146:, all inside a well-sealed box (the "case"). This carburizing package is then heated to a high temperature—but still under the melting point of the iron—and left at that temperature for a length of time. The longer the package is held at the high temperature, the deeper the carbon will diffuse into the surface. Different depths of hardening are desirable for different purposes: sharp tools need deep hardening to allow grinding and resharpening without exposing the soft core, while machine parts like gears might need only shallow hardening for increased wear resistance.
270:
a hot furnace for a variable length of time. Time and temperature determines how deep into the surface the hardening extends. However, the depth of hardening is ultimately limited by the inability of carbon to diffuse deeply into solid steel, and a typical depth of surface hardening with this method is up to 1.5 mm. Other techniques are also used in modern carburizing, such as heating in a carbon-rich atmosphere. Small items may be case-hardened by repeated heating with a torch and quenching in a carbon rich medium, such as the commercial products
535:. In order for the screws to be able to drill, cut and tap into other materials like steel, the drill point and the forming threads must be harder than the material(s) that it is drilling into. However, if the whole screw is uniformly hard, it will become very brittle and it will break easily. This is overcome by ensuring that only the surface is hardened, and the core remains relatively softer and thus less brittle. For screws and fasteners, case-hardening is achieved by a simple heat treatment consisting of heating and then quenching.
880:
302:
178:, generated by the breakdown of the carburising compound and the oxygen packed into the sealed box. This takes place with pure carbon but too slowly to be workable. Although oxygen is required for this process it is re-circulated through the CO cycle and so can be carried out inside a sealed box (the "case"). The sealing is necessary to stop the CO either leaking out or being oxidised to CO
38:
87:
This matrix then required re-heating and hammering to extract as much of the slag as possible, in order to produce a low-carbon malleable wrought iron which could then be forged into tools etc. Due to its low carbon content, wrought iron is quite soft, so something like a knife blade could not be kept very sharp; it would blunt quickly and bend easily.
329:
Typical uses are for the shackle of a lock, where the outer layer is hardened to be file resistant, and mechanical gears, where hard gear mesh surfaces are needed to maintain a long service life while toughness is required to maintain durability and resistance to catastrophic failure. Flame hardening
269:
is derived from the practicalities of the carburization process itself, which is essentially the same as the ancient process. The steel work piece is placed inside a case packed tight with a carbon-based case-hardening compound. This is collectively known as a carburizing pack. The pack is put inside
86:
which converted iron ore into metallic iron by heating it in a furnace which burnt wood and charcoal. Because the temperatures that could be achieved by this method were generally below the melting point of iron, it was not truly smelted, but instead converted into a spongy metallic iron/slag matrix.
66:
In order to produce a hard skin on steels which have less than ~0.2% carbon, carbon can be introduced into the surface by heating steel in the presence of some carbon rich substance such as powdered charcoal or hydrocarbon gas. This causes carbon to diffuse into the surface of the steel. The depth of
165:
Case-hardened steel combines extreme hardness and extreme toughness, which is not readily matched by homogeneous alloys since hard homogeneous steels tend to be brittle, especially those steels whose hardness relies on carbon content alone. Alloy steels containing nickel, chromium, or molybdenum can
453:
This process produces a thin, hard shell (between 0.25 and 0.75 mm; 0.0098 and 0.0295 in) that is harder than the one produced by carburizing, and can be completed in 20 to 30 minutes compared to several hours so the parts have less opportunity to become distorted. It is typically used on
391:
Nitriding heats the steel part to 482–621 °C (900–1,150 °F) in an atmosphere of ammonia gas and dissociated ammonia. The time the part spends in this environment dictates the depth of the case. The hardness is achieved by the formation of nitrides. Nitride forming elements must be present
362:
Carburization is a diffusion-controlled process, so the longer the steel is held in the carbon-rich environment the greater the carbon penetration will be and the higher the carbon content. The carburized section will have a carbon content high enough that it can be hardened again through flame or
149:
