Hot-rolled TRIP steel with tensile strength being 900 MPa level and preparation method thereof

Abstract

The invention provides hot-rolled TRIP steel with tensile strength being the 900 MPa level and a preparation method thereof. The steel comprises, by chemical mass percentage, 0.10-0.30% of C, smallerthan or equal to 0.10% of Si, 4-8% of Mn, smaller than or equal to 0.01% of P, smaller than or equal to 0.008% of S, 1.0-2.0% of Al, smaller than or equal to 0.04% of Nb, smaller than or equal to 0.10% of V and the balance Fe and inevitable impurities. By means of control over chemical components, hot-rolling technology parameters and the heat treatment technology, after ferrite and austenite two-phase areas (Ac1-Ac3) are annealed, the finished product TRIP steel with the texture state being ferrite, bainite and residual austenite, by means of addition of micro alloy element Nb and V, C and Nin the steel can be fixed, the adverse influence of AlN to thermoplasticity is eliminated, and the refined crystalline strengthening and precipitation strength functions are played effectively. The rare earth element is added, and the functions of reducing alloy segregation and refining as-cast structure can be achieved. The tensile strength of the product is larger than or equal to 900 MPa, the ductility after breakage is larger than or equal to 25%, the product of strength and elongation can reach 25-30 GPa%, the requirements for the light weight, energy saving and consumption reducing of car industry are fully met, and the steel has good economy and application prospect.

Description

technical field

[0001] The invention belongs to the technical field of hot-rolled strip steel production technology, and in particular relates to a hot-rolled TRIP steel with a tensile strength of 900MPa and a preparation method thereof. Background technique

[0002] With the development trend of automobile lightweight, energy saving and safety improvement, high-strength steel has become the focus of steel material research in recent years and has been widely used in automobile manufacturing. However, in order to meet the forming conditions of body components, the elongation of high-strength steel must be guaranteed, so the strength level of high-strength steel used is limited, and some parts with complex shapes that require high strength can only be produced by welding after forming .

[0003] The TRIP steel with medium manganese content, that is, the phase transformation induced plasticity steel, induces the TRIP effect during deformation, so that the retained austenite f...

Examples

preparation example Construction

[0044] The second aspect of the present invention provides a method for preparing the above-mentioned hot-rolled TRIP steel with a tensile strength of 900MPa, the steps comprising:

[0045] S1, obtaining the molten steel with the above composition and then casting to obtain a slab;

[0046] S2, heat-treating the obtained cast slab under nitrogen protection, the heating temperature of the heat treatment is 1230-1270°C, and the holding time is 1 hour;

[0047] S3. The hot-rolled plate is obtained by hot-rolling by two-stage rolling process, the starting rolling temperature is 1120-1170°C, and the finishing rolling temperature is 850-930°C;

[0048] S4. Cool the hot-rolled sheet at a cooling rate of 20-30°C / s, cool it to 570-630°C, put it into a furnace (furnace temperature is 200-400°C) and keep it warm for 25-35 minutes, then cool it with the furnace to obtain a finished product, hot-rolled After 7 passes of rolling, the thickness range of the plate is controlled at 4-6mm; the...

Embodiment 1

[0053] This embodiment provides a method for preparing hot-rolled TRIP steel with a tensile strength of 900 MPa. The steps include:

[0054] After obtaining the molten steel, cast it to obtain a slab; the chemical composition of the molten steel is: by mass percentage, C: 0.11%, Si: 0:060%, Mn: 5.03%, P: 0.005%, S: 0.003%, Al: 1.82%, Nb: 0.036%, V: 0.060%, and the rest are Fe and unavoidable impurities.

[0055] The obtained slab was heated under the protection of nitrogen, the heating temperature was 1238° C., and the holding time was 1 hour.

[0056] The hot-rolled plate is hot-rolled by two-stage rolling process, the rolling start temperature is 1150°C, the thickness specification variation range of the hot-rolled plate is controlled at 4-5 mm after 7 passes of rolling, and the rolling termination temperature is controlled as 895°C. The hot-rolled plate is cooled at a cooling rate of 25°C / s, cooled to 600°C by laminar flow, put into the furnace (furnace temperature is 330...

