Tin Terne Coated Steel

3. There are two processes used in the United State for the production of Tin Plate. One is by hot dipping and accounts for about 3% of the US volume, and the second is electroplating which accounts for about 97% of the volume. After tin plating the sheets may be sold directly or they may be given a number of top surface coatings.There are two processes used in the United State for the production of Tin Plate. One is by hot dipping and accounts for about 3% of the US volume, and the second is electroplating which accounts for about 97% of the volume. After tin plating the sheets may be sold directly or they may be given a number of top surface coatings.

4. There are a couple of common plating mills. In this mill, the individual �black plate� (uncoated usually cold rolled material) is dipped into and electrolytic pickling bath to clean the surface, then plunged through a fluxing material and into the tin pot. Upon withdrawal from the tin pot the sheet goes through a palm oil bath to put a protective coating on the sheet and is wet washed and sent through some banishing rolls to add surface texture.There are a couple of common plating mills. In this mill, the individual �black plate� (uncoated usually cold rolled material) is dipped into and electrolytic pickling bath to clean the surface, then plunged through a fluxing material and into the tin pot. Upon withdrawal from the tin pot the sheet goes through a palm oil bath to put a protective coating on the sheet and is wet washed and sent through some banishing rolls to add surface texture.

5. A second production method involve the feeding of individual black plate into a flux bath where scrubbing rolls help to clean the surface and apply the flux, followed by immersion into the tin pot. The sheets are brought through a palm oil for final coating.A second production method involve the feeding of individual black plate into a flux bath where scrubbing rolls help to clean the surface and apply the flux, followed by immersion into the tin pot. The sheets are brought through a palm oil for final coating.

6. From the equilibrium phase diagram, it can be seen that at these molten tin temperatures, there will be some inter-diffusion of material to form some iron-tin phases, Zeta and Eta.From the equilibrium phase diagram, it can be seen that at these molten tin temperatures, there will be some inter-diffusion of material to form some iron-tin phases, Zeta and Eta.

7. This is a schematic cross section of the tin coating. Note the iron-tin alloy layer of Zeta and Eta and the FeSn2 high tin containing layer. On top of this is a tin oxide layer and the palm oil film.This is a schematic cross section of the tin coating. Note the iron-tin alloy layer of Zeta and Eta and the FeSn2 high tin containing layer. On top of this is a tin oxide layer and the palm oil film.

8. A second method of producing tin plate (actually most used in the US) is an electrolytic method. This method is continuous so it starts with joining of coils back to front and accumulating the strip in a looper type tank. Strip is then removed at a constant (fairly fast) speed of about 2000 ft/min, forced over a bridle roll to break scale and goes though a cleaning tank. From there it goes into a pickler to remove and remaining adherent oxide, into a rinse tank, a scrubber and then into the electrolytic plating tanks. It is then conducted into a muffle furnace to promote a small amount of diffusion for coating adherence and quenched.A second method of producing tin plate (actually most used in the US) is an electrolytic method. This method is continuous so it starts with joining of coils back to front and accumulating the strip in a looper type tank. Strip is then removed at a constant (fairly fast) speed of about 2000 ft/min, forced over a bridle roll to break scale and goes though a cleaning tank. From there it goes into a pickler to remove and remaining adherent oxide, into a rinse tank, a scrubber and then into the electrolytic plating tanks. It is then conducted into a muffle furnace to promote a small amount of diffusion for coating adherence and quenched.

9. The coil then goes into a tank for application of a chromate passivation film and final oiling and is then finally processed for shipping. A typical tin plate product has strip thickness of 0.006-0.012 cold rolled product with a coating thickness of 6 to 30 micro-inch.The coil then goes into a tank for application of a chromate passivation film and final oiling and is then finally processed for shipping. A typical tin plate product has strip thickness of 0.006-0.012 cold rolled product with a coating thickness of 6 to 30 micro-inch.

10. Typical Applications of Tin Coated Steels Black Plate (no Tin) Temper Roll Start Material Tin Coated Ornamental Uses Tin Coated & Chromate Oil filter Heater components Food Storage Containers Tin Coated & Painted Gas Tanks This slide lists some typical use of tin coated steel.This slide lists some typical use of tin coated steel.