The resulting case-hardened part may show distinct surface discoloration, if the carbon material is mixed organic matter as described above. The steel darkens significantly and shows a mottled pattern of black, blue, and purple caused by the various compounds formed from impurities in the bone and
118:
but not very hard, nor capable of being hardened by heating and quenching. This led to the introduction of case hardening. The resulting case-hardened product combines much of the malleability and toughness of a low-carbon steel core with the hardness and resilience of the outer high-carbon steel
90:
As smelting techniques improved, higher furnace temperatures could be achieved which were sufficient to fully melt iron. However, in the process, the iron picked up carbon from the charcoal or coke used to heat it. This resulted in molten iron with a carbon content of around 3%, which was termed
325:
on the surface. A carbon content of 0.3–0.6 wt% C is needed for this type of hardening. Unlike other methods, flame or induction hardening does not change chemical composition of the material. Because it is merely a localized heat-treatment process, they are typically only useful on high-carbon
358:
Carburizing is a process used to case-harden steel with a carbon content between 0.1 and 0.3 wt% C. In this process iron is introduced to a carbon rich environment at elevated temperatures for a certain amount of time, and then quenched so that the carbon is locked in the structure; one of the
468:
Carbonitriding is similar to cyaniding except a gaseous atmosphere of ammonia and hydrocarbons is used instead of sodium cyanide. If the part is to be quenched, it is heated to 775–885 °C (1,427–1,625 °F); if not, then the part is heated to 649–788 °C (1,200–1,450 °F).
95:. This liquid iron could be cast into complex shapes, but due to its high carbon content, it was very brittle, not at all malleable, and totally unsuitable for something like a knife blade. Further processing was required to remove the excess carbon from cast iron and create malleable
67:
this high carbon layer depends on the exposure time, but 0.5mm is a typical case depth. Once this has been done the steel must be heated and quenched to harden this higher carbon 'skin'. Below this skin, the steel core will remain soft due to its low carbon content.
483:
Ferritic nitrocarburizing diffuses mostly nitrogen and some carbon into the case of a workpiece below the critical temperature, approximately 650 °C (1,202 °F). Under the critical temperature the workpiece's microstructure does not convert to an
58:
Iron which has a carbon content greater than ~0.02% is known as steel. Steel which has a carbon content greater than ~0.25% can be direct hardened by heating to around 600C and then quickly cooling, often by immersing in water, this being known as
519:
Firearms were a common item case-hardened in the past, as they required precision machining best done on low carbon alloys, yet needed the hardness and wear resistance of a higher carbon alloy. Many modern replicas of older firearms, particularly
538:
For theft prevention, lock shackles and chains are often case-hardened to resist cutting, whilst remaining less brittle inside to resist impact. As case-hardened components are difficult to machine, they are generally shaped before hardening.
241:
for more information). These mild steels are not normally hardenable due to the low quantity of carbon, so the surface of the steel is chemically altered to increase the hardenability. Case-hardened steel is formed by diffusing carbon
63:. Hardening is desirable for metal components because it gives increased strength and wear resistance, the trade off being that hardened steel is generally more brittle and less malleable than when it is in its softer state.
373:. Packing low carbon steel parts with a carbonaceous material and heating for some time diffuses carbon into the outer layers. A heating period of a few hours might form a high-carbon layer about one millimeter thick.
376:
Liquid carburizing involves placing parts in a bath of a molten carbon-containing material, often a metal cyanide; gas carburizing involves placing the parts in a furnace maintained with a methane-rich interior.
212:
fallacy that case-hardening was done with bone but this is misleading. Although bone was used, the main carbon donor was hoof and horn. Bone contains some carbonates but is mainly calcium phosphate (as
366:
It is possible to carburize only a portion of a part, either by protecting the rest by a process such as copper plating, or by applying a carburizing medium to only a section of the part.
404:. The advantage of this process is that it causes little distortion, so the part can be case-hardened after being quenched, tempered and machined. No quenching is done after nitriding.
412:
Cyaniding is a case-hardening process that is fast and efficient; it is mainly used on low-carbon steels. The part is heated to 871–954 °C (1,600–1,749 °F) in a bath of
55:
is the process of introducing carbon to the surface of a low carbon iron or much more commonly low carbon steel object in order to enable the surface to be hardened.