Embodiment 2- Embodiment 6

[0060] Embodiments 2-6 all provide a method for preparing hot-rolled TRIP steel with a tensile strength of 900 MPa. The preparation method is basically the same as that of Example 1, the difference lies in the chemical composition of molten steel and some preparation process parameters. Specifically, Example 2 The chemical composition of the slab used in -6 is shown in Table 1, the control requirements of the preparation process parameters are shown in Table 2, and the preparation process of the other unmentioned parts is the same as that of Example 1.

[0061] Each embodiment of table 1 molten steel chemical composition mass percent (%)

[0062] serial number

[0063] Each embodiment process parameter of table 2

[0064] serial number

[0065] The microstructure of the product obtained in Examples 2-6 is basically consistent with Example 1.

technical field

[0001] The invention belongs to the technical field of hot-rolled strip steel production technology, and in particular relates to a hot-rolled TRIP steel with a tensile strength of 900MPa and a preparation method thereof. Background technique

[0002] With the development trend of automobile lightweight, energy saving and safety improvement, high-strength steel has become the focus of steel material research in recent years and has been widely used in automobile manufacturing. However, in order to meet the forming conditions of body components, the elongation of high-strength steel must be guaranteed, so the strength level of high-strength steel used is limited, and some parts with complex shapes that require high strength can only be produced by welding after forming .

[0003] The TRIP steel with medium manganese content, that is, the phase transformation induced plasticity steel, induces the TRIP effect during deformation, so that the retained austenite f...

Examples

preparation example Construction

[0044] The second aspect of the present invention provides a method for preparing the above-mentioned hot-rolled TRIP steel with a tensile strength of 900MPa, the steps comprising:

[0045] S1, obtaining the molten steel with the above composition and then casting to obtain a slab;

[0046] S2, heat-treating the obtained cast slab under nitrogen protection, the heating temperature of the heat treatment is 1230-1270°C, and the holding time is 1 hour;

[0047] S3. The hot-rolled plate is obtained by hot-rolling by two-stage rolling process, the starting rolling temperature is 1120-1170°C, and the finishing rolling temperature is 850-930°C;

[0048] S4. Cool the hot-rolled sheet at a cooling rate of 20-30°C / s, cool it to 570-630°C, put it into a furnace (furnace temperature is 200-400°C) and keep it warm for 25-35 minutes, then cool it with the furnace to obtain a finished product, hot-rolled After 7 passes of rolling, the thickness range of the plate is controlled at 4-6mm; the...

Embodiment 1

[0053] This embodiment provides a method for preparing hot-rolled TRIP steel with a tensile strength of 900 MPa. The steps include:

[0054] After obtaining the molten steel, cast it to obtain a slab; the chemical composition of the molten steel is: by mass percentage, C: 0.11%, Si: 0:060%, Mn: 5.03%, P: 0.005%, S: 0.003%, Al: 1.82%, Nb: 0.036%, V: 0.060%, and the rest are Fe and unavoidable impurities.

[0055] The obtained slab was heated under the protection of nitrogen, the heating temperature was 1238° C., and the holding time was 1 hour.

[0056] The hot-rolled plate is hot-rolled by two-stage rolling process, the rolling start temperature is 1150°C, the thickness specification variation range of the hot-rolled plate is controlled at 4-5 mm after 7 passes of rolling, and the rolling termination temperature is controlled as 895°C. The hot-rolled plate is cooled at a cooling rate of 25°C / s, cooled to 600°C by laminar flow, put into the furnace (furnace temperature is 330...

Embodiment 2- Embodiment 6

[0060] Embodiments 2-6 all provide a method for preparing hot-rolled TRIP steel with a tensile strength of 900 MPa. The preparation method is basically the same as that of Example 1, the difference lies in the chemical composition of molten steel and some preparation process parameters. Specifically, Example 2 The chemical composition of the slab used in -6 is shown in Table 1, the control requirements of the preparation process parameters are shown in Table 2, and the preparation process of the other unmentioned parts is the same as that of Example 1.

[0061] Each embodiment of table 1 molten steel chemical composition mass percent (%)

[0062] serial number

[0063] Each embodiment process parameter of table 2

[0064] serial number

[0065] The microstructure of the product obtained in Examples 2-6 is basically consistent with Example 1.

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