JPH01221A - How to continuously process cold rolled carbon manganese steel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Today there exists a family of steels that are characterized by inter alia higher mechanical properties, including yield point and tensile strength, than IIA building carbon steels. They are known as high strength low alloy (TR5LA) steels. Various H8LA steels are available, including C--Mn steels and steels that have been microalloyed with the addition of elements such as Nb, V, and Ti to enhance mechanical properties. Demand for H8LAII originally arose from the need to improve the strength-to-weight ratio and reduce dead weight in transportation equipment. Today, H8LA steel is used in a wide variety of applications, including vehicles, construction equipment, material handling equipment, bridges, and buildings in addition to its original use.

Commercially available H8LA steel has a hook-shaped yield point of 275-345 MPa or more and a tensile strength of 410-480 MPa or more. The mechanical properties and other properties of H8LA steel are rated 5AEJJI (5ociety of＾tomo
tive Engineers) J 410 c
It is stated in standards such as H8 added with microalloying (licroallOvinQ) elements
LA steel has a yield point of 345 to 550 MPa or more and a yield point of 45
It has even higher strength, such as tensile strength of 0-655 MPa or more. These steels generally contain alloying elements such as Nb, V, Ti, 7r, and rare earth elements in o, io~0
．． It has been added at concentrations below 15% to achieve higher strength levels. The properties of the microalloyed H8LASM are obtained from continuous rolling in a continuous hot strip mill, so no heat treatment is involved.

There are grades 950A, B, C, and D in the SAE standard J410c^ strength low alloy steel, which is 34
Proof strength of 5 MPa or more (0.2% offset), 480
Tensile strength of MPa or more and elongation of 22% or more (51:
It is characterized by having a 1 m test piece). This material exhibits its mechanical properties in the as-hot-rolled state, and when it is further cold-worked to a thin plate thickness, it is subjected to a long-term low-temperature recovery annealing to maintain the mechanical properties in the as-rolled state.

Another grade of high-quality low-alloy steel with trace alloy additions to SAE standard J410c is grade 970 % or more (5I:Il test piece). As mentioned above, this material exhibits its mechanical properties in the as-hot-rolled state.

Furthermore, when cold working to a thin sheet thickness, a long period of low-temperature recovery annealing is similarly applied to maintain the mechanical properties achieved by controlled rolling. In addition to the cost increase due to the addition of microalloying elements, this recovery annealing is
This is disadvantageous due to the long time required for the annealing process or the huge investment required in continuous annealing equipment.

Thus, there is a need today for a steel that has the desired strength and ductility necessary for H8LΔ steel applications, yet can be economically produced from cold-worked sheet stock without the need for extended recovery annealing. .

Furthermore, there is a need for steels with improved mechanical properties, particularly yield point and tensile strength, without significantly increasing the cost of steel by eliminating the intentional addition of microalloying elements such as Nb, Ti, and ■. There is.

It is characterized by a relatively low carbon content and does not contain expensive microalloying agents, yet still contains e.g.
AE standard J 410 c grade 950A, B, C1
D and 970X micro-70-sized l-I
It is an object of the present invention to provide a method for processing a cold-worked steel composition characterized in that the processed state exhibits mechanical properties such as yield point, tensile strength and elongation that satisfy the specifications for SLA steel. This is the main purpose of the invention. Furthermore, we provide a method for producing cold-worked steels that can be produced in a continuous process relatively constraint and very economically, yet have uniformly higher mechanical properties than microalloyed H3LΔ steels. This is also a main objective of the present invention.

To this end, the present invention proposes a low C without microalloying
- Mn steel compositions and methods of heat treatment thereof. One copper phase included in the present invention or 0.04-0
．． 15 double beating%C10,25~0.701ffi%Mn. Microalloying elements such as Nb1Ti and ■ are not added to the steel composition to enhance mechanical properties. Desired plate thickness, e.g. 0.078-0.236m
Steel that has been cold-worked to a + range is successively passed through three heating stages. The first stage is a preheating stage which raises the temperature of the cold rolled sheet to a temperature in the range of about 700°F to below 1000°F.

The steel is then heated to a temperature ranging from below 1625°F to below 1725°F, quenched to a temperature ranging from below 650°F to 750°F, and then cooled to vm. Another steel composition included in the invention is 0.11 to 0.18 wt.% C and 1.20 to
1.40wt%n.