722:
122:
The traditional method of applying the carbon to the surface of the iron involved packing the iron in a mixture of carbon-rich material such as ground
359:
simpler procedures is repeatedly to heat a part with an acetylene torch set with a fuel-rich flame and quench it in a carbon-rich fluid such as oil.
674:
516:. In these cases, the surfaces requiring the hardness may be hardened selectively, leaving the bulk of the part in its original tough state.
330:
uses direct impingement of an oxy-gas flame onto a defined surface area. The result of the hardening process is controlled by four factors:
1228:
658:
715:
166:
have very high hardness, strength, or elongation values, but at a greater cost than a case-hardened item with a low-carbon core.
174:
Carbon itself is solid at case-hardening temperatures and so is immobile. Transport to the surface of the steel was as gaseous
454:
small parts such as bolts, nuts, screws and small gears. The major drawback of cyaniding is that cyanide salts are poisonous.
1190:
305:
A flame-hardened sprocket. The discoloration around the teeth delineates the area that was rapidly heated and then quenched.
262:) into the outer layer of the steel at high temperature, and then heat treating the surface layer to the desired hardness.
668:
678:
313:
are processes in which the surface of the steel is heated very rapidly to high temperatures (by direct application of an
708:
627:
602:
1208:
369:
The carbon can come from a solid, liquid or gaseous source; if it comes from a solid source the process is called
1249:
663:
17:
504:
Parts that are subject to high pressures and sharp impacts are still commonly case-hardened. Examples include
1218:
1198:
990:
31:
1151:
296:
1027:
682:
1223:
1075:
478:
675:"MIL-S-6090A, Military Specification: Process for Steels Used In Aircraft Carburizing and Nitriding"
642:
1166:
964:
217:). This does not have the beneficial effect of encouraging CO production and it can also introduce
1213:
1203:
1090:
752:
41:
1105:
1037:
1022:
1014:
980:
548:
104:
847:
844:
528:, which simulates the mottled pattern left by traditional charcoal and bone case-hardening.
110:
After the removal of almost all carbon from cast iron, the result was a metal that was very
1176:
1140:
1095:
985:
959:
573:
558:
8:
1145:
1135:
1131:
1080:
1070:
954:
933:
820:
787:
568:
553:
310:
850:
747:
532:
238:
100:
864:
623:
598:
318:
205:
increasing the overall abundance of CO and the activity of the carburising compound.
949:
928:
209:
186:
416:
and then is quenched and rinsed, in water or oil, to remove any residual cyanide.
1156:
909:
813:
278:
or "Cherry Red". Older formulations of these compounds contain potentially toxic
214:
175:
1060:
918:
914:
860:
509:
463:
413:
154:, providing a degree of corrosion resistance, as well as an attractive finish.
151:
597:. Engineering Metallurgy (5th ed.). Hodder & Stoughton. p. 474.
1243:
1004:
793:
521:
353:
243:
158:
refers to this pattern and is commonly encountered as a decorative finish on
52:
700:
1118:
1113:
879:
840:
836:
645:
Hemmings Sports & Exotic Car — MARCH 1, 2006 - BY CRAIG FITZGERALD
563:
96:
301:
233:
are suitable for case-hardening; typically mild steels are used, with low
1161:
1065:
922:
888:
586:
230:
531:
Another common application of case-hardening is on screws, particularly
1050:
893:
803:
505:
485:
397:
322:
321:) then cooled rapidly, generally using water; this creates a "case" of
218:
1171:
1085:
856:
808:
765:
386:
251:
111:
92:
60:
1055:
797:
783:
775:
513:
489:
401:
393:
259:
247:
159:
127:
83:
79:
282:
compounds, while the more recent types such as Cherry Red do not.
314:
279:
131:
115:
234:
735:
524:
revolvers, are still made with case-hardened frames, or with
255:
143:
37:
731:
326:
steels that will respond sufficiently to quench hardening.
