CN101255492A - Production method for preventing no remarkable yield point of niobium micro-alloyed hot-rolled rib steel bar - Google Patents

Abstract

The invention provides a production method for a niobium-microalloying-preventing hot-rolled ribbed steel bar of no obvious yield point, comprising reasonably controlling heating temperature and post-rolling temperature on cooling bed, when the environment temperature is less than 0 DEG C, the control objective of heating temperature of a rolling billet is 1060 DEG C to 1120 DEG C, the control objective of post-rolling temperature on cooling bed is 910 DEG C to 960 DEG C; when the environment temperature is 0 DEG C to 30 DEG C, the control objective of heating temperature of the rolling billet is 1040 DEG C to 1100 DEG C, the control objective of post-rolling temperature on cooling bed is 870 DEG C to 910 DEG C; when the environment temperature is greater than 30 DEG C, the control objective of heating temperature of the rolling billet is 1040 DEG C to 1100 DEG C, the control objective of post-rolling temperature on cooling bed is 820 DEG C to 865 DEG C. According to the produced niobium-microalloying-preventing hot-rolled ribbed steel bar, no obvious yield point phenomena can be effectively prevented, occurring probability of which is lower than 1%.

Description

The production method of prevention niobium micro-alloyed hot-rolled rib steel bar no remarkable yield point

Technical field

The invention belongs to the stress metal manufacture field, relate in particular to the production method of prevention niobium micro-alloyed hot-rolled rib steel bar no remarkable yield point.

Background technology

The fast development of Chinese national economy has driven China's construction(al)steel growth of requirement, and this provides good opportunity for the development of construction(al)steel.Along with China's development of the West Regions, infrastructure construction and quickening of urbanization process, the construction industry of China will sustained and rapid development.Construction industry is the industry of China's steel consumption amount maximum, is main raw because the Infrastructure of China remains with Steel Concrete, so hot rolled ribbed steel bar consumption maximum in construction(al)steel always for many years.In recent years, China develops aspect hot rolled ribbed steel bar rapidly, the GB1499 standard is dressed to international advanced standard, stipulated the requirement of 400MPa, 500MPa rank reinforcing bar, the output of China's HRB400 reinforcing bar in 2006 has reached more than 1,000 ten thousand tons, account for 15% of reinforcing bar ultimate production, existing just further broadened application scope.

For a long time, the HRB400 high strength cast iron of China's production 400MPa level mainly adopts vanadium iron or VN alloy microalloying technology.Because the demand to vanadium iron and VN alloy increases considerably, and has caused vanadium iron and VN alloy resource anxiety, price goes up significantly.In order reasonably balancedly to utilize resource, to reduce production costs, promote applying of HRB400 reinforcing bar, the manufacturing enterprise of China has begun to produce in batches the 400MPa niobium micro-alloyed hot-rolled rib steel bar.But the phenomenon of no remarkable yield point often appears in the Nb-microalloying HRB400 reinforcing bar of producing, and ratio can reach 9-25%.No remarkable yield point because being used for the common tensile testing machine of reinforcing bar examination and quality surveillance, present domestic market generally do not possess the survey Rp0.2 condition of (being used to replace yield strength ReL), so cause difficulty can for user acceptance and quality supervision and test.Add the user and use the reinforcing bar of not approving no remarkable yield point in idea, existing market is not generally accepted the HRB400 reinforcing bar of no remarkable yield point.In addition, the reinforcing bar of no remarkable yield point often is accompanied by that elongation is low, brittle rupture during tension test, even defectively, actual during cold bending test ruptures when using bending.Therefore, need take measures to prevent the phenomenon of 400MPa niobium micro-alloyed hot-rolled rib steel bar no remarkable yield point.

Chinese patent application " trace niobium-containing steel for cooling-control reinforced bar and production method thereof " [application number: 200510094835.9] has proposed a kind of production method of niobium micro-alloyed hot-rolled rib steel bar: " billet heating temperature is controlled at 1050-1220 ℃ of scope when rolling; finish more than more than 950 ℃ rolling ... the temperature of cold bed is controlled at 800-1050 ℃ on the reinforcing bar usually.Though " provided the production method of 400MPa niobium micro-alloyed hot-rolled rib steel bar; by this explained hereafter the yield-point phenomenon might appear still not having; need the process combination control that propose Heating temperature more specifically, go up cold bed temperature by different envrionment temperatures, effectively the phenomenon of prevention reinforcing bar no remarkable yield point.

Summary of the invention

The technical problem to be solved in the present invention provides a kind of production method of preventing the niobium micro-alloyed hot-rolled rib steel bar no remarkable yield point, according to said method produces, and can effectively prevent the phenomenon of reinforcing bar no remarkable yield point.

For solving the problems of the technologies described above, the technical scheme that the present invention proposes is: rationally control Heating temperature and roll upward cold bed temperature of back, when envrionment temperature＜0 ℃, billet heating temperature controlled target value is 1060-1120 ℃ when rolling, and last cold bed temperature controlled target value is 910-960 ℃; In the time of envrionment temperature 0-30 ℃, billet heating temperature controlled target value is 1040-1100 ℃ when rolling, and last cold bed temperature controlled target value is 870-910 ℃; During envrionment temperature＞30 ℃, billet heating temperature controlled target value is 1040-1100 ℃ when rolling, and last cold bed temperature controlled target value is 820-865 ℃.Use the watercooler controlled chilling after the finish to gauge, control cold bed temperature by adjusting the process for cooling parameter, last cold bed temperature is meant cold bed place or near its top temperature of reinforcing bar on cold bed, reinforcing bar behind naturally cooling on the cold bed, shearing, bundling, warehouse-in.