Similarly, the desired thickness of steel, e.g. 0.078 to 0.2
It is cold worked to a temperature range of 36411+ and passed through three successive heating stages. The first stage is the preheating stage, which raises the temperature of the cold rolled sheet to a temperature in the range of about 700°F to below 1000°F. Next, lower the steel to 1500 to 157
Heat to a temperature in the range below 5°F, rapidly cool to a temperature in the range from 850°F to below 950°F, and then cool to room temperature.

In either case, the heat treatment is performed continuously at a line speed in the range of 50 to 300 feet/min, so that a continuous thin steel plate of the desired thickness and width is passed through three heating stages continuously and sequentially. .

One of the currently preferred steel compositions is a steel having 0.10-0.15% by weight C1 to about 0.25-0.70Φ%Mn and the balance Fe and the usual residual components associated with deoxidation. . When treated according to the first heat treatment plan above,
The treated steel is SAE standard J410C grade 950A,
It satisfies the yield strength of 345 MPa or more, the tensile strength of 480 MPa or more, and the elongation of 22% or more specified in B, C, and D. Another low carbon composition containing about 0.04 to 0.07:aft% C and about 0.25 to 0.40 wt% Mn has a Mn of 345 MP when processed with the method of the present invention.
proof stress of more than a, tensile strength of more than 410 MPa and 28
% showing a relatively high elongation rate.

One currently preferred steel composition is about 0.11-0.
There is a steel containing 18% by weight C1, about 1.20 to 1.40% Mn, and the balance Fe and the usual residual components associated with deoxidation. When treated according to the second heat treatment plan above, the treated steel G;! S A E standard J410c (D
/Rade 970X1. : Specified 4 80 MP
proof stress of a to L, tensile strength of 585 MPa or more and 1
Satisfies growth of 4% or more.

The method of the present invention for treating steels with relatively low carbon content and Mn content as described above and without the addition of micro-70 alloying agents corresponds to the existing H3LA steel standard for micro-alloyed steels or To obtain a cold-worked product having mechanical properties that surpass those of the above. Thus, the present invention aims to achieve higher mechanical properties than certain commercially available micro-70 alloyed high-strength low-alloy steels in a cold-open worked low carbon steel that does not undergo microalloying. It is characterized by the absence of added curing agents and by the economy derived from the continuous processing of the cold-worked product.

C--Mn steel compositions treated by the method of the present invention in one case have about 0.04-0.15 wt.% C and 0.25-0.25 wt.
0.70@ff1% Mn, in another case about 0.11-0.18%C and 1.20-1.4
Contains 0% Mn.

The steel is a guild steel, preferably a cold-killed steel, and is continuously cast to achieve uniform mechanical properties.

As a result, the composition has residual Si and Aj! can contain. The steel may be 3i guild steel or semi-killed steel.

As shown in Figure 1, hot-dipped rolled steel coils, which may be pickled and oiled, are rolled from a series of cold-rolled steel coils to a desired thickness, e.g. Cold work the root 10 to the desired thickness. The cold-rolled root 10 then passes through rollers 11 and rolls between 700" and 10".
It passes into a preheating tower 12, which may be a molten Pb bath maintained at a temperature in the range of 0.000°F. The Pb bath may be heated by any of several methods, such as natural gas or electricity. Other media capable of providing a liquid bath with a temperature in the range of 700° to below 1000° may be used in place of the Pb bath. The material then exits the bath upwardly and passes over the rollers 14 located above. The material then falls into a second molten Pb bath, which is a quenching bath.

The heating stage heats the material to a temperature ranging from 1625 to 1725 below, depending on its composition. The quenching stage quenches the material to a temperature ranging from 650° to below 950°C, depending on the composition. That is, the low Mn composition is between 1625° and 1725°F.
heating to a temperature range of 650° to 750°,
^Mn composition is heated in the range of 1500a to 1575T-
Rapidly cool to below r800° to 950°. The material in the heating stage is heated by resistance heating. That is,
The preheating tower 12 and the quenching bath 16 have a voltage of about 90V and a
Maintain a current of 000 A and ground the quench bath.