139:
135:
123:
76:
185:
Adding an easily decomposed carbonate "energiser" such as
592:
27:Process of hardening the surface of a metal object
1241:
392:for this method to work; these elements include
150:charcoal. This oxide surface works similarly to
290:
730:
716:
617:
99:(the ultimate developments of this being the
472:
44:, showing discoloration from case-hardening
723:
709:
300:
36:
14:
1242:
343:Composition of the metal being treated
704:
237:content, usually less than 0.3% (see
221:as an impurity into the steel alloy.
679:United States Department of Defense
595:Part I: Applied Physical Metallurgy
24:
193:and this encourages the reaction:
25:
1261:
652:
492:phase, which is why it is called
457:
878:
673:
340:Target temperature to be reached
643:Case Hardening in a Home Garage
499:
669:Case Hardening Steel and Metal
636:
611:
347:
30:For the woodworking term, see
13:
1:
748:History of ferrous metallurgy
681:. 7 June 1971. Archived from
579:
224:
991:Argon oxygen decarburization
593:Higgins, Raymond A. (1983).
407:
380:
291:Flame or induction hardening
285:
169:
32:case hardening (woodworking)
7:
1152:Differential heat treatment
664:Surface Hardening of Steels
542:
297:Differential heat treatment
10:
1268:
476:
461:
384:
351:
294:
70:
29:
1189:
1127:
1104:
1076:Ferritic nitrocarburizing
1036:
1013:
1003:
973:
942:
902:
887:
876:
829:
774:
761:
743:
479:Ferritic nitrocarburizing
473:Ferritic nitrocarburizing
1167:Post weld heat treatment
488:phase, but stays in the
334:Design of the flame head
753:List of steel producers
197:C (from the donor) + CO
189:breaks down to BaO + CO
182:by excess outside air.
981:Electro-slag remelting
618:Roy F. Dunlap (1963).
549:Differential hardening
306:
45:
1250:Metal heat treatments
1191:Production by country
363:induction hardening.
304:
40:
1177:Superplastic forming
1096:Quench polish quench
986:Vacuum arc remelting
965:Basic oxygen process
960:Electric arc furnace
574:Von Stahel und Eysen
559:Quench polish quench
533:self-drilling screws
496:nitrocarburization.
130:or a combination of
1132:Cryogenic treatment
955:Open hearth furnace
943:Primary (Post-1850)
934:Cementation process
821:Direct reduced iron
622:. Stackpole Books.
569:Surface engineering
554:Diffusion hardening
337:Duration of heating
311:induction hardening
903:Primary (Pre-1850)
307:
239:plain-carbon steel
101:Bessemer converter
46:
1237:
1236:
1185:
1184:
999:
998:
874:
873:
865:Induction furnace
688:on 29 August 2019
512:faces, or engine
319:induction heating
16:(Redirected from
1257:
1011:
1010:
950:Bessemer process
900:
899:
882:
772:
771:
725:
718:
711:
702:
701:
697:
695:
693:
687:
646:
640:
634:
633:
615:
609:
608:
590:
371:pack carburizing
229:Both carbon and
210:common knowledge
187:barium carbonate
21:
1267:
1266:
1260:
1259:
1258:
1256:
1255:
1254:
1240:
1239:
1238:
1233:
1181:
1157:Decarburization
1123:
1100:
1041:
1032:
995:
969:
938:
910:Pattern welding
891:
883:
870:
825:
814:Anthracite iron
763:
762:Iron production