Adopting the content of niobium of the present invention's design is the production method of the 400MPa niobium micro-alloyed hot-rolled rib steel bar of 0.01-0.04%, can effectively prevent the phenomenon of reinforcing bar no remarkable yield point, makes the phenomenon probability of occurrence of reinforcing bar no remarkable yield point be lower than 1%.

Embodiment

Specify the content of technical scheme below:

Billet heating temperature control: Heating temperature is crossed the low then content of niobium minimizing of solid solution in the steel austenite when heating, is unfavorable for bringing into play it in rolling and crystal grain thinning and precipitation strength effect process of cooling; The alligatoring of growing up of the too high then austenite crystal of Heating temperature is unfavorable for the refinement of final room temperature texture.General continuous merchant bar mill operation of rolling rolled piece temperature does not reduce even raises, the too high meeting of Heating temperature causes finishing temperature higher, can be unfavorable for the refinement of room temperature texture on the one hand, can increase the formation of low temperature phase change products such as austenitic stability, promotion bainite on the other hand, be prone to the phenomenon of no remarkable yield point.The too high control that also is unfavorable for cold bed temperature on the reinforcing bar of finishing temperature.When envrionment temperature＜0 ℃, billet heating temperature controlled target value is 1060-1120 ℃, and when envrionment temperature＞0 ℃, billet heating temperature controlled target value is 1040-1100 ℃.When envrionment temperature＞0 ℃, billet heating temperature is lower slightly, is that it is lower that it goes up cold bed temperature subsequently owing to considered to be convenient to the control that it goes up cold bed temperature subsequently.Above-mentioned Heating temperature is meant the soaking zone temperature.

Last cold bed temperature control: go up cold bed temperature and must be controlled at more than the Ar3 temperature, this is in order to prevent that too much low temperature phase change products such as bainite from appearring occurring on tempered structure and the reinforcing bar section in surface of reinforced bar.Last cold bed temperature is on the low side then can to make the reinforcing bar cooling temperature field change, and makes reinforcing bar roll the back austenite and cool off quickening when room temperature texture changes, and promotes bainite to form, and is prone to the phenomenon of no remarkable yield point; Last cold bed temperature is too high then can be made phase transformation time cooling is slow, be unfavorable for the refinement of room temperature texture, last cold bed temperature height then finishing temperature is also high, the preceding crystal grain of phase transformation is thicker during cooling, can be unfavorable for the refinement of room temperature texture on the one hand, can increase the formation of low temperature phase change products such as austenitic stability, promotion bainite on the other hand, be prone to the phenomenon of no remarkable yield point.When envrionment temperature＜0 ℃, last cold bed temperature controlled target value is: 910-960 ℃; In the time of envrionment temperature 0-30 ℃, last cold bed temperature controlled target value is: 870-910 ℃; During envrionment temperature＞30 ℃, last cold bed temperature controlled target value is: 820-865 ℃.When envrionment temperature was low, reinforcing bar rolled the back austenite and cools off when room temperature texture changes comparatively fast, and for preventing too much bainite, the no remarkable yield point phenomenon occurring, last cold bed temperature is controlled higherly, to reduce cooling rate; When envrionment temperature was higher, reinforcing bar rolled the back austenite and cool off slowlyer when room temperature texture changes, is crystal grain thinning, raising intensity, and last cold bed temperature is controlled lowlyer, with the increase cooling rate.

Whether processing parameter of the present invention and reinforcing bar have the situation embodiment of sharp yield point to see Table 1, and working condition is that 50 tons of converter smeltings, continuous castings become the 150mm square billet, rolling on the merchant bar mill continuously.

Whether table 1 processing parameter of the present invention and reinforcing bar have the situation embodiment of sharp yield point

The content of niobium of producing with the present invention is that the microstructure of the 400MPa niobium micro-alloyed hot-rolled rib steel bar of 0.01-0.04% is ferrite+perlite, or ferrite+perlite+bainite, and bainite comprises granular bainite.Rebar surface has the thin crystal layer of one deck≤2mm thickness.

Claims (4)

1, a kind of production method of preventing the niobium micro-alloyed hot-rolled rib steel bar no remarkable yield point, comprise reasonable control Heating temperature and roll upward cold bed temperature of back, it is characterized in that: when envrionment temperature＜0 ℃, billet heating temperature controlled target value is 1060-1120 ℃ when rolling, and last cold bed temperature controlled target value is 910-960 ℃; In the time of envrionment temperature 0-30 ℃, billet heating temperature controlled target value is 1040-1100 ℃ when rolling, and last cold bed temperature controlled target value is 870-910 ℃; During envrionment temperature＞30 ℃, billet heating temperature controlled target value is 1040-1100 ℃ when rolling, and last cold bed temperature controlled target value is 820-865 ℃.

2, the production method of prevention niobium micro-alloyed hot-rolled rib steel bar no remarkable yield point according to claim 1, it is characterized in that: described billet heating temperature is meant the soaking zone temperature.

3, the production method of prevention niobium micro-alloyed hot-rolled rib steel bar no remarkable yield point according to claim 1, it is characterized in that: the content of niobium of producing with the present invention is that the microstructure of the 400MPa niobium micro-alloyed hot-rolled rib steel bar of 0.01-0.04% is ferrite+perlite, or ferrite+perlite+bainite.

4, the production method of prevention niobium micro-alloyed hot-rolled rib steel bar no remarkable yield point according to claim 1 is characterized in that: there is the thin crystal layer of one deck≤2mm thickness on the 400MPa niobium micro-alloyed hot-rolled rib steel bar surface of producing with the present invention.