11. When we look at the Black Plate starting product which was produced by cold rolling and then given a temper roll to produce a hardened roughened finish we find that the static resistance measured before welding is fairly high as a result of the roughness, cold worked structure and oxides. Higher wheel electrode forces slightly reduce this static resistance. The hot dipped tin product first of all has an annealed steel substrate (because of the hot dipping) and the tin has smoothed out the surface. The static resistance is very low. There is a thin tin oxide layer, and as additional electrode force is applied this layer fractures further reducing the static resistance. When the weld is actually made and the dynamic resistance is measured, it is seen that the resistance of the Black Plate drops as a result of the heat of welding annealing the cold worked structure ahead of the weld. The dynamic resistance of the Hot Dipped Tin product however is increased because of the bulk heating of the steel.When we look at the Black Plate starting product which was produced by cold rolling and then given a temper roll to produce a hardened roughened finish we find that the static resistance measured before welding is fairly high as a result of the roughness, cold worked structure and oxides. Higher wheel electrode forces slightly reduce this static resistance. The hot dipped tin product first of all has an annealed steel substrate (because of the hot dipping) and the tin has smoothed out the surface. The static resistance is very low. There is a thin tin oxide layer, and as additional electrode force is applied this layer fractures further reducing the static resistance. When the weld is actually made and the dynamic resistance is measured, it is seen that the resistance of the Black Plate drops as a result of the heat of welding annealing the cold worked structure ahead of the weld. The dynamic resistance of the Hot Dipped Tin product however is increased because of the bulk heating of the steel.

12. Let us look at some work from Japan which examined some variations in coating thickness on the Weldability of tin coated steel. The tin was electrolytically deposited followed by the chromate treatment. This left a layer of tin, metallic chromium and topped with a layer of chromium oxide. The thickness of each layer was varied and in some cases only one side was coated.Let us look at some work from Japan which examined some variations in coating thickness on the Weldability of tin coated steel. The tin was electrolytically deposited followed by the chromate treatment. This left a layer of tin, metallic chromium and topped with a layer of chromium oxide. The thickness of each layer was varied and in some cases only one side was coated.

13. This chart lists the variation in coating thickness used in this seam welding study. The tin thickness varied from zero on both sides to 2.8 g/m2 on both sides (note that a one sided Sn coating was also included). The total chromium (metallic chromium plus chromium oxide) varied from a level of 6 to 90 mg/m2 . The resistance was measured across the weldment for each material combination. In the case where there was no tin coating and fairly high levels of total chromium, the resistance was quite high as a result of the insulating properties of the chromium oxide. No weld current range could be found where good seam welds were made. In the presence of the tin coating, welds could be made, and with thicker tin coatings and thinner chromium coating the welding properties improved. Thus, it was found that the available current range extends as the tin coating weight increased; and contact current decreased with tin coating it is felt because the soft tin allows the chromium oxide to break and be moved out of the way thus promoting a current path.This chart lists the variation in coating thickness used in this seam welding study. The tin thickness varied from zero on both sides to 2.8 g/m2 on both sides (note that a one sided Sn coating was also included). The total chromium (metallic chromium plus chromium oxide) varied from a level of 6 to 90 mg/m2 . The resistance was measured across the weldment for each material combination. In the case where there was no tin coating and fairly high levels of total chromium, the resistance was quite high as a result of the insulating properties of the chromium oxide. No weld current range could be found where good seam welds were made. In the presence of the tin coating, welds could be made, and with thicker tin coatings and thinner chromium coating the welding properties improved. Thus, it was found that the available current range extends as the tin coating weight increased; and contact current decreased with tin coating it is felt because the soft tin allows the chromium oxide to break and be moved out of the way thus promoting a current path.

14. In the case of the one sided coating it was observed that the unbalance of resistance characteristics of the sheet caused an unbalance in the heating and the seam weld nugget fell outside the interface making no usable current range.In the case of the one sided coating it was observed that the unbalance of resistance characteristics of the sheet caused an unbalance in the heating and the seam weld nugget fell outside the interface making no usable current range.

