MXPA99000370A - Hot laminated steel band and procedure for your producc - Google Patents

Abstract

The invention relates to a hot-rolled strip with a maximum thickness of 5 mm of steel with high tensile strength, which contains 0.08 to 0.25% C, 1.20 to 2.0% Mn and 0.02 to 0.05% Al and mainly has a martensitic microstructure.

Description

HOT LAMINATED STEEL BAND AND PROCEDURE FOR ITS PRODUCTION DESCRIPTION OF Lft INVEffCIQff The invention relates to a hot strip with a maximum thickness of 5 mm, made of high strength steel and a process for its production. The "hot" band refers to a hot rolled strip According to the present state of the art, the hot rolled strip is produced only with a strength of approximately 800 N / mm *. Thermo-mechanically laminated alloy For applications requiring higher strengths, the soft-rolled strip is used and the required strength for the component is obtained by subsequent heat treatment, for thickness intervals below 2.0 mm usually required additional cold rolling in order to obtain the desired thickness In this case the required strength is also obtained by means of an adequate heat treatment It is known from the patent of US 4 406 713 the high strength and high ductility steel with good manageability, which consists of 0.005 to 0.3% C, 0.3 to 2.5% Mn, up to 1.5% if and at least one carbide and nitride former from the Nb, v, Ti and Zr group in cant idades up to?.?%, to 0.15%, up to 0.3% and 0. 3% respectively. After austenitizing, this steel is quenched to such a degree that it contains 5 to 65% ferrite, being REF. 29227 the rest martensite. it is intended to be used above all for the production of wires and bars. From GB 2 195 658 Al there are known forged parts of steel with 0.01 to 0.20% C Ijasta 1.0% yes, 0.5 to 2.25% Mn, up to 1.5% Cr, up to 0.05% Ti, up to 0.10% Nb, 0.005 a o. oi5% N and up to 0.06% Al. The cooling of the steel of the austenitic region has to be controlled in such a way that the microstructure is completely martensitic. To be sure, only examples with carbon contents below ü.lü% and silicon contents above o.17% are described. Sulfur contents above ü.01% are relatively high. The well-known steels of EPO 072 867 Al also have of camo per p tajo ds OJJ0 & and a-ptaúd-s ds si lirio by e_ na de u_L3 &.

The hot tench, after the gradual phase, has a dual phase phase of polygonal ferrite and a mixture of pearlite and bainite. The hot-rolled strip known from DE 30 07 560 Al, after hot rolling, is also cooled at a cooling rate of i K / s or faster in order to produce a dual-phase microstructure of ferrite and martensite. In view of the satisfactory properties related to ductility and durability, carbon contents are recommended in the range between 0.02 and 0.09%. The preferred silicon content is relatively high at 1.0%. The object of the invention is to produce a band hot rolled with tensile strength values greater than 800 N / mm2 and at the same time good ability to cold reduce its thickness in the range of < . 5mm This would mean an extension of the direct use of the hot strip for cold reduction purposes, such as cold pressing, obtaining significant economic advantages from the fact that the laminate and the cold treatment would be made without heat. This objective is fulfilled according to the invention by means of a proposed hot strip with a thickness of less than s mm, in particular less than 2 mm, with a tensile strength of 800 to 1400 N / mm1, of an aaero with the following composition (in% by mass): 0.08 to 0.25% carbon, 1.20 to 2.0% manganese, 0.02 to 0.05% aluminum less than 0.07% silicon, the rest being iron and unavoidable impurities, including up to 0.015% phosphorus and up to 0.003% sulfur, and martensitic structure with less than 5% in total of other structural components. if desired, the steel may additionally contain at least one of the following elements in mass%: up to 1.0% chromium up to 0.1% copper up to 0.5% molybdenum up to or .1% nickel to o.ooy% nitrogen preferably with a carbon content of q.oa to ü.15%, manganese of 1.75 to 1.90%, chromium of 0.5 to p.6% and nitrogen of 0.005 a 0.009%. For the stoichiometric determination of nitrogen present in the steel, titanium (Ti = 3.4% N) can be added in an appropriate amount in order to protect an additive of up to ü 0.0025% B from being bound to N, in such a way that it can contribute to the highest mechanical strength and the ability to be hardened. The limitation of silicon content to less than 0.04% helps improve surface conditions. a process for producing a hot strip with a final thickness of less than 5 mm, in particular less than 2 mm, of the steel with the composition presented with tensile strength values above 800 N / mm1 consists of the following measures: a plate is it is heated to 1300 uc, pre-rolled within the temperature range of 950 to 1150 ° C and terminated at a final rolling temperature above Ar3. The hot band produced in this manner is cooled to a winding temperature in the range of 20UC to below the winding temperature of the martensite to convert it into a martensite structure with a total content of other structural components of less than 5%, and then it is rolled.

