High-Strength Sheet Steels”, Welding Journal 59 (January 1980), Baker & Sawhill]

  8. Effect of Carbon and Phosphorous on Current Range Drop due to interfacial nugget tears 4000 0.31 in. 3000 0.28 in Current Range, Amp (0.15 in. Minimum Button) 2000 0.25 in Electrode [Reference: “Spot Weldability of High-Strength Sheet Steels”, Welding Journal 59 (January 1980), Baker & Sawhill] 1000 0.05 0.10 0.15 %C + %P

  9. Hardness Transverses in a Spot Weld between Rephosphorized and Plain Carbon Steels Hardness, HV1.0 [Reference: “Spot Weldability of High-Strength Sheet Steels”, Welding Journal 59 (January 1980), Baker & Sawhill] Base Metal HAZ Distance from Fusion Line, in.

  10. Chemistry (CONT.) Max. Tensile Shear Stress Centerline Tears Max. Cross- Tension Strength Tensile-Shear Test Maximum Strength Maximum Button Diameter Welding Range, % Max. Button Dia. in Peel Test Peel Test Weight, %Ti Weight, %Ti [Reference: Welding in the Automotive Industry, p.156, D. W. Dickinson ]

  11. OTHER ELEMENTS • NITROGEN • Promotes Interfacial Tears • More Critical in Unkilled Cold-Rolled Gages • N Tied up by Al in Killed Steels • OXYGEN • Promotes Interfacial Tears • Kill Heats to Reduce • Get Rid of Rust • HYDROGEN • Usually not a problem except in High Carbon • Remove Surface Oils

  12. Empirical Carbon Equivalent Equation CE = C + Mn/36 + (Cr + Mo + Zr)/10 + Ti/2 + Cb/3 + V + T.S.(ksi)/900 + t(in.)/20 For Best Results CE < 0.30

  13. Effect of Boron Babu, S et Al, “Effect of Boron on the Microstructure of Low-Carbon Steel Resistance Seam Welds” Welding Journal, 1997

  14. Questions? • Turn to the person sitting next to you and discuss (1 min.): • The chemistry effects in spot and seam welding of carbon steels are similar to those in GTAW at high travel speeds but somewhat more exaggerated. Considering solidification morphology, why should this be?

  15. Process Parameters: Weld Current Weld Time Hold Time Upslope/Downslope Pulsing Electrode Force Postweld Temper Electrode Designs Material Parameters: Chemistry Cleanliness Surface Condition Material Processing Thickness Process Variables

  16. Steel Cleanliness [Reference: Welding in the Automotive Industry, p.160, D. W. Dickinson ]

  17. Process Parameters: Weld Current Weld Time Hold Time Upslope/Downslope Pulsing Electrode Force Postweld Temper Electrode Designs Material Parameters: Chemistry Cleanliness Surface Condition Material Processing Thickness Process Variables

  18. Surface Condition Hot Spots Alloying & Cavitation Surface Expulsion Electrode Eroding Oils/Dirt Oxide Steel

  19. Effect of Surface Oxide on Electrode THICK SHEET - High Currents Weld on Scale Scale Cleaned Weld on Scale - No Upslope With Upslope THIN SHEET Lower Current Scale Cleaned

  20. Effect of Surface Oxide on Lobe

  21. Effect of Surface Carbon on Button Tear Interface Failure Dirty Solid State Bond HAZ Nugget Clean

  22. Weld Lobes of Two HSLA SteelsBatch Annealed (high surface C) vs Continuous Annealed (low surface C) Accu-form 50XK Batch-Annealed B50XK Weld Time, cycles [Reference: “Forms of Dynamic Resistance Curves Generated During Resistance Spot Welding”, Watney & Nagel] Lower Surface Carbon No Partial Nuggets Current, kA

  23. Questions? • Turn to the person sitting next to you and discuss (1 min.): • What are some ways that a steel company can get cleaner steels both internally and on the surface?