As a result, the plate material 10 passing between the preheating tower and the quenching bath
represents the current and is resistively heated by it. The length, current, and speed of movement of the material through the heating stage are controlled to bring the material in the heating stage to the desired processing temperature. Atmosphere housing 18 which is a sink for exothermic protective gas
By enclosing the plate material 10 inside, a protective atmosphere is maintained in the heating stage. The gas prevents oxidation of the sheet material as it passes from preheating tower 12 to quench bath 16. Material 1 can be heated by other heating methods such as induction heating, infrared heating and gas heating instead of resistance heating.
0 may be heated.

The quenching bath 16 is a Pb bath, and can be heated to a desired temperature using a method such as an immersion electric heater or a radiant gas tube. After quenching, the material exits the quench bath 16 vertically upwards.
Beyond the lathe 20 it passes through a charcoal chute 22 containing lighted charcoal to prevent the PB from getting onto the board and being drawn out of the quench bath. The plate material, which is at a temperature of about 500°F, is then passed through a downstream water tank or water jet (not shown) to reduce its temperature to about 150°F. but,
All transformation of the steel is complete by the time the material leaves the quench bath 16. After cooling, it may be rolled up for shipping or processed by known methods such as pickling and/or polishing, painting, plating, stretching, tension leveling, or combinations thereof.

The plate material passes through preheating, heating and quenching stages successively. Typical line speed is 15-100TrL/
It is an order of minutes. The preheating, heating and quenching stages are approximately 3-8 m long. As a result, the material at each stage is only 6 to
Heating or rapid cooling takes place on the order of 15 seconds.

A typical device for performing such heating is Wood et al.
U.S. Patent No. 2.224°98 to Wood et al.
No. 8 Specification 1 and No. 2.304.225. Overlapping, heating and cooling other than molten Pb]
Media can be used for preheating and quenching baths.

It is believed that the relatively short cycle times of the preheating, heating, and quenching stages result in grain refinement and, as a result, increased strength. In other words, the strain generated in the material by cold rolling causes recrystallization of ferrite in the preheating and heating stages, resulting in fine crystals IfrI.
It becomes a structure. Short cycle times limit grain growth and result in small grain sizes, typically less than 0.01aIII, often 0.003-0.004m and finer. Furthermore, during heating, a small amount of austenite is formed at the grain boundaries, suppressing movement of the grain boundaries and further restricting grain growth, resulting in higher strength levels.

At the same time, the carbides in pearlite are spheroidized and defects are removed, improving the ductility of the steel. Carbides precipitate during quenching, providing ductility and eliminating the possibility of subsequent strain aging.

Example 1 A thin steel plate having an S cta width of 0.11 cs+thickness, which was cold-worked from a material of 0.21 using the same tVi shown in FIG. 1, was subjected to hot tJX processing. The steel has uniform properties to A1 kill, and the composition is 0.10% C10, 40% Mn, 0.012% 3i and 0.057% AI, with Si and AI acid components remaining from deoxidation of the steel before casting. It's a minute.

The sheet material was moved at a speed of 3371 L/min. The length of the thin plate under the Pb in the preheating bath was 3 m, 67 FL in the quenching bath and 7.3 m in the heating stage.

Roller 14 was 2.4 m above the PB bath. The sheet temperature was measured using an optical pyrometer. The treatment plan and mechanical properties obtained are shown in Table 1.

As can be seen from Table 1, the mechanical properties obtained from the processing step are grade 950A, B.

Minimum mechanical properties specified in C1D (yield strength 345MP
a, tensile strength 480 MPa, elongation 22%) f exceeded.

A second similar composition test was conducted using the same conditions.

This composition is 0.0410.06% C and 0.2510
．． It was 35% Mn. The treatment plan and mechanical properties obtained are shown in Table 2.

This material is characterized by a lower tensile strength but an excellent level of elongation than the previous sample, and would thus be considered to have a high degree of processability.

Example 2 A thin steel plate with a saA width of 0.113 and a thickness of 0.113 was cold-worked from a material of 0.2 CII using the apparatus shown in FIG. 0.
14% C, 1,33% Mn, 0°22% Si and 0.
019% AI and is the residue from the 12 acid of the steel before casting the 3i and AI acid components. Thin plate material is 337FL/
Moved at a speed of 1 minute. The thickness of the thin plate under the PB in the preheating bath is 3m, the quenching bath is 6TrL, and the heating stage is 7.
It was 3m. 0-Ra14 was 2.4 m above the PB bath. The thin plate temperature was measured using a 9B lagoon meter. The treatment plan and mechanical properties obtained are shown in Table 3.