15. As with other coated steels, the welding of tin coated steel can effect electrode life because the coating material alloys with the cooper base electrodes to form low melting phases. Looking at this Cu-Sn equilibrium phase diagram indicates that one might predict very serious lowering of electrode melting temperature as alloying with tin proceeds. Some method to preserve the integrity of the electrode is required.As with other coated steels, the welding of tin coated steel can effect electrode life because the coating material alloys with the cooper base electrodes to form low melting phases. Looking at this Cu-Sn equilibrium phase diagram indicates that one might predict very serious lowering of electrode melting temperature as alloying with tin proceeds. Some method to preserve the integrity of the electrode is required.

16. The soudronic welding process has been adapted as a method for continuously welding tin coated steel of �tin can� applications. In this process, a continuously fed wire serves as the welding electrode, thus minimizing the effect of alloying and low melting Cu-Sn alloys on the electrode face.The soudronic welding process has been adapted as a method for continuously welding tin coated steel of �tin can� applications. In this process, a continuously fed wire serves as the welding electrode, thus minimizing the effect of alloying and low melting Cu-Sn alloys on the electrode face.

17. Schematically illustrated here, the wire which is used as the electrode is continuously fed over grooved electrode wheels so that a new fresh electrode face is continuously presented to the seam weld. The contour of the wire varies slightly when converting from an overlap seam weld to a mash lap seam weld.Schematically illustrated here, the wire which is used as the electrode is continuously fed over grooved electrode wheels so that a new fresh electrode face is continuously presented to the seam weld. The contour of the wire varies slightly when converting from an overlap seam weld to a mash lap seam weld.

18. The next few slides will describe some common weld problems encountered when welding tin plated steel. Careful welding engineers specify each of these production parameters in order to assure consistency in welding operations.The next few slides will describe some common weld problems encountered when welding tin plated steel. Careful welding engineers specify each of these production parameters in order to assure consistency in welding operations.

19. The micrograph in this slide shows the tin flowing around the edges of the seam weld. Excessive heat will vaporize the Sn and reduce corrosion protection. Proper heat and weld speed produces good flow as seen here. Note that the molten Sn occurs very close to the molten steel nugget thus allowing some Sn alloying of the weld metal. Small levels of Sn in the weld metal can cause embrittlement.The micrograph in this slide shows the tin flowing around the edges of the seam weld. Excessive heat will vaporize the Sn and reduce corrosion protection. Proper heat and weld speed produces good flow as seen here. Note that the molten Sn occurs very close to the molten steel nugget thus allowing some Sn alloying of the weld metal. Small levels of Sn in the weld metal can cause embrittlement.

20. Surface cracking of seam welded tin coated steel occurs as a result of liquid metal embrittlement of tin infiltration of steel grain boundaries, particularly in the course grained region of the weld heat affected zone. The higher the heat and the larger the grain growth, the worse the LME appears. The cracks tend to occur at the knurl marks left by the welding electrode in AC and DC welding. The use of Soudronic welding where fresh wire electrodes are continually fed to the weld area seems to reduce this form of cracking.Surface cracking of seam welded tin coated steel occurs as a result of liquid metal embrittlement of tin infiltration of steel grain boundaries, particularly in the course grained region of the weld heat affected zone. The higher the heat and the larger the grain growth, the worse the LME appears. The cracks tend to occur at the knurl marks left by the welding electrode in AC and DC welding. The use of Soudronic welding where fresh wire electrodes are continually fed to the weld area seems to reduce this form of cracking.

21. Terne plate is sheet steel which has been coated with an alloy of lead and tin. The normal composition is 80% Pb and 20% Sn; however wide variations in compositions are not uncommon. The reason for the proportion of tin in terne metal is that lead by itself, is insoluble in both solid and liquid iron, so there is no tendency for lead to wet the steel or bond itself to a steel surface by alloying. The addition of Sn enhances the adhering property of the lead-alloy coating to such an extent that by weight, only a half or a third as much is required to achieve the same protection as would be required for lead. {Greer H, Begeman M, �Resistance Seam Welding of Terne Plate� Welding Journal, June 1960}Terne plate is sheet steel which has been coated with an alloy of lead and tin. The normal composition is 80% Pb and 20% Sn; however wide variations in compositions are not uncommon. The reason for the proportion of tin in terne metal is that lead by itself, is insoluble in both solid and liquid iron, so there is no tendency for lead to wet the steel or bond itself to a steel surface by alloying. The addition of Sn enhances the adhering property of the lead-alloy coating to such an extent that by weight, only a half or a third as much is required to achieve the same protection as would be required for lead. {Greer H, Begeman M, �Resistance Seam Welding of Terne Plate� Welding Journal, June 1960}

22. This table lists the designations for some standard terneplate coatings.This table lists the designations for some standard terneplate coatings.