  24. Process Parameters: Weld Current Weld Time Hold Time Upslope/Downslope Pulsing Electrode Force Postweld Temper Electrode Designs Material Parameters: Chemistry Cleanliness Surface Condition Material Processing Thickness Process Variables

  25. Heat-Affected Zone Property Loss in HSLA Steels Martensitic Zone Aged Zone Base Metal Recrystallized Ferritic Zone Transformation Martensite Tempering Knoop Hardness HSLA Controlled Rolled Grain Refinement Ppt Strength Plain Carbon [Reference: Welding in the Automotive Industry, p.162, D. W. Dickinson ] Distance From Fusion Line

  26. Microstructure Near Outside Edge of HAZ in SRA Steel Spot Weld [Reference: “Spot Weldability of High -Strength Sheet Steels”, Welding Journal 59 (January 1980), Baker & Sawhill]

  27. Process Parameters: Weld Current Weld Time Hold Time Upslope/Downslope Pulsing Electrode Force Postweld Temper Electrode Designs Material Parameters: Chemistry Cleanliness Surface Condition Material Processing Thickness Process Variables

  28. High Hardness at Weld Edge Water Cooled Copper Electrode 230 250 350 300 400

  29. martensite m + p + f p + f carbon % HARDNESS 0.5 0.3 0.1 THICKNESS

  30. Thickness Temperature Temperature Temperature Time (cycles) Time (cycles) Time (cycles) 0.5 mm Steel 1.1 mm Steel 1.5 mm Steel

  31. Spot Welding of Extra Heavy Gage Mild Steel Plate (12 mm) • Machine Characteristics • Power Source: 3 phase Freq Convert • Rated Capacity : 150 kVA • Max Capacity : 1,000 kVA • Max Current : 150 KA • Max Force : 20 Tons • Uses • Architecture • Bridges • Off Highway Vehicles Yamamoto, T “A study of spot welding of heavy gauge mild steel”, Welding In the World, July/Aug, 1971

  32. Spot Welding of Extra Heavy Gage Mild Steel Plate (12 mm) • Welding Procedure Modified • Squeeze time heat and Pre-heat, High Squeeze Force added to Set Parts. (20 Ton Force Press) • Welding Done With Frequency Changer – Very Long Weld Times • Forge and Q&T Added Yamamoto, T “A study of spot welding of heavy gauge mild steel”, Welding In the World, July/Aug, 1971

  33. Spot Welding of Extra Heavy Gage Mild Steel (12 mm) • 1mm Thick steel reaches peak in nugget diameter in 12 cycles • But, 12 mm Thick Steel peak is 150 – 5 cycle pulses = 750 cycles • Weld Strength = f (Nugget dia + Corona Dia) Corona Diameter Nugget Diameter Indentation Penetration Yamamoto, T “A study of spot welding of heavy gauge mild steel”, Welding In the World, July/Aug, 1971

  34. Effect of Electrode Force on Spot Welding of Extra Heavy Gage Mild Steel (12 mm) • Increased Force • Reduces Nugget Diameter (lower R) • Almost no effect on Corona Dia • Only Slightly Lowers TSS • The Corona Diameter Plays a large Role in Strength of Very Thick Materials >F Yamamoto, T “A study of spot welding of heavy gauge mild steel”, Welding In the World, July/Aug, 1971

  35. Spot Welding of Extra Heavy Gage Mild Steel (12 mm) • The thermal time constant for 12 mm thick steel plate is remarkably high (10 sec. vs 1 mm at 0.1 sec) • Increased electrode force leads to decreased heat • The corona bond around the weld contributes a great deal to mechanical strength • The incidence of blow holes or shrinkage cavities decreases as electrode force increases Yamamoto, T “A study of spot welding of heavy gauge mild steel”, Welding In the World, July/Aug, 1971

  36. Questions? • Turn to the person sitting next to you and discuss (1 min.): • What factors might limit the thickness of shet or plate steel that can be spot welded?

  37. RW Hot Rolled Steel

  38. RW Cold Roiled Steel

  39. Structure Property

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