US3701694A - Heat treatment method for ferrite-pearlite steel - Google Patents

Heat treatment method for ferrite-pearlite steel Download PDF

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US3701694A
US3701694A US878261A US3701694DA US3701694A US 3701694 A US3701694 A US 3701694A US 878261 A US878261 A US 878261A US 3701694D A US3701694D A US 3701694DA US 3701694 A US3701694 A US 3701694A
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steel
ferrite
treatment
steels
hot forming
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US878261A
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Tatsumi Osuka
Chiaki Oouchi
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JFE Engineering Corp
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Nippon Kokan Ltd
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    • 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

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  • 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.

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  • 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)

Abstract

THE INVENTION RELATES TO A HOT FORMING METHOD FOR PRODUCING STEEL WITH A FERRITE-PEARLITE STRUCTURE. THE STEEL OF THE INVENTION HAS IMPROVED TOUGHNESS.

Description

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.
BACKGROUND OF THE INVENTION The present invention relates to a heat treatment method for improving the toughness of ferrite-pearlite steels.
DESCRIPTION OF PRIOR ART In the prior art, many and varied methods have been proposed for improving the toughness of ferrite-pearlite steels, such as adjusting the hot forming conditions or using a normalizing treatment.
There are many objections to making adjustments to the heating conditions for the steel during the hot forming process, e.g. processing temperature, or time of processing. With lower processing temperature, the deformation resistance and work hardening rate of the steels increase thus resulting in lower working efiiciency. Moreover, it is very diflicult to carry out industrially the required processing because of the limited processing capacities of rolling machines. A normalizing treatment is quite a good heat treatment method, although various technical and financial short-comings having still to be removed. In a normalizing treatment, a steel after being processed, is cooled down to a normal temperature and then reheated to an austenitic temperature. Thus, not only is the quantity of heat used very high, but also much space is required to cool the steel. Also, the time lag between hot forming and the heat treatment is liable to lower the working efiiciency. Finally, 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.
SUMMARY OF THE INVENTION 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.
DESCRIPTION OF THE PREFERRED EMBODIMENTS 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:
Carbon: 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: 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 percentages of other elements are set out as follows:
Less than 0.50% for Ni, Cr, Cu; less than 0.30% for Mo,
W; less than 0.15% for V, Nb, Ti, Zr, Al. These elements, if they exceed the mentioned percentages, will greatly lower the transformation points. This is not de sirable in this treatment, as it reduces the toughness of the steel.
After hot forming, 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.
Within this temperature range, 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.
It structures other than ferrite-pearlite increase in the finally produced steels, the toughness of the steels will be lowered. Accordingly, the maximum is fixed at 90%.
In additiomafter A3 transformation point, steels could Example The table shows the comparison of characteristics obtained by various treatments of a 20 mm. thick steel Thus the present invention provides many technical and economic advantages in improving the toughness of steels.
We claim:
1. 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,
0.012% of P, 0.010% of S and 0.05% of Al.
TABLE 1 Tensile test 2 mm. V notch Austenitic (1 IS No. 4 steel) impact test transformation amount Thick- Yield, Tensile Elongain intermediness of oint, strength, tion rate, E0, Trs, Tr 15, ate cooling, scale, kg. mm. kgJmm. percent kgJm. 0. C. percent mm.
1. 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,
heated at 900 C. for 15 min. and cooled by air ,(normaiizing)- 36. 3 51. 9 38. 8 20. 0 68 -100 100 0.
In the table, 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.
More particularly, in treatment 3, 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. Further, in the treatment 4 in which a steel is cooled down to 550 C., the 15 ft.-1b. transition temperature Tr 15 is almost equal to that of the conventional treatment 5.
As will be seen from the above description 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.
comprising the steps of hot forming the steel with an austenitic structure, air cooling the formed steel to a temperature within the range of 700 to 500 C. and sufiicient to transform 50%-90% of the austenitic structure to the ferrite-pearlite structure, heating the tseel to a temperature above the A3 transformation point for austenification and air cooling the steel to obtain a product having substantially 90% of ferrite-pearlite structure.
2. The method of claim 1, wherein said hot formed steel with an austenitic structure, is air cooled to 650 C.
3. The method of claim 1, wherein said hot formed steel with an austenitic structure, is air cooled to 550 C.
References Cited UNITED STATES PATENTS 3,432,368 3/1969 Nakamura 148134 2,858,206 10/1958 Boyce et a1. 148-12 3,010,822 11/1961 Altenburger et a1. -123 3,102,831 9/1963 Tisdale 148-l2 3,163,565 12/1964 Wada 148-143 3,201,288 8/1967 Grange 148l2.4 3,388,988 6/1968 Nagashima et a1. 148--12 3,492,173 1/ 1970 Goodenow 14812 WAYLAND W. STALLARD, Primary Examiner US. Cl. X.R. 148134 y 3 s R; t "1v n w 6 m t d t a... n n a Mm 4 m a K P M n w m u M 9 w t t H 0 N 1 d o n C n v e l S i S T m .3 1 e i o 3 T e w l v b. P W Wm H 3 v {V mm w 1 6.1 3 r e o i d s M 4 e m m h l V/ T S a PM b W e a Ri o e S .1 M E m w t v a n Y B m W WHHM C w d 2 H M 0 O R O 1 v RC PU f & .m 3 g m a 8 m W m t r I d d t n w e a .w M n C t e eh m 3 VJ 1 9 n n rb e r 2 T. .H? a e d e PU e r d s S 1 WM n .1 W 1 a a 1 u h PM I m 9 ,t a L o W mi a m a M m2 d g ANA r t b 3 e m e n a l l e T O a R u J1 U .E t C 6 Wm a a J W; s h P 3 t S 9 1 O t 3 e r R T T V1 4 s h e d E e MAL m y OJ I d r n t S n H C W mm 6 M .mm. m n a Ci mwl q U PI t n Rm 1 S i e 1 1 d E 1 O T t L o e e 7 A r C e C n P T w m u h w g A Q s M m m P 5 Mn an O (x 1 t V S )t D .t M N u t a t t L w m MW w t t I m. s i A t W t o n n r E t D .t 4 e e l n S n 0 t V (A E P a n n f l M P I a R o F
US878261A 1968-11-22 1969-11-19 Heat treatment method for ferrite-pearlite steel Expired - Lifetime US3701694A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4144379A (en) * 1977-09-02 1979-03-13 Inland Steel Company Drawing quality hot-dip coated steel strip
US4437902A (en) 1981-10-19 1984-03-20 Republic Steel Corporation Batch-annealed dual-phase steel
FR2551369A1 (en) * 1983-06-09 1985-03-08 Huck Mfg Co STARTING TYPE FIXING DEVICE AND METHOD FOR MANUFACTURING THE SAME
US5542995A (en) * 1992-02-19 1996-08-06 Reilly; Robert Method of making steel strapping and strip and strapping and strip
WO1998048061A1 (en) * 1997-04-17 1998-10-29 Aspector Oy Heat treatment of steel

