Since the 1980 s, the thermal mechanical rolling direct drawing of low alloy steel or cold forging process carried out extensive research, such as some other studies focused on the cut high carbon and bearing steel rolling temperature austenitic has begun to close to the critical temperature interval of pearlite transformation. This kind of rolling technology for industrial production to bring inconvenience, due to the high rolling force and large frame, thus requiring special mill can achieve.

17 no memorial arch frame short stress line mill press flat vertical layout, alternately use rapid change overall frame, within 5 min, you can change the product size. Two automatic steel rolling workshop and roll workshop automatically connect. Steel rolling workshop is equipped with five descaling machine, improve the quality of the product surface. Installed in the mill at the entrance of the first descaler can return. Rolling of round bar final size tolerance can reach 1/8 DIN 1013, this is due to the adopted a set of 5 ℃ ks - including a K of agnelli units (RSB) of reducing diameter and 2 sets of automatic measurement equipment used for product size control automation. Arrangement in front of the RSB cooling line (LTR low-temperature rolling) ensure finishing passes in front of the temperature and the temperature uniformity requirements. Cold rolling strip material refers to finishing in 700 ~ 820 ℃ temperature range. More importantly to along the length direction of the rolling bar to achieve the uniformity of the temperature, avoid due to different finishing temperature changes in the internal structure.

Need to adopt cold rolling for fine grained rolling, then the ultimate online heat treatment. Rolling temperature is thermal deformation in the process of one of the three basic parameters that affect grain refinement. Take control of grain refinement in cold rolling and grain growth, influence the time - temperature - phase transformation (CCT) curve, so as to adjust the length of the grain boundary and subsequent nucleation position. Especially the temperature parameter, it affects the whole process of thermal dynamic conditions.

And cooling in a production line of online annealing furnace is a gas stove, bar here to complete the heat treatment (in cold rolling line has been completed the slow, softening annealing, spheroidizing annealing and tempering process). Burner layout optimization and the use of the fan, can make the furnace temperature distribution uniformity, ensure no decarburization reaction, and ensure the length direction of bar and rod of each process performance is uniform.

Rods after cut into fixed-length, online testing and finishing is an important process of continuous production line. Rod finishing line by an online shot blast machine, four mill cutter, a nondestructive testing station, a clear burrs and strapping machine, a stacking stand and a collection point.

Latest technology for bearing steel annealing process, the progress of the actual installation, use online annealing furnace made a summary and analysis of results. The most common bearing steel AISI 52100 is studied in this paper. And more varieties of alloy after online annealing furnace for annealing and tempering treatment.

2 discuss

AISI52100 basic composition is 1% 1% carbon and chromium steel, usually by spheroidizing annealing or softening annealing state delivery. Spheroidizing annealing mode is very suitable for the organization, such as drilling and cutting processing, the reason was that the structure of the continuous ferrite spherical cementite with high plasticity. Has this organization bearing in the final after hardening treatment, has the proper hardness and fatigue strength. Because of the cementite are dispersed in the ferritic matrix, thus has high plasticity. After such heat treatment hardness value is 200 hb. If the delivery with softening annealing, the hardness of more than 200 HB, but anyway, softening annealing of bearing can process and shear won't appear the phenomenon of cracking and reduce the tool life. Spheroidizing annealing time is long, and is also the most expensive annealing process, the reasons are the following:

. Need long total processing cycles;

. A long raw material processing time; .

Due to oxidation material loss; .

Surface decarbonization; The bar straightening is required after annealing.

3 conclusion

Develop AISI52100 steel from the mill directly after the whole process of the spheroidizing annealing process. Of finishing temperature, isothermal transformation start temperature and annealing temperature and annealing time is optimized, the spheroidization rate is greater than 80%, and the organizational structure of the final hardness is lower than 220 hb. In the process of production use of ONA furnace for isothermal annealing and tempering treatment, heat treatment all the time about 2 hours, to get the hardness and the distribution of the carbide result is satisfied.

Current for all materials for isothermal annealing and tempering treatment, common practice is to install using on-line heat treatment furnace, such as ONA equipment, this equipment can also be used to achieve productivity as the first target production purpose.