Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment

Definitions

• United States Patent 1m. (:1. czid 7/14 US. Cl. 148l2 3 Claims ABSTRACT OF THE DISCLOSURE
• the invention relates to a hot forming method for producmg steel with a ferrite-pearlite structure.
• the steel of the invention has improved toughness.
• the present invention relates to a heat treatment method for improving the toughness of ferrite-pearlite steels.
• a normalizing treatment is quite a good heat treatment method, although various technical and financial short-comings having still to be removed.
• a normalizing treatment a steel after being processed, is cooled down to a normal temperature and then reheated to an austenitic temperature.
• the time lag between hot forming and the heat treatment is liable to lower the working efiiciency.
• the prolonged heating produces scales on the surface of the steel during the heating stage which cause the surface quality of the steel to deteriorate.
• the object of the present invention is to overcome various defects of the known methods. More particularly, according to the present invention there is provided a method for improving the toughness of steels having a ferrite-pearlite structure in which the steel, after hot forming, is at once cooled down to 700-500 C. to transform the austenitic structure into the ferrite-pearlite structure by about 5090%, and then again is heated to above the A3 transformation point for austenitization, and cooled by air or by some other suitable cooling methods.
• the treatment of the present invention can be applied "ice to any steels with a ferrite-pearlite structure, so that there is no particular need to use a steel with the standard range of components. However, when there are too many alloy elements involved, the transformation point is lowered and the application of this treatment difficult. Accordingly, in practice, it will be generally desirable to fix the range of components, by weight, as follows:
• the upper limit of C content is fixed at 0.25%. As the percentage of carbon increases, the toughness is reduced and the transformation point is lowered so making the application of this treatment more diiiicult.
• the lower limit is fixed at 0.05% due to the limitations of industrial steel making for structural steels which require great toughness.
• Si The upper limit of Si content is 1.00%. Si is very effective as a deoxidizer in steel making and makes the treatment of the invention easier as it serves to raise the starting temperature of ferrite transformation. On the other hand, more than 1.00% of Si will lower the toughness of the steel. Therefore, the upper limit is fixed at 1.00%.
• Mn is a cheap but very effective element for improvin the toughness of steels. However, a higher percentage of Mn content causes the transformation point to go down and hinders the successful application of the treatment of the invention.
• the upper limit is fixed at 1.50%.
• the lower limit is fixed at 0.40% which is generally regarded as an essential percentage of Mn content as a deoxidizer in steel making.
• the maximum for the intermediate cooling temperature is limited to 700 C. A temperature exceeding this maximum results in the slowing of the transformation from austenitic to ferrite-pearlite structure, hence lowering the working efiiciency. (Refer to treatment 2 in Table l.)
• the minimum cooling temperature is set at 500 C. Below this temperature, the loss of heat retained in the steel will be greater. Moreover, the subsequent heating will be prolonged so increasing the formation of scales.
• the amount of transformation from austenitic to a ferrite-pearlite structure after hot rolling is about 50-90%. If it is less than 50%, the treatment will be less effective as the after effect of hot rolling is still very pronounced, while if it is more than the transformation speed will be slower, so that the treatment time will be prolonged and lose its industrial advantages.
• a hot forming method for producing a steel consisting essentially of 0.050.25% of C, less than 1.00% of Si, 0.40-1.50% of Mn, and one or more of the following elements in the stated percentages: less than 0.50% of Ni, Cr and Cu, less than 0.30% of Mo and W, and less than 0.15% of Nb, V, Ti, Zr and A1, with the resheet containing 0.14% of C, 0.37% of Si, 1.26% of Mn, mainder essentially Fe with -a ferrite-pearlite structure,
• Air cooling after hot forming (as formed) 33. 2 51. 1 88. 8 8. 4 -10 -73 0. 10 2. Cooled down to 700 C. after hot forming, heated at I 900 C. for min. andthen cooled by air 35. 4 51. 2 38. 1 9. 4 ---10 74 5 0. 17 3. Cooled down to 650 C. after hot forming, heated at 900 C. for 15 min. and cooled by air 33. 4 50. 8 40. 5 17. 4 56 78 65 0. 18 4. Cooled down to 550 C. after hot forming, heated at 900 C. for 15 min. and cooled by air 38. 2 51. 0 40. 5 18. 4 -61 99 90 0. 19 5. Cooled down to normal temperature after hot forming,
• treatment shows thestate of a steel as hot rolled and treatment 5 is the conventional normalizing treatment.
• treatment 3 and 4 embody the present invention and clearly indicate the great improvement of toughness in comparison with other treatments.
• the steel is cooled down to 650 C. after hot forming.
• the austenitic transformation obtained is 65% which is a great improvement over the treatment 1. It shows almost the same value of absorbing energy E, and a 50% brittle fracture percentage ,Trs as produced by the conventional normalizing treatment 5.
• the 15 ft.-1b. transition temperature Tr 15 is almost equal to that of the conventional treatment 5.
• the present invention provides a method for producing steels with various advantages over the prior art; the quantity of heat used can be reduced as the heat retained by a steel after hot forming can be effectively utilized in reheating; operating efiiciency of a hot treatment furnace can be improved by drastically shortening the heat treatment time, and the working efficiency can be improved by reducing the space for transferring steels and shortening the time lag between forming and heat treatment.
• Another advantage, as will be apparent from the table, is that the shortening of the heating time serves to reduce the scale formation on the surface of the steels.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=13851419

Family Applications (1)

Country Status (5)

Cited By (5)

Families Citing this family (6)

• 1969
  • 1969-11-17 SE SE15694/69A patent/SE349059B/xx unknown
  • 1969-11-18 GB GB56258/69A patent/GB1268798A/en not_active Expired
  • 1969-11-19 US US878261A patent/US3701694A/en not_active Expired - Lifetime
  • 1969-11-21 FR FR6940169A patent/FR2023915A1/fr not_active Withdrawn
  • 1969-11-21 DE DE19691958548 patent/DE1958548B2/de not_active Ceased

Also Published As

Similar Documents