WEARFACING MATERIALS A surfacing operation using a copper-base alloy filler metal produces a relatively soft surface. Work- hardening  bronzes  are  soft  when  applied  and  give excellent  resistance  against  frictional  wear.  Other  types of alloys are available that produce a surface that is corrosion and wear resistant at high temperatures. Wear- facing materials are produced by many different manu- facturers; therefore, be sure that the filler alloys you select for a particular surfacing job meet Navy specifi- cations. Two types of hard-surfacing materials in general use in  the  Navy  are  iron-base  alloys  and  tungsten  carbide. Iron-Base  Alloys These materials contain nickel, chromium, manga- nese,  carbon,  and  other  hardening  elements.  They  are used for a number of applications requiring varying degrees of hardness. A Steelworker frequently works with iron-base alloys when he builds up and resurfaces parts of construction equipment. Tungsten  Carbide You use this for building up wear-resistant surfaces on  steel  parts.  Tungsten  carbide  is  one  of  the  hardest substances known to man. Tungsten carbide can be applied in the form of inserts or of composite rod. Inserts are not melted but are welded or brazed to the base metal, as shown in figure 6-18. The rod is applied with the same surfacing technique as that used for oxygas welding;  a  slightly  carburizing  flame  adjustment  is  nec- essary. WEARFACING  PROCEDURES Proper preparation of the metal surfaces is an im- portant  part  of  wearfacing  operations.  Make  sure  that scale, rust, and foreign matter are removed from the metal surfaces. You can clean the metal surfaces by grinding, machining, or chipping. The edges of grooves, corners,  or  recesses  should  be  well  rounded  to  prevent base  metal  overheating  and  to  provide  a  good  cushion for the wearfacing material. Weafacing material is applied so it forms a thin layer over the base metal. The thickness of the deposit is usually from one sixteenth to one eighth of an inch and is seldom over one fourth of an inch. It is generally deposited in a single pass. Where wear is extensive, it may  become  necessary  to  use  a  buildup  rod  before wearfacing. If in doubt as to when to use a buildup rod, you should check with your leading petty officer. Preheating Most parts that require wearfacing can be preheated with a neutral welding flame before surfacing. You should  use  a  neutral  flame  of  about  800°F.  Do  not preheat to a temperature higher than the critical tem- perature of the metal or to a temperature that can cause the formation of scale. Application In general, the torch manipulations and the wearfac- ing procedures are similar to brazing techniques. How- ever,  higher  temperatures  (about  2200°F)  are  necessary for wearfacing, and tips of one or two sizes larger than normal are used. To begin, you heat a small area of the part with a sweeping torch movement until the surface of the base metal takes on a sweating or wet appearance. When the surface of the base metal is in this condition, bring the end of the surfacing alloy into the flame and allow it to melt. Do not stir or puddle the alloy; let it flow. When the  surface  area  has  been  properly  sweated,  the  alloy flows freely over the surface of the base metal. Being able to recognize a sweated surface is essen- tial  for  surfacing.  Sweating  occurs  when  you  heat  the steel with a carburizing flame to a white heat tempera- ture. This carburizes an extremely thin layer of the base metal, approximately 0.001 inch thick. The carburized layer has a lower melting point than the base metal. As a result, it becomes a liquid, while the underlying metal remains a solid. This liquid film provides the medium for flowing the filler metal over the surface of the base metal. The liquid film is similar to and serves the same purpose as a tinned surface in soldering and braze weld- ing. When you heat steel with a carburizing flame, it first becomes  red.  As  heating  continues,  the  color  becomes lighter  and  lighter  until  a  bright  whiteness  is  attained.  At this point, a thin film of liquid, carburized metal appears on the surface. Surfacing alloy added at this time flows over the sweated surface and absorbs the film of carbur- ized metal. This surface condition is not difficult to recognize, but you should make several practice passes before you try wearfacing for the first time. When you use an oxygas torch for surfacing with chromium cobalt, the torch flame should have an excess fuel-gas feather about three times as long as the inner 6-16