Preferably the cooling of the final rolling temperature to the winding temperature takes place with t8 / 5 = less than 10 s. (t 8/5 at cooling time from 800wc to 500UC) The temperature Ar3 can be estimated by means of the following formula: Ar3 = 910-310x (% C) -80x (% Mn) -20x (% Cu) -15x ( % Cr) -55x (% Ni) -80x (% Mo) The initial temperature of the martensite s can be estimated by means of the following formula: Ms = 500-300x (% C) -33x. { % Mn) -22x (% Cr) -17? (% NÍ) -llx (% Sii-llx (% M?) By means of the respective selection of the cooling temperature within the aforementioned temperature range, the tensile strength of the hot band is preferably set at a value in the range of 800 to 1400 N / mm2. The hot band can be galvanized to make it more resistant to corrosion. Galvanized high tensile strength laminates with a good capacity to be cold reduced are preferably used for mechanical parts subjected to high stresses in automotive construction, for example for side impact shock absorbers and bumpers. The steel according to the invention achieves high mechanical strengths without expensive alloying elements and without the need for annealing, as is the case with known steels. The invention is illustrated by means of the following examples. e emlo i: a steel containing o.15% C, o.01% yes, 1.77% Mn, 0.014% P, 0.003% S, 0.028% Al, 0.0043% N, 0.526% Cr, 0.017% Cu, 0.003% Mo, 0.027% Ni, the rest Fe is molded into a plate. The plate was heated to about 1250UC, pre-rolled to approximately 1120 ° C and at a final temperature of 840 ° C it was laminated to a final thickness of 2 mm. Then it cooled and rolled at 50 ° C. This resulted in a microstructure with more than 95% martensite. The elastic limit reached values of 1120 N / mm3 and tensile strength values of 1350 N / rare * with values of elongation Aβ0 of up to 11.1%. Example; A steel with the same composition as Example 1 is processed to give a hot strip with a thickness of 3.5 mm. The data is shown in table l. The values related to the mechanical strength were significantly higher. The winding is carried out at a temperature of up to 95 ° C, instead of higher than 40 ° C.

Table l * E n g lish Comparative Before reducing to the final shape by means of cooling, the hot rolled strip can be galvanized. The heat treatment cycle during the galvanization of the martensite is tempered. Starting with a band laminated in hot with tensile strengths between 1200 to 1400 N / mm2, depending on the heat treatment cycle during ßí galvanized, tensile strengths between 800 and 1100 N / mm2 are obtained. 6jerop or 3; A hot rolled strip with a thickness of 2.0 to 1.6 mm. It was galvanized. Table 2 given below shows a comparison of properties in the rolling stage and after galvanizing. Table 2 B or a hot rolled strip with a thickness of 1.6 to 1.8 mm was produced in the manner described in Example 1. The production parameters and the deter- mined mechanical properties are listed in table 3, which also contains the gu omj ^ a com m on of the material examined. B eg 5; Table 4 lists the respective data for the hot-rolled strip with a thickness of 1.4 m. iaoi 3 or *) Comparative example Table 4 It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (11)

1. RBIVIMPICAGIQNBS l.- Hot-rolled strip with a thickness of less than 5 mm, in particular less than 2 mm, with a tensile strength of 800 to 1400 N / mm3 characterized because it is formed with a steel with < % by mass): 0.08 to 0.25% carbon 1.20 to 2.00% manganese 0.02 to 0.05% aluminum less than 0.07% silicon, the rest being iron and unavoidable impurities, including 0. 015% phosphorus and up to 0.003% sulfur, and martensitic structure with less than 5% in total of other structural components.
2. 2. Hot-rolled strip according to claim 1, characterized in that, however, the steel has a carbon content of 0.12 to 0.25%.
3. 3. - Hot rolled strip according to claim 1, characterized in that the steel additionally contains at least one of the following elements (mass%): up to 1.% chromium up to 0.1% copper up to 0.5% molybdenum up to 0.1% nickel up to 0.009% nitrogen.
4. 4. - Hot rolled strip made of a steel according to claim 3, characterized in that it has carbon contents of 0.08 to 0.15%, manganese of 1.75 to 1.90%, chromium of 0.5 to 0.6% and nitrogen of 0.00
5. 5. to 0.009%. 5. Hot-rolled strip made of a steel according to claim 3, characterized in that it contains titanium in an amount suitable for the stoichiometric fixing of the nitrogen contained in the steel (ti »3.4% N) and up to 0.0025% B. .- Hot rolled strip according to claim 1 or 2, characterized in that the content of silicon is limited to less than 0.04%. 7. - A process for producing a hot rolled strip with a final thickness of less than 5 mm, in particular less than 2 mm, with a steel with the composition according to one of claims 1 to 6, with tensile strength values greater than 800 N / mm2, characterized in that the following measurements are carried out: a plate is heated to 1000 to 1300 ° C, - it is pre-rolled within the temperature range of 950 to 1150 ° C, it is finished at a rolling temperature final above Ar3; the hot band produced in this way is cooled to a winding temperature in the range of 20 ° C to below the initial temperature of the raartensita and rolled, obtaining a structure with more than 95% of martensite. 8. A process according to claim 7, characterized in that the cooling to the final rolling temperature at the winding temperature is carried out with t8 / 5 < l0s. 9. -. A process according to claim 7 or 8, characterized in that by the respective selection of the cooling temperature within the temperature range mentioned in claim 7, the tensile strength of the hot rolled strip is set at a value in the range from 800 to 1400 N / mm3. 10. Hot rolled strip according to one of claims 1 to 6, characterized? because it is galvanized, use of the hot-rolled galvanized strip made of a steel according to one of claims 1 to 6 and produced in a process according to claims 7 to 9 for components subjected to high mechanical stress in automotive construction, for example for side impact and bumper shock absorbers.