Background technology
The high-strength engineering machines steel is to serve as the Hi-Stren steel of basis adding Mo, Nb, microalloy elements such as V, Ti with the C-Mn steel.At present, high tensile steel plate is used widely at construction machinery industry and coal mine machinery industry, and demand thickness is based on 4-80mm, wherein, the following thickness steel plate of 20mm is mainly coiled sheet and opens flat series products, and the overwhelming majority is applied to construction machinery industry, is used to make crane arm, vehicle frame etc.; The above thickness steel plate of 20mm is mainly the plate of moderate thickness series products, and majority is applied to the coal mine machinery industry.Because hot-rolled sheet coil does not have the such strong control of plate of moderate thickness to control cold means, often need to add more alloying elements, improved cost, and coiled sheet in use needs out flat, unrelieved stress is very big to the influence of plate shape, influence in order to reduce or to eliminate unrelieved stress, in process of production smooth alignings and the thermal treatment process of adopting of coiled sheet have also increased cost more.Domestic have only several families such as Baosteel, Anshan iron and steel plant, Wuhan Iron and Steel Plant to produce 600 grades of High Strength Steel Plates, adds precious metals such as Mo, V mostly, and the controlled rolling and controlled cooling heat treated is produced, and its complex procedures, cost are higher.
Summary of the invention
The purpose of this invention is to provide a kind of 600MPa grade high-strength engineering machines steel and production method thereof, need not to add expensive elements such as Mo, V, adopt the technology of dynamically gently depressing, effective control center's segregation and center porosity, make it have the high-intensity high toughness that keeps simultaneously, and adopt the method for going into the holding pit slow cooling after rolling to eliminate unrelieved stress, and produce the high-strength engineering machines steel hot-rolled sheet coil of yield strength more than 600MPa, hot-rolled sheet coil is at-20 ℃ of V-type Charpy-V impact power 〉=40J.
Purpose of the present invention can realize by following measure:
The present invention relates to a kind of 600MPa level high-strength engineering machines uses the chemical ingredients of steel hot-rolled sheet coil to be C:0.06-0.09%, Si:0.15-0.25%, Mn:1.4-1.6%, P by weight percentage: S≤0.020% :≤0.010%, Alt:0.020-0.060%, Nb:0.040-0.060%, Ti:0.09-0.12%, surplus is Fe and unavoidable impurities.
600MPa level high-strength engineering machines of the present invention need not to add expensive elements such as Mo, V with steel hot-rolled sheet coil, only compound interpolation Nb, Ti microalloy element on C-Mn base steel plinth, Nb+Ti≤0.18%.
Produce the production method of 600Mpa level high-strength engineering machines, comprise smelting, rolling, it is characterized in that with steel hot-rolled sheet coil:
(1) smelt employing full guard pouring technology, promptly ladle adopts long nozzle to add the argon envelope to the tundish protection, utilizes seal washer and argon to seal and prevents that air from infiltrating; Tundish adopts the connection of SEN to add the argon envelope to the beam protection of crystallizer, P≤0.020%, S≤0.010%, [the o]≤20ppm of control strand, [N]≤30ppm.Adopt and dynamically gently to depress technology, effectively control center's segregation and center porosity guarantee that coiled sheet keeps high toughness simultaneously high-intensity.
(2) adopt two frame roughing and six frame finish rolling mode of manufacture, rough rolling step adopts six passages rolling, and the finish rolling stage is adopted six passage finish rolling, and at austenite non-recrystallization district draught 65%~70%, finishing temperature is controlled at 820~860 ℃.
(3) adopt front end laminar flow cooling mode, be as cold as target temperature soon after going out finish rolling, coiling temperature is controlled in 550~600 ℃ of scopes, and speed of cooling is controlled at 5~10 ℃/s.
(4) batch and carried out slow cooling with the interior holding pit of putting in back 30 minutes.