As can be seen from Table 3, the mechanical properties obtained from the treatment process are in line with the minimum mechanical properties specified for grade 970x (yield strength 480 MPa, tensile strength 585 MPa).
and elongation exceeded 14%). Both samples exhibited superior ductility with higher levels of strength.

The method of the invention is applicable to a range of steel compositions within the composition limits mentioned above. As the specific examples described above demonstrate, the processing method involves hot rolling of commercially available trace alloys to provide a low C, high Mn cold worked steel with the desired combination of strength and ductility that characterize low strength low alloy steels. .

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an apparatus used in the treatment process of the present invention. DESCRIPTION OF SYMBOLS 11... Roller, 12... Preheating bath, 14... Roller, 16... Rapid cooling bath, 18... Atmosphere housing.

Claims (7)

[Claims] (1) having a composition of about 0.04-0.18% by weight carbon and 0.25-1.40% manganese without the addition of microalloying agents for the purpose of improving mechanical properties; A method of treating cold-worked steel in a continuous process, comprising: (a) preheating the steel to a temperature in the range of 700° to 1000°F; (b) heating the steel to a temperature in the range of 1500° to 1725°F. and (c) rapidly cooling the steel to a temperature in the range of 650° to 950°F, such that the treated steel has a yield strength of 275 MPa or more, a tensile strength of 345 MPa or more, and a tensile strength of 14% or more. A method for processing steel characterized by having an elongation of . (2) having a composition of about 0.11-0.18% by weight carbon and 1.20-1.40% manganese without the addition of microalloying agents for the purpose of improving mechanical properties; A method of treating cold-worked steel in a continuous process, comprising: (a) preheating the steel to a temperature in the range of 700° to 1000°F; (b) heating the steel to a temperature in the range of 1500° to 1575°F. and (c) rapidly cooling the steel to a temperature in the range of 800° to 950°F, so that the treated steel has a yield strength of 480 MPa or more, 58
A method for treating steel, characterized by having a tensile strength of 5 MPa or more and an elongation of 14% or more. (3) approximately 0.14% by weight of carbon and 1.3% by weight without the addition of microalloying agents for the purpose of improving mechanical properties;
A method of treating cold-worked steel having a composition of 3% by weight manganese in a continuous process, comprising: (a) preheating the steel to a temperature in the range of 700° to 1000°F; (b) (c) rapidly cooling the steel to a temperature in the range of 800° to 950°F, such that the treated steel has a yield strength of 480 MPa or more; , 58
A method for treating steel, characterized by having a tensile strength of 5 MPa or more and an elongation of 14% or more. (4) having a composition of about 0.04-0.15% by weight carbon and 0.25-0.70% manganese without the addition of microalloying agents for the purpose of improving mechanical properties; A method of treating cold-worked steel in a continuous process, comprising: (a) preheating the steel to a temperature in the range of 700° to 1000°F; (b) heating the steel to a temperature in the range of 1625° to 1725°F. and (c) rapidly cooling the steel to a temperature in the range of 650° to 750°F so that the treated steel has a yield strength of 275 MPa or more, 34
A method for treating steel, characterized by having a tensile strength of 5 MPa or more and an elongation of 22% or more. (5) having a composition of about 0.10-0.15% by weight carbon and 0.25-0.70% manganese without the addition of microalloying agents for the purpose of improving mechanical properties; A method of treating cold-worked steel in a continuous process, comprising: (a) preheating the steel to a temperature in the range of 700° to 1000°F; (b) heating the steel to a temperature in the range of 1625° to 1725°F. and (c) rapidly cooling the steel to a humidity in the range of 650° to 750°F, so that the treated steel has a yield strength of 345 MPa or more, 48
A method for treating steel, characterized by having a tensile strength of 0 MPa or more and an elongation of 22% or more. (6) Preheating the material by passing it through a molten lead bath and heating it by means of a resistor, each heating step lasting less than about 15 seconds. the method of. (7) The method according to any one of claims 1 to 5, wherein the material is a plate or thin plate of aluminum killed steel.