HEAT TREATMENT OF LOW CARBON STEEL

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Yasser Mohamed abbas elkelawy

Yasser Mohamed abbas elkelawy

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发布日期: 2019年8月18日

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1. Low carbon steel is easily available and cheap having all material properties that
2. are acceptable for many applications. Heat treatment on low carbon steel is to
3. improve ductility, to improve toughness, strength, hardness and tensile strength
4. and to relive internal stress developed in the material. Here basically the
5. experiment of harness and ultimate tensile strength is done to get idea about
6. heat treated low carbon steel, which has extensive uses in all industrial and
7. scientific fields.
8. Carbon steel:
9. Carbon steel (plain carbon steel) is steel which contain main alloying element is
10. carbon. Here we find maximum up to 1.5% carbon and other alloying elements like
11. copper, manganese, silicon. Most of the steel produced now-a-days is plain carbon
12. steel. It is divided into the following types depending upon the carbon content.
13. 1. Dead or mild steel (up to 0.15% carbon)
14. 2. Low carbon steel (0.15%-0.45% carbon)
15. 3. Medium carbon steel(0.45%-0.8% carbon)
16. 4. High carbon steel (0.8%-1.5% carbon)
17. Steel with low carbon content has properties similar to iron. As the carbon
18. content increases the metal becomes harder and stronger but less ductile and
19. more difficult to weld. Higher carbon content lowers the melting point and its
20. temperature resistance carbon content cannot alter yield strength of material
21. LOW CARBON STEEL:-
22. Low carbon steel has carbon content of 1.5% to 4.5%. Low carbon steel is the
23. most common type of steel as its price is relatively low while its provides material
24. properties that are acceptable for many applications. It is neither externally brittle
25. nor ductile due to its low carbon content. It has lower tensile strength and
26. malleable.
27. HEAT TREATMENT:-
28. The process of heat treatment is carried out first by heating the material and
29. then cooling it in the brine, water and oil. The purpose of heat treatment is to
30. soften the metal, to change the grain size, to modify the structure of the material
31. and to relieve the stress set up in the material after hot and cold working.
32. The various heat treatment processes commonly employed in engineering
33. practice as follows:-
34. ANNEALING:-
35. Spherodizing:-
36. Spherodite forms when carbon steel is heated to approximately 700 for
37. over 30 hours. The purpose is to soften higher carbon steel and allow
38. more formability. This is the softest and most ductile form of steel. Here
39. cementite is present.
40. Full annealing:-
41. Carbon steel is heated to approximately above the upper critical
42. temperature (550-650) for 1 hour. Here all the ferrite transforms into
43. austenite. The steel must then cooled in the realm of 38 per hour. This
44. results in a coarse pearlite structure. Full annealed steel is soft and ductile
45. with no internal stress.
46. Process annealing:-
47. The steel is heated to a temperature below or close to the lower critical
48. temperature (550-650), held at this temperature for some time and then
49. cooled slowly. The purpose is to relive stress in a cold worked carbon
50. steel with less than 0.3%wt c.
51. Diffusion annealing:-
52. The process consists of heating the steel to high temperature (1100-
53. 1200). It is held at this temperature for 3 hours to 20 hours and then
54. cooled to 800-850 inside the furnace for a period of about 6 to 8 hours. It
55. is further cooled in the air to room temperature. This process is mainly
56. used for ingots and large casting. It is also called isothermal annealing
57. NORMALISING:-
58. The process of normalizing consist of heating the metal to a temperature of 30
59. to 50 c above the upper critical temperature for hypo-eutectoid steels and by the
60. same temperature above the lower critical temperature for hyper-eutectoid steel.
61. It is held at this temperature for a considerable time and then quenched in
62. suitable cooling medium. The purpose of normalizing is to refine grain
63. structure, improve machinibility and improve tensile strength, to remove strain
64. and to remove dislocation.
65. HARDENING:-
66. The process of hardening consist of heating the metal to a temperature of 30-50
67. c above the upper critical point for hypo-eutectoid steels and by the same
68. temperature above the lower critical temperature for hyper-eutectoid steels. It
69. is held this temperature for some time and then quenched. The purposes of
70. hardening are to increase the hardness of the metal and to make suitable cutting
71. tools.
72. AUSTEMPERING:-
73. It is a hardening process. it is also known as isothermal quenching. In this
74. process, the steel is heated above the upper critical temperature at about 875 c
75. where the structure consists entirely of austenite. It is then suddenly cooled by
76. quenching it in a salt bath maintained at a temperature of about 250 c to 525 c.
77. MARTEMPERING:-
78. This process is also known as steeped quenching or interrupted quenching. It
79. consists of heating steel above the upper critical temperature and quenching it
80. in a salt bath kept at a suitable temperature.
81. TEMPERING:-
82. This process consists of reheating the hardened steel to some temperature below
83. the lower critical temperature, followed by any desired rate of cooling. The
84. purpose is to relive internal stress, to reduce brittleness and to make steel tough
85. to resist shock and fatigue.
86. SURFACE HARDENING:-
87. In many engineering applications, it is desirable that steel being used should
88. have a hardened surface to resist wear and tear. At this time, it should have soft
89. and tough interior or core so that it can absorb any shocks. Case hardening is
90. the process of hardening the surface of metal, often a low carbon steel by
91. infusing elements into the metal surface forming a hard, wear resistance skin
92. but preserving a tough and ductile interior. This type of treatment is applied to
93. gears, ball bearings, railway wheels. The various case hardening processes are
94. as follows:-
95. A. Carburizing
96. B. Cyaniding
97. C. Nitriding
98. D. Carbonitriding
99. E. Flame/induction hardening

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