23. Typical Applications of Terne Coated Steels Listed here are typical applications for Terne Coated Steels.Listed here are typical applications for Terne Coated Steels.

24. Terne coated steels can be difficult to weld.Terne coated steels can be difficult to weld.

25. This slides lists some typical seam welding parameters for Terne Coated Steels. This slides lists some typical seam welding parameters for Terne Coated Steels.

26. The presence of the low-melting-point coating on the surface of a weldment involves some difficulty in seam welding in that the coating tends to alloy with the wheel electrodes, and some provision in necessary for cleaning the wheel surface. The problem of electrode pickup may be countered by employing a knurled driving roller to break up the alloyed material on the electrode face.The presence of the low-melting-point coating on the surface of a weldment involves some difficulty in seam welding in that the coating tends to alloy with the wheel electrodes, and some provision in necessary for cleaning the wheel surface. The problem of electrode pickup may be countered by employing a knurled driving roller to break up the alloyed material on the electrode face.

27. Alloying of terne metal with electrodes occurs in the seam welding operation and produces a marked change in weld surface appearance and electrode contour. The first welds made with new electrodes are accompanied by flashing and a tendency for electrode sticking. As welding continues the alloy coating on the electrodes increases and the weld surfaces loose their sticky, melted appearance. The electrodes begin to show distinct center depressions. For the concave electrode face shape to have developed, more allying must have occurred at the center than at its edges. The center of the electrode face is less affected by cooling, its higher temperature is conducive to more alloying and wear. Wear is noted to be considerably faster than similar welds made on Zinc coated galvanized steel. A comparison of boiling point of the coating materials show that Zinc vaporization would remove it from the weld area so little remained to alloy with the electrodes; whereas, with the melting of terne alloy, the coating remains in close contact with the electrodes and is readily available for electrode pickup.Alloying of terne metal with electrodes occurs in the seam welding operation and produces a marked change in weld surface appearance and electrode contour. The first welds made with new electrodes are accompanied by flashing and a tendency for electrode sticking. As welding continues the alloy coating on the electrodes increases and the weld surfaces loose their sticky, melted appearance. The electrodes begin to show distinct center depressions. For the concave electrode face shape to have developed, more allying must have occurred at the center than at its edges. The center of the electrode face is less affected by cooling, its higher temperature is conducive to more alloying and wear. Wear is noted to be considerably faster than similar welds made on Zinc coated galvanized steel. A comparison of boiling point of the coating materials show that Zinc vaporization would remove it from the weld area so little remained to alloy with the electrodes; whereas, with the melting of terne alloy, the coating remains in close contact with the electrodes and is readily available for electrode pickup.

28. With the first generation of heat, the low-melting-point coating liquefies and is squeezed away from the weld area by the force applied by the electrodes. Ideally, the displacement of the liquid coating results in a steel-to-steel contact at the sheet interface and welding then proceeds as in uncoated materials. There is, however, the possibility that some of the coating will be trapped in the weld area and remain as inclusion defects. The requirement that the liquefied coating be forced from the weld area dictates the use of higher electrode forces when welding terne coated material. The melting of the coating produces cooling in the weld area and represents a heat loss to the base metal. As the liquefied coating is squeezed out it take heat from the weld area as well by convection. To compensate for the heat deficit, either the electrical resistance or the welding current must increase. In addition, the higher electrode forces already have reduced the interfacial resistance. The increased heating required for the welding can be achieved only by an increase in the welding current. Thus as seen in this figure, an increase in electrode force requires an increase in current to maintain a given penetration.With the first generation of heat, the low-melting-point coating liquefies and is squeezed away from the weld area by the force applied by the electrodes. Ideally, the displacement of the liquid coating results in a steel-to-steel contact at the sheet interface and welding then proceeds as in uncoated materials. There is, however, the possibility that some of the coating will be trapped in the weld area and remain as inclusion defects. The requirement that the liquefied coating be forced from the weld area dictates the use of higher electrode forces when welding terne coated material. The melting of the coating produces cooling in the weld area and represents a heat loss to the base metal. As the liquefied coating is squeezed out it take heat from the weld area as well by convection. To compensate for the heat deficit, either the electrical resistance or the welding current must increase. In addition, the higher electrode forces already have reduced the interfacial resistance. The increased heating required for the welding can be achieved only by an increase in the welding current. Thus as seen in this figure, an increase in electrode force requires an increase in current to maintain a given penetration.