757:
739:
729:
691:
689:
685:
655:
650:
649:
641:
637:
630:
616:
612:
605:
591:
587:
582:
545:
502:
481:
475:
466:
460:
448:
442:
438:
434:
430:
423:
410:
389:
383:
356:
350:
299:
293:
288:
227:
215:hydroxylapatite
200:
192:
181:
176:carbon monoxide
172:
105:Siemens process
73:
42:Colt Peacemaker
35:
28:
23:
22:
15:
12:
11:
5:
1265:
1264:
1253:
1252:
1235:
1234:
1232:
1231:
1226:
1221:
1216:
1211:
1206:
1201:
1195:
1193:
1187:
1186:
1183:
1182:
1180:
1179:
1174:
1169:
1164:
1159:
1154:
1149:
1143:
1138:
1128:
1125:
1124:
1122:
1121:
1116:
1110:
1108:
1102:
1101:
1099:
1098:
1093:
1088:
1083:
1078:
1073:
1068:
1063:
1061:Carbonitriding
1058:
1053:
1047:
1045:
1043:Case-hardening
1034:
1033:
1031:
1030:
1025:
1019:
1017:
1008:
1005:Heat treatment
1001:
1000:
997:
996:
994:
993:
988:
983:
977:
975:
971:
970:
968:
967:
962:
957:
952:
946:
944:
940:
939:
937:
936:
931:
929:Tatara furnace
926:
919:Damascus steel
915:Crucible steel
912:
906:
904:
897:
885:
884:
877:
875:
872:
871:
869:
868:
861:Cupola furnace
854:
833:
831:
827:
826:
824:
823:
818:
817:
816:
811:
806:
791:
780:
778:
769:
759:
758:
756:
755:
750:
744:
741:
740:
728:
727:
720:
713:
705:
699:
698:
671:
666:
661:
659:Case Hardening
654:
653:External links
651:
648:
647:
635:
628:
610:
603:
584:
583:
581:
578:
577:
576:
571:
566:
561:
556:
551:
544:
541:
501:
498:
477:Main article:
474:
471:
464:Carbonitriding
462:Main article:
459:
458:Carbonitriding
456:
451:
450:
446:
443:
440:
436:
432:
428:
425:
421:
414:sodium cyanide
409:
406:
385:Main article:
382:
379:
352:Main article:
349:
346:
345:
344:
341:
338:
335:
295:Main article:
292:
289:
287:
284:
267:case-hardening
226:
223:
203:
202:
201:<—> 2 CO
198:
190:
179:
171:
168:
156:Case colouring
72:
69:
49:Case-hardening
26:
18:Case hardening
9:
6:
4:
3:
2:
1263:
1262:
1251:
1248:
1247:
1245:
1230:
1229:United States
1227:
1225:
1222:
1220:
1217:
1215:
1212:
1210:
1207:
1205:
1202:
1200:
1197:
1196:
1194:
1192:
1188:
1178:
1175:
1173:
1170:
1168:
1165:
1163:
1160:
1158:
1155:
1153:
1150:
1147:
1144:
1142:
1139:
1137:
1133:
1130:
1129:
1126:
1120:
1117:
1115:
1112:
1111:
1109:
1107:
1103:
1097:
1094:
1092:
1091:Precipitation
1089:
1087:
1084:
1082:
1079:
1077:
1074:
1072:
1069:
1067:
1064:
1062:
1059:
1057:
1054:
1052:
1049:
1048:
1046:
1044:
1039:
1035:
1029:
1028:Short circuit
1026:
1024:
1021:
1020:
1018:
1016:
1012:
1009:
1006:
1002:
992:
989:
987:
984:
982:
979:
978:
976:
972:
966:
963:
961:
958:
956:
953:
951:
948:
947:
945:
941:
935:
932:
930:
927:
924:
920:
916:
913:
911:
908:
907:
905:
901:
898:
895:
890:
886:
881:
866:
862:
858:
855:
852:
849:
846:
845:Reverberatory
842:
838:
835:
834:
832:
828:
822:
819:
815:
812:
810:
807:
805:
802:
801:
799:
795:
794:Blast furnace
792:
789:
785:
782:
781:
779:
777:
773:
770:
767:
760:
754:
751:
749:
746:
745:
742:
737:
733:
726:
721:
719:
714:
712:
707:
706:
703:
684:
680:
676:
672:
670:
667:
665:
662:
660:
657:
656:
644:
639:
631:
629:0-8117-0770-9
625:
621:
614:
