THE INFLUENCE OF COMPOSITION AND THERMAL PROCESSING FOR STRUCTURE AND PROPERTIES NIKELCHROMIUM STEEL
At present is uninterrupted augmentation of rolled production processes, which create a more strained condition of rolls exploitation and produce increased demand to it quality, stability and to preservation of essential level of mechanical properties at work. High work speeds, loading at contact zones of working roll with processed metal, it cyclic changes, deflections and work temperatures increase lead to defects formation on body of roll and early outage, which bring down a mill productivity and rolling quality. The main ways to roll stability increase - create and use new, stronger materials for it making, improvement of making technology and exploitation.
The main demand for rolls for hot rolling there are high wear resistance, small inclination to heat checking cracks initiation, high mechanical properties. For this usually use high-strength cast iron working rolls, wear-resisting steels, bimetal rolls with welding deposition. For finishing stands shape rolling mills now use powder hard alloys based on refractory metal carbides because it have high abrasive wear resistance. However was ascertain that for leader pass in a number of cases more preferable may be using of high-carbon nickel-chromium steels because it have smaller inclination to make a fire cracks.
In this work a behavior of high-carbon nickel-chromium cast steels was studied depending on chemistry and heating temperature during heat treatment, structure and properties of cast steels with different temper and alloying elements. The same characteristics was studied for one of investigated steels - Cr12Ni4 - after oil quenching with heating temperatures 850 to 1100°Ñ. In all steels chromium and nickel is in approximate the same ratio, one of steels subsidiary doped of molybdenum, tungsten and vanadium.
Table 1 - Chemistry of investigated steels, %
| Steel | Ñ | Mn | Si | Ñã | N1 | Ìî | W | V |
|---|---|---|---|---|---|---|---|---|
| Cr12Ni4 | 1,03 | 0,25 | 0,06 | 11,9 | 3,83 | - | - | - |
| Cr15Ni4 | 0,64 | 0,12 | 0,08 | 14,8 | 3,45 | - | - | - |
| Cr15Ni4MoTgV | 1,95 | 0,2 | 0,14 | 15,2 | 3,4 | 0,65 | 1,1 | 0,18 |
| 150Cr15Ni5 | 1,5 | 0,4 | 0,3 | 14 | 5 | - | <1 | <1 |
In work quantitative parameters of structure are gave: quantity of eutectic component, defined with dotted method, quantity of residual austenite and a period of austenite lattice, defined with X-ray structure analysis, hardness and microhardness of structure components.
All cast steels which studied are correspond with austenite class, at the same time steel hardness primarily depend of quantity of eutectic. Following heat treatment is notably brought down austenite stability (for example Õ12Í4 steel), lead it in martensite class, and heating temperature make an sufficiently standard impact on steel hardness, but with hardness maximum after quenching from relatively low temperatures, about 900-950°Ñ.
For the next phases planed to investigate a dependence of stability nonequilibrium structures of high-carbon nickel-chromium steels from it temper and will take a subsequent investigate of heat treatment influence at structure and properties of this steels too.