29. The shaded areas indicate regions of optimum weld quality for 22 gage material as a function of current, force and travel speed for welds made with current pulses with 3 cycle on and 2 cycles off. The limits of the optimum region were set by excessive flashing and electrode sticking at the higher penetrations and by insufficient boning or joining at the lower penetration. The lateral boundaries of the optimum region were not so easily defined, for the change in weld quality was gradual. The boundaries were drawn in the light of the observation that acceptable welds could be achieved with electrode forces 100 lb above and below the designated optimum electrode force.The shaded areas indicate regions of optimum weld quality for 22 gage material as a function of current, force and travel speed for welds made with current pulses with 3 cycle on and 2 cycles off. The limits of the optimum region were set by excessive flashing and electrode sticking at the higher penetrations and by insufficient boning or joining at the lower penetration. The lateral boundaries of the optimum region were not so easily defined, for the change in weld quality was gradual. The boundaries were drawn in the light of the observation that acceptable welds could be achieved with electrode forces 100 lb above and below the designated optimum electrode force.

30. The acceptable electrode force range for gages other than 22 gage (0.031 inc thick) material are presented in this table.The acceptable electrode force range for gages other than 22 gage (0.031 inc thick) material are presented in this table.

31. Welds made outside the optimum range resulted in a variety of defects. Where defects were present, these were similar in all gages of material except that transverse cracks were detected more frequently in the thinner material. The types of defects and their causes are presented in this figure.Welds made outside the optimum range resulted in a variety of defects. Where defects were present, these were similar in all gages of material except that transverse cracks were detected more frequently in the thinner material. The types of defects and their causes are presented in this figure.

32. Change in heat time (while holding the cool time constant) was found to have little effect on penetration obtained. The amount of penetration obtained depends primarily upon the welding current used to make the weld as determined by the current timing and the percent heat. Increased time was found to produce a slight increase in nugget size which helped improve nugget overlap, but tended to cause large voids in the nugget interior. The effect of increased cool time (while holding the heat time constant) was to sharply reduce the amount of current required to produce a given nugget penetration. This result is expected because the increased cool time increased nugget spacing thereby reducing shunting effects and allowing more time for heat dissipation between current impulses. The time available for heat dissipation is important for it lowers the temperature and the electrical resistance of the weldment at the point of the next current impulse. The slight reduction in resistance tends to cause less total heat to be generated between the electrodes; however, this loss is more than offset by the heating effect produced by the proportional increase in the current which flows through the weld area.Change in heat time (while holding the cool time constant) was found to have little effect on penetration obtained. The amount of penetration obtained depends primarily upon the welding current used to make the weld as determined by the current timing and the percent heat. Increased time was found to produce a slight increase in nugget size which helped improve nugget overlap, but tended to cause large voids in the nugget interior. The effect of increased cool time (while holding the heat time constant) was to sharply reduce the amount of current required to produce a given nugget penetration. This result is expected because the increased cool time increased nugget spacing thereby reducing shunting effects and allowing more time for heat dissipation between current impulses. The time available for heat dissipation is important for it lowers the temperature and the electrical resistance of the weldment at the point of the next current impulse. The slight reduction in resistance tends to cause less total heat to be generated between the electrodes; however, this loss is more than offset by the heating effect produced by the proportional increase in the current which flows through the weld area.