The present invention has the following advantages compared to existing technology:
Mainly adopts at present both at home and abroad on Nb, Ti basis, add alloying elements such as a certain amount of Mo, V, adopt roll after modified mode heat-treat production 600MPa level high-strength engineering machines steel hot-rolled sheet coil.Using great advantage of the present invention is to need not to add expensive alloying elements such as Mo, V can produce 600MPa level high-strength engineering machines steel hot-rolled sheet coil cheaply, and eliminate unrelieved stress by coiled sheet slow cooling mode, reduce the plate shape fraction defective of opening after putting down, need not smooth aligning and other heat treatment mode.Use the lumber recovery that the present invention can reduce cost, simplify Production Flow Chart greatly, improve opening plate, energy-saving and cost-reducing, be specially:
1, the present invention is route with the low cost, need not to add expensive elements such as Mo, V, only compound interpolation Nb, Ti microalloy element on C-Mn base steel plinth, and Nb+Ti≤0.18%, cost of alloy is saved about 210 yuan than domestic prior art.
2, adopt the full guard pouring technology, P≤0.020%, S≤0.010%, [the o]≤20ppm of control strand, [N]≤30ppm.Adopt and dynamically gently to depress technology, effectively control center's segregation and center porosity guarantee that coiled sheet keeps high toughness simultaneously high-intensity.
3, the present invention adopts six frame finish rolling, than seven frame finish rolling, can obtain bigger compression ratio, especially at austenite non-recrystallization district draught greater than 65%, impel separating out of microalloy element carbonitride, increase lattice defects such as non-recrystallization austenite grain boundary, deformed belt and dislocation, to increase effective grain boundary area, improve the ferrite nucleation rate, thereby ferrite crystal grain after the refinement phase transformation obtains better refined crystalline strengthening effect.Refined crystalline strengthening is unique reinforcement means that can obtain high strength and high tenacity, can reduce cost in the use that reduces expensive elements such as Mo, V like this.
4, the present invention puts into the holding pit slow cooling rapidly to eliminate unrelieved stress after coiled sheet rolls off the production line, and need not smooth aligning and other thermal treatment means.Coiled sheet goes out the hole after holding pit nature slow cooling to 100 ℃, fully discharge unrelieved stress.All being controlled in the 5mm, satisfy the requirement of engineering machinery with steel to opening plate volume back transverse and longitudinal roughness.
Embodiment
Below in conjunction with example to 600MPa level high-strength engineering machines with further auspicious the stating of steel hot-rolled sheet coil and production method thereof:
Table 1 has been listed the present invention and has been used to produce the chemical ingredients of low-cost 600Mpa high-strength engineering machines with steel hot-rolled sheet coil.Production method is as follows: adopt desulfurizing iron, 210t converter smelting, the refining of LF stove at steelworks, make the chemical ingredients in the steel as shown in table 1 after the processing, surplus is Fe and inevitably is mingled with.The molten steel casting that table 1 is required becomes the slab of 230mmX1300~1800mm section again, delivers to hot continuous rolling factory.
Table 1 chemical ingredients of the present invention, wt%
Sequence number |
C |
Si |
Mn |
P |
S |
Alt |
Nb |
Ti |
1 |
0.08 |
0.19 |
1.48 |
0.012 |
0.0044 |
0.043 |
0.04 |
0.10 |
2 |
0.076 |
0.19 |
1.51 |
0.012 |
0.0046 |
0.036 |
0.04 |
0.09 |
Adopt the hot continuous rolling mode of production of controlled rolling and controlled cooling, go into the burial pit slow cooling after coiled sheet batches.The cold significant parameter of control control comprises: (1) adopts two frame roughing and six frame finish rolling mode of manufacture, rough rolling step adopts six passages rolling, the finish rolling stage is adopted six passage finish rolling, and greater than 65%, finishing temperature is controlled at 820~860 ℃ at austenite non-recrystallization district draught; (2) adopt front end laminar flow cooling mode, be as cold as target temperature soon after going out finish rolling, coiling temperature is controlled in 550~600 ℃ of scopes, and speed of cooling is controlled at 5~10 ℃/s; (3) batch and put into holding pit in back 30 minutes and carry out slow cooling.
Low-cost 600MPa level high-strength engineering machines of the present invention is tabulated in 2 with the manufacturing parameter and the test-results of steel hot-rolled sheet coil.Yield strength is greater than 600MPa as can be seen from the table, and tensile strength is greater than 700MPa, and unit elongation is greater than 19%, ,-20 ℃ of V-type Charpy-V impact power 〉=100J.
Table 2 technology controlling and process of the present invention and test-results