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2949124C2 (en) * 1979-12-06 1985-11-21 Stahlwerke Peine-Salzgitter Ag, 3150 Peine Denitrided steel hot rolled strip or heavy plate and process for its manufacture
DE3127373C2 (en) * 1981-07-09 1985-08-29 Mannesmann AG, 4000 Düsseldorf Process for the manufacture of seamless steel tubes for the petroleum industry
DE3535886A1 (en) * 1985-10-08 1987-04-16 Tischhauser Max W Method for the production of steel prestressing elements
CH667104A5 (en) * 1984-10-30 1988-09-15 Max Willy Prof Tischhauser Method for producing spannstaehlen.
DE3719569C2 (en) * 1986-07-05 1988-06-23 Thyssen Edelstahlwerke Ag Microalloyed steels.
US5221373A (en) * 1989-06-09 1993-06-22 Thyssen Edelstahlwerke Ag Internal combustion engine valve composed of precipitation hardening ferritic-pearlitic steel

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4144379A (en) * 1977-09-02 1979-03-13 Inland Steel Company Drawing quality hot-dip coated steel strip
US4437902A (en) 1981-10-19 1984-03-20 Republic Steel Corporation Batch-annealed dual-phase steel
FR2551369A1 (en) * 1983-06-09 1985-03-08 Huck Mfg Co STARTING TYPE FIXING DEVICE AND METHOD FOR MANUFACTURING THE SAME
US4540447A (en) * 1983-06-09 1985-09-10 Huck Manufacturing Company Method of making a multigrip fastener and fastener made thereby
US5542995A (en) * 1992-02-19 1996-08-06 Reilly; Robert Method of making steel strapping and strip and strapping and strip
WO1998048061A1 (en) * 1997-04-17 1998-10-29 Aspector Oy Heat treatment of steel

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GB1268798A (en) 1972-03-29
DE1958548A1 (en) 1970-12-03
DE1958548B2 (en) 1977-11-17
FR2023915A1 (en) 1970-08-21

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