by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
button in toolbar for more information.
Metal Casting Technologies : June 2006
42 PROCESS IRON TYPE REASON SOAK TEMP. TIME* COOL RATE Stress Relief Anneal Unalloyed irons Stress relieving 510-565º C 1-5 hours Furn. cool down (950-1050ºF) to 150-100º C; then cool in air. Stress Relief Anneal Low alloy irons Stress relieving 565-595º C 1-5 hours Furn. cool down (1050-1100º F) to 150-100º C; then cool in air. Stress Relief Anneal High alloy irons Stress relieving 595-650º C 1-5 hours Furn. cool down to (1100-1200º F) 150-100º C; then cool in air. Low Temperature Plain and low alloy Breakdown of 700-760º C 45mins.to1hr Furnace cool at 55º C Anneal (a.k.a. alloy irons pear-lite to ferrite (1300-1400º F) per inch of (100º f) per hour Ferri-tizing annealing) and graphite for cross section. to between 540 and maxi-mum machinability 290º C (1000 and 550 F) Medium Tempera-ture Alloy irons and those Breakdown of pear-lite 790-900º C About 45 mins. Furnace cool Anneal (a.k.a. Full or not re-sponsive to low to ferrite and graphite (1450-1650º F) per inch of cross from annealing medium an-nealing) temperature anneal for maxi-mum section tempersture machinability to 290º C (550º F) High Temperature Mottled or Elimination of massive 900-955º C 1to3hrs.+ ***Air cool to Anneal -- A ** chilled iron carbides retaining (1650-1750º F) 1 hr. per inch 540º C (1000º F), (a.k.a. Graphitizing maximum strength of section size then furnace cool annealing) and hard-ness to 290º C (550º F) High Temperature Mottled or For maximum 900-955º C 1to3hrs.+1hr. Furnace cool Anneal -- B chilled iron ma-chinability (1650-1750º F) per inch of from annealing temp. (a.k.a Graphitizing section size to 290º C (550º F) anneal-ing) METAL Casting Technologies June 2006 Back to the is necessary, a minimum temperature of 595º C (1100º F) can be employed, but except in low carbon equivalent, high-duty irons, possible sacrifice in the mechanical properties must be considered. It is a fortunate circumstance, however, that the higher carbon equivalent, soft irons normally exhibit a lower level of internal stress and a comparatively low creep resistance. In fact, high carbon equivalent irons can be satisfactorily stress relieved at the lower end of the suggested temperature range, that is, at temperatures not exceeding 538º C (1000º F). Suggested Procedure in Stress Relief Anneal It is best to place the castings so that there would be no undue forces exerted or bearing on them. 1. Raise the furnace temperature at the rate of about 100º C (212º F) per hour to 520º C (970º F). 2. Soak the castings at about 520º ± 20º C (970º ± 70º F) for one to five hours. 3. Cool in furnace to 150º C (300º F) and then cool in air. Alternatively, if a faster anneal is desired: 1. Raise the furnace temperature at the rate of about 100º C (212º F) per hour to 730º C (1350º F). 2. Soak the castings at about 730º ± 20º C (1350º ± 70º F) for thirty minutes. 3. Cool in furnace to 400º C (750º F) and then cool in air. ● * Some foundries habitually employ a lower temperature range for stress relieving, i.e., 370º-455º C (700º-850º F). Holding periods in excess of one hour are common using these lower temperatures. The resultant 15-30% relief is apparently adequate for their type of castings. In cases where equipment or time for slow cooling is not available, these lower temperatures are helpful. ANNEALING PRACTICES FOR GRAY IRONS (Reference: Charles F. Walton, editor. The Gray Iron Castings Handbook, Gray Iron Founders' Society.) The annealing process is done for gray irons for a specific purpose, so the procedure varies depending on this. * Shorter times may be used with modern radiant heating furnaces. ** If the microstructure of gray iron contains massive carbides, higher annealing temperatures are necessary. Graphitizing annealing may have the purpose simply of converting massive carbide to pearlite and graphite. It is general practice to employ holding temperatures of 900-955º C (1650-1750º F). However, at 925º C (1700º F) and above, the phosphide eutectic (steadite) present in irons containing ≥ 0.10% P may melt. Steadite is hard and improves resistance to some types of wear. If continuous, it may somewhat improve resistance to corrosion and oxidation, also. *** Carbides may often be eliminated in shorter times REFERENCES: 1 Charles F. Walton, ed., Gray Iron Castings Handbook, (Cleveland: Gray Iron Founders' Society.) 2 Richard W. Heine and Philip C. Rosenthal, Principles of Metal Casting. McGraw- Hill Book Co., Inc. 3 Samuel L. Hoyt, ed., ASME Handbook: Metal Properties. McGraw-Hill Book Co., Inc. 4 J. H. D. Bautista, Metal Engineering, Technonology & Management. 5 American Society for Metals, Metals Handbook, Supplement; and ASM, Metals Handbook, 8th edition. 6 American Society for Metals, Metals Handbook, 7th edition.