606:
604:0-340-28524-9
600:
596:
589:
585:
575:
572:
570:
567:
565:
562:
560:
557:
555:
552:
550:
547:
546:
540:
536:
534:
529:
527:
526:case coloring
523:
522:single action
517:
515:
511:
507:
497:
495:
491:
487:
480:
470:
465:
455:
444:
426:
419:
418:
417:
415:
405:
403:
399:
395:
388:
378:
374:
372:
367:
364:
360:
355:
354:Carburization
342:
339:
336:
333:
332:
331:
327:
324:
320:
317:flame, or by
316:
312:
303:
298:
283:
281:
277:
273:
268:
263:
261:
257:
253:
249:
245:
244:carburization
240:
236:
232:
222:
220:
216:
211:
206:
196:
195:
194:
188:
183:
177:
167:
163:
161:
157:
153:
147:
145:
141:
137:
133:
129:
125:
120:
117:
113:
108:
106:
102:
98:
94:
88:
85:
81:
78:
68:
64:
62:
56:
54:
53:carburization
50:
43:
39:
33:
19:
1119:Martempering
1114:Austempering
1042:
1023:Low hydrogen
841:Finery forge
837:Wrought iron
690:. Retrieved
683:the original
638:
619:
613:
594:
588:
564:Shot peening
537:
530:
525:
518:
503:
500:Applications
493:
482:
467:
452:
411:
390:
375:
370:
368:
365:
361:
357:
328:
308:
275:
271:
266:
264:
231:alloy steels
228:
207:
204:
184:
173:
164:
155:
148:
121:
109:
97:wrought iron
89:
82:made use of
74:
65:
57:
48:
47:
1162:Forming gas
1066:Carburizing
923:Wootz steel
889:Steelmaking
788:sponge iron
620:Gunsmithing
506:firing pins
348:Carburizing
1219:Luxembourg
1199:Bangladesh
1141:Deflashing
1051:Ausforming
894:Steel mill
804:Cold blast
796:(produces
786:(produces
738:production
580:References
510:rifle bolt
486:austenitic
427:2NaCNO + O
398:molybdenum
323:martensite
225:Modern use
219:phosphorus
84:bloomeries
1172:Quenching
1146:Hardening
1136:Deburring
1106:Tempering
1086:Nitriding
1081:Induction
1071:Cryogenic
1038:Hardening
1015:Annealing
974:Secondary
857:Cast iron
830:Secondary
809:Hot blast
766:Ironworks
514:camshafts
420:2NaCN + O
408:Cyaniding
387:Nitriding
381:Nitriding
309:Flame or
286:Processes
265:The term
252:nitriding
170:Chemistry
112:malleable
93:cast iron
61:quenching
1244:Category
1056:Boriding
848:Puddling
798:pig iron
784:Bloomery
776:Smelting
543:See also
494:ferritic
490:ferritic
445:2CO → CO
439:+ CO + N
424:→ 2NaCNO
402:aluminum
394:chromium
276:Casenite
260:boriding
248:nitrogen
208:It is a
160:firearms
128:charcoal
103:and the
80:smelting
1224:Nigeria
1007:methods
851:Furnace
692:20 June
315:oxy-gas
280:cyanide
272:Kasenit
132:leather
116:ductile
71:History
626:
601:
400:, and
235:carbon
152:bluing
136:hooves
119:skin.
75:Early
1214:Italy
1209:India
1204:China
859:(via
839:(via
736:steel
686:(PDF)
256:boron
254:) or
144:urine
843:or
734:and
732:Iron
694:2012
624:ISBN
599:ISBN
508:and
431:→ Na
142:and
140:salt
126:and
124:bone
114:and
77:iron
863:or
449:+ C
246:),
107:).
51:or
1246::
1040:/
921:,
800:)
677:.
435:CO
396:,
274:/
162:.
138:,
134:,
1148:)
1134:(
925:)
917:(
896:)
892:(
867:)
853:)
790:)
768:)
764:(
724:e
717:t
710:v
696:.
632:.
607:.
447:2
441:2
437:3
433:2
429:2
422:2
258:(
250:(
242:(
199:2
191:2
180:2
34:.
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