33. For the 22 gage terne coated material studies here using a 3 cycle heat time, the cool time of 2 cycles normally produced a good weld with moderate penetration an just overlapping without significant defects. Welds made with 3 cycle cool time allowed greater spacing between the welds, and when the welds were made, resulted in greater penetration. Welds made with the shorter 1 cycle weld time tended to overheat the entire sheet, but producing irregularly shaped welds with less total penetration and the existence of porosity and shrinkage cracks.For the 22 gage terne coated material studies here using a 3 cycle heat time, the cool time of 2 cycles normally produced a good weld with moderate penetration an just overlapping without significant defects. Welds made with 3 cycle cool time allowed greater spacing between the welds, and when the welds were made, resulted in greater penetration. Welds made with the shorter 1 cycle weld time tended to overheat the entire sheet, but producing irregularly shaped welds with less total penetration and the existence of porosity and shrinkage cracks.

35. This table lists some spot welding parameters.This table lists some spot welding parameters.

37. Let us now take a look at the comparison of seam welding of a series of coated materials including: A terne Coated material with paint on both sides An un-painted hot dipped tin coated material A painted hot dipped tin coated steel Painted ZnNi and Galvannealed Steel (for comparison) We will look at the three common seam welding processes for tin and terne seam welding, AC DC and Soudronic Welding. The weld parameters are listed above. Let us now take a look at the comparison of seam welding of a series of coated materials including: A terne Coated material with paint on both sides An un-painted hot dipped tin coated material A painted hot dipped tin coated steel Painted ZnNi and Galvannealed Steel (for comparison) We will look at the three common seam welding processes for tin and terne seam welding, AC DC and Soudronic Welding. The weld parameters are listed above.

38. The welding lobe for AC seam welding is represented by a region of weld current and weld speed over which acceptable seam welds are attained. The lower bound is represented by parameters which result in non-continuous seam welds, the upper bound represents parameter combinations where expulsion, overheat or surface eruptions occur. At higher welding speeds either the coating or painted surfaces can reduce the range of currents over which acceptable welds are attained. One way of comparing materials is to examine the current range at one weld speed where the largest current range is obtained. In the data presented above, it is seen that as the thickness of a tin coating increases or a paint is added to terne coating, the resistance increase, causing the nominal weld current to be reduced. In addition the current range also reduces.The welding lobe for AC seam welding is represented by a region of weld current and weld speed over which acceptable seam welds are attained. The lower bound is represented by parameters which result in non-continuous seam welds, the upper bound represents parameter combinations where expulsion, overheat or surface eruptions occur. At higher welding speeds either the coating or painted surfaces can reduce the range of currents over which acceptable welds are attained. One way of comparing materials is to examine the current range at one weld speed where the largest current range is obtained. In the data presented above, it is seen that as the thickness of a tin coating increases or a paint is added to terne coating, the resistance increase, causing the nominal weld current to be reduced. In addition the current range also reduces.

39. As the substrate thickness of tin coated steels increases, the current level and weld width both increase. Note the tin coated and unpainted material has current levels far exceeding the painted terne material as a result of the lower coating resistance of the tin coating.As the substrate thickness of tin coated steels increases, the current level and weld width both increase. Note the tin coated and unpainted material has current levels far exceeding the painted terne material as a result of the lower coating resistance of the tin coating.

40. As a painted coating is added to the tin coating, the resistance increases and current level decreases.As a painted coating is added to the tin coating, the resistance increases and current level decreases.

41. DC seam welding produces a heat cycle which is much more uniform with less heat losses and thus requires less welding current to produce the same size seam weld. Here also note the comparison with other types of coated products.DC seam welding produces a heat cycle which is much more uniform with less heat losses and thus requires less welding current to produce the same size seam weld. Here also note the comparison with other types of coated products.

42. The results presented here illustrate how well the soudronic welding process performs with unpainted hot dipped tin coated steel. Note the comparison with the DC welding process and that the soudronic process allows weld speed several times that of the AC and DC process. Only a slight penalty is paid with increases in welding speed.The results presented here illustrate how well the soudronic welding process performs with unpainted hot dipped tin coated steel. Note the comparison with the DC welding process and that the soudronic process allows weld speed several times that of the AC and DC process. Only a slight penalty is paid with increases